IN-PLACE AIR PERMEAMETER FOR OPEN-GRADED DRAINAGE LAYERS

A RAPID FIELD TEST IS PROPOSED TO EVALUATE THE PERMEABILITY OF OPEN-GRADED ROAD BASES AND OTHER DRAINAGE LAYERS. THE SAME TEST ALSO SHOULD BE ADAPTABLE TO EVALUATE PERMEABILITIES OF OTHER EXPOSED PAVEMENT LAYERS INCLUDING THOSE COMPOSED OF BITUMINOUS OR PORTLAND CEMENT CONCRETES, AS AN INDEX TO PERMEATION AND POSSIBLY TO DETERIORATION. IT IS PROPOSED THAT THE PERMEABILITY BE EVALUATED THROUGH USE OF AIR AS A PERMEANT RATHER THAN A LIQUID. ADVANTAGES OF MEASURING AIR INSTEAD OF LIQUID PERMEABILITY INCLUDES (1) FLOW RATES INCREASED BY THE REDUCED VISCOSITY, GREATLY REDUCING TESTING TIME, (2) NO NEED TO TRANSPORT THE PERMEANTTO THE TEST SITE, (3) NO REQUIREMENT FOR SATURATING THE TEST AREA, (4) AVOIDING CAPILLARY SUCTION AND WETTING EFFECTS, (5) REMOVING GRAVITATIONAL DRIVE, AND (6) A POSSIBILITY FOR UTILIZING THE COMPRESSIBILITY OF AIR TO DRIVE THE SYSTEM FOR ONE-SHOT DETERMINATIONS. DETERMINATION OF AIR PERMEABILITY BY BOTH STEADY STATE AND DYNAMIC FLOW CONDITIONS IS PROPOSED. THE DYNAMIC OR ONE-SHOT PROCEDURE WOULD PROVIDE GREATER TESTING SPEED AND COULD ALLOW DEFINITION OF PERMEABILITY AS A FUNCTION OF AIR PRESSURE WHICH CAN BE EXTRAPOLATED TO GIVE A MEASURE OF PERMEABILITY OF AN INCOMPRESSIBLE FLUID.