Architectural Precast Concrete Joint Details

Home , Joint (building), Precast concrete

ARCHITECTURAL PRECAST CONCRETE JOINT DETAILS

Reported by PCI Committee on Architectural Precast Concrete Joint Details

Raymond J. Schutz Chairman James Engleҟ Albert Litvin James G. Grossҟ R. L. Pare Abraham GutmanҟJohn S. Parrish J. A. Hansonҟ Irwin J. Speyer Kai Holbekҟ Ivan L. Varkay Felix Kulkaҟ Lloyd 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 recommendations will result in a good design and a durable, waterproof, and economical joint.

10 CONTENTS Chapter1—Joint design ...... 12 1.1 Scope 1.2 Types of joints 1.3 General design concepts for joints 1.4 Number of joints 1.5 Location of joints Chapter 2—Planning check lists ...... 14 2.1 Definitions 2.2 Joint planning 2.3 Water runoff planning Chapter3—Joint details ...... 15 3.1 General 3.2 One-stage joints 3.3 Two-stage joints 3.4 Cavity wall 3.5 Floor and roof slab joints 3.6 Precast parapets 3.7 Precast panel window details Chapter 4—Sealant materials ...... 24 4.1 General 4.2 Field-molded sealants and their uses 4.3 Accessory materials 4.4 Preformed sealants and their uses 4.5 Compression seals and their uses 4.6 Joint design 4.7 Determination of joint movements and locations 4.8 Selection of butt joint widths for field-molded sealants 4.9 Selection of butt joint shape for field-molded sealants 4.10 Selection of size of compression seals for butt joints 4.11 Limitations on butt joint widths and movements for various types of sealants 4.12 Lap joint sealant thickness

References ...... 36

PCI Journal/March-April 1973ҟ 11 CHAPTER 1 —JOINT DESIGN

1.1 Scope that it generally provides the lowest first cost, and it is suitable for use be- The design of joints must be exe- tween precast panels as shown in Figs. cuted as an integral part of the total 3.2.1 to 3.2.6. wall design. Some specific guidelines The success of one-stage joints de- for joints do govern their ultimate suc- pends on the quality of materials and cess. This chapter highlights and illus- proper installation at the building site. trates several cases of interdependence This type of joint is in common use in with other wall design criteria. most of North America. One-stage In all cases, the designer should as- joints should be regularly inspected and sess his requirements for joints realisti- may demand fairly frequent mainte- cally with respect to both performance nance to remain weathertight. and cost. If joint designs and details are contemplated which differ from those 1.2.2 Two-stage joints. These joints normally used in the area where the have two lines of defense for weather- project is located, local producers proofing. The typical joint consists of a should be consulted. rain barrier near the exterior face and an air seal normally close to the interior The following discussion will deal face of the panels. The rain barrier is mainly with joints which are designed designed to shed most of the water to accommodate local wall movements from the joint and the air seal is the de- only, rather than an accumulation of marcation line between outside and in- such movements which would require side air pressures. Between these two properly designed expansion joints. stages is an equalization or expansion chamber which must be vented and drained to the outside. Section 3.3 gives 1.2 Types of joints typical details of two-stage joints. It can be seen that the simplest form of a hor- Joints between precast wall panels izontal two-stage joint is the well prov- may be divided into two basic types: en shiplap joint. 1. One-stage joints The rain barrier prevents most of the 2. Two-stage joints rain and airborne water from entering A cavity wall design is considered a the joint. If airborne water (wind-driv- further application of the two-stage en rain) penetrates this barrier, it will joint. drain off in the expansion chamber as the kinetic energy is dissipated and the 1.2.1 One-stage joints. As the name air loses its ability to carry the water. implies, this joint has one line of de- Any water which penetrates the rain fense for its weatherproofing ability. barrier should be drained out of the This occurs normally in the form of a joint by proper flashing installations. sealant close to the exterior surface. In order to avoid vertical movement The advantage of this type of joint is of the air in the expansion chamber

12 (stack effect) caused by wind or outside The two-stage joint is gaining accep- air turbulences, it is advisable to use tance particularly for buildings subject these flashing details as dampers and to severe climatic exposure or tempera- provide them at regularly spaced inter- ture and humidity control. vals along the height of the vertical A disadvantage of the two-stage joint joints. Such flashing is sometimes in- for concrete wall panels is the higher stalled at each floor level, but a greater cost. For projects with good repetitive spacing (two or three stories) may be joint design properly integrated with sufficient for low-rise buildings and in other panel details, and having efficient areas with moderate wind velocities. production and erection procedures, it Since the air seal is the plane where may well approach the cost of one-stage the change in air pressures between the joint installations. In these instances, outside and inside atmospheres occurs, the safety factors and lower mainte- it would normally be subject to water nance costs should also be considered. penetration through capillary action. A minimum precast wall panel thick- Inasmuch as the outside air reaching ness of 4 in. (10.2 cm) (with field- this seal has lost its water content, no molded sealants), preferably 5 in. (12.7 moisture can enter by such action. cm) (with gaskets and compression The danger of humidity traveling seals), is required to accommodate both from inside the building and through the rain barrier and the air seal. For the air seal should be investigated for two-stage joints with compression seals, buildings with relatively higher interior connection detail allowance should be humidity, and for tall buildings, where made for slight horizontal movements the interior air pressure may occasion- of the panels after initial fastening for ally be substantially higher than the air seal compression.5 The joints must outside atmospheric pressure. This con- be fully accessible from the inside of dition is normally solved by using a the panels for later installation of the cavity wall design. air seal. The simplest form of a horizon- A cavity wall (Fig. 3.4.1) is the most tal two-stage joint is the shiplap joint. effective wall for the optimum separa- tion and control of both outside and inside air and humidity conditions. When 1.3 General design concepts precast concrete wall panels are used in for joints cavity wall designs, they will normally serve as the rain barrier. An air space is The purpose of joint design is to pro- maintained between the precast exteri- vide weathertightness of the joint con- or and the interior wall. Insulation, sistent with the exposure of the joint. In when required, is applied to the outside addition, as part of the overall perfor- face of the interior wall, eliminating mance requirements of the building, condensation problems and, thereby, the purpose for which the building is making the inner wall subject only to built will also determine design require- the relatively constant interior tempera- ments for the joint. ture. Cavity wall construction is nor- Thus, joint design will be governed mally expensive when compared with by its exposure (orientation and climatic conventional walls. On the basis of their conditions), the purpose of the building, lower maintenance costs and their ex- and appearance. The following guide- cellent performance records, they may lines must all be evaluated in relation well be justified for specific types and to the relative importance of these cri- locations of buildings. teria.

