Manuel Celaya

Seismic Testing to Determine Quality of Hot-Mix Asphalt

Existing practices for acceptance of hot-mix asphalt are based on parameters such as adequate density, adequate thickness, and adequate air voids of the placed and compacted materials. Current mechanistic routines for structural design of flexible pavements consider mainly the modulus of each layer. Therefore, a procedure to measure the modulus of each pavement layer shortly after placement is highly desired. Laboratory tests on specimens prepared from material retrieved during construction, such as the simple-performance tests, can be used to determine these moduli. However, these methods are time-consuming, and the equipment costs are high. In addition, prepared specimens may not be representative of as-placed materials. Seismic tests are more practical because they are rapid to perform and are nondestructive, immediate results are obtained, and the material is tested in its natural state. The portable seismic property analyzer (PSPA) is an example of such a device. The PSPA is presented as a real-time ...

Assessment of Debonding in Concrete Slabs Using Seismic Methods

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.

Concrete Bridge Deck Quality Mapping with Seismic Methods: Case Study in Texas

The state of practice for acceptance of newly constructed concrete bridge decks is typically based on the compressive or flexural strength of specimens prepared and cured under ideal conditions. These tests do not address how the quality of construction is affected by placement, compaction, curing, and environmental conditions during construction. Cores obtained from the finished product can also be used for quality assessment, but coring is expensive and specimens may suffer from internal damage. Several nondestructive testing (NDT) technologies are readily available that can be used to evaluate the quality of concrete slabs under field conditions. These technologies are typically based on seismic–sonic or electromagnetic principles. Seismic–sonic methods rely on measuring the velocity of propagation of elastic waves within the concrete. Velocities can be converted to modulus of elasticity and related with confidence to strength. A case study is presented in which seismic–sonic methods were used to detect construction problems along a bridge deck. On the basis of the NDT results, several candidate cores were extracted. Cores were tested for abrasion durability and chloride ion penetration. Overall lower modulus concrete exhibited unacceptably high abrasion and chloride ion permeability, confirming that seismic methods may be a reliable means of determining concrete quality for in-place structures.

Stripping Detection in Asphalt Pavements with Seismic Methods

Stripping of hot-mix asphalt pavements has been a significant problem for many transportation agencies. The detection of stripping has been carried out by using either visual observation or laboratory strength tests of cores retrieved from the field. Ground-penetrating radar also has been used for this purpose. Seismic methods are presented here as a nondestructive tool to detect the extent of stripping. Seismic tests are beneficial because they are rapid to perform and nondestructive and because the material is tested in its natural state. The portable seismic property analyzer (PSPA) is an example of a device that uses two methods of analysis to detect stripping: ultrasonic surface wave (USW) and impact echo (IE). PSPA results and field cores retrieved (ground-truth data) from two sites were compared. PSPA, with the standard receiver spacing of 6 in., correlated well with cores when they were located in the first 10 in. of the asphalt layer (shallow). For deeper stripping, longer spacing between the receivers should be used. From the two methods of analysis, the USW method was found to be more effective than the IE in visualizing the extent and depth of low-quality layers in terms of asphalt stiffness.

Evaluation of Asphalt Damage and Cracking Development with Seismic Pavement Analyzer

Fatigue cracking in asphalt pavements is an indicator of structural failure, and early detection of fatigue cracking would allow for improved preventive maintenance. The evaluation of cracking relies on the distresss being visible and possibly in advanced stages. Detection of load-related cracking at an early stage or before initiation is greatly needed. The portable seismic property analyzer (PSPA), a nondestructive device that monitors the change in modulus in pavement surface layers, was used in this study to measure the change in pavement stiffness response at the same time as the development of load-associated cracking. PSPA tests were conducted at the FHWA Turner–Fairbank Highway Research Center accelerated loading facility on full-scale test pavements being subjected to repeated wheel loading to induce cracking. PSPA measurements taken at a predetermined number of loading passes were evaluated to find crack initiation or propagation. The patterns for the amount of modulus reduction before and after the initiation of cracking were measurable and different for modified and unmodified binders. An unmodified asphalt section lost only between 25% and 33% of the original modulus before the initiation of surface cracks, whereas a polymer-modified asphalt lost between 62% and 57%. The cracking was top-down given the aged condition of the test sections.

