Section 2001. General Equipment Requirements
Equipment shall be subject to approval of the Engineer and shall be maintained in satisfactory working condition. Except as provided in Article 1105.12, G, equipment operating on pavement or on primed or unprimed subgrade, subbase, or base course shall not exceed the legal axle load, as defined herein. Tractors with lugs shall not be used for manipulating or spreading subbase or base material except when traveling on uncompacted material deposited by spreaders or spreader boxes.
Equipment that comes in contact with bituminous materials or bituminous mixtures shall be kept clean by heating, scraping, or by the use of an approved release agent described in Materials I.M. 491.15. When kerosene, distillates, or other solvents are used, the equipment shall be allowed to drain for a minimum of 5 hours after cleaning. Cleaning agents shall be collected and disposed of in accordance with Federal and State regulations.
Field laboratories shall comply with requirements of Section 2520.
TRUCKS FOR TRANSPORTING BITUMINOUS MIXTURES.
Trucks for transporting bituminous mixtures shall be motor trucks with tight metal or metal lined dump bodies. For hot mixes on unusually long hauls or for work after October 1, the Engineer may require the truck bodies to be insulated adequately to retain heat in the mixture. All trucks for transporting hot mixes shall have a cover of canvas or other suitable material, but covering will not normally be required between May 15 and October 1.
In areas inaccessible to rollers where compaction is required and hand tamping is not permitted, a mechanical tamper of a size suitable for the work shall be used. Pneumatic tampers shall not be operated at pressures lower than recommended by the manufacturer.
Rollers shall be subject to restrictions imposed in the specifications for the various types of construction. Rollers which are not in good repair, or which are not designed to do the work required fully and satisfactorily, shall not be used. They shall be subject to approval of the Engineer. Rollers shall comply with the following requirements:
Soil Compaction Rollers.
Sheepsfoot type rollers shall consist of one or more drums having studs or feet projecting not less than 6-1/2 inches (165 mm) from the surface of the drum. The roller shall be loaded so that not less than 200 psi (140 g/mm2) is exerted on a single row of feet parallel to the axle of the drum.
Self Propelled, Smooth, Steel Tired Rollers.
Self propelled, smooth, steel tired rollers may be of the 3 wheel type, 2 axle tandem type, or 3 axle tandem type. For natural subgrade, rollers shall not be less than the 3 ton (2.7 Mg) weight class.
For hot asphalt mixtures, the driving drum shall not be less than 60 inches (1500 mm) in diameter. On tandem type rollers, the driving drum shall be capable of being filled with liquid ballast, and the Engineer may require that it be partially or entirely filled.
For all other types of work, the rollers shall be of a weight class not less than 8 tons (7.3 Mg), and the driving drum shall be loaded to produce a compactive effort not less than 200 pounds per inch (3.5 kg/mm) of width of the roller. When required by the Engineer, the steering drum shall also be weighted to 200 pounds per inch (3.5 kg/mm) of width of the steering drum.
Self Propelled, Pneumatic Tired Rollers.
Self propelled, pneumatic tired rollers shall have tires not smaller than the 7.50 x 15 size.
For hot asphalt mixtures, the rollers shall be capable of producing contact pressures of 80 psi (550 kPa) and shall be operated when specified or directed by the Engineer. The 80 psi (550 kPa) contact pressure shall be obtainable with a legal axle load.
For all other types of work, the rollers shall be loaded to produce a compactive effort not less than 200 pounds per inch (3.5 kg/mm) of width of the roller, based on the maximum ground contact width. The tire inflation pressure used shall not be less than 60 psi (410 kPa). Rollers complying with the requirements for hot asphalt mixtures may also be used.
The tire pressures shall not vary more than 5 psi (35 kPa). An information plate shall be attached to each roller, which shows the tire size and ply and the correlation of wheel load and tire pressure with contact pressure. The roller shall be equipped with wheel sprinklers, scrapers, or mats, and during cooler weather, protective skirting around the tires.
Pull Type, Pneumatic Tired Rollers.
Pull type, pneumatic tired rollers shall have tires not smaller than the 7.50 x 15 size. The rollers shall be loaded to produce a compactive effort not less than 200 pounds per inch (3.5 kg/mm) of width of the roller, based on the maximum ground contact width. The tire inflation pressure used shall not be less than 60 psi (410 kPa).
Trench rollers used in trench operations shall have a compacting roller of a width not less than 15 inches (380 mm). The rollers shall be equipped with a leveling mechanism to maintain the compacting surface of the roller in the desired plane while compacting surfaces below the edge of the old pavement. If used only to compact the bottom of a trench for widening, the leveling mechanism will not be required, provided the roller is built to fit the slope of the trench bottom.
The Engineer may require the roller loaded to produce the compactive effort best adapted to the work, to a maximum of 250 pounds per inch (4.5 kg/mm) of width of the tire. Pneumatic tired rollers shall be operated with an inflation pressure not less than 60 psi (410 kPa).
Self Propelled Vibratory Rollers.
Self propelled vibratory rollers shall be suitable for the use intended. The manufacturer's handbook should be available to the operator. The speed of the roller shall be controlled so there is a minimum of 10 impacts per linear foot ( 35 impacts per meter).
Other types of rollers will be considered for approval by the Engineer.
For the purpose of this Article, the word "bin" shall be defined as any structure in which materials are stored. The requirements shall apply to any bin that an inspector, while performing sampling or inspection duties, might work upon or beneath.
