National Academies Press: OpenBook

Preservation Approaches for High-Traffic-Volume Roadways (2011)

Chapter: Appendix D - Other Pavement Preservation Treatments

« Previous: Appendix C - Summary of Preservation Questionnaire Responses
Page 165
Suggested Citation:"Appendix D - Other Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Preservation Approaches for High-Traffic-Volume Roadways. Washington, DC: The National Academies Press. doi: 10.17226/14508.
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Page 165
Page 166
Suggested Citation:"Appendix D - Other Pavement Preservation Treatments." National Academies of Sciences, Engineering, and Medicine. 2011. Preservation Approaches for High-Traffic-Volume Roadways. Washington, DC: The National Academies Press. doi: 10.17226/14508.
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Page 166

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174 A few other types of preservation treatments were identified and examined as part of the literature review. These included polymer-modified asphalt concrete (PMAC) overlays, epoxy asphalt, high-performance cementitious materials (HPCM), high-friction surface (HFS), undersealing, cross stitching, ultra-thin epoxied laminates, and shot abrading. These treat- ments fall under one of the following categories: (a) lengthy existence but limited overall use, (b) lengthy existence but use limited to one or two agencies, (c) international use with recent trials in the United States, or (d) new/innovative with recent trials in the United States. Known details regarding each of these treatments are provided below. • Polymer-modified asphalt concrete (PMAC; also known as Smoothseal) is a thin surfacing material composed of polymer-modified asphalt cement and fine-graded aggre- gate mixed in a conventional HMA plant and placed using a conventional asphalt paving machine. It is primarily used in Ohio as a PM treatment capable of retarding raveling and oxidation, reducing the intrusion of water, improving surface friction, and removing minor surface irregulari- ties. It is reportedly suitable for all levels of traffic and is available in two mixture forms. Type A PMAC is used for low-speed (<45 mph) urban applications and is typically placed 0.625 in. thick. Type B PMAC is placed between 0.75 and 1.25 in. thick and is intended for high-speed (≥45 mph) applications. • Epoxy asphalt is a product made with aggregate and a modified binder that can be applied in thin layers on exist- ing pavement. It has been used worldwide as a bridge deck surface, but is relatively untested on a large scale on road- ways because of its high material cost and special construc- tion considerations. However, laboratory testing has shown it to be stiffer than conventional asphalt pavement, giving better load distribution. Additionally, it is resistant to rut- ting, low-temperature cracking, surface abrasion, and fatigue cracking. It is less susceptible to water damage than con- ventional asphalt pavement. Aggregates must be carefully selected for compatibility, and mixing time and tempera- ture must be closely monitored. These special construction considerations can be overcome through experience with the material. The initial cost of epoxy asphalt is estimated to be two to three times higher than conventional asphalt, but the treatment is expected to have a longer life span. • HPCM is a new treatment method where a thin layer of high-performance, fiber-reinforced mortar is placed on the existing pavement, and then hard aggregate particles are embedded in the mortar, similar to a chip seal. The strength of the bond between the HPCM and the underly- ing asphalt concrete is critical, but laboratory tests have shown that a strong bond is possible if the asphalt is thor- oughly cleaned prior to applying the HPCM. Small cracks are inevitable as shrinkage occurs, but the fibers minimize the width of crack opening. Because this method is new, work still needs to be completed to make it viable on a large scale. HPCM is estimated to cost two to three times more than a conventional asphalt treatment. • HFS treatments have been widely used in Great Britain. It is relatively new in the United States, but several test proj- ects have proved effective. The treatment consists of a layer of resins and polymers mixed with a binder and topped with small, hard aggregate. One common HFS treatment feature is the use of an epoxy resin and bauxite aggregate. The construction process can be completed during a single shift or an overnight closure, as the epoxy- resin cures in about 3 hours. It is recommended that cracks be sealed before placing the HFS treatment and, as with a chip seal, the surface should be swept to remove excess stones before opening to traffic. HFS treatments are designed to improve surface friction at problem sec- tions such as tight curves and steep grades especially at intersection approaches and on and off ramps. HFS treat- ments can be applied over surface distortions such as rut- ting or faulting, but will not address those problems. A P P E N D I X D Other Pavement Preservation Treatments

