【摘要】 采用多通道椭圆环收缩开裂测试手段、自由收缩和强度试验综合评价了聚羧酸类、萘系和木质素系减水剂对水泥砂浆早期收缩开裂和强度的影响.结果表明,掺减水剂均延长了砂浆初始开裂时间,从而降低了砂浆的开裂敏感性.就减水剂降低砂浆开裂敏感性而言,聚羧酸类和高浓型萘系高效减水剂是行之有效的.掺聚羧酸类和掺木质素系减水剂都减小了砂浆的最大裂纹宽度,而掺萘系则加快了砂浆最大裂纹宽度的发展速度.掺高效减水剂均增大了砂浆自由收缩值,且萘系比聚羧酸类减水剂更能增大砂浆自由收缩值,而掺木质素系减水剂能稍微降低砂浆的自由收缩值.在干燥养护条件下,掺高效减水剂比掺木质素系减水剂更能有效地提高砂浆抗折和抗压强度,且掺聚羧酸类减水剂又比掺萘系高效减水剂更为有效.更多还原

【Abstract】 High range water-reducing admixture is an important ingredient of high performance concrete.Early-age cracking due to shrinkage accelerates obviously the deteriorations of concrete.The effect of polycarboxylate type superplasticizer(PC),high thickness type polynaphthalene sulphonate superplasticizer(PNS) and calcium lignosulphonate(CL) on shrinkage cracking of mortars has been investigated by means of multi-channel ellipse ring shrinkage cracking test,free shrinkage and strength test under drying conditions.The general effect of PC,PNS and CL is to increase initial cracking time of mortars,and decrease cracking sensitivity of mortars.As for decreasing cracking sensitivity,PC and PNS are quite effective.Maximum crack width of mortars with PC and PNS is lower,but the development rate of maximum crack width of mortars with PNS is faster in comparison with control mortars.The effect of PC and PNS is to increase free shrinkage of mortars when keeping the constant W/B ratio and the content of cement pastes.Furthermore,free shrinkage of mortars with PC is lower than those with PNS,but CL has slightly lowered free shrinkage of mortars.Superplasticizer is more effective to improve flexural and compressive strength of mortars than CL under drying conditions,and PC is more effective than PNS.更多还原