Mixture Design and Testing of Fiber-Reinforced Self-Consolidating Concrete

An extensive testing program was undertaken to evaluate the applicability of a mixture-proportioning method proposed for shrinkage control in fiber-reinforced concrete (FRC) in proportioning fiber-reinforced self-consolidating concrete (FR-SCC). The study also proposed test methods to evaluate workability of FR-SCC. The investigated fibers included polypropylene, steel, and hybrid fibers of different properties with fiber lengths of 5 to 50 mm (0.20 to 1.97 in.). Fiber volume V-f ranged between 0.25 and 0.75%. The study also aimed to determine the impact of fiber type and addition on key properties of the fresh and hardened concrete. Hardened properties included compressive, splitting tensile, and average residual strengths. Test results indicate that the proposed methodology to maintain constant mortar thickness over coarse aggregate and fibers can reduce any significant drop in workability of FR-SCC, resulting from an increase in fiber factor. In general, a V-f of 0.5% is found to be an upper limit for the production of SCC. A greater V-f can hinder the self-consolidating characteristics. For the assessment of the passing ability of FR-SCC, a modified J-ring setup containing six or eight bars instead of 16 bars is proposed. The passing ability of FR-SCC can be expressed as the ratio of diameter:height at the center of the J-ring test. The passing ability can also be evaluated using the L-box with a single bar instead of three bars. A superworkable concrete (SWC) requiring low consolidation energy can still be produced with a V-f of 0.75% when a viscosity-modifying admixture is incorporated to prevent segregation and blockage. For the tested fiber types, the average residual strength (ARS) in flexure is shown to increase with V-f. Steel fibers exhibited the highest ARS value.