HOT IN-PLACE ASPHALT SURFACE RECYCLING
Hot surface recycling has proven to be the most effective method of resurfacing in the industry. The objective of Hot in-place asphalt surface recycling is to reduce the amount of new asphalt used in a resurfacing project. The new technology of 100% radiant heat to soften the asphalt pavement, has dramatically changed the process to allow every pavement manager, rural urban and private, to take advantage of this method.
USES OF HOT IN-PLACE ASPHALT SURFACE RECYCLING
* Correct gradation deficiencies
* Correct asphalt deficiencies (too little or too much)
* Correct asphalt properties
* Block cracking
* After a surface has been milled to proper grade
* To add a soft cushion for a new asphalt lift where additional structural needs are required
This statement, taken from the United States Department of Transportation, Federal Highways Administration, National Highway Institute Techniques for Pavement Rehabilitation Training Course, revised January 1984, states as follows:
It is a commonly accepted rule of thumb that a one inch overlay over once inch of recycled material out performs a
2 1/2 inch overlay.
CONSIDERATION BEFORE BIDDING
HOT IN-PLACE ASPHALT SURFACE RECYCLING
1. The streets to be recycled should be available for the bidding contractor to look at so that a good determination can be obtained to avoid costly change orders. In a contract that contains an optional, annual bid extension, the streets should be available for the contractor to see before agreeing to extend each additional annual contract and the contractor should sign an affidavit that he has seen the streets to be recycled and knows their condition. The contractor should also test the streets to determine the proper amount of rejuvenating agent. As obvious as this may seem, there are contractors that have convinced the Engineers that this is not necessary. The only reason I could think a recycling contractor would not want to see the streets, contrary to the (ARRA) Asphalt Recycling and Reclaiming Association Handbook, or to test them, is because when they recycle there is no need to make the necessary testing required for a good job. If the owner tests the recycled street after they are completed and finds the recycling very poor what does he have to compare it to? Is this the reason these same recycling contractors recommend that one place a minimum of 11/2 to 2 inches of new asphalt over the asphalt they recycle? Then what is the point of recycling? There is no money saved, in fact, now its going to cost even more money to resurface, unless the street needs more asphalt for strength. I have witnessed this type of poor quality control from a recycling company that uses a single machine that recycles and lays the new asphalt mix with no separation between the recycled asphalt and the installation of the new asphalt. This type of machine prohibits proper inspection and quality control and is not recommended.
2. Many asphalt pavement projects are appropriate for the hot-in-place asphalt surface recycling. Suitable pavements that have good stability and an adequate base, but often exhibit cracks, deterioration, and other surface characteristics not conductive to good riding qualities or appearance.
3. In some hot-in-place asphalt surface recycling, pavements that have received prior treatments with special seal coatings, slurries or chip seals, may require removal of these contaminates, determined by the engineer prior to any hot surface treatment.
4. My recommendation to all Pavement Managers is to keep all the miracle surfaces, fabrics, sealants, slurries and fiber off and out of your asphalt so a Hot in-place asphalt surface recycling contractor can recycle your streets every 20 years the way we are about to do in the fine City of Orlando, Florida.
5. Painted lines, which will interfere with the recycling process, must be removed.
6. Additional hot asphalt mix can be installed at the same time using an approved paver, following the hot-in-place asphalt surface recycling and if it is installed immediately behind the hot-in-place asphalt surface recycling, before the recycled asphalt is rolled, one can place as little as 1/2 inch of additional hot mix asphalt using a mix with the largest stone, maximum 3/8. If the hot mix asphalt is not immediately installed, to be installed at a later date or after the recycled hot surface treatment is compacted, then a minimum of 1 inch of hot asphalt mix is recommended.
7. When recycling and adding 3/4 new asphalt, some machines have a screed that will take the recycled asphalt away from the curb or gutter and no milling would be required.
8. Milling. If the street to be recycled has to keep the same level with the curb or gutter then it would be necessary to mill 3/4, or whatever thickness is required of the new asphalt. Example: 3/4 mill at the gutter, 3/4 out 5 to 0. If the existing street is 1 higher than the curb or gutter and the job calls for an additional 3/4, it is recommended that the street be milled 1 3/4 at the curb or gutter out 10 to 0.
