掺合料对混凝土体积稳定性的影响

以实际铁路大桥工程为背景,以解决大体积混凝土开裂问题为目的,通过试验分析了矿粉、粉煤灰对水泥化学收缩和干燥收缩的影响,结果显示：内掺50%的矿粉能够大幅度降低早期塑性阶段的化学收缩,对减少后期的化学收缩也有一定作用,矿粉与粉煤灰复合后对降低7 d以内的化学收缩都有显著作用,粉煤灰比例越高,作用越明显;单掺加矿粉会增加干燥收缩值,而采用矿粉与粉煤灰复掺的方法则能够有效提高体积稳定性。根据掺合料对混凝土强度影响的试验分析,并结合工程要求和化学收缩、干燥收缩试验结果与分析,提出了优化大桥原设计混凝土配合比的方案,经过实际施工检验,有效避免了大体积混凝土开裂的出现。

Effect of Admixture on Volume Stability of Concrete

Based on the actual railway bridge engineering background and for the purpose of solving the mass concrete cracking problem,the effects of ground blast furnace slag（GBFS） and fly ash on chemistry contraction and drying shrinkage of hardened cement are analyzed through tests.The results show that 50% cement replaced by the same amount of GGBFS can greatly reduce early plastic deformation stage chemical contraction,and can also reduce some late chemical contraction.Mix of GBFS and fly ash can reduce chemical contraction within 7 days significantly.The higher the proportion of fly ash,the more obvious the effects are.Single GBFS will increase dry shrinkage while mix of GBFS and fly ash can effectively improve the volume stability.According to the experimental analysis of influence of admixtures on strength of concrete,and combined with engineering requirements and the testing result of chemical shrinkage and drying shrinkage,the optimization design of the bridge concrete is offered to avoid the crack of mass concrete effectively in actual construction.