Experimental investigation on the impact properties and microstructure of recycled steel fiber and silica fume reinforced recycled aggregate concrete

With the continuous development of the economy and society, the production of solid waste is increasing. Construction and demolition waste (CDW), used tires and silica fume are the main components of solid waste. Recycling these materials will reduce resource pressure, decrease carbon emissions and protect the environment, while bringing certain economic benefits. This study focused on the influence of the synergistic effect of recycled steel fibers (RSF) and silica fume on the mechanical properties and impact resistance of recycled aggregate concrete (RAC). The mathematical statistical model of Weibull distribution was adopted to depict the impact results. In addition, the microstructure of the interfacial transition zone (ITZ) between the cement paste and the aggregate/fiber was researched by scanning electron microscopy (SEM). Results revealed that the synergistic effect of RSF and silica fume significantly improved the impact resistance of RAC. Especially the specimen containing 10% silica fume and 0.75% RSF performed the best properties, the first crack impact and failure impact energy increased by 421.9% and 461.3%, the net-gain in them by the synergistic action of silica fume and RSF with values of 102.7% and 115.3%. The distribution law of the impact life for RSF reinforced RAC can better describe by the two-parameter Weibull distribution function. Impact resistance life was predicted corresponding to reliability levels. SEM investigations revealed that the ITZ between cement and aggregate/RSF significantly improved by mixing silica fume.