ABSTRACT
If concrete is to be used in practice it is necessary that it performs as designed throughout its service life, i.e. maintains its designed strength and serviceability. However, during the service life of concrete structures it is common that elements are subjected to external factors that cause deterioration and wear which may lead to an unserviceable structure if left untreated. Hence, the durability of concrete determines the concrete’s ability to resist such attacks and subsequent deterioration. One of the most common forms of concrete deterioration is from sulphate attack, which occurs due to the presence of sulphates in surrounding ground water (Wild et al. 1997, Mangat & El-Khatib 1992, Matthews 1995). Sulphate attack occurs through the reaction of aggressive sulphate ions with constituents of the hydrated material such as tricalcium aluminate hydrate (C-A-H) and calcium hydroxide (CH) (Bureau 1970, Mehta 1986, Lea 1998, Collepardi 2001). These reactions generally result in the formation of gypsum (CaSO4·H2O) and ettringite
(C3A·3CS·H32). This can cause excessive expansion, which can lead to cracking and strength loss. Magnesium sulphate reacts with the calcium aluminate hydrate (C-A-H) phases to form ettringite as shown in Equation 1.
