Effect of alkali activated limestone-silica fume blended precursor on performance enhancement of recycled aggregate concrete

The utilization of Recycled Aggregates (RA) from Construction and Demolition (C&D) waste, has been reported to be an efficient way of dealing with the environmental issues encountered by our planet nowadays. However, due to the poor quality of RA, its incorporation in high – grade civil engineering applications been limited. It is essential that adequate process of treatment methods be incorporated into the production of RA to enhance its properties and optimize its use. This study is carried out to determine the effects of an alkaline NaOH activated by limestone powder (LSP) and silica fume (SF) to improve the properties of various concrete mixes produced with either recycled concrete aggregate (RCA), or recycled cement block aggregate (CBA). Fifteen mixes were designed to examine the effects of different parameters, RA replacement levels, various w/c ratios and different enhancement methods on the properties of recycled aggregate concrete (RAC). The study examined the effects of the proposed enhancement method on the physical characteristics of RCA and CBA. Compressive strength, splitting tensile strength, flexural strength, pull-out, and water absorption of the different concrete mixes were measured to determine the effectiveness of the enhancement method proposed. The enhanced RAC produced by CBA and RCA showed an increased 28-day compressive strength at 0.35 w/c ratio of up to 51 MPa and 44 MPa, respectively, suitable for structural applications. The flexural strength, tensile splitting strength, and bonding strength values at 0.35 w/c ratio of the enhanced RAC produced with treated CBA were 28%, 6%, and 8% higher than that of the RAC produced with treated CBA. Whereas, the flexural strength, tensile strength, and bonding strength of the enhanced RAC produced with treated RCA were 1%, 3%, and 5% higher compared to the RAC produced with treated RCA. The improved mechanical performance of the enhanced RAC produced by CBA or RCA was attributed to the effects of the geopolymer solution treatment in filling and sealing the voids and gaps on the CBA and RCA surface, leading to a better packed structure, reducing the water absorption, and improving the aggregate impact value. The treatment technique proposed can be a powerful tool for promoting the use of RA in the construction industry and expanding its application.