Abstract: A composition includes an admixture of a cementitious component and a cellulosic component. The cellulosic component includes a cellulosic fibrous material and water. The admixture is suitable for mixing with a second amount of water to form a hardened material. A method includes reducing a cellulosic fiber material to produce a fiber fragment material, treating the fiber fragment material, and rinsing the treated fiber fragment product with water to form a rinsed fiber fragment material. Treating the fiber fragment material includes admixing the fiber fragment material and water to form an admixture, heating the admixture, agitating the admixture, and separating a treated fiber fragment product from the admixture. The method is effectively controlled so that the rinsed fiber fragment material is suitable for reacting with a cementitious component to form a hardened material.