"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:bf642704-ee39-4d2e-93ba-3735bd79bc62","http://resolver.tudelft.nl/uuid:bf642704-ee39-4d2e-93ba-3735bd79bc62","基于分段步进式弹塑性格构模型的混凝土破坏过程细观模拟","Zhang, H. (Shandong University); Jin, Zuquan (Qingdao University of Technology); Jiang, Nengdong (Shandong University); Ge, Zhi (Shandong University); Schlangen, E. (TU Delft Materials and Environment); Ling, Yifeng (Shandong University); Šavija, B. (TU Delft Materials and Environment); Wang, Zheng (Shandong Hi-Speed Group)","","2023","The classically lattice model assumes the local elements behave elastic brittle, neglecting the ductility of the mortar matrix. This leads to the simulated load⁃displacement response more brittle than the realistic. To solve the aforementioned issue, a piece⁃wise approach was introduced to describe the elastic⁃plastic constitutive relation of lattice element. The fracture process and the load⁃displacement response were obtained through the sequentially⁃linear solution approach. The model was calibrated using the uniaxial tension and compression tests. It is found that the model can precisely simulate the fracture process and load⁃displacement response. Moreover, the model was used to model the size effect in uniaxial tension and the influence of the specimen’s slenderness and boundary confinement on the fracture behavior under compression. It offers a new theoretical method and approach for studying the fracture of concrete.","concrete; elastic⁃plastic constitutive relation; fracture process; lattice model; meso⁃scale","zh","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-10-25","","","Materials and Environment","","",""
"uuid:bd2cec63-0d51-4829-8232-476b2d717d39","http://resolver.tudelft.nl/uuid:bd2cec63-0d51-4829-8232-476b2d717d39","Verduurzaming tunnelgietbouw: Beperkte aanpassing, grote impact","Schuurman, A.C.B. (TU Delft Applied Mechanics); Robbemont, Arnold (Zonneveld ingenieurs)","","2023","Met tunnelgietbouw kunnen snel en tegen lage kosten woningen worden gerealiseerd. Het is dan ook een veel toegepaste bouwmethodiek. Er valt potentieel veel terrein te winnen ten aanzien van milieu-impact door de betonsector.","tunnel formwork; concrete; sustainability; Concrete mix design","nl","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-06-20","","","Applied Mechanics","","",""
"uuid:949a6032-ddbf-4e2d-9308-8ee30bf9fe84","http://resolver.tudelft.nl/uuid:949a6032-ddbf-4e2d-9308-8ee30bf9fe84","From waste to self-healing concrete: the missing PHA-link","Rossi, E. (TU Delft Materials and Environment)","Jonkers, H.M. (promotor); Kleerebezem, R. (promotor); Copuroglu, Oguzhan (copromotor); Delft University of Technology (degree granting institution)","2022","Self-healing concrete has attracted increasing attention of researchers and industry over the last decades. Given the brittle nature and the relatively low tensile strength of concrete, the occurrence of cracks is an almost unavoidable phenomenon affecting (reinforced) concrete structures. Cracks allow harmful agents present in the environment
to penetrate more easily in structures, accelerating the material degradation and compromising their service life. Repair and maintenance interventions are often needed in practice to maintain the serviceability of structures and to avoid any premature collapse. However, the costs of these interventions are socially and economically impactful. The
aim of both academia and industry is (and it has been) therefore to limit the need of these interventions through different technologies such as, among others, self-healing
concrete. Several technologies (or healing agents) have been proposed and investigated to improve the self-healing capacity of concrete, such as mineral and crystalline admixtures, superabsorbent polymers, micro- or macro-encapsulated polymers, and bio-concrete. Any technology has its own working principle, and the beneficial effects that the healing agents have on concrete properties are continuously under investigation. Despite the relatively high amount of available healing agents, this research focuses on the potential of innovatively using waste-derived polyhydroxyalkanoates (PHAs) as bacterial substrate for self-healing bio-concrete applications. Differently from other healing agents, PHAs are biodegradable and they can be extracted from biomass. The application of PHAs as substrate for bacterial healing agents in concrete does not ideally need high material requirements (e.g., purity) as other applications may do, hence opening the possibility to obtain efficient and relatively low costs healing agents, of which production would significantly contribute to the principles of circular economy. The aim of this research is, therefore, to investigate the applicability of PHAs as bacterial
substrate for self-healing agents in concrete. To do so, a PHAs extraction procedure has been designed, as well as the healing agent particle formulation process, as reported
in Chapter 3. This chapter aimed to formalize the production of PHAs-based healing agents (AKD), and to demonstrate its compatibility with bacterial metabolic activity. In Chapter 4, an extensive experimental campaign on the compatibility between AKD and Ordinary Portland Cement (OPC) mortar has been conducted. The feasibility of this application was demonstrated by the marginal effect that AKD healing agents have on some fundamental functional properties of cementitious materials (e.g., strength) and
by the improved self-healing capacity of the proposed system compared to plain mortar. In Chapter 5, the effect of self-healing on chloride penetration resistance in mortar specimens has been investigated. The results of this chapter firstly showed that the chloride penetration resistance in sound specimens increased thanks to the formation of a
thin calcium carbonate layer at the surface of the specimens and through a slight densification of the matrix. Secondly, self-healing of cracks was beneficial since it delayed the penetration of chlorides. Nevertheless, the initial chloride penetration resistance (e.g., that of sound specimens) could not be completely restored through self-healing.
In Chapter 6, the applicability of AKD in Blast Furnace Slag Cement (BFSC) mortar was investigated. Results of this chapter demonstrated the compatibility between AKD and low-alkaline mixtures, since functional properties did not get negatively affected and the self-healing capacity significantly improved. These results are different from those
observed when applying poly-lactic acid (PLA) healing agents in BFS mixtures, which on the contrary showed incompatibility with the mixture due to its lower alkalinity. In
Chapter 7, analysis and reflections on the potentially positive impact that self-healing could have on the service-life of infrastructures have been conducted based on idealized
scenarios. The environmental impact of AKD healing agents has been also discussed based on the eco-costs related to available processing treatments of PHAs. In Chapter 8, a methodology based on gas chromatography has been proposed to detect and quantify bio-based healing agents in added in cementitious materials. Even though the applicability of this methodology has been demonstrated for PLA healing agent, gas chromatography can be extended to AKD healing agent as well. In Chapter 9 conclusions based on the analysis conducted over the whole research have been drawn, and recommendations for future research have been made. With the present research the author hopes to provide a valuable contribution for those interested in the field of self-healing materials.","self-healing; concrete; bacteria; healing agent","en","doctoral thesis","","978-94-6419-667-2","","","","","","","","","Materials and Environment","","",""
"uuid:19aad3b1-ceb8-4bee-b03a-6f588b146377","http://resolver.tudelft.nl/uuid:19aad3b1-ceb8-4bee-b03a-6f588b146377","Gaussian models for bond strength evaluation of ribbed steel bars in concrete","Prem, Prabhat R. (CSIR-Structural Engineering Research Centre, Chennai); Šavija, B. (TU Delft Materials and Environment)","","2022","A precise prediction of the ultimate bond strength between rebar and surrounding concrete plays a major role in structural design, as it effects the load-carrying capacity and serviceability of a member significantly. In the present study, Gaussian models are employed for modelling bond strength of ribbed steel bars embedded in concrete. Gaussian models offer a non-parametric method based on Bayesian framework which is powerful, versatile, robust and accurate. Five different Gaussian models are explored in this paper-Gaussian Process (GP), Variational Heteroscedastic Gaussian Process (VHGP), Warped Gaussian Process (WGP), Sparse Spectrum Gaussian Process (SSGP), and Twin Gaussian Process (TGP). The effectiveness of the models is also evaluated in comparison to the numerous design formulae provided by the codes. The predictions from the Gaussian models are found to be closer to the experiments than those predicted using the design equations provided in various codes. The sensitivity of the models to various parameters, input feature space and sampling is also presented. It is found that GP, VHGP and SSGP are effective in prediction of the bond strength. For large data set, GP, VHGP, WGP and TGP can be computationally expensive. In such cases, SSGP can be utilized.","bond strength; concrete; gaussian; modelling; steel bars","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-06-10","","","Materials and Environment","","",""
"uuid:19077cdf-3246-4f7e-bd69-c0bfb4fd8a82","http://resolver.tudelft.nl/uuid:19077cdf-3246-4f7e-bd69-c0bfb4fd8a82","Making it Concrete: Analysing the Role of Concrete Plants’ Locations for Circular City Policy Goals","Van den Berghe, K.B.J. (TU Delft Urban Development Management); Verhagen, Teun (Universiteit Leiden)","","2021","Increasingly, space for remanufacturing is seen as the most valuable resource to achieve circular economy (CE) policy goals, in particular for cities. However, in many cities, industrial urban areas are increasingly subject of – mostly circular designed - residential redevelopment. The proposition of this paper is that these diminishing industrial areas host, at least potentially, essential functions necessary to “close the material loop.” The reason why policy makers neglect the necessity of remanufacturing capacity, is because it is difficult to pinpoint the “ideal” geography of a circular loop. Most (circular) products can be transported limitless, thus their remanufacturing functions can be located around the world. But what if a critical material cannot be transported limitless and has circular potential? Therefore, this paper focusses on concrete for two reasons. First, concrete is by far the most abundant material in urban areas. Second, newly/circular made fluid concrete can only be transported for a limited time and distance. The hypothesis of this paper is that concrete plants are and will become essential for circular cities. Subsequently, we focus on the Dutch city of The Hague and combine a Material Flow Analysis with the locations of the concrete resupply chain. Our results show that potentially The Hague has a 100% circular concrete chain, but the importance of its concrete plant is (implicitly) neglected. We conclude that The Hague is illustrative for the problem of many circular cities that are without (implicitly) taking into account the whole circular resupply chain, jeopardized today a future urban CE.","(re)supply chain; circular city; circular washing; concrete; urban metabolism","en","journal article","","","","","","","","","","","Urban Development Management","","",""
"uuid:fa7f616f-ea4a-40bc-85ba-76128cef7829","http://resolver.tudelft.nl/uuid:fa7f616f-ea4a-40bc-85ba-76128cef7829","URL 2003 - Betonrestauratie - advies: Uitvoeringsrichtlijn","Jonker, Martin; Quist, W.J. (TU Delft Heritage & Technology)","","2021","Deze uitvoeringsrichtlijn (URL) beschrijft de werkzaamheden (diensten) van een adviseur in het werkveld restauratie van historisch beton, toegepast in rijks-, provinciale of gemeentelijke monumenten of karakteristieke gebouwen en objecten in beschermde gezichten.","concrete; conservation; preservation","nl","report","Stichting Erkende Restauratiekwaliteit Monumentenzorg","","","","","","","","","","Heritage & Technology","","",""
"uuid:59f3bf13-1474-45da-8bbc-8d3b2e019b28","http://resolver.tudelft.nl/uuid:59f3bf13-1474-45da-8bbc-8d3b2e019b28","On the Applicability of a Precursor Derived from Organic Waste Streams for Bacteria-Based Self-Healing Concrete","Rossi, E. (TU Delft Materials and Environment); Vermeer, C.M. (TU Delft BT/Environmental Biotechnology); Mors, R.M. (TU Delft Materials and Environment; Green Basilisk); Kleerebezem, R. (TU Delft BT/Environmental Biotechnology); Copuroglu, Oguzhan (TU Delft Materials and Environment); Jonkers, H.M. (TU Delft Materials and Environment)","","2021","Bacteria-based self-healing concrete has the ability to heal cracks due to the bacterial conversion of incorporated organic compounds into calcium carbonate. Precipitates seal the cracks, theoretically increasing the service life of constructions. The aim of this paper is to propose a precursor for bacteria-based self-healing concrete derived from organic waste streams, produced is in line with the circular economy principle and ideally more affordable than other substrates. To verify the applicability of the proposed healing agent, some fundamental requirements of the proposed system are studied, such as its influence on functional properties, crack sealing capacity and evidence of bacterial activity in concrete.","bacteria; concrete; crack sealing; durability; self-healing; sustainability","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:944a07ac-81a5-4be0-b06a-4676ae4f05c8","http://resolver.tudelft.nl/uuid:944a07ac-81a5-4be0-b06a-4676ae4f05c8","Overview of Torsion Design Methods","Granda Valencia, Camilo (University of British Columbia); Lantsoght, E.O.L. (TU Delft Concrete Structures; Universidad San Francisco de Quito; Adstren)","Lantsoght, Eva (editor); Greene, Gary (editor); Belarbi, Abdeldjelil (editor)","2020","Large torsional moments, which need to be considered in a design, can result among others, in structures with an asymmetric layout or loading. To find the required longitudinal and transverse reinforcement to resist these torsional moments, the link between the three-dimensional action of the torsional moment and sectional analysis methods is necessary. This paper reviews the existing methods and code provisions for torsion. First, an overview of the principles of torsion from the mechanics perspective is given. Then, a survey of the available mechanical models for torsion is presented. Finally, the code provisions for torsion of ACI 318-19, CSA-A23.3-04, AASHTO-LRFD- 17, EN 1992-1-1:2004, and the fib Model Code 2010 are summarized. Additionally, current research topics on torsion in structural concrete are summarized. It is expected that with this paper, engineers will have a useful overview and background knowledge for the design and assessment of torsion-critical elements.","codes; concrete; reinforcement; shear; torsion","en","conference paper","American Concrete Institute","","","","","Accepted Author Manuscript","","","","","Concrete Structures","","",""
