Transportation Research Board 90th Annual MeetingTransportation Research Board, 2011
This paper discusses how the method of compaction (laboratory, gyratory or field) affects the mea... more This paper discusses how the method of compaction (laboratory, gyratory or field) affects the measured resilient modulus of hot-mix asphalt. The specific research presented was conducted on the asphaltic mixtures placed on the Virginia Smart Road. Three types of laboratory compacted asphaltic mixture specimen, representing different mix production methods, were compared to field compacted asphaltic mixture specimen obtained from coring. In general, irrespective of the mix production method, the resilient modulus values of laboratory-compacted specimens were 50% higher than the resilient modulus values of field-compacted specimens. A model relating asphaltic mixture resilient modulus to its volumetrics was developed using laboratory-compacted specimens’ data. The statistical approach considers both fitting and predicting measures. The model was then used to predict resilient modulus values of field-compacted specimens from their volumetric properties. The calculated resilient modulus values, using the developed model, were 15% higher than the measured resilient modulus values for field-compacted specimens. For the considered mixes, 70% of the difference between laboratory-compacted and field-compacted specimens’ resilient modulus values is attributed to a difference in volumetrics (mainly air voids), while the remaining 30% (or 15% difference) is due to the compaction method (field vs. laboratory).
In order to better understand reflected ground-penetrating radar (GPR) signals from sound concret... more In order to better understand reflected ground-penetrating radar (GPR) signals from sound concrete and delaminated concrete structures, 5 bare concrete slabs and 9 slabs with simulated delaminations were built. Five concrete mixtures were used; all were cast at 1.5 x 1.5 x 0.127 m. Delamination was simulated by placing polystyrene plastic pieces inside slabs during casting. A method was developed to determine the complex dielectric constant of the 5 concrete mixtures. The effect of delamination was studied by comparing signals obtained from the bare concrete slabs with those obtained from slabs with embedded polystyrene pieces. It was found that modeling the reflected signals using an average complex dielectric constant over the entire radar frequency range results in waveforms comparable to the measured ones. It was also found that reflections from air voids located at 50 mm from the surface overlap with the surface reflection. The distorted shape of the reflected signal, however, serves as an indication of the void pressure.
This paper presents the description, calibration procedures, installation, and performance of the... more This paper presents the description, calibration procedures, installation, and performance of the instrumentation used at the Virginia Smart Road to measure flexible pavement response to loading. Also presented are the measured horizontal transverse and longitudinal ...
Ninth International Conference on Asphalt PavementsInternational Society for Asphalt Pavements, Aug 1, 2002
One of the 12 instrumented sections of the Virginia Smart Road was used to evaluate the effect of... more One of the 12 instrumented sections of the Virginia Smart Road was used to evaluate the effect of several loading parameters on the measured stresses at different layers and the measured horizontal transversal strain in the bottom of the hot-mix asphalt (HMA) layer. It was found that speed does not affect the measured vertical compressive stress in all layers, but does significantly affect the measured horizontal transversal strain under the HMA layer. Strain was found to decrease by a factor of 2.7 when the speed increases from 8km/h to 72.4km/h at 25 deg C. Variation in tire inflation from 551.6kPa to 724kPa was found not to affect the measured vertical compressive stress in all the layers and the measured horizontal transversal strain in the bottom of the HMA layer. Vertical stresses under the HMA layer were found to vary linearly with the applied tires' load at 25 deg C.
... Imad L. Al-Qadi Charles A. Via Jr. ... Environmental Engineering Virginia Polytechnic Institu... more ... Imad L. Al-Qadi Charles A. Via Jr. ... Environmental Engineering Virginia Polytechnic Institute and State University, 200 Patton Hall, Blacksburg, VA 24061-0105 voice (540) 231 5262, fax (540) 231 7532, email: alqadi@vt.edu ... Seattle, WA: American Society for Testing and Materials ...
ABSTRACTPortland cement concrete (PCC) structures deteriorate with age and need to be maintained ... more ABSTRACTPortland cement concrete (PCC) structures deteriorate with age and need to be maintained or replaced. Early detection of deterioration in PCC (e.g., alkali-silica reaction, freeze/thaw damage, or chloride presence) can lead to significant reductions in maintenance costs. However, it is often too late to perform low-cost preventative maintenance by the time deterioration becomes evident. By developing techniques that would enable civil engineers to evaluate PCC structures and detect deterioration at early stages (without causing further damage), optimization of life-cycle costs of the constructed facility and minimization of disturbance to the facility users can be achieved.Nondestructive evaluation (NDE) methods are potentially one of the most useful techniques ever developed for assessing constructed facilities. They are noninvasive and can be performed rapidly. Portland cement concrete can be nondestructively evaluated by electrically characterizing its complex dielectric constant. The real part of the dielectric constant depicts the velocity of electromagnetic waves in PCC. The imaginary part, termed the “loss factor,” describes the conductivity of PCC and the attenuation of electromagnetic waves.Dielectric properties of PCC have been investigated in a laboratory setting using a parallel plate capacitor operating in the frequency range of 0.1 to 40.1MIHz. This capacitor set-up consists of two horizontal-parallel plates with an adjustable separation for insertion of a dielectric specimen (PCC). While useful in research, this approach is not practical for field implementation. A new capacitor probe has been developed which consists of two plates, located within the same horizontal plane, for placement upon the specimen to be tested. Preliminary results show that this technique is feasible and results are promising; further testing and evaluation is currently underway.
Civil Engineering Studies, Illinois Center for Transportation Series, 2016
A series of five experimental projects were constructed to better determine the life-cycle cost a... more A series of five experimental projects were constructed to better determine the life-cycle cost and performance of pavement overlays using various types and combinations of recycled materials—namely, reclaimed asphalt pavement (RAP), recycled asphalt shingles (RAS) and crushed concrete. The asphalt binder replacement (ABR) varied from 15% to 48% in the experimental sections. The study of these projects prior to construction, during construction, and for a short monitoring period after construction is intended to determine the impact of various pavement conditions, pavement cross-sections, mix designs, and material properties on the ultimate performance of the hot-mix asphalt (HMA) overlay. This interim report documents the construction and testing to date on two of the five projects in the study—Crawford Avenue/Pulaski Road and US 52 (IL 52 to Laraway Road)—that were constructed in 2014. Distress and profile surveys were conducted before and after construction. Samples were obtained...
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Journal Papers by Imad L . Al-Qadi