Structures. Existing manholes, water valve boxes, junction boxes, etc. that do not conform to the finished pavement grade, shall be adjusted by the contractor by using riser rings and boxes or as directed by the Engineer. It is important to order these extensions well in advance to allow for manufacturing and shipping.
ADVANTAGES OF SEPARATING HOT-IN-PLACE ASPHALT SURFACE RECYCLING AND RIDING SURFACE APPLICATIONS OTHER THAN AN ASPHALT OVERLAY
1. With the exception of additional hot mix asphalt, which, as an option, can be included in the hot-in-place asphalt surface recycling, all the additional asphalt surface applications such as sand seal, slurry seal, chip seal and micro surfacing, should be considered a distinct and separate application and should be bid and inspected as a separate item to be applied sometime after the hot-in-place asphalt surface recycling has been completed, inspected and accepted.
2. The hot-in-place asphalt surface recycling contractor and the other surface application contractor can operate apart from each other to achieve the maximum efficiency of operations and avoid scheduling conflicts.
3. Inspection and acceptance of the Hot in-place asphalt surface recycling can be readily accomplished to ensure full compliance before any other type of surface is installed.
4. Inspection and acceptance of the other riding surface can be completed without being confused with the hot surface treatment. Once again, this provides ready inspection to ensure quality performance on this portion of the job.
5. Scheduling of the hot-in-place asphalt surface recycling with a time interval before the overlay of another riding surface can be achieved by separating the items on the bid or by letting separate bids.
6. Separating these items will also give you the true unit price for each item showing the actual cost savings of hot-in-place asphalt surface recycling.
OPTION #1 (By Owner)
All testing of the asphalt surfaces will be completed by the owner to determine the optimum quantity per unit of recycling agent, the depth of asphalt to be recycled and the required thickness of the new asphalt to be placed. This information will be given for each street area and made a part of the invitation for bidding documents.
OPTION #2 (By Contractor)
General. Immediately after receiving a Notice to Proceed, the Contractor shall arrange for testing of the asphalt surface to determine the optimum type and quantity per unit area of recycling agent, and the density of the surface asphalt. The Contractor shall request approval of a testing laboratory experienced in asphalt technology and receive approval from the Agency in writing before authorizing any testing.
Sampling. The Contractor shall instruct the testing laboratory to obtain one core in every 1000 feet of street. Core shall be alternated from lane to lane and be distributed uniformly on both sides of the street. Core points shall be indicated on the contract plans and submitted to the City with other test results. Enough cores shall be taken to provide sufficient asphalt concrete to perform the necessary tests.
Test Methods. Extraction of asphalt shall be performed under Method ASTM D 2172 and shall be performed only on the top one inch of the core. The extracted asphalt shall be reclaimed from solution by Method ASTM D 1856. Penetration tests shall be performed as needed under test Method ASTM D 5 to determine the optimum amount of recycling agent for each street, whichever is less.
The testing laboratory shall provide a recommendation for the quantity of recycling agent necessary to provide optimal properties for the recycled asphalt on each street. An asphalt content test shall be performed on each segment of pavement to verify that total asphalt content in the recycled pavement does not exceed 7 percent by weight. Enough tests shall be provided such that the testing laboratory can make proper recommendations on each street. A brief report of all test results and criteria used as basis for the determination shall be submitted to the Engineer at least two working days prior to the scheduled start of work.
All time required for testing, including the two days for City review of the testing laboratory’s initial report for the recommended recycling agent, shall be included in the “Time for Completion” set forth in the General Specifications of the contract documents.
