EPDXY ADHESIVES INPRECAST PRESTRESSEDCONCRETE CONSTRUCTIONFelix HugenschmidtMarketing ManagerConstruction Industry ProductsPlastics & Additives DivisionCiba-Geigy LimitedBasle, Switzerland

Although epoxy adhesives have been used for manyyears in the construction industry, they are nowbeing used to an increasing degree in precastprestressed concrete applications. This is especiallyevident in segmental bridge construction.The author reviews the properties of structuraladhesives and lists the important criteria for selectingepoxy adhesives.In particular, he emphasizes the importance ofobtaining reliable data on creep deformation, heatstability, and moisture resistance.The properties of epoxies are greatly influenced byvariations in temperature.The test results of a comprehensive laboratoryprogram on the creep behavior of epoxy mortars arepresented.Suggested items for specifications are listed togetherwith several pointers in applying the adhesive.For example, it is very important not to exceed theallowable time period between mixing and epoxyapplication.Some suggestions are given on field testing and itemsneeded to be tested.Finally, the application of epoxies to two specificbridge projects is described.

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Epoxy resins have been employed inthe construction industry for manyyears. For example, they have beenused as anti-corrosion coatings, indus-trial flooring, interlayer sealing mem-branes, anti-skid surface dressings, ad-hesives, injection and grouting systems.

There are, therefore, great variationsin the properties required of the binderor the ready-for-use products in the dif-ferent types of applications.

When epoxies are used to transmitloads, they must possess very uniqueproperties since both the stability anddurability of a structure must be guar-anteed over its life span.

Segmental precast concrete bridgesfit into this category. For some practi-cal applications of epoxy adhesives insegmental construction refer to the endsection of this paper.

Felix Hugenschmidt

CRITERIA FOR SELECTINGEPDXY ADHESIVES

What properties should an engineerconsider in selecting an epoxy resin?Which properties have an importantbearing in formulating the job specifica-tions?

To answer these questions we mustcarefully weigh two separate aspects ofthe problem.

1. The anticipated requirements ofthe adhesive demanded by the job.

2. The known physical and chemicalproperties of the selected cold-curingepoxy resin system.

Because cement has been used as abinder for a very long time, we are fa-miliar with its properties. Unfortunate-ly, this is not the case with epoxy resins.

Therefore, it is helpful to comparethe influence temperature has on theproperties of cement and epoxies.

In general, cement (an inorganicbinder) is largely insensitive to tempera-tures ranging up to 350 C (662 F).

On the other hand, the properties of

epoxies (organic binders) are greatly in-fluenced by variations in temperature.For example, viscosity, workability, potlife, processing time, curing speed, de-gree of cross-linking, durability, andshort-term and long-term behavior areall gravely affected by large tempera-ture variations.

Because of this sensitivity to temper-ature, the testing of epoxies is expensiveand time consuming.

Ideally, a structural adhesive shouldpossess the following properties:

1. Easy workability at different tem-peratures and in various kinds ofweather.

2. Proper consistency to allow appli-cation of desired coat thickness.

3. Long processing time.4. Curing independent of tempera-

ture and humidity.5. Good adhesion to concrete with

passage of time and varying humidityconditions.

6. Negligible creep deformation.7. Resistance to temperature varia-

tions.

PCI Journal/March-April 1974 113

IV

V

1P

Test ispecmen:epoxy mortar prism

E `^' P = 6.4 tcp U O

O

^P

10

5

1

O.E

0.11 5 10 50 100 500 1000 days

Fig. 1. Creep deformation of three epoxy mortars at a compressive stress of 400

kp/cm2 (5690 psi) at 20 C (68 F); Systems I, IV, and V. Note: I in. = 2.54 cm.

t E ° I ( X10 3^

C

10

5

1

0.E

0.111 5 10 50 100 500 1000 days

Fig. 2. Creep deformation of an epoxy mortar at a compressive stress of 400

kp/cm2 (5690 psi) at 20 C and 40 C (68 F and 104 F); System I (see Fig. 1).

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8. High early strength relative tomethod of construction used and speedof erection.

Unfortunately, in practice, a fewcompromises must be made dependingon the job concerned. Not all the aboveproperties can be met simultaneouslywith any given epoxy system. Becausethe performance of an epoxy adhe-sive (especially cold-curing syntheticresins) is dependent on temperature,when selecting an epoxy it is helpful toclassify the properties into "not primar-ily decisive" and "primarily decisive"categories.

