Aggregate Retention in Chip Seal

Chip sealing is a commonly used pavement maintenance treatment that aims to delay pavement deterioration by reducing water infiltration and restoring skid resistance. Loss of aggregate and bleeding are considered the major failure mechanisms in chip seal, and therefore, are the main design criteria for this treatment method. The objective of this study was to evaluate the laboratory and short-term field performance of chip seals prepared with different types of asphalt emulsions, application rates, and aggregate blends. A newly introduced crumb-rubber modified asphalt emulsion was evaluated that allows chip seal installation at the same temperature of a standard emulsion. Types of emulsion included a crumb-rubber modified asphalt emulsion (CRS-2TR), an asphalt rubber (AC20-TR), a polymer-modified emulsion (CRS-2P), and a conventional unmodified emulsion (CRS-2). Application rates were selected based on the Louisiana Department of Transportation and Development (LaDOTD) and the Texas Department of Transportation (TxDOT) specifications, as well as, from the chip seal design method recommended in NCHRP Report 680. A 90-10 aggregate blend of lightweight aggregate (LWA) and rubber aggregate (RA) was also investigated. The loss of aggregate was measured using two laboratory performance tests: the sweep test (ASTM D 7000) and the Pennsylvania Aggregate Retention Test (PART). The strength of adhesion of the four emulsions was also evaluated using the Bitumen Bond Strength (BBS) test. While asphalt rubber was the best performer in terms of aggregate loss, CRS-2P and CRS-2TR performed similarly followed by the conventional emulsion. Results of the BBS test showed a similar rank for the bond strength of the emulsions. It was also observed that the loss of aggregate in chip seal decreased with the increase in application rate. However, incorporation of rubber as aggregate in chip sealing increased the loss of aggregate in the chip seal specimens indicating poor adhesion between the emulsions and the rubber aggregate. Field application of chip seals was also conducted to assess the short-term field performance of chip seal sections. Manual distress survey was conducted on the chip seal sections after three months of construction, after six months of construction, and after 12 months of construction. Field distresses associated with chip seals such as, bleeding, rutting, longitudinal cracking, and transverse cracking were measured and the PCI for each chip seal section was calculated. Results indicated that chip seal sections constructed with CRS-2P and CRS-2TR had performed well whereas the chip seal sections constructed with CRS-2 had the worst performance. Furthermore,

Chip seal construction has received increased attention recently because of rising construction costs and reduced funding for new asphalt pavement projects. The cost and carbon footprint of chip seal applications can be reduced using reclaimed asphalt pavement (RAP). In this paper, the suitability of RAP material for chip seal applications was evaluated through laboratory experiments. Aggregate retention performance and bleeding susceptibility of chip seal samples were investigated using two different aggregate sources and emulsion types. The gradation of the collected aggregates was matched with RAP aggregates using sieving and batching. Modified sweep, Vialit, and pull-off tests were conducted to determine the aggregate retention performance of RAP-modified chip seal samples. To evaluate the effect of RAP on bleeding susceptibility, a Hamburg wheel tracker (HWT) device with a rubber wheel was used. Macrotexture values were measured at specific HWT passes using a laser texture scanner, and the number of passes until chip seal failure was iterated. According to the results, the aggregate retention performance of RAP was found to be comparable with that of natural aggregates when a binder with an appropriate charge was used. RAP material showed higher aggregate retention with the cationic binder compared to the anionic binder. The bleeding test results indicated that RAP is more susceptible to bleeding. Overall, laboratory test results showed that RAP can be a good alternative to virgin aggregate and may reduce the need for virgin binders used in chip seal construction.

Companies in the United States need to mine billions of tons of raw natural aggregate each year. At the same time, billions of scrap tires are stockpiled every year. As a result, replacing the natural aggregate with recycled aggregate is beneficial to the construction industry and the environment. This paper is part of a comprehensive project that developed, and field implemented, a new eco-friendly rubberized chip seal where the mineral aggregate in chip seal is partially or totally replaced with crumb rubber made of recycled tires. This paper presents an extensive study of the environmental impact of using rubber aggregate in chip seal pavement in terms of leaching under different pH conditions, including simulated acid rain. The results are compared with those of conventional chip seal. Leaching from the constituents of chip seal, that is, rubber aggregate and emulsion, was investigated. Two types of rubber and two types of asphalt emulsions were studied. The leaching performance of rubberized chip seal was also investigated. This study revealed that the toxic heavy metals leached from the rubberized chip seal, for pH ranging from 4 to 10, were below that of the EPA drinking water standards. In addition, a significant reduction of heavy metal leaching was recorded when rubber was used with emulsion in the form of chip seal pavement under different pH conditions. Finally, the metal leaching in all types of samples (including rubber, asphalt emulsion, and chip seal) decreased with the increase in pH value.

