Evaluating Structural Performance of Base/Subbase Materials at the Louisiana Accelerated Pavement Research Facility

Transcription

1 Evaluating Structural Performance of Base/Subbase Materials at the Louisiana Accelerated Pavement Research Facility Zhong Wu, Ph.D., P.E. Louisiana Transportation Research Center 2007 Transportation Engineering Conference Baton Rouge, February 11-14, 2007

2 Outline Background Objectives Project Layout and Instrumentation Discussion of Results Conclusions

3 Background Blended Calcium Sulfate (BCS) material is by-product from hydrogen fluoride production used as base materials in Louisiana low-volume roads. When raw BCS materials is used, the major engineering concern water susceptibility A previous laboratory study at LTRC indicates that The water susceptibility of BCS materials can be improved by mixing with granulated ground furnace slag, flyash, cement and etc. In fact, 10% slag (by weight) stabilized minus 4 BCS materials showed significant improvement on both water susceptibility and strength However, field performance of stabilized BCS base materials is unknown

4 Background (contd..) In-place cement- or lime- treated soil subgrade normally 12 thick used in wet conditions of pavement construction in Louisiana The treated subgrade contains 4 to 10% cement or lime by volume considered as a working table in pavement design no structure value assigned However, Laboratory results indicated cement treated soils showed significantly higher modulus and strength than lime-treated soils Can cement-treated soil be considered as a subbase layer and provide certain structure value in a pavement design?

5 Objective To evaluate the structural performance of thin flexible pavements containing different chemically stabilized base and subbase materials under accelerated loading.

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, LA Total Load = 9,750 lbs Tire Pressure = 105 psi

7 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 1 Section 2 Section 3 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 Section 5 Section 6

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

9 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).

10 Stabilized BCS Base Materials Section 1 BCS stabilized with the grade 120 ground granulated blast furnace slag (GGBFS) 10% by volume Section 2 BCS stabilized with Class C flyash (15% by volume) BCS/Slag Section 1 2 in. 19 mm Superpave Mixture 19 mm Superpave Mixture 8.5 in. BCS/Slag Base BCS/Flyash Base 12 in. Lime-treated Soil Subbase Lime-treated Soil Subbase BCS/flyash Section 2

11 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 3 is a FA stabilized base Design Standard Wirtgen Cold Recycling Manual Components 2.8% PG asphalt binder 3% water 48.6% RAP, and 48.6% recycled soil cement 19 mm Superpave Mixture Foamed Asphalt Base I Cement-treated Soil Subbase 2 in. 8.5 in. 12 in. Section 3

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

13 Instrumentation & Field Data Collection

14 Instrumentation Control Data Acquisition Hardware MEGADAC 3415AC Up to 25,000 samples per second Data Acquisition Software TCS Windows 1,000 samples per second

15 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

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

17 Multi-Depth Deflectometer (MDD) SnapMDD Construction Technology Laboratories, Inc. Illinois Measure compressively elastic & plastic deformations up to seven depths Installation bore hole 3-in in diameter 10-ft deep

18 NDT Tests Dynatest 8002 model FWD 9 sensors (0, 8, 12, 18, 24, 36, 48, 60, 72 ) Every 25,000 repetitions Dynaflect 1,000-lb dynamic load 5 geophones at 1 ft interval Every 25,000 repetitions

19 ALF Loading & Condition 9,750-lbs for 175,000 passes Equivalent to 241,039 ESALs 12,050-lbs from 175,000 to 225,000 passes Equivalent to 401,713 ESALs Un-controlled in situ environment Testing period from Oct. Aug. Air temperature from 30 to 93 o F Total rainfalls only 16.8 inches

20 Field Test Results

21 Rut Depth (mm) Average Measured Rut Depths section 1 section 2 section Load (ESALs)

22 Instrumentation Results

23 Measured Vertical Stresses 9,750 lb 9,750 lb 9,750 lb S1 S2 S3 HMA BCS/ Slag σ v1 =0.8psi HMA BCS/ Flyash σ v1 =5.0psi HMA Foam Asphalt σ v1 =10.2psi Lime Soil σ v2 =0.5psi Lime Soil σ v2 =1.7psi Cement Soil σ v2 =0.4psi Subgrade Subgrade Subgrade 9,750 lb 12,050 lb

24 Measured Vertical Stresses (Contd..) 12,050 lb 12,050 lb 12,050 lb S1 S2 S3 HMA BCS/ Slag σ v1 =0.9psi HMA BCS/ Flyash σ v1 =? psi HMA Foam Asphalt σ v1 =12.4psi Lime Soil σ v2 =0.6psi Lime Soil σ v2 =2.5psi Cement Soil σ v2 =0.8psi Subgrade Subgrade Subgrade

25 Depth (mm) MDD Displacements, mm MDD Results (Elastic Deformation) Time, seconds MDD1 MDD2 MDD3 MDD4 MDD5 MDD6 0 Deflection (mm) Section 1 Section 2 Section

26 NDT Test Results

27 Permanent Deformation (mm) Permanent Deformation (mm) MDD Results (Plastic Deformation) BCS/flyash lime-treated Subgrade MDD on Section Load (ESALs) Foam Asphalt Cement-treated Subgrade MDD on Section Load (ESALs)

28 Structure Number (SN) Kinchen 6.0 and Temple in 1980 developed Dynaflect-deflection based approach for structural evaluation of flexible pavements 5.0 Dynaflect Results (SN) ESALs Section 1 Section 2 Section 3

29 D0 at 25C (mm) Spreadability (%) FWD Load FWD Results d0 d1 d2 d3 d4 d5 d6 d7 d8 Spreadability, d0 d2 d4 d5 d6 Sp 100percent D d0 (mm) 80 Spreadability (%) ESALs ESALs Section 1 Section 2 Section 3 Section 1 Section 2 Section 3

30 Prediction of Rutting

31 Rut Depth (mm) M-E PDG Predicted Rut Depths section 1(measured) section 2 (measured) section 3(measured) section 1(M-E PDG predicted) section 2(M-E PDG predicted) section 3(M-E PDG predicted) ESALs

32 Rutting Prediction Model Damage A MN resp resp E resf E i Rut Depth( mm) 5.08mm MN D 0 0.3mm S p 80% (n=212, R 2 =0.89) MN = 1 million load applications, resp = pavement response (e.g. stress or strain), resp ref = reference response. E = modulus, E i = initial modulus, and A,,, = model constants.

33 Rut Depths (mm) Model Predicted Rut Depths section 1(measured) section 2 (measured) section 3(measured) section 1(Eq.4 predicted) section 2(Eq.4 predicted) section 3(Eq.4 predicted) ESALs

34 Conclusions The BCS/Slag base material performed significantly better than its counterpart material - BCS/Flyash, whereas BCS/flyash better than foam-asphalt base. The cement-treated subbase possessed higher load-induced structural capacity than the lime-treated subbase, in terms of higher resilient modulus, greater load carrying capability, and smaller permanent deformation. A heavier load would cause higher percent increase of vertical stresses on top of the subgrade than upper pavement layers. The M-E PDG software generally overestimated the rut depths developed in the three test sections of this study The proposed model, which relates flexible pavement rutting development to the in-situ surface deflection characteristics, has a potential to be directly utilized in a mechanisticempirical pavement design and analysis.

35 Acknowledgment Financial Support is provided by Louisiana Transportation and Development (LaDOTD) Louisiana Transportation Research Center (LTRC) Questions?