Chip Seal Research Articles

Performance of Flexible Pavement Maintenance Treatments in the Long-Term Pavement Performance SPS-3 Experiment

A study was conducted to assess the relative performance of different flexible pavement maintenance treatments, including the influence of pretreatment condition and other factors. The data used in the study were drawn from the Long-Term Pavement Performance Studies' Specific Pavement Studies (SPS) SPS-3 experiment. The maintenance treatments used in the SPS-3 experiment are thin overlays, slurry seals, crack seals, and chip seals. The initial and long-term effects of the maintenance treatments on international roughness index (IRI), rutting, and cracking were analyzed, as were the influences of time, truck traffic, pretreatment condition, and climate. Thin overlays were found to be the most effective of the treatments studied, followed by chip seals and slurry seals. Crack sealing did not demonstrate any beneficial initial or long-term effect with respect to IRI, rutting, or cracking.

Otta Seals and Gravseals as Low-Cost Surfacing Alternatives for Low-Volume Roads: Experiences in South Africa

The geology of the northeastern part of the province of KwaZulu–Natal, South Africa, is predominantly alluvial with vast deposits of sands. Suitable gravel sources are hard to come by, which results in high graveling and regraveling costs brought about by long haul distances and accelerated gravel loss. Most gravel roads carry fewer than 500 vehicles per day of which less than 10% are heavy vehicles. The high cost of regraveling has led to consideration of upgrading such roads to surfaced standard, even though traffic volumes do not justify upgrading. Traditional chip seals are expensive and cannot be economically justified on roads that carry fewer than 500 vehicles per day. The KwaZulu–Natal Department of Transport is actively involved in efforts to identify cost-effective alternative surfacing products for low-volume roads. Field trials were conducted with Otta seals and Gravseals, which have been used successfully in other countries, as low-cost surfacing products for low-volume roads. The Otta seal is formed by placing graded aggregates on a relatively thick film of soft binder that, because of traffic and rolling, works its way through the aggregates. Gravseal consists of a special semipriming rubberized binder that is covered by a graded aggregate. Both Otta seals and Gravseals provide relatively flexible bituminous surfaces suitable for low-volume roads. Cost savings are derived mainly from the broad aggregate specifications, which allow for the use of marginal materials.

Solution for Distressed Pavements and Crack Reflection

It is commonly accepted that cracks in aged asphalt pavements will reflect through seal coat and overlay applications. Pavement fabric placed under asphalt concrete overlays will slow this crack reflection, but not stop it. Nineteen years of experience working with the same fabric under a double chip seal has shown that using a modified technique, developed through trial and experimentation, adds substantial pavement life at a reduced cost over typical methods of repair used in the industry. In addition, pavement deterioration due to oxidation and stripping has been eliminated because air and water are unable to penetrate the surface. The subgrade dries out and regains its original strength, minimizing deflection under traffic loadings. This method reduces crack reflection by more than 90% over alternate methods. The reduction is due mainly to a regaining of the subgrade strength along with an increase in the flexibility of the surface through the use of a higher percentage of oil in the total mix. The most surprising aspect of this process is that alligatored pavement can be repaired without having to remove and replace the damaged pavement.

Determination of the Effectiveness of Preventative Maintenance Treatments

The main goal of a pavement maintenance program is to provide timely maintenance and promote cost-effectiveness in the pavement life cycle. The success of a maintenance program relies on accurate information on the relative performance of treatment methods. LTPP's SPS-3 test sections were built in 1990 to address the cost-effectiveness of various maintenance treatments such as a thin overlay, slurry seal, crack seal, and chip seal. Two SPS-3 sites on US175 and US62 were selected to evaluate the cost-effectiveness of these four treatments. TxDOT's distress collection and rating systems were applied to judge the effectiveness of these four treatments. Both the TxDOT system and the historical distress data were used in this study. Distress data collection criteria are slightly different between TxDOT and LTPP, which result in different distress scores. Based on TxDOT distress survey results from Summer 2000, it was found that the ride and distress scores yield a similar trend, in that the best performer is a thin overlay. The next best treatments are a slurry seal and chip seal. The crack seal yielded the lowest (worst) distress and ride scores. Although the distress score for a thin overlay is higher (better) than for a chip seal, the average difference is only about nine points. LTPP distress data shows that the chip seal is the best performer. Sound underlying structural condition is one of the keys to the success of preventative maintenance treatments. With this condition on US175 and US62: all maintenance treatments lasted for 10 years. Among the chip seal, slurry seal, and 25 mm overlay, chip seal is the most cost-effective alternative.

