Concrete Pavement Fundamentals Concrete Pavement Types Jointed Plain

Concrete Pavement Fundamentals

Concrete Pavement Types • Jointed Plain – Undoweled – Doweled • Jointed Reinforced • Continuously Reinforced

Jointed Plain Plan 12 - 20 ft Profile or

Jointed Reinforced Plan 24 -30 ft Profile

Continuously Reinforced Plan 3 – 7 ft Profile

Stresses in Rigid Pavements • • • Traffic loads Thermal and moisture gradients Drying shrinkage Thermal heating and cooling of the slab Foundation movements

Calculating Stresses • Westergaard –closed form solutions 1. Medium-thick plate theory • • 2. 3. 4. 5. 6. Sufficiently thick to carry a transverse load by flexure Not so thick that transverse shear deformation occurs (assuming L/tslab < 100) Neutral axis is located at mid-depth Slab dimensions are infinite Winkler foundation No shear forces on surface Homogenous, isotropic, elastic slab

Calculating Stresses • Westergaard –closed form solutions Corner Load Edge Load Midslab Load

Calculating Stresses • Westergaard –Limitations – – – Only, edge, corner, midslab calculations Foundation only extends to edge of slab Fully supported slab Load transfer not considered No multiple wheel loads Uniform thickness

Calculating Stresses • Finite element – – Slab can be any size Non-uniform thickness Non-uniform support and voids Single & multiple loads can be placed anywhere on the slab – Slab discontinuities (jts & cracks) with various levels of load transfer

Critical Stress Locations • Traffic – Full uniform support – Highest stress directly under load for edge and interior loads Max. bending stress when full supported

Critical Stress Locations • Traffic – Full uniform support – Highest stress directly under load for edge and interior loads Max. bending stress when full supported

Critical Stress Locations • Non-traffic – Drying shrinkage – Temperature changes – Moisture and temperature gradients Traffic and non-traffic induced stresses are not additive!!!!

Design of Concrete Pavements

Concrete Pavement Design • • Geometrics Thickness(es) Joints Materials

Concrete Pavement Design • • Geometrics ` Thickness(es) Joints Materials Most Often Influence Cost & Selection of Projects C O S T

Concrete Pavement Design • • Geometrics Thickness(es) Joints Materials Most Often Influence Real-world Performance PERFORMANCE

Subgrade and Bases • Base – Layer of material directly below the concrete pavement. • Subgrade – Natural ground, graded, and compacted on which the pavement is built. Concrete Section Base Subgrade

Subgrade and Bases Design – Subgrade strength is not a critical element in the thickness design. • Has little impact on thickness. – Need to know if pavement is on: • • Subgrade (k 100 psi/in. ), Granular subbase (k 150 psi/in. ), Asphalt treated subbase (k 300 psi/in. ) Cement treated/lean concrete subbase (k 500 psi/in. ).

Base • May be constructed as: – Granular • Principal criteria is to limit fines passing #200 sieve – Cement-treated or Lean concrete – Permeable • Stabilized or Unstabilized • Not needed with low traffic volumes – Residential and Secondary roads – Parking lots

Subgrade and Bases Performance – Proper design and construction are absolutely necessary if the pavement is to perform. • Must be uniform throughout pavement’s life. – Poor subgrade/base preparation can not be overcome with thickness. • Any concrete pavement, built of any thickness, will have problems on a poorly designed and constructed subgrade or subbase.

UNIFORMITY: The Key To GOOD PAVEMENT PERFORMANCE

Design for Uniform Support Sources of Non-Uniform Support • Expansive soils • Frost susceptible soils • Pumping (loss of Support) • Cut-fill transitions • Poorly compacted excavations – Utility work – Culverts

Pumping • Conditions for Pumping – Subgrade Soil that will go into suspension – Free water between Slab and subgrade – Frequent, rapid, and large deflections • Use Subbase to control

