ARCHITECTURAL PRECAST CONCRETE JOINT DETAILS

ARCHITECTURAL PRECASTCONCRETE JOINT DETAILS

Reported by

PCI Committee on Architectural PrecastConcrete Joint Details

Raymond J. SchutzChairman

James Engleҟ Albert LitvinJames G. GrossҟR. L. PareAbraham GutmanҟJohn S. ParrishJ. A. Hansonҟ Irwin J. SpeyerKai Holbekҟ Ivan L. VarkayFelix Kulkaҟ Lloyd Wright

Correct joint design and proper selection of materialsand installation are vital for the successfulperformance and esthetic appeal of precast concretewall systems. This report recommends the properprecast concrete joint details and sealants forspecific situations. In writing these recommendations,architectural treatment and economy in mold designwere considered but are not included, since theseare covered in the PCI Manual on ArchitecturalPrecast Concrete. Following these recommendationswill result in a good design and a durable,waterproof, and economical joint.

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

1.1 Scope1.2 Types of joints1.3 General design concepts for

joints1.4 Number of joints1.5 Location of joints

Chapter 2—Planning check lists ............................ 142.1 Definitions2.2 Joint planning2.3 Water runoff planning

Chapter3—Joint details ................................... 153.1 General3.2 One-stage joints3.3 Two-stage joints3.4 Cavity wall3.5 Floor and roof slab joints3.6 Precast parapets3.7 Precast panel window details

Chapter 4—Sealant materials ............................... 244.1 General4.2 Field-molded sealants and

their uses4.3 Accessory materials4.4 Preformed sealants and

their uses4.5 Compression seals and

their uses4.6 Joint design4.7 Determination of joint

movements and locations4.8 Selection of butt joint widths

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

for field-molded sealants4.10 Selection of size of compression

seals for butt joints4.11 Limitations on butt joint widths

and movements for various typesof sealants

4.12 Lap joint sealant thickness

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

PCI Journal/March-April 1973ҟ 11

CHAPTER 1 —JOINT DESIGN

1.1 Scope

The design of joints must be exe-cuted as an integral part of the totalwall design. Some specific guidelinesfor joints do govern their ultimate suc-cess. This chapter highlights and illus-trates several cases of interdependencewith other wall design criteria.

In all cases, the designer should as-sess his requirements for joints realisti-cally with respect to both performanceand cost. If joint designs and details arecontemplated which differ from thosenormally used in the area where theproject is located, local producersshould be consulted.

The following discussion will dealmainly with joints which are designedto accommodate local wall movementsonly, rather than an accumulation ofsuch movements which would requireproperly designed expansion joints.

1.2 Types of joints

Joints between precast wall panelsmay be divided into two basic types:

1. One-stage joints2. Two-stage joints

A cavity wall design is considered afurther application of the two-stagejoint.

1.2.1 One-stage joints. As the nameimplies, this joint has one line of de-fense for its weatherproofing ability.This occurs normally in the form of asealant close to the exterior surface.The advantage of this type of joint is

that it generally provides the lowestfirst 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 andproper installation at the building site.This type of joint is in common use inmost of North America. One-stagejoints should be regularly inspected andmay demand fairly frequent mainte-nance to remain weathertight.

1.2.2 Two-stage joints. These jointshave two lines of defense for weather-proofing. The typical joint consists of arain barrier near the exterior face andan air seal normally close to the interiorface of the panels. The rain barrier isdesigned to shed most of the waterfrom the joint and the air seal is the de-marcation line between outside and in-side air pressures. Between these twostages is an equalization or expansionchamber which must be vented anddrained 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 therain and airborne water from enteringthe joint. If airborne water (wind-driv-en rain) penetrates this barrier, it willdrain off in the expansion chamber asthe kinetic energy is dissipated and theair loses its ability to carry the water.Any water which penetrates the rainbarrier should be drained out of thejoint by proper flashing installations.

In order to avoid vertical movementof the air in the expansion chamber

12

(stack effect) caused by wind or outsideair turbulences, it is advisable to usethese flashing details as dampers andprovide them at regularly spaced inter-vals along the height of the verticaljoints. Such flashing is sometimes in-stalled at each floor level, but a greaterspacing (two or three stories) may besufficient for low-rise buildings and inareas with moderate wind velocities.

Since the air seal is the plane wherethe change in air pressures between theoutside and inside atmospheres occurs,it would normally be subject to waterpenetration through capillary action.Inasmuch as the outside air reachingthis seal has lost its water content, nomoisture can enter by such action.

The danger of humidity travelingfrom inside the building and throughthe air seal should be investigated forbuildings with relatively higher interiorhumidity, and for tall buildings, wherethe interior air pressure may occasion-ally be substantially higher than theoutside atmospheric pressure. This con-dition is normally solved by using acavity wall design.

A cavity wall (Fig. 3.4.1) is the mosteffective wall for the optimum separa-tion and control of both outside and in-side air and humidity conditions. Whenprecast concrete wall panels are used incavity wall designs, they will normallyserve as the rain barrier. An air space ismaintained between the precast exteri-or and the interior wall. Insulation,when required, is applied to the outsideface of the interior wall, eliminatingcondensation problems and, thereby,making the inner wall subject only tothe relatively constant interior tempera-ture. Cavity wall construction is nor-mally expensive when compared withconventional walls. On the basis of theirlower maintenance costs and their ex-cellent performance records, they maywell be justified for specific types andlocations of buildings.

The two-stage joint is gaining accep-tance particularly for buildings subjectto severe climatic exposure or tempera-ture and humidity control.

