Many Paths to Low-Energy Asphalt Mixes

This article describes how in-plant foamed asphalt processes have grow in popularity as producers, contractors and agencies embrace warm mix asphalt. Warm mix asphalt (WMA) is created by mixing a solid chemical compound additive with hot mix asphalt in the plant, except when a liquid additive is used to make WMA. But ask a contractor in different parts of the United States if he produces warm mix asphalt, and he may say, “Yes, we foam our asphalt.” That’s because in-plant foamed asphalt using plant-mounted equipment also is known as warm mix asphalt. This dedicated equipment foams the liquid asphalt in the drum during mixing. But foamed asphalt also is created in a cold mix plant, and even in situ in the field, using as much as 100-percent reclaimed asphalt pavement (RAP). That technology antedates in-plant foamed processes, but also is called foamed asphalt or foamed bitumen. And some asphalt producers are creating warm mixes by using liquid additive combined with dedicated in-plant foaming equipment. Welcome to the sometimes confusing new world of what might be better termed low-energy mixes; that is, asphalt mixes produced at significantly lower temperatures, with substantial benefits to the producer and consumer in terms of energy costs and environmental impact. The confusion is exacerbated by the fact that few state Departments of Transportation (DOTs) have specifications for warm mix asphalts, leaving their composition up to the contractor, so long as their use is permitted by the contract, and the contractor stands behind his or her work.