Degradation of Natural Fiber in Cement Composites Containing Diatomaceous Earth

Abstract

This paper reports the results of an investigation carried out to understand the influence of two different diatomaceous earths on the service life of natural fibers in cement composites. Deterioration of the embedded natural fiber was determined using two methods: development of flexural properties of natural fiber-reinforced mortar under accelerated aging, and direct investigation of fiber strength and components by means of micro-force tensile testing and thermogravimetric analysis. By replacing 2% cement with natural mineral admixture (diatomaceous earths), the cement hydration was enhanced and 24.4% calcium hydroxide was consumed, generating a mild environment for the natural reinforcement. The tensile strength of the aged natural fiber after 2 wetting and drying cycles was improved by 3.8 times. Due to fiber degradation, the flexural strength and toughness of fiber-reinforced cement mortar decreased by 9% and 98%, respectively, after 1 wetting and drying cycles. By incorporating diatomaceous earths, after 1 wetting and drying cycles, flexural strength and toughness as high as 5.3 and 7.9 times, respectively, of those of the control group were observed, suggesting that the degradation in the flexural properties of the cement composites was effectively mitigated. The influence of diatomaceous earths on the hydration of cement and its correlations with the durability of the fiber and composites were also studied. Investigations of the deterioration in interfacial bonding between cement matrices and aged natural fibers and the optimization of the pozzolanic activity of diatomaceous earths in cementitious systems are recommended as future work.