An Innovative Study on Lightweight Concrete for the Complete Replacement of Conventional Coarse Aggregates by Waste Tire Rubber Particles

An all-encompassing endeavor has been commenced to incorporate waste tire rubber particles as a replacement for conventional aggregates and binders in concrete, comprehending the sustainable prospects of addressing environmental and economic concerns. Waste tire rubber is favored in non-structural applications due to the intimidation of fundamental concrete property, i.e., strength, and thus, practicing a concept of its partial incorporation. Thereby, very limited work is found in the available literature on structural lightweight concrete (SLWC) with the complete replacement of conventional aggregates by waste tire rubbers. In addition, there is no available study addressing the properties of SLWC with 100% rubber content, a major gap in sustainable construction. This study aims to manufacture novel LWC with 100% waste coarser tire rubber to replace conventional coarse aggregates and set an inaugurating move identifying its properties. Two steel mould rigs were newly designed for manufacturing normal and compressed rubberized concrete (RuC) samples. Three different mix designs containing 100% replacement of conventional coarse aggregates were prepared using (i) two different sizes of rubber particles and (ii) the addition of steel fibers. The workability of different fresh RuC mixes varied from 84 to 122 mm, maintaining the requirement denoted by ACI 213R for SLWC. Density, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity were undertaken to evaluate mechanical performances. The experimental results depict that this novel preloading method can bring a maximum of 97%, 59%, and 20% increase in compressive strength, flexural and tensile strength compared to that of the normal RuC, respectively. Hardened density and compressive strength of newly developed SLWC were determined at 28-, 56-, 90-, and 180-day. This study demonstrates the efficient scientific recycling procedures in manufacturing the RuC with a maximum compressive strength of 18 MPa (density of 2000 kg/m3), which can be considered SLWC as per ACI 213R-14 and Eurocode 2 recommendations. The durability properties, including water absorption, sorptivity, shrinkage, sulfate attack, and rapid chloride penetration, were evaluated at 28-, 56-, 90-, and 180-day for normal and compressed RuC samples. Water absorption rates were determined at two stages, i.e., the initial stage (for 30 min) and final stage (for 72 hrs), where compressed RuC samples exhibited improved transportation properties compared to the normal RuC samples. Sorptivity index for all the RuC samples was below 0.21 mm/√min, satisfying the maximum permissible limit prescribed by Cement Concrete & Aggregates Australia (2009). Drying shrinkage was determined by subtracting autogenous shrinkage from the total shrinkage, and the total, drying, and autogenous shrinkage strains of newly developed SLWC were 509, 372, and 137.9 μ, respectively. Submersion and drying processes of 4 weeks were considered for one Cycle, and in this study, the sulfate attack test was continued for up to 5 Cycles for all the normal and compressed RuC samples. The novel LWC samples with smaller rubber particles and steel fiber were in the moderate chloride ion penetrability category at 180-day, following the standard code of practice ASTM C1202 (2019). The obtained experimental results demonstrate that the newly designed casting method is very effective in enhancing the durability performances of RuC with 100% waste tire rubber. The material characterizations for different normal and compressed RuC samples were also conducted in terms of scanning electron microscope (SEM), X-ray fluorescence (XRF), energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), and X-ray CT analysis. The microstructure analysis shows a significant improvement in the interfacial transition zone between the matrix and rubber particles. Thermal insulation and carbonation were also determined to prioritize its application both in structural and non-structural elements. Decisively, this study effort to promote waste tire rubbers in concrete to a greater extent, identifying the service life and stimulating sustainable development.