Asphalt emulsions are a key material used for pavement preservation. Over time, asphalt concrete pavements become oxidized, which can lead to cracking and other surface deterioration. The addition of pavement maintenance treatments, such as scrub seals, chip seals, or fog seals, can rejuvenate the pavement surface as the asphalt emulsion penetrates the oxidized layer of pavement. However, most existing test methods for asphalt emulsions are empirical in nature and do not directly address field performance. With the aim of improving material characterization and testing so as to better capture field properties, this research explored using a bending beam rheometer (BBR) to measure the stiffness and rate of change of the stiffness (or m-value) of asphalt concrete mixture beams treated with asphalt emulsions. There were three components of this study. First, procedures for fabricating BBR beams from field asphalt concrete samples were developed, as the top portion of pavement is often brittle after field aging and oxidation. It was determined that beams could be successfully fabricated with reasonable geometric variability. Second, asphalt concrete BBR specimens compacted and fabricated in the laboratory were sawn and tested, with and without asphalt emulsion, to determine whether the addition of emulsion could be detected. Third, the same emulsion applied to the laboratory fabricated specimens was applied to field mixes to determine the influence of asphalt emulsion on candidate materials for pavement preservation. Overall, beam fabrication was repeatable, and coefficient of variation values for test results were lower for the laboratory compacted plant mix (10 % to 25 %) than for the field mixtures (9 % to 57 %). Emulsion addition increased the m-value and decreased the stiffness of all pavements, which indicates rejuvenation of the asphalt concrete. BBR mixture beams appear to be able to capture the effect of adding emulsion to both lab produced and field specimens, but more types of emulsions, a more comprehensive conditioning regime, and more asphalt concrete mixtures should be examined in order to determine the effectiveness of the measured performance properties of asphalt concrete with the addition of asphalt emulsion.

The paper presents a study on the performance of innovative synthetic lightweight aggregates (SLAs) made from recycled plastic and biomass fly ash when used in road embankment construction on soft soil. It was ascertained that the SLAs behave just like a granular soil with compressibility and shear strength properties comparable to those exhibited by other natural lightweight aggregates. Two different applications were considered. The first deals with the use of the SLAs as back-fill material of compacted aggregate columns to improve soft soil under the embankment. In this case, the behavior of the embankment in terms of stability, settlements and consolidation time was evaluated using the basic concepts of stone columns method. In the second application, SLAs are used as fill material of the embankment constructed in a single stage on a soft soil improved by vertical drains. The performance of this latter solution was compared to that obtained with the adoption of traditional granular materials by a stage construction method. The results obtained allow the conclusion that SLAs can be used as an effective alternative to traditional natural aggregates NAs in either case. The advantages of using the SLAs instead of NAs as fill material of the embankment were analyzed not only in terms of geotechnical features but also in terms of improvement in road constructive aspects such as time, costs and environmental burdens.

The use of lightweight aggregate (LWA) instead of ordinary aggregate may make lightweight aggregate concrete, which possesses many advantages such as lightweight, lower thermal conductivity, and better fire and seismic resistance. Recently the developments of LWA have been focused on using industrial wastes as raw materials to reduce the use of limited natural resources. In view of this, the intent of this study was to apply Taguchi optimization technique in determining process condition for producing synthetic LWA by incorporating waste thin film transition liquid crystal displays (TFT-LCD) glass powder with reservoir sediments. In the study the waste TFT-LCD glass cullet was used as an additive. It was incorporated with reservoir sediments to produce LWA. Taguchi method with an orthogonal array L16(45) and five controllable 4-level factors (i.e., cullet content, preheat temperature, preheat time, sintering temperature, and sintering time) was adopted. Then, in order to optimize the selected parameters, the analysis of variance method was used to explore the effects of the experimental factors on the performances (particle density, water absorption, bloating ratio, and loss of ignition) of the produced LWA. The results showed that it is possible to produce high performance LWA by incorporating waste TFT-LCD glass cullet with reservoir sediments. Moreover, Taguchi method is a promising approach for optimizing process condition of synthetic LWA using recycled glass cullet and reservoir sediments and it significantly reduces the number of tests.

