Effect of Acidic Curing Environment on the Strength and Durability of Concrete

Abstract

This paper investigates the effect of acidic curing environment on the strength and durability of concrete cured in water containing various percentages of Nitric acid.  60 number grade M20 concrete cubes of sizes 150mm x 150mm x 150mm, 18 number 150mm x 150 mm x 450mm concrete beams and 18 number 150mm x 300mm concrete cylinders are casted for compressive, flexural and tensile strength tests respectively, using a water cement ratio of 0.69 and mix ratio of 1:3:4, and cured in water containing 0, 5, 10, 15, and 20% of nitric acid by volume of water for 7, 14, 28 and 60 days. The result shows that the compressive strength of the cubes at all percentage concentration of the acid decreases with curing age. Also, the percentage decrease in strength increases with both percentage of acid and curing age. Thus the rate of deterioration is highest at 60 days curing in 20% acid concentration (47.8%). Tensile and Flexural strength tests at 28 days curing revealed that the strength decreased with increase in percentage concentration of acid, with a decrease of 22% at 20% concentration of acid in the case of flexural strength and 41% in the case of tensile strength. For a particular curing age, both the strength and mass of Concrete decrease with an increase in the concentration of acid. Also, for a particular concentration of acid, the strength and weight of concrete decrease with curing age. A near linear relationship exists between weight loss and loss in compressive strength. It can therefore be concluded that deterioration of concrete cured in acidic medium increases with concentration of acid and curing age. The durability decreases faster as the concrete ages. Thus, concrete structures cannot stand the test of time in acidic environment unless special cements are used.

Keywords: Acidic curing environment, Compressive Strength, Flexural Strength, Tensile Strength, Durability and Weight loss