The recycling of ultralight foam concrete (ULFC), both with and without phase-change material (PCM), involves crushing it and using the resulting recycled foam concrete powder (RFCP) as a partial substitute for cement or sand in cement composites. These recycling paths remain insufficiently explored in the literature regarding practical feasibility. Since both RFCP and PCM reduce the flowability of fresh mortars, incorporating RFCP with PCM is, in practice, only feasible with the addition of a superplasticizer (SP). The primary objectives of this study were to determine: (1) the effect of RFCP with PCM, when used to replace cement or sand, on mortar properties, and (2) its influence on the performance of the superplasticizer (SP), to assess the feasibility of using RFCP with PCM in cement composites. The addition of RFCP, both without PCM (RFCP_0) and with PCM (RFCP_PCM), deteriorates the properties of fresh and hardened mortars compared to reference mortars. The negative impact of RFCP is less pronounced when it replaces sand rather than cement. Compared to RFCP_0 mortars, RFCP_PCM mortars exhibit reduced flowability. PCM delays setting and reduces heat evolution during the first 48 h of hardening. PCM does not significantly affect strength or water absorption but increases shrinkage and lowers thermal conductivity. While RFCP_PCM does not impair SP efficiency, PCM causes SP to significantly retard setting and hardening.

Cow-dung is a widely used stabiliser applied in traditional earthen buildings with one objective to improve water resistance. However, most research has focused on explaining its mechanical strength, with only one study suggesting water resistance mechanism via formation of insoluble compounds at high pH, a phenomenon uncommon in natural cow dung and soil mixtures. This article investigates the water-resistance behaviour of cow-dung stabilised compressed earthen blocks (CD-CEBs) through an extensive experimental programme to understand the influence of cow-dung and soil related factors and to characterise the components of cow-dung responsible for its water resistance. It was found that the small-sized microbial aggregates (SSMA) present in cow-dung, which are negatively charged hydrophobic aggregates of low specific surface area, are responsible for enhanced water resistance of CD-CEBs. The insights gained from experiments are compiled to recommend the following strategies for improved performance of CD-CEBs: (i) The use of wet cow-dung is advised over dry cow-dung as it provided over 80 times better water resistance; (ii) Adopting a higher compaction liquid content (by 3%) improved the water resistance by over 40 times; (iii) The water resistance of CD-CEBs was improved over 30 times by using soils rich in low-swelling clay minerals such as kaolinite. A case study applying these findings demonstrates the successful scaleup from the lab to field showcasing potential of cow-dung and soil in low-carbon construction.

Concrete production is a major contributor to global CO₂ emissions, responsible for approximately 80% of the emissions in the construction sector. This high emission level is primarily due to the use of clinker, an energy-intensive component of cement. Reducing the environmental impact of concrete therefore depends on producing and reusing high-quality residual cementitious fines (RCF) derived from End-of-Life (EoL) concrete. The process of obtaining high-quality RCF begins before concrete demolition, where identifying the cement type in existing concrete is crucial for high-value downstream processing. This study explores the suitability of currently available methods for identifying binder types in (destructively obtained) RCF and evaluates which of these methods could potentially be suitable for non-destructive identification of binder types in the original concrete. The methods investigated include handheld X-ray fluorescence (HXRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), titration and selective dissolution. To assess their binder type identification potential, RCF powder samples obtained from concretes of known composition were analysed first. Results show that all five methods can distinguish and identify three binder types (Portland cement, blast furnace slag cement and fly ash cement) based on variations in the chemical and mineralogical properties of the RCFs derived from their respective concretes. HXRF currently shows the greatest potential for rapid, non-destructive, in-situ identification of binder types present in EoL concrete, while XRD and FTIR also show potential.

