Study on bending properties of coir fiber magnesium phosphate cement immersed in water

Magnesium phosphate cement (MPC), possessing the characteristics of fast setting and early strength, but has the disadvantages of poor toughness and easy cracking. Our previous studies found that these shortcomings could be improved by adding coir fiber (CF). In practical projects, chances are that CF-MPC might work in watery environment like rainy day. Therefore, it is important to understand the effect of water on the properties of CF-MPC. This paper was then committed to investigate the effect of water immersion on the bending performance of CF-MPC. A three-point bending test was employed to capture the flexural strength, flexural stiffness, and toughness of MPC with different CF contents cured in air and water respectively. The results demonstrated that CF-MPC cured in water and in air displayed a similar failure mode. Specimens' failure mode varied from brittle failure to ductile failure with CF content increasing. Moreover, the first and second peak loads of specimen load-displacement curves gradually decreased as the water curing time increased. The flexural strength dropped, different from the performances observed in specimens cured in air. But when CF content was smaller than 3%, this flexural property deterioration of specimens in water was relieved as CF content increases.