Strengthening mechanism and microstructure of fibre-reinforced coral mortar and concrete

The effects of different dosages and lengths of carbon fibre (CF), sisal fibre (SF) and polypropylene fibre (PPF) on the microstructure and mechanical properties of mortar and concrete made with coral sand were studied through mechanical tests and scanning electron microscopy. In total, 37 groups of coral mortar and concrete specimens with the addition of CF, SF and PPF in four different dosages and three different lengths were tested. Based on mechanical tests and microstructure analysis, the strengthening effect and strengthening mechanism of fibre in coral mortar and concrete, and the mechanical properties of coral mortar and concrete were investigated. It was found that – compared with normal mortar and concrete – the workability of the coral mortar and concrete was poor due to its light weight, high porosity and rough surface. The strengthening effect of the fibres was reduced due to difficulty in dispersing the fibres evenly in the mortar and concrete. The addition of fibres significantly enhanced the flexural strength and toughness of the coral mortar and concrete, but an excessively high fibre dosage and the use of extra-long fibres significantly reduced its working performance due to the fibre curling and clustering, especially for CF. The optimal length and content of the different fibres were also investigated. The addition of SF was found to have the best strengthening effect.