Effect of silica fume fineness on the improvement of Portland cement strength performance

• Interaction between SF fineness and amorphous SiO2 on mortars has been assessed.
• The mortar compressive strength rises with the SF fineness increase.
• SF size distribution is a key factor regarding the compressive strength development.
• The addition of fine SF to PC improves the microstructure of hardened pastes.
• Higher strength and lower permeability have been assessed.

This paper presents both a study on the effect of silica fume (SF) fineness on the pozzolanicity of blended cement and a method for improving coarse SF performance in making high-strength and high-performance concrete. The coarse SF, having a 45 μm sieve residue of 32.11%, yields a low pozzolanic reaction. In order to enhance its quality, the coarse SF was ground until the average particle size was reduced to a 45 μm sieve residue of 4.13% and 0.98%. It was then mixed with Portland cement type CEM I 52.5 N-SR 3 by a weight of 25% to determine the strength activity index for it to be used to produce high-performance concrete.The pozzolanic reaction and quantitative influence of SF fineness on the mechanical strength in the SF containing composite cement system were examined in detail. XRF results indicated that reactive SiO2 content has a clear influence on pozzolanic performance, though not as important as the SF grain size. Several methods, including the pozzolanicity test (EN 196-5:2011), chemical analysis (XRF) and strength activity index techniques, were used comprehensively for evaluation of the SF containing composite cement system.The results suggest that the SF with high fineness is suitable for use in making CEM II/A–D cement in percentages of SF lower than 10%, according to the European Standard EN 197-1:2011 in producing a good quality, high-strength and high-performance concrete.