The continuous mobile mixer shall be calibrated to the satisfaction of the Engineer prior to starting work. The frequency of calibration will be determined by the Engineer. All special equipment required for calibration shall be furnished by the contractor. The calibration sheets may be provided by the Department or the mixer operator.

The mixer shall be set at the appropriate operating revolutions per minute as determined by the mixer manufacturer or mixer operator. The unit discharging the cement shall be operated until an even flow of cement has been discharged. It shall then be stopped and the cement meter reset to zero. A suitable container shall be set below the discharge of cement. The time required to discharge 94 lbs. (43 kg) cement shall be measured with a stop watch, the number of counts on the cement meter shall be recorded, and the weight of the discharged cement determined. The process shall be repeated at least three times or until trials have proved consistent with one another

With the mixer set at the required operating rpm, calibrate the delivery of the latex modifier into a suitable container. The latex throttling valve shall be adjusted to deliver the required amount of latex emulsion admixture for each 94 lbs. (43 kg) of cement. For the calculated seconds per 94 lbs. of cement the latex shall be discharged into a container. The weight of the latex shall be determined and the throttling valve adjusted such that the amount of latex discharge is within 0.5 lb. of the weight of latex of 29.4 lbs., the amount required per 94 lb. of cement or 3.5 gallons per 94 lb. of cement (Based on the latex being 8.4 lbs. per gallon).

With the mixer set at the required operating rpm, calibrate the accuracy of the water flow meter into a suitable container. The accuracy of the water flow meter shall be verified by setting the flow meter at 2 gallon per minute and discharging into a container during a one minute interval. Weighing the amount and dividing by 8.33 will determine the number of gallons. This procedure shall be repeated with the flow meter adjusted to 3 gallons per minute. A theoretical water setting on the flow meter can be determined by calculating total water required according to the mix design and then deducting for aggregate moisture and water in the latex emulsion.

Based on the approved mix design the aggregates shall be weighed out separately to meet the desired weights per cubic yard. The seconds per bag of cement for each mixer may be reduced by one half to reduce the weight of aggregates per bag to one half for more manageable handling. Yield checks shall be performed using a 36” x 36” x 9” open box to verify gate settings.

Continuous mobile mixers which entrap unacceptable volumes of air shall be allowed to use anti-foaming additive as prescribed by the latex emulsion manufacturer. Batch type mixers will not be used. Drum type mixers or rotating drum batch mixers shall not be used under any circumstances. The continuous mixer shall be kept clean and free of partially dried or hardened materials.