氧化钙-碳酸钠复合激发矿渣砂浆的自收缩机制

Mechanism of autogenous shrinkage of hybrid calcium oxide and sodium carbonate-activated slag mortars

为探究氧化钙和碳酸钠复合激发矿渣对碱激发水泥自收缩的影响机制,采用氧化钙和碳酸钠(摩尔比1∶1)为复合激发剂制备碱矿渣砂浆(AM),研究复合激发剂Na_(2)O质量分数(CaO和Na_(2)CO_(3)反应生成的Na_(2)O质量与矿渣质量比,为2.5%、4.5%、6.5%和8.5%)对AM自收缩的影响;通过XRD、TG-DTG、MIP和NMR分析其水化产物与微观结构。结果表明:随着Na_(2)O质量分数的增加,激发剂反应耗水量增加,孔结构细化,孔隙压力增大;Al^(3+)对C-(A)-S-H中Si^(4+)的取代量增多导致Na^(+)的吸附量增多,C-(A)-S-H滑移增大;水化程度提高,水化产物数量增多,AM的自收缩增大。Na_(2)O质量分数为6.5%的AM为最优组,其力学性能高于普通硅酸盐水泥砂浆(OM),但由于较低的晶体含量和致密的孔结构,其自收缩大于OM。

To investigate the mechanism of the effect of calcium oxide and sodium carbonate activated slag on the autogenous shrinkage of alkali-activated cement,an alkali-activated slag martar(AM)was prepared using calcium oxide and sodium carbonate(molar ratio of 1∶1)as the combined activator.The effect of combined activator Na_(2)O equivalent(i.e.the by weight ratio of Na_(2)O produced by the reaction of the combined activators to slag,i.e.2.5%,4.5%,6.5% and 8.5%)on the autogenous shrinkage of AM was investigated.The hydration products and microstructure were characterized by X-ray diffraction,thermogravimetric analysis,mercury intrusion porosimetry,and nuclear magnetic resonance.The results indicate that with the increase of Na_(2)O equivalent,the increase of water consumption due to the reaction of activators and pore structure refinement leads to the increase of pore pressure,and the amount of absorbed Na+increases due to the increase of amount of Si^(4+)in C-(A)-S-H replaced by Al^(3+),resulting in the increase of C-(A)-S-H slippage.The increase of hydration degree induces the increase of the amount of hydration products,resulting in the increase of the autogenous shrinkage.AM with Na_(2)O equivalent of 6.5% is the best group with its mechanical properties higher than those of ordinary Portland cement mortar(OM),but its autogenous shrinkage greater than that of OM due to its lower crystal content and denser pore structure.