随着高强混凝土在工程中的不断应用，混凝土的水灰比越来越小，减小水灰比虽然可以提高混凝土或砂浆的抗压强度，但同时也会使其脆性增强、抗裂性变差。矿物掺合材料在工程中使用很广泛，它们的掺入对混凝土的脆性、强度都会产生影响。选取三种工程中较常采用的矿物掺合材料———粉煤灰、硅灰和MgO粉末，通过改变掺量和掺加方式来研究它们对砂浆强度、脆性的影响。试验结果表明，砂浆脆性随着自身强度的提高和养护龄期的延长而不断增强。随着胶凝材料含量的增大，砂浆的抗压强度提高，同时其脆性有一定程度下降。粉煤灰掺量越高，砂浆脆性下降得越多，但粉煤灰的掺入对砂浆早期强度的发展会产生不利影响。掺入一定量的硅灰不仅能提高砂浆的抗压强度，而且能很好地降低其脆性，提高抗裂性。掺入MgO粉末也能降低砂浆的脆性，但同时对其抗压强度特别是早期抗压强度有明显降低作用。因此，在实际工程中，建议双掺适量粉煤灰和硅灰，这不仅可以显著降低砂浆的脆性，而且可以弥补粉煤灰对早期强度的不利影响，使中后期强度不低于甚至高于基准砂浆的强度。%With the continuous application of high strength concrete in engineering, concrete water⁃cement ratio is getting smaller and smaller. Although water⁃cement ratio can be reduced to improve the compressive strength of concrete or mortar, but will also make it more brittle so that crack resistance deteriorates. Mineral admixture materials are widely used in the project, and their incorporation will have an impact on brittleness and strength concrete. In this paper, three kinds of mineral admixture materials( fly ash, silica fume and MgO powder) often used in the actual project were selected to study their effects on the strength and brittleness of mortar by changing the content and adding ways. Test results show that the mortar brittleness increases with the increasing of compressive strength and curing age. When the content of cementitious materials rises,the compressive strength also increases, but the brittleness decreases at the same time. The more the content of fly ash is, the more the brittleness falls. However, the incorporation of fly ash will have an adverse impact on the development of early strength of mortar. Silica fume added can not only increase compressive strength but also reduce brittleness of mortar and enhance its crack resistance. MgO added can cut down the brittleness, but can reduce the compressive strength significantly at the same time, especially for early compressive strength. Therefore, double mixed the right amount of fly ash and silica fume is proposed in the actual project, which can not only significantly reduce the brittleness of mortar, but also can compensate for the adverse impact on the early strength of fly ash so that the late strength is not less than or greater than the strength of the reference mortar.
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