Study of Pozzolanic Admixtures Effects in the Concretes Under Chemical Attack

Abstract

The alkaline nature of concrete makes it highly vulnerable to acidic attack. The chemical attack occurs due to the decomposition of hydration products, forming soluble products that can be leached, or insoluble products than can expand in their formation site. The use of cements with pozzolan and blast furnace slag in concrete mixtures reduces their permeability, as well as their porosity, besides consuming part of the calcium hydroxide. These characteristics are signs of benefits for the reduction of the effects of corrosion caused by acid in the concretes. In this study, the effect of the presence of pozzolanic materials on the resistance of concrete against acidic attack had been investigated by considering two different acids. The concretes studied were inserted in lactic and formic acid solutions, thus simulating environments commonly found in the dairy, paper and cellulose industries, respectively. The tests were made with concretes with two water/cementitious materials ratios and two different content of replacement of cement by silica fume, 8 and 15 %, apart from pozzolanic cement. Test specimens with 100 mm × 200 mm cylindric dimensions were immersed in acid solutions after the curing process, and then subjected to cycles of wetting and drying. Mass loss and compressive strength tests were carried out between cycles of exposure to the acids. At each water/cementitious materials ratio, the mass loss and compressive strength loss of concrete with silica fume were less than the concrete without pozzolan. The presence of pozzolan decreased the detrimental effect of both acids in concrete. And besides, it was verified that formic acid is more aggressive for all concrete mixtures.