Fiber-optic laser speckle-intensity crack sensor for embedment in concrete

The development of a fiber-optic displacement/strain sensor using the intensity variation of laser speckle pattern has been demonstrated. This sensor can be embedded in concrete for the detection and measurement of crack opening displacements. The transduction mechanism is based on the correlation between the external axial perturbation to the optical fiber and the integrated light intensity variation of speckle patterns due to mode redistribution in a multimode fiber. Calibration tests indicated that the sensor possesses sufficient sensitivity and dynamic range for application in cementitious composite. Application of the sensor has been demonstrated by embedment of the sensor in concrete beams for measurement of the crack tip opening displacements. Experimental results have been validated with analytical formulations. The proposed sensor is simplistic in design and offers a method for the measurement of internal strains and displacements in concrete.