Hosin David Lee

Effects of Recycled Materials on Long-Term Performance of Cold In-Place Recycled Asphalt Roads

Within three to five years following construction of asphalt pavements, reflected cracks may be observed, one of the primary forms of distress in hot-mix asphalt overlays of flexible pavements. Reflected cracks affect ride quality when rolled down and allow water to penetrate into the pavement and the base, causing the asphalt mix to deteriorate and the base to soften. Consequently, the service life of pavements is reduced. Cold in-place recycling (CIR) provides an economical rehabilitation method that mitigates crack reflection by pulverizing the asphalt pavement surface, thus destroying the old crack pattern in the recycled layer. While the performance of recycled roads is generally good, there is some inconsistency. Several years after recycling, some roads are in excellent condition, while more cracking and rutting is observed on other roads. These differing behaviors can be observed on roads constructed in the same county by the same contractor in the same construction season. Thus, the difference in performance is probably not from such factors as weather, equipment, contractor experience, and construction procedures. Rather, other factors more prominently affect pavement performance, such as recycled pavement age, traffic volume, support conditions, and aged engineering properties of the CIR materials. This paper discusses a partially completed investigation to identify how aged engineering properties of the CIR materials and other factors affect pavement performance. A selection matrix consisting of 18 sample roads was developed based on previous study. These 18 sample roads represent various ages (young/medium/old), traffic volumes (high/medium/low), and support conditions (strong/weak) in a geographically balanced sampling in Iowa. Pavement condition index (PCI) ratings were collected using an automated pavement distress digital image collection and analysis system. Engineering properties of CIR materials (density, compressive strength, indirect tensile strength, resilient modulus, and asphalt and aggregate content) will be examined through field and lab tests. Statistical analysis will be conducted to describe the relationships between pavement performance and the prominent factors. It is expected that the conclusions and recommendations from this study can be used to improve the performance of future CIR projects in Iowa and other states.

Long-Term Field Performance of Cold In-Place Recycled Roads in Iowa

Cold in-place recycling (CIR) is one of the most effective methods to rehabilitate asphalt pavements. In fact, most CIR roads have performed well at low cost in Iowa since the first CIR road was constructed in 1986. However, some CIR roads have reached failures earlier than their expected design lives because there is no design standard for designing CIR roads with a limited amount of past performance information. Some of the most prominent problems seemed to have come from selecting CIR in areas where there are poor subgrades. Therefore, it is critical to collect CIR performance data along with Falling Weight Deflectometer (FWD) data in order to develop performance models. The main purpose of this paper is to document that effort. The performance models were developed on the basis of historical data collected from CIR roads in Iowa. First, an inventory of CIR roads was created which includes construction information, subgrade and base characteristics, and traffic levels. In consideration of pavement age, level of traffic and subgrade condition, twenty-six test sections were selected from the inventory of CIR roads and pavement surface distress surveys were conducted on these roads using an automated image collection system (AICS). Distress data were then compiled to compute Pavement Condition Index (PCI) for each test section. FWD data were collected from each test section to determine its relative soil support condition. Finally, to determine their long-term performance, the PCI values were plotted against pavement age for each group of pavements categorized by their soil support conditions and traffic levels. Overall, it can be concluded that the CIR roads in Iowa, all under traffic level of AADT of 2,000, have performed very well and predicted to last up to 25 years before reaching the poor condition (PCI = 40) when the pavements are to be rehabilitated. The CIR roads with a good subgrade support, however, are predicted to last up to 35 years.

Development of Moisture Loss Index Based on Field Moisture Measurement using Portable Time Domain Reflectometer (TDR) for Cold In-place Recycled Pavements

The practice of asphalt pavement recycling has grown rapidly over the decade, one of which is the cold in-place recycling with the foamed asphalt (CIR-foam) or the emulsified asphalt (CIR-emulsion). Particularly, in Iowa, the CIR has been widely used in rehabilitating the rural highways because it significantly increases the service life of the existing pavement. The CIR layer is typically overlaid by the hot mix asphalt (HMA) to protect it from water ingress and traffic load and obtain the required pavement structure and texture. Most public agencies have different curing requirements based on the number of curing days or the maximum moisture contents for the CIR before placing the overlay. The main objective of this study is to develop a moisture loss index that the public agency can use to monitor the moisture content of CIR layers in preparation for a timely placement of the wearing surface. First, the moisture contents were measured in the field using a portable time domain reflectometry (TDR) device. Second, the weather information in terms of rain fall, air temperature, humidity and wind speed was collected from the same location. Finally, a moisture loss index was developed as a function of initial moisture content, air temperature, humidity and wind speed. The developed moisture loss index based on the field measurements would help the public agency to determine an optimum timing of an overlay placement without continually measuring moisture conditions in the field.

