Effect of long-term ageing by temperatures on mechanical behaviour of Fibre Reinforced Concretes

This study examines the effect of ageing by operating temperatures on the mechanical properties of Fibre Reinforced Concretes (FRCs) when exposed during long-term periods (180 days of conditioning). There is little information in the literature about long-term mechanical performance of steel (SFRC), and especially, macro synthetic fibre reinforced concretes (MSFRCs), which may be affected due to this exposure. One type of steel fibre and three types of macro synthetic fibres were selected to reinforce an ordinary concrete in this work. An extensive experimental campaign (with a total of 260 specimens) which includes compression and flexural tests performed at temperatures, was carried out to investigate the influence of a range of temperature from-15 to 60 degrees C. Additionally, the interaction between cracking conditions (up to 0.5 mm) and temperature was analyzed for both type of FRC beams. The compression results obtained show higher strengths at low temperatures (25-30 %) and a decrease on the strengths at higher temperatures (15-20 %), but these variations are not crucial on the ageing of FRCs. Similar effects were detected for the strength at the peak load, and to a minor extent, for the residual flexural strengths, for all the FRCs. Specimens with a pre-existing crack (cracked condition) exposed to the studied temperature had the same results as uncracked specimens. Thus, both FRCs have the potential to obtain appropriate results for structural applications when exposed to the studied temperatures.