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Long-term durability of concrete structures
Mailvaganam, N. P.; Litvan, G. G.
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Long-t e rm dura bilit y of c onc re t e st ruc t ure s
N R C C - 4 0 6 1 5
M a i l v a g a n a m , N . P . ; L i t v a n , G . G .
D e c e m b e r 1 , 1 9 9 6
A version of this document is published in / Une version de ce document se trouve dans:
Construction Specifier,
49, (12), December, pp. 24-28,31, December 01, 1996
The material in this document is covered by the provisions of the Copyright Act, by Canadian laws, policies, regulations and international agreements. Such provisions serve to identify the information source and, in specific instances, to prohibit reproduction of materials without
written permission. For more information visit http://laws.justice.gc.ca/en/showtdm/cs/C-42
Les renseignements dans ce document sont protégés par la Loi sur le droit d'auteur, par les lois, les politiques et les règlements du Canada et des accords internationaux. Ces dispositions permettent d'identifier la source de l'information et, dans certains cas, d'interdire la copie de
by
Noel
P.
Mailvaganam and
G. G.
Litvan
e ures
ing. A plan for all stages of the work is impemtin'.
SllCl'('ssfnl eXl'l'ution of a project requires a l'Omprehl'nsiveｬｬｮ､･ｲｳｴ｡ｮｾｬｩｮｧ
of Illl\tl'rial properties. A､･ｾ｜ｬｴｨ Dl'inl(lr-illiltion Oil the long-term per/(lrI11anCl' of ｴｯ､｡ｾＧｳｴｮｬ｜｜ｻＧｲｩ｡ｬｳ oftl'll forces engineers to
E
ngineers are concerned not only with
creating new structures but with
pre-serving their functionality against all types
of deterioration for long service life. The
cOluplexity involved in current design, the
proliferation of new luaterials, and
Envi-ronmental Protection Agency
require-ments Inake this a demanding task.
PriJperly spedJ)'lng technical perfor-mance will help a\"oid or Ininimizl' tleteli-oration. The specil"ication must hl' n"alis· tie, expressed in terllls of perf()f]nance eharatleristics of the il1<lteriuls tobp used, and inclnde the preparatioil and lllising of concrete materials, application, and
Cllr-Ｒﾷｾ Th(' C:onstI" .. {,t j l l i l ｓｰＮｾﾷＨＭｪ fit'r!DI'(""lIlhl"r ]UU(1
Long-Term
ofDurability
with
pre-ypes
The
the
,nvi-
lre-I\"(lrk is [lroject -allding f infor-mct" of t'i'rs toUnifonn
concrete
quality
depends to a
large
extent on the
promptness
in which
changes
in factors
influencing
unffonnlty
are observed
and
corrections
are
made.
, <',rely on judgment, past experience, and common sense when dealing with mater-ial deterioration problems.
Matching the Material to the Environment
Materials are not inherently durable or susceptible to deterioration. Durability problems arise when the materials resis-tance is less than required for the envi-ronment. Steelwill nut corrode in adry;
salt-free environment but will in the pres-ence of moisture and chloride ions. It would be meaningless to
label
steel as durable or nondurable without defining exposure conditions. Concrete made with type 10 cement will not resist sulfate attack; therefore, this concrete is unsuit-able for sulfate-rich soils but is appropri-ate for low-sulfappropri-ate soils.The characteristics of the environment must be determined before the suitabillty of a material can be established. Often the microclimate in the immecllate vicin-ity of the exposed material differs from the overall environment and can be of greater influence on the material's perfor-mance. Careful consideration must be given to the general environmental para-meters as well as to their values near the exposed material.
Difficulties also exist in establishing standards for new materials. Standards usually are established only after experi-ence has been gained with the new mate-rial and in comparison with an established material used in a novel application. In the absence of standards, the follOWing aspects must be criticaUyevaluated:
• relevance of test data provided in product literature
• limitations and requirements that will be imposed by weather conditions such as temperature, rain, and winds dur-ing application
• the product's fIeld history under con-ditions similar to the present job
• the availability, when possible, of long-standing successful applications
• compatibility of the product with other materials that will form the com-posite unit
• the applied and long-tE'rrn mainte-nance costs of the prouucts.
ConcreteMix Design Considerations
After establishing the environmental parameters, the mix must be prepared. The major considerations are:
• With the water/cement ratio selected to satislY strength requirements, will the<
concrete be durable for the stnrct u,e's life span?
• If freeze/thaw action is expected during construction or the service life of the structure, is the concrete properly air entrained?
