相对分子质量对脂肪族高效减水剂分散增强性能的影响

Influence of Molecular Weight of Sulfonated Acetone-Formaldehyde Polycondensate on Its Dispersing Performance

采用超滤法将脂肪族高效减水剂（SAF）切割为相对分子质量（以下简称分子量）范围依次为〈2 500、2 500-10 000、10 000-50 000和〉50 000的4个级分,测试结果表明,随级分分子量的增大,重均分子量、特性黏度依次增加,磺化度依次降低。对不同级分减水剂的应用性能研究表明,级分分子量增大,对水泥的减水分散性能显著提高,但对流动度的保持能力降低,同时磺酸根与羟基对Ca2＋的络合作用逐渐减弱,使缓凝作用减小。与空白砂浆比较,掺4种级分的7 d和28 d硬化砂浆抗压强度均增大,增幅在30%-60%,并随分子量的增大而增加;掺量（减水剂相对水泥的质量分数）大于0.3%时,由于分子量较大的两个级分对掺量及用水量较敏感,使砂浆泌水严重,抗压强度比低掺量时略低。

Sulfonated acetone-formaldehyde polycondensate（SAF） was fractioned by ultrafitration into four fractions with the molecular weight range of 〈2 500,2 500～10 000,10 000～50 000 and 〉50 000.Structural analysis showed the average molecular weight and the intrinsic viscosity of the four fractions successively increased while their sulfonation degree decreased.Meanwhile,properties of SAF fractions with different molecular weights as the water reducer of cement were investigated.Results showed with the increase of molecular weight of SAF fractions,the water-reducing ratio of cement paste containing SAF fractions increased significantly,but the paste tended to lose fluidity easier with the time-lapse.The retardation effect of SAF fractions decreased because the content of sulfonic groups,hydroxyl reducer and the complexation of these two groups to calcium ion was weakened.The 7 d and 28 d compressive strength of the harden mortar added SAF fractions were enhanced by 30%～60% in contrast with the reference and the strength increased as the molecular weight of SAF fractions increased.The two fractions of higher molecular weight had the dosage and water-amount sensitivity,and when their dosage was above 0.3%（ratio of mass of SAF to cement）,the mortar became bleeding.It thus decreased the compressive strength.