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362.1R·28 ACI COMMITTEE REPORT
Fig 3 7 Typical sealant detail Mer construction joint incast in place structural slab
3 6 G uldellnes for selection of durability systems
for f loors and roofs3 6 1 Introduction The performance of parking structures
requires special attent ion to durability systems in all envi
ro nments . Selecting the right combination of protection
systems is not a prescriptive process. This section is provided
to assist the designer in selecting an appropriate combination
of pro tective measures .
Recommendations in the text differentiate between
parking levels exposed directly to the elements roof and
parking levels not exposed directly to the weather floor .
The recommendations re fer to general park ing area and
adjacent drive lane s. Isolated ramps, helixes, or access lanes
with concentrated traffic may require protection greater than
the minimum recommendations. Other physical or functionalcharacteristics that may justify exceeding these minimum
recommendations arc:
I. Multiple-usc structure;
2. Perimeter of park ing level exposed to the wea ther;
3. Occupied space direc tly below parking level ;
4. Heated space above or below parking level
5. Isolated single-lane entrance or ex it without alternate
acce ss; and
6. High traffic volumes.
Section 3.6.4 provides descriptions of these characteristics
and their effects on the durability system.
Not all available protection measures arc appropriate or
compatible. Tables 3.1 through 3.4 provided minimum recom
mended durability measures for different types of structural
systems and service env ironments.
3 6 2 Structural llsideratiolls Recommended durability
meas ures are dependent on the structural system chosen and
their service environmen t For example, slabs that tend to
crack thin slabs and nonprestressed slabs should be
provided with traffic grade membranes on the roo f in certain
conditions and on all floors in others. Measures to isolate and
protect internal metal elements in the slab will also vary from
system to sys tem.
3 6 3 Environmental considerations hapter I discusses
various exposure conditions and types of deterioration that
may occur. Figure 3.1 defies various exposure zones to
provide the designer with initial guidance to address each of
specific cracks that continue to leak at a later date with the
rout and seal method .
Another method of sealing cracks is the use of epoxy
injection. This process involves injecti ng epoxy into a crack
under pressure to fill the void and adhere the surfaces back
together. Th is approach should be consi dered if the crack is
static and it is desirable to restore the structural integrity of
the cracked section. A varia tion on this method is to gravity
feed a low-viscosity epoxy, methacrylate, or other polymer
into the crack to fill the void and make it watertight In either
case, it is important that the underlying cause of the crack be
determined and corrected prior to the repair, or a new crack
may develop to replace the one being fixed. Epoxy injection is
nor a recommended procedure for repairing moving cracks.
CONSTJitU T ON JOINT f AeONCRETE SL/o.8
SLA8 REINf ORCING
3 5 2 4 Construe/ion join s Construction jo ints are
created at predetermin ed locati ons where one concrete
placement is terminated and another is begun later. Depending
on structural design. joints may be monolithic that is. the
interfaces of the joint are soundly bonded to ensure complete
struc tural integrity of the slab , or function as isolation or
contractionjoints.
Construction joints arc often sources of leakage in parking
structures. Deicers allowed to penetrate through the joint may
result in corrosion of reinforcement or otherembedded metals.
Leakage at monolithic construction joi nts may be reduced
if, before the second cast ing, laitance is removed to promote
a positive bond.Following placement, monolithic construction jo ints
should be tooled and sealed. Sealing should be accomplished
by filling the construction jo int with an elastorneric sealant
refer to Fig. 3.7 . Monolithic construction joints are usually
restrained from movementbecause of the amount of reinforce
ment crossing the jo int.
Optimum configuration of the jo int sealant is dependent
on the amount of movement anticipated during the servic e
life of the structure refer to ACI 504R .
3.5.2.5 Cracks racks in concrete occur for a variety
of reasons . Because cracks are a source of mois ture and
chlo ride intrusion into the concr ete , sealing them is an
important issue.
The re arc several common methods of scaling cracks . The
effectiveness of a given method is dependent upon the
underlying cause and behavior of the crack. Refer to ACT
224R and ACI 224.IR for a more complete discussion of the
causes of cracki ng. Many cracks in parki ng structures are
subject to dynamic movement due to temperature change.
