A portable, submersible, MR sensor - The Proteus magnet.

This paper details the design, fabrication, and testing of a new portable magnet, generically termed the Proteus magnet, that can undertake a wide range of MR measurements. The Proteus magnet is intended for 1H measurements of liquids and is fully functional when submersed in the sample of interest. The Proteus magnet is fabricated from a pair of low-cost, commercial, NdFeB disk magnets, axially polarized, with their North and South poles aligned. The two N52 NdFeB magnets - 31.75 mm diameter and 6.35 mm thickness were separated by 10 mm. The gap between the magnets is sufficient for a RF shield and transverse rectangular solenoid RF probe. The sensor was evaluated through a series of measurements including bulk CPMG, saturation recovery T1, self-diffusion, T1 - T2, and D - T2.

Ultrasound frequency analysis for identification of aggregates and cement paste in concrete.

The aim of the present study was to identify specific frequencies related to aggregates and cement paste during concrete hydration, by performing a Fourier analysis of the ultrasonic response of concrete specimens to different excitation frequencies. This identification will reduce the high influence of aggregates in the ultrasound signal analysis, enabling a better assessment of changes occurring in the cement paste. Thirty-five cylindrical specimens with a diameter of 100mm and a length of 200mm were cast with a water to cement ratio=0.60. Thirty specimens were destructively tested at 1, 3, 5, 7, 14 and 28days for their compressive strength. The remaining five specimens were non-destructively tested at 1, 3, 5, 7, 14, 28 and 56days using longitudinal and transversal ultrasonic wave transducers with frequencies from 50kHz to 500kHz. Analysis of the evolution in frequency observed in the specimens identified variations related to progressive hydration of the cement paste, in contrast with the invariant behavior of the inert aggregates. Results show that it is possible to distinguish the behavior of cement paste and aggregates in the frequency domain. As a consequence, it should be possible in future research to evaluate more efficiently different phenomena that affect only the cement paste.