Determining the moisture content in concrete with a fibre optic Mach-Zehnder interferometer: a feasibility study

This paper proposes and demonstrates the use of a fibre optic Mach-Zehnder interferometer to determine the average bulk moisture content of concrete. The principle of operation is based on the moisture dependence of the propa gation velocity of shock waves in the concrete. A spring-loaded gun with st ainless steel balls of various diameters created the shock waves. The time delay of the shock waves between the two arms of the interferometer embedde d in an experimental concrete block could be determined from the autocorrel ation function of the interference signal obtained at the optical detector. The average velocity at room temperature measured in dry concrete was 3.54 +/- 0.34 km s(-1), and for moist concrete it was 5.00 +/- 0.45 km s(-1). T hese values indicate that the discrimination between moist and dry concrete is large enough, and the standard deviations in the measurements small eno ugh, to make this a feasible approach to determine the moisture content in concrete.