Mechanistic performance evaluation of chip seal

Slag as waste material of steel-making process has similar characteristics with aggregate that has been widely used in pavement construction. The use of slag as chip seal aggregate to provide skid resistance needs to be analyzed. In this laboratory study, the chip seal samples are made using steel slag and natural aggregate. The bonding materials used are asphalt and epoxy resin. Skid resistance tests for all chip seal samples and also hot rolled sheet pavement without chip seal application are performed using the Portable British Pendulum Tester. The results show the variations of chip seal aggregate weight are inconsistent. The natural aggregate used as chip seal material could produce high skid resistance value of 10.3% higher than that using steel slag. Also the skid resistance of chip seal with the ALD 3 mm are not significantly different with that of ALD 6 mm. Similar results occur on the skid resistance of chip seals using epoxy resin and asphalt. Keywords: steel slag, waste material, chip seal, the Portable British Pendulum Tester, skid resistance.

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.

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,

Evaluation of the causal effect of the surface performance-graded (SPG) specification for chip seal binders on performance

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.

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.

Over time, new pavements deteriorate due to the effect of traffic loads and the environment. If appropriate treatments are applied during the early stages of deterioration, it is possible to extend the service life of the pavement without incurring in costly rehabilitation or reconstruction activities. Chip seals are preservation treatments that can help protect the pavement structure, reduce the rate of pavement deterioration, improve skid resistance, and address minor surface problems. As part of the National Center for Asphalt Technology Pavement Preservation Study, chip seal test sections were placed in a low traffic volume road (Lee County Road 159) in Auburn, Alabama. The location consists of a two-lane county road that provides dead end access to a quarry and an asphalt plant, resulting in a high percentage of heavy loads. At the time of treatment, the existing pavement was 14 years old and consisted of a 5.5 in. hot-mix asphalt layer over a 6.0 in. granular base. Treatments were applied in the summer of 2012 and have been in service for approximately 4.5 years. During this time, cracking, roughness, rutting, and macrotexture data were collected weekly to evaluate pavement performance. The results determined that the performance of the treated sections is highly dependent on the initial condition of the pavement, particularly the percentage of area cracked. Pavements that are treated while still in good condition tend to remain in that category for a longer time. Macrotexture may also be used to evaluate the functional performance of the chip seals.

Chip seal, as the most widespread pavement preventive treatment, is regularly applied on existing pavements that are still in good structural condition to increase the pavement serviceability. The most effective key parameter on chip seal performance is binder application rate, which directly governs chip seal distresses such as bleeding and raveling. How this rate is calculated mainly depends on the value of least dimension (LD) of aggregate particles. However, the available measuring methods of LD value are slow, laborious, and subjective. This study presents the development of a new high-speed line laser scanner (LLS) prototype to measure the LD value of particles more quickly and accurately. The LD values of aggregate particles were also measured using a digital caliper and considered as control data. The repeatability and reliability of the developed LLS prototype were evaluated, as well as the speed of the prototype in calculating the LD values of 100 aggregate particles. The findings indicate that the measurements of the developed prototype are highly correlated with those of the caliper. In addition, it was found that the developed prototype is efficient and capable of calculating the LD values of several particles simultaneously.

Low-volume roads require cost-effective maintenance methods to minimize the amount of money spent on them while maximizing the engineering properties required to furnish the required levels of service. Skid resistance is an engineering property that is important for any road. Because chip sealing is a tried-and-true pavement preservation method, it often is used as the primary maintenance treatment of these roads. Unfortunately, chip seals are prone to flushing in the wheelpaths, which creates a loss of skid resistance. The economics of replacing strip sealing using conventional chip seal in the wheelpaths with the ultra-high-pressure watercutter used in New Zealand are explored. An economic analysis of typical low-volume roads on the basis of case studies found in Texas is conducted to determine the life-cycle costs of using both options on each case study project. The study applies the FHWA pavement life-cycle cost methodology, and the results are reported on a net-present-value basis to permit assessment of both methodologies. The analysis is conducted on two levels. First, a traditional deterministic life-cycle cost analysis is performed, and that is followed by a stochastic analysis of life-cycle cost using a Monte Carlo simulation. It is concluded that the watercutter is an economically viable alternative to strip sealing with the benefit of restoring the macrotexture without exacerbating the condition that caused the loss of skid resistance in the first place. It also allows the desired engineering objective to be achieved without additional consumption of asphalt binder or aggregate, thus making an environmentally sustainable alternative as well.

Numerical Simulation of Tire-Pavement Interaction

To preserve the existing asphalt pavement and extend its service life, various preventive maintenance methods, such as chip seal, slurry seal, fog seal, and microsurfacing, have been commonly applied. Sand fog seal is one of such maintenance methods, which is based on the application of bitumen emulsion and sand. Thus, its performance is largely dependent on the properties of the bitumen emulsion and sand. This study aims to develop an improved sand fog seal method by using waterborne epoxy resin as an emulsion modifier. To this end, both laboratory tests and field trials were conducted. In the laboratory, the wet track abrasion and British pendulum test were performed to determine the optimum sand size for the sand fog seal, and the rubbing test was carried out to evaluate the wearing resistance of the sealing material. In the field, pavement surface regularity before and after the sand fog seal application was measured using the 3 m straightedge method, and the surface macrotexture and skid resistance were evaluated with the sand patch method and British pendulum test, respectively. The laboratory test results indicated that the optimum sand size range is 0.45–0.9 mm, and the sand fog seal with waterborne epoxy resin showed good wearing resistance and skid resistance. The field test results verified that both the pavement texture and skid resistance were substantially improved after sand fog sealing.

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.

Influence of pavement surface macrotexture on pavement skid resistance

The chip seal refers to the technology of using the layer-pave method to directly spread asphalt binder and crushed stone with single particle size, and then form a thin layer after rolling. The asphalt in the chip seal is covered with a continuous film on the surface of the underlying layer, so it can effectively prevent the road surface from seeping underwater and reduce road water damage; it has a good follower deformation ability and can adapt to the relatively poor underlying layer conditions; The stone in the gravel seal is directly exposed on the road surface, so it has excellent anti-sliding performance and abrasion resistance. Fiber seal is an upgraded version of the chip seal. It refers to the use of synchronous fiber seal construction equipment, spraying two layers of asphalt cement and a layer of glass fiber at the same time, and then spread the crushed stones on it, forming new wear after rolling. Layer or stress-absorbing layer (SAMI) is a rapid pavement maintenance technology. Compared with the crushed stone seal layer, the fiber seal has a better ability to prevent reflection cracks due to the addition of glass fiber. This chapter mainly introduces the material, construction, construction equipment, construction process, use conditions, quality inspection and acceptance of chip seal and fiber seal.

A fluid mechanics explanation of the effectiveness of common materials for respiratory masks