Each part of each bin, including foundations and connections, shall have adequate strength to withstand any stress to which it might be subjected while in use.
The Engineer may inspect each portable bin each time it is erected. The Engineer may reject the use of any bin that does not perform as intended, or otherwise exhibits any unsafe condition.
WEIGHING EQUIPMENT AND PROCEDURES.
This Article describes equipment capability and procedures to be used when payment for an item is based on weight (mass).
Weighing equipment for measuring a pay item shall meet requirements of the Iowa Department of Agriculture. Truck weighing equipment shall be of sufficient length to weigh, at one time, the maximum truck and trailer combination, or separate equipment shall be situated so that both truck and trailer can be weighed at the same time. Upon request, the Contractor shall make available, at least 10 standard 50 pound (22.68 kg) test weights and suitable cradles and platforms for the purpose of testing weighing equipment.
Weighing equipment shall be accurate to 2 pounds per 1000 pounds of weight (2 kg per 1000 kg) sensitive to a weight (mass) equal to 0.1% of the quantity being weighed but not less than a weight (mass) equal to one of the minimum graduations on a beam or dial scale and not to exceed 20 pounds (10 kg). When electronic devices such as load cells, computers, and printers are a part of the weighing equipment, they shall be sealed or otherwise protected to prevent any unauthorized adjustment. Any weighing system which has been tampered with may be rejected from further use until the system has been checked and/or recalibrated. Contractors using electronic type weighing equipment and devices shall furnish a copy of the manufacturer's detailed step by step instructions for adjusting and/or checking for accuracy, sensitivity, and tolerance of the equipment.
All trucks to be weighed shall be initially tared before being loaded. These trucks shall be tared daily thereafter, preferably on a random time basis. The tare for the previous day shall be used until a new tare is determined.
A scale ticket shall accompany each load to be furnished to the Engineer for project records. A scale ticket shall also be furnished when tares are determined, for verification and check weighing. Verification weighing is defined as a second weighing of the same load on the same equipment. Check weighing is defined as a second weighing of the same load on different weighing equipment. Check weighing shall be performed on a certified truck scale. Scale tickets, as a minimum, shall identify project number, date, truck number and type of material. They also shall include a total net weight (mass).
Except for automatic weighing, a weighmaster, as defined in Chapter 214, Code of Iowa, shall weigh all loads or load increments. The weigh master, or operator for automatic weighing, shall sign the first scale ticket of each day and shall initial all subsequent tickets or cause them to be printed by automatic equipment.
Check weighing and verification weighing may be made at any time as directed by the Engineer. The Engineer may check the operation of the equipment at any time.
The verification weight (mass) should not be different from the initial weight (mass) by more than 0.1%. When check weighing on a platform scale, the check weight (mass) should not be different from the initial weight (mass) by more than 0.3%. When the material is not weighed in the truck, (such as weighing in a weigh hopper or from initial and final weighing of a weigh silo) check weighing shall be made on a certified truck scale and the net check weight (mass) should not be different from the initial net weight (mass) by more than 100 pounds (45 kg). A suitable fuel adjustment may be made.
If the weight (mass) is not within these tolerances, the Engineer may adjust the weight (mass) of loads previously weighed on the weighing equipment that day and the previous day by the difference greater than the specified tolerance. Verification and check weighings shall be made at no additional cost to the Contracting Authority.
Special Procedures for Asphalt Mixtures,
Aggregates, and Binders.
Automatic or semi automatic weighing shall be used on projects with contract quantities of asphalt mixtures totaling 10,000 tons (10,000 Mg) or more; or aggregates totaling 10,000 tons (10,000 Mg) or more from a single source.
1. Automatic Weighing.
The weighing equipment shall be self balancing and shall include an automatic weight (mass) recorder. All tickets shall be printed automatically with net weight (mass) and all weights (mass) needed to determine total net weight (mass).
2. Semi Automatic Weighing.
The weighing equipment may be self balancing or manually balanced. Equipment shall include an automatic weight (mass) recorder which will not print until the equipment is balanced, and which prints the gross weight (mass) or the batch weights (mass) and number of batches. For weigh hoppers, the printout shall include the empty weight (mass) after each discharge.
For measurement of asphalt binders by tank stick or in-line flow meter, the Contractor shall meet the requirements of Materials I.M. 509 for calibration and measurement.
For asphalt mixtures, the Contractor shall furnish to the Engineer each day, a total quantity of mixture used for the project. The Contractor shall furnish daily totals to the Engineer for all mixture quantities produced and not incorporated into the project. This total shall also identify the quantity of asphalt binder used but not incorporated.
EQUIPMENT FOR PREWETTING AGGREGATES AND AGGREGATE MIXTURES.
The equipment shall comply with one of the following:
The equipment used for this purpose shall provide accurate control of the proportions of water and aggregate, and positive, thorough mixing of the materials. Dow boxes will be approved as a Standard Mixer.
When this equipment is specified, it shall provide accurate control of the proportions of water and aggregate and shall be designed so that the material can be retained in the mixing chamber under vigorous mixing action for at least 15 seconds. If the mixer is the continuous flow type, it shall have twin mixing shafts and shall be equipped with a hopper or bin at the discharge end of the mixer designed to minimize segregation of the mixed materials.
A distributor mounted on a truck or trailer equipped with pneumatic tires shall be used for applying water to the roadway.
The distributor shall be equipped with an adequate pressure pump and flush or spray bars to distribute water evenly over the intended area.
