掺合料混凝土早期碳化的微观分析

Microscopic analysis of early carbonization of mineral admixture concrete

为探明掺合料混凝土早期碳化过程中微观性能的变化,通过测试pH值研究了掺合料混凝土早期碳化后内部pH值沿试件深度的分布规律;对比pH值和酚酞试剂测试结果的差异,探讨了酚酞试剂测试早期碳化测试方法的适用性;通过化学成分分析研究了早期碳化过程中物质成分的变化规律。研究表明:从表面向内部方向,混凝土试块pH值不断增大并稳定于一定值;随着掺合料掺量的增加,混凝土孔隙液的pH值沿着试件的深度方向减小,掺合料混凝土的碱性减弱,砂浆试件可碳化的Ca(OH)2含量减小;混凝土孔隙液的pH值随着养护时间的延长而逐渐增大,且其增大量随着试件深度的增加而减小;随着试验龄期的延长,表层混凝土孔隙液pH值逐渐减小,而混凝土内部孔隙液的pH值随试验龄期的延长变化不大;酚酞溶液测得的碳化深度约为pH值法测得的完全未碳化深度的0.53倍;沿砂浆试件表层向内部方向,CaCO3含量逐渐减小而Ca(OH)2含量逐渐增大,二者最终都趋于定值。

In order to ascertain the change of micro-performance change of mineral admixture concrete during early carbonation,the pH value distribution along the depth of concrete specimen after early carbonation was studied through pH value test.By comparing pH value test results with phenolphthalein test results,the applicability of phenolphthalein reagent test method was discussed. The change pattern of material composition during early carbonation was analyzed by chemical composition analysis.Results show that along the direction from surface to inner part,pH value of concrete specimen increases and gradually tends to be a certain value.With the increase of admixture content,pH value of concrete pore solution decreases,the alkalinity of mineral admixture concrete weakens,the Ca(OH)2 content of mortar specimen which can be carbonized decreases,pH value of concrete pore solution increases with the increase of curing time,and its increment deceases with the increase of specimen's depth.As the concrete age increases,the pH value of specimen's surface decreases gradually while the pH value of specimen's deep doesn't change obviously.The carbonation depth by phenolphthalein solution test is about 0.53 times of the non-carbonated depth by pH value test.Along the side surface to inner direction of mortar specimen,the CaCO3 content decreases gradually and tends to be a constant value while the Ca(OH)2 content increases gradually and tends to be a constant value.