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
Outline Background Objectives Project Layout and Instrumentation Discussion of Results Conclusions
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
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?
Objective To evaluate the structural performance of thin flexible pavements containing different chemically stabilized base and subbase materials under accelerated loading.
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 - 10.5 mile per hour Operated by Pavement Research Facility (PRF) in Port Allen, LA Total Load = 9,750 lbs Tire Pressure = 105 psi
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
Pavement Materials Hot Mix Asphalt (HMA) mixture Stabilized BCS materials Foamed asphalt stabilized materials Lime or cement treated soil materials Subgrade soils
HMA Mixture 19-mm Superpave Level II mixture Polymer-modified PG 76-22 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).
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
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 58-22 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
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 91 23.5 60.3 31 12 18.5 17.1 CL-ML A-6
Instrumentation & Field Data Collection
Instrumentation Control Data Acquisition Hardware MEGADAC 3415AC Up to 25,000 samples per second Data Acquisition Software TCS Windows 1,000 samples per second
Field Instrumentation Layout 107.5 ft 0+52.5 0+57.0 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
Earth Pressure Cell Geokon model 3500 Hydraulic type 9 in. diameter 5 lbs designed to measure total pressure in earth fills up to 100psi
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
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
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
Field Test Results
Rut Depth (mm) Average Measured Rut Depths 14 12 10 8 6 section 1 section 2 section 3 4 2 0 0 50000 100000 150000 200000 250000 300000 350000 400000 450000 Load (ESALs)
Instrumentation Results
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
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
Depth (mm) MDD Displacements, mm MDD Results (Elastic Deformation) Time, seconds -0.1 23.8 23.9 23.9 24.0 24.0 24.1 24.1 24.2 24.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 MDD1 MDD2 MDD3 MDD4 MDD5 MDD6 0 Deflection (mm) 0 0.1 0.2 0.3 0.4 0.5 0.6 400 800 1200 1600 2000 2400 Section 1 Section 2 Section 3 2800
NDT Test Results
Permanent Deformation (mm) Permanent Deformation (mm) MDD Results (Plastic Deformation) 15 12 9 BCS/flyash lime-treated Subgrade MDD on Section 2 6 3 0 0 100000 200000 300000 400000 500000 Load (ESALs) 15 12 9 Foam Asphalt Cement-treated Subgrade MDD on Section 3 6 3 0 0 100000 200000 300000 400000 500000 Load (ESALs)
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) 4.0 3.0 2.0 1.0 0 100000 200000 300000 400000 500000 ESALs Section 1 Section 2 Section 3
D0 at 25C (mm) Spreadability (%) FWD Load FWD Results 8 4 6 6 12 12 12 12 d0 d1 d2 d3 d4 d5 d6 d7 d8 Spreadability, d0 d2 d4 d5 d6 Sp 100percent D 5 0 1.0 0.8 0.6 0.4 0.2 0.0 d0 (mm) 80 Spreadability (%) 70 60 50 40 30 20 10 0 0 100000 200000 300000 400000 500000 0 100000 200000 300000 400000 500000 ESALs ESALs Section 1 Section 2 Section 3 Section 1 Section 2 Section 3
Prediction of Rutting
Rut Depth (mm) M-E PDG Predicted Rut Depths 14 12 10 8 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) 6 4 2 0 0 100000 200000 300000 400000 500000 ESALs
Rutting Prediction Model Damage A MN resp resp E resf E i Rut Depth( mm) 5.08mm MN 0.1663 D 0 0.3mm 2.1433 S p 80% 3.5293 (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.
Rut Depths (mm) Model Predicted Rut Depths 14 12 10 8 6 section 1(measured) section 2 (measured) section 3(measured) section 1(Eq.4 predicted) section 2(Eq.4 predicted) section 3(Eq.4 predicted) 4 2 0 0 100000 200000 300000 400000 500000 ESALs
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.
Acknowledgment Financial Support is provided by Louisiana Transportation and Development (LaDOTD) Louisiana Transportation Research Center (LTRC) Questions?