Accelerated Loading Evaluation of Base & Sub-base Layers

Transcription

1 Accelerated Loading Evaluation of Base & Sub-base Layers Zhong Wu, Ph.D., P.E. Louisiana Transportation Research Center (LTRC) April 2006

2 What is Accelerated Loading? Accelerated loading refers to Accelerated Pavement Testing (APT). It represents an outdoors, full-scale pavement test A specialized wheel loading device applies repeated heavy loads on pavements. Pavement structure fails in a fraction of the time required under normal traffic.

3 Why Use APT? The average gross weight of trucks increased over time Pavement life shortened due to Heavier axle loads Increased tire pressures Laboratory material tests do not contain Full-scale paving technologies Repeated heavy loads APT is an advance research tool

4 APT Programs in U.S. Reported as early as 1909 a test track built in Detroit. Currently, about 15 APT test facilities national wide.

5 Major APT Loading Devices (a) Heavy Vehicle Simulator (HVS) (b) Texas MLS

6 Louisiana Accelerated Loading Facility (ALF) Approximately 100-ft long and 55-ton One half of a single axle Load adjustable from 9,750 lbs ~ 18,950 lbs Simulate traffic wander Speed mile per hour Operated by Pavement Research Facility (PRF) in Port Allen Total Load = 9,750 lbs Tire Pressure = 105 psi

7 LTRC Project No. 03-2GT Accelerated Loading Evaluation of A Subbase Layer on Pavement Performance State Project No

8 Objectives For Base Layers: to assess field performance of Blended Calcium Sulfate (BCS) materials stabilized with fly ash and furnace slag. to evaluate field performance of foamed asphalt treated materials.

9 Objectives For Subbase Layer to prove that a cement treated subbase layer will provide a working table for pavement construction; also provide a layer that contributes to the pavement s overall structural bearing capacity.

10 Pavement Structures 2 in. 19 mm Superpave Mixture 19 mm Superpave Mixture 19 mm Superpave Mixture 2 in. 8.5 in. BCS/Slag Base BCS/Flyash Base Foamed Asphalt Base I 8.5 in. 12 in. Lime-treated Soil Subbase Lime-treated Soil Subbase Cement-treated Soil Subbase 12 in. Section 4-1A Section 4-2A Section 4-3A 2 in. 19 mm Superpave Mixture 19 mm Superpave Mixture 19 mm Superpave Mixture 2 in. 8.5 in. Crushed Stone Base Crushed Stone Base Foamed Asphalt Base II 8.5 in. 12 in. Lime-treated Soil Subbase Cement-treated Soil Subbase Cement-treated Soil Subbase 12 in. Section 4-1B Section 4-2B Section 4-3B

11 Pavement Structures

12 Factors in Experimental Design Pavement Structure and Materials Loading and Sequence Failure Criteria e.g. for asphalt pavements, rutting and fatigue cracking Performance Data Collection Surface Distress Survey Field Non Destructive Test (NDT) Instrumentation

13 Loading and Failure Criteria Loading consideration Two phase testing Phase-I- A sections: 4-1A, 4-2A and 4-3A Phase-II- B sections: 4-1B, 4-2B and 4-3B 9,750-lb load for first 175,000 passes Use 7.5 wander function Move the device at every 25,000 passes Failure Criteria Rut depth >= 0.75 in Fatigue cracks in 50% loading area >= 5 ft /ft 2

14 Pavement Materials Hot Mix Asphalt (HMA) mixture Stabilized BCS materials Foamed asphalt stabilized materials Lime or cement treated soil materials Subgrade soils

15 HMA Mixture 19-mm Superpave Level II mixture Polymer-modified PG Supplied by Marathon Optimum binder content: 4.4% Aggregate blend 45.4% #67 coarse granite aggregate, 17.1% #11 crushed siliceous limestone, 10.3% coarse sand, 12.9% crushed gravel, and 14.3% reclaimed asphalt pavement (RAP).

16 Stabilized BCS Base Materials BCS material is Short for Blended Calcium Sulfate by-product from hydrogen fluoride production. Major engineering concern water susceptibility. BCS stabilized with the grade 120 granulated ground blast furnace slag (GGBFS) Section 4-1A 10 percent by volume BCS stabilized with flyash (15% by volume) Section 4-1B Field performance: UNKNOWN

17 Foamed Asphalt Base Foamed asphalt (FA) process When cold water injected into the hot asphalt, it turns to steam: contains thousands of tiny asphalt bubbles causes the asphalt expands many times in volume decreases the binder viscosity. Section 4-3A is a FA stabilized base Components 2.8% PG asphalt binder 3% water 48.6% RAP, and 48.6% recycled soil cement

