guide selection of polymer adhesives with concretethe

McHale Peter Mendis* This guide provides the engineer, contractor, and architect with a de-scription of thevarious types of polymer adhesives epoxy, polyester, acrylic, plyurethane, pol

ACI 503.5R-92

Raymond J Schutz

Milton D Anderson*

Roger W Black

John P Cook

Floyd E Dimmick

Wolfgang D Eisenhut

Jack J Fontana*

Paul R Hollenbach

Guide for Polymer Adhesives with Concrete

Reported by ACI Committee 503

*Members of Subcommittee who prepared the report.

Robert W Gaul*

Subcommittee chairman David P Hu T.Michael Jackson Troy D Madeley Albert Mayer Joseph A McElroy*

Paul F McHale Peter Mendis*

This guide provides the engineer, contractor, and architect with a

de-scription of thevarious types of polymer adhesives (epoxy, polyester,

acrylic, plyurethane, polysulfide, silicone, vinyl acetate, and styrene

butadiene) most frequently used for adhesive bonding of fresh

crete to cured concrete, repair of cracks in concrete, bonding

con-crete to other materials, and adhesive grouting of bolts and other

in-serts into concrete.

The guide emphasizes the factors that should be considered where

selecting astructural adhesive, including characteristics during

instal-lation and in service.The benefits and limitations of adhesive

bond-ing are discussed for each application.

CONTENTS

Chapter 1 - General, pg 503.5R-2

1.1-Organization of the Guide

1.2-Caution

1.3-Advantages/disadvantages of adhesive bonding

1.4-Glossary of terms

Chapter 2 - Solvent-free adhesives, pg 503.5R-4

2.1-Application characteristics

2.2-Properties during cure

2.3-Properties of cured adhesive

2.4-Distinguishing Characteristics

ACI Committee Reports, Guides, Standard Practices, and

Commentaries are intended for guidance in designing,

plan-ning, executing, or inspecting construction and in preparing

specification Reference to these documents shall not be made

in the Project Documents If items found in these documents

are desired to be part of the Project Documents they should

be phrased in mandatory language and incorporated into the

Project Documents.

Mylcs A Murray Secretary Richard Montani Joseph M Plecnik Hamid Saadatmanesh

W Glenn Smoak Joe Solomon Michael M Sprinkel Douglas G Walters*

Chapter 3 - Water-borne adhesives (latex and latex powder adhesives), pg 503.5R-8

3.1-Application characteristics 3.2-Properties of cured adhesive 3.3-Distinguishing characteristics

Chapter 4 - Adhesive selection criteria, pg.

503.5R-10

4.1-Type and magnitude of loads 4.2-Conditions during application

Chapter 5 - Adhesive for bonding of hardened concrete to hardened concrete, pg 503.5R.10

5.1-Important application characteristics 5.2-Important bond-strength considerations

Chapter 6 - Adhesives for bonding of plastic concrete to hardened concrete, pg 503.5R-11

6.1-Important application characteristics 6.2-Important bond-strength considerations

Chapter 7 - Adhesives for repair of cracks in concrete, pg 503.5R-11

7.1-Important application considerations 7.2-Important strength considerations

Chapter 8 - Adhesives for bonding inserts into concrete, pg 503.5R-12

8.1-Important application considerations 8.2-Important strength considerations

Chapter 9 - Adhesives for bonding concrete and other materials, pg 503.5R-13

9.1-Important application considerations Copyright 01992 American Concrete Institute.

All rights reserved including rights of reproduction and use in any form or

by any means including the making of copies by any photo process or by any electronic or mechanical device, printed written, or oral, or recording for sound

or visual reproduction or for use in any knowledge or retrieval system or de-vice, unless permission in writing is obtained from the copyright proprietors.

503.5R-1

503.5R-2 ACI COMMITTEE REPORT

503.5R-14

Chapter 11 - References, pg 503.5R-15

11.1-Specified and/or recommended references

11.2-Cited references

11.3-Additional references

CHAPTER 1 - GENERAL

This guide is intended to aid the engineer,

contrac-tor, and architect in choosing a proper polymer

adhe-sive for adheadhe-sive bonding applications encountered in

joining concrete members in construction, repair, and

rehabilitation of concrete structures

1.1- Organization of the Guide

Sections 2 and 3 of the guide describe the properties

of the two major classes of polymer adhesives in use

(solvent-free adhesives and water-borne adhesives) and

identifies the distinguishing features of the specific

pol-ymers (e.g., epoxy, acrylic, and polyvinyl acetate)

within each class Section 4 lists the basic criteria that

should be used in all adhesive selections Sections 5

through 9 provide additional guidance specific to the

selection of adhesives for bonding fresh or hardened

concrete to hardened concrete, repairing cracked

con-crete, bonding other materials to concon-crete, and

bond-ing inserts into concrete Section 10 is a quick reference

guide to help narrow the search for a proper adhesive

This guide includes more data and information on

epoxy adhesives than on other types because epoxy

ad-hesives are the most versatile and by far the most

widely used with concrete Information on other types

is included where there is a choice

1.2 - Caution

The Guide presents data on the various polymer and

copolymer types (epoxy, polyester, acrylic,

polyure-thane, silicones, vinyl acetate, and styrene-butadiene)

either as typical values, as a range of values, or as

rel-ative values Because of the ease of tailoring polymer

products by formulation, some very special products

within a group may possess values for a particular

characteristic that differ widely from the typical value

or fall outside of the range To include all extremes

would lead to a less accurate perception of the true

na-ture of these groups of products as they are commonly

used The cited characteristics of classes of polymer

adhesives are only a guide to help narrow the field in a

search for an appropriate adhesive

When using an adhesive, the manufacturer’s

litera-ture should always be reviewed Manufaclitera-turer’s

rec-ommendations should be followed because the

adhe-sive may differ from other adheadhe-sives in its class

Many adhesives contain hazardous ingredients

Ma-terial Safety Data Sheets (MSDS) and labels should

al-ways be consulted before using the adhesive

1.3 - Advantages/disadvantages of adhesive

bonding

The major advantage of adhesive bonding is that it

allows distribution of an applied load over much larger areas compared to other methods of fastening, thus re-ducing the unit stress on the elements that are bonded

