guide selection of polymer adhesives with concretethe

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 the Selection of (Reapproved 1997,2003) 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 concrete to cured concrete, repair of cracks in concrete, bonding concrete to other materials, and adhesive grouting of bolts and other inserts into concrete. The guide emphasizes the factors that should be considered where selecting a structural adhesive, including characteristics during installation and in service.The benefits and limitations of adhesive bonding 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 0 1992. 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 device, unless permission in writing is obtained from the copyright proprietors. 503.5R-1 503.5R-2 ACI COMMITTEE REPORT Chapter 10 - Quick reference guide, pg. 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, contractor, and architect in choosing a proper polymer adhesive for adhesive 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 polymers (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 concrete, bonding other materials to concrete, and bonding 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 adhesives 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, polyurethane, silicones, vinyl acetate, and styrene-butadiene) either as typical values, as a range of values, or as relative 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 literature should always be reviewed. Manufacturer’s rec- ommendations should be followed because the adhesive may differ from other adhesives in its class. Many adhesives contain hazardous ingredients. Ma- terial Safety Data Sheets (MSDS) and labels should always 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 reducing 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 catalyst 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 (usually 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 second 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 viscous 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 temperature at which a plastic material reaches an arbitrary deflection when subjected to an arbitrary load and test condition. It can be an indication of the glass transition temperature, although these two temperatures are not necessarily equal. Initiator - A substance that causes a chemical reaction (such as polymerization 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 copolymer to reduce its minimum film forming temperature and/or its glass transition temperature. Polyester - One of a large group of synthetic resins, mainly produced by reaction of unsaturated dibasic acids 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 laminates (mainly glass), adhesives, and the like. Polymer - The product of polymerization; more commonly a rubber or resin consisting of large molecules 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 thermoplastic 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 increase 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 concrete, 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 substrate 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 surface area. Surfactant - A contraction of the term “surface-active agent". Thermoplastic - Becoming soft when heated and hard when cooled. Thermosetting - Becoming rigid by chemical reaction 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 produced 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 Working life - The period of time which an adhesive, 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 characteristics 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 achieving and maintaining an adhesive bond. Section 2.3 describes the features that distinguish each of the polymeric 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 curing time. Automatic metering and mixing 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 polymerization 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 because 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 curing adhesives. Epoxies and two-component polyurethanes cure by the chemical reaction of the base resin and a curing agent. Polyesters, one-component polyurethanes, methacrylates, polysulfides, and silicones cure by the addition of a catalyst or release of a catalyst included 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 available 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 depends 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 affected 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 containment. 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 hazard 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, adhesives 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 before 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 curing, 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, resulting in the adhesive reaching the gel state at an elevated 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 characteristics 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 attraction 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 - T he strength of an adhesive bond depends on: a. Adhesion of the adhesive to the substrate materials. 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 formation 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 adhesives that are more viscous or that have relatively poor molecular attraction to concrete. The low-viscosity primer can provide more intimate contact with the substrate, resulting in better adhesion. Adhesive strengths with concrete are usually measured 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 concrete, 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 measured 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 adhesive joint is not the same as in the test specimen. In fact, at most it can only be a small fraction of the elongation 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 polymer adhesives varies from rubber-like with some silicones and polyurethanes to glass-like with some methacrylate and polyesters (see Table 1). However, the modulus of all polymer adhesives is affected by temperature, 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 adhesives 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 10 3 psi at 73 F - ASTM D 695 Heat deflection degF temperature - ASTM D 648 Coefficient 10 6 /in./in./deg C of thermal expansion - ASTM D 696 Acrylic Epoxy Polyester Polyurethane 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. NR: Not reported. 