PCI Journal/March-April 1973ҟ 13 1.4 Number of joints manufactured and erected to close tolerances. Hence, it is recommended that It is generally advantageous to plan joints be placed in any ribbed projec- for the fewest number of joints, due to tions of panels. the lower overall joint cost, potentially lower maintenance cost, and the econ- If ribs are too narrow to accommo- omy of large panel erection. date joints, the full rib may be located in one panel only (Fig. 3.2.6). Another Optimum panel sizes must, however, solution is to design every second panel also be determined from erection condi- with ribs at both edges using the bal- tions and established limitations of ance as infill units. weight and sizes for transportation.7 An important factor in locating and If the desired appearance requires detailing joints is a proper assessment additional joints, this may be achieved of the predicted weathering pattern for through the use of false or dummy the structure. To limit weathering ef- joints. In order to match the appear- fects on the building, it is advisable to ance of both false and real joints, an emphasize the joints by making them applied finish should be chosen to sim- wide and recessed from immediately ulate sealants or gaskets in the real adjacent surfaces.8 Joints in forward joints. Caulking of the false joints adds sloping surfaces are difficult to weather- an unnecessary expense. proof, especially where they may col- lect snow or ice. When these surfaces 1.5 Location of joints cannot be avoided, the architect should include a second line of defense against Joints are easier to design and exe- water penetration. This may be cute if they are located where maximum panel thickness occurs. Except for achieved by sealing the front of the sur- one-stage joints and joints in precast face and using a two-stage joint. If a panels performing as rain barriers in one-stage joint is used, the owner must cavity walls, the minimum panel thick- accept regular inspection of such joints ness at joints should be 4 in. (and pref- and be prepared to perform frequent erably 5 in.) for panels which can be maintenance.

CHAPTER 2—PLANNING CHECK LISTS

2.1 Definitions 2.2 Joint planning Joint planning is recognition of, and 1. Determination of amount of provision for, movement or isolation of movement that can be anticipated. movement in a building or other struc- A. Initial movement ture based on an analysis of esthetic, 1. Shrinkage structural and mechanical require- 2. Foundation ments. 3. Elastic deflection Water runoff planning is the visuali- 4. Other zation of the paths that moisture may B. Life of structure movement take, or its entrapment, and the provi- 1. Temperature sions of safe channels for its flow and 2. Moisture discharge. 3. Wind

14 4. Earthquake or other founda- qualities tion movement 4. Differing exposure to heat or 5. Live load deflections moisture 6. Creep B. Isolation of vibrations 7. Other 1. Internal (machinery or activ- 2. Architectural (esthetic) considera- ity) tions 2. External A. Accentuated jointing C. Other B. Hidden joints 5. Material considerations C. Spacing (a few large or many A. Field-molded sealants small) 1. Mastics D. Environmental needs 2. Thermoplastics 1. Water control 3. Thermosetting 2. Air control (circulation) 4. Accessory materials 3. Temperature control B. Preformed sealants 4. Noise (vibration control) 1. Rigid waterstops 3. Structural considerations 2. Flexible waterstops A. Elimination of stress in structur- 3. Gaskets al materials through relief of al- C. Other lowed movement. 6. Tolerances B. Design to resist movement A. Production through the accumulation of B. Erection stress. C. Adjacent construction C. Location of expansion-contraction joints to maintain the structural integrity. 2.3 Water runoff planning 1. Expansion-contraction joints 1. Resistance to penetration 2. Construction joints A. Seal 3. Articulating joints B. Shape of joint 4. Mechanical considerations 2. Channelization of moisture and A. Differential movement potential discharge 1. Differing coefficients of ex- A. Planned channelizing joints pansion (two-stage system) 2. Differing heat absorption B. Channelization of inadvertent rates or seepage penetration (one- 3. Differing moisture absorption stage system)

CHAPTER 3-JOINT DETAILS

3.1 General oped within the recommendations of This chapter shows typical details for this report that will provide satisfactory one-stage and two-stage joints, for floor service. Thus, it is not intended that and roof slab joints, for precast concrete these details be used to the exclusion of parapets, and for windows in precast all others, but rather that they be taken concrete panels. The committee recog- to illustrate the features of good joint nizes that other details can be devel- planning and design.

PCI Journal/March-April 1973ҟ 15 3.2 One-stage joints

p P ^ Pҟe .D. b.

p • P O p ' 6 a G DD 1 s p D . pɁD . D .ҟP 3/8°MIN. D• 3/ $MIN. VERTICAL HORIZONTAL JOINT WIDTH JOINT WIDTH p • pҟD ^ a p. ° • b.°

pDp D .,°P D^.pɁ.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. D ҟD, D P MIN. s aɁ ° JOINT WIDTH °ҟ.D-^ • D p D • p ' ° e• ' e D•

D ° • 0 .p •p . p Q a D Q D• • A.

° - (1112" X MAX. 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 ^N N • D- d. a..a P 3/8" MIN. a ^ D°o oa >a JOINT WIDTH ° a P 'D 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 ROPE 1.5 TIMES THE THEORETICAL JOINT WIDTH EXPANSION 4"MIN ^4 ^2 I CHAMBER 1ҟ1ҟ,

w • D Via. ° rn^a ^ ^ AIR SEAL N N W K o •d. .•d, • \ \ r ,Aҟ vҟ

^ ^N -0J d W . Q • p^ - ^W Z r ' d a f W • d pҟ- a iD v a d.