"uuid:e80be72f-3d9f-4838-9852-dcacc5763a7a","http://resolver.tudelft.nl/uuid:e80be72f-3d9f-4838-9852-dcacc5763a7a","Torsion Design Example: Inverted Tee Bent Cap","Granda Valencia, Camilo (University of British Columbia); Lantsoght, E.O.L. (TU Delft Concrete Structures; Universidad San Francisco de Quito; Adstren)","Lantsoght, Eva (editor); Greene, Gary (editor); Belarbi, Abdeldjelil (editor)","2020","This paper provides a practical example of the torsion design of an inverted tee bent cap of a three-span bridge. A full torsional design following the guidelines of the ACI 318-19 building code is carried out and the results are compared with the outcomes from CSA-A23.3-04, AASHTO-LRFD-17, and EN 1992-1-1:2004 codes. Then, a summary of the detailing of the cross-section considering the reinforcement requirements is presented. The objective of this paper is to illustrate the application of ACI 318-19 when designing a structural element subjected to large torsional moments.","bridge; codes; concrete; design; inverted tee bent cap; reinforcement; shear; torsion","en","conference paper","American Concrete Institute","","","","","Accepted Author Manuscript","","","","","Concrete Structures","","",""
"uuid:e06bd615-7fc4-481b-a334-37627f142e3d","http://resolver.tudelft.nl/uuid:e06bd615-7fc4-481b-a334-37627f142e3d","Autogenous shrinkage of early age cement paste and mortar","Lu, T. (TU Delft Materials and Environment)","van Breugel, K. (promotor); Delft University of Technology (degree granting institution)","2019","Concrete is a brittle composite material that easily fractures under tension. Due to the fact that the early-age deformation of the concrete member is restrained by adjoining structures, cracking can occur throughout the concrete prior to application of any load. The cracks would provide preferential access for aggressive agents penetrating in the concrete and then cause corrosion of reinforcement and degradation of concrete. As a result, the service life of concrete structure would be decreased. There are many different types of early-age deformation of concrete, e.g. temperature induced strain, drying shrinkage and autogenous shrinkage. Among these types of early-age deformation, autogenous shrinkage is a consequence of the self-desiccation during the cement hydration process. For a long time autogenous shrinkage was considered negligible compared with drying shrinkage. In recent years, autogenous shrinkage has drawn more and more attention due to the increasing use of concretes with low water-binder ratios. Despite the fact that phenomenon of autogenous shrinkage has been recognized for several decades, the mechanism behind it is still not fully understood and no consensus has yet been reached. Three is a general agreement about the existence of a relationship between autogenous deformation and relative humidity change in the capillary pores of the hardening cement paste. Many simulation models were built based on this relationship to predict the development of autogenous shrinkage. The reliability of these predictions, however, is not always satisfactory. The discrepancy between the measured and calculated autogenous deformation becomes very pronounced at later ages. In those simulation models, cement paste was considered as an elastic material and only the elastic part of autogenous shrinkage was predicted. In fact, cement paste is not ideal elastic material. When a cement paste is subjected to a sustained load, it will deform elastically and continue to deform further with time, which process is known as creep. Creep plays an important role in autogenous shrinkage of hydrating cement paste. The ignorance of creep would lead to an underestimation of the autogenous shrinkage. The aim of this project is to study the autogenous shrinkage of Portland cement pastes and blended pastes with supplementary materials. The autogenous shrinkage is supposed to consist of two parts, elastic part and time-dependent part (creep), which are simulated separately. Based on the autogenous shrinkage of cement pastes, autogenous shrinkage of cement mortars and concretes were simulated by taking the restraining effect of rigid sand/aggregate particles into consideration.","autogenous shrinkage; capillary tension; creep; silica fume; fly ash; blast furnace slag; cement paste; cement mortar; concrete","en","doctoral thesis","","978-94-6384-040-8","","","","","","","","","Materials and Environment","","",""
"uuid:1607467e-1df5-407f-853c-69eda1339043","http://resolver.tudelft.nl/uuid:1607467e-1df5-407f-853c-69eda1339043","Life Cycle Assessment of 3D Printing Geo-polymer Concrete: An Ex-ante Study","Yao, Yue (Universiteit Leiden); Hu, Mingming (Universiteit Leiden; Chongqing University); Di Maio, F. (TU Delft Resources & Recycling); Cucurachi, Stefano (Universiteit Leiden)","","2019","Three-dimensional (3D) printing and geo-polymers are two environmentally oriented innovations in concrete manufacturing. The 3D printing of concrete components aims to reduce raw material consumption and waste generation. Geo-polymer is being developed to replace ordinary Portland cement and reduce the carbon footprint of the binder in the concrete. The environmental performance of the combined use of the two innovations is evaluated through an ex-ante life cycle assessment (LCA). First, an attributional LCA was implemented, using data collected from the manufacturer to identify the hotspots for environmental improvements. Then, scaled-up scenarios were built in collaboration with the company stakeholder. These scenarios were compared with the existing production system to understand the potential advantages/disadvantages of the innovative system and to identify the potential directions for improvement. The results indicate that 3D printing can potentially lead to waste reduction. However, depending on its recipe, geo-polymer likely has higher environmental impacts than ordinary concrete. The ex-ante LCA suggests that after step-by-step improvements in the production and transportation of raw materials, 3D printing geo-polymer concrete is able to reduce the carbon footprint of concrete components, while it does still perform worse on impact categories, such as depletion of abiotic resources and stratospheric ozone depletion. We found that the most effective way to lower the environmental impacts of 3D concrete is to reduce silicate in the recipe of the geo-polymer. This approach is, however, challenging to realize by the company due to the locked-in effect of the previous innovation investment. The case study shows that to support technological innovation ex-ante LCA has to be implemented as early as possible in innovation to allow for maintaining technical flexibility and improving on the identified hotspots.","3D printing; concrete; emerging technologies; ex-ante LCA; geo-polymer; industrial ecology","en","journal article","","","","","","","","","","","Resources & Recycling","","",""
"uuid:dc6c5aad-5a4a-4286-bec6-46f8c929f28d","http://resolver.tudelft.nl/uuid:dc6c5aad-5a4a-4286-bec6-46f8c929f28d","Micromechanical modeling of tension stiffening in FRP-strengthened concrete elements","Ghiassi, B. (TU Delft Materials and Environment); Soltani, Masoud (Tarbiat Modares University); Rahnamaye Sepehr, Sara (Tarbiat Modares University)","","2018","This article presents a micromodeling computational framework for simulating the tensile response and tension-stiffening behavior of fiber reinforced polymer–strengthened reinforced concrete elements. The total response of strengthened elements is computed based on the local stress transfer mechanisms at the crack plane including concrete bridging stress, reinforcing bars stress, FRP stress, and the bond stresses at the bars-to-concrete and fiber reinforced polymer-to-concrete interfaces. The developed model provides the possibility of calculating the average response of fiber reinforced polymer, reinforcing bars, and concrete as well as the crack spacing and crack widths. The model, after validation with experimental results, is used for a systematic parameter study and development of micromechanics-based relations for calculating the crack spacing, fiber reinforced polymer critical ratio, debonding strength, and effective bond length. Constitutive models are also proposed for concrete tension stiffening and average response of steel reinforcing bars in fiber reinforced polymer–strengthened members as the main inputs of smeared crack modeling approaches.","concrete; Fiber reinforced polymer; local stress field approach; micromechanics; smeared crack; tension stiffening","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:9ab8bdfd-63ef-4ab4-b88a-56ec30470851","http://resolver.tudelft.nl/uuid:9ab8bdfd-63ef-4ab4-b88a-56ec30470851","Modelling the mechanical response of adobe components under uniaxial loadings","li Piani, T. (TU Delft Applied Mechanics; TNO; Netherlands Defence Academy); Weerheijm, J. (TU Delft Applied Mechanics; TNO); Koene, L. (Netherlands Defence Academy); Sluys, Lambertus J. (TU Delft Materials- Mechanics- Management & Design)","","2018","This paper presents a constitutive relationship to describe the uniaxial response in statics of brick and mortar samples of Adobe. This defines a traditional masonry whose components are made of soil mixture reinforced with fibres. Only recently Adobe has started attracting scientific attention, primarily as a consequence of the dramatic failures these structures have suffered in regions prone to earthquakes due to dynamic loadings. Furthermore, it possesses eco-friendly material properties which are attractive features for western countries forced to reduce the environmental impact of modern building industry. Nevertheless, the mechanical properties of Adobe are still largely neglected, especially with regards to the influence of soil mixture components. The study of the structural performance of masonry starts from the assessment of the material performance of its components. Thus, an extensive characterization campaign was organized and performed by Delft University of Technology and the Military Engineering Laboratory of the Netherlands, in order to characterize the material properties of Adobe components. Three types of bricks and one type of mortar, made with different mixture components proportions, were subjected to granulometry, moisture content, density tests and uniaxial compressive and three point bending tests. Predictive formulations for compressive and tensile strength and deformation values have been proposed by the authors [1]. These relations include the dependency of mixture components and moisture contents. In this paper, constitutive laws are developed for Adobe in pure compression and tension according to the experimental results. In compression, the force-displacement curves were interpolated according to several existing constitutive laws and the model originally developed by Priestley for concrete masonry elements was finally selected as best fitting. Despite the differences in terms of mechanical parameters, the analytical assessment revealed that the experimental force-displacement graphs of all the different types of bricks could be interpolated using the same model with the same calibrating values. Furthermore, the uniaxial response in tension was derived according to an inverse approach. A numerical model recently developed and calibrated with respect to the compressive and bending tests was used to simulate uniaxial tensile tests [2]. Also in this case, a common trend among types was observed. The results of the constitutive modelling frames components of Adobe within the class of quasi brittle (geo)materials, with particular reference to concrete-like materials. This paper presents the experimental results of the tested samples and the related analytical and numerical modelling.","Adobe; brick; mortar; Priestley; tension; compression; Adobe delta model; concrete; quasi brittle","en","abstract","","","","","","","","","","Materials- Mechanics- Management & Design","Applied Mechanics","","",""
"uuid:2113768d-6b00-4b13-91f0-d338dac9e47a","http://resolver.tudelft.nl/uuid:2113768d-6b00-4b13-91f0-d338dac9e47a","Fly ash from coal and biomass for use in concrete: Origin, properties and performance","Saraber, A.J. (TU Delft Materials and Environment)","van Breugel, K. (promotor); Jonkers, H.M. (copromotor); Delft University of Technology (degree granting institution)","2017","Coal fly ash is widely used in as raw material in concrete industry because it can replace part of the cement and fly ash contributes to improve certain properties of concrete. As a way to reduce the contribution of coal fired power plants to the climate change, more and more coal is replaced by biomass. To keep fly ash as a valuable resource for concrete it is essential to create thorough understanding of the relation between the compositions of co-fired biomass, the combustion process, the properties of fly ash and concrete made with it. Fly ashes derived from co-combustion teste on both pilot-scale and real-scale were characterized physically, chemically and mineralogically. Further, the properties of cement paste, mortar and concrete made with these fly ashes were determined. The chemical composition of the fly ash is influenced due to co-combustion of biomass. Especially the content of the elements Ca, Mg, K and P increases when biomass from vegetable or animal origin is co-fired. The influence of biomass from industrial origin varied from type to type. It was possible to identify the aimed relation in the case of co-biomass from vegetable and animal origin. However, this was not always the case with biomass from industrial origin. Finally, the application of fly ashes from co-combustion is assessed from the point of view of a circular economy (technical and biological cycle).","fly ash; co-combustion; concrete; biomass; wood ash","en","doctoral thesis","","978-94-6186-867-1","","","","","","","","","Materials and Environment","","",""
