Hydration And Micro Performance Of Ordinary Portland Cement Blending With Calcium Sulfoaluminate Cement At Low Temperature

The problem of slow early age strength development or even frost damage is a technical problem ofen encounteres in winter construction when Portland cement concrete is used. Commonly used methods as mixed with early strength agent, antifreezer and heat storage maintenance are with problems like high construction costs and potential hazards for long-term durability. Therefore, a technical idea of adding a small amount of sulfur cement into cementitious material system to encourage early strength development. Strength development and hydration mechanism for this combined system under different temoerature are discussed, providing basic data for further practical application.The paper discusses the strength development rules of the composite mortar after temperature recovery from early frost with different proportional relationship at different temperatures to achieve the purpose of preventive maintenance and discover the effect of early strength on the resistance of frozen damage. As more Sulphoaluminate cement added, the composite condensation became faster, the early strength became higher and achieved faster. However, excessive Sulphoaluminate cement delayed the strength development which had a severe impact on long-term strength after early strength. It is also found that excessive Sulphoaluminate cement results in decreased sensitivity of low temperature and frost.Based on the analysis of hydration heat, mercury intrusion porosimetry, x-ray diffraction, thermogravimetric analysis and scanning electron microscopy, the research into the hydration mechanism and microstructure of the cement paste with different composite ratios has indicated that Portland cement can promote the hydration of Sulphoaluminate cement. In contrast, the hydration of Portland cement is restricted by Sulphoaluminate cement. Additionally, the combination causes volume expansion, increased total porosity in early stages and decreased total porosity in late stages. Therefore, as the proportional relationship between the two materials is changed, the components and content of the hydration products are different.The paper investigates the influence of composition cementing material to the frost resistance of concrete frozen in early stages to compare with the antifreeze- calcium nitrite. To be specific, to simply add 20% Sulphoaluminate cement to Portland cement can make a marked improvement to the frost resistance of concrete, thus making the damage degree of frozen concrete minimal in late stages. Besides, to mix with the antifreeze enables the concrete to even lower temperatures. Furthermore, coarse aggregate in concrete resists the cracks from the interface of the cement paste and aggregate caused by early expansion of the composite. Due to the crack and the change of hydration products, dynamic elasticity modulus shows no characterization of the compressive strength of the negative temperature concrete.