Wood pulp microfibers in cement-based composites: Improving fiber distribution and characterizing composite behavior

As an alternative to more expensive steel, glass, and synthetic polymer fibers, wood fibers are well-suited for reinforcing cement-based products due to their high strength-to-cost ratio, availability, renewability and recyclability, and non-hazardous nature. The goals of this study were: (1) to improve fiber distribution, (2) to assess how different wood pulp microfibers influence the behavior of cement-based composites, and (3) to develop a practical method for characterizing the toughness of cement-based composites measured in flexure. Toward the first objective, a method involving mechanically and chemically tailoring the fiber surface was developed to improve pulp fiber dispersion in cement-based matrices. By overcoming common problems with fiber clumping, the development of this low-cost method for improving dispersion should broaden the use of pulp fibers in cement-based composites. Assessment of the effect of pulp fiber reinforcement made through measurements of compressive strength, toughness in compression, stiffness, flexural strength and toughness, and free and restrained shrinkage showed that the use of wood fibers in cement-based composites significantly improved the toughness in both flexure and compression without having a great detrimental effect on the strength or shrinkage. Also, reinforcement with longer softwood fibers, as compared to shorter hardwood fibers, was found to produce larger increases in toughness. Finally, a new simple and practical method that uses a new set of parameters to characterize toughness in flexure has been proposed.