Embedded NMR Sensor to Monitor Compressive Strength Development and Pore Size Distribution in Hydrating Concrete

Sensors

Floriberto D໚z-D໚z²  Prisciliano F. de J. Cano-Barrita²  Bruce J. Balcom³  Sergio E. Solís-Nájera¹ 

[1] Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico Distrito Federal 04510, Mexico; E-Mail:;Instituto Politécnico Nacional-CIIDIR Unidad Oaxaca, Hornos No. 1003, Sta. Cruz Xoxocotlán, Oaxaca 71230, Mexico; E-Mail:;MRI Centre, Department of Physics, University of New Brunswick, Fredericton, NB E3B 5A3, Canada

关键词: embedded NMR sensor;    RF coil;    external tuning circuit;    T₂ relaxation time;    cement paste;    concrete;    compressive strength;    pore size distribution;   

DOI  :  10.3390/s131215985

来源: mdpi

【 摘 要 】

In cement-based materials porosity plays an important role in determining their mechanical and transport properties. This paper describes an improved low–cost embeddable miniature NMR sensor capable of non-destructively measuring evaporable water loss and porosity refinement in low and high water-to-cement ratio cement-based materials. The sensor consists of two NdFeB magnets having their North and South poles facing each other, separated by 7 mm to allow space for a Faraday cage containing a Teflon tube and an ellipsoidal RF coil. To account for magnetic field changes due to temperature variations, and/or the presence of steel rebars, or frequency variation due to sample impedance, an external tuning circuit was employed. The sensor performance was evaluated by analyzing the transverse magnetization decay obtained with a CPMG measurement from different materials, such as a polymer phantom, fresh white and grey cement pastes with different w/c ratios and concrete with low (0.30) and high (0.6) w/c ratios. The results indicated that the sensor is capable of detecting changes in water content in fresh cement pastes and porosity refinement caused by cement hydration in hardened materials, even if they are prepared with a low w/c ratio (w/c = 0.30). The short lifetime component of the transverse relaxation rate is directly proportional to the compressive strength of concrete determined by destructive testing. The r² (0.97) from the linear relationship observed is similar to that obtained using T₂ data from a commercial Oxford Instruments 12.9 MHz spectrometer.

【 授权许可】

CC BY   
© 2013 by the authors; licensee MDPI, Basel, Switzerland.