内养护剂和膨胀剂组合对混凝土收缩的影响

Effect of Internal Curing Agent and Expansion Agent on Concrete Shrinkage

为在等抗压强度前提下调控混凝土的早期收缩开裂,以膨胀剂(HP-CSA)和由高吸水树脂(SAP)引入的内养护水占胶凝材料相同比例进行组合,设计了各自的内掺量均为0%、4.5%、6.0%、9.0%共4种混凝土配合比,研究了其对混凝土早期收缩的调控规律,并分析了混凝土收缩、力学强度、内部相对湿度和干燥失水率之间的关系.结果表明:混凝土早期收缩和内部相对湿度发展均呈2阶段规律;随“HP-CSA+SAP”组合掺量增加,其对混凝土早期收缩的调控作用逐渐增强,且在阶段I的调控作用更为显著,但28 d时仍不能根除混凝土的净干燥收缩;组合掺量对混凝土早期内部湿度发展的整体影响较小;混凝土28 d内的净干燥收缩与干燥失水率之间基本呈线性正相关.从调控收缩、强度保持和经济性等方面综合考虑,6.0%为最优调控组合掺量.

To control early-age shrinkage induced cracking for concrete with equivalent compressive strength,four concrete mixtures were prepared with co-addition of expansion agent(HP-CSA)and internal curing water introduced by superabsorbent polymer(SAP),both of them at the rate of 0%,4.5%,6.0%and 9.0%by mass to the dosage of total cementitious materials.The regulation effect of"HP-CSA+SAP"combination on early-age shrinkage of concrete was experimentally investigated.The relationships between shrinkage,mechanical strength,internal relative humidity and water loss rate during drying of concrete were analyzed.The test results show that the developments of early-age shrinkage and internal relative humidity of concrete both follow a two-stage rule.The more the dosage of"HP-CSA+SAP"combination,the better the controlling effect on early-age concrete shrinkage,especially in shrinkage developing stage I.However,as the net drying shrinkage of concrete could not be completely eliminated in 28 d,the influence of the combination dosage of"HP-CSA+SAP"on the development of early-age internal humidity of concrete is relatively small.The net drying shrinkage of concrete is positively linearly correlated to the water loss rate within 28 d.Considering the performances in shrinkage reducing,strength retention and cost-effectiveness,6.0%is considered to be the optimal dosage of"HP-CSA+SAP"combination.