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Effective use of bonding agents
Mailvaganam, Noel P.
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b y Noe l P. Ma ilv a ga na m
The main types of bonding agents used in construction are latex emulsions
and epoxies. This Update review s the properties of each and guides the user
and the specifier on their advantages and limitations.
C o n s t r u c t i o n T e c h n o l o g y U p d a t e N o . 1 1
Bon d in g agen ts are n atu ral, com p ou n d ed or synthetic materials used to enhance the joining of in d ivid u al m em bers of a stru ctu re w ith ou t em p loyin g m ech an ical fasten ers. Th ese products are often used in repair applications su ch as th e bon d in g of fresh con crete, sp rayed con crete or san d / cem en t rep air m ortar to h ard en ed con crete.
Tw o of th e critical factors affectin g th e bon d in g betw een n ew an d old con crete, p rovid ed sou n d con crete p ractices are follow ed , are (i) th e stren gth an d in tegrity of th e old su rface an d (ii) th e clean lin ess of th e old su rface.
Wh en a w eak layer of con crete (laitan ce) exists on th e old su rface or w h en th e old su rface is d irty, a p oor bon d is obtain ed . Th e su rface con d ition th u s p lays a critical role in bon d d evelop m en t, alth ou gh th e stren gth of th e bon d d ep en d s on oth er factors su ch as p rop er com p action of th e n ew con crete an d p rop er su rface p rep aration th at takes in to accou n t th e d en sity of th e base con crete. For a sou n d base con crete, for exam p le, acid etch in g w ill su ffice, w h ile m ech an ical clean in g w ill be essen tial if th e old con crete con tain s a w eak or d eteriorated su rface.
Th e m ain typ es of bon d in g agen ts u sed in th e con stru ction in d u stry are latex em u lsion s an d ep oxies. Alth ou gh good ad h esion m ay be obtain ed w ith ou t a bon d in g agen t, gen erally a bon d in g layer con sistin g of cem en t an d san d slu rry, cem en t/ latex slu rry or ep oxy in creases bon d stren gth .
La t e x Em ulsions
Th ere are a variety of ap p lication s for latex em u lsion s u sed as bon d in g agen ts (see Table 1). Some have a greater degree of water resistance th an oth ers. Th e latex em u lsion s gen erally u sed in cem en titiou s com p osition s are of th e oil-in -w ater typ e, an d som etim es con tain m ore th an 50% w ater. Th ey are gen erally stable in th e cem en t/ w ater system . How ever, n ot all em u lsion s are com p atible w ith cem en t, an d th e selection of an ap p rop riate p rod u ct for a given ap p lication requ ires an u n d erstan d in g of its ch em istry or, altern atively, con su ltation w ith th e m an u factu rer.
Th ree m eth od s can be u sed to m od ify a latex to m ake it a u sefu l bon d in g agen t: (i) Prep are a n eat cem en t slu rry u tilizin g
th e latex as p art of th e m ixin g w ater; (ii) Use a 1:1 w ater:latex d ilu ted m aterial; (iii) Use a re-em u lsifiable latex, w h ich can
be soften ed an d re-tackified u p on con tact w ith w ater.
Th e u se of m eth od (ii) is n ow d iscou raged becau se of th e lack of bon d in g en cou n tered in field ap p lication s (corroborated by labo-ratory stu d ies). Th e u se of th e latex w ith ou t an y cem en t in th e m ix p rod u ces a failu re p lan e becau se of th e lack of film form ation at th e bon d in terface.
Th e follow in g d escrip tion of th e ad van -tages an d lim itation s of th e variou s typ es of em u lsion s u sed as bon d in g agen ts is in ten d ed to serve as a p relim in ary gu id e for th e u ser an d sp ecifier.
Effective Use of
Bonding Agents
2
Styrene Butadiene (SBR)
Styren e bu tad ien e (SBR) latex, w h ich is com p atible w ith cem en titiou s com p ou n d s, is a cop olym er. Th is typ e of latex sh ow s good stability in th e p resen ce of m u ltiva-len t cation s su ch as calciu m (Ca2+) an d
alu m in u m (Al3+), an d is u n affected by th e
ad d ition of relatively large am ou n ts of electrolytes (e.g., CaCl2). SBR latex m ay coagu late if su bjected to h igh tem p eratu res, freezin g tem p eratu res, or severe m ech an ical action for p rolon ged p eriod s of tim e.
