PORTLAND CEMENT & READY MIX
PLANT CALIBRATION CHECKLIST
References: IM 527, 528 and noted Specifications
STORAGE & HANDLING OF MATERIALS
Aggregates: 2301.02
· Certified compliance
· Separation of materials
· Storage area floor shall be a minimum of 18” of similar material
· Fine aggregates shall drain a minimum of 24 hours on new bridge deck floors-2412.02
Cementitious Material: 2301.02
· Approved certified sources
· No intermingling of products or sources
· Stored in suitable weather proof enclosures
WATER
· Sample when required
ADMIXTURES
· Verify acceptance of lot
· Circulate 5 min. per 100 gal. of solution
· Proper storage to prevent freezing
PLANT REQUIREMENTS
Safety:
· Guards, ladders, railings and walkways
· Sampling location
· Proper template if belt sample
· Safety switches and belt lockouts in place
· Bins are structurally safe: 2001.06
· Settlement of footings is uniform
· Suitable wind protection for scale operation
· Automatic interlocks for projects over 6000 sq. yds: 2001.20 & 2301.13
· Weight indicator or digital readouts are in full view of the plant operator.
Scale Calibration: 2001.20
Calibration of batch plant scales as required by the specifications is performed by incrementally loading the scales with standard test weights and partial batches through the operating range of the scales. As each increment of load is applied, the actual observed weight and the required weight are compared. The differences plus or minus, are determined and converted to percentages of the required weight. If the percentage deviations are less than the tolerance allowed by the specifications and the scales are sensitive to the test loads, the scales will be considered in calibration. If the scales do not meet the various requirements, the contractor should be notified immediately and required to make the necessary repairs or adjustments. The engineer may order recalibration if the scale equipment malfunctions, material quantities do not agree with actual material quantities, or any repairs or replacement of equipment occurs.
· Calibrate scales to include the maximum weight for projected batches
· Commercially manufactured weights that have the weight stamped on the exterior and appear to be unaltered and in good condition may be assumed to meet the requirements of ASTM E617.
· Non-commercially manufactured test weights may be used in providing accumulating weight for loading the scales, if validated against commercially manufactured test weights, or a certified scale, a minimum of once every two years. Some manufactured weights may vary and require more frequent validation.
Example: Aggregate Scale Calibration.
As a guide, a working form to help record field calibration measurements is on page 4. Certified scale company reports may be used or use District Materials Engineer Excel spreadsheets.
Water Calibration: 2001.20B
· Equipment shall be such that accuracy will not be affected by variations in pressure of the water supply.
· Weighing equipment to verify water calibration shall meet specification
· Repairs or adjustments will require equipment to be recalibrated.
Equipment for Dispensing Liquid Admixtures: 2001.20C
· Calibrate per Specification
· Measuring container of digital readout shall be on view of plant operator.
Truck Mixer & Agitator: 2001.21B
· Meet the requirements of specification
· Truck mixer certification (Form #820907) kept in truck and is up to date.
CONCRETE PLANT CALIBRATION WORKSHEET
DATE PAVING PLANT
LOCATION READY MIX PLANT
CEMENT SCALE – ACCURATE TO 0.5% OF BATCH WEIGHT
SENSITIVITY – EMPTY FULL LBS. @ LBS.
TOLERANCE – 0.1% OF BATCH WEIGHT OR 2 LBS., WHICHEVER IS GREATER
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applied weight |
scale reading |
Error, % |
applied weight |
scale reading |
Error, % |
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AGGREGATE SCALE – ACCURATE TO 0.5% OF BATCH WEIGHT
SENSITIVITY – EMPTY FULL LBS. @ LBS.
TOLERANCE – 0.1% OF BATCH WEIGHT OR 2 LBS., WHICHEVER IS GREATER
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applied weight |
scale reading |
Error, % |
applied weight |
scale reading |
Error, % |
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WATER-ACCURATE TO +/-1.0% OR 2 LBS., ADMIXTURES-ACCURATE TO +/-3.0%
WHICHEVER IS GREATER OF QUANTITY REQUIRED
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metered gal. lbs. |
scale reading |
Error. % |
area meter meas. oz. oz. |
water reducer meter meas. oz. oz. |
Retarder meter meas. oz. oz. |
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