Curtis F Berthelot

Mechanistic Laboratory Evaluation and Field Construction of Recycled Concrete Materials for Use in Road Substructures

Given the renewal of urban infrastructure and the increased costs of landfilling concrete rubble materials, opportunities exist to optimize the reclamation and recycling of portland cement concrete (PCC) and hot-mix asphalt concrete (HMAC) rubble through their innovative use in road rehabilitation. The primary objective of this study was to demonstrate the ability to reclaim, process, and recycle stockpiled concrete materials to provide improved structural mechanistic–climatic material properties and to meet or exceed the mechanical properties of conventional granular road materials. This research was based on advancements made in 2009 as part of the Green Streets Infrastructure Program in the city of Saskatoon, Saskatchewan, Canada. A second objective of this research was to pilot the field application of reclaimed and recycled HMAC and PCC rubble in typical urban road reconstruction applications. Recycled HMAC and PCC materials were used in the pilot reconstruction of a road that was exhibiting substructure moisture problems and structural failure. This study showed that recycled HMAC and PCC rubble materials could be processed to achieve mechanistic laboratory properties that exceeded those of conventional granular-based materials. This study also demonstrated efficient constructability and high end-product structural asset value of a typical rehabilitated urban road structure test section in the city of Saskatoon by using recycled HMAC and PCC rubble. On the basis on these findings, the use of quality processed HMAC and PCC rubble materials for road reconstruction was found to be a technical and environmentally sustainable solution.

Mechanistic Comparison of Cement- and Bituminous-Stabilized Granular Base Systems

The Saskatchewan, Canada, Department of Highways and Transportation is investigating alternative recycling and strengthening systems for inservice thin granular pavements. This research is being performed to improve the granular pavement structural integrity and to reduce the dependence on new source aggregates. A pilot project investigated the mechanistic-climatic laboratory characterization of materials used to construct test sections on Control Section Highway 15-11 (C.S. 15-11). This research demonstrated the use of ground-penetrating radar and falling weight deflection measurements to select uniform field test section locations. In situ recycled granular base was sampled and found to be a typical thin granular pavement requiring strengthening because it is relatively high in fine sand fraction and has a high portion of intermediate plastic clay fines. These two properties are known to cause marginal performance of granular bases in the field. This research showed that cement and bitu-minous stabilization significantly improved the mechanistic primary response and climatic durability properties of marginal granular base materials. However, it was found that the asphalt emulsion with cement stabilization showed the highest performance improvement. It also was found that the addition of cement to emulsified and foamed asphalt stabilization systems significantly improved the mechanistic-climatic durability of the marginal granular base aggregate. This study demonstrated the rapid triaxial tester to be a pragmatic and cost-efficient methodology to characterize the mechanistic constitutive relations of granular base materials for performing mechanistic road structural modeling.

Life-Cycle Economic Evaluation of Alternative Road Construction Methods on Low-Volume Roads

The province of Saskatchewan has the largest number of public roads per capita in Canada and one of the largest in the world. Over the past decade, pressures on the road network have increased, resulting in accelerated road damage and increased demand to upgrade portions of the highway network. To address transportation infrastructure sustainability issues, Saskatchewan Highways and Transportation (DHT) and Pavement Scientific International, Inc., are researching more cost-effective methods. The research work involves evaluating the technical and economic feasibility of undertaking alternative road construction techniques. A critical component of this research effort is to evaluate the economic feasibility associated with different road construction techniques. The ability to perform whole-life economic analysis associated with long-term infrastructure assets is important to long-term sustainability. By comparing the present value of initial construction and future preservation costs across different road structures and technologies, an accurate assessment of construction and design options is achievable. On the basis of performance predictions and projected structural performance, resource allocation can be optimized more reliably across limited resources and alternative road strengthening systems, providing technically sound solutions that are more economically attractive. With an ability to predict whole life-cycle performance on the basis of future maintenance treatments, road managers can more reliably assess alternative surfacing and structural preservation strategies. The primary focus of this paper is to demonstrate the economic considerations undertaken in evaluating alternative road design and construction methods. This longer-term evaluation approach allows strategic investments in highway infrastructure and allows DHT and other agencies to consider innovative road structural rehabilitation and management strategies more effectively.

