Insights on the use of recovered aggregates for concrete production

The construction industry is a great source of waste generated in the production and demolition phases. The most common type of waste generated on construction sites is Construction and Demolition Waste (C&DW), typically composed of concrete and bricks mixed with minor quantities of steel and timber, depending on the geographical area, site organization and local recycling practices. In addition to direct waste production generated in the construction phase, indirect waste, comprising by-products and materials produced during manufacturing and processing, also poses a significant environmental burden. Steel slags are an example of this kind of waste, which includes Blast Furnace Slags, Basic Oxygen Furnace Slags and Electric Arc Furnace Slags (EAFS). EAFS is generated in Electric Arc Furnaces, primarily used to recycle steel from scrap. Once cooled, the EAFS assumes a stone-like appearance with high-density. Batching plants are another significant source of waste, particularly through the accumulation of leftover concrete and washing residues, usually called Concrete Sludge Waste (CSW). At the same time, the construction industry is a great consumer of raw materials, and aggregates are the most consumed overall because of concrete production, which is the most produced and consumed substance on the planet after water. To save raw materials and limit the need for waste landfilling, recovered aggregates, e.g. those obtained from C&DW or EAFS, can effectively replace conventional gravel and sand for concrete production. However, landfilling is still quite common for most of this waste due to the reluctance of builders and stakeholders, absence of specific guidelines and insufficient information. The aim of this thesis is to address several mechanical challenges that may hinder the widespread adoption of recovered aggregates in concrete production. EAFS is here adopted to replace the coarse fraction of the natural aggregates, and to investigate specific mechanical properties which are unexplored in literature, i.e. the shear strength and the cyclic loading behavior. Furthermore, additional tests were performed on mortars with fine EAFS to evaluate and predict the yield stress in the fresh state. The results demonstrate usually superior performance than the conventional counterpart. Recycled concrete made with recycled aggregates recovered from C&DW shows some issues typically linked to higher shrinkage and inferior mechanical performance compared the conventional counterparts. In this thesis, a method is proposed to enhance recycled concrete properties with the addition of Raw Crushed Wind Turbine Blade (RCWTB), a waste obtained from the recovery and crushing of decommissioned wind turbine blades. The results demonstrate substantial reductions in plastic shrinkage and notable enhancements in flexural strength. Finally, hardened leftover concrete (CSW) is also explored as both partial and total aggregate replacement, reporting satisfactory results.