Shear Behavior of Modified Reactive Powder Reinforced Concrete Beams

Abstract

This thesis presents, the first systematic (due to the researcher’s knowledge) study that considers the shear behavior of modified reactive powder concrete (MRPC) beams (without shear reinforcement) containing red bricks waste aggregates (RBWA) (as coarse aggregates ( and hybrid steel fiber (mix of hooked-end steel fibers with straight steel fibers), and compares it with the reactive powder concrete (RPC) beams. The present study can be divided into two stages. The first stage is to study the effect of steel fibers type and replacing silica sand (fine aggregate) partially with RBWA (coarse aggregate) for MRPC on some mechanical properties (cube and cylinder compressive strength, splitting tensile strength, and flexural strength), flowability, and also ultrasonic pulse velocity (UPV) (non-destructive test) and compares it with the RPC. Where nine mixes were prepared, they were divided into three groups and each mix in a group has a different type of fibers (straight steel fibers, hybrid-steel fibers, and hooked-end steel fibers). The first group had no RBWA, the second group silica sand was replaced by 25% of RBWA, and in the last group silica sand was replaced by 50% of RBWA. While the second stage is to study the shear behavior of simply supported MRPC beams (without shear reinforcement) and compare it with RPC beams. This study included the following variables: steel fibers type, replacement ratio of silica sand with RBWA, shear span to effective depth (a/d) ratio, and longitudinal reinforcement (ρ) ratio. In addition, study the effect of the above-mentioned variables parameters on the deformation characteristics of the test beams including the failure mode, cracks pattern, ultimate shear load, deflection characteristics, first diagonal cracking load, a principal strain of concrete, width of the cracks. Experimental results indicated that replacing 25% of silica sand with RBWA increased the mechanical properties, ultrasonic pulse velocity, and reduced the percentage of water /cement at a constant flowability for MRPC mixture when compared with the RPC mixtures. The highest experimental results obtained from the tested MRPC mixtures, which were higher than RPC mixtures were as follows: compressive strength (fcu) =138.06 MPa (higher by 6.6%), splitting tensile strength (ft) =15.44 MPa (higher by 13.58%), flexural strength (fr) =20.16 MPa (higher by 6.1%), and ultrasonic pulse velocity (UPV) = 4.7 km/sec (higher by 2.17%). ii On the other hand, test results indicated that replacing 25% of silica sand with RBWA increases the ultimate shear load (Vu) when compared to the RPC beam made without RBWA but with the same fiber (S, HS, and H) by around (6.12%, 6.6%, and 26.43%) respectively. This result reflects the positive effect of the RBWA on shear performance. Experimental results indicated that the ultimate shear load of the beams that contained hybrid-fibers was higher than beams that contained hooked-end fibers but lower than beams that contained straight fibers. This result reflects the positive effect of mixing straight fibers with hooked-end fibers in the RPC and MRPC mixtures when compared with the RPC and MRPC mixtures contained hooked-end fibers (single fibers) on shear performance. Also, it was found that the efficiency of the straight fibers is superior to the hooked-end fibers. The results showed that the ultimate shear load for MRPC beams decreases when (a/d) ratio increases from (2.5) to (3.5 and 4) around by (26.44% and 34.3%) respectively. Moreover, the ultimate shear load for the MRPC beams increases when (ρ) ratio increases from (1.25%) to (1.82% and 3.29%) around by (38.2% and 100.86%) respectively. Finally, it was observed that when replacing 50% of silica sand with RBWA, the mechanical properties and (water /cement) ratio at a constant flowability decreased but the ultimate shear load increased by 9.03%.