Architectural Precast Joints

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ARCHITECTURAL PRECAST

CONCRETE JOINT DETAILS

Reported by

PCI Committee on Architectural PrecastConcrete Joint Details

Raymond J. SchutzChairman

James Engleҟlbert Litvin

James G. Grossҟ. L. Pare

Abraham Gutmanҟohn S. Parrish

J. A. Hansonҟrwin J. Speyer

Kai Holbekҟvan L. Varkay

Felix Kulkaҟloyd Wright

Correct joint design and proper selection of materials

and installation are vital for the successful

performance and esthetic appeal of precast concrete

wall systems. This report recommends the proper

precast concrete joint details and sealants for

specific situations. In writing these recommendations,

architectural treatment and economy in mold design

were considered but are not included, since these

are covered in the PCI Manual on Architectural

Precast Concrete. Following these recommendationswill result in a good design and a durable,

waterproof, and economical joint.

10



CONTENTSChapter1—Joint design.................................. 12

1.1cope1.2ypes of joints1.3eneral design concepts for

joints

1.4umber of joints

1.5ocation of joints

Chapter 2— Planning check lists........................... 142.1efinitions2.2

oint planning2.3ater runoff planning

Chapter3—Jointetails.................................. 153.1eneral3.2ne-stage joints3.3wo-stage joints3 .4avity wall3.5loor and roof slab joints

3.6recast parapets

3.7recast panel window details

Chapter 4— Sealant materials.............................. 244.1eneral4 .2ield-molded sealants and

their uses

4.3ccessory materials4 .4reformed sealants and

their uses4 .5omp ression seals and

their uses4 .6oint design

4 .7etermination of joint

movements and locations4.8election of butt joint widths

for field-molded sealants4.9election of butt joint shape

for field-molded sealants

4.10 Selection of size of compression

seals for butt joints4.11 Limitations on butt joint widths

and mo vements for various typesof sealants

4.12 Lap joint sealant thickness

References ............................................... 36

PCI Journal/March-A pril 1973 1



CHAPTER 1 —JOINT DESIGN

1.1Scope

The design of joints must be exe-

cuted as an integral part of the total

wall design. Some specific guidelines

for joints do govern their ultimate suc-

cess. This chapter highlights and illus-trates several cases of interdependence

with other wa ll design criteria.

In all cases, the designer should as-

sess his requirements for joints realisti-

cally with respect to both performance

and cost. If joint designs and details are

contemplated which differ from those

normally used in the area where the

project is located, local producersshould be consulted.

The following discussion will deal

mainly with joints which are designed

to accommodate local wall movements

only, rather than an accumulation of

such movements which would require

prope rly designed expan sion joints.

1.2 Types of joints

Joints between precast wall panels

may be divided into two basic types:

1. One-stage joints

2. Two-stage joints

A cavity wall design is considered a

further application of the two-stage

joint.

1.2.1 One-stage joints. As the name

implies, this joint has one line of de-

fense for its weatherproofing ability.

This occurs normally in the form of a

sealant close to the exterior surface.

The advantage of this type of joint is

that it generally provides the lowest

first cost, and it is suitable for use be-

tween precast panels as shown in Figs.

3.2.1 to 3.2.6.

The success of one-stage joints de-

pends on the quality of materials and

proper installation at the building site.This type of joint is in common use in

most of North America. One-stage

joints should be regularly inspected and

may demand fairly frequent mainte-

nance to rem ain weathertight.

1.2.2 Tw o -stage joints. These joints

have two lines of defense for weather-

proofing. The typical joint consists of arain barrier near the exterior face and

an air seal normally close to the interiorface of the panels. The rain barrier is

designed to shed most of the water

from the joint and the air seal is the de-

marcation line between outside and in-

side air pressures. Between these two

stages is an equalization or expansion

chamber which must be vented and

drained to the outside. Section 3.3 givestypical details of two-stage joints. It canbe seen that the simplest form of a hor-

izontal two-stage joint is the well prov-

en shiplap joint.

The rain barrier prevents most of the

rain and airborne water from entering

the joint. If airborne water (wind-driv-

en rain) penetrates this barrier, it will

drain off in the expansion chamber asthe kinetic energy is dissipated and the

air loses its ability to carry the water.

Any water which penetrates the rain

barrier should be drained out of the

joint by p roper flashing installations.

In order to avoid vertical movement

of the air in the expansion chamber

12



(stack effect) caused by wind or outsideair turbulences, it is advisable to use

these flashing details as dampers and

provide them at regularly spaced inter-

vals along the height of the verticaljoints. Such flashing is sometimes in-

stalled at each floor level, but a greater

spacing (two or three stories) may be

sufficient for low-rise buildings and in

areas with moderate w ind velocities.

Since the air seal is the plane where

the change in air pressures between the

outside and inside atmospheres occurs,

it would normally be subject to waterpenetration through capillary action.

Inasmuch as the outside air reaching

this seal has lost its water content, no

mo isture can enter by such action.

The danger of humidity traveling

from inside the building and through

the air seal should be investigated for

buildings with relatively higher interior

humidity, and for tall buildings, wherethe interior air pressure may occasion-

ally be substantially higher than the

outside atmospheric pressure. This con-

dition is normally solved by using a

cavity wall design.

