硅烷改性聚羧酸减水剂对水泥-硅灰浆体分散性能影响及机理

Influence of silanized polycarboxylate superplastizers on fluidity of cement-silica fume pastes and its mechanism

硅灰是超高强混凝土(UHSC)中最难被分散的组分,超高强混凝土性能提升需要硅灰的有效分散。通过自由基反应,将乙烯基三乙氧基硅烷接枝引入了主链结构中,合成了一种含有硅烷基团的聚羧酸减水剂(PCES)。采用微坍落度法研究了PCES对水泥-硅灰浆体流动性的影响规律。用有机碳分析仪研究了PCES在水泥净浆和硅灰表面的吸附性能。研究结果表明,聚羧酸减水剂分子结构中引入硅烷基团后,分散水泥-硅灰浆体的能力明显提高,在水泥颗粒表面吸附量增加幅度不大,而在硅灰表面的吸附量有较大幅度增加。PCES能够在含有羟基的硅灰表面同时发生物理吸附和化学吸附,硅灰表面吸附更多的减水剂分子后,其空间排斥能增加,这可能是PCES分散能力提升一个机理。相较普通聚羧酸减水剂,硅烷改性的聚羧酸减水剂更适宜配制超高强混凝土。

Silica fume is the hardest dispersing component in ultra high strength concrete( UHSC),and improvement of UHSC performance need effective dispersion of silica fume. In this study,silanized polycarboxylate superplastizer(PCES)was synthesized through radical copolymerization,which Vinyltriethoxysilane was introduced to backbone structure of polymer. The influence of PCES on fluidity of cement-silica fume pastes was analysed by mini-slumps method. Adsorption properties of PCES on surface of cement and silica fume were investigated by TOC. Results shows: compared with traditional polycarboxlate,PCES showed a higher dispersing capability in cement-silica fume pastes,Adsorption amount increased marginally in cement,while sharply in silica fume. The surface of silica fume existed hydroxyl,chemical adsorption and electrostatic adsorption of PCES happened simultaneously. Owing to additional chemical adsorption,more molecules existed in surface of particles,they can offer stronger steric hindrance repulsive force,this may be a mechanism that PCES possessed high dispersion effectiveness in cement-silica fume pastes. Compared to traditional polycarboxlate,PCES was more suitable for ultra high strength concrete.