A Computational Model for Predicting the Effect of Tire Configuration on Asphaltic Pavement Life

ABSTRACT This paper proposes a model for predicting the mechanical behavior and performance life of asphalt pavements subjected to various tire configurations, layer thickness, and material properties. A viscoelastic two-dimensional finite element model was developed and utilized in order to predict pavement life depending on different combinations of these design variables. The effects of truck loads on the pavement performance were studied by simulating three tire configurations: two types of the new generation wide-base single tire and one conventional dual tire configuration. Also, two different types of hot mix asphalt (HMA) and three variations of the HMA layer thickness were evaluated. Results showed that the use of conventional dual tires produces approximately 50 per cent longer asphalt service life when compared to the use of wide tires. The service life is shown to increase by increasing the HMA layer thickness. In fact, simulation results suggest that a 200 mm thick HMA layer provides a 15 per cent longer life than a 100 mm thick layer. Asphalt material results also suggest that the quality of materials can significantly affect pavement performance and service life. Furthermore, service life is significantly reduced when a poor quality material is combined with a thin asphalt layer. The simulation model presented here will be useful for future pavement design and material selection.

Cold in-place recycling and full-depth strengthening of clay-till subgrade soils: Results with cementitious waste products in northern climates

Saskatchewan is experiencing significant increases in commercial truck traffic due to grain transportation rationalization, consolidation of the rural grain elevator system, rural economic diversification, and expansion of resource industries. Although increasing truck traffic has longterm implications for the primary pavement system, significant increases hold immediate implications for thin paved roads; many were not originally designed to accommodate heavily loaded commercial trucks. There is a clear need to strengthen many Saskatchewan thin pavements. However, conventional structural strengthening typically involves regrading and granular subbase-base overlay systems, often too expensive because of the cost associated with aggregate hauls and regrading. As a result, the Saskatchewan Department of Highways and Transportation is investigating the use of cold in-place recycling and full-depth cementitious stabilization to strengthen Saskatchewan thin pavements. To this end, industrial waste coproducts such as coal fly ash, bottom ash, and kiln dusts are being investigated as structural cementitious soil stabilizers. The results are presented from preconstruction site investigation methods, laboratory materials characterization, and in situ quality assurance test results. Field performance after 2 years shows cold in-place recycling and cementitious stabilization to be a technically and economically feasible solution for strengthening Saskatchewan thin paved roads built on clay-till subgrades.

Saskatchewan Field Case Study of Triaxial Frequency Sweep Characterization to Predict Failure of a Granular Base across Increasing Fines Content and Traffic Speed Applications

Approximately one-third of the Saskatchewan provincial highway system is comprised of granular base structures with a thin asphaltic or double seal surfacing. Unfortunately, significant portions of the Saskatchewan thin granular system were not constructed to primary legal weight limit standards and are now exhibiting varying degrees load related distresses and in many cases, structural failures. Based on field performance observations, many of the failures are commonly observed within the granular base layer, particularly when the base is comprised of high fines content, and/or when exposed to high deviatoric stress states. A recent increase in load spectra due to increasing truck traffic has resulted in much of the Saskatchewan granular base systems needing structural rehabilitation. In order to optimize the road structure upgrade treatment, it is desirable to better understand the material constitutive relations of granular base materials across fines content, triaxial stress states, and load frequencies representative of those induced within thin granular base pavements in the field. This research employed triaxial frequency sweep characterization to characterize the mechanical material constitutive behavior of a typical Saskatchewan Type 33 granular base across increasing fines content, triaxial stress state, and load frequency. Based on the findings of this study, increased fines content was found to significantly degrade the mechanical behavior of the standard Saskatchewan Type 33 granular base material in terms of dynamic modulus and phase angle. This research showed that under realistic field state conditions in Saskatchewan, phase angle may be an indicator of elevated viscous behavior within the granular base. Based on the mechanical material properties measured, it was also found that the current specified limits for fines content may not be sufficient to ensure optimal mechanistic structural behavior of thin granular pavement systems under severe traffic load conditions.

