Resilient Behavior of Unbound Granular Materials Subjected to a Closed-System Freeze-Thaw Cycle

The resilient modulus of a base course granular material is an important input parameter for pavement design and analysis. In recent decades, numerous studies have been performed to characterize and model the resilient behavior of base course materials under unfrozen conditions. In cold regions, frost heaving and subsequent thawing significantly affect the resilient behavior of base course materials. Due to the complex nature of the problem, relatively less effort was dedicated to characterize and model the resilient behavior of base course materials after seasonal freeze-thaw cycles. Among the limited studies, very often the soil specimens were prepared in an open system with free water access to simulate the frost heave, which represented the worst-case scenario in terms of stiffness reduction during thawing. Sometimes omnidirectional freeze tests were performed to simplify the testing procedures. In reality, soils in the field often experience one-dimensional freeze and thaw. When the permeability of the soil is very low, the groundwater table is far from the freezing front, or the freezing temperature gradient is high, the freezing process can be considered to be in a closed system (i.e., limited or no water exchange). The closed system represented the best-case scenario in terms of stiffness reduction during thawing, which has rarely been investigated. Hence, an in-depth understanding of the seasonal resilient behavior of base course materials in a closed system is essential for cold region pavement design and analysis. In this study, repeated loading triaxial tests were performed to investigate the effects of nonplastic fines content, moisture content, temperature, thermal gradient, and freeze-thaw cycling on the resilient modulus of unbound granular base course materials under seasonal frost conditions. Soil specimens were prepared in the laboratory using a one-dimensional frost heave chamber with temperature-thermal gradient control. Specimens were subjected to a closed-system freezing (undrained) condition. Test results were analyzed and discussed, and models were developed to predict granular materials\u27 resilient moduli as a function of the state of stress, temperature, moisture, and fines content to complement the previous study

Characterizing the Permanent Deformation Behavior of Alaskan Granular Base Course Materials

Permanent deformation of granular base course materials under repeated vehicle load is an important characteristic that is required to be considered in pavement design. In Alaska, due to the extreme climatic condition, the granular base course materials in a pavement structure usually undergo significant permanent deformation which is typically reflected by the rutting, cracking, and eventually pothole problems on the pavement surface during spring. Over the years, research effort on the permanent deformation behavior of base materials, especially for cold regions pavements, is very limited. In this study, to investigate the permanent deformation behavior of granular base course materials in cold regions, a series of one-dimensional frost heave tests under two extreme water access conditions (i.e. limited and free water access conditions) were conducted on Alaskan granular material specimens with different fines and initial moisture contents using a one-dimensional frost heave cell. After the freezing process, the repeated load triaxial test was then performed to evaluate the permanent deformation behavior of these specimens under frozen and subsequent thawing conditions. With the results from the repeated load triaxial tests, the influences of fines and water content, temperature, temperature gradient, stress state, and water access condition during freezing on the permanent deformation behavior of the base course materials were evaluated. Also, regression was performed to predict the permanent deformation of granular materials with different fines content, water content, and temperature conditions for the granular materials under unfrozen and frozen conditions. Finally, recommendations were provided to mitigate the cold region pothole problem due to accumulated permanent deformation under repeated vehicle load

Variability of Composition, Volumetric, and Mechanic Properties of Hot Mix Asphalt for Quality Assurance

As hot mix asphalt (HMA) is the major paving material worldwide, how the quality of this material is assured is a critical issue. The current quality assurance (QA) practices include testing programs that yield inevitable variability as a result of, e.g., different operators, equipment, and methods. So far, very little research has focused on the variance and testing variability of HMA properties with respect to the material types and climatic conditions that are typical of Alaska. This study presents research to evaluate the variance in composition, volumetric, and mechanical properties between plant-produced and lab-designed mixtures of Alaska HMA, which was produced with various production/compaction scenarios and tested by different operating parties. The variability level of each tested property was quantified, compared with nationwide levels, and tested for influencing factors. This study further evaluated the method proposed in the National Cooperative Highway Research Program (NCHRP) 9-22 project, to predict the means and variability of mechanical properties with the measured composition and volumetric properties of Alaska HMA. According to the results, clear differences were observed between the plant-produced and lab-designed mixtures, and the magnitudes of the differences were higher for the volumetric and mechanical properties than for the composition properties. The variability of properties of Alaska HMA was within the nationwide range, with the lowest levels found on composition properties, followed by volumetric properties, and the highest on mechanical properties. The effects of the operating party and production/compaction scenario were also reported. The predicted results of the mechanical properties were found to deviate from the measured ones