It allows attachment without having to alter the shape

or deface the elements to be attached The adhesive

bond line can also act as a moisture barrier 1,2 The major disadvantage of adhesive bonding is that the bonded elements cannot be disturbed after being joined, because the adhesive cures for hours or days depending on the cure rate of the adhesive used and the temperature of the elements being bonded Thus, work progress may be slowed down if the other work tasks cannot be scheduled to accommodate the adhesive cure time

1.4 - Glossary of terms

This glossary gives definitions of some terms which are used in adhesive bonding in the concrete industry Other terms may be found in ASTM D 907

Accelerator-A material that increases the rate of a

chemical reaction

Acrylic - One of a group of resins formed by

poly-merizing the esters or amides of acrylic acid

Adhesives - The group of materials used to join or

bond similar or dissimilar materials; for example, in concrete work, the epoxy resins

Age hardening - The progressive change in the

chemical and physical properties of an adhesive, lead-ing to embrittlement

Bond line - The interface between two surfaces

bonded together with an adhesive

Catalyst - A substance whose presence increases the

rate of a chemical reaction In some cases the catalyst

is consumed and regenerated, in other cases the cata-lyst seems not to enter into the reaction, but functions

by virtue of some other characteristic

Cohesive - The type of molecular attraction that

holds adhesives and other materials together

Cohesive failure - A failure by separation within the

adhesive itself, or within the substrate, rather than in the adhesive’s bond to the substrate

Copolymerization - Polymerization of two or more

dissimilar monomers

Crosslinking agent - A substance that increases the

molecular weight of a polymer by chemically linking and bridging the polymer chains

Cure- To change the properties of a chemical

(usu-ally a polymer) by increasing its molecular weight by polymerization or crosslinking, usually accomplished by the action of heat, catalyst, crosslinking agent, curing agent, or any combination, with or without pressure

Curing agent - A substance that accelerates or

par-ticipates in the curing of chemicals, sometimes referred

to as a hardener

Elastomeric- Pertaining to a substance which has

rubberlike properties

Emulsion - A two-phase liquid system in which

small droplets of one liquid (the internal phase) are im-miscible in, and dispersed uniformly throughout, a sec-ond continuous liquid phase (the external phase)

POLYMER ADHESIVES 503.5R-3

Epoxy resins -A class of organic chemical bonding

systems used in the preparation of special coatings or

adhesives for concrete or as binders in epoxy resin

mortars and concretes

Exothermic -Pertaining to a chemical reaction

which occurs with the evolution of heat

Flexibilizer - A substance that is mixed with a more

brittle material to make the latter more ductile

Gel -A colloid in which the dispersed phase has

combined with the continuous phase to produce a

vis-cous jelly-like material

Glass transition temperature - The temperature or

range of temperature at which polymeric materials

change from a rigid, glass-like state to an

elastomeric-like state

Heat deflection temperature (HDT) - The

tempera-ture at which a plastic material reaches an arbitrary

de-flection when subjected to an arbitrary load and test

condition It can be an indication of the glass

transi-tion temperature, although these two temperatures are

not necessarily equal

Initiator- A substance that causes a chemical

reac-tion (such as polymerizareac-tion or curing) to start The

term usually applies to free-radical polymerization-type

reactions

Latex - A dispersion of organic polymer particles in

water

Minimum-film-forming temperature (MFFT) - The

lowest temperature at which the polymer particles of a

latex have sufficient mobility and flexibility to coalesce

into a continuous film

Monomer -An organic liquid, of relatively low

molecular weight, that creates a solid polymer by

react-ing with itself or other compounds of low molecular

weight or both

Plasticizer - A substance added to polymer or

co-polymer to reduce its minimum film forming

tempera-ture and/or its glass transition temperatempera-ture

Polyester - One of a large group of synthetic resins,

mainly produced by reaction of unsaturated dibasic

ac-ids with dihydroxy alcohols; commonly prepared for

application by mixing with a vinyl-group monomer and

free-radical catalysts at ambient temperatures and used

as binders for resin mortars and concretes, fiber

lami-nates (mainly glass), adhesives, and the like

Polymer - The product of polymerization; more

commonly a rubber or resin consisting of large

mole-cules formed by polymerization

Polymerization - The reaction in which two or more

molecules of the same substance (monomer) combine to

form a compound containing the same elements, but of

high molecular weight

Polyol - -A polhydric alcohol, i.e., one containing

two or more hydroxyl groups

Polysulfide - Synthetic polymers obtained by the

reaction of sodium polysulfide with organic

dichlo-rides

Polyurethane - Reaction product of an isocyanate

with any one of a wide variety of other compounds

containing an active hydrogen group; used to formu-late tough, abrasion-resistant coatings

Polyvinyl acetate - Colorless, permanently

thermo-plastic resin; usually supplied as an emulsion or water-dispersible powder characterized by flexibility, stability towards light, transparency to ultraviolet rays, high di-electric strength, toughness, and hardness; the higher the degree of polymerization, the higher the softening temperature; may be used in paints for concrete

Promoter - Substances, which added in small

quan-ities, increase the activity of catalysts, as well as in-crease or promote polymerization activity