Self-healing concrete, with its ability to autonomously repair damages, holds promise in enhancing its structural durability and resilience. Research on self-healing concrete in the past decade has advanced in understanding the mechanisms behind healing, exploring various healing agents, and assessing their effectiveness in concrete structures. However, the full potential of self-healing concrete remains untapped unless its effects are effectively integrated into the design practices of reinforced concrete structures. Realizing this challenge, this paper synthesizes the current research progress and discusses the possibilities to consider self-healing into design codes. The focus was placed on two specific benefits of applying self-healing concrete: one centered on durability and the other on mechanical performance. Specifically, the effect of self-healing on impeding chloride penetration into cracked reinforced concrete was discussed first. Modifications of parameters in existing predictive models based on different types of healing approaches were recommended. Furthermore, the possible impact of the self-healing capacity in mitigating the stiffness reduction of concrete was also discussed. Equations that can describe the stiffness regained due to healing action are presented. In each part of the case study, limitations and challenges still hindering standardization and wider application in the construction field are discussed.

Bioreceptive concrete supports biological growth on its surface, but natural colonisation takes years, and indoor cultivation followed by outdoor translocation often results in poor long-term survival. This research aimed to develop a method for rapidly establishing a moss layer on bioreceptive concrete while ensuring long-term persistence and survival. The developed method comprised a two-step approach. First is the rapid establishment of moss on bioreceptive concrete indoors. Then, it is hardened and translocated outdoors. Findings indicate that the most effective method for growing moss on concrete indoors is to grow them at low light intensity (70 μmol m−2 s−1 full-spectrum), while watering daily for the first six weeks. Subsequently, watering can be gradually reduced to once every 4 days, inducing drought hardening. This resulted in significant coverage and growth for both acrocarp (Mcoverage = 15.1 %; Mgrowth = 11.2 mm) and pleurocarp species (Mcoverage = 51.7 %; Mgrowth = 15.5 mm). Finally, after outdoor translocation, the moss should be covered with a light-blocking cloth for a 3-month period to allow for adaptation to UV and high light intensity conditions. When applying this method to moss species (mixtures), it was found that T. muralis showed slow indoor growth but the best adaptation to outdoor conditions on both north- and south-facing surfaces. Contrarily, both P. capillare and B. rutabulum displayed faster growth under indoor conditions but showed poor surface adhesion when translocated outdoors, which can, in some cases, be improved by using species mixtures. This research is a first step towards identifying the factors influencing moss growth and survival on bioreceptive concrete in the built environment.

Phase change materials (PCM) are receiving ever-growing attention as a promising construction material for improving building energy performance through thermal storage and peak load shifting. The analysis of PCM performance and decision-making related to PCM implementation in building envelopes often relies on building energy simulation software such as EnergyPlus – a de facto standard in the academic world and the industry. For a precise modelling of the dynamic PCM behaviour, it is essential to correctly account for PCM hysteresis. This work introduces two new implementations of PCM hysteresis models in EnergyPlus. Further, it provides an in-depth analysis of four publicly available EnergyPlus-based hysteresis models, including the two newly introduced ones, and identifies the existing limitations for each of them. Finally, it explores the effects of PCM model selection on decision-making using the example of novel PCM-embedded material development. The results of this study show that the current built-in hysteresis model in EnergyPlus is not implemented correctly, and none of the other analysed models is completely free of limitations. Moreover, this work draws attention to the existing contradictions between different PCM modelling approaches, highlighting the critical impact the selection of a PCM model has on PCM-related decision-making. We conclude that while the existing hysteresis models in EnergyPlus are operable – albeit with great caution – they are not yet at the stage where they could be used as a reliable decision-making support tool. Practical real-world integration of PCM in building envelopes is hardly possible without having dependable modelling tools to back it up, and the development of such tools requires far more attention than it is given at the moment.

