高吸水树脂对高强混凝土早期减缩效果及机理研究

研究了预吸水高吸水树脂(super absorbent polymer, SAP)作为内养护剂掺入高强混凝土后对其早期收缩及力学性能的影响.预吸水SAP额外引入的水量分别控制为水泥质量的5%和10%.研究结果表明：（1）预吸水SAP对高强混凝土自收缩及早期干燥条件下的总收缩有明显的减缩作用，14d自收缩减缩率可达90%以上，干燥条件下总收缩可减少75%，其机理主要在于掺入SAP后可大大提高相同龄期混凝土的内部相对湿度，减小自收缩和干燥收缩产生的驱动力；（2）预吸水SAP的加入会对高强混凝土的强度发展造成不利影响，但对其后期强度影响不大；当SAP额外引入的水量控制在水泥质量的5%时，高强混凝土28d抗压强度可达基准组的95%以上，因此不会影响SAP作为内养护剂在高强混凝土中的工程应用；（3）与简单增加拌和水量相比，加入预吸水SAP对于混凝土的减缩作用更为显著，掺量适中时对其强度的不利影响更小.

Investigation on the Shrinkage Reducing Effect of Super absorbent Polymerin High Strength Concrete and Its Mechanism

Pre soaked super absorbent polymer(SAP) was incorporated into high strength concrete(HSC) as internal curing agent to study its effects on early age shrinkage and mechanical properties. The amount of additional water introduced by SAP was fixed at 5% and 10% of the mass of cement respectively. Results show that pre soaked SAP significantly decreases autogenous shrinkage(AS) and early age drying shrinkage(DS) of HSC. The main mechanism is that the pre soaked SAP effectively reduces the driving force of AS and DS by heightening the inner relative humidity(RH) in concrete via releasing water when inner RH drops. The shrinkage reducing ratio can reach above 90% for AS and up to 75% for total shrinkage under dry condition. Nevertheless, addition of SAP has an unfavorable effect on strength development of HSC to some extent and late strength is less affected by addition of SAP. When the amount of additional water introduced by SAP is 5% of the mass of cement, the compressive strength at 28d reaches 95% of the control HSC. Thus, it would not impede engineering application of SAP in HSC. In addition, compared with simply increasing the water cement ratio, the effectiveness of pre soaked SAP in shrinkage reduction of HSC is much more pronounced and the harmful effect on strength is obviously less.