Pseudoplastic - Often referred to as thixotropic, a

substance whose viscosity decreases with increasing shear

Rheology - The science dealing with the flow of

materials

Silicone - A resin, in which the main polymer chain

consists of alternating silicon and oxygen atoms, with carbon containing side groups; silicones may be used in caulking or coating compounds, admixtures for con-crete, or as adhesives

Substrate - A material upon the surface of which an

adhesive is spread for the purpose of bonding

Surface-active agent - A substance that markedly

affects the interfacial or surface tension of solutions even when present in very low concentrations

Surface energy - The interfacial free energy per unit

area of the boundary between the surface of a sub-strate and the air above it

Surface tension - A measure of surface energy,

arising from molecular forces at the surface of a liquid, which tend to contain the volume to a minimum sur-face area

Surfactant - A contraction of the term

“surface-ac-tive agent"

Thermoplastic - Becoming soft when heated and

hard when cooled

Thermosetting - Becoming rigid by chemical

reac-tion and not remeltable

Thixotroping agents - A substance incorporated

into an adhesive to impart thixotropy

Thixotropy - The property of a material that

ena-bles it to stiffen in a short period of time on standing, but to acquire a lower viscosity on mechanical agita-tion, the process being reversible; a material having this property is termed thixotropic or shear thinning (see

Rheology).

Vinyl ester - One of a group of synthetic resins

pro-duced by the reaction of acrylic with epoxy resin or

Bisphenol A, and commonly prepared for application

by mixing with a vinyl group monomer and free-radical catalysts at ambient temperatures, and used as binders for resin mortars and concretes, and fiber laminates (mainly glass) adhesives

Viscosity - The property of a material which resists

change in shape or arrangement of its elements during flow, and the measure thereof Specifically the ratio of the shear stress existing between laminae of moving fluid and the rate of shear between these laminae

503.5R-4 ACI COMMITTEE REPORT

adhe-sive, after mixing with a curing agent or other

ingredi-ent, remains sufficiently workable to permit spreading

and application

CHAPTER 2 - SOLVENT-FREE ADHESIVES

Solvent-free adhesives cure by polymerization of

monomeric resins Section 2.1 describes the

character-istics of polymeric adhesives prior to curing which are

important in applying or installing the adhesive

Sec-tion 2.2 describes properties of these materials during

and after curing which affect their suitability in

achiev-ing and maintainachiev-ing an adhesive bond Section 2.3

de-scribes the features that distinguish each of the

poly-meric adhesives

2.1- Application characteristics

2.1.1 Working life - Working life can vary from as

little as 2 min to as long as 8 hr from one adhesive to

another within each type of solvent free adhesive In

general, the longer the working life, the longer the

cur-ing time Automatic metercur-ing and mixcur-ing equipment

makes practical the use of adhesives with a very short

working life.3

The temperatures of the adhesive components, the

ambient temperature, and the substrates also influence

working time High temperatures shorten working time

and low temperatures lengthen working time.4 The

po-lymerization reaction is exothermic Holding a mixed

adhesive in a mass in a mixing container increases the

temperature of the adhesive because the heat cannot

dissipate efficiently This significantly shortens the

working life Applying the adhesive to the substrate

immediately after mixing lengthens the working life

be-cause most of the exothermic heat can be dissipated

into the substrate without raising the temperature of the

adhesive

2.1.2 Curing -There are two mechanisms for

cur-ing adhesives Epoxies and two-component

polyure-thanes cure by the chemical reaction of the base resin

and a curing agent Polyesters, one-component

polyur-ethanes, methacrylates, polysulfides, and silicones cure

by the addition of a catalyst or release of a catalyst

in-cluded in the formulation.5

The curing reaction of a monomer/curing agent is

very temperature-dependent.6

Lower temperatures ex-tend the curing time and higher temperatures shorten

the curing time Although special adhesives are

availa-ble that will cure at temperatures down to 0 F (-18 C),

most adhesives will not effectively cure in a practical

time at temperatures below 40 F (4 C)

Catalytic curing is less temperature-dependent than

the monomer/curing agent reaction, and the cure rate

can be increased by the addition of an accelerator.7

The adhesive must cure quickly enough to obtain

strength levels that can resist stresses that develop from

removal of support of the bonded composite, or from

temperature changes in the bonded composite; and

from exposure to moisture due to precipitation, tides,

or other sources which could cause degradation

2.1.3 Viscosity - Polymeric adhesives are available

with viscosities ranging from 15 centipoise (cps) to a paste-like consistency The viscosity of the adhesive de-pends on the inherent viscosity of the base monomers and curing agents, fiiers, and thixotroping agents The viscosity of any adhesive can be lowered by raising its temperature This can be achieved either by heating the adhesive itself or by heating the substrate

2.1.4 Thixotropy - Very viscous adhesives are not

necessarily thixotropic When thixotropic properties of

an adhesive are desired, an adhesive must be chosen that has been manufactured to include thixotroping agents Generally, high temperatures will lower the thixotropic characteristic of the adhesive and lower temperatures will increase the thixotropy, but is not af-fected to the same extent as viscosity by temperature.8 Adhesives are available that will stand in a bond line

as thick as 1/4 in (6.4 mm) without external contain-ment

2.1.5 Toxicity and safety - Most components of

solvent-free adhesives prior to curing have some degree

of toxicity and some are flammable Toxicity and haz-ard potentials vary widely from product to product The manufacturer’s literature and Material Safety Data Sheet (MSDS) for each product should be consulted, and all cautions should be observed In general, adhe-sives require the use of protective clothing, good venti-lation, good housekeeping, and personal cleanliness

