Two Layer Pavement Preservation System
A pavement preservation system comprises two layers of specialized chip seal applications. The first layer is a Polymer Modified Asphalt Rubber chip seal application. This layer is composed of an application of Polymer Modified Asphalt Rubber binder followed by a hot pre-coated ⅜ or ½ inch aggregate placed at 28 to 34 pounds per square yard and rolled into the binder material. The second layer is a Rubberized Asphalt Binder chip seal application. This layer is composed of an application of Rubberized Asphalt Binder followed by a hot pre-coated ⅛ inch aggregate placed at 10 to 14 pounds per square yard and rolled into the binder material.
This Application claims the benefit of U.S. Provisional Patent Application No. 61/251,725, filed on Oct. 14, 2010.
BACKGROUND OF THE INVENTIONFlexible pavement roadways, such as those made of asphalt cement mixtures, usually require periodic surface treatment so the pavement system, which deteriorates under wear and weathering, may successfully achieve its design life. Chip seals are a common preventive maintenance treatment for both low-volume and high-volume pavements.
A chip seal is essentially a single layer of asphalt binder that is covered by embedded aggregate (one stone thick), with its primary purpose being to seal the fine cracks in the underlying pavement's surface and prevent water intrusion into the base and subgrade. The aggregate protects the asphalt layer from damage and combines with the asphalt to develop a macrotexture that results in a skid-resistant surface for vehicles. Chip seals are expected to provide about 5 years of service.
BRIEF SUMMARY OF THE INVENTIONThe present invention comprises two layers of specialized chip seal applications, resulting in a unique two layer system that has specific physical advantages and improved binder properties. The combination of the physical aggregate interlock and highly modified binder materials results in a high performance pavement preservation system that can be utilized to rehabilitate badly deteriorated pavements at very low cost compared to the alternative, and at the same time reduce maintenance costs along with extending service life, allowing for significant improvements in life cycle costs.
The first layer of the inventive system is a Polymer Modified Asphalt Rubber chip seal application. This layer is composed of an application of Polymer Modified Asphalt Rubber binder at a rate of about 0.60 to 0.70 gallons per square yard. The actual application rate is project specific and is determined by the existing pavement condition after the proper pre-maintenance (crack sealing and patching) has been done. Immediately following the application of the Polymer Modified Asphalt Rubber binder a hot pre-coated ⅜ or ½ inch aggregate is placed at 28 to 34 pounds per square yard and rolled into the binder material. Once the rolling is complete and this first layer has had sufficient cure time the loose aggregate is removed and the Polymer Modified Asphalt Rubber chip seal is ready to receive the second layer of the inventive system.
The second layer of the inventive system is a Rubberized Asphalt Binder chip seal application. This layer is composed of an application of Rubberized Asphalt Binder at a rate of 0.20 to 0.23 gallons per square yard. Immediately following the application of the Rubberized Asphalt Binder a hot pre-coated ⅛ inch aggregate is placed at 10 to 14 pounds per square yard and rolled into the binder material. Once the rolling is complete and this second layer has had sufficient cure time the loose aggregate is removed and the Two Layer Pavement Preservation System is complete in place.
Aspects and applications of the invention presented here are described below in the drawings and detailed description of the invention.
In the following description, and for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various aspects of the invention. It will be understood, however, by those skilled in the relevant arts, that the present invention may be practiced without these specific details. In other instances, known structures and devices are shown or discussed more generally in order to avoid obscuring the invention.
The inventive system comprises a bituminous surface Stress Absorbing Membrane Interlayer (SAMI) composed of a single application of Polymer Modified Asphalt-Rubber material and pre-coated aggregate (first layer) followed by a second bituminous surface Stress Absorbing Membrane (SAM) composed of a single application of Rubberized Asphalt Binder and pre-coated aggregate (second layer) in accordance with the following specification. Pre-maintenance (crack sealing and patching) of the existing pavement surface may be desirable, depending upon the local conditions.
