Pavement Design and Construction AASHTO Background

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Pavement Design and ConstructionAASHTO Background

• July 2007
• Newton C. Jackson
• Joe P. Mahoney

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AASHO Road Test
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AASHO Road Test
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AASHO Road Test
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In the 1950s, asphalt concrete thicknesses were
generally much thinner than today.
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AASHO Road Test
Test Site and Annual Frost Depth (inches)
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AASHO Road Test
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AASHO Road Test Goals

• Pavement performance related to number, type, and
  magnitude of loads
• Axle and gross vehicle load effects on bridges
• Special studies on
• Paved shoulders
• Base types
• Tire size and pressures
• Heavy military vehicles
• Pavement maintenance effects
• Develop instrumentation, test procedures, charts,
  formulas which characterize the test sections.

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AASHO Road Test Flexible Experiment

• Factorial design factors
• Surfacing thickness (3 levels)
• Base thickness (3 levels)
• Subbase thickness (3 levels)
• 3X3X3 (Loops 3-6)
• Total number of flexible sections 468

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AASHO Road Test Rigid Experiment

• Factorial design factors
• Surfacing reinforcement (2 levels)
• Surfacing thickness (4 levels)
• Subbase thickness (3 levels)
• 2X4X3 (Loops 3-6)
• Total number of rigid sections 368

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Climates
AASHO Site Central America Central America AASHO Site Central America Central America
AASHO Site Panama City San Jose, CR AASHO Site Panama City San Jose, CR
Average Mean Temperature (July) 76 F 80F 81F Annual Average Rainfall (in.) 34 70 71
Average Mean Temperature (January) 27 F 80F 67F Average Depth of Frost (in.) (fine-grained soil) 28 0 0
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Test Trucks
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Flexible Sections
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Rigid Sections
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Illustration of the Performance Concept
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AASHTO Flexible Design
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AASHTO Flexible Design Equation
Structural Number
? Present Serviceability Index
Reliability
ESALs
Resilient Modulus of the subgrade
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AASHTO Flexible Design Equation
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Terminology
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Terminology
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Terminology
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AASHO Road Test Findings

• Layer and load equivalencies developed
• Construction variability quantified
• Showed that pavements could be designed to carry
  high volumes of heavy loads
• AASHO design equation in effect an early
  performance equation
• Showed impact of spring thaw on performance
• Benefits associated with thicker HMA and PCC
  slabs.

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Flash Based Tool for Flexible Pavements
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Flash Based Tool for Rigid Pavements
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Flash Based Tool for Calculation ESALs