Joseph Anochie-Boateng

Aggregate Morphology Affecting Resilient Behavior of Unbound Granular Materials

The resilient modulus (MR) defines the nonlinear elastic response of pavement geomaterials, such as the unbound aggregate base-subbase materials, under repeated traffic loading. The resilient behavior of unbound aggregate layers is affected by the stress states experienced because of wheel loading and physical properties of aggregate materials. Among the physical properties, the influence of aggregate morphology on the resilient behavior of base-subbase materials is not yet well understood because of a lack of quantitative measurements of shape, angularity, and surface texture characteristics of aggregate particles. This paper focuses on investigating the influence of aggregate angularity and surface texture properties on the resilient behavior of unbound granular materials expressed by a nonlinear, stress-dependent resilient response model. With an image analysis approach, two important aggregate morphological indices [the angularity index (AI) and the surface texture index (ST)] were defined to quantify...

Aggregate Surface Areas Quantified through Laser Measurements for South African Asphalt Mixtures

For several decades, efforts have been made by engineers and researchers in road and airfield pavements and railroads to develop methods/procedures for accurate quantification of aggregate shape and packing properties. The difficult part of the process has been the fact that aggregate particles have irregular and nonideal shapes. New research capabilities, including laser-based technology, can effectively address the difficulties associated with aggregate shape measurements to optimize asphalt mix design. This paper introduces the use of a three-dimensional (3D) laser scanning method to directly measure the surface area of aggregates used in road pavements in South Africa. As an application of the laser-based measurements, the asphalt film thicknesses of five typical South African mixtures were calculated and compared with the film thicknesses calculated from traditional methods. Based on the laser scanning method, new surface area factors were developed for coarse aggregates used in the asphalt mixtures. Overall, the study demonstrated applicability of 3D laser scanning method to characterize coarse aggregates.

Analytical and Laser Scanning Techniques to Determine Shape Properties of Aggregates

The fundamental shape attributes of aggregates used in pavements (i.e., form, angularity, and surface texture) have not been accurately quantified historically because of their irregular and nonideal shapes. This paper presents selected results from the use of a laser-based scanning technique to determine the form of aggregates employed in construction of pavements in South Africa. A three-dimensional (3-D) laser scanning system was used to examine aggregate materials from various sources, and the data were processed to reconstruct 3-D models of the aggregate particles. The models were further analyzed to determine the properties of the forms. Two analysis approaches based on physical properties of the aggregate and spherical harmonic analysis were employed to determine the form indices, and the results were compared. The indices based on the physical properties included (a) sphericity computed from the surface area and volume, (b) sphericity computed from three orthogonal dimensions, and (c) the flat-and-elongated ratio computed from the longest and shortest dimensions of an aggregate particle. Good correlations were observed between the form indices from the aggregate physical properties and the spherical harmonic form index. One conclusion of the research is that the laser scanning technique can be employed to quantify better the form properties of aggregate materials used in pavements.

Sustainable Use of Oil Sands for Geotechnical Construction and Road Building

Oil sands are natural deposits of bituminous sand materials that are mined and processed for crude oil. They are routinely used in oil sand fields for building temporary and sometimes permanent roads serving mining and hauling activities. Although the principal application of these materials for road building has been in the unbound layers of the pavement structure, the full benefits of oil sands, particularly their sustainability and environmental friendliness, are yet to be realized. In their natural state, oil sands have similarities to cold mix asphalt mixtures which are often comprised of uniformly graded fine to medium sands and used for pavement repair and patching applications. Yet, they may exhibit complex stress dependent characteristics and viscoelastic and plastic behavior under dynamic loading of mining and off-road construction equipment. This paper presents findings from a comprehensive laboratory research program conducted on three types of oil sand materials with the main goal to characterize their engineering behavior. The research efforts focused on establishing a suite of tests to determine strength, modulus, and deformation characteristics under realistic traffic loading and climatic conditions. The developed suite of tests established essential trends in oil sand behavior for developing laboratory guidelines and test protocols and typical material characterization models for their sustainable use in geotechnical and road building applications.

Long-Term Pavement Performance Monitoring and the Revision of Performance Criteria for High Modulus Asphalt in South Africa

Enrobe a Module Eleve (EME) technology, a High Modulus Asphalt (HiMA), was originally developed in France. The technology is primarily suitable for construction of heavily trafficked routes, airports and container terminals. The key performance characteristics of EME are high stiffness, high resistance to permanent deformation and fatigue cracking. EME is also designed to offer good moisture resistance and good workability. The EME technology has been successfully introduced to South Africa. The development of EME design guidelines in South Africa started in 2006. A major outcome was the publication of Sabita Manual 33: “Interim design procedure for high modulus asphalt in South Africa.” The performance criteria/specifications stipulated in Manual 33 were based on limited data. Based on further work against French mix design and analysis of data collected in South Africa, a revised fatigue and stiffness specifications were adopted in July 2015. Implementation of EME technology in South Africa started in 2011, when a trial section consisting of an EME base layer was constructed on the heavily trafficked South Coast Road in Durban. The section is a major entry route for heavy vehicles travelling to the Durban harbour. Several attempts to rehabilitate the section using conventional asphalt mixes had failed as a result of premature rutting due to the heavy traffic volumes entering the Durban harbour. The heavy traffic volumes at the section offered an ideal setting for an experiment in Accelerated Pavement Testing (APT) without the use of a Heavy Vehicle Simulator (HVS), which enabled the accelerated validation of the South African EME design procedure. The objective of this paper is to present the outcomes of the Long-Term Pavement Performance (LTPP) monitoring programme that was undertaken to assess the field performance of EME, and discuss the development of the newly adopted South African EME performance specifications.

