Early-age shrinkage of cement pastes with polypropylene and curaua fibres

The aim of this research was to investigate the effect of the addition of discrete polypropylene fibres (PPF) and curaua fibres (CF) on the early-age autogenous and drying shrinkage of cement pastes. The fibres used were 12 mm long and the volume fraction varied from 0.3 kg/m³ (0.03%) to 2.7 kg/m³ (0.30%). Autogenous, unrestrained and restrained drying shrinkage tests were performed and it was found that the addition of these fibres influenced the different shrinkage behaviours. A significant reduction in autogenous shrinkage was observed in the specimens with 2.7 kg/m³ of CF, especially in the first few hours of curing. Regarding the unrestrained drying shrinkage, the addition of 2.7 kg/m³ of CF led to only a slight improvement (by about 8.5%) and lower fibre contents had little or no influence. The addition of PPF slight reduced the unrestrained drying shrinkage (by about 8.13%) for all the evaluated fibre contents. Both fibres delayed the development of cracks and reduced crack opening during the restrained drying tests. The addition of 2.7 kg/m³ of PPF or CF delayed cracking by 23% and 18%, respectively. The results indicate that discrete CF can be potentially used to restrain the autogenous and drying shrinkage of cementitious materials.