Use of highly reactive rice husk ash in the production of cement matrix reinforced with green coconut fiber

This study evaluated the influence of partial replacement of Portland cement by rice husk ash (RHA) to enable the use of green coconut husk fiber as reinforcement for cementitious matrix. The use of highly reactive pozzolanic ash contributes for decreasing the alkaline attack on the vegetable fiber, originated from waste materials. The slurry dewatering technique was used for dispersion of the raw materials in aqueous solution, followed by vacuum drainage of water and pressing for the production of pad composites, as a simplified simulation of the Hatschek process for industrial manufacture. Five formulations were evaluated, two of them without any mineral additions. One of the mixtures served as a reference (without green coconut fibers) and the remaining ones were reinforced with the green coconut fibers (5% by weight of binder) and with the content of Portland cement replacement by RHA equal to 0, 30, 40 and 50%. The composites were analyzed at 28 days of age and after aging by immersion in warm water (65 °C), which lasted for 28 additional days. Physical and mechanical tests were applied for assessment of the performance of composites. Thermogravimetric analysis was used to observe the consumption of portlandite and chemically combined water content in the hydrated products for pastes presenting the same levels of Portland cement replacement by RHA (i.e., 0-50%) and with the water/binder ratio kept constant and equal to 0.5. The mechanical performance evaluated by bending test after 28 days reached the MOR of 15.7 MPa after the accelerate aging, for the composites reinforced with the green coconut fiber and with high levels of Portland cement replacement by RHA demonstrating that the use of green coconut fiber for reinforcement can be very promising for the production of binary cement based matrix. The thermogravimetry showed that the replacement of Portland cement by the RHA helped in maintaining the mechanical behavior of the green coconut fiber in the composite subjected to the accelerated aging tests, and resulted in improved mechanical performance, providing a lightweight composite.