The role of hardwood pulp fibers in mitigation of early-age cracking

The availability, relative consistency, and renewability of hardwood pulp fibers have prompted interest in their use in fiber–cement composites, in which they may be used for a variety of purposes. This study clarifies the ability of hardwood pulp to reinforce mortar, its capacity to provide internal curing, and its role as early-age crack-control reinforcement through a coordinated series of restrained shrinkage, free shrinkage, and mechanical testing on mortar samples. It finds that hardwood pulp improves the restrained shrinkage behavior of mortar at an early age. That is, 0.5% and 0.75% (by volume) hardwood pulp-reinforced mortars exhibited a lower rate of stress development and lengthened time-to-cracking by about 1.6 times and 2.3 times, respectively, compared to a companion crack-prone ordinary mortar. The initial crack width also decreased by 88% in 0.75% hardwood pulp-reinforced mortar samples, which suggested an application aimed at assisting self-healing in cement-based materials with an appropriate binder composition. Hardwood pulp successfully provided internal curing to crack-prone mortar and thus reduced autogenous shrinkage. This reduction in shrinkage, together with a combination of increased early tensile capacity, reduced stiffness, and improved post-cracking toughness were identified as the key contributions of hardwood pulp in the improved resistance of mortar to early-age cracking.