|FHWA > Engineering > Pavements > HIF-10-002 > Chapter 8, Other Materials|
Advanced High-Performance Materials for Highway Applications: A Report on the State of Technology
Chapter 8, Other Materials
Ultra-Thin Bonded Wearing Course
Also referred to as an ultra-thin friction course, an ultra-thin bonded wearing course consists of a thin (0.375- to 0.75-in. [9.5 to 19 mm] thick) gap-graded, polymer-modified HMA layer placed on a polymer-modified emulsified asphalt membrane. This material was originally developed in France in 1986 and introduced in the United States in the early 1990s as the proprietary product NovaChip®.
An ultra-thin bonded wearing course is typically applied as a preventive maintenance or minor rehabilitation treatment for the purpose of sealing the surface, correcting surface distresses (e.g., raveling, block cracking), or restoring key surface characteristics, such as friction, smoothness, and transverse profile. The polymer-modified HMA layer uses crushed aggregate chips sized 0.25 to 0.5-in. (6.4 to 12.7 mm) with binder contents in the range of 4.5 to 5.5 percent.
Similar to HMA, an ultra-thin bonded wearing course is easily produced at a HMA facility and placed with little difficulty (Kandhal and Lockett 1997). The main difference in placement is the use of a specialized paver, which is capable of applying the asphalt membrane and the polymer-modified HMA surfacing in a single pass. Once placed, the material is lightly rolled to orient and seat the aggregate chips.
Recent research on the performance of ultra-thin bonded wearing course indicates life expectancies between 7 and 12 years when placed on HMA-surfaced pavements and 5 to 10 years when placed on concrete-surfaced pavements (Peshkin et al. 2009). A study on the performance of ultra-thin bonded wearing courses placed on concrete surfaces in North Carolina suggested services lives of 6 to 10 years (Corley-Lay and Mastin 2007).
Ultra-thin bonded wearing course is most suitable for use on existing HMA-surfaced pavements that are in structurally good condition (Peshkin et al. 2009). While it can also be used with success on concrete pavements, its performance on concrete pavements is often compromised because of joint reflection cracking issues. Ultra-thin bonded wearing course can be used on a variety of pavement facilities, ranging from parking lots and low-volume roads to high-volume rural and urban highways.
In addition to preserving existing pavements via sealing and correction of surface distresses, ultra-thin bonded wearing courses provide benefits in the areas of user safety (improved friction, reduced splash/spray, and reduced hydroplaning potential) and comfort (increased smoothness and reduced noise). In addition, unlike certain surface treatments, ultra-thin bonded wearing courses do not experience aggregate chip loss due to their excellent adhesion properties.
Although the cost of ultra-thin bonded wearing course depends largely on the location, specific application, and size of the project, typical construction costs may range from about $4.00/yd2 to $6.00/yd2 ($4.78/m2 to $7.18/m2) (Peshkin et al. 2009).
The use of ultra-thin bonded wearing course in the United States is fairly significant. In 2001, upwards of 6.6 million yd2 (5.5 million m2) of NovaChip® were reportedly placed, with key users being Alabama, Arkansas, Illinois, Maryland, Michigan, Ohio, and Pennsylvania (Russell et al. 2008). Since then, a number of other highway agencies (including Minnesota, Washington, Texas, California, and New Mexico) have used ultra-thin bonded wearing courses in a number of applications with generally good success. A project in Minnesota shows excellent performance after 7 years of service (Ruranika and Geib 2007).
For More Information
Corley-Lay, J., and J. N. Mastin. 2007. "Ultrathin Bonded Wearing Course as a Pavement Preservation Treatment for Jointed Concrete Pavements." Paper presented at the 2007 Annual Meeting of the Transportation Research Board, Washington, DC.
Kandhal, P. S., and L. Lockett. 1997. Construction and Performance of Ultrathin Asphalt Friction Course. NCAT Report No. 97-5. National Center for Asphalt Technology, Auburn, AL.
