What are Crack Treatments?
TITLE: Recommended Performance Guidelines for Crack Treatment
Download A-175 Guidelines
Crack treatments consist of placing specialized materials into prepared cracks to prevent water and incompressible intrusion into the cracks and underlying pavement layers, and to reinforce the adjacent pavement. Restriction of water entry into underlying pavement base and sub-grade layers serves to maintain pavement strength and prolong pavement life. Pavements in different climate zones, with different construction types, and with different traffic loadings experience different types of cracking. The various crack types experience different movement ranges depending mostly on crack spacing and temperature variations. Different types of crack treatment materials and installation geometries are required for the different conditions.
Types of Crack Treatment Materials
There are several types of materials used for crack treatments ranging from unmodified asphalts and emulsions, to polymer and rubber modified asphalts and specialty chemically curing polymeric materials. Hot applied rubber and polymer modified asphalts are the most widely used materials. Crack treatment materials must have appropriate properties for the climate in which they are used and need to be able to accommodate expected movement. Proper materials are available for use in all climatic areas.
Crack treatment materials can be installed in a range of configurations and with varying preparation methods. Configurations range from filling unprepared cracks and capping with a narrow overband, to specifically designed reservoirs that widen the crack to provide the correct geometry for the expected movements.
How are Crack Treatments selected?
The first step is to examine the pavement to determine the cracking type, extent and severity. This examination indicates if the pavement is an appropriate candidate for crack treatment and indicates the type of treatment method to use. Generally, pavements with low and moderate severity cracking are the best candidates. Crack treatments may not be appropriate for pavements with high amounts of severe cracking.
Crack Filling — Filling treatments are used for pavements that primarily have non working cracks (less than1/8 inch annual movement). Filling treatments generally consist of cleaning the cracks and placement of appropriate material in a fill and slight overband application. Filling treatments are generally used for cracks spaced at less than 20 feet for block, random closely spaced thermal, and longitudinal cracking.
Crack Sealing-— Crack sealing treatments are used for pavements that primarily have working cracks (greater than 1/8 inch annual movement). Sealing treatments consist of creating a widened reservoir to provide proper geometry and placement of flexible, extensible material that can accommodate the expected movements. Sealing treatments are generally used for thermal cracking spaced at over 20 feet. For all sealing or filling installations, the treatment material needs to have appropriate properties for the specific temperature ranges at the project site.
How are Crack Treatment materials applied?
Application consists of 3 basic steps– cleaning the cracks, cutting the reservoir if needed, and installing the material. Cleaning is generally accomplished using compressed air. Reservoir cutting is performed using a crack saw or router that can cut varying widths and depths as required. Hot applied products heated to the appropriate temperature in a melter unit equipped with agitation and a temperature monitoring device. The heated material is then pumped into the crack or placed using pour pots or wheeled applicators. Cold applied materials can be installed using pour pots, or other containers. For all installations, cracks must be clean and dry for the best performance.
How long do crack treatments last?
Properly designed and installed crack treatments have been proven to last between 5 and 7 years.
How long do crack treatments extend pavement life?
Properly designed and installed crack treatments have been proven to increase pavement life up to 7 years
What is Chip Seal?
TITLE: Recommended Performance Guideline for Chip Seal
Download A-165 Guidelines
Chip Seal is an application of a bituminous binder covered with an application of clean graded aggregate to an existing asphalt surface. It is also known as armor coat, bituminous sealing or seal coat, to name a few. The binders may be emulsions, paving grade asphalt cements, and modified versions of each being modified with various polymers such as latex, tire and natural rubbers.
The aggregates commonly vary in size from a maximum of 5/8 of an inch to a minimum of ¼ inch with less than 5% passing the No. 4 screen. Aggregate must be durable with the use of crushed stone, gravels or manufactured aggregates. Aggregates may be precoated with a small % of asphalt cement when used with hot asphalt binders. Chip Seal has been used in various forms since at least the early 1900’s. The quality has improved over the years with better binder technology, cleaner aggregates, and improved equipment and a better understanding of how the materials perform together.
How is Chip Seal designed?
By making use of the best local aggregates with the most compatible binders while considering climate, traffic count and type to
maximize results with awareness of cost with the funds that are available. Once the binder and aggregate are selected there are
procedures to determine the rates of application for each.