Characterizing Influence of Water Access Condition during Freezing on Resilient Behavior of Alaskan Base Course Materials

Accurate characterization of the resilient behavior of the base course materials under different climatic conditions is critical for the design of reliable and cost-effective pavement structures. In Alaska, the resilient behavior of base course materials usually undergoes significant variation due to seasonal change and extreme climatic conditions. Previous studies have revealed that the resilient behavior of base course materials could be significantly influenced by the freezing process. In this study, the freezing process under two extreme conditions (i.e., free and no water access conditions) that base course materials could possibly experience in the field was simulated using a one-dimensional frost heave cell. The influences of the water access condition during freezing on the frost heave and resilient modulus (MR) of the base course materials with different fines and initial water contents was assessed based on the results from the freezing process and repeated load triaxial tests. A pressure plate test was also performed to build the relationship between suction and water content of soils with different fines content. Suction was then introduced to model MR of the materials tested under unfrozen conditions before and after a freeze–thaw cycle. The adoption of suction significantly simplified the equation for MR prediction. Finally, structural analyses were conducted using BISAR and Alaska Flexible Pavement Design (AKFPD) software and the results revealed that free water access during freezing can significantly accelerate cracking and reduce pavement service life

Low Temperature Cracking Analysis of Asphalt Binders and Mixtures

Low temperature cracking (LTC), or thermal cracking, is one of the most prevalent asphalt concrete (AC) pavement distresses in northern states and countries. Extensive efforts have been made on the characterization of LTC of AC pavements and specification development for pavement design. With the recent update of binder cracking temperature approach in AASHTO specification M 320, this study aimed at conducting a comprehensive LTC analysis of typical Alaskan asphalt materials including both laboratory tests and analytical assessment. The critical cracking temperatures for both binders and mixtures were correlated and compared. The pavement temperatures in winter time for typical Alaskan AC pavements were predicted using the TEMPS software and compared with the critical cracking temperatures of mixtures. Findings and recommendations were provided regarding adaptation of binders and mixtures to better address the LTC in Alaskan pavements

Characterizing Permanent Deformation of Alaskan Granular Base-Course Materials

Permanent deformation of granular base-course materials under repeated vehicle load is an important characteristic that is required to be considered in pavement design. In Alaska, due to the extreme climatic condition, the granular base-course materials in a pavement structure usually undergo significant permanent deformation, which is typically reflected by rutting, cracking, and eventually pothole problems on the pavement surface in spring. Over the years, research efforts on the permanent deformation of base materials, especially for cold regions pavements, have been very limited. To investigate the permanent deformation of granular base-course materials in cold regions, a series of one-dimensional frost heave tests under two extreme water access conditions (i.e., limited and free water access) were conducted on Alaskan granular materials with different fines and initial moisture contents using a one-dimensional frost heave cell. After the freezing process, the repeated-load triaxial test was then performed to investigate the permanent deformation under frozen and subsequent nonfrozen conditions. Test results indicated that frost heave and subsequent permanent deformation of base-course materials were highly dependent on the water access condition during freezing. The fines and water contents, temperature, temperature gradient, stress state, and their coupling effect also played important roles in the permanent deformation of the base-course materials. In addition, regression analyses using a mechanistic-empirical design guideline and Sweere models were performed to predict the permanent deformation of the granular base-course materials with consideration of the influences of fines content, water content, and temperature conditions under thawed and frozen conditions. Compared with the equation from the guideline, the Sweere model provided a better prediction in the material permanent deformation under the unfrozen condition. Using the guideline equation may lead to inaccurate prediction of permanent deformation, especially for granular base-course materials at a relatively higher water content