硫酸盐对聚羧酸减水剂吸附-分散性能的影响

系统研究了硫酸盐对掺聚羧酸减水剂水泥浆体流变性及水化性能的影响.结果表明:硫酸盐降低了聚羧酸减水剂在水泥颗粒表面的吸附量,削弱了聚羧酸减水剂对水泥浆体的分散作用.随着硫酸盐掺量的增加,聚羧酸减水剂分散性能下降.少量硫酸盐延缓了水化加速期最大水化放热速率峰的出现,并且提高了最大水化放热速率.而大量硫酸盐则使得水泥水化诱导期缩短,最大水化速率峰显著提前.大量硫酸盐的加入促进了水泥浆体中钙矾石(AFt)的生成,削弱了水化铝酸钙(CAH)的生成.MgSO4对于水泥浆体中水化产物生成的促进作用最明显.掺加MgSO4的水泥水化产物中含有大量细丝状水化硫铝酸盐产物.MgSO4对水泥水化具有显著延缓作用,水化产物结晶成核作用较缓慢,从而使得水化产物生成及分布更加均匀,形状更加细小.

Effects of Sulfates on the Adsorption and Dispersing Properties of Polycarboxylate Superplasticizer

The effects of sulfates on the adsorption and dispersing properties of cement paste of polycarboxylate superplasticizer (PCE) were studied. The effects of sulfates on the hydration process of cement paste were systematically investigated through TAM air isothermal calorimetry, XRD, DTA/TG, FTIR as well as SEM. The results show that the addition of sulfates reduces the adsorption of PCE on cement particles and hence impairs the dispersing capability of PCE. Among the sulfates, alkali sulfates (Na2SO4 and K2SO4) most significantly influence the dispersing capability of PCE, while the poorly soluble CaSO4?2H2O slightly influences the dispersing capability of PCE. A small amount of sulfates retards induction period, promotes the maximum hydration rate, and increases the heat evolution rate due to the transformation from AFt to AFm. A high amount of sulfates significantly advances the maximum hydration rate peak at acceleration period, promotes the formation of AFt, and impairs the formation of CAH. Among the sulfates, the addition of MgSO4 greatly retards the hydration heat peak at acceleration period and significantly promotes the transformation from AFt to AFm. After cement paste is hardened, a large number of filamentous hydrated sulphoaluminate phases are present due to the addition of MgSO4, because MgSO4 greatly retards the hydration process and slows the nucleation and precipitation of hydration products.