Load Transfer • A slabs ability to share its load with neighboring slabs – Dowels – Aggregate Interlock – Concrete Shoulders • Decrease edge & corner stresses & deflections. • Tied Concrete, curb & gutter, and extended lane have same effect. – Stabilized Subbases – Keyways L= x U= 0 Poor Load Transfer L= x/2 Good Load Transfer U = x/2

Concrete Properties Flexural Strength (S’c) Determination Third-point Loading Center-point Loading Head of Testing Machine d=L/3 Span Length = L L/2 Span Length = L

Concrete Properties Compressive Strength f’c S’c = 8 -10 Ö f’c = Compressive Strength (psi) S’c = Flexural Strength (psi) Head of Testing Machine Cylinder Depth

Thickness Design

Design of Concrete Pavements • Thickness Design Considerations: – Traffic Loads and Traffic Growth – Subgrade and Bases – Drainage – Concrete Properties – Load Transfer – Reliability

Thickness Design Procedures • Empirical Design Procedures – Based on observed performance • AASHTO Design Procedure • Mechanistic Design Procedures – Based on mathematically calculated pavement responses • PCA Design Procedure (PCAPAV)

Differences Between Design Procedures • Traffic Classification: – AASHTO - uses 18 -kip ESALs – PCA - uses axle load distribution • Reliability – AASHTO - Reliability – PCA - Load Safety Factors • Drainage

Typical Concrete Pavement Thickness • Depends on traffic load, subgrade, and climate. – City streets, secondary roads, and small airports • 100 to 175 mm (4 to 7 in. ) – Primary roads and interstate highways • 175 to 280 mm (7 to 12 in. ) – Large airports • 200 to 460 mm (8 to 18 in. )

AASHTO Design Procedures AASHTO Guide for Design of Pavement Structures - 1993

AASHTO Design Procedures & Changes • 1961 -62 AASHO Interim Guide for the Design of Rigid and Flexible Pavements • 1972 AASHTO Interim Guide for the Design of Pavement Structures - 1972 • 1981 Revised Chapter III on Portland Cement Concrete Pavement Design • 1986 Guide for the Design of Pavement Structures • 1993 Revised Overlay Design Procedures • 1998 Revised Portland Cement Concrete Pavement Design

1986 -93 Rigid Pavement Design Equation Standard Normal Deviate Overall Standard Deviation Change in Serviceability é é DPSI ù ù ê Logê ú ú ë 4. 5 - 1. 5û ú Log(ESALs) = ZR * s o + 7. 35 * Log(D +1) - 0. 06 + ê ê 1. 624 * 107 ú ê 1+ 8. 46 ú Modulus of êë (D + 1) úû Drainage Rupture Terminal Coefficient é ù Serviceability ê ú 0. 75 S'c * C d * D - 1. 132 ê ú + (4. 22 - 0. 32 pt ) *Log ê ú é ù 18. 42 ú ê 0. 75 0. 25 ú ú ê 215. 63* J * êD (Ec / k) úû û êë ë Load Depth [ Transfer Modulus of Elasticity ] Modulus of Subgrade Reaction

AASHTO DESIGN Concrete Properties Use average, in-field strength for design (not minimum specified) If specify minimum flexural strength at 28 -day of 550 psi & allow 10% of beams to fall below minimum: STEP 1 Estimate SDEV: 9% for typical ready mix. SDEV = 550 * 0. 09 = 50 psi STEP 2 S’c design = S’c minimum + z * SDEV S’c design = 550 + 1. 282 * 50 S’c design = 614 psi

AASHTO DESIGN Traffic - ESALs Equivalent Number of 18 k Single Axle Loads

AASHTO DESIGN Reliability The statistical factors that influence pavement performance are: – RELIABILITY, R = f(functional class, urban vs rural) • The statistical probability that a pavement will meet its design life. (use table 2. 2 p II-9) – STANDARD DEVIATION, So • The amount of statistical error present in the design equations resulting from variability in materials, construction, traffic, etc. (use So = 0. 35, unless exact traffic is know then So=0. 25)

AASHTO DESIGN SERVICEABILITY Reliability po Performance Curve Design Curve pt ZR * s o Log ESALs Win. Pas

AASHTO DESIGN Base Effects The current Design does not model the contribution of bases accurately. At the AASHO Road Test, it was found that the concrete pavements with granular bases could carry about 30% more traffic. The current design procedures allows concrete pavements built with granular bases to carry about 5 - 8% more traffic.