"uuid:5b78d71b-708f-405f-b3b3-ca664b141ce0","http://resolver.tudelft.nl/uuid:5b78d71b-708f-405f-b3b3-ca664b141ce0","The spalling mechanism of fire exposed concrete","Lottman, B.B.G. (TU Delft Steel & Composite Structures)","Walraven, J.C. (promotor); Koenders, E.A.B. (promotor); Delft University of Technology (degree granting institution)","2017","The spalling damage observed to concrete structures after severe fire exposure has been the topic of scientific research for the past decades. This phenomenon is commonly characterised by the sudden and in some cases violent breaking off of concrete pieces from the cross-section. In this thesis the derivation and the numerical results of a finite element based model are presented, using a coupled pore pressure and fracture mechanics approach. The crack patterns obtained are found to be sufficient to reduce the pore pressure to a level representing only a minor contribution. The fracture behaviour during severe fire exposure also revealed that the continued compression of the heated surface layer promotes the formation of thermal instabilities. Based on simulated results, observations from full-scale tests and a conceptual model, a philosophy is argued proposing thermal buckling as the spalling mechanism of fire exposed concrete. --- NEDERLANDSE VERSIE --- De na een ernstige brand waargenomen spatschade aan betonnen constructies is het onderwerp van wetenschappelijk onderzoek in de afgelopen decennia geweest. Dit fenomeen kenmerkt zich algemeen door het plotseling en in sommige gevallen heftige afbreken van betonnen stukken van de doorsnede. In dit proefschrift worden de afleiding en de numerieke resultaten van een op de eindige elementen gebaseerd model gepresenteerd dat gebruik maakt van een gekoppelde benadering tussen de poriëndruk en de breukmechanica. De verkregen scheurpatronen blijken voldoende te zijn om de gasdruk te reduceren tot een niveau hetgeen alleen een geringe toevoeging vertegenwoordigd. Het scheurgedrag gedurende brandbelasting onthulde ook dat de zich continuerende samendrukking van de verhitte oppervlaktelaag de vorming van thermische instabiliteiten bevordert. Gebaseerd op simulatieresultaten, waarnemingen tijdens grootschalige testen en een conceptueel model wordt een filosofie verdedigd die thermische knik voorstelt als het spatmechanisme van aan brand blootgesteld beton.","concrete; fire; (explosive) spalling; pore pressure; fracture mechanics; finite element method; thermal buckling mechanism","en","doctoral thesis","","978-94-028-0623-6","","","","","","","","","Steel & Composite Structures","","",""
"uuid:a2f8bcc8-d524-45eb-91e6-ff9e05c930d6","http://resolver.tudelft.nl/uuid:a2f8bcc8-d524-45eb-91e6-ff9e05c930d6","Determination of Chloride Content in Cementitious Materials: From Fundamental Aspects to Application of Ag/AgCl Chloride Sensors","Pargar, F. (TU Delft Materials and Environment); Koleva, D.A. (TU Delft Materials and Environment); van Breugel, K. (TU Delft Materials and Environment)","","2017","This paper reports on the advantages and drawbacks of available test methods for the determination of chloride content in cementitious materials in general, and the application of Ag/AgCl chloride sensors in particular. The main factors that affect the reliability of a chloride sensor are presented. The thermodynamic behaviour of silver in the presence or absence of chloride ions is described and kinetic restrictions are addressed. The parameters that can affect the activity of chloride ions in the medium and/or the rate of ion exchange and dissolution/precipitation processes at the sensor’s surface are also considered. In this regard, the contribution of morphology and microstructure of the AgCl layer, binding of chloride ions and the compactness of hydration products around the chloride sensor are highlighted. The important parameters for a reliable sensor’s response are discussed and the possible causes of inaccuracies are evaluated","Ag/AgCl electrode; cement; concrete; chloride sensor; OA-Fund TU Delft","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:6f7b7c39-fff0-4011-aa3b-808180e0cfc0","http://resolver.tudelft.nl/uuid:6f7b7c39-fff0-4011-aa3b-808180e0cfc0","Polarization Behaviour of Silver in Model Solutions","Pargar, F. (TU Delft Materials and Environment); Koleva, D.A. (TU Delft Materials and Environment)","","2017","When studying chloride-induced corrosion in reinforced concrete structures, essential information of interest is the concentration of chloride ions in the system. The absence of a reliable method for monitoring the free chloride ions justifies the attempts towards establishing a feasible practice in the application of the already known Ag/AgCl electrode, as a chloride sensor. To identify the governing mechanism and cognition of causes for instability of the chloride sensors in highly alkaline medium (as concrete), it is necessary to study the polarization behaviour of silver in different aqueous solutions resembling the concrete environment. Following expectations and well-known fundamental background, the results from this work confirm that in the presence of chloride ions, silver chloride is the predominant reaction product, forming on the silver surface. Whereas, in the absence of chloride ions and/or presence of interfering ions, such as hydroxide ions, the oxidation process of AgCl formation is significantly dependent on the chloride concentration in the medium. Therefore, the formation of a stable AgCl layer on a Ag substrate (as would be required for sensors application for example) is a function of the presence and amount of interfering ions, together with the chloride concentration in the medium.","Ag/AgCl electrode; chloride sensor; concrete; potentiodynamic polarization; alkaline solution","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:28a5bb7f-ee5b-4961-a0dc-2b70d7ebbe88","http://resolver.tudelft.nl/uuid:28a5bb7f-ee5b-4961-a0dc-2b70d7ebbe88","Convective Concrete: Additive Manufacturing to facilitate activation of thermal mass","de Witte, D. (TU Delft Design of Constrution); de Klijn-Chevalerias, M.L. (Eindhoven University of Technology); Loonen, R.C.G.M. (Eindhoven University of Technology); Hensen, J.L.M. (Eindhoven University of Technology); Knaack, U. (TU Delft Design of Constrution); Zimmermann, G. (G.techz engineering GmbH)","","2017","This paper reports on the research-driven design process of an innovative thermal mass concept: Convective Concrete. The goal is to improve building energy efficiency and comfort levels by addressing some of the shortcomings of conventional building slabs with high thermal storage capacity. Such heavyweight constructions tend to have a slow response time and do not make effective use of the available thermal mass. Convective Concrete explores new ways of making more intelligent use of thermal mass in buildings. To accomplish this on-demand charging of thermal mass, a network of ducts and fans is embedded in the concrete wall element. This is done by developing customized formwork elements in combination with advanced concrete mixtures. To achieve an efficient airflow rate, the embedded lost formwork and the concrete itself function like a lung. The convection takes place with separate pipes on both sides of the concrete’s core to increase the charge/discharge of the thermal storage process. The first stage of the research, described in this paper, is to simulate the Convective Concrete at the component level, whereupon a mock-up is tested in a climate test set-up. The paper concludes with describing planned activities for turning this concept into a real building product.","concrete; thermal mass activation; computational design support; Additive Manufacturing; advanced formwork; Optimization; heat exchange; heat storage","en","journal article","","","","","","","","","","","Design of Constrution","","",""
"uuid:af8e4836-e0c0-4b26-9f61-cee2c705a1e5","http://resolver.tudelft.nl/uuid:af8e4836-e0c0-4b26-9f61-cee2c705a1e5","Simulation-Aided Design of Tubular Polymeric Capsules for Self-Healing Concrete","Šavija, B. (TU Delft Materials and Environment); Feiteira, J. (Universiteit Gent); Araújo, M. (Universiteit Gent); Chatrabhuti, S. (Université de Mons); Raquez, JM (Université de Mons); van Tittelboom, K (Universiteit Gent); Gruyaert, Elke (Universiteit Gent); de Belie, N (Universiteit Gent); Schlangen, E. (TU Delft Materials and Environment)","","2017","Polymeric capsules can have an advantage over glass capsules used up to now as proof-of-concept carriers in self-healing concrete. They allow easier processing and afford the possibility to fine tune their mechanical properties. Out of the multiple requirements for capsules used in this context, the capability of rupturing when crossed by a crack in concrete of a typical size is one of the most relevant, as without it no healing agent is released into the crack. This study assessed the fitness of five types of polymeric capsules to fulfill this requirement by using a numerical model to screen the best performing ones and verifying their fitness with experimental methods. Capsules made of a specific type of poly(methyl methacrylate) (PMMA) were considered fit for the intended application, rupturing at average crack sizes of 69 and 128 m, respectively for a wall thickness of ~0.3 and ~0.7 mm. Thicker walls were considered unfit, as they ruptured for crack sizes much higher than 100 m. Other types of PMMA used and polylactic acid were equally unfit for the same reason. There was overall good fitting between model output and experimental results and an elongation at break of 1.5% is recommended regarding polymers for this application.","polymers; capsules; self-healing; concrete; cracks; simulation","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:165a98cf-7d74-42bf-9fd7-ef7782829eb0","http://resolver.tudelft.nl/uuid:165a98cf-7d74-42bf-9fd7-ef7782829eb0","Societal Burden and Engineering Challenges of Ageing Infrastructure","van Breugel, K. (TU Delft Materials and Environment)","","2017","Ageing is an inherent feature of nature and, hence, of materials, structures and systems. Yet, it seems a rather new topic in both science and engineering. The main reason for increasing attention for ageing as a topic is the growing awareness that, particularly in industrialized countries, ageing of our assets is a financial burden for the society. It touches our environment and a country's economy. It affects the overall sustainability of our planet and deserves, therefore, our utmost attention. In this contribution the urgency and challenges of ageing of concrete structures are addressed. Recent estimates of the extent of the issue and how ageing problems are dealt with in different disciplines, reactive or pro-active, are mentioned. The complexity of ageing problems will be evaluated by looking in more detail to the evolution in concrete mix design and the consequences thereof for the long-term performance of concrete structures. In this evaluation different kinds of driving forces contributing to ageing will be identified. Emphasis will be on ageing of concrete infrastructure and the need of research on ageing phenomena will be addressed.","ageing; concrete; infrastructure; research investment; risks; societal impact","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:efb45c8d-e8a2-4840-8aa5-a6fd5f4999f0","http://resolver.tudelft.nl/uuid:efb45c8d-e8a2-4840-8aa5-a6fd5f4999f0","Toward Bio-based geo- & Civil Engineering for a Sustainable Society","Jonkers, H.M. (TU Delft Materials and Environment)","","2017","The since 2010 running research program 'Bio-Based Geo & Civil Engineering for a Sustainable Society (BioGeoCivil)', funded by the Dutch technology foundation STW, aims to develop novel bio-based construction materials that can be used in Civil- and Geo-engineering constructions to enhance the sustainability performance of the sector. Rationale is that the sector produces still today excess amounts of waste in all life cycle phases of a construction, from building to use phase as well as end-of-life phase. Aim of the program is to mimic nature as 'building' processes in nature do not produce any waste as all elements, also residual material. is considered a high grade resource. In order to substantially improve the sustainability profile of the sector, upgrading of secondary- or byproducts must be achieved to allow functional performance similar to primary materials and resources. The challenge of the six currently running projects within the BioGeoCivil program is therefore not only to mimic nature but also to include bio-based materials or processes in civil- or geo-engineering applications which result, in comparison to traditional building products, in drastically improved performance both on sustainability and durability level. The six projects comprise: 1. Fungal biofilms (coating) for wood protection, 2. Bacteria-based repair and performance improvements of aged concrete structures, 3. Bacteria-based ground stabilization to mitigate liquefaction and piping of granular sediments, 4. Engineering of bacterial biofilms on buildings and infrastructure as a basis for natural protection, 5. Lift up Lowlands: upgrading of natural materials (bio-remediation of sludge) for sustainable lift up of low lying polder areas, and 6. Towards the development of carbon dioxide neutral renewable cement.","Bio-based processes; cement; civil- and geo-engineering; concrete; soil","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:48997b72-4d2b-4b45-8919-a150bb1486df","http://resolver.tudelft.nl/uuid:48997b72-4d2b-4b45-8919-a150bb1486df","Autogeneous healing and chloride ingress in cracked concrete","Savija, B.; Schlangen, E.","","2016","An experimental study of the influence of autogeneous healing on chloride ingress in cracked concrete is presented. In the study, two concrete mixtures (a Portland cement mix and a blast furnace slag mix), two healing regimes (submerged and fog room regime), two cracking ages (14 and 28 days), and multiple crack widths are used as parameters. An adapted Rapid Chloride Migration testing procedure is used after the healing period to assess the effectiveness of healing. It was found that small bending-type (i.e. tapered) cracks can heal fully, and larger cracks partially under tested conditions. The obtained results provide a good starting point for further study of the influence of autogeneous or self-healing on concrete durability","concrete; cracking; autogeneous healing; durability; marine environment","en","journal article","Heron","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:c39c8ff0-ea30-4de4-9b53-d3ce9242625a","http://resolver.tudelft.nl/uuid:c39c8ff0-ea30-4de4-9b53-d3ce9242625a","Topology optimisation of a concrete floor slab guided by manufacturability constraints from a vacuumatic formwork","Magan, Christopher; Coenders, J.L. (TU Delft Steel & Composite Structures; White Lioness Technologies); Huijben, F (ABT); Nijsse, R. (TU Delft OLD Structural Design; TU Delft Steel & Composite Structures); van der Horst, A.Q.C. (TU Delft Integral Design & Management)","Kawaguchi, K. (editor); Ohsaki, M. (editor); Takeuchi, T. (editor)","2016","This paper presents a design for a topology-optimised concrete floor slab, of which the structural optimisation process is guided by manufacturability constraints from a vacuumatic formwork. Ihe design has been obtained using an open-source, tliree-dimensional topology optimisation algorithm. Traditional floor systems are cost-optimised but can have the disadvantage of being structirrally inefficient. Topology opthnisation allows for efficient material distribution, and thus a reduction in weight. Topology-optimised floors are typically regarded as being difficuft to produce, however, and cost too much to be considered in building designs. In order to reach a compromise between a low self-weight and low production costs, two features are included in the optimisation process. First, manlifacftirability is directly incorporated in the optimisation, rather than afterwards. Secondly, the highly malleable vacuumatic formwork system by Huijben [7] has been used as a premise. Its advantages may cause the formwork costs to be reduced considerably when producing floor slabs.","structural optimisation; topology optimisation; SIMP; vacuumatic formwork; concrete; floor slab","en","conference paper","IASS","","","","","","","","","","Steel & Composite Structures","","",""
