干燥状态下混凝土孔隙结构研究

Pore structure of concrete under dry condition

【目的】研究105℃恒温干燥115.5 h前后混凝土内部孔隙结构的演化规律,分析混凝土干燥前后孔隙结构对其强度的影响机理,为混凝土干燥工艺的确定提供参考。【方法】基于不同干燥温度下混凝土强度变化规律所确定的105℃恒温干燥115.5 h的干燥工艺,应用X-ray CT三维扫描技术分别对干燥处理前后的混凝土试件进行三维扫描,并对混凝土扫描数据进行三维重构,通过VG Studio MAX 2.2软件对其内部孔隙个数、直径、体积进行系统对比研究。【结果】经105℃恒温干燥处理115.5 h后,与干燥处理前相比,干燥后混凝土的孔隙率和孔隙个数均有所提高,其中孔隙率较干燥前增加了19.77%,孔隙个数增加了41.61%,单个最大孔隙体积增大了4.72%;大孔径孔隙个数所占比例降低,直径5.0~15.0 mm的大孔径孔隙所占比例仅为总孔隙数量的0.73%;小孔径孔隙比例增大,其中以直径0.5~1.0 mm的小孔径孔隙增长较为显著,为干燥前的2.08倍。【结论】混凝土于105℃恒温干燥115.5 h,该干燥工艺的机理是总孔隙率增加,且小孔径孔隙比例增加而大孔径孔隙比例降低。总孔隙率增大对混凝土强度有降低效应,但小孔径孔隙比例的提高却对强度有增大效应,两种效应的叠加使混凝土强度损伤达到最小化。

【Objective】The evolution of internal pore structure of concrete before and after constant temperature drying at 105℃for 115.5 h was studied and the influence mechanism of concrete pore structure on its strength was analyzed to provide support for improving the drying process of concrete.【Method】The drying process with constant temperature drying at 105℃for 115.5 h was studied based on the changing of concrete strength under different drying temperatures.The three-dimensional scanning technique of X-ray CT was used to scan the concrete specimens before and after the drying,and the three-dimensional reconstruction of the concrete scanning data before and after the drying was carried out.The VG Studio MAX 2.2 software was used to systematically and quantitatively analyze the number,diameter and volume of concrete internal pores.【Result】The porosity and number of pores of concrete after constant temperature drying at 105℃for 115.5 h increased compared with those before drying.The porosity increased by 19.77%compared with that before drying,the number of pores increased by 41.61%,and the volume of single maximum pore increased by 4.72%.The proportion of large pores in the number of pores decreased,and the proportion of large pores in the diameter range of 5.0-15.0 mm was only 0.73%of the total number of pores.The proportion of small pores increased,and the small pores in the diameter range of 0.5-1.0 mm increased significantly after drying,which was 2.08 times of that before drying.【Conclusion】The mechanism of drying process with constant temperature drying at 105℃for 115.5 h was the increase of total porosity and proportion of small pores increased with decrease of proportion of large pores.The increase of total porosity decreased concrete strength,while the increase of small pores proportion increased concrete strength.The superposition of the two effects minimized the damage to concrete strength.