18 Subbase and Subgrade Subbase Materials: in-place lime treated soils (10 % by volume) Sections 4-1A, 4-1B & 4-2A in-place cement treated soils (8 % by volume) Sections 4-2B, 4-3A & 4-3B Soil Properties Passing # 200 (%) Clay (%) Silt (%) LL(%) PI W opt (%) γ d (kn/m 3 ) USCS Classification AASHTO CL-ML A-6

19 Surface Distress Survey Rut Measure Device A Frame Crack Mapping Profiler Moving profiler 1ft 1ft

20 Field NDT Tests Falling Weight Deflectometer (FWD) Test Dynatest 8002 model DYNAFLECT Test

21 Field Instrumentation Layout ft Plan View 2 HMA 8.5 Base 12 Subbase Base Pressure Cell Subbase Pressure Cell D6 D5 D4 D3 D2 D1 Multi Depth Deflectometer Vertical View

22 Earth Pressure Cell Geokon model 3500 Hydraulic type 9 in. diameter 5 lbs designed to measure total pressure in earth fills up to 100psi

23 Multi-Depth Deflectometer (MDD) Snap MDD Construction Technology Laboratories, Inc. Illinois Measure compressively elastic & plastic deformations up to seven depths Installation bore hole 5-in in diameter 10-ft deep

24 Current Test Sections Current testing on Section 4-1A Section 4-2A Section 4-3A 4-1A 4-2A 4-3A 2 HMA 8.5 BCS/Slag Base 12 Lime treated soil (10%) 2 HMA 8.5 BCS/Flyash Base 12 Lime treated soil (10%) 2 HMA 8.5 Foamed Asphalt Base (50%SC+50%RAP) 12 Cement treated soil (8%)

25 Covered: Discussion of Test Results 125,000 ALF load repetitions three test sections: 4-1A, 4-2A, and 4-3A. Includes: Instrumentation Results NDT Test Results Surface distress survey

26 Instrumentation Results

27 Typical MDD Potentiometer Readings

28 MDD Test Results MDD Displacements, mm Time, seconds D1 D2 D3 D4 D5 D6 Plastic Deformation (in Plastic Deformation (Potentiometer D1) No. Passes Section 4-1A Section 4-2A Section 4-3A

29 Earth Pressure Examples Cell Results P=9,000lb p=100psi P=9,000lb p=100psi 2 in. 8.5 in. HMA E=450ksi BASE E=800ksi σ v =7.3psi 2 in. 8.5 in. HMA E=450ksi BASE E=80ksi σ v =20psi 12 in. Subbase E=40ksi σ v =2.4psi 12 in. Subbase E=40ksi σ v =4.3psi Subgrade E=15ksi P=9,000lb p=100psi Subgrade E=15ksi 2 in. 8.5 in. HMA E=450ksi BASE E=80ksi σ v =34.5psi 12 in. Subbase E=400ksi σ v =2.2psi Subgrade E=15ksi

30 Measured Vertical Stresses 4-1A 4-2A 4-3A HMA BCS/ Slag σ v1 =0.9psi HMA BCS/ Flyash σ v1 =5.2psi HMA Foam Asphalt σ v1 =9.5psi Lime Soil σ v2 =0.5psi Lime Soil σ v2 =1.8psi Cement Soil σ v2 =0.6psi Subgrade Subgrade Subgrade

31 NDT Test Results Dynatest 8002 model (a) FWD (b) Dynaflect

32 Average Measured Center FWD Deflection Results FWD Load d1 d2 d3 d4 d5 d6 d7 d8 d9 25 Center Deflection (m ils) K (86/74F) 25K (94/81F) 50K (71/68F) 75K (65/60F) 100K (88/71F) 125K (89/78F) 0 4-1A 4-2A 4-3A

33 DYNAFLECT Results Pavement structure number (SN) is defined as SN=a 1 *H 1 +a 2 *H 2 +a 3 *H 3 SN determined from center deflection deflection basin parameter Structure Number K 100K A 4-2A 4-3A Ave. Structure Number

34 Cracking Surface Distress Survey 1ft Rutting 1ft

35 Cracking Only Section 4-2A developed some hairline-type cracks not severe No visual cracks found on either Section 4-1A or 4-3A

36 Rutting Rutting on "A" Sections Average Rut depth (in.) A A A K 50K 75K 100K 125K 4-1A A A ALF Passes (K=1,000)

37 Summary and Conclusions 1. BCS/Slag Base perform better than BCS/Flyash Base 2. Evidenced by Surface distresses FWD center deflections Dynaflect Structure Number Measured vertical stresses, and Measured MDD deformations. Cement-treated Soil Subbase superior than Lime-treated Soil Subbase Evidenced by Measured vertical stresses

38 APT Research to Implementation Local and international technology Industry innovation Performance history APT Practice Research assessment Acceptable confidence Performance Construction quality control Reduce risk Increase expertise Build confidence Specifications Guideline documents Material and pavement design

39 Questions?