"uuid:bc319492-0e12-41cf-a30c-fcfb2c79f6b4","http://resolver.tudelft.nl/uuid:bc319492-0e12-41cf-a30c-fcfb2c79f6b4","Defining loading criteria for proof loading of existing reinforced concrete bridges","Koekkoek, R.T. (TU Delft Steel & Composite Structures); Lantsoght, E.O.L. (TU Delft Steel & Composite Structures); Yang, Y. (TU Delft Steel & Composite Structures); Boer, A. de (Ministry of Infrastructure and the Environment); Hordijk, D.A. (TU Delft Steel & Composite Structures)","Beushausen, H. (editor)","2016","As the bridge stock in The Netherlands and Europe is ageing, various methods to analyse existing bridges are bemg studied. Proof loading of bridges is an option to study the capacity when crucial information about the structure is lacking. This information could be related to the material (for example, the effect of alkali-silica reaction on the structural capacity) as well as to the structiu-al system (for example, the effect of restraints at the supports or transverse redistribution capacity). When it is decided to proof load a bridge, the question arises which maximum load should be attained diuing the experiment to approve the capacity of tiie bridge, and which criteria, based on the measiurements during the test, would indicate that the proof loading needs to be aborted before reaching the maximum desired load (the so-called stop criteria). To defme the requked loading criteria, a review of the literature has been made, finite element models of existing viaducts have been made, and on tiiese viaducts, proof loading tests have been carried out. These bridges were heavily instrumented, with a goal of leaming as much as possible about the structural behaviour during proof loading. As a result of the analysis and experiments, recommendations are given for proof loading of bridges with respect to the required maximum load and the stop criteria. These recommendations are important, since they form the basis of a guideline for proof loading of existing concrete bridges that is under development in The Netherlands.","assessment; concrete; proof loadmg; viaduct","en","conference paper","","","","","","","","","","","Steel & Composite Structures","","",""
"uuid:9258fa96-7e6b-4815-8952-dafd51baf91a","http://resolver.tudelft.nl/uuid:9258fa96-7e6b-4815-8952-dafd51baf91a","The influence of moisture on the fracture behaviour of concrete loaded in dynamic tension","Vegt, I. (TU Delft Materials and Environment); Weerheijm, J. (TU Delft Applied Mechanics; TNO)","Saouma, V. (editor); Bolander, J. (editor); Landis, E. (editor)","2016","Dynamic tests demonstrate an extensive rate effect on the tensile strength as well as the post-peak behaviour beyond loading rates of about 50 GPa/s. One of the possible explanations for the observed rate effects on the fracture behaviour is enhanced resistance by moisture in the pores. To study the influence of the moisture content and pore structure on the rate dependency, different moisture contents and concrete types are used and tested at three loading rates. From the test results it is concluded that the moisture volume, porosity and pore structure play an important role for tensile strength as well as the fracture process. The NMR tests showed that the water in the capillary pores causes the strength increase and not the water in the gel-pores. From the analysis of the experimental results it is concluded that for loading rates < 50 GPa/s, the main cause for the observed strength increase is the viscous behaviour of concrete. For loading rates beyond 50 GPa/s, also rate effects due to limitations on crack propagation contribute to the observed strength increase for all moisture contents and concrete types. Concerning the post peak response for rates > 50 GPa/s, the additional resistance is due to additional micro cracking, the moisture in the capillary pores and the limited crack propagation velocity.","rate effects; concrete; tension; moisture; experiments; fracture characteristics","en","conference paper","","","","","","","","","","","Materials and Environment","","",""
"uuid:2f0756a1-6d6c-4186-8889-5c861d589eae","http://resolver.tudelft.nl/uuid:2f0756a1-6d6c-4186-8889-5c861d589eae","Uncracked joints in plain concrete pavements: causes, effects and possibilities of improvements","Pradena, M.A. (University of Concepcion); Houben, L.J.M. (TU Delft Pavement Engineering)","","2016","During the construction of Jointed Plain Concrete Pavements (JPCPs) in Chile, it was observed that joints remained uncracked. The objectives of this paper are to evaluate the effects of uncracked joints (UnCrJ) in JPCPs and to propose possible solutions or improvements to avoid or minimize this phenomenon. Considering low thermal amplitude as cause of UnCrJ, a rational-based, detailed and empirically validated model is used to predict UnCrJ and crack width. The modelled results are not only due to material changes but also to the location of the series of cracks in time in the JPCP system. The paper contributes with this rational approach, instead of an empirical-simplified one, to achieve the objectives. For the modelled conditions, the “as-built” slab length range is 8 m to 56 m instead of the 4 m designed one. Then, more curling, joint faulting, water infiltration in sealed joints and load transfer efficiency ≤ 70% are expected.
The alternative solutions proposed are associated to innovations as short joints spacing, unsealed joints and saw-cuts up to 50% thickness made with thin blade (≤ 3mm), which was verified with new field evidence provided in the article.","pavements; concrete; uncracked; joints; crack width","en","journal article","","","","","","","","","","","Pavement Engineering","","",""
"uuid:b256e5eb-37c9-47df-a6d2-48203a602bf1","http://resolver.tudelft.nl/uuid:b256e5eb-37c9-47df-a6d2-48203a602bf1","Lattice Modelling of the Onset of Concrete-Ice Abrasion","Ramos, N.; Shamsutdinova, G. (Norwegian University of Science and Technology (NTNU)); Hendriks, M.A.N. (TU Delft Applied Mechanics); Jacobsen, S. (Norwegian University of Science and Technology (NTNU))","Colombo, M. (editor); di Prisco, M. (editor)","2016","","Lattice Modelling; concrete; ice; abrasion","en","conference paper","Trans Tech Publications","","","","","","","","","","Applied Mechanics","","",""
"uuid:b4eecfcd-d2aa-4ff3-9301-520450f329a3","http://resolver.tudelft.nl/uuid:b4eecfcd-d2aa-4ff3-9301-520450f329a3","Reduction of water permeation through cracks in mortar by addition of bacteria based healing agent","Mors, R.M.; Jonkers, H.M.","","2015","","self-healing; concrete; bacteria; crack; permeability","en","conference paper","","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:9416ec6a-08a8-4782-89d3-07316e299bd5","http://resolver.tudelft.nl/uuid:9416ec6a-08a8-4782-89d3-07316e299bd5","How to measure path length?","Stroeven, P.","","2015","Path length measuring is a relevant engineering problem. Leonardo Da Vinci designed for the military appropriate equipment, the podometer, to do so. Modern equipment such as step meters and map meters are quite similar to Da Vinci?s design, despite geometrical statistical - stereological - methods based on theorems of Cauchy and Buffon that were potentially available for a long period of time for doing a better job. The theorems have moreover been applied earlier for the engineering purposes indicated in this paper. Even Saltikov?s reintroduction for quantitative image analysis purposes in 1945 was ignored. Gradually, the last half of a century, stereological methods became more popular in concrete technology. Nevertheless, the stereology-based global averaging operation required to make the step from materials technology to engineering properties is inherent to making errors, as the literature demonstrates. The methodological framework has been described in earlier papers by this author as to path length measurements in sections of cracked concrete and on X-ray images of steel fibre reinforced concrete (SFRC). By laying side by side in this paper the direct engineering approach (from Da Vinci to map meter) and the science (stereology)-based approaches, the profit in economy and reliability can nevertheless be stressed. Particularly the element of geometric averaging based on simple mathematical-statistical notions is highlighted, because the literature reflects still major violations to these scientific principles. Three-dimensional information in the indicated fields of materials engineering is also readily obtained, provided proper sampling is guaranteed.","concrete; fibres; cracks; podometer; map meter; Cauchy; Buffon; Saltikov; image analysis; geometric averaging","en","conference paper","Institute of Fundamental Technological Research PAS","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:612c1bca-3234-421b-bca9-09ca7533580a","http://resolver.tudelft.nl/uuid:612c1bca-3234-421b-bca9-09ca7533580a","Nonlinear structural analysis as an assessment tool for existing concrete structures","De Boer, A.; Hendriks, M.A.N.; Van der Veen, C.; Belletti, B.","","2015","","nonlinear analysis; concrete; assessment; re-examination; guideline","en","conference paper","IABSE","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:cc231be1-662c-4b1f-a1ca-8be22c0c4177","http://resolver.tudelft.nl/uuid:cc231be1-662c-4b1f-a1ca-8be22c0c4177","Double-curved precast concrete elements: Research into technical viability of the flexible mould method","Schipper, H.R.","Vambersky, J.N.J.A. (promotor); Van Breugel, K. (promotor)","2015","The production of precast, concrete elements with complex, double-curved geometry is expensive due to the high costcosts of the necessary moulds and the limited possibilities for mould reuse. Currently, CNC-milled foam moulds are the solution applied mostly in projects, offering good aesthetic performance, but also resulting in waste of material, relatively low production speed and fairly high costs per element. The flexible mould method aims to offer an economic alternative for this state of art technology by allowing repeated reuse of the same mould, and if necessary, reuse in adapted shape. A patent and literature review and comparison of state-of-art formwork methods reveals that, although the idea of a flexible formwork already dates from the mid-20th century, in building industry it has not yet found widespread application, and is still experimental to a large extent. In other industries, such as aerospace and automotive, flexible moulds are occasionally used for rapid prototyping purposes, mostly for the forming of thin metal sheets. The understanding of the flexible mould principle in terms of mechanics is still in development. In combination with concrete, the flexible mould has been industrially applied only on occasion. Deliberately imposed deformation of concrete after casting allows the use of only one single-sided flexible mould, but - being a method quite alien to normal precast concrete production - has hardly been investigated. Therefore, models are needed both for the flexible layer as well as it's use in combination with concrete. By analysing a number of architectural cases in terms of geometrical aspects, more information is gathered about building size, element thickness, curvature radius and number and type of elements. This information is used to define the type of shapes for which the flexible mould method would be suitable. Through the last 80 years, the shape of curved architecture has changed; whereas the early famous shell designers such as Isler and Torroja aimed for structurally optimized and material-efficient shapes, nowadays these shapes have mostly made place for free-form curves, in which parametric design or sculptural influences are leading. For larger projects, several hundreds to even thousands of uniquely curved elements are manufactured, varying in curvature radius in a range between 0.75 m and 45 m. Furthermore the contours and edge position can vary from element to element. Prediction of each element's edge position is non-trivial for the flexible mould method, especially not for elements with strong curvature. The deformation process can be described mathematically by analysing thecurvature parameters. An important and meaningful parameter is the Gaussian curvature. Depending on the change in Gaussian curvature, the imposed deformation of the mould surface and the concrete results in certain amounts of bending action (B) and in-plane surface stretching (S). Bending tensile strains in the still plastic concrete can be in the range of 25 to 50 for an element with 50 mm thickness, which is far more than the values normally encountered in concrete after casting. The application of in-plane shear deformation appears to be helpful to deform the mould from flat to double-curved. The exact positioning of the element edges can be determined from this in-plane shear deformation. The shape of the mould, in the present research, is controlled by a grid of actuators - extendible support points that follow the intended architectural shape. As mould surface, a thin rubber layer can be used, that, however, has to be supported by a material that is capable of carrying the weight of the concrete without visible deflection between the actuators. Various solutions are investigated for this support material, of which the strip mould offers the most accurate results and predictability. As said, the concrete in this method is deliberately deformed after casting in an open, single-sided mould. This requires control over both the fluidity and strain capacity of the fresh concrete: if the concrete is too fluid, it will flow out of the mould after deformation due to the slope of the mould, if it is already too stiff, cracks may occur. Various experiments are conducted to investigate the viability of the principle as well as the parameters that influence the risk of either flow or cracking. It appears that the use of a self-compacting concrete with thixotropic properties reduces both the risks: as a result of quick stabilisation after casting, the yield strength build-up will prevent flow once the mould is deformed and put at a certain slope. Thanks to it's plastic strain capacity, this type of concrete will be able to undergo the imposed deformation without