Not primarily decisive properties1. Reactivity.2. Short-term mechanical strength.3. Adhesion to concrete.

Primarily decisive properties1. Long-term behavior.

(a) Creep.(b) Temperature resistance.(c) Resistance to water and alkalis.

2. Relative insensitivity ' to incorrectmixing ratio.

Reactivity, i.e., pot life and curingspeed, is heavily dependent on thetype of system used and the prevailingfield temperature. However, reactivityis not a reliable criterion for selectionbecause it provides little indication ofthe other properties.

The short-term strengths (compres-sion, flexure, shear strength, lap shearstrength, and modulus of elasticity) areusually deceptively high. Furthermore,they can easily give the erroneous im-pression that the mechanical strengthof an epoxy system is always greaterthan that of the concrete to be bonded.

If the concrete is being bonded un-der mild conditions, the requirement"failure in concrete" is easy to fulfill un-der most prevailing stresses. The adhe-sive strength of the epoxy can be as-sumed to be greater than the ultimate

strength of the concrete and is thereforenot a governing criterion.

TEST RESULTS

Creep deformation under permanentload is one of the most important prop-erties in selecting an epoxy system. Al-though creep is very hard to measure ina joint, data on plastic deformation areessential. This is because such data pro-vide basic information on long-term be-havior and loading capacity.

A comprehensive laboratory programwas undertaken at Ciba-Geigy Limitedto test the long-term creep behavior ofepoxy mortars under high temperaturevariations.

Figs. 1 through 4 show some typicalcreep deformation curves obtained withvarious epoxy systems. An explanationof these systems is given below:

System I—Highly reactive systemcuring at low temperatures. Maximumtemperature resistance. Filling ratio(binder/aggregates) 1:3.5.

System IV—Highly reactive systemcuring at 0 C (32 F) and above. Goodadhesion to wet concrete. Filling ratio1:4.3.

System V—Suitable system for appli-cation at elevated temperatures up to35 C (95 F). Filling ratio 1:3.7.

It can be assumed that, at a tempera-ture of 20 C (68 F) and lower, the ulti-mate creep rate of highly cross-linkedepoxy systems is about three to fourtimes as high as that of the concrete tobe bonded.

The most important criterion for se-lecting an appropriate adhesive is itsbehavior under rising temperature con-ditions. This is the critical point for allcold-curing binders (and not only forepoxy resins).

Data on creep deformation with ris-ing temperature (such as Fig. 5) is es-sential prior to selecting an adhesive.

Measurements on 4 x 4 x 16 cm (ap-

PCI Journal/March-April 1974 115

X – 310 l7:1)

X1:2)

(1:3.5)

(1:7)

Test specimen:as for Fig. 1

10ҟ50ҟ100ҟ500 days

Fig. 3. Creep as a function of filling ratio (binder/aggregates) at 20 C (68 F);compressive stress 400 kp/cm 2 (5690 psi); System I (see Fig. 1).

10

0.5

0.1

prox. 11 x 11 x 6% in.) epoxy mortarprisms [see Fig. 5 and Table 1, Note(a)] indicate that highly cross-linkedsystems start to lose their strength attemperatures of about 45 C to 55 C(113 F to 131 F).

Nevertheless, thin layers of adhesivein bonded joints perform much betterthan prisms when exposed to rising tem-peratures. Compression tests on diago-nally bonded concrete prisms, with ajoint width up to 5mm [see Table 1,Note (b)], and also lap shear tests onbonded metal strips [see Table 1, Note(c)], have shown that a loading of 25percent of the short-term ultimate loaddoes not cause failure in the highest

quality epoxy adhesives until a tem-perature of 95 C to 100 C (203 F to212 F) is attained.

SUPPLEMENTARYCONSIDERATIONS

Another important criterion in select-ing an adhesive is its resistance to waterand alkalis. To test this property, bond-ed cement mortar prisms are immersedin water for periods up to 2 years. Atthe end of this testing period, goodbinder systems should show no loss ofstrength.

In some applications (e.g., in thebuilding industry), errors in the mixing

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x 10 -3

400 kp/cm2

200 kp/cm2

100 kp/cm2

Test specimen:as for Fig. 1

LL

E

0.5

0.11 5 10 50 100 500 1000 days

Fig. 4. Creep as a function of compressive stress of 400, 200, and 100 kp/cm2(5690, 2845, and 1423 psi) at 20 C (68 F); System I (see Fig. 1).

