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.

The paper describes a study of reinforced concrete bridge decks that addresses the need for an accurate evaluation method that is not hindered by an asphalt cover or extensive operator experience. The use of two antennas for Subsurface Interface Radar (SIR) surveys allows for more accurate evaluations by reducing false readings that may be associated with the use of a single antenna. A more accurate determination of the amount of deterioration is also achieved, because the different frequency antennas will detect different types and severities of defects. To assess the use of dual frequency radar for evaluation of bridge decks, both laboratory studies and field studies were conducted. The results of the research indicate that false readings are reduced by using dual frequency radar such that bridge deck repair jobs can be prioritized. The added information on the extent of deterioration also allows more accurate predictions of the time, effort and money necessary for bridge deck rehabilitation.

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.