Effect of silica fume inclusion on the strength, shrinkage and durability characteristics of natural pozzolan-based cement concrete

In the present work, effect of inclusion of silica fume on the performance of natural pozzolan-based cement concrete was investigated. Natural pozzolan, obtained from volcanic rocks, was used as the main supplementary cementitious material to partially replace the Portland cement. Silica fume was admixed at an optimum dosage, optimally selected based on the performance of several trial mixtures, in an attempt to improve the performance of the natural pozzolan-based cement concrete. Compressive strength, drying shrinkage, water penetration depth, coefficient of chloride diffusion, carbonation depth, reinforcement corrosion, loss of strength due to exposure to sulfate and salt weathering were measured to evaluate the performance of the concrete mixtures. Inclusion of silica fume to the blend of natural pozzolan and Portland cement significantly improved the performance of concrete. Reduction in the early age compressive strength of natural pozzolan-based cement concrete was compensated for by the addition of silica fume. Inclusion of silica fume to the natural pozzolan-based concrete significantly improved the durability characteristics without significant increase in the shrinkage. Though the addition of silica fume increased the carbonation depth, the increased carbonation depth was much less than the cover thickness normally provided over reinforcing steel, ruling out the possibility of reinforcement corrosion.