Experimental Observation of Hardening Process of Engineering Materials by Optic Fiber Sensor

A new optic fiber sensor for detection of the change in the difference between refractive indices of plastic optic fibers and that of the surrounding material is proposed. The sensor is made of two plastic optic fibers in the following way: the light emitted from a constant light source travels through the first fiber, gets reflected and/or refracted on the boundary between the fiber tips and arbitrary material around them, and comes back through the second fiber to a photo sensor. Therefore, the recorded light intensity becomes a function of ??, the difference between the refractive index of the plastic optic fiber and that of the material around the fiber tip. This implies that the sensor may be applicable to various events of interest in which ? changes with time. Some of the examples of such events are listed as follows: 1) pore space in soil being filled with water, 2) water becoming ice, 3) wet ground becoming frozen, 4) cement mortar hardening, etc. After demonstrating the sensing principle of the proposed sensor, several laboratory tests were performed to prove its ability to monitor the progress of phase change of water and mortar, which is of great engineering value.