A cavity wall (Fig. 3.4.1) is the most

effective wall for the optimum separa-

tion and control of both outside and in-

side air and humidity conditions. When

precast concrete wall panels are used in

cavity wall designs, they will normally

serve as the rain barrier. An air space is

maintained between the precast exteri-

or and the interior wall. Insulation,

when required, is applied to the outside

face of the interior wall, eliminating

condensation problems and, thereby,

making the inner wall subject only to

the relatively constant interior tempera-ture. Cavity wall construction is nor-

mally expensive when compared with

con vention al walls. On the basis of their

lower maintenance costs and their ex-

cellent performance records, they may

well be justified for specific types and

locations of buildings.

The two-stage joint is gaining accep-

tance particularly for buildings subject

to severe climatic exposure or tempera-

ture and humidity control.

A disadvantage of the two-stage jointfor concrete wall panels is the higher

cost. For projects with good repetitive

joint design properly integrated with

other panel details, and having efficient

production and erection procedures, it

may w ell approach the co st of one-stagejoint installations. In these instances,

the safety factors and lower mainte-

nance costs should also be considered.A minimum precast wall panel thick-

ness of 4 in. (10.2 cm) (with field-

molded sealants), preferably 5 in. (12.7

cm) (with gaskets and compression

seals), is required to accommodate both

the rain barrier and the air seal. For

two-stage joints with com pression seals,connection detail allowance should be

made for slight horizontal movementsof the panels after initial fastening for

air seal compression. 5 The joints must

be fully accessible from the inside of

the panels for later installation of the

air seal. The simp lest form of a horizon-tal two-stage joint is the shiplap joint.

1.3 General design conceptsfor joints

The purpose of joint design is to pro-

vide weathertightness of the joint con-

sistent with the exposure of the joint. In

addition, as part of the overall perfor-

mance requirements of the building,

the purpose for which the building is

built will also determine design require-ments for the joint.

Thus, joint design will be governed

by its expo sure (orientation and climaticconditions), the purpose of the building,and appearance. The following guide-

lines must all be evaluated in relation

to the relative importance of these cri-

teria.




4. Earthquake or other founda-

t ion mo vement5. Live load deflections6. Creep7. Other

2. Architectural (esthetic) considera-tions

A . Acc entuated jointingB. Hidden jointsC. Spacing (a few large or many

small)D. Environmental needs

1. Water control2. Air control (circulation)3. Temperature control

4. Noise (vibration con trol)3. Structural considerations

A. Elimination o f stress in structur-al materials through relief of al-

lowed movement.B. Design to resist movement

through the accumulation ofstress.

C. Location of expansion-contrac-

tion joints to maintain the struc-tural integrity.1. Expansion-contraction joints2. Construction joints3. Articulating joints

4. Mechanical considerations

A. Differential movement potential1. Differing coefficients of ex-

pansion

2. Differing heat absorptionrates

3. D iffering m oisture absorption

qualities

4. Differing exposure to heat or

moistureB. Isolation of vibrations

1. Internal (machinery or activ-

ity)2. ExternalC. Other

5. Material considerationsA. Field-molded sealants

1. Mastics2. Thermoplastics3. Thermosetting4. Accessory materials

B. Preformed se alants1. Rigid waterstops2. Flexible waterstops3. Gaskets

C. Other6. Tolerances

A. ProductionB . E re ctio nC. Adjacent construction

2.3 Water runoff planning

1. Resistance to penetrationA . SealB. Shape o f joint

2. Channelization of moisture and

discharge

A. Planned channelizing joints

(two-stage system)

B. Channelization of inadvertentor seepage penetration (one-

stage system)

CHAPTER 3-JOINT DETAILS

3.1 General

This chapter shows typical details forone-stage and two-stage joints, for floorand roo f slab joints, for prec ast conc reteparapets, and for windows in precast

concrete panels. The committee recog-

nizes that other details can be devel-

oped within the recommendations of

this report that will provide satisfactory

service. Thus, it is not intended that

these details be used to the exclusion of

all others, but rather that they be taken

to illustrate the features of good joint

planning and design.




3.2 One-stage joints

pP Pҟ.D.

b

p • P O

p' 6 a G DD 1 s p'

D

p Ɂ .' .ҟ 3/8°MIN.

.'D•

3/$MIN. VERTICALHORIZONTAL

JOINT WIDTHJOINT WIDTH ° • °p. ҟa• b.

pDp °P D.pɁD•., P

pɁpp

D `p o 'a 'p D • D

Fig. 3.2.1. Recessed vertical butt joint Fig. 3.2.2. Recessed horizontal butt joint

b •• : DV•°

pҟ , p

° v °_ ' 3/8" MIN.

•ҟ•-'ҟ JOINT WIDTH

.A

sD

ҟ, DMIN.

P '°JOINT WIDTH °ҟ D

aɁ

ep •' p ' ° e• '

•

D•

D• 0 '.p •p . p Q

°

'a

D Q D••

(1'12"

A.

° - X AX. SIZE

AGGREGATE OR 3/4 MIN.

Fig. 3.2.3. Flush butt joint Fig. 3.2.4. Recessed corner joint

D• D ,p,° Z _

•D D , p ^NN

'• D- 'd.

^'

a..a P3/8" MIN.