Reducing CO2 emissions from concrete production requires effective recycling of cement, particularly its clinker component. Significant emission reductions depend on innovative techniques that extract high-quality cement fractions from recycled concrete, beginning with source separation strategies before demolition. This study developed a practical measurement approach using handheld X-ray fluorescence (HXRF) to identify cement types (i.e. cement classifications such as CEM I, CEM II/B-V, CEM III/B) in End-of-Life concrete. The research was conducted in two phases: First, laboratory testing of seven powder samples (milled river gravel and sand, three cement types: CEM I, CEM II/B-V and CEM III/B along with blast furnace slag and fly ash) and three cement paste prism types containing the three cement types established optimal measurement parameters and assessed moisture influence. Second, field measurements were taken on outdoor concrete blocks, containing the three cement types, after one year of weather exposure. Measurements were conducted on both the exposed surface and subsurface layers (after removing 0.1–5 mm of material). Results showed that powder samples can be accurately characterized with 10-second measurements, while concrete blocks require at least 20 s. HXRF measurements demonstrated good reproducibility with low coefficients of variation (CV) values, ensuring reliable cement type identification. Surface measurements are reliable only when the concrete is unaltered: coatings, paint, or weathering negatively affect accuracy, necessitating removal of the surface layer. Cement types were successfully distinguished using oxide concentrations (Al₂O₃, Fe₂O₃, P₂O₅, MgO) and their ratios (CEM III/B: Al2O3/Fe2O3 > 9.0, MgO/Fe2O3 > 3.0, MgO/CaO > 0.11, Fe2O3/Al2O3 < 0.11 and Fe2O3/CaO < 0.04; CEM II/B-V: P2O5/CaO > 0.005 and P2O5/Fe2O3 > 0.1; CEM I: P2O5/CaO < 0.005 and P2O5/Fe2O3 < 0.1). This study demonstrates that handheld XRF enables fast and reliable in-situ identification of the three studied cement types, supporting improved source separation and cement recycling strategies.

Moss-covered bioreceptive concrete is a novel green vertical structure which can be applied to a wide variety of structures due to its low structural and maintenance requirements. One of the potential benefits of using moss-covered concrete is its ability to absorb sound, the extent of which is currently unknown. Therefore, the effectiveness in attenuating (urban) noise of six moss species in different hydration states was assessed and compared to bare concrete and other vertical green structures. Results show that using moss-covered concrete increases sound absorption compared to bare concrete in nearly all situations. The best-performing mosses overall were acrocarp species, particularly P. capillare, which reached a peak sound absorption coefficient of 0.86 and an average of up to 0.48 (50–6400 Hz). Its results are also relatively constant across hydration states. On the other hand, G. pulvinata outperformed P. capillare when dry, but not when hydrated or wet. The pleurocarp species showed the lowest sound absorption. Finally, the thickness of the moss layer has a minor impact on absorption. The acrocarp moss species compare favourably to (in)direct vertical green structures using climbing plants, whereas the sound absorption of the pleurocarp species is slightly lower. However, the sound absorption of moss-covered concrete is significantly lower than that of vertical green structures using a growing substrate (Living Wall Systems), as the substrate provides the bulk of the absorption in this case. In conclusion, the moss-covered bioreceptive concrete presents a viable alternative to (in)direct green structures, although benefits are mostly limited to frequencies above 1000 Hz.

The environmental footprint of concrete is largely influenced by the binder. It is therefore of high interest to investigate the potential reuse of the binder retrieved by modern separation techniques. However, studies found that the recycled cement fraction (RCF) still contained a certain amount of siliceous concrete aggregates, which forms an obstacle in the upcycling of RCF. In this study, the potential of electrostatic separation as a method to separate cementitious binder (hydrated and unhydrated) and sand (silica) is evaluated. Different cementitious powders and silica (sand) were prepared, resulting in a total of 9 powders and 8 mixtures. The mixtures consisted of a combination of silica and one of the cementitious powders (50/50 wt%) with a particle size of the components <125 μm. The potential of the studied technique was evaluated through charging measurements and x-ray fluorescence (XRF). Silica was assumed to contain no CaO and the detected CaO was therefore assigned to the cementitious powders. Results showed that silica and silica-rich fly ash (FA) particles became negatively charged, blast furnace slag (BFS) particles remained largely charge neutral and all other cementitious particles obtained a positive charge. Through electrostatic separation an enrichment of the cementitious binder fraction for all mixtures was obtained at the negative electrode. FA-Silica achieved the highest enrichment (89.9%), CEM III/B-Silica the lowest (4.7%) and the hydrates were enriched ranging from 28.0 to 31.8%.