cracking. An important measure to prevent this cracking is the curing of the concrete directly after casting and a deformation that takes place before initial setting time. Thin steel rebar, glass-fibre textiles or mixed fibres are all applicable as reinforcement, the latter two giving the best results. For the measurement of yield strength development of the concrete mixture before and after casting, various methods are investigated. Literature research and experiments demonstrate that, once the rheological behaviour of a mixture has been determined with a viscometer accompanied with slump (flow) tests, the correct moment of deformation of the flexible mould can later be determined from repeated slump (flow) tests with sufficient reliability. However, as soon as the mixture constituents will be adapted, new viscometer measurements have to be carried out again. The flexible mould method has been successfully tested on single- and double-curved precast concrete elements with a radius down to 1.50 m and an element thickness up to 50 mm. Until this moment, the maximum element size tested was approximately 2 x 1 m2, but larger elements are expected to be feasible. An integrated design-to-production process is required: due to the complex geometry and the impact of this geometry on all aspects of the manufacturing, all parties involved should cooperate to make the use of this method possible. Computational skills are needed to determine design parameters and control the manufacturing process. Several new questions were identified during the research, but at this moment, implementation of the flexible mould method in an industrial environment in cooperation with a concrete product manufacturer is the best way to determine the priorities for further research. From the full research it is concluded that the flexible mould method is viable for the production of double-curved concrete elements.","concrete; precast; double-curved; doubly curved; curved; panels; cladding; elements; rheology; thixotropy; complex geometry; architecture; structural engineering; building; fabrication; CNC; mould; mold; file-to-factory; production; gaussian curvature; panelisation; panelization; beton; dubbelgekromd; prefab; geprefabriceerd; architectuur","en","doctoral thesis","","","","","","","","2015-08-14","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:af86512f-af53-42df-ac2d-807559753621","http://resolver.tudelft.nl/uuid:af86512f-af53-42df-ac2d-807559753621","Kine-Mould: Manufacturing technology for curved architectural elements in concrete","Schipper, H.R.; Eigenraam, P.; Grünewald, S.; Soru, M.; Nap, P.; Van Overveld, B.; Vermeulen, J.","","2015","The production of architectural elements with complex geometry is challenging for concrete manufacturers. Computer-numerically-controlled (CNC) milled foam moulds have been applied frequently in the last decades, resulting in good aesthetical performance. However, still the costs are high and a large volume of waste is produced. This paper describes the first outcomes of an R&D project funded by STW, the Dutch Technology Foundation, that was executed in close cooperation with industry. The work aimed at offering a viable alternative technology for CNC-milling, reducing cost and material waste at the same time. By constructing a prototype of a flexible mould system, and evaluating its viability in the production environment of a concrete factory, conclusions could be drawn concerning its feasibility. The context for the R&D project was a real ongoing project at the start of the research - a subway station in London - for which double-curved cladding elements needed to be produced. This paper discusses the principles of the technology, the construction of the prototype and the performance evaluation and accuracy. Some of the more fundamental technical aspects of the technology are discussed in a second paper in this ISOFF conference.","concrete; precast; complex geometry; double-curved; architecture; flexible mould","en","conference paper","","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:650616c5-ff06-49b4-8db0-076df52a9ea1","http://resolver.tudelft.nl/uuid:650616c5-ff06-49b4-8db0-076df52a9ea1","Field application of self-healing concrete with natural fibres as linings for irrigation canals in Ecuador","Sierra Beltran, M.G.; Jonkers, H.M.; Mors, R.M.; Mera-Ortiz, W.","","2015","This paper describes the first field application of self-healing concrete with alkaliphilic spore-forming bacteria and reinforced with natural fibres. The application took place in the highlands in Ecuador in July 2014. The concrete was cast as linings for an irrigation canal that transports water from glaciers in the Andean mountains to agricultural fields. This canal has been used for over a century by the local farmers. Until not long ago the walls and bottom of the canals were simply made out of compressed soil without any concrete. The yield of the canal was therefore very low: about 70% of the water was lost due to evaporation and infiltration into the soil. In order to improve the functionality of the canal it was then decided to line it with concrete. Unfortunately within one year the concrete cracked so that water was now wasted through the cracks. Self-healing concrete reinforced with natural fibres was proposed as a solution to this problem. The use of fibres in concrete increases the tensile capacity of concrete and assures a controlled crack width. Abaca fibres were selected due to their mechanical properties and availability as they are a fibre indigenous to Ecuador. Additionally, Abaca fibres have already been studied as reinforcement for mortar to improve the structural behaviour of houses in Ecuador under seismic loads. The bacteria are included in the concrete in order to seal possible cracks. The mechanical properties of the concrete with fibres and bacteria were first evaluated in the laboratory by means of flexural and compression tests. The compressive strength fulfilled the requirements for the intended application in irrigation canals. The selfhealing capacity of the concrete with and without bacteria was studied by monitoring the crack-healing. The concrete was designed to favour the use of locally available materials and following mixing procedure that could be replicate by the local communities. The self-healing concrete was mixed and cast in-place. Following this successful application, new sites in Ecuador are being evaluated by the local authorities for more field applications of this material.","concrete; self-healing; bacteria; field application; natural fibres","en","conference paper","","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:e6664554-4169-4c24-91b9-6f3d911fa9bf","http://resolver.tudelft.nl/uuid:e6664554-4169-4c24-91b9-6f3d911fa9bf","Modelling the influence of cracking and healing on modal properties of concrete beams","Savija, B.; Schlangen, E.","","2015","Concrete structures are commonly cracked when in service. To overcome issues arising from cracking, self-healing concrete is being developed. Together with the development of the material, techniques to verify and quantify self-healing are being developed. A number of destructive techniques have been used in the past. It would be beneficial to use non-destructive testing for continuous monitoring of self-healing. It is well known that cracking causes changes in natural frequencies of structural elements. A change in natural frequencies can be, therefore, used as an indication of damage. Consequently, the recovery of natural frequencies can be used as an indication of healing. In this work, a model which enables calculation of mode shapes and natural frequencies is presented. First, it is shown that the proposed 2D model can reasonably mimic modal behavior of thin structures under different boundary conditions [6]. It is then used to assess the influence of cracking and healing on the change of modal properties of concrete beams. Finally, based on the modelling results, conclusions are drawn.","concrete; modelling; modal analysis; lattice model; self-healing","en","conference paper","","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:41987a91-1726-495e-b024-2e204567d75e","http://resolver.tudelft.nl/uuid:41987a91-1726-495e-b024-2e204567d75e","ESEM-BSE coupled with rapid nano-scratching for micro-physicochemical analysis of marine exposed concrete","Palin, D.; Thijssen, A.; Wiktor, V.; Jonkers, H.M.; Schlangen, H.E.J.G.","","2015","Ordinary Portland cement (OPC) mortar specimens submerged in sea-water were analysed through environmental scanning electron microscopy (ESEM) in back scattered electron (BSE) mode and nano-scratching. Results from both sets of analysis show the presence of distinct phases associated with aragonite, brucite and cement paste. Phases associated with porosity and aggregates were also distinguishable through the BSE analysis and less defined in the nano-scratch data. This study indicates the powerful nature of coupling BSE image analysis with nano-scratching to obtain information on the quality of concrete. Work is underway to improve the method in order to apply it for better understand on the micro-physicochemical properties of marine exposed concrete.","marine environment; concrete; ESEM-BSE; nano-scratches; micro-physicochemical","en","conference paper","Delft University of Technology","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:b92471c4-2a8e-4643-9c59-0bca35957025","http://resolver.tudelft.nl/uuid:b92471c4-2a8e-4643-9c59-0bca35957025","The ITZ in concrete with natural and recycled aggregates: Study of microstructures based on image and SEM analysis","Bonifazi, G.; Capobianco, G.; Serranti, S.; Eggimann, M.; Wagner, E.; Di Maio, F.; Lotfi, S.","","2015","Aim of this work was to investigate the microstructure of the Interfacial Transition Zone (ITZ) between cement paste and aggregate in concrete utilizing Scanning Electron Microscope (SEM) in order to identify possible effects on the ITZ related to different recipes and production parameters. SEM is an important tool to carry out concrete, cement and aggregate microstructure characterization. SEM imaging facilitates identification of elements in concrete. Thanks to the higher spatial resolution, and the analytical capabilities, it allows to perform a materials-imaging-related analysis. Many information can thus be extracted from these data, such as composition, phase abundance and distribution. In particular, during the last years, backscattered electron imaging of polished surfaces became an important method for the study of cement and concrete microstructures. The technique has many advantages, as the possibility to visualize representative cross-sections over a wide range of magnifications and to correlate image contrast with materials composition (i.e. atomic number). Comparing the information acquired starting from SEM imaging and X-ray microanalysis, the complex microstructure of concrete can be analyzed and images with sub-micrometer definition acquired and processed, obtaining compositional, morphological and morphometric information allowing to understand and evaluate the mechanism affecting the interaction of the aggregates with the cement paste. A common image representative of the ITZ in concrete involves approximately a domain of about 30 ?m surrounding each aggregate and showing, theoretically, an increase of the porosity at the aggregate interface. In order to study this transition zone, 12 different types of concrete mixtures were analyzed, characterized by different combination of cement and virgin/recycled aggregates. The influence of these aggregates (i.e. virgin and recycled) on the resulting concrete microstructure was studied. The significant morphological and overall textural characteristics (i.e. area with higher porosity around aggregate, micro-cracks, size of the crystals in the ITZ) were detected by SEM analysis. Image analysis and SEM investigation, obtained from different concrete samples, provided very interesting results due to the different porosity and the possible interactions between the aggregates and the cement paste.","recycled aggregates; concrete; Interfacial Transition Zone (ITZ); SEM; image analysis","en","conference paper","Delft University of Technology","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:56daf2b5-05c9-46f9-9d83-d97333142385","http://resolver.tudelft.nl/uuid:56daf2b5-05c9-46f9-9d83-d97333142385","Assessment of the functionality of bacteria-based repair system for concrete through ESEM analysis","Wiktor, V.; Jonkers, H.M.","","2015","Biodeposition, a method by which calcium carbonate (CaCO3) precipitation is induced by bacteria, has been proposed as an interesting approach to protect building materials. The liquid-based system presented in this paper aims at the sealing of cracks and decrease of the porosity due to the production of a calcium-based biomineral. In this system, a silicate-based compound, which has a composition similar to concrete, is associated with Microbial Induced Precipitation (MIP), without involving urea hydrolysis pathway. Instead, the metabolic conversion of organic salts through bacterial respiration is used for MIP. The novelty of such system is to combine advantages of both, traditional repair system for concrete (fast reacting, and short term efficiency), and bio-based methods (more sustainable, slow process, and long-term efficiency). This paper presents how environmental scanning electron microscope (ESEM) has been used in the development of the bacteria-based repair system. It is a good evaluation technique to assess the functionality of the bacteria-based repair system and to evidence the involvement of bacteria in the mineral production. The functionality of the bacteria-based repair system has first been assessed in the repair system alone, and then after injection into porous concrete. These results bring more insight regarding the formation of the biomineral. Though the bacteria are active after 1 day, it requires longer time to indeed observe mineral formation. Several days are needed to bacteria to actively convert the feed and produce substantial amount of CO2, leading to favorable chemical environment for calcium carbonate precipitation. The results also showed how FTIR and ESEM analysis are complementary. Vaterite and calcite have been identified thank to FTIR while ESEM observation highlighted the unique features of the biomineral in size, shape and texture.","bacteria-based system; repair; concrete; biomineral; bacteria imprints","en","conference paper","Delft University of Technology","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:1207b07c-aa48-4992-9bbb-f972e1451a72","http://resolver.tudelft.nl/uuid:1207b07c-aa48-4992-9bbb-f972e1451a72","Microstructure Development and Transport Properties of Portland Cement-fly Ash Binary Systems: In view of service life predictions","Yu, Z.","Van Breugel, K. (promotor)","2015","Fly ash is a by-product of burning coal in electric power generating