Effects of silica fume on mechanical strength and microstructure of basalt fiber reinforced cementitious composites (BFRCC)

In this study, the effect of different silica fume contents (0%, 5%, 10%, 15% by binder mass) as a replacement for cement on the mechanical strength and microstructure of cementitious composites containing chopped basalt fibers (0%, 1% and 1.5% by volume) has been evaluated. Flowability, compressive strength, flexural strength, toughness, water absorption and specific electrical resistivity of cementitious composites specimens have been investigated. The quality of fiber bonding in microstructure of cementitious matrix at 28-day age have been also analyzed and evaluated by the scanning electron microscope images (SEM). The results showed that clumping occurred at high amounts of fibers (1.5%) and silica fume (15%) which caused mixing and casting problems. Adding basalt fibers increased the flexural strength and toughness 2 and 6 times, respectively; however, it caused 47% decrease in compressive strength. Including silica fume had positive effects on fiber-matrix transition zone structure while increasing mechanical strength and specific electrical resistivity up to 20 times due to production of pozzolanic reactions and decreased portlandite so that it raised uniformity and density as well as bond quality.