Effects of low calcium bentonite on the strength development of recycled aggregate concrete

The negative environmental impact of high cement use and aggregate extraction can be minimized by the use of greener materials and recycled aggregate (RA) instead of conventional materials. In this study, the effects of a low-calcium bentonite (LCB) binder on the strength development and workability of recycled aggregate concrete are investigated. RA is used as 0, 50, and 100% by volume replacement of natural aggregate concrete (NAC), whereas bentonite is used as 0, 5, 10, 15 and 20% by weight replacement of cement for each level of RA. LCB addition significantly improved the 90-day compressive, flexural, and splitting tensile strengths of normal and RA concrete, whereas at 28 days, the results of the LCB mixtures were comparable to those of the control. The RA mixtures had slightly reduced compressive strengths, similar tensile strengths, and superior flexural strengths to those of NAC after 90 days. Higher correlations between all strength results with successively higher RAs. These results can be attributed to the pozzolanic properties of LCB and their symbiotic relationship with the mortar adhered to the surface of the RA, along with greater bonding surface regions for the cement matrix. The response surface methodology (RSM) confirmed the trend in strength.