The technical (service) lifespan of concrete is a crucial element in the construction sector, where the quality of the concrete mix and execution technology plays a decisive role in the performance throughout the entire functional life of structures. This presentation explores the importance of a well-designed concrete mix and how it contributes to the sustainability (overall environmental impact) and longevity of structures. We will examine the influence of reducing the environmental impact of concrete, resistance to environmental exposure conditions, and maintenance needs of concrete structures. By providing insights into the relationships between mix composition and lifespan performance, we emphasize the necessity of careful material selection and precise execution technology as the foundation for sustainable construction practices. The presentation will offer practical recommendations for improving the technical lifespan and reducing the environmental impact of concrete by focusing on the quality of the concrete mix and execution technology.

Given the rising popularity of foam concrete (FC) for both structural and insulating purposes, evaluating the feasibility of recycling after its lifespan is crucial in the context of the growing emphasis on sustainable building practices. One approach to recycling FC incorporating microencapsulated phase change material (MPCM) involves utilizing recycled foam concrete powder (RFCP) as an additive in cement composites. This article aims to investigate the impact of RFCP without and with MPCM when employed as a partial replacement for cement in mortars. Furthermore, the study verifies various processing methods such as crushing, grinding, and heat treatment for RFCP. The results reveal that introducing RFCP, regardless of the MPCM presence and processing method, significantly affects the properties of both cement and mortar. The presence of MPCM in RFCP negatively influences the flowability of fresh mortars, delays the setting time, and reduces the hydration heat within the first 48 h. However, the presence of MPCM does not significantly affect mortars' strength and water absorption but simultaneously it increases shrinkage and decreases thermal conductivity. Grinding RFCP mitigates the adverse effects of MPCM, while thermal processing removes MPCM from RFCP, albeit with an associated increase in water demand. A noteworthy finding is that mortars having 20 % RFCP, with or without MPCM, exhibit compressive strengths exceeding 16 MPa and 42.5 MPa after 2 and 28 days, respectively. These results meet the requirements outlined in EN-196-1 for cement of class 42.5, highlighting the potential to produce CEM II/A-F 42.5 using RFCP with MPCM.

This study investigates the structural behaviour and self-healing performance of hybrid reinforced concrete (RC) beams, enhanced with a 1.5-cm-thick self-healing cover composed of bacteria-embedded strain hardening cementitious composite (SHCC), for its potential in crack width control and crack healing. The research focuses on the performance under both flexural and shear loading, examining aspects such as load-bearing capacity, surface crack pattern, crack propagation between layers, and healing effectiveness. Results demonstrate the successful activation of the healing function, alongside improvements in structural performance. Under flexural loading, hybrid beams exhibited greater load-bearing capacity and significantly improved crack control ability. The maximum crack width of the hybrid beams exceeded 0.3 mm at 124.7 kN load, whereas in the control beam the largest crack exceeded 0.3 mm at only 59.8 kN load. Under shear loading, while the influence of the cover on structural capacity was minimal, it notably improved post-peak ductility and energy dissipation. Interface delamination was not observed in both cases. The results of the current study demonstrate the potential of delivering the self-healing mechanism precisely where it is most needed, which presents a scalable and economically viable strategy for integrating self-healing technology into standard construction practices.