Polyvinyl acetate latex (PVA)
Tw o m ain typ es of PVAs are u sed in rep air: n on -re-em u lsifiable an d em u lsifiable. Non -re-em u lsifiable PVA form s a film th at offers good w ater resistan ce, u ltraviolet stability, an d agin g ch aracteristics. Becau se of its com p atibility w ith cem en t, it is w id ely u sed as a bon d in g agen t an d as a bin d er for cem en titiou s w ater-based p ain ts an d w aterp roofin g coatin gs. Em u lsifiable PVA produces a film that can be softened and re-tackified w ith w ater. Th is typ e of latex
Table 1.Latex bonding agents comparative chart
Property/ Acrylic Polyvinyl- Butadiene- Polyvinylacetate test method acetate (non- styrene (re-emulsifiable)
re-emulsifiable)
Ap p earan ce Milky w h ite Milky w h ite Milky w h ite Milky w h ite or clear
Solid s Con ten t 45% 55% 48% 50%
Prim ary Use Bon d in g fresh Bon d in g fresh Bon d in g fresh Bon d in g to p laster con crete to con crete to concrete to old concrete,
old con crete old con crete, con crete ad m ixtu re, th in layer top p in gs th in layer top p in gs
Ap p lication Bru sh , broom , Bru sh , broom , Bru sh , sp ray, Bru sh , sp ray, Meth od s sp ray, roller sp ray, roller roller as ad h esive, roller
as ad h esive, as ad h esive, trow el as top p in g. trow el as top p in g trow el as top p in g
Ap p lication s <—Un d erlaym en ts, stu cco, grou tin g-m ortar, terrazzo, crack fillers—> Clean in g, Su rface Rem ove oil, grease; Rem ove oil, grease Rem ove oil, grease
Prep aration w et su rface Com p . Stren gth (MPa)
2 in . (50 m m ) cu bes 22.0 23.45 22.75 22.0 (air)
ASTM C109 28.27 24.82 27.58 20.68 (w et)
Ten sile Stren gth (MPa) 1 in . (25 m m ) th ick
briqu ettes 4.0 2.41 3.10 2.06 (air)
ASTM C190 4.24 3.10 4.0 2.83 (w et)
Flexu ral Stren gth
Bar (MPa) 6.55 6.90 8.62 6.38 (air)
ASTM C-348-61T 9.65 8.62 11.38 5.17 (w et)
Wh ere to Use In d oor an d ou t- In d oor an d ou t- In d oor an d ou t- In d oor ceilin gs d oor exp osu res; d oor exp osu res; d oor exp osu res; p rim arily, on con crete, on con crete, on con crete, lim ited u se as steel, w ood ; steel, w ood ; steel, w ood ; con crete bon d in g gu n itin g; th in gu n itin g; th in gu n itin g; th in agen t
section top p in g. section top p in g. section top p in g. May be u sed as May be u sed as May be u sed as a p laster bon d a p laster bon d a p laster bon d w ith in 45-60 m in . w ith in 45-60 m in . w ith in 45-60 m in .
Wh ere Not to Use Not for extrem e Not for extrem e Not for extrem e Do n ot u se as an ch em ical exp osu re, ch em ical exp osu re, accelerators, ad m ixtu re. Do n ot n ot for con d ition s n ot for con d ition s n ot for extrem e u se u n d er w et or of h igh h yd rostatic of h igh h yd rostatic ch em ical exp osu re, h u m id con d ition s. p ressu re p ressu re n ot for con stan t Do n ot u se at
w ater tem p eratu res below 10°C. From P. Maslow, Ch em ical Materials for Con stru ction (w ith p erm ission ).
Epox y Bonding Age nt s
Variou s ep oxy p rod u cts are available for th e bon d in g of fresh ly p laced con crete to cu red con crete an d of con crete to steel. Most p rod u cts con tain resin s th at are 100% solid s. Th ey m ay or m ay n ot con tain fillers, su ch as calciu m carbon ate or silica flou r, an d oth er ad d itives to en h an ce a p articu lar p rop erty or red u ce cost. Prod u cts are avail-able in a variety of con sisten cies, ran gin g from a h igh ly filled p aste (for overh ead w ork) to liqu id s w ith a viscosity of 100 cp (0.1 Pa•s), w h ich is sim ilar to th at of w ater.
Becau se th e form u lation s can com bin e d ifferen t resin s, h ard en ers an d m od ifiers to p rod u ce a great variety of en d p rod u cts, th e u ser an d sp ecifier n eed gu id an ce on th e op tion s available to th em . Th e ASTM stan -d ar-d ASTM C881-78 “Ep oxy-resin -base-d Bon d in g System s for Con crete” is qu ite in form ative in th is resp ect. It is a p erfor-m an ce sp ecification based on en d u se an d th ere are n o sp ecific lim its on ch em ical com p osition . In stead , th e m aterial selected m u st m eet requ irem en ts related to p h ysical p rop erties su ch as viscosity, bon d stren gth , sh rin kage an d th erm al com p atibility.
