Acid corrosion resistance of different cementing materials

This study has investigated the corrosion of different hardened cementing materials, such as Portland cement (PC), alkali-activated blast furnace slag cement (ASC), lime-fly ash (LFA) blend and high alumina cement with gypsum and lime (HAC), in pH 3 nitric acid, pH 3 acetic acid, and pH 5 acetic acid solutions. Experimental results indicated that PC pastes were corroded faster than ASC and LFA pastes, and pastes consisting of HAC were quickly dissolved in these acid solutions. PC pastes are more porous than ASC pastes but much less porous than LFA pastes. Thus, the corrosion of hardened cementing materials in acid solutions depends on the nature of the hydration products rather than the porosity of the hardened cementing materials: calcium silicate hydrate (C-S-H) with a low C/S ratio is the main hydration product in ASC and LFA pastes, while C-S-H with a high C/S ratio and Ca(OH)(2) are the main hydration products in hardened PC pastes. Ca(OH)(2) decomposes as the pH drops below 12, and C-S-H decalcifies as the pH decreases, and decomposes for pH values below 9. The mixture of high alumina cement, gypsum, and lime results in the formation of an ettringite-based matrix, which was dissolved very quickly in these acid solutions. (C) 2000 Elsevier Science Ltd. All rights reserved.