Optimizing the Acid Resistance of Concrete with Granulated Blast-Furnace Slag

Abstract

Concrete for agricultural or industrial applications is often subject to intense acid attack. Most affected structures are sewage structures and biogas plants, natural draught cooling towers or silage silos. Widely independent from acid type, in most cases the acid attack on concrete runs the same way, starting with dissolution of easily soluble calcareous phases like calcium hydroxide. With ongoing attack, calcium-silicate-hydrate crystals (CSH) are also affected by acidic media. In contrast, siliceous phases like silicon-dioxide (SiO2) are widely unaffected by acid attack. While the dissolution of the matrix is increasing with ongoing attack, quarzitic aggregates remain unchanged. Beside the use of coarse SiO2-aggregates, the resistance against acid attack is mainly increased by a minimization of the porosity. For this purpose on one hand, a low water/cement-ratio has to be sought, on the other hand also the fines should be distributed with an optimized grading curve (e.g. Fuller-principle). In practice, this results in a combination of various fine and ultra-fine components, e.g. fly ash, GGBS, silica fume or metakaolin. Such binder compositions lead to a particularly dense microstructure, especially at pore sizes below 1 micron, and a higher chemical resistance due to a lower Ca(OH)2 content. This paper gives an overview on typical acid-resistant concretes, most common applications as well as the effects of the related acid attack and points out the potential of granulated blast furnace slag addition to such concretes.