Impacts of Laboratory Curing Condition on Indirect Tensile Strength of Cold In-Place Recycling Mixtures Using Foamed Asphalt

Cold in-place recycling (CIR) layer is normally covered by a wearing surface in order to protect it from water ingress and traffic abrasion while obtaining the required pavement structure and texture. Currently, various agencies have differing moisture content requirements prior to placement of the wearing surface based either on the total moisture content in the mixture or the increase in moisture content from the pavement prior to recycling. The industry standard for this curing time is 10 to 14 days or a maximum moisture content of 1.5 percent. The main objective of this research is to develop technically sound methods to identify minimum in-place CIR properties necessary to permit placement of the HMA overlay through the laboratory curing process. Indirect tensile strength and moisture content of CIR mixtures were measured from the specimens with two different curing procedures: uncovered and semi-covered. Based upon the limited test results, both the length of the curing time and the moisture content significantly affect the indirect tensile strength of the CIR mixtures. It should be noted that, given a similar moisture level, the longer curing period would produce the higher indirect tensile strength.

Influences of Binder and RAP Temperatures and Foaming Water Content on Cold In-Place Recycling Mix Design Process Using Foamed Asphalt

The Cold-In-Place Recycling using foamed asphalt (CIR-foam) is becoming more common in rehabilitating the existing asphalt pavements due to its cost effectiveness, the conservation of paving materials, and its environmental friendliness. The main objective of this research is to identify the influences of binder and RAP temperatures and foamed water content on the wet indirect tensile strength. Although the optimum foaming water content and temperature can be found through the experiment which would produce the highest expansion ratio and longest half-life, it may not necessarily produce the optimum foamed asphalt mixture. Therefore, these asphalt foam design parameters such as foaming water content and binder temperature were considered as part of the foamed asphalt mix design process which is to determine the optimum foamed asphalt content for varying RAP temperatures. Based on the limited test data collected from Johnson County in Iowa, RAP temperature was found to have a significant impact on the wet indirect tensile strength whereas either foamed asphalt temperature of foaming water content did not significantly affect the wet indirect tensile strength. It is recommended that the amount of foamed asphalt content should be adjusted depending on the existing pavement temperature during CIR construction.

Effects of High Reclaimed Asphalt-Pavement Content on the Binder Grade, Fatigue Performance, Fractionation Process, and Mix Design

AbstractThe primary objective of this research is to examine the effects of reclaimed asphalt pavement (RAP) amounts and fractionation methods on the mix design of high-RAP content surface mixes. T...

Laboratory and Field Evaluation of HMA with High Contents of Recycled Asphalt Pavement

In an attempt to conserve natural resources such as materials and energy there is a trend to increase the amount of recycled asphalt pavement (RAP) in asphalt pavement construction. Currently in Iowa, the amount of RAP materials allowed for the surface layer is limited to 15% by weight. The objective of this paper is to develop quality standards for inclusion of RAP content higher than 15% in asphalt mixtures. To determine if the higher percentage of RAP materials greater than 15% can be used in Iowa’s state highways, three test sections with target amounts of RAP materials of 30%, 35% and 40% were constructed on Highway 6 in Iowa City. To meet Superpave mix design requirements for mixtures with high RAP contents, it was necessary to fractionate the RAP materials. Based on an extensive sieve-by-sieve analysis of RAP materials, the optimum sieve size to fractionate RAP materials was then identified. Three test sections with actual RAP contents of 30.0%, 35.5% and 39.2% were constructed and the average field densities measured from the cores were 95.3%, 94.0%, and 94.3%, respectively. Field mixtures were compacted in the laboratory to evaluate moisture sensitivity using a Hamburg Wheel Tracking Device and rut depths after 20,000 passes were less than 3 mm for all three test sections. The binder was extracted from the field mixtures from each test section and tested to identify the effects of RAP materials on the performance grade of the virgin binder. Based on Dynamic Shear Rheometer and Bending Beam Rheometer tests, the virgin binders (PG 64-28) from test sections with 30.0%, 35.5% and 39.2% RAP materials were stiffened to PG 76-22, PG 76-16, and PG 82-22, respectively. Finally, a condition survey of the test sections was conducted to evaluate their short-term pavement performance.

Determining the Optimum Content and Stirring Time of Emerging Dry Polymer for Asphalt Using Rotational Viscometer, Dynamic Shear Rheometer, and Atomic Force Microscopy

During the past decades, styrene-butadiene-styrene (SBS) triblock copolymer has been used to produce Polymer-Modified Asphalt (PMA) to make asphalt pavements more resistant to both rutting at a high temperature and cracking at a low temperature. However, the process of adding SBS copolymer to asphalt requires additional equipment such as high-shear mixing equipment, and the produced PMA is required to be stored in a separate tank. To overcome these limitations associated with the production handling, the pelletized SBS-based compound was developed. It can be added to the pugmill using a dry process together with asphalt and aggregates at the asphalt plant. The main objective of this study is to identify the proper melting time for the pelletized SBS-based compound in asphalt and to determine the optimum amount of the pelletized SBS-based compound. In this study, to characterize the pelletized SBS-based compound, atomic force microscopy (AFM), a dynamic shear rheometer (DSR), and a rotational viscometer (RV) were used. Based on the laboratory test results, optimum quantity and mixing time of pelletized SBS-based compound were identified.