• Will the structure be exposed to chloride ions origi-nating either from deicing salts or saltwater spray?
• Is the reinforcing steel post-tensioning cables or pre-stressing steel protected from corrosion?
• In case of elevated sul-fate conte nt in the environ-ment, is the cement used sul-fate-resistant Type 5? Or have other precautionary measures (e,g., use of supplementary cementing materials) been taken?
Compatibility ofMaterials
Avoid embedding dissimilar materials in concrete. The incompatibility of diverse materials, whether physically connected or merely in
con-tact, can result in cracking and spalling,
causing expensive maintenance.
In-compatibility gives rise to variance in responses to changes in the environmen-tal parameters (e.g., moisture content, temperature, extent of loading, vibration, or usage).
Galvanic; corrosion is the most common type of metal deterioration. The presence of dissimilar metals, in addition to mois· hIre and electric contact, are essential for the operation ofa galvanic cell. There-fore, dissimilar metals should not be embedded in concrete, If this is unavoid-able, electric contact between them should be avoided.
While the operation of a galvanic
ｾ･ｬｬ
is well known, the consequences of the ratio of the anode to cathode areas is oftenneglected. For example, care is usually taken to avoid the contact ofcopper flash-ings with aluminum; however, it is often forgotten that to protect aluminum gut-ters from destruction in the vicinity of copper on roofs, no coating should be applied to the aluminum because a pin-hole in the coating could lead to a large cathode/small anode condition and severe local attack.
A material's modulus of elasticity is a measure of its stiffness. Low-modulus materials deform more under a given load than high-modu-lus materials. When materials with widely differing moduli are in contact, the significant difference in deformance may cause problems.
InFigureA,the drawing on the left shows that in loading perpendicular to the bond line, difference in modulus is not troublesome. However, when the load is applied par-allel to the bond line, as shown in the drawing on the right, deformation of the
lower modulus material trans-fers the load to the higher modulus material, which may then fracture. This type of problem can occur at the edge of a concrete patch and is par-ticularly likely when dynamic (impact or vibration) forces are present.
Differential shrinkage or thermal movement can cause loss of bond unless the modulus of one material is low enough to permit differential movement
without exerting excessive stress at the bond line. During significant temperature change, composite materials with two components having dissimilar thennal coefficients often fail at the bond inter-face or within the lower-strength mater-iaL
When making large or thick patches or when placing an overlay, it is important to closely match the coefficient of thermal expansion of the repair material with that of the concrete substrate. Although this is most important under conditions where frequent, large temperature changes
oec atk is iJ QUi ｔｨｾ pIa< tiar
mm
•
be
t aisI•
and U larg., char are' reco' factc resl!' that enc€: um!!AL
usu,'i:ｾ pJekj dabll afterＮｾ orpI
temp affec: ness» coneI!
Sri
main; the becmH const:! AsaIt:
perfoj! , •ｉｾＬ reqUlI," availa'; Mil II: waterJ of th! entnu! f ｭｯｳｴｾ aｱｵ｡ｾ ｾ ｍｯｬｳｾＺ ConCh rain,I;
Figure A. Materials with low modulus of elasticity defonn more under given unit load
\
\
Deterioration
Steel and reinforced concrete are prone to cbcmical attack in C'orrOSl\'e ｃＧｭｾｲｯｮﾭ
ments and must he protected to prevent deterioration, This can be accomplished through a comprehensh'e prevention pro-gram that prO\ides chemical resistan('c and watell)l'Oofing and includes tbe fol-lowing core elements:
o Pro\'ide good dminageand effective
drainage hardware, Ensure that water is not "Bowed to pond.
o Control cracking \\ith sealed control joints, correctlY placed where cracking is likelY to occur, and repair existing cracks by routing and sealing. The expan>ion joint sealant system should be deSigned to handle both the mOl-ement of the con-erC'te and traffie conditions to whichitwill hc expose'd.
o Prodde a durable reinforccment
co\'('r (.50 mm [2 in,]: by using a low waterleement ratio dessthan 0.4), air entrained (6 percent ± 1 perc-ent)
con-crete,
o Seal the surface "ith a penetrating
concrete sealer or an elastomeri c traffic deck coating s\'stem to prel'ent the ingress of water and waterborne salts.
