Traditional methods of collecting data on the condition of bridges are expensive and time consuming, and the results are not always dependable. Since the early 1980’s, the Ministry of Transportation, Ontario (MT01 and the Communications Research Laboratory (CRL) at McMaster University have been involved in the use of impulse radar for the assessment of asphalt-covered bridge decks through a program called Deck Assessment by Radar Technology (DART). In this paper, a correlation study involving comparisons between the predictions of the DART survey and the actually observed conditions of the decks (after removal of asphalt during rehabilitation) is discussed with emphasis on the processing of the radar waveforms. Since a large volume of radar data is collected from bridge decks, it is important to develop strategies to extract the salient features from the reflected signal. These strategies include: first, a thresholding method and strata plot which are very effective in locating subsurface layers; and, second a differencing technique which has the capability of discriminating between sound concrete and damaged concrete. The comparisons demonstrate that there is a good correlation between the DART survey and the actual condition of bridge decks.

Acoustic emission (AE) has the potential to be an effective tool in evaluation of concrete structures under the action of loads causing cracking. In conventional testing, several AE parameters are investigated to elucidate microfracturing behavior in concrete. To identify internal cracks, the AE location technique is available, which is based on measuring arrival time differences. By employing multi-channel AE observations, the location of a crack responsible for an AE source can be determined. To obtain quantitative information on crack kinematics, the procedure is further studied and a technique for kinematic characteristics of internal cracks is developed. The AE source is mathematically represented by a moment tensor, by which the classification of cracks into tensile and shear cracks and the determination of crack directions can be made. To implement the procedure into a conventional AE system, software named SiGMA (Amplified Green’s function for moment tensor malysis) has been developed. The analysis is readily available on an AE waveform analyzer system consisting of a digital waveform-recorder and a microcomputer (controller). The procedure is applied to a uniaxial compression test of a plate specimen with a through-thickness slit and to a tensile test of a reinforced concrete rigid frame. The crack locations, the classification of crack types, and the determination of the directions of crack motion are in good agreement with experimental findings. The results show the procedure certainly provides a new technique for kinematic identification of internal cracks.

Two 16-story reinforced concrete apartment blocks founded on drilled shafts (CIP piles) were damaged in the 1994 Northridge earthquake. In order to assess the viability of the buildings for retrofit, it was considered necessary to evaluate the integrity of the existing concrete drilled shaft foundations, which were only partially reinforced. This paper describes the use of various nondestructive testing methods for the foundation evaluation, including ground penetrating radar, parallel seismic and impulse response tests. The selected test methods proved to be successfir!, and provided an economical approach while obtaiuing maximum informatron about the integrity and future performance of the hidden foundation.

A test method, which uses pull-off test and partial coring techniques, was developed in this study. This test method is particularly suitable for assessing the durability of bonding new to old concrete subjected to freeze-thaw cycling and exposed to deicing salt. This test method also combines bond evaluation and ASTM C-672 test ( Standard Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing Chemicals ) into one test method. Laboratory experimental research investigated important factors which influence the test results and their scatter. Test results show that this test method is very promising.

The contact electrical resistivity was found to correlate with the shear bond strength between steel rebar and concrete, between stainless steel fiber and cement paste, and between carbon fiber and cement paste. For the bond between steel rebar and concrete and that between stainless steel fiber (untreated or acetone washed) and cement paste, the contact resistivity increased linearly with increasing bond strength, due to an interfacial phase of high volume resistivity that helped the bonding. For the bond between stainless steel fiber (acid washed) and cement paste and that between carbon fiber (untreated) and cement paste, the contact resistivity decreased with increasing bond strength, due to the bond degradation by interfacial voids, which were high in volume resistivity. The acid washing of the stainless steel fiber decreased the contact resistivity, but had little effect on the bond strength. The high volume resistivity interfacial phase that enhanced the bonding between the untreated or acetone washed stainless steel fiber and cement paste apparently required for its formation the oxide layer on the stainless steel surface. The removal of the oxide layer by acid washing eliminated this phase, thus decreasing the contact resistivity and causing the contact resistivity to decrease with increasing bond strength. For a given interface at a given curing age, the correlation between bond strength and contact resistivity allows the bond strength to be nondestructively measured via contact resistivity measurement.