plants. It is commonly known that owing to its pozzolanic properties fly ash is widely used as a partial replacement for Portland cement in concrete. The use of fly ash in concrete not only reduces the landfill costs of fly ash, but also reduces the use of Portland cement in concrete, consequently reduces CO2 emission per ton concrete. More important, the presence of fly ash improves the durability of concrete and extends the service life of concrete structures. Today, there is a demand for concrete structures with a service life of 80, 100, or even 200 years. In many cases chloride-induced rebar corrosion is assumed to be the dominant mechanism determining the service life of reinforced concrete structures. It is commonly believed that fly ash concrete has a better resistance to chloride penetration than Portland cement concrete, since the microstructure development of Portland cement-fly ash binary systems is different from that of pure Portland cement system. The resistance of concrete to chloride penetration is highly related to their microstructure. The studies on Portland cement-fly ash binary systems (concrete or paste) have been carried out for many years. Most studies are based on experimental results at a relative short curing period (i.e. 3 months) or from different concrete mixtures with different fly ash and Portland cement. The advantage of using fly ash, however, becomes evident at later ages, i.e. beyond 90 days. Systematic long-term investigations on Portland cement-fly ash binary systems are still limited. In this thesis the research on these binary systems starts from the hydration process (chapter 3), the microstructure development (chapter 4) to transport properties (water permeability and chloride penetration) (chapter 5- chapter 8) in view of service life predictions of concrete structures made with fly ash-blended cements. In a fly ash cement paste there are two types of chemical reactions: hydration of cement and pozzolanic reaction of fly ash. The pozzolanic reaction of fly ash needs calcium hydroxide (CH), produced by the hydration of cement, to occur. The evolution of the amount of CH with time reflects the rate of hydration of cement and pozzolanic reaction of fly ash in binary systems. As discussed in chapter 3 at early ages, i.e. before 7 days, the CH content of blended cement paste was higher than that of Portland cement paste. It indicated that the presence of fly ash leaded to faster hydration of cement in binary systems. After about 7 days, the CH content in blended cement paste decreases significantly. It suggests that in binary systems the rate of the pozzolanic reaction of fly ash (consuming CH) is faster than that of the hydration of cement (producing CH). At later ages, i.e. beyond 180 days, the CH content in blended cement paste stays at a constant low level. It is inferred that beyond 180 days the rate of the pozzolanic reaction of fly ash in binary systems becomes very slow. The pozzolanic reaction of fly ash results in a different microstructure development of blended cement paste compared with pure Portland cement paste. In chapter 4 the evolution of the pore structure of Portland cement paste and blended cement paste was investigated at ages up to 3 years. The porosity of blended cement paste was higher than that of pure Portland cement paste, even at an age of 3 years. At later ages, i.e. after about 28 days, the presence of fly ash results in the formation of a large amount of small capillary pores in the range between 10 and 100 nm. At later ages, i.e. after 180 days, blended cement paste had a lower connectivity of the pores than Portland cement paste. The pore structure of blended cement paste was refined at later ages while the porosity of blended cement was still higher than that of Portland cement paste (at ages up to 3 years). The microstructure of paste determines the transport properties. In chapter 5 the water permeability of Portland cement paste and blended cement paste was studies. At early age the pastes containing fly ash exhibit a higher capillary porosity than pure Portland cement paste. The initial water permeability of blended cement paste is higher than that of Portland cement paste. However, after about 180 days blended cement paste is less permeable than pure Portland cement paste, even though the capillary porosity of blended cement paste is higher than that of Portland cement paste. The water permeability of pure cement paste and blended cement paste depends on the connectivity of the pores. At later ages, i.e. after 180 days, the connectivity of the pores of blended cement paste is lower than that of pure Portland cement paste, resulting in a less permeable microstructure. In chapter 6 the resistance of Portland cement concrete and fly ash concrete to chloride penetration was investigated. Under moist curing conditions the DRCM values of Portland cement concrete made with different w/c ratios (0.4, 0.5 and 0.6) decrease with time at early ages, i.e. from 28 to 180 days. After that the DRCM values of Portland cement concrete increase and then turn to decrease again after around 1 year (Figure 6.6). The possible reason might be the delayed ettringite formation in Portland concrete when limestone powder (as filler) is blended with Portland cement clinker and when it is cured under moist conditions (see chapter 7). The DEF results in a change of the microstructure of hydrated cement paste and an increase of DRCM at later ages. At ages beyond about 28 days the concrete mixtures made with fly ash have better resistance against chloride penetration than Portland cement concrete. Ettringite forms in fly ash concrete at later ages. This ettringite is found in voids initially present in the paste and in the spaces left after the reaction of fly ash particles. Formation of ettringite in empty spaces explains why DEF in fly ash concrete does not lead to expansion and micro-cracking and an associated increase of the DRCM values as observed for Portland cement concrete. Based on the measured DRCM values for Portland cement concrete and fly ash concrete, the ageing factor n was determined (see chapter 8). It represents how rapidly the chloride migration coefficient of the concrete decreases with time. In DuraCrete the 28 days values of DRCM and n are two important input parameters to predict the service life of concrete structures. An important question is whether new n-values, as those determined in this study, can directly be adopted in the currently used version of DuraCrete for service life predictions. In DuraCrete it is assumed that the chloride diffusion (migration) coefficient of concrete, D(t), decreases considerably with increasing age of the concrete. This decrease is quantified with a constant value of n. It means that D(t) would go to zero as time tends to infinity (t ? ?), which is known not to be realistic. In reality, the chloride diffusion coefficient D(t) is directly determined by the microstructure of concrete. In fact, the decrease of the diffusion coefficient cannot be described adequately with a constant value of n. A more accurate description of the evolution of the diffusion coefficient D(t) with an not constant value of n, however, will affect the consistency of the currently used version of DuraCrete. A reconsideration of n-values should be accompanied by reconsidering the values of other model parameters values (e.g. environmental factor ke and curing factor kc in DuraCrete), since these parameter, ke, kc and n, are mutually interdependent.","fly ash; concrete; microstructure development; ageing factor","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","Materials & Environment","","","",""
"uuid:310abf7c-73c7-4363-80f7-b92212030919","http://resolver.tudelft.nl/uuid:310abf7c-73c7-4363-80f7-b92212030919","Modelling dynamic tensile failure of quasi-brittle materials using stress-enhanced nonlocal models","Magalhaes Pereira, L.F.; Weerheijm, J.; Sluys, L.J.","","2015","The development of realistic numerical tools to efficiently model the response of concrete structures subjected to close-in detonations and high velocity impacts has been one of the major quests in defense research. Under these loading conditions, quasi-brittle materials undergo a multitude of failure (damage) mechanisms. Dynamic tensile failure (e.g. spalling), characterized by a significant strength increase associated with loading rate, has revealed to be particularly challenging to represent. This phenomenon has been modeled by means of continuous damage mechanics in the last decades. To minimize pathological mesh sensitivity, a nonlocal formulation is generally considered. Nevertheless, these models fail to properly represent damage initiation and growth around discontinuities, such as notches, damage areas and free boundaries. These inconsistencies are the consequence of using a fixed interaction domain (characteristic length) in the nonlocal formulation. In spite of limited experimental knowledge about the definition of the characteristic length parameter, there is now consensus that this quantity is not constant. In this contribution, an enhanced nonlocal model, where the interaction domain of any gauss point contracts or expands according to the stress-state of its neighbors, is used. This formulation was coupled to the well-known Mazars damage model and implemented within the framework of LS-DYNA using a fully explicit computation scheme. Two sets of numerical studies are presented in this paper. One shows the applicability and limitations of the implemented explicit algorithm to compute nonlocal quantities. The other shows that with this stress-enhanced regularization model it is possible to represent damage initiation and growth more realistically and correct the inconsistencies emerging from the traditional nonlocal formulations.","concrete; damage; nonlocal; erosion; tensile failure","en","conference paper","","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:b6dcf405-1591-4202-b744-f833cef4541d","http://resolver.tudelft.nl/uuid:b6dcf405-1591-4202-b744-f833cef4541d","Porous Network Concrete: A bio-inspired building component to make concrete structures self-healing","Sangadji, S.","Schlangen, E. (promotor)","2015","The high energy consumption, its corresponding emission of CO2 and financial losses due to premature failure are the pressing sustainability issues which must be tackled by the concrete infrastructure industry. Enhancement of concrete materials and durability of structures (designing new infrastructures for longer service life) is one solution to overcome the dilemma. Concrete is a quasi-brittle material with properties that are high in compression but weak in tension, therefor concrete is prone to cracking. In the case that a continuous network of cracks is formed, the permeability of concrete will increase and the reinforcement bars may be open to the ambient atmosphere. This opening provides easy means for aggressive substances to enter into concrete and reach rebars which may start to corrode. Further cracks may threaten the tightness of the retaining structures, e.g. liquid containing structures tank wall, aqueducts, underground spaces, tunnels, etc., which undergo tensile forces. In these cases cracks may facilitate the flow of fluid – liquid or gas – into and out of the structures which considerably alters its serviceability, leads to unhealthy environments within a structure, and diminishes its functionality. In case the container or reservoir contains waste, highly toxic materials or radioactive materials, leakage through the concrete is catastrophic and unacceptable. One promising concept to design new concrete structures to achieve higher durability is incorporating self-healing mechanisms that are found in nature into the cement-based materials or the concrete structural element. If unavoidable cracks due to inherent brittleness in concrete could be self-sealed/healed/repaired, concrete will certainly serve longer and be more durable and sustainable. In general, on attempting to solve engineering problems, one can (always) seek inspiration from biology (nature). Though, borrowing nature’s idea to enhance our living environment is as old as humankind, the post-industrial technical advent makes the process more systematic and deliberate, hence makes use of bio-mimicry to solve problems and inspire innovation. Observing the domain of biology, there are several wound healing mechanisms found in nature: cut skin and bone fracture healing in human and animal, and plant response to injury. The present work takes inspiration from studies on bones of present-day mammals and birds and its healing mechanism. Two of appropriate principles that might be constructive are identified; (1) bone morphology comprises of cortical (solid) bone and trabecular (spongious) bone and (2) a feedback loop process is present in the remodelling and healing process. These two principles formed the basis for the development of a healable concrete material and for a method for healing it with healing agents. The idea behind this is that cortical bone may be mimicked with solid concrete and trabecular bone may be imitated by porous concrete. The combination of the two types of concrete resembles Porous Network Concrete, a bone-like concrete able to self-heal by the mechanism of feedback loop. These are the points addressed in the chapter 1 which explores the success story of concrete in serving society and civilization for millennia, the present challenge to make modern concrete more durable, and the bio-inspired solution of self-healing concrete Porous Network Concrete (PNC) is a hybrid system in which high permeability porous concrete is embedded in the interior or exterior of normal dense concrete. The porous network core constitutes alternate means for [1] channelling temporary or permanent materials to form a dense layer in the later stage and [2] distributing healing agent from the point of injection to cracks in the concrete main body. In chapter 2 the concept of the PNC is elaborated by setting up criteria and realized by creating a fabrication procedure. The production process – the making of the PNC – follows the current standard for both of the main and porous part and seemingly there is no complicated fabrication procedure. PNC characterization was carried out to study its pore and mechanical properties. The autonomous healing mechanism in the PNC is designed by incorporating the feedback mechanism; once a certain crack width is sensed, an action to heal takes place. As a proof-of-concept, in chapter 3, a simple and intuitive approach to design a feedback system for PNC self-healing mechanism has been carried out. When a concrete structure receives loads and builds up internal stress, it deflects, cracks and deforms. Once the crack mouth opening reaches a certain prescribed value the healing agent is injected automatically. The proposed working principle is verified by mechanical and leakage (permeability, infiltration) testing. The