不同养护制度下大掺量石灰石煅烧黏土UHPC早期水化及力学性能发展

Hydration and Mechanical Properties Development of UHPC with Large Substitution Level of Limestone and Calcined Clay at Early Stage under Different Curing Regimes

采用大掺量(60%,质量分数)石灰石煅烧黏土替代水泥熟料设计制备了超高性能混凝土(UHPC),通过抗压强度测试、X射线衍射(XRD)分析、等温量热分析以及综合热分析研究了其在标准养护和蒸汽养护下的早期水化行为和力学性能发展。研究发现,蒸汽养护显著改善了由高水泥替代量造成的1 d及3 d抗压强度损失,标准养护则使7 d抗压强度更为优异,煅烧黏土和石灰石质量比为2∶1时各个龄期的强度发展最佳。在蒸汽养护条件下水化进程得到大幅提前,出现明显的铝酸盐相反应放热峰。蒸汽养护加剧了煅烧黏土对氢氧化钙的消耗,煅烧黏土和石灰石质量比为2∶1时才检测到单碳型碳铝酸盐的形成,表明在低水胶比环境下,早期煅烧黏土与石灰石的协同作用主要取决于活性组分煅烧黏土的含量。

Ultra-high performance concrete(UHPC)was designed and prepared by using large substitution level(60%,mass fraction)of limestone and calcined clay instead of cement.Its early hydration behavior and mechanical properties under standard curing and steam curing were studied by compressive strength test,X-ray diffraction(XRD)analysis,isothermal calorimetry analysis and comprehensive thermal analysis.It is found that steam curing significantly improves the loss of compressive strength caused by high cement substitution at 1 d and 3 d,while standard curing brings more excellent compressive strength at 7 d.When the mass ratio of calcined clay to limestone is 2∶1,the strength development of each age is the best.The hydration process is greatly accelerated under the condition of steam curing,and there is an obvious exothermic peak of aluminate phase reaction.Steam curing intensifies the consumption of calcium hydroxide by calcined clay,and the formation of monocarboaluminate is detected only when the mass ratio of calcined clay to limestone is 2∶1,indicating that in the environment of low water to binder ratio,the synergistic effect of early calcined clay and limestone mainly depends on the content of calcined clay.