Optimization of the acid resistance of slag-rich concrete

Project duration: 2015 to 2019

It is well known that concrete has a fundamentally high resistance to many media. As a rule, structures subject to high chemical stresses, such as wastewater engineering plants, cooling tower shells or catch basins, are made of concrete, since many properties of this building material are initially advantageous for this purpose. A considerable disadvantage, however, is the only limited resistance of concrete, especially Portland cement concrete, to acid attack. Even if an "acid-resistant" concrete cannot be produced with known systems, an "increased resistance to acid attack" would offer significant technical and economic advantages.In principle, it is known that to increase acid resistance, the use of granulated blastfurnace slag in place of the Portland cement releasing Ca(OH)2 during hydration offers technical advantages, since from a chemical point of view the potential weak point of the cement paste, the easily soluble large Portlandite crystals, is reduced. The scientific and technical problem is now to optimize the granulated blastfurnace slag content of the binder to such an extent that maximum chemical resistance is achieved, while at the same time ensuring practical processing properties and appropriate strength development of the concrete, without any technical and economic disadvantages.In order to avoid high costs as a result of repair measures and shutdowns, the protection of concrete components exposed to high chemical stress is currently mostly ensured by additional measures. However, these are disadvantageous due to their limited service life and cost- or time-intensive execution. It is therefore necessary to optimize the acid resistance of the concrete structure and, in particular, of the binder matrix. Various approaches have already been developed for this purpose, but they are problematic from an economic point of view, among other things. Optimization through the use of granulated blastfurnace slag, on the other hand, is advantageous from an economic point of view. In addition to specific technical advantages, blastfurnace slag offers the ecological advantage that, as a by-product of pig iron production, it has a significantly lower "ecological rucksack" than Portland cement clinker, particularly with regard to process-related CO2 emissions and the demand for natural resources.