A disadvantage of the two-stage jointfor concrete wall panels is the highercost. For projects with good repetitivejoint design properly integrated withother panel details, and having efficientproduction and erection procedures, itmay well approach the cost 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. (12.7cm) (with gaskets and compressionseals), is required to accommodate boththe rain barrier and the air seal. Fortwo-stage joints with compression seals,connection detail allowance should bemade for slight horizontal movementsof the panels after initial fastening forair seal compression.5 The joints mustbe fully accessible from the inside ofthe panels for later installation of theair seal. The simplest 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. Inaddition, as part of the overall perfor-mance requirements of the building,the purpose for which the building isbuilt will also determine design require-ments for the joint.

Thus, joint design will be governedby its exposure (orientation and climaticconditions), the purpose of the building,and appearance. The following guide-lines must all be evaluated in relationto the relative importance of these cri-teria.


1.4 Number of jointsIt is generally advantageous to plan

for the fewest number of joints, due tothe lower overall joint cost, potentiallylower maintenance cost, and the econ-omy of large panel erection.

Optimum panel sizes must, however,also be determined from erection condi-tions and established limitations ofweight and sizes for transportation.7

If the desired appearance requiresadditional joints, this may be achievedthrough the use of false or dummyjoints. In order to match the appear-ance of both false and real joints, anapplied finish should be chosen to sim-ulate sealants or gaskets in the realjoints. Caulking of the false joints addsan unnecessary expense.

1.5 Location of jointsJoints are easier to design and exe-

cute if they are located where maxi-mum panel thickness occurs. Except forone-stage joints and joints in precastpanels performing as rain barriers incavity walls, the minimum panel thick-ness at joints should be 4 in. (and pref-erably 5 in.) for panels which can be

manufactured and erected to close tol-erances. Hence, it is recommended thatjoints be placed in any ribbed projec-tions of panels.

If ribs are too narrow to accommo-date joints, the full rib may be locatedin one panel only (Fig. 3.2.6). Anothersolution is to design every second panelwith ribs at both edges using the bal-ance as infill units.

An important factor in locating anddetailing joints is a proper assessmentof the predicted weathering pattern forthe structure. To limit weathering ef-fects on the building, it is advisable toemphasize the joints by making themwide and recessed from immediatelyadjacent surfaces. 8 Joints in forwardsloping surfaces are difficult to weather-proof, especially where they may col-lect snow or ice. When these surfacescannot be avoided, the architect shouldinclude a second line of defense againstwater penetration. This may beachieved by sealing the front of the sur-face and using a two-stage joint. If aone-stage joint is used, the owner mustaccept regular inspection of such jointsand be prepared to perform frequentmaintenance.

CHAPTER 2—PLANNING CHECK LISTS

2.1 DefinitionsJoint planning is recognition of, and

provision for, movement or isolation ofmovement in a building or other struc-ture based on an analysis of esthetic,structural and mechanical require-ments.

Water runoff planning is the visuali-zation of the paths that moisture maytake, or its entrapment, and the provi-sions of safe channels for its flow anddischarge.

2.2 Joint planning1. Determination of amount of

movement that can be anticipated.A. Initial movement

1. Shrinkage2. Foundation3. Elastic deflection4. Other

B. Life of structure movement1. Temperature2. Moisture3. Wind

14

4. Earthquake or other founda-tion movement

5. Live load deflections6. Creep7. Other

2. Architectural (esthetic) considera-tions

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

small)D. Environmental needs

1. Water control2. Air control (circulation)3. Temperature control4. Noise (vibration control)

3. Structural considerationsA. Elimination of stress in structur-

al materials through relief of al-lowed movement.

B. Design to resist movementthrough 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 considerationsA. Differential movement potential

1. Differing coefficients of ex-pansion

2. Differing heat absorptionrates

3. Differing moisture absorption

qualities4. 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 sealants1. Rigid waterstops2. Flexible waterstops3. Gaskets

C. Other6. Tolerances

A. ProductionB. ErectionC. Adjacent construction

2.3 Water runoff planning1. Resistance to penetration

A. SealB. Shape of joint

2. Channelization of moisture anddischarge

A. Planned channelizing joints(two-stage system)

B. Channelization of inadvertentor seepage penetration (one-stage system)

CHAPTER 3-JOINT DETAILS

3.1 GeneralThis chapter shows typical details for

one-stage and two-stage joints, for floorand roof slab joints, for precast concreteparapets, and for windows in precastconcrete panels. The committee recog-nizes that other details can be devel-

oped within the recommendations ofthis report that will provide satisfactoryservice. Thus, it is not intended thatthese details be used to the exclusion ofall others, but rather that they be takento illustrate the features of good jointplanning and design.


3.2 One-stage joints

pP ^ Pҟe

.D. b.

p • P Op ' 6 a G DD 1 s p'

D

pɁD .' D .ҟP 3/8°MIN..'D'•

3/$ MIN. VERTICALHORIZONTAL JOINT WIDTHJOINT WIDTH ° • °p.pҟD ^ ap • b.

pDp °P D^.pɁ.D•D ., P

pɁ•'p`p. 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 •°

pҟD , p° v ° _ ' ° 3/8" MIN.

• ҟ° •-'ҟp JOINT WIDTH

.A.s

D ҟD, DMIN. P '°JOINT WIDTH °ҟ.D-^

aɁ

eD p' D •' p ' ° e• '

•

D•

D• 0 '.p •p . p Q

°'a

D Q D••

(1'112"

A.

