Application of Low-Field NMR to the Pore Structure of Concrete

In the present study, we used low-field nuclear magnetic resonance (LF-NMR) measurements and mercury intrusion porosimetry (MIP) to evaluate the influence of the water-binder (w/b) ratio, fly ash (FA) replacement and curing regimes on the pore structure of concrete. The main advantage of LF-NMR is that it is nondestructive and suitable for large concrete samples compared with other traditional methods, such as MIP, adsorption methods and scanning electron microscopy methods. Hence, the LF-NMR relaxometry method measures the pore structures that are closer to reality. The LF-NMR relaxation time,T-2, represents the change in the pore structure during the hydration and hardening processes of concrete. The results showed that theT(2)spectrum of the concrete sample was mainly composed of 3-5 signal peaks. Additionally, thew/bratio, FA replacement and the curing regimes have significant effects on theT(2)spectrum, porosity, and pore size distribution of concrete. In addition, the compressive strength of concrete has a close relationship with its pore structure. Based on the LF-NMR test results, the relationship between the compressive strength and the porosity, pore size distribution of concrete was established.