SELECTING THE PROPER HEATING MACHINE
This is one of the most important decisions of any hot surface project. Many pavement managers in the past have had considerable problems with the open flame type heating machine. If the new 100% radiant heaters were used when Hot in-place asphalt surface recycling started in the 1960s, the process would be the dominating process of resurfacing streets today. For example, the open flame heaters burn and scorch the asphalt being recycled, which destroys all the prior testing to establish the proper amount of recycling agent, the uneven heat to asphalt being recycled creating uneven and insufficient scarification, blue/black smoke spilling into the air, the burning of vegetation adjacent and overhanging the street, the burning of the bark off the roadside of the trees and other vegetation, some of which are destroyed and the danger to bystanders and even pedestrians walking past the Heaters. This is one of the most damaging stages in hot surface recycling and some agencies that have realized the savings of HSR in the past, have chosen not to continue because of this damage caused by these fire breathing dragons. It has also deterred many other agencies from even trying the recycling method. The only way to eliminate the risk is to specify a heating system that is 100% radiant, (no flame) and has the capabilities to contain the heat under the heating panel and spread the heat under the chamber so that every square foot produces the same amount of BTUs per hr.and can be adjustable from 40,000 to 100,000 BTUs per hr., for the various conditions of the asphalt being heated and the conditions of the environment. Even the Asphalt Recycling and Reclaiming Association has addressed the open flame problem and go on to say that most recycling machines have converted to LPG liquid propane fuel, infrared or Radiant heating systems. All recycling machines should be infrared or radiant heat. The 100% radiant heat is capable of heating to the full depth of the asphalt to be recycled so that only viscous shearing (having a heavy, gluey quality) occurs. Scarifiers or milling heads with carbide teeth should not be allowed. The average temperature as measured by a thermometer located 18 inches from the pavement surface and 24 inches from the heater chamber shall not exceed 180° F. under wind of less than two miles per hour in velocity. Under no condition shall this temperature reading exceed an average 180° F. in the vicinity of plants either alive or not. In no case shall there be protruding flames. Any plants subject to temperature over 140° F. shall be sprayed with water such that they are damp during the period of high temperatures. Most of all, infrared and radiant heating systems are the only heating systems that will ensure protection of the properties and vegetation adjacent or overhead of the pavement being recycled and proper depth of the asphalt being recycled is obtained..
GUIDELINES FOR ASPHALT RECYCLING AGENTS
The intent of adding a rejuvenating agent is to increase the penetration and lower the viscosity of the recycled asphalt.
The conventional Emulsified Rejuvenating agents do not increase their measurement much, but there are new rejuvenating agents that are 300% better and can bring the recycled asphalt up to minimum standards for new FDOT asphalt.
The rejuvenating agent must be a straight oil product. It is the only rejuvenator that can increase penetration and viscosity standards close to or equal new asphalt. Emulsion type rejuvenator or any rejuvenating agent that has water and is not 100% oil can not be used because it requires so much in volume such that voids will be filled, leaving excess with no place to go. This can cause (1) lower penetration, (2) higher viscosity, (3) most important, it will cause bleeding of the rejuvenator to the top of the additional new asphalt surface if not enough voids are left in the recycled asphalt.
SELECTING THE PROPER REJUVENATOR APPLICATION SYSTEM
The machines should be equipped with a rejuvenating spinner type applicator adjustable from .02 gallons per square yare to .15 gallons per square yard. The rate of application shall be determined by the engineer, based on preconstruction laboratory analysis and adjustments for varying field conditions.
The specified application of the rejuvenating agent shall be meticulously measured. First the speed of the machine shall be measured giving an accurate foot per minute reading. Then the rejuvenating agent is to be properly calculated and applied to the recycled asphalt by spinners that will allow the application in droplets which is heavy enough that any wind will not move the recycling agent off target which happens when a fine mist spraying type application is used. Because of the potency of the new 100% oil rejuvenator, it is applied very thin. Trying to apply it by a fine mist from spraying nozzles allows even the slightest wind to disperse the spray everywhere but where it is intended to go.
New Bituminous Concrete
The mix designs for the application of the new bituminous concrete layer will vary in accordance with the thickness of the bituminous concrete being laid.
The mix design of the new bituminous concrete surface, by owner, less than 1” shall have a maximum size aggregate of 3/8”.
The mix design of the new bituminous concrete surface, by owner, 1” or thicker shall have a maximum size aggregate of 5/8”.
Depth of the asphalt being recycled will vary in accordance with the thickness of the existing asphalt and other factors determined by the owner.
It is the owner’s intention to raise the penetration and lower the viscosity of the recycled asphalt to minimum FDOT standards for new asphalt.
In the past, under the standard practices in the Industry, there have been surface areas that have not been included in the recycling portion of the paving, such as the radius at intersections, cul-de-sacs, cross overs and other areas not practical for a recycling train. Rather than scarifying, contractors have been tacking and resurfacing or milling, tacking and resurfacing. Pavement Savers recommends that this no longer be considered acceptable and that these areas should be Hot in-place recycled by means of a smaller, single machine that will heat the surface up to not less than 350°F. and before the temperature drops below 300°F. the surface shall be scarified to a depth reasonable to accept the rejuvenating agent, and recompacted.