° - X MAX. SIZEAGGREGATE 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 D ° a

JOINT WIDTHoaa 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 SPONGENEOPRENE SQUARE STRIP OR ROPE1.5 TIMES THE THEORETICAL JOINTWIDTH

^4 ^2 IEXPANSIONCHAMBER

w^• D Via. ° rn a ^

•d. .•d, • \N \N W K

^' d. Q • 'p^^N -0J^W Z Wr-

f W

iD v

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

EXTERIORҟRAIN BARRIERFACE

4"MIN

1ҟ1ҟ,

r ,Aҟvҟo

' d a• d pҟ-

a d. a

d d^ d

AIRSEAL

(MIN. I /16"/ 1° )

Fig. 3.3.1. Two-stage joint vertical Fig. 3.3.2. Two-stage joint horizontalgaskets gasket

'2"MIN. z

• 1 dҟ'

• O0 1 ' 0Ɂo •. d

• D'D .ҟPҟe Dҟ•ҟ9SEALANT(IF USED)MUST BEDISCONTINUED AT INTERVALS

SEALANT DISCONTINUED(VERTICAL JOINTS) TO DRAIN

AT HORIZONTAL JOINT AREA BETWEEN IT AND AIR SEAL

Fig. 3.3.3. Two-stage joint vertical Fig, 3.3.4. Two-stage joint horizontalsealants sealants

3.4 Cavity wall

INSULATION IF REQUIREDҟ .^'p I ° ,d

2 ҟI j2„SEALANT-ALTERNATE RAINBARRIERS(TUBE)

Fig. 3.4.1. Horizontal section through cavity wall

PCI Journal/March-April 1973 17

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

O D D• D e

Fig. 3.5.2

STEEL PLATES

4 ` d b`,D, 4 , p , p D.

p , 0 D 1. D D. 0 D• D •p'

O' D

PREFORMED COMPRESSION SEAL NEOPRENE(SOMETIMES COMBINED WITH P.V.C. SHEETOR SHEET NEOPRENE SECONDARYSYSTEMS.)

Fig. 353 Fig,3.5.4

COVERPLATE

ADHESIVE

•aҟ•ҟ4 ° ••d'DDS• °•°vҟ°.• a g o d- p D

TREATED NEOPRENE

WIDTH OF NEOPRENE OR HYPALON SHEET SHALLEQUAL JOINT WIDTH PLUS ANTICIPATED MOVEMENTPLUS 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

JOINTGASKET

SECTION A-A

Fig. 3.6.1. Precast parapet joint with cap flashing


STUD

BENTCUR

3IIY2MIN. N

t a a o CLOSED CELLSPONGENEOPENE

r'

Îa

.: o SEALANT

(' I° MAX.

FLASH. 8°MIN.

PC. PANELBELOW

JOINTGASKE

2 ' X 3°CONT

NN

)N

2-PC. MET. FLASH.DETAIL /

CONT. BENTPLATE — A..

' D

oy'•D

u`D

•e .A.D

. '4..4.e:

CONT. MET.CAP FLASH

Î to • D .^ II

JOINTGASKETҟII. D vll

ellp.•D,^

Îlpô'U.v.D•a

o o

ALTERNATE PARAPETCAP FLASHING

Fig. 3.6.2. Precast parapet with guarded roof flashing

20

s •o

GASKETҟ'li ' n DÌ 2DIҟ,

D

I I , r

° Qd

vi I OḏQ.

oli . D • D •4

• (l a . D o l u

ol^ ,d .', D .a

IA

III • ^' o

/

CLOSED CELL NEOPRENESPONGE - HOLD IN PLACE WITHMASTIC ADHESIVE

2 PC. MET. FLASH.

112..

ry -CONT. 314° X 4" NAILER WIMECHANICAL FASTENER

"— ADVISABLE TO PROVIDEP.V.C. FLEXIBLE FLASHINGACROSS PANEL JOINT POINTS

Fig. 3.6.3. Precast parapet with flush roof flashing

FIELD-MOLDED SEALANT

RAINBARRIE -ROOFING DETAILS

=E FIGS. 3.6.2 a 3.6.3)

R SEAL

Fig. 3.6.4. Precast para-pet two-stage joint


3.7 Precast panel windows details

ANis" -SHIA11,

CAULK1, C PANEL

Iru1i.JlHEAD (JAMB 1SIMILAR)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 ONLY

GLASS

AIR SPACE

CAULEING1I

BUTYL,,

i

11W HEATING

COVER

\CAULKING

'-BACKINGCLOSED CELLFOAM

Fig. 3.7.3. Fixed window in precastpanel

22

• j2 PLASTIC TUBE

+4 Y° ° a EXTRUSION

SNAP-ON VINYL PREFORMEDSEALANTS

PREFORMEDSEALANTS

JAMB ALTERNATE JAMB(HEAD SIMILAR) (HEAD SIMILAR)

PREFORMEDSEALANTS NEOPRENE

II SHIMS

SILL

Fig. 3.7.4. Fixed- ALTERNATEDRAINAGE window in precast

concrete panel

Fig. 3.7.5. Panel with PVC reglet andspline gasket


CHAPTER 4—SEALANT MATERIALS

4.1 GeneralNo one material has the perfect com-

bination of properties necessary to fullymeet each and every one of the require-ments for each and every application. Ifthere were, and its price were reasona-ble, obviously it would be in universaluse. It therefore is a matter of selecting,from among a large range of materials,a particular material that offers theright properties at a reasonable price tosatisfy the job requirements.

