U.S. Department Advisory of Transportation 

Federal Aviation 

Administration Circular 

Subject: AIRPORT PAVEMENT DESIGN AND Date: 6/3/02 AC No: 150/5320-6D 

EVALUATION Initiated by: AAS-100 Change: 2 

1. Purpose of this advisory circular. Advisory Circular (AC) 150/5320-6D, AIRPORT PAVEMENT DESIGN AND 

EVALUATION, has been revised to incorporate recent changes and corrections.

2. Principal changes. In addition to necessary typographical changes, this AC includes the following revisions:

a. Paragraph 203b(4) has been changed to agree with AC 150/5370-10A, Standards for Specifying Construction 

of Airports; 60,000 pounds is now the decision point between heavy-load and light-load pavements.

b. Paragraph 337, JOINTING OF CONCRETE PAVEMENTS, has been changed to refer to Table 3-10A, 

PAVEMENT JOINT TYPES, which has been added as page 86-2.

c. Figures 3-42 and 3-42A, RIGID PAVEMENT TYPES AND DETAILS, have been revised to change the depth, 

noted as "T/5" in DETAIL 2, to "T/4"; add a chamfer joint detail; and add new detail "PLAN VIEW - Position of 

Dowels at Edge of Joint Type A, D, F."

d. Paragraph 337b(1) has been updated to reflect a conservative recommendation for maximum joint spacing. A 

definition for the symbol for radius of relative stiffness has been included.

e. Paragraph 337b(2) has been changed to reflect the maximum recommended ratio of joint spacing in inches to 

radius of relativity from 6.0 to 5.0.

f. The formula for steel area in paragraph 344a has been corrected.

g. Figure 3-43 has been revised to indicate joint and fillet alternatives.

h. Paragraph 406b(1) has been revised to indicate the correct value for Cr and Cb.

i. Figure 4-3, GRAPH OF "F" FACTORS VS. MODULUS OF SUBGRADE REACTION FOR DIFFERENT 

TRAFFIC LEVELS, has been updated to include departure levels on the graph.

j. The formulas for overlay thickness in paragraphs 411a and 411b have been corrected.

k. Paragraph 502c has been updated to correct the paragraph reference and update the ASTM title.

l. The example problem in paragraph 503d (1), (2), and (3) has been updated to agree with the referenced figure.

m. The reference in paragraph 503f to paragraph 323 has been corrected to paragraph 322.

n. Paragraph 505a has been updated to include an explanation of tension ring design employment.

o. Paragraph 508 has been added to address thermal resistant pavements for vertiports.

p. The formula for split tensile strength in paragraph 604b(1)(i) has been updated.

iii 
AC 150/5320-6D CHG 2 6/3/02 

The change number and date are shown at the top of each page. 

PAGE CONTROL CHART

Remove Pages Dated Insert Pages Dated 

iv 7/7/95 iv 6/3/02 

8 7/7/95 8 6/3/02 

85, 86, 87, 88, 89, 90 7/7/95 85, 86, 86-1, 86-2, 87, 88, 89, 90 6/3/02 

106 7/7/85 106 6/3/02 

108 7/7/95 108 6/3/02 

113, 114 7/7/95 113, 114 6/3/02 

125 7/7/95 125 6/3/02 

129, 130, 131, 132 7/7/95 129, 130, 130-1, 131, 132 6/3/02 

138 7/7/95 138 6/3/02 

The following pages are reprinted for convenience iii, 8, 105, 107, 126, and 137.

DAVID L. BENNETT

Director, Office of Airport Safety and Standards
7/7/95 AC 150/5320-6D

317. DESIGN INPUTS ........................................................................................................ 49

TABLE 3-4. MINIMUM BASE COURSE THICKNESS........................................ 49

318. CRITICAL AND NONCRITICAL AREAS.................................................................. 49

TABLE 3-5. PAVEMENT THICKNESS FOR HIGH DEPARTURE LEVELS ...... 49

319. DESIGN EXAMPLE.................................................................................................... 49

320. STABILIZED BASE AND SUBBASE......................................................................... 51

321. SUBBASE AND BASE EQUIVALENCY FACTORS ................................................. 51

TABLE 3-6. RECOMMENDED EQUIVALENCY FACTOR RANGES FOR

HIGH QUALITY GRANULAR SUBBASE ................................................................. 52

TABLE 3-7. RECOMMENDED EQUIVALENCY FACTOR RANGES FOR

STABILIZED SUBBASE............................................................................................. 52

TABLE 3-8. RECOMMENDED EQUIVALENCY FACTOR RANGES FOR

GRANULAR BASE ..................................................................................................... 52

TABLE 3-9. RECOMMENDED EQUIVALENCY FACTOR RANGES FOR

STABILIZED BASE .................................................................................................... 52

322. FULL-DEPTH ASPHALT PAVEMENTS.................................................................... 53

323. FROST EFFECTS ........................................................................................................ 53

SECTION 3. RIGID PAVEMENT DESIGN ........................................................................... 55

324. GENERAL ................................................................................................................. 55

325. CONCRETE PAVEMENT........................................................................................... 55

326. SUBBASE .................................................................................................................. 55

TABLE 3-10. CONDITIONS WHERE NO SUBBASE IS REQUIRED ................... 55

327. SUBBASE QUALITY.................................................................................................. 55

328. STABILIZED SUBBASE............................................................................................. 55

329. SUBGRADE ............................................................................................................... 55

330. DETERMINATION OF FOUNDATION MODULUS (k VALUE) FOR

RIGID PAVEMENT .................................................................................................... 56

FIGURE 3-16. EFFECT OF STABILIZED SUBBASE ON SUBGRADE 

MODULUS .................................................................................................................. 56

331. DETERMINATION OF CONCRETE SLAB THICKNESS ......................................... 58

332. USE OF DESIGN CURVES......................................................................................... 58

333. CRITICAL AND NONCRITICAL AREAS.................................................................. 58

FIGURE 3-17. RIGID PAVEMENT DESIGN CURVES, SINGLE WHEEL

GEAR .......................................................................................................................... 59

FIGURE 3-18. RIGID PAVEMENT DESIGN CURVES, DUAL WHEEL

GEAR .......................................................................................................................... 60

FIGURE 3-19. RIGID PAVEMENT DESIGN CURVES, DUAL TANDEM

WHEEL GEAR ............................................................................................................ 61

FIGURE 3-20. RIGID PAVEMENT DESIGN CURVES, A-300 MODEL B2 ........... 62

FIGURE 3-21. RIGID PAVEMENT DESIGN CURVES, A-300 MODEL B4 ........... 63

FIGURE 3-22. RIGID PAVEMENT DESIGN CURVES, B-747-100, SR, 

200 B, C, F ................................................................................................................... 64

FIGURE 3-23. RIGID PAVEMENT DESIGN CURVES, B-747-SP.......................... 65

FIGURE 3-24. RIGID PAVEMENT DESIGN CURVES, B-757................................ 66

FIGURE 3-25. RIGID PAVEMENT DESIGN CURVES, B-767................................ 67

iii 
AC 150/5320-6D CHG 2 6/3/02 

FIGURE 3-26. RIGID PAVEMENT DESIGN CURVES, C-130................................68

FIGURE 3-27. RIGID PAVEMENT DESIGN CURVES, DC 10-10, 10CF................69

FIGURE 3-28. RIGID PAVEMENT DESIGN CURVES, DC 10-30, 30CF, 

40, 40CF.......................................................................................................................70

FIGURE 3-29. RIGID PAVEMENT DESIGN CURVES, L-1011-1, 100 ...................71

FIGURE 3-30. RIGID PAVEMENT DESIGN CURVES, L-1011-100, 200 ...............72

FIGURE 3-31. OPTIONAL RIGID PAVEMENT DESIGN CURVES, 

DUAL TANDEM GEAR..............................................................................................73

FIGURE 3-32. OPTIONAL RIGID PAVEMENT DESIGN CURVES, A-300 

MODEL B2 ..................................................................................................................74

FIGURE 3-33. OPTIONAL RIGID PAVEMENT DESIGN CURVES, B-747-100, 

SR, 200 B, D, F.............................................................................................................75

FIGURE 3-34. OPTIONAL RIGID PAVEMENT DESIGN CURVES, B-747-SP ......76

FIGURE 3-35. OPTIONAL RIGID PAVEMENT DESIGN CURVES, A300 

MODEL B-4.................................................................................................................77

FIGURE 3-36. OPTIONAL RIGID PAVEMENT DESIGN CURVES, B-757............78

FIGURE 3-37. OPTIONAL RIGID PAVEMENT DESIGN CURVES, B-767............79

FIGURE 3-38. OPTIONAL RIGID PAVEMENT DESIGN CURVES, 

DC 10-10, 10CF ...........................................................................................................80

FIGURE 3-39. OPTIONAL RIGID PAVEMENT DESIGN CURVES 

DC 10-30, 30CF, 40, 40CF ...........................................................................................81

FIGURE 3-40. OPTIONAL RIGID PAVEMENT DESIGN CURVES, 

L1011-1, 100 ................................................................................................................82

FIGURE 3-41. OPTIONAL RIGID PAVEMENT DESIGN CURVES, 

L1011-100, 200 ...........................................................................................................83

334. DESIGN EXAMPLE ....................................................................................................84

335. FROST EFFECTS ........................................................................................................84

336. HIGH TRAFFIC VOLUMES........................................................................................84

337. JOINTING OF CONCRETE PAVEMENTS.................................................................85

FIGURE 3-42. RIGID PAVEMENT JOINT TYPES AND DETAILS ........................86

FIGURE 3-42A.RIGID PAVEMENT JOINT TYPES AND DETAILS ........................86-1

TABLE 3-10A. PAVEMENT JOINT TYPES..............................................................86-2

TABLE 3-11. RECOMMENDED MAXIMUM JOINT SPACINGS 

RIGID PAVEMENT WITHOUT STABILIZED SUBBASE ........................................87

338. SPECIAL JOINTING CONSIDERATIONS.................................................................87

339. JOINTING STEEL .......................................................................................................88

TABLE 3-12. DIMENSIONS AND SPACING OF STEEL DOWELS......................88

340. JOINT SEALANTS AND FILLERS.............................................................................88

341. JOINT LAYOUT..........................................................................................................88

342. REINFORCED CONCRETE PAVEMENT..................................................................89

343 TYPE AND SPACING OF REINFORCEMENT..........................................................89

344 AMOUNT OF REINFORCEMENT..............................................................................89

FIGURE 3-43. TYPICAL JOINT LAYOUT PATTERN FOR RUNWAY,

PARALLEL TAXIWAY AND CONNECTOR.............................................................90

TABLE 3-13. YIELD STRENGTHS OF VARIOUS GRADES OF 

REINFORCING STEEL...............................................................................................91

iv 
 6/3/02 AC 150/5320-6D CHG 2

(1) Dry Preparation of Soil Samples for Particle-Size Analysis and Determination of Soil 

Constants (ASTM D 421) or Wet Preparation of Soil Samples for Grain-Size Analysis and Determination of Soil 

Constants (ASTM D 2217). The dry method (D 421) should be used only for clean, cohesiveless granular materials. 

The wet method (D 2217) should be used for all cohesive or borderline materials. In case of doubt, the wet method 

should be used. 

(2) Particle-Size Analysis of Soils (ASTM D 422). This analysis provides a quantative 

determination of the distribution of particles sizes in soils. 

(3) Liquid Limit, Plastic Limit, and Plasticity Index of Soils (ASTM D 4318). The plasticity 

and liquid limits of soil define in a standard manner the lowest moisture contents at which a soil will change from a 

semisolid to a plastic state and at which a solid passes from a plastic to a liquid state, respectively. The plasticity index 

is the numerical difference between the plastic limit and the liquid limit. It indicates the range in moisture content over 

which a soil remains in a plastic state prior to changing into a liquid. The plastic limit, liquid limit, and plasticity index 

of soils are used in engineering classification in accordance with the Unified Soil Classification System (ASTM D 

2487). In conjunction with particle size analysis, natural moisture content and other soil properties or conditions, the 

limits may be used to estimate engineering properties or behavior of soils, such as shrink/swell potential, consolidation 

characteristics, construction/stabilization characteristics, permeability, and strength characteristics. 

(4) Moisture-Density Relations of Soils (ASTM D 698, D 1557). For purposes of compaction 

control during construction, tests to determine the moisture-density relations of the different types of soils should be 

performed. 

(i) Heavy-Load Pavements. For pavements designed to serve aircraft weighing 60,000 pounds 

(27,000 kg) or more, use ASTM D 1557. 

(ii) Light-Load Pavements. For pavements designed to serve aircraft weighing less than 60,000 

pounds (27,000 kg), use ASTM D 698. 

(5) Bearing Ratio of Laboratory-Compacted Soils (ASTM D 1883). This test is used to 

assign a California Bearing Ratio (CBR) value to subgrade soils for use in the design of flexible pavements. 

(6) Modulus of Soil Reaction (AASHTO T 222). This test is used to determine the modulus of 

soil reaction, K, for use in the design of rigid pavements. 

c. Supplemental Tests. In many cases, additional soil tests will be required over those listed in 

Paragraph 203b above. It is not possible to cover all the additional tests that may be required; however, a few examples 

are presented below. This list should not be considered all-inclusive. 

(1) Shrinkage Factors of Soils (ASTM D 427). This test may be required in areas where 

swelling soils might be encountered. 

(2) Permeability of Granular Soils (ASTM D 2434). This test may be needed to assist in the 

design of subsurface drainage. 

(3) Determination of Organic Material in Soils by Wet Combustion (AASHTO T 194). This 

test may be needed in areas where deep pockets of organic material are encountered or suspected. 

(4) California Bearing Ratio, Field In-Place Tests (Mil-Std 621, Method 101). Field-bearing 

tests can be performed when the in-situ conditions satisfy density and moisture conditions that will exist under the 

pavement being designed. The method is also described in Manual Series No. 10, Soils Manual, The Asphalt Institute, 

College Park, MD. 

7
AC 150/5320-6D 7/7/95

204. UNIFIED SOIL CLASSIFICATION SYSTEM. 

a. Purpose. The standard method of classifying soils for engineering purposes is ASTM D 2487, 

commonly called the Unified system. The primary purpose in determining the soil classification is to enable the 

engineer to predict probable field behavior of soils. The soil constants in themselves also provide some guidance on 

which to base performance predictions. The Unified system classifies soils first on the basis of grain size, then further 

subgroups soils on the plasticity constants. Table 2-2 presents the classification of soils by the Unified system. 

b. Initial Division. As indicated in Table 2-2, the initial division of soils is based on the separation of 

coarse- and fine-grained soils and highly organic soils. The distinction between coarse and fine grained is determined 

by the amount of material retained on the No. 200 sieve. Coarse-grained soils are further subdivided into gravels and 

sands on the basis of the amount of material retained on the No. 4 sieve. Gravels and sands are then classed according 

to whether or not the fine material is present. Fine-grained soils are subdivided into two groups on the basis of liquid 

limit. A separate division of highly organic soils is established for materials which are generally suitable for 

consideration purposes. 

TABLE 2-2. CLASSIFICATION OF SOILS FOR AIRPORT PAVEMENT APPLICATIONS 

MAJOR DIVISIONS GROUP SYMBOLS 

Coarse-grained soils more 

than 50% retained on No. 

200 sieve1 

Gravels 50% or more of coarse fraction 

retained on No. 4 sieve 

Clean 

Gravels 

GW 

GP 

Gravels with 

Fines 

GM 

GC 

Sands less than 50% of coarse fraction retained 

on No. 4 sieve 

Clean 

Sands 

SW 

SP 

Sands with 

Fines 

SM 

SC 

Fine-grained soils 50% or 

less retained on No. 200 

sieve 

Silts and clays liquid limit 50% or less ML 

CL 

OL 

Silts and clays liquid limit greater than 50% MH 

CH 

OH 

Highly Organic Soils PT 1

Based on the material passing the 3-in (75-mm) sieve 

c. Soil Groups. Soils are further subdivided into 15 different groupings. The group symbols and a brief 

description of each is given below: 

(1) GW Well-graded gravels and gravel-sand mixtures, little or no fines.

(2) GP Poorly graded gravels and gravel-sand mixtures, little or no fines.

(3) GM Silty gravels, gravel-sand-silt mixtures.

(4) GC Clayey gravels, gravel-sand-clay mixtures.

(5) SW Well-graded sands and gravelly sands, little or no fines.

(6) SP Poorly graded sand and gravelly sands, little or no fines.

(7) SM Silty sands, sand-silt mixtures.

(8) SC Clayey sands, sand-clay mixtures.

(9) ML Inorganic silts, very fine sands, rock flour, silty or clayey fine sands.

(10) CL Inorganic clays of low to medium plasticity, gravelly clays, silty clays, lean clays.

(11) OL Organic silts and organic silty clays of low plasticity.

(12) MH Inorganic silts, micaceous or diatomaceous fine sands or silts, plastic silts.

8
6/3/02 AC 150/5320-6D CHG 2

uniform, stable foundation. 

b. Thickness. Pavements subjected to traffic intensities greater than the 25,000 annual departure level 

shown on the design curves will require more thickness to accommodate the traffic volume. Additional thickness can be 

provided by increasing the pavement thickness in accordance with Table 3-5. 

c. Panel Size. Slab panels should be constructed to minimize joint movement. Panel sizes given in 

Paragraph 337 should be selected conservatively. Small joint movement tends to provide for better load transfer across 

joints and reduces the elongation the joint sealant materials must accommodate when the slabs expand and contract. 

High-quality joint sealants should be specified to provide the best possible performance. 

337. JOINTING OF CONCRETE PAVEMENTS. Variations in temperature and moisture content can cause 

volume changes and slab warping, resulting in significant stresses. In order to reduce the detrimental effects of these 

stresses and to minimize random cracking, it is necessary to divide the pavement into a series of slabs of predetermined 

dimensions by means of joints. These slabs should be as nearly square as possible when no reinforcement is used. 

a. Joint Categories. Pavement joints are categorized according to the function that the joint is intended 

to perform. The categories are expansion, contraction, and construction joints. All joints, regardless of type, should be 

finished in a manner that permits the joint to be sealed. Pavement joint details are shown in Figures 3-42 and 3-42A 

and are summarized in Table 3-10A. These various joints are described as follows: 

(1) Expansion Joints. The function of an expansion joint is to isolate intersecting pavements 

and to isolate structures from the pavement. There are two types of expansion joints. 

(i) Type A. Type A is used when load transfer across the joint is required. This joint 

contains a 3/4-inch (19 mm) nonextruding compressible material and is provided with dowel bars for load transfer. 

(ii) Type B. Type B is used when conditions preclude the use of load transfer devices 

that span across the joint, such as where the pavement abuts a structure or where horizontal differences in movement of 

the pavements may occur. These joints are formed by increasing the thickness of the pavement along the edge of slab. 

No dowel bars are provided. 

(2) Contraction Joints. The function of contraction joints is to provide controlled cracking of 

the pavement when the pavement contracts due to decrease in moisture content or a temperature drop. Contraction 

joints also decrease stresses caused by slab warping. Details for contraction joints are shown as Types F, G, and H in 

Figure 3-42. 

(3) Construction Joints. Construction joints are required when two abutting slabs are placed at 

different times, such as at the end of a day’s placement, or between paving lanes. Details for construction joints are 

shown as Types C, D, and E in Figure 3-42. 

b. Joint Spacing. 

(1) Without Stabilized Subbase. A rule-of-thumb for joint spacing given by the Portland 

Cement Association is applicable for rigid pavements without stabilized subbase: “As a rough guide, the joint spacing 

(in feet) should not greatly exceed twice the slab thickness (in inches).” Table 3-11 shows the recommended maximum 

joint spacings. Shorter spacings may be more convenient in some instances and may be required to provide minimum 

clearance between pavement joints and in-pavement obstructions such as light cans. The recommended maximum 

spacing for slabs thicker than 12 inches (305 mm) should only be used when historical records can verify satisfactory 

performance. In lieu of historical performance records, a maximum spacing of 20 feet (6.1 m) is recommended. The 

ratio of slab length to slab width should not exceed 1.25 in unreinforced pavements. 

85
FIGURE 3-42. RIGID PAVEMENT JOINT TYPES AND DETAILS

AC 150/5320-6D CHG 2 6/3/02 

86
Longitudinal Joint Type A or D

Transverse Joint

Type A, D, or F

PLAN VIEW

Position of Dowels at Edge of Joint 

Type A, D, F

Bar Length Varies

3" (76mm) Minimum

10" (254mm) Minimum

Bar Length Varies

Construction Joint Between Slabs

Rod Backup 

Material

Sealant Material 1/4" - 3/8" 

(6-10mm) Below Surface

1 1/4" (32mm)

Minimum

W

D

DETAIL 3

CONSTRUCTION JOINT

Sealant Material 1/4" - 3/8"

(6-10mm) Below Surface

1 1/4" (32mm)

Minimum

Rod Backup Material

DETAIL 2

CONTRACTION JOINT

D

W

T/4±1/4"

(±6mm)

3/4"±1/8"

(19±3mm)

Sealant Material 1/4" - 3/8" 

(6-10mm) Below Surface

Non-Extruding Premolded Compressible 

Material 

1/4" (6mm) Radius

or Chamfer

DETAIL 1

EXPANSION JOINT

3/4"±1/8"

(19±3mm)

NOTES:

1. 

SHAPE FACTORS FOR OPTIMUM PERFORMANCE.

2. 

3. 

4. 

HIGH TRAFFIC VOLUMES.

Optional

1/4" X 1/4" Chamfer

Rod Backup Material

FIGURE 3-42A. RIGID PAVEMENT JOINT TYPES AND DETAILS

 6/3/02 AC 150/5320-6D CHG 2 

86-1

ASTM D-1751 or 1752

SEALANT RESERVOIR SIZED TO PROVIDE PROPER SHAPE FACTOR, W/D. FIELD POURED AND PREFORMED SEALANTS REQUIRE DIFFERENT 

ROD BACKUP MATERIAL MUST BE COMPATIBLE WITH THE TYPE OF SEALANT USED AND SIZED TO PROVIDE THE DESIRED SHAPE FACTOR.

RECESS SEALER 3/8" - 1/2" FOR JOINTS PERPENDICULAR TO RUNWAY GROOVES

CHAMFERED EDGES ARE RECOMMENDED FOR DETAILS 2 AND 3 WHEN PAVEMENTS ARE SUBJECT TO SNOW REMOVAL EQUIPMENT OR 
AC 150/5320-6D CHG 2 6/3/02

TABLE 3-10A PAVEMENT JOINT TYPES

JOINT TYPES - DESCRIPTION AND USE (Chapter 3 designations) 

TYPE DESCRIPTION LONGITUDINAL TRANSVERSE 

A Doweled Expansion 

Joint 

Not used. Use near intersections to isolate different 

pavement areas. Not recommended to 

isolate different joint patterns. 

B Thickened Edge 

Expansion Joint 

Use at intersections where dowels are 

not suitable and where pavements abut 

structures. Consider at locations along 

a pavement edge where future 

expansion is possible. 

Provide thickened edge where pavement 

extension is likely. On thinner pavement 

sections the thickened edge will provide 

additional section for placement of future 

dowel bars. Recommended to isolate 

different joint patterns. 

C Keyed Construction 

Joint 

Acceptable for all construction joints 

except where type E is required. 

Not used. 

D Doweled 

Construction Joint 

Acceptable for all construction joints. Use at locations where paving operations 

are delayed or stopped. 

E Hinged Construction 

Joint 

Acceptable for use on all construction 

joints of taxiways and for all other 

construction joints placed 25' or less 

from the pavement edge unless wide 

body aircraft are expected. See 

paragraph 338b for wide body aircraft 

requirements. 

Not used. 

F Doweled Contraction 

Joint 

May be considered for general use. Use on all contraction joints for a 

distance of at least three joints from a 

free edge, for the first two joints on each 

side of expansion joints, and for all 

contraction joints in reinforced 

pavements. May be considered for 

general use. 

G Hinged Contraction 

Joint 

For all contraction joints of the taxiway 

and for all other contraction joints 

placed 25' or less from the pavement 

edge unless wide body aircraft are 

expected. See paragraph 338b for wide 

body aircraft requirements. 

Not used. 

H Dummy Contraction 

Joint 

For all other contraction joints in 

pavement. 

For all remaining contraction joints in 

non-reinforced pavements. 

86-2
6/3/02 AC 150/5320-6d CHG 2 

TABLE 3-11. RECOMMENDED MAXIMUM JOINT SPACINGS -

RIGID PAVEMENT WITHOUT STABILIZED SUBBASE

Slab Thickness Transverse Longitudinal 

Inches Millimeters Feet Meters Feet Meters 

6 150 12.5 3.8 12.5 3.8 

7-9 175-230 15 4.6 15 4.6 

9-12 230-305 20 6.1 20 6.1 

> 12 >305 25 7.6 25 7.6 

Note: Joint spacings shown in this table are maximum values that may be acceptable under ideal 

conditions. Smaller joint spacings should be used if indicated by past experience. Pavements subject 

to extreme seasonal temperature differentials or extreme temperature differentials during placement 

may require smaller joint spacings. See also Chapter 5 for light-load rigid pavement jointing. 

(2) With Stabilized Subbase. Rigid pavements supported on stabilized subbase are subject to higher 

warping and curling stresses than those supported on unstabilized foundations. When designing a rigid pavement 

supported on a stabilized subbase a different procedure is recommended to determine joint spacing. Joint spacing should 

be a function of the radius of relative stiffness of the slab. The joint spacing should be selected such that the ratio of the 

joint spacing, in inches, to the radius of relative stiffness is 5.0 or less to control transverse cracking. In the absence of 

conclusive local experience, a maximum joint spacing of 20 feet (6.1 m) is recommended. The radius of relative stiffness 

is defined by Westergaard as the stiffness of the slab relative to the stiffness of the foundation. It is determined by the 

following formula: 

1 

� Eh3 � 4 

l = �

�

Ł12(1 - u 2 ) k ł

�

� 

Where: 

l = radius of relative stiffness, inches.

E = modulus of elasticity of the concrete, usually 4 million psi.

h = slab thickness, inches. 

u = Poisson’s ratio for concrete, usually 0.15.

k = modulus of subgrade reaction, pci.

338. SPECIAL JOINTING CONSIDERATIONS. A number of special considerations are required when 

designing the jointing system for a Portland cement concrete pavement. Several considerations are discussed below. 

a. Keyed Joints. Keyed construction joints should not be used for slabs less than 9 inches (230 mm) in 

thickness. Keyed joints in slabs of lesser thickness result in very small keys and key-ways with limited strength. 

b. Jointing Systems for Wide Body Jet Aircraft. Experience indicates poor performance may result from 

keyed longitudinal construction joints supported on low-strength foundations when wide body aircraft loadings are 

encountered. Special jointing recommendations are discussed below. 

(1) Low Strength Foundations. For foundation moduli of 200 pci (54 MN/m3) or less, a doweled or 

thickened edge construction joint, Type D or B, is recommended. Keyed joints should not be used as poor performance 

will likely result. In areas of low traffic usage, such as extreme outer lanes of runways and aprons, keyed joints, Type C, 

may be used. 

(2) Medium Strength Foundations. For foundation moduli between 200 pci (54 MN/m3) and 400 pci 

(109 MN/m3

), hinged construction joints, Type E, may be used as well as doweled or thickened edge. The maximum 

width of pavement that can be tied together depends on several factors such as subgrade frictional restraints, pavement 

thickness, and climatic conditions. Normally, the maximum width of tied pavement should not exceed 75 feet (23 m). 

Type C joints may be used in low traffic areas. 

(3) High Strength Foundations. For foundation moduli of 400 pci (109 MN/m3) or greater 

conventional keyed joints, Type C, may be used regardless of traffic usage. Note, however, that the prohibition 

87 
AC 150/5320-6D 7/7/95

against keyed joints in pavements less than 9 inches (230 mm) thick shall still remain in effect. 

c. Future Expansion. When a runway or taxiway is likely to be extended at some future date, it is 

recommended that a thickened edge joint be provided at that end of the runway or taxiway. Likewise, if any pavement is 

to be widened in the future, a key-way or thickened edge should be provided at the appropriate edge. 

339. JOINTING STEEL. 

a. Tie Bars. Tie bars are used across certain longitudinal contraction joints and keyed construction joints to 

hold the slab faces in close contact. The tie bars themselves do not act as load transfer devices. By preventing wide 

opening of the joint, load transfer is provided by the keyed joint or by aggregate interlock in the crack below the groovetype joint. Tie bars should be deformed bars conforming to the specifications given in Item P-501. The bars should be 

5/8 inches (16 mm) in diameter and 30 inches (760 mm) on center. 

b. Dowels. Dowels are used at joints to provide for transfer of load across the joint and to prevent relative 

vertical displacement of adjacent slab ends. Dowels permit longitudinal movement of adjacent slabs. 

(1) Where used. Provision for load transfer by dowels is provided at all transverse expansion joints and 

all butt-type construction joints. Dowels for contraction joints should be provided at least three joints from a free edge. 

Contraction joints in the interior of the pavement may be the dummy groove type. 

(2) Size Length and Spacing. Dowels should be sized such that they will resist the shearing and bending 

stresses produced by the loads on the pavement. They should be of such length and spacing that the bearing stresses 

exerted on the concrete will not cause failure of the concrete slab. Table 3-12 indicates the dowel dimensions and 

spacing for various pavement thicknesses. 

Table 3-12. DIMENSIONS AND SPACING OF STEEL DOWELS 

Thickness of Slab Diameter Length Spacing 

6-7 in 

(150-180 mm) 

8-12 in 

(210-305 mm) 

13-16 in 

(330-405 mm) 

17-20 in 

(430-510 mm) 

21-24 in 

(535-610 mm) 

3/4 in 18 in 12 in 

(20 mm) (460 mm) (305 mm) 

1 in 19 in 12 in 

(25 mm) (480 mm) (305 mm) 

1 1/4 in1 20 in 15 in 

(30 mm) (510 mm) (380 mm) 

1 1/2 in1 20 in 18 in 

(40 mm) (510 mm) (460 m) 

2 in1 24 in 18 in 

(50 mm) (610 mm) (460 mm) 1

Dowels noted may be solid bar or high-strength pipe. High-strength pipe dowels must 

be plugged on each end with a tight-fitting plastic cap or with bituminous or mortar mix. 

(3) Dowel Positioning. The alignment and elevation of dowels is extremely important in obtaining a 

satisfactory joint. Transverse dowels will require the use of a fixture, usually a wire cage or basket firmly anchored to 

the subbase, to hold the dowels in position. During the concrete placement operations, it is advisable to place plastic 

concrete directly on the dowel assembly immediately prior to passage of the paver to prevent displacement of the 

assembly by the paving equipment. Some paving machines have a dowel placer, which can be used to accurately 

position dowels. 

340. JOINT SEALANTS AND FILLERS. Sealants are used in all joints to prevent the ingress of water and 

foreign material in the joint. Premolded compressible filler are used in expansion joints to permit expansion of the 

slabs. Joint sealants are applied above the filler in expansion joints to prevent infiltration of water and foreign material. 

In areas subject to fuel spillage, fuel-resistant sealants should be used. Specifications for joint sealants are given in Item 

P-605. 

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6/3/02 AC 150/5320-6D CHG 2

341. JOINT LAYOUT. Pavement joint layout is a matter of selecting the proper joint types and dimensions so that 

the joints can perform their intended function. Construction considerations are also vitally important in determining the 

joint layout pattern. Paving lane widths will often dictate how the pavement should be jointed. Generally speaking, it is 

more economical to keep the number of passes of the paving train to a minimum while maintaining proper joint 

function. Figure 3-43 shows a typical jointing plan for a runway end, parallel taxiway, and connector. In-pavement 

light fixtures may also affect joint spacing. Joint patterns should be such that the nearest edge of a light fixture is 

approximately 2 feet (610 mm) from any joint. It is impossible to illustrate all of the variations that can occur at 

pavement intersections. Reference 8 in Appendix 4 contains further information on jointing patterns. Two important 

considerations in designing joint layouts for intersections are isolation joints and odd-shaped shapes. More discussion 

on these follows: 

a. Isolation Joints. Two intersecting pavements, such as a taxiway and runway, should be isolated to 

allow the pavements to move independently. Isolation can best be accomplished by using a Type B expansion joint 

between the two pavements. The expansion joint should be positioned such that the two pavements can expand and 

contract independently; normally this can be accomplished by using a Type B expansion joint where the two pavements 

abut. One isolation joint is normally sufficient to allow independent movement. 

b. Odd-Shaped Slabs. Cracks tend to form in odd-shaped slabs; therefore, it is good practice to 

maintain sections that are nearly square or rectangular in shape. Pavement intersections that involve fillets are difficult 

to design without a few odd-shaped slabs. In instances where odd-shaped slabs cannot be avoided, steel reinforcement is 

recommended. Steel reinforcement should consist of 0.050 percent steel in both directions in slabs where the length-towidth ratio exceeds 1.25 or in slabs that are not rectangular in shape. The steel reinforcement should be placed in 

accordance with the recommendations given in paragraph 342, Reinforced Concrete Pavement. Fillets may also be 

defined by constructing slabs to the normal, full dimensions and painting out the unused portion of the slab with 

bitumen. 

342. REINFORCED CONCRETE PAVEMENT. The main benefit of steel reinforcing is that, although it does 

not prevent cracking, it keeps the cracks that form tightly closed so that the interlock of the irregular faces provides 

structural integrity and usually maintains pavement performance. By holding the cracks tightly closed, the steel 

minimizes the infiltration of debris into the cracks. The thickness requirements for reinforced concrete pavements are 

the same as plain concrete and are determined from the appropriate design curves, Figures 3-17 through 3-41. Steel 

reinforcement allows longer joint spacing; thus the cost benefits associated with fewer joints must be considered in the 

decision to use plain or reinforced concrete pavement. 

343. TYPE AND SPACING OF REINFORCEMENT. Reinforcement may be either welded wire fabric or bar 

mats installed with end and side laps to provide complete reinforcement throughout the slab panel. End laps should be a 

minimum of 12 inches (305 mm) but not less than 30 times the diameter of the longitudinal wire or bar. Side laps 

should be a minimum of 6 inches (150 mm) but not less than 20 times the diameter of the transverse wire or bar. End 

and side clearances should be a maximum of 6 inches (150 mm) and a minimum of 2 inches (50 mm) to allow for nearly 

complete reinforcement and yet achieve adequate concrete cover. Longitudinal members should be spaced not less than 

4 inches (100 mm) nor more than 12 inches (305 mm) apart; transverse members should be spaced not less than 4 

inches (100 mm) nor more than 24 inches (610 mm) apart. 

344. AMOUNT OF REINFORCEMENT. 

a. The steel area required for a reinforced concrete pavement is determined from the subgrade drag 

formula and the coefficient of friction formula combined. The resultant formula is expressed as follows: 

A = (3.7 )L Lt 

S f s 

Where:

As = area of steel per foot of width or length, square inches 

L = length or width of slab, feet

T = thickness of slab, inches 

fs = allowable tensile stress in steel, psi

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6/3/02 AC 150/5320

-6D CHG 2

Expansion Joint 

Doweled or Dummy Joint 

Tied or Doweled Joint 

Doweled Contraction Joint 

Reinforce 

Odd Shaped Slabs 

2 Feet (0.61m) 

Minimum 

2 Feet (0.61m) Minimum 

Fillet May Be Marked On Full 

Or Partial Panels 

All 

FIGURE 3-43. TYPICAL JOINT LAYOUT PATTERN FOR RUNWAY, PARALLEL TAXIWAY, AND CONNECTOR

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7/7/95 AC 150/5320-6D

404. DESIGN OF STRUCTURAL HOT MIX ASPHALT OVERLAYS. Structural hot mix asphalt overlays can 

be applied to either flexible or rigid pavements. Certain criteria and design assumptions are different for hot mix 

asphalt overlays of flexible or rigid pavements. The design procedures are presented separately. 

405. HOT MIX ASPHALT OVERLAYS ON EXISTING FLEXIBLE PAVEMENT. The design of structural 

hot mix asphalt overlays on existing flexible pavements is based on a thickness deficiency approach. That is, the 

existing pavement is compared to what is needed for a new pavement, and any deficiency is made up in the overlay. 

a. Calculate New Pavement Requirements. Using the appropriate flexible pavement design curves 

(Figures 3-2 through 3-15), calculate the thickness requirements for a flexible pavement for the desired load and number 

of equivalent design departures. A CBR value is required for the subgrade material and subbase. Thicknesses of all 

pavement layers must be determined. 

b. Compare New Pavement Requirements With Existing Pavement. The thickness requirements for a 

new pavement are compared with the existing pavement to determine the overlay requirements. Adjustments to the 

various layers of the existing pavement may be necessary to complete the design. This is particularly difficult when 

overlaying old pavement. Hot mix asphalt surfacing may have to be converted to base, and/or base converted to 

subbase. Note that a high-quality material may be converted to a lower quality material, such as surfacing to base or 

base to subbase. A lesser-quality material may not be converted to a higher-quality material. For example, excess 

subbase cannot be converted to base. The equivalency factors shown in Tables 3-6 through 3-8 may be used as guidance 

in the conversion of layers. It must be recognized that the values shown in Tables 3-6 through 3-8 are for new 

materials, and the assignment of factors for existing pavement must be based on judgment and experience. Surface 

cracking, high degree or oxidation, evidence of low stability, etc. are a few of the considerations that would tend to 

reduce the equivalency factor. Any hot mix asphalt layer located between granular courses in the existing pavement 

should be evaluated inch for inch as granular base or subbase course. 

c. Example. To illustrate the procedure of designing a hot mix asphalt overlay, assume an existing 

taxiway pavement composed of the following section: the subgrade CBR is 7, the hot mix asphalt surface course is 4 

inches (10 mm) thick, the base course is 6 inches (150 mm) thick, the subbase is 10 inches (250 mm) thick, and the 

subbase CBR is 15. Frost action is negligible. Assume the existing pavement is to be strengthened to accommodate a 

dual wheel aircraft weighing 100,000 pounds (45,000 kg) and an annual departure level of 3,000. The flexible 

pavement required (referring to Figure 3-3) for these conditions is: 

Hot mix asphalt surface 4 inches (100 mm) 

Base 9 inches (230 mm) 

Subbase 10 inches (250 mm) 

Total pavement thickness 23 inches (585 mm) 

The total pavement thickness must be 23 inches (585 mm) in order to protect the CBR 7 subgrade. The combined 

thicknesses of surfacing and base must be 13 inches (330 mm) to protect the CBR 15 subbase. The existing pavement 

is 3 inches (75 mm) deficient in total pavement thickness. All of the thickness deficiency is in the base course. For the 

sake of illustration, assume the existing hot mix asphalt surface is in such condition that surfacing can be substituted for 

base at an equivalency ratio of 1.3 to 1. Converting 2.5 inches (64 mm) of surfacing to base yields a base course 

thickness of 9.2 inches (234 mm) leaving 1.5 inches (40 mm) of unconverted surfacing. A 2.5-inch (54-mm) overlay 

would be required to achieve a 4-inch (100-mm) thick surface. 

d. Summary. Structurally, a 2.5-inch-thick overlay should satisfy the design conditions. The overlay 

thickness calculated from structural considerations should be compared with that required to satisfy geometric 

requirements. Geometric requirements include, for example, provision of drainage, correcting crown and grade, 

meeting grade of other adjacent pavements and structures, etc. The most difficult part of designing hot mix asphalt 

overlays for flexible pavements is the determination of the properties of the existing pavement. Subgrade and subbase 

CBR values can be determined by conducting field in place CBR tests. Field CBR tests should be performed in 

accordance with the procedures given in Manual Series No. 10 (MS-10 by the Asphalt Institute. See Appendix 4.). The 

subgrade and 

105
AC 150/5320-6D CHG 2 6/3/02 

subbase must be at the equilibrium moisture content when field CBR tests are conducted. Normally, a pavement that 

has been in place for at least 3 years will be in equilibrium. Procedures for calculating CBR values from NDT tests are 

also available. Layer conversions (i.e., converting base to subbase, etc.) are largely a matter of engineering judgment. 

When performing the conversions, it is recommended that any converted thicknesses not be rounded off. 

406. HOT MIX ASPHALT OVERLAY ON EXISTING RIGID PAVEMENT. The design of a hot mix asphalt 

overlay on an existing rigid pavement is also based on a thickness deficiency approach. However, new pavement 

thickness requirements for rigid pavements are used to compare with the existing rigid pavement. The formula for 

computing overlay thickness is as follows: 

t = 2.5(Fhd - Cbhe ) 

Where:

t = thickness of hot mix asphalt overlay, inches (mm).

F = a factor which controls the degree of cracking in the base rigid pavement.

hd = thickness of new rigid pavement required for design conditions, inches (mm). Use the exact 

value for hd; do not round off. In calculating hd use the k value of the existing foundation and 

the flexural strength of the existing concrete as design parameters. 

Cb = a condition factor that indicates the structural integrity of the existing rigid pavement. Values 

range from 1.0 to 0.75. 

he = thickness of existing rigid pavement, inches (mm). 

a. F Factor. The "F" factor is an empirical method of controlling the amount of cracking that will occur 

in the rigid pavement beneath the hot mix asphalt overlay. It is a function of the amount of traffic and the foundation 

strength. The assumed failure mode for a hot mix asphalt overlay on a existing rigid pavement is that the underlying 

rigid pavement cracks progressively under traffic until the average size of the slab pieces reaches a critical value. 

Further traffic beyond this point results in shear failures within the foundation, producing a drastic increase in 

deflections. Since high strength foundations can better resist deflection and shear failure, the F factor is a function of 

subgrade strength as well as traffic volume. Photographs of various overlay and base pavements shown in Figure 4-2 

illustrate the meaning of the F factor. Figures 4-2a, b, and c show how the overlay and base pavements fail as more 

traffic is applied to a hot mix asphalt overlay on an existing rigid pavement. Normally an F factor of 1.0 is 

recommended unless the existing pavement is in quite good condition, see paragraph 406b(1) below. Figure 4-3 should 

be used to determine the appropriate F factor for pavements in good condition. 

b. Cb Factor. The condition factor "Cb" applies to the existing rigid pavement. The Cb factor is an 

assessment of the structural integrity of the existing pavement. 

(1) Selection of Cb Factor. The overlay formula is rather sensitive to the Cb value. A great deal 

of care and judgement are necessary to establish the appropriate Cb. NDT can be a valuable tool in determining a proper 

value. A Cb value of 1.0 should be used when the existing slabs contain nominal structural cracking and 0.75 when the 

slabs contain structural cracking. The designer is cautioned that the range of Cb values used in hot mix asphalt overlay 

designs is different from the "Cr" values used in rigid overlay pavement design. A comparison of Cb and Cr and the 

recommended F factor to be used for design is shown below: 

Cr Cb Recommended F factor 

0.35 to 0.50 0.75 to 0.80 1.00 

0.51 to 0.75 0.81 to 0.90 1.00 

0.76 to 0.85 0.91 to 0.95 1.00 

0.86 to 1.00 0.96 to 1.00 Use Figure 4.3 

The minimum Cb value is 0.75. A single Cb should be established for an entire area. The Cb value should not be varied 

along a pavement feature. Figures 4-4 and 4-5 illustrate Cb values of 1.0 and 0.75, respectively. 

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7/7/95 AC 150/5320-6D

SURFACE OF OVERLAY BASE PAVEMENT

SURFACE OF OVERLAY BASE PAVEMENT

SURFACE OF OVERLAY BASE PAVEMENT

FIGURE 4-2. ILLUSTRATION OF VARIOUS "F" FACTORS FOR HOT MIX ASPHALT OVERLAY

107
AC 150/5320-6D CHG 2 6/3/02 

[ MN/m3] 

[ 0 ] [ 25 ] [ 50 ] [ 75 ] [ 100 ] 

1.00 

0.90 

0.80 

0.70 

0.60 

0 100 200 300 400 

pci

Modulus of Subgrade Reaction 

FIGURE 4.3 GRAPH OF "F" FACTOR VS. MODULUS OF SUBGRADE REACTION 

FOR DIFFERENT TRAFFIC LEVELS F-Factor 

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6/3/02 AC 150/5320-6D CHG 2

410. CONCRETE OVERLAY ON FLEXIBLE PAVEMENT. The design of concrete overlays on existing 

flexible pavements assumes the existing flexible pavement is a foundation for the overlay slab. Overlay slab thickness is 

based on the design curves in Figures 3-17 through 3-40. The existing flexible pavement should be assigned a k value 

using Figure 2-4 or 3-16 or by conducting a plate-bearing test on the existing flexible pavement or by NDT testing. In 

any case, the k value assigned should not exceed 500. When frost conditions require additional thickness, the use of 

nonstabilized material below the rigid pavement overlay is not allowed, as this would result in a sandwich pavement. 

Frost protection must be provided by stabilized material. 

411. CONCRETE OVERLAY ON RIGID PAVEMENT. The design of concrete overlays on existing 

rigid pavements is also predicated on the rigid pavement design curves, Figures 3-17 through 3-40. The rigid 

pavement design curves indicate the thickness of concrete required to satisfy the design conditions for a single 

thickness of concrete pavement. Use of this method requires the designer to assign a k value to the existing 

foundation. The k value may be determined by field NDT tests or by bearing tests conducted in test pits cut 

through the existing rigid pavement, they may also estimated from construction records for the existing 

pavement. The design of a concrete overlay on a rigid pavement requires an assessment of the structural integrity 

of the existing rigid pavement. The condition factor, Cr , should be selected after an extensive pavement 

condition survey. The selection of a condition factor is a matter of engineering judgment. The use of 

nondestructive testing can be of considerable value in assessing the condition of an existing pavement. NDT can 

also be used to determine sites for test pits. NDT procedures are given in Advisory Circular 150/5370-11, Use of 

Nondestructive Testing Devices in the Evaluation of Airport Pavements. See Appendix 4. In order to provide a 

more uniform assessment of condition factors, the following values are defined: 

Cr = 1.0 for existing pavement in good condition - some minor cracking evident, but no structural 

defects 

Cr = 0.75 for existing pavement containing initial corner cracks due to loading but no progressive 

cracking or joint faulting 

Cr = 0.35 for existing pavement in poor structural condition, badly cracked or crushed and faulted 

joints 

The three conditions discussed above are used to illustrate the condition factor rather than establish the only values 

available to the designer. Conditions at a particular location may require the use of an intermediate value of Cr within 

the recommended range. Sketches of three different values of Cr are shown in Figures 4-6, 4-7, and 4-8. 

a. Concrete Overlay Without Leveling Course. The thickness of the concrete overlay slab applied 

directly over the existing rigid pavement is computed by the following formula. 

h = c 

Where:

hc = required thickness of concrete overlay 

h = required single slab thickness determined from design curves

he = thickness of existing rigid pavement 

Cr = condition factor

1.4 1.4 

r e 

1.4 h - C h

Due to the inconvenient exponents in the above formula, graphic solutions are given in Figures 4-9 and 4-10. These 

graphs were prepared for only two different condition factors, Cr = 1.0 and 0.75. The use of a concrete overlay 

pavement directly on an existing rigid pavement with a condition factor of less than 0.75 is not recommended because of 

the likelihood of reflection cracking. The above equation assumes the flexural strength of the concrete used for the 

overlay will be approximately equal to that of the base pavement. If the flexural strengths differ by more than 100 psi 

(0.7 MN/m2

), the following modified equation should be used to determine the required thickness of the overlay 

h = 1.4 c 

1.4 

e 

b 

r 

1.4 h 

h 

h h C �

� 

ł 

� 

�

� 

Ł 

� - ·

Where: 

113
AC 150/5320-6D CHG 2 6/3/02 

hb = required single slab thickness determined from design curves based on the flexural strength of the base 

pavement 

Other factors are the same as previous formula. 

b. Concrete Overlay With Leveling Course. In some instances it may be necessary to apply a leveling 

course of hot mix asphalt concrete to an existing rigid pavement prior to the application of the concrete overlay. Under 

these conditions a different formula for the computation of the overlay thickness is required. When the existing 

pavement and overlay pavement are separated, the slabs act more independently than when the slabs are in contact with 

each other. The formula for the thickness of an overlay slab when a leveling course is used is as follows: 

h = c 

2 

r e

2 h - C h 

Where: 

hc = required thickness of concrete overlay

h = required single slab thickness determined from design curves

he = thickness of existing rigid pavement 

Cr = condition factor

When the flexural strength of the overlay and the existing pavements differ by more than 100 psi (0.7 MN/m2), the 

equation is modified as follows: 

h = c 

2

e 

b 

r 

2 h 

h 

h h - C �

� 

ł 

� 

�

� 

Ł

� · 

Where: 

hb = required single slab thickness determined from design curves based on the flexural strength of 

the base pavement 

The leveling course must be constructed of highly stable hot mix asphalt concrete. A granular separation course is not 

allowed as this would constitute sandwich construction. Graphic solutions of the above equation are shown in Figures 

4-11 and 4-12. These graphs were prepared for condition factors of 0.75 and 0.35. Other condition factors between 

these values can should be computed as part of the design. 

412. BONDED CONCRETE OVERLAYS. Concrete overlays bonded to existing rigid pavements are sometimes 

used under certain conditions. By bonding the concrete overlay to the existing rigid pavement, the new section behaves 

as a monolithic slab. The thickness of bonded overlay required is computed by subtracting the thickness of the existing 

pavement from the thickness of the required slab thickness determined from design curves. 

hc = h - he 

Where: 

hc = required thickness of concrete overlay

h = required single slab thickness determined from design curves using the flexural strength of

the existing concrete 

he = thickness of existing rigid pavement 

Bonded overlays should be used only when the existing rigid pavement is in good condition. Defects in the existing 

pavement are more likely to reflect through a bonded overlay than other types of concrete overlays. The major problem 

likely to be encountered with bonded concrete overlays is achieving adequate bond. Elaborate surface preparation and 

exacting construction techniques are required to ensure the bond. 

413. JOINTING OF CONCRETE OVERLAYS. Where a rigid pavement is to receive the overlay, some modification 

to jointing criteria may be necessary because of the design and joint arrangement of the existing pavement. The following 

points may be used as guides in connection with the design and layout of joints in concrete overlays. 

114 
6/3/02 AC 150/5320-6D CHG 2

500. GENERAL. Pavements for light aircraft are defined as those intended to serve aircraft weights of less than 

30,000 pounds (13,000 kg). Aircraft of this size are usually engaged in nonscheduled activities, such as agricultural, 

instructional, or recreational flying. Pavements designed to serve these aircraft may be flexible or rigid-type pavements. 

The design of pavements serving aircraft of 30,000 pounds (13,000 kg) gross weight or more should be based on the 

criteria contained in Chapter 3 of this publication. Some areas of airports serving light aircraft may not require paving. 

In these areas, the development of an aggregate-turf or turf surface may be adequate for limited operations of these light 

aircraft. Aggregate-turf surfaces are constructed by improving the stability of a soil with the addition of aggregate prior 

to development of the turf. Aggregate-turf construction is covered in some detail in the latter part of this chapter. 

Information on stabilization of soils can be found in Chapter 2 of this circular and in AC 150/5370-10, Standards for 

Airport Construction. 

501. TYPICAL SECTIONS. Typical cross-sections for light aircraft pavements are shown in Figure 5-1. No 

distinction is made between critical and noncritical pavement sections for pavements serving light aircraft. 

502. FLEXIBLE PAVEMENT MATERIALS. Flexible pavements for light aircraft are composed of hot mix asphalt 

surfacing, base course, subbase, and prepared subgrade. The function of these layers and applicable specifications are 

discussed below. 

a. Hot Mix Asphalt Surfacing. The function of the hot mix asphalt surface or wearing course is the 

same as discussed earlier in Chapter 3. Specifications covering the composition and quality of hot mix asphalt mixtures 

are given in Item P-401, Plant Mix Bituminous Mixtures. Note that under certain conditions, state highway hot mix 

asphalt mixtures may be used for pavements intended to serve aircraft weighing 12,500 pounds (5,700 kg) or less. 

b. Base Course. As in heavy loaded pavements, the base course is the primary load-carrying component 

of a flexible pavement. Specifications covering materials suitable for use as base courses for light-load pavements are 

as follows: 

(1) Item P-208 - Aggregate Base Course 

(2) Item P-209 - Crushed Aggregate Base Course 

(3) Item P-220 - Caliche Base Course 

(4) Item P-211 - Lime Rock Base Course 

(5) Item P-212 - Shell Base Course 

(6) Item P-213 - Sand-Clay Base Course 

(7) Item P-301 - Soil-Cement Base Course 

(8) Item P-304 - Cement-Treated Base Course 

(9) Item P-306 - Econocrete Subbase Course 

(10) Item P-401 - Plant Mix Bituminous Pavement 

Note: Use of some of the above materials in areas where frost penetrates into the base course may 

result in some degree of frost heave and/or may require restricted loading during spring thaw. 

c. Subbase Coarse. A subbase course is usually required in flexible pavement except those on subgrades 

with CBR value of 20 or greater (usually GW or GP type soils). Materials conforming to specification Item P-154, 

Subbase Course, may be used as subbase course. Also any items listed above in paragraph 502b may be used as subbase 

course if economy and practicality dictate. Since the loads imposed on these pavements are much less than those on 

pavements designed for heavier aircraft, compaction control for base and subbase layers should be based upon ASTM D 

698, Test Method for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft3

 [600 kNm/m3

]). 

d. Stabilized Base and Subbase. Stabilized base and subbase courses may be used in light-load 

pavements. Reduced thicknesses of base and subbase may result. Thickness equivalencies for stabilized materials are 

given in Chapter 3. 

125
AC 150/5320

-6D 7/7/95 RUNWAY AND TAXIWAY WIDTHS IN ACCORDANCE WITH APPROPRIATE ADVISORY CIRCULARS. TRANSVERSE SLOPES IN ACCORDANCE WITH APPROPRIATE ADVISORY CIRCULARS. SURFACING, BASE, PCC, ETC., AS REQUIRED. MINIMUM 12" (30cm) TYPICAL [ UP TO 30" (76cm) ALLOWABLE FOR SLIP - FORMED PCC] RUNWAY 

TAXIWAY 

TAXIWAY ALL PAVEMENT AREAS SAME THICKNESS " T " 

PCC 

SUBBASE 

BASE

SUBBASE

SURFACE 

12" 

(30cm) 

12" 

(30cm) 

3 2 

4 

PAVEMENT WIDTH 

1 

1 

2 

3 

4 

FIGURE 5-1. TYPICAL SECTIONS FOR LIGHT AIRCRAFT PAVEMENTS

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6/3/02 AC 150/5320-6D CHG 2

d. Example. As an example of the use of Figure 5-2, assume a pavement is to be designed for the 

following conditions: 

Aircraft gross weight = 24,000 pounds (10,900 kg) 

Subgrade CBR = 7.5 

(1) Total Pavement Thickness. Enter the upper abscissa of Figure 5-2 with the subgrade CBR 

value of 7. Make a vertical projection downward to the aircraft gross weight line of 24,000 pounds (10,900 kg). At the 

point of intersection of the vertical projection and the aircraft gross weight line, make a horizontal projection to the 

pivot line. At the point of intersection of the horizontal projection and the pivot line, make a vertical projection down to 

the lower abscissa and read the total pavement thickness required, in this example 12.3 inches (312 mm). 

(2) Thickness of Surfacing and Base. To determine the thickness of surfacing and base, 

proceed as in the steps above using a CBR value of 20. In this example, a thickness of 6.7 inches (170 mm) is read on 

the lower abscissa. This represents the combined thickness of surfacing and base. 

(3) Final Design Section. The design section would thus consist of 2 inches (50 mm) of hot mix 

asphalt surfacing, 5 inches (102 mm) of base, and 6 inches (152 mm) of subbase. Should difficulties be anticipated in 

compacting the 5-inch (102-mm) base course, the base course thickness should be increased. The thickness increase can 

be accomplished by substituting some of the subbase material with base course. If base material is substituted for 

subbase material, a thickness credit can be taken. The thickness credit should be determined using the equivalency 

factors given in Table 3-7. 

e. Omission of Hot Mix Asphalt Surfacing. Under certain conditions, it may be desirable to utilize a 

bituminous surface treatment on a prepared base course in lieu of hot mix asphalt. In such instances, the strength of the 

pavement is furnished by the base, subbase, and subgrade. Additional base course thickness will be necessary to make 

up for the missing surface course. Additional base should be provided at a ratio of 1.2 to 1.6 inches (30 to 41 mm) of 

base for each 1 inch (25 mm) of surfacing. 

f. Full-Depth Asphalt Pavements. Pavements to serve light aircraft may be constructed of full-depth 

asphalt using the criteria specified in paragraph 322. The Asphalt Institute has published guidance on the design of full 

depth asphalt pavements for light aircraft in Information Series No. 154, Full Depth Asphalt Pavements for General 

Aviation. Use of the Asphalt Institute method of design for full-depth asphalt pavements requires approval on a case-bycase basis. 

g. Local Materials. Since the base and subbase course materials discussed in Chapter 3 are more than 

adequate for light aircraft, full consideration should be given to the use of locally available, less-expensive materials. 

These locally available materials may be entirely satisfactory for light-load pavements. These materials may include 

locally available granular materials, soil aggregate mixtures, or soils stabilized with portland cement, bituminous 

materials, or lime. The designer is cautioned, however, if the ultimate design of the pavement is greater than 30,000 

pounds (13,000 kg), higher quality materials should be specified at the outset. 

504. RIGID PAVEMENT MATERIALS. Rigid pavements for light aircraft are composed of Portland cement 

concrete surfacing, subbase, and prepared subgrade. The functions of these layers and applicable specifications are 

discussed below: 

a. Portland Cement Concrete. Specifications concerning the quality and placement of Portland cement 

concrete should be in accordance with Item P-501, Portland Cement Concrete Pavement. Local state highway 

specifications for paving quality concrete may be substituted for Item P-501 if desired. 

b. Subbase. Rigid pavements designed to serve aircraft weighing between 12,500 pounds (5,700 kg) and 

30,000 pounds (13,000 kg) will require a minimum subbase thickness of 4 inches (100 mm) except as shown in Table 3-

4 of Chapter 3. No subbase is required for designs intended to serve aircraft weighing 12,500 pounds (5,700 kg) or less, 

except when soil types OL, MH, CH, or OH are encountered. When the above soil types are present, a minimum 4-inch 

(100-mm) subbase should be provided. The materials suitable for subbase courses are covered in Item P-154, Subbase 

Course. 

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AC 150/5320-6D CHG 2 6/3/02 

c. Subgrade. Subgrade materials should be compacted in accordance with Item P-152 to the following 

depths. For cohesive soils used in fill sections, the entire fill shall be compacted to 90-percent maximum density. For 

cohesive soils in cut sections, the top 6 inches (150 mm) of the subgrade shall be compacted to 90-percent maximum 

density. For noncohesive soils used in fill sections, the top 6 inches (150 mm) of fill shall be compacted to 100-percent 

maximum density, and the remainder of the fill shall be compacted to 95-percent maximum density. For cut sections in 

noncohesive soils, the top 6 inches (150 mm) of subgrade shall be compacted to 100-percent maximum density and the 

next 18 inches (460 mm) of subgrade shall be compacted to 95-percent maximum density. For treatment of swelling 

soils refer to paragraph 3-14. 

505. RIGID PAVEMENT THICKNESS. No design curves for light-duty rigid pavements are presented since 

there are only two thickness requirements. Rigid pavements designed to serve aircraft weighing 12,500 pounds (5,700 

kg) or less should be 5 inches (127 mm) thick. Those designed to serve aircraft weighing between 12,501 pounds (5,700 

kg) and 30,000 pounds (13,000 kg) should be 6 inches (150 mm) thick. 

a. Jointing of Light Load Rigid Pavements. The maximum spacing of joints for light-load rigid 

pavements should be 12.5 feet (3.8 m) for longitudinal joints and 15 feet (4.6 m) for transverse joints. Jointing details 

are shown in Figure 5-3. Note that several differences exist between light-load and heavy-load rigid pavement joints. 

For instance, butt-type construction and expansion joints are permitted when an asphalt or cement stabilized subbase is 

provided. Also, half-round keyed joints are permitted even though the slab thicknesses are less than 9 inches (230 mm). 

Odd-shaped slabs should be reinforced with 0.05 percent steel in both directions. Odd-shaped slabs are defined as slabs 

that are not rectangular in shape or rectangular slabs with length-to-width ratios that exceed 1.25. Two recommended 

joint layout patterns are shown in Figure 5-4 for 60-foot (18-m) and Figure 5-5 for 50-foot (15-m) wide pavements. 

The concept behind the jointing patterns shown is the creation of a “tension ring” around the perimeter of the pavement 

to hold joints within the interior of the paved area tightly closed. A tightly closed joint will function better than an open 

joint. The last three contraction joints and longitudinal joints nearest the free edge of the pavement are tied with #4 

deformed bars, 20 inches (510 mm) long, spaced at 36 inches (1 m) center to center. At the ends of the pavement and in 

locations where aircraft or vehicular traffic would move onto or off the pavement, a thickened edge should be 

constructed. The thickened edge should be 1.25 times the thickness of the slab and should taper to the slab thickness 

over a distance of 3 feet (1 m). 

The intent of this paragraph is to allow the use of the tension ring design but limit it to pavements less than 60 feet in 

width. Also, the use of the half-round keyway is limited to those pavements utilizing the tension ring concept. Use of 

the half-round keyway as a standard construction joint is not acceptable in pavements that do not use the tension ring 

concept. 

Pavements that do not use the tension ring design should be designed in a manner similar to Chapter 3. The designer is 

reminded that the use of any type of keyway is not permitted in pavements less than 9 inches thick (except with the 

tension ring concept). The general recommendations of Table 3-10A may be employed for Chapter 5 pavements not 

using the tension ring concept; however, the designer should note that the joint designations and steel sizes and spacing 

discussed in Chapter 5 are different those in Chapter 3. 

506. AGGREGATE TURF. Aggregate-turf differs from normal turf in that the stability of the underlying soil is 

increased by the addition of granular materials prior to establishment of the turf. The objective of this type of 

construction is to provide a landing areas that will not soften appreciably during wet weather and yet has sufficient soil 

to promote the growth of grass. Aggregate-turf should be considered only for areas designed to serve aircraft having 

gross weights of 12,500 pounds (5,700 kg) or less. 

a. Materials. Construction details and material requirements are covered in Item P-217, Aggregate-Turf 

Pavement. A minimum CBR of 20 is recommended for aggregate-soil layers. 

b. Thickness. The thickness to be stabilized with the granular materials varies with the type of soil and 

the drainage and climatic conditions. The total thickness of aggregate stabilized soil should be read directly from the 

thickness scale of Figure 5-2 using the CBR of the subgrade, (disregard the note concerning the surfacing course). 

507. OVERLAYS. Overlays of pavements intended to serve light aircraft are designed in the same manner as 

overlays for heavy aircraft. 

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6/3/02 AC 150/5320-6D CHG 2

508. HELIPORT/VERTIPORT DESIGN. The guidance contained in paragraph 500 of this section is appropriate 

for pavements designed to serve rotary-wing aircraft. Where direct thermal effects of jet blast is a concern (e. g., at 

vertiports serving tiltrotor traffic), incorporation of unique pavement formulations specific to thermal resistance may be 

required. Any pavement that is subjected to the direct thermal effects of high temperature exhaust gases can become 

progressively damaged with repeated thermal cycles, resulting in surface spalling, a potential for foreign object damage 

(FOD), as well as subsequent deterioration of the affected slab. An example formulation for thermal resistant pavement 

can be found in TR-2079-SHR, Development of Mix Designs for F/A-18 Resistant Pavement Systems, Naval Facilities 

Engineering Service Center, July 1997. 

130-1
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CHG 2 

FIGURE 5-3. -LOAD RIGID PAVEMENT

131

6/3/02 AC 150/5320-6D 

JOINTING DETAILS FOR LIGHT
6/3/02

Rod Backup 

Material

Sealant Material 1/4" - 3/8" 

(6-10mm) Below Surface

1 1/4" (32mm)

Minimum

W

D

DETAIL 3

CONSTRUCTION JOINT

Sealant Material 1/4" - 3/8"

(6-10mm) Below Surface

1 1/4" (32mm)

Minimum

Rod Backup Material

DETAIL 2

CONTRACTION JOINT

D

W

T/4±1/4"

(±6mm)

3/4"±1/8"

(19±3mm)

Sealant Material 1/4" - 3/8" 

(6-10mm) Below Surface

Non-Extruding Premolded Compressible 

Material 

1/4" (6mm) Radius

or Chamfer

DETAIL 1

EXPANSION JOINT

3/4"±1/8"

(19±3mm)

NOTES:

1. 

W/D. 

DIFFERENT SHAPE FACTORS FOR OPTIMUM PERFORMANCE.

2. 

SEALANT USED AND SIZED TO PROVIDE THE DESIRED SHAPE 

FACTOR.

Rod Backup Material

Key Centered

at T/2 for type 

H and HT

0.1 T

Figure 5-4. -LOAD RIGID PAVEMENT (CONT.)

132

AC 150/5320-6D CHG 2 

ASTM D-1751 or 1752

SEALANT RESERVOIR SIZED TO PROVIDE PROPER SHAPE FACTOR, 

FIELD POURED AND PREFORMED SEALANTS REQUIRE 

ROD BACKUP MATERIAL MUST BE COMPATIBLE WITH THE TYPE OF 

JOINTING DETAILS FOR LIGHT
7/7/95 AC 150/5320-6D

3 4 5 6 7 8 9 11 13 16 20

F10 F9 F8 F7 F6 F5 F4 F3 F2 F1 Fa 

SUBGRADE CLASS 

FIGURE 6-1. CBR -- FAA SUBGRADE CLASS COMPARISONS 

(1) Subbase and Base Equivalencies. Equivalency factor ranges shown in Tables 3-6 through 3-9 

for subbase and base are recommended for evaluation purposes. The actual value selected will depend on the 

composition, quality, and condition of the layer. In instances where experience or physical test results show that other 

values are valid, they may be used in lieu of the values recommended here. Subbase or base courses should not be 

assigned a higher equivalency factor than a layer above it in the pavement structure. Conversion of material to a higher 

classification, such as subbase to base, will not be permitted, except where excess stabilized base course (P-401or P-304) 

exists immediately under a flexible surface; in this instance, the stabilized material may be counted as an equal thickness 

of surface. 

(2) Surfacing. Broken hot mix asphalt surface course (shrinkage cracks due to age and 

weathering, without evidence of base failure) shall be evaluated as an equal thickness of nonstabilized base. A hot mix 

asphalt surface, with limited cracking and well maintained, may justify use of an equivalency between the limits noted. 

603. APPLICATION OF FLEXIBLE PAVEMENT EVALUATION PROCEDURES. After all of the evaluation 

parameters of the flexible pavement have been established using the guidance given in the above paragraphs, the 

evaluation process is essentially the reverse of the design procedure. The design curves presented in Chapter 3 or 5 are 

used to determine the load-carrying capacity of the existing pavement. Required inputs are subgrade and subbase CBR 

values, thicknesses of surfacing, base, and subbase courses; and an annual departure level. Several checks must be 

performed to determine the load-carrying capacity of a flexible pavement. The calculation that yields the lowest allowable 

load will control the evaluation. 

a. Total Pavement Thickness. Enter the lower abscissa of the appropriate design curve in Chapter 3 or 5 

with the total pavement thickness of the existing pavement. Make a vertical projection to the annual departure level line. 

For light-load pavements, Chapter 5, a single pivot line is used. At the point of intersection between the vertical 

projection and the departure level line, or a single pivot line in the case of light-load pavements, make a horizontal 

projection across the design curve. Enter the upper abscissa with the CBR value of the subgrade. Make a vertical 

projection downward until it intersects with horizontal projection made previously. The point of intersection of these two 

projections will be in the vicinity of the load lines on the design curves. An allowable load is read by noting where the 

intersection point falls in relation to the load lines. 

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AC 150/5320-6D CHG 2 6/3/02 

b. Thickness of Surfacing and Base. The combined thickness of surfacing and base must also be checked 

to establish the load-carrying capacity of an existing flexible pavement. This calculation requires the CBR of the subbase, 

the combined thickness of surfacing and base, and the annual departure level as inputs. The procedure is the same as that 

described in subparagraph a above, except that the subbase CBR and combined thickness of surfacing and base are used to 

enter the design curves. 

c. Minimum Base Course Thickness. The thickness of the existing base course should be compared with 

the minimum base course thicknesses in Table 3-4 or Figure 5-2. Notice that the minimum base course thickness is 4 

inches (100 mm) for heavy-load pavements and 3 inches (75 mm) for light-load pavements. If there is a deficiency in the 

thickness of the existing base course, the pavement should be closely monitored for signs of distress. The formulation of 

plans for overlaying the pavement to correct the deficiency should be considered. 

d. Minimum Surface Thickness. The thickness of the existing surface course should be compared with 

that shown on the appropriate design curve. If the existing surface course is thinner than that given on the design curve, 

the pavement should be closely observed for surface failures. It is recommended that correction of the deficiency in 

surfacing thickness be considered. 

604. RIGID PAVEMENTS. Evaluation of rigid pavements requires, at a minimum, the determination of the 

thickness of the component layers, the flexural strength of the concrete, and the modulus of subgrade reaction. 

a. Layer Thicknesses. The thickness of the component layers is sometimes available from construction 

records. Where information is not available or of questionable accuracy, thicknesses may be determined by borings or test 

pits in the pavement. 

b. Concrete Flexural Strength. The flexural strength of the concrete is most accurately determined from 

test beams sawed from the existing pavement and tested in accordance with ASTM C 78. Quite often this method is 

impractical as sawed beams are expensive to obtain and costs incurred in obtaining sufficient numbers of beams to 

establish a representative sample is prohibitive. Construction records, if available, may be used as a source of concrete 

flexural strength data. The construction data will probably have to be adjusted for age as concrete strength increases with 

time. Strength-age relationships can be found in Portland Cement Association, Engineering Bulletin, Design of Concrete 

Airport Pavement. 

(1) Correlations With Other Strength Tests. Correlations between concrete flexural strength 

and other concrete strength tests are available. It should be noted that correlations between flexural strength and other 

strength tests are approximate and considerable variations are likely. 

(i) Tensile Split Strength. An approximate relationship between concrete flexural 

strength and tensile splitting strength (ASTM C 496) exists and can be computed by the following formula: 

R = 1.02( T ) + 117 

Where: 

R = flexural strength, psi. 

T = tensile split strength, psi. 

Note: For conversions in metric units, the above formula remains the same, except the +117 psi constant 

should be changed to +0.81 Mpa. 

(ii) Compressive Strength. Flexural strength can be estimated from compressive strength 

(ASTM C 39) using the formula below: 

R = 9 ' 

c f 

Where: 

R = flexural strength ' f = compressive strength c

138