Carbon Fiber Reinforced Concrete as an Intrinsically Smart Concrete for Damage Assessment During Dynamic Loading
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PU-WOEI CHEN AND D.D.L. CHUNG Composite Materials Research Laboratory, State University of New York at Buffalo, Buffalo, NY 14260-4400 ABSTRACT
Concrete containing short carbon fibers (0.2-0.5 vol.%) was found to be an intrinsically smart concrete that can sense elastic and inelastic deformation, and fracture. The signal provided is the change in electrical resistance, which is reversible for elastic deformation and irreversible for inelastic deformation and fracture. The presence of electrically conducting short fibers is necessary for the concrete to sense elastic or inelastic deformation, but the sensing of fracture does not require fibers. The fibers serve to bridge the cracks and provide a conduction path. The resistance increase is due to conducting fiber pull-out in the elastic regime, conducting fiber breakage in the inelastic regime, and crack propagation at fracture. INTRODUCTION
Smart structures capable of damage assessment in real time are important due to the need to maintain the functions of critical civil infrastructure systems. The sensing provides an electrical, optical or acoustic response to damage in real time during dynamic loading. Requirements of the sensor include (1) low cost for both materials and implementation, (2) durability and reliability, (3) measurement repeatability and stability, (4) ability to provide
quantitative signals with high sensitivity and resolution, (5) ability to provide spatial resolution, (6)fast response, (7) sensitivity to a wide dynamic range of strain, covering both the elastic and inelastic regimes of deformation, (8) not weakening the structure, (9) not requiring expensive peripheral equipment, and (10) applicability to both old and new structures. No. 7 above refers to the ability to detect and distinguish between inelastic deformation (which corresponds to permanent damage) and elastic deformation. This ability is valuable for monitoring damage occurrence during dynamic loading, as it provides monitoring of the dynamic loading in its complete range, covering both the elastic and inelastic regimes. Thus, it allows determination of exactly in which part of which loading cycle damage occurs and does not require the load cycling to be periodic in time. No. 5 above refers to the ability to provide a measure of the degree and location of damage. This measure can be in terms of the inelastic strain, as strain in the inelastic regime is associated with damage. The greater is the inelastic strain, the greater is the damage. Due to the ability described in No. 7, the response due to the inelastic strain can be distinguished from that due to the elastic strain. Thus, the inelastic strain (or degree of damage) can be monitored in real time during dynamic loading. 317 Mat. Res. Soc. Symp. Proc. Vol. 360 01995 Materials Research Society
In a new sensor technology [1], concrete itself is the sensor, which satisfies all of the requirements listed above. Moreover, the intrinsically smart concrete exhibits high flexural strength and toughness, and low drying shrinkage [2]
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