D , I/6 ^2 I/8 PERFORATED ^N NEOPRENE TUBE EXTERIORҟ d d^ d FACE RAIN BARRIER (MIN. I /16"/ 1° ) Fig. 3.3.1. Two-stage joint vertical Fig. 3.3.2. Two-stage joint horizontal gaskets gasket

2"MIN. z • 1dҟ'

0 1 ' 0Ɂ• O o •. d

• D ' D .ҟPҟe Dҟ•ҟ9 SEALANT(IF USED)MUST BE DISCONTINUED AT INTERVALS (VERTICAL JOINTS) TO DRAIN SEALANT DISCONTINUED AREA BETWEEN IT AND AIR SEAL AT HORIZONTAL JOINT Fig. 3.3.3. Two-stage joint vertical Fig, 3.3.4. Two-stage joint horizontal sealants 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 MEMBRANE PREFORMED ELASTOMER (STEEL REINFORCED) (OPTIONAL) (STEEL REINFORCED)

p 4 •Q .4 Q

.. a• ' D D . 4

O D D• D e

Fig. 3.5.1 Fig. 3.5.2

STEEL PLATES

4 ` d b`, D, 4 , p , p D. D •p p ,0 D 1. D D. 0 D•

O D

PREFORMED COMPRESSION SEAL NEOPRENE (SOMETIMES COMBINED WITH P.V.C. SHEET OR SHEET NEOPRENE SECONDARY SYSTEMS.) Fig. 353 Fig,3.5.4

COVERPLATE

ADHESIVE

•aҟ•ҟ4 ° ••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

PCI Journal/March-April 1973ҟ 19 NN

STUD

BENT CUR )N PC. PANEL 3IIY2MIN. BELOW 2-PC. MET. FLASH. N DETAIL /

t a a o CLOSED CELL JOINT SPONGENEOPENE GASKE ^Ia o SEALANT r.: ( I° MAX. 2' X 3°CONT FLASH. 8°MIN. CONT. BENT PLATE — A.. D e: . 4..4.

oy CONT. MET. •D CAP FLASH

u`D

•e . ^I to • D .^ II A.D JOINT GASKETҟII. D vll ellp.•D,^

^Ilp^o U. v.D•a

o o ALTERNATE PARAPET CAP FLASHING

Fig. 3.6.2. Precast parapet with guarded roof flashing

20 CLOSED CELL NEOPRENE SPONGE - HOLD IN PLACE WITH / s •o MASTIC ADHESIVE

GASKETҟli n D`I 2 2 PC. MET. FLASH. DIҟ, 112.. D I I , ° Qd r vi I Q. ry -CONT. 314° X 4" NAILER WI Oḏ MECHANICAL FASTENER oli . D • D •4

• (l a . D o l u

., D ol^ ,d .a "— ADVISABLE TO PROVIDE IA P.V.C. FLEXIBLE FLASHING ACROSS PANEL JOINT POINTS

III • ^ o

Fig. 3.6.3. Precast parapet with flush roof flashing

FIELD-MOLDED SEALANT

RAIN BARRIE -ROOFING DETAILS =E FIGS. 3.6.2 a 3.6.3)

R SEAL

Fig. 3.6.4. Precast parapet two-stage joint

PCI Journal/March-April 1973 21 3.7 Precast panel windows details

-PVCDE I HEAD ONLY

AN is" -SHIA11,

HEAD

CAULK 1, C PANEL Iru1i.Jl CAULK HEAD (JAMB1 SIMILAR)i

JAMB

CAULK

PANEL

SILL SILL

Fig. 3.7.1. Wood casement in pre- Fig. 3.7.2. Aluminum sash in precast concrete panel cast concrete panel

AIR SPACE

GLASS

CAULEING1I

BUTYL,,

HEATING 11W COVER

\CAULKING -BACKING CLOSED CELLFOAM i

Fig. 3.7.3. Fixed window in precast panel

22 • j2 PLASTIC TUBE

+4 Y ° ° a EXTRUSION SNAP-ON VINYL PREFORMED SEALANTS PREFORMED SEALANTS

JAMB ALTERNATE JAMB (HEAD SIMILAR) (HEAD SIMILAR)

