Acid resistance of concrete

Sewers and sewage disposal systems in particular place high demands on the acid resistance of concrete. Practical application shows that ordinary pipe concrete is attacked chemically if it is permanently exposed to concentrated acids having a pH of less than 6.5. For that reason, improved acid resistance of pipe concrete is desirable for operating conditions in which long-term acid attacks in a pH range between 6.5 and 4.5 occur.

In a research project sponsored by the AiF, the Research Institute investigated possible ways of improving the chemical resistance of concrete in general and of concrete pipes in particular. This resulted in the development of concrete compositions that possess higher chemical resistance.

The fundamental concrete technology options for increasing chemical resistance by aiming at higher strength and, more in particular, higher impermeability of the concretes were examined more closely with the objective of optimising concrete mix formulations.

In reference to practice, most of the concretes were made from Portland cement CEM I 42.5 R. The concrete additions used were substances that react like pozzolana, such as silica fume and fly ash. Silica fume input totalled up to 8 wt.% relative to the cement content, and fly ash accounted for up to 60 wt.% relative to the cement content.

The investigations also served to determine the potential of cements with a high blastfurnace slag proportion to improve the chemical resistance of concrete. To that effect, investigations on blastfurnace cement CEM III/B 42.5 N were carried out.