175 They are designed to be extremely durable and withstand heavy braking and snow plows while maintaining their surface friction characteristics. A similar treatment uses an epoxy-resin and a specially designed hard aggregate to create a rigid spongelike texture that holds anti-icing treat- ments near the surface to release more as needed. This cre- ates a high-friction surface that resists ice and snow and requires less frequent treatment. • A fiber-reinforced seal (FRS) is a sprayed-on surface treat- ment consisting of a layer of glass fiber strands sandwiched between two coats of a polymer-modified asphalt emulsion (Austroads 2005). The system includes a layer of fine aggre- gate that is spread and rolled on top. The proprietary treat- ment was originally developed in Britain and has been used extensively throughout that and other European countries for treating cracked and aged HMA pavements covering a range of applications (parking lots to major roadway and airport pavements). • Undersealing is the pressure insertion of a flowable material beneath a PCC slab to fill voids between the slab and base, thereby reducing deflections and, consequently, deflection- related distresses such as pumping or faulting. This treatment performs best if applied before faulting starts to develop. Given the higher cost of the treatment, undersealing has not received extensive use. When used, the treatment is most often performed at areas where pumping and loss of sup- port occur, such as beneath transverse joints and deterio- rated cracks. The voids filled by this technique are generally less than 0.12 in. thick. • Cross stitching is a longitudinal crack and joint repair tech- nique that consists of grouting tie bars in holes drilled across nonworking longitudinal cracks or joints at an angle to the pavement surface. Cross stitching prevents horizontal and vertical crack and joint movements. Use of this treat- ment is growing because cross stitching has proven effec- tive at strengthening longitudinal cracks, preventing slab migration, mitigating the omission of tie bars from longi- tudinal contraction joints, tying separating roadway lanes or shoulders, and tying together faulted center-lane joints. The treatment is not appropriate for slabs that have multiple cracks or are considered shattered (broken into more than four or five pieces). When the treatment is properly applied, it is expected to last approximately 15 years. • Ultra-thin (0.12 to 0.25 in. [3.0 to 6.0 mm]) epoxied lami- nates (i.e., Italgrip System proprietary treatment) have been used for concrete roads for surface texture restoration pri- marily in Europe, but with some success in the United States. The Italgrip method, which uses an epoxy for binding a 0.01-in. (0.25-mm) hard, synthetic stone to the road surface, has been used in Italy for the past 15 years. Benefits/strengths reportedly associated with the Italgrip system include good anti-skid microtexture properties, good macro-texture for water removal and reduced hydro- planing, early opening time to traffic under summer condi- tions, fast application rate, reduced pavement-tire noise, and elimination of bridge clearance and curb-and-gutter prob- lems due to thin layer. Reported weaknesses/disadvantages include high initial cost and durability that is sensitive to the combination of low initial temperatures and early traffic application. • Shot abrading was originally developed in 1979–1980 as a way of preparing concrete surfaces before applying bonded concrete overlays but has been more recently used for restoring friction on PCC highways. The process uses a machine (called a Skidabrader) that hurls steel abrasive materials at the road surface to increase the texture of con- crete surfaces. This method has been used on many high- profile concrete road texture restoration projects in the United States, including the shuttle runway for NASA, major airport runways, tunnels, Interstates, and the Lake Pontchartrain Bridge in Louisiana. Benefits and strengths of the shot-abrading method include increased macro-texture levels for friction restora- tion, relatively high production rate, and relatively low cost. Reported concerns/weaknesses include microtexture wear if the coarse aggregate is susceptible to polishing, increased noise if larger aggregates are exposed, and limited ability to restore ride quality.

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TRB’s second Strategic Highway Research Program (SHRP 2) Report S2-R26-RR-1: Preservation Approaches for High-Traffic-Volume Roadways documents the state of the practice of preservation treatment on asphalt and concrete pavements. The report focuses on treatments suitable for application on high-traffic-volume roadways but also discusses current practices for low-volume roadways.

The same project that produced SHRP 2 Report S2-R26-RR-1 also produced SHRP 2 Report S2-R26-RR-2: Guidelines for the Preservation of High-Traffic-Volume Roadways. The report provides suggested guidelines for the application of preservation treatments on high-traffic-volume roadways and considers traffic volume, pavement condition, work-zone requirements, environmental conditions, and expected performance.

An e-book version of this report is available for purchase at Google, iTunes, and Amazon.

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