The influence of sodium hydrogen carbonate on the hydration of cement

The presence of Ca(OH)2 may adversely influence resistance to sulfates, while its absence reduces the pH, leading to corrosion of the steel in reinforced concrete. Test results of the present study showed that adding NaHCO3 allowed carbonation to occur uniformly within the cement paste, resulting in the consumption of Ca(OH)2. Despite the consumption of Ca(OH)2, the pH was found to increase by production of NaOH. Strength test results showed that an addition of NaHCO3 of less than 5% enhanced the strength, but that exceeding 5% had an adverse effect. The results here provide new insight into potential means to improve the durability of concrete.