For many years oil-based mastics orbituminous compounds and metallicmaterials were the only sealants avail-able. For many applications these tra-ditional materials do not perform welland in recent years there has been ac-tive development of many types of elas-tomeric sealants whose behavior islargely elastic, rather than plastic, andwhich are flexible rather than rigid atnormal service temperatures. Elasto-meric materials are available as field-molded and preformed sealants.Though initially more expensive, theymay be more economical over an ex-tended period due to longer service life.Furthermore, as will be seen, they canseal joints where considerable move-ments occur which could not have beensealed by the traditional materials. Thishas opened up new engineering andarchitectural possibilities to the design-er of concrete structures.

No attempt has been made in thischapter 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 madefor various materials can be assessedand 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 asfield-molded sealants:

4.2.1 Mastics. Mastics are composedof viscous liquid rendered immobile bythe addition of fibers and fillers. Theydo not usually harden, set or cure afterapplications, but instead form a skin onthe surface exposed to the atmosphere.

The vehicle in mastics may includedrying 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 varietyof fillers is used, including asbestos fi-ber, fibrous talc or finely divided cal-careous or siliceous materials. The func-tional extension-compression range forthese materials is approximately ± 3percent.

They are used in buildings for gener-al caulking and glazing where only verysmall joint movements are anticipatedand economy in initial cost outweighsthat of maintenance or replacement.With passage of time, most mastics tendto harden in increasing depth as oxida-tion and loss of volatiles occur, thus re-ducing their serviceability. Polybuteneand polyisobutylene mastics have asomewhat longer service life than dothe 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 onexposure to air. Sometimes they areheated to a temperature not exceeding120 F (49 C) to facilitate applicationbut usually they are handled at ambient

24

temperature. Release of solvent or wa-ter can cause shrinkage and increasedhardness with a resulting reduction inthe permissible joint movement and inserviceability. Products in this categoryinclude 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 hardeningmay, however, reduce this figure.

These materials are restricted in useto joints with small movements. Acryl-ics and vinyls are used in buildings pri-marily for caulking and glazing.

4.2.3 Thermosetting (chemically cur-ing). Sealants in this class are eitherone- or two-component systems whichcure by chemical reaction to a solidstate from the liquid form in whichthey are applied. They include polysul-fide, silicone, urethane and epoxy-basedmaterials. The properties that makethem suitable as sealants for a widerange of uses are: resistance to weather-ing and ozone; flexibility and resilienceat both high and low temperatures; andinertness to a wide range of chemicalsincluding, for some, solvents and fuels.In addition, the abrasion and indenta-tion resistance of urethane sealants isabove average. Thermosetting, chemi-cally curing sealants have an expansion-compression range of up to -!- 25 per-cent depending on the one used, attemperatures 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 ofuses in buildings and containers forboth vertical and horizontal joints, andmay be used in pavements. Though ini-tially more expensive, thermosetting,chemically curing sealants can accom-modate greater movements than otherfield-molded sealants, and generallyhave a much greater service life.

4.2.4 Thermosetting (solvent re-

lease). Another class of thermosettingsealants are those which cure by the re-lease of solvent. Chlorosulfonated poly-ethylene and certain butyl and neo-prene materials are included in thisclass and their performance character-istics generally resemble those of ther-moplastic solvent release materials (seeSection 4.2.2). They are, however, lesssensitive to variations in temperatureonce they have set up on exposure tothe atmosphere. Their maximum exten-sicn-compression range does not, how-ever, exceed ± 7 percent. They areprimarily used as sealants for caulkingand for horizontal and vertical joints inbuildings which have small movements.Their cost is somewhat less than that ofother elastomeric sealants, and theirservice life is likely to be satisfactory,though for some recent products thishas 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 usedas field-molded sealants for joints andcracks. These include portland cementmortar and modified epoxy resins.

4.3 Accessory materials4.3.1 Primers. Where primers are re-

quired, a suitable proprietary materialcompatible with the sealant is usuallysupplied with it. To overcome dampsurfaces, wetting agents may be includ-ed in primer formulations, or materialsmay be used that preferentially wetsuch surfaces, such as polyamide-curedcoal tar epoxies. For oleoresinous mas-tics, shellac can be used.

4.3.2 Bond breakers. Many backupmaterials do not adhere to sealants andthus, where these are used, no separatebond breaker is needed. Polyethylenetape, coated papers and metal foils areoften used where a separate bondbreaker is needed.


4.3.3 Backup materials. These mate-rials serve to limit the depth of the seal-ant; support it against sagging, indenta-tion, and displacement by traffic, fluidpressure, and other forces; facilitatetooling; and may serve as a bond break-er to prevent the sealant from bondingto the back of the joint. Suitable mate-rials are listed in Table 2. The backupmaterial should preferably be compres-sible so that the sealant is not forcedout as the joint contracts, and it shouldrecover as the joint expands. Care mustbe taken to select the correct width andshape of material so that, after installa-tion, it is in approximately 50 percentcompression. Stretching, twisting, orbraiding of tube or rod stock should beavoided. Backup materials and fillerscontaining bitumen or volatile materialsshould not be used with thermosetting,chemically curing field-molded sealants,since these additives migrate to and/orare absorbed at joint interfaces, thusimpairing adhesion. In the selection of abackup material, it is advisable to fol-low the recommendations of the sealantmanufacturer to insure compatibility.Backup materials necessary to controlthe depth of field-molded sealants orprovide support are usually preformed.

4.4 Preformed sealants andtheir uses

Strictly speaking, compression sealsshould be included with the flexiblegroup of preformed sealants. However,because their functional principle is dif-ferent and because the compartmental-ized neoprene type can be used in al-most all joint sealant applications as analternate to field-molded sealants, it isincluded in Table 1 and treated sepa-rately.

