ASPHALT PLANT INSPECTION
The overall responsibility for plant inspection remains with the Contractor. The Contractor’s Certified Technician should witness the contractor operations. Any deficiencies, which are observed with regard to specification compliance or safety, shall be reported to the contractor and the engineer.
Refer to IM 213 Appendix D for a list of the duties of a Certified Plant Inspector.
A. Preliminary Inspection
The first phase of the contractor operations consists of preparing the plant site and building stockpiles.
Stockpiles should be inspected for segregation, contamination and intermingling. If evidence of segregate and/or contamination is found, report to the contractor’s quality control manager. Inspect Plant Site for safe working conditions.
B. Job Mix Formula (JMF)
The plant inspector must be thoroughly familiar with the information provided by the Job Mix Formula Report (Form #956 & 955). Sample mix design documentation can be found in IM 510 Appendix B.
C. Sampling and Testing
The Contractor’s Laboratory Technician is responsible for meeting all sampling, testing, and documentation requirements as set forth by Specification 2303 and IM 511. Sampling frequencies are provided for in IM 204 and the Standard Specifications. Sampling and testing methods are provided for in IM 300 series.
D. Plant Equipment
Items of equipment to be checked for specification compliance prior to beginning operations are listed below:
1. Truck Scales or weigh hoppers
2. Aggregate Bins and Belts
4. Dust Collector
5. Revolution Counters, and/or Scales
6. Thermometer Equipment
7. Equipment for Heating, Storing and Measuring Asphalt Binder (Asphalt Pump, Surge Tank, and/or Scales)
8. Testing Laboratory
9. Safety Requirements
See IM 514 for plant calibration.
E. Production Inspection Duties
1. Temperature Control
Observe and control the temperature of the various material components to document specification compliance, to prevent damage to the material, and to produce uniform workable mixtures. The specifications contain the ranges and tolerances for each type and class of mixture. The specification limits for mix temperature are the same for all plant types. Production above or below these limits must be approved in advance by the Engineer, and documented as set out in Section 1108.04 of the Standard Specifications.
Point of Test (Temperature)
· Asphalt Binder
Delivery units and storage tanks
· Final Mixture
Point of Discharge from mixer (May be obtained from the internal instrumentation providing real-time information to the control house)
· Final Mixture (on road)
2. Gradation Control
Aggregate proportioning will be monitored and verified as part of the overall plant inspection activity. When the sieve analysis test indicates the combined material does not comply with the gradation requirements, the plant inspector shall take the following steps:
a. Recheck test procedures and computations.
b. Check gate settings and feeder operations.
c. Check the materials and material handling procedures.
d. Notify the RCE, the DME and the contractor of the results.
e. Obtain a second sample and test promptly.
If the gradation tests and/or inspection observations indicate that proportioning irregularities are occurring, the contractor is required to take corrective action immediately. Adjustments in proportions and other job mix formula changes must be documented, in accordance with IM 511.
3. Asphalt Content Control
IM 509 provides the detailed procedure for determining asphalt content and IM 509 Appendix A for making tank measurements. Refer to IM 511 Appendix D for troubleshooting. Separate check systems are used for drum-mix and batch plants as follows:
a. Drum Mixing Type Plants
At start-up and during periods when asphalt or aggregate delivery is questionable, it is advisable to perform proportioning checks in addition to the measurements required in IM 204. The specifications require drum-mixing plants to be equipped with totalizing asphalt meters and aggregate scales.
This equipment and information should be utilized for making continuous checks. Total asphalt delivered as indicated by the meter should be periodically compared with quantities used as determined by tank measurements.
(1) Compare asphalt delivered by metering pump or scale with outage shown by 2 or 4 hour tank measurement (compare by pounds, gallons, or percent).
(2) Compare total mix produced, including waste, to asphalt and aggregate delivered by plant for a given period of time.
b. Batch Type Plants
The operation of batch type plants should also be verified when work begins on a project. This is done by checking the operation and sensitivity of the scale equipment.
