Effect of grain size on the mechanical properties and crack formation of HPFRCC containing deformed steel fibers

This research investigated the influence of sand grain size on the behavior of high-performance fiber-reinforced cementitious composites (HPFRCC). Four types of sand with different grain sizes were investigated using the same matrix composition containing 2.0% hooked and twisted fibers by volume. The compressive strength was significantly greater for the finer sand grains, despite little difference in the packing density. The better compressive strength was mainly due to the denser calcium silicate hydrate (CSH) resulting from an intensive pozzolanic reaction with the finer silica sand, rather than to an improvement in packing density. The interfacial bond strength of those fibers was notably improved, having favorable effects on the mechanical properties and multiple crack formation of HPFRCCs. Although both fibers showed superior properties in mortars with a finer sand grain, twisted fiber produced more sensitive behavior according to the sand grain size.