Here, the 12.5 mm (0.5 inch) Superpave surface course and the 25 mm (1 inch) dense-graded binder course are structurally equivalent. It is interesting to note that in most empirical design procedures HMA, no matter what the specific mix designation or size, is treated equally. Notice also that a change in reliability level from 90% to 99% results in a SN increase of about 1.0 and a resultant increase in HMA thickness of about 55 mm (2 inches). In this particular example, which only shows one set of possible solutions, the HMA surface course and base course layer depths were kept constant and the HMA binder course depth was varied depending upon requirements. Layer coefficients used were 0.44 for HMA and 0.13 for crushed stoneįrost design requirements must be checked if subgrade soil frost susceptible Pavements are typically designed for the critical lane or “design lane”, which accounts for traffic distribution.ĮSALs per year = (Vehicles/day) (Lane Distribution Factor) (days/yr) (ESALs/Vehicle) Composite samples can be manufactured by combining small portions of each subgrade. This step involves converting the daily traffic volume into an annual ESAL amount. Groupings shall not consist of samples with different AASHTO Classifications. Work can be verified by using the Flexible Pavement Structural Design Utility. Truck trains – trucks with more than 2 units (assume 1.75 ESALs per truck) = 247/dayīy looking at several different design periods and reliability levels this example gives an idea of the relative influence of these inputs. Single unit trucks (assume 0.40 ESALs per truck) = 1872/dayĭouble unit trucks (assume 1.00 ESALs per truck) = 1762/day ![]() This represents a typical range of reliability levels encountered for Interstate highways. Investigate three levels: R = 90%, R = 95%, R = 99%. M R = 86 MPa (12,500 psi) in the wet months of November through April M R = 103 MPa (15,000 psi) in the dry months of May through October ![]() Use E = 3,447 MPa (500,000 psi) Base course: Crushed aggregate with M R= 193 MPa (28,000 psi)Subbase course: None used Surface course: 12.5 mm (0.5 inch) Superpave with E = 3,447 MPa (500,000 psi)Binder course: Dense-graded HMA mix with a nominal maximum aggregate sizeof 25 mm (1 inch). AASHTO values are 4.5 for rigid pavement and 4.2 for flexible pavement. ![]() Investigate 20, 30 and 40 year design periods ![]() Assume 80% of the loading occurs in the design lane
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