Micro surfacing pavers require calibration due to their continuous mix operation. Pavers deliver a continuous feed of raw ingredients (aggregate, asphalt emulsion, fines, 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 micro surfacing 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.
As there are multiple manufacturers of micro surfacing pavers, each manufacturer has their preferred calibration method, however all methods follow the same theory:
Mineral Filler Calibration
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.