Performance of Louisiana’s Chip Seal and Microsurfacing Program, 2002

A 5-year field performance study was conducted of the 1995–1996 Chip Seal and Microsurfacing projects with a summary of data generated by the Louisiana Department of Transportation and Development’s pavement management group. The pavement management data set includes performance indicators such as the international roughness index, crack analysis, rut depth, and ground-penetrating radar thickness. A subjective survey designed for maintenance surfacing was developed and used on this same set of projects. The pavement condition rating was examined from the point of pretreatment and annually until spring of 2001. The survey suggests that treatments will improve a pavement’s initial condition, but no conclusion can be drawn on the effect on pavement condition index (PCI) over time compared with untreated pavements, as all pavements’ PCI curves are similar and are independent of PCI before treatment. General observations for chip seal projects are as follows: the median PCI was 75 after 52 months with a significant reduction in cracking; 20% of the projects showed moderate to heavy bleeding; rutting was not evident; and measurement for skid resistance was very good. For a life expectancy of 5 years, the equivalent annual cost (EAC) of a chip seal is approximately 27 cents a year. For micro-surfacing projects, the median PCI of microsurface sections is approximately 85 after 60 months of service with significantly fewer cracks detected after treatment. Projects with 0.5-in. initial rut showed substantial reduction after treatment. The friction numbers (FN) for smooth tire are in the low teens to low thirties on 50% of the projects. The lower numbers are attributed to a combination of the use of limestone and high asphalt content. Sandstone sections exhibited FNs in the 50s. For a life expectancy of 6 years, the EAC is about 49 cents a year.

Field Evaluation of Pavement Surface Treatments

The application of surface treatments (chip seals) is a highly economical highway maintenance option. Surface treatments offer protection against deterioration caused by traffic and weather. There are several material types used in surface treatments. A few years ago, the Wyoming Department of Transportation (WYDOT) initiated a comprehensive field experiment to determine the effect of materials selection on the field performance of surface treatments. Twenty-three test sections were constructed as part of this experiment. The materials used in the experiment represented the most widely used aggregates and binders in the state of Wyoming. Monitoring these sections over five years indicated that surface friction is affected by aggregate type alone while transverse cracks are predominately affected by the choice of the binder. Other interesting findings are described in the paper.

Pavement Preventive Maintenance: Key to Quality Highways

Highway funding is inadequate to maintain current road conditions under traditional maintenance and rehabilitation policies. Through a preventive maintenance program, pavements can be maintained in a cost-effective manner leading to a better pavement quality at lower total costs. Preventive maintenance is a program strategy that arrests light deterioration, retards progressive failures, and reduces the need for routine maintenance activities. The objective of this strategy is to extend the pavement’s functional life by applying treatments before the pavement deteriorates to a condition requiring a corrective treatment, such as a structural overlay. An effective strategy would feature a combination of treatments, such as periodic crack treatment followed by chip sealing. Several highway agencies have used preventive maintenance strategies successfully for both low-volume and high-volume roads. Flexible-pavement preventive maintenance treatments include fog seal, chip seal, slurry seal, microsurfacing, crack treatment, and thin hotmix overlays. The selection of a preventive maintenance treatment should be based on the condition of the existing pavement, traffic volume, and environmental conditions. Other factors include experience, budget constraints, and political reality. The Strategic Highway Research Program demonstrated that preventive maintenance is cost-effective for roads in the National Highway System. FHWA sponsored an implementation project to develop a preventive maintenace workshop and assist states with evaluation of preventive maintenance treatments. The workshop was presented in more than 20 states.

Effectiveness of Maintenance Treatments of Flexible Pavements

To achieve effective pavement maintenance, the life expectancy and timing of treatment applications need to be determined. The Long Term Pavement Performance (LTPP) program includes the Specific Pavement Study-3 (SPS-3), which focuses on this subject. The treatments applied are chip seals, crack seals, slurry seals, and thin overlays. In studying the life expectancy it is not feasible to wait for all the sections in the experiment to fail. Thus, there is a need to determine the life expectancy while making efficient use of the available data collection funds. Survival data analysis is a statistical technique that meets this need by accounting for the portion of the sections in which the exact time the treatment lasted is not known. The application of this technique to flexible-pavement maintenance is presented. In addition, some results of the LTPP SPS-3 experiment are presented to the highway community. The focus is on the LTPP Southern Region. The results showed that the probability of failure was two to four times higher for the sections that were in poor condition at the time the treatment was applied than those sections that were in better condition. The median survival times for thin overlays, slurry seals, and crack seals were 7, 5.5, and 5 years, respectively. The chip-seal sections had not yet reached the 50 percent failure probability after 8 years of the SPS-3 experiment. Accordingly, chip seals appear to have outperformed the other treatments investigated in this study in delaying the reappearance of distress.

