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水泥净浆、砂浆和混凝土等温干燥过程对抗压强度的影响
作者:杜向琴 李宗利 韩进生   
单位:(西北农林科技大学水利与建筑工程学院 陕西 杨凌 712100) 
关键词:混凝土 等温干燥 抗压强度 干燥变形 微观结构 
分类号:TU528.36
出版年,卷(期):页码:2019,47(5):0-0
DOI:
摘要:

 研究了水泥净浆、砂浆和混凝土的等温干燥过程对抗压强度的影响,从微观尺度上分析了干燥对强度的影响机理。结果表明:等温干燥对水泥基材料抗压强度影响显著;干燥后混凝土抗压强度的增长主要来自水泥净浆的强度提高,且增强效应与净浆质量分数呈对数关系;水泥净浆、砂浆、混凝土的干燥变形具有先膨胀后收缩特征,混凝土干燥过程及其变形取决于水泥净浆的干燥失水与变形;干燥后水泥净浆和砂浆孔隙率与平均孔径均显著增大,净浆孔隙率增大主要源于<100 nm小孔的增多,而砂浆孔隙率增大主要源于100~1 000 nm毛细孔的增多;干燥后水泥水化产物密实度提高,但骨料与水泥水化产物间粘结减弱,混凝土干燥后强度的改变是水泥水化产物密实度提高引起的强化效应和孔隙率增大、微裂纹扩展引起的劣化效应共同作用的结果。

 Effect of isothermal drying on the compressive strength of cement paste, mortar and concrete was investigated, and the mechanism in micro-scale was analyzed. The results show that isothermal drying has an effect on the compressive strength of cement-based materials, and the increase in compressive strength of concrete mainly is due to the strength improvement of cement paste. There is a logarithmic relationship between drying-strengthening effect and the mass fraction of paste. The drying deformation of cement paste, mortar and concrete all exhibit obvious characteristics of firstly expansion and then shrinkage. The drying process and deformation of concrete depend on the water removal and drying deformation of cement paste. The time required to the fully drying state, water-losing rate and drying deformation decrease with the decrease of mass fraction of cement paste. The porosity and average pore diameter of cement paste and mortar increase after drying. The increased porosity of cement paste is mainly attributed to the increase of pores with the diameters of less than 100 nm, and the increased porosity of mortar is attributed to the increase of pores with the diameters of 100–1 000 nm. The hydration products of cement become more dense after drying, however, the bond between aggregates and paste weakens. The increased strength of concrete after isothermal drying is the competition result between strengthening effect due to the densification of hydration products and weakening effect due to the porosity increasing and microcracks propagation.

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