Peshkin, D., K. L. Smith, A. Wolters, J. Krstulovich, J. Moulthrop, and C. Alverado. 2009. Guidelines for the Preservation of High Traffic Volume Roadways. Draft Final Report, Strategic Highway Research Program 2 Project R-26. Strategic Highway Research Program, Washington, DC.
Ruranika, M. M., and J. Geib. 2007. Performance of Ultra-Thin Bounded Wearing Course (UTBWC) Surface Treatment on US-169, Princeton, MN. MN/RC-2007-18. Minnesota Department of Transportation, Maplewood, MN.
Russell, M. A., L. M. Pierce, J. S. Uhlmeyer, and K. W. Anderson. 2008. NovaChip®. Report No. WA-RD 697.1. Washington State Department of Transportation, Olympia, WA.
Advanced Curing Material
The SINAK Corporation recently developed a lithium-based curing compound called Lithium Cure™, which is a water-based lithium compound with a proprietary formula in solution that contains no volatile organic compounds or solvents and requires no mixing or agitation (SINAK 2009). The compound can be placed earlier than conventional curing materials and, when applied to freshly placed concrete prior to initial set, the accompanying lithium reaction produces additional gel that significantly reduces moisture loss, thereby producing a more efficient hydration process and eliminating surface restraint cracking (SINAK 2009).
SINAK Lithium Cure™ can be used on virtually any type of concrete material, including roadway pavements, bridges, pre-cast elements, and cast-in-place elements (SINAK 2009). The material is purportedly particularly effective for slip-form pavements, in which it can be applied directly behind the paving equipment in a single coat. If a separate texturing machine is used, Lithium Cure is applied immediately after the final texturing. Typical application rates vary, but typically range between 300 and 400 ft2 per gallon (7.4 to 9.8 m2/L) for slip-form paving, between 500 and 700 ft2 per gallon (12.3 to 17.2 m2/L) for pre-cast concrete, and between 400 to 500 ft2 per gallon (9.8 to 12.3 m2/L) for cast-in-place concrete (SINAK 2009).
According to the manufacturer, Lithium Cure provides the following benefits (SINAK 2009):
The benefits of Lithium Cure are expected to be most evident in hot, windy, low-humidity environments. The application of Lithium Cure does not interfere with the bonding of joint sealants, patching or surface coating materials, paints, or lane markers (SINAK 2009).
Cost data are currently not available.
Lithium Cure is a relatively new product and has not yet seen widespread use. It has been applied on a new concrete pavement construction project on the North-South Road in Honolulu, Hawaii (Gomaco 2009).
For More Information
Gomaco World (Gomaco). 2009. "A Big Project on a Small Island." Gomaco World, Vol. 37, No. 2. Gomaco Corporation, Ida Grove, IA.
SINAK Corporation (SINAK). 2009. Product Information Sheet - Lithium Cure™. SINAK Corporation, San Diego, CA.
The BASF Construction Chemical Company recently developed a new concrete admixture formulated to retain slump and control workability without retardation. The product, RheoTEC™ Z-60, provides more consistent concrete that helps producers achieve more cost-effective and efficient operations, even under changing materials and environmental conditions (CM 2009). In essence, the admixture is dosed to provide workability retention for a desired length of time, with improvements in both early and later-age strength development while minimally affecting set. RheoTEC meets the requirements of ASTM C 494/C494M, Standard Specification for Chemical Admixtures for Concrete - Type S, Specific Performance Admixtures.
RheoTEC™ Z-60 is recommended for use in virtually all types of concrete, including ready-mixed concrete, precast concrete, and SCC mixtures. It may be particularly effective in concrete with varying slump requirements, concrete mixtures that employ supplementary cementitious materials, and concrete where high flowability, increased stability, and improved durability are required (BASF 2009). The recommended dosage range for RheoTEC is between 3 and 12 fl oz (88.7 to 355 mL) per cwt of cementitious materials.