Design of Rehabilitation Treatments for New Zealand’s Thin-Surfaced Unbound Granular Pavements

Most thin-surfaced unbound granular pavements are rehabilitated by overlaying with an unbound granular material and surfaced with a chip seal (thin-surfacing). The unbound granular overlay thickness is the difference between the total granular thickness required for future traffic and the granular thickness required for past traffic as determined from the design chart. However, where there are signs of shoving or other indications of a weak and degraded aggregate base layer then a smoothing treatment will not be adequate. For this situation the appropriate rehabilitation is either in situ stabilization (to improve the strength of the aggregate base material) or to cover with a minimum thickness of unbound granular material (determined from the thickness design chart by assuming the existing pavement acts as a subbase). This method of unbound granular overlay design has resulted in significant cost savings over the past 20 years in rehabilitation treatments for New Zealand roads, as the existing pavement has been fully utilized. In 1995 New Zealand adopted the Austroads (the Association of State, Territory and Federal Road and Traffic Authorities in Australia) procedures for pavement design. The Austroads procedures encourage the use of mechanistic procedures for pavement design. By using the same assumptions as the design chart method for determination of granular overlay depths, a mechanistic design procedure for rehabilitation treatments was developed. This method produces comparable results and has the advantage of being able to design a range of rehabilitation treatments.

Optimum Decision Policy for Management of Pavement Maintenance and Rehabilitation

An effective practical decision policy has been developed for use in the selection of an optimum maintenance and rehabilitation program. Its main objective is the optimization of pavement condition under constrained budgets. The developed policy utilizes a discrete-time Markovian model with five condition states labeled a, b, c, d, and f. State a represents pavements in excellent condition, and State f indicates pavements in bad condition. Several decision options have been introduced based on either maximizing the proportion of “good” pavements or minimizing the proportion of “bad” pavements. State probabilities at some desired future time have been used as the main objective functions in the development of optimum maintenance and rehabilitation programs. The unknown variables in these programs are those representing improvements to pavement condition through implementation of maintenance and rehabilitation work. The resulting optimum programs are nonlinear in form, and therefore the penalty function method with functional evaluations has been successfully used to yield optimum solutions. The optimum solution to a particular program defines the type and extent of maintenance and rehabilitation work required for annual or biennial implementation. Pavement maintenance is mainly defined as routine maintenance consisting of filling cracks, patching potholes, and other applicable techniques such as chip seal coat or slurry seal. Pavement rehabilitation is defined as major rehabilitation actions to include resurfacing (overlay), resurfacing with partial reconstruction (localized reconstruction), and complete reconstruction applied to pavements in States c, d, and f, respectively.

Framework for Selecting Effective Preventive Maintenance Treatments for Flexible Pavements

Preventive maintenance techniques are considered useful in extending the life of a pavement if applied at the right time. Discussed here is a framework for a process that can be used to select the proper maintenance strategies for different distress types in asphalt pavements, depending on traffic level and environment. Maintenance treatments addressed include only crack seals, fog seals, slurry seals, microsurfacings, chip seals, thin asphalt concrete overlays, and other thin surface treatments. Types of distress considered include roughness, rutting, fatigue cracking, longitudinal cracking, raveling, weathering, and bleeding. Decision trees, based on the authors' experiences, are presented to illustrate the process in selecting appropriate maintenance treatments. A framework for evaluating the cost-effectiveness of the various maintenance treatments is presented. Existing methods for evaluating cost-effectiveness of maintenance are discussed together with their strengths and weaknesses. An example of cost-effectiveness for different maintenance treatments is also briefly presented.