1.2

1.0

0.8

0.6

0.4

0.2

System IV I' V Temperature rising 1 °C/10 min.Load 200 ku/cm

P

E°

°

v

^P

Test specimen:E epoxy mortar prism° P=3.2t

I

100 _O ^v °_ _ 20 300TI 400 500 minvv w v^ ^.1 no cu on /u 15 "l.

Fig. 5. Epoxy mortar creep with rising temperatures.

X 10 -3

1.4

PCI Journal/March-April 1974 117

Table 1. Behavior of epoxy mortars and adhesives at elevated temperatures. Note:1 in. = 2.54 cm.

System Properties Epoxyḏmortar, Epoxyḏadhesives,fillingḏratio fillingḏratio1:3.5-1:4.3 1:1.8Transition Failureḏattemperature

1 2

I Highlyḏreactive system 54ḏCḏ(129.2ḏF) 103ḏCḏ(217.4ḏF)curing atḏlowḏtemperatures.Highestḏtemperatureresistance.

IV Highlyḏreactiveḏsystem 47ḏCḏ(116ḏF) 62ḏCḏ(143.6ḏF)curingḏatḏ0ḏCḏ(32ḏF)ḏandabove.ḏGoodḏadhesionḏtowetḏconcrete.

V Systemḏfor application 44ḏCḏ(111.2ḏF) 103ḏCḏ(217.4ḏF)at elevatedḏtemperaturesupḏtoḏ35ḏCḏ(95ḏF).

(a)ḏEpoxyḏmortarḏprism,ḏ4x4x16ḏcm.

(b)ḏDiagonallyḏbondedḏcementmortar prismḏ(4x4xl6ḏcm)ḏorcylinder ofḏadequateḏsize(Arizonaḏcylinderḏtest).

(c)ḏMetal-to-metalḏlapḏshearḏjoint.

(a) (b) (c)

* To facilitate comparison between the various epoxy mortar andadhesive systems, the tests carried out were given the characterof discontinued long-term tests under the loadings cited. In eachcase, the maximum permissible service temperature as a functionof loading would have to be determined by supplementary long-termtests.

ratio can have a detrimental effect onthe end product.

To test the effect of mixing errors,the author's company instigated a labo-ratory program on normally-cured andhot-cured specimens. Data were ob-tained on short-term strengths at 20 Cand 70 C (68 F and 158 F), as well asthe effect of mixing ratio errors oncreep, water absorption, and reactivity.

The test results showed that thebinder systems performed well even

with a margin of error of 20 percent inthe mixing ratio. However, this relativeinsensitivity should not be regarded asa license to indulge in careless mixing.

From the governing criteria, it is seenthat only highly cross-linked epoxy res-in systems (high strength, rapid curing,and high heat stability) should be usedas structural adhesives.

Unfortunately, highly cross-linkedsystems are usually extremely reactive,their pot life is relatively short, and

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their "contact time" is relatively lim-ited. On the job site, this means that themixing and application of the adhesiveshould be carried out just before theelement being bonded is ready for in-stallation.

The dependency of binder perfor-mance on temperature also means thatdifferent reactive systems should beused at different seasons of the year. Asa rule, it is sufficient to use one formu-lation for the summer and a differentone for the winter.

SUGGESTED SPECIFICATIONS

Now, having reviewed the significantproperties of a quality adhesive, wewould like to know what data weshould include in a job specification.

Let us first list what does not belongin a specification. Data that give us lit-tle information on the properties of res-ins and hardeners are: epoxy equiva-lent, ash content, specific gravity, vis-cosity of H-active equivalent, watercontent, and alkalinity. As for the curedadhesive, data on water absorption,Martens point, tensile strength andelongation, strengths at high tempera-tures, and resistance to chemical agentsare not only of little value, but oftenmisleading.

Data that should be included in aspecification are as follows:

1. Pot life and contact time at vari-ous temperatures.

2. Compressive and flexural strength,and possibly shear strength, tested aftercuring for 7 days at 20 C (58 F).

3. Development of mechanicalstrength at various temperatures.

4. Modulus of elasticity at 20 C (68F).

5. Shear strength of bonded concreteprisms at 20 C (58 F). The actual timewhen failure occurs in the concrete isalso significant.

6. Lap shear strength of bonded

metal strips cured for 7 days at 20 C(68 F).

