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Sensors 2013, 13(12), 15985-15999; doi:10.3390/s131215985
Article

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

1
, 1,* , 2,* , 3
 and 4
Received: 8 October 2013; in revised form: 12 November 2013 / Accepted: 14 November 2013 / Published: 25 November 2013
(This article belongs to the Special Issue Magnetic Resonance Sensors)
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Abstract: 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.
Keywords: embedded NMR sensor; RF coil; external tuning circuit; T2 relaxation time; cement paste; concrete; compressive strength; pore size distribution embedded NMR sensor; RF coil; external tuning circuit; T2 relaxation time; cement paste; concrete; compressive strength; pore size distribution
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Díaz-Díaz, F.; de J. Cano-Barrita, P.F.; Balcom, B.J.; Solís-Nájera, S.E.; Rodríguez, A.O. Embedded NMR Sensor to Monitor Compressive Strength Development and Pore Size Distribution in Hydrating Concrete. Sensors 2013, 13, 15985-15999.

AMA Style

Díaz-Díaz F, de J. Cano-Barrita PF, Balcom BJ, Solís-Nájera SE, Rodríguez AO. Embedded NMR Sensor to Monitor Compressive Strength Development and Pore Size Distribution in Hydrating Concrete. Sensors. 2013; 13(12):15985-15999.

Chicago/Turabian Style

Díaz-Díaz, Floriberto; de J. Cano-Barrita, Prisciliano F.; Balcom, Bruce J.; Solís-Nájera, Sergio E.; Rodríguez, Alfredo O. 2013. "Embedded NMR Sensor to Monitor Compressive Strength Development and Pore Size Distribution in Hydrating Concrete." Sensors 13, no. 12: 15985-15999.


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