Assessing Pavement Rolling Resistance by FWD Time History Evaluation

Transcription

1 Assessing Pavement Rolling Resistance by FWD Time History Evaluation C.A. Lenngren Lund University 2014 ERPUG Conference 24 October 2014 Brussels 20Nm 6 Nm 2 Nm

2 Background: Rolling Deflectometer Tests During 1990:ies a test of pavement dynamic response was carried out with a Road Deflection Tester. These test required pavement dynamic response evaluations.

3 RDT history Prototype and FWD correlation study in 1995 New vehicle built in 1996 Lack of funding in 1997 First continuous test (2*120km) in 1998 Additional tests in

4 RDT history (continued) New RDT data evaluation started in 1999 Advanced modeling in 2000 More data 2000 rough road and correlation with GPR moisture measurements evaluated Funding stopped for political reasons. Huge data base with FWD correlation left behind. 4

5 Deflection = Rear profile - Front profile Sensor Bars Wheel Base 6m Note longitudinal sensors for maximum lag! 5

6 Rolling Deflectometer Tests The RDT was validated by Falling Weight Deflectometer Tests (over 120 test sections) Also initiated FWD dynamic response evaluation

7 One site in the 1990:ies test consisted of flexible and rigid pavements on the same subgrade Linear elastic layer solutions mu Torsby E4.65 AC E4.65 PCC 45 V Ämtervik 63 Lindfors mm Transverse deflection profiles from truck load

8 Anno 1995 Field Test Objective Two different pavement types on the same type of subgrade designed for the same traffic!

9 First results Test verified significant difference between pavement types.

10 By plotting load vs. displacement hysterises curves are attained Load [kn] D0 D20 D30 D45 D60 D90 D Displacement [mu]

11 2007 Field Test Objective Find two different pavement types on the same type of subgrade designed for the same traffic!

12 Find two different pavement types on the same type of subgrade! On Highway E4 north of Uppsala, Sweden there are PCC over AC and AC only pavements with the same traffic and soil.

13 FWD Field Test in Early September About 30 tests per pavement type 10 Drops per test Three load levels at kn

14 Field Conditions Overcast Pavement temperature 18 C (Near Annual Average). No gradients I.e. almost perfect conditions

15 Backcalculated Layer Stiffness Layer Thickness Modulus [mm] [MPa] PCC (Fixed) Asphalt Base Unbound layers Subgrade Semi infinite 370 Layer Thickness Modulus [mm] [MPa] Asphalt Layers Unbound layers Subgrade Semi infinite 375

16 Dissipated work Previous Experience 4 8 kn is a common range. About 3 Nm was recorded on a hot 40 C asphalt pavement on a stiff elastic layer. I.e. visco elastic AC contribution is about 50 to 70 % when hot.

17 Flexible 4.2 Nm Load [kn] D0 D20 D30 D45 D60 D Deformation [mu] Rigid 1.04 kn Load [kn] D0 D20 D30 D45 D60 D90 D Displacement [mu]

18 Rolling Resistance About five percent of the total fuel consumption on the road is attributed to rolling resistance The losses occur in the drive train, wheels, tires, road texture and damping in the pavement layers and soil About a third is attributed to the road, e.g. the texture and damping in the pavement layers Lots of studies have been done on the texture but very little on internal pavement effects.

19 Drive Tests Fuel consumption tests have been made with trucks E.g. comparing asphalt concrete and PCC pavements Generally, less fuel used on stiffer PCC However, tests are inconclusive due to Temperature fluctuations Wind speed and direction Different materials and varying soils

20 Note! The Load Displacement Loops are not a direct measure of hysteresis, but they reflect: Visco elastic properties Soil Damping Material movement Inertia mu Sagån 70 kn Load kn

21 Example: Asphalt Concrete on Stiff Subgrade Load [kn] Displacement [mu]

22 Example: 180 mm Thick Asphalt Concrete Load Deflection Diagram at 40 C Load [kn] Deflection [micrometer]

23 New 200 mm 70 kn 10 degrees C mu Sagån 70 kn Load kn

24 Intermediate 2-lane (new) 80 Hästbo Section: 2750 Drop: 10;Height: 4 Int 3863 mnm 70 D0 60 D20 Load [kn] D30 D45 D60 10 D Displacement [mu] D120

25 Low Volume Trunk Road X512 Section: 265 Drop: 10;Height: 4 Int 9374 mnm Load [kn] D0 D20 D30 D45 D60 D90 D Displacement [mu]

26 Effect of Curling of Jointed Slabs? First study was done near average temperature and no curling was anticipated. Tests were done far from joints. A morning test was performed with upward curling on a JPCC from the edge and inwards.

27 Effect of Curling Load [kn] D0 edge D0 mid Deformation 40 [mu] The edge effect was only apparent at the joint. overall contribution estimated to about 10 % higher for the moving vehicle.

28 Different offsets Different Off-sets from Edge Mid-slab Load [kn] cm from edge At edge Displacement [mu]

29 Relative Difference for Various Pavement Types, Soft Soils Flexible Semi Rigid Jointed Rigid Continuously Reinforced Flexible Semi Rigid Jointed Rigid Continuously Reinforced

30 Relative Difference for Various Pavement Types, Stiff Soils Flexible Semi Rigid Jointed Rigid Continuously Reinforced Flexible Semi Rigid Jointed Rigid Continuously Reinforced

31 Conclusions In the first comparison test the PCC pavement exhibited about four times less work loss as AC pavement at the mean annual average temperature. Other tests show that thick asphalt pavements have high hysteresis at hot temperatures. By theory they should also be less sensitive at lower temperatures.

32 Conclusions The rolling resistance for a certain pavement type should be considered in a LCC analysis and Life Cycle Assessment when choosing pavement type. The FWD can be used for Life Cycle Inventory purposes and Rating Systems.

33 Conclusions The effect of rolling resistance in JPCC is higher when slabs curl upward; it corresponds to the strain energy calculated for edge cracking. The results can be used to improve AC and PCC pavements as well, and motivate higher investment costs for e.g. continuously reinforced pavements.

34 Conclusions For construction control time histories reveal: Water present Poor compaction Helps improving sustainable pavements

35 Thank You! Questions?