Material Components
PG Asphalt Cement. The type and grade of PG (Performance Graded) asphalt cement utilized to manufacture the Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder will be PG 64-16, PG 58-22 or PG 58-28 which should comply with requirements in Table #1.
Granulated Reclaimed Tire Rubber. The CRM (Crumb Rubber Modifier) should be produced primarily from the processing of whole automobile and truck tires. The rubber should be produced by ambient temperature grinding processes only. The SBS (styrene butadiene styrene) polymer should be a linear or radial type of polymer with a molecular weight sufficient enough to meet the end result physical binder requirements. The gradation of the CRM and SBS Polymer when tested in accordance with ASTM C-136 (dry sieve only) and using a 100 gram sample, should meet the requirements in Table #2.
The use of CRM from multiple sources is acceptable provided that the overall blend of rubber meets the gradation requirements. The individual CRM particles, irrespective of diameter, should not be greater in length than 3/16 of an inch (5 mm).
The CRM should have a specific gravity of 1.15±0.05, and should be free of loose fabric, wire and other contaminants except that up to 4 percent (by weight of rubber) calcium carbonate or talc may be added to prevent the rubber particles from sticking together. The rubber should be sufficiently dry so as to be free flowing and not produce a foaming problem when blended with the hot asphalt cement. The Reclaimed Tire CRM material should conform to the chemical analysis in Table #3.
Polymer Modified Asphalt Rubber Binder and Rubberized Asphalt Binder. The temperature of the blended PG asphalt cement should not be less that 375° F. nor more than 450° F. when the CRM and the SBS Polymer are homogenously blended and/or milled with either binder, in the field. The combined materials should be reacted for a minimum of 90 minutes after the incorporation of all the CRM and SBS Polymer. The Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder should meet the requirements in Table #4 and Table #5, when the reaction/interaction is complete.
The viscosity test should be conducted by using a hand held HAAKE viscometer (or equal), with rotor 1, 24 mm in depth×53 mm in height, or equivalent. The fully reacted Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder should be maintained at a temperature of not less than 375° F. nor more than 425° F.
If material in a batch of Polymer Modified Asphalt Rubber binder or Rubberized Asphalt Binder is not used within six hours after the reaction period is complete, heating of the material should be discontinued. When the Polymer Modified Asphalt Rubber binder or Rubberized Asphalt Binder temperature cools below 375° F. and is then reheated, it should be considered a reheat cycle. The total number of reheat cycles should not exceed two (2). The binder materials should be uniformly reheated to a temperature of not less than 375° F. Additional scrap tire CRM may be added to the reheated Polymer Modified Asphalt Rubber binder and reacted for a minimum of 30 minutes and should not exceed 10 percent of the total binder weight. Reheated Polymer Modified Asphalt Rubber binder should conform to the requirements for blended Polymer Modified Asphalt Rubber binder.
Aggregate Cover Material. Aggregate should be composed of clean and durable crushed rock or crushed gravel conforming to the following requirements:
Proposed aggregate samples should be tested for compatibility and stripping characteristics (vialit testing). The test method is described below.
If the aggregate is to be crushed stone, it should be manufactured from sound, hard, durable material of accepted quality and crushed to specification size. All strata, streaks and pockets of clay, dirt, sandstone, soft rock or other unsuitable material accompanying the sound rock should be discarded and not allowed to enter the crusher.
If the aggregate material is to be crushed gravel, it should consist of hard, durable fragments of stone or gravel of accepted quality and crushed to specification size. All strata, streaks, pockets of sand, excessively fine gravel, clay or other unsuitable material including all stones, rocks and boulders of inferior quality should be discarded and not allowed to enter the crusher. The crushing of the gravel should separate the #4, ⅜ and ½ inch sieves and should have a minimum 95% of the particles with a minimum of one mechanically fractured face and 90% of the particles should have a minimum of two mechanically fractured faces.