Distributors shall have a spray bar with correct size and pattern of nozzles, a means to maintain uniform nozzle pressure, a means to control application rates between 0.05 to 0.50 gallon per square yard (0.20 to 2.50 L/m2), and a positive sprayer shutoff mechanism.
Distributors used for trench operations shall have an offset spray bar with replaceable nozzles so the width to which water is applied can be adjusted to the work.
WATER SUPPLY EQUIPMENT.
Water supply equipment, including pipe lines and water trucks, shall be of a capacity and nature to insure an ample supply and sufficient pressure for all the requirements of the work. When pumping is necessary, backup pumping equipment may be required.
EQUIPMENT FOR HEATING BITUMINOUS MATERIALS.
Equipment for heating bituminous material shall have adequate capacity to heat the material to the temperatures specified. Heating shall be under control and shall be accomplished by circulating steam or a liquid through coils in the car or tank, by electric heat, by circulating the bituminous material through a separate heating unit, or by other means so that no flame is applied to metal with which the bituminous material comes in contact. The heating equipment shall be equipped with an accurate thermometer which will indicate the temperature of the bituminous material in the unit in which heat is being applied. The heating equipment shall not damage the bituminous material by local overheating or by contamination with the material used for the transfer of heat.
Equipment for heating asphalt binder shall insure continuous circulation between the storage tank and the mixer during the operating period. All pipe lines shall be jacketed or insulated to prevent heat loss.
EQUIPMENT FOR DISTRIBUTING BITUMEN.
Distributors shall be mounted on motor trucks or trailers. They shall be subject to the restrictions imposed in the specifications for the various types of construction. Distributors which are not in good repair or which are not designed to do the work required shall not be used. Distributors and trucks shall be subject to the approval of the Engineer.
Distributors shall be equipped with adequately sized burners and flues for heating the bituminous material and with means for circulating the material in the tank when the burners are in operation. They shall be equipped with adequate and safe catwalks or ladders for use in making stick measurements.
Each unit shall be equipped with an accurate thermometer for indicating the temperature of the bitumen in the tank, a tachometer operated by a wheel independent of the truck wheels, a calibrated or verified measuring stick, a quick opening gate in the dome of the distributor tank, and quick cutoff valves at the nozzles or other means for reversing the direction of flow through the nozzles.
The power for the pressure pump shall be supplied by a unit independent of the one which provides motive power for the distributor. However, pressure equipment which is dependent on the motive power may be approved provided special devices are installed to insure that variation from the designated rates of application will not exceed 0.02 gallon per square yard (0.10 L/m2). The pressure system shall have capacity sufficient to produce a uniform, fine, even spray from all the nozzles for the maximum width of the spray bar used. It shall be capable of distributing bitumen at rates varying from 0.03 to 0.50 gallon per square yard (0.15 to 2.50 L/m2). The size of the nozzles shall be such that bitumen may be spread in a uniform coating without the forward speed exceeding 20 mph (30 km/h).
The spray bars shall be adjustable for the widths of application required by the work. They shall be equipped with a means of lateral shifting during the application of bitumen of at least 6 inches (150 mm) each way from the center position. They shall be adjustable vertically to insure uniform transverse application of the bitumen. Distributors used for applying bituminous seal coat binder bitumen shall be equipped with a positive means for maintaining a constant nozzle height, within ± 1/2 inch (15 mm), during discharge of the load. If dollies are used for maintaining the constant nozzle height, the spray bar mounting shall be adjustable vertically.
The Contractor shall provide, with each distributor, the manufacturer's instructions for use which shall include specific recommendations for the following:
1. Spray bar height above road surface.
2. Nozzle size and angle of spray fan with spray bar axis.
3. Tables showing rates of distribution in gallons per square yard (liters per square meter) for tachometer readings, spray bar pressure, or pump revolutions, and for various widths of spray bars.
The tanks of all distributors that have not been previously checked shall be calibrated or verified before being initially used and after any damage or alteration which may affect the calibration. Distributors shall be calibrated initially at the Iowa DOT Materials Laboratory. Verification of a manufacturer's calibration may be made by the Iowa DOT Materials Laboratory or by a District Materials Office. Distributor calibrations shall be certified annually by either the Iowa DOT Materials Laboratory or District materials personnel; if they are found to have inaccurate calibrations, they shall be recalibrated by the Iowa DOT Materials Laboratory before further use.
This article applies to equipment used for distribution of certain materials, other than liquids, where it is required that the material be distributed on a roadbed at a specified uniform rate.
Non-Self-Propelled Cover Aggregate Spreaders.
Non-self-propelled cover aggregate spreaders shall have a mechanical feed of a length at least equal to the width to which aggregate is spread at a single passage of the spreader. They shall be capable of depositing aggregate from the transporting vehicle directly upon freshly applied bitumen in a smooth, uniform layer, at the rate required and in a manner that equipment will not come in contact with the bitumen until the bitumen is covered with a layer of aggregate. The spreaders shall be equipped so that they may be filled and moved without discharging aggregate.
1. They shall be self-propelled and shall be mounted on pneumatic tires.
2. The width of spread shall be not less than 13 feet (3.9 m).
3. Cutoff plates shall be provided to permit the width of spread to be reduced in increments of 1 foot (0.3 m) from the maximum to 4 feet (1.2 m).
4. The unit shall be capable of spreading aggregate of 1 inch (25 mm) maximum size at any rate desired from 3 to 50 pounds per square yard (1.5 to 27 kg/m2) of surface covered.