°a

P ' D ° aJOINT WIDTH

oaa o >

a p'

s D 4 . ^ v' e

Fig. 3.2.6. Joints in panels with narrow

Fig. 3.2.5. Corner joint detail ribs

16



3.3 Two-stage joints

AIR SEAL : CLOSED CELL SPONGE

NEOPRENE SQUARE STRIP OR ROPE1.5 TIMES THE THEORETICAL JOINTWIDTH

^4 ^2 IEXPANSIONCHAMBER

w

^D Via. ° rn a^

• d. .•d, •\\W K

^' d. Q • 'p

^N -0J^W Z

Wrf W

iD v

D , I /6 ^2 I/8 PERFORATED NNEOPRENE TUBE

EXTERIORҟAIN BARRIERFACE

4"MIN

1ҟҟr ,Aҟҟ

' a

• d pҟa d.

a

d d ^ d

AIRSEAL

(MIN. I /16"/ 1° )

Fig..3.1.wo-stageointertical Fig. 3.3.2. Two-stage joint horizontal

gaskets gasket

'2"MIN. z

• 1dҟ• O 1 ' 0Ɂ•. d

• D' D ҟҟҟҟ SEALANT(IF USED)MUST BE

DISCONTINUED AT INTERVALS

SEALANT DISCONTINUED(VERTICAL JOINTS) TO DRAIN

AT HORIZONTAL JOINT

AREA BETWEEN IT AND AIR SEAL

Fig..3.3.wo-stageointertical Fig, 3.3.4. Two-stage joint horizontal

sealants sealants

3.4 Cavity wall

INSULATION IF REQUIREDҟ'p I ° ,d

2 ҟj 2 „

SEALANT-ALTERNATE RAINBARRIERS(TUBE)

Fig. 3.4.1. H orizontal section through cavity w all

PCI Journal/March-April 19737



3.5 Floor and roof slab joints

PREFORMED ELASTOMER(STEEL REINFORCED)

p 4 Q .4 Q

..a •' D D

Fig. 3.5.1

MEMBRANE(OPTIONAL)

PREFORMED ELASTOMER(STEEL REINFORCED)

. 4 D D• D e

Fig. 3.5.2

STEEL PLATES

4 ` db, 4 , pp D

p, 0D 1. D D. 0 D• D •p'

O D

PREFORMED COMPRESSION SEAL NEOPRENE

(SOMETIMES COMBINED WITH P.V.C. SHEET

OR SHEET NEOPRENE SECONDARYSYSTEMS.)

Fig. 353 Fig,3.5.4

COVERPLATE

ADHESIVE

•aҟҟ° ••dDDS•°•°

vҟ.• a g o d- p D

TREATED NEOPRENE

WIDTH OF NEOPRENE OR HYPALON SHEET SHALL

EQUAL JOINT WIDTH PLUS ANTICIPATED MOVEMENT

PLUS I INCH PLUS BOND AREA

Fig, 3.5.5

is



3.6 Precast parapets

COMMERCIAL P.V.C. FLASH.OVER P.C. PANEL JOINTS.

SECURE WITH COMPATIBLE

JOINT

GASKET

SECTION A-A

Fig. 3.6.1. Precast parapet joint with cap flashing




STUD

BENT

C UR

3IIY2MIN. N

t a a o CLOSED CELL

SPONGENEOPENE

r'

Îa

. :o SEALANT

(' I° MAX.

FLASH. 8°MIN.

PC. PANEL

BELOW

JOINT

GASKE

2 ' X 3°CONT

NN

)N

2-PC. MET. FLASH.

DETAIL /

CONT. BENT

PLATE — A..

'oy

'•D

u`D

•e

A.D

. '4.4:

CONT. MET.

CAP FLASH

Î to • D .^ II

JOINT

GASKETҟI.Dvlelp•D

Îlpô'U.v.D•a

o

ALTERNATE PARAPET

CAP FLASHING

Fig. 3.6.2. Precast parapet with guarded roof flashing

20



3.7 Precast panel windows details

AN

is" -SHA11,

CAULK

1, C PANEL

Iru1i.Jl

HEAD (JAMB SIMILAR)i

SILL

Fig. 3.7.1. Wood casement in pre-

cast concrete panel

HEAD

CAULK

JAMB

CAULK

PANEL

SILL

Fig. 3.7.2. Aluminum sash in pre-

cast concrete panel

am

-PVC

DE IHEAD ONL Y

GLASS

AIR SPACE

CAULENG1

BUTYL,,i1 W HEATINGC O V E R

\CAULKING

'-BACKING

CLOSED CELLFOAM

Fig. 3.7.3. Fixed window in precast

panel

22



•j2 PLASTIC TUBE

+ 4 Y° ° a EXTRUSION

SNAP-ON VINYLPREFORMED

SEALANTSPREFORMED

SEALANTS

JAMB ALTERNATE JAMB(HEAD SIMILAR) (HEAD SIMILAR)

PREFORMED

SEALANTS NEOPRENEI I SHIMS

SILL

Fig. 3.7.4. Fixed-LTERNATE

DRAINAGE window in precast

concrete panel

Fig. 3.7.5. Panel with PVC reglet andspline gasket

PCI Journal/March-April 1973 3



CHAPTER 4—SEALANT MATERIALS

4.1 General

No one material has the perfect com-

bination of properties necessary to fully

meet each and every one of the require-

ments for each and every application. If

there were, and its price were reasona-

ble, obviously it would be in universal

use. It therefore is a matter of selecting,

from among a large range of materials,a particular material that offers the

right properties at a reasonable price to

satisfy the job requirem ents.

