ITEM 402 ASPHALT CONCRETE MIXING PLANTS
402.01 Description. This specification consists of the minimum requirements for an asphalt
concrete mixing plant, including approval, calibration, RAP and RAS management, Warm Mix Asphalt methods, polymer binders, loading and hauling, and mixing and production to produce asphalt concrete mixes according to Department specifications. Control all production processes at the asphalt concrete mixing plant such that the mixture delivered to the paving site meets all specification requirements.
402.02 Mixing Plants. The Department will approve mixing plants before preparation of the
mixtures. Schedule a date with the Department for approval inspection to take place at least 1 week before mix production. Do not produce mixtures for projects from un-approved plants. Asphalt mixtures may be produced using the warm mix asphalt method according to 402.05 except as restricted by specification. Store and introduce additives into the plant according to Supplement 1053. Obtain Department approval of the additive storage and feed systems before the start of production.
402.03 Calibration . Document all company owned plants and their individual high and low
manufacturer recommended operating rates in the Quality Control Plan (403.03). Ensure the plant is calibrated and adheres to the procedures according to Supplement 1101 when producing any asphalt concrete for the Department. Verify the calibrations biweekly using a quick calibration method outlined in S1101. Document all data from calibrations by means of data logger or mix plant controls printouts and post the results in plain view in the plant control room and plant laboratory for reference by the Monitoring Team. Store and have available for review all plant quick calibration results for the previous 12 calendar months at the mix plant . Store all remaining records in accordance with 403.03. If issues arise within quick calibration results, documentation, mix production problems or plant operation concerns, Department personnel may request additional quick calibrations, or a full calibra tion and verification procedure outlined in Supplement 1101.05.
402.04 RAP and RAS Processing Requirements. Process and use RAP by one of the following
two methods.
A.RAP Processing Method 1 -Standard RAP. For surface courses process RAP to less than 0.75 inches (19 mm) and place a 0.75 -inch (19 mm) screen on the cold feed. For other courses place a 2 - inch (50 mm) screen on the cold feed. Ensure that the RAP is the proper size to allow for complete breakdown in the plant. If mixing is incomplete, place a smaller screen on the cold feed.
B.RAP Processing Method 2 -Extended RAP. Use Method 2 only with counter flow drum plants or mini-drum batch plant configurations meeting 402. Process RAP by means of fractionation or by additional in line processing. Fractionate RAP from one pile into multiple piles of various sieve sizes by processing over specific screens as specified in the approved Quality Control Plan. Typically, fractionated RAP is sized into two (coarse or fine) or three (oversize, coarse, or fine) piles. Test fractionated piles to show uniformity. For additional in line processing only process RAP from a uniform, tested and approved stockpile by passing the RAP over a d ouble deck screen placed in -line between the RAP cold feed bin and the mixer. Use a 9/16 -inch (14.3 mm) screen for surface and intermediate mixes and a 1.5-inch (37.5 mm) screen for base mixes. Do not use concurrent project RAP in a stream process.
C.RAS Processing and Usage. Ensure RAS is processed to have 100 percent passing the 1/2 -inch (12.5 mm) sieve and at least 90 percent passing the No. 4 (4.75 mm) sieve. Ensure RAS has less than 1.0 percent deleterious materials and 0.1 percent metals by weight. Do not blend RAS from manufacturing waste and RAS from roofing tear-offs. Introduce and control RAS in asphalt plants in the same manner as RAP is introduced and controlled. RAS for base courses may be preblended with RAP if using rate control equipment to ensure uniformity of blending and if satisfactory blend and production is achieved. RAS may be preblended with a small amount of virgin aggregate meeting 703.05 to minimize stockpile agglomeration. Other methods must be approved by OMM.
