Measurement of shrinkage in concrete samples by using digital photogrammetric methods

This paper shows the use of digital photogrammetry for measurement of shrinkage in concrete sample (4x4x22 cm) during the hydration process. A vision system consist of two digital video cameras was established to measure vertical displacement. The system was calibrated because of the cameras were designed for high accuracy measurement purposes. This was done by imaging a calibration object placed within the workplace. A least squares bundle adjustment determines the camera calibration parameters as well as the exterior orientation parameters of the cameras. Measurements were conducted at 2 epochs over 24 h. The estimated precision of the 3-D points positions is in the order of 0,1 mm, which is sufficient for this application. The resulting points can then be used for a deformation analysis.