Flexural strength and impact resistance study of fibre reinforced concrete in simulated aggressive environment

Abstract

In addition to being exposed to chloride and sulphate attacks, marine structures are subject to seismic and impact loads resulting from waves, impact with solid objects, and water transports. Therefore, the flexural behaviour and impact resistance of Fibre-Reinforced Concrete (FRC) in marine environment must be elucidated. However, such information is scarcely reported. Therefore, this study aims to explore the effects of simulated aggressive environments on flexural strength and impact resistance of FRC and to identify the relationship between the two parameters. Three types of fibres, namely, coconut fibre, Barchip fibre (BF), and alkali-resistant glass fibre, were used in this study. The fibre dosage ranged from 0.6% to 2.4% of the binder volume. All mixes have constant water/binder ratio of 0.37 and their compressive strengths were all exceeding 60MPa. The specimens were prepared and exposed to three different aggressive exposure environments, namely, tropical climate, cyclic air and seawater conditions, and seawater environment for up to 180days. Results indicate that flexural strength and impact resistance of FRC have a direct relationship with fibre content. Nonetheless, change in fibre type is more significant than increasing fibre dosage in enhancing flexural strength but alteration in both matters would significantly impact the impact resistance. Tensile strength of an individual BF (640MPa) is much higher than the flexural strength of the BFRC composite. Thus, failure of concrete matrix was observed to occur prior to the rupture of the fibre which in turn resulted in fibre pull out from the concrete matrix. Among the various FRC examined, FRC containing the highest BF content (2.4%) demonstrated the best flexural strength performance. The flexural strength of the Barchip FRC was observed to be increased by 11–13% in all exposure environments after 180days. The pre-crack energy absorptions, which were determined through impact load test were found to increase by 60–63% as compared to the control concrete, which exhibited no post-crack energy absorption. Meanwhile, the post-crack energy absorptions of the 2.4BF were found to range between 3.67J and 3.71J for various environmental exposure conditions. Analysis of variance (ANOVA) results showed that flexural strengths were significantly increased after six months of exposure to the various aggressive environment conditions, especially in seawater. This could be due to formation of salt crystals which contributed towards enhancing the fibre/matrix frictional bond. However, the exposure environments have no significant effect on impact resistance performance. A logarithmic relationship was found between flexural strength and total impact energy absorption.