Design Criteria
ｾｉＧｬｩｮｴｬＧｮ｡ｮｬＧｦＧ dollars are spent e\'el'}' day in an attempt to correct deSign deflcien-cies, often shortly alter the structure is commissioned,
Dnring the senice life of a stmcture, the cmironment ,mel the occupancy of the building change It is a mistah' not to make allowance for such changes and not to havE' a margin of safety in the inherent
high modlilus
from the t€'mperat1l1'e decreasing helow the dew point, and other sourct?s. Contrett? absorbs moisture until it becomes satu ratcd. :Vloisturt? ingress can be prelt'nted, or at lrast Significantly rt?duced. by the applic,\tionof,lmoisture
banier.
\ Yater content also can be recluc{>d bv pre\'enting ponding, The structure's design should accentuate watrr sh('dcling characletistics for vertical elements and incorpomte slopes and drain holes for hOtizontal surfaces.
The drain holes sbould be iu the lowest pOt1ion of the are'l to II(' drained ('\'('n after settlement. and they must be large enough for water and dehris to run freely through them,
One of the most eflective ways of pro-tecting reinforcing steel from corrosion is to prodde an adequate cover of good quality concrl'tc--one ｜｜ｾｴｨ low perme' ability to moisture, carbon dioxide, chlo, lides. and other aggrt?ssive agents and \dth the proper air-void parameters to resist damage due to freeze/thaw action. Keeping Il'ater out eliminates the elec-troh11' required to support an\' cormsiou cd!: it r"duccs the moisture content and hence the potential for freeze/thm\' {hm, age and alkali/aggregate attack.
Quality concrete, however, is difficult to ,lchien- \Iith current field-qllalily con-trol procedlll'es, ｃｯｮｳ･ｱｵ･ｮｴｬｾＧＬ in some ell\ironments. the \lsefullil(' of tlw con-crete \lil1 be shOl1ened unless it is pro-tected to prf'wnt detelioratioll. A pre\'en-th'e maintenance program, including periodic inspection and correctil'e actions. \\ill be necessary.
Quality of the Placed Concrete
occur. it should not be OH'rlooked in situ-ations wlwre such a tr'm!wrature change is iufrequent (e,g" cold storagp rooms),
Thpre are scvural rcasous ｜｜ｾｨｶ concrete placed in the field fails to meet speciAca-tions, Concrete's quality depends on man\' factors:
o The various mateJials selected must be thoroughly tested ,md inspected,
o Proportioning andｬｬｬ｢ｾｩｬｬｧ of mated-als must be accurately performed.
o Handllng, plaCing, consolidating,
and curing mustbe carefullv executed, Uniform concretequ,tlit\'depcnds to a large extent on the promptness in which changes in factors influencing uniformity are observed and corrections made. Late recognition of a change in anyone of the factors or delay in making a change will result in inferior concrete. It is essential that personnel on the job site are expeti-enced and that the work is carried out under an engineer's supel'\ision.
Although the water content of concrete usually is more than required for the COIll-plete hydration of the cement, an appre-ciable loss of this water by evaporation after initial set has taken placewilldelay or prevent complete ｨｾＧ｣ｬｲ｡ｴｩｯｮＬ Curing temperature and insufficient moist cuting affect the water tightness (impervious-ness), strength, and abrasion resistance of concrete,
Specil1cations h,1\'e been estabhshed to maintain quality during COllstmction, but the tendency is not to follow them because testing is expensi\'e and time consuming and causes production delays. As a result, often only minimum testing is performed, Just meeting the minimum reqUirements is construed as the hest available technology.
Mistakes in proportioning, adding water at the site to improve the harshness of the mix, and inadequate quantity of entrained air are a few examples of the most common problems. The presence of a qualilled field inspector is essentiaL
Moisture and Free.zejThaw
Concrete contains water originating Ii'om rain. melting sno\\', spillage. condensation
, I ,s usuaHy ;,per flash-! is often ,!Urn gut-idnity of ｬ［ｾｵｬ､ be se a pin-() II large 'ld severe jcity isa ｾｭｯ､ｵｬｵｳ ,re under ｾｨＭｭｯ､ｵﾭ materials Ｇｾ moduli gnificant lOee may awing on 1loading 'Ie bond odulus is lowever, ,lied par-line, as g on the of the ial trans-, higher lich may type of the edge ld is par-dynamic resent. thermal d unless is low ｾｶ･ｭ･ｮｴ 5at the ,rerature ith two thermal d inter-I mater-tches or lrtant to thermal rith that ;h this is • where :hanges T ht' C(J1'1t't!"neti(Jn Spl ' (:irit'rII)ｾｾ (.C, IIIhj 'r 1ｾｊ D() 2.7
in:
p(
01
Safety Awards
Staying on
the Fast Track
Since in>lth'ntion to5al'etvmenSlLres
leads to ilccid{'nts, injuries, and delay,
the first of llianagcnH'nfsｭｻＩｮｴｨｪｾ
pany.
