Fresh, mechanical, sorptivity and rapid chloride permeability properties of self-compacting concrete with silica fume and fly ash

The effects of the use of silica fume (SF) and fly ash (FA) on the fresh, mechanical and durability properties of self-compacting concrete (SCC) were experimentally examined. Combinations of F-class FA ranging from 15 to 45% and SF ranging from 5 to 15% were replaced for Ordinary Portland. The effects of FA and SF replacement on fresh concrete parameters (slump flow, L-box, V-funnel and U-box), mechanical properties (compressive and flexural strength) and durability properties (capillary water permeability, and rapid chloride ion permeability) were investigated. Test results showed that, replacement of cement with SF and by up to 30% FA increased mechanical properties of SCC series at 28 and 180 days, compared to the control group. With increased amounts of FA in SCC mixtures, however, a decrease in the compressive and flexural strengths was observed. The increased ratios of FA and SF in SCC mixtures significantly decreased the rapid chloride permeability and water absorption values of concrete in 180 days. Especially, in SCC mixtures prepared with FA, very low chloride permeability resistance was obtained at 180 days. The lowest chloride permeability resistance was observed to be 345 Coulomb at 180 days for SCC with 45% FA content. Minimum sorptivity coefficient was obtained as 0.062 mm/min(0.5) at 180 days for SCC with 15% SF content. Although the sorptivity coefficients of the FA-containing mixtures decreased on the 180th day compared to the control sample, these values were higher than the reference sample on the 28th day. Therefore, it may be misleading to take the 28th day sorptivity coefficient values as a basis for mixtures containing FA. The results showed that the curing time had a significantly effect on the sorptivity coefficient of the FA-added mixtures. Also, unlike the SF-added SCC mixtures, no obvious correlation was found between the compressive strength and sorptivity coefficient of the FA-added mixes.