Dynamic and Quasi-Static Loading Behavior of Low-Strength Concrete Incorporating Rubber Aggregates and Polymer Fiber

This study evaluates low-strength concrete incorporating recycled rubber aggregates from waste tires and polymer fiber for use as “forgiving” safety barriers that enhance road safety while promoting environmental sustainability. Incorporating the rubber and fiber enables recycling the tires close to the source where they were originally used—the road. These barriers are designed to absorb collision energy, reduce vehicle deceleration, and minimize the severity of accidents. The key requirements for such concrete are low strength, low elastic modulus, high ductility, high toughness, and minimal dispersion of large fragments upon failure. The study investigated various concretes containing different percentages of recycled rubber (0–20% by volume) and polymer fibers (0–1.2% by volume). We conducted compression, flexural, and dynamic impact tests to assess the effects of these additions on the properties of the concrete. Dynamic tests were carried out in a cantilever loading scheme with strain rates of 2.5–3 s−1, to emulate barrier loading during car crush. Key findings include indications that recycled rubber decreases concrete strength, while its contribution to energy absorption is limited. In contrast, polymer fibers enhance the concrete’s elongation and toughness, increasing energy absorption. The quantity of fibers present in the fracture area is critical for energy absorption. Notably, energy absorption under dynamic loads is more significant than that under quasi-static loads; however, the difference between these results diminishes as the fiber percentage increases. Furthermore, quasi-static tests on fiber-reinforced concrete can effectively evaluate its response to impact loads. In conclusion, the combined use of recycled rubber and polymer fibers in low-strength concrete offers a sustainable solution for developing safer and more environmentally responsible roadside infrastructure by repurposing waste materials and reducing the ecological footprint of construction. Careful attention should be paid to the distribution of fibers within the concrete, as this significantly influences energy absorption.