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

Abstract

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, T2, represents the change in the pore structure during the hydration and hardening processes of concrete. The results showed that the T2 spectrum of the concrete sample was mainly composed of 3–5 signal peaks. Additionally, the w/b ratio, FA replacement and the curing regimes have significant effects on the T2 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.