碱对水泥基材料早期收缩性能的影响

用椭圆型开裂环自动测试装置和非接触式电阻率测定仪以及JAF量热计,分别测试不同水灰比、不同碱度水泥砂浆的初始开裂时间以及水泥浆体早期水化的电阻率与水化放热速率。结果表明：碱度增加虽然加速水泥的水化,但削弱了水泥基材料抵抗收缩变形的能力,在低水灰比下表现更为明显。水泥基材料的初始开裂时间与电阻率曲线上的特征点以及最大放热峰之间存在一定的联系。所提出的阻率步长与热率步长之比值K与水泥基材料的开裂敏感性及碱含量密切相关。

EFFECTS OF ALKALINITY ON EARLY AGE SHRINKAGE CHARACTERISTIC OF CEMENT-BASED MATERIALS

Initial cracking time, electrical resistivity and rate of heat evolution of cement-based materials with different alkalinities were measured by an ellipsis-ring cracking apparatus with an automatic monitoring system, non-contact resistivity instrument and JAF calorimeter, respectively. Results show that the alkali accelerates the hydration process of portland cement but shortens greatly the initial cracking time of mortar, especially at a lower watercement ratio. Moreover, there is an interactive effect between the initial cracking time and resistivity inflexion, as well as maximum heat peak. A ratio of resistivity step/heat step (as K value) indicates a relation between early-age deformation and alkali content of cement-based materials.