How is Chip Seal applied?
The binder is applied by an asphalt distributor which has the capability of applying the design rate at the desired width. The binder application is followed by a mechanical aggregate spreader that is also capable of applying a design rate at the desired width. Then rolling is performed with pneumatic rollers to set the cover aggregate into the binder. Finally if there is any loose aggregate, it is removed by a rotary broom.
Types of Chip Seal:
There are virtually an unlimited number of Chip Seal combinations depending on what type of binder and aggregate are available. Chip Seal is normally one application but can be applied in double or even triple applications if needed. Multiple applications commonly use different sizes of aggregates to help “lock” the applications together.
Why Use Chip Seal?
Chip Seal is a comparatively low cost method of maintaining an asphalt surface indefinitely that can make use of local materials, and be performed by contract or by using local maintenance personnel. Traffic can be back on the road in minutes. A finished Chip Seal is very pleasing in appearance and traffic markings show up very well.
Chip Seal Best Practices Pay Off for End User – PPJ Article
What is Micro Surfacing?
TITLE: Recommended Performance Guidelines for Polymer Modified Micro Surfacing, 2010
Download A-143 Guidelines
One of the most versatile tools in the road maintenance arsenal, Micro Surfacing is a polymer-modified cold-mix paving system that can remedy a broad range of problems on today’s streets, highways, and airfields.
Like its parent product, slurry seal, Micro Surfacing begins as a mixture of dense-graded aggregate, asphalt emulsion, water, and mineral fillers. While conventional slurry seal is used around the world as an economical treatment for sealing and extending the service life of both urban and rural roads, Micro Surfacing has added capabilities, thanks to the use of high-quality, carefully monitored materials, including advanced polymers and other modern additives.
A History of Expanding Service
Micro Surfacing was pioneered in Germany in the late 1960s and early 1970s. German scientists began experimenting with conventional slurry to find a way to use it in thicker applications which could be applied in narrow courses for wheel ruts, and not destroy the expensive road striping lines on the autobahns.
When the scientists used highly selected aggregates and bitumen, and then incorporated special polymers and emulsifiers that allowed the product to remain stable even when applied in multi-stone thicknesses, the result was Micro Surfacing.
Introduced in the United States in 1980, Micro Surfacing now is recognized not only as the most cost-effective way to treat the surface wheel-rutting problem, but also a variety of other road surface problems. Micro Surfacing is now used throughout Europe, the United States, and Australia and is making inroads into many other areas.
How is Micro Surfacing Made and Applied?
Micro Surfacing is made and applied to existing pavements by a specialist machine, which carries all components, mixes them on site, and spreads the mixture onto the road surface. Materials are continuously and accurately measured, and then thoroughly combined in the Micro surfacing machine’s mixer. As the machine moves forward, the mixture is continuously fed into a full-width “surfacing” box which spreads the width of a traffic lane in a single pass. Or specially engineered “rut” boxes, designed to deliver the largest aggregate particles into the deepest part of the rut to give maximum stability in the wheel path, may be used. Edges of the Micro Surfacing are automatically feathered.
The new surface is initially a dark brown color and changes to the finished black surface as the water is chemically ejected and the surface cures, permitting traffic within one hour in most cases.
Continuous-load pavers utilize support units which bring the materials to the job site and load the machine while it is working, thus maximizing production and minimizing transverse joints.
A Proven Problem Solver
Using various design mixes, techniques, and equipment, Micro Surfacing can be used successfully in these situations:
- In quick-traffic applications as thin as 3/8 inch (9.5mm), Micro Surfacing can increase skid resistance, color contrast, surface restoration, and service life to high-speed roadways (interstates and autobahns). Such projects are often reopened to traffic within an hour.
- Modern, continuous-load pavers can lay 500 tons of Micro Surfacing per day, with no long traffic delays. This equates to an average 6.6 lane miles (10.6 lane kilometers) per day for surfacing applications.
- On airfields, dense-graded Micro Surfacing produces a skid-resistant surface without loose rock that damages aircraft engines.
- As a thin, restorative surface source on urban arterials and heavy traffic intersections, Micro Surfacing does not alter drainage; there is no loss of curb reveal.
- Micro Surfacing is applied to problem sections of roads or runways to eliminate hydroplaning problems that occur during periods of rain. The Micro Surfacing restores the proper surface profile and makes the area safe to use.
