Guy Doré

Gradation influence on frost susceptibility of base granular materials

Base granular materials are generally considered non-frost susceptible, which is an adequate assumption based on widely recognised frost criterions. However, their frost susceptibility is influenced by the presence of water that can unavoidably penetrate pavement structures. Even if unsaturated, freezing of unbound granular materials causes a net volume gain and an increase in water content which affect pavement performance during the spring period. This paper presents the results of a laboratory investigation on the effect of gradation on frost susceptibility, quantified with the segregation potential (SP), of three aggregate sources. The results suggest that SP values for all sources are strongly related to a fine particles state parameter. Moreover, the source influence was found to be described adequately with a parameter describing fine particles grain size distribution uniformity and fines specific surface. A model is proposed which combines gradation and mineralogical source effects on frost susceptibility of base granular materials.

Role of Deicing Salt in Pavement Deterioration by Frost Action

Frost action is a major cause of pavement deterioration in cold climates. Thermal cracking, differential heaving, and loss of bearing capacity during spring thaw are often identified as the main mechanisms involved. Except for thermal cracking, frost-susceptible subgrade soils are generally considered to be the source of the problems. Field observations suggest that frost action within the pavement granular layers could also contribute to pavement deterioration. Differential freezing conditions associated with the contamination of the base material by deicing salt are believed to be the cause of this problem. Indeed, field observations of heaved pavement surfaces near discontinuities, such as cracks or pavement edges, suggest that an ice enrichment process is occurring in pavement granular layers during the freezing season. In a laboratory testing program, salt concentration gradients reproduced in freezing temperature create conditions favorable to an ice enrichment process and contribute to a substantial increase in the frost susceptibility of granular materials. Under steady isothermal cooling conditions, samples placed in layers of increasing salinity have exhibited heave at rates as high as 6 mm/day. Normal freezing tests on the same material free of salt have shown no significant segregation potential. Surface heave resulting from ice enrichment can be highly detrimental to pavement performance. Induced distortion contributes to rapid deterioration of the pavement surface. When occurring along transverse cracks, the phenomenon may seriously alter the ride quality of the pavement.

Deterioration Model for Pavements in Frost Conditions

Pavements in cold climates are often subjected to transverse differential heaving. This phenomenon is the result of the more severe frost action under the unprotected road surface. It induces bending stresses in the pavement structure and ultimately causes longitudinal cracking at the pavement surface. A simple model to predict the initiation and the propagation rate of cracking induced by frost heave is proposed. The model is based on mechanistic principles and calibrated using field performance data. It can be used in designing and managing pavements in frost conditions.

Development and Validation of the Thaw-weakening Index

In northern climates, frost action is a major cause of pavement deterioration. It is well known that frost action in frost susceptible subgrade soils can cause considerable heaving in pavements. When spring thaw occurs, segregation ice melts generating high pore pressures in frost susceptible subgrades. The bearing capacity loss can be substantial, leading to important structural damage to pavement exposed to severe and uncontrolled loading conditions. Extensive research efforts have been devoted to the characterization of soils and material properties and their variation as a function of moisture and temperature variations. These research initiatives are typically conducted in the field using deflexion measurements or in the laboratory using cyclic triaxial testing. The results of these tests are used for the assessment of seasonal fatigue damage using analytical techniques to compute stresses and strains at critical location in pavement structures combined with empirical damage models. A new approach based on a mechanistic index, the thaw weakening index, is proposed. The index takes into consideration the amount of water accumulated by the freezing process, the rate of thawing in pavement layers and in the subgrade soil and the rate of consolidation of the pavement structure. Based on a number of observations found in the literature and on measurements made on test roads, good correlation was found between the index and the increase in pavement total deflection during spring thaw. A good correlation was also found between the index and the loss of stiffness (resilient modulus) of the subgrade soil. The paper will describe the theoretical development of the new index and will present correlations between the thaw-weakening index and observed weakening on in-service test roads during spring thaw.

Use of falling weight deflectometer time history data for the analysis of seasonal variation in pavement response

This paper presents the results of an exploratory analysis of falling weight deflectometer (FWD) data collected on a large project about the spring thaw behaviour of pavements. The test site includes four test sections, two of which are conventional flexible pavement structures, whereas the other two are built with a cement-treated base. The aim of this study is to verify the applicability of using FWD time history data to evaluate damage to a road during the thawing period. The applicability of the analysis techniques is verified through the phase angle and dissipated energy. The data analyzed were obtained from tests conducted with an FWD on one flexible pavement test section. The results obtained showed a clear difference between the winter, thawing, and summer periods. It was found that the phase angle and dissipated energy can be used to evaluate the road damage during the thawing period through quantification of the phase angle and dissipated energy. These factors can also be used to describe the pa...

