Please use this identifier to cite or link to this item: https://hdl.handle.net/11681/4684
Title: New technologies for improving the consolidation of concrete
Authors: Haskins, Richard W.
Soroushian, Parviz, 1956-
Alexander, A. Michel
Sari, Al
Hsu, Jer-Wen
Keywords: Concrete
Concrete consolidation
Concrete testing
Vibratory consolidation
Construction Productivity Advancement Research Program (U.S.)
Publisher: U.S. Army Engineer Waterways Experiment Station
Series/Report no.: Technical Report (Construction Productivity Advancement Research Program (U.S.)) ; no.Technical Report CPAR-SL-97-2
Abstract: Under the Construction Productivity Advancement Research (CPAR) Program, a new two-part system for improving the consolidation of concrete has been developed. First, a new vibratory consolidation subsystem was developed to enhance the efficiency and effectiveness of concrete consolidation in the context of a slipform paver. The system uses the phenomenon of resonance to efficiently vibrate a rigid and relatively large consolidation volume within concrete to relatively high-vibratory displacement amplitudes at a frequency appropriate for concrete consolidation. Dynamic finite-element analysis and optimization techniques were used to design a mechanical system baaed on this concept which also satisfied the geometric requirement for installment in slipform pavers. The vibratory consolidation subsystem was then constructed, evaluated, and subjected to a comparative experimental study which revealed its advantages over conventional internal vibrators. A strain-gauge monitoring system was also devised and evaluated for real-time monitoring of the consolidation process of concrete under the action of the new system. A connection mechanism to interface between the new consolidation system and slipforrn pavers was devised, manufactured, and installed on a slipform paver. A large-scale field simulation was constructed for the purpose of evaluating the whole connection system under realistic operating conditions that closely simulated those of slipform pavers. Refinement of the hydraulic control and cooling system of the shakers that drive the resonant vibrators is going on cumently. This will be followed by long-term longevity and fatigue evaluation of the complete system under realistic operation conditions on a slipform paver. Second, significant progress was made in the development of the other subsystem. It is an ekctricaI impedance device that provides results in real-time for measuring the degree of consolidation of concrete during vibration for mechanical pavers. The device operates on the principle that since air is an insulator and fresh concrete is a conductor, electrical impedance measurements can detect the release of air during the consolidation of fresh concrete. When the entrapped air is released from the fresh concrete through the process of vibration, then the alternating-current impedance of the concrete drops in value. Two prototype consolidation meters appropriate for the field were constructed. The device is simple to operate, portable, battery-powered, and noise resistant. The heart of the device is based on the impedance bridge. Fresh concrete has been found to be equivalent to a parallel resistor-capacitor 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 alternating-current-resistance-against-time-of-vibration curve. The intersection of these two parts of the curve represents the point in time at which consolidation is complete. The system has a 0- to 15-V analog meter to indicate that point of completion. Before paving begins, a couple of zero-controls on the front panel of the meter are adjusted so that the analog needle falls on zero volts to represent the impedance of the unconsolidated concrete. Then, that same volume of concrete is consolidated before the paver begins to move, and the gain control on the front panel is adjusted to represent the consolidated impedance on a full-scale setting of 15-V. The setting is arbitrary. When the paver begins to move at a rate sufficient to maintain the meter near the full-scale setting, then the entrapped air has been removed, and only the entrained air remains. The concrete has been properly consolidated. The system has not yet been tested in the field on a slipform paver. Provisional plans are for CMI of Oklahoma City, OK, to commercialize both subsystems assuming they follow through with their stated purpose within a reasonable time frame.
Description: Technical Report
Gov't Doc #: Technical Report CPAR-SL-97-2
Rights: Approved for public release; distribution is unlimited
URI: http://hdl.handle.net/11681/4684
Appears in Collections:Technical Report

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