Nano-mechanical properties of internally cured kenaf fiber reinforced concrete using nanoindentation

Kenaf fiber reinforced concrete (KFRC) is being considered as a more sustainable fiber reinforced concrete. The effect of water-absorbing kenaf fibers on the microstructure of concrete was studied using nanoindentation. Results showed that cement hydration products found in KFRC are similar to those in conventional concrete, but relative volume fractions of these hydration products differ in KFRC. KFRC samples have more CH/Csingle bondSsingle bondH and less LD Csingle bondSsingle bondH in bulk than would be expected for plain concretes with similar water–cement ratios. Further nanoindentation experiments were performed in the interfacial transition zones around individual kenaf fibers, revealing a porous phase, a high percentage of LD Csingle bondSsingle bondH, and a lack of HD Csingle bondSsingle bondH in the fiber interfacial zones. The water absorbance of kenaf fibers and associated internal curing effects explain both results. Enhanced production of higher density hydration products in KFRC may provide a pathway for optimal design of these materials.