为深入揭示水泥基材料渗透率与孔结构间的关系,以不同水灰比、不同温度水养的白水泥砂浆为研究对象,利用低场磁共振与压汞技术分别测试了砂浆在饱水与干燥状态下的孔径分布,并利用稳态渗透法测试其水分渗透率。结果表明:砂浆在饱水与干...为深入揭示水泥基材料渗透率与孔结构间的关系,以不同水灰比、不同温度水养的白水泥砂浆为研究对象,利用低场磁共振与压汞技术分别测试了砂浆在饱水与干燥状态下的孔径分布,并利用稳态渗透法测试其水分渗透率。结果表明:砂浆在饱水与干燥状态下的孔结构差异显著,临界孔径相差1个数量级左右,原因在于水化硅胶钙(C-S-H)凝胶具有显著的水敏性。经历56 d 80℃热水养护后,由于C-S-H凝胶高温老化加速,饱水砂浆的孔隙率及临界孔径显著增大,孔结构明显粗化,水分渗透率增大,对耐久性不利。干燥预处理对压汞测试所得孔结构的影响可能远超高温老化,在分析孔结构变化时必须考虑水敏性的影响,否则可能得出错误结论。将孔隙视作不同大小的毛细管束,经典Kozeny-Carman模型可基于低场磁共振测试所得饱水孔径分布曲线来准确预测水分渗透率,将比例系数取为1.09所得理论值与实测值的相对误差在[–42.7%,71.1%]范围内,预测精度接近极低渗透率测试的误差水平。展开更多
Long-term continuous cropping of soybean （Glycine max）, spring wheat （Triticum aesativum） and maize （Zea mays） is widely practiced by local farmers in northeast China. A field experiment （started in 1991） was ...Long-term continuous cropping of soybean （Glycine max）, spring wheat （Triticum aesativum） and maize （Zea mays） is widely practiced by local farmers in northeast China. A field experiment （started in 1991） was used to investigate the differences in soil carbon dioxide （CO2） emissions under continuous cropping of the three major crops and to evaluate the relationships between CO2 fluxes and soil temperature and moisture for Mollisols in northeast China. Soil CO2 emissions were measured using a closed-chamber method during the growing season in 2011. No remarkable differences in soil organic carbon were found among the cropping systems （P〉0.05）. However, significant differences in CO2 emissions from soils were observed among the three cropping systems （P〈0.05）. Over the course of the entire growing season, cumulative soil CO2 emissions under different cropping systems were in the following order： continuous maize （（829±10） g CO2 m2）〉continuous wheat （（629±22） g CO2 m^2）〉continuous soybean （（474±30） g CO2 m-2）. Soil temperature explained 42-65% of the seasonal variations in soil CO2 flux, with a Q10 between 1.63 and 2.31; water-filled pore space explained 25-47% of the seasonal variations in soil CO2 flux. A multiple regression model including both soil temperature （T, ~C） and water-filled pore space （W, %）, log（]）=a＋bT log（W）, was established, accounting for 51-66% of the seasonal variations in soil CO2 flux. The results suggest that soil CO2 emissions and their Q10 values under a continuous cropping system largely depend on crop types in Mollisols of Northeast China.展开更多
文摘为深入揭示水泥基材料渗透率与孔结构间的关系,以不同水灰比、不同温度水养的白水泥砂浆为研究对象,利用低场磁共振与压汞技术分别测试了砂浆在饱水与干燥状态下的孔径分布,并利用稳态渗透法测试其水分渗透率。结果表明:砂浆在饱水与干燥状态下的孔结构差异显著,临界孔径相差1个数量级左右,原因在于水化硅胶钙(C-S-H)凝胶具有显著的水敏性。经历56 d 80℃热水养护后,由于C-S-H凝胶高温老化加速,饱水砂浆的孔隙率及临界孔径显著增大,孔结构明显粗化,水分渗透率增大,对耐久性不利。干燥预处理对压汞测试所得孔结构的影响可能远超高温老化,在分析孔结构变化时必须考虑水敏性的影响,否则可能得出错误结论。将孔隙视作不同大小的毛细管束,经典Kozeny-Carman模型可基于低场磁共振测试所得饱水孔径分布曲线来准确预测水分渗透率,将比例系数取为1.09所得理论值与实测值的相对误差在[–42.7%,71.1%]范围内,预测精度接近极低渗透率测试的误差水平。
基金supported by the Key Research Program of the Chinese Academy of Sciences (KZZD-EW-TZ-16-02)the Foundation for Young Talents of the Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences (DLSYQ13001)the National Natural Science Foundation of China (41101283)
文摘Long-term continuous cropping of soybean （Glycine max）, spring wheat （Triticum aesativum） and maize （Zea mays） is widely practiced by local farmers in northeast China. A field experiment （started in 1991） was used to investigate the differences in soil carbon dioxide （CO2） emissions under continuous cropping of the three major crops and to evaluate the relationships between CO2 fluxes and soil temperature and moisture for Mollisols in northeast China. Soil CO2 emissions were measured using a closed-chamber method during the growing season in 2011. No remarkable differences in soil organic carbon were found among the cropping systems （P〉0.05）. However, significant differences in CO2 emissions from soils were observed among the three cropping systems （P〈0.05）. Over the course of the entire growing season, cumulative soil CO2 emissions under different cropping systems were in the following order： continuous maize （（829±10） g CO2 m2）〉continuous wheat （（629±22） g CO2 m^2）〉continuous soybean （（474±30） g CO2 m-2）. Soil temperature explained 42-65% of the seasonal variations in soil CO2 flux, with a Q10 between 1.63 and 2.31; water-filled pore space explained 25-47% of the seasonal variations in soil CO2 flux. A multiple regression model including both soil temperature （T, ~C） and water-filled pore space （W, %）, log（]）=a＋bT log（W）, was established, accounting for 51-66% of the seasonal variations in soil CO2 flux. The results suggest that soil CO2 emissions and their Q10 values under a continuous cropping system largely depend on crop types in Mollisols of Northeast China.