503.5R-6 ACI COMMITTEE REPORT polymer adhesive formulation has a specific HDT. Fre- quently, manufacturers’ literature and technical references report physical properties at only one temperature. When this is so, it is important to know the HDT to be able to anticipate if the physical properties at actual service temperatures will be substantially different from those strengths reported in the published literature. Modulus of elasticity, adhesive strength, bond strength, creep resistance, and chemical and radiation resistance all begin to change at about 18 F (10 C) below the HDT and begin to fall off rapidly in a region beginning about 18 F (10 C) above the HDT 16-18 (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 aggregate 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. 2.3.8 Coefficient of thermal expansion - Polymer adhesives have coefficients of thermal expansion two to ten times that of concrete (see Table 1). When the adhesive 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 expansion and contraction than that of concrete, the difference can cause failure in the concrete if the bonded elements are subjected to low temperatures (below 30 F). Problems caused by the differences in thermal expansion 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 expansion 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 adhesively 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 magnitude and direction of stress on the bond line. An anal- ysis should be performed to estimate the actual temperature that may be reached, and consideration should be given to the possibility that some of the bonded material may be consumed or removed by the fire. Through 4 cn a UY 3 2 a B 105 lo4 lo3 -50 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 structures 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 2.3.10 Age hardening - Most polymer adhesives develop over 90 percent of their strength at normal ambient 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 modulus, 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 precise 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 resistance to water. Relative water resistance 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 Epoxy/Aromatic Amine Curing Agent I 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 materials such as concrete. Within a polymer type formulation, variations can greatly influence radiation resistance. 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 generally composed of an epoxy resin, an amine or polyamid curing agent, reactive diluents and, in some cases, inorganic 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 temperatures 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 equipment . 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 normal 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 adhesives. 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 peroxide. TypicaIly, promoters or accelerators are used to ac- tivate the decomposition of the initiator at room temperature, thus enabling rapid low-temperature curing. Because of their relatively high shrinkage while curing, polyesters have found only limited use as adhesives. 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 polyester 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 during 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 addition of an accelerator component which can provide full cure in approximately 2 min. The use of accelerators 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 required to achieve full cure. Generally polyesters have excellent resistance to acid environments. Some polyesters have relatively poor resistance to alkalis and solvents. Although water resistance of the polymer itself is good, most polyester adhesive bonds to concrete deteriorate under constant wet conditions. Polyesters, in general, are considered flammable, with flash points below 100 F (38 C). However, products 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 decomposition 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 monomer 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 formulations. 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 adhesives 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 adhesives 30 ; 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 latex to cement is about one part latex solids to four parts of cement by weight. Both types of adhesives are generally used for bonding fresh, unhardened concrete to hardened concrete. However, Type II adhesives have occasionally been used for bonding hardened concrete to hardened concrete. Latexes and latex powders are generally made by emulsion polymerization techniques which have been described in the literature .31 The types in use today include 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 generally 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 copolymers. The more common comonomers are ethylene, butyl acrylate, and the vinyl ester of versatic acid. POLYMER ADHESIVES 503.5R-9 Type II latex adhesives are usually made with nonionic surfactant systems such as alkyl phenols reacted with various levels of ethylene oxide. Often, low levels of anionic surfactants are incorporated to assist in polymerization or to result in specific latex properties. This type of latex gives a dried film that is not redispersible. Polyacrylic esters and styrene-butadiene copolymers are included in this category. 3.1 - Application characteristics 3.1.1 Surface preparation - For both Type I and II 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 applied 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 obtained 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 conditions. 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 adhesives cure by drying. The drying occurs as water is removed either by evaporation or by hydration of the cement in the fresh concrete. Curing of Type II adhesives depends on the rate of hydration of the cement in the slurry and also on evaporation of the water. 3.1.4 Methods of application - Type I and Type II adhesives are usually applied by brush or roller, although other techniques such as spraying and troweling have also been used. It is essential that the surface being coated be thoroughly damp, and that the application 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 temperatures 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 environmental 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 surface, 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 because these materials, when properly applied, completely 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 suspect because the latex film is redispersible and vinyl acetate 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 concrete “wets out” the hardened concrete 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 hydraulic 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 surfactant 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 polyvinyl acetate. Films of the latex are redispersible. 