solidification process of the self-healing agent is important and even critical for the success of the healing strategy and mechanism designed. Instead of developing new healing agent and investigating its behaviour, this present study aims to examine the effectiveness and efficiency of the healing process in the Porous Network Concrete with different classes of agents. Three groups of healing agents are then studied and its healing efficiency is tested by leakage and mechanical testing. The first type of agent is a single- and double-component chemical based which mostly works through poly-condensation or cross-link polymerization upon contact with the atmosphere, with the concrete matrix or within the reactants. In this case, epoxy resin is used. The second healing agent used is grout material made of a cementitious powder mix. Cementitious grout material can be thought of as healing agent for concrete structures since it functions as crack sealant and void filler with the objective to restore structural integrity. The use and healing performance of PNC by both healing agents is discussed in chapter 4. The third agent is bacteria-based repair solution. It contains alkaliphilic bacteria able to facilitate bio-mineralization, nutrients and transport solution. It was originally developed as a bio-based repair material for cracked concrete. This is discussed in the dedicated chapter 5. It has been demonstrated in this thesis that the Porous Network Concrete has a good prospect in making concrete structural elements self-healing. This is the concluding point presented in the final chapter. Some recommendations for improving the work are presented such as; modelling work, larger and realistic experimental campaign and improved damage sensing.","concrete; porous concrete; porous network concrete; self-healing concrete; biomimetic; bio-inspired engineering; closed-loop feedback; autonomous healing mechanism; autogeneous healing mechanism","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:25de2059-a967-4a8c-9e2c-bde02c9489ee","http://resolver.tudelft.nl/uuid:25de2059-a967-4a8c-9e2c-bde02c9489ee","Field performance of bacteria-based repair system: Pilot study in a parking garage","Wiktor, V.A.C.; Jonkers, H.M.","","2015","This paper presents the field performance in a parking garage of the recently developed bacteria-based repair system for concrete. This liquid-based repair system aims at the sealing of cracks and decrease of the porosity due to the production of a calcium-based biomineral. The system combines advantages of both a traditional repair system for concrete (fast reacting and short term efficiency), and bio-based methods (more sustainable, slow process, and long-term efficiency). The bacteria-based repair system has been sprayed onto the surface of cracks and on concrete pavement. The crack-sealing efficiency and improvement of frost salt scaling were assessed by water permeability and freeze/thaw resistance tests respectively. The results were very promising as only cracks that had not been treated with the bacteria-based repair system were still heavily leaking. In addition, the freeze/thaw resistance of concrete that was treated with the bio-based repair system was higher than the untreated concrete.","concrete; repair; bacteria-based system; crack","en","journal article","Elsevier","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:c8074c0f-7261-489d-8355-b923a2b6d50d","http://resolver.tudelft.nl/uuid:c8074c0f-7261-489d-8355-b923a2b6d50d","Autogenous shrinkage of HPC and ways to mitigate it","Van Breugel, K.; Van Tuan, N.","","2014","","shrinkage; concrete; microstructure; water/cement ratio; cracking; RHA; codes","en","conference paper","Trans Tech Publications Ltd","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:e848a933-4dc2-4976-bd51-2f9d69b441a6","http://resolver.tudelft.nl/uuid:e848a933-4dc2-4976-bd51-2f9d69b441a6","Application of acoustic emission measurements in the evaluation of prestressed cast in-between decks","Van Hemert, P.H.A.; Fennis-Huijben, S.A.A.M.; Hordijk, D.A.","","2014","A large number of concrete structures, that is built in the sixties and seventies of the twentieth century, need to be re-evaluated. It should be judged whether their capacity is still sufficient for the increased traffic loads. Acoustic emission (AE) is a non-destructive technique that can possibly be used to get a better insight in the structural state of these concrete structures. However, interpretation the AE measurements is challenging and is even more difficult when the concrete is cracked by for example alkali–silica reaction. Due to the existing cracks the wave attenuation affects the acoustic emission measurements. For an investigation into the capacity of pre-stressed cast in-between decks a 1:2 scale bridge was loaded in the Stevin laboratory of Delft University of Technology under two-way shear. In this preliminary research it was investigated whether AE-measurements can be used to get an idea about the structural condition of a structure, or more precise, to what extent the ultimate capacity is reached. For testing the concrete in-between decks a cyclic loading procedure is applied. It appeared that cyclic loading resulted in a lower capacity in comparison with the previously performed static loading experiments. There was no AE indication of early failure due to cyclic loading. Usually applied parameters, like ‘Kaiser Effect’ and ‘Calm Ratio’ are investigated. Furthermore, it was investigated whether the location of cracks could be determined by the emitted sound during the fracture process and applying a relatively large numbers of AE-sensors (so-called source location). In this article the performed AE measurements are reported and results discussed.","acoustic emission; concrete; in-between decks; (punching) shear and cyclic loading","en","conference paper","Engineering Technics Press","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:b0508df0-47f0-463c-96ac-b55c3426ce0b","http://resolver.tudelft.nl/uuid:b0508df0-47f0-463c-96ac-b55c3426ce0b","Innovations in concrete pavements for a sustainable infrastructure","Pradena, M.; Houben, L.J.M.","","2014","Concrete pavements (CPs) are durable and they do not need periodic invasive maintenance interventions. Nevertheless, CPs are hardly chosen when only initial costs, instead of life-cycle costs, are considered in the evaluation. Nowadays, there are innovations in Jointed Plain Concrete Pavements (JPCPs) that reduce initial costs about 25% with respect to alternatives with equivalent structural capacity. This paper addresses the question if the innovations early-entry saw-cutting of joints, joints without seals and shorter joint spacing (without dowels bars) are able to maintain the traditional life-cycle performance of CPs. All these innovations affect the joints of the JPCP, and these ones the JPCP performance. Accordingly, the objective of the present paper is to analyse the effects of the joints behaviour on the performance of the JPCPs innovations. The joint behaviour is characterized by the joint activation and opening, the joint capacity to transfer traffic loads and the joint deterioration. The calculations of the joints activation and opening are made with a model developed by the authors. For the estimation of the joint transfer capacity; the results of finite-element software are used. The analysis is completed with field data of the JPCPs innovations. The innovations analysed contribute to a sustainable infrastructure as they can maintain, and even improve, the traditional life-cycle performance of CPs with lower initial costs. Nevertheless, for the design hypotheses to be valid, it is necessary to assure the joints activation and to limit the joints opening to 1.2 mm. With this purpose, for the analysed conditions, it is recommended to cut the joints at least at 30% of the JPCP thickness.","innovations; concrete; pavements; sustainable","en","conference paper","City Net Scientific Research Center","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:c00c74f6-d138-4e7d-a284-9932df03c025","http://resolver.tudelft.nl/uuid:c00c74f6-d138-4e7d-a284-9932df03c025","Protection of aged concrete structures: Application of bio-based impregnation system","Wiktor, V.A.C.; Jonkers, H.M.","","2014","This paper focuses particularly on the ageing of concrete due to micro-crack formation or freeze/thaw which results in an increased permeability of the concrete. The bacteria-based repair system presented in this paper aims at recovering the concrete permeability thanks to bacteria-induced calcium carbonate precipitation inside cracks/porosity. The performance of the bacteria-based repair system in laboratory and field application were very promising. The laboratory results showed that the crack sealing capacity of the repair system is very good as the cracks were completely sealed after impregnation. Results from field application are also very good as treated concrete had a significant higher resistance to freeze/thaw and only cracks that were not impregnated with the bacteria-based repair system were still heavily leaking.","concrete; crack-repair; bio-based system; biodeposition","en","conference paper","DCMat Ageing Centre, Delft University of Technology","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:3273b5ee-bd17-4586-bba0-da5ee04a75c4","http://resolver.tudelft.nl/uuid:3273b5ee-bd17-4586-bba0-da5ee04a75c4","Shear Resistance of Reinforced Concrete Beams without Shear Reinforcement under Sustained Loading","Sarkhosh, R.","Walraven, J.C. (promotor); Den Uijl, J.A. (promotor)","2014","","shear; concrete; beam; time; sustained loading; long-term; crack; RC","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:02735288-ca84-451a-8e39-0f7a5f36fe32","http://resolver.tudelft.nl/uuid:02735288-ca84-451a-8e39-0f7a5f36fe32","Bio-inspired control of material properties in civil engineering: Current concept for corrsoion protection via the application of bacteria and bio-polymers","Koleva, D.A.; Jonkers, H.M.; van Breugel, K.","","2013","The improvement of material properties of cement-based materials e.g. reduced permeability, porosity, uniform distribution of hydration products, etc. is of a significant importance and related to durability and sustainability of concrete and reinforced concrete structures. With this respect, a recent and novel approach is to ""create"" self-healing systems that will be able to recover at leastpartly their originally designed performance. Bio-based cement-based materials were already proven to have the capacity of reduced crack width and permeability respectively as a result of bacterial activity in the cement matrix. New approaches, related to corrosion control for offshore structures, involve the application of bacterial, hydrogen consuming organisms, bio-polymers and nano-composite or sol-gel coating for increased service life and improved resistance to microbiological corrosion (MIC). The aper will briefly mention already established self-healing mechanism in ""bio-concrete"" and will resent the concept and approach of recently initiated research with respect to MIC corrosion control.","bio-corrosion; concrete; steel; bacteria; cathodic; bio-polymers","en","journal article","Journal of International Scientific Publications","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:1624342e-c059-45b7-9cb0-ecb45b479d14","http://resolver.tudelft.nl/uuid:1624342e-c059-45b7-9cb0-ecb45b479d14","The use of SCC and textile reinforcement","Schipper, H.R.; Grünewald, S.; Kok, M.A.D.; Nijsse, R.; Raghunath, P.","","2013","In an earlier article (CPI issue of August 2011 [1]) a method was presented for producing precast curved panels with a thickness of a few centimeters using the 'flexible mould method'. This method is the central theme in the PhD study of the first author on the realization of freeform architecture in concrete. The concrete panels manufactured with the flexible mould method can be applied for many architectural purposes in which curvature is present, such as facade cladding, precast plank floors or roof elements. The method essentially comprises a reusable and bendable smooth surface that can be deformed into a wide range of geometries, including variable curvatures in one or two directions and freely shaped edge contours. In the earlier article in CPI it was concluded that some aspects needed further research, among which were the choice of suitable concrete mixtures and the investigation of fibre reinforcement. This article discusses the results of experiments investigating these aspects: the mixture choice was guided by measuring the workability in time and the ability to undergo deformations after casting without cracking. Furthermore, AR-glass textile was used to strengthen the panels with a flexible reinforcement that allowed deformation in the non-hardened state. Experimental work has been done to check the position of the reinforcement after deformation and the contribution of the textiles to the strength of the panels.","concrete; precast; free-form; complex geometry; cladding; flexible mould; architecture; flexible mold; double-curved","en","journal article","Ad-media GmbH","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:b105c9a1-09d9-4aaf-8bc4-c26d85a1dd4c","http://resolver.tudelft.nl/uuid:b105c9a1-09d9-4aaf-8bc4-c26d85a1dd4c","Practical approach for production of bacteria-based agent-contained light weight aggregates to make concrete self-healing","Mors, R.M.; Jonkers, H.M.","","2013","A functional experimental concrete system has been developed in our lab, in which a two component bacteria-based healing agent contained in a protective reservoir is included in the concrete mixture. Incorporated bacteria have the potential to produce copious amounts of calcium carbonate based crystals from supplied mineral precursor compounds. Precipitates of the carbonate mineral seal and block occurring cracks. Particles of expanded clay, a type of light weight aggregate (LWA), were chosen as protective reservoir in which the bacteria and precursor compound are contained. Most effective method for intrusion of healing agent in LWA is by vacuum impregnation, a rather expensive process. In this work a more economically feasible in-situ approach is proposed, still gaining the required healing capacity. Prior to mixing LWA are pre-wetted with a warm liquid impregnation solution (80°C) carrying bacterial spores and mineral precursor compounds. This alternative production process is economical and practically more straightforward and functionally additionally beneficial as water-saturated LWA contribute to internal curing. Benefit of the novel approach is the reduced cost of healing agent production and improved practicality directly at a concrete plant, as commonly available equipment can be used. First tests indicate sufficient healing capacity remains after the wet mixing stage and internal drying by cement hydration.","self-healing; concrete; bacteria; agent; LWA","en","conference paper","Magnel Laboratory for Concrete Research","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:2062e452-beab-43da-9422-b162f3de142c","http://resolver.tudelft.nl/uuid:2062e452-beab-43da-9422-b162f3de142c","Interactive mathematical model of self-healing in carbonated cementitious materials","Zemskov, S.V.; Copuroglu, O.; Vermolen, F.J.","","2013","A mathematical model for the post-damage recovery of carbonated cement is described. The model is based on a two-dimensional initial-boundary value problem for a system of partial differential equations. The study is embedded within the framework of investigating the effect of using lightweight expanded clay aggregate, which is incorporated into the impregnation of the sodium monofluorophosphate (Na-MFP) solution. The model of the self-healing process is built under the assumption that the position of the carbonation front changes in time. Here the rate of diffusion of Na-MFP into the carbonated cement matrix and the reaction rates of the free phosphate and fluorophosphate with the components of the cement are comparable to the speed of the carbonation front. The main modeling results presented in the paper are related to the autonomous improvement of the structure of carbonated blast furnace slag cement. Nevertheless, the parameters of the model can be set for various types of cement paste and different conditions of the healing process (including both carbonation under natural conditions and accelerated carbonation). The governing diffusion-reaction equations are solved using a Galerkin finite-element method. For usage convenience, the model is completed as an interactive application on the basis of computer algebra system Mathematica.","numerical modeling; finite-element method; concrete; self-healing; carbonation","en","conference paper","Magnel Laboratory for Concrete Research","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Delft Institute of Applied Mathematics","","","",""
