RESIDUAL STRENGTH OF EPOXY-COATED PINEAPPLE LEAF FIBER EXPOSED TO HIGH ALKALINE ENVIRONMENT

Abstract

Employing plant fibers to reinforce cementitious materials is feasible but not ubiquitous as fibers degrade rapidly when exposed to the alkaline-rich environment in cement composites. To alleviate such degradation and promote the use of natural fibers, processes to enhance the alkaline resistance of the fibers are of great interest. In this study, a process of coating fibers with epoxy was researched, and its efficacy was compared with two typical fiber treatment processes – boiling in water at 100°C for 60 minutes and bleaching in 10% w/w NaOH solution for 30 minutes. Pineapple leaf fiber (PALF) was the natural fiber chosen for the experiment due to its excellent mechanical properties. An untreated PALF (controlled sample) and treated PALF were examined by means of a single fiber tension test and bonding test. From the test results, the epoxy-coated PALF (EPALF) exhibited the highest average tensile loading capacity and the highest bonding force. Therefore, only EPALF was selected for further alkaline degradation testing. As the curing process of the epoxy (at room temperature) was time-consuming, it was shortened by being cured at elevated temperatures. The optimum temperature is 100 ^oC, which was thus used to prepare EPALF for later study, named EPALF100. To predict the fiber degradation in high alkaline environment, EPALF100 samples were submerged in 10% w/w NaOH solution at temperature of 30 ^oC, 50 ^oC, and 70 ^oC for 30, 60, and 90 days, and then examined the residual tensile strength. An empirical equation to estimate fiber residual strength was then proposed.