4.4.1 Gaskets and miscellaneousseals. Gaskets and tapes are widely usedsealants between glazing and its frame,around window and other openings inbuildings, and at joints between precastconcrete panels in curtain walls. Suit-

able materials and their uses are listedin Table 3. Sealing action is obtainedeither because the sealant is com-pressed between the joint faces (gas-kets) or because the surface of the seal-ant, as in the case of polyisobutylene,is pressure sensitive and thus adheres.

4.5 Compression seals andtheir uses

These are preformed compartmental-ized or cellular elastomeric deviceswhich, when in compression betweenthe joint faces, function as sealants.

4.5.1 Compartmentalized. Neopreneextruded to the required configurationis currently used for most compressionseals (see Tables 1 and 3). For this ap-plication, the neoprene formulationused must have special properties. 14 Foreffective sealing, sufficient contact pres-sure must be maintained at the jointface. This requires that the seal experi-ences some degree of compression.Good resistance to compression set (thatis, the material must recover sufficientlywhen released) is required. In addition,the neoprene must be crystalization-re-sistant at low temperatures (the resul-tant stiffening may make the seal tem-porarily ineffective though recoverywill occur on warming). If, during themanufacturing process the neoprene isnot fully cured, the interior webs mayadhere together during service, oftenpermanently, when the seal is com-pressed.

To facilitate installation of compres-sion seals, liquid neoprene based lubri-cants are used. For machine installa-tions, additives to make the lubricantthixotropic have been found necessary.Special lubricant adhesives, which bothprime and bond, have been formulatedfor use where improved seal to jointface contact is required. Neoprene com-pression seals are effective joint sealantsover a wide range of temperature in al-most all applications.

26

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

Group Field-molded PreformedType Mastic Cold-applied Thermosetting Compression

thermoplastics Chemically-curina Solvent release seat(F) Polysulfide

Composition (A) Drying oils (E) Acrylics (G) Polyurethane (J) Neoprene (M) Neoprene(B) Nondrying Contain 75-90 (H) Silicones (K) Butadiene rubberoils percent solids (F) (H) Contain styrene(C) Polybutenes and a solvent 95-100 per- (L) Chlorosulf-(D) Polyisobuty- 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) Contains 85asbestos fiber or ponent system 90 percentsiliceous ma- solidsterials.

All contain 100percent solids,except C & Dwhich may con-tain solvent.

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

may be treatedto give variedcolors.

Setting or Noncuring, re- Noncuring, sets Two component Release ofCuring mains viscous on release of system-catalyst. solventA 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 Low Moderate High High Highresistance

Increase inhardness inrelation to(1) Age High High Moderate High Lowor (2) Lowtemperature High High Low High LowRecovery Low Low (F) Moderate Low High

(G) (H) HighResistance to Low Moderate (G) (H) High Moderate Highwear (F) ModerateResistance to Low Low at high High Low Highindentation temperaturesand intrusionof solids

Shrinkage after High High Low High Noneinstallation

Resistance to High except to High except to (F) (G) Low to Low to sol- Highchemicals solvents and alkalis and solvents, fuels, vents, fuels

fuels, oxidizing acids oxidizing acids and oxidizing(H) Low to alkalis acids

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

Allowable i- 3 percent ± 7 percent -± 25 percent -!- 7 percent Must be corn-extension and pressed at allcompression times 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 first cost (A) (B) Very low High Very high Low High(C) (D) Low


Table 2. Preformed materials used for fillers and backup

Composition and type Uses and governing properties InstallationNatural rubber Expansion joint filler. Readily High pliability may(a) Sponge compressible and good recov- cause installation prob-(b) Solid ery. Closed cell. Non-absorp- lems. Weight of plastic

tive. Solid rubber may function concrete may precom-as filler but primarily Intended press it. In constructionas gasket. joints attach to first

placement with adhesive.Neoprene or butyl Backup Compressed into jointsponge tubes Where resilience required in with hand tools.

large joints. Check for com-patibility with sealant as tostaining.

Neoprene or butyl Backup Compressed into jointsponge rods Used in narrower joints. with hand tools or

Check for compatibility with roller.sealant as to staining.

Expanded poly- (a)ҟExpansion joint fillers. Must be rigidly sup-ethylene, poly- Readly compressible, good ported for full lengthurethane, polyvinyl recovery, non-absorptive, during concreting.chloride, or poly- (b) Backup. Compressed into jointpropylene flexible Compatible with most with hand tools.foams sealants.Expanded poly- Expansion joint filler. Support 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. Sometimes

removed after concret-ing where no longerneeded.

Glass fiber or (a)ҟExpansion joint filler. Installed as for wood ormineral wool Made in board form by im- fiberboard materials.

pregnating with bitumen orresins. Easily compressed.

(b) Backup. Insert without In mat form, packedimpregnation so as not loose material or yarn.to damage sealant.

Oakum, jute, or The traditional material for Packed In joint to re-manila yarn and rope packing joints before Installing quired depth.

sealant. Where used as back-up should be untreated withoils, etc.

Portland cement Used at joints in precast units Bed (mortar)grout or mortar and pipes to fill the remaining Inject (grout)

gap when no movement Isexpected and sometimes be-hind waterstops.

4.6 Joint designThe location and width of joints that

require sealing can only be specified byconsidering whether a sealant is avail-able which will take the anticipatedmovement, and what shape factor or,

in the use of preformed sealants, whatsize is required. If the sealants can nottake the anticipated movement, thenthe joint system for the structure mustbe redesigned to reduce the movementat 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 concrete structure.

