The combined effect of coir and superplasticizer on the fresh, mechanical, and long-term durability properties of recycled aggregate concrete

Abstract

The investigations to resolve the issue of low ductility and toughness of concrete led to the invention of fiber-reinforced concrete (FRC) by utilizing scattered fibers in a cementitious matrix. Besides offering a higher ductility, FRC developed with natural aggregates and industrial fibers is ecologically challenged and contributes to the depletion of natural reserves. The use of recycled aggregates (RA) instead of natural ones with waste coconut fibers (CF) can lead to the production of a cheap and eco-friendly FRC. For this purpose, concrete mixes were prepared with 50% and 100% incorporation of coarse RA as the replacement of coarse natural aggregates (NA) with and without CF. The CF-reinforced mixes were also studied with and without the effect of superplasticizer (SP) addition. Mechanical properties (compressive strength, bi-surface shear strength, and splitting tensile strength) and durability properties (water absorption and chloride ion penetration) of all mixes were examined. SEM technology was employed to observe the bond of CF with cementitious paste. Besides that, the effect of indoor and outdoor exposure on the compressive strength of CF reinforced concrete was also examined. The results revealed that the 2% CF (by weight of cement) advanced the shear strength of plain concrete by 40% and 60% with and without SP, respectively. The combined use of CF and SP provided 100% RA concrete (RAC) with noticeably higher mechanical performance compared to that of plain NA concrete (NAC). Chloride permeability and water absorption were increased due to the solo addition of CF, however, the permeability of CF-reinforced mixes was noticeably controlled by SP addition. This research found no degradation in the compressive strength of CF reinforced mixes exposed to subtropical outdoor conditions for 365-days. SEM observations revealed insignificant shrinkage of CF filaments in cement paste.