偏高岭土对硅酸盐水泥浆体干燥收缩行为的影响及机理

Effect of Metakaolin on Drying Shrinkage Behaviour of Portland Cement Pastes and its Mechanism

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 mechanism of the effect of the metakaolin （MK） effect on the drying shrinkage of cementitious ma- terials, the drying shrinkage and mass loss of blended Portland cement pastes with various MK contents （0, 5%, 10%, 15%） and different maturities （precured in water for 3 d and 28 d, respectively）, were investigated by drying at 20 ℃ and 55% relative humidity. The composition and microstructure of cement pastes were determined by thermal analysis and mercury intrusion porosimetry. The results show that the effect of MK on the drying shrinkage of cement pastes is closely related to the MK content and maturity of the pastes. The late-age drying shrinkage of cement pastes with different maturities decreased with the increase of MK contents. However, the effect on the early age drying shrinkage depended on the maturity of paste. The MK increased slightly the early age drying shrinkage of the paste pre-cured for 3 d, and decreased the early age shrinkage of the paste pre-cured for 28 d. The drying shrinkage of cement paste was proportional to its mass loss and the mechanism of water loss and its relation with the drying shrinkage varied. The decrease of drying shrinkage of blended cement paste with the MK was due to the result of less and slower evaporation of water in the MK blended cement paste with low porosity and refined pores structure by the micro-filler effect, nuclear effect and/or pozzolanic reaction of the MK.