For many years oil-based mastics or

bituminous compounds and metallic

materials were the only sealants avail-

able. For many applications these tra-

ditional materials do not perform well

and in recent years there has been ac-

t ive developm ent of man y types of elas-tomeric sealants whose behavior is

largely elastic, rather than plastic, and

which are flexible rather than rigid at

normal service temperatures. Elasto-

meric materials are available as field-

molded and preformed sealants.Though initially more expensive, they

may be more economical over an ex-

tended period due to longer service life.Furthermore, as will be seen, they can

seal joints where considerable move-

ments occur which could not have been

sealed by the traditional materials. This

has opened up new engineering and

architectural possibilities to the design-

er of concrete structures.

No attempt has been made in this

chapter to list or discuss every attributeof every sealant on the market. Discus-

sion is limited to those features consid-

ered important to the designer, speci-

fier, and user so that the claims made

for various materials can be assessed

and a suitable choice for the applicationcan be made.

4.2 Field-molded sealants andtheir uses

The following types of materials list-

ed in Table 1 are currently used as

field-molded sealants:

4.2.1 Mastics. Mastics are composed

of viscous liquid rendered immobile by

the addition of fibers and fillers. They

do not usually harden, set or cure after

applications, but instead form a skin on

the surface expose d to the atmosphere.The vehicle in mastics may include

drying or nondrying oils (including ole-

oresinous compounds), polybutenes,

polyisobutylenes, low-melting point as-

phalts, or combinations of these mate-

rials. With any of these, a wide variety

of fillers is used, including asbestos fi-ber, fibrous talc or finely divided cal-

careous or siliceous materials. The func-tional extension-compression range for

these materials is approximately ± 3

percent.

They are used in buildings for gener-

al caulking and glazing where only verysmall joint movements are anticipated

and economy in initial cost outweighsthat of maintenance or replacement.

With passage of time, most m astics tendto harden in increasing depth as oxida-

tion and loss of volatiles occur, thus re-

ducing their serviceability. Polybutene

and polyisobutylene mastics have a

somewhat longer service life than do

the other mastics.

4.2.2 Thermoplastics (cold-applied,solvent or emulsion type). These mate-

rials are set either by the release of sol-

vents or the breaking of emulsions on

exposure to air. Sometimes they are

heated to a temperature not exceeding

120 F (49 C) to facilitate application

but usually they are handled at ambient

24



temperature. Release of solvent or wa-

ter can cause shrinkage and increased

hardness with a resulting reduction in

the permissible joint movement and in

serviceability. Products in this category

include acrylic, vinyl and modified bu-tyl types which are available in a vari-

ety of colors. Their maximum exten-

sion-compression range is ± 7 percent.

Heat softening and cold hardening

may , how ever, reduce this figure.

These materials are restricted in use

to joints with small movements. Acryl-

ics and vinyls are used in buildings pri-

ma rily for caulking and glazing.4.2.3 Thermosetting (chemically cur-

ing). Sealants in this class are either

one- or two-component systems which

cure by chemical reaction to a solid

state from the liquid form in which

they are applied. They include polysul-

fide, silicone, urethane and epoxy-basedmaterials. The properties that make

them suitable as sealants for a widerange of uses are: resistance to weather-ing and ozone; flexibility and resilience

at both high and low temperatures; and

inertness to a wide range of chemicals

including, for some, solvents and fuels.

In addition, the abrasion and indenta-

tion resistance of urethane sealants is

above average. Thermosetting, chemi-

cally curing sealants have an expa nsion-compression range of up to -!- 25 per-

cent depending on the one used, at

temperatures from —40 F to +180 F

(-40 C to +82 C). Silicone sealants re-

main flexible over an ever wider tem-

perature range.

These sealants have a wide range of

uses in buildings and containers for

both vertical and horizontal joints, and

may be used in pavements. Though ini-

tially more expensive, thermosetting,

chemically curing sealants can accom-

modate greater movements than other

field-molded sealants, and generally

have a muc h greater service life.

4.2.4 Thermosetting (solvent re-

lease). Another class of thermosetting

sealants are those which cure by the re-

lease of solvent. Chlorosulfonated poly-ethylene and certain butyl and neo-

prene materials are included in this

class and their performance character-istics generally resemble those of ther-

moplastic solvent release materials (see

Section 4.2.2). They are, however, less

sensitive to variations in temperature

once they have set up on exposure to

the atmosphere. Their maximum exten-

sicn-compression range does not, how-

ever, exceed ± 7 percent. They are

primarily used as sealants for caulkingand for horizontal and vertical joints in

buildings which have small movements.Their cost is somewhat less than that of

other elastomeric sealants, and their

service life is likely to be satisfactory,

though for some recent products this

has not yet been established by expe-

rience.

4.2.5 Rigid. Where special propertiesare required and movement is negligi-

ble, certain rigid materials can be used

as field-molded sealants for joints and

cracks. These include portland cement

mortar and m odified ep oxy resins.

4.3 Accessory materials

4.3.1 Primers. Where primers are re-quired, a suitable proprietary material

compatible with the sealant is usually

supplied with it. To overcome damp

surfaces, wetting agents may be includ-

ed in primer formulations, or materials

may be used that preferentially wet

such surfaces, such as polyamide-cured

coal tar epoxies. For oleoresinous mas-

tics, shellac can be use d.

