Automated Determination of Entrained Air-Void Parameters in Hardened Concrete

摘要

Development of an automated linear traverse system for determination of air-void parameters in hardened concrete is described. The technique is comprised of an image analysis system for acquisition of surface images through a microscope, methodology for detection and identification of entrained air voids, and a computer-controlled two-dimensional motorized actuator for bringing the sampling points in line with the microscope. In addition to the sample preparation procedures involved in ASTM C 457, the automated technique requires an additional step that includes pigmenting of the sections to create color contrast between the voids and the concrete matrix. Following the sample preparation steps, the process requires approximately 15 min for the complete determination of air-void parameters along a 2642 mm (104 in.) traverse length. Data are automatically analyzed, and air-void parameters in terms of air content, specific surface, spacing factor, void frequency, and other parameters of importance are displayed and stored in a worksheet for reporting. Evaluation of the system included experimentation with a range of concretes with varying degrees of air content using both automated and manual measurements for the determination of air-void parameters.