Implementation of quality management of hot-mix asphalt with seismic methods

Existing practices for field quality management of hot-mix asphalt layers rely on the adequacy of parameters such as thickness, air voids, and density. Because mechanistic–empirical pavement design is primarily based on the modulus of the pavement layers, methods of measuring the asphalt modulus in the field shortly after construction may lead to the more reliable implementation of the design. Seismic methods of modulus-based quality management may be more beneficial than traditional techniques because they are nondestructive, they can be performed rapidly, results are obtained immediately, and the material is tested in its natural state. The approach presented here includes a six-step procedure that combines design, laboratory, and field quality management processes. To evaluate the proposed method, 10 new construction sites were investigated to corroborate its usefulness and convenience. On the basis of the information collected, transportation organizations can implement the method along with their traditional methods to develop quality control and acceptance criteria. Performance of the simplified seismic laboratory and field tests along with more traditional tests may result in a database that can be used to smoothly unify the design procedures with pavement evaluation.

Accelerated Moisture Conditioning Process of Lime-Stabilized Clays

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.

Implementation of Quality Management of Base Materials with Seismic Methods: Case Study in Texas

Existing practices for field quality management of unbound layers (base, subbase, and subgrade) rely on the adequacy of parameters such as density and moisture content. However, increasingly accepted mechanistic–empirical pavement design is primarily based on the strength and stiffness of the pavement layers. Therefore, methods to measure the modulus or stiffness of soil layers in the field shortly after construction may lead to a more reliable implementation of that design process. Modulus-based quality management methods may be more beneficial than traditional techniques because they test materials in their natural state. Nondestructive testing methods allow researchers to obtain modulus of pavement layers in a rapid way. Seismic methods are one example of available methods that can be used to measure the modulus of finished unbound layers. Seismic methods are particularly attractive because they yield the same parameter (low-strain modulus) for the lab and field tests and do not require any backcalculation process. Performing the simplified seismic laboratory and field tests, with more traditional tests, may lead to a smooth integration of design procedures with pavement evaluation. An overall approach that integrates design, laboratory, and field quality management processes is presented. To evaluate the proposed method, a case study was incorporated to corroborate its usefulness and convenience.

Nondestructive quality control of geo-materials using seismic methods

Stiffness is the main engineering parameter generally used in the structural design of highways. However, adequate in-place density is normally used for acceptance criteria. Several nondestructive Testing (NDT) methods have been recently developed to supplant the conventional methods. Seismic methods are one example. In this paper, a procedure to measure the modulus of each pavement layer after placement with seismic technology is presented. Field and laboratory tests are incorporated so their results can be reconciled without any scaling or simplifying assumptions. The overall procedure and a case study are described here.

Damage Assessment of Tunnel Lining by Mobile Laser Scanning: Pittsburgh, Pennsylvania, Implementation Phase of FHWA SHRP 2 R06G Project

This paper presents the results of a nondestructive (NDT) laser scanner investigation that was conducted in one night by using the SPACETEC TS3 laser scanner in one tube of each of the Liberty and Armstrong Tunnels in Pittsburgh, Pennsylvania. A portable seismic property analyzer (PSPA), a hand-held NDT ultrasonic seismic device, was used to investigate a 200-ft-long segment of the lining of the Liberty Tunnel, for which results are also presented. The investigation was complemented with a limited inspection with traditional techniques (e.g., hammer sounding, coring) to validate NDT findings. This work was funded by FHWA under the auspices of Round 4 of the Implementation Assistance Program of the SHRP 2 R06G project. Both technologies incorporated in this study were also used and reviewed in the original SHRP 2 R06G project. With the use of the SPACETEC TS3 scanner and the supporting suite of software, the study obtained high-resolution imagery, thermal imagery, and three-dimensional profiles for the full length of the tunnels. The deliverables included complete mapping and inventory of distresses and moisture intrusion behind the lining. In the Armstrong Tunnel, SPACETEC technology was successful at detecting cold anomalies (tile debonding, water intrusion, etc.). However, in the Liberty Tunnel, detection of debonding or delamination was less effective as a result of the insufficient temperature gradient at the time of scanning within this particular tunnel. The PSPA results correlated well with results obtained from traditional techniques. Areas with a lower seismic modulus correlated well with areas showing debonding or delamination. Areas of severe debonding were also clearly identified with the PSPA device.