Fillers, such as limestone or quartz powder, are used as a replacement of Portland cement. Their application can make concrete more environment friendly and possibly cheaper. Additions of limestone or quartz powder have been reported to exert a limited chemical effect on cement hydration. The main quasi-chemical effect of added limestone and quartz powder is that they accelerate cement hydration by facilitating nucleation and growth of reaction products at their surfaces. Fine fillers in cement paste can result in improvements in strength because of a lower porosity and a denser packing. At the same time, however, the use of fillers results in dilution of Portland cement particles and their strength-providing reaction products in the paste. This ‘dilution’ effect will lead to an increased porosity. Above a critical amount of fillers, the effect of dilution exceeds the effect of packing, resulting in a lower strength of the hardened paste or concrete. These effects (porosity, packing and dilution) on the strength of cement paste have been studied intensively, but they (porosity, packing and dilution) cannot explain difference in performance of different fillers. Also adhesion between filler particles and reaction products has an influence on the strength of blended cement paste. However, filler-hydrates adhesion properties and their effect on the strength of blended cement paste are not quite well understood yet. The basic questions why filler particles and reaction products adhere to each other in blended cement paste, and how the chemistry and surface characteristics of fillers affect this adhesion, are rarely addressed and need further research. The aim of this project is to study the filler-hydrates adhesion properties in blended cement paste system. Firstly, the influence of the filler-hydrates adhesion properties on the strength of blended cement paste has been analysed. The compressive strength of cement paste blended with limestone powder and micronized sand was studied experimentally. The contact area between different solid phases in these cement pastes was quantified numerically. The relationship between the measured compressive strength and simulated contact area was analysed (“contact area concept”). Based on this relationship, the influence of the filler-hydrates adhesion properties on the strength of blended cement paste was quantified. It was found that micronized sand-hydrates contact area had no contribution to the compressive strength. By contrast, the limestone-hydrates contact area in cement paste had a substantial contribution to the compressive strength. Secondly, the filler-hydrates adhesion properties were studied at the microscale. Crack paths and fracture surfaces of loaded cement pastes were investigated by scanning electron microscopy (SEM) observation. Parallel with the SEM observations, the influence of interface’s mechanical properties on crack propagation, tensile strength and fracture energy was studied numerically by using a lattice model. Based on these SEM observations and simulation results, the mechanical properties of the interface between filler particles and hydration products were evaluated. Meanwhile, this provided a validation of the ‘contact area concept’. Then, the filler-hydrates adhesion mechanisms in blended cement paste system were investigated. The influence of the chemical nature of fillers on the interaction between main ions, i.e., Ca2+, SO42-, in the pore solution of blended cement paste and filler surfaces was investigated via zeta potential measurements. Meanwhile, microscopic observations of the nucleation and growth of C-S-H on the surface of these filler particles were performed by SEM. It was concluded that Ca2+ ions chemically adsorbed at limestone surfaces led to the formation of a relatively strong bond (most likely, ‘ionic-covalent’ bond) between a limestone particle and C-S-H. By contrast, Ca2+ ions electrostatically adsorbed at micronized sand surfaces resulted in an attractive ion-ion correlation force and hence a relatively weak bond between a micronized sand particle and C-S-H. This information about the filler-hydrates adhesion mechanisms is very important for the search for new fillers and for improving the performance of existing fillers. For example, based on the knowledge acquired in this study, carbonation can improve the performance of hardened cement paste powder when it is used as a filler in cement paste. This is because carbonation can turn the silicate and CH phase of the surface of the recycled hardened cement paste powder into calcite phase. This can enhance the adhesion properties between hardened cement paste particle and new hydration products. Finally, the fracture behaviour of cement paste with strong and weak filler-matrix interfaces was simulated at microscale by using a lattice model. The simulations indicated that the bond strength between filler particles and C-S-H matrix plays a more important role in the crack propagation and the strength of blended cement paste compared to the role of the particle size distribution, size (5, 10, 15 and 20 µm), shape, surface roughness and volume fraction (5, 15, 25, 35 and 45%) of the filler. These findings provided support to the previous findings that the strong interfaces between limestone particles and hydration products are due to the superior bond between limestone and hydration products rather than the physical surface properties, such as shape and surface roughness. Moreover, this study indicated the direction for optimization of the performance of fillers in cement paste in view of strength. To improve the performance of fillers, priority should be given to improving the bond strength between filler particles and hydration products. Modifying microstructural features (i.e., shape, surface roughness) of filler is less effective.@en