- Because Micro Surfacing can be effectively applied to most surfaces at 3/8 inches (9.5mm) or less, more area per ton of mix is covered, resulting in cost-effective surfacing.
- Micro Surfacing creates a new, stable surface that is resistant to rutting and shoving in summer and to cracking in winter.
- Applied to both asphalt and Portland cement concrete surfaces (usually preceded by a tack coat on concrete), Micro Surfacing is often used to restore a skid-resistant surface to slick bridge decking with minimum added dead weight.
- Used as a scratch (leveling) course, to be followed by a surface course, Micro Surfacing can provide transverse surface leveling.
- Because of its quick-traffic properties, Micro Surfacing can be applied in a broad range of temperature and weather conditions, effectively lengthening the paving season. It is particularly suitable for night applications on heavy-traffic streets, highways, and airfields.
- Applied at ambient temperatures, Micro Surfacing has low energy requirements. And it is environmentally safe, emitting nopollutants.
- Micro Surfacing life expectancy usually exceeds seven years.
- Capable of filling wheel ruts up to 1-1/2 inches (38mm) deep when the pavement has stabilized and is not subject to plastic deformation, Micro Surfacing has the unique ability to solve this problem without milling.
A Product of Quality
Successful Micro Surfacing incorporates carefully selected materials, scientific mix designs, advanced technical specifications, and problem field practices.
Micro Surfacing begins with the selection of high-quality materials – asphalt, aggregate, emulsifiers, water, and additives – which must pass special laboratory tests, both individual and when combined, as a Micro Surfacing system.
The International Slurry Surfacing Association’s (ISSA) broad range of specialized mix design tests help to insure that the mixture has these Micro Surfacing characteristics:
1. Is capable of being spread in various thick cross-sections (wedges, ruts, scratch course), which
2. After initial traffic consolidation, does not further compact (i.e. resists compaction) throughout the entire design tolerance
range of bitumen content and variable thicknesses to be encountered, and
3. Maintains good macro-texture (high wet coefficient of friction) in variable thick sections throughout the service life of the Micro Surfacing.
Successful Micro Surfacing projects depend on strict adherence to technical specifications. Many users find it helpful to design their individual job specifications around those recommended by ISSA (Technical Bulletin A-143) The resulting “mix design” and job specifications are carefully adhered to in the field, where ISSA member contractors use specialized job-calibrated equipment and thoroughly trained crews to maintain consistent quality control
What Is Slurry?
TITLE: Recommended Performance Guidelines for Emulsified Asphalt Slurry Seal Surfaces, 2010
Download A-105 Guidelines
TITLE: Slurry Seal Consistency Template
The principal materials used to create slurry seal are aggregate, asphalt emulsion, and filler, which are mixed together according to a laboratory’s design-mix formula. Water is also added for workability.
Asphalt emulsions serve as a binder, holding the crushed aggregate together and adhering the new slurry surfacing to the old surface over which it is being applied. Various emulsions and aggregates are used to meet the conditions, specifications, and requirements of individual projects.
The aggregate must be clean, crushed, durable, properly graded, and uniform. The asphalt emulsion is a three-part system consisting of asphalt, water, and emulsifier. Fillers such as Portland cement, hydrated lime, or aluminum sulfate liquid are often used in small quantities as stabilizers or chemical modifiers.
History of Slurry
In the early 1930s, a coating consisting of a mixture of very fine aggregates, asphalt binder, and water was laid out on a road in Germany. It proved to be a novel approach, a new and promising technique in maintaining road surfaces, and marked the beginning of slurry seal development.
Later in that decade, extensive worldwide experimentation begin in earnest. But it was not until the 1960s, with the introduction of improved emulsifiers and continuous flow machines, that real interest was shown in the usage of slurry seal for a wide variety of applications.
Continuing advancements in mixing methods, emulsions and machinery have made slurry seal today’s choice in providing highly durable, low cost paving and surface maintenance. As a treatment for everything from residential driveways to public roads, highways, airport runways, parking lots, and a multitude of other paved surfaces, slurry seal is now used extensively throughout the world. Local, state, and federal agencies — including the military — have a growing and ongoing commitment to the use of slurry seal in their maintenance programs, attesting to its effectiveness and economy.
