Cellulose fiber-reinforced cement paste, mortar, and concrete

Fiber-reinforced concrete is a fast-growing technology. The use of cellulose fibers as an inexpensive alternative to synthetic fibers is considered. This study characterizes the behavior of cellulose fiber-reinforced paste, mortar, and concrete and investigates rheological, dispersion, and mechanical properties of the materials.;Fibers are treated with special coatings to enhance dispersion, bond, and mechanical performance. Coatings are not found to change the behavior of the fiber-reinforced material. Flexural strengths and toughnesses are obtained for cellulose fiber-reinforced cementitious materials. When cellulose fibers are added to a cementitious material, they stiffen the matrix. This stiffening limits the maximum usable fiber volume. At fiber volumes tested, fibers offer little improvement in flexural strength, but increase toughness late in the post-peak region.;A partial factorial statistical design is employed to optimize matrix properties and thereby enhance fiber performance. Silica fume, fly ash, and superplasticizer are added at two levels each. Matrix changes do not affect fiber performance at the fiber volumes tested.;Shrinkage tests are performed on paste and mortar to evaluate the ability of fibers to control plastic and drying shrinkage cracking over a range of fiber volumes. At low fiber volumes, plastic shrinkage cracking is entirely eliminated in cement paste. Fibers are found to reduce the width of restrained ring shrinkage cracks in mortar and paste. Shrinkage crack control is seen as the best application for cellulose fibers in cast cementitious materials.;Optical and scanning electron microscopy are used to inspect fiber dispersion. A technique is developed to locate fibers in a hardened, polished specimen. This enables the use of statistical point processes to quantify fiber dispersion. Correlations among fiber dispersion, mechanical performance, and rheology are investigated.;Fiber dispersion cannot be correlated positively with matrix rheological parameters, such as yield stress and viscosity, nor can matrix rheology be correlated directly with mechanical performance. Fibers disperse well under normal mixing conditions, regardless of matrix rheological properties.