4.3.2 Bond breakers. Many backup

materials do not adhere to sealants and

thus, where these are used, no separate

bond breaker is needed. Polyethylene

tape, coated papers and metal foils are

often used where a separate bond

breaker is neede d.




Table 1. Materials used for sealants in joints open on at least one surface

Group Field-molded Preformed

Type Mastic Cold-applied Thermosetting Compressionthermoplastics Chemically-curina Solvent release seat

(F) Polysulf ideComposition (A) Drying oils (E) Acrylics ( G) P o lyureth an e ( J) Ne op re ne (M) Neoprene

(B) Nondrying Contain 75-90 (H) Sil icones (K) B utadiene rubberoils percent solids (F) (H) C ontain styrene(C) P olybutenes and a solvent 95-100 per- (L) Chlorosulf-(D) Poly isobuty- cent solids onated poly-

lenes or corn- (G) Contains 75- ethylenebination of 100 percent (J) (L) ContainC & D solids 80-90 per-

All used with fill- May be either cent solidsera such as one or two corn- (K) Co ntains 85asbestos fiber or ponent system 90 percentsi liceous m a- solidsterials.Al l contain 100percent solids,except C & Dwhich may con-tain solvent.

Colors (A) (B) Varied Varied (F) (H) V aried (J) Limited Black(C) (D ) Limited (G) Limited (L) Varied Exposed surfaces

may b e treatedto give variedcolors.

Setting or Noncu ring, re- Noncu ring, sets Tw o co mp onent Release ofCuring mains viscous on release of system-catalyst. solvent

A and B form solvent or One componentskin on exposed evaporation of system-moisturesurface, water; remains pickup from the

soft except for air.surface.skin.

Aging andweathering Lo w Moderate High High High

resistanceIncrease inhardness inrelation to(1) Age High High Moderate High Low

or (2) Lowtemperature High High Lo w High Low

Recovery Lo w Lo w (F) M oderate Lo w High(G) (H) High

Resistance to Lo w Moderate (G) (H) High Moderate Highwear (F) Moderate

Resistance to Lo w Low at high High Lo w Highindentation temperaturesand intrusionof solids

Shrinkage after High High Lo w High Noneinstallation

Resistance to High except to High except to (F) (G) Low to Low to sol- Highchemicals solvents and alkalis and so lv en ts, fu els, v en ts, fu els

fuels, oxidizing acids oxidizing acids and oxidizing(H) Lo w to a lk alis a cids

Modulus at Not applicable Lo w (F) (G) Low Moderate100 percent (H) Highelongation

Allowable i- 3 percent ± 7 percent -± 25 percent -!- 7 percent M ust b e corn-extension and pressed at al lcompression t imes to 45 -85

percent of itsoriginal width.

Other (A) (B) (C) (D ) Nonstaining (K) (L) Non-properties Nonstaining staining

(C) (D) Pick up (L) Good vapordirt; use in-con- and dust sealercealed locationonly.

Unit f irst cost (A) (B) Very low High Very high Lo w High(C) (D) Low




Table 2. Preformed materials used for fillers and backup

Composition and type Uses and governing properties Installation

Natural rubb er Expansion jo in t fille r. Read ily H igh p liab ility may(a) Sponge compress ib le and good recov - cause insta lla tion p rob-

(b) So lid e ry . C losed cell. Non -absorp - lem s. W e ight o f p lastict ive. Solid rub ber may function concrete may precom-as fille r bu t p rimarily In tended press it. In construc tionas gasket. joints attach to first

placemen t with adhesive.

Neoprene or bu tyl Backup Co mpressed into jointsponge tubes W here resilience requ ired in w ith hand to ols.

large joints. C heck for com -patibility w ith sealant as tostaining.

Neoprene or butyl Backup Co mpressed into joint

sponge rods Used in narrower joints. with hand tools orCh eck for comp atib ility with roller.sealant as to staining.

Expanded poly- (a)ҟxpansion joint fillers. M ust b e rigid ly sup-ethylene, poly- Readly compressible, good po rted for full lengthurethane, polyvinyl recovery, no n-absorptive, during concreting.chloride, or poly- (b) Backup. Co mpressed into jointprop ylene flexible Com patible with mo st with hand tools.foams sealants.

Expanded poly- Expansion joint filler. Sup port In place duringethylene, poly- Useful to form a gap after sig- concreting. In construc-urethane or poly-

nificant compression will not tion joints attach to firststyrene rigid foams recover. placement. Som etimesremoved after concret-ing where no longerneeded.

Glass fibe r or (a)ҟxpansion joint filler. Installed as for wood o rmineral wool Made in board form by im- fib erbo ard m aterials.

pregnating with bitume n orresins. Easily compressed.

(b) B ackup. Insert without In mat form, packedimpregnation so as no t loose m aterial or yarn.to damage sealant.

Oakum, jute, or The traditional material for P acked In joint to re-manila yarn and rope packing joints b efore Installing quired depth.

sealant. W here used as b ack-up shou ld be u ntreated withoils, etc.

P ortland cement Used at joints in precast u nits Bed (mortar)grout or mo rtar and p ipes to fil l the rem aining Inject (grout)

gap when no m ovement Isexpected and sometimes be-hind waterstops.

4.6 Joint design

The location and width of joints that

require sealing can only be specified by

considering whether a sealant is avail-

able which will take the anticipated

movement, and what shape factor or,

in the use of preformed sealants, what

size is required. If the sealants can not

take the anticipated movement, then

the joint system for the structure must

be redesigned to reduce the movement

at the joints. Sealing systems currently

28



available can accommodate (at increas-

ing cost) movements up to about 15 in.