The ⅜ inch crushed aggregate or crushed gravel should not contain more than 8% by weight of flat or elongated pieces and should be free from wood, roots and vegetable or other organic extraneous matter. The ⅜ inch crushed aggregate or crushed gravel should have a minimum Cleanness Value (CV) of 80, the ⅛ inch crushed aggregate or crushed gravel should have a minimum Cleanness Value (CV) of 88, and should have a percentage of wear not more than 7 percent at 100 revolutions and not more than 30 percent at 500 revolutions, as determined by ASTM C131 or California Test Method 211. Note: When performing the percentage of wear testing for the ⅛ inch aggregate Schedule “D” Sizing will be required as indicated in California Test Method 211. Modified Fine Durability testing should also be required for the ⅛ inch aggregate, with a minimum acceptable value at 76, as required by California Test Method 229.
The aggregate should show no evidence of disintegration nor show a total loss greater than 12% when subjected to 5 cycles of the sodium sulfate accelerated soundness test specified in ASTM C88.
The crushed aggregate for Polymer Modified Asphalt Rubber binder applications should meet the requirements for gradation given in Table 6. The crushed aggregate for Rubberized Asphalt Binder should meet the requirements for gradation given in Table 7, when tested in accordance with ASTM C136. The ⅛ inch aggregate should be a porphyritic olivine basalt with a specific gravity (coarse bulk SSD) ranging from 2.6-2.8, California Test Method 206. Gray or light colored aggregate should not be used as part of the Rubberized Asphalt Binder chip seal surface course.
The aggregate to be utilized for both binder materials should be hot pre-coated with 0.5 to 1.0 percent PG asphalt cement. The pre-coated aggregate should have a “salt and pepper” appearance and supplied to the project site at 225° F. to 325° F.
There needs to be insurance that good adhesion occurs between binder and aggregate, at the time of placement. The Vialit Retention Test provides a method to assess the active adhesivity of the binder and the aggregate being utilized in conditions, which simulate actual project variables and environment. This method is an indicator of aggregate retention for hot applied chip seal, pavement preservation surface treatments. It is a modification of European Standard EN12272-3, adapted to hot spray applied rubberized/polymer chip seal binders.
Vialit Retention Test. Hot applied, modified binder materials are applied at 79 grams (0.42 gal/sy) to standard size, clean and dry, stainless steel plates. Exactly one hundred (100) washed and graded aggregate particles are embedded into the required binder type. The sample is allowed to cure under specified conditions. Following this cure, the individual plates are conditioned at three different temperatures for 30 minutes. Then a 500 gram steel ball is dropped three (3) times from a distance of 50 cm (20 inches) onto the inverted stainless steel plates. The results are recorded at % aggregate retention with 90% retention being the minimum allowable value.
Steps for Modified Test Method
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- 1) Hot asphalt cement, Polymer Modified Asphalt Rubber or Rubberized Asphalt Binder is pre-heated to approximate application temperature 330° F. (165° C.) to 375° F. (190° C.).
- 2a) Tare weight of plate is recorded.
- 2b) Individual plates are pre-heated in an oven to a minimum of 330° F. (165° C.).
- 2c) 79 grams of asphalt cement/modified binder applied to each plate.
- 2d) Plates are returned to the 330° F. (165° C.) minimum temperature oven for 15 minutes.
- 2e) Plates are removed from the oven and placed on a warm hotplate and the binder is spread and smoothed with a hot blade.
- 2f) Application weight is verified and adjusted as needed.
- 2g) 100 particles of washed and graded aggregate, meeting the project specification requirements, are applied in a 10×10 matrix, with the plate still on the warm hotplate.
- 2h) Three (3) plates are prepared for each combination of binder and aggregate.
- 3) Plates are again returned to the 330° F. (165° C.) minimum temperature oven for 15 minutes.
- 4a) Plates are removed from the oven and allowed to cool at room temperature for four to six hours.
- 4b) Once the room temperature cure is complete, individual plates are conditioned for 30 minutes at each of the following temperatures: 41° F. (5° C.), 14° F. (−10° C.) and −8° F. (−22° C.).
- 5) After the 500 gram steel ball has been dropped three times on each of the three samples, report the number of stones attached as percent aggregate retention at test temperature.
