This study investigated the possibility of enhancing immobilization of heavy metals in hazardous fly ashes by mineral carbonation. The research initially investigated five different fly ashes for their chemical composition and carbonation potential. The highest lime content resulted in the highest carbonation potential, but mineral carbonation occurred also in other fly ashes with very limited free lime. One of the municipal solid waste incineration (MSWI) fly ash (FA) with a high heavy metal content and the highest carbonation potential was selected for further carbonation and immobilization investigations.
The selected MSWI FA was carbonized following the first three out of four possible different routes:

1.Pre-carbonation of fly ash and casting with binder
2.Pre-carbonation of fly ash-binder mixture and casting after carbonation
3.Curing of the sample in the carbonation chamber
4.Carbonation of fresh mixture during mixing

The materials were tested for their crystalline composition before and after curing as well as for effective carbon-uptake. The second route resulted in the highest effective carbonation for the MSWI FA but also in the lowest compressive strength. The third route showed an increase in strength compared to the reference sample and effective reduction of final pH on the leachate and electrical conductivity. A fast shake leaching test was used to determine the leachability of relevant anions and cations from the mix designs. The results were compared with a reference sample prepared following a procedure used in industrial-scale applications and with the Dutch Soil Quality Decree and Regulation (Ministerie van Infrastructuur en Waterstaat, 2022).
The leaching tests resulted in an increased immobilization of lead, copper, and zinc for both a MSWI FA and a biomass (BM) FA also selected for its high carbonation potential. The highest total immobilization was reached for the MSWI FA through pre-carbonation of fly ash-binder mixture as the high reduction of pH of the sample cured in the carbonation chamber increased the solubility of other heavy metals. The immobilized BM FA through carbon-curing resulted in the optimal immobilization solution, followed by the pre-carbonation of the mixture of binder and fly ash. For both tested materials, the addition of carbonation outperforms the reference samples.
The comparison with the Dutch soil decree showed promising outcomes for future development of mineral carbonation for immobilization of hazardous materials. The carbonized specimens met most of the requirements for construction materials, which were expected to be more stringent than those for landfill use. The materials were evaluated under a worst-case scenario, showing the effective reduction of lead leachability. The carbonation of hazardous materials offered potential for application in highly lead-polluting waste streams to reduce carbon emissions and contribute to a cleaner environment.

This graduation project investigates the integration of green concrete in construction projects for sustainable development. Green concrete, characterized by the use of recycled materials, reduced cement content, and environment-friendly processes, is crucial in minimizing the construction industry's environmental impact. The study addresses the central question of how green concrete can be effectively implemented in construction projects, considering industry-specific challenges.
A mixed-methods approach, incorporating literature review, an online survey, and expert interviews, was utilized. The study extends the definition of green concrete to encompass lower energy and water consumption, a longer lifespan, and contributions to environmental, social, and economic sustainability.
The results indicated moderate awareness of green concrete among industry professionals, highlighting the need for further education. Despite this, the relevance and importance of green concrete were acknowledged. Environmental considerations were found to be the most influential factors in decision-making, followed by social and economic aspects. Seven critical factors affecting the decision-making process were identified, including industry support, personal attitudes, resources, market conditions, leadership, collaboration, and communication barriers. The most significant barrier to innovation was short-term thinking.
Expert interviews reaffirmed the significance of green concrete, though they also emphasized challenges such as high costs, performance concerns, and the lack of established norms.
In response to these findings, the study introduces the Green Concrete Integration Model (GCIM), an adaptive, six-step iterative framework to streamline the incorporation of green concrete into construction projects. The GCIM focuses on adaptability and continuous improvement, addressing technical, economic, socio-cultural, and regulatory challenges through identification, estimation, planning, testing, refinement, scaling up, and monitoring. The model also stresses the importance of stakeholder management and continuous assessment of environmental, social, and economic impacts.
In conclusion, the study offers a pioneering framework in the form of GCIM to facilitate the effective implementation of green concrete, promoting sustainable advancements in the construction industry.

