CONCRETE PLANT MIX COURSES
409.01 Mineral Aggregates. Mineral aggregate for Asphalt
Concrete Hot Mix Base Course, Asphalt Concrete Hot Mix Binder Course, Asphalt Concrete Hot Mix Surface Course, an d Asphalt Concrete Cold Plant Mix shall consist of combinatio ns of coarse aggregate, fine aggregate and mineral filler as pro vided for in the respective mix designs. Mineral aggregate shall co nsist of clean, hard, durable fragments of aggregate of uniform qua lity, free from an excess of soft particles, deleterious material a nd adherent films of clay. Eighty-five percent of the mineral aggregate shall be produced from larger particles by mechanical crushing operat ions. Coarse aggregate shall comply with Table 409-1. Table 409-1 Coarse Aggregate Properties Coarse Aggregate Type Size Fractured Faces One Face Two Faces LA Abrasion (AASHTO T 96) Sodium Sulfate Soundness Note 1 (AASHTO T 104, 5 cycle) Flat, Elongated Particle Wearing Surface Aggregate Limestone Other Note 2 Gravel Other Note 3 Crushed Gravel; Crushed Stone; Steel Slag Plus No. 8 (2.36 mm) 98 % min. 80 % min. 40 % max. 12% max. 10 % max. 60 % max. 40 % min. 60 % max. 40 % min. NOTE 1: Sodium Sulfate Soundness does not apply to Crushed Gravel. 263 NOTE 2: Crushed sandstone, crushed siliceous gravel , syenite, novaculite, crushed steel slag, or mineral aggregat e which has an insoluble residue not less than 85% when tested in a 1:1 solution of hydrochloric acid and water according to ASTM D3 042 shall be used as the remaining coarse mineral aggregate. NOTE 3: Crushed steel slag, crushed sandstone, syen ite, novaculite, or other crushed quarry stone which has an insoluble residue not less than 85% when tested in a 1:1 solu tion of hydrochloric acid and water according to ASTM D3042 shall be used as the remaining coarse mineral aggregate. The fine aggregate shall comply with Table 409-2. Table 409-2 Fine Aggregate Properties Fine Aggregate Type Note 1 Manufactured Sand; Natural Sand Size Minus No. 8 (2.36 mm) Fine Aggregate Angularity Note 2 & 3 As specified in AASHTO M 323 Sand Equivalent As specified in AASHTO M 323 Natural Sand Content 15% max. Coal and/or Lignite Note 4 2% max. NOTE 1: Manufactured sand shall be angular particl es that have been produced from larger particles by mechanical c rushing operations. NOTE 2: Test to be performed according to AASHTO T 304 using the aggregate blend specific gravity of the m inus No. 8 (2.36 mm) sieve through plus No. 100 (0.15 mm) siev e material. NOTE 3: If any part of an ACHM Binder Course or an ACHM Base Course is used within 4 inches (100 mm) of the pavement surface, the binder or base course lift shall compl y with the angularity requirements for the top 4 inches (100 m m) of pavement. NOTE 4: The amount of coal and lignite shall be de termined according to AASHTO T 113. 264 409.02 Asphalt Binder. Asphalt binder shall be according to AASHTO M 320 Table 1, except the Direct Tension req uirement is deleted. If required, the asphalt binder shall contain a hea t-stable anti- stripping additive. The additive shall be approved by the Engineer. It shall be added at the rate of 0.5% to 0.75% by w eight of asphalt binder as determined by laboratory analysis and lab oratory mix design procedures. The anti-stripping additive sha ll be added by an in-line blending process just before introduction o f the asphalt binder to the mixer.
409.03 Mixing Plants. (a) General. The plant used in the
production of the mixture shall be of the separate weigh batch type, the continuous mixing type, or the drum mixing type . The separate weigh batch type and the continuous mixing type may be operated without screens.
b.Requirements of All Plants.
1.Uniformity. The plant shall be so designed, coordinated, and operated as to produce mixtures within the job mix tolerances fixed by these specifications.