These areas are to be recycled before the recycling is done by the recycling train
SELECTING THE PROPER SCARIFICATION SYSTEM
This is another important step to ensure a good Hot-in-place asphalt recycling program. The scarifying should take place using spring equalized scarifiers not harder than a #12 hardened 1/2 inch bolt. This will ensure pure viscous (having a heavy, gluey quality) shearing of the heated asphalt only. Scarifiers and milling heads using carbide teeth can not be allowed to reach the proper depth of the recycled asphalt specified in the bid in place of proper heating of the asphalt. Doing so will (a) break the stone, (b) loosen asphalt too cold to recompact, (c) leaving uncoated sides of the stone, (d) change the mix design, (e) segregate the mix (f) create a powder-like unviscous material that will not bond to the pavement below the recycled pavement (g) resist compaction for proper density (h) leaving a porous area under the surface where moisture can collect and freeze, and a loose bond between the surfaces. Using the proper heating equipment will allow scarification without carbide scarifier/milling/mixing equipment.
DEPTH OF SCARIFICATION
The recommended depth of scarification according to the (ARRA) Asphalt Recycling and Reclaiming Association has been a minimum of 3/4 inch or 9 lbs per sq ft. Tests have shown that is where 90% of the oxidation of the asphalt to be recycled occurs. There have been specifications requiring a minimum of 1 1/2 inches. The 1 1/2 inch specification surfaced in the early 1980s. Even when the specification called for 1 1/2 inches, very few, if any, succeeded. What it did do was eliminate competitive competition, because all of the reputable recycling contractors knew that these depths could not be accomplished without converting to carbide teeth, which causes the recycling contractor to lose the viscous shearing which defeats the purpose of deeper scarification, so they did not bid. Next a specification surfaced calling for a maximum of 1 1/2inches, but no minimum. Can you imagine? Now, most of the so called 1 1/2 recycling contractors have come back to the original and more attainable spec of 3/4 to 1 inch deep, others went out of business. Pavement Savers recommends that for the best job, for the most competitive price, a specification of 1 inch depth be required. It has been proven that 3/4 inch is where 90% of the oxidation of the asphalt occurs. We have a 30 minute video available on the oxidation of asphalt pavement. If one wishes to require a deeper scarification, then we recommend that the depth not exceed deeper than 1/4 inch from the interface between the surface course and the base course. The reason for this is (a) there is usually a moisture barrier between the two courses which will prevent an economical scarification just for an additional 1/4 inch and (b) the scarifying could get into the base asphalt, mixing the larger stone and contaminating the surface mix.
AIR QUALITY PROVISIONS
Hot in-place asphalt surface recycling projects that require liquid propane gas, 100% radiant, (no flame) heating units have conformed to the most stringent local and regional air quality standards that open flame heaters can not, for example the South Coast Air Quality Board (California). These standards may vary, but a typical standard is as follows:
1. Visible emissions of more than 20% opacity should not be discharged into the atmosphere for a period or periods totaling more than two minutes in any one hour. For this purpose of this rule, visual emissions are to be viewed by an observer from the ground up.
2. All heating units of equipment should be fired with liquid propane gas (LPG).
The engineer shall require the successful bidder to submit a list of at least 5 (five) comparable size projects performed using the equipment and techniques specified. Said list shall include at least 1 (one) job to be over 15 years old where less than 1 inch of asphalt was placed over the recycled asphalt, the agency name, address, telephone number of the engineer in charge, and pictures of the adjacent properties before and after the hot surface treatments to ensure that the heat system being used did not damage the adjacent properties.
In lieu of the above, the Contractor may qualify his equipment by a demonstration on this or comparable work to the satisfaction of the engineer. Equipment not approved by the engineer shall be removed from the project and acceptable machines supplied. The cost of this demonstration shall be borne by the contractor.
Weather. Ambient temperature does not play as much of a factor when Hot in-place asphalt surface recycling versus conventional paving. Attention is to be directed to the surface temperature of the pavement to be recycled. If the surface temperature is 50° F and rising, one can recycle. The contractor still has the responsibility to meet the minimum required temperature of the recycled and new asphalt before compaction. If the surface is below 50° F, but the ambient temperature is rising, the contractor can raise the temperature of the surface to be recycled to specification with the heaters and continue recycling.
Wet surfaces can be dried off by the heaters before starting the recycling process.