PREFORMED SEALANTS NEOPRENE II SHIMS

SILL

- ALTERNATE Fig. 3.7.4. Fixed DRAINAGE window in precast concrete panel

Fig. 3.7.5. Panel with PVC reglet and spline gasket

PCI Journal/March-April 1973ҟ 23 CHAPTER 4—SEALANT MATERIALS

4.1 General 4.2 Field-molded sealants and No one material has the perfect com- their uses bination of properties necessary to fully The following types of materials list- meet each and every one of the require- ed in Table 1 are currently used as ments for each and every application. If field-molded sealants: there were, and its price were reasonable, obviously it would be in universal 4.2.1 Mastics. Mastics are composed use. It therefore is a matter of selecting, of viscous liquid rendered immobile by from among a large range of materials, the addition of fibers and fillers. They a particular material that offers the do not usually harden, set or cure after right properties at a reasonable price to applications, but instead form a skin on satisfy the job requirements. the surface exposed to the atmosphere. For many years oil-based mastics or The vehicle in mastics may include bituminous compounds and metallic drying or nondrying oils (including ole- materials were the only sealants avail- oresinous compounds), polybutenes, able. For many applications these tra- polyisobutylenes, low-melting point as- ditional materials do not perform well phalts, or combinations of these mate- and in recent years there has been ac- rials. With any of these, a wide variety tive development of many types of elas- of fillers is used, including asbestos fi- tomeric sealants whose behavior is ber, fibrous talc or finely divided cal- largely elastic, rather than plastic, and careous or siliceous materials. The func- which are flexible rather than rigid at tional extension-compression range for normal service temperatures. Elasto- these materials is approximately ± 3 meric materials are available as field- percent. molded and preformed sealants. They are used in buildings for gener- Though initially more expensive, they al caulking and glazing where only very may be more economical over an ex- small joint movements are anticipated tended period due to longer service life. and economy in initial cost outweighs Furthermore, as will be seen, they can that of maintenance or replacement. seal joints where considerable move- With passage of time, most mastics tend ments occur which could not have been to harden in increasing depth as oxida- sealed by the traditional materials. This tion and loss of volatiles occur, thus re- has opened up new engineering and ducing their serviceability. Polybutene architectural possibilities to the design- and polyisobutylene mastics have a er of concrete structures. somewhat longer service life than do the other mastics. No attempt has been made in this chapter to list or discuss every attribute 4.2.2 Thermoplastics (cold-applied, of every sealant on the market. Discus- solvent or emulsion type). These mate- sion is limited to those features consid- rials are set either by the release of sol- ered important to the designer, speci- vents or the breaking of emulsions on fier, and user so that the claims made exposure to air. Sometimes they are for various materials can be assessed heated to a temperature not exceeding and a suitable choice for the application 120 F (49 C) to facilitate application can be made. but usually they are handled at ambient

24 temperature. Release of solvent or wa- lease). Another class of thermosetting ter can cause shrinkage and increased sealants are those which cure by the re- hardness with a resulting reduction in lease of solvent. Chlorosulfonated poly- the permissible joint movement and in ethylene and certain butyl and neo- serviceability. Products in this category prene materials are included in this include acrylic, vinyl and modified bu- class and their performance character- tyl types which are available in a vari- istics generally resemble those of ther- ety of colors. Their maximum exten- moplastic solvent release materials (see sion-compression range is ± 7 percent. Section 4.2.2). They are, however, less Heat softening and cold hardening sensitive to variations in temperature may, however, reduce this figure. once they have set up on exposure to These materials are restricted in use the atmosphere. Their maximum exten- to joints with small movements. Acryl- sicn-compression range does not, how- ics and vinyls are used in buildings pri- ever, exceed ± 7 percent. They are marily for caulking and glazing. primarily used as sealants for caulking and for horizontal and vertical joints in 4.2.3 Thermosetting (chemically cur- buildings which have small movements. ing). Sealants in this class are either Their cost is somewhat less than that of one- or two-component systems which other elastomeric sealants, and their cure by chemical reaction to a solid service life is likely to be satisfactory, state from the liquid form in which though for some recent products this they are applied. They include polysul- has not yet been established by expe- fide, silicone, urethane and epoxy-based rience. materials. The properties that make them suitable as sealants for a wide 4.2.5 Rigid. Where special properties range of uses are: resistance to weather- are required and movement is negligi- ing and ozone; flexibility and resilience ble, certain rigid materials can be used at both high and low temperatures; and as field-molded sealants for joints and inertness to a wide range of chemicals cracks. These include portland cement including, for some, solvents and fuels. mortar and modified epoxy resins. In addition, the abrasion and indentation resistance of urethane sealants is above average. Thermosetting, chemi- 4.3 Accessory materials cally curing sealants have an expansion- 4.3.1 Primers. Where primers are re- compression range of up to -!- 25 per- quired, a suitable proprietary material cent depending on the one used, at compatible with the sealant is usually temperatures from —40 F to +180 F supplied with it. To overcome damp (-40 C to +82 C). Silicone sealants re- surfaces, wetting agents may be includ- main flexible over an ever wider tem- ed in primer formulations, or materials perature range. may be used that preferentially wet These sealants have a wide range of such surfaces, such as polyamide-cured uses in buildings and containers for coal tar epoxies. For oleoresinous mas- both vertical and horizontal joints, and tics, shellac can be used. may be used in pavements. Though ini- 4.3.2 Bond breakers. Many backup tially more expensive, thermosetting, materials do not adhere to sealants and chemically curing sealants can accom- thus, where these are used, no separate modate greater movements than other bond breaker is needed. Polyethylene field-molded sealants, and generally tape, coated papers and metal foils are have a much greater service life. often used where a separate bond 4.2.4 Thermosetting (solvent re- breaker is needed.

PCI Journal/March-April 1973 25 4.3.3 Backup materials. These mate- able materials and their uses are listed rials serve to limit the depth of the seal- in Table 3. Sealing action is obtained ant; support it against sagging, indenta- either because the sealant is com- tion, and displacement by traffic, fluid pressed between the joint faces (gas- pressure, and other forces; facilitate kets) or because the surface of the seal- tooling; and may serve as a bond break- ant, as in the case of polyisobutylene, er to prevent the sealant from bonding is pressure sensitive and thus adheres. to the back of the joint. Suitable materials are listed in Table 2. The backup 4.5 Compression seals and material should preferably be compres- their uses sible so that the sealant is not forced out as the joint contracts, and it should These are preformed compartmental- recover as the joint expands. Care must ized or cellular elastomeric devices be taken to select the correct width and which, when in compression between shape of material so that, after installa- the joint faces, function as sealants. tion, it is in approximately 50 percent 4.5.1 Compartmentalized. Neoprene compression. Stretching, twisting, or extruded to the required configuration braiding of tube or rod stock should be is currently used for most compression avoided. Backup materials and fillers seals (see Tables 1 and 3). For this ap- containing bitumen or volatile materials plication, the neoprene formulation should not be used with thermosetting, used must have special properties. 14 For chemically curing field-molded sealants, effective sealing, sufficient contact pres- since these additives migrate to and/or sure must be maintained at the joint are absorbed at joint interfaces, thus face. This requires that the seal experi- impairing adhesion. In the selection of a ences some degree of compression. backup material, it is advisable to fol- Good resistance to compression set (that low the recommendations of the sealant is, the material must recover sufficiently manufacturer to insure compatibility. when released) is required. In addition, Backup materials necessary to control the neoprene must be crystalization-re- the depth of field-molded sealants or sistant at low temperatures (the resul- provide support are usually preformed. tant stiffening may make the seal tem- porarily ineffective though recovery 4.4 Preformed sealants and will occur on warming). If, during the their uses manufacturing process the neoprene is Strictly speaking, compression seals not fully cured, the interior webs may should be included with the flexible adhere together during service, often group of preformed sealants. However, permanently, when the seal is com- because their functional principle is dif- pressed. ferent and because the compartmental- To facilitate installation of compres- ized neoprene type can be used in al- sion seals, liquid neoprene based lubri- most all joint sealant applications as an cants are used. For machine installa- alternate to field-molded sealants, it is tions, additives to make the lubricant included in Table 1 and treated sepa- thixotropic have been found necessary. rately. Special lubricant adhesives, which both 4.4.1 Gaskets and miscellaneous prime and bond, have been formulated seals. Gaskets and tapes are widely used for use where improved seal to joint sealants between glazing and its frame, face contact is required. Neoprene com- around window and other openings in pression seals are effective joint sealants buildings, and at joints between precast over a wide range of temperature in al- concrete panels in curtain walls. Suit- most all applications.

