Joints for Concrete Pavements

8/9/2019 Joints for Concrete Pavements

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Joints for Concretepavements



Introduction

All concrete, once placed, will contract slightlyduring the curing process; this is the primary cause

of small surface cracks that appear during thecuring process. When set, concrete will expand

and/or contract slightly with ambient temperature.

Movement oints are also useful when layingconcrete within an area bounded by walls or

buildings, or when an obect such as a manhole

cover has to be incorporated within the slab, asthey allow the concrete to expand and/or contract

without transferring pressure onto the other

structures, causing cracks within the concrete

slab, or the wall, M! cover, etc..



Contants

INTRODUCTION

SPACING

TYPES

MATERIALSDOWELLED

EXPANSION

CONTRACTION

NON-DOWELLEDEXPANSION

CONTRACTION

CONSTRUCTION JOINTS





Types of Joint

• Expansion joints

• Contraction joints

• Construction joints



Expansion joints

E%$ansion "oints are usuall& a com$lete 34a$3

#et2een ad"acent #a&s+ i*e+ there is a de5nite#rea) in the concrete and an& reinorcin4 steelthat ma& #e $resent* Where ad"acent #a&s are3tied3 to4ether #& means o do2el #ars+ these

do2els are slee!ed in one o the #a&s to allo2e%$ansion to ta)e $lace 2ithout 4eneratin4stresses 2ithin the sla#*



C k l



Crack control joints

as some 2it once remar)ed+ 6There are onl& t2o

t&$es o concrete7 that 2hich has crac)ed+ andthat 2hich is a#out to crac)*6 Crac) control "ointsare a $artiall&-ormed contraction "oint that aimsto ensure that 2hen the concrete does crac)+ it

crac)s in a $redicta#le manner at a $reciselocation



Construction joints

Construction "oints can #e hori8ontal or !ertical

and are ormed 2hen $lacement o the concreteis interru$ted or some reason* It ma& #e the endo a da&3s 2or) or it ma& #e that some other 2or)needs to #e com$leted #eore resumin4 the

$lacement*



Materials for Concrete Joints

Flexible board: a fibrous, compressible, flexible board,such as "#lexcell", $t is cheap and readily

available from %uilders" merchants in pre&

cut strips of the re'uired depth, expressly

for creating expansion oints. $t istypically ()mm, )*mm or )+mm thick.

Dowels: **&-**mm long, )*&)mm in diameterand manufactured from rade )+* steel.

Sealants: hot poured, usually bituminous in origin.



Dowelled JointsWhere a large area is being covered with concrete, the slab is normally divided into

a number of bays and adacent bays are tied to each other by means of dowels,short lengths of steel bar embedded half in one bay and half in its neighbour.

$n alternate bay construction, the dowels

are positioned in the first bay and leftprotruding, to be concreted over whenthe second bay is poured.

0he dowels should be -**mm long and

manufactured from mild steel 1rade)+*2. $n expansion oints, the dowels are)+mm diameter at **mm centres, butfor contraction oints, the dowels may beslightly shorter, **mm in length and)*mm diameter, again at **mmcentres.



Dowelled Expansion Joints3xpansion 4oints consist of a flexible piece of compressible board, such

as "#lexcell", topped with a waterproof sealant and sandwiched betweenadacent bays or between the concrete slab and another fixed obect.

#or a dowelled expansion oint, thedowel should be de&bonded to half&

length to prevent it "sticking" to theconcrete and thereby limiting free

movement. $n heavy duty

applications, such as roadways, thede&bonded half is sleeved and

capped, or sheathed in plastic film,

to ensure free movement.



Dowelled Contraction JointsWith dowelled contraction oints,

again the dowels are de&bondedto one half. $n some cases, the

sleeving will extend into the first

bay so that when the completed oint is formed, the steel dowel isfully insulated from any water or

salts that may find their way into the oint.

