Effect of Gypsum-Contaminated Aggregate on Long Term Properties of Mortar

Abstract

Contamination of aggregates with gypsum occurs frequently. Fine aggregate has more detrimental effect due to its large surface area. An experimental work had carried out to investigate the behavior of mortar made from six SO3 contents in the fine aggregate, five size fractions of gypseous aggregate and three C¬3A contents in the cement. The results show that significant expansions do not occur within mortar bars if the content of SO3 lies below 1.25% by the weight of fine aggregate and the reduction in strength is higher in later ages and for higher SO3 contents. The size fraction of gypseous aggregate also affects the degree of expansion, especially in the case of fine particles. The cement with C3A content lower than 5% can tolerate a higher level of contaminant gypsum.

Understanding the adsorption of calcium sulfate on tetracalcium aluminoferrite and tricalcium aluminate surfaces

“…11,12 The sources of sulfate are also from aggregates, groundwater, and seawater, and it reacts with C 4 AF, C 3 A, and its hydration products, causing volume expansion and generating cracks (known as delayed ettringite formation or internal sulfate attack). 13,14 An optimal sulfate content contributes to the highest mechanical properties and the lowest shrinkage. 15 It is beneficial to fully understand the differences in hydration mechanisms between C 4 AF and C 3 A to regulate the balance between C 4 AF/C 3 A and CaSO 4 and to ensure the best performance in using cementitious materials.…”