Effect of MgO and gypsum content on long-term expansion of low heat Portland slag cement with slight expansion

摘要

The expansion of low heat Portland slag cement with slight expansion (LSE cement) was studied by XRD, SEM and test methods for strength and expansion. Results indicated that under the condition of 4.5-5.0 percent MgO in clinker and 2.8-3.4 percent SO_3 in cement, ettringite expansion and brucite expansion produced by periclase hydration in the paste had continuity, entirety and stability. Periclase hydration in the paste started at about 60 days and was completed up to 2000 days and ettringite was stable from 3 to 2000 days. At the ages of 28, 90, 365, 730 and 2000 days the expansion of the paste reached 0.08-0.13 percent, 0.09-0.14 percent, 0.12-0.17 percent, 0.13-0.18 percent and 0.15-0.21 percent, respectively. At the ages of 2, 28 and 180 days the autogenous volume deformation of mass concrete made out of LSE cement was positive and was 0.0042 percent, 0.0050 percent and 0.0066 percent, respectively and the prestress of the concrete with 2.0 percent steel bar content was 0.069, 0.060 and 0.082 MPa, respectively. The results suggest that using this cement in mass concrete may compensate for a part of its thermal shrinkage and autogenous shrinkage.