Durability of fibre concrete containing high-volume fly ash in complicated environment

The deterioration of engineered cementitious composites (ECCs) incorporating ultra-high-volume fly ash (FA) under the coupled action of freeze–thaw (F–T) cycles and sulfate attack is explored in this paper. Three mixes, with FA/cement ratios of 1.2 (FA1.2), 1.8 (FA1.8) and 2.4 (FA2.4), were investigated. ECC specimens were subjected to F–T cycles under 10% sodium sulfate (NaSO₄) solution and 10% magnesium sulfate (MgSO₄) solution. In addition, loss of weight, variation of relative dynamic elastic modulus (RDEM) and compressive strength were determined at different numbers of F–T cycling. What is more, the microstructure of ECCs was investigated after the final 150 F–T cycles. It was observed that RDEM decreased with the increase of the FA content in sodium sulfate solution; on the contrary, specimens of FA1.8 showed the highest RDEM in magnesium sulfate solution. It can be found that the residual compressive strength of specimens in magnesium sulfate solution declined firstly and then increased within all F–T cycles, while it continued to decrease in sodium sulfate solution. The residual compressive strength was higher in magnesium sulfate solution than in sodium sulfate solution, achieving a maximum of 34.7 MPa.