5. A hopper having a capacity not less than 5 tons (4.5 Mg), integral with the spreader unit, shall be provided to receive aggregate from transporting vehicles without the wheels of such vehicles coming in contact with uncovered bitumen on the road surface. Suitable conveyors shall convey the aggregate from the hopper to the spreading element. Augers or agitators shall distribute aggregate uniformly to the spreading element without segregation of aggregate particles.
6. Power shall be adequate to propel the spreader at uniform speed on gradients up to 6%.
The spreader used for sand cover of tack and seal coat shall have one or more horizontal rotating disk fed by a conveyor and driven by power takeoff or by a separate unit.
Materials Spreader for Base Widening Work.
The material used in base widening shall be placed by machine without being dumped on the pavement. The machine shall spread the base materials in a uniform layer of the desired thickness and width in a uniformly loose condition. Wheels of the spreader shall be located so they do not operate on the 1 foot (0.3 m) width of pavement where curb has been removed.
Brooms shall be of the rotary type, and the broom shall be driven by an auxiliary motor or by a power takeoff from the power plant of the unit propelling the broom.
Motor graders used in trimming edges of subbases or bases shall be equipped with an offset blade with supplementary cutting edge designed so the wheels of the motor grader will be operated entirely on the surface of the base or subbase.
Scarifying equipment used shall be designed and operated to loosen the material to the depth specified.
Pulverizing equipment shall be designed and operated to pulverize the material to the degree specified.
TRENCH EXCAVATING MACHINES.
The equipment used shall be a machine designed for the required purpose. The equipment used to excavate shall be capable of excavating the material to the full, normal design depth and suitable width.
ASPHALT PAVING MACHINE.
All asphalt mixtures to be placed 8 feet (2.4 m) or more in width shall be spread by a self- propelled finishing machine which will receive the hot mixture and spread the mixture in a layer of uniform density to the desired elevation.
The finishing machine shall consist of a tractor unit and a screed unit.
The tractor unit will provide the motive power and may be mounted on crawler treads or pneumatic tires. If mounted on pneumatic tires, sufficient inflation pressure shall be maintained to keep vertical movement to a minimum. The length of crawler treads or distance between axles, if mounted on pneumatic tires, shall be sufficient to allow the tractor unit to pass over small irregularities in the base without abrupt vertical movement. The tractor unit shall have dual controls to permit operation of the finishing machine from either side.
The screed unit shall be attached to the tractor unit in such a manner that it is free floating on the mixtures being placed. It shall be equipped with vibrators or tampers for giving the initial consolidation to the material, and this equipment shall be operated at the frequency recommended by the manufacturer. The screed unit shall be adjustable to the crown of the finished surface, and shall be equipped with an approved device which will indicate the slope of crown. A screed extension may be used, provided it has a screed plate with vibration. If the extension exceeds 1 foot (0.3 m), the auger shall also be extended. Other extensions will be allowed only for use in placing fillets or short or irregular tapers. The screed unit operation shall produce a smooth surface, free from surface tears or voids, and within the permissible variation specified for the type of work involved.
Machines which operate with rollers on the freshly placed mixture shall not be used.
At least a 2 foot (0.6 m) straightedge shall be provided for checking the installation of screed extensions.
Unless otherwise provided, the finishing machine shall have automatic screed controls, except for the following uses:
1. Wedge courses.
2. Curb fill resurfacing.
3. Urban type sections containing fixtures or other permanent grade control features.
4. Surface layers 1 inch (25 mm) or less in thickness.
5. Special leveling course in which the screed rests entirely on the high spots of the underlying base during the paving procedure.
6. Single course resurfacing on Secondary projects.
The automatic controls shall have grade and slope control systems which shall operate with an approved grade reference system. The controls shall work in conjunction with a ski type device, traveling stringline, or other approved, self contained grade referencing system. The self contained grade referencing system shall not be less than 30 feet (9 m) in length. Both the grade and slope controls shall be adequately sensitive and in proper working order at all times, however, during malfunctions the Engineer may permit the completion of the day's work using manual controls. When placing a single lift only, with a thickness of 1 1/2 inches (40 mm) or less, or for placement in conjunction with heater scarification work, a special commercial joint matching shoe may be used when constructing longitudinal joints on surface courses.
Finishing machines or pavement widening machines for placing the final lift of paved shoulders shall have an automatic grade and slope control system approved by the Engineer. The joint matching shoe may be used when placing any paved shoulder.
Machines for spreading mixtures on other areas less than 8 feet (2.4 m) in width shall be subject to approval of the Engineer. Machines which are less than standard size for highway work shall not be used except with permission of the Engineer.
Use of material transfer vehicles shall be subject to approval by the Engineer based on bridge and pavement structural evaluation of resultant axle and wheel loads.
When a windrow pick-up process is used, the process shall be controlled to produce a windrow that is uniform and does not extend more than two truck dumps ahead of the paver. All hot mix material shall be picked up from the windrow and deposited in the paver. Windrow placement shall be balanced to maintain a uniform quantity of material in the paver hopper.
EQUIPMENT FOR WEIGHING AND PROPORTIONING PORTLAND CEMENT CONCRETE MATERIALS.
