General Parameters & Advice
Slurry seal pavers require calibration due to their continuous mix operation. Pavers deliver a continuous feed of raw ingredients (aggregate, asphalt emulsion, mineral filler, water and additive) to the front of the pugmill (mixer), while a homogeneous mixture of all ingredients is continuously delivered to the spreader box from the back of the pugmill.
Calibration is a process in which the actual output of the paver is measured by weight for aggregate, emulsion, and fines. These actual outputs are correlated to the revolutions of the aggregate belt since the laboratory specifies all material ratios by weight, to the amount of aggregate.
By performing the calibration process, the slurry seal paver is set to deliver precise ratios of emulsion and fines with respect to the aggregate, as specified in the mix design from the laboratory. By doing this, the contractor and buyer agency know what they can expect from the mix being applied, since the tests performed in the laboratory determined the ratios. It also allows a precise record of the amounts of materials that were applied on the project for payment purposes.
Calibration Guidelines
As there are multiple manufacturers of slurry seal pavers, each manufacturer has their preferred calibration method, however all methods follow the same theory:
Asphalt Emulsion Calibration:
- Capture the output of the emulsion pump accurately while tracking fractions of a revolution of the pump.
- Weigh the output, repeat several times and average the results to ensure there are no errors in the calibration process.
- Determine the weight of asphalt emulsion delivered for each fraction of a revolution (referred to as ‘count’) of the pump.
- Utilize this weight/count in the operating system of the paver.
Mineral Filler Calibration
- Capture the output of the mineral filler hopper accurately while tracking fractions of a revolution of the auger.
- Weigh the output, repeat several times and average the results to ensure there are no errors in the calibration process.
- Determine the weight of mineral filler delivered for each fraction of a revolution (referred to as ‘count’) of the auger.
- Utilize this weight/count in the operating system of the paver.
Aggregate Calibration
- Capture the output of the aggregate hopper accurately while tracking fractions of a revolution of the conveyor belt. This will include determining the moisture content of the aggregate, as the dry weight of the aggregate must be known.
- Weigh the output, repeat several times and average the results to ensure there are no errors in the calibration process. For pavers with an adjustable aggregate gate, this will be performed at three different gate settings.
- Determine the weight of aggregate delivered for each fraction of a revolution (referred to as ‘count’) of the conveyor belt.
- Utilize this weight/count in the operating system of the paver.
Water and Additive
A similar process will be followed for the water and additive, however the amount of these materials in the mix will vary (within an acceptable range) as project conditions change, and different brands of pavers will track the amounts in different ways.
Upon completion of the above process, the output of the asphalt emulsion pump and of the mineral filler system is correlated to the output of the aggregate conveyor belt. This is a critical step, as the Job Mix Formula derived from the mix design performed by the laboratory will specify the amount of asphalt emulsion and mineral filler as a percentage of the weight of the aggregate. Follow the manufacturer’s guidelines to complete the configuration of the paver for the specific Job Mix Formula. Once completed, the paver will be configured such that every time mixing is started, the materials will be delivered in the proportions specified in the Job Mix Formula.
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