The increasing global demand for construction materials has raised concerns about the sustainability of natural sand, a key component in concrete production. In the Netherlands and across Europe, the long term availability of sand is uncertain, and the environmental and social impacts of sand extraction are becoming more apparent. One promising alternative is the use of recycled aggregates, particularly construction and demolition waste (CDW) fines, as a replacement for natural fine aggregates in mortar and concrete. This master thesis investigates the potential of Dutch CDW fines to address this challenge, with a focus on their characterisation, performance, and impact on microstructure.

The study begins with a comprehensive characterisation of CDW fines provided by Miner-
alz/Renewi, assessing their chemical, physical, and mineralogical properties using techniques such thermogravimetric analysis (TGA), X-ray fluorescence (XRF), X-ray diffraction (XRD), and
polarised light microscopy. These analyses revealed that CDW fines are highly heterogeneous but largely consistent in composition over time. Quartz is the dominant phase at 72.5% according to qXRD, with smaller amounts of calcite, gypsum, and amorphous material also being present. The presence of contaminants such as glass and metals was confirmed and quantified using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

Performance tests on mortar samples incorporating varying percentages of CDW fines demonstrated a notable reduction in compressive and flexural strength of about 25% when 100% of natural aggregates are replaced with CDW fines. The compressive strength of 24.7 Mpa (100% CDW fines) still falls into the highest defined strength class in the European standard for masonry mortar. A decrease in strength while other parameters are kept constant is consistent with previous studies. The setting time does drastically increase with the replacement percentage of CDW fines, by as much as 100%. The workability on the other hand remains the same, contrary to what other is reported in other literature. All this would make CDW fines viable for plenty of applications. Before knowing more about the durability aspects though it is recommended to start with non-structural ones like pavement tiles.

Microstructural analyses using SEM indicated no significant changes in hydration products
but highlighted the presence of impurities, microcracks, and damaged and low quality interfacial transition zones (ITZs). The impurities such as brick, various metals and attached old cement paste contribute to the observed strength performance differences. The low amount of old cement paste (4-6%) observed with EDS also makes the low water absorption, high density, and stable workability more plausible. Furthermore, calorimetry testing on mortar samples shows significant differences in the hydration process over time. One difference is that the reaction of C3A is slowed down by the presence of gypsum in the CDW fines. This is in line with the previously mentioned increase in setting time.

This research provides insights into the properties and behaviour of CDW fines and extends the foundation for their improved utilisation in sustainable construction practices. By leveraging this abundant waste stream, the construction industry can make meaningful steps toward reducing its environmental footprint and conserving natural resources.

Carbon dioxide can be used during concrete production, which leads to stronger concrete as well as a sequestration method for CO2. While these technologies are developed quite far, they are currently not being used within society nor is there any systemic overview of the system and a reason why these technologies are not used. This thesis performs a Technological Innovation System analysis to investigate the Dutch concrete system and find barriers to the transition from conventional to carbon-cured concrete. The three located barriers are knowledge exchange, guidance of the search and the formation of markets. Intervention tools are presented to decrease the barriers and stimulate the technology within the system to enable further growth.

The increasing demand for sand in the construction sector underscores the need for sustainable alternatives to natural sand. This bachelor's thesis explores the application of Fine Recycled Concrete Aggregate (fRCA) produced by Heating air and classification system (HAS) from the Concrete To Cement and Aggregate (C2CA) technology as a sustainable substitute for natural sand. fRCA consists of pure sand and cementitious material, with the removal of extraneous substances such as timber and steel. While fRCA finds applications in various sectors, the challenges in its use in mortar include property variations, cost considerations, and the absence of quality control standards. Addressing these challenges would be crucial for the wider adoption of fRCA in mortar applications. This research aims to characterize fRCA properties, enhance fRCA quality through acid treatment and milling, determine optimal milling parameters, investigate the influence of the water-cement (W/C) ratio on mortar workability, and assess the compressive and tensile strength of mortar with fRCA. The central inquiry pertains to identifying the optimal approach for enhancing fRCA properties and integrating it into concrete mixes for civil engineering applications. The study is exploring the effects of untreated fRCA, milled fRCA, and acid-washed fRCA on mortar properties. It is also determined the ideal quantity of milled fRCA to replace natural sand in mortar mixtures. The theoretical evaluation of sustainability in mortar mixes utilizing this specific fRCA have been conducted. This research did not investigate the chemical properties of fRCA. Notably, the quality of fRCA differs from that of Natural Aggregate (NA), characterized by distinct particle size distributions and water absorption properties. While fRCA can effectively replace NA in mortar mixtures, it does affect compressive strength due to higher water absorption and the partial retention of cementitious material. However, by milling or treating it with ACID, the quality of fRCA can be improved, making it possible to use fRCA as a replacement for NS in mortars. The optimal substitution rate of NA with fRCA is identified as 25%, with the possibility of an increase to 100%, depending on the specific application. The integration of fRCA in concrete holds potential for sustainability by reducing reliance on natural resources and curbing waste generated by the construction industry.

Construction and demolition waste form a significant problem in terms of environmental pollution and material depletion. Concrete, as part of construction and demolition waste, is already responsible for 9% of the total anthropogenic carbon dioxide emissions. Consequently, it is important to alleviate the environmental stress of concrete by replacing virgin aggregates and cement by recycled aggregates and liberated cement. This study determines how the properties of recycled aggregates and virgin (new) aggregates compare for using recycled aggregates in a new concrete mixture.
Recycled aggregate properties are examined by performing a variety of experiments, namely
water absorption and specific gravity, Los Angeles abrasion, flakiness and shape index and
compressive strength. Each experiment describes a different characteristic of the aggregates
creating a clear picture of their properties. The properties of virgin aggregates have been
obtained from literature.
In addition, a milling method has been examined as a possible new step in the recycling chain
for liberating cement paste from the fine recycled aggregates.
Water absorption and interfacial transition zone formed problems for the recycled aggregates,
but they show excellent properties in terms of compressive strength, resistance to abrasion,
grain interlocking and shape characteristics.
While very different from each other, recycled aggregates show very good properties when
compared to virgin aggregates giving them potential to be used in new concrete mixtures.