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

摘要:

采用超滤法将脂肪族高效减水剂（SAF）切割为相对分子质量范围依次为＜2500、2500~10000、10000~50000和＞50000的四个级分，测试结果表明随级分相对分子质量的增大，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，级分相对分子质量增大，对水泥的减水分散性能快速提高，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，掺四种级分的7d和28d硬化砂浆抗压强度均增大，增幅在30%~60%，并随相对分子质量的增大而增加；掺量＞0.3%时，由于相对分子质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。

Abstract:

Sulfonated acetone–formaldehyde polycondensate(SAF) was fractioned by ultrafitration into four fractions with molecular weight range of ＜2500、2500~10000、10000~50000 and ＞50000. Structural analysis showed the weight-average molecular weight and intrinsic viscosity of the four fractions successively increased while their sulfonation degree decreased. Meanwhile, properties of SAF with different molecular weight as water reducer of cement were studied. Results showed with the increasing of molecular weight of SAF, the water-reducing ratio of cement paste containing SAF increased remarkably, but the paste tended to lose fluidity easier with time-lapse. And the retardation effect of SAF decreased because the content of sulfonic groups and hydroxyl reduced and the complexation of these two groups to calcium ion was weakened. The 7d and 28d compressive strenght of harden mortar added fracioned SAF were enhanced by 30%~60% in contrast with the reference and the strenght increased as molecular weight of SAF increased. The two fractions of higher molecular weight had dosage and water-amount sensitivity ,and when their dosage was above 0.3%, mortar became bleeding. It thus decreased the compressive strenght.