THE EFFECTS OF FIBERS ON CONCRETE BEAMS FLEXURE AND SHEAR CAPACITIES

An experiment program was created to determine the effectiveness of fibers as reinforcement in concrete beams. Premixed concrete was used instead of creating a new mix design. Steel fibers and synthetic macrofibers were used in this experiment. Three tests were conducted on various elements using three different fiber volume fractions of 0.736%, 1.105%, and 1.473%. Specifically, large scale beams with longitudinal reinforcement were tested to determine shear and moment capacities; small beams without longitudinal reinforcement were tested to find the modulus of rupture; and concrete cylinders were tested to determine the compressive strength.  

From the cylinder test, it was shown that as the volume fraction increased, the compressive strength decreased. Also, the steel fibers increased the compressive strength significantly. On the other hand, the synthetic macrofibers only increased it 1.04% for a volume fraction of 0.736%. In fact, after the volume fraction increased beyond 0.736% for the synthetic macrofibers, the compressive strength value started to decrease. 

The small beams test showed that the steel fiber beams had a higher residual capacity than the synthetic macrofiber beams. It was also shown that a fiber volume fraction of 1.105% resulted in the highest modulus of rupture out of the three volume fractions. This fiber volume fraction also showed a higher load capacity than the other volume fractions. It was also shown that the crack location impacted the modulus of rupture.

The test on large scale beams showed that as the fiber volume fraction increased, the moment and shear capacities increased as well. It was also shown that steel fiber beams had higher shear and moment capacities as well as maximum load capacity compared to synthetic macrofiber beams.