This thesis addresses the topic of ongoing (excessive) deformations observed in balanced cantilever prestressed concrete bridges all over the world. Many authors attribute this behavior to the time-dependent phenomena of creep and shrinkage. Balanced cantilever bridges are classified as creep-sensitive structures, and for that reason, a detailed analysis of the long-term structural behavior, such as deformations and prestress losses, is recommended. However, during the design of these bridges, commonly used code-based models generally tend to underestimate the long-term creep and shrinkage effects. Additionally, various (simplifying) assumptions are made when modeling these bridges, making their actual creep and shrinkage behavior unclear.

This work aims to investigate whether the long-term effects of creep and shrinkage are indeed a plausible explanation for the excessive and ongoing deflections detected in a specific balanced cantilever bridge in the Netherlands: the Rooyensteinse Brug. This bridge, inaugurated in 1977 in Zoelen, currently exhibits a deflection at midspan of 0.43 m, more than two times what was anticipated in bridge design. To investigate this behavior, a detailed two-and-a-half-dimensional finite element model was developed, incorporating a time-dependent phased analysis accounting for the construction phases. Creep and shrinkage effects were incorporated into the concrete material model through creep compliance and shrinkage strain curves.

A sensitivity study is conducted to analyze the impact of: (i) different code-based models for creep and shrinkage, (ii) accounting for the large creep and shrinkage model uncertainties, (iii) different maturities on the creep compliance curve, and (iv) considering cross-sectional variability in the drying characteristics. The main findings showed that commonly used code-based models, including the current standard Eurocode 2, significantly underestimate the long-term (multi-decade) deflections observed in the Rooyensteinse Brug by 30%. Notably, only the RILEM B4 model (B4), considered the most theoretically grounded creep and shrinkage model, was able to capture the long-term deflection trend reasonably well. Further, acknowledging the inherent uncertainties in B4 significantly widened the range of potential deflections and prestress losses. Using the bounds of the 90% credible interval, the midspan deflections after 60 years range between 0.514 m and 2.91 m, compared to a mean of 0.895 m. The prestress losses range between 18% and 30% in the shear-critical zone, against a mean of 23%. Additionally, accounting for the cross-sectional variability in drying characteristics led to an improvement in both the short-term (first 10 years of service life) and long-term (multi-decade) deflection prediction when comparing the results to in-situ measurements, with differences of 14% and 6.1%, respectively. Based on these predictions, it is expected that the current deflection trend of the Rooyensteinse Brug will continue to decrease linearly (log-scale) for the next two decades.

This study demonstrates that a detailed finite element model incorporating time-dependent phased analysis, in combination with the RILEM B4 model and accounting for cross-sectional variability, can explain the observed behavior in the Rooyensteinse Brug. The results support the hypothesis that the long-term effects of creep and shrinkage are the cause of the ongoing trend of excessive deformations in this balanced cantilever prestressed concrete bridge.

Upscaling of two geopolymer concrete mixtures in an individual prestressed girder in self-compacting geopolymer concrete (SCGC) with a topping layer cast in-situ by a ready-mix geopolymer concrete provider. The objective is to study the different material properties of the mixtures, determine their impact in the structural performance and define the extent of applicability of current methods of analysis for conventional concrete structures, as defined in EN 1992-1-1 and the Rijkswaterstaat’s Guidelines for NLFEA, for geopolymer concrete. The structural performance of the elements subjected to flexural (at 28 days and 9 months) and shear (at 28 days) tests is studied by analytical methods and 2D plane stress nonlinear finite element analyses, which are compared to experimental results in terms of deformations, load-deflection response, principal strains, normal stresses, damage evolution, cracking stages, maximum load and failure mechanism; the effect of the long-term material properties (e.g. elastic modulus, creep and shrinkage) of the geopolymer concrete mixtures in the prestressing losses, cracking load and maximum load carrying capacity is analyzed. The elastic modulus of both geopolymer concrete mixtures decreases when exposed to drying and is lower than the estimates from EN 1992-1-1 for OPC concrete of the same strength class. The increase of creep and shrinkage between 30 and 60 days suggest a pronounced viscous mechanical response. The prediction models from EN 1992-1-1 for conventional concrete to determine the material properties from the 28-day compressive strength do not capture the long-term material properties. The isotropic elasticity-based prediction models underestimate considerably the creep coefficient and shrinkage strains leading to unsafe design assumptions. The short-term flexural resistance is higher (8% by analytical model and 3% for the numerical simulation) than the maximum load during testing. The stress distributions at characteristic phases and the cracking load (3% higher than the experiment) are practically equal from the analytical and numerical model. The flexural cracking pattern in the topping in the NLFEA shows more cracks at smaller spacing because higher stresses transfer from the precast girder due to perfect bond. The short-term shear resistance was 12% higher from the numerical simulation and 16% lower from the analytical model, as compared to the experiment. The cross-section of the numerical simulation is stiffer since the precast girder and the topping are perfectly bonded, in the experiment debonding occurred. The position and orientation of the shear critical crack causing failure from the NLFEA was consistent with the DIC observations. The prestress losses at 28 days are higher than for conventional concrete and increase from 26% after 28 days to 38% after 270 days. The variation in the elastic modulus at 28 days has a marginal effect in the short-term response to the flexural test. The cracking load is decreased by 15% in the specimen after 9 months but the prestress losses will continue to increase over time and the cracking resistance will decrease which is critical for the performance over the service lifetime. The design criteria of conventional concrete result in non-conservative estimates of the cracking resistance and flexural load carrying capacity.

