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为探究偏高岭土(metakaolin,MK)影响水泥基材料干燥收缩(干缩)机理,研究了不同MK掺量(0、5%、10%、15%)、不同成熟度(水中分别预养护3 d和28 d)硅酸盐水泥浆体在20℃、55%相对湿度下的干缩和质量损失行为,并采用综合热分析和压汞法研究了不同成熟度水泥浆体的组成和微观结构。结果表明:MK对浆体干燥收缩行为的影响与掺量和浆体成熟度密切相关;MK使不同成熟度水泥浆体长期(28 d以上)干缩均减小,且掺量越大干缩越小;对早期干缩的影响则随浆体成熟度不同而有差异,MK使预养护3d的浆体早期干缩略有增大,预养护28d则相反;浆体干缩与质量损失在一定范围内呈线性相关,浆体在不同阶段的内在失水机制及其引起的收缩大小有差异;MK通过微填充效应、晶核效应和/或火山灰效应使不同成熟度浆体孔隙率下降、孔径细化,导致浆体蒸发失水减少、减缓而减小浆体干缩。
In order to explore the effect of metakaolin (MK) on the drying shrinkage (dry shrinkage) of cement-based materials, the effect of different MK contents (0, 5%, 10%, 15% And 28 d) shrinkage and mass loss of Portland cement paste at 20 ℃ and 55% relative humidity respectively. The composition and microstructure of cement paste with different maturity were studied by comprehensive thermal analysis and mercury intrusion. The results showed that the effect of MK on the drying and shrinkage behavior of the slurry was closely related to the dosage and the maturity of the slurry. MK reduced the dry shrinkage of cement slurry with different maturity for more than 28 days The effect of early drying shrinkage is different with the maturity of the slurry, MK pre-curing 3d slurry early shrinkage increased slightly, pre-curing 28d is the opposite; slurry shrinkage and mass loss in the Linear relationship was found within a certain range, and there was a difference in the internal water loss mechanism and the shrinkage caused by slurry at different stages. MK decreased the porosity of slurry with different maturity through micro-filling effect, nucleation effect and / or volcanic ash effect, Aperture refinement, leading to loss of slurry evaporation loss, reduce and reduce the slurry shrinkage.