Research On Calcium Strontium Sulphoaluminate Cement And Its Durability

In this paper, the relationship between property and structure of calcium strontium sulphoaluminate(CSS) was studied by changing the factors such as mineral composition and burning condition. Industrial waste containing strontium were used to burn calcium strontium sulphoaluminate cement. The influence of gypsum for hydration and strength of CSS cement was discussed, and affect of CaF₂ for dead burn and property of CSS cement was researched. On this basis, the impact of admixture for durability of CSS cement was considered. The results showed that:In the series of CSS mineral, Ca_1.50Sr_2.50A₃(S|-) formed by displacing 2.50 mol Sr²⁺ to Ca²⁺ in C₄A₃(S|-) had the highest strength. The compressive strength of its paste hydrated 3d and 28d were 76.6 MPa and 89.6 MPa, respectively. The burning temperature could affect the property of CSS, and strength of CSS burnt at 1300℃was higher than it burnt at 1350℃. The hydrated rate of CSS was fast, and its hydrated products were AFt, CAH₁₀, Ca(OH)₂ and Al₂O₃ (aq).CSS cement with strontium slag as raw material was gelling capacity material with performance in high-early strength and high-strength. Hydrated 3d and 28d compressive strength of CSS paste were respectively 67.75 MPa and 89.63 MPa. The optimum mineral proportion of CSS cement clinker was: Ca_1.50Sr_2.50A₃(S|-) 65%;β-C₂S 25%; C4AF 5%. Best sintering temperature was 1300℃and optimal firing time was 90 min. The clinker mineral grain was about 1μm and distinct outline in this burning conditions. CSS cement hydrated rapidly and the hydrated product were mainly AFt, CAH₁₀, AH₃(gel), SrSO₄, C–S–H and Ca(OH)₂.The addition of gypsum in the CSS cement clinker could promote hydration of Ca_1.50Sr_2.50A₃(S|-) and other minerals. The optimum content of gypsum in CSS cement was 6%, which had high early strength and steady later increasing strength. The compressive strength of cement paste hydrated 3d and 28d were 64.58 MPa and 79.86 MPa, respectively. Much more content of gypsum in CSS cement promoted rapid hydration of cement, which was benefit for early strength of cement. However, it led to retraction of later strength.Because of adulteration of CaF₂ in sintering process, decomposition of CaCO₃ and formation of Ca_1.50Sr_2.50A₃(S|-) were accelerated, and the burnability of CSS cement was improved. When the content of CaF₂ was 0.2%, strength of CSS cement was the highest. The compressive strength of paste hydrated 3d and 28d were 65.0 MPa and 86.2 MPa separately. Excessive CaF₂ could promote hydrated product CAH10 turning into C₃AH₆, and destroy instability of cement paste structure. The strength of cement decreased with the content of CaF₂ increasing when the amount of CaF₂ was more than 0.2%.After cured in 5% sulfate solution,the quality loss of samples that adding fly ash and slag were less than CCS cement, and quality loss of mortar and pasted samples decreased with the mixing amount of ash and slag increasing, which was benefit to improve the resistance of sulfate erode. The CCS cement adding fly-ash mortar had good freezethaw resistance capability and the physical performance degradation was small after 300 freeze-thaw cycles. The freeze-thaw resistance increased with the amount of ash increasing. The admixture was helpful to improve anti-permeability of CSS cement, and the anti-permeability of fly ash cement was superior to slag cement.