A system for controlling the Laboratory's pilot scale "continuous dryer" asphalt mixing plant has been developed with the aim of producing a more uniform product than is possible with other available systems. The report describes a detailed evaluation of the performance of the final prototype system carried out over a period of four years on a wide variety of materials. Comparisons of material produced under automatic and manual control have shown that the variability of composition and temperature is much improved under automatic control, as is the accuracy of batching mix components. The trials have also shown the benefits, and a few limitations, of the various sequencing and monitoring programs that help the smooth running of the plant and thereby the production of a correct and consistent product. However, to fulfil the original aim of this project completely, it is necessary to implement the control system on a suitable full-scale plant to compare it with other available systems. The Report also contains a detailed description of the plant and details of modifications that have been made to the instrumentation and control system since the last published information.

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