Effect of Steel Fibers, Polypropylene Fibers and/ or Nanosilica on Mechanical Properties of Self-Consolidating Concrete

Abstract

This research concerned studying the combined effect of using nano-silica and/ or hybrid fibers on key mechanical properties of self-consolidating concrete SCC. A comprehensive experimental work has been carried out, using steel fiber (SF) with volume fraction (0, 0.5% and 1.5%), polypropylene fiber (PPF) (0%, 0.05% and 0.15%) and SiO2 nanoparticles (0%, 2% and 4%) by weight of powdered material (silica fume- Sf ) with constant w/c ratio (0.48) to produce eleven different mixtures and tested at different ages (7, 28 and 90 days). Results showed that adding fibers adversely affect SCC workability and thus more dosage of super plasticizer (SP) should be added to stay within the standard limits. comparable to conventional concretes, the presence of steel fibers with SCC provide slight increase in compressive strength at 28 days, (up to 11%), while significant enhancement in tensile properties were observed (up to 24% and 32% for splitting and flexural strength respectively). Polypropylene or hybrid fibers however, provide lower enhancement compared with steel fibers. In contrast, implementation of nanosilica leads to significant improvement in concrete strengths particularly at 4% dosage. Combined effect of 4% nanosilica and 1.5% of steel fibers provide the superior hardening effect on the flexural performance compared with softening effect provided by other added dosages. Scanning Electron Micrograph (SEM) images confirm the matrix densification effect due to nanosilica adding. Flexural strength of SCCs without nanosilica was generally higher than splitting testing results. This fact does not change even with the presence of nanosilica and/ or fibers.