5nce the first bay has hardened

sufficiently and the former and

shuttering has been removed,the second bay can bepoured.0he tight oint between

the adacent bays generates ahigh degree of interlock between

the aggregates.



Dowelled Control Joints

6owelled control oints 1dummy oints2 are most commonly used

on highway and airport runway

constructions, where continuousrun concrete trains are used and

the dowels can be automatically

inserted.A crack inducer at thebase of the concrete slab may be

incorporated and a "starter" ointcreated by sawing at a critical

point during the curing process orinsertion of a wet&former when

the concrete is placed.



on!dowelled Joints

Non-do2elled "oints tend onl& to #e ound inli4ht-use a$$lications+ such as residential

$aths+ $atios and dri!e2a&s* There is a 4oodar4ument or all "oints to #e do2elled unlessthere are e%tenuatin4 circumstances+ #ut site$ractice and tradition tends to ollo2 thesim$lest+ chea$est o$tion 2hen let to its o2nde!ices*



Expansion Joints7on&dowelled expansion oints

are not particularly commonbetween two new concrete

bays, but they are occasionally

encountered as the oint

between a new concrete slaband another fixed feature, such

as a wall, as the wall 1or otherfeature2 is not capable of being

dowelled.0his series of diagrams illustrates the

formation of an expansion ointbetween two new slabs, but the

same principles apply forconstructing an expansion ointbetween a wall and a slab.



Contraction Joints

8ontraction oints are thesimplest of oints in that they are

basically a break in the concrete

and the reinforcement created toallow the natural shrinkage of

concrete 1because of curing

and/or temperature change2 totake place without generating

crack&inducing tensile forceswithin the slab.0hey are formed

by embedding a )+9)+mm

timber or plastic oint&former intothe still wet concrete, thenremoving it once hardening has

taken place, and filling the void

with a suitable sealant.



Construction JointsAs mentioned above, 8onstruction 4oints are breaks in the continuity of

a concrete structure, rather than control features, such as 3xpansion,

8ontraction or 8rack 8ontrol 4oints, that is, they are there throughnecessity rather than because of any critical engineering consideration.

Simple Vertical Construction Joint

0he most common reason for theexistence of a 8onstruction oint is the

cessation of work for the day. 8onsider alarge slab that is being poured as part of a

road scheme: work cannot continue )hours per day, and so, when the end of a

working shift is reach, the pour comes to

an end, and this end, often known as a"top 3nd", "tunt 3nd" or "6ay 4oint",

needs to be relatively neat and tidy so that

work can be continued the following day,continuing on from the previous day"s top

3nd. 0he simplest form of a 8onstruction

4oint in such a scenario is shown opposite.



Joggle Joint

$n some situations, it may be

preferable to "lock together" the

slab across the construction oint insuch a way that shearing forces can

be transferred across the oint.5ften, this would be done bymeans of some form of dowelled

oint as described above, but analternative is to use what is known

as a "4oggle 4oint".With this type of construction oint,

a <trape=oidal key< is created in the

stop end by using a "former"attached to the stop end

shuttering.

http://www.pavingexpert.com/concjnt1.htm#dowexp

http://www.pavingexpert.com/concjnt1.htm#dowexp



Joint

0his type of construction oint is mostcommonly found in minor civil engineering

works. the example shown here is from

the construction of a manhole chamber.0he base concrete is placed first, and may

be left for a period of time or may havethe first chamber section placed andlevelled, or one or two courses of

engineering brickwork laid more or lessimmediately. ome time later, the channel

and its immediate haunching may be

placed, further chamber sections orbrickwork added as re'uired to bring up

the chamber to soffit level , and theexternal haunching concrete put in place.

0his will result is a simple, hori=ontal

construction oint at the interface of the

two phases of work.

http://www.pavingexpert.com/drain05.htm

http://www.pavingexpert.com/concjnt1.htm#01

http://www.pavingexpert.com/concjnt1.htm#01

http://www.pavingexpert.com/drain05.htm



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Joints for Concrete Pavements