The clinker in cement largely determines the environmental footprint of concrete. Therefore, concrete recycling should focus on retrieving high-quality cementitious fractions to replace clinker. This requires a shift from current traditional recycling techniques towards innovative recycling methods, enabling recovery of not only clean secondary aggregates, but also residual cementitious fines (RCF), potentially eliminating the carbon dioxide emissions associated with them. The production and upcycling of RCF offer new implementation routes that were previously deemed unfeasible. However, the properties of RCF may vary based on their origin, affecting their replacement and upcycling potential. Consequently, assessing the original concrete quality, with a focus on the binder type, before demolition is important. A handheld x-ray fluorescence technique appears promising for this purpose. To achieve effective separation of clean secondary aggregates from the original cementitious content, innovative crushing and separation techniques are needed. Additionally, electrostatic separation shows significant research potential for further optimizing RCF.

This study compares Enzyme-Induced Calcium Carbonate Precipitation (EICP) and Microbially Induced Calcium Carbonate Precipitation (MICP) for repairing external cracks in cement-based materials. Cracks in cement-base members can compromise structural integrity and increase maintenance costs. Thus, cement-base specimens with controlled cracks were treated using EICPs and MICP, with organic and non-organic additives to enhance calcium carbonate formation. Results show that both methods were effective in sealing cracks smaller than 0.35 mm. While incorporated additives improved the overall precipitation effectiveness, influence the crystallite size and altern the morphology of precipitated calcium carbonate. MICP generated more consistent crystal structures, while EICPs resulted in diverse crystal shapes influenced by enzyme sources and additives. Both methods offer promising, sustainable solutions for crack repair, with EICP providing greater flexibility and easier preparation. Presented research gives the comprehensive insights into the field of crack repair via bio-based methods reveals its potential in this area.

Research into bioreceptive materials is gaining increased interest. However, while advances are being made on the material side of bioreceptivity, the underlying ecology of urban mosses is still underexposed. This research aimed to determine how the local environment affects the species composition of urban epilithic moss communities and assess which moss species are most suitable for the colonisation of pristine (bioreceptive) concrete surfaces, leading to recommendations for moss species selection to designers and engineers of bioreceptive structures. We conducted a field survey of 137 moss communities on concrete in the Dutch cities of Amsterdam, Rotterdam and The Hague. A total of 26 different species were found, of which the acrocarp species Tortula muralis, Grimmia pulvinata, Ptychostomum capillare, and Orthotrichum diaphanum and the pleurocarp species Brachythecium rutabulum, Hypnum cupressiforme, and Rhynchostegium confertum acted as most common pioneers and also formed a part of the climax community. We found some positive associations between acrocarp species but negative associations between acrocarp and pleurocarp species. Local environmental factors only played a small role in the community composition at a species level; however, when comparing acrocarp and pleurocarp species, the former preferred more exposed sites, whereas the latter preferred more shaded habitats. As such, we recommend that bioreceptive concrete structures use acrocarp pioneers for exposed locations and pleurocarp pioneers for more shaded locations.

Given the ongoing global urbanization and the rise of heat, flooding, and drought in cities, the integration of climate adaptive measures based on “ecosystem functions and services” becomes imperative in design. This study details the implementation process of a microclimate design model in the design and retrofitting of the housing project Ecohof Noorderveer in Wormerveer, the Netherlands. The model, which quantifies local urban heat and mitigating measures through ecosystem functionalities, was incorporated into the program of requirements. The design process followed a research-by-design trajectory, involving iterative creative collaboration among all stakeholders, including future residents, the municipality, the water board, and the architect. The research employed the CFIR method to compare anticipated implementation outcomes with actual results. The findings suggest that introducing the microclimate design model into the program of requirements proved beneficial for the implementation process in the early design stage. The research-by-design approach was also deemed helpful, contingent on careful involvement of all participants in the knowledge-sharing process. This implementation method demonstrates significant potential for scaling up to standard urban development projects.

Implementing nature in cities has great potential to improve urban liveability by providing ecosystem services, which can help mitigate heat stress, improve air quality, attenuate noise, and reduce rainwater run-off. However, widespread adoption of urban nature and green building typologies is still limited due to their costs, environmental impact, and space constraints. Bioreceptive concrete can form the basis of a new green building typology, where the concrete mixture is adjusted to allow for biological growth, specifically mosses, to occur on its surface.