2.Storage Tanks for Asphalt Binder. Storage tanks shall be equipped to heat the asphalt binder, under effec tive and positive control at all times, to the temperature r equirements set forth in the specifications. Heating shall be acco mplished by steam or oil coils, electricity, or other means suc h that no flame comes into contact with the heating tank. A circulating system for the asphalt binder shall b e provided of adequate size to ensure proper and continuous ci rculation during the entire operating period. Pipe lines and fittings shall be steam or oil jacke ted or otherwise properly insulated to prevent heat loss. Provisions shall be made for sampling storage tanks . The asphalt storage system shall be provided with s ignal devices and controls that will warn of low levels i f the asphalt storage level is lowered to the point of exposing t he feed end of the asphalt suction line. 265 (3) Mineral Filler and Dust Return. Dry storage shall be provided for mineral filler, when required, and pro vision shall be made for accurate proportioning. If the asphalt plant is equipped with a baghouse du st collector, the fines, if elected to be reintroduced to the mix ture, shall be added to the mixture at the approximate rate at whi ch collected. In addition baghouse fines may be stored in a silo for use in mixes. If baghouse fines from a silo are incorpora ted into a mix, the baghouse fines shall be added at the rate that is shown on the mix design. Direct return from the baghouse to the hot elevator will be permitted only when it can be demonstrated that the flow can be controlled at a uniform rate. Intermittent feeding of baghouse fines into the mixture will not be permitt ed.
4.Cold Feed Bins and Cold Feeder for Dryer. A minimum of 3 cold feed bins shall be used with weig h batch and continuous mixing type plants, and a minimum of 4 c old feed bins shall be used with drum mixing type plants, we igh batch type plants without screens, and continuous mixing type plants without screens. The bins shall be of sufficient si ze to store the amount of aggregate that is required for continuous plant operations. The unit shall have a mechanical feede r control mounted under the cold feed bins capable of control ling cold aggregate feeds at the rates shown on the job mix d esign. A scalper screen of the dimensions necessary to rem ove oversize aggregates shall be provided.
5.Dryer. The plant shall include a dryer or dryers that wi ll continuously agitate the aggregate during the heati ng and drying process. The dryer shall be capable of heating and drying the aggregate to the moisture and temperature requireme nts without leaving any visible unburned fuel or carbon residue on the aggregate when discharged from the dryer.
6.Asphalt Control Unit. Satisfactory means, either by weighing, metering, or the taking of volumetric mea surements, shall be provided to obtain the proper amount of as phalt binder in the mixture within the tolerance specified for the job mix. Suitable means shall be provided, either by steam j acketing or other insulation, for maintaining the specified tem perature of asphalt binder in the system. 266 (7) Thermometric Equipment. An armored automatic recording thermometer covering a range from 200° F to 400° F (90° C to 205° C) shall be fixed in the asphalt bin der feed line at a suitable location near the discharge valve at the mixer unit. An armored recording thermometer shall be placed as to register and record automatically the temperature o f the heated aggregates.
8.Pollution Control Equipment. Asphalt mixing plants shall be so designed, equipped, and operated that t he quality and quantity of pollutants emitted will conform to the requirements of applicable Federal, State, and local laws, ordinanc es, and regulations.
