K^+/Na^+摩尔比对高碱含量水泥基材料早期开裂敏感性的影响

Influence of potassium-sodium ratio on the early age cracking sensitivity of cementitious materials with high alkalinity

利用椭圆环开裂仪、比长仪、等温量热仪、压汞仪(MIP)及扫描电子显微镜(SEM),重点研究了在高碱含量水泥基材料中,K^+/Na^+摩尔比对其早期开裂敏感性的影响及机制,并探究了粉煤灰对不同K^+/Na^+摩尔比高碱水泥基材料早期开裂敏感性的影响。结果表明:K^+/Na^+摩尔比每增加1倍,水泥基材料初始开裂时间缩短3%左右,主要作用机制在于,更高的K^+/Na^+摩尔比增加了水泥基材料水化速率和对收缩影响较大的孔径小于50 nm的孔分布,导致浆体内部毛细孔水含量降低,孔隙压力增加,早期收缩率增加,收缩应力增大同时水泥基材料抗拉强度和结晶度的下降,降低了水泥基材料基体抵抗拉应力的能力,使水泥基材料开裂敏感性增加;粉煤灰并不能改变水泥基材料早期开裂随K^+/Na^+摩尔比的增加而增加这种规律,但能有效降低水泥材料开裂敏感性,其作用机制在于粉煤灰延缓了水泥早期水化,在一定程度上降低了孔压力,早期收缩率降低,同时增加了水泥基材料基体抵抗拉应力的能力,使水泥基材料具有良好抵抗早期开裂能力。

The influence of potassium-sodium ratio on early age cracking sensitivity of cementitious materials in high alkalinity added with and without fly ash was investigated,using techniques of multi-channel ellipse ring shrinkage cracking apparatus,comparator,isothermal calorimeter and mercury intrusion porosimetry（MIP）.The results indicate that initial cracking time of cementitious materials shortens by about 3% with each doubling of potassium-sodium ratio,the mechanism of which is that high potassium-sodium ratio accelerates hydration and increases content of pores that under 50 nm of diameter,which reduces the amount of capillary water and raises pore pressure,resulting in increasing of early shrinking ratio and shrinkage stress,and tensile strength and crystalhnity of cementitious materials are reduced,resulting in the decreasing of ability of tensile stress resistance,and increasing sensibility of early cracking.Fly ash has little impact on the influence of potassium-sodium ratio on early age cracking sensitivity of cementitious materials,but it can efficiently improve early age cracking sensitivity of cementitious materials by delaying early hydration,and reducing pore pressure to some degree,fly ash can also help to increase ability of tensile stress resistance of cementitious materials,and thus,improving the ability of resistance of early age cracking of cementitious materials.