超高强混凝土中各组分与聚羧酸系超塑化剂之间的相互作用(英文)

超高强混凝土(ultra-high strength concrete,UHSC)的水灰比小于0.25,含有大量的硅灰等微细组分,这有利于颗粒的最优紧密堆积。硅灰的表面化学效应以及较大的表面积使其成为UHSC中最难被分散的组分。由甲基丙烯酸、甲基丙烯酸酯及甲代烯丙基磺酸合成的聚羧酸系超塑化剂能使水泥颗粒被有效润湿,然而烯丙醚-马来酸酐合成的聚羧酸系超塑化剂可以很好地分散硅灰。这2种不同的聚羧酸系超塑化剂的复合可以使其拥有不同的分子结构,从而赋予超高强混凝土很好的流动性。当只加入1种聚羧酸系超塑化剂时其掺量为1%(质量分数,下同),而当加入这种复合聚羧酸系超塑化剂时掺量为0.5%就足够了。这2种类型的聚羧酸系超塑化剂的协同效应是由于它们的选择性吸附:甲基丙烯酸盐基的聚羧酸系超塑化剂主要吸附在水泥颗粒表面,而烯丙醚基聚羧酸系超塑化剂主要吸附在硅灰颗粒表面。实验表明:小分子量的有机酸阴离子(如:柠檬酸盐、葡萄糖酸盐及酒石酸盐中的阴离子)与聚羧酸系超塑化剂之间具有潜在的协同作用。只需加入0.1%的这些阴离子即可显著提高烯丙醚基聚羧酸系超塑化剂的作用效果。这些阴离子可以起到一种辅助作用,它们同时吸附在水泥颗粒表面以及硅灰颗粒表面。水泥颗粒的表面首先由这些阴离子所占据,而硅灰颗粒表面吸附了烯丙醚基聚羧酸系超塑化剂和这些阴离子。这些阴离子起到了一种很强的静电分散效应,使烯丙醚基聚羧酸系超塑化剂的空间位阻效应得到加强。虽然聚羧酸系超塑化剂阴离子具有缓凝作用,但是使用这种复合聚羧酸系仍能制备出高早强混凝土。

INTERACTIONS BETWEEN POLYCARBOXYLATE SUPERPLASTICIZERS AND COMPONENTS PRESENT IN ULTRA-HIGH STRENGTH CONCRETE

The ultra-high strength concrete (UHSC) is eharacterized by a water cement ratio of below 0.25 and a high content of frees such as silica fume for optimized packing density. In the UHSC, due to its surface chemistry and large surface area, silica fume is the most difficult component to be dispersed. Polycarboxylates (PCEs) made of methacrylie acid, MPEG methaerylate ester and methal-lylsulfonic acid effectively liquefies cement, whereas allyl ether-maleic anhydride based PCEs disperse silica fume well. Thus, a combination of these PCE types which possess different molecular architectures provides superior flowability to UHSC. A low dosage of 0.5% by mass of cement of this combination is sufficient, whereas about 1% (by mass of cement) is required when the individual PCEs are utilised. The reason for this synergistic effect of these of PCEs is their selective adsorption: the methacrylate-based PCE preferentially adsorbs on cement while the allyl ether-type PCE is strongly attracted by the silica surface. Additional experiments were conducted to probe a potential synergism between organic anions (citrate, gluconate, tartrate, with small molecular mass) and PCE. It was found that addition of only 0.1% by mass of cement of these anions further enhances the effectiveness of the allyl ether-based PCE, resulting in an even lower PCE dosage. It was mechanistically identified that these anions act as supplemental effect which ad-sorb simultaneously on both cement and silica fume. This way, the surface of cement is primarily occupied by the anion, whereas on the surface of silica, concomitant adsorption of the allyl ether-based PCE, and the anion occurs. The anion exercises a strong electro-static dispersion effect which compliments the steric effect of the allyl ether-based PCE. This admixture combination was found to sprovide a high early strength, in spite of the known retarding effect of the carboxylate anions.