碳化作用下水泥浆内亚硝酸根离子的含量分布

Effect of carbonation on nitrite ion distribution in cement paste

通过电子探针微区分析(EPMA)和X射线衍射分析(XRD)技术探明了碳化对硬化水泥浆内亚硝酸根离子分布的影响,阐明了游离亚硝酸根离子的迁移和吸附规律,有利于精确评价亚硝酸根离子在混凝土中的阻锈作用。结果表明:含亚硝酸盐的水泥浆体水化后生成新的水化产物结晶相NO2-AFm,并均匀分布于水泥浆内。NO2-AFm在碳化过程中重新分解生成亚硝酸根离子并向未碳化区扩散,致使碳化区NO2-含量减少,非碳化区NO2-含量增加。由于碳化过程中C-S-H凝胶分解,吸附于凝胶表面的游离亚硝酸根离子重新转变成游离态,碳化区游离态亚硝酸根离子含量增多,同时硅元素从碳化区向未碳化区迁移,未碳化区C-S-H凝胶非晶态含量增加,提高了游离态亚硝酸根离子的固化率,使碳化区游离态亚硝酸根离子含量高于未碳化区。

The influence of carbonization on the distribution of nitrite ions in hardened cement paste is verified by electron probe microanalysis(EPMA)and X-ray diffraction(XRD),and the migration and adsorption of free nitrite ions in cement paste is clarified,which is important to accurately evaluates the corrosion-resistant effect of nitrite ion on reinforced concrete.The results reveal that a new hydrated crystallization phase NO2-AFm is produced after the hydration of nitrite-containing cement paste and is evenly distributed.During the carbonation process,NO2-AFm re-decomposes and generates nitrite ions,diffusing to non-carbonized area.This results in a decrease of NO2-content in carbonized area and an increase in non-carbonized area.Nevertheless,due to the decomposition of C-S-H gel during the carbonization process,the free nitrite ions adsorbed on its surface are re-transformed into free nitrite ion,increasing the content of free nitrite in the carbonization area.Meanwhile,the migration of silicon from carbonized area into non-carbonized area,contributes to a higher amorphous content of C-S-H gel in noncarbonized area,which increases the solidified effect of nitrite ion,and eventually leads to a higher nitrite ion content in carbonized area than that in non-carbonized area.