Road-mix vs. Plant-mix in Bituminous Road Construction

below the surface through scarifier teeth. Emulsions and medium-curing and slow-curing asphalts were used. The travelling plant-mix was not entirely satisfactory because of conditions existing on this project. It is necessary to have the windrow of material quite wet in order to get it through the travelling pug-mill mixer. The project was built late in the fall, and the water did not evaporate from the mixture. In soil-bituminous stabilization, water may be necessary to facilitate mixing, but the resulting mixture is no good until the water has been reduced to the optimum or below. This is a point worth remembering, because it has been responsible for poor results in a number of states. The costs varied from $4,300 per mile for the sub-oiled section and slow-curing oil to $8,900 per mile for the section mixed with a travelling mixer and asphalt emulsion. It seems probable that costs lower than this might be obtained on future projects after the contractors have become more familiar with the process. Recent reports from Kentucky indicate that this type of con­ struction has not been very satisfactory. The cause of the poor performance has not been determined. All of us would like to know how to build a good low-cost road. That seems to be one of the most difficult problems a highway engineer has to solve. It has often been said that the lower the type of road desired, the higher the grade of engineering required. No doubt this is true. I am sorry that I am not a good enough engineer to tell you definitely how to build a good road cheaply. I hope, however, that some of the things I have suggested will be found useful in constructing a more stable road at a reasonable cost.