(38.8 cm) and are presently being de-

signed for even greater movements.

With due forethought it should, there-

fore, be possible to design and specify asuitable sealed joint for almost any typeof co ncrete structure.

4.7 Determination of jointmovements and locations

The anticipated length (volume)

changes within the structure must be

determined and translated into joint lo-

cations and movements that not only fitthe structural design and maintain the

integrity between the individual struc-

tural units, but also consider the fact

that each type of sealant currently

available imp oses spe cific limitations onboth the shape of joint that can be

sealed and the movement that can be

accommodated. When using the appli-

cable structural design codes and stan-

dards for these calculations, it should

be remembered that the sources of

movement and the nature of the move-

ment, both long and short term, can be

very complex in other than simple

structures. Both experience and judg-

ment are necessary in the design of

joints that function satisfactorily. A

more complete discussion of this is be-

yond the scope of this report. The fol-lowing simple facts will, if properly

co nsidered , result in goo d joint seal pe r-formance:

1. The movement of the end of a

unit depends on its effective length,

that is, on the length of that part of the

unit that is free to move in the direction

of the joint.

2. Except where a positive anchor isa feature of the design, experience

shows that the only safe assumption is

that a joint between two units may be

called upon to takethe total movement

of both units. Based on joint movement

measured on actual buildings, the

Building Research Station in England

calculated that movement of each joint

should be multiplied by two for design

purposes. Egon Tons of the University

of Michigan suggests r 5 a multiplication

factor of 1.7.

3. The actual service temperaturesof the materials being joined, not the

ambient range, must be used in calcu•

lating joint movements.

4. Where units to be joined are of

dissimilar materials, they may not be at

the same surface temperature and the

appropriate coefficient for each m aterialmust be used in calculating its contri-

hution to the joint movement. Differ-

ential movements resulting from this

may, depending on the joint configura-

tion, result in secondary strains in the

sealant.5. Where knowledge exists of actual

movements that have occurred in simi-

lar joints in similar structures under

similar service conditions, these should

be used in the new design to supple-

ment those indicated by theory alone.6. Allowance must be made for the

practical tolerances that can be

achieved in constructing joint openings

and po sitioning pre cast units.

7. In butt joints, the movement to

which the sealant can properly respond

is that at right angles to the plane of

joint faces.

8. The width of the joint sealant res-ervoir must always be greater than the

movement that can occur at the joint.9. When viewing a structure, the

joints, either sealed or unsealed, are

readily noticeable. It is, therefore, de-

sirable to either locate and construct

them as a purposeful feature of the ar-

chitectural design or to conceal them bystructural or architectural de tails.

4.8 Selection of butt jointwidths for field-molded

sealants

The selection of the width and depth

of field-molded sealants, for the com-

puted movement in a joint, is based on




Table 3. Preformed materials used for waterstops, gaskets, and miscellaneoussealing purposes

Composition P roperties significant Available in Usesand type to ap plication

Butyl— High resistance to water, Beads, rods, W aterstops. Corn-conventional vapor and weathering, tubes, flat sheets, b ined crack inducerrubb er cured Low p ermanent set and tapes and pur- and seal. Pressure

mo dulus o f elasticity form- pose-made sensitive du st andulations possible, giving shapes. water sealing tapeshigh cohesion and recov- for glazing andery. Tough. Color— curtain walls.b lack, can be p ainted.

Butyl—raw, High resistance to water, Beads, tapes, Glazing seals, lappolymer- vapor and w eathering, gaskets, grom- seams in metalmodified with Goo d adhesion to metals, mets. cladding. Curtainresins and glass, plastics. Mo ldable wall panels.plasticisers into place b ut resists dis-

placement. Tough andcohesive. Color—b lack,can be p ainted.

Neoprene— High resistance to o il, Beads, rods, tub es, Waterstops, glazingconventional water, vapor and w eather- flat-sheets, tapes, seals, insulationrubb er cured ing. Low perm anent set, purpose-made and isolation o f

Color—b asically b lack b ut shapes. Either service lines.other surface colors can solid or open or Tension-compres-be incorporated, closed cell sion seals. Co m-

sponges. pression seals.Gaskets.

P VC (polyvinyl High water, vapor, b ut only Beads, rods, tubes, W aterstops, gaskets,chloride) moderate chemical resis- flat sheets, tapes, comb ined crack in-Extrusions tance. Low permanent set gaskets, pu rpose- ducer and seal.or moldings and m odu lus of elasticity made shapes.

formulations p ossible, giv-ing high cohesion and re-covery. Tough. Can besoftened by heating forsplicing. Color— pigmentedblack, brow n, green, etc.

Polyiso- High water, vapor resis- Beads, tapes, Gaskets, glazingbutylene- tance. High flexib ility at grommets, gaskets. seals. Cu rtain wall

non-curing low temperature. Flows panels. Aco usticalunder pressure, surface partitions.pressure sensitive, highadhesion. Sometimes usedwith b utyl compounds tocontrol degree of cure.Color—black, grey, white.

