ASSESSING APPROPRIATE LOADING CONFIGURATION IN APT Byron – Choubane - Tia
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ASSESSING APPROPRIATE LOADING CONFIGURATION IN APT Byron – Choubane - Tia
ASSESSING APPROPRIATE LOADING CONFIGURATION IN APT Byron – Choubane - Tia APT?  Controlled application of realistic wheel loading  Allows monitoring the performance of pavement systems within short time  Eliminates/reduces the need for in-service experimental sections APT ADVANTAGES  Time  Control of Variables  Economy and Flexibility FLORIDA’S APT PROGRAM  Housed within State Materials Research Park  Test site consists of 8 linear tracks 150x12 ft.  2 additional tracks with water table control capability  Loading using a Heavy Vehicle Simulator (HVS) APT SITE APT PITS HVS Weight: 50+ tons Length: 75 feet Height: 13 feet Width: 12 feet LOADING CAPABILITIES ¾ ¾ ¾ ¾ Loading: 7 to 45 kips Wheel speed: 8 mph Sinusoidal loading Maximum passes/day: 29,000 bidirectional 14,000 unidirectional TESTING CAPABILITIES ¾ ¾ Test Track Length: 20’ Wander From 0 – 30” ¾ ¾ Super-Single vs. Dual Maximum Rut Depth: 4” LASER PROFILING ENVIRONMENTAL CHAMBER  2” thick Styrofoam w/ aluminum sheeting  Windows & doors provided  Easily removable HEATING SYSTEM 6 elements, 9 ft long, attached to HVS test beam & moving transversely with beam.  Independently controlled to provide 6 heating zones.  SYSTEM PERFORMANCE Temperature (C) 60 50 Ambient Air 40 Surface 30 20 10 0 0 10 20 INITIAL EXPERIMENT INITIAL EXPERIMENT SBS modifier Binders: PG 67-22 PG 76-22 SP 12.5 fine graded mixes LOADING CONFIGURATION ASSESSMENT UNI-DIRECTIONAL LOADING BI-DIRECTIONAL LOADING UNI-DIRECTIONAL w/ WANDER BI-DIRECTIONAL w/ WANDER LOADING CONFIGURATION ASSESSMENT  Good Year G165 super-single tire  Tire load of 9000 lbs  Test speed of 8 mph  Tire pressure of 112 psi RUT DEPTH – NO WANDER bi-directional loading uni-directional loading 10 5 Number of Passes, (x 1000) 100 90 80 70 60 50 40 30 20 0 10 R u t D e p th (m m ) 15 RUT ILLUSTRATIONS Bi-Directional, No Wander (above)  Uni-Directional, No Wander (Left)  RUBBER BUILD-UP TIRE TREAD PATTERN TIRE TREAD STRIPS Contac t % TIRE CONTACT 100% 80% 60% 40% 20% 0% 0 1 2 3 4 5 6 7 8 Footprint Width (in) 9 10 11 12 % CONTACT - 2” VS. 1” STEPS 100% C ontac t 80% 60% 40% 20% 2" Step 1" Step 0% 0 2 4 6 8 10 12 Test Footprint Width (in) 14 16 CONCLUSIONS  W/o wander, uni-directional - rut developed at rate of 65% greater per-pass basis.  W/o wander, uni-directional mode placed considerable wearing forces. As much as 25% of tread depth worn away at very localized locations.  Uni-directional loading, pattern matched very closely the general tire tread pattern. CONCLUSIONS (Con’t)  W/ wheel wander, wander increments differently affected the tire-pavement contact.  Importance of using both wheel wander & appropriate wander incremental step.  It is recommended that, in order to determine an appropriate loading configuration, a thorough pavement-tire tread investigation be conducted any time the tire brand and/or type is changed. WEBSITE LINKS  http://www11.myflorida.com/statematerialsoffice/ PavementEvaluation/APT/aptresearch.htm Questions???