Engineer
AASHTO Terminology
AASHTO soil terminology comes from AASHTO M 145, “Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes”. Aggregate terminology comes from AASHTO M 147, “Materials for Aggregate and Soil-Aggregate Subbase, Base and Surface Courses”. Basic terms include: Boulders & Cobbles: Material retained on a 75-mm (3-inch) sieve. Gravel: Material passing a 75-mm (3-inch) sieve … Read more
AASHO Road Test
The AASHO Road Test, a $27 million (1960 dollars) investment and the largest road experiment of its time, was conceived and sponsored by the American Association of State Highway Officials (AASHO) as a study of the performance of highway pavement structures of known thickness under moving loads of known magnitude and frequency (Highway Research Board, … Read more
Frost Action
Frost action can be quite detrimental to pavements and refers to two separate but related processes: Frost heave. An upward movement of the subgrade resulting from the expansion of accumulated soil moisture as it freezes. Thaw weakening. A weakened subgrade condition resulting from soil saturation as ice within the soil melts. Frost Heave … Read more
Present Serviceability Index
The present serviceability index (PSI) is based on the original AASHO Road Test PSR. Basically, the PSR was a ride quality rating that required a panel of observers to actually ride in an automobile over the pavement in question. Since this type of rating is not practical for large-scale pavement networks, a transition to a … Read more
Foamed Asphalt
Foamed asphalt is formed by combining hot asphalt binder with small amounts of cold water. When the cold water comes in contact with the hot asphalt binder it turns to steam, which becomes trapped in tiny asphalt binder bubbles (World Highways, 2001[1]). The result is a thin-film, high volume asphalt foam with approximately 10 times … Read more
Thin-Film Oven
The thin-film oven (TFO) test simulates short-term aging by heating a film of asphalt binder in an oven for 5 hours at 163° C (325° F). The effects of heat and air are determined from changes incurred in physical properties measured before and after the oven treatment by other test procedures. Standard Test Methods AASHTO … Read more
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