Experimental study of the effect of different types of industrial steel fibers on the mechanical properties of reactive powder concrete

The present research aimed to evaluate the effect of industrial steel fibers on the mechanical properties of reactive powder concrete (RPC). A series of reinforced RPC specimens containing different percentages of steel fibers having different diameters were built. By performing resistance tests on the samples, the mechanical properties (compressive, bending and tensile strengths) of RPC were determined. The results of the compressive tests showed that by increase in the curing age from 7 to 42 days, the strength of RPC containing group 2 steel fibers (medium fibers: diameter 0.6 mm) increases compared to the control concrete. This is attributed to the continued reactions between the cement paste and the interlocking of most of the quartz-silica sand aggregates and micro-silica powder in the RPC specimens with steel fibers. The highest compressive strength of RPC compared to the control concrete was obtained for the sample containing 2% group 1 steel fibers (small fibers: diameter 0.4 mm) equal to 421 MPa (29.11% growth compared to the control concrete). By reduce in the diameter of fibers, the number of fibers in the sample and subsequently the interlocking between aggregates and fibers increases and the replacement distribution of aggregates improves. Based on the flexural strength tests, 2% of groups 1 and 2 steel fibers and 3% of group 3 (large fibers: diameter of 0.8 mm) were determined as the optimal value of fibers to achieve the maximum flexural strength of RPC. Based on the tensile tests, it was found that with the addition of 1%, 2% and 3% of groups 1, 2 and 3 steel fibers, the growth of RPC tensile strength is completely upward. The reason was attributed to the bridging effect of steel fibers in the concrete matrix. Empirical equations obtained from regression analysis have high accuracy for estimating resistance properties.