Effect of accelerated aging on the properties of microconcrete reinforced with sisal fibers

Abstract In this study, two microconcrete samples, with and without metakaolin, were designed for the production of laminated composites reinforced with long sisal fibres. In addition to the reference microconcrete, another microconcrete was produced by replacing cement by metakaolin.The ideal metacaolin content that would guarantee a free calcium hydroxide matrix was determined by thermogravimetric analysis of blends with 20%, 30% and 40% substitution contents at the ages of 4 h, 10 h, 24 h, 7 days, 28 days and 730 days. Laminates produced with cement substitution by 30% metakaolin were submitted to flexural test after 28 days of curing in water, and after 12 and 25 wetting and drying cycles. The analysis of the microstructure was performed by scanning electron microscopy and dispersive energy X-ray spectroscopy (EDS). The results demonstrate that in the microconcrete containing only cement, the calcium hydroxide was leached from the matrix and deposited on the surface of the fibre. Thus, the aged composites showed a sudden rupture due to the weakening of the fibres. With the incorporation of metakaolin, the matrix showed to be free of calcium hydroxide, and the mechanical behaviour after cracking was not altered by aging. However, the temperature and humidity variation due the wet-drying cycle has induced cracking of the microconcrete, which detrimentally affected the strength at crack initiation of these composites and their rupture mode.