Munir Nazzal

Estimation of Resilient Modulus of Subgrade Soils for Design of Pavement Structures

Field and laboratory testing programs were conducted to develop an efficient methodology for estimating resilient modulus ( Mr ) values of subgrade soils for use in the design of pavement structures. The field testing program consisted of obtaining Shelby tube samples of subgrade soils from different pavement projects throughout Louisiana. The laboratory program included conducting repeated load triaxial Mr tests as well as physical property tests on the collected samples. The validity of the correlation equations developed by the long-term pavement performance (LTPP) to predict the Mr was examined. In general, the LTPP model underestimated the values of Mr coefficients obtained in this study. A comprehensive regression analysis was conducted to develop models that predict the Mr coefficients of different subgrade soils in Louisiana using different physical properties. A good agreement was observed between the measured and predicted Mr coefficient values. Furthermore, the developed models had a better pre...

Mechanistic Approach to Pavement–Vehicle Interaction and Its Impact on Life-Cycle Assessment

The accuracy and the comprehensiveness of any pavement life-cycle assessment are limited by the ability of the supporting science to quantify the environmental impact. Pavement–vehicle interaction represents a significant knowledge gap that has important implications for many pavement life-cycle assessment studies. In the current study, the authors assumed that a mechanistic model that linked pavement structure and properties to fuel consumption could contribute to closing the uncertainty gap of pavement–vehicle interaction in life-cycle assessment of pavements. The simplest mechanistic pavement model, a Bernoulli–Euler beam on a viscoelastic foundation subjected to a moving load, was considered. Wave propagation properties derived from falling weight deflectometer time history data of FHWAs Long-Term Pavement Performance program were used to calibrate top-layer and substrate moduli for various asphalt and concrete systems. The model was validated against recorded deflection data. The mechanistic response was used to determine gradient force and rolling resistance to link deflection to vehicle fuel consumption. A comparison with independent field data provided realistic order-of-magnitude estimates of fuel consumption related to pavement–vehicle interaction as predicted by the model.

Estimation of Resilient Modulus of Subgrade Soils Using Falling Weight Deflectometer

Field and laboratory testing programs were conducted to develop models that predict the resilient modulus (Mr) of subgrade soils from the falling weight deflectometer (FWD) test results. Mr is used in the design and evaluation of pavement structures. The field testing program included testing various sections in 10 pavement projects within Louisiana. The tested sections covered the common subgrade soil types found in Louisiana. Three backcalculation software packages were used to interpret the FWD data: ELMOD 5.1.69, MODULUS 6.0, and EVERCALC 5.0. In addition, the AASHTO and Florida backcalculation equations were used for comparison. The laboratory testing program consisted of conducting repeated load triaxial Mr tests, physical properties, and compaction tests on soil samples obtained from tested sections. Statistical models were developed that can relate the laboratory measured Mr to FWD moduli backcalculated (EFWD) using each of the methods considered. The results of this study showed that the EFWD/Mr ratio ranged from 0.51 to 8.1 for the tested subgrade soils. Furthermore, this ratio was higher at lower Mr values and hence weaker subgrade soils. The EFWD/Mr ratio was also found to be significantly affected by the backcalculation method. The results of the regression analysis showed that among all backcalculated FWD moduli, those backcalculated using ELMOD 5.1.69 software had the best correlation with Mr. Furthermore, the results showed that the Mr prediction was significantly enhanced when soil properties were included as variables within the regression model.

Evaluation of Warm Mix Asphalt Mixtures Containing RAP Using Accelerated Loading Tests

This paper presents the results of a study that was conducted to evaluate the performance and constructability of warm mix asphalt (WMA) mixtures containing reclaimed asphalt pavement (RAP). Four sections were constructed at the indoor Accelerated Pavement Loading Facility at Ohio University. Aspha-min, Sasobit, and Evotherm WMA mixtures were used in the wearing course layer of the first three sections. In addition, the fourth section had a conventional hot mix asphalt (HMA) mixture, which was used as a control. Temperature was monitored during the production, placement, and compaction of WMA and HMA mixtures. Furthermore, emission tests were conducted at the asphalt plants during the production of each of the evaluated mixtures. Falling weight deflectometer (FWD) and rolling wheel tests were conducted at different temperatures on all evaluated sections. The results of this study showed that emissions were reduced during the production of the Aspha-min and Sasobit WMA mixtures by at least 50 % for volatile organic compounds, 60 % for carbon monoxide, 20 % for nitrogen oxides, and 83 % for sulfur dioxide, when compared to the control HMA mixture. In addition, although WMA mixtures were produced and compacted at much lower temperatures, they achieved better field densities than the control HMA mixture. The FWD test results showed that at 40°F (4°C) test temperature, the control HMA mixture had significantly lower stiffness than that of the WMA mixtures. However, the FWD stiffness measurement of the HMA and the WMA mixtures were statistically indistinguishable at the intermediate and high test temperatures of 70°F (21.1°C) and 104°F (40°C), respectively. Finally, the rolling wheel test results indicated that the three WMA sections, especially the Evotherm section, exhibited more rutting than the control HMA section during the post primary compaction stage. However, the rutting rate of the HMA section was higher than those of the WMA sections in the secondary stage, which suggests that the rutting difference may slowly be mitigated.

