Silica fume and crumb rubber as partial replacement of cement and fine aggregate concrete

This study investigated nine mixes containing 0 or 15% silica fume as the cement replacement and 0 or 10% treated and untreated crumb rubber as the fine aggregate replacement. The fresh and mechanical properties of these concrete mixes were correlated with non-destructive test results including rebound hammer and Ultrasonic Pulse velocity (UPV). One curing scheme was adopted here in this study which was normal curing. Microstructure characterization was carried out using X-ray diffraction Analysis (XRD) and Scanning Electron Microscope (SEM). The XRD showed that the crumb rubber must be washed in clean water after pretreatment with sodium hydroxide (NaOH) to avoid ettringite formation in the concrete pores. The results showed that combining the silica fume and crumb rubber enhanced the compressive strength of the rubberized concrete. The rebound hammer numbers were closely correlated linearly with the compressive strength of the test mixes