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

Group Field-molded Preformed Type 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 rubber oils 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- ethylene bination of 100 percent (J) (L) Contain C D solids 80-90 per- All used with fill- May be either cent solids era such as one or two corn- (K) Contains 85 asbestos fiber or ponent system 90 percent siliceous ma- solids terials. All contain 100 percent solids, except C D which may contain solvent. Colors (A) (B) Varied Varied (F) (H) Varied (J) Limited Black (C) (D) Limited (G) Limited (L) Varied Exposed surfaces may be treated to give varied colors. Setting or Noncuring, re- Noncuring, sets Two component Release of Curing mains viscous on release of system-catalyst. solvent A and B form solvent or One component skin on exposed evaporation of system-moisture surface, water; remains pickup from the soft except for air. surface.skin. Aging and weathering Low Moderate High High High resistance Increase in hardness in relation to (1) Age High High Moderate High Low or (2) Low temperature High High Low High Low Recovery Low Low (F) Moderate Low High (G) (H) High Resistance to Low Moderate (G) (H) High Moderate High wear (F) Moderate Resistance to Low Low at high High Low High indentation temperatures and intrusion of solids Shrinkage after High High Low High None installation Resistance to High except to High except to (F) (G) Low to Low to sol- High chemicals 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 Moderate 100 percent (H) High elongation Allowable i- 3 percent ± 7 percent -± 25 percent -!- 7 percent Must be corn- extension and pressed at all compression times to 45-85 percent of its original width. Other (A) (B) (C) (D) Nonstaining (K) (L) Non- properties Nonstaining staining (C) (D) Pick up (L) Good vapor dirt; use in-con- and dust sealer cealed location only. Unit first cost (A) (B) Very low High Very high Low High (C) (D) Low

PCI Journal/March-April 1973ҟ 27 Table 2. Preformed materials used for fillers and backup

Composition and type Uses and governing properties Installation Natural 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 construction as gasket. joints attach to first placement with adhesive. Neoprene or butyl Backup Compressed into joint sponge tubes Where resilience required in with hand tools. large joints. Check for compatibility with sealant as to staining. Neoprene or butyl Backup Compressed into joint sponge 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 length urethane, polyvinyl recovery, non-absorptive, during concreting. chloride, or poly- (b) Backup. Compressed into joint propylene flexible Compatible with most with hand tools. foams sealants. Expanded poly- Expansion joint filler. Support In place during ethylene, poly- Useful to form a gap after sig- concreting. In construc- urethane or poly- nificant compression will not tion joints attach to first styrene rigid foams recover. placement. Sometimes removed after concreting where no longer needed. Glass fiber or (a)ҟExpansion joint filler. Installed as for wood or mineral wool Made in board form by im- fiberboard materials. pregnating with bitumen or resins. Easily compressed. (b) Backup. Insert without In mat form, packed impregnation 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 backup should be untreated with oils, 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 Is expected and sometimes behind waterstops.

4.6 Joint design in the use of preformed sealants, what The location and width of joints that size is required. If the sealants can not require sealing can only be specified by take the anticipated movement, then considering whether a sealant is avail- the joint system for the structure must able which will take the anticipated be redesigned to reduce the movement movement, and what shape factor or, at the joints. Sealing systems currently

28 available can accommodate (at increas- calculated that movement of each joint ing cost) movements up to about 15 in. should be multiplied by two for design (38.8 cm) and are presently being de- purposes. Egon Tons of the University signed for even greater movements. of Michigan suggestsr5 a multiplication With due forethought it should, there- factor of 1.7. fore, be possible to design and specify a 3. The actual service temperatures suitable sealed joint for almost any type of the materials being joined, not the of concrete structure. ambient range, must be used in calcu• lating joint movements. 4.7 Determination of joint 4. Where units to be joined are of movements and locations dissimilar materials, they may not be at The anticipated length (volume) the same surface temperature and the changes within the structure must be appropriate coefficient for each material determined and translated into joint lo- must be used in calculating its contri- cations and movements that not only fit hution to the joint movement. Differ- the structural design and maintain the ential movements resulting from this integrity between the individual struc- may, depending on the joint configura- tural units, but also consider the fact tion, result in secondary strains in the that each type of sealant currently sealant. available imposes specific limitations on 5. Where knowledge exists of actual both the shape of joint that can be movements that have occurred in simi- sealed and the movement that can be lar joints in similar structures under accommodated. When using the appli- similar service conditions, these should cable structural design codes and stan- be used in the new design to supple- dards for these calculations, it should ment those indicated by theory alone. be remembered that the sources of 6. Allowance must be made for the movement and the nature of the move- practical tolerances that can be ment, both long and short term, can be achieved in constructing joint openings very complex in other than simple and positioning precast units. structures. Both experience and judg- 7. In butt joints, the movement to ment are necessary in the design of which the sealant can properly respond joints that function satisfactorily. A is that at right angles to the plane of more complete discussion of this is be- joint faces. yond the scope of this report. The fol- 8. The width of the joint sealant res- lowing simple facts will, if properly ervoir must always be greater than the considered, result in good joint seal per- movement that can occur at the joint. formance: 9. When viewing a structure, the 1. The movement of the end of a joints, either sealed or unsealed, are unit depends on its effective length, readily noticeable. It is, therefore, de- that is, on the length of that part of the sirable to either locate and construct unit that is free to move in the direction them as a purposeful feature of the ar- of the joint. chitectural design or to conceal them by 2. Except where a positive anchor is structural or architectural details. a feature of the design, experience shows that the only safe assumption is 4.8 Selection of butt joint that a joint between two units may be widths for field-molded called upon to takethe total movement sealants of both units. Based on joint movement The selection of the width and depth measured on actual buildings, the of field-molded sealants, for the com- Building Research Station in England puted movement in a joint, is based on