Effective repairs for these cracks must be able to withstand
ongoing movement in the crack. 1he most effective method to
accomplish this repair is to provide a groove of approximately
1/2 in. wide by 1/2 in. deep sealed with an elastomeric sealant.
For small c racks approx imately 0.0 15 in. or less that
show little or no movement, treatment with a penetrating
silane or sucxane sealer may render the crack hydrophobic.
One course o f action to repair multiple smallc racks is to treat
the surface area with a silane or suoxane sealer, then retreat
SlOP E TOOL EOO£S s.oME fIEASONSSTATEDIN 3 5.2.3
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DeSIGN OF DURA lE PARKING STRUCTURES
Fig. .7- Scaling of floor surface:
Concrete Bridgl Du b for conversion factors expressing
chloride content.
Corrosion can occur in uncracked concrete due to chloride
ions. moisture, and oxygen permeating into the concrete
(refer to Section3.3.2). However, corrosionofreinforcement is
generally more severe and begins earlier at cracks and places
where water can easily penetrate. Information on corrosion
of metals in concrete is available in AO 222R. Corros ion
of Metals in Concrete
1.4.1.2 Bonded prestressing sud - The corrosion of
prestressing strand in pretensioned double-tees and inverted
lee-beams used in parking structures has normally occurredwhere there is a breach in the scaled joints and where
brackish water reaches the bottoms of members.
Corrosion of grouted prestressing steel has occurred where
the grout did not encase the wires, bar, or strand within a
grout duct, and moisture or chlorides gained access to the
open void.
1.4.1.3 Unbonded prestressing fflel- Most cases of
corrosion of unbonded prestressing steel in parking structures
have involved either natural saltwater or deicer salt exposure
to loosely sheathed systems with inadequate amounts of
grease. Other areas most susceptible to corrosion include
poorly grouted stressing end anchorages. intermediate
stressing points at construction joints. and regions of insuffi
cient concrete cover.
1.4.1.4 Other I mIHddl d n l tals orroded electrical
conduits have been observed in structures exposed to deicer
salts. Likewise. uncoated aluminum has been observed 10
corrode in concrete containing chloride and particularly
where the aluminum has been in contact with the steel
reinforcement. Embedded metals of all kinds should be
specifically reviewed for their durability and function.
1.4.2 Freezing and thawing damagl S caling of concrete
is a deterioration observed in parking structures exposed to a
freezing and thawing environment. Cyclic freezing and
deicer scaling is discussed extensively in ACI 201.2R.
Guide to Durable Concrete. The phenomenon usually
begins withthelossof thinflakes at the surface.Asdeteriorationprogresses. coarse aggregates may be exposed. In advanced
Fig. .S Spalling of beam SOff i l beside ll ahng isolanonjo int.
stages, the surface may progress from an exposed aggregate
appearance to that of rubble. Frequently. with prolonged
water saturation and repeated freeze-thaw cycles, theconcrete will develop fine cracks paralleling the exposed
surface.The presence of deicers willacceleratethisdeterioration
f jg 1.7) .
The addition of air entrainment is the most effective
method of increasing the resistance of concrete to damage
due to freezing and thawing. The entrained air-void size and
spacingin the concrete is also important (refer to ACt 345R).
Severe abrasion accelerates the deterioration of concrete
undergoing scaling. Good drainage (pitch of surface 10
drains) diminishes the severity of freezing and thawing
exposure by reducing the moisture content of the concrete .
1.4_3 Cracking and l l n pt lll tTcltio l Cracking of
concrete exists in many forms. Some common types are:
mtcrocracking. partial depth cracks in the top of members.
and through-slab cracks. Observations of parking structures
suggest that corrosion will occur earlier and is much more
likely at wide cracks than at uacracked or finely cracked
areas. For information on resistance 10 cracking. refer 10
Section 3.5.2.5.
In addition to abetting corrosion. water penetration through
the slab is undesirable. When substantial amounts of water
penetrate completely through the slab at cracks and jo ints.
corrosion and freeze-thaw damage of the sides or bouoms of
underlying members may occur. Damage to ribs, jo ists, webs,
beams, columns, heavily loaded joints, and bearings is more
critical to structural integrity than damage to the slab because
these elements support larger tributary areas. Severe damageto a beam at an isolation joint is shown in Fig. 1.8.
