High-strain rate compressive behavior of Fiber-Reinforced Rubberized Concrete

The compressive mechanical properties of concrete-based materials are strongly affected by the presence of additions in the mix and load application velocity. Fiber-Reinforced Rubberized Concrete (FRRC) was recently proposed in the literature as a concrete-based material with the aim of obtaining a ductile material with reduced environmental burden and characterized by excellent energy absorption performances during impact loading. FRRC joins and balances the advantages and drawbacks of Fiber Reinforce Concrete (FRC) and Rubberized Concrete (RuC). However, its behavior has rarely been investigated under dynamic loadings, although gaining sufficient knowledge on their high strain rate behavior is crucial for their full-scale application. This study aims to investigate the high-strain rate compressive behavior of FRRC with fine rubber aggregates and micro-straight steel fibers. Tests were performed using conventional quasi-static loading with a compressive testing machine and high-strain rate tests with a 080-mm Split Hopkinson Pressure Bar (SHPB) for strain rates up to 200 s(-1). The experimental program comprises the characterization of Plain Concrete (PC), FRC, RuC, and FRRC with a full test matrix (a total of 192 specimens) covering fiber contents up to 1.5% and rubber volume substitution ratios up to 30%. The micro-scale characterization of the material using SEM scans provided a complete understanding of the observed macro-scale behavior. A high-speed camera was used to capture the cracking development processes. The measurements both for quasi-static and dynamic tests indicate that the addition of fibers improves the ductility or toughness with a slight increase in the compressive strength and the substitution with rubber aggregates significantly reduces the compressive strength with improved ductility or toughness. The combination of fiber and rubber (FRRC) leads to a combination of the previously described single marginal effects. The dynamic tests reveal the marked strain rate dependency, although specimens with large rubber volume substitution were more sensitive to the strain rate effect within the considered test range. Based on the test data, data-driven models for strength reduction factor (SRF) and dynamic increase factor (DIF) are proposed for different types of FRRC. The image-based waveform discussion provides evidence of the "double-peak" phenomenon highlighting the different features of the observed signals and damage evolution. Ultimately, this study indicates that FRRC has an excellent high-strain rate compressive behavior and can be a promising material to be employed to protect structures against impact and blast loads.