PCI Journal/March-April 1973ҟ 29 Table 3. Preformed materials used for waterstops, gaskets, and miscellaneous sealing purposes

Composition Properties significant Available in Uses and type to application Butyl— High resistance to water, Beads, rods, Waterstops. Corn- conventional vapor and weathering, tubes, flat sheets, bined crack inducer rubber cured Low permanent set and tapes and pur- and seal. Pressure modulus of elasticity form- pose-made sensitive dust and ulations possible, giving shapes. water sealing tapes high cohesion and recov- for glazing and ery. Tough. Color— curtain walls. black, can be painted. Butyl—raw, High resistance to water, Beads, tapes, Glazing seals, lap polymer- vapor and weathering, gaskets, grom- seams in metal modified with Good adhesion to metals, mets. cladding. Curtain resins and glass, plastics. Moldable wall panels. plasticisers into place but resists displacement. Tough and cohesive. Color—black, can be painted. Neoprene— High resistance to oil, Beads, rods, tubes, Waterstops, glazing conventional water, vapor and weather- flat-sheets, tapes, seals, insulation rubber 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, giving high cohesion and recovery. Tough. Can be softened by heating for splicing. Color—pigmented black, brown, green, etc. Polyiso- High water, vapor resis- Beads, tapes, Gaskets, glazing butylene- tance. High flexibility at grommets, gaskets. seals. Curtain wall non-curing low temperature. Flows panels. Acoustical under pressure, surface partitions. pressure sensitive, high adhesion. Sometimes used with butyl compounds to control 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-made NBR (nitrile shapes. Either butadiene solid or cellular rubber) and sponges. polyisoprene polydlene conventional rubber cured

25)

z d d / (DEPTH OF LU wi "3ҟ U SEALANT) Wi -2 w WI 200 JOINT WIDTH WHEN FILLED) d wi LU LU

>- d=o }-0 a o 150

0 WLL z

100 N W J m

PROBLEM: I ASSUME Wi=1.0 IN.(25.4mm)

50 COMPUTED EXPANSION 0.5 IN.(12.7mm),(50%) 0 MAXIMUM STRAIN FROM LAB.TESTS= 60%

FROM CURVES d MAX =1 Wi

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

ON 0 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 the which extends the sealant is that which sealant. This occurs in the outer fibers, increases the width of the joint at the usually when the sealant is extended, time the sealant is installed to the though in some cases maximum strain width of the joint at its maximum open- may occur while the sealant is com- ing. The temperature difference be- pressed. The part of the total movement tween that at installation and at maxi-

PCI Journal/March-April 1973ҟ 31 W Z7 mm IN mm IN IN mm .l 51/2 !A 40 It/. 5% o 3 13/e E Z E 125 5 5 -125 (i) Coefficient of Thermal Expansion of Concrete 3s 6.6 x 10 6 in./in./°F (11.9 x 10 6 mm./mm./ C) q Z (iii Shrinkage neglected 41/2 4 (iiil Temperature Range L T 150°F (83°C) 41/n ( iv) 101 x LL< SW at 90 0 F (82°C) Q3 308 E 90 x AL < % W at 40 O F (4 WC) 100 4 4 -100 Z O ^ 1 31/. 31/2 25 d ^^ Z ^O^ O 1 75-I 3 "p. 3 75 20 3/4 O 1- O• coo Z 21/2 21/2 n 21/4

p 15 8 50-) 2 •2 5(

p 1/2 13/4 n coo 11/2 11/2 10 3/8 11/4 11/4 25 1 1 2: 1/4 3/q 5 4 _ Z 1/2 1/ 4 0 0 0 40 60 80 100 FEET 0 -20 0 20 40 60 80 100 121 1 1 0 F 0 20 + 0 5 10 15 20 25 30 METERS -29 -18 -7 +4 16 27 38 49 54°C TEMPERATURE IN °F ANDC EFECTIVE LENGTH (L) OF UNIT IN FEET AND METERS -