"uuid:dd41e46c-c101-4310-9069-614103eacd2d","http://resolver.tudelft.nl/uuid:dd41e46c-c101-4310-9069-614103eacd2d","Injecting a liquid bacteria-based repair system to make porous network conrete healed","Sangadji, S.; Wiktor, V.A.C.; Jonkers, H.M.; Schlangen, H.E.J.G.","","2013","Bacteria induced calcite precipitation has been proven to be effective in making concrete structure self-healing. In Microlab TU Delft, the concept has been enhanced by developing a liquid bacteria-based concrete repair system. The solution contains calcite precipitating bacteria, nutrients and buffer compound which may demonstrate high potential as healing agent to be injected into porous network concrete (PNC). This type of concrete has a porous core which can be used as a media to transport healing agents into the fracture zone. The concept was tested in the 55×55×285 mm PNC prisms with 23×23×285 mm porous concrete core in the interior. Ø2 mm threaded steel rebar was installed below the core. A crack was formed by three-point bending loading and the solution was injected through porous network until it reached and flew out through the crack opening. The bacteria then precipitated calcium carbonate blocking the crack. The healing efficiency was measured by water permeability test before and after injection at several time intervals. Second cycle mechanical loading was carried out to assess regain of mechanical properties. Eventually, calcite precipitation in the crack wall was examined by polished section with ESEM. Preliminary results showed more than 90% permeability reduction has been achieved at 11 days which appeared to be temporary since after 19 days permeability reduction drop to 70%.This could be attributed to the flushing of the solution after 11 days as the process could be not yet complete. However, bacteria imprints obtained from ESEM observation of polished section of Ø26-30 mm cylindrical porous core 21 days after injection with the solution provided strong evidence of bacterial activity and confirm the previous observation. The on-going research program has been devised implementing tap water and bacteria-based solution injected specimens with wet and dry curing. The results showed that wet cured bacteria series exhibited 99% permeability reduction while dry cured specimen only shows 60% reduction.","porous network concrete; self-healing; concrete; liquid bacteria-based repair system","en","conference paper","Magnel Laboratory for Concrete Research","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:feee94db-aecb-446b-a1d4-1a09c464bd7a","http://resolver.tudelft.nl/uuid:feee94db-aecb-446b-a1d4-1a09c464bd7a","Potential of bacteria-based repair solution as healing agent for porous network concrete","Wiktor, V.A.C.; Sangadji, S.; Jonkers, H.M.; Schlangen, H.E.J.G.","","2013","Bacterially induced calcium carbonate precipitation has received considerable attention for its potential application in enforcing or repairing construction material. The mechanism of bacterially mediated calcite precipitation in those studies is primarily based on the enzymatic hydrolysis of urea. Besides calcite precipitation, this reaction mechanism leads also to the production of ammonium ions which may result in excessive environmental pressure. More recently, bacterially mediated calcite precipitation thanks to metabolic conversion of calcium lactate has been successfully applied in self-healing concrete. This concept is also now considered for the development of bio-based repair system for concrete structures. The bio-based repair system as presented in this paper is a liquid-based system which transports the bio-based agent into concrete. This paper presents the recent advances on the development of the bacteria-based repair system and especially its possible application as healing agent in porous network concrete. To assess the repair capacity of the system the bacteria-based solution is injected into porous cores, and the production of the biomineral in time is monitored by X-ray micro-tomography. In parallel, water permeability testing is conducted before and after the injection of the bacteria-based solution to determine the sealing efficiency of the system. The precipitate is analyzed with FTIR and thermal analysis for identification and quantification. Finally, at the end of the healing period, polished sections of injected specimens are observed with ESEM/EDS to analyze and locate precipitated biominerals. FTIR results coupled with thermal analysis and ESEM observations showed that CaCO3 has been formed in pores after 21 days, with increased amount after 28 days. Moreover, the evidence that CaCO3 precipitation was indeed mediated by bacteria has been found with observations of bacteria imprints on Ca based minerals. It can be concluded that the bacteria-based repair system can successfully be injected as healing agent into porous network concrete.","concrete; self-healing; cracks; bacteria-based system; porous network","en","conference paper","Magnel Laboratory for Concrete Research","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:cd5dca54-ecdc-4121-a531-810343d812e5","http://resolver.tudelft.nl/uuid:cd5dca54-ecdc-4121-a531-810343d812e5","Bacteria-based self-healing concrete for application in the marine environment","Palin, D.; Wiktor, V.; Jonkers, H.M.","","2013","Marine concrete structures are exposed to one of the most hostile of natural environments. Many physical and chemical phenomena are usually interdependent and mutually reinforcing in the deterioration of marine exposed concrete: expansion and microcracking due to physical effects increases concrete permeability paving the way for harmful chemical interactions between seawater, concrete and embedded steel reinforcement. Early research in self-healing concrete has focused on the autogenous ability of hydrates to heal cracks over time, this form of healing is however restricted to early and small cross sectional crack width reductions, while limited research is available on the autogenous healing of concrete incorporating GBFS (Ground blast furnace slag). A novel approach to self-heal concrete is a bioinspired technique, where bacteria immobilized in the concrete are activated through crack induced water ingress, forming a mineral healing precipitate [1]. The current study characterises the autogenous healing of blast furnace slag cement (CEM III/B 42.5 N) mortar cubes submerged in both fresh- and synthetic sea- water, as the first step towards developing a bacteria-based self-healing concrete for application in the marine environment.","bacteria; self-healing; marine environment; concrete; cracks","en","conference paper","Magnel Laboratory for Concrete Research","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:8c1129bc-6c75-4add-82b0-0c366d01ca2e","http://resolver.tudelft.nl/uuid:8c1129bc-6c75-4add-82b0-0c366d01ca2e","Polymeric nano-materials for corrosion control of steel in concrete","Varini, M.; Koleva, D.A.; Denkova, A.G.; Mol, J.M.C.; Terryn, H.; Van Breugel, K.","","2013","Polymeric nano-materials utilization in reinforced concrete, aiming to deal with steel corrosion was developed in previous works. Promising results were obtained with PEO–b–PS nano-formations, both in terms of enhanced bulk matrix properties and improved steel corrosion resistance. Recent research has been focusing on a cheaper and commercially available polymer, Pluronic P123. Pluronic is able to self assemble into micelles and/or vesicles but their sensitivity towards the environmental medium is a drawback: for this reason, a study on Pluronic micelles stability in different solutions has been carried out. A stabilization process against dissociation of micelles was also performed. Both stabilized and non-stabilized micelles were tested in model solutions in terms of their influence on steel corrosion resistance.","concrete; self-healing; corrosion","en","conference paper","Magnel Laboratory for Concrete Research","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:f421fecf-205e-45d3-8e3b-c07c8e0ace64","http://resolver.tudelft.nl/uuid:f421fecf-205e-45d3-8e3b-c07c8e0ace64","A testing preocedure for the evaluation of directional mesh bias","Slobbe, A.T.; Hendriks, M.A.N.; Rots, J.G.","","2013","This paper presents a dedicated numerical test that enables to assess the directional mesh bias of constitutive models in a systematic way. The test makes use of periodic boundary conditions, by which strain localization can be analyzed for different mesh alignments with preservation of mesh uniformity and with exclusion of boundary disturbances. After an exploratory study of the proposed test, the test is demonstrated by applying it to the classical and still widely used crack band model. An analysis series is performed on five meshes with different alignments. The meshes consist of squared quadrilateral elements with varying interpolation function and numerical integration scheme. From the results it can be concluded that the test identifies a significant mesh-induced directional bias.","directional mesh bias; concrete; fracture; finite elements; crack band model","en","conference paper","International Center for Numerical Methods in Engineering","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:553407d3-cb5b-4aa2-99b8-09474c6b5346","http://resolver.tudelft.nl/uuid:553407d3-cb5b-4aa2-99b8-09474c6b5346","Dynamic tensile resistance of concrete-split Hopkinson bar test","Weerheijm, J.; Sharma, A.; Ozbolt, J.","","2013","The behavior of concrete structures is strongly influenced by the loading rate. Compared to quasi-static loading, on meso and macro-scale concrete loaded by impact loading acts in a different way. First, there is a strain-rate influence on strength, stiffness, ductility, and, second, there are inertia forces activated which influence the resistance and failure mode of concrete structure. The experimental and theoretical studies show that the influence of loading rate on tensile behavior of concrete is relatively strong. In dynamic testing the split Hopkinson bar (SHB) is used to measure concrete tensile resistance. The results of the experimental measurements show that after reaching some critical strain rate tensile resistance progressively increases with increase of strain rate. The questions discussed in the paper are: (i) what is the reason for progressive increase of tensile resistance ? and (ii) can the resistance be attributed only to material strength or are there some other effects ? To answer these questions the numerical analysis on a simple elastic-cohesive FE model is carried out. Moreover, simulation of the compressive pulse in a concrete bar, which is reflected from the free end-surface of the bar and causes tensile fracture, is carried out for different loading rates. The evaluation of the results clearly shows that the progressive increase of tensile resistance (apparent strength) can be attributed to structural inertia of the fracture zone, which is invoked by cracking of concrete and is not to the true material strength. It is shown that the size of the fracture process zone significantly influence apparent strength. Similar as the true strength it is also discussed that with the increase of strain rate concrete fracture energy does not increase progressively.","concrete; dynamic fracture; rate sensitivity; Hopkinson bar; true and apparent strength; finite elements; microplane model","en","conference paper","Cimne","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:474d8991-7e57-49e9-80aa-a71066cb884a","http://resolver.tudelft.nl/uuid:474d8991-7e57-49e9-80aa-a71066cb884a","A mesoscale modelling perspective of cracking process and fracture energy under high strain rate in tension","Weerheijm, J.; Lu, Y.; Xu, J.","","2013","This paper presents a numerical modelling study on the simulation of the cracking process and fracture energy in concrete under high strain rate. To capture the stress wave effect and the damage evolution at the meso-length scale, both a homogeneous model with a millimetreresolution mesh and an explicit heterogeneous mesoscale model with random polygon aggregates are employed. The tendency of development of a) discrete multiple cracks, and b) spread tensile damage across adjacent element layers, in the high strain rate tension regime is scrutinised. This phenomenon generally gives rise to an increase in the dynamic fracture energy, which is consistent with experimental observations. Relative comparison between the homogeneous and heterogeneous mesoscale simulations suggests a sensible effect of the mesoscopic heterogeneity in the dynamic fracture process.","concrete; dynamic tension; high strain rate; fracture energy; mesoscale model","en","conference paper","Cimne","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:11252649-96db-4dbd-bda6-b79509320f9f","http://resolver.tudelft.nl/uuid:11252649-96db-4dbd-bda6-b79509320f9f","Packing of non-spherical aggregate particles by DEM","Stroeven, P.; He, H.","","2013","Loose random and dense random mono-size pacl