Equivalent CO₂ Emission and Cost Analysis of Green Self-Compacting Rubberized Concrete

Global warming and climate changes are the major environmental challenges globally. With CO₂ emission being one of the main greenhouse gases emitted to the environment, and cement and concrete production amounting to about 10% of the global CO₂ emission, there is a need for the construction industry to utilize an environmentally sustainable material as an alternative to cement. This study analyzed the cost, CO₂ emission and strength properties of green self-compacting concrete (SCC) ternary blend containing fly ash, calcium carbide residue (CCR), and crumb rubber (CR) as a replacement material by volume of cement, cementitious material, and fine aggregate, respectively. Cement was replaced with fly ash at 0% and 40% by volume. CCR was used as a replacement at 5% and 10% by volume of cementitious materials, CR replaced fine aggregate in proportions of 10% and 20% by volume. The result indicated that the mix with 0% fly ash and 20% CR replacement of fine aggregate was the most expensive and had the highest CO₂ emission. However, the mix with 10% CR, 40% fly ash, and 10% CCR had the lowest CO₂ emission and was therefore the greenest SCC mix. The 28-day maximum compressive strength of 45 MPa was achieved in a mix with 0% CR, 0% fly ash, and 10% CCR, while the utmost 28-day splitting tensile strength of 4.1 MPa was achieved with a mix with 10% CR, 0% fly ash, and 5% CCR, and the highest flexural strength at 28 days was 6.7 MPa and was also obtained in a mix with 0% CR, 0% fly ash, and 5% CCR. In conclusion, a green SCC can be produced by substituting 40% cement with fly ash, 10% fine aggregate with CR, and 10% CCR as a replacement by volume of cementitious material, which is highly affordable and has an acceptable strength as recommended for conventional SCC.