Weighing and proportioning equipment shall meet the requirements of this Article. The Engineer shall be allowed every opportunity to witness calibration of the equipment during the Engineer's normal working hours, or at a mutually agreeable time. This schedule limitation will be modified, if necessary, for work to be done according to an accelerated work schedule. The Engineer may consider a report concerning equipment and its calibration certified by a Professional Engineer licensed in the State of Iowa in lieu of this calibration. The Engineer may, at any time, perform such tests or checks as necessary to verify a report or to assure continued compliance. Coarse aggregate sampling facilities which permit collecting representative portions of a ribbon or stream will be required at the proportioning plant site. The sampling point shall be as designated by the Engineer and shall be prior to loss of individual material identity in the proportioning mixing process and after delivery to the plant or after delivery to a plant site stockpile, whichever is nearest the mixer. Personnel, test weights, and equipment for calibration of the plant and for verifying accuracy of proportions shall be furnished by the Contractor. Arrangements for weighing water to calibrate the water meter shall be made by the Contractor.
Proportioning equipment shall comply with the following requirements:
1. The equipment shall be accurate to 0.5% of the batch weight (mass).
2. The equipment shall be sufficiently sensitive so that 0.1% of the batch weight (mass) or 2 pounds (1 kilogram), whichever is greater, will be detectable.
3. The equipment shall weigh each individual material within ± 1.0% of the batch weight (mass) and return to zero within ± 0.5% of the batch weight (mass).
4. The equipment shall be protected from air currents, vibration, etc. which may affect the accuracy of weighing. All fulcrums, clevises, and similar working parts shall be kept clean and in proper working condition.
There shall be reasonably available upon request, at the plant site, standard
test weights for calibrating weight equipment according to the following table:
|Nominal Scale Capacity
|Minimum Test Weights (Mass) Required
Total lb (kg)
|0 to 500 (0 to 225)||2 @ 50 lbs. ea. (2 @ 22.68 kg ea.)|
|Over 500 to 5000 (Over 225 to 2250)||500 (225)|
|Over 5000 to 10,000 (Over 2250 to 4500)||1000 (450)|
|Over 10,000 (Over 4500)||2000 (900)|
Suitable devices shall be made available for conveniently applying test loads.
6. Cement shall be weighed in an independent hopper. The weigh hoppers shall have a dust tight seal between the charging mechanism and the batching hopper which will not affect the accuracy of weighing, and a discharge hose or device which will prevent the loss of cement during discharge. Any part of the discharge device which comes in contact with the receiving equipment shall not be supported by the weigh hopper. Cement hoppers shall be equipped with a vibrator and with a vent which will adequately release any air pressure which may affect weighing.
7. Fly ash and GGBFS shall be weighed in accordance with the requirements of weighing cement. Fly ash and GGBFS may be weighed in the same hopper as the cement, provided the cement is introduced into and weighed in the hopper first.
8. Automatic weighing equipment shall be set and operated with the following interlocks:
a) The charging mechanism cannot be opened until the equipment has returned to zero balance within ± 0.5% of the batch weight (mass).
b) The charging mechanism cannot be opened if the discharge mechanism is open.
c) The discharge mechanism cannot be opened if the amount in the hopper is over or under by more than 1.0% of the batch weight (mass).
When automatic weighing equipment is required, manual controls may be used for emergencies. Manual controls will be permitted no longer than 1 working day after automatic batching equipment failure.
When automatic weighing equipment is required, fly ash shall be weighed in accordance with the requirements for cement.
B. Water Measuring Equipment.
Water shall be measured with equipment which will clearly indicate the volume or weight (mass) being measured with an accuracy of 2 pounds (1 kg) or ± 1.0%, whichever is greater. The equipment shall be arranged so that the accuracy of the measurement will not be affected by variations in pressure of the water supply line. Unless water is measured by weight (mass), the Contractor shall provide containers in which the entire quantity of water required for one batch of concrete may be weighed for calibration purposes.
Equipment that measures moisture in the fine aggregate and adjusts the batch amounts of fine aggregate and batch water on a continuous basis will be allowed provided satisfactory calibration and correlation procedures are met.
C. Equipment for Admixtures.
Equipment for dispensing liquid admixtures shall be accurate within ± 3.0% of the quantity required. The visual inspecting chamber requirement may be waived in lieu of admixture dispensing systems utilizing positive electronic flow metering and computer controlled delivery that prevents improper admixture incorporation into the mix. Dispensing equipment shall have a means for routine diversion of a measured quantity into a suitable vessel for calibration and for periodic verification of the batch quantity.
When liquid admixtures are proportioned and introduced into the mix, the equipment and procedures shall meet the following requirements:
1. Each individual admixture shall be measured and automatically introduced separately into the mixer with the mixing water.
2. The dispenser shall be equipped with a measuring chamber which provides a means of determining the batch quantity by visual inspection.
D. Equipment for Volumetric Proportioning.
Volumetric proportioning equipment shall meet the applicable requirements of ASTM C 685, Sections 5, 6, 7, and 8 and the applicable requirements of Article 2413.03, B. This equipment shall be calibrated each time, when in the opinion of the Engineer, material or condition changes may affect the calibration. It is not intended that this equipment be used in lieu of conventional drum mixing equipment normally used for structures and paving applications.
PORTLAND CEMENT CONCRETE MIXING EQUIPMENT.
The mixing equipment shall meet requirements of this Article for the type specified. The Engineer shall be allowed every opportunity to witness the calibration of the equipment during the Engineer's normal working hours, or at a mutually agreeable time. This schedule limitation will be modified, if necessary, for work to be done under an accelerated work schedule.
A. Construction or Stationary Mixer.
Only batch type mixers shall be used.
The total volume of the batch shall not exceed the designated size of the mixer or the rated capacity as shown on the manufacturer's rating plate.
