MECHANICAL PROPERTIES OF CONCRETE MADE FROM CUPOLA FURNACE SLAG AND RECYCLED CONCRETE AGGREGATES

Abstract

Concrete is an undeniably versatile and practical material for the construction and infrastructural development of any nation. Nonetheless, the adverse environmental effects involved in the production of cement and the aggregate fraction of concrete, and the short-fall in the building supply are some of the downsides of concrete use. Cupola furnace slag and recycled concrete (fine and coarse) wastes from industrial processes and construction and demolition sites are disposed into the environment, resulting in the pollution that threatens marine, agriculture, and public health. Therefore, the utilization of cupola furnace slag and recycled concrete aggregates (binder and coarse aggregate) waste in concrete production would help protect the environment. This study presents the outcome of an experimental investigation of the effect of partial replacement of ordinary Portland cement at percentage levels of 0% to 25% in steps of 5% with granulated cupola furnace slag, coarse aggregate, and fine aggregate from 0% to 50% in steps of 10%; with coarse cupola slag, recycled aggregates. The fresh and hardened properties of concrete such as workability, compressive strength and microstructural characteristics were tested. The test results generally showed that the workability increases with increase in percentage replacement while the concrete’s compressive strength decreased with an increased replacement level. However, at 7, 14, 28 and 56 days concrete produced from the partial replacement of ordinary portland cement with granulated cupola slag (C-G) had the optimum compressive strength of 9.65 N/mm 2 , 15.85 N/mm 2 , 20.37 N/mm 2 and 22.15 N/mm 2 at 10% replacement (C- G 10 ). The strength however increased by 13.67%, 23.54%, 29.42% and 25.42% compared to the control sample. Similarly, concrete produced from the partial replacement of river sand with fine cupola slag (S-F), had the optimum compressive strengths of 11.74 N/mm 2 , 20.12 N/mm 2 , 22.81 N/mm 2 and 23.72 N/mm 2 at 7, 14, 28 and 56 days respectively. When the fine cupola slag content increased to 20%, the strength improved by 39.60%, 54.75%, 56.82% and 34.31% respectively when compared with the control. In contrast, granite’s partial replacement with coarse cupola slag (G-C) gave the optimum compressive strength at 10% replacement (G-C 10 ) with a value of 14.89 N/mm 2 at 28 days. The compressive strength gotten from the complete replacement of fine and coarse aggregate with cupola slag, recycled fine aggregate (R-F) and recycled coarse aggregate (R-C) respectively were lower compared with the control samples at 7, 14, 28 and 56 days. The image analysis of the scanning electron microscope (SEM) result of the specimens with optimum compressive strengthfrom each mix design was used to calculate the percentage area of pores in the concrete. The analysis reveal that the percentage area of concrete pores produced containing granulated cupola slag was lower when compared with others, hence leading to higher compressive strength. The Analysis of Variance (ANOVA) for the combine effect of CFS when used to partially replace OPC, NS and NG showed that FCS, GCS and CCS had a p-value of 0.020, 0.016 and 0.049 respectively which were below 0.05 and this meant there was statistically significant differences in the mean of various groups. A model was developed to predict the compressive strength of concrete produced, containing CFS as binder, fine and coarse aggregate. In addition, the effect of RFA, RCA, CFS, NS and NG on the compressive strength of concrete showed the p-value of RFA to be 0.0461 while that of RCA to be 0.8076. It meant the addition of RFA had a significant effect on the compressive strength while RCA does not have.