Application of Low-Field NMR to the Pore Structure of Concrete
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Applied Magnetic Resonance
ORIGINAL PAPER
Application of Low‑Field NMR to the Pore Structure of Concrete Lei Liu1 · Zhen He1,2 · Xinhua Cai1 · Shaojun Fu2 Received: 15 February 2020 / Revised: 11 July 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
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.
1 Introduction The pore structure characteristics of concrete mainly include the porosity, pore size distribution, pore geometry or morphology, connectivity and arrangement. Previous methods to test the pore structure of concrete primarily include mercury intrusion porosimetry (MIP), adsorption methods (the nitrogen adsorption method and the water vapor adsorption method), electrical methods, X-ray microtomography, * Zhen He [email protected] 1
State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China
2
Shaanxi Key Laboratory of Safety and Durability of Concrete Structures, Xijing University, Xian 710123, China
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small-angle X-ray scattering and small-angle neutron scattering, scanning electron microscopy and low-field nuclear magnetic resonance (LF-NMR) [1–5]. It can be seen from Fig. 1 that the pore size range of all test methods is limited except for LF-NMR. The use of LF-NMR to test the concrete pore structure has emerged in recent years. Concrete samples, including the matrix, aggregates and interfacial transition zones, can be used for LF-NMR measurements, which are more representative than cement paste or mortar. LF-NMR characterizes the pore structure of concrete by detecting the hydrogen proton signal of pore water. Therefore, LF-NMR can test both the connected pores and the non-connected pores, which is an advantage that other measurement devices do not have at present. In addition, LF-NMR testing has a high efficiency and go
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