Abstract: This paper investigated the effects of Na₂SO₄ on setting time, slump flow, hydration heat, expansion rate, compressive strength, and micromechanical properties of gas sealing composite cement (composed of ordinary Portland cement and sulphoaluminate cement). The results show that Na₂SO₄ accelerated the setting and hydration processes of composite cement, and its setting acceleration effect is positively correlated with the dosage (0.5%~2.0%, mass fraction). Meanwhile, both the expansion rate and compressive strength of composite cement increase with the increase in Na₂SO₄ dosage. By incorporating 0.5%~2.0% Na₂SO₄, the increase rates of compressive strength of the composite cement are 23.3%~100.0% (1 d), 10.4%~30.8% (3 d), 6.8%~23.9% (7 d), and 11.0%~29.9% (28 d). Micromechanical property analysis indicates that the hydration of composite cement is more complete, with a more uniform distribution of elastic modulus and a notable increase in the formation of gel-like products with low elastic modulus. These findings provide a technical basis for performance regulation of high-performance gas sealing materials.

Key words: gas sealing material, composite cement, setting time, micromechanical property, compressive strength