2.2 - Properties during cure

2.2.1 Gel - Cure of an adhesive is accompanied by

an increase in viscosity and formation of a gel state be-fore full cure In the gel state, the adhesive does not possess the physical or chemical properties it will ulti-mately achieve If the adhesive is stressed during cur-ing, irreversible damage can be done to the bond with the substrate or the adhesive itself, resulting in lower strength.9,10

2.2.2 Exothermic reaction - The chemical reaction of

curing is exothermic and can accelerate cure rate, re-sulting in the adhesive reaching the gel state at an ele-vated temperature If this happens, internal stresses are induced in the bond when the adhesive cools to normal temperature

On a practical level, this condition occurs only in bond lines greater than 0.125 in (3.2 mm) in thickness, because in narrow bond lines the heat dissipates into the substrates

2.2.3 Shrinkage - All adhesives shrink when they

cure The addition of fillers to an adhesive system will reduce volumetric shrinkage but the inherent character-istics of a particular polymer system have by far the greatest influence on shrinkage.11 Volumetric shrinkage from the uncured to the cured state varies from as low

as 2 percent for filled epoxy systems to over 20 percent for some unfilled polyester systems

Shrinkage works against good adhesion It reduces the intimate contact between adhesive and substrate that is important for mechanical interlock and attrac-tion of the adhesive molecules to the substrate surface;

it also builds internal stress in the bond line.12

POLYMER ADHESIVES 503.5R-5

2.3 - Properties of cured adhesive

2.3.1 Bond strength - The strength of an adhesive

bond depends on:

a Adhesion of the adhesive to the substrate

materi-als

b Cohesive strength of the adhesive

c Cohesive strength of the substrate materials

The bonded joint is only as strong as the weakest of

these three strengths.13,14

In all bonding/repair applications, the surface of the

hardened concrete must be sound and clean Grease

and oil-type contaminants will interface with the

for-mation of a sound bond

The condition and strength of concrete at the surface

is particularly important If the larger aggregate is not

exposed, the surface layer is considerably weaker than

the concrete below the surface The application of

low-viscosity primers improves adhesion of solvent-free

ad-hesives that are more viscous or that have relatively

poor molecular attraction to concrete The

low-viscos-ity primer can provide more intimate contact with the

substrate, resulting in better adhesion

Adhesive strengths with concrete are usually

meas-ured in tension as a pulloff, in flexure in a bond line

parallel with the direction of the applied load, or in

shear The slant-shear test described in ASTM C 882 is

the most useful and commonly used test See Table 1

for typical adhesive bond strengths

The pipe cap pulloff test described in ACI 503R-80,

Appendix A, is useful for field testing adhesive bonds

2.3.2 Tensile strength and elongation - Because of

the higher tensile strength of polymers relative to

con-crete, the tensile strength of an adhesive material itself

is seldom a controlling factor

Tensile strength of adhesives is most commonly

measured by ASTM D 638 Tensile elongation as

meas-ured in ASTM D 638 is an indication of the relative

stiffness of the adhesive

The numerical value determined in the test method

for percentage of elongation should not be taken as the

elongation that will take place in an adhesive joint The

elongation in the test specimen is measured over a

length of 1 in (25 mm) with an intial cross section of

1/2 x 1/8 in (12.7 x 3.2 mm) or less As the test specimen

is loaded, the cross section can become smaller without

any external constraints In an actual adhesive joint loaded in tension, the “length” of the adhesive in the direction of the tensile load can vary from a few thou-sandths to a tenth of an inch The “cross section” per-pendicular to the tensile force can be literally thousands

of square inches Because the adhesive is bonded to the substrates it is not free to change its cross section by

“necking down.” Thus, its ability to elongate is se-verely restricted and the elongation achieved in the ad-hesive joint is not the same as in the test specimen In fact, at most it can only be a small fraction of the elon-gation measured in ASTM D 638.15

2.3.3 Shear strength - Shear strength is the most important property of adhesive materials commonly used to bond concrete Shear strength is usually the only strength property for short-time loads that may be exceeded without the bonded concrete substrate failing first If the shear forces in the bond line can be calcu-lated, shear strength data can be used to determine if the adhesive has the strength required

2.3.4 Flexural strength - As with tensile strength,

adhesive materials have high flexural strength relative

to concrete Flexural strength of an adhesive is seldom

a critical factor in adhesive bonding of concrete

2.3.5 Modulus of elasticity - The stiffness of

poly-mer adhesives varies from rubber-like with some sili-cones and polyurethanes to glass-like with some meth-acrylate and polyesters (see Table 1) However, the modulus of all polymer adhesives is affected by tem-perature, especially near or above the heat-deflection temperature (HDT) Below the HDT the change in modulus with temperature is modest (Fig 1)

Although the modulus of elasticity of polymeric ad-hesives used with concrete ranges from about 2 percent

to no more than 20 percent of the modulus of elasticity

of concrete, this difference has an insignificant effect

on transfer of load because of the very small volume of adhesive per unit area of bond line

2.3.6 Heat-deflection temperature (HDT) - Each

Table 1 - Polymer materials - Typical physical properties*

Tensile strength ASTM 638 psi

Tensile elongation ASTM D 638 percent

Compressive Strength ASTM D 695 psi

Compressive modulus 103psi

at 73 F

-ASTM D 695

Heat deflection degF

temperature

-ASTM D 648

Coefficient 106/in./in./deg C

of thermal

expansion

-ASTM D 696

5000-9000 4000-13,000 600-13,000 175-10,000

20-70 3-6 2-6 100-1000

4000-14,000 15,000-25,000 13,000-30,000 20,000

290-370 NR 300-400 10-100

165-209 115-550 140-400 NR

48-80 45-65 55-100 100-200

Styrene-butadiene

300-800 67-140

*From Reference 26.

