Recycled coarse aggregate and silica fume used in sustainable self- compacting concrete

When used in conjunction with cementitious mortar, recycled coarse aggregates (RCA) from demolition and rubble debris have numerous financial and environmental advantages by reducing carbon dioxide (CO2) emissions, minimising wasteful resource consumption, and assisting in a cleaner concrete manufacturing process. This paper evaluates fresh properties, durability properties and compressive strength (CSs) of self-compacting concrete (SCC) using RCA and silica fume (SF). Therefore, in this study, the effects of partial replacements of natural coarse aggregate (NCA) by RCA and ordinary Portland cement (OPC) by SF in the SCC mixes, cured in normal tap-water and also, in the presence of sodium sulphate (Na2SO4) solutions (2.0 g/l) for the exposure period of 28, 180 and 270 days, are investigated. Three different SCC mixes – control mix (CM) [OPC (100%) +NCA (100%)] whereas the other mixes have been designated as Mix-SF10 [OPC (90%) + SF (10%) + NCA (100%)] and Mix-SF10RCA25 [OPC (90%) + SF (10%) + NCA (75%) + RCA (25%)]. The fresh and hardened properties of the mixes, along with their microstructural properties were determined. The change in microstructure of the SCC mixes due to sulphate attack were investigated by X-ray diffraction (XRD). It is concluded that fresh properties are increased up to an optimum level of SF content (SF-10%) and in case of RCA, the trend reverses; the gain in CSs of different SCC in normal tap-water is lies between 6.76-25.00%, and reductions in CSs of SCC mixes exposed to Na2SO4 solution is in the range of 0.75-7.01 % in comparison to the SCC mixes's strength in normal tap-water. In contrast to the CM, the Na2SO4 attack had a smaller impact on the SCC mix, which contained SF viz., SF10 and SF10RCA25.