7. Heat stability of bonded metalstrips cured for 7 days at 20 C (68 F)at 25 percent of the ultimate load [nor-mally 40 kp/cm2 (570 psi)].

In addition, information should he re-quested on the formulation of the bind-er (resin/hardener system) used to for-mulate the adhesive, data on creep andmechanical behavior of bonded cementmortar prisms following immersion inwater.

The above suggestions might deviatesomewhat from past practice. However,the important point to remember is thatan adhesive must be structurally com-patible with the material being bonded(i.e., the concrete).

POINTERS IN APPLYINGTHE ADHESIVE

These suggestions come from experi-ences in segmental bridge construction.

1. In the liquid state, the epoxy actssimultaneously as a lubricant, which fa-cilitates joining, and as an equalizationlayer, which evens out irregularities.

2. In the cured state, the epoxy func-tions as a sealer to protect the post-ten-sioning tendons, and transmits shearforces.

Several important checks must bemade and various points observed dur-ing the mixing and application of theadhesive, and during the installation ofthe bridge segment.

1. The condition of the surfaces tobe joined must be checked.

2. The resin and hardener compo-nents of the adhesive should be sup-plied to the job site in closed cans.

3. Damaged cans should never beused.

4. Mixing should only be st._rtedwhen the element to be joined is aboutto be installed.

5. The adhesive mortar should be

PCI Journal/March-April 1974 119°

mixed until it has a uniform color. (Res-in and hardener components should becolored differently, e.g., white/black.)

6. A slow mixer should be used(about 600 revolutions per minute) sothat a minimum of air is stirred in.

7. The temperature of the mixshould be checked.

8. The adhesive should be appliedimmediately after mixing and before itspot life elapses (15 to 30 minutes).

9. The adhesive should be applied ina uniform layer and preferably to bothconcrete surfaces.

10. The surfaces around the cableducts should be left sufficiently free sothat an adhesive will not be pressed in-to the ducts during prestressing.

11. Temporary prestressing shouldbe done within the contact time of theadhesive (75 to 90 minutes).

12. The joint should be checked. Ifthe right amount of adhesive has beenapplied, a small amount of it will bepressed out of the joint during the post-tensioning operation.

13. Preferably the same work crewshould be used on the entire job.

14. The work crew should be trainedcarefully. They must know how to mixand apply the adhesive properly.

15. Tools should be cleaned im-mediately after use and the work areacleaned up.

FIELD TESTING

In general, epoxy adhesives are notfield tested to the same degree as con-crete materials. This is an area whichthe author believes needs improving.For example, to make sure that fieldtest data are interpreted reliably, thetemperature at the construction sitemust always be recorded.

SupervisionIn general, responsibility for super-

vising the application of the adhesive

rests with the epoxy supplier or hisagent.

Preparation of test specimensThese should be prepared jointly by

the epoxy supplier and the general con-tractor.

Conduct of testsAs a rule, the laboratory tests are car-

ried out by an independent testingagency. The general contractor and theepoxy supplier should agree on thetypes of tests to be carried out and onthe number of test specimens to be pre-pared.

What should be tested?The following is a suggested list of

items that should be tested. These sug-gestions are based on experiencesgained during the construction of theRio-Niteroi Bridge in Brazil.

1. Pot life of the adhesive (spotchecks).

2. Condition of the concrete ele-ments being joined.

3. Dryness of the concrete (assessedvisually).

4. Mixing of the mortar and color ofthe ready-to-use mix. Resin and harden-er components have different colors(white/black). The mixed adhesive isgray similar to concrete. By checkingthis mixed color visually, an incorrectmixing ratio can be detected, thusavoiding unnecessary mixing errors..

5. Application of the adhesive.6. Preparation of specimens (prisms)

to be tested for flexural strength as afunction of temperature and reactivityof the adhesive. (Even more useful re-sults are obtained if the shear strengthand/or the splitting tensile strengthcan be determined.)

7. Joining of diagonally cut concretecylinders or prisms (e.g., the Arizonacylinder test) for testing under axialcompression.

8. Lastly, testing of the cured joints

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Fig. 6. Launching trusses used in construction of Rio-Niteroi Bridge (Brazil).The precast concrete segments were ferried to the site by raft and then joined

together with an epoxy adhesive.

("drill cores") for crushing strength.The drilled concrete cylinders shouldhave an axial bond line.

Finally, the test reports should becompiled and signed by both the epoxysupplier and the independent testingagency.