503.5R-6 ACI COMMITTEE REPORT

polymer adhesive formulation has a specific HDT

Fre-quently, manufacturers’ literature and technical

refer-ences report physical properties at only one

tempera-ture When this is so, it is important to know the HDT

to be able to anticipate if the physical properties at

ac-tual service temperatures will be substantially different

from those strengths reported in the published

litera-ture Modulus of elasticity, adhesive strength, bond

strength, creep resistance, and chemical and radiation

resistance all begin to change at about 18 F (10 C)

be-low the HDT and begin to fall off rapidly in a region

beginning about 18 F (10 C) above the HDT16-18

(also see Fig 1) Heatdeflection temperature is determined

byASTM D 648

2.3.7 Creep resistance - Polymer adhesives have a

much higher tendency to creep than inorganic materials

such as concrete Sustained loads at temperatures more

than 18 F (10 C) above the HDT can result in creep to

failure.19 Creep resistance can always be improved by

reducing bond-line thickness, by increasing fiber

con-tent of the adhesive as supplied by the manufacturer, or

by adding aggregate in the field The amount of

aggre-gate that can be added is limited by the degree that

workability is reduced and/or air voids result from too

high an aggregate to adhesive ratio Physical testing is

required to quantify the effect of filler addition for

each specific adhesive

adhesives have coefficients of thermal expansion two to

ten times that of concrete (see Table 1) When the

ad-hesive is confined in a narrow [ 1/8 in (3.2 mm)] or less

bond line between two concrete elements or between

concrete and steel, this difference has not proven to be

a problem However, when placed in thicker sections or

used to bond materials with a greater thermal

expan-sion and contraction than that of concrete, the

differ-ence can cause failure in the concrete if the bonded

el-ements are subjected to low temperatures (below 30 F)

Problems caused by the differences in thermal

ex-pansion of the adhesive and concrete can always be

lessened by reducing bond line thickness Choosing an

adhesive with a lower modulus of elasticity also helps to

minimize stress caused by differences in thermal

expan-sion but increases the danger of creep failure if the

bond line is subjected to sustained loads

2.3.9 Fire resistance - Polymers are combustible, as

are most organic materials Incorporation of special

fire-retardent additives and inorganic fillers allows the

formulation of adhesives with fire resistance acceptable

for some applications The performance of a bonded

concrete structure or of an assembly of concrete

adhe-sively bonded to other materials will depend on the

in-sulation value and thermal conductivity of each of the

bonded materials, as well as the temperature level (see

Section 2.3.6), duration of exposure, and the

magni-tude and direction of stress on the bond line An

anal-ysis should be performed to estimate the actual

temper-ature that may be reached, and consideration should be

given to the possibility that some of the bonded

mate-rial may be consumed or removed by the fire Through

4 cn

a UY 3

2

a

B

105

lo4

lo3

- 5 0 0 50 100 150

Temperature, deg C

Fig 1 - Modulus of amine-cured epoxy (from Refer-ence 38)

appropriate design, including plaster coating of the concrete member to prevent burn out of the adhesive, the fire resistance of adhesively bonded concrete struc-tures can be maintained within desired levels Test data for a specific application and configuration should be required when a fire rating is required 20-21

de-velop over 90 percent of their strength at normal am-bient temperature, 68 to 100 F (20 to 38 C) within 7 days after placement However, curing continues and results in higher strength accompanied by higher mod-ulus, or by hardening.22 Age hardening is undesirable with flexible, low-modulus adhesives that are expected

to maintain their flexibility over a long period of time Adhesives are available for which long-term test data are available Accelerated aging data using elevated temperature aging for several days is often used as an indication of a susceptibility to aging However, a pre-cise correlation between long-term tests at the expected service temperature and accelerated tests can be estab-lished only by conducting both tests

2.3.11 Chemical resistance - The degree of chemical

resistance varies greatly, not only between polymer groups, but also from formulation to formulation within a polymer group; see Table 2 for comparison of the polymer groups Chemical resistance of an adhesive

in a bond line is often better than chemical resistance tables would indicate because only a very small surface area (the edges of the bond line) of the entire mass of adhesive is exposed to the chemical environment

2.3.12 Water resistance - Cured polymer adhesives

have generally good water resistance As with chemical resistance there can be a wide variation both between polymer groups and within a polymer group for resis-tance to water Relative water resisresis-tance can be

meas-POLYMER ADHESIVES

Table 2 - Chemical and water resistance - Polymer materials*

Nonoxidizng acids

Oxidizing acids

Aqueous salt solution

Aqueous alkalies

Polar solvents

Nonpolar solvents

Water

Acrylic xy

65 C S U s

Poly

25 c

s S

s S

ester

65 C

Poly

25 c

s S U S ure

I

thane

65 C

Sili

25 C

s :

S

cone

65 C 25 C

Styrene-S = satisfactory; Q = questionable; U = unsatisfactory.

l Sourcc: Reference 37.

Polyurethane I

UTILITY

buta iene

65 C

Incipient to Mild Nearly Always Usable Silicone Mineral Filled

Mild to Moderate Often Satisfactory IEpoxy/Aromatic Amine Curing Agent

Moderate to Severe Not Recommended Silicone Unfilled

Polyester Mineral Filled

Gy (Gray) - 1 J/Kg - 100 rad.