3.3.2 Vinyl acetate copolymers - Copolymers of vinyl acetate with such materials as butyl acrylate, ethylene, and the vinyl ester of versatic acid are Type I adhesives but can also be used as Type II adhesives. They are generally made in polyvinyl alcohol surfactant systems and are available in latex and redispersible powder 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 comonomer to vinyl acetate. The comonomer 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 latex adhesives. It has been postulated 32 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 adhesives, but this is not recommended because the dried film are usually not redispersible. If the latex dries before 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-butadiene copolymer latexes are Type II adhesives. They could be used as Type I adhesives but are not recommended 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 incorporated in the polymerization. Such groups can improve adhesion and latex stability, but may also retard the initial hydration of the hydraulic cement. CHAPTER 4 - ADHESIVE SELECTION CRITERIA This chapter describes the factors that can be important 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 applications, if adequate test data are not available, a test program should be conducted that simulates the load 4.2 - Conditions during application 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 materials 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 under the specific applications and service conditions expected. 13-14 4.2.2 Temperature of the contact surfaces - The temperature of the contact surfaces and of the adhesive, 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 together 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 selection of the adhesive. CHAPTER 5 - ADHESIVES FOR BONDING OF 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 applied 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. [...]... Coefficient of thermal expansion Elastic modulus Vinyl acetate copolymer latexes E E E,PP E - E,P,M CAUTION: The listing of a particular type of adhesive as suitable for an adhesive requirement indicates that many adhesive products of that type meet the requirement It does not mean that all adhesives of that type meet the application or performance requirement The purpose of the chart is to guide the... other construction materials such as aluminum, wood, glass, rubber, and plastics, a wider variety of adhesives is required because of the very different characteristics of each of these materials 9.1 - Important application considerations There are innumerable combinations of types of adhesive and types of construction materials that can be bonded to concrete Which application conditions are important... and the hardened substrate The primary use of all types of water-borne adhesives with concrete is to bond plastic concrete to hardened concrete The only solvent-free adhesives used for bonding plastic concrete to hardened concrete are epoxy adhesives because, unlike other solvent-free adhesives, they can be readily formulated to cure and bond in the presence of water 6.1 - Important application considerations... range of 15 to 20 cps at 77 F (25 C) However, if injection adhesives with viscosities lower than 100 cps are used the adhesive can penetrate into the concrete so far that it leaves a starved bond line In this case, there must be a continual reservoir of adhesive available to the crack until the adhesive gels fill to the bond line Liquid adhesives without thixotropic properties will also drain out of a... through the adhesive joint CHAPTER 6 - ADHESIVES FOR BONDING PLASTIC CONCRETE TO HARDENED CONCRETE Polymer adhesives provide a better bond of plastic concrete to hardened concrete than can be obtained by relying on the cement itself or on a cement slurry, because polymer adhesives shrink less than cement paste upon curing, and because they tolerate a wider range of moisture conditions in the plastic... adhesive cures Because of the much higher modulus of elasticity of the steel compared to the polymer adhesive, the steel can exert stresses on the bond line that exceed the strength of the adhesive Even if the adhesive does not fail immediately upon removal of the clamps, constant stresses will be built into the bond line, which can cause creep failure at a later time Because of its high heat capacity,... bond-strength considerations Epoxy adhesives provide higher bond strengths than water-borne adhesives In thicker bond lines, epoxy adhesives, as opposed to water-borne adhesives, can bond to a greater surface area of the larger aggregate As an example, ASTM C 881 requires a minimum slant-shear strength of 1500 psi (10.3 MPa) for an epoxy adhesive while ASTM C 1059 requires a minimum of 400 psi (2.8 MPa) for... requirement of each particular project POLYMER ADHESIVES CHAPTER 11 - REFERENCES 11.1 - Specified and/or recommended references The documents of the various standards-producing organizations referred to in this document are listed with their serial designation, including year of adoption or revision The documents listed were the latest effort at the time this document was revised Since some of these... Irving, Handbook of Adhesives, 2nd Edition, Van Nostrand Reinhold Company, New York, 1977, “Introduction to Adhesives, ” by I Skeist and J Miron, pp 3-4 3 Lee, Henry, and Neville, Kris, Handbook of Epoxy Resins, McGraw-HiIl Book Company, New York, 1967, pp 25-7-25-I 1 4 Skeist, Irving, Handbook of Adhesives, 2nd Edition, Van Nostrand Reinhold Company, New York, 1977, “Introduction to Adhesives, ” by I... psi (8.6 MPa) for Type II water-borne adhesives CHAPTER 7 - ADHESIVES FOR REPAIR OF CRACKS IN CONCRETE Epoxy adhesives are the most common adhesives 503.5R-12 ACI COMMITTEE REPORT used for crack repair They are usually introduced into cracks by injection High-molecular-weight methacrylates are also used on some flat surface applications by flooding the surface with adhesive, and they have been used . 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. resistance of such adhesives is suspect because of hydrolysis of the polyvinyl acetate. Films of the latex are redispersible. 3.3.2 Vinyl acetate copolymers - Copolymers of vinyl acetate with. laminates (mainly glass), adhesives, and the like. Polymer - The product of polymerization; more commonly a rubber or resin consisting of large molecules formed by polymerization. Polymerization -

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