Permeability of Asphalt Surface Seals and Their Effect on Aging of Underlying Asphalt Concrete

Asphalt surface seals are defined as slurry seals, micro-surfacings, and chip seals (seal coats). The relative aging abatement effects of surface seals on the upper 13 mm (½ in.) of an asphalt pavement were estimated. A laboratory aging experiment was devised wherein a surface seal was simulated by a membrane that could be easily removed after the artificial aging process without affecting the uppermost layer of asphalt in the asphalt concrete. By comparing laboratory aging data with existing field data on aged asphalt pavements it was possible to make inferences about the number of years an asphalt surface seal will delay hardening of an underlying asphalt concrete layer. Compacted asphalt concrete slab specimens (40 × 60 × 13 mm) were prepared in the laboratory. Half of each slab was covered with an impermeable membrane; then the specimens were exposed to hot air to accelerate oxidative aging. Following the heat exposure, asphalt was extracted and physical and chemical tests were performed to measure hardening of the covered and uncovered specimens. Permeabilities of laboratory prepared slurry seal, micro-surfacing, and seal coat specimens were measured. By knowing the amount of oxidative aging that occurred in uncovered and covered specimens of asphalt concrete and the permeability of the surface seals, the effects of the surface seals on aging of an underlying asphalt concrete layer were interpolated. Testing indicated that a surface seal can retard oxidative hardening of an underlying asphalt concrete layer by 0 to 2 years, depending on the situation. However, most of the oxidative aging in the upper stratum of an asphalt concrete pavement occurs during the first 4 years after construction. After this period, the asphalt aging rate decreases significantly. Therefore, for a surface seal to significantly delay oxidative hardening of the underlying pavement, it must be placed during the first 2 years (approximately) of the pavement's life. It was demonstrated that ultraviolet (actinic) light penetrates asphalt cement only a few microns and, therefore, does not contribute materially to hardening of the uppermost 13 mm of an asphalt concrete pavement. Permeability of a slurry seal or micro-surfacing after sufficient traffic to effect maximum compaction is less than 1 × 10−5 cm/sec. Permeability to water and air of an asphalt seal coat (chip seal) is essentially zero. For practical purposes, these three surface seals will protect the top 13 mm of an underlying pavement from oxidation as if they were impermeable to air and water.

Permeability of Asphalt Surface Seals and Their Effect on Aging of Underlying Asphalt Concrete

Asphalt surface seals are defined as slurry seals, micro-surfacings, and chip seals (seal coats). The relative aging abatement effects of surface seals on the upper 13 mm (1/2 in.) of an asphalt pavement were estimated. A laboratory aging experiment was devised wherein a surface seal was simulated by a membrane that could be easily removed after the artificial aging process without affecting the uppermost layer of asphalt in the asphalt concrete. By comparing laboratory aging data with existing field data on aged asphalt pavements it was possible to make inferences about the number of years an asphalt surface seal will delay hardening of an underlying asphalt concrete layer. Compacted asphalt concrete slab specimens (40 X 60 X 13 mm) were prepared in the laboratory. Half of each slab was covered with an impermeable membrane; then the specimens were exposed to hot air to accelerate oxidative aging. Following the heat exposure, asphalt was extracted and physical and chemical tests were performed to measure ...

ASPHALT DURABILITY: FROM LABORATORY TEST TO FIELD IMPLEMENTATION

ABSTRACT Spray and chip seals are the most important form of road surfacings in Australia. The long term hardening of the asphalt binder (its durability) is of critical importance in determining their life. The Australian Road Research Board (ARRB) Durability Test measures the intrinsic resistance of an asphalt cement to oxidative hardening and has been used in specifications for many years. A model which allows calculation of the rate of asphalt hardening in a sprayed seal has already been presented. It is based on data from road trials monitored for up to 15 years. A second model now permits calculation of the viscosity level at which seal distress occurs in a particular climatic area. By using the combined models it is possible to predict surfacing life. The parameters required for the calculation are the average temperature at the site and the asphalt Durability Test result. Application of the models to sites; in the U.S. suggests that, if seal lives comparable to those in Australia are to be achieved...

Plastic-Reinforced Asphalt Seepage Barrier

This report is concerned with laboratory equipment development, laboratory testing, and field investigations of a water seepage barrier consisting of plastic-reinforced asphalt. Three testing methods were utilized and evaluated in the asphalt-plastic-asphalt-chip-coated (APAC) membrane investigation. The first test method evaluated the hydrostatic puncture resistance of an asphalt-polyethylene combination. This test confirmed the hypothesis that the asphalt effectively increases the puncture resistance of the APAC membrane over that of plain polyethylene. The second test investigated the slope stability of a protective APAC chip seal. It was found that a typical 3/8-in. (9.5-mm) cover aggregate remained stable on constructed slopes of 3:1 and 4:1 and also remained stable on a 2:1 slope up to a surface temperature of 122°F (50°C). The third test method evaluated adhesive materials and determined the best suited adhesive for sealing polyethylene overlaps. Subsequent field investigations resulted in equipment development that increased construction efficiency in the installation of the APAC membrane.