9.Storage Silos and Surge Bins. Storage silos or surge bins may be used to store production mixture provided th at it is not detrimental to the quality of the mixture placed on the roadway. Open Graded Asphalt Base Course mixtures shall not be stored. Mixtures that are determined by visual observation to be segregated will be rejected. The system shall be capable of conveying the hot mi x from the plant to the silo by means of a drag-slat conveyor system or other approved system. The conveyor may be enclosed and heated to prevent a drop in the mixture temperature; however, hot air shall not be blown on the mixture. The atmosphere within the silo may be air or inert gas. The storage silo heating system shall be capable of mai ntaining the mixture temperature without localizing heating (hot spots). If inert gas is used, the inert gas system must be cap able of purging the silo with an oxygen-free (inert) atmosphere and then sealing the silo to prevent loss of the inert gas. Permissible storage times shall be as follows: Storage Time (Hours)* Maximum Aggregate Size ¾" (19.0 mm) 1½" (37.5 mm ) Air in bin 36 18 Inert gas in bin 144 72 267 *Note: Asphalt binder shall be treated with a sili cone that is on the Department’s QPL at the rate of 1 ounce/5000 gallons (1 g/668 L). Longer storage times than those permitted above may be allowed based upon the results of tests on the mixt ure. All sampling and testing of the mixture shall be perfor med by an approved independent laboratory and certified corre ct. To qualify the silo or storage bin for longer storage times, the mixture must be sampled immediately after it is mix ed and again after it has been stored at the requested longer ti me. Penetration loss in storage shall not exceed 20 per cent. Comparative tests shall be performed according to A ASHTO T 49. The minimum limits for Rolling Thin Film Oven (RTFO ) residue when tested with a Dynamic Shear Rheometer (DSR) in accordance with AASHTO T 315, from samples of disch arge from the surge or storage bin, shall be as follows: GRADES MINIMUM PG 64-22 0.3 psi @ 147°F (2.2 kPa @ 64°C) PG 70-22 0.3 psi @ 158°F (2.2 kPa @ 70°C) PG 76-22 0.3 psi @ 169°F (2.2 kPa @ 76°C) Once a silo or storage bin has qualified for longer storage times for particular types of mixes, the requested longer storage times may be used on other jobs without additional testing. Testing of mixture for permitting longer storage ti me will be at no cost to the Department. If changes or alterations to a qualified surge or s torage system are made, the Engineer shall be notified of the mod ifications. Any departure or alteration will require reevaluati on. The storage silo or surge bin unloading gates shall not cause segregation or be detrimental to the mixture in any way.
10.Safety Requirements. Adequate and safe access to all parts of the plant shall be provided for plant insp ection. Moving parts shall be shielded. A clean, free from drippi ngs, and unobstructed passage shall be maintained at all tim es in and around the truck loading space 268 (11) Anti-strip Additive Measuring System. An anti-strip additive measuring system shall be placed in the an ti-strip additive line prior to introduction into the asphal t binder loading line. The meter shall be capable of handling the a nti-strip additive at temperatures up to 162° F (72 ° C) and shall be capable of withstanding the corrosiveness of the an ti-strip additive. Meters having working internal component s exposed to the additive shall not be composed of aluminum, bra ss, bronze, or copper. Permanent provisions shall be made for che cking the accuracy of the meter. The meter shall be designed so that the cumulative amount of anti-strip additive can be acc urately determined. The anti-strip additive pipe line shall be insulate d.
12.Scales. All approved plant and truck scales shall be furnished by the Contractor according to Subsection 109.01(f).
c.Additional Requirements for Batch Plants.
1.Hot Bins. The plants shall include hot bins of sufficient capacity to supply the mixer when it is operating a t full capacity. Hot Bins shall be divided into at least three compa rtments unless otherwise specified. Each compartment shall be provided with an overflow pipe that shall be of such size and at such location as to prevent any backing up of material into other bins.
2.Proportioning Equipment. Mineral aggregate shall be proportioned by weight. The weighing unit shall consist of one hopper or we igh box large enough to hold one batch without running over or without requiring manual placement. The weigh box or hopper shall be supported on fulcr ums and knife edges so constructed that they will not be ea sily thrown out of alignment or adjustment. The gate shall close tightly when the hopper is emp ty so that no material will be allowed to leak into a batch in the mixer during the process of weighing the next batch.
3.Scales. Scales for weigh box or hopper shall be of the digital or springless dial type and shall be of sta ndard make and design. 269 The capacity of the dial shall not exceed twice the full capacity of the mixer. The dials shall be of compo unding type having full complements of index pointers. Scales shall be equipped with a tare beam. Weight indicators shall be plainly visible and easi ly read by the operator. Pointers so placed as to give excessive parallax er rors shall not be used. Scale indicators placed at locations other than the mixer platform shall be operated by a satisfactory electr onic system. A mechanical arrangement such as cables and pulleys f or operating the scale indicators will not be permitted. Asphalt shall be measured by weight in a heated buc ket suspended from a springless dial scale. Scales for weighing asphalt shall conform to the specifications for the scales for aggregate, and shall read to the nearest pound (kil ogram). In lieu of plant and truck scales, the Contractor m ay provide an approved automatic printer system that will prin t the weights of the material delivered, provided the system is u sed in conjunction with an approved automatic batching and mixing control system. Such weights shall be evidenced by a weight ticket for each load.