4.7 Determination of jointmovements and locations

The anticipated length (volume)changes within the structure must bedetermined and translated into joint lo-cations and movements that not only fitthe structural design and maintain theintegrity between the individual struc-tural units, but also consider the factthat each type of sealant currentlyavailable imposes specific limitations onboth the shape of joint that can besealed and the movement that can beaccommodated. When using the appli-cable structural design codes and stan-dards for these calculations, it shouldbe remembered that the sources ofmovement and the nature of the move-ment, both long and short term, can bevery complex in other than simplestructures. Both experience and judg-ment are necessary in the design ofjoints that function satisfactorily. Amore complete discussion of this is be-yond the scope of this report. The fol-lowing simple facts will, if properlyconsidered, result in good joint seal per-formance:

1. The movement of the end of aunit depends on its effective length,that is, on the length of that part of theunit that is free to move in the directionof the joint.

2. Except where a positive anchor isa feature of the design, experienceshows that the only safe assumption isthat a joint between two units may becalled upon to takethe total movementof both units. Based on joint movementmeasured on actual buildings, theBuilding Research Station in England

calculated that movement of each jointshould be multiplied by two for designpurposes. Egon Tons of the Universityof Michigan suggests r5 a multiplicationfactor of 1.7.

3. The actual service temperaturesof the materials being joined, not theambient range, must be used in calcu•lating joint movements.

4. Where units to be joined are ofdissimilar materials, they may not be atthe same surface temperature and theappropriate coefficient for each materialmust be used in calculating its contri-hution to the joint movement. Differ-ential movements resulting from thismay, depending on the joint configura-tion, result in secondary strains in thesealant.

5. Where knowledge exists of actualmovements that have occurred in simi-lar joints in similar structures undersimilar service conditions, these shouldbe used in the new design to supple-ment those indicated by theory alone.

6. Allowance must be made for thepractical tolerances that can beachieved in constructing joint openingsand positioning precast units.

7. In butt joints, the movement towhich the sealant can properly respondis that at right angles to the plane ofjoint faces.

8. The width of the joint sealant res-ervoir must always be greater than themovement that can occur at the joint.

9. When viewing a structure, thejoints, either sealed or unsealed, arereadily noticeable. It is, therefore, de-sirable to either locate and constructthem as a purposeful feature of the ar-chitectural design or to conceal them bystructural or architectural details.

4.8 Selection of butt jointwidths for field-moldedsealants

The selection of the width and depthof 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 Properties significant Available in Usesand type to application

Butyl— High resistance to water, Beads, rods, Waterstops. Corn-conventional vapor and weathering, tubes, flat sheets, bined crack inducerrubber cured Low permanent set and tapes and pur- and seal. Pressure

modulus of elasticity form- pose-made sensitive dust andulations possible, giving shapes. water sealing tapeshigh cohesion and recov- for glazing andery. Tough. Color— curtain walls.black, can be painted.

Butyl—raw, High resistance to water, Beads, tapes, Glazing seals, lappolymer- vapor and weathering, gaskets, grom- seams in metalmodified with Good adhesion to metals, mets. cladding. Curtainresins and glass, plastics. Moldable wall panels.plasticisers into place but resists dis-

placement. Tough andcohesive. Color—black,can be painted.

Neoprene— High resistance to oil, Beads, rods, tubes, Waterstops, glazingconventional water, vapor and weather- flat-sheets, tapes, seals, insulationrubber cured ing. Low permanent set, purpose-made and isolation of

Color—basically black but shapes. Either service lines.other surface colors can solid or open or Tension-compres-be incorporated, closed cell sion seals. Com-

sponges. pression seals.Gaskets.

PVC (polyvinyl High water, vapor, but only Beads, rods, tubes, Waterstops, gaskets,chloride) moderate chemical resis- flat sheets, tapes, combined crack in-Extrusions tance. Low permanent set gaskets, purpose- ducer and seal.or moldings and modulus of elasticity made shapes.

formulations possible, giv-ing high cohesion and re-covery. Tough. Can besoftened by heating forsplicing. Color—pigmentedblack, brown, green, etc.

Polyiso- High water, vapor resis- Beads, tapes, Gaskets, glazingbutylene- tance. High flexibility at grommets, gaskets. seals. Curtain wallnon-curing low temperature. Flows panels. Acoustical

under pressure, surface partitions.pressure sensitive, highadhesion. Sometimes usedwith butyl compounds tocontrol degree of cure.Color—black, grey, white.

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

purpose-madeNBR (nitrile shapes. Eitherbutadiene solid or cellularrubber) and sponges.polyisoprenepolydleneconventionalrubber cured

30

zLUUw

200

LULU

>-

0}-ao 150

J

0WLL

z

100N

WJm

500

d(DEPTH OF

SEALANT)

WIJOINT WIDTHWHEN FILLED)

25)

dwi "3ҟ

/' Wi -2

PROBLEM: IASSUME Wi=1.0 IN.(25.4mm)COMPUTED EXPANSION 0.5 IN.(12.7mm),(50%)MAXIMUM STRAIN FROM LAB.TESTS= 60%

FROM CURVES d MAX =1Wi

dM A X- 1x1.0=1 INCH (25.4 mm)

dwi

d=o

ON0

50 100 150

200

COMPUTED LINEAR EXPANSION — PERCENT

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

(ii) sealant free to assume parabolic shape on both 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: American Concrete Institute)

the maximum allowable strain in thesealant. This occurs in the outer fibers,usually when the sealant is extended,though in some cases maximum strainmay occur while the sealant is com-pressed. The part of the total movement

which extends the sealant is that whichincreases the width of the joint at thetime the sealant is installed to thewidth 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 contributionto the extension of the sealant; but anyresidual drying shrinkage of the con-crete that has yet to occur, and shrink-age in the sealant as it sets or cures,will also impose additional extension onthe sealant.

