Degradation behavior and kinetics of sisal fiber in pore solutions of sustainable cementitious composite containing metakaolin

Degradation of cellulose is the primary cause for the premature failure of natural fibers in the alkaline environment of cementitious systems. However, the degradation behavior and kinetics of cellulosic fibers in cementitious composites have not been thoroughly understood. In this study, the aging kinetic of cellulose exposing to pore solutions of cementitious materials is experimentally investigated and a model for service-life prediction of cellulose in cement is developed. To assess the impact of cement hydration on degradation behavior of cellulosic fibers and understand the correlations between fiber degradation and alkaline environment of cement, an approach to directly assess degradation rate of the embedded fibers was developed by determining fiber's tensile properties, thermal decompositions, crystallinity, and microstructures. The results indicate a strong dependence of degradation of sisal fiber on alkalinity of cement pore solutions. By incorporating 30 wt% metakaolin clay, the hydration of cement was modified and a mild environment was generated. Concentration of OH- was reduced and the pore solution becomes from oversaturated to unsaturated for calcium hydroxide after 7 days. As a result, tensile strength loss of the aged fiber was mitigated and the service life of cellulose was extended by 13.7 times.