Investigating the effect of borax on the hydration and properties of Portland cement

Portland cement is known as the third most important material in the construction industry. In this research, the effect of borax on the properties of Portland cement including setting time, hydration percentage and compressive strength has been investigated. For this purpose, borax was used in amounts of 0.2, 0.4, 0.6 and 1 wt%. The obtained results showed that the setting time of Portland cement increases with increasing the amount of borax. The addition of 0.6 wt% of borax increased the setting time of Portland cement by about 50%, and the initial setting increased from 120 minutes to 170 minutes. The presence of borax in amounts less than 0.6 wt% led to an increase in the percentage of hydration and compressive strength of cement. The highest values of degree of hydration and compressive strength were obtained for the sample containing 0.6 wt% of borax. The 28-day compressive strength was 57 MPa for this sample, which was 42 MPa for the pure Portland cement sample. The increase in strength is attributed to the higher degree of hydration and lower porosity. By increasing the amount of borax to 1 wt%, there was a significant drop in the compressive strength of cement, which is related to the lower degree of hydration and a higher percentage of porosity.