Implementation of a Critical State Two-Surface Model to Evaluate the Response of Geosynthetic Reinforced Pavements

A finite-element model was developed using ABAQUS software package to investigate the effect of placing geosynthetic reinforcement within the base course layer on the response of a flexible pavement structure. A critical state two-surface constitutive model was first modified to represent the behavior of base course materials under the unsaturated field conditions. The modified model was then implemented into ABAQUS through a user defined subroutine, UMAT. The implemented model was validated using the results of laboratory triaxial tests. Finite-element analyses were then conducted on different unreinforced and geosynthetic reinforced flexible pavement sections. The results of this study demonstrated the ability of the modified critical state two-surface constitutive model to predict, with good accuracy, the response of the considered base course material at its optimum field conditions when subjected to cyclic as well as static loads. The results of the finite-element analyses showed that the geosyntheti...

EVALUATING THE POTENTIAL USE OF A PORTABLE LFWD FOR CHARACTERIZING PAVEMENT LAYERS AND SUBGRADES

An evaluation of the Light Falling Weight Deflectometer (LFWD) device to reliably measure the in-situ elastic modulus of pavement layers and subgrades is presented in this paper. For this purpose, field tests were conducted on selected highway sections from different periods within Louisiana. In addition, six test sections were constructed and tested at the Louisiana Transportation Research Center (LTRC) Pavement Research Facility (PRF) site. All sections were tested using the Prima 100 model - LFWD in comparison with other standard tests including the Falling Weight Deflectometer (FWD) and the Plate Load Test (PLT) that were used as reference measurements. Regression analyses were conducted to determine the best correlations between the elastic modulus obtained from LFWD and those obtained from FWD and PLT tests. Good correlations were obtained, which demonstrated that the LFWD can be a promising device for in-situ characterizing of highway layers and subgrades.

Using Atomic Force Microscopy to Evaluate the Nanostructure and Nanomechanics of Warm Mix Asphalt

AbstractIn this paper, various Atomic Force Microscopy (AFM) techniques are utilized to study the effects of different warm mix asphalt (WMA) additives on the nanostructure and microstructure as well as the adhesive and cohesive properties of an asphalt binder. To achieve this objective, a control asphalt binder was modified with three different types of WMA additives, which included: Advera (a synthetic zeolite), Evotherm, and Sasobit (a commercial wax). The AFM tapping-mode imaging technique was used to examine the nanostructure and microstructure of the different asphalt material considered. In addition, AFM force spectroscopy experiments were conducted using chemically functionalized AFM tips to measure the nanoscale level adhesive and cohesive forces for the control and WMA asphalt binders before and after moisture conditioning. The results of the AFM imaging showed that while the Sasobit additive has reduced the width of the so-called “bee-like” structures within the asphalt binder, the other WMA ad...

Reliability of Piezocone Penetration Test Methods for Estimating the Coefficient of Consolidation of Cohesive Soils

The current piezocone penetration test (PCPT) interpretation methods were evaluated for their capability to estimate the vertical coefficient of consolidation (cv) of cohesive soils reasonably by using the piezocone dissipation tests. Seven PCPT methods were evaluated. Six sites in Louisiana were selected for this study. At each site, in situ PCPT tests were performed, and soundings of cone tip resistance, sleeve friction, and pore pressures at different locations were recorded. Piezocone dissipation tests also were conducted at different penetration depths. High-quality Shelby tube samples were collected close to the PCPT tests and were used to carry out a comprehensive laboratory testing program. The (cv) values predicted by the different interpretation methods were compared with the reference values determined from the oedometer laboratory tests. The results of this study showed that two methods can estimate cv better than the other prediction methods.

Evaluating the use of neural networks and genetic algorithms for prediction of subgrade resilient modulus

This paper investigates the use of artificial neural networks (ANNs) and genetic algorithms to improve the accuracy of the prediction of subgrade resilient modulus (M r) based on soil index properties. Furthermore, it also examines the effect of the accuracy of the M r estimation on the mechanistic empirical pavement design guide (MEPDG) performance prediction. The results of this paper showed that the ANN models had much better prediction of the M r coefficients of subgrade soils than that of the regression models. In addition, the use of the genetic algorithms in the selection of the input variables of the ANN models enhanced the accuracy of the prediction of those models. The results of the MEPDG analyses indicated that the prediction model used to estimate the subgrade M r input value can have a significant effect on the predicted performance of pavements. Furthermore, those results showed that the use of ANN models yielded much more accurate pavement performance prediction than using regression models; in particular when genetic algorithms were used in developing those models.

Non-Nuclear Methods for Compaction Control of Unbound Materials

Proper compaction of unbound materials, such as soils, aggregate, and recycled materials, is a critical component in the performance of highway pavements and embankments. The most commonly used device to test for proper compaction is the nuclear density gauge. However, due to the costs associated with regulatory compliance and radiation safety training, there is an increased effort to find acceptable non-nuclear devices. This synthesis documents information on national and international experience with non-nuclear devices and methods for measuring compaction of unbound materials. Information used in this study was gathered through a literature review, a survey of state departments of transportation (DOTs) and Canadian provincial transportation agencies, and interviews with selected state DOTs.