Distribution of Fiber-Reinforcement in Thin Concrete Overlays

The spatial distribution and orientation of fibers in concrete materials can be linked with the measured fracture performance of the fiber-reinforced concrete (FRC). For FRC pavements, the improved toughness performance is used for adjusting the structural design and expected service life of the pavement. The prediction of toughness performance and pavement serviceability can be improved with a better characterization of fiber dispersion in the concrete pavement. In this research study, a flowable fibrous concrete (FFC) mixture was developed containing a synthetic macrofiber at a volume fraction higher than found with existing thin concrete pavements. This FFC mixture is anticipated to have greater toughness induced by more fiber alignment in a thinner (5 cm thickness) concrete inlay pavement. Quantification of synthetic fiber dispersion and alignment in the FFC mixture was made using x-ray computed tomography and imaging analyses. The influences of placement technique and proximity of cast or mold surfaces were investigated and found to impact the fiber spatial distribution and orientation. The image analysis revealed that the number of fibers crossing any vertical plane, which increased for FFC placed under directional flow, was directly related to the measured fracture performance. Fibers were verified to have the desired alignment, allowing more fibers to become engaged in crack opening resistance, when the FRC was placed as a thinner pavement layer and therefore resulting in a more cost-effective use of FRC for pavements.