On Apil 24, 1995, Rudolph/Libbe, Inc., of Toledo, contractors for
ealth-works and the shell,b0ganremoving
764,000m'(I million ydl
)of earth
from the223hectare(550acre) site,
launching the project.
by Mary Kincaid
W
hat happens to schedulingwhen several key workers have an accident? 'Vhen a dozen or so don't show up? When the concrete deliveties are late?
At the$4i2million North Star
BHPSteel project near Delta, Ohio,a
safety award program, a consortium of concrete plants, and an on-site testing lab all helped minimize delays.
ｓｰ･｣ｩｾＱｮｧＬ scheduling, and el'en parking at the site for the flat-roll minimill demanded adroit arrange-ments. At peak times, over a thousand field workers a day swarmed on the former pasture in northwest Ohio. Project Manager Eric Kolatchew real,
ized the project｣ｯｵｬ､ｮｾｴ be
com-pleted by October]996without
attention to safety and
clearcommu-nieation among
an
workers andsup-pliers.
This joint venture between North Star Steel and the Australian finn
BHPSteel brought workers from the
East Coast and the South to augment Ohio union locals, Equipment came in from Italy; subcontractors arrived from Great Blitain and South Afllca.
Casting machiner)' andmillelectlics
came from Japanese firms, the tunnel furnace came from Pittsburgh, other furnaces came from Germany, con-veyers were made in Canada, and
controls came fromaMexican
COIl1-Maintenance
the n('cessmy evaluatiolJ and tests
fol-lowed by major rehabilitation,
This situation can be avoided by per-forming routine walk-through inspections to record the progressive condition of thc various structund components.lhe feed-back from such monitOling will ensure that maintenance and repair are cartied out in a timely, cost-effective manner,
Figure B represents a struc-ture's typical performance
over time, Performance
decreases rapidly helo\\' the critical limit, at which time rehabilitation is needed to restore per/annance, ideally to its design level of senice-ability. Because of the grad-ual chemical, physical, and
mechanical changes that
degrade each material or
component, deterioration ｲ･ｾ
occurs and eventually ,mother repair \\ill be necessary,
The timing of the rehabili-tation \\ith respect to the rate of deterioration is of
para-lllount importance. In pnlCtice, a
struc-ture is repaired when its performance is unacceptable to the nsers Dr some time after that when funding is available. Many owners mistakenly believe that a major rehabilitation not only corrects
defiC'ien-des but also providefiC'ien-des trouble-freeｰ･ｬｦｯｲｾ
Because of
the gradual
chemical,
physical, and
mechanical
changes that
degrade each
material or
component,
deterioration
reoccurs,
and
eventu-ally another
repair
will
be
necessary.
ＭＭＭＭＭｾＬ｟｟Ｋ｟ＭＭＭＭＭＧＢＧＢＢＭＫ｟ＭＭＭｾＭ｟ＢＺ｟｟｟｟｟ＫＭＭＭＭ critical nihilresistancc' of the chosen matelials and the
protecti\'I"measures,
t.:ncertuinties in the evaluation of the propeltic's of materhtls and discrepancies bet"l'-een the lahoratory and field-sen·ice conditions also make a sufety margin in the protective measures necessary,
Inspections
EarlY detection of deHciencies proddc's technical and ,'co-nomi£' ackantages, Leal1ling to recognize problems will make it possible to prel"ent or at !ellst minimize further dete-rioratioll and catastrophes,
\'isual observations and
other supporting test dat,l determine theundr,r1)ing fac-tors ('allsing and controlling dL'tc'lioration. Many deficien-cies nre Cilused by more than one mechanism, An under-standing of tbe causes of con-erett' deterioration is
neces-s,m'. Proper evaluation of the
problem i, crucial and often
the deciding factor inｲ･ｨ｡｢ｩｬｾ
itation.
Propert\ owners are
sel-dfJm equipped with sufficient technical expertise to evaluate their structural
con-crete. The.\ Teact only whcn distress
becomes unacceptable or user inconve-nience occurs. At this point, usually a con-sultant specialiZing in the cvalu,ltion of
stmdural concrete is called to jJ",donn
.1!