Naturally, day time hours are the best to do hot in-place recycling. The sun helps to warm the asphalt. Just ask any contractor that cold mills what happens when they go into the shade. There is nothing wrong with night work as long as the agency understands that production will drop, sometimes as much as 10% or 1.5 FPM (feet per minute) off of 15 FPM equaling 13.5 FPM.
The heater scarifier should be capable of heating the surface to the proper depth at a minimum travel rate of 15 feet per minute under normal working conditions. Only the last heater scarifier shall do the scarifying.
The existing asphalt surface should be heated from 6 inches to 12 inches wider than the widths to be recycled. The temperature of the scarified material shall be a minimum of 225 degrees and shall not exceed 350 degrees when measured with a thermometer immediately behind the scarifier.
The specified grade of recycling agent shall be applied. The rate of application shall be determined by the engineer, based on pre-construction laboratory analysis and adjustments for varying field conditions.
Scarification should be deemed acceptable when the average of five consecutive measurements in an area across the recycled mat, one on each side, one on each side 1/4 of the way to the center, and one probe in the center. The depth of the five probes shall average 1 inch and should be checked by the contractor every 100 yards.
The scarified material shall be distributed and leveled. The temperature of the recycled asphalt immediately behind the recycling screed should read a minimum of 225° F. The width recycled shall be rolled immediately while it possesses a minimum temperature of 170°, for proper compaction.
The recycled asphalt shall be scraped off by means of a flat asphalt shovel to verify that a black viscous finish exists at the interface between the recycled asphalt and the asphalt below. Any kind of powdery material will not be acceptable.
RESURFACING WITH THE APPLICATION OF ADDITIONAL ASPHALT
(ARRA) GUIDELINE BID SPECIFICATION BOOK (CALLED METHOD B REPAVE)
A. The asphalt shall be placed by a paver immediately behind the recycler, before the recycled asphalt has been rolled, and while it still has a minimum temperature of not less than 170 degrees F.
B. Resurfacing with additional asphalt of 1 inch or more, the asphalt can be placed immediately, as in (A) above, or can be completely separate from the recycling operation to be placed at another time.
C. All new asphalt should be 100% virgin when placing under 1, maximum stone size 3/8, over 1 maximum stone size 5/8. Although virgin asphalt may cost more, one can install less, making up for the additional cost.
MEASUREMENT AND PAYMENT
1. It has been determined that for the most economical price one should call for a job of a minimum of 100,000 square yards.
2. Items, such as the removal of paint markings shall be paid for on a square foot basis. Other asphalt treatments deemed necessary to be removed before the recycling or any other milling is to take place, shall be paid for on a square yard basis.
3. Heating, scarifying, leveling, compacting of the pavement and installation of additional bituminous concrete, shall be paid for at the contract unit price per square yard (all under one item). Such price shall constitute full compensation for the item as herein described and specified, with the exception of the new asphalt material which shall be paid for and delivered to the job site by the owner. If the new asphalt is to be installed at a later time it and if any other coatings such as chip seal, slurry seal, and seal coating is called for, it shall be a separate contract and be paid for at a separate contract unit price per square yard or per ton. Such price shall constitute full compensation for the item as described and specified.
4. Recycling agent will be paid for at the contract unit price per gallon by certified weight. The certified weight shall be determined by weighing on sealed scales, regularly inspected by the State Bureau of Weights and Measures. The unit price shall include full compensation for furnishing and applying the recycling agent.
Thermal Power Corporation is dedicated to manufacturing the finest Pavement Saving equipment in the world.
The primary purpose of these specifications is to develop a clean, clear, quiet, high quality Hot in-place asphalt surface recycling reputation and raising to the highest standards of such treatments so that every pavement manager, rural, urban or private, can take advantage of the savings.
We have made the most economical method for resurfacing an asphalt street, Hot in-place asphalt surface recycling, a science with stringent tests and inspections. It is no longer the gosh and by golly process that it was. If you wanted to know where they were working, look for the smoke.
Since 1978, we at Thermal Power Corporation have set the best specifications possible and then built the machinery to perform these specifications. We have made this machinery available to everyone, by offering them for purchase, lease or rent. We do not try to single source to make a profit. We can make a profit competing, by being the best.
Thermal Power Corporation is constantly striving to improve its products and methods. Therefore, we reserve the right to change design, materials, and/or specifications without notice.