Equipment
Primary equipment utilized in the production and application of Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder materials is as follows:
A PG asphalt cement heating tank with a hot oil heat transfer system or a retort heating system capable of heating the PG asphalt cement to the proper temperature for blending/milling with the CRM and SBS Polymer.
A Polymer Modified Asphalt Rubber/Rubberized Asphalt Binder mechanical blender and a Supraton 549-5.03 mill (or equal) should have a two stage continuous mixing process capable of producing a homogenous blend of PG asphalt cement CRM and SBS Polymer, at the mix design specified ratios, as directed by the engineer. The mechanical blender should be equipped with a dual hopper granulated rubber feed system capable of supplying the PG asphalt cement feed system, as not to interrupt the continuity of the blending process. The maximum capacity of the primary blending vessel should be 500 gallons. Both the primary and secondary blenders should be equipped with an agitation device orientated horizontally in the blending vessel. The mechanical blender and Supraton 549-5.03 mill should be capable of fully blending or milling the individual modifier particles (CRM and SBS Polymer) with the PG asphalt cement. A separate PG asphalt cement feed pump and finished product pump are required. This unit should have a PG asphalt cement totalizing meter in gallons and a flow rate meter in gallons per minute.
A distributor truck equipped with a heating unit, and an internal mixing device capable of maintaining a uniform mixture of PG asphalt cement, CRM and SBS Polymer. It should be equipped with a full circulating spreader bar and pumping system capable of applying the Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder material within a 1% tolerance of the specified application rate, and must achieve a uniform covering of the surface to be treated. The distributor should have a boot board on the rear of the vehicle and a bootman should accompany the distributor. The bootman should ride in a position so that all the spray bar tips are in full view and readily assessable for unplugging, if a plugged tip should occur. The distributor truck should also require a thermometer and a computer rate control (CRC) interlinked with a Coriolis Flow Measuring System to ensure and confirm binder application rate accuracy.
The cover material (chip) spreader should be a self-propelled machine with an aggregate receiving hopper in the rear, belt conveyors to carry the pre-coated aggregate to the front, and a full width spreading hopper. The spreader should be in good mechanical condition and should be capable of applying the cover aggregate uniformly across the spread width and at the specified application rate, and heat-treated belts should be installed on the chip spreader. A minimum of three continually operated self-propelled pneumatic-tired rollers (and one steel wheel roller) should be used for the required rolling of the cover material. The pneumatic-tired rollers' should carry a minimum loading of 3,000 pounds on each wheel and a minimum pressure of 90 pounds per square inch in each tire. Foam filled tires can be utilized.
Construction Methods
Immediately prior to the application of the Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder chip seal applications, the surface should be clean in order to insure adequate adhesion of the Polymer Modified Asphalt Rubber to the existing pavement surface and the Rubberized Asphalt Binder chip seal to the Polymer Modified Asphalt Rubber chip seal. Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder material should be applied only when the existing surface is dry and the atmospheric temperature is above 60° F. and rising.
Concerning the Polymer Modified Asphalt Rubber binder, the percentage of Reclaimed Tire Rubber CRM should be 15-18 percent by weight of the total Polymer Modified Asphalt Rubber mixture; the exact CRM content should be determined by the binder design submitted by the Polymer Modified Asphalt Rubber supplier. During Polymer Modified Asphalt Rubber binder manufacture the CRM percentage should not fluctuate by more than 1 (one) percent by weight of total Polymer Modified Asphalt Rubber mixture, as determined by the original laboratory binder design. The SBS Polymer should be 2 percent by weight of the Polymer Modified Asphalt Rubber mixture. Concerning the Rubberized Asphalt Binder, the percentage of Reclaimed Tire Rubber CRM should be 5-10 percent by weight of the total Rubberized Asphalt Binder mixture, the exact CRM content should be determined by the binder design submitted by the Rubberized Asphalt Binder supplier. The SBS Polymer should be 2-4 percent by weight of the total Rubberized Asphalt Binder mixture. During Rubberized Asphalt Binder manufacture the CRM percentage should not fluctuate by more than 1 (one) percent by weight of total Rubberized Asphalt Binder mixture, as determined by the laboratory binder design.
