Hot-Mix Asphalt Paving Handbook, 2000 Flashcards
(56 cards)
What improves rutting resistance in the mix?
The rougher the texture of the aggregate.
What is the ‘one third’ rule for nominal maximum aggregate size?
If nominal max aggregate size exceeds 1/3 of compacted pavement layer thickness, surface texture may be reduced.
What is an advantage of method specifications?
They offer an advantage when a measure of quality is difficult to define.
List two disadvantages of method specifications.
1) Contractors may not use economical procedures.
2) Inspection is labor-intensive.
What happens if product quality is poor under method specifications?
Contractor has no legal responsibility to improve it.
Who assumes specification risk under method specifications?
The agency
What is the greatest advantage of QC/QA specifications to agencies?
They place responsibility for quality on the contractor or producer.
What is the primary advantage of QC/QA specs to both agency and contractor?
Risks to both parties can be quantified and balanced.
Who performs QC testing and who is responsible for QA?
The contractor performs QC; the owner agency is responsible for QA.
Purpose of counter-flow drum mix plant design?
To improve heat transfer and reduce emissions.
How should aggregate be stored?
On a sloped, clean, stable surface with coarse and fine kept separate.
What increases drying costs and reduces plant capacity?
Excess moisture in fine aggregates.
Why cover aggregate stockpiles?
To reduce moisture accumulation from rain.
Why should tarps not be placed directly on aggregate?
Moisture collects under the tarp instead of evaporating.
Why place tarp on fine aggregate if only one roof is used?
Fine aggregate has higher moisture content.
What causes aggregate problems?
Mishandling during stockpiling and load-out.
How should stockpiles be constructed?
In horizontal or gently sloping layers.
What reduces moisture damage in HMA mixes?
Adding 1 - 2 Percent hydrated lime by weight.
What is the slurry proportion for hydrated lime?
1 part lime to 3 parts water.
How often should moisture content be tested?
At least twice a day and after moisture changes.
How should the front-end loader remove aggregate?
Perpendicular to flow to minimize segregation.
Purpose of liquid antistrip materials?
Improve adhesion and resistance to moisture damage.
Ideal moisture content after drying aggregates?
Less than 0.5%, ideally less than 0.2%.
What limits RAP fed into hot elevator?
Heating process as material travels to top.
