Juanyu Liu

Laboratory Evaluation of Sasobit-Modified Warm-Mix Asphalt for Alaskan Conditions

A number of completed or ongoing studies on different aspects of warm-mix asphalt (WMA) have being conducted in the United States, indicating pavement professionals’ strong interest in exploring the application of this innovative technology. In the summer of 2008, a field trial project using Sasobit-modified WMA was established in the southeastern region of Alaska, which was Alaska’s first experience with a WMA technology. In line with this field experimental feature project, this paper presents a systematic laboratory study of both Sasobit-modified WMA binders and mixes. Engineering properties of Sasobit-modified WMA binders and mixes were experimentally evaluated, and the effects of Sasobit addition on the WMA’s performance in terms of low temperature behavior, rutting resistance, and moisture susceptibility were investigated. Research results identified a number of engineering benefits of Sasobit-modified WMAs over conventional HMA. Sasobit-modified WMAs reduced mixing and compaction temperatures, improved workability and rutting resistance, and had insignificant effect on moisture susceptibility. These effects indicated the suitability of this WMA technology for central and southeastern regions of the Alaska Department of Transportation and Public Facilities (AKDOT&PF). The indirect tension test results showed a decrease of WMAs tensile strength at low temperatures. Additional tests at lower temperatures, along with a more complete thermal cracking analysis need to be performed to obtain a more definitive answer regarding the low temperature performance of these mixes for the northern region of AKDOT&PF.

Low Temperature Performance of Sasobit-Modified Warm-Mix Asphalt

In the summer of 2008, a field trial project using Sasobit-modified warm-mix asphalt (WMA) was established in Alaska, which was Alaska’s first experience with a WMA technology. Previous studies conducted by writers identified a number of engineering benefits of Sasobit-modified WMAs over conventional hot-mix asphalt (HMA). This paper presents a further assessment focusing on low temperature performance of both Sasobit-modified WMA binders and mixes. A series of binder tests including bending beam rheometer (BBR), direct tension test (DTT), and asphalt binder cracking device (ABCD) tests were conducted. Indirect tension tests (IDT) of mixtures along with a thermal cracking analysis were performed to obtain a more definitive answer regarding the WMA application for cold-weather conditions. Results showed a decrease of tensile strength for both WMA binders and mixtures at low temperatures, and the cracking temperatures of both WMA binders and mixtures increased with the increase of Sasobit content. However, the increase in cracking temperature was very slight, which indicated that Sasobit addition had an insignificant effect on resistance to low temperature cracking. Therefore, Sasobit-modified WMA should be suitable for the Northern Region of the Alaska Department of Transportation and Public Facilities (AKDOT&PF) without compromising the resistance to low temperature cracking.

Effect of fibers on expansion of concrete with a large amount of high f-CaO fly ash

The effects of different types of fibers on expansion of cement paste, in which a large amount of high content of f-CaO fly ash (HFA) was added, were investigated and the way to prevent cement paste with HFA from expansion was proposed. The results showed that the effects of different fibers on expansion of cement paste are related to the properties of fibers. Carbon fiber and alkali-resistant glass fiber, which have high elastic modulus, can effectively restrain the expansion, while nylon fiber with low elastic modulus has no restraint effect on the expansion. In addition, the restraint effect of alkali-resistant glass fiber increases with the increase of fiber content.

Materials and Temperature Effects on the Resilient Response of Asphalt-Treated Alaskan Base Course Materials

Asphalt-treated bases (ATBs) are the most commonly used type of stabilized layer in Alaska because of locally available asphalt resources and its relatively lower cost. As an essential material input parameter for pavement design, resilient modulus ( MR ) of ATBs has been studied in laboratory evaluations, field investigations, and empirical and mechanistic modeling. However, most ATBs’ MR values available in the database of the Alaska flexible pavement design software were obtained from in-service roadways through nondestructive testing and back calculation. Therefore, there was a need to characterize these stabilized materials by taking into account the main factors that influence their engineering behavior. In this study, the MR characterization of two types of ATBs was achieved through laboratory testing: hot asphalt-treated base (HATB) and foamed asphalt-treated base (FATB). The effects of loading amplitude, confining pressure, temperature, binder content, and aggregate source and properties on the r...

Pavement Preservation Practices in Cold Regions

Pavement preservation is an emerging approach in road upkeep. The State of Alaska Department of Transportation and Public Facilities (AKDOT&PF) aim to spend wisely the funding for its road upkeep by integrating pavement preservation concept into its Pavement Management System. To do this, a literature review was conducted on the performance and cost effectiveness of pavement preservation treatments in cold regions. This paper presents the results of the literature review. The following include the main findings: Pavement preservation treatments, Crack Sealing, Patching, Fog Seals, Chip Seals, Slurry Seals, AST/BST, Microsurfacing, Thin Overlays, Bonded Wearing Courses, Interlayers and In-place Recycling, are all used widely in cold regions. Crack sealing and patching are the most extensively used pavement preservation treatments. Use of chip seals, fog seals, and slurry seals should be considered job specifically. The service life of the treatments varies from about 3 years to 12 years. Microsurfacing and thin overlays have the longest service life. The costs of treatments vary from a region to another as well as from project to another. Other issues despite the cost effectiveness include sustainability and traffic safety.

