Changes in long-term performance of fibre reinforced shotcrete due to corrosion and embrittlement

Abstract

The post-crack performance of fibre reinforced shotcrete (FRS) differs from that of conventionally reinforced concrete in that the post-crack pull-out characteristics of fibres depend on the properties of the concrete matrix. Changes in the concrete matrix with time can effect substantial changes in the post-crack performance of the fibres in a way that is independent of external exposure conditions. When cracks occur in the FRS matrix, fibres may also be exposed to aggressive agents that can reduce their already small cross-sectional area at the crack and thereby diminish their post-crack performance, particularly at larger levels of deformation. The present investigation has examined how the post-crack energy absorption capacity of fibre reinforced shotcrete is affected by the interaction of aging of the concrete matrix and corrosion at cracks. The findings show that changes in performance characteristics are related to crack width and fibre type. The majority of fibre types show negligible changes in performance at low deformations over time. However, following aging, some fibre types exhibit significantly lower post-crack performance at high deformations than is evident at 28 days. The use of fibre reinforcement in shotcrete therefore needs to address aging effects, the exposure conditions regarding potential corrosion, as well as the in-service conditions of use in order to specify an appropriate maximum crack width limit that will enable the chosen fibre type to perform without risk of corrosion or embrittlement.