Effect of short-term exposure to moderate temperatures on the residual strength of cracked fibre reinforced concretes

Abstract

This work studies the effect of short-term exposure to the temperatures of -15°C, 5°C, 40°C and 60°C on the flexural performance of Fibre Reinforced Concretes (FRCs) with steel and synthetic fibres in cracked conditions. The results will be compared with the performance in cracked conditions at 20°C (submerged and air environments). The content of the fibres was chosen to guarantee similar residual strength in all the mixes. The beams were pre-cracked following EN 14651 at ambient temperature after 28 days, up to a crack mouth opening displacement (CMOD) of 0.5 mm. Afterwards, these beams were exposed for 3 days to moderate temperatures, and they were re-loaded up to failure maintaining the target temperature during the test. The residual strength at CMODs of 1.5, 2.5 and 3.5 mm was analysed. Concrete mixes were also characterised by compressive strength, air content, fresh density, and workability. The results show that residual strengths of cracked FRC are more sensitive to sub-zero temperatures than to warm temperatures, similar to the behaviour of uncracked specimens. Synthetic and steel FRCs presented enough flexural response after short-term exposure to moderate temperatures under cracked conditions.