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在混凝土中,使用低钙粉煤灰或高炉矿渣部分取代水泥时,其早期抗压强度一般较低,特别是在头3天或7天。最好的方法是用少量的硅灰来解决这个问题。Mehta和Gyorv首先提出了这种方法。除了进行掺粉煤灰和硅灰的混凝土强度试验之外,他们还进行掺相同比例的火山灰和水的净浆体的研究,以资对比。他们用ASTMC114测定了干浆试体的游离氧化钙量,用水银压人法进行孔径分布的分析。表1是他们得到的各种混凝土抗压强度。仅掺用粉煤灰时,3、7、28和90天的强度始终低于对照
In concrete, when low-calcium fly ash or blast-furnace slag is partially replaced by cement, its early compressive strength is generally low, especially in the first 3 days or 7 days. The best way is to solve this problem with a small amount of silica fume. Mehta and Gyorv first proposed this method. In addition to conducting concrete strength tests with fly ash and silica fume, they also conducted a study of the same proportion of pozzolan and water paste to compare. They used ASTM C114 to determine the amount of free calcium oxide in dry pulp samples and the mercury pressure method to analyze the pore size distribution. Table 1 shows the compressive strength of various concretes they obtained. In the case of fly ash alone, the strength at 3, 7, 28, and 90 days is always lower than that of the control.