Comparative life cycle assessment of chip seal preventive maintenance techniques: Cost and environmental implications

Chip seals are mostly designed on the basis of empirical methods, which fail to account for the effect of microstructural factors (i.e. percent embedment of aggregates and aggregate shape) on chip seal performance. Two-dimensional (2-D) viscoelastic Finite Element (FE) analyses coupled with laboratory-based sweep tests as per ASTM D7000 were performed to evaluate the impact of such factors on the performance of chip seals. The factors considered in this study were percent embedment, two different aggregate shapes (cubical and flaky), temperature, and aggregate application rates. The 2-D FE models were developed from actual images of the chip seal specimens with cubical and flaky aggregates. The analyses revealed that the maximum tensile strain at the aggregate-binder interface for the chip seals with cubical aggregates follows an asymptotic trend after the percent embedment level of 50%. The trend was not evident in the case of the chip seals with flaky aggregates. The FE simulations also indicated that the chip seals with cubical aggregates outperformed the chip seals with flaky aggregates, which was also observed through the laboratory tests. Furthermore, it was determined that excess aggregate application rates, i.e. higher than that of the optimum design rates, are detrimental to the chip seal performance.

This paper presents the findings from a study conducted to develop a simple quantitative test method to characterize the stability of asphalt emulsions. The proposed method uses electrokinetic techniques to determine the rate at which an asphalt emulsion breaks when subjected to an electric field. The test method was used with different types of emulsion as well as emulsions that were modified by further dilution or mechanical agitation. Results demonstrate that the parameters obtained from these tests were repeatable and different for different types of asphalt emulsions. Results also demonstrate that for a given type of emulsion the test method is sensitive to factors such as water content and partial breaking due to mechanical agitation. The proposed electrokinetics-based method and concomitant parameters provide a repeatable, rapid, and quantitative method by which to characterize asphalt emulsions.

This paper presents properties of new synthetic lightweight aggregates (SLAs), made of plastic and fly ash, and their implications for use as aggregate in pavements systems. These aggregates are manufactured through a thermal process that combines and co-extrudes plastic and coal fly ash. The plastic acts as a matrix material that binds and encapsulates the fly ash particulates. In this study, index and compression properties are presented for SLAs made with different plastic types. All aggregates have an approximate fly ash to plastic ratio, by weight, of 80:20 and use fly ash with carbon contents of 15% to 30%. Index properties presented for the various SLAs include gradation, specific gravity, and water absorption capacity. A series of one dimensional compression tests, at moderate and elevated stresses, were performed to compare the compression behavior of SLAs with that of traditional aggregate (sand). The results shows that SLAs have relatively substantial elastic deformation and rates of secondary compression but also exhibit substantial rebound upon unloading when compared to sand. However, at elevated stresses, the rate of secondary compression for both the SLAs and sand approach similar values, with some SLAs actually exhibiting a slower rate of secondary compression. Overall, the compression results show that SLAs will have advantages (e.g., lightweight, stress absorption) and disadvantages (e.g., excessive deformation ) over the use of traditional granular materials in pavement systems.

The objective of this study is to investigate how moisture content affects the stiffness of a gravelly-sandy soil stabilized with asphalt emulsion, considering different types of emulsion (medium- and slow-setting) and modified compaction energy. Dynamic triaxial tests were carried out to determine the stiffness of specimens at different moisture contents, considering the dry and wet branches of the compaction curve, all stabilized with 2% asphalt emulsion. The influence of moisture content and emulsion type was assessed using robust analysis of variance (ANOVA), allowing the evaluation of statistical significance and the interaction between factors. The results showed that the stiffness of the stabilized soil is strongly influenced by moisture content, with a peak value observed near the optimum moisture (~8.2%). The slow-setting (SS) emulsion achieved the best performance, reaching 938.94 MPa, representing a 452.32% increase compared to the untreated soil. The medium-setting (MS) emulsion also produced a significant stiffness gain (375.29%). Statistical analysis indicated that emulsion type was the most influential factor (Q = 1747; p = 0.001). This study contributes to the literature by experimentally and statistically demonstrating how moisture content and emulsion type affect the stiffness of stabilized soils.