The temperature of the PG asphalt cement should be between 375° F. and 450° F. at the addition of the CRM and SBS Polymer. The PG asphalt cement, CRM and SBS Polymer should be combined and mixed together in the Polymer Modified Asphalt Rubber binder/Rubberized Asphalt Binder blending unit and/or field Supraton Mill, and reacted in the distributor truck or a reaction vessel for a minimum period of 90 minutes from the time the CRM and SBS Polymer are blended with the PG asphalt cement. The temperature of the Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder mixture should be above 375° F. during the reaction period, but should not exceed 425° F. at any time.
When a job delay occurs after full reaction, the Polymer Modified Asphalt Rubber binder and Rubberized Asphalt Binder may be allowed to cool. The Polymer Modified Asphalt Rubber binder or Rubberized Asphalt Binder should be re-heated slowly just prior to application to a temperature between 375° F. and 400° F. An additional quantity of PG asphalt cement and/or CRM may be added to only to the Polymer Modified Asphalt Rubber binder as required to produce a material with the appropriate viscosity.
Placement of the Polymer Modified Asphalt Rubber and Rubberized Asphalt Binder should proceed only under the following conditions: The pavement surface temperature should be 60° F. and rising. The pavement surface is clean and dry. The wind conditions do not exceed 20 mph. All of the construction equipment such as the Polymer Modified Asphalt Rubber/Rubberized Asphalt Binder distributor, aggregate spreader, haul trucks loaded with cover material, rollers and brooms are in position and ready to commence placement operations. Chance of rain does not exceed 75%.
The Polymer Modified Asphalt Rubber binder should be applied to the existing roadway immediately following mixing and reaction, at a temperature of 375° F. to 400° F. at a rate of 0.60 to 0.65 gallons per square yard, with a maximum of 1% application rate variance allowed. The Rubberized Asphalt Binder should be applied to the Polymer Modified Asphalt Rubber chip seal surface immediately following mixing and reaction, at a temperature of 375° F. to 400° F. at a rate of 0.23 to 0.27 gallons per square yard, with a maximum of 1% application rate variance allowed.
Transverse joints should be constructed by placing building paper across and over the end of the previous Polymer Modified Asphalt Rubber binder or Rubberized Asphalt Binder chip seal application. Once the application has progressed beyond the paper, the paper should be removed immediately and disposed of. The use of paper may be discontinued if the contractor chooses to squeegee the excess Polymer Modified Asphalt Rubber binder material at the transverse joints prior to the placement of the cover aggregate. All longitudinal joints should not exceed a 12-inches (30 cm) overlap and should be staggered from initial Polymer Modified Asphalt Rubber and Rubberized Asphalt Binder application. At no time should the contractor be allowed to place longitudinal joints one on top of the other.
The ⅜ inch or ½ inch pre-coated aggregate should be applied immediately onto the Polymer Modified Asphalt Rubber membrane at a rate of 26 to 34 pounds per square yard and the ⅛ inch pre-coated aggregate should be applied immediately to the Rubberized Asphalt Binder, at a rate of 8 to 12 pounds per square yard. The actual rate selected within this range will be determined in the field based on the appearance of the Polymer Modified Asphalt Rubber chip seal and the Rubberized Asphalt Binder chip seal after initial rolling. At all times the application rate of the cover aggregate should be kept to a minimum. At the time of application the temperature of the aggregate should range from 225° F. to 325° F.
At least three operational pneumatic-tired rollers (and one steel wheel roller) should be provided to accomplish the required embedment of the aggregate cover material. At some project locations, or when production rates dictate, additional or fewer rollers may be utilized. The pneumatic tire rollers should be operated in front of the steel wheel roller. There should always be at least 3 (three) operational pneumatic-tired rollers and 1 (one) 12 to 14 ton operational steel wheel roller on a project. Sufficient rollers should be used for the initial rolling to cover the width of the aggregate spread with one pass. The first pass should be made immediately behind the cover material spreader (chip-box) as the aggregate is being placed. If the spreading is stopped for an extended period, the cover material spreader (chip-box) should be moved ahead or off the chip seal surface so that all cover material may be immediately rolled. Three complete passes with rollers should be made with the pneumatic rollers and one pass with the steel wheel roller.