----'---t---+-,"'-'- - - i l - - ｾ
ｾ
10 11 \14
5
time(yearsI ｾ
Figure B. Performance of a garage over time ｾ
L....-
-'8
100 75 -8"
!so-ｾJ
to
25 f ",
Ｇｾ
I
F"li\lreC.ｐ･ｲｦｯｮｮ｡ｾ ofa garage-the effectofongoing repairs A B C 12 10 m;caIDmit
\vith the other components of the ｣ｯｭｾ posite system. A detailed description of maintenance procedures is essential. •
References
Concrete Manl/tII, A Water Resources Techniazl Publication.8thed.(Washington, D.C., U.S. Departmentof Interior, 1979), 211-214.
Emmons, P. H. and A. M. VaysLurd, "Performance CriteriaforConcrete Repair
NOEL P. MAILVAGANAM works for the Institute for Research in Construction, National Research Council, in Ottawa,Canada
GERALD G.UTVANis a materials (:onsultant in Ottawa.
Materials. Phase 1." Technical Repdrt R EMR-CS;,\47 (Vicksburg, Miss., U.S.Army EngineersWaterways Experiment Station,
(995).
- Feld.
J,
I,esso,.1 from Failures of ConcreteStructures.AC1 Monograph No. 1 (1967): 21-39,
Fulton, F. S. Concrete Techrwlogy. Portland
Cement Institute (1977), 307-310. Litvan, G_ G. Deterioration of Parking
Srnlctllres RP-Iearc/' Project. NRC Client Report CR 549315,517/551815519.9 (1992). Mailvaganam. :-;. P Repair aJul Protection of
Concrete Stmctures(BocaRaton,Fl.: CRC Press, 1992). 6 8 time (years} ｏＫＭＭＭＭＫＭＭＭｾＭＭＭｾＭＭ｟Ｋ｟ＭＭ｟｟ＬｾＭＭ｟Ｋ｟ＭＭ｟｟ｉ o 100
lllance for a long time. Numerous case histories where the stfllctures were Icft in a state of disrepair (Inti! the structure required extensive rep'air show that this practice is the least cost eHective.
FigureC shows the benefits of
contin-uous rehabilitation. Curve A represents performance overtimeifrepairs are car-ded out at frequent intervals, with full restoration. Curve B also represents repairs camed out at frequent intervals
25
but without full restoration, while curveC
represents infrequent, major repairs. Even if full restoration is eventually needed (C\lJve B), the benefits of on-going rehabilitation are realized in good performance at a fraction of the cost of major renovation (curveC),
Conclusion
The cause of widespread material-related problems of the last two decades may be .the use of mah.,rials with properties inad-equate for changed environments or usage. Significant advances must still be made in correctly matching newer mate-rials with traditional matemate-rials to ensure acceptable long-term service.
Designer\; must understand the prop-erties of the materials to ensure satisfac-tory performance for the entire service life. They must know how materials are to be used, how they will f('spond to the environment, and how they will interact
MARYKINCAIDisaｴｲ･･ｬ｡ｮｾＧ･ writerin Ann Arbor, Michigan.
I
On-Slte Testing
Another help in keeping the jobon scheduleｗＱｬｾ the pair uf trailers housing the on-site office andlab of Bowser Momer,Inc., of Toledo. Up to four people at atime worked in the converted semitrailer under guid-auce from Robert White, manager of constructio;, services. He explained that thelln'nfollows ASTM testing guidelines.
'Wetest both fresh and hardened concrete for strength in compression on site. We test for strength at time intervals, sampling it up to 10 times a day, doing this at least once for every 150 cubic y"rds (115 m']. Since the concrete batch quality control is suc-cessful, very few rejections are required," White sai.d.
Placement details duriug hot and cold weather changes brought chal-lenges, but cracking-related problems carlyon were solved by different cur-ing proc'Cdures and placement tech-niques.
'We are expected at the North Star site to provide a wide range of
COII-struction observation, including earthwork, soil preparation, and veri-fying bearing capacity of the soil in footings, and structural steel weld and bolt torque monitoring," White continued.
"Aninteresting aspect of the job is
the 50-plusf(Xltdeep pits for descal-ing steel, holddescal-ing water for the steel to move through. The pits' thickｷ｡ｬｬｾ and base mats were more compli-cated than the main floor slabs and pavements.It was intricate work doing the foundations for heavy machinery bases," he said.
According to White, even though the early logistics of the setup were challenging, once up and running, communication between suppliers, subcontractors, and contractors r,\n smoothly. • Inicrowave \lkon,