Chip seals generally deteriorate as a result of asphalt oxidation, wear and polishing of aggregates, bleeding, and raveling (loss of aggregates). In this study, two major environmental effects on chip seal performance, freeze-thaw, and asphalt aging were investigated based on laboratory tests and field distress survey. For freeze-thaw evaluation, laboratory chip seal samples were prepared for 18 combinations (6 aggregates X 3 asphaltic materials). A simple freeze-thaw protocol was developed and evaluation of freeze-thaw effect on aggregate types reveals that both the precoated and uncoated expanded shale lightweight aggregates perform comparatively very well against freeze-thaw. Evaluation of freeze-thaw effect on asphaltic material types reveals that CRS-2P, an emulsion performs significantly better than hot asphalts, namely PAC-15 and AC20-5TR. For aging evaluation, asphaltic materials were extracted from 15 (5 aggregates X 3 asphaltic materials) field test sections and increase in stiffness due to aging were determined using a dynamic shear rheometer. For each of the five aggregates, CRS-2P shows the lowest G*/sinδ, indicating minimum field aging susceptibility among the three asphaltic materials while AC20-5TR shows slightly higher G*/sinδ than PAC-15, indicating maximum field aging susceptibility. Overall field distress ratings of the CRS-2P sections (sum of distress ratings of all the CRS-2P sections) are better than those of PAC-15 and AC20-5TR. The overall distress ratings of PAC-15 sections are better than overall distress ratings of AC20-5TR. In case of aggregate types, precoated expanded shale lightweight test sections performed the best, while expanded clay lightweight sections performed very poorly. Both freeze-thaw and asphalt aging tests closely reflect field performances and it can be concluded that the freeze-thaw and aging performances can be used as effective tools for predicting long term chip seal performances.

Chip seal is a pavement surface treatment, consisting of a combination of asphalt binder or emulsion and a layer of aggregate compacted on top of a pavement substrate. Raveling and bleeding are the two major distresses that affect the performance of chip seals. Studies have shown that these distresses can be related to the embedment depth, among a few factors. Embedment depth is the depth that rock is lodged into binder and is a key parameter that significantly affects the performance of chip seals. Currently, embedment depth is evaluated by pulling out the rock from the binder (often by a plier) and visually estimating the percentage of embedment. However, this method is subjective and does not provide accurate and reliable results. This study evaluated the use of laser texture scanner as quality control of chip seal construction. The mean profile depth (MPD), which is inversely related to percent embedment in the field, was measured and used to correlate with chip seal performance for raveling and bleeding. It was found that MPD is sensitive to compaction efforts of chip seals. The shoulder MPD value of chip seals after sweeping should be at a minimum of 0.150 in. to prevent bleeding from happening for the traffic volume experienced by the selected field project. When MPD in the wheelpath drops below 0.05 in., bleeding has occurred. More field experiments are needed to cover different construction practices and conditions to validate the findings from this study.

When applied at the right time, pavement preservation treatments can restore a smooth, safe driving surface while delaying the cost for rehabilitation, resulting in reduced life cycle cost. The purpose of this study was to evaluate the performance of three preventive maintenance treatments applied to US 301 in Sussex County, Virginia, to extend pavement life. This paper documents the installation of a Cape seal application of fiber-reinforced chip seal (with microsurfacing on top) over an existing asphalt pavement. A performance comparison was made with more conventional surface treatment options: regular Cape seal (modified single chip seal with microsurfacing), and microsurfacing without a chip seal. Five years after the treatment application, a visual survey complemented by automated distress data from the Virginia Department of Transportation Pavement Management System showed that the section with fiber-reinforced chip seal and microsurfacing performed well with very little reflective cracking. The modified single chip seal with microsurfacing (i.e., regular Cape seal) also performed well, but reflective cracking was higher compared with the fiber-reinforced section. The control section (microsurfacing only) showed extensive cracking after 5 years. This study showed that pavement preservation activities such as the use of fiber-reinforced chip seal with microsurfacing and modified single seal with microsurfacing improved both the pavement condition and the surface characteristics in a very cost-effective manner (based on initial cost). However, long-term performance data are needed to evaluate the benefit/cost of each treatment.

Fourteen Texas SPS-3 test sites were studied to determine the effectiveness of preventative maintenance treatments. These sections were built on four highway classifications (IH, US, SH, and FM) in different climates and with different levels of traffic and subgrade support. Almost all 14 SPS-3 sites were given preventative maintenance treatments (thin overlay, slurry seal, crack seal, and chip seal) in Fall 1990. The distress score concept used by the Texas Department of Transportation (TxDOT) was adopted in this study to judge the effectiveness of preventative maintenance treatments. TxDOT has used this concept since the early 1980s, though the utility factors have been revised few times. The distress score quantifies the visible surface wear due to traffic and environmental influences. Only very few sections experienced premature failures on the SPS-3 sites in Texas. In many cases, superior underlying pavement conditions have been found. The chip seal has the most sites in which it is rated the best pe...