This literature review aims to give an overview of the current state of the art on bioreceptive concrete as a material in general and specifically the (potential) ecosystem services provided by the mosses growing on this bioreceptive concrete.

This review shows that bioreceptivity can be achieved in concrete in several ways, including minor adjustments to standard concrete recipes. While quantitative data on the ecosystem services provided by mosses in an urban context is still limited, potential gains appear significant. The main challenges lie in the durable long-term development of mosses on the bioreceptive concrete and the valuation through quantification of the ecosystem services they provide. However, moss-receptive concrete shows promise as a new green building typology if these challenges are bridged.

In the current study, experiments were carried out to investigate the structural performance of reinforced concrete (RC) beams with a self-healing cover zone. The cover zone consists of a 1.5-cm-thick layer of bacteria-embedded strain hardening cementitious composite (SHCC) for a combination of crack width control and crack healing. The aim is to bring together two emerging technologies (i.e., self-healing and strain-hardening) that show great potential for realizing highly efficient concrete structures. RC beam without the self-healing cover was also prepared as the control specimen for comparison purposes. The experimental program includes loading the beams to failure in four-point bending configuration and sawing the beams to segments for crack pattern analysis and crack healing. Results show that the beams with self-healing cover exhibited a 45-60% improvement in structural capacity. The crack patterns of the hybrid beams were also largely modified. While the reference beam formed only a few major cracks, the hybrid beams formed around 40 fine cracks in the constant bending moment region with an average crack width smaller than 0.2 mm even at maximum load. By having an improved cracking behavior and an enhanced self-healing capacity, it is expected that the beams with a self-healing cover will possess an extended service life at the expense of minimal additional cost.

The current study investigates short-term and long-term crack-healing behaviour of mortars embedded with bacteria-based poly-lactic acid (PLA) capsules under both ideal and realistic environmental conditions. Two sets of specimens were prepared and subjected to different healing regimes, with the first set kept in a mist room for varying short durations (i.e., 1 week, 2 weeks, 3 weeks and 8 weeks) and the second set placed in an unsheltered outdoor environment for a long-term healing process (i.e., 1 year). Alteration of microstructure because of self-healing was characterized by backscattered electron (BSE) imaging and energy dispersive X-ray spectroscopy (EDS) via crack cross-sections. Results show that visible crack healing enabled by bacteria began after 2 weeks in a humid environment. The healing products initially precipitated at crack mouths and gradually moved deeper into cracks, with the precipitated calcium carbonate crystals growing larger over time. After 8 weeks, healing products can be found even a few millimetres deep inside cracks. Observations of crack healing in a realistic environment revealed significant differences compared to healing under controlled conditions. While no healing products can be found at crack mouths, a substantial healing process was observed throughout the entire crack depth. It is likely that the environmental actions such as rainfall and/or freeze and thaw cycles may have worn away the healing products at crack mouths and thus led to a deeper ingress of oxygen into cracks, which promoted the activation of healing agents and associated calcium carbonate precipitation deep inside a crack.

This study presents an early-stage design exploration of NRG-Foam, an innovative insulation material composed of cementitious foam doped with microencapsulated phase change materials (MPCMs). The study comprises the static part that utilizes life cycle assessment and life cycle costing assessment for getting insight into the impacts of the NRG-Foam production process and the dynamic part that identifies the trade-offs between performance characteristics of NRG-Foam using multi-objective optimization. The production of MPCMs was found to be a major contributor to environmental impacts while the addition of small amounts of reduced graphene oxide amplifies the impacts even further. The hot spot analysis pinpointed high electricity consumption as the main driver of environmental impacts. A multi-objective optimization analysis revealed trade-offs between performance characteristics, emphasizing the necessity of compromises during material development. The selection of the MPCM type was shown to be determinative of the final properties of NRG-Foam.