Impact of Cement Hydration on Durability of Cellulosic Fiber‐Reinforced Cementitious Composites in the Presence of Metakaolin

Degradation of cellulosic fiber in the alkaline environment of concrete generated in the process of cement hydration is the primary reason for the low durability of such composites. However, the impact of cement hydration on cellulosic fiber's degradation in cementitious systems has not been thoroughly understood. This paper presents the dependence of deterioration behavior of cellulosic fiber‐cement systems on cement hydration in the presence of metakaolin. Experimental investigations, such as isothermal calorimetry, thermogravimetric analysis and energy dispersive X‐ray spectroscopy, and thermodynamic simulations are carried out to investigate cement hydration kinetics and hydration products. Durability of cellulosic fiber‐reinforced cement composite is assessed based on the degradation in flexural properties. The results indicate that, in the presence of metakaolin, the hydration of cement is enhanced accompanied by consumption of calcium hydroxide, low release of hydration heat, decreased Ca/Al and Ca/Si ratios of C–S–H phase, and reduced OH^‐ and Ca²⁺ amounts in pore solution. A cement substitution by 30 wt% metakaolin results in an improvement of flexural toughness and durability of cellulosic fiber‐reinforced cement composites by 42 and 269%, respectively. The correlations between composite durability and hydration of Portland cement are established.