Physicomechanical properties of nano-silica effect on geopolymer composites

Addition of Nano-SiO2 (NS) to geopolymer composites has been studied through measurement of compressive strengths, Fourier Transformer Infra-Red (FTIR) and X-ray diffraction (XRD) analysis. Alumino–silicate materials are coarse aggregate included waste concrete and demolished walls with its cementing binder, cement kiln dust (CKD) used and can possess a pronouncing activation for the geopolymer reaction resulting from the high alkali contents within. Materials prepared at water/binder ratios in a range of 0.30: 0.40 under curing of 40 oC and 100% R.H, while the used activator is sodium hydroxide in the ratio of 2 wt. %. First, CKD is added in the ratio from 10 up to 50 wt., %, and the demolished walls was varied depending on the used CKD content, while using constant ratio of waste concrete (40 wt., %). Second step, depending on the optimum CKD ratio resulted from the first one (40 wt. %), so the control geopolymer mix composed of CKD, demolished walls and waste concrete in the ratio (40:20:40, wt %). NS partially replaced waste concrete by 1 up to 8%. Results indicated that, compressive strengths of geopolymer mixes incorporating NS were obviously higher than those control one, especially at early ages and specially with 3%NS.