D.RAP and RAS QC and Management Requirements. Provide enough space for meeting all RAP and RAS handling requirements at a mix plant facility. Provide a clean, graded base for stockpiles that does not collect water. Test processed stockpiles to ensure uniform gradation and asphalt binder content. Sample at the face of stockpiles and test at least every month or once every 5,000 tons of RAP or RAS used, whichever occurs first. This includes an inspection to ensure no deleterious materials are in the stockpile. Ensure stockpiles adhere to a maximum tolera nce from the established stockpile average on the JMF of ± 5 percent passing the No. 4 (4.75 mm) sieve and ± 0.50 percent for asphalt binder content by centrifuge extraction before continued use of the processed stockpile. If the stockpile is out of tolera nce based on testing, immediately stop using the stockpile and notify District Testing until the issue is resolved. If the issue cannot be resolved, the stockpile will be rejected and all JMFs using the stockpile with be withdrawn or rescinded. Provide all test results and forms on the TE -199. Include a summarized table of the data with date tested for each stockpile and include the stockpile identification(s). Ensure the summarized table is posted in the testing facility and mix plant control room and easily available for review by the Department for the life of the stockpile. If desired, when applying Method 1 Standard RAP requirements, use concurrent Department project RAP in a stream process in place of stockpiling and testing for uniformity but do so in the following manner. Concurrent project RAP must be taken from one exis ting mix type on the concurrent project or two existing mix types if both mix types are taken at the same time in one pass of the milling machine. If these requirements are not met, blend and test for uniformity and apply the stockpile requirements of this specification. Maintain in the plant lab and control room an up to date and dated site map of all tested and untested RAP and RAS stockpiles. Give each stockpile a unique identification using the following format: Year processed, company abbreviations, plant location and number where the stockpile was processed, screen size, “GR” if the pile contains coarse gravel, and A, B, etc. based on number of stockpiles processed (e.g., 2023, ODOT, Columbus -614, ½”, GR, A). Identify if RAS stockpiles are from un - used manufactured shingle waste or used roofing tear -off shingles. Provide in the plant lab RAP and RAS properties for each uniform, blended stockpile cross referenced with its identification. In addition, provide the date the stockpile processing was completed and the stock pile estimated size in tons. For all RAP and RAS established stockpiles, provide a log for each stockpile of the tonnage used and subtracted from the initial measured stockpile versus the measured stockpile tonnage to date that is updated weekly and is available at the testing facility and mix plant control room and easily available for review by the Department for the life of the stockpile. Ensure the measured tonnage is within ten (10.0) percent tolerance of the actual. If the tolerance is exceeded, immediately stop production and notify District Testing until the issue is resolved. If the issue cannot be resolved, the stockpile will be rejected and all JMFs using the stockpile with be wit hdrawn or rescinded. Provide signage at all RAP and RAS stockpiles. Do not add to a stockpile once it is tested for uniformity. Provide signage at all uniform stockpiles to inform haulers that uniform stockpiles are not to be added to. Stockpiles and processing methods are subject to inspection and approval by the Department at any time. Rejection of stockpiles can occur for the presence of foreign or deleterious materials, lack of uniformity, incomplete mixing in the asphalt mixture, adding to stockpiles, or moving RAP or RAS in a way not traceable through the QCP records and methods. OMM will resolve disputes over acceptability of RAP or RAS.
402.05 Warm Mix Asphalt. Notify District Testing before using and ensure the daily TE-199
Quality Control Report reports that WMA was used during production. Warm Mix Asphalt (WMA) is defined as asphalt mixtures produced with various technologies, including water foaming and chemical additives, that have the capacity to be used with lower production temperatures (below 300 degree F), but can also be used at nor mal production temperatures to achieve improved compactability, in -place density, and sustainability and without a diminution of short - and long -term performance. WMA technologies may be used to produce asphalt concrete. Specify the use of warm mix asphal t in the QCP for approval by OMM.
A.Water Injection System . Use a water injection system approved by OMM for the purpose of foaming the asphalt binder. Only use equipment that has been proven stable and effective through project use on non -ODOT projects. Ensure equipment for water injection meets the following requirements:
1.Injection equipment computer controls are in the plant control room and are tied to the plant computer metering.
2.Injection equipment has variable water injection control controlled by the plant operation rate and the water injection can never exceed 2.2 percent by weight of asphalt binder.
3.Water injection rate cannot be manually overridden by the plant operator once in the computer.
4.Injection equipment stops water flow when a control or equipment failure in the injection system occurs.
5.The water injects into the asphalt binder flow before the asphalt binder spray hits aggregate. Do not allow water to touch aggregate before the binder spray.
6.Injection equipment includes water storage and pump control tied to the injection computer controls.
7.Water storage low water alarm installed in the control room.