Resilient Modulus Characterization of Hot Asphalt Treated Alaskan Base Course Material

In many areas of Alaska, clean, durable aggregates normally utilized for base course either require long hauls from outside, or are difficult to obtain within the project limits. Asphalt treatment is the most commonly used type of stabilization for the available lower quality materials to increase their strength thus extending their life and saving money to the state in the long run. This paper presents the resilient modulus characterization of hot asphalt treated base (HATB) course material in northern region of Alaska. Experimental studies were conducted to evaluate the resilient modulus of HATBs through repeated load triaxial tests. Effect of different stabilization levels (i.e. asphalt content) on the performance of HATB materials was investigated and a model was developed to reflect the influence of confining pressure and deviator stress on HATBs.

Experimental Study on Gilsonite-Modified Asphalt

This paper presents an experimental study on investigating the properties of Alaskan asphalt binder modified with different percentages of gilsonite over a wide range of climatic conditions by addressing the performance grade (PG) of gilsonite-modified binders according to Superpave specifications. The base asphalt used in this study was the neat asphalt with PG 52-28, and 5 different percentages of gilsonite (0, 3%, 6%, 9%, and 12% of total binder content) were introduced. With the increase of gilsonite content from 0% to 12%, the PG high temperature increased from 52°C to 70°C. However, the PG low temperature also increased from −28°C to −22°C. The results indicated that the addition of gilsonite tends to improve the rutting resistance of asphalt binders, however, increases the tendency for fatigue cracking and low temperature cracking. Adding low content of gilsonite (i.e. 3% within the scope of this study), the modified binder presents improved rutting resistance without any compromise of resistance to low temperature cracking.

Field Evaluation of Crack Sealing of AC Pavements in Alaska

Sealing cracks in asphalt concrete (AC) pavements is a widely used preventive maintenance strategy, and has long been regarded as a necessary annual procedure in most of the United States and other countries. However, many years of careful observations in Alaska have conjectured that certain thermal crack types may sometimes be ignored, i.e., left completely unsealed, for the life of the pavement with no negative effects. This paper presents a recently completed field study on evaluating crack sealing of thermal cracks in older AC pavements in northern and central Alaska. Two distinct types of thermal cracks, differentiated as 1) lesser thermal cracks and 2) major transverse thermal cracks, were formally recognized and assessed using a special thermal crack evaluation (STCE) method. Based on field data collection, analysis, and interpretation, it was concluded that significant maintenance funds can be saved or redirected by not sealing or by reduced sealing of certain types of thermal cracks in AC pavements. The study recommends that lesser thermal cracking receive no maintenance except on delaminating pavements. Maintenance treatment of major transverse thermal cracks can be greatly reduced based on inexpensive, long-term assessments following new pavement construction.

Predictive Model for Nonlinear Resilient Modulus of Emulsified Asphalt Treated Base

Emulsified asphalt treated base (EATB) is a cold mixture of emulsified asphalt (emulsion) and granular material. The resilient modulus (M sub R) of EATB is an essential parameter for both material evaluation and pavement design. Triaxial tests can be used to measure M sub R and capture its nonlinear property affected by the stress state. However, such complicated test is not available for most routine practices. In this study, triaxial tests were conducted to measure M sub R of EATB at different stress states. The effects of influencing factors, such as residual binder contents, aggregate property, dry density and temperature, on resilient property of EATB were also investigated. The nonlinear predictive models were further developed based on the modified universal soil model and all factors and interactions among them were incorporated.

Permanent Deformation Behavior of Alaskan Granular Base Materials

Permanent deformation of the unbound granular base course layer is a major factor that influences the structural response and performance of asphalt pavements. It is one of the pavement distress types that require special attention especially in the springtime in Alaska. In the past few decades, research efforts have focused on the resilient characteristics of base course materials. However, less effort has been spent on the permanent deformation behavior of base materials, especially for cold-region pavements. In Alaska, D-1 base course materials have been commonly used in pavement construction. Under traffic loading, permanent deformation of these materials exhibited significant variations due to seasonal conditions. Base materials’ saturation and weakening due to thawing usually resulted in significant permanent deformation of pavement structures. This paper describes a series of repeated load triaxial tests which were conducted on D-1 base course materials from the central region of Alaska. These tests aimed at evaluating the effects of the stress state, temperature, freeze-thaw cycling, moisture and non-plastic fines content on the permanent strain of laboratory prepared specimens. Test results and analyses showed that the increase of fines and moisture contents, and freeze-thaw cycling significantly increased permanent deformation.