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A combination of impact echo (IE) and ultrasonic surface waves techniques was used to locate the debonding in concrete slabs at several locations on TX-225 near Houston, Texas. A portable seismic pavement analyzer (PSPA), a hand-held automated system, was used for seismic data collection in the field. Field measurements are presented in the time and frequency domains in the form of time records and amplitude spectra. The characteristics differentiating the response (time records) of fully bonded and debonded slabs are discussed. The frequency domain (spectral) analysis was shown to be superior to time domain analysis in describing the response of slabs in marginal condition (i.e., slabs showing partial debonding or horizontal cracks). On the basis of the spectral characteristics of their surface response, the slabs were categorized into four different categories: good, fair, poor, and bad conditions (in terms of debonding). Time–frequency analysis was proposed as a complementary tool for the analysis of IE signals. The test records were analyzed by a time–frequency analysis method and are presented in a two-dimensional time–frequency plane. The advantages of using a time–frequency technique over a spectral analysis are described. Finally, the debonding assessments made on the basis of PSPA measurements were verified by ground truth data.

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In this paper, the use of seismic nondestructive methods to map the quality of a concrete structure is demonstrated. Seismic methods measure the modulus, which can be related to the strength of the concrete. The portable seismic property analyzer (PSPA) is the device used in this study to correlate concrete moduli with concrete durability. The results are presented through a case study.A faulty concrete placement operation during construction led to exposed aggregates, poorly consolidated concrete, segregation, and plastic shrinkage cracks on extended areas of a bridge deck. Nondestructive testing with the PSPA and GPR was used initially to locate problem areas and visual inspections were used to confirm obvious blemishes. Results of the analyses were used to locate candidate core locations to conduct advanced laboratory tests. Cores taken to represent various concrete qualities as suggested by PSPA results were tested for abrasion durability using ASTM C944 and chloride ion penetration using ASTM C1202 as an indicator of material durability. Background information and the results of this study are presented here. BACKGROUNDReinforced concrete structures such as bridge decks and their reinforcing steel experience losses in their integrities over time caused by damage due to deicing salts, overloading, freeze-thaw cycles, induced stresses, and fatigue. El-Safty estimates that the cost of repairing and replacing deteriorating highway bridges in the United States is approximately $100 billion (1). Poor initial quality of construction plays a major role in accelerating the loss of integrity, which eventually affects the long-term health and functionality of bridges. This is especially true for bridge decks that are the major component of bridges with which the traveling public is in contact.Means for rapid, nondestructive, and accurate quality management of bridges during construction can minimize the need for frequent maintenance and premature rehabilitation of bridge decks. Proper quality management can reduce the financial resources required for operation and reduce the frequency and duration of traffic interruptions significantly. Data collected during construction from NDT of bridge decks can complement other information, leading to a better understanding of the deterioration mechanisms and the effectiveness of preservation techniques and, most important, prevention of premature and unexpected failure. Table 1 contains a partial list of the NDT technologies that have the potential to detect or quantify the quality of concrete. The methods can be categorized into two broad groups: electromagnetic and seismic-sonic. GPR, the prime electromagnetic method, measures the propagation of electromagnetic waves that are affected by the change

Lime stabilization is a common procedure currently used in road construction. This technique is particularly attractive for improving the subgrade material for low-volume unpaved or low-cost paved roads. Selection of the proper concentration of lime for stabilization of clays is primarily based on achieving a target pH value. A number of parameters—such as the interaction between the mineralogy of the clay materials and the additives in the presence or absence of moisture, construction methods, and curing processes—significantly affect the performance of stabilized clays. If the selected concentration of additives is not adequate to ensure shortand long-term strength and durability, the stabilization will be ineffective, and pavement rehabilitations, requiring costly repairs and road closures, will be necessary. Many state highway agencies supplement this design process with other tests to ensure that proper strength, stiffness, and durability can be achieved. The most common parameter considered for this purpose is the unconfined compressive strength of laboratory-prepared specimens that are cured for several days and subjected to capillary moisture conditioning for several additional days. This procedure is perceived as time-consuming to implement. To establish whether the stabilization method is effective in field construction projects, this paper addresses some shortcomings in the current protocols. Several accelerated testing methods that could potentially minimize the time required for soil specimen preparation, curing, conditioning, and testing to complete the stabilizer design process are evaluated. From this study, the most appropriate method was found to be backpressure saturation.