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CAUSES EVALUATION AND REPAIR OF CRACKS 224.1R·17
monomer or resin can bepoured onto the surface and spread
with brooms, rollers, or squeegees. The material should be
worked back and forth over the cracks to obtain maximum
filling because the monomer or resin recedes slowly into thecracks . The use of this methodon elevated slabs will require
sealing of the cracks on the bottom of the slab to contain
material from leaking through the crack. Excess material
should be broomed off the surface to prevent slick, shining
areas after curing . If surface friction is important, sand
should be broadcast over the surface before the monomer or
resin cures.
If the cracks contain significant amounts of silt, moisture,
or other contaminants, the sealant cannot fill them. Water
blasting followed by a drying time may be effective in
cleaning and preparing these cracks. Cores may be taken to
verify crack filling and the depth of penetration measured.
Cau tion should be employed to avoid cutting existingreinforcement during the coring process. Cores can be tested
to give an indication of the effectiveness of the repair
method. The accuracy of the results may be limited,
howeve r, as a function of the crack orientation or due to the
presence of reinforcing steel in the core. For some polymers,
the failure crack will occur outside the repaired crack.
3 e G routlng3.8.1 Portland cement grouting W ide cracks, particularly
in gravitydams (Warner 20 ) and thick concrete walls,may
be repaired by fill ing with portland-cement grout. This
method is effective in stopping water leaks, but it will not
structurally bond crackedsections. The procedure consists ofcleaning the concrete along the crack; installing built-up
seats (grout nipples) at intervals astride the crack (to provide
a pressure-tight connection with the injection apparatus);
sealing the crack between the seats with a cement paint,
sealant, or grout; flushing the crack to clean it and test the
seal; and then grouting the whole area. Grout mixtures may
contain cement and water or cement plus sand and water,
depending on the width of the crack. The wlcm however,
should be kept as low as practical to maximize the strength
and minimize shrinkage. Water reducers or other admixtures
may be used to improve the properties of the grout. For small
volumes, a manual injection gun may be used; for larger
volumes, a pump may be used . After the crack is filled , the
pressure should be maintained for several minutes to ensure
good penetration.
3.8.2 Chemical grouting hemical grouts, such as
urethanes and acrylomides , arc activated by catalysts or
water to form a gel, a solid precipitate, or foam that will fill
void spacewithin concrete. The materials are primarily used
for scaling cracks from water penetration. Bondstrengths are
typically low, so structural repairs are not madewhh chemical
grouts. Cracks in concrete as narrow as 0.002 in. (0.05 mm)
have been filled with chemical grout.
The advantages of chemical grouts include applicability in
moist environments (excess moisture available). wide limits
of control of gel time, and thei r ability to be applied in vel)
fine fractures. Disadvantages are the high degree of skillneeded for satisfactory usc, and lack of strength.
3 DrypacklngDrypacking is the hand placement of a low water content
mortar followed by tamping or ramming of the mortar into
place, producing intimate contact between the mortarandtheexisting concrete (U.S. Bureau of Reclamation 1975; C rack
Repair Method: Drypacking 1985). Because of the low w/cm
of the material. there is little shrinkage. and the patch
remains tight and can have good quality with respect to
durability, strength, and watertightness.
Drypack can be used for filling narrow slots cut for the
repair of dormant cracks .The use of drypack is not advisable
for filling or repai ring active cracks.
Before a crack is repaired by drypacking, theportionadjacent
to the surface should be widened to a slot about 1 in. (25 mm)
wide and I in. (25 mm) deep. The slot should be undercut so
that the base width is slightly greater than the surface width.
After the slot is thoroughly cleaned and dried, a hond coat,consisting of cement slurry or equal quantities of cement and
fine sand mixed with water to a fluid paste consistency, or an
appropriate latex bonding compound (ASTM C 1059),
should be applied. Placing of the drypack mortar should
begin immediately. The mortar consists of one part cement,
one to three parts sand passing a No. 16 (1.18 mm) sieve, and
just enough water so that the mortar will stick together when
molded into a ball by hand.
the patch must match the color of the surrounding
concrete, a blend of gray portland cement and white portland
cement may be used. Normally, about 3 while cement is
adequate, but the precise proportions can be determined only
by trial.To minimize shrinkage in place, the mortar should stand
for 1/2 hour after mixing, and then be remixed before use.
