Influence of accelerator type and dosage on the durability of wet-mixed sprayed concrete against external sulfate attack

Abstract External sulfate attack in concrete comprises a series of interdependent processes resulting from the interaction of sulfate ions from the external environment and cement phases, resulting in matrix degradation. To obtain a sulfate-resisting matrix, C3A content in cement and water/cement ratio must be controlled. In sprayed concrete, accelerator type and dosage and the interaction between cement and accelerator are important parameters that control sprayed concrete strength and may influence the durability of the matrix. In this context, the objective of this study is to evaluate how accelerator type and dosage influence the durability of sprayed concrete exposed to a sulfate solution. Samples were analyzed by XRD, TGA, SEM, length change, US propagation velocity, compressive strength and water accessible porosity for 270 days. Results showed that sprayed concrete produced with accelerators presents a high deterioration rate due to sulfate attack. Kinetics of specimen expansion and reduction of compressive strength are directly related to the final SO3/Al2O3 ratio of the matrix. This study may be useful to understand how external sulfate attack occurs in sprayed concrete and to develop prediction models and guidelines.