How do many WMA additives affect compaction compared to HMA?

• A. They increase viscosity and make compaction more difficult
• B. They decrease viscosity and ease compaction
• C. They have no effect on compaction
• D. They prevent compaction entirely

Answer: (A)

Many WMA additives are designed to make the asphalt binder flow more readily at lower temperatures. By lowering the binder viscosity (or enabling temporary foaming that reduces viscosity in the mix), the material can be placed and compacted more easily than hot mix asphalt at the same reduced temperature. This improved workability leads to easier, more consistent compaction and better density outcomes as the mix cools. So the expected effect is decreased viscosity and easier compaction. The idea that additives would increase viscosity or prevent compaction goes against how WMA technologies are intended to operate, and claiming no effect ignores the observed improvements in workability at lower temps.