After all solid materials are assembled in the drum, the mixing time shall be a minimum of 60 seconds and a maximum of 5 minutes. The mixing time may be increased by the Engineer if the mixer efficiency tests show that the concrete is not satisfactory for uniformity or strength. The minimum mixing time shall be indicated by an accurate timing device which shall be automatically started when the mixer is fully charged, and when applicable, shall lock the discharge chute until the expiration of the required time. Mixers shall be operated at the speed recommended by the manufacturer as mixing speed. The batch shall be charged into the mixer so that some water will enter in advance of cement and aggregates, and all water shall be in the mixing chamber by the end of the first 25% of the specified mixing time.
The mixing drums of tilting drum mixers shall be operated at an angle no steeper than that recommended by the mixer manufacturer. Mixers shall not be used if the drum is not clean or if the mixing blades are damaged or badly worn.
When a construction or stationary mixer is used for mixing pavement concrete the quantities of fine aggregate, coarse aggregate, cement, mineral admixture, liquid admixture and water for each batch shall be automatically documented on individual batch tickets or on a daily summary. The time of discharge for each batch shall also be recorded automatically. These proportioning documents shall become property of the Contracting Authority.
Truck Mixer and Agitator.
The capacities and mixing capabilities shall be as defined in ASTM C 94, and each unit shall have an attached plate containing the information described therein. The plate may be issued by the Truck Mixer Manufacturers Bureau; if not, compliance shall be determined by an independent, recognized laboratory as defined in Article 4103.01, and complete test results may be required. The mixer or agitator capacity shall not be exceeded, and the mixing and agitator speeds shall be within the designated limits. Truck mixers shall be equipped with a reliable reset revolution counter. If truck mixers are used for mixing while in transit, the revolution counter shall register the number of revolutions at mixing speed.
An authorized representative of the concrete producer shall certify that the interior of the mixer drum is clean and reasonably free of hardened concrete, that the fins or paddles are not broken or worn excessively, that the other parts are in proper working order, and that the unit has been checked by the representative within the previous 30 calendar day period to substantiate this certification. The current, signed certification shall be with the unit at all times.
For bridge floor concrete, the required mixing shall be between 70 and 90 revolutions. For other structural concrete and pavement concrete, the required mixing shall be between 60 and 90 revolutions with satisfactory preblending of the materials or between 70 and 90 revolutions without preblending. The mixing shall be at the rate designated by the manufacturer. The mixing rate shall be of a duration between the above stated limits, to produce uniform, thoroughly mixed concrete.
The Engineer may inspect mixer units at any time to assure compliance with certification requirements, and removal of inspection ports may be required. Should the Engineer question the quality of mixing, the Engineer may check the slump variation within the batch. Should the slump variation between two samples taken, one after approximately 20% discharge and one after approximately 90% discharge of the batch, show a variation greater than 3/4 inch (20 mm) or 25% of the average of the two, whichever is greater, the Engineer may require the mixing to be increased, the batch size reduced, or the unit removed from the work.
PLANT EQUIPMENT FOR HOT MIX ASPHALT MIXTURES.
The plant equipment shall proportion each aggregate, dry and heat the aggregate, except mineral filler, proportion the aggregate and hot asphalt, and mix all materials. The plant may be of a batch type, continuous type, or drum mixing type, and it shall be equipped to produce uniform mixtures of required composition, heated to the desired temperature. The plant shall conform to the following requirements for the respective type.
Aggregate Feeders for Dryer or Drum Mixer.
Except for mineral filler added without heating, each aggregate shall be accurately fed by a mechanical means to a central elevator or conveyor in the proportion prescribed by the formula. Feeders shall be of the belt type and be equipped with adjustable gates or adjustable drive systems that can be calibrated and controlled satisfactorily. The feeder throats shall be of sufficient size to insure positive and continuous flow. All feeders shall be mechanically or electrically interlocked during operation. On some types of feeders, revolution counters capable of registering to a tenth of a revolution may be necessary for accurate calibration and control and may be required. When drum mixing plants are used, the central conveyor shall be equipped with a continuous weighing system with a recorder that can be monitored by the plant operator. The weighing system shall be interlocked with the asphalt control unit.
If a drum mixing plant is used for recycling, a dual weigh belt system will be required to control delivery of virgin aggregates and recycled material to the dryer. The system shall be equipped with interlocking control mechanisms in a manner that will assure positive and accurate delivery of recycled and virgin materials in proper proportions at all times. Included in this system shall be recorders that will record the total amount of material being delivered by each belt system separately. The belt weighing controls shall be connected to a totalizer which is interlocked with the asphalt delivery system in a manner which will assure that asphalt delivered to the mix is at all times within ± 0.3% of the intended amount. The system shall be subject to approval of the Engineer. A schematic diagram of the control system shall be furnished for the Engineer's information prior to plant calibration.
B. Dryer and Drum Mixer.
The plant shall be equipped with means for drying and heating the aggregate and/or mixture. Heating shall be controlled to avoid damage to the aggregate and asphalt. Operation of the equipment shall be controlled so the desired temperature is maintained as specified.
The plant shall be equipped with adequate means to remove objectionable oversize and foreign material from the aggregate before entering into the hot aggregate bin or drum.
The plant shall have aggregate bins of sufficient capacity to insure uniform and continuous operation. The aggregate storage shall be provided with sufficient ventilation by means of a stack or connection to the dust collection system so that moisture from the hot aggregate will be removed before condensing in the aggregate storage. When mineral filler is added without heating, adequate additional dry storage shall be provided for the mineral filler, and provisions shall be made for proportioning the filler uniformly in the desired proportion for the mixture.
