偏高岭土对硅酸盐水泥浆体干燥收缩的影响

为探究偏高岭土(MK)影响水泥基材料干燥收缩机制,研究不同MK掺量、不同成熟度硅酸盐水泥浆体在20℃、55%湿度下的干燥收缩和质量损失,并采用压汞法(MIP)研究不同成熟度水泥浆体的孔结构。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;虽然MK使不同成熟度水泥浆体长期(28 d以上)干缩均减小,掺量越大,干缩越小,但对早期干缩的影响则存在差异。MK使预养护3 d的浆体早期干缩略有增大,而预养护28 d则相反。MK对浆体的干燥收缩与质量损失的影响有明显的一致对应关系,浆体质量损失越大,则收缩越明显。MK通过微填充效应、晶核效应和火山灰效应使不同成熟度浆体孔隙率下降、孔径细化,导致浆体在干燥条件下蒸发失水减少、过程减缓,从而减小浆体干燥收缩。

Effect of metakaolin on drying shrinkage behaviour of cement pastes

For exploring the mechanism of the effect of metakaolin(MK) on drying shrinkage of cementitous materials,the drying shrinkage and weight loss of blended cement pastes with various replacement levels of MK and different maturities,were studied by being dried at 20 ℃,55% RH.The pore structure of cement pastes was measured by mercury intrusion porosimetry(MIP).Results showed that the effect of MK on drying shrinkage of cement pastes was closely related to the MK content and maturity of cement paste.The long-term drying shrinkage of cement pastes with different maturities decreased with the increasing MK contents.The early age drying shrinkage of the paste pre-cured increased with MK for 3 d,while the early age shrinkage of the paste procured decreased for 28 d.The effect of MK on the mass loss of paste agreed well with its effect on drying shrinkage,the higher the mass loss,the larger the shrinkage.The decrease of drying shrinkage of blended cement paste with MK was due to the less and slower evaporation of water in the paste with lower porosity and refined pore structure,resulting from the micro-filler effect,nuclear effect and pozzolanic reaction of MK with lower porosity and refined pore structure.