减水剂与低硫酸盐含量水泥的相容性

Compatibility of Surerplasticizers in Cement Paster with Low Sulfate Content

研究了硫酸盐含量不超过2.00%的胶凝材料中,硫酸盐含量变化对减水剂与胶凝材料相容性的影响规律及微观机理。通过测定0.39%～3.00%硫酸盐含量的浆体在相同流动度下的水胶比和减水剂掺量,确定硫酸盐含量降低对减水剂作用效果的影响规律。研究了减水剂的吸附行为和硫酸盐含量低于2.00%的水泥浆体早期水化产物的变化情况。结果表明:当水泥浆体中硫酸盐含量低于1.50%时,浆体硫酸盐含量的降低使水泥早期生成大量Ca(OH)2,新拌浆体Zeta电位显著提高,增加了减水剂的吸附量和早期水化产物对减水剂分子的包裹与吞噬作用。硫酸盐含量降低对低电荷密度的聚羧酸减水剂影响较小,因此,当胶凝材料中硫酸盐含量低于2.00%时,应尽量选取低电荷密度的聚羧酸减水剂,以避免相容性问题的出现。

The influence mechanism of sulfate content on the compatibility of cement with naphthalene and polycarboxylate superplasti- cizer was investigated in the cement slurry with sulfate content lower than 2.00 %. The water-cement ratio and dosage of each super- plasticizer was measured in cement pastes with 0. 39%-3. 00% sulfate content. The effect of sulfate on the performance superplasticizer is clarified. The adsorption of superplasticizer was investigated and the change of early hydration products in cement paste was observed in cement paste with sulfate content lower than 2.00%. The results show that the early hydration products were changed in low sulfate content cement. Huge amount of Ca{OH）z was observed when sulfate content is less than 1.50%. The Zeta potential declined and the adsorption of superplasticizers increased. Superplasticizer was dramatically consumed by absorbing into the hydration products in cement paste with sulfate content lower than 2.00%. Superplasticizer with lower charge density is less affected by lower sulfate content. Therefore, in the composite cementitious material with sulfate content lower than 2. 00 %, the superplasticizer with lower charge densi- ty should be chosen to avoid the incompatibility problems.