低水胶比对复合胶凝体系水化特性和动力学影响研究

Effect of Low Water-Binder Ratio on the Hydration Properties and Kinetics of Composite Cementitious System

低水胶比复合胶凝体系的水化机理和水化行为较普通水胶比胶凝体系存在一定差异,该条件下传统的水化结论往往不再适用.以不同低水胶比水泥-粉煤灰-矿渣复合胶凝体系为研究对象,通过测试净浆试件7d水化热,结合水化动力学模型探明了低水胶比、矿物掺合料掺量对其水化行为和水化机理的影响,并通过透射电子显微镜(TEM)和X射线衍射(XRD)分析了低水胶比复合胶凝体系的水化产物差异.研究结果表明:水胶比为0.2、粉煤灰-矿渣复掺量小于50%时,复合胶凝体系早期和后期的放热速率无明显差异,此时复掺粉煤灰-矿渣对水泥水化存在一定促进作用,当水胶比增至0.25和0.3时,复掺粉煤灰-矿渣在10~17h抑制了水泥水化;当水胶比由0.3降低至0.2时,胶凝体系最大放热速率呈增大趋势,且水化过程由NG-I-D改变为NG-D,不再经历相边界反应;水化至28d时,水化硅酸钙(C-S-H)的形貌随着水胶比的降低,由纤维状向球状转变.

The hydration mechanism and behavior of composite cementitious system with low water-binder ratios(W/B)are different from those of ordinary cementitious system,and the traditional conclusions about cement hydration are no longer appropriate under this condition.The hydration heat of composite cementitious system of cement-fly ash-slag with different low W/B ratios was measured in 7 days,based on which the effects of low W/B ratio and mineral admixture content on its hydration behavior and mechanism were explored by the cement hydration kinetics.TEM and XRD were also conducted to analyze the hydration products difference of composite cementitious system with low W/B ratio.Results show that the early and late hydration exothermic rates of the composite cementitious system do not change significantly when its W/B ratio is 0.2 and the fly ash-slag content is less than 50%,and the compound mineral admixture could slightly promote the cement hydration under this condition.The addition of fly ash and slag inhibits the hydration of composite cementitious system in 10~17h when the W/B ratio is 0.25 or 0.3.The maximum hydration exothermic rate of the cementitious system increases with the decrease of W/B ratio from 0.3 to 0.2,and the hydration process changes from NG-I-D to NG-D,no longer experiencing the phase boundary reaction.With the decrease of W/B ratio,the fibrous hydrated calcium silicate(C-S-H)will transform into spherical structures after hydrating 28 days.