The specification classifies the epoxy-resin bon d in g system by typ e, grad e an d class. Th e typ e is d eterm in ed by en d u se (see ASTM C881, Table 1, “Physical Requirements of Bon d in g System s”). System s can be su m m arized as follow s:
Typ e I, for bon d in g h ard en ed con crete an d oth er m aterials to h ard en ed con crete;
Typ e II, for bon d in g fresh ly m ixed con crete to h ard en ed con crete; Typ e III, for bon d in g skid -resistan t
m aterials to h ard en ed con crete (or for u se as a bin d er in ep oxy m ortars or con cretes).
Th e grad e of a system is d efin ed by its flow ch aracteristics. For exam p le, m ateri-als of low viscosity su itable for in jection in to cracks, an d w h ere flow is requ ired , are grou p ed in Grad e 1. Grad e 2 com p rises m ed iu m -viscosity m aterials for gen eral-p u reral-p ose u se, an d Grad e 3 m aterials are of a n on -saggin g con sisten cy for overh ead w ork or for bon d in g n on -m atin g su rfaces. Th e m aterials are fu rth er d ivid ed in to classes by th e test tem p eratu re at w h ich th e gel tim es are d eterm in ed (gel tim e is th e in terval betw een th e begin n in g of m ixin g an ep oxy system an d th e first form ation of a gelatin ou s p erm its th e ap p lication of a film to a su rface
lon g before th e su bsequ en t ap p lication of a w ater-based overlay. Its u se is lim ited to sp ecific ap p lication s w h ere th e p ossible in filtration of m oistu re to th e bon d lin e is p reclu d ed . It is m ost w id ely u sed as a bon d in g agen t for p laster, an d to bon d fin ish -or base-coat gyp su m , -or P-ortlan d cem en t p laster, to in terior su rfaces of cu red cast-in -p lace con crete.
Acrylic latex
Acrylic ester resin s are p olym ers an d cop olym ers of th e esters of acrylic an d m eth acrylic acid s. Th eir p h ysical p rop erties ran ge from soft elastom ers to h ard p lastics. Th is typ e of em u lsion is u sed in cem en ti-tiou s com p ou n d s in m u ch th e sam e m an n er as SBR latex.
Epoxy latex
Epoxy emulsions are produced from liquid ep oxy resin m ixed w ith th e cu rin g agen t. In ad d ition to servin g as an em u lsifyin g agen t, th e cu rin g agen t also serves as a w et-tin g agen t. From th e tim e of m ixin g u n til gellation occu rs, th e em u lsion s are stable an d can be d ilu ted w ith w ater. Pot life can be varied from 1 to 6 h ou rs d ep en d in g on th e cu rin g agen t selected an d on th e am ou n t of w ater ad d ed . Most ep oxy em u lsion s are p rep ared on th e job site ju st before u se becau se p h ase sep aration occu rs in p re-p ackaged em u lsion s. Equ al re-p arts of ere-p oxy an d cu rin g agen t are m ixed , th en blen d ed for 2 to 5 m in u tes an d allow ed to set for 15 minutes to enable polymerization to begin. Wh ile th e m ixtu re is bein g m ech an ically agitated , w ater is ad d ed slow ly to form th e em u lsion .
As an altern ative to th ese liqu id -based system s, w h ich requ ire on -site m easu rem en t an d p re-d ilu tion , it is n ow p ossible to obtain factory-blen d ed p ow d ers con tain in g a m ixtu re of cem en t, sp ray-d ried latex p ow d ers, san d an d oth er ad d itives, w h ich are sim p ly m ixed w ith w ater on site. Th e resu ltan t “stip p le” fin ish p rovid es a good “key” for rep air m ortar or overlays. Th e stip p led grou t coat m in im izes th e loss of w ater from th e overlay to th e su bstrate, p reven tin g d esiccation of th e cem en t an d th e resu ltan t p oor bon d . Alth ou gh th e grou t coat d oes p rovid e p oin ts of an ch orage for bon d in g, th e ap p lication of th e rep air m ortar or overlay w h ile th is key coat is still tacky is stron gly recom m en d ed .
m ass w ith in th e system ). Th e m aterials are n ot, h ow ever, restricted to u se at th e tem p eratu re d esign ated for each class.