When the suitability of a new jointsealant is first being considered, and aprecise determination of the dimensionsof the sealant reservoir is required, theapproach using Fig. 4.8.1 may be fol-lowed. The curves relate the maximumallowable strain in a sealant to an as-sumed joint width and various shapefactors. First, the maximum allowablestrain for the sealant under considera-tion must be determined by testing ata specified temperature. Usually thistemperature is 0 F (-18 C) and the testis performed in accordance with therequirements of Federal SpecificationSSR-406-C. Next, a likely approxima-tion to the joint width is assumed, andthe linear extension and compressionthat the sealant will experience, as re-lated to the installed width, are thencalculated.

The various curves then permit thecomputed extension and shape factor tobe interrelated so that the maximumallowable 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. Inpractice, a safety factor of four shouldbe applied in using this chart to allowfor unforeseen circumstances.

The detailed procedure of Fig. 4.8.1is simplified for practical use by usingthe percentage extension-compressionshown in Table 1 for each group ofsealants. This figure has been devel-oped through consideration of the maxi-mum allowable strains for materials inthe group and application of the sug-gested safety factor. The percentage ex-tension-compression of the sealant isthe percentage increase or decrease of

the installed width of the sealant thatcan be safely accommodated as thejoint subsequently opens and closes.The width of the joint to be formed,which becomes the sealant mold andthus determines the sealant width asinstalled, can then be obtained by asimple calculation so that the permis-sible extension-compression range is notexceeded in service. This calculationshould, of course, consider the antici-pated temperature at the time of form-ing the joint, the temperature at seal-ant installation, and any additional jointopening caused by drying shrinkage ofthe abutting concrete units as well asby the extremes of service temperature.

When the joint width is designed, aprecise installation temperature canncusually be known or specified; other-wise, an intolerable restriction wouldbe 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 temperaturecircumstances for installation; for ex-tension the top of the range is used, andfor compression the bottom of therange. A practical range of installationtemperatures is assumed for this andother factors, such as moisture conden-sation at low temperatures and reducedworking life at high temperatures, to befrom 40 to 90 F (4 to 32 C). Generally,because the tension condition, as thejoint opens with a decrease in temper-ature, is the most critical in sealant h^-havior, joint sealants installed a, thelow end of this range may be expectedto perform best. A warning note shouldbe included on the plans that, if sealingmust take place for any reason at tem-peratures above or below the specifiedrange, then a wider than specified jointmay have to be formed, or changes inthe type of sealant or shape factor maybe required to secure greater extensi-bility.

Detailed calculations for selection of


the joint width for sealants with an ex-pansion-compression range of -!- 25percent (which is the most common onefor the widely used class of thermo-setting, chemically curing sealants) canbe dispensed with by the use of Fig.4.8.2. Where a reasonable joint width(see Section 4.11) is not possible byeither of the above considerations or bythose that follow in Section 4.9 as tosealant depth, the proposed joint layoutfor the structure must be redesigned toproduce movements tolerable to sealant.

4.9 Selection of butt jointshape for field -moldedsealants

When a suitable joint width has beenestablished (see Section 4.8), the ap-propriate depth for the sealant reservoirmust be determined so that the sealanthas a good shape factor. 16 Fig. 4.8.1can be used for this purpose. Curves fordepth-to-width ratios of 1:1, 2:1, and3:1 are shown on this chart. Any depth-to-width ratio may be used providedthat the maximum allowable strain isnot exceeded at the computed exten-sion or compression expected in thesealant. The benefits in both betterperformance and economy of mate-rial by using the smallest possibledepth-to-width ratio have alreadybeen discussed in the preceding sec-tion. In general, the depth of sealedjoints should not exceed joint width andthat on wide joints (up to say 4 in.)depth at midwidth should not exceed1/z in., with concave shape giving greaterthickness at panel faces. The depth ofsealant is controlled by using a suitablebackup material as described in Section4.3.3. To obtain full benefit of a well-designed shape factor, a bond breakermust be used behind the sealant (seeSection 4.3.2),

4.10 Selection of size ofcompression seals forbutt joints

A positive contact pressure must be

exerted against the joint faces at alltimes for compression seals to functionproperly. The development of suitableseal configurations to achieve this, whilefollowing the principles explained byDreher, ls has been largely based onthe results of trial and error laboratoryand field experiments in both Americaand Europe. 1719 Neoprene compressionseals must remain compressed approxi-mately 15 percent of the uncompressedseal width at maximum joint opening tomaintain sufficient contact pressure forsealing and to resist displacement; gen-erally, not more than 55 percent of theuncompressed seal width is permitted atmaximum closing to prevent overcom-pression. For larger sizes of compressionseals, the 55 percent value may be ex-ceeded. The allowable movement isthus approximately 40 percent of theuncompressed seal width. The allow-able movement for impregnated foamsis much less, about 5 to 20 percent.