E. Equipment for Heating and Storing Bituminous Materials.
Article 2001.11 shall apply. Unless the asphalt binder is supplied to the project from transports measured by weight (mass), duplicate storage facilities shall be provided, each of sufficient capacity to permit complete unloading of a tank car or truck transport at a single operation. Filling and withdrawal of material from each tank shall be conducted as a separate, definite operation which will permit the Engineer to measure the quantity of asphalt binder used from each tank for each cycle of operation. Each storage tank shall be installed and maintained in a level position. Measurement devices and gauging tables shall be furnished so accurate determinations of quantities used and stored can be made at regular intervals.
Suitable means shall be provided for maintaining the specified temperature of the asphalt binder in the pipe lines, meters, weighing buckets, spray bars, and other containers and flow lines.
The system shall include a spigot for removing asphalt samples from the delivery line to the mixer before the asphalt binder is metered into the mixer or weighed.
F. Asphalt Binder Control Unit.
Satisfactory means, by weighing, metering, or volumetric measurements, shall be provided to obtain the proper amount of asphalt binder. All measuring devices shall be operated within a delivery tolerance of 1.5%.
1. Batch Plants.
For batch plants, the quantity of asphalt binder for each batch shall be weighed on equipment meeting the appropriate requirements of Article 2001.07, A, or shall be measured by an approved automatic batch metering system. When used for proportioning only, the equipment shall meet the appropriate requirements of Article 2001.20.
The means of heating shall be sufficiently flexible so it will not affect the weighing. The container shall be arranged so that it will deliver the asphalt binder in a thin, uniform sheet or in multiple streams the full width of the mixer, except in the case of a mixer into which the asphalt binder is sprayed. If deposited on a flow or spreader sheet, the sheet shall be heated and shall have sufficient slope to discharge promptly into the mixer.
2. Continuous Plants.
Continuous plants shall use a pump to supply asphalt binder to the mixer, which is constructed to be under a positive pressure sufficient to maintain uniform delivery from the pump. The pressure shall be maintained within ± 0.5 psi (5 kPa) of the mean operating pressure.
Accurate pressure gauges shall be installed in readily accessible locations in lines feeding the metering pump and the mixer spray bars. The gauges shall be such size that the normal operating pressure can be easily read to the nearest psi (10 kPa).
The mixer unit shall be equipped with a surge tank or a deaeration chamber for supplying a constant pressure flow of asphalt binder to the metering pump. The surge tank or the deaeration chamber shall be approved by the Engineer and shall be of dimensions and capacity to provide the pressure specified. The capacity shall be at least a 6 minute supply of asphalt binder at the normal mixing rate of the mixer unit. The surge tank or the deaeration chamber shall be fitted with baffles and other appurtenances necessary to prevent the incorporation of air bubbles into the asphalt binder as the tank is being filled to ensure deaeration and escape of any air bubbles that may be present. When the surge tank system is used, the pressure at the spray bar shall not be greater than 20 psi (140 kPa). When a deaeration chamber system is used, the pressure difference between the return line and the spray bar shall not be greater than 20 psi (140 kPa). Separate return lines shall be provided for each tank.
3. Drum Mixing Plants.
Drum mixing plants shall use a pump to supply asphalt binder to the mixer, which is constructed to be under positive pressure sufficient to maintain uniform delivery from the pump. A totalizing flow meter shall be placed in the line between the metering pump and mixer unit. The asphalt control unit shall be interlocked with the aggregate weighing system specified in Article 2001.22, A, and shall be equipped to automatically adjust for variation in aggregate delivery. The plant shall be operated with automatic controls except when approved by the Engineer. The asphalt control unit shall be equipped so the plant operator can monitor and adjust the flow rate of aggregate or asphalt binder.
G. Thermometer Equipment.
An accurate, registering pyrometer or other approved thermometric instrument shall be installed in the discharge chute of the dryer or drum mixer in a manner so that the temperature of the heated aggregate or mixture is automatically indicated. This instrument shall be located where it is in clear view of the plant or dryer operator and readily accessible to the Engineer.
H. Control of Mixer Capacity and Mixing Time.
The plant shall be equipped with positive means to govern and maintain the time of mixing.
I. Dust Collector.
Proper housings, mixer covers, and dust collecting systems and returns shall be installed and properly maintained. The method of returning dust collected by dry type collection systems to the hot aggregate mixture shall be subject to the approval of the Engineer. If not required in the mixture, the bag house fines shall be removed from the project and plant site. When wet type collection systems are used, the Contractor shall remove all wet material from the project and plant site.
J. Hot Aggregate Proportioning.
Batch plant equipment shall include a means for accurately weighing the mineral filler and dried aggregate from each bin in a weighing hopper that is of ample size to hold a full batch without hand raking or running over. The weighing hopper shall be supported so it will not be easily thrown out of alignment or adjustment. Gates on bins and hoppers shall be constructed to prevent leakage when closed.
Mineral filler which is added cold shall be proportioned separately from a hopper and arranged to be fed uniformly into the heated aggregate before delivery to the feeder for the mixer.
For batch plants, the quantity of aggregate for each batch shall be weighed on equipment meeting the appropriate requirements of Article 2001.07, A. When used for proportioning only, the equipment shall meet the appropriate requirements of Article 2001.20.
The requirements of this Paragraph J do not apply to drum mixing plants.