SBR (styrene High water resistance. Beads, rod s, flat Waterstops.butadlene NB R has high oil re- sheets, tapes, gas-rubber) sistance. kets, grommets,

purpose-madeNBR (nitrile shapes. E ither

butadiene solid or c ellularrubb er) and sponges.polyisoprenepolydleneconventionalrubb er cured

30



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SEALANT)

WIJOINT WIDTH

WHEN FILLED)

25)

dwi "3ҟ' i -2

PROBLEM: IASSUME Wi=1.0 IN.(25.4mm)

COMP UTED EXPANSION 0.5 IN.(12.7mm),(50%)

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FROM CURVES d MAX =1

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COMPUTED LINEAR EXPANSION — PERCENT

Note, (i) ifdmax is less than id in. (12.7mm.) sealant may, with age lose extensibility.

Redesign joint system.

( ii ) sea lant free t o assume parabo l ic shape on bo th faces .

(iii) factor of safety of4 should be used in applying this chart

Fig. 4.8.1. Selection of dimensions for field-molded sealants in butt joints (Cour-

tesy: A m erican Concrete Institute)

the maximum allowable strain in the

sealant. This occurs in the outer fibers,

usually when the sealant is extended,

though in some cases maximum strain

may occur while the sealant is com-

pressed. The part of the total movement

which extends the sealant is that which

increases the width of the joint at the

time the sealant is installed to the

width of the joint at its maximum open-

ing. The temperature difference be-

tween that at installation and at maxi-




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mum opening is the main contribution

to the extension of the sealant; but any

residual drying shrinkage of the con-

crete that has yet to occur, and shrink-

age in the sealant as it sets or cures,

will also im pose additional extension onthe sealant.

When the suitability of a new joint

sealant is first being considered, and a

precise determination of the dimensionsof the sealant reservoir is required, the

approach using Fig. 4.8.1 may be fol-

lowed. The curves relate the maximum

allowable strain in a sealant to an as-

sumed joint width and various shapefactors. First, the maximum allowable

strain for the sealant under considera-

tion must be determined by testing at

a specified temperature. Usually this

temperature is 0 F (-18 C) and the test

is performed in accordance with the

requirements of Federal Specification

SSR-406-C. Next, a likely approxima-

tion to the joint width is assumed, and

the linear extension and compression

that the sealant will experience, as re-

lated to the installed width, are thencalculated.

The various curves then permit the

computed extension and shape factor to

be interrelated so that the maximum

allowable strain will not be exceeded.

More than one solution is usually possi-

ble and, where the upper limits of thecurves are approached, a wider as-

sumed joint width should be tried. In

practice, a safety factor of four should

be applied in using this chart to allow

for unforeseen circumstances.

The detailed procedure of Fig. 4.8.1

is simplified for practical use by using

the percentage extension-compression

shown in Table 1 for each group ofsealants. This figure has been devel-

ope d through consideration of the m axi-mum allowable strains for materials in

the group and application of the sug-

gested safety factor. The percentage ex-tension-compression of the sealant is

the percentage increase or decrease of

the installed width of the sealant that

can be safely accommodated as the

joint subsequently opens and closes.

The width of the joint to be formed,

which becomes the sealant mold and

thus determines the sealant width asinstalled, can then be obtained by a

simple calculation so that the permis-

sible extension-compression range is notexceeded in service. This calculation

should, of course, consider the antici-

pated temperature at the time of form-

ing the joint, the temperature at seal-

ant installation, and any additional joint

opening caused by drying shrinkage ofthe abutting concrete units as well as

by the extrem es of service temp erature.When the joint width is designed, a

precise installation temperature cannc

usually be known or specified; other-

wise, an intolerable restriction would

be placed on the installation operation.

Normally a general installation temper-

ature range is specified. This can bedone safely by checking the dimension-

al range under the worst temperature

circumstances for installation; for ex-

tension the top of the range is used, and

for compression the bottom of the

range. A practical range of installation

temperatures is assumed for this and

other factors, such as moisture conden-

sation at low temperatures and reduced

working life at high temperatures, to be

from 40 to 90 F (4 to 32 C). Generally,

because the tension condition, as the

joint opens with a decrease in temper-

ature, is the most critical in sealant h^-

havior, joint sealants installed a, the

low end of this range may be expected

to perform best. A warning note should

be included on the plans that, if sealing

must take place for any reason at tem-peratures above or below the specified

range, then a wider than specified joint

may have to be formed, or changes in

the type of sealant or shape factor may

be required to secure greater extensi-bility.

Detailed calculations for selection of




the joint width for sealants with an ex-

pansion-compression range of -!- 25

percent (which is the most common onefor the widely used class of thermo-

setting, chemically curing sealants) can

be dispensed with by the use of Fig.4.8.2. Where a reasonable joint width

(see Section 4.11) is not possible by

either of the above considerations or by

those that follow in Section 4.9 as to

sealant depth, the proposed joint layout

for the structure must be redesigned to

produce m ovem ents tolerable to sealant.