Gamma dose Gy

Fig 2 - Radiation resistance of polymer materials (from Reference 23)

ured by water absorption tests such as ASTM D 570

However, water resistance in service also depends on

the degree of exposure of the adhesive to water, either

through the substrates or at the edge of the bond line

(Table 2 gives a comparison of polymer groups)

2.3.13 Radiation resistance - Polymer materials are

much more susceptible to radiation than inorganic

ma-terials such as concrete Within a polymer type

formu-lation, variations can greatly influence radiation

resis-tance See Fig 2 for relative radiation resistance for

polymer type groups.23-26

2.4 - DISTINGUISHING CHARACTERISTICS

2.4.1 Epoxy adhesives - Epoxy adhesives are

gener-ally composed of an epoxy resin, an amine or polyamid

curing agent, reactive diluents and, in some cases,

in-organic fillers and thixotroping agents They are the

most commonly used polymeric adhesives

Epoxy adhesives generally have excellent adhesion

because of relatively low curing shrinkage, with low

surface tension and molecular properties that enhance

their attraction to a wide variety of substrates They are

very tolerant of the alkalinity of concrete

Epoxy adhesives can be formulated to cure at tem-peratures as low as 0 F (- 18 C) or to have a working life allowing use at 100 F (38 C)

Most epoxy adhesives have very low ratios of resin to curing agent, which allows proper metering and mixing within the tolerances of available automatic equip-ment

Epoxy adhesives conforming to ASTM C 881 will bond to concrete substrates and some will cure and bond underwater.27

Since resin systems (resin/curing agent) are available with viscosities lower than 100 cps and in semi-solid form, they can be formulated into adhesive products that pour and penetrate but require containment in a bond line or into products that can fill gaps without being contained

Epoxies can be formulated with HDTs as low as 10 F (- 12 C) or as high as 180 F (82 C) after curing at nor-mal ambient temperatures This means that they can be tailored to a wide variety of strength and modulus re-quirements for a broad range of service temperatures Water and chemical resistance of epoxy adhesives

af-503.5R-8 ACI COMMITTEE REPORT

ter cure, as a class, is second only to polyester

adhe-sives

2.4.2 Polyester adhesives - Unsaturated polyester

resins are generally dissolved in styrene monomer They

are cured with initiators, usually an organic peroxide,

such as methyl ethyl ketone peroxide or benzoyl

per-oxide

TypicaIly, promoters or accelerators are used to

ac-tivate the decomposition of the initiator at room

tem-perature, thus enabling rapid low-temperature curing

Because of their relatively high shrinkage while

cur-ing, polyesters have found only limited use as

adhe-sives.28

Epoxy or modified-urethane primers may be

used to improve the overall bond strengths to concrete

substrates if the primers are compatible with the

poly-ester resin prior to use Resistance to bond failure can

also be increased by increasing the flexibility of the

polyesters, thus providing some local stress relief

dur-ing the application of external forces Most polyesters

do not bond well to damp or wet substrates and should

not be used when these conditions exist? However,

re-cent research has shown that some vinyl esters, a type

of polyester, can bond under such conditions

Curing of polyesters can be accelerated by the

addi-tion of an accelerator component which can provide

full cure in approximately 2 min The use of

accelera-tors that provide very short cure times requires mixing

with automatic equipment The accelerator is usually

added at a very high ratio of resin/accelerator (100/ 1 to

100/10) Since the accelerator does not become an

in-tegral part of the polymer system, intimate mixing with

the monomer resin at a precise proportion is not

re-quired to achieve full cure

Generally polyesters have excellent resistance to acid

environments Some polyesters have relatively poor

re-sistance to alkalis and solvents Although water

resis-tance of the polymer itself is good, most polyester

ad-hesive bonds to concrete deteriorate under constant wet

conditions

Polyesters, in general, are considered flammable,

with flash points below 100 F (38 C) However,

prod-ucts with flash points over 100 F (38 C) are available

The peroxides used as initiators, when in the pure state,

may decompose rapidly at elevated temperatures over

90 F (32 C) and may even cause fire or explosion

Pow-der peroxides, such as benzoyl peroxide, are extended

with inert fillers, or are supplied as emulsions, or in

paste form in combination with water or inert organic

liquids, thus minimizing the explosion hazard In any

event, prolonged storage of the initiators at elevated

temperatures should be avoided to avoid

decomposi-tion of the peroxide

2.4.3 Acrylic adhesives - Methyl methacrylate and

high-molecular-weight methacrylate monomers of the

acrylic family are used as solvent-free adhesives for

concrete These adhesives generally share the same

characteristics as polyester adhesives They are most

commonly used by mixing with fine aggregate to form

an easily flowable adhesive mortar

The flowability of the mortar can be controlled by

the amount of aggregate added The mortar can be

used as an adhesive to fill wide bond lines and provide

a cure adequate for service in 30 min to 2 hr In almost all cases, a primer composed of the methacrylate mon-omer cured with an organic peroxide is used to provide

an improved bond to concrete

2.4.4 PoIysulfide adhesives - Polysulfides are most

frequently used as flexibilizers in epoxy resin formula-tions These formulations are sometimes referred to as

“polysulfide adhesives,” but they fit properly into the

“epoxy adhesive” category Polysulfide materials that are primarily joint sealants can be used to bond glass to concrete.29

2.4.5 Polyurethane adhesives - Polyurethane

adhe-sives are available as both rigid and flexible materials When combined with an aromatic amine, the urethane forms a rigid polymer similar to epoxy adhesives When combined with a polyol, they form an elastomer They have limited use with concrete because of their low bond strength The flexible types have been used in membrane systems and for bonding ceramic tile to concrete where impact resistance is required

2.4.6 Silicone adhesives - Silicones that have the

ability to cure in a wide temperature range are almost exclusively used as flexible joint sealants.29

