Implementing a novel procedure of ACI 544.2R drop-weight impact test to measure the residual compressive strength after impact of multi-layered fiber-reinforced concrete with different patterns

The main drawbacks of ACI 544.2 R repeated impact test are the time and effort consumed. This paper proposes the compressive after-impact (CAI) test concept to eliminate such disadvantages, i.e., to markedly reduce the number of blows, which can reach thousands in certain cases. The test procedure was to measure the CAI of the disc specimens before and after being subjected to a few blows by the same setup of the ACI 544.2 R test, i.e., the load is transmitted to the disc specimen through the metallic ball resting on it. Another notable achievement in the current work is the investigation of the CAI of multi-layered fiber-reinforced concretes (FRCs) with different patterns, i.e., layers, sequences, and types of fibers—to obtain optimal impact resistance for FRCs. Three different types of concrete were used: plain concrete (PC), polypropylene (PP) FRC, and steel (ST) FRC. Single-, two-, and three-layered FRCs were made from these concretes with different sequences/patterns for facing the impactor. The ultimate static compressive loads measured by the proposed and standard tests showed a logical relationship between them. ST FRC showed the best kind of concrete for resisting such contact stress. The Weibull distribution was used to analyze the scattered test results. The statistical results showed good consistency of the present results, as the coefficient of variation was less than 0.25. For single-layered specimens, the ST specimen showed the highest Residual Strength Indicator (RSI), at 91 %, followed by the PP specimen, at 80 %, and finally, the PC specimen at 65 %. CAI of two-layered specimens with an outer ST layer (subjected to the impactor) showed higher impact capacity (RSI = 88 %) than other two-layered specimen patterns. Furthermore, a three-layered specimen with two layers of ST FRC and an inner PC layer showed the highest three-layered patterns resist the impact load (RSI = 90 % after two blows). Therefore, the thickness of the shielded layer is the main parameter controlling the improvement of a structural element's impact resistance. Finally, the proposed ACI 544.2 R test procedure can be adopted to measure the impact resistance of multi-layer FRCs or other FRCs, consuming significantly less time and effort.