4.Mixer Unit. The plant shall include a batch mixer of an approved twin pugmill type and capable of producing a uniform mixture within the job mix tolerances. The mixer shall have an accurate time lock to contr ol the operation of a complete mixing cycle by locking the weigh box gate. It shall lock the asphalt bucket throughout the dry mixing period and shall lock the mixer gate throughout the dry and wet mixing periods. The dry mixing period is defined as the interval of time between the opening of the weigh box gate and the s tart of introduction of asphalt material. The wet mixing p eriod is the interval of time between the start of introduction of asphalt material and the opening of the mixer gate. The time control shall be capable of being set at intervals of not more than 5 seconds. 270 (d) Additional Requirements for Continuous Mixing Plants.
1.Hot Bins. If hot bins are included as part of the design of the plant, they shall be of sufficient capacity to supply the mixer when it is operating at full capacity. Hot Bins sh all be divided into at least three compartments unless otherwise s pecified. Each compartment shall be provided with an overflow pipe that shall be of such size and at such location as to prevent any backing up of material into other bins.
2.Mixer Unit. The plant shall include a continuous mixer of an approved twin pugmill type or rotary drum mixer and capable of producing a uniform mixture within the job mix t olerances Unless otherwise required, determination of mixing time shall be by weight method under the following formula: /g1839/g1861/g1876/g1861/g1866/g1859/uni0009/g1846/g1861/g1865/g1857/uni002C/g1871/g1857/g1855/g1867/g1866/g1856/g1871/g3404/g1842/g1873/g1859/g1865/g1861/g1864/g1864/uni0009/g1856/g1857/g1853/g1856/uni0009/g1855/g1853/g1868/g1853/g1855/g1861/g1872/g1877/uni002C/g1864/g1854/uni0009 /g4666/g1863/g1859 /g4667 /g1842/g1873/g1859/g1865/g1861/g1864/g1864/uni0009/g1867/g1873/g1872/g1868/g1873/g1872/uni002C/g1864/g1854/uni0009 /g4666/g1863/g1859 /g4667/uni0009/g1868/g1857/g1870/uni0009/g1871/g1857/g1855/g1867/g1866/g1856 The weights shall be determined for the job by test s made by the Engineer.
e.Additional Requirements for Drum Mixer Plants. The system shall provide a positive weight measurement of the cold aggregate feed by use of belt scales or other devic es that will allow regulation of feed gates and permit correction for variations in load. The asphalt feed control shall be interlocked with the total aggregate weight measuring device in such manner as to automatically vary the asphalt feed rate as require d to maintain proper asphalt content in the mixture.
f.Additional Requirements for All Plants Without Screens. Cold Feed Control. The cold feed control shall be considered acceptable when the results of tests conducted on t hese cold feed samples indicate that the individual aggregates hav e been combined within the allowable tolerances for the job mixture limits.
