Lightweight concrete (LWC) has been used for more than 2000 years, and the technical development of waste-based LWC is still proceeding. Notably, the very first representative concrete mix of infrastructural LWC was introduced for building a family house in Berlin, Germany, a few decades ago. The unique and distinctive combination of waste-based LWC successfully creates an appealing alternative to traditional concrete aggregates in terms of durability, robustness, cost, energy-saving, transportation, environmental advantages, innovative architectural designs and implementations, and ease of construction. Numerous researchers have attempted to utilize waste materials to produce LWC, aiming to bring both ecological and economical solutions to the construction industry over the past few decades. Waste materials, such as crushed glass, waste tire rubber, masonry rubber, chip rubber, plastics, coconut shells, palm oil fuel ash, palm kernel shells, fly ash, and rice husks, possess lower specific gravity than traditional concrete aggregates. Thus waste-based LWC can be a significant replacement for conventional raw materials (cementitious material and aggregates) as it requires less strength than conventional concrete for both structural and non-structural applications. Although waste-based LWC is well recognized and has proven its scientific potential in a broad range of applications, there are still uncertainties and hesitations in practice. Therefore, the primary objective of this study was to demonstrate the current state-of-the-art understanding and advancement of waste-based LWC over the past decades. Furthermore, an equally critical discussion is reported to shed light on the potential benefits of LWC. We highlight how the performance of LWC has been enhanced significantly over the period, and understanding of the properties of waste-based LWC has advanced.

The widespread disposal of scrap tires has become a major environmental problem that necessitates finding an effective way of using recycled crumb rubber (CR) in concrete. Rubberized concrete, however, exhibits reduced mechanical strength compared to conventional concrete, which restricts its application in structures. This research adopted a mix design strategy based on the Taguchi method to overcome these drawbacks and improve the performance of rubberized concrete. A total of ten mixes, including one for normal concrete (NC) mix, were formulated by varying the CR content (10%, 20%, and 30% by weight of fine aggregate), cement content (400, 425, and 450 kg/m ³ ), admixture dosage (0.5%, 1%, and 1.5% by weight of cement), and polypropylene (PP) fiber content (0.2%, 0.25%, and 0.3% by weight of cement). The impact of these factors was assessed on concrete workability, density, mechanical properties, flexural performance of beams, and axial load capacity of columns. The use of CR reduced workability, density, and strength; however, the optimized mix combinations successfully alleviated these deficiencies. Based on the experimental results, four mix combinations were recommended, comprising different contents of CR, cement, admixture, and PP fiber. These combinations increased the slump by up to 7% and improved the compressive, split tensile, and flexural strengths of rubberized concrete by up to 16%, 15%, and 20%, respectively, compared with the NC. In addition, the bending strength of the beams and the axial load-carrying capacity of columns increased by up to 24% and 13%, respectively. Therefore, the test outcomes suggest that rubberized concrete can be modified from a non-structural material to a load-bearing structure with this strategic mix design.