Mohammad Jamal Khattak

Durability and mechanistic characteristics of fiber reinforced soil–cement mixtures

Over the years, field experiments and research information have been collected and studied on the behavior of soil–cement mixtures, and quite a few studies have been conducted for fiber reinforcement in soil–cement mixtures. This research study focuses on the laboratory durability and mechanistic evaluation of soil–cement mixtures reinforced with Processed Cellulose fibers (PCFs) and polypropylene fibers (PFs). Four soil types from various project sites in the state of Louisiana were acquired. Laboratory tests including the durability, unconfined compressive strength (UCS), indirect tensile strength (ITS), and indirect tensile cyclic load tests (ITCTs) were conducted. The results indicated that the mechanistic characteristics of the soil–cement–fiber mixtures were functions of fiber dosage, soil type and curing time. In general, the durability, UCS, ITS and fracture toughness, and resilient modulus values of soil–cement–fiber mixtures either remained the same or were greater than soil–cement mixtures. Moreover, the horizontal plastic deformation (HPD) rate was significantly lower for soil–cement–fiber mixtures. The implication of the results is that the fiber reinforcement at optimum fiber percentage may resist the tensile or shrinkage crack formation in the soil–cement mixtures for road bases thereby, improving the structural capacity and performance of pavements.

ENGINEERING PROPERTIES OF POLYMER-MODIFIED ASPHALT MIXTURES

A large research program sponsored by the Michigan Department of Transportation was designed and completed to evaluate the effect of polymer modification on the various properties of asphalt mixtures. These include the micro- and macrostructural, morphological, chemical, and engineering properties. Some of the engineering properties of the styrene-butadiene-styrene and styrene-etylene-butylene-styrene polymer-modified asphalt mixtures are presented and discussed. The elastic, fatigue, tensile, and permanent deformation properties were investigated at 60, 25, and –5°C. It was found that, for some polymer systems, the fatigue life and the indirect tensile strength increased considerably at 25°C while the elastic properties at -5°C were not affected by the addition of polymer. The implication of this is that the use of some polymer systems in asphalt mixtures enhances their fatigue cracking and rutting resistance without affecting the low temperature cracking potential.

Fatigue and Permanent Deformation Models for Polymer-Modified Asphalt Mixtures

For the past 2 decades, significant research has been conducted on polymer-modified asphalt (PMA) mixtures. Polymers can successfully improve the performance of asphalt pavements at low, intermediate, and high temperatures by increasing mixture resistance to fatigue cracking, thermal cracking, and permanent deformation. Most of the research has been concentrated on the characterization and relative comparison of neat and PMA mixtures, and little work has been done toward the development of fatigue and permanent deformation models for PMA mixtures. A 3-year study that was sponsored by the Michigan Department of Transportation was conducted at Michigan State University to characterize PMA mixtures. It was found that the rheological and engineering properties of PMA mixtures largely depend on the polymer type and content. The improvements in the fatigue lives and resistance to permanent deformation are mainly due to the improvements in the rheological properties of the binders. Fatigue life and permanent deformation models were developed. These models show that the laboratory fatigue life and permanent deformation are strongly related to the rheological properties of binders and the engineering properties of PMA mixtures.

Variability of Air Voids and Mechanistic Properties of Plant-Produced Asphalt Mixtures

The results of a laboratory and field evaluation of the variability of physical and mechanistic properties of plant-produced asphalt mixtures are presented. Three asphalt mixtures from two overlay rehabilitation projects were selected. Comparison analyses were conducted on density measurements between two laboratory (AASHTO T166 and ASTM D6752-02, or CoreLok) and one in situ (pavement quality indicator) test methods. In addition, two laboratory mechanistic tests—indirect tensile (IDT)-strength and frequency-sweep-at-constant-height tests—and two field nondestructive tests with falling weight deflectometer (FWD) and light falling weight deflectometer (LFWD) were performed to characterize the variability of the plant-produced mixtures evaluated in this study. Superpaver gyratory compactor (SGC) samples and field cores were used in the laboratory testing program. A strong correlation was observed between the two laboratory bulk specific gravity test methods: AASHTO T166 and CoreLok. The IDT strengths of SGC samples were higher than those of field cores. A good correlation was found between the complex shear moduli of SGC samples and field cores. Field test results indicated that the LFWD test may be used as an alternative to the FWD test in pavement structure evaluation.

Viscoelastic Behavior of Hydrated Lime-Modified Asphalt Matrix and Hot-Mix Asphalt Under Moisture Damage Conditions

This paper characterizes the viscoelastic response of asphalt matrix (AM) and hot-mix asphalt (HMA) mixtures under dry and moisture-damaged conditions. The AM and HMA mixtures were made with two types of aggregates and one asphalt grade. The hydrated lime was used as a binder additive to reduce the moisture sensitivity of the mixtures. A dynamic shear rheometer was used to conduct frequency sweep and creep tests at various temperatures with AM specimens. The indirect tensile load test was conducted to characterize the creep response, tensile strength, elastic and plastic, and fatigue properties of the HMA mixtures. The results indicated that the generalized creep compliance mechanical model can effectively characterize the viscoelastic response of the AM and HMA mixtures under both wet and dry conditions. The AM testing demonstrated that the lime modification significantly improves the viscoelastic properties of the moisture-damaged AM. The fatigue life of the HMA mixtures improved because of the decrease in the rate of accumulation of tensile plastic deformation as a result of the addition of hydrated lime to the mixtures.