4.9 Selection of butt jointshape for field -moldedsealants

When a suitable joint width has been

established (see Section 4.8), the ap-

propriate depth for the sealant reservoir

must be determined so that the sealant

has a good shape factor. 1 6 Fig. 4.8.1

can be used for this purpose. Curves for

depth-to-width ratios of 1:1, 2:1, and

3:1 are shown on this chart. Any depth-to-width ratio may be used provided

that the maximum allowable strain is

not exceeded at the computed exten-

sion or compression expected in the

sealant. The benefits in both better

performance and economy of mate-

rial by using the smallest possible

depth-to-width ratio have already

been discussed in the preceding sec-tion. In general, the depth of sealed

joints should not exceed joint width andthat on wide joints (up to say 4 in.)

depth at midwidth should not exceed

1/z in., with concave shape giving greaterthickness at panel faces. The depth of

sealant is controlled by using a suitable

backup material as described in Section

4.3.3. To obtain full benefit of a well-

designed shape factor, a bond breaker

must be used behind the sealant (see

Section 4.3.2),

4.10 Selection of size ofcompression seals forbutt joints

A positive contact pressure must be

exerted against the joint faces at all

times for compression seals to function

properly. The development of suitable

seal con figurations to achieve this, whilefollowing the principles explained by

Dreher,ls has been largely based onthe results of trial and error laboratory

and field experiments in both America

and Europe. 1719 Neoprene compression

seals must remain compressed approxi-

mately 15 percent of the uncompressed

seal width at maximum joint opening tomaintain sufficient contact pressure for

sealing and to resist displacement; gen-

erally, not more than 55 percent of theuncompressed seal width is permitted at

maximum closing to prevent overcom-

pression. For larger sizes of com pressionseals, the 55 percent value may be ex-

ceeded. The allowable movement is

thus approximately 40 percent of the

uncompressed seal width. The allow-

able movement for impregnated foams

is much less, about 5 to 20 percent.

The critical condition exists when thejoint is fully open at low temperature

since compression set or lack of low

temperature recovery may adversely

affect sealant performance. The prin-

ciple of size selection is similar to that

for field-molded sealants in that the

original uncompressed width of seal

is required to maintain the seal within

the specified compression range con-sidering the installation temperature,

width of formed opening, and the ex-

pected movement. A simplified chart

applicable to the conditions specified in

this section is shown in Fig. 4.10.1.

4.11 Limitations on butt jointwidths and movements

for various types ofsealants

Field-molded sealants generally re-

quire a minimum joint width of 1/4 in.

(6.4 mm) to provide an adequate re-

serve against loss of material due to ex-trusion or to accommodate unexpected

service conditions.

34



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The upper limit of joint width and

permissible movement varies with the

type of material used. Mastic, thermo-

plastic, and thermosetting, solvent re-

lease sealants may be used in joints up

to 1 1/a in. (3.8 cm) wide with a permis-

sible movement not exceeding Y4 in .

(6.4 mm). Thermosetting, chemically-

curing materials have been used in

joints up to 4 in. (10.2 cm) wide with

movements in the order of 2 in. (5.1

cm), though it is more usual to confine

them to joints of half that size to ensure

good performance and economy in ma-

terials. In wide joints, increasing carewith sealant installation is necessary

and, where subject to traffic, protection

of the upper surface against damage

with a steel plate or other means is re-

quired.

4.12 Lap joint sealant thickness

Shear governs sealant behavior in lapjoints and its magnitude is related to

both the movement that occurs and the

thickness of the sealant between thetwo faces. For installations made at nor-

mal temperatures of 40 to 90 F (4 to

32 C), the thickness of the sealant

should be at least one half the antici-

pated movement and, where higher or

lower temperatures prevail at installa-

tion, the thickness of the sealant should

be equal to the anticipated movement.

Where there will be no movement,

the sealant thickness can be as little as

½o in. (1.6 mm). However, in assem-

bling concrete units, a minimum thick-

ness of ' 1/z in. (12.7 mm) is desirable to

com pensate for casting tolerances or any

irregularities in the faces.

REFERENCES

1. "Weathertight Joints for Walls,"

CIB Symposium, Oslo, Norway,

Norwegian Building Research In-

stitute, 196 7.

2. Bishop, D., "Weatherproo fing Joints

Between Precast Concrete Panels,"

Building Research Station, United

Kingdom, The Builder, Jan. 5,1962,

3. Latta, J. K., "Precast Concrete

Walls—A New Basis for Design,"

Canadian Building Digest #93,

National Research Council, Otta-

wa, Canada, Septem ber 1967.

4. Garden, G. K., "Rain Penetration

and its Control," Canadian Build-

ing Digest #40, National Research

Council, Ottawa, Canada, April

1963.

5. Garden, G. K., "Look at Joint Per-

formance," Canadian Building Di-

gest #97, National Research Coun-cil, Ottawa, Canada, January 1968.

6. Malstrom, P. E., "Jointing Prob-

lems in Facades," Fifth Internation-

al Congress of the Precast ConcreteIndustry, London, England, British

Precast Concrete Federation, May

1966.

7. PCI Design Handbook, Precast and

Prestressed Concrete, Prestressed

Concrete Institute, Chicago, Illi-

nois, 1971.

8. "Aspects of Design in Concrete,"

Seminar for Architects, Cement &

Concrete Association, London,

England, 1971.

9. "The Weathering of Concrete,"

Proceedings, Sym posium, Royal In-

stitute of British Architects, The

Concrete Society, London, En-

gland, 197 1.

10. "Guide to Joint Sealants for Con-crete Structures," ACI Committee

504,ACI Journal, Proceedings,

Vol. 67, No. 7, July 1970, pp. 489-

536.

11. Karpati, Klara K., "Literature Sur-

vey of Sealants," Journal of Paint

Technology, V ol. 40, No. 523, Aug.

36

Architectural Precast Joints

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Transcript of Architectural Precast Joints