Influence of fiber orientation and dispersion on flexural behavior of UHPFRC in the full-scale slab: Image analysis, magnetic test and constitutive model

This study aimed to analyze and predict the variation in fiber orientation and dispersion within a full-scale ultra-high performance fiber reinforced concrete (UHPFRC) slab in relation to the extraction angles and flow distances, as well as the resulting variation in flexural behavior. Initially, fiber volume fraction and orientation within the slab were measured using magnetic test. Then, four-point flexural test was carried out on prism specimen, extracted from the slab at different angles and locations, to characterize the flexural behavior of UHPFRC. Meanwhile, the fiber orientation and dispersion were quantitatively evaluated based on the image analysis. The test results indicated that the flexural behavior of UHPFRC was more influenced by fiber dispersion than fiber orientation. The sensitivity analysis also indicated that the fiber dispersion had the greatest impact on flexural strength. A prediction model for fiber dispersion considering the effects of fiber length, volume fraction, and orientation was developed. When the variations in flexural-to-tensile strength ratio of UHPFRC were considered as the function of fiber dispersion, orientation, aspect ratio, volume fraction, and flexural-to-tensile strength ratio of the matrix, the peak flexural strength, as well as the flexural strength at the deflections of 1/1200, 1/900, 1/600, 1/300, 1/200, and 1/150 of specimen span, can be predicted using the modified Composite Theory. Additionally, a prediction model for deflection was proposed. Based on the above prediction results, the flexural constitutive model of UHPFRC was established. All prediction models were successfully validated using the test data.