Internal and external sources of sulfate ions in portland cement mortar: two types of chemical attack

This paper compares the effects of chemical attack on portland cement mortar from internal and external sulfate sources. Factors such as cement type, cement content, water to cement ratio, and addition of fly ash are studied with respect to expansion and strength development and it is found that substantial differences exist between the two types of sulfate attack. Expansion values used to evaluate both external and internal attack are discussed and a low bound of maximum expansion corresponding to the beginning of strength loss for internal sulfate attack is proposed. This threshold is a function of cement content rather than a constant.