150_5320_6d_part3

150_5320_6d_part3 - AC150/5320-6D 7l7l95 C. Stabilized...

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AC150/5320-6D 7l7l95 C. Stabilized Subbase. Stabilized subbases also offer considerably higher strength to the pavement than P-154. Recommended equivalency factors associated with stabilized subbase are presented in Table 3-7. -/ TABLE 3-7. RECOMMENDED EQUWALENCY FACTOR RANGES FOR STABILIZED SUBBASE Material Equivalency Factor Range P-301, Soil Cement Base Course 1.0 - 1.5 P-304, Cement Treated Base Course 1.6 - 2.3 P-306, Econocrete Subbase Course 1.6 - 2.3 P-401, Plant Mix Bituminous Pavements 1.7 - 2.3 d. Granular Base. The FAA standard for granular base is Item P-209, Crushed Aggregate Base Course. In some instances it may be advantageous to utilize other nonstabilized granular material as base course. Other materials acceptable for use as granular base course are as follows: TABLE 3-8. RECOMMENDED EQUIVALENCY FACTOR RANGES FOR GRANULAR BASE Material Equivalency Factor Range P-208, Aggregate Base Course 1.0’ P-21 1, Lime Rock Base Course 1.0 ‘Substitution of P-208 for P-209 is permissible only if the gross weight of the design aircraft is 60,000 lbs (27 000 kg) or less. In addition, if P-208 is substituted for P-209, the required thickness of hot mix asphalt surfacing shown on the design curves should be increased 1 inch (25 mm). e. Stabilized Base. Stabilized base courses offer structural benefits to a flexible pavement in much the same manner as stabilized subbase. The benefits are expressed as equivalency factors similar to those shown for stabilized subbase. In developing the equivalency factors Item P-209, Crushed Aggregate Base Course, with an assumed CBR of 80 was used as the basis for comparison. The thickness of stabilized base is computed by dividing the granular base course thickness requirement by the appropriate equivalency factor. The equivalency factor ranges are given below in Table 3-9. Ranges of equivalency factors are shown rather than single values since variations in the quality of materials, construction techniques, and control can influence the equivalency factor. In the selection of equivalency factors, consideration should be given to the traffic using the pavement, total pavement thickness, and the thickness of the individual layer. For example, a thin layer in a pavement structure subjected to heavy loads spread over large areas will result in an equivalency factor near the low end of the range. Conversely, light loads on thick layers will call for equivalency factors near the upper end of the ranges. -- TABLE 3-9. RECOMMENDED EQUIVALENCY FACTOR RANGES FOR STABILIZED BASE Material Eauivalencv Factor Range P-304, Cement Treated Base Course 1.2 - 1.6 P-306, Econocrete Subbase Course 1.2 - 1.6 P-401, Plant Mix Bituminous Pavements 1.2 - 1.6 Note: Reflection cracking may be encountered when P-304 or P-306 is used as base for a flexible pavement. The thickness of the hot mix asphalt surfacing course should be at least 4 inches (100 mm) to minimize reflection cracking in these instances.
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150_5320_6d_part3 - AC150/5320-6D 7l7l95 C. Stabilized...

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