摘要
在不同养护温度条件下,采用X射线衍射、微量热分析、扫描电子显微镜等研究了硝酸钙对铝酸盐水泥强度及水化性能的影响。结果表明:硝酸钙(CN)能延缓铝酸盐水泥的水化进程,在20℃其延缓程度随CN掺量提高,呈现先增大后降低。其中10%CN延缓程度最显著。在50℃其延缓程度随CN掺量提高而增大。在硝酸钙存在下,铝酸盐水泥会优先形成Gibbs自由能更低的硝酸盐钙钒石相(NO_3-AFm和NO_3-AFt),从而抑制铝酸盐水泥的相转变。CN的掺量和养护温度显著影响硝酸盐型钙钒石的形成和演变。硝酸钙大幅提高了50℃养护条件下铝酸盐水泥的抗压强度。硝酸钙的最佳掺量为10%,此时50℃养护条件下铝酸盐水泥的28 d抗压强度达到66.8 MPa,而未掺CN的铝酸盐水泥抗压强度仅为28.7 MPa。
Effect of calcium nitrate(CN) on the strength and hydration of calcium aluminate cement(CAC) at different curing temperatures was investigated. The CAC additions of CN were analyzed by X-ray diffraction, scanning electron microscopy,isothermal calorimetry and compressive strength measurement. The results show that CN can retard CAC hydration. For cured at 20 ℃, the retardation degree increases up to the ‘optimum CN' value and decreases at a higher dosage of CN with increasing the dosage of CN. The ‘optimum CN' value is 10%; For cured at 50 ℃, the retardation degree increases with increasing the dosage of CN.In the presence of CN, NO_3-AFm and NO_3-AFt are more preferred than CAH_(10) and C2_AH_8, and they are more thermostable than those typically hydrates, thus avoiding the phase conversion to a large extent. The CN addition and curing temperature affect the formation and evolution of NO_3-AFm and NO_3-AFt. For cured at 50 ℃, the compressive strength of CAC systems with CN is improved. CAC with 10% CN systems has the maximum strength(i.e., 66.8 MPa) at 28 d, while the CN-free system has the minimum strength(i.e., 28.7 MPa), the optimum dosage for CN is 10 %.
引文
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