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OCR for page 165
A P P E N D I X D Other Pavement Preservation Treatments A few other types of preservation treatments were identified ventional asphalt pavement. Aggregates must be carefully and examined as part of the literature review. These included selected for compatibility, and mixing time and tempera- polymer-modified asphalt concrete (PMAC) overlays, epoxy ture must be closely monitored. These special construction asphalt, high-performance cementitious materials (HPCM), considerations can be overcome through experience with high-friction surface (HFS), undersealing, cross stitching, the material. The initial cost of epoxy asphalt is estimated ultra-thin epoxied laminates, and shot abrading. These treat- to be two to three times higher than conventional asphalt, ments fall under one of the following categories: (a) lengthy but the treatment is expected to have a longer life span. existence but limited overall use, (b) lengthy existence but use · HPCM is a new treatment method where a thin layer of limited to one or two agencies, (c) international use with high-performance, fiber-reinforced mortar is placed on recent trials in the United States, or (d) new/innovative with the existing pavement, and then hard aggregate particles recent trials in the United States. Known details regarding are embedded in the mortar, similar to a chip seal. The each of these treatments are provided below. strength of the bond between the HPCM and the underly- ing asphalt concrete is critical, but laboratory tests have · Polymer-modified asphalt concrete (PMAC; also known shown that a strong bond is possible if the asphalt is thor- as Smoothseal) is a thin surfacing material composed of oughly cleaned prior to applying the HPCM. Small cracks polymer-modified asphalt cement and fine-graded aggre- are inevitable as shrinkage occurs, but the fibers minimize gate mixed in a conventional HMA plant and placed using the width of crack opening. Because this method is new, a conventional asphalt paving machine. It is primarily used work still needs to be completed to make it viable on a large in Ohio as a PM treatment capable of retarding raveling scale. HPCM is estimated to cost two to three times more and oxidation, reducing the intrusion of water, improving than a conventional asphalt treatment. surface friction, and removing minor surface irregulari- · HFS treatments have been widely used in Great Britain. It ties. It is reportedly suitable for all levels of traffic and is is relatively new in the United States, but several test proj- available in two mixture forms. Type A PMAC is used for ects have proved effective. The treatment consists of a low-speed (<45 mph) urban applications and is typically layer of resins and polymers mixed with a binder and placed 0.625 in. thick. Type B PMAC is placed between 0.75 topped with small, hard aggregate. One common HFS and 1.25 in. thick and is intended for high-speed (45 mph) treatment feature is the use of an epoxy resin and bauxite applications. aggregate. The construction process can be completed · Epoxy asphalt is a product made with aggregate and a during a single shift or an overnight closure, as the epoxy- modified binder that can be applied in thin layers on exist- resin cures in about 3 hours. It is recommended that ing pavement. It has been used worldwide as a bridge deck cracks be sealed before placing the HFS treatment and, as surface, but is relatively untested on a large scale on road- with a chip seal, the surface should be swept to remove ways because of its high material cost and special construc- excess stones before opening to traffic. HFS treatments tion considerations. However, laboratory testing has shown are designed to improve surface friction at problem sec- it to be stiffer than conventional asphalt pavement, giving tions such as tight curves and steep grades especially at better load distribution. Additionally, it is resistant to rut- intersection approaches and on and off ramps. HFS treat- ting, low-temperature cracking, surface abrasion, and fatigue ments can be applied over surface distortions such as rut- cracking. It is less susceptible to water damage than con- ting or faulting, but will not address those problems. 174
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175 They are designed to be extremely durable and withstand The treatment is not appropriate for slabs that have multiple heavy braking and snow plows while maintaining their cracks or are considered shattered (broken into more than surface friction characteristics. A similar treatment uses four or five pieces). When the treatment is properly applied, an epoxy-resin and a specially designed hard aggregate to it is expected to last approximately 15 years. create a rigid spongelike texture that holds anti-icing treat- · Ultra-thin (0.12 to 0.25 in. [3.0 to 6.0 mm]) epoxied lami- ments near the surface to release more as needed. This cre- nates (i.e., Italgrip System proprietary treatment) have been ates a high-friction surface that resists ice and snow and used for concrete roads for surface texture restoration pri- requires less frequent treatment. marily in Europe, but with some success in the United States. · A fiber-reinforced seal (FRS) is a sprayed-on surface treat- The Italgrip method, which uses an epoxy for binding a ment consisting of a layer of glass fiber strands sandwiched 0.01-in. (0.25-mm) hard, synthetic stone to the road surface, between two coats of a polymer-modified asphalt emulsion has been used in Italy for the past 15 years. (Austroads 2005). The system includes a layer of fine aggre- Benefits/strengths reportedly associated with the Italgrip gate that is spread and rolled on top. The proprietary treat- system include good anti-skid microtexture properties, ment was originally developed in Britain and has been used good macro-texture for water removal and reduced hydro- extensively throughout that and other European countries planing, early opening time to traffic under summer condi- for treating cracked and aged HMA pavements covering a tions, fast application rate, reduced pavement-tire noise, and range of applications (parking lots to major roadway and elimination of bridge clearance and curb-and-gutter prob- airport pavements). lems due to thin layer. Reported weaknesses/disadvantages · Undersealing is the pressure insertion of a flowable material include high initial cost and durability that is sensitive to the beneath a PCC slab to fill voids between the slab and base, combination of low initial temperatures and early traffic thereby reducing deflections and, consequently, deflection- application. related distresses such as pumping or faulting. This treatment · Shot abrading was originally developed in 19791980 as a performs best if applied before faulting starts to develop. way of preparing concrete surfaces before applying bonded Given the higher cost of the treatment, undersealing has not concrete overlays but has been more recently used for received extensive use. When used, the treatment is most restoring friction on PCC highways. The process uses a often performed at areas where pumping and loss of sup- machine (called a Skidabrader) that hurls steel abrasive port occur, such as beneath transverse joints and deterio- materials at the road surface to increase the texture of con- rated cracks. The voids filled by this technique are generally crete surfaces. This method has been used on many high- less than 0.12 in. thick. profile concrete road texture restoration projects in the · Cross stitching is a longitudinal crack and joint repair tech- United States, including the shuttle runway for NASA, nique that consists of grouting tie bars in holes drilled major airport runways, tunnels, Interstates, and the Lake across nonworking longitudinal cracks or joints at an angle Pontchartrain Bridge in Louisiana. to the pavement surface. Cross stitching prevents horizontal Benefits and strengths of the shot-abrading method and vertical crack and joint movements. Use of this treat- include increased macro-texture levels for friction restora- ment is growing because cross stitching has proven effec- tion, relatively high production rate, and relatively low cost. tive at strengthening longitudinal cracks, preventing slab Reported concerns/weaknesses include microtexture wear migration, mitigating the omission of tie bars from longi- if the coarse aggregate is susceptible to polishing, increased tudinal contraction joints, tying separating roadway lanes noise if larger aggregates are exposed, and limited ability to or shoulders, and tying together faulted center-lane joints. restore ride quality.