Mixing the components of a bituminous mixture, proportioned by weight from hot — bins, in a batch asphalt plant takes place in a pugmill. Contemporary batch plants have pugmills of various sizes, usually from 1 ton to 8 tons. Despite the different sizes of pugmills and the resulting output of the plants, mixing time, by and large, remains at the same level for all plants (USACE Handbook, 2000). Determining the suitable amounts of materials to batch given the pugmill’s volume is quite a significant step
Recommended Maximum Production Temperatures of an SMA Mixture for example binders according to various Regulations
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Maximum Mixture Temperature in Asphalt Plant (°С)
Note: PMB = Polymer modified binder.
and is one of the decisive actions undertaken during the plant’s calibration. The quantity of material intended for mixing in one cycle may neither be too large nor too small in comparison with the pugmill’s volume. In the case of an excessive charge of material, the mixing will be ineffective; the mixture will remain partially unmixed and the stabilizer will not be distributed throughout the mixture. An insufficient amount of material in the pugmill will result in throwing the mixture out of the mixing chamber instead of mixing it properly, an acceleration of the binder-aging process and, again, the potential of destroying the stabilizer.
In a drum-mix plant, components are continually delivered into a constantly mixing drum. Thus the control of the constituents’ proportions is exercised through the adjustment of the batching rate. The mixing time depends on the shifting rate of materials inside the drum, which can be affected by a variety of factors such as the length of the drum and the angle of the drum.