How is Slurry Made?
Slurry is made in specially designed equipment, either truck-mounted or self-propelled. This equipment carries a quantity of unmixed materials which are blended together in a continuous flow pugmill. The use of this technologically advanced machinery insures a smooth, consistently uniform mixture.
Slurry is made quickly and accurately at the project site. Mixing and spreading are accomplished in one continuous operation, with the surface being reopened to travel within a few hours.
How is Slurry Applied?
Slurry seal is applied to an existing pavement surface by means of a spreader box linked to the surface slurry-mixing unit. Slurry is introduced into the spreader box, which then lays down the slurry coating as the mixer/spreader is driven forward.
The box is capable of spreading the slurry seal over the width of a traffic lane in a single pass, and is constructed so that close contact with the existing surface is maintained. This insures uniform application of the new coating on a variety of configurations encompassing various crowd shapes, superelevated sections, and shoulder slopes.
Trained operators continually monitor the automatic mixing procedure. Other personnel clean the surface before slurry applications, barricade the street, inspect the operation in progress for uniformity, clean metal utility covers after application, and complete slurry seal spreading in any area inaccessible to the spreader box.
Types of Slurry
Emulsions of varying composition and setting times are mixed with any one of three grades of aggregates to create slurry seal mixes for specific purposes.
Aggregate types are I (fine), II (general), and III (coarse). Fine aggregate mixtures are used for maximum crack penetration and sealing in low-density/low-wear traffic areas. Type II aggregates are the most commonly used and are widely employed where moderate-to-heavy traffic is found. They seal, correct moderate-to-severe ravelling, oxidation and loss of matrix, and improve skid resistance. Type III corrects severe surface conditions — preventing hydroplaning and providing skid resistance under very heavy traffic loads.
A slurry seal for nearly any need or condition can be custom designed to satisfy the most difficult requirements.
Why Use Slurry?
Pavement Performance Histograph
As shown below, slurry seal maintenance dramatically extends pavement life. Although the serviceability of an untreated asphalt pavement is still adequate after several years of use, pavement deterioration has already begun.
A slurry seal maintenance program undertaken before significant pavement deterioration has begun is essential to proper pavement maintenance.
Preventive maintenance is more cost-effective than corrective maintenance.
Advantages of Using Slurry
As the most versatile of any pavement surface treatment system, slurry seal is also unique in its ability to deposit a durable bituminous mixture in accordance with the demands of a variably textured surface – filling cracks and voids, sealing weather-tight, and providing color and texture delineation in a single pass.
- Low cost
- Economical to install, highly cost-effective to use.
- Rapid usability
- Easy, swift application of a new overlay makes slurry especially attractive for rehabilitating busy thoroughfares, parking lots, and airport runways. The new surface is ready for use just hours after application.
- Preventing problems
- Used over newly laid pavements, slurry seal will prevent surface distresses such as the effects of weathering from occurring. Oxidation, loss of oils, loss of matrix, and embrittlement of the mix are minimized. It also provides special durability and texture not available in the underlying mix.
- Correcting problems
- Existing distresses in older pavements — surface cracking, ravelling, loss of matrix, increased water and air permeability, and slipperiness due to flushing and aggregate polishing — can be corrected through a slurry application. Waterproofing is also achieved, preventing further deterioration. An all-weather, long-lasting surface is created that offers skid resistance and improved handling characteristics for drivers.
- Aesthetic value
- With one simple application, existing pavement receives a new wearing surface of uniform black color and texture. Enhanced appearance means increased property value, marketing potential, and buyer acceptance. Thoroughfares, shopping center parking lots, and other public or commercial pavements treated with slurry seal become more attractive and eye-appealing.
Benefits of Pavement Maintenance
Even the best of surfaces are subject to the wear and tear caused by time, weather, and traffic. No surface is permanent.
By undertaking a program of planned pavement maintenance, considerable savings in rehabilitation costs may be achieved. Your pavement surface will remain sound, usable, and safe. Extensive downtime needed to repair deep cracks and potholes will be reduced or eliminated.
The application of slurry seal will significantly extend the life of existing pavements by protecting the under-surface from damage caused by water seepage. Improved surface performance is an added bonus.
A pavement maintenance program using slurry seal will not only help to protect your pavement, it will help to protect your paving investment.