Main considerations for the determination and evaluation of the acid resistance of cementitious materials

The paper reports on the development of an accelerated test method for determining and evaluating acid resistance of highly alkaline cementitious materials. The test method was derived through extensive laboratory experiments on hardened cement pastes, mortars and concretes, in order to determine the acid specific modes of action and to evaluate the related deterioration mechanisms for cementitious materials when subjected to acid attack. From the experimental study it can be concluded that the pH value of the acid solution is not the only decisive parameter. For example organic acids, such as acetic acid, cause a higher damaging effect compared to so-called "strong" acids (such as sulphuric or hydrochloric acid) because of the acid buffer action and the high solubility of the reaction products. In order to enable a constant deterioration rate the pH value during testing conditions has to be regulated at a stationary level, the degree of saturation in the acid solution needs to be regularly examined, and in particular for organic acids, the acid solution needs to be continuously stirred. The degree of degradation can be quantified by using visual methods or through measuring the residual mechanical properties, e.g. the compressive and/or flexural tensile strength. It should be noted that different damage mechanisms are possible, which are strongly dependent on the applied acid solution and constituents of the cementitious materials.