F. Checking Scales
1. Batch Scales
Batch scale sensitivity shall be checked once per day during a normal working day by placing a weight equal to 1/10 percent of the batch weight but not greater than 20 lbs. on the fully loaded scales and observing the movement of the indicator. A properly sensitive scale will exhibit a visible indicator movement when so tested. If no indicator movement is visible, immediate corrective action must be taken by the contractor.
The specified scale delivery tolerance limits should be checked by periodically witnessing the batch weighing operations. Each scale indicator should consistently indicate the required weight within the specified delivery tolerance, and return to zero when unloaded within the specified 0.5 percent tolerance.
When automatic batch weighing equipment is used, the interlock system shall be set at the 1.0 percent limit as specified. They may be manually overridden to continue plant operation if the specified delivery tolerance is not exceeded. When the delivery tolerances are exceeded, the asphalt or aggregate batch sizes shall be adjusted manually to bring the batch into compliance, or it shall be wasted.
The plant superintendent or other authorized contractor representative must make all necessary scale and equipment settings and/or adjustments. Before the plant operation begins or resumes the plant inspector will independently determine for himself that the settings and/or adjustments are accurate and that the weights of material being delivered to the batch are correct.
Normal plant operation causes vibration, which tends to change these adjustments. Accumulation of material clinging to the inside of the weighing hopper can also cause these adjustments to drift. If the amount exceeds one percent of the material batch weight it must be removed and the empty weight readjusted to indicate a zero load.
2. Truck Scales
Truck scales shall be checked as provided in Standard Specification 2001.07.
G. Specification Compliance
All materials shall be inspected prior to being incorporated in a pavement structure. Some materials are being shipped to projects under certification programs and others must have a report. In either case it is necessary to check and file the reports or certifications such that each final product component is properly identified and incorporated with the proper documentation. This is accomplished by obtaining the documents for each lot of material before incorporation. All shipments of all materials incorporated shall be logged as they are received.
H. Reporting Requirements
1. Computer programs are provided to document what is required.
Daily Plant Report. This form is submitted daily to document plant operations, job control testing, and material placement. (http://www.iowadot.gov/Construction_Materials/hma/HMAplantreport.xlsm)
2. Testing Worksheets. All worksheets and other original documents used by inspection personnel are to include identification of:
a. Individuals associated with sampling and testing,
b. County and Project No.,
c. Material and sampling point,
d. Date and time of sampling and testing and,
e. Source, producer or contractor.
All documents other than field notebooks are to be filed with the appropriate report and retained per the file retention schedule.
I. Mixture Segregation
Segregation of the mix results in non-uniform distribution of the material in the pavement. Coarse, lean mixtures are more subject to segregation than fine-rich mixtures; therefore more care must be exercised when coarse mixtures are being produced. Segregation at the plant may be caused by:
1. Pugmill discharge being too high above the truck bodies.
2. Depositing into very large truck bodies, causing the mixture to cone and roll. In this case trucks should be moved back and forth during loading.
3. Pugmill or storage gates opening improperly. They may not open or close quickly or to the full extent of the opening.
4. Inadequate mixing. This may be caused by short mixing cycle, improper mixer paddle positioning, worn paddles, or low level in the mixing chamber.
5. Improperly designed, maintained, and operated surge and storage bins and conveyors. Example - material discharge into conveyor must be centered into the bucket or belt.
6. Failure to provide near level truck charging platform.
J. Asphalt Binder Contamination
Alert inspection and proper supervision can prevent contamination by the contractor since most of the problems are associated with the use of cleaning fluids and improper material combination. Contamination may be caused by:
1. Allowing fuel oil used for cleaning pumps and lines to enter the storage tanks.
2. Accepting delivery of non-specification material or material of a different grade.
3. Leakage of plant heating oil into the storage tanks.
4. Contaminated delivery tanks.
5. Improper sampling, and sample catching container, refer to IM 323.
6. Residual products left in the tank.
K. Completed Project
When a project is completed, the plant inspector shall check all documentation for accuracy and completeness. It is also necessary to determine at this time the net quantity of materials incorporated in the project. The field records and plant records should be compared and final determinations made. Furnish copies of all required documentation to the RCE and DME.