Mechanistic Characteristics of Asphalt Binder and Asphalt Matrix Modified with Nano-Fibers

The Hot Mix Asphalt (HMA) mainly consists of air voids, coarse aggregate and asphalt matrix (AM), which includes asphalt cement (AC) and fine aggregates. The coarse aggregate is stiffer than the AM and is elastic in nature, whereas, the AM makes the HMA a visco-elastic material. The AM is considerably weaker than the coarse aggregate and highly susceptible to damage due to external loads and environment. This study focuses on the preparation and mechanistic characterization of AC and AM mixtures modified with Carbon Nano-fibers (CNF). The AM mixtures were made using lime-stone aggregates and three AC types, neat, processed and CNF-modified. The AC was modified with varying percentage of CNF by weight of AC. To achieve the highest degree of CNF dispersion in AC, two different dispersion techniques were utilized. First, the CNF were sonicated for a specified time to initially disperse them into a solvent. Then the mixture was mixed with AC using a mechanical mixer at medium to high temperature. The dynamic shear rheometer was utilized to determine complex shear modulus (G*) and creep compliance (J[t]) of AC and AM mixtures for a range of temperatures and loading frequencies. The G*-master curve and J[t] analysis revealed that the AC modified with CNF significantly improves the visco-elastic response of the AC and AM. It is recommended to expand the research to different types of aggregate, aggregate gradation, and types of asphalt in order to identify key parameters that can facilitate the understanding of improvements in HMA performance using nano-fibers.

Review of Louisiana's Pavement Management System: Phase I

“Louisiana–Vision 2020” serves as a benchmark for improving highway pavements over a 20-year period. Cost-effective pavement preservation is emphasized in current Louisiana state law and federal law. The Louisiana Department of Transportation and Development (LADOTD) and the FHWA strategic plans also emphasize cost-effective pavement preservation. In an effort to improve the pavement management system (PMS), the Louisiana Transportation Research Center initiated a two-phase research study to evaluate the overall performance and effectiveness of the system. This paper focuses on the Phase I study and addresses the state-of-the-art practice of LADOTDs PMS and the results of a departmental survey to assess the needs of the various districts. The use of various location reference systems by different units in the department makes linking to different database sets difficult. Although many of the districts’ engineers have no concerns about all the referencing systems, most would prefer to have a unified reference location system. All the districts have access to the PMS data and most of them use it; however, the degree of use varies from one district to another. This paper also discusses the types of PMS output and reports, the degree to which the outputs are analyzed, the accuracy of the information currently available, and the degree to which the current PMS data track and differentiate between different preservation actions.

International roughness index models for HMA overlay treatment of flexible and composite pavements

Timely rehabilitation and preservation of pavement systems are imperative to minimising agencys costs and maximising benefits. Reasonable estimates of treatment life and pavement life extension can be made possible by developing reliable treatment performance models. Louisiana Department of Transportation and Development initiated a three-phased study to develop pavement treatment performance models in support of cost-effective selection of pavement treatment type and the time of treatment. As a result of the study, international roughness index (IRI) models for overlay treatment of composite and flexible pavements were developed. Various factors affecting the IRI of overlay treatment were identified. Climatic indices pertaining to Louisiana were developed which exhibited strong statistical significance along with the other variables as used in the IRI models. The developed IRI models provided good agreement between the measured and predicted IRI values with the majority of data within 5% of prediction error. The models could be used as a good pavement management tool for pavement maintenance and rehabilitation actions.

Rigid and composite pavement index-based performance models for network pavement management system in the state of Louisiana

The Louisiana Department of Transportation and Development (LADOTD) in conjunction with the Federal Highway Administration initiated a study to evaluate the existing Pavement Management System (PMS) of LADOTD. The study evaluated and updated the performance models for different pavement types and highway classifications as used by LADOTD. This paper discusses the development of index-based rigid and composite pavement models. Distress data collected over the last 10 years at 2-year intervals were sorted based on control sections, distress type, pavement type and four new LADOTD highway classifications: Interstate, National, State and Regional Highway System. The data were sorted and analysed based on the historical records of the construction/reconstruction and resurfacing year. Regression analyses were conducted and a methodology was adopted to develop generalised models, based on the fundamental concept of pavement rate of deterioration as a function of age. The newly developed models provide good prediction capabilities that will assist in assessing the deterioration of pavements. It is believed that improving the performance models will enhance the efficiency of the PMS of LADOTD.

Micromechanical Modeling of Hot-Mix Asphalt Mixtures by Imaging and Discrete Element Methods

This study focused on the application of a clustered micromechanical discrete-element modeling (DEM) technique to predict the uniaxial compression dynamic modulus of hot-mix asphalt (HMA) mixtures. Six HMA mixtures were made with two types of asphalts and two gradations for limestone and gravel aggregates. The dynamic modulus of HMA was determined at three temperatures by using the indirect tensile test (IDT). Similarly, a frequency sweep test was used to determine the shear complex modulus (G*) of the asphalt matrix (AM) at various temperatures. The master curves for both AM and HMA mixtures were generated at 25°C, and results were analyzed. A two-dimensional, synthetic, heterogeneous microstructure of HMA was reconstructed with scanned images of IDT specimens. Bulk characteristics were used to determine the microproperties of the AM and aggregate structure in order to conduct virtual compressive test simulations. The results indicated that the DEM simulation accurately predicted the dynamic modulus of AM and aggregates at 25°C through the quasi-elastic approach. However, the HMA moduli were underpredicted by the model for a range of AM moduli and loading frequencies at 25°C. Calibration factors for aggregate volume concentrations and particle point contacts were developed and have been discussed here.