EXPERIMENTAL INVESTIGATION ON MINERAL ADMIXTURE IN IMPROVING THE PROPERTIES OF CONCRETE TO SULFATE ATTACK

This paper presents an experimental investigation on the performance of mineral admixture in improving the resist-properties to sulfate attack, by measuring the relative dynamic modulus of elasticity index of concrete suffered long-term immersion and dry-wet cycle in saturated sodium sulfate solution. The mineral admixture, such as fly ash and silica fume, were added into concrete to replace various amount of cement. At the 90 dry-wet cycles, the ingressive depths of sulfate physical attack and the flexural/compressive strength ratio of specimens are investigated after the measuring of the relative dynamic modulus of elasticity. Experimental results indicate that the addition of mineral admixture can improve the performance of concrete in sulfate environment, and the silica fume combined with ultra-fine fly ash is effective in improving the resistance of concrete to sulfate attack for the formation of secondary C-S-H and various properties of pozzolanic reaction between silica fume and fly ash. The secondary C-S-H depositing in pores thereby makes the concrete dense and impermeable, therefore, the sulfate ions cannot easily penetrate through the matrix. The silica fume entitles the concrete a high strength in early time and fly ash endues the concrete with a great latency strength increasing, therefore, the bi-addition silica fume and fly ash concrete has enough strength to resist the swelling stress by salt crystallization.