A study was conducted in which a reactive powder concrete was reinforced with a combination of nanocellulose and microcellulose fibers to increase the toughness of an otherwise brittle material. These fibers could provide the benefit of other micro- and nanofiber reinforcement systems at a fraction of the cost. An empirical investigation into the effects of several different reinforcement schemes on processing parameters and mechanical properties of a reactive powder concrete mixture was conducted. In particular, notched-beam tests were performed under crack-mouth opening displacement control to measure fracture energy under stable crack-growth conditions. Preliminary results show that the addition of up to 3% micro- and nanofibers in combination increased the fracture energy by more than 50% relative to the unrein-forced material, with little change in processing procedure. Splitting tensile tests were also performed for comparison with beam-bending tests. Current work focuses on applying high-resolution three-dimensional imaging techniques to better quantify the physical microstructures and the corresponding shifts in damage mechanisms that lead to higher toughness.