8.Provide a PG binder sampling valve between the last piping tee on the tank side of the line and the injection equipment to sample PG binder before water is injected.
B.Other WMA Technologies. All other WMA methods or technologies will be reviewed by OMM for approval. Chemical WMA may be used where WMA is allowed. Use chemical WMA additives on the approved list only at the recommended rates listed on the approved list. When chemical WMA is required by specifications for cold temperature paving, produce mix using HMA mixing temperatures. Ensure bill of lading from terminal and TE-199 documents that chemical WMA additive was used, the amount used, and the product name used. Include on the weight ticket in Supplement 1101.02 that chemical WMA is being used. This can be added after the JMF number.
402.06 In-line Blending of Modifiers and Additives . Provide in-line blending at the asphalt
concrete mix plant of modifiers such as SBR polymer binders and additives such as liquid antistrips. Ensure asphalt concrete mix plants meet the following if the mix plant plans to use modifiers or additives. Include in the QCP what mix plant facilities will use modifiers or additives and how they will be incorporated into the mix. Ensure modifier and additive rates are not consistently on the low or high side and adjust to meet target rate and note change on the TE-199. Ensure in-line blending pumps and flow meters meet Supplement 1053 and also meet or exceed the modifier or additive manufacturer's recommendations. Provide a written statement from the manufacturer that the pump and flow meter meet Supplement 1053 and also meet or exceed the modifier or additive manufacturer's recommendations.
A.Post Blended SBR Polymer Binders. If an asphalt binder is modified by SBR at an asphalt concrete mixing plant, equip the plant with an automated SBR flow control and monitoring system. Obtain OMM’s approval of the system before operating and demonstrate the system calibration to District Testing. If District Testing waives the demonstration, provide a letter documenting calibration data for the flow system to District Testing for each project. Obt ain written approval from OMM for the use of SBR and ensure the QCP contains methods for properly controlling and sampling SBR binder blends. For drum mix plants, introduce the SBR directly into the asphalt binder line through means of an in- line motionless blender or other device approved by OMM that is able to provide a homogeneous blend. Ensure the in-line motionless blender design provides aggressive interaction of asphalt binder and SBR emulsion to provide a homogenous blend at the sampling port. Do not use swirl type blend. Locate a sampling valve between the in -line blender and the plant drum, at least 12 ft (3 m) downstream of the in -line blender and at least 5 ft (1 m) downstream of a piping elbow. Ensure the sampling valve port is at least 1 inch (25.4 mm) in diameter. Ensure the sampling valve can be opened quickly for maximizing sample flow for the purpose of obtaining a proper sample. In place of an in -line sampling valve, a sample may be taken from a 3 to 5 gal (11 to 19 L) surge tank as long as the tank is downstream of the required blender and the in-line flow can be quickly and directly diverted to the surge tank. Continue mixing for a minimum of 20 seconds after SBR is added and long enough to provide a uniform mixture. Ensure the SBR pumping and metering system is capable of adding the SBR within the limits of
702.01 For drum plants ensure the SBR pump is automatically controlled by an independent computer
and interfaced with the asphalt binder flow to automatically maintain the SBR flow within specification limits. Produce asphalt mixtures for placement in automatic SBR control mode only. Ensure the SBR meter is a magnetic flow meter consisting of a metering flow tube which utilizes Faraday’s Law of Induction to measure the flow and includes a transmitter to transmit the flow signal to a totalizer located in the control room of the asphalt plant. Obtain OMM approval for use of any other type of SBR meter. Locate the SBR meter downstream of any recirculation lines. Provide a means for removing the SBR line at the in-line blender to be able to obtain a sample of the SBR for calibration purposes. Ensure the SBR meter is accurate to ± 2.0 percent over a flow range typical of that used at the asphalt plant (typically 0.8 to 12 gpm (0.05 to 0.76 L/s) at drum plants and 10 to 25 gpm (0.63 to 1.58 L/s) at batch plants). Ensure the totalizer displays total volume measured and flow rate in standard engineering units. Ensure the totalizer is interfaced with a data logger that produces printouts of the logged data every five minutes for a drum plant or every batch for a batch plant. Ensure the logged data includes time, date, flow rate, and flow total except flow rate is not necessary for batch plant production.