(S Method of Use Ill Enter at L to diagonal line 131 Follow slope to vertically projected Installation Temp. (2) Horizontal to intercept Max Joint Width line (4) Follow horizontal intercept right to Min Joint Width line to determine joint width at installation CM) mum opening is the main contribution the installed width of the sealant that to the extension of the sealant; but any can be safely accommodated as the residual drying shrinkage of the con- joint subsequently opens and closes. crete that has yet to occur, and shrink- The width of the joint to be formed, age in the sealant as it sets or cures, which becomes the sealant mold and will also impose additional extension on thus determines the sealant width as the sealant. installed, can then be obtained by a When the suitability of a new joint simple calculation so that the permis- sealant is first being considered, and a sible extension-compression range is not precise determination of the dimensions exceeded in service. This calculation of the sealant reservoir is required, the should, of course, consider the antici- approach using Fig. 4.8.1 may be fol- pated temperature at the time of form- lowed. The curves relate the maximum ing the joint, the temperature at seal- allowable strain in a sealant to an as- ant installation, and any additional joint sumed joint width and various shape opening caused by drying shrinkage of factors. First, the maximum allowable the abutting concrete units as well as strain for the sealant under considera- by the extremes of service temperature. tion must be determined by testing at When the joint width is designed, a a specified temperature. Usually this precise installation temperature cannc temperature is 0 F (-18 C) and the test usually be known or specified; other- is performed in accordance with the wise, an intolerable restriction would requirements of Federal Specification be placed on the installation operation. SSR-406-C. Next, a likely approxima- Normally a general installation temper- tion to the joint width is assumed, and ature range is specified. This can be the linear extension and compression done safely by checking the dimension- that the sealant will experience, as real range under the worst temperature lated to the installed width, are then circumstances for installation; for ex- calculated. tension the top of the range is used, and The various curves then permit the for compression the bottom of the computed extension and shape factor to range. A practical range of installation be interrelated so that the maximum temperatures is assumed for this and allowable strain will not be exceeded. other factors, such as moisture conden- More than one solution is usually possi- sation at low temperatures and reduced ble and, where the upper limits of the working life at high temperatures, to be curves are approached, a wider as- from 40 to 90 F (4 to 32 C). Generally, sumed joint width should be tried. In because the tension condition, as the practice, a safety factor of four should joint opens with a decrease in temper- be applied in using this chart to allow ature, is the most critical in sealant h^- for unforeseen circumstances. havior, joint sealants installed a, the The detailed procedure of Fig. 4.8.1 low end of this range may be expected is simplified for practical use by using to perform best. A warning note should the percentage extension-compression be included on the plans that, if sealing shown in Table 1 for each group of must take place for any reason at tem- sealants. This figure has been devel- peratures above or below the specified oped through consideration of the maxi- range, then a wider than specified joint mum allowable strains for materials in may have to be formed, or changes in the group and application of the sug- the type of sealant or shape factor may gested safety factor. The percentage ex- be required to secure greater extensi- tension-compression of the sealant is bility. the percentage increase or decrease of Detailed calculations for selection of

PCI Journal/March-April 1973 33 the joint width for sealants with an ex- exerted against the joint faces at all pansion-compression range of -!- 25 times for compression seals to function percent (which is the most common one properly. The development of suitable for the widely used class of thermo- seal configurations to achieve this, while setting, chemically curing sealants) can following the principles explained by be dispensed with by the use of Fig. Dreher,ls has been largely based on 4.8.2. Where a reasonable joint width the results of trial and error laboratory (see Section 4.11) is not possible by and field experiments in both America either of the above considerations or by and Europe. 1719 Neoprene compression those that follow in Section 4.9 as to seals must remain compressed approxi- sealant depth, the proposed joint layout mately 15 percent of the uncompressed for the structure must be redesigned to seal width at maximum joint opening to produce movements tolerable to sealant. maintain sufficient contact pressure for sealing and to resist displacement; gen- 4.9 Selection of butt joint erally, not more than 55 percent of the shape for field-molded uncompressed seal width is permitted at sealants maximum closing to prevent overcom- When a suitable joint width has been pression. For larger sizes of compression established (see Section 4.8), the ap- seals, the 55 percent value may be ex- propriate depth for the sealant reservoir ceeded. The allowable movement is must be determined so that the sealant thus approximately 40 percent of the has a good shape factor. 16 Fig. 4.8.1 uncompressed seal width. The allow- can be used for this purpose. Curves for able movement for impregnated foams depth-to-width ratios of 1:1, 2:1, and is much less, about 5 to 20 percent. 3:1 are shown on this chart. Any depth- The critical condition exists when the to-width ratio may be used provided joint is fully open at low temperature that the maximum allowable strain is since compression set or lack of low not exceeded at the computed exten- temperature recovery may adversely sion or compression expected in the affect sealant performance. The prin- sealant. The benefits in both better ciple of size selection is similar to that performance and economy of mate- for field-molded sealants in that the rial by using the smallest possible original uncompressed width of seal depth-to-width ratio have already is required to maintain the seal within been discussed in the preceding sec- the specified compression range con- tion. In general, the depth of sealed sidering the installation temperature, joints should not exceed joint width and width of formed opening, and the ex- that on wide joints (up to say 4 in.) pected movement. A simplified chart depth at midwidth should not exceed applicable to the conditions specified in 1/z in., with concave shape giving greater this section is shown in Fig. 4.10.1. thickness at panel faces. The depth of sealant is controlled by using a suitable 4.11 Limitations on butt joint backup material as described in Section widths and movements 4.3.3. To obtain full benefit of a well- for various types of designed shape factor, a bond breaker sealants must be used behind the sealant (see Field-molded sealants generally re- Section 4.3.2), quire a minimum joint width of 1/4 in. 4.10 Selection of size of (6.4 mm) to provide an adequate re- compression seals for serve against loss of material due to ex- butt joints trusion or to accommodate unexpected A positive contact pressure must be service conditions.