The critical condition exists when thejoint is fully open at low temperaturesince compression set or lack of lowtemperature recovery may adverselyaffect sealant performance. The prin-ciple of size selection is similar to thatfor field-molded sealants in that theoriginal uncompressed width of sealis required to maintain the seal withinthe specified compression range con-sidering the installation temperature,width of formed opening, and the ex-pected movement. A simplified chartapplicable to the conditions specified inthis section is shown in Fig. 4.10.1.

4.11 Limitations on butt jointwidths and movementsfor 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 unexpectedservice conditions.

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Enter

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to Dia

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l Line

.(1

)Ba

sed o

n com

pressi

on ra

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t of u

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Horiz

ontal

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pt sta

ndard

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ine.

seal

width

(may

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eat s

ize an

d man

ufactu

rer).

(3)

Vertic

al to

next

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ard se

al siz

e (no

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t metr

ic eq

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nt).

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Depth

of se

al go

verne

d by s

pecifi

c man

ufactu

rer's d

esign

. This

and

(4)

Follo

w slo

pe to

vertic

ally p

rojec

ted in

stalla

tion t

empe

rature

.ins

et req

uired

for th

e sea

l belo

w the

open

surfa

ce of

the j

oint,

(5)

Horiz

ontal

inter

cept

at rig

ht giv

es jo

int w

idth i

nfo w

hich s

electe

dde

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nes p

ositio

n ofsu

pport

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lders

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al.

size o

f sea

l shou

ld be

insta

lled to

main

tain s

pecifi

ed co

mpres

sion r

ange

.

The upper limit of joint width andpermissible movement varies with thetype of material used. Mastic, thermo-plastic, and thermosetting, solvent re-lease sealants may be used in joints upto 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 injoints up to 4 in. (10.2 cm) wide withmovements in the order of 2 in. (5.1cm), though it is more usual to confinethem to joints of half that size to ensuregood performance and economy in ma-terials. In wide joints, increasing carewith sealant installation is necessaryand, where subject to traffic, protectionof the upper surface against damagewith a steel plate or other means is re-quired.

4.12 Lap joint sealant thicknessShear governs sealant behavior in lap

joints and its magnitude is related toboth the movement that occurs and thethickness of the sealant between thetwo faces. For installations made at nor-mal temperatures of 40 to 90 F (4 to32 C), the thickness of the sealantshould be at least one half the antici-pated movement and, where higher orlower temperatures prevail at installa-tion, the thickness of the sealant shouldbe equal to the anticipated movement.Where there will be no movement,the sealant thickness can be as little as½o in. (1.6 mm). However, in assem-bling concrete units, a minimum thick-ness of '1/z in. (12.7 mm) is desirable tocompensate for casting tolerances or anyirregularities in the faces.

REFERENCES

1. "Weathertight Joints for Walls,"CIB Symposium, Oslo, Norway,Norwegian Building Research In-stitute, 1967.

2. Bishop, D., "Weatherproofing JointsBetween Precast Concrete Panels,"Building Research Station, UnitedKingdom, The Builder, Jan. 5,1962,

3. Latta, J. K., "Precast ConcreteWalls—A New Basis for Design,"Canadian Building Digest #93,National Research Council, Otta-wa, Canada, September 1967.

4. Garden, G. K., "Rain Penetrationand its Control," Canadian Build-ing Digest #40, National ResearchCouncil, Ottawa, Canada, April1963.

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, BritishPrecast Concrete Federation, May1966.

7. PCI Design Handbook, Precast andPrestressed Concrete, PrestressedConcrete 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, Symposium, Royal In-stitute of British Architects, TheConcrete Society, London, En-gland, 1971.

10. "Guide to Joint Sealants for Con-crete Structures," ACI Committee504, ACI Journal, Proceedings,Vol. 67, No. 7, July 1970, pp. 489-536.

11. Karpati, Klara K., "Literature Sur-vey of Sealants," Journal of PaintTechnology, Vol. 40, No. 523, Aug.

36

1968, pp. 337-347.12. de Courcy, J. W., "Movement in

Concrete Structures," Concrete(London), Vol. 3, No. 6, June 1969,pp. 241-246; No. 7, July 1969, pp.293-297; and No. 8, August 1969,pp. 335-338.

13. "Causes, Mechanism, and Controlof Cracking in Concrete," SP-20,American Concrete Institute, De-troit, Michigan, 1968, 246 pp.

14. Hall, Kenneth F., Ritzi, Jack H.;and Brown, Delmont D., "Study ofthe Factors Governing ContactPressure Generating in NeoprenePreformed Compression Seals,"Highway Research Record 200,Highway Research Board, 1967.

15. Tons, Egon, "A Theoretical Ap-

proach to Design of a Road JointSeal," Bulletin No. 229, HighwayResearch Board, 1959, pp. 20-44.

16. Schutz, Raymond J., "Shape Fac-tor in Joint Design," Civil Engi-neering, Vol. 32, No. 10, October1962, pp. 32-36.

17. Watson, Stewart C., "CompressionSeals for Bridges," ACI Journal,Proceedings, Vol. 65, No. 9, Sep-tember 1968, pp. 721-729.

18. Dreher, D., "A Structural Ap-proach to Sealing Joints in Con-crete," Highway Research Record80, Highway Research Board,1965, pp. 57-73.

19. PCI Manual on Architectural Pre-cast Concrete, Prestressed ConcreteInstitute, Chicago, Illinois, 1973.

Discussion of this committee report is invited.Please forward your discussion to PCI Headquarters by August 1, 1973, to permitpublication in the September-October 1973 issue of the PCI JOURNAL.

PCI Journal/March-April 1973 :37

Documents

ARCHITECTURAL PRECAST CONCRETE JOINT DETAILS