Low field NMR technique was applied to investigate the hydration of cement pastes with different water to cement ratios or addition of superplasticizer. As a nondestructive method, this technique can be used to monito...Low field NMR technique was applied to investigate the hydration of cement pastes with different water to cement ratios or addition of superplasticizer. As a nondestructive method, this technique can be used to monitor the hydration kinetics process by following the changes of longitudinal relaxation time （T1） of water constrained in the pastes. The experimental results indicate that the T1 distributions of water in the fresh paste normally exhibite bimodal distribution, where the large peak is corresponding to the free water while the small one is contributed by the water stored in the flocculations. Time dependence of the weighted average T1 has a good agreement with the hydration process and could be divided into four stages, i e, initial period, dormant period, accelerated period and steady period. The hydration mechanism of each stage was described based on the theory of cement chemistry. In addition, the total signal intensity, which is proportional to the content of the physically bound water in the samples, decrease successively during the hydration reflecting the consumption of physically bound water by hydration reactions.展开更多
Development of microstructure of early cement paste （0-6 h） was investigated with 1H low- field NMR. It was found that T2 （transverse relaxation time） distributions of fresh cement paste were bimodal and two peaks...Development of microstructure of early cement paste （0-6 h） was investigated with 1H low- field NMR. It was found that T2 （transverse relaxation time） distributions of fresh cement paste were bimodal and two peaks were ＇long component＇ and ＇short component＇. Separation degree of two peaks was a sign of exchange of water within flocculation and outside flocculation. Factors such as water cement ratio, specific surface area and dosage of superplasticizer had influences on the separation degree： the separation degree increased with the water cement ratio; the separation degree of cement paste prepared with cement with a high specific surface area was zero; dosage of superplasticizer will decrease separation degree. Results also suggested that T2 distribution gradually moved to the left and T2 of long component and initial fluidity were linearly correlated.展开更多
Development of microstructure of early cement paste (0–6 h) was investigated with 1H low-field NMR. It was found that T 2 (transverse relaxation time) distributions of fresh cement paste were bimodal and two peaks we...Development of microstructure of early cement paste (0–6 h) was investigated with 1H low-field NMR. It was found that T 2 (transverse relaxation time) distributions of fresh cement paste were bimodal and two peaks were ‘long component’ and ‘short component’. Separation degree of two peaks was a sign of exchange of water within flocculation and outside flocculation. Factors such as water cement ratio, specific surface area and dosage of superplasticizer had influences on the separation degree: the separation degree increased with the water cement ratio; the separation degree of cement paste prepared with cement with a high specific surface area was zero; dosage of superplasticizer will decrease separation degree. Results also suggested that T 2 distribution gradually moved to the left and T 2 of long component and initial fluidity were linearly correlated.展开更多
将低场核磁共振(low field nuclear magnetic resonance,LF-NMR)分析技术应用于煎炸油脂总极性化合物(total polar compounds,TPC)含量的预测。采用柱层析方法测定油脂样品的TPC含量作为测定值,采集油脂样品的LF-NMR弛豫特性(峰起始时间...将低场核磁共振(low field nuclear magnetic resonance,LF-NMR)分析技术应用于煎炸油脂总极性化合物(total polar compounds,TPC)含量的预测。采用柱层析方法测定油脂样品的TPC含量作为测定值,采集油脂样品的LF-NMR弛豫特性(峰起始时间T21、T22、T23相应的峰面积比例S21、S22、S23、单组分弛豫时间T2W),分别利用向后筛选多元回归分析、主成分回归分析和偏最小二乘回归分析建立LF-NMR弛豫特性与TPC含量的回归方程,比较3种模型的校正集和预测集的决定系数与均方根误差,最终确定最优模型为偏最小二乘回归模型。应用此模型预测预测集样品TPC含量,决定系数R2可达0.928,预测集均方根误差为0.568%,模型稳定。展开更多
基金Funded by the Major State Basic Research Development Program of China(‘973’ Program) (No. 2009CB623105)
文摘Low field NMR technique was applied to investigate the hydration of cement pastes with different water to cement ratios or addition of superplasticizer. As a nondestructive method, this technique can be used to monitor the hydration kinetics process by following the changes of longitudinal relaxation time （T1） of water constrained in the pastes. The experimental results indicate that the T1 distributions of water in the fresh paste normally exhibite bimodal distribution, where the large peak is corresponding to the free water while the small one is contributed by the water stored in the flocculations. Time dependence of the weighted average T1 has a good agreement with the hydration process and could be divided into four stages, i e, initial period, dormant period, accelerated period and steady period. The hydration mechanism of each stage was described based on the theory of cement chemistry. In addition, the total signal intensity, which is proportional to the content of the physically bound water in the samples, decrease successively during the hydration reflecting the consumption of physically bound water by hydration reactions.
基金Funded by the National Natural Science Foundation of China （No. 51178339）, and the National Basic Research Program （No. 2009CB623104-5）
文摘Development of microstructure of early cement paste （0-6 h） was investigated with 1H low- field NMR. It was found that T2 （transverse relaxation time） distributions of fresh cement paste were bimodal and two peaks were ＇long component＇ and ＇short component＇. Separation degree of two peaks was a sign of exchange of water within flocculation and outside flocculation. Factors such as water cement ratio, specific surface area and dosage of superplasticizer had influences on the separation degree： the separation degree increased with the water cement ratio; the separation degree of cement paste prepared with cement with a high specific surface area was zero; dosage of superplasticizer will decrease separation degree. Results also suggested that T2 distribution gradually moved to the left and T2 of long component and initial fluidity were linearly correlated.
基金Funded by the National Natural Science Foundation of China(No.51178339)the National Basic Research Program(No.2009CB623104-5)
文摘Development of microstructure of early cement paste (0–6 h) was investigated with 1H low-field NMR. It was found that T 2 (transverse relaxation time) distributions of fresh cement paste were bimodal and two peaks were ‘long component’ and ‘short component’. Separation degree of two peaks was a sign of exchange of water within flocculation and outside flocculation. Factors such as water cement ratio, specific surface area and dosage of superplasticizer had influences on the separation degree: the separation degree increased with the water cement ratio; the separation degree of cement paste prepared with cement with a high specific surface area was zero; dosage of superplasticizer will decrease separation degree. Results also suggested that T 2 distribution gradually moved to the left and T 2 of long component and initial fluidity were linearly correlated.
文摘将低场核磁共振(low field nuclear magnetic resonance,LF-NMR)分析技术应用于煎炸油脂总极性化合物(total polar compounds,TPC)含量的预测。采用柱层析方法测定油脂样品的TPC含量作为测定值,采集油脂样品的LF-NMR弛豫特性(峰起始时间T21、T22、T23相应的峰面积比例S21、S22、S23、单组分弛豫时间T2W),分别利用向后筛选多元回归分析、主成分回归分析和偏最小二乘回归分析建立LF-NMR弛豫特性与TPC含量的回归方程,比较3种模型的校正集和预测集的决定系数与均方根误差,最终确定最优模型为偏最小二乘回归模型。应用此模型预测预测集样品TPC含量,决定系数R2可达0.928,预测集均方根误差为0.568%,模型稳定。