g.Additional Requirements for Batch Plants Withou t Screens. The discharge into the weigh hopper shall be made from 1 bin only, which shall discharge into the center of the weigh hopper. The amount of material stored in the bin at any one time shall be such that sloughing or segregation is minimized. 271 (h) Plant Inspection. The Engineer shall have access to all parts of the plant. The Contractor shall provide and maintain a laborat ory facility for the exclusive use of the Engineer. This facili ty shall be located at the plant site. The dimensions and other requir ements specified herein are minimums. The facility may be built by the Contractor for the specific purposes stated. It is not intend ed, however, to preclude the use of commercially built trailers or prefabricated buildings that may deviate in minor dimension or de tail from the requirements listed but may in some features exceed these requirements and in all major respects be entirely suitable for the purpose intended. The Contractor may furnish, in l ieu of a separate building, a facility having sufficient space in a b uilding, parts of which are used for other purposes, provided that th e facility furnished meets all other requirements of this subs ection; is physically separated from the remainder of the buil ding; and has an outside entrance with unrestricted access allowed a nd reserved for the exclusive use of the Engineer. Adequate space shall be provided for parking of at least three Department vehicles i n the vicinity of the facility. The Engineer will determine the suit ability of any facility furnished. General requirements for the laboratory facility ar e: • 208 square feet (20 sq m) floor space, with a width of 8' (2.5 m) or greater and a ceiling height of 7' (2 m) . • Floored, weatherproof, and reasonably dustproof. • At least two glazed windows capable of being opened and locked only from the inside. • At least one door with a substantial lock and all k eys placed in the possession of the Engineer. • Windows and doors shall be screened. • Adequate electric lights and power outlets suitable for the purposes intended. At least one power outlet shall provide 220 VAC. • Adequate heating in cold weather and air conditioni ng in hot weather. Heating, cooling, and utility service shall be provided at no cost to the Department. • Suitable toilet facilities in reasonably close prox imity to the facility. 272 Detailed requirements: • A work counter approximately 30 ″ (750 mm) high built-in along one wall and across one end. Total length of the work counter shall be approximately 20' (6 m). • A single sink, approximately 20 ″ (500 mm) square, with outside drain, suitable for washing samples, instal led in the end section of the work counter. • A water supply providing a minimum of 50 gallons (200 liters) storage capacity (or connected to a pu blic or private water system), discharging through a faucet above the sink. • Adequate shelves and/or cabinets for storage of tes ting equipment. • A storage area for storing nuclear equipment, compl ete with a substantial lock and all keys to this area p laced in the possession of the Engineer. • A desk or table approximately 24" x 36" (600 mm x 900 mm), with at least two drawers, each approximat ely 13" x 13" x 18" (330 mm x 330 mm x 450 mm) for stor ing records. • At least three chairs. • At least one Type C fire extinguisher (10-pound siz e minimum). • An exhaust fan shall be installed over the equipmen t clean up area. The exhaust fan shall be rheostatically c ontrolled and capable of exhausting in one minute a volume of air equal to the volume of the entire laboratory. The exhaust fan shall be maintained operational. • A local access touchtone telephone line (with acces s to toll free telephone numbers but otherwise blocked for ou t- going long distance calls), with a landline modular jack and touchtone telephone, shall be provided in the labor atory facility for use by Department personnel. The loc al landline telephone service will be furnished at no cost to the Department. The field laboratory for asphalt mixing plants will not be paid for directly, but will be considered a part of the asph alt mixing plant. 273 409.04 Equipment. (a) Mechanical Spreading and Fini shing Equipment. Mechanical spreading and finishing equipment shall consist of a self-powered paver, capable of spreadi ng and finishing the mixture true to line, grade, and cross section. The paver shall be capable of laying a uniform mixture to the full wid th being laid. The paver shall be equipped with mechanical devices such as equalizing runners, straightedge runners, evener ar ms, or other compensating devices to adjust the grade and confin e the edges of the mixture to true lines. The paver shall be equi pped with hoppers and distributing screws adequate to place the mixtu re evenly ahead of the screed for the full width being laid. Pavers used for shoulders and similar construction shall be capable of uniformly spreading and finishing course s of asphalt material to the full width being laid. The paver s hall be equipped with a receiving hopper and distribution system to place the mixture uniformly across the entire width of the screed. The term "screed" shall include any strike-off devi ce, operated by cutting, crowding, or other practical action that e ffectively places and spreads the mixture without tearing, shoving, g ouging, or segregating. Screeds shall be adjustable to crown and grade and shall have an indicating level attached. The paver shall be equipped with an automatic scree d control system for the control of grade and slope. The sen sor for grade control may be operated from a reference stringline , from a ski-type grade reference system, or by any other appropriate method that will produce the desired results. Final approval of spreading and finishing equipment will be based upon satisfactory performance during actual c onstruction. If equipment becomes unsatisfactory, it shall be repla ced before proceeding with the work.
