Returned concrete, a waste product of ready-mixed concrete (RMC), is generally washed to reclaim coarse aggregates from the finer portion consisting of fine aggregate, hydration products of cement, and un-hydrated cement particles, if any. In searching for environmentally sustainable construction materials, this finer part, termed as washed fines (WF), may substitute natural sand in producing mortar and concrete. An extensive study was conducted to determine the feasibility of replacing sand with WF by testing mortar cubes (50 mm x 50 mm x 50 mm) and prisms (285 mm x 25 mm x 25 mm) at replacement levels of natural sand by WF at 5%, 10%, 15%, and 20% for compressive strength, sorptivity, and drying shrinkage. The specimens were made with different types of cement. The microstructure of hardened mortar around WF was also examined using scanning electron microscope (SEM). Field trials reusing WF in concrete were conducted at an RMC plant to validate the laboratory results. Findings indicate compressive strength of mortar increased up to 19% with partial sand replacement by WF. The incorporation of WF reduced shrinkage and sorptivity coefficient. SEM images revealed a dense microstructure around WF in hardened mortar.
Read full abstract