NUCLEAR MAGNETIC RESONANCE PROFILING OF HIGH-STRENGTH CONCRETE SAMPLES

Abstract

The present work proposes an indirect way of identifying and monitoring the evolution of inter C-S-H and capillary pores from the surface layer of some high-strength concrete samples with different water to cement ratios as a function of depth. The method is based on measuring the nuclear magnetic resonance spin-spin relaxation of the water confined inside the porous matrix of the cementitious material. The concrete samples were prepared using a mixture of cement (CEM I 52.5 R), quartz sand, sillica fume (Elkem Microsillica), water and superplasticizer (Glenium ACE 30 - BASF). All experiments were performed in low fields using a single-sided NMR-MOUSE (MObile Universal Surface Explorer) operating at the protons resonance frequency of 11.7 MHz. The NMR profiles were acquired for each sample with a maximum depth of 2.4 mm, and the evolution of the moisture content versus depth was extracted. The relaxation time distributions were obtained from the echo decays using a regularized numerical Laplace inversion algorithm. The results show a decrease of the relaxation time with the increase of the measuring depth, proving that the moisture content decays along with the measuring depth. The method can easily be applied for nondestructive in situ monitoring of the curing, setting and hardening processes of concrete structures.