After water, concrete is the most used substance on the planet. Approximately three tonnes of concrete is produced per person annually (Gagg, 2014). Traditionally, large amounts of Ordinary Portland Cement (OPC) are needed for the production of concrete. The production of OPC is very energy intensive and therefore a major generator of carbon dioxide, which is considered to be a potent greenhouse gas. High CO2-emissions are caused by calcination of limestone and combustion of fossil fuel during an energy intensive production process.
To reduce the CO2-emissions caused by the concrete manufacturing, there is a growing interest in alternative and low CO2-binders. A great example of alternative binders are alkali-activated materials (AAMs), often referred to as geopolymers. Alkali-activated materials are inorganic polymers acting as the binder agent in concrete, often containing by-products from the industry such as fly ash and blast furnace slag (Davidovits, 1989). Unlike OPC, AAMs are synthesized by activation of an aluminosilicate source (fly ash, slag, metakaolin) with alkaline activators. AAMs have attracted a lot of attention in the industry because of its superior mechanical properties, excellent resistance to sulphate attack, low creep and low drying shrinkage compared to OPC.
Besides sustainability, the total amount of costs is also a relevant factor for the construction industry. 3D-printing of concrete removes the need for formwork and enables the industry to create complex shapes as well as optimization of material use. It also provides an opportunity for an automated building process with a minimal amount of labour and material wastage. Combining the use of alkali-activated materials (AAMs) in an innovative and automated 3D-printing process may therefore offer many advantages for the construction industry...

Global climate change has been a huge matter of concern today. While there are several factors that contribute to greenhouse gases, adversely affecting the planet, CO2 emission is one of them. It is said that 8% of total carbon dioxide emission is caused due to the production of Ordinary portland cement used for concrete in construction. The construction industry highly relies upon concrete as a major and widely used construction material. Solutions to reduce the production of Portland cement without having to entirely remove concrete as a building material has been an important discussion. A possible solution is to replace the Portland cement in concrete with industrial by-products further activating the binder with alkali activators producing a green concrete called ‘Geopolymer concrete’ (GPC) which would reduce CO2 emission.  The biggest challenge yet is that, designing any structure, a standard validated code/regulation is required and GPC doesn’t have a standard code of practice. All the concretecodes till now are formulated taking the parameters for Ordinary Portland cement concrete. This lack of design models specifically formulated for GPC restricts contractorsand engineers to use GPC in structures. This is why GPC has not gained much acceptance in practice.  This research was done in collaboration with Boskalis. A bridge (KW15-N69) has beenconstructed using geopolymer concrete in North Brabant province of the Netherlands.To make the bridge sustainable and circular, the GPC used contained no cement andaggregates were fully replaced by thermally recycled asphalt aggregates. For design ofthe bridge, Eurocode 2 for concrete structures was used and additionally regulations by Dutch ministry of transport and infrastructure was followed.This research will act asone of the pioneer studies to investigate the overall structural behaviour of geopolymerconcrete beams with respect to standard codes which should help design engineers upto some extent to execute and design structures using GPC in future.   

