Effects of sodium carbonate admixture and mix design ratios on the compressive strength of concrete

Abstract

This study aimed to investigate the impact of sodium carbonate (Na₂CO₃) admixture on the acceleration and long-term compressive strength of ordinary Portland cement (OPC) concrete at different mix ratios. Concrete cube specimens (150 × 150 × 150mm3 size) were cast at three different mix ratios (1:1.5:3, 1:2:4, and 1:3:6) with sodium carbonate admixture added in increasing dosage of 0.5% from 0 to 2.0% by weight of OPC. Compressive strength tests were conducted on the cast specimens after curing under water for 7, 28, 56 and 90days. Additionally, tests were done to see how sodium carbonate would accelerate setting times of OPC paste. The results of the tests showed that Na₂CO₃ decreased the initial and final setting times of cement paste from 96 to 67mins and 543 to 387mins respectively. Compressive strength test results for 1:2:4 and 1:3:6 mix ratios showed an increasing trend up to 1.0% Na₂CO₃ admixture, after which there was a decrease. Meanwhile, 1:1.5:3 mix ratio showed a decrease in strength from 21.87 N/mm2 at 0% to 14.90 N/mm2 at 1.0% Na₂CO₃ addition, after which the strength increased with Na₂CO₃ percent addition. These results suggest that sodium carbonate has an accelerating effect on concrete setting time, and may aid its early strength development, but has negative long-term effects on concrete strength with increasing dosage. An optimal percentage of 1% Na₂CO₃ by weight of OPC is advised for accelerating effects in concrete, based on the results of this study.