These reports should include dataon: number of the joint, date, weather,temperature, batch number of adhesive,time period of use, flexural strength,breaking load and type of fracture ofthe: diagonally bonded cylinders orprisms.

APPLICATIONS

The epoxy adhesives discussed in thispaper have been applied successfully inmany different types of concrete con-struction. For example, in prestressed

segmental construction these epoxiesare particularly advantageous in splic-ing the precast concrete elements to-gether.

Segmental construction is very effi-cient in congested urban areas and overlong stretches of water or rugged ter-rain. Expensive falsework is eliminatedand there is minimal interference withthe environment.

Two major projects (Brazil's Rio-Niteroi Bridge and Switzerland's Chil-lon Viaduct) are particularly significantbecause they showed that epoxies canbe used efficiently and economically insegmental construction.

Rio-Niteroi BridgeBrazil's Rio-Niteroi Bridge is 14 km

(about 8.7 miles) long and has two 3-lane roadways. The precast concrete

PCI Journal/March-April 1974 121

Fig. 7. Epoxy resin and hardener be-ing readied for stirring (Rio-NiteroiBridge, Brazil). In general, it is prefer-able to use a low-speed stirrer. On thisjob electric drill motors were mountedin line to mix six 11-lb batches of

epoxy.

Fig. 8. Upended pan of thixotropic ad-hesive being handed to worker on deckof Rio-Niteroi Bridge (Brazil), Theepoxy adhesive was applied to adjoin-ing segment surfaces using woodenspatulas. Note post-tensioning tendon

in gap at left.

segments were ferried to the site by raftfrom an on-shore factory. In additionto being glued together with epoxy ad-hesive, the segments were post-ten-sioned longitudinally. Subsequently, theparallel bridge decks were coupled us-ing transverse post-tensioning. Thebridge was finished in about 18 months.

Fig. 6 shows the two steel launchingtrusses used in the construction of theRio-Niteroi Bridge. These launchingtrusses were employed in transportingand adjusting the segments into posi-tion.

Prior to application the epoxy adhe-sive must be mixed. In general, theepoxy resin and hardener are bestmixed with a low-speed stirrer. On theRio-Niteroi job, the electric drill motorswere mounted in line to mix six 5 kg(11 lb.) batches of epoxy (see Fig. 7).

Fig. 8 shows a construction manhanding over an upended pan of thixo-tropic adhesive to his partner on thedeck of the Rio-Niteroi Bridge. To hisleft, in the gap, can be seen a post-tensioning tendon.

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Fig. 9. Manual application of epoxy adhesive on precast concrete segment (Chil-lon Viaduct, Switzerland). On an average it takes about 30 minutes using two

men to complete the epoxy coating and initial post-tensioning operation.

The epoxy adhesive was applied toadjoining segment surfaces with wood-en spatulas. During this operation theadjoining segments are about 30 to 40cm (approx. 12 to 16 in.) apart.

In general, only two men are re-quired to apply the epoxy. However,on the Rio-Niteroi job, two men wereemployed on the deck and four to sixmen inside the segment. It took about45 mintes per segment to mix andapply the epoxy (including the in-itial post-tensioning operation). How-ever, on other jobs this time has beensomewhat reduced.

Chillon Viaduct

The other noteworthy project usingepoxy bonded segments is Switzerland's

Chillon Viaduct, located near the his-toric Chillon Castle. In such a scenicsetting it was important to leave thenatural environment unscathed. Seg-mental construction proved to be anideal mode of erection.

Fig. 9 shows a construction man, on afinished deck, manually applying anepoxy adhesive to a new segment as itis gradually lowered into place. On theChillon job, the mixing and applica-tion of the epoxy (including the initialpost-tensioning) took about 30 minutes.

In Fig. 10 the adhesive has been ap-plied to the far side of the segment.Simultaneously, the tendons and stress-ing equipment are being readied for theinitial post-tensioning operation.

PCI Journal/March-April 1974 123

Fig. 10. Dramatic shot of precast concrete segment being lowered into positionjust after the epoxy adhesive was applied to the far side of the segment (Chillon:Viaduct, Switzerland). In the background one can see the famous Chillon Castle_

TECHNICAL INQUIRIES

Technical inquiries within North Americaregarding the epoxies discussed in thispaper should be directed to:

Ren Plastics5656 South Cedar StreetLansing, Michigan 48909Tel: 517-3931-1500

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