As facilities in the Dutch North Sea are approaching the end of their production life, the focus shifts from the developing to the decommissioning of facilities. The legislation on offshore pipeline decommissioning in the Dutch North Sea is currently unclear. The Minister can decide whether pipelines are to be removed or are allowed in situ. In situ decommissioning is considered unwanted by major external stakeholders. Besides, the pipeline owner holds an extensive liability for the pipeline after decommissioning. Full removal options, on the other hand, are accompanied with large environmental, technical and financial impact. This graduation thesis Accelerated pipeline degradation aims to investigate how accelerated degradation of steel can contribute to offshore pipeline decommissioning. By accelerated degradation it is aspired to limit the environmental impact and seabed disturbance. Furthermore, the costs and technical impact can be reduced. After evaluating the current decommissioning methods, a series of alternative options is assessed. The assessment has resulted in a further investigation of galvanic corrosion for steel degradation. With this investigation, it is aspired to evaluate the mechanism of galvanic corrosion to accelerate the corrosion of the steel pipeline. By doing so, the liability period at the sea bottom would decrease dramatically with respect to in situ decommissioning. The materials that could be applicable for galvanic coupling were considered. Due to its high standard potential and low costs, the use of graphite (carbon) is determined to be most suitable. Subsequently, several small-scale tests on low carbon steel. In a laboratory setting the galvanic corrosion of steel was investigated by coupling steel samples to carbon electrodes. Coupling with platinum electrodes is also tested to provide reference scenarios. The results of the tests show an increase of corrosion current with addition of a galvanic couple. However, with increasing cathodic surface the steel dissolution is limited by corrosion kinetics and diffusion limitations. A preliminary schematisation for implementation is designed. Accordingly, the main challenges are identified. The test results and identified challenges are the motivation for a field test. This field test is to be designed to investigate the potential feasibility issues that arise in the practical situation. Furthermore, the operational challenges can be addressed on the test site.

This work is an overview of the state of art on Ageing of Materials and structures in the world. Ageing of materials is a natural phenomenon. Each material we use will age. This ageing will influence the performance of the object where the materials is used. Furthermore, the ageing will be affected by the surroundings in which the object is placed. The main focus of the book is on materials used in infrastructure, energy, buildings and industry. The book in effect establishes the definition of ageing and its main research topics that are relevant for society.@en

A long standing research field in material science has been the trade-off between strength and ductility of steels. Advanced High Strength Steels (AHSS) aim to combine these two properties and provide steels that can increase safety and lower CO2 consumption in automotive applications, by decreasing weight. To further decrease the environmental impact, novel quenched and partioned (Q&P) martensitic stainless steel is considered to prevent corrosion. Quenching and partitioning is a heat treatment that aims for a martensite/retained austenite microstructure with specific phase fractions to optimize strength and ductility. While mechanical properties are well researched for Q&P treated martensitic stainless steel, the corrosion properties are not that widely documented. This thesis aims to discover the influence of the microstructural development in terms of phase fractions due to the Q&P treatment, and the manganese content on the corrosion properties of martensitic stainless steel. Two alloys with chemical composition 0.2C-12.5Cr-0.35Si-XMn, where X stands for 0.7 for the low manganese alloy, and 3 for high manganese alloy, are considered for this study, and are compared to a commercial AISI 420 martensitic stainless steel. The microstructure was investigated by the use of optical microscopy, energy dispersive X-ray spectroscopy (EDS), electron probe microanalysis (EPMA), scanning Kelvin probe force microscopy (SKPFM). This was combined with electrochemical experiments including Open-circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). When compared to commercially available AISI 420 martensitic stainless steel, the novel Q&P MSS showed improved corrosion properties. This can mainly be attributed to the lack of chromium rich carbides (Cr23C6 or Cr7C3) in the Q&P treated MSS. However, this improvement in corrosion properties was only observed for the samples with low manganese content. The increase of fraction retained austenite did show an increase in corrosion potential, making the steel more cathodic, but the improvements in terms of pitting potential and passive film properties are limited. Samples with high fresh martensite fractions also showed an increase in corrosion potential, but only marginally increased in terms of length of the passive region. EIS data shows that the addition of fresh martensite reduces the passivity properties of the material. Volta-potential measurements done by SKPFM showed a clear difference between primary martensite and fresh martensite of up to 20mV and were overlapping with the topography maps. This can be an indication of increased tendency to form micro-galvanic cells between martensite phases. Manganese was found to be detrimental for the corrosion properties of the Q&P treated MSS. A clear drop in the length of the passive region shows that the high manganese samples are more susceptible to pitting. EDS measurements and EPMA elemental distribution maps showed local zones of decreased chromium and increased manganese and silicon. This indicates that there are secondary phase particles present in the material in the form of manganese silicide or manganese sulfide. Volta-potential measurements done by SKPFM showed these particles behave more anodic in comparison to the matrix of the material. The number of particles per unit area was increased for the samples with high manganese content. These inclusions greatly reduce corrosion performance, showing that the addition of manganese is detrimental for corrosion performance. Several other microstructural features are discussed in terms of influence on the corrosion performance of the material. Which include prior austenite grain boundaries, elemental banding of chromium and manganese and Volta-potential differences between martensite laths.

In this research, the effect of curing with different types of current, current densities/voltage intensity on mortar is studied. The main objective is to explore the outcomes of electric curing on the setting time of CEM-I mortar. For achieving the main objective, an electrical curing setup is designed to accommodate curing with direct current, alternating current and pulsed direct current and the conventional vicat apparatus and its test procedure are modified in order to carry out the testing while a sample is being cured with current. Additionally, the effect of passing current on material properties such as compressive strength and resistivity is also studied. The temperature development during the curing process has also been monitored in the research. The electric charge and power calculation are done, for possible current/voltage regimes. The experiments revealed that the setting time can be altered by electrical curing of CEM-I mortar. The influence of electric curing for the chosen curing period is not significant as revealed from the compressive strength testing while the development of resistivity and temperature reveals that there is a correlation between these two properties. The effect of electric power applied to a sample is reflected in the results of the setting times. In the last chapter the findings of the study are summarised and recommendations, keeping in mind the possibility of expanding research in this field of study, have been made.