Thaumasite sulfate attack on concrete: Mechanisms, influential factors and mitigation

Thaumasite sulfate attack (TSA) is a special form of sulfate attack typically occurring due to the availability of carbonates/bicarbonates in the cementitious matrix with abundance of moisture and a prevailing low temperature. It transforms concrete into a non-cohesive mass without any binding or load carrying capacity. Field and laboratory data show that the extent of TSA depends on multiple critical factors including exposure conditions (e.g. type and concentration of sulfate, change of temperature and relative humidity, location of structure/element relative to grade level) and constituents of concrete (e.g. type of cement, inclusion of limestone materials, type and dosage of supplementary cementitious materials). The current paper compiles and analyzes current knowledge/research on the topic from various field and laboratory studies. TSA on concrete is discussed in terms of the mechanisms of damage, test methods, most influential factors and code provisions in North America and Europe. In addition, a mitigation strategy for TSA is proposed based on the balance of physical and chemical resistances of concrete as controlled by key mixture design parameters.