Effect of sodium sulfate on some properties of blended portland cement

Abstract

The objective of this study is to evaluate the effect of sodium sulfate (Na₂SO₄) content on certain properties of blended Portland cement. The Na₂SO₄ content was varied from 0% to 3%. The investigated properties include water of consistency, setting time, heat of hydration during the first 24 hours, compressive strength at 1, 3, 7, and 28 days, and soundness. The results show that increasing the Na₂SO₄ content from 0% to 3% reduces the water of consistency by approximately 3%, shortens the initial setting time by 40 minutes, and reduces the final setting time by 60 minutes. The addition of Na₂SO₄ accelerates cement hydration at early ages. At 1 day, Na₂SO₄ significantly increases compressive strength, with an increase of approximately 32% at 1% and 2% Na₂SO₄, and 24% at 3% Na₂SO₄. However, compressive strength decreases at 3, 7, and 28 days, with the 1% Na₂SO₄ sample showing a smaller reduction compared to those with 2% and 3%. Moreover, Na₂SO₄ increases expansion, with the highest observed increase being 0.4 mm compared to the control sample. Among the Na₂SO₄ dosages studied, 1% is considered optimal as it significantly enhances early-age strength while minimizing the reduction in long-term strength relative to higher dosages.