mm) IN. 60 DL = q■^TxL IN. mm n ^' 21h a 6.6 x 10-6 IN./IN. °F(11.9x10- 6mm/mm°C) r. 3^ s r14° WMIN^0.50xWn I I Ip -I h Q O 2 WMAX<0.85xWn \ 5 125 W0 = WIDTH Of JOINT `^ I -I 3 J I 3F 41/2 • 45 13/4 PROBLEM : er^^ n o E E E E A B C D ^hO 4 1C Z 40 11/2 80 88 80 — LA=168 — -lp 80 OA a 35 4 3%2 T=120°F(-20.°F,100°F) I I% APPROACH SLAB WILL BE PLACED 31 0 A ^ 0 30 LAST AFTER THE DECK) AT 65 °F /2 alp 3 75 JOINT A 3 " p N Z O O O 25 1 ALA=1.99" _ TNN 21/2 Wrl , 6^. I O Z 21/ Wj -3/8 AT 65-F W 20 3/4 ^- 2 5C O JOINT D w 2 N 13/4 15 6LD=0.95" I I 13/ 1/2 15/8 11/2 Wi- 2" o 1 4 n 2 10- I I 11/4 ^ p AT I ? 1 25 1/ 65F (5) 13^ o R 5 4 6 4 3/4 2 1/2 n ^v 0 1/4 N ti" 0 50 100 150 200 FEET -20 0 +20 40 60 80 100 •130 •F ^ o ) ( I I 0 15 30 45 60 METERS _29 _18 -7 +4 -q 16 27 38 +54 •C EFECTIVE UNIT LENGTH ( L), FEET (METERS) TEMPERATURE IN •F AND •C Method of use: Notes: (1) Enter at Effective Length L to Diagonal Line. (1) Based on compression range of 15 to 50 percent of uncompressed (2) Horizontal to intercept standard inch seal size tine. seal width (may vary with seat size and manufacturer). (3) (2) Depth of seal governed by specific manufacturers design. This and Vertical to next standard seal size (no direct metric equivalent). Cn OC (4) Follow slope to vertically projected installation temperature. inset required for the seal below the open surface of the joint, (5) Horizontal intercept at right gives joint width info which selected determines position ofsupport shoulders (S/ to underside ofseal. size of seal should be installed to maintain specified compression range. The upper limit of joint width and 4.12 Lap joint sealant thickness permissible movement varies with the Shear governs sealant behavior in lap type of material used. Mastic, thermo- joints and its magnitude is related to plastic, and thermosetting, solvent re- both the movement that occurs and the lease sealants may be used in joints up thickness of the sealant between the to 11/a in. (3.8 cm) wide with a permis- two faces. For installations made at nor- sible movement not exceeding Y4 in. mal temperatures of 40 to 90 F (4 to (6.4 mm). Thermosetting, chemically- 32 C), the thickness of the sealant curing materials have been used in should be at least one half the antici- joints up to 4 in. (10.2 cm) wide with pated movement and, where higher or movements in the order of 2 in. (5.1 lower temperatures prevail at installa- cm), though it is more usual to confine tion, the thickness of the sealant should them to joints of half that size to ensure be equal to the anticipated movement. good performance and economy in ma- Where there will be no movement, terials. In wide joints, increasing care the sealant thickness can be as little as with sealant installation is necessary ½o in. (1.6 mm). However, in assem- and, where subject to traffic, protection bling concrete units, a minimum thick- of the upper surface against damage ness of '1/z in. (12.7 mm) is desirable to with a steel plate or other means is re- compensate for casting tolerances or any quired. irregularities in the faces.

REFERENCES

1. "Weathertight Joints for Walls," al Congress of the Precast Concrete CIB Symposium, Oslo, Norway, Industry, London, England, British Norwegian Building Research In- Precast Concrete Federation, May stitute, 1967. 1966. 2. Bishop, D., "Weatherproofing Joints 7. PCI Design Handbook, Precast and Between Precast Concrete Panels," Prestressed Concrete, Prestressed Building Research Station, United Concrete Institute, Chicago, Illi- Kingdom, The Builder, Jan. 5, nois, 1971. 1962, 8. "Aspects of Design in Concrete," 3. Latta, J. K., "Precast Concrete Seminar for Architects, Cement & Walls—A New Basis for Design," Concrete Association, London, Canadian Building Digest #93, England, 1971. National Research Council, Otta- 9. "The Weathering of Concrete," wa, Canada, September 1967. Proceedings, Symposium, Royal In- 4. Garden, G. K., "Rain Penetration stitute of British Architects, The and its Control," Canadian Build- Concrete Society, London, En- ing Digest #40, National Research gland, 1971. Council, Ottawa, Canada, April 10. "Guide to Joint Sealants for Con- 1963. crete Structures," ACI Committee 5. Garden, G. K., "Look at Joint Per- 504, ACI Journal, Proceedings, formance," Canadian Building Di- Vol. 67, No. 7, July 1970, pp. 489- gest #97, National Research Coun- 536. cil, Ottawa, Canada, January 1968. 11. Karpati, Klara K., "Literature Sur- 6. Malstrom, P. E., "Jointing Prob- vey of Sealants," Journal of Paint lems in Facades," Fifth Internation- Technology, Vol. 40, No. 523, Aug.

36 1968, pp. 337-347. proach to Design of a Road Joint 12. de Courcy, J. W., "Movement in Seal," Bulletin No. 229, Highway Concrete Structures," Concrete Research Board, 1959, pp. 20-44. (London), Vol. 3, No. 6, June 1969, 16. Schutz, Raymond J., "Shape Fac- pp. 241-246; No. 7, July 1969, pp. tor in Joint Design," Civil Engi- 293-297; and No. 8, August 1969, neering, Vol. 32, No. 10, October pp. 335-338. 1962, pp. 32-36. 13. "Causes, Mechanism, and Control 17. Watson, Stewart C., "Compression of Cracking in Concrete," SP-20, Seals for Bridges," ACI Journal, American Concrete Institute, De- Proceedings, Vol. 65, No. 9, Sep- troit, Michigan, 1968, 246 pp. tember 1968, pp. 721-729. 14. Hall, Kenneth F., Ritzi, Jack H.; 18. Dreher, D., "A Structural Ap- and Brown, Delmont D., "Study of proach to Sealing Joints in Con- the Factors Governing Contact crete," Highway Research Record Pressure Generating in Neoprene 80, Highway Research Board, Preformed Compression Seals," 1965, pp. 57-73. Highway Research Record 200, 19. PCI Manual on Architectural Pre- Highway Research Board, 1967. cast Concrete, Prestressed Concrete 15. Tons, Egon, "A Theoretical Ap- Institute, Chicago, Illinois, 1973.

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

PCI Journal/March-April 1973 :37