According to the manufacturer, RheoTEC Z-60 provides the following benefits (BASF 2009):
RheoTEC Z-60 will neither initiate nor promote corrosion of steel reinforcement embedded in the concrete.
Cost data are currently not available.
RheoTEC Z-60 was introduced in mid-2009 and is being promoted to concrete producers and consumers. No information is immediately available regarding its use in actual construction projects.
For More Information
BASF Construction Chemicals (BASF). 2009. Product Data Sheet - RheoTEC Z-60. BASF Construction Chemicals, Cleveland, OH.
Concrete Monthly (CM). 2009. "New BASF Admixture Retains Workability Without Retardation." Concrete Monthly, August 2009 Issue. Publications and Communications, Inc., Austin, TX.
Concrete Surface Sealers
Concrete surface sealers effectively reduce or prevent the ingress of moisture, chloride ions, sulfate ions, and other substances that may contribute to damaging reactions in the concrete (Sutter et al. 2008). Concrete surface sealers may be divided into a number of different families, with one such grouping as follows (Cady 1994):
Satisfactory performance of the concrete is still strongly dependent on the development of durable mix designs and effective construction, and surface sealers may be considered in areas where significant deicing chemicals are applied or where concrete durability is suspect. For concrete bridge elements, it is recommended that for the use of sealers to be economical, the chloride ion content at the depth of the shallowest 1 percent of the reinforcing steel should be less than 1 lb/yd3 (0.59 kg/m3) and the corrosion potential (half-cell) should be more positive than -250 mV (Cady 1994).
Although all surface sealers can slow the penetration of deicing chemicals, one study showed that siloxane sealants were particularly effective at slowing the ingress of deicing chemicals into concrete or mortar; silane sealants were also effective, but to a lesser extent (Sutter et al. 2008). The FHWA's ASR program notes that the application of silane (or siloxane) compounds has been effective in reducing the rate of ASR development in field applications (FHWA 2008).
Surface sealers may be applied to any horizontal concrete structure exposed to deicing chemicals or other adverse contaminants, but may be most appropriate where very high concentrations of such contaminants are expected, such as bridge decks, parking lots, and perhaps intersections, or on concrete whose durability is suspect. The effectiveness of surface sealers is lost after they are exposed to traffic and environmental forces, and they may need to be reapplied after 3 to 5 years.
The primary benefit provided by surface sealers is to reduce the ingress of deleterious substances that would contribute to degradation of the concrete and reduced service life.
Costs for surface sealers are highly variable depending on the type of material and the application rate, but can range from about $0.10 to $0.70 per ft2 ($1.08/m2 to $7.53/m2).
A number of highway agencies are evaluating concrete surface sealers, particularly for use on their bridge decks. Generally speaking, silanes and siloxanes have exhibited the best performance. Wisconsin, Minnesota, Florida, and Illinois are among the highway agencies with active research in this area.
For More Information
Cady, P. D. 1994. Sealers for Portland Cement Concrete Highway Facilities. NCHRP Synthesis of Highway Practice 209. Transportation Research Board, Washington, DC.
Federal Highway Administration (FHWA). 2008. "Got ASR? Mitigation Options for Concrete Structures Affected by ASR." Reactive Solutions - An FHWA Alkali-Silica Reactivity News Publication, Vol. 1, No. 3. FHWA, Washington, DC. Available at http://www.fhwa.dot.gov/pavement/concrete/reactive/issue04.pdf.
Sutter, L. L., K. Peterson, G. Julio-Betancourt, D. Hooton, T. Van Dam, and K. Smith. 2008. The Deleterious Chemical Effects of Concentrated Deicing Solutions on Portland Cement Concrete. Final Report SD2002-01F. South Dakota Department of Transportation, Pierre, SD.
PDF files can be viewed with the Acrobat® Reader®