掺合料与减缩剂对混凝土早期收缩的影响

Effects of Admixtures and SRA on Early Age Shrinkage of Concrete

目的研究减水剂、矿粉、粉煤灰和减缩剂对混凝土早期收缩的影响及其作用机理,以期降低混凝土早期收缩和控制早期收缩裂缝.方法采用自行设计的混凝土早期收缩测试装置,用位移传感器测量从初凝开始的早期收缩,试验研究了12组不同配合比的混凝土早期收缩.结果单掺减水剂使混凝土早期收缩增大4倍左右.掺减水剂并保住水胶比不变时,粉煤灰和矿粉等量取代水泥10%～50%,混凝土早期收缩率分别下降8%～20%和5%～15%.减缩剂使混凝土早期收缩减小45%以上.结论减水剂极大地增加混凝土早期收缩.粉煤灰和矿粉等量取代水泥,均能降低混凝土早期收缩.减缩剂与减水剂、矿粉和粉煤灰相容性好,并能有效减小早期收缩,是控制混凝土早期收缩裂缝的有效措施之一.

Effects and mechanics of superplasticizer, pulverized fly-ash and blast furnace slag on the early age shrinkage of concrete were studied to reduce the early age shrinkage and control the early age shrinkage crack. The early age shrinkage of 12 different part mixture of concrete was measured by means of self-designed and manufactured early self-shrinkage testing plant. Testing results indicated that the early age shrinkage of concrete with superplasticizer was about 4 times more than that without superplasticizer. It reduce by 5 % -15 % and 8 % -20 % for fly-ash and slag respectively. And the shrinkage reducer agent could reduced the early age shrinkage of concrete by more than 45 %. The early age shrinkage of concrete increased greatly with superplasticizer and reduced when fly-ash or blast furnace slag were added as the replacement of cement. The compatibility of shrinkage reducer agent with superplasticizer and slag powder and fly-ash was preferable. The shrinkage reducer agent could reduce the early age shrinkage, so it was one of the effective methods to control the early age shrinkage crack of concrete.