SBR乳液对水泥砂浆长期收缩性能影响及机理分析

采用螺旋弓形测量仪分别测量了普通水泥砂浆和SBR（styrene-butadiene rubber）乳液改性水泥砂浆长期（1～90d）收缩变形，并通过孔径分布法、密度法和SEM图像法对28d砂浆的微观形貌及孔结构特征进行了分析，并对SBR乳液水泥净浆的水化热进行了测试。结果表明，乳液掺量超过水泥质量的3％后能有效改善砂浆长期收缩性能，特别是改善砂浆28d龄期前的收缩性能，且乳液掺量越大，砂浆收缩长期变形越小。SBR乳液对砂浆收缩性能改善机理主要有以下几点：1）SBR乳液的掺入减小了砂浆早期（72h前）水化热，起到减少收缩开裂的效果；2）在水泥水化过程中，乳液水分的丧失，形成了聚合物薄膜，起到了“微纤维”作用，限制了收缩；3）SBR乳液的掺入使砂浆的平均孔径、最可几孔径及中值孔径等特征孔径减小、有害孔及多害孔数量减少，而无害孔增多。表明乳液的掺入起到了改善砂浆微观结构的作用效果；4）使砂浆的总孔隙率略有下降，闭口孔隙率在总孔隙中所占比重大幅度增加，起到了保持砂浆内部水分的作用。

Effect and Mechanism of Styrene-butadiene Rubber Latex on the Long Term Shrinking Performance of Mortar

The long term shrinking strain(1~90 d) of ordinary cement mortar and styrene-butadiene rubber(SBR) latex modified cement mortar were tested by micrometer calipers,and the micro-image and microstructure of mortar aged at 28 d was analyzed by pore size distribution method,density method and scanning electron microscope(SEM) image.The hydration heat of SBR latex modified neat cement mortar was measured.It was shown that the long term shrinking performance of mortars was improved when the content of SBR latex w...