Upon completion of the Polymer Modified Asphalt Rubber chip seal treatment, the pavement cross section should look as in
The foregoing description has been presented and is intended for the purposes of illustration and description. It is not intended to be exhaustive nor limit the invention to the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application and to enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed for carrying out the invention
Claims
1. A method for installing a dual layer pavement preservation system, comprising the steps of
- preparing the pavement to receive an asphalt surface;
- applying a layer of hot polymer modified asphalt rubber binder;
- applying a layer of ⅜ inch or ½ inch aggregate that is hot pre-coated with 0.5 to 1.0 percent asphalt cement;
- rolling the aggregate into the binder material;
- allowing the combined binder and aggregate to cure;
- removing any loose aggregate;
- applying a layer of hot rubberized asphalt binder;
- applying a layer of ⅛ inch aggregate that is hot pre-coated with 0.5 to 1.0 percent asphalt cement;
- rolling the ⅛ inch aggregate into the rubberized asphalt binder material;
- allowing the combined binder and ⅛ inch aggregate to cure; and
- removing any loose aggregate.
2. The method of claim 1 wherein the polymer modified asphalt rubber binder is applied at a rate of about 0.60 to 0.70 gallons per square yard.
3. The method of claim 1 wherein the ⅜ or ½ inch aggregate is placed at about 28 to 34 pounds per square yard.
4. The method of claim 1 wherein the rubberized asphalt binder is applied at a rate of about 0.20 to 0.23 gallons per square yard.
5. The method of claim 1 wherein the ⅛ inch aggregate is placed at about 10 to 14 pounds per square yard.
6. The method of claim 1 wherein the polymer modified asphalt rubber binder comprises about 15 to 18 percent by weight of reclaimed tire rubber crumb rubber modifier and about 2 percent by weight of SBS polymer, and the rubberized asphalt binder comprises about 5 to 10 percent by weight of reclaimed tire rubber crumb rubber modifier and about 2 to 4 percent by weight of SBS polymer.
7. The method of claim 6 wherein the polymer modified asphalt rubber binder is prepared in a blender unit in which asphalt cement is combined with crumb rubber modifier and SBS polymer at a temperature between about 375° F. and 450° F., reacted in a distributor truck or reaction vessel at a temperature between about 375° F. and 425° F., and applied to the pavement at a temperature between about 375° F. and 400° F.
8. The method of claim 6 wherein the rubberized asphalt binder is prepared in a blender unit in which asphalt cement is combined with crumb rubber modifier and SBS polymer at a temperature between about 375° F. and 450° F., reacted in a distributor truck or reaction vessel at a temperature between about 375° F. and 425° F., and applied to the pavement at a temperature between about 375° F. and 400° F.
9. A dual layer pavement preservation system comprising a polymer modified asphalt rubber chip seal layer in contact with the pavement; and a rubberized asphalt binder chip seal layer on top of the polymer modified asphalt rubber chip seal layer.
10. The system of claim 9 wherein the polymer modified asphalt rubber chip seal layer includes a binder comprising performance graded asphalt cement and about 15 to 18 percent by weight of reclaimed tire rubber crumb rubber modifier and about 2 percent by weight of SBS polymer.
11. The system of claim 10 wherein the rubberized asphalt binder comprises performance grade asphalt cement and about 5 to 10 percent by weight of reclaimed tire rubber crumb rubber modifier and about 2 to 4 percent by weight of SBS polymer.
Type: Application
Filed: Oct 14, 2010
Publication Date: Dec 15, 2011
Inventors: Gregory Reed (Modesto, CA), Marc A. Bertsch (Ripon, CA), Jeffrey Smith (Queen Creek, AZ)
Application Number: 12/905,010
International Classification: E01C 7/32 (20060101); E01C 7/22 (20060101);