In floors without dilation joints drying shrinkage cracking can occur. Shrinkage reducing agents (SRAs) can reduce the amount of drying shrinkage and improve the durability of the concrete structure. The mechanism of shrinkage reduction and the influences on the hydration process and development of mechanical properties of the SRA Sika Control 40 were researched. Shrinkage reducing agents lower the surface tension of water which reduces the capillary tensile stresses and ultimately reducing the drying shrinkage. Experiments were performed on cement paste samples to investigate influences on the hydration process of cement (surface tension, rate of hydration, porosity, shrinkage, flexural and compressive strength). In addition experiments were performed on concrete samples to investigate the influences of applying shrinkage reducing agents on the mechanical properties of concrete (compressive strength, shrinkage, elastic modulus). Overall, the experimental results showed that applying Sika Control 40 is an effective method for reducing drying shrinkage when concentrations of 1.56 w% and 2.61 w% are used. The shrinkage reducing agent has positive effects on the surface tension, weight loss and drying shrinkage for concentrations of 1.56 w% and 2.61 w% of cement. It has negative effects on rate and degree of hydration, porosity, pore size distribution, compressive and flexural strength for concentrations of 1.56 w% and 2.61 w%. The elastic modulus lacks adequate data to observe a trend, however the results are within the range of expected values for concrete for mixtures 156 and 261. , An SRA concentration of 0.52 w% of cement resulted in unpredictable and contradicting results.

Ordinary Portland Cement (OPC) consumption has grown nearly exponentially in the last twenty years. OPC has become the highest-volume manufactured product on the planet. Production of OPC is energy-intensive, consumes unrenewable natural resources and is one of the primary contributors to global warming (accounting for at least 5-8% of worldwide anthropogenic CO2 emissions). An alternative for OPC concrete is Alkali-Activated Concrete (AAC), for which Portland cement is completely substituted by an alternative binder. Instead of using OPC and water, precursors (raw materials) like Blast Furnace Slag (BFS) or Fly Ash (FA) are activated with an alkaline activator solution.
Although AAC seems to have promising qualities for structural application in terms of sustainability, worldwide use is not yet established. One of the reasons for this is the fact that there are no available regulations or codes to apply it, the material is relatively new and limited research has been conducted. For OPC concrete, the design codes are based on compressive strength at 28 days (strength at later ages stays either constant or is higher) and most other mechanical properties used in calculations are estimated based on this compressive strength. For AAC it is not yet sure if the same relations and assumptions as for OPC are also valid. First, because mechanical properties that have been reported for AAC in literature vary a lot, depending on mixture composition and curing conditions. Second, the long-term strength development of AAC is scarcely investigated and it is not clear if the compressive strength at 28 days can be used as a safe reference for design. Namely, a few researchers reported a decrease of strength or stiffness over time, for AAC mixtures that contain blast furnace slag. The observed decrease might not be a very desirable phenomenon and should be well-understood prior to wider structural application of AAC. Therefore, the main research question of this thesis is: Can a decrease of stiffness and strength over time, as sometimes reported in literature for AAC, also be found for AAC used at TU Delft and if so, what could be an explanation for this behaviour? Does the amount of BFS in the binder play a role, as a decrease over time has only been reported for AAC containing BFS? And if not, what other cause could lead to a decrease of properties over time? The intention is to make some first steps towards a better understanding of this phenomenon.
The research question is investigated in an experimental manner. Compressive strength, elastic modulus, splitting tensile strength and flexural strength are tested at different ages (28, 56 and 91 days) after being wet-cured (20°C and 95% RH) for 28 days. Two different AAC mixtures are investigated, S100 and S50, characterized by a BFS/FA binder ratio of 100:0 and 50:50 respectively. Furthermore, the flexural behaviour of reinforced beams is investigated by conducting four-point bending tests on both S100 and S50 concrete of two different ages (33/34 days and 69/70 days) and compared to an OPC concrete control beam.