Effect of expansive agent on the mechanical properties of carbon-fibre-reinforced cement-based composites

Improving the flexural strength of a cement-based composite (CBC) reinforced with chopped carbon fibre (CF) while maintaining good workability is highly attractive for building high-rise large-span structures. A sulfoaluminate-based expansive agent (EA) was used to optimise the mechanical properties of CBCs reinforced with chopped CF by improving the fibre–matrix interfacial properties. The results of single-fibre pull-out tests showed that the interfacial frictional bond strength was improved by up to 51% owing to the addition of the EA, whereas the chemical debonding energy remained nearly unchanged. The effects of various concentrations of EA on the strength of cement pastes containing various lengths and volume fractions of CF were then investigated. The results indicated that, benefitting from the EA-induced high interfacial bond strength, the flexural strength and fluidity of the CF-reinforced cement paste could be further optimised. For example, utilising the EA, the flexural strength could be improved by 28% for a cement paste containing 0.5% CF of length 15 mm.