The mixer shall comply with the following:
1. Batch Mixer.
A batch mixer shall be a twin shaft pugmill and shall be capable of producing a uniform mixture within the job mix or other specified limits. The clearance of the blades from all fixed and moving parts shall not exceed 3/4 inch (20 mm), and the orientation of the blades shall be as recommended by the manufacturer. If not enclosed, the mixer shall be equipped with a dust hood to prevent loss of dust by dispersion. The mixer shall be constructed to prevent leakage of contents until the batch is to be discharged. The mixer shall have an accurate time lock to control the operation of a complete mixing cycle by locking the weighing hopper gate when the mixer is charged and until the mixer gate is closed at the completion of the cycle. It shall also lock the outlet of the asphalt binder delivery system throughout the dry mixing period and the mixer gate throughout the dry and wet mixing periods.
The dry mixing period is the interval of time between the opening of the weighing hopper gate and the application of asphalt binder. The wet mixing period is the interval of time between the application of asphalt binder and the opening of the mixer gate. Control of the timing shall be flexible and capable of being set at intervals of not more than 5 seconds. A mechanical batch counter shall be installed as part of the timing device and shall be designed to register only completely mixed batches.
For recycling, batch plant equipment shall be modified to provide for accurate proportioning of the recycled material and for adding it directly into the weigh hopper, with weighing as a separate increment of the total batch, and with no preheating necessary.
The recycled material may be added to the hot elevator with no preheating necessary. In any method where preheating is being done, the equipment must be specifically designed for this purpose.
Any proportioning system shall also meet the requirements of Paragraph A.
When the heat transfer method is used, the new aggregate shall be superheated so that, when combined with the recycled material, the temperature of the resultant mixture will meet all requirements for mixing and placing the hot mixture.
Each plant modified for recycling mixtures shall initially be subject to approval of the Engineer.
2. Continuous Mixer.
A continuous mixer shall be an approved twin shaft pugmill capable of producing uniform mixtures within the job mix or other specified limits. The paddles shall be of a type adjustable for angular position on the shafts and reversible to retard the flow of mix. The mixer shall be equipped with a discharge hopper holding approximately 1 ton (1 Mg) and discharging intermittently by means of quick acting gates. Distance to the receiving vehicle shall be regulated to minimize segregation.
Satisfactory means shall be provided to afford positive interlocking control between the flow of aggregate from the bins and the flow of asphalt binder from the meter or other proportioning source. This control shall be accomplished by interlocking mechanical means or by any positive method for accurate control. The equipment shall include an accurate revolution counter, operating continuously during production.
The plant shall be equipped with positive means to govern and maintain a constant time of mixing.
3. Drum Mixer.
A drum mixer shall be capable of producing uniform mixtures within the job mix or other specified limits. The aggregate, asphalt binder, and additives, when furnished, shall be introduced continuously and uniformly and shall be subject to control of the plant operator. The mixture shall be discharged continuously and uniformly onto an elevator or conveyor that discharges into a hot mixture storage unit meeting requirements of Article 2001.22, L. The mixing shall be continued until the asphalt binder is uniformly distributed, and the aggregate particles are uniformly coated.
The plant may be modified with a pugmill coater added to the drum mixer. When so modified, the coater must be inclined and positioned as an integral built-in unit, located between the drum and the hot elevator of the plant setup. The asphalt binder, and additives when furnished, shall be introduced continuously and uniformly at the lower end of the coater, subject to control by the plant operator. Each modified plant shall be initially subject to approval of the Engineer.
For recycling, drum mixing equipment shall be modified to process recycled mixtures in accordance with Paragraph A.
Hot Mixture Storage.
When the hot mixture is not hauled immediately to the project and placed, suitable bins shall be provided. These bins shall be either surge bins to balance production capacity with hauling and placing capacity, or storage bins which are heated and/or insulated and which have a controlled atmosphere around the mixture. Either type of bin shall be round or octagonal in shape, shall be designed for the intended use, shall fill using an enclosed system unless skip conveyors are used, shall dump material directly into trucks through quick opening and quick closing gates, and shall not result in significant segregation, damage, or cooling. Affixed to each bin and visible to the loading operator shall be an indicating or control device which will allow control of material remaining in the bin.
When surge bins are used, the holding time shall be limited to 4 hours.
Hot mixture placed in storage bins shall be used within 24 hours of production unless otherwise approved by the Engineer.
M. Safety Requirements.
Adequate and safe stairways, platforms, and guarded ladders to plant units shall be placed at points required for accessibility to sampling locations and other plant operations. All gears, pulleys, chains, sprockets, and other moving parts shall be guarded and protected. Ample and unobstructed passage for personnel shall be maintained at all times in and around the truck loading area. This area shall be protected from falling material. Bins shall comply with requirements of Article 2001.06.
N. Plant Calibrations.
Personnel, weighing devices, test weights, and equipment for calibration of the plant and for verifying accuracy of proportions shall be furnished by the Contractor. Sufficient space shall be provided between aggregate feeds and elevators to permit taking of samples of the discharge for accurate calibration and control of rate of feed. Samples of sufficient size, for calibration and checking of proportions, shall be weighed. Truck sampling and weighing will be acceptable. The Engineer shall be allowed every opportunity to witness calibration of the equipment during the Engineer's normal working hours, or at a mutually agreeable time. This schedule limitation will be modified, if necessary, for work to be done under an accelerated work schedule. The Engineer's representative shall indicate witnessing the calibration by signing the calibration documents and charts.