New Field System for Measuring Degree of Consolidation of Concrete During Vibration

Abstract

Significant progress has been made in the development of a field prototype device for slipform pavers to measure the degree of consolidation of concrete during vibration. The device operates on the principle that since air is an insulator and fresh concrete is a conductor, electrical impedance measurements can indicate the release of air during the consolidation of fresh concrete. When the air is released from the fresh concrete through the process of vibration, the electrical impedance of the concrete drops in value. The device, which is based on the impedance bridge, is portable, battery-powered, noise resistant, and easy to operate. Fresh concrete has been found to be equivalent to an RC (resistor and capacitor in parallel) circuit in terms of its electrical response. Limited tests indicate that the entrapped air is released at a faster rate than entrained air, creating two distinct parts to the AC-resistance curve against time of vibration. The intersection of these two curves represents the point at which consolidation is complete. The system has a 0- to 15-V analog meter to indicate that point of completion. Project constraints did not permit the research to be completed by testing its performance on a slipform paver. However, the likelihood of commercialization has been augmented since a prototype and specifications now exist for a portable field meter.