B.Liquid Antistrip Additives . Use liquid antistrip additives on the approved list only. When liquid antistrip additives are required by specifications, in-line blend at the asphalt concrete mix plant only according to Supplement 1053.
C.Chemical WMA Additives . When using chemical WMA additives, in -line blend according to Supplement 1053. In-line blending may occur at asphalt binder terminals as long as in - line blending equipment meets Supplement 1053 and the system is approved by OMM.
402.07 Mixing and Production . Do not start mix production without a preliminary JMF
approval and 48 hour notification of District Testing. Do not start each production day without the moisture contents of the aggregate, RAP, and RAS stockpiles to be used in the JMF tested according to 403.06. Ensure the moisture contents are entered into computerized plant controls. Ensure new moisture contents are tested and entered after weather events and as outlined in the Contractor’s QCP. Set the plant controls for the computerized plant at the JMF design total and virgin asphalt binder contents, recycled materials, and any other additives used at all times unless a change is authorized by District Testing. Follow 403.07 for JMF field adjustments. Maintain the temperature of the mix at the plant within the range in JMF or according to the specification. Ensure the mixture is workable and temperature is sufficient for compaction at the point of placement. For batch plants, after all of the aggregate is in the mixer, add the asphalt binder in an evenly spread sheet over the full length of the mixer. The mixing time is defined as the interval between the start of application of the asphalt binder and the open ing of the mixer gate. Discharge all asphalt binder required for one batch in 30 seconds or less. After the asphalt binder is added, apply the mixing time determined by OMM but not less than 30 seconds. When using a batch plant for base mix production, use screens with openings of sizes that result in a reasonably balanced separation of the dried and heated aggregate into a minimum of two bins.
A.Aggregate Preparation. Feed aggregates in their proper proportions and at a rate to permit correct and uniform control of heating and drying. Remove all aggregates in the plant that will produce a mix outside the temperature limits or that contain excessive moisture or expandi ng gases causing foaming in the mixture and return them to the proper stockpiles.
B.Asphalt Binder. Heat the asphalt binder and deliver it to the mixer within the temperature range specified in Table 702.00-1. Do not use asphalt binder while it is foaming in a storage tank. For drum mix plants, introduce the SBR binder directly into the asphalt binder line as described in
402.06 For batch plants, add the SBR binder after the aggregate has been completely coated with
asphalt binder. Continue mixing for a minimum of 20 seconds after SBR is added and long enough to provide a uniform mixture. Take samples using approved, new, containers from the binder line between the last piping ‘tee’ and inlet into the plant unless a different storage method requires a different sampling location. At a minimum, take a split sample of asphalt binder whenever the Department requests a sample. For sampling SBR binder, the contents of the tank should be drained into a 5 gal (19 L) sampling bucket and stirred before filling the required sample container. Provide a sampling valve port that is in a position to safely obtain the required sample volum e in the required 5 gal (19 L) sampling bucket. Provide a stable sampling rack to obtain a sample. Balling or wadding of SBR or uncoated aggregate indicates improper mixing; cease production immediately and until corrected to District Testing satisfaction.
C.Stopped Production. Do not restart production after a shutdown required by 403 until OMM or District Testing accepts the proposed remedy. Following a shutdown restart production in a manner acceptable to District Testing. When production problems cannot be solved within one day after a plant shutdown, a Contractor’s approved Asphalt Level 3 Technician is required to be at the asphalt plant until a full production day is achieved with results satisfactory to the Monitoring Team as established in 403.06.
402.08 Loading and Hauling. Before loading, apply a thin coating of an approved release agent to
the inside surfaces of the truck bed to prevent adhesion of mixture to the bed surfaces. OMM maintains a list of approved release agents. Do not use diesel or fuel oil for this purpose. Any use of non-approved release agent, diesel, or fuel oil may result in suspension of truck, driver, or both for up to one year. Drain truck beds after applying the release agent and before loading. Load trucks in manner to minimize segregation of the mixture. Equip all truck beds with a securely fastened, waterproof cover of suitable material to protect the mixture from wind and weather. Cover truck beds with the secure, waterproof cover after loading.
Referenced in this section
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Source: Construction and Material Specifications, 2023 (rev. 7/17/2026) Edition. Pages 165–171 of 892. View official source ↗