Effect of Crystalline Admixtures in the Mass Transport of Concrete with Polypropylene Microfibers

This article aims to evaluate the mass transport properties in concretes with different contents of polypropylene microfiber (0% and 1%, by concrete volume) and crystalline admixture (0%, 1%, and 3%, by cement mass). Water absorption by immersion, water absorption by capillarity, and air permeability tests were performed to evaluate the properties of mass transport. Images of the microstructure of the concretes were used to support the hypotheses discussed. The tests were performed immediately after curing (28 days) and after curing plus 35 and 70 days of wetting and drying cycles. The combined use of polypropylene microfibers and crystalline admixtures may increase the properties of mass transport at an early age. Nevertheless, the nucleation of hydrated phases around polypropylene microfibers contributed to the densification of the concrete pores over time. The crystalline admixture can close larger pores and reduce connectivity between them in the first ages (first 35 days). However, the effect of crystalline admixtures in filling capillary voids requires more time to occur (around 70 days). The void index was reduced between 0 and 70 days by 47%, 42%, and 44% for reference, F + 1CA, and F + 3CA concrete mixtures, respectively.