Characterizing Resilient Behavior of Naturally Occurring Bituminous Sands for Road Construction

Oil sand is a generic name given to natural deposits of bituminous sand materials that are mined for crude oil production. These materials are currently used as subgrade materials of temporary and permanent roads in oil sand fields for operating large capacity haul trucks and shovels. This paper focuses on determining in laboratory the resilient behavior of three oil sand materials with bitumen contents of 8.5, 13.3, and 14.5% by weight. The resilient modulus ( MR ) properties were obtained using a newly established repeated load triaxial test procedure. From the test results, nonlinear MR models were successfully developed in the forms of K-theta, Witczak-Uzan, and the mechanistic empirical pavement design guide (MEPDG) models to properly characterize temperature and stress dependent resilient behavior. The modified K-theta model predicted the overall MR dependency on applied stress states and temperature quite satisfactorily for all the three oil sands when compared to the modified Witczak-Uzan and MEPD...

Permanent Deformation Behavior of Naturally Occurring Bituminous Sands

Oil sand, or tar sand, is a generic name given to bituminous sand deposits that are rich in bitumen or asphalt content to the extent that oil can be extracted from these deposits. The typical 8% to 15% presence of bitumen in the soil composition makes these naturally occurring sands low load-bearing materials. In this study, repeated load triaxial tests were conducted on three types of oil sand materials with natural bitumen contents of 8.5%, 13.3%, and 14.5% by weight. The oil sand specimens were compacted close to field densities and then tested for permanent deformation at two temperatures using a newly proposed test procedure. The procedure applied stress states and ratios determined from field-loading characteristics of haul trucks and mining equipment at two different load pulse durations or loading frequencies (related to field-trafficking speeds). Both the test data and axial permanent strain models developed in the form of power functions of the number of repeated load applications indicated a strong dependency of oil sand permanent strain development on the applied vertical to horizontal (or major to minor principal) stress ratio. Using the test data, permanent strain and deformation models were developed with high correlation coefficients to account for the applied stress states and ratios, test temperature, and bitumen content. These models generalized for oil sand deformation behavior may be used as practical predictive equations to estimate the amount of rutting in oil sand materials and to alleviate potential sinkage problems faced by off-road haul trucks, shovels, and other mining equipment in the field.

Geomaterial Characterizations of Full Scale Pavement Test Sections for Mechanistic Analysis and Design

Resilient modulus is a key input property of pavement foundation geomaterials, i.e., subgrade soil and base/subbase unbound aggregate, for the mechanistic-empirical design of flexible pavements. Recent research at the University of Illinois has focused on the development of a mechanistic model for the response analysis of geogrid reinforced flexible pavements. This model utilized the finite element approach and considered the nonlinear, stress dependent pavement foundation behavior in a similar way to the level I analysis approach in the 2002 Pavement Design Guide. To validate the response model as well as to develop pavement distress models, nine full-scale flexible pavement test sections, geogrid reinforced and unreinforced, were recently constructed. To quantify the effectiveness of geogrid reinforcement on low volume flexible pavements, the finegrained subgrade soils were carefully constructed and maintained at California Bearing Ratio (CBR) values 4% or lower throughout the test sections. A complete suite of laboratory and field tests were performed to characterize the pavement geomaterials for mechanistic analysis of the test section response. This required both monitoring of the pavement layer properties during construction and also development of modulus characterization models from multiple regression analyses of the laboratory test data.

Advanced Testing and Characterization of Shear Modulus and Deformation Characteristics of Oil Sand Materials

Oil sands are natural deposits of sand materials that are rich in bitumen. Limited studies have been conducted to determine the dynamic behavior of oil sand materials. Recent difficulties encountered in oil sand mine fields in Canada substantiated the need to characterize the stress dependent, visco-elastic, and plastic behavior of oil sand materials under dynamic loading of off-road construction and mining equipment. This paper introduces a new cyclic triaxial test procedure for determining shear modulus and deformation characteristics of oil sand materials. The test procedure was used to characterize shear moduli of three oil sand materials with varying bitumen contents. From the test results, nonlinear shear modulus models were successfully developed to characterize temperature and stress dependent behavior of the tested oil sand materials. The research findings indicate that the new laboratory approach is an improvement on conventional tests, especially when oil sand materials need to be evaluated in the field for subgrade construction and equipment mobility.