Multi-scale computational model for design of flexible pavement – part II: contracting multi-scaling

Abstract A computational multi-scale procedure for designing flexible pavements is developed in this, the second of a three-part series. In this study, computational analyses are performed on sequentially smaller length scales, termed contracting multi-scaling. The model is constructed by utilising the finite element method on each length scale, thereby creating a one-way coupled multi-scale algorithm that is capable of accounting for the effects of cyclic loading on the initiation and evolution of cracks on multiple length scales within the roadway. For example, the algorithm can be utilised to predict the effects of small-scale design variables such as aggregate volume fraction, as well as the effects of large scale design variables such as asphalt concrete thickness on pavement cracking due to external loading. The model for predicting roadway cracking is briefly described herein, including the experimental properties required to deploy the cracking model within a computational framework. The article concludes with demonstrative examples intended to elucidate the power of this predictive technology for the purpose of designing more sustainable roadways.

Effectiveness of Truck Rollover Warning Systems

Different types of intelligent rollover system deployed by road agencies across North America are investigated. The importance of weight is addressed for maximum effectiveness of rollover warning messages for commercial vehicles in a potential rollover situation on sharp curves or exit ramps. The type of information that may be used to activate a rollover is discussed to analyze the number of correctly warned vehicles compared with the number of false warnings generated by the rollover warning system. A case study of the effectiveness of an intelligent rollover system is presented. On the basis of this case study, it was found that speed-based rollover warning systems generated anywhere from 44 percent to 49 percent more false rollover warnings for commercial vehicles than did rollover warning systems that employed weight information in the rollover decision criteria.

Ground-Penetrating Radar Evaluation of Moisture and Frost across Typical Saskatchewan Road Soils

This study was undertaken to evaluate the effect of soil type, moisture content, and the presence of frost on road substructure permittivity. Permittivity sensitivity of typical road soils was characterized in the laboratory to provide baseline dielectric constant values which were compared to field ground penetrating radar (GPR) survey results. Both laboratory devices, the complex dielectric network analyzer and the Adek Percometer, as well as the field GPR system were used in this study to measure the dielectric constant of soils. All three systems differentiated between coarse-grained and fine grained soils. In addition, at temperatures below freezing, all three systems identified an increase in water content in soils; however, when frozen, the sensitivity of dielectric constant across soil type and moisture content was significantly reduced. Based on the findings of this study, GPR technology has the ability to characterize in situ substructure soil type and moisture content of typical Saskatchewan road substructure soils. Given the influence of road soil type and moisture content on in-service road performance, this ability could provide road engineers with accurate estimates of in situ structural condition of road structures for preservation and rehabilitation planning and optimization purposes.

Multi-scale computational model for design of flexible pavement – part III: two-way coupled multi-scaling

Abstract A computational multi-scale procedure for designing flexible roadways is developed in this part, the third of a three-part series. In this study, a two-way coupled multi-scale algorithm was developed and utilised to predict the effects on pavement performance caused by variations in local and global design variables. The model is constructed by utilising the finite element method at two simultaneous and two-way coupled length scales, thereby creating a multi-scale algorithm that is capable of accounting for the effects of variations in design parameters on both length scales. Energy dissipation mechanisms such as viscoelasticity in the asphalt mastic, plasticity in the base layer and crack propagation in the asphalt concrete are incorporated within the model for the purpose of predicting permanent deformations in typical roadways subjected to cyclic tyre loadings. The algorithm is briefly described herein, including the experimental properties required to deploy the computational scheme for the purpose of pavement design. The algorithm is subsequently utilised to predict the effects on pavement performance of variations in design variables on the global length scale (metres) such as asphalt concrete layer thickness and base layer yield point as well as design variables on the local length scale (centimetres) such as aggregate volume fraction and asphalt mastic fracture toughness. These demonstrative examples elucidate the power of this new technology for the purpose of designing more sustainable roadways.