That is why they are usually omitted when computing ESAL values LEFs Lecture 8

# That is why they are usually omitted when computing

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That is why they are usually omitted when computing ESAL values.
LEFs Lecture 8 13/04/14 15
Lecture 8 13/04/14 16 PAVEMENT DESIGN Estimating ESALs for Occasional Traffic: The use of load equivalency factors for facilities such as residential streets and parking lots, where expected traffic is predominantly automobiles (cars) with only occasional trucks, will result in low ESAL and consequently thin pavements that may not be capable of carrying the occasional heavy traffic or environmental effects. A good estimate of the occasional traffic will be required. Where this is not possible, the minimum pavement thickness recommended by the Asphalt Institute must be adopted. If it is reckoned that the truck percentage is less than 2%, Asphalt Institute recommends that the design ESAL may be obtained by multiplying total traffic by a truck factor of 0.06.
Lecture 8 13/04/14 17 PAVEMENT DESIGN Step 1.4: Determine Subgrade Engineering Properties : This is either the natural soil or soil imported to form an embankment. The imported or even local soil may be improved through stabilisation. The main engineering property required for the subgrade is its RESILIENT MODULUS, which gives the resilient characteristic of the soil when it is repeatedly loaded with an axial load. This is determined in the laboratory by loading specially prepared samples of the soil with a deviator stress of fixed magnitude, frequency, and load duration while the specimen is triaxially loaded in a triaxial chamber. To facilitate the use of the more direct CBR, the Asphalt Institute has determined conversion factors: M r (MPa)= 10.342 CBR ; where M r is the equivalent resilient modus Step 1.5 Determine Subbase and Base Engineering properties : The material used for subbase and base courses must meet certain criteria, which are given in terms of CBR, PI, LL, particle size distribution (maximum percentage passing through the sieve No.200), and minimum sand equivalent. Refer to relevant standards; e.g. Thickness Design – Asphalt Pavements for Highways and Streets, Manual Series No. 1, by the Asphalt Institute. CBR (MINIMUM) 20 (subbase) 80 (base) LL (MAX) 25 (subbase) 25 (base)
Lecture 8 13/04/14 18 PAVEMENT DESIGN Step 2: Choose Surface and Base Materials The materials to be specified here would depend, first and foremost on the materials economically available. But generally the designer can choose an asphalt concrete surface and any other, from asphalt to bound and unbound natural materials for the base. For pavements that will carry very heavy traffic a crushed rock/ gravel base may be used. The grade of asphalt (bitumen) used for the asphalt concrete must be selected primarily on its ability to satisfactorily coat the aggregates at different temperatures. Step 3: Minimum Thickness Requirements: The minimum thickness required for the design ESAL and the type of surface, base, and subbase selected is obtained by entering the appropriate design charts or table with the design ESAL and M r of the subgrade and selecting the required minimum thickness.
Lecture 8 13/04/14 19 DBM = Dense Bitumen Macadam HRA = Hot Rolled Asphalt DTM = Dense Tar Macadam DBM50 = DBM+50 penetration bitumen HDM = Heavy Duty Macadam

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• Fall '08
• Devine,D
• Road, Truck, Tarmac, Asphalt concrete

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