Sustainable self compacting concrete from C&D waste by improving the microstructures of concrete ITZ

This paper presents the microstructural changes and the improvement in mechanical properties of self compacting recycled aggregate concrete (SCRAC) which is prepared with the use of construction and demolition (C&D) waste. Experimental investigation reveals that with 7% replacement of fly ash by silica fume yields required fresh properties and improved mechanical properties. Proportional amount of cement is added with 7% silica fume to prepare a silica fume-cement slurry for making a proper mix with RCA in premix stage. Two stage mixing approach((silica fume, fly ash and cement)) (TSMA(sfc)) is followed, where the silica fume-cement slurry fills up the weak areas in the recycled concrete aggregate (RCA) and improved interfacial transition zones (ITZs) are developed resulting higher strength in concrete. Electron probe micro-analyzer (EPMA) is used to investigate the microstructure of SCRAC by indentifying different constituents of concrete (C-S-H, CH, unhydrated cement and epoxy). This analysis confirms the improvement of ITZ because of two stage mixing approaches. Wavelength dispersive X-ray spectroscopy (WDS) is used for quantitative and chemical analysis of ITZ. Improvement in properties of SCRAC obtaining with 100% RCA and 7% silica fume using TSMA(sfc) is confirmed by EPMA examination and WDS. (C) 2017 Elsevier Ltd. All rights reserved.