However, they can be used to bond elements such as windows to concrete where a highly flexible adhesive is required to minimize concentration of stresses Silicone should not

be used in applications requiring resistance to sustained loads

CHAPTER 3 - WATER-BORNE ADHESIVES (LATEX AND LATEX-POWDER ADHESIVES)

The only water-borne adhesives currently used to bond concrete are latex and latex-powder adhesives There are two types of latex and latex-powder adhe-sives30; Type I, which is designed to be used without further formulation, and Type II, which is designed to

be used in slurry form with a hydraulic cement, usually portland cement For Type II adhesives, the ratio of la-tex to cement is about one part lala-tex solids to four parts

of cement by weight

Both types of adhesives are generally used for bond-ing fresh, unhardened concrete to hardened concrete However, Type II adhesives have occasionally been used for bonding hardened concrete to hardened con-crete Latexes and latex powders are generally made by emulsion polymerization techniques which have been described in the literature 31 The types in use today in-clude the following:

l Polyvinyl acetate (PVA)

l Vinyl acetate copolymers (VAC)

l Polyacrylic esters (PAP)

l Styrene-butadiene copolymers (SB) Type I latex and latex-powder adhesives are gener-ally made using a polyvinyl alcohol (PVOH) surfactant system This type of adhesive gives a dried film that is redispersible upon application of water This category includes most polyvinyl acetate and vinyl acetate co-polymers The more common comonomers are ethyl-ene, butyl acrylate, and the vinyl ester of versatic acid

POLYMER ADHESIVES 503.5R-9

Type II latex adhesives are usually made with

non-ionic surfactant systems such as alkyl phenols reacted

with various levels of ethylene oxide Often, low levels

of anionic surfactants are incorporated to assist in

po-lymerization or to result in specific latex properties

This type of latex gives a dried film that is not

redis-persible Polyacrylic esters and styrene-butadiene

co-polymers are included in this category

3.1 - Application characteristics

adhesives, the surface should be damp, but without any

standing water This damp condition is conducive to

penetration by the polymer particles of the adhesives

into the hardened concrete

3.1.2 Working life -Type I latex adhesives have

a virtually unlimited working life because of their

redispersible characteristic The adhesive is usually

ap-plied by brush or roller, and the fresh, unhardened

concrete can be applied whether the latex is still wet or

has dried In the latter occurrence, water from the

fresh, unhardened concrete causes redispersion of the

latex polymer Although it is recommended that the

fresh, unhardened concrete be placed within 24 hr of

applying the latex, satisfactory bonds have been

ob-tained when the fresh, unhardened concrete was placed

up to 7 days after latex application Note that the dried

film of the Type I latex adhesive must be kept clean

from dust and other contaminants between the times of

film forming and the application of the fresh concrete

Type II adhesives have a limited working life, the

length of which wiIl depend on the type of latex, the

type of hydraulic cement, and the environmental

con-ditions Typically, the working life of the slurry, in a

relatively closed container, will be from one to several

hours; however, in an open environment, drying can

occur quickly and shorten working life to less than 30

min It is important that the fresh concrete be placed

while the latex-cement slurry is still wet If the slurry

has dried, it may act as a bond breaker rather than an

adhesive

3.1.3 Curing -Curing of Type I adhesives depends

on the cure of the fresh concrete because Type I

adhe-sives cure by drying The drying occurs as water is

re-moved either by evaporation or by hydration of the

ce-ment in the fresh concrete

Curing of Type II adhesives depends on the rate of

hydration of the cement in the slurry and also on

evap-oration of the water

3.1.4 Methods of application - Type I and Type II

adhesives are usually applied by brush or roller,

al-though other techniques such as spraying and troweling

have also been used It is essential that the surface

be-ing coated be thoroughly damp, and that the

applica-tion technique be such that the adhesive completely

“wets” the surface

3.1.5 Application conditions - It is essential that the

latex adhesive, whether Type I or II, coalesces to form

a polymer film Consequently, application

tempera-tures must either be above the minimum film-forming

temperature (MFFT) or above 50 F (10 C), whichever

is higher, when the adhesive and the fresh concrete are placed

Although the surface must be thoroughly damp when the latex adhesive is applied, the adhesive and fresh concrete should not be placed during wet environmen-tal conditions, such as in rain or snow

3.2 - Properties of cured adhesive

3.2.1 Bond strength -The bond strength of Type I

and Type II latex adhesives will depend on the latex, the type of cement, the quality of the hardened sur-face, and the quality of the fresh concrete When tested

by ASTM C 1042 method, Type I adhesives usually give bond strengths in excess of 300 psi (2.1 MPa), while Type II adhesives give strengths usually in excess of

1200 psi (8.3 MPa).32

3.2.2 Shrinkage -There is virtually no shrinkage

associated with Type I and Type II latex adhesives be-cause these materials, when properly applied, com-pletely migrate into the hardened surface and the fresh concrete Consequently, any shrinkage that occurs is caused by shrinkage of the fresh concrete

3.2.3 Water resistance - The water resistance of

Type I latex adhesives has always been considered sus-pect because the latex film is redispersible and vinyl ac-etate hydrolyzes in the presence of moisture and high

pH values to give water-soluble products (vinyl alcohol and a metallic acetate) However, this type of adhesive has been successfully used without apparent problems

in areas exposed to moisture It is postulated that the function of the adhesive is to insure that the fresh con-crete “wets out” the hardened concon-crete surface The resulting bond is obtained from the penetration of the cement paste of the fresh concrete into the surface If this postulation is correct, it explains why moisture failures of Type I adhesives have not occurred where expected

Type II latex adhesives (slurries of latex and hydrau-lic cement) have excellent water-resistance In fact, such slurries are used for waterproofing swimming pools and for corrosion protection of steel members.33

