Effect of Microcracking on Frost Durability of High-Volume- Fly-Ash- and Slag-Incorporated Engineered Cementitious Composites

Abstract

This paper reports the durability performance of high-volume-fly-ash (FA)- and slag (S)-incorporated engineered cementitious composites (ECCs) when subjected to mechanical loading and freezing-and-thawing cycles. Composites containing two different contents of FA and slag as a replacement of cement (55 and 70% by weight of total cementitious materials) are examined. To find out the effect of mechanical preloading on the frost durability of ECCs, prism specimens were preloaded up to a certain deformation level under four-point bending loading to generate microcracks. Then, the preloaded and pristine (sound) specimens were subjected to the freezing-and-thawing test in accordance with ASTM C666/C666M. Experimental tests consisted of measuring the change in mass and ultrasonic pulse velocity (UPV) and residual flexural properties of ECC specimens exposed to the freezing-and-thawing cycles up to 300. Test results revealed that the frost resistance of ECCs was significantly influenced by the mineral admixture type and amount and preloading deformation. The deterioration with an increasing number of freezing-and-thawing cycles was relatively more for ECC mixtures with FA than for slag mixtures at the same replacement level. In addition, an increase in the FA replacement rate was observed to exacerbate the deterioration caused by freezing-and-thawing cycles. Apart from some reduction in flexural properties and UPV and an increase in mass loss and residual crack width, the results presented in this study, however, confirm the durability performance of ECC material under freezing-and-thawing cycles, even in cases where the material experiences mechanical loading that deforms it into the strain hardening stage prior to exposure. It is important to note that this durability of ECCs under freezing and thawing was achieved without deliberate air entrainment, and contrary to conventional concrete, no relationship of frost resistance was found to the air-void structure of the ECC mixtures.