Properties of SCC containing pozzolans, Wollastonite micro fiber, and recycled aggregates

Self compacting concretes (SCC) containing higher volumes of pozzolanic materials possess compressive strengths up to 30MPa. Fibers like steel, polypropylene, and carbon fibers are added in small volumes ranging from 0.25-2% v/v of concrete to increase the strength (>40MPa) of such concretes as higher volumes of fiber cause balling effect on account of inhomogeneity, thereby reducing the strength and workability. Hence higher volume of cement substitution either with mineral admixtures or fibers, or with both, to increase strength and workability is limited in the case of SCC. The condition worsens further if recycled aggregates replace normal aggregates. Wollastonite micro fiber (WMF) is a promising material that could be used in higher contents but its interaction with recycled aggregates to affect workability and strength has not been studied. Therefore this study tries to obtain a high strength concrete (>M40) by use of WMF along with flyash @ 5%, maximally up to 10% each. Microsilica was added @ 2.5%, maximally up to 10% to improve the interphase strength and make the concrete homogeneous. Results indicated that in order to obtain a high strength mix for such composites, higher amounts of WMF (>= 10% by weight of binder) such that WMF:flyash varies from 1:1 to 2:1 is required, along with microsilica contents >= 7.5%. Literature suggests 5% microsilica along with either 20% WMF or 10% flyash, for yielding high strength SCC without recycled aggregates. Hence use of nearly equal amounts of WMF, flyash, and microsilica such that nearly 30% of cement is substituted, is recommended.