Class A – system s for u se below 5°C Class B – system s for u se betw een
5 an d 15°C
Class C – system s for u se above 15°C. Th ree p rop erties stip u lated in th e ASTM sp ecification are of great im p ortan ce, n am ely: bon d stren gth , sh rin kage an d th er-m al coer-m p atibility. ASTM tests C882, C883 an d C884 d eterm in e th e resp ective valu es for th ese p rop erties requ ired by th e sp ecifi-cation . Th e tests are an effective m ean s of screen in g p rod u cts th at are u n su itable for th e in ten d ed u se. For exam p le, th e bon d stren gth test (ASTM C882) w ill elim in ate system s th at are ad versely affected by bleed w ater from p lastic con crete if th e in ten d ed u se is th e bon d in g of fresh con crete to h ard -en ed con crete. Th e sh rin kage test (ASTM C883) w ill elim in ate system s con tain in g solven ts, excessive qu an tities of d ilu ten ts or oth er ch em icals th at w ill in d u ce sh rin kage. If a bon d in g system h as a h igh m od u lu s of elasticity, a p atch or overlay m ay d elam in ate as a resu lt of ch an ges in tem p eratu re. Th e ASTM C884 test m easu res th is ten d en cy.
Alth ou gh th e ASTM C881 sp ecification p rovid es a m ean s of screen in g ou t m aterials th at are likely to p erform p oorly, oth er p rop erties n ot ad d ressed in th e sp ecification sh ou ld be taken in to accou n t w h en m akin g a fin al ch oice am on g sim ilar ep oxy resin system s.
Most ep oxy bon d in g p rod u cts h ave a p ot life or settin g tim e of 15–30 m in u tes at 25°C, m akin g it n ecessary to m ix on ly th e am ou n t th at can be p rop erly u sed in th at p eriod of tim e. At tem p eratu res below 0°C, th e settin g tim e is con sid erably lon ger (4–5 h ou rs). Som e of th e ap p lication factors th at sh ou ld be con sid ered are sh ow n in Table 2.
Wh ere exten sive rep air w ork is n eces-sary — su ch as slab rep lacem en t or resu r-facin g of vertical w alls or colu m n s — ep oxy bon d in g agen ts, in com bin ation w ith n ew con crete, often p rovid e th e m ost eco-n om ical solu tioeco-n . Th e u se of th e boeco-n d ieco-n g agen t en su res th at th e rep air w ill h ave th e stren gth of m on olith ically cast con crete. Conc lusion
On e of th e critical factors govern in g th e ach ievem en t of an effective rep air is good ad h esion at th e in terface of th e rep air m aterial an d th e con crete su bstrate. Good ad h esion is im p erative for stru ctu ral rep airs w h ere m on olith ic ch aracter is requ ired for th e tran sfer of load . A p rop er bon d betw een th e rep air m aterial an d th e su bstrate can be obtain ed by d iligen t w ork-m an sh ip — in volvin g su rface p rep aration , con solid ation an d cu rin g — w ith ou t th e u se of bon d in g agen ts. How ever, bon d in g agen ts p lay a sign ifican t role w h ere it is critical to en su re bon d at th e in terface. For exam p le, a w eak an d p liable su bstrate m ay n eed stren gth en in g to m atch th e m od u lu s of th e rep air m aterial. A bon d in g agen t m ay be requ ired becau se of th e p revailin g p oor am bien t con d ition s. Notw ith stan d in g th e ad van tages p rovid ed by bon d in g agen ts, th ey sh ou ld n ot be u sed to com p en -sate for p oor w orkm an sh ip .
Mr. Noe l P. Ma ilv a ga na mis th e m an ager of Evalu ation an d Rep air in th e Bu ild in g En velop e an d S tru ctu re Program at th e N ation al Research Cou n cil’s In stitu te for Research in Con stru ction .
“Construction Te chnology Up d a te s” is a se rie s of te chnica l a rticle s conta ining p ra ctica l inform a tion d istille d from re ce nt construction re se a rch.
For more information, contact Institute for Research in Construction, National Research Council of Canada, Ottaw a K1A 0R6
Telephone: (613) 993-2607; Facsimile: (613) 952-7673; Internet: http://irc.nrc-cnrc.gc.ca
© 1997
Nation al Research Cou n cil of Can ad a Decem ber 1997
ISSN 1206-1220
Table 2.Application factors for epoxy bonding agents Mixin g ratios Vary from 100:1 to 1:1
Pot life In stan tan eou s to several m on th s; also in flu en ced by am ou n t of m aterial m ixed an d am bien t tem p eratu re.
Exoth erm Can vary from 0°C to over 100°C, in w h ich case th e cu red system is literally ch arred . Viscosity Can vary from liqu id of 100 cp (0.1 Pa•s), th e con sisten cy of w ater, to very h eavy p aste. Pen etrability A fu n ction of viscosity an d lu bricity — varies w id ely.
Cu re tim e Varies from a few m in u tes to several d ays an d is d irectly d ep en d en t u p on th e ap p lication tem p eratu re. (Som e system s w ill n ot cu re u n less exp osed to very h igh tem p eratu res.) From J. Warn er, Magaz in e of A S CE, Febru ary 1978 (w ith p erm ission ).
