A Method for Characterizing the Early Hydration Process of Cement Using Low Field NMR

Abstract

The invention belongs to the field of building materials, and specifically relates to a method for quickly and conveniently researching and characterizing the early hydration process of cement by using low-field nuclear magnetic resonance technology, which includes the following steps: a) putting a sealed sample tube containing cement slurry into Low-field nuclear magnetic resonance instrument, set different parameters and sampling intervals and start the test; b) Use CPMG pulse sequence to collect nuclear magnetic relaxation decay signals at different hydration time t; c) Automatically collect each attenuation signal at hydration time t The amplitude A(t) of the first echo peak of the curve; d) Fit the obtained data points of A(t) and t to make a fitting relationship curve between A(t) and t; e) Make a part of the fitting curve First-order and second-order differential curves, and divide the different stages of hydration according to the zero point of the second-order differential; f) Combining the three curves and their stage time points to characterize the cement hydration process. This method combines the mathematical differential processing method to analyze the experimental results, accurately obtains the turning point of the hydration reaction stage, overcomes the subjectivity of human judgment, is more accurate and intuitive, and also lays the foundation for quantitative research on the cement hydration process.

Description

technical field [0001] The invention belongs to the field of building materials, and in particular relates to a method for characterizing the early hydration process of cement based on low-field nuclear magnetic resonance technology. Background technique [0002] Cement is one of the largest building materials in the civil construction industry. Cement starts to undergo hydration reaction when water is added, gradually solidifies and hardens, and consolidates sand, stones, etc. together to form finished materials such as concrete. In the field of building materials, the characterization of the cement hydration process has always been one of the routine experimental projects for scientific research personnel in the industry and for enterprise R&D personnel to develop new products. Therefore, the research and development of new technologies and methods for characterizing the cement hydration process has broad application prospects. [0003] Water is an indispensable componen...

AI Technical Summary

Problems solved by technology

These previous studies usually used the longitudinal relaxation time T of the hydrogen proton in the water molecule 1 or the transverse relaxation time T 2 To study the hydration process of cement, its disadvantages are: 1) The longitudinal relaxation time T 1 and the transverse relaxation time T 2 The test process is more complicated, and the inversion calculation of the original data is required, and the data processing is tedious and heavy; 2) use T 1 or T 2 The change of the weighted average is used to characterize the hydration process of cement, and the data calculation is complicated and difficult to understand and implement, especially if the T 1 or T 2 Improper handling of miscellaneous peaks in the distribution spectrum can easily introduce errors; 3) T 1 or T 2 The test is limited by the sample. Due to the presence of different contents of ferromagnetic substances in the cement, it is easy to cause the acceleration of the relaxation decay process, reduce the signal-to-noise ratio, etc., resulting in signal distortion.

4) The method of dividing the hydration stage is too rough. Generally, the turning point of the hydration process is judged subjectively by the experimenter based on the trend of the data points, which lacks accuracy

5) The collected T 1 or T 2 The change with the hydration time essentially reflects the change of the bound degree of water molecules, that is, the process of the pores in the cement paste gradually changing from large pores to small pores. This process is related to the hydration process, but It is not as direct as directly testing the changes in the content of physically bound water

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