b.Materials Transfer Device (MTD) / Materials Tr ansfer Vehicle (MTV). A Materials Transfer Device or Materials Transfer Vehicle (MTD/MTV) shall be used on all State, US, a nd Interstate highways for the placement of all ACHM courses. AC HM quantities exempt from this requirement are project s or phases of work with less than 1000 tons of hot mix, leveling, parking lots, driveways and turnouts, temporary pavements (such a s detours and crossovers), and ACHM placement in trench widening areas less than 11 ′ (3.3 m) in width. At the Engineer’s discretion, i solated 274 portions of a project may be exempted from use of t he MTD/MTV if the weight or operation of the MTD/MTV is detriment al to the roadway. Exemptions will not be made prior to the beginning of paving operations and initial use of the MTD/MTV. The MTD/MTV may not be removed from the project during the paving operations over the exempted location; rather it mu st be on-site and available to resume work once the paving operation moves out of the isolated area. The ACHM mixture shall be transferred mechanically to the paver by means of a MTD/MTV. The material shall be continuously remixed or reblended either internally in the transfer vehicle, in a paver hopper insert, or in the paver’ s hopper. Remixing/reblending shall be accomplished by the us e of remixing augers, paddles or screens capable of continuously blending the hot mix asphalt. The MTD/MTV, haul units, and paver shall work toget her to provide a continuous, uniform, segregation free flo w of material. The number of haul units, speed of the paver, plant production rate, and speed of the MTD/MTV shall be coordinated to av oid stop and go operations. The wings of the paver receiving ho pper shall not be raised (dumped) at any time during the paving opera tion. If a MTD/MTV or remixing/reblending unit malfunctio ns during lay-down operations, the Contractor may continue ho t mix lay-down operations until any hot mix asphalt in transit or stored in a silo (up to a maximum of 500 tons [500 metric tons]) has bee n laid and until such time as there is sufficient hot mix placed to maintain traffic in a safe manner. Lay-down operations shall cease there after, until such time as the equipment is operational. The Engineer will evaluate the performance of the M TD/MTV and remixing/reblending equipment by measuring the temperature profile of the mat immediately behind the screed of the paver during placement of the rolling pattern test strip. The A CHM to be placed for the temperature profile test shall be held in t he haul truck(s) for at least 45 minutes, measured from the time of load ing to the time of discharging into the MTD/MTV. If the bed of the ha ul truck is covered, the cover will be removed once arriving at the test strip location. The temperature profile measurements sha ll be taken of the surface of the mat at six 50 ft. (13 m) interva ls during test strip construction using a non-contact thermometer. Each temperature profile shall consist of three surface temperature measurements 275 taken transversely across the mat in a straight lin e at a distance of 1 foot to 3 feet (0.3 m to 1 m) from the screed while the paver is operating. The three temperature measurements in e ach profile shall be taken approximately one foot (0.3 m) from each e dge and one in the middle of the mat. The difference between the m aximum and minimum temperature of each individual profile shal l not be more than 10 °F (6 ° C). If any two temperature measurement profiles within the test strip do not comply with the 10 °F (6 ° C) temperature differential requirement, the paving operation shall be halted a nd adjustments made to the MTD/MTV or remixing/reblending equipmen t to ensure that the hot-mix placed by the paver is within the above temperature requirements. Once adjustments are made, the Engin eer will repeat this procedure to verify that the mix placed by the paver is within specifications. Additional surface temperature profile measurements may be taken transversely across the mat at any time durin g the project to determine if the MTD/MTV and remixing/reblending eq uipment are working properly. During this verification testing , if two consecutive temperature measurement profiles do not comply with the 10 °F (6 ° C) temperature differential requirement, the pavin g operation shall be halted and adjustments made to t he MTD/MTV or remixing/reblending equipment to ensure that the ho t-mix placed by the paver is within the above temperature requireme nts.
c.Rollers. Rollers shall be of the size and type to produce the density required and a surface that is smooth and f ree from check cracking. Rollers shall have a system for moisteni ng the full width of each tire or drum and devices for cleaning the t ires or drums. Petroleum products shall not be used on the surface s of the roller that will be in contact with the pavement.
Source: , Edition.