掺膨胀剂粉煤灰混凝土的碳化性能与微观机理

Carbonation of fly ash concrete with expansive admixtures

混凝土的抗碳化性能是其耐久性研究的重要内容。研究了复掺膨胀剂和粉煤灰对混凝土抗碳化能力的影响规律,并通过压汞分析、热重-差示扫描量热(TG-DSC)分析等微观分析方法研究碳化反应前后混凝土微结构的改变。研究结果表明:大掺量粉煤灰将降低混凝土内部Ca(OH)2含量,加速混凝土的碳化,掺入膨胀剂加速粉煤灰混凝土的碳化速率。掺入粉煤灰能减小混凝土大孔的分布,转化成为小孔,对混凝土的孔结构分布具有明显的改善作用。膨胀剂的掺入会增加粉煤灰混凝土的孔隙率及大孔分布,并加速碳化速率。混凝土的Ca(OH)2含量是影响粉煤灰混凝土碳化速率的主要因素。膨胀剂引起粉煤灰混凝土的孔结构改变,进而影响其抗碳化性能。

Carbonation resistance of concrete is an important part of concrete durability.This paper mainly studies the complex mixed with ex-pansive agent and fly ash on the carbonation resistance of concrete discipline,and analyzes microstructure changes of concrete before and after car-bonation by mercury intrusion analysis,thermogravimetric-differential thermal scanning（TG-DSC）coupled analysis methods.The results show that high volume fly ash concrete will reduce the internal C（aOH）2 content,and accelerate carbonation of concrete,meanwhile,expansive admixture will accelerate carbonation of fly ash concrete.Fly ash can reduce the large pore distribution of concrete,and translated into small holes,which markedly improves the pore structure distribution of concrete.Expansive agent will increase the porosity of fly ash concrete and large pore distribu tion,and speed up the carbonation rate.The C（aOH）2 content of concrete is the main factor on controlling carbonation rate.Expansive agent will cause the pore structure changes and affect the carbonation ability of fly ash concrete further.