3.3 - Distinguishing characteristics

3.3.1 Polyvinyl acetate - Polyvinyl acetate latexes

are Type I adhesives and are usually formulated with a plasticizer such as dibutyl phthalate or dipropyl glycol dibenzoate The plasticizers are added to decrease the minimum film-forming temperature (MFFT) This type

of adhesive is usually made in a polyvinyl alcohol sur-factant system and is available both in the latex form and as a redispersible powder Water resistance of such adhesives is suspect because of hydrolysis of the poly-vinyl acetate Films of the latex are redispersible

3.3.2 Vinyl acetate copolymers - Copolymers of

vi-nyl acetate with such materials as butyl acrylate, ethyl-ene, and the vinyl ester of versatic acid are Type I ad-hesives but can also be used as Type II adad-hesives They are generally made in polyvinyl alcohol surfactant sys-tems and are available in latex and redispersible pow-der forms Their water resistance is much better than

503.5R-10 ACI COMMITTEE REPORT

that of polyvinyl acetate, both because the comonomer conditions expected Alternately, field experience of an

reduces the hydrolysis of the vinyl acetate grouping, adhesive under similar service and environmental

con-and because the resultant product is not as water solu- ditions can indicate the suitability of a polymer adhe-ble as polyvinyl alcohol The water resistance of such sive for a particular use

polymers will depend on the type and ratio of

comon-omer to vinyl acetate The comoncomon-omer also causes a

reduction in the minimum film forming temperature,

which eliminates the need for addition of plasticizers

When used as Type II adhesives, bond strengths

(ASTM C 1042) usually exceed 1000 psi (6.9 MPa)

This value is slightly lower than most other Type II

la-tex adhesives It has been postulated32

that these lower values may be caused by the larger particle size of such

latexes

3.3.3 - Polyacrylic esters and acrylic copolymers

-Polyacrylic ester latexes, such as polyethyl acrylate, and

acrylic copolymer latexes are Type II latex adhesives

They are generally made using primarily a nonionic

surfactant system They could be used as Type I

adhe-sives, but this is not recommended because the dried

film are usually not redispersible If the latex dries

be-fore placement of the fresh concrete, the dried film can

act as a bond breaker rather than as an adhesive Glass

transition temperatures for such latexes are normally

less than 18 F (10 C) Low levels (less than 2 percent)

of reactive groups, such as vinyl carboxylic acids, may

be incorporated in the polymerization of these polymer

latexes These groups can improve adhesion by ionic

reaction with metallic radicals in the surface of the

fresh concrete However, it has been observed that such

groups may retard the initial hydration of the hydraulic

cement

3.3.4 Styrene-butadiene copolymers -

Styrene-buta-diene copolymer latexes are Type II adhesives They

could be used as Type I adhesives but are not

recom-mended for this category, because their films are not

redispersible In addition, their surfactant system is

primariIy of the nonionic type Small levels of reactive

groups, such as vinyl carboxylic acids, can be

incorpo-rated in the polymerization Such groups can improve

adhesion and latex stability, but may also retard the

in-itial hydration of the hydraulic cement

CRITERIA

This chapter describes the factors that can be

impor-tant in choosing an adhesive for a specific application

4.1 - Type and magnitude of loads

For permanent adhesive bonds the adhesive should

be able to transfer loads to the same degree as the

structural elements that are bonded together For each

load a determination should be made of:

l Direction (tension, compression, shear, flexure)

l Rate (static, dynamic)

l Duration

l Frequency

Most often data are available only for a single load

rate while information on creep, fatigue, or dynamic

loading is not available For very critical adhesive

ap-plications, if adequate test data are not available, a test

program should be conducted that simulates the load

Equally as important as the strength characteristics

of the adhesive is whether it can be installed to provide the strengths that are achieved in controlled laboratory tests Factors that affect the installation and that the adhesive must be able to tolerate are described in the following sections

4.2.1 Surface contamination - The presence of oils, greases, chemicals, dirt, dust, or any other foreign ma-terials can interfere with achieving a good bond If a foreign substance cannot be completely removed the adhesive chosen must be able to tolerate its presence This tolerance can be demonstrated only by testing un-der the specific applications and service conditions ex-pected.13-14

temperature of the contact surfaces and of the adhe-sive, when it is applied during the curing period of the adhesive, will affect the rate of bond-strength develop-ment Low temperatures may make the adhesive too viscous to apply properly High temperatures may cause the adhesive to gel before it can be properly placed and the substrates joined

4.2.3 Wetness of the substrates - The presence of

water can seriously affect the ability of adhesives to bond to concrete or other construction materials If there is any chance that the surfaces to be bonded to-gether will be damp, have residual water on them, or be submerged, the adhesive specified must be compatible ’

with moisture to achieve the required bond strength

4.2.4 Surface accessibility - The accessibility of the

surfaces to be bonded may dictate an adhesive with a long working time The length of time that external supports for bonded elements may be in place during the curing of the adhesive can also influence the selec-tion of the adhesive

HARDENED CONCRETE TO HARDENED

CONCRETE

Polymer adhesives are frequently used in segmental construction to bond together broken concrete, and to attach elements such as facades to concrete structures

In most critical situations the adhesive bond is used in conjunction with mechanical attachments, with rein-forcing steel, or with tendons which cross the bond line

5.1 - Important application characteristics

5.1.1 Viscosity and thixotropy - An adhesive for

bonding hardened concrete to hardened concrete must

be viscous and thixotropic enough not to run out of the bond line prior to forming a gel It must also be ap-plied in a thickness that will completely fill any irregu-larities that exist between the surfaces to be bonded Except for match cast segments, the bond line between concrete elements is seldom uniform