AASHTO DESIGN Base (Subbase) • Determine composite effective k-value (neglect thin layers) • Slab built on subgrade k = Mr/19. 4

AASHTO DESIGN Drainage coefficient, Cd = f(Percent time structure is exposed to saturated conditions, overall quality of drainage of the pavement structure) Obtain from table 2. 5 p II-26

AASHTO DESIGN Load transfer coefficient, J = f(load transfer device, shoulder type, pavement type) Obtain from table 2. 6 p II-26

AASHTO DESIGN Loss of serviceability, DPSI = po – pt po = 4. 5 unless otherwise stated by the individual agency

AASHTO DESIGN Sensitivity analysis 1. Slab thickness sensitive 2. 3. 4. 5. Ec fairly sensitive Sc very sensitive R very sensitive at levels above 90% So little affect 6. Jo sensitive 7. Cd sensitive 8. k not very sensitive

AASHTO DESIGN Limitations 1. Variability – more localized failures would occur then observed at AASHO Road test 2. Limited material and subgrade 3. Loss of support- sections exhibited severe pumping 4. Short road test performance period 5. Jt design 1. 2. 3. 4. Joint spacing Rational for determining dowel size/spacing When are load transfer devices are required Load transfer mechanisms other than dowels 6. Climate 7. LEF –limited to conditions under which they were developed 8. No mixed traffic

PCAPAV Design Procedure Design Basics • Mechanistic stress analysis • Calibrated to field tests, test roads • Control criteria can be either: – Fatigue (cracking) – Erosion (pumping) • Available computer program (PCAPAV)

PCAPAV Design Traffic Categories Two-way ADTT Category LSF 3 LR 1. 0 10 - 30 1 1. 0 50 - 500 2 1. 1 Minor Arterial Sts. Primary roads 300 - 600 2 1. 2 Major Arterial Sts. 700 - 1500 3 1. 2 Light Residential Rural & secondary rds. Collector streets Rural & secondary rds. (heavy trucks)

PCAPAV Design Traffic • Axle loads Distribution – The number of single and tandem axles over the design period – Expressed as Axles per 1000 trucks – Does not include panel and pickup trucks and other four-tire vehicles. Axle load Axles/1000 Axles in Kips Trucks design period Single Axles 28 -30 26 -28 24 -26 22 -24 20 -22 18 -20 16 -18 14 -16 12 -14 10 -12 Tandem Axles 48 -52 44 -48 40 -44 36 -40 32 -36 28 -32 24 -28 20 -24 16 -20 12 -16 0. 58 1. 35 2. 77 5. 92 9. 83 21. 67 28. 24 38. 83 53. 94 168. 85 6, 310 14, 690 30, 140 64, 410 106, 900 235, 800 307, 200 422, 500 586, 900 1, 837, 000 1. 96 3. 94 11. 48 34. 27 81. 42 85. 54 152. 23 90. 52 112. 81 124. 69 21, 320 42, 870 124, 900 372, 900 885, 800 930, 700 1, 656, 000 984, 900 1, 227, 000 1, 356, 000

PCAPAV Design Traffic • Numbers & weights of heavy axle loads expected during the design life – ADT (average daily traffic in both directions) – ADTT (average daily truck traffic in both directions) • Includes only trucks with six tires or more • Does not include panel and pickup trucks and other four-tire vehicles. – Axle loads of trucks

PCAPAV Design Load Safety Factors Recommended values • Interstate, interprovincial, multilane projects – LSF = 1. 2. • Highways and arterial streets – LSF = 1. 1 • Roads, residential streets, and other streets that carry small volumes of truck traffic – LSF = 1. 0 PCAPAV

AASHTO DESIGN Traffic For a Given Load: