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Airfield PavementsConcrete Joints & Joint Sealing

GUIDANCE N O T E S

1



In an un-reinforced rigid pavement a regular arrangement of

joints are required in the concrete slab. These joints serve a

number of purposes; the main ones being to control cracking

due to restrained shrinkage in the concrete after laying, to

divide the pavement into suitably sized sections for ease of

laying and then to accommodate any slab movement and

cracking due to thermal and moisture effects in the slab

(Reference 9).

A well-designed pavement joint will adequately control cracking, as well

as providing a degree of load transfer between the adjoining slabs.

It will also be designed in such a way as to prevent the ingress of

foreign objects into the joint.

The Britpave Airport Task Group has prepared this Guidance Note

relating to the design, specification, construction, maintenance and

performance of airfield pavement concrete joints in the UK.

As part of the development of this Guidance Note, questionnaires were

sent out to a number of airfield operators to ascertain current practice

and issues of concern and scope for improvement on matters relating to

concrete joints and we would like to thank those who kindly responded.

1. Introduction

2.1 Joint Types

In the UK, the majority of concrete airfield pavements are in plain un-

dowelled, un-reinforced Pavement Quality (PQ) Concrete. There are

three principal types of joints, namely:

• Expansion joints,

• Transverse (or contraction) joints, and

• Longitudinal (or construction) joints.

2.2 Purpose of Pavement Joints

As outlined above, the principle purpose of these joints are as follows:

• To control shrinkage induced cracking after laying,

• To accommodate the contraction and expansion of the slab

resulting from temperature and moisture changes

• To enable load transfer between slabs longitudinally and

transversely,

• Provide a natural break between two paving sessions.

2.3 Joint Design

The majority of concrete pavements in the UK are designed in accordance

with either the PSA (Reference 1) or BAA (Reference 2) methods.

2.4 Load Transfer

Load transfer at transverse joints is provided at aggregate interlock,

though to improve load transfer of both longitudinal and transverse

joints in plain PQ Concrete pavements a number of techniques are used

and these include:

• Dowels

• Tie Bars

• Sinusoidal

• Keys

• Thickened Edges

For guidance on the use of dowels in concrete pavements refer to

Section 5.7 of PSA Guide (Reference 1). Details of thickened edges are

contained in References 5 and 15.

It should be noted that experience has shown that keyed joints do not

perform adequately for high volume medium and heavy loads inpavements constructed on low and medium strength subgrades

(References 5 and 15).

2. Concrete Joint Types and Joint Design

All faces to be cleaned and primed

Saw cut (3 wide as detailed

in table) to be finalised by

Contractor following site trials.prior to the installation of joint

sealant, as described in Section 11.13

Bond breaker tape

1 5

5

Joint sealant to BS2499 type F1 or

BS5212 type F (recess for sealant

to be formed by sawing), as

described in Section 11.

Pavement surface

Finish both sides

with bullnose not exceeding 5mm radius

Coat of bitumen emulsion

complying with BS 434

Figure. 3.1: Sealed Transverse Joint (BAA) Figure. 3.2: Longitudinal Unsealed Butt Joint (PSA)

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Guidance Notes



All faces to be cleaned and primed

prior to the installation of joint

sealant, as described in Section 11.

Formed edge

13

Bond breaker tape

1 5

5

Joint sealant to BS2499 type F1 or

BS5212 type F (recess for sealant

to be formed by sawing), as

described in Section 11.

Pavement surface

Saw cut depth 40mm or

one fifth depth of slab which ever is greater

Induced Crack

Saw cut 3mm maximum width

Figure. 3.3: Longitudinal Joint (BAA) Figure. 3.4: Unsealed Transverse Joint (DE)

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3.1 Joint Details

Guidance on the size, details and spacing of concrete joints is given in

the following documents:

• Defence Works Functional Standard Specification 033 “Pavement

Quality Concrete for Airfields” (1996), and in particular:

- Section 5.7 Layout of Joints

- Section 5.20 Expansion Joints

- Section 5.21 Construction Joints

- Section 5.27 Contraction Grooves

- Section 5.29 Sealing of Expansion Joints

- Figure 5.1 – Details of Joints (Sheet 1)

- Figure 5.2 - Details of Joints (Sheet 2)

- Appendix C – Tests for Manufactured Joint Fillers

• PSA Design Guide Section 5.3 and Figures 14 to 21 (Reference 1),

• US FAA AC150/5320-6D Sections 337 to 341 (Reference 5).

• BAA Standard Detail Drawings.

Examples of typical joint details currently in use are shown in Figures

3.1, 3.2, 3.3 and 3.4 (reproduced from References 1 & 3 and BAA Standard

Detail Drawings).

3.2 Joint Spacing

Typically, the spacing of longitudinal and transverse joints in the UK isbetween 3 and 7.5 metres. The actual spacing is a function of slab

thickness, slab support, radius of relative stiffness, temperature and

construction technique. US practice has found that joint spacing

between 4 to 6 times the radius of relative stiffness perform

satisfactorily on a stabilised sub-base. (Reference 5 - Section 337 (b)).

The radius of relative stiffness is a measure of a concrete slab’s

resistance to deformation, and is defined as:

l = [ (E.h3) / (12.k.(1- 2)) ] 0.25

where: l = the radius of relative stiffness

E = the Young’s Modulus

h = the slab thickness

k = the modulus of subgrade reaction, and

= the Poisson’s ratio for concrete.

US military practice is to limit the maximum size of slabs to between

6.1 and 7.6m for slab thickness in excess of 300mm (Reference 15).

Other factors determining the spacing of concrete joints include:

• Pavement horizontal geometry,

• Structural design of the pavements,

• The type of coarse aggregate used in the concrete - more

specifically the coefficient of thermal expansion of the aggregate.

• Aspect ratio - bays to be ideally square (typically, the maximum

aspect ratio is limited to 1.5:1 (Reference 3) or 2:1 (BAA)). Where

unavoidable, “odd” shaped bays should be reinforced with a layer

of steel mesh.

• Changes of pavement type and thickness,

• Pavement ridge and valley lines,

• Differential settlement,

• Construction phasing,

• Limits and capabilities of construction paving plant and methods

of construction,

• Maintaining consistent slab widths as far as possible in each

construction phase,

• Direction of laying,

• Location of AGL Fittings (bay joints typically offset by some

1000mm from the fittings),• Pavement penetrations (e.g. slot drains, pits, manholes, fuel

hydrants, maintenance access shafts, etc) – ideally this should fit

in to the slab layout

• Location and type of surface water drainage system adopted (e.g.

edge slot drain, inset valley with gullies, etc).

Detailing of the bay layout will also take account of the following:

• Irregular edge bays - aspect ratio - (maximum 2:1)

• Included angle - minimum 60° (Reference3) and minimum 80°

(BAA).

• Minimum length of joint - 1.0m (Reference 3 and BAA).

3. Concrete Joint Details


Guidance Notes



4.1 Aggregate Types

Typically in the UK, PQ Concrete is now manufactured using crushed

rock coarse aggregate, such as limestone and basalt. Prior to the early

1990s, flint and gravel coarse aggregate was used, due to its local

availability, particularly in the south-east of England. The use of flint

and gravel waned after this time, mainly due to the fact that concrete

slabs using these coarse aggregate could not be readily sawn (without

“plucking”). As flint and gravel has a higher coefficient of thermal

expansion this leads to greater movement/higher stresses within the

slab in hot weather than an identical slab with a lower coefficient, such

as one using limestone coarse aggregate.

4.2 Transverse Joints

Transverse, or contraction, joints are primarily used to relieve tensile

stresses due to the thermal contraction and warping of the concrete

slab. The joint is commonly left un-dowelled; aggregate interlock being

generally sufficient to transfer load between the slabs, especially if a

stiff base layer is being used, such as lean concrete. If load transfer is

felt to be critical in the pavement and dowels are to be used, then one

end of the dowel bar should be lubricated to allow the longitudinal

movement of the slabs relative to one another (Reference 13).

For concrete with crushed rock coarse aggregate, transverse joints aretypically formed by sawing the concrete some 8-24 hours after placing,

a time when the concrete is still “green” and easy to saw, but is

sufficiently set to prevent marking of the surface or the dislodging of

coarse aggregate by the sawing process. The exact timing is a function

of concrete mix, slab depth, temperature, use of slip membrane etc.

The sawing of transverse joints is used in preference to wet forming

the joints at the time of laying as wet-forming joints has been found to

generate a number of problems on site, such as the over-working of

adjacent concrete and consequential joins spalling (Reference 1).

The initial saw cut is typically some 3mm wide and typically, a quarter

or a fith of the PQ Concrete slab depth. If the joints are to be sealed,

these are typically widened to 13mm for a depth of 20mm to form the

sealant recess/reservoir (see Figure 4.1). The actual size of the recess

is dependent on the sealant used and consequently, the manufacturers

specific product recommendations on width-to-depth ratio should be

followed.

For concrete using flint coarse aggregate, the joints are typically

formed by the use of plastic (or timber) crack inducers, though recent

developments in “soff-cut” saw technology has allowed flint aggregate

concrete to be sawn, as soon as, the concrete has sufficiently hardened

to accommodate pedestrian loading.

4.3 Longitudinal Joints

Longitudinal, or construction joints are typically vertical joints and areformed by either fixed forms or slip forming. These joints are used at

a transition between concrete slabs, such as at the end of a day’s

construction and between alternate rows of slabs (Reference 13). The

spacing of longitudinal joints is usually the same as the spacing of the

transverse joints as the effect of warping and wheel load effects has

been seen to be reduced in square bays (Reference 1).

During the late 1990s, longitudinal joints with sinusoidal profiles have

been trialled at a number of UK civil airports to improve load transfer

(see Figure. 4.2) and their performance is currently under review.

The vertical face is typically coated with bitumen emulsion after initial

curing is complete. Widening and sealing of longitudinal joints on civil

airfields is current common practice, details of which are shown in

Figure 3.3

4.4 Expansion Joints

As their name suggests, expansion joints are provided to

accommodate the expansion of the concrete due to thermal effects. In

pavements over 250mm thick, expansion joints are not generally

required, though may be needed in certain circumstances. General

guidance on the spacing of expansion joints is contained in Section 5

of the PSA Design Guide (Reference 1). Expansion joints are alsotypically provided around pavement intrusions and major changes in

the direction of paving.

4. Concrete Joint Construction

Figure. 4.1: Joint Recess Sawing Figure. 4.2: Vertical Sinusoidal Joint

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Guidance Notes



Joint finished

with bullnose

not exceeding

5mm radius

Joint to be fitted flush with

surface level in summer &

autumn and 6mm below

surface level in winter & spring

Manufactured

joint filter board

Hot poured joint seal Cold poured joint seal

Separator

Membrane

Separator

Membrane

25mm

Figure. 4.3: Undowelled expansion joint with hot or cold poured joint sealant

P.4

Expansion joints are typically formed against already cast vertical

faces. A filler board of some 25mm width is provided against the

vertical face of the pavement intrusion or concrete slab (and lean

concrete base). In the case of slip formed pavements, recent practice

has been to form the expansion joint by full depth saw cutting of the

finished concrete and subsequent installation of the filler board.

Care must be taken with selection of the filler board width, as a 25mm

board will accommodate more expansion than a 13mm board and so

the spacing between expansion joints can be greater. There are three

main types of filler board typically used in the UK:

• Bitumen impregnated fibreboard

• Closed cell polyethylene filler board

• Cork based filler board

Each of the above have relative merits and, consequently, the choice

should be made on economic and performance grounds.

Expansion joints are typically sealed. Expansion joint details are

typically as shown in Figure 4.3 below. It should be noted that whilst

not current UK practice, US practice is to provide slab thickenings

either side of an expansion joint (References 5 and 15).


Guidance Notes

In the UK, it has been common practice to seal concrete joints on civil

airfields. However, based on experience from military airfields in the

UK, where the policy is not to seal new longitudinal and transverse

joints (unless the airfield overlies an aquifer), it is understood that a

number of airport operators are now questioning the need and benefits

in sealing joints in new concrete pavements. If joints are not sealed, thelongitudinal joint should be finished with a radiussed arris to reduce the

risk of spalling. Transverse joints with a width of over 5mm (i.e. a 3mm

saw cut and a 2mm joint opening) should be sealed.

The purpose of sealing the joints has typically been to:

• Prevent water ingress leading to damage of the pavement

foundation,

• Prevent the ingress of “harmful” liquids, such as fuel and de-icers

from entering groundwater,

• Preventing the ingress of grit, small stones and other debris which

may inhibit the performance of the joint and cause spalling orresult in a “blow-up”.

A number of different types of joint sealant have been used, each with

their own attributes in terms of ease of installation, cost, life

expectancy, performance and H&S issues. Joint sealants used in

concrete pavements are typically fuel resistant in nature and in certain

circumstances are flame resistant. In the case of expansion joints,

sealants should be carefully selected to accommodate the movementanticipated.

Concrete joint sealant types include:

• Hot poured to BS2499 – typically elastomeric, pitch PVC based.

Some sealants to BS2499 have had service problems.

• Hot poured to American ASTM - requires standard pitch in the

sealant. Hot-poured sealants to the ASTM generally perform better

than those to BS2499.

• Cold poured to BS5212 – typically elastomeric one and two part

pitch polyurethane or polysulphide,

• Silicone seals,• Neoprene compression seals,

• Self expanding cork,

• Neoprene expanding foam.

5. Concrete Joint Sealing



Historically, hot and cold poured fuel resistant elastomeric joint

sealants, other than compression seals, perform well for between 5

and 10 years. The life and performance of the sealant is highly

dependent on the preparation of the joint surfaces, the age of the

concrete at the time of sealing, the temperature and movement range

of the concrete. Recent Health and Safety concerns have resulted in

the declining use of pitch based joint sealant products.

Based on feedback from a number of airport operators, the resealing

of joints is not always their highest maintenance priority and some

airports do not reseal joints due to lack of maintenance funds. The

cost of joint resealing varies but typically is £5 -10 per linear metre.

Recesses for joint sealants should be formed to the dimensions

recommended by the sealant manufacturer. Typically, in the UK

transverse and longitudinal joint sealant recesses are 13mm wide and

20mm deep and the joint sealant is finished 5mm below the surface.

Figure. 6.2: Joint and Corner Spalls Figure. 6.3: Corner Spalls Figure 6.4: Corner Spalls

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Guidance Notes

The most common concrete joint failures in the UK are:

• Edge spalling – typically caused by manual over-working of

longitudinal joints and/or late saw cutting of transverse joints.

• Durability (D) cracking.

• Debonding joint sealant, due to poor preparation and also age

hardening of the joint sealant.

• Excessive extrusion of the sealant, due to compression of the joint

(or overfilling of the joint reservoir in winter months).

• Tearing of the sealant, due to expansion of the joint (usually,

where the spacing between expansion joints is too great).

Typical examples of some of the above defects are shown below:

6. Concrete Joint Failures



P.6


Guidance Notes

The following documents provide useful details on the design,

construction and maintenance of concrete joints.

1. Property Services Agency (PSA) “A Guide to Airfield Pavement

Design & Evaluation” (1989).

2. BAA plc “Pavement Design Guide for Heavy Aircraft Loading” (1993).

3. Defence Works Functional Standard Specification 033 “Pavement

Quality Concrete for Airfields” (1996).

4. Defence Works Functional Standard 06 “Guide to Airfield

Pavement Maintenance” (1994) – Section 4 “Maintenance of

Concrete Pavements”.

5. US Federal Aviation Administration (FAA) AC150/5320-6D “Airport

Pavement Design & Evaluation” (1995).

6. US Federal Aviation Administration (FAA) AC150/5370-10A

“Standards for Specifying Construction of Airports Item P-501

Portland Cement Concrete Pavement”.

7. US Federal Aviation Administration (FAA) AC150/5380-6 “Guidelines

and Procedures for Maintenance of Airport Pavements”.

8. American Concrete Pavement Association “Joint and Crack

Sealing and Repair for Concrete Pavements” (1995).

9. Packard, R.G. - “Design of Concrete Airport Pavement”, Portland

Cement Association (1973).

10. Concrete Society TR 45 “Mechanised Construction of Concrete

Pavements & Ancillary Works” (1996).

11. Highways Agency / Britpave “Concrete Pavement Maintenance

Manual” (2001).

12. Shober, S.F. “The Great Unsealing - A perspective on PCC Joint

Sealing”.

13. Yoder, E.J. “Principles of Pavement Design”. John Wiley and Sons,

Inc. (1959).

14. TRL RR349 “The Performance of Joint Sealants in Concrete

Pavements” (1992).

15. US Army / Air Force Technical Manual “Rigid Pavements for

Airfields” TM 5-825-3 / AFM 88-6, Chap. 3 (August 1988)

7. References & Publications

The Britpave Technical Committee would like to thank John Cairns (TPS

Consult), Paul Mallows (TPS Consult) and Richard Moore (TPS Consult)

for their assistance in the preparation of this Guidance Note and

to Andy Delchar (Amec), Joe Quirke (SIAC), Graham Woodman (WSP)

and Tim Gibbs (Fitzpatrick) for their contribution to this Guidance Note

July 2002.

Further details on Britpave are available at

www.britpave.org.uk

8. Acknowledgements

11.8.1. 4.2.



Century House, Telford Avenue, Crowthorne, Berkshire RG45 6YS

Tel. 01344 725731 Fax. 01344 761214

www.britpave.org.uk

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