Feasibility Study of In-situ Characterization of Size Distribution of Air Voids in Concrete Pavements

Abstract

This report concerns a feasibility study on the use of a non-destructive and non-invasive method to determine the size distribution of air voids in fresh concrete, which will be used for laying concrete pavement. A preliminary review of different techniques suggested that the measurement of the p-wave velocity of ultrasound pulses transmitted through a fresh concrete specimen offers the most straightforward approach. This report describes an experimental study to address the design of an experimental test rig, the selection of appropriate equipment, and the determination of the p-wave velocity in fresh cementitious materials. The paper starts with the ultrasound characterization of fresh cement and mortars. Then, the feasibility of using the ultrasound method to determine the air-void content in a fresh concrete specimen with a minimum thickness of 4" is examined. In addition to the discussions of the ultrasound characterization of fresh cementitious materials, this paper also reports on the development of a suite of MATLAB programs to characterize the air-void systems of hardened cementitious materials. The approach is based on image processing techniques used to analyze digital images of polished specimens collected with a flatbed scanner. The results will provide pertinent information on the air-void systems in hardened cementititous materials.