The mortar should be placed in layers about 3/8 in. (10 mm)
thick. Each layer should be thoroughly compacted over the
surface using a blunt stick or hammer and each underlying
layer scratched to facilitate bonding with the next layer.
There need be no time delays between layers.
The repair should be cured by using either water or a curing
compound. The simplest method of moist curing is to support a
strip of foldedwet burlap along the length of the crack.
3 1o Ctack arrestDuring construction of massive concrete struc tures, cracks
due to surface cooling or other causes may develop and
propagate into new concrete as construction progresses.
Such cracks may he arrested by blocking the crack and
spreading the tensile stress over a larger area (U.S. Army
Corps of Engineers 1945).
A piece of bond-breaking membrane or a grid of steel mat
may be placed over the crack as concreting continues . A
semicircular pipe placed over the crack may also be used
(Fig. 3.7). A description of installation procedures for semi
circular pipes used during the construction of a massive
concrete structure follows:
I The semicircular pipe is made by splitting an 8 in .
(200 mm), 16 gauge pipe and bending it to a semicirc ular
section with an appro ximately 3 in . (75 mm) flange oneach side;
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GUIDETODUR LE CONCRETE 201.2R-5
When consolidating concrete, the duration of vibration
can have a significant effect on the air content of concrete,
with the effect being influenced by the initial slump of the
concre te Kosmatka et aI. 2002). Increasing the time ofvibration leads to a reduc tion in the overall air content.
Consolida tion, however, is normally necessary to obtai n the
strength and durability properties required over the service
life of the concrete structure. Provided that the concrete is
proportioned and vibra ted properly, internal vibration will
mainly remove the larger airvoids, so that the air-void spacingfactor will not be affected adversely. Placement and consoli
dation methods should be carefully evaluated to ensure thatthe desired fresh concrete properties are attained ACI 309R).
Good consolidation is a prerequisite for obtaining low
permeability , which is critical for making concre te resistant
to weathering and most agents of deterioration. Low pcrmc
ability can be achieved more readily with concrete mixturesdesigned for good workability and placeability. ACI 211.1
and 21I,2 provide guidance for selecting mixture proportions,
andACI 309R provides guidance for consolidating concrete.
3 5 B leedlngOnce concrete is in place, but before the time of initlal
setting, particles denser than water su ch as cement and
aggregates) may settle due to the force of gravity. displacing
part of the mixing water which may reach the top surface as
bleed water. This condition is more pronounced in mixtures
with excessive water content. Also, non-air-entrained
concrete mixtures will exhibitmore bleeding than air-entrained
mixtures of similar composition. It is the difference in densitybetweenwater and other components in themixture thatcauses
bleeding to occur. Just as entrapped air moves to the surface
Lankard 1995) during vibration, waterwill be displaced due
to settling of the solid components of the concrete.
Defective hardened concrete surfaces are frequen tly the
result of finishing fresh concrete while bleed water is present
on the surface . If bleed water is worked into the concre te
near thesurface byfinishing opera tions, the surface concrete
can suffe r from increased w m and decreased air conte nt.
Premature finishing of the concrete surfa ce while bleeding is
still active may result in an accumulation of bleed water
below the sealed surface that can result in subsequent spalling,
scaling, or delam ination. Problems such as craze cracks anddusting can occur, and abrasion resistance can be reduce d.
Scaling of the surface from freezing and thawing is a
common result of reduced air conte nt in the surface concrete .
3 6 Cracklng of fresh conc reteCracks can fonn in fresh concrete as a result of plastic
shrinkage, settlement, or temperature differential between
the exposed surface and the interior. Insulating blankets can
prevent tempe rature differential-induced cracking.
Plastic shrinkage cracking is characterized by a series of
short, discontinuous cracks that fonn before initial setting of
the concrete.Plasticshrinkage cracks may occur approximately
parallel to each other, but will typically occur in a random,
irregular pattern, Plastic shrinkage cracks may be only
superficial, or they may extend more deeply int o a slab,even
to its full depth .
Plastic shrinkage cracking is caused by rapid evaporation of