Erosion susceptibility of granular pavement materials

Turbulent flows, such as wind and runoff water, affect the integrity of base granular materials in paved roads shoulders and unpaved roads. This paper presents the results of a laboratory investigation on the effect of base granular gradations on their erosion resistance under turbulent flows. The tests were performed with the turbulent flow test designed to be used with conventional geotechnical laboratories equipment. Several gradations curves, within and outside the Quebec Ministry of Transportation grading envelope, were tested in order to examine the influence of the variation of base granular materials gradation characteristics on the erosion susceptibility. For unbound materials, it was found that properties related to material voids and the permeability of the material (uniformity coefficient, fine fraction porosity and estimated permeability) and property related to the fine particles content are strongly related to the erosion rates (ER) measured with the turbulent flow test. It was demonstrated that the performance of base granular materials under turbulent flows can be controlled using these specific parameters.

Wide-Base Single-Tire and Dual-Tire Assemblies: Comparison Based on Experimental Pavement Response and Predicted Damage

Past studies suggest that wide-base single tires [WBSTs (455/55R22.5)] induce pavement strains that can be either more or less severe than those caused by dual tires of similar sizing, as strain depends on both the spatial direction of the strain and where the strain is located in the pavement. An experimental assessment of strain basins occurring at various positions within the hot-mix asphalt (HMA) layer, as well as within pavement unbound layers, was undertaken to further this understanding. The method and the results of this assessment, along with the pavement damage predicted by using available models are presented. Four failure mechanisms were considered: HMA rutting, both bottom-up and top-down fatigue cracking, and structural rutting. Testing was conducted at two sites on four roads over a range of loads, pressures, and temperatures by using WBSTs and different sizes of dual tires. Data analysis showed several critical strain zones near the tire edges and at the tire center. Optic-fiber sensors were used to analyze these phenomena. HMA rutting was calculated by considering vertical shear strain near the surface under the edge of the tires. Other failure mechanisms were calculated by using maximum strain. The results predicted that the WBSTs tested may induce less damage in the upper part of the HMA layer and more damage when fatigue cracking and rutting of soils and unbound materials are considered. Data collected were from specific tires, and all tests were conducted only under smooth, steady-state rolling conditions. Thus, results should neither be generalized to all tires nor extrapolated to the prediction of actual field performance.

Pavement Performance Evaluation of Three Canadian Low-Volume Test Roads

New and improved pavement technologies are developed through laboratory investigations, construction and maintenance, theoretical analyses, long-term performance studies such as the Strategic Highway Research Program (SHRP) and the Canadian SHRP, and integrated programs of laboratory and field research. The latter, integrated approach is the subject of this study. Although various test roads have been placed in Canada over the past several decades, this study focuses on three test roads that examine low-volume road performance. These test roads are located in Ontario, Quebec, and Alberta and are being monitored by three Canadian universities. The background, test road objectives and location, design of the test roads and instrumentation, construction, and vehicle testing are first summarized briefly. Then, some ongoing projects at the three test roads and how results from the three test roads can be used either individually or collectively to improve current practices within Canada are discussed, with a focus on low-volume road technologies. Particular emphasis is placed on the performance of low-volume resource roads with respect to both traffic loading and environmental conditions. Findings from these studies will also be useful in the Canadian national calibration of the new Mechanistic–Empirical Pavement Design Guide.

Prediction of Winter Roughness Based on Analysis of Subgrade Soil Variability

Frost action is a major cause of pavement deterioration in cold climates. Thermal cracking, differential heaving, and loss of bearing capacity during spring thaw have often been mentioned as the main mechanisms involved. Frost heave observed on pavements built over frost-susceptible subgrades can reach 200 mm in the Canadian climatic context. The problem is mainly because frost heave is rarely uniform. As a result, pavements tend to become rough during winter. Research recently conducted at Laval University in Quebec City, Quebec, Canada, has shown that winter roughness is related to the variability of subgrade-soil properties. A relationship between the variability of soil frost susceptibility and the ratio of winter and summer roughness has been developed. A new approach, based on the relationship, is proposed to help pavement designers to predict and mitigate winter roughness problems.

Thermal Effectiveness of the Mitigation Techniques Tested at Beaver Creek Experimental Road Site Based on a Heat Balance Analysis: Yukon, Canada

To better understand permafrost degradation under roadways, 12 experimental sections were constructed on the Alaska Highway near Beaver Creek in April 2008. These techniques designed to prevent permafrost thawing are: air convection embankments, heat drains, snow/sun sheds, longitudinal culverts, light-coloured aggregate for road surfacing, snow plowing techniques and grass-covered embankments. This paper presents the results of the analysis on heat balance for each section during the first three years in service to determine the short term effectiveness of the techniques.