Sustainable precast concrete blocks incorporating recycled concrete aggregate, stone crusher, and silica dust

Due to rapid urbanization and onset of various infrastructure projects, construction and demolition waste management is a key challenge to related stakeholders. The utilization of stone crusher dust (SCD) and silica dust (SD) generated as wastes in stone processing units is also a matter of concern as it leads to air pollution. As per the published research articles, these industrial wastes can replace a significant proportion of natural aggregates in concrete, however, the authors could not find a study on utilization of coarse (4.75-10 mm) recycled concrete aggregates (RCA) in combination with SCD, and SD in making zero-slump concrete for producing M-40 grade paver blocks. This study evaluates the effect of incorporating (0%, 15%, 30%, 45%, 60%, 75%) coarse RCA. Then, the feasibility of incorporating (0%, 20%, 40%, 60%, 80%, 100%) SCD, and SD with optimum coarse RCA was investigated. The workability, fresh density, compressive strength, flexural strength, split tensile strength, dynamic modulus, water absorption, void ratio, abrasion resistance, and sulphate and acid resistance properties of paver blocks were evaluated. As per the results, the workability increased 2.6% at 45% coarse RCA, however, it decreased 4.6% and 10.2% at 100% SD and 100% SCD, respectively. The compressive strength decreased 6% at 45% coarse RCA, whereas it increased 2.8% and 3.8% at 100% SD and 100% SCD. Microstructure analysis (TGA, FT-IR, SEM) was performed to observe the changes in mass loss, chemical properties, pore analysis, shape, and texture of aggregates. Based on the observations, coarse RCA can replace up to 45% natural aggregates, whereas SD, and SCD can replace even 100% river sand without having significant impact on the properties. The environmental and economic assessment of 1 m3 of selected concrete mixes were also performed. The incorporation of 45% coarse RCA reduced 1% GWP and 3% primary energy consumption. The use of 100% SD with 45% coarse RCA can reduce 4.8% GWP and 11.8% primary energy consumption, whereas 100% SCD with 45% coarse RCA can reduce 5% GWP and 12% primary energy consumption. The production cost of 1 m3 control mix increased 24% at 45% coarse RCA , whereas it increased 5% and decreased 3% at 100% SD, and SCD, respectively. So, utilization of coarse RCA, SD, and SCD can save significant number of natural resources and pave the way to sustainable development by converting these industrial wastes into resources.