聚羧酸系超塑化剂对铝酸三钙–石膏水化行为的影响

通过水化热、热分析等手段研究了两种具有相同侧链长度,但桥接基团不同(酯基、醚键)的聚羧酸系超塑化剂(PCs)对铝酸三钙(C3A)–石膏水化行为的影响。结果表明:当石膏与C3A的摩尔比为0.3时,PCs的加入能促进硫酸根的消耗,加快C3A的溶解,有利于单硫型硫铝酸盐(AFm)的沉淀,但对水榴石(C3AH6)的生长具有抑制作用。PCs的化学结构与其吸附能力息息相关,侧链桥接基团为酯基时,PCs在C3A–石膏体系中的吸附量较大,对C3AH6的生长抑制作用更强。由于PCs与硫酸根离子在C3A颗粒表面发生竞争吸附,PCs部分占据颗粒表面的溶解点,进而释放出额外的自由硫酸根离子,这是PCs促进硫酸根消耗并加速AFm相形成的原因。

Effect of Polycarboxylate-Type Superplasticizer on Hydration Behavior of C3A–Gypsum Suspension

The impact of two comb-like copolymer dispersants (PCs) with either ester (–COO–) or ether (–C–O–C–) linkages on the hydration behavior of C3A–gypsum suspension was investigated via conduction calorimetry and thermal analysis. The addition of PCs accelerated the depletion of sulphate as well as the dissolution of C3A at the gypsum/C3A molar ratio of 0.3, resulting in an increase of the formation of monosulfoaluminate phase and a decrease of C3AH6 precipitation. Moreover, the chemical structure of PCs was correlated to its adsorption behavior. The PCs with ester linkage induced a greater adsorption on the C3A–gypsum system, leading to a stronger retardation of C3AH6 precipitation. It was assumed that the competitive adsorption between PCs and sulphate could cause the dissolution sites of C3A that were partly occupied by PCs. The AFm precipitation and sulphate consumption both increased at a greater amount of extra sulphate released in the pore solution.