Application background
As a multi-phase composite material, cement-based materials have been the focus of attention in the hydration and hardening process. As an important component of the cement-based material, water is initially mixed with the cement powder and filled in the gap between the cement particles in the liquid phase. In the subsequent hydration hardening process, a part of the water hydration reaction becomes chemically bound water and becomes condensed. A part of the colloidal crystallites, which cannot be removed by dry evaporation, and is therefore also referred to as non-evaporable water; modern cement-based materials science studies have shown that the amount of non-evaporable water is related to the degree of hydration reaction of the material and The crystal structure of the product is related, and the content and state of the evaporable water are closely related to the frost resistance, corrosion resistance, creep and drying shrinkage of the material. Due to the continuity of the cement hydration reaction with time, it cannot be evaporated. The content and state of water and evaporable water are also constantly changing. Studying the phase transition of water in cement-based materials, exploring the evolution of water in different states, and fully understanding the composition and structure of cement-based materials, revealing the degradation mechanism of materials. Significance.
The application of low-field NMR technology in water in porous media has gradually expanded from the fields of life sciences and geophysics to the field of building materials. This method can study the relaxation characteristics of protons in water molecules without destroying the samples. The change in water content and its distribution has the advantages of rapid, continuous and non-destructive.
The following is a brief introduction to the 1H NMR relaxation characteristics and state evolution of evaporable water in cement slurry using NMR test system.
Nuclear magnetic resonance analysis
The distribution of the relaxation signals of each sample after inversion is shown in Figure 1.
The relaxation time distribution of all samples is 1 or 2 main peaks with a small number of weak secondary peaks. The main peak is distributed in the range of 0.1 to 10.0 ms. As the curing time increases, the relaxation peak gradually moves to the left, that is, the distribution tends to a short relaxation time. The shorter relaxation time distribution of the sample is due to the increasing hydrated product with the increase of age, gradually refining the original larger pores, and the unreacted evaporable water is gradually distributed in the smaller pores.
As shown in Fig. 2, the average relaxation time of each sample decreased with the increase of age, and it decreased rapidly in the early 1-7 days, and then the change was gentle.
It can be seen from the above figure that the three curves in the trend have the same trend, and the average relaxation time of the sample with the water-cement ratio is larger than that of the water-cement ratio, and the saturated water conservation is larger than the closed curing .
(Reference: 1H NMR relaxation characteristics and state evolution of evaporable water in cement pastes) Journal of the Chinese Ceramic Society 2009, Vol.37, NO.10
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