Flowable fibrous concrete for thin pavement inlays

Synthetic fibers within a flowable fibrous concrete (FFC) mixture were characterized by relating their spatial distribution and orientations, determined from x-ray computed tomography (CT), with the measured toughness or fracture energy response of a FFC specimen. This new type of concrete, FFC, was developed to provide a workable, flowable mixture that could be utilized to rapidly construct thin concrete pavement inlays. A full-scale demonstration project verified the feasibility of constructing the FFC as a 5 cm thick inlay bonded to an existing asphalt pavement. In order to quantify this new FFC material, flexural beam properties were measured to determine the material?s toughness and fracture properties. Unnotched beams of the FFC material verified that the measured nominal strength and measured toughness increased as the specimen size was reduced. A high energy x-ray CT and image processing technique were utilized to identify the synthetic fibers in the hardened FFC through contrast and shape-based filtering from the 3D images. The filtered images showed the number of fibers across any given vertical plane in a FFC specimen was directly correlated with the measured total fracture energy. Fibers located near a surface (cast or mold) within a boundary zone size estimated at ? to ? of the fiber length, were found to have a higher alignment parallel to the surface with a lower number of fibers in this boundary zone, than the interior of the specimen. Fiber alignment in the FFC fracture beams had a less significant contribution, relative to the number of fibers, on the measured total fracture energy. For the FFC mixture, volumetric segregation of fibers occurred within a 15 cm cast beam, based on the analysis of the CT images. A finite element analysis using a tri-linear softening model successfully simulated the behavior of FFC for larger (15 cm) notched beam specimens and for some smaller (5 cm) beam specimens. However, a deflection hardening response occurred in some of these other 5 cm beam FFC specimens due to the higher local fiber content, for which the tri-linear softening modeling approach could not accurately simulate this post-cracking response.