SULFATE RESISTANCE OF HIGH FLY-ASH CONTENT CONCRETE

Changes in length, compressive strength, dynamic modulus of elasticity and pulse velocity of high fly ash content concrete with replacement levels of up to 50 % when completely immersed in the 10 % Na2SO4 solution were periodically measured for 2 years. It Was found from the measurements of mechanical properties that the 50 % replacement by fly ash was very effective in the improvement of the sulfate resistance of concrete. During 2 years of exposure to the 10 % Na2SO4 solution, high fly ash content concrete with the binder content of 400 kg/m(3) and with replacement level of 50 % was steadily gaining the compressive strength, and no detectable deterioration was observed. Chemical analysis data also showed that the excellence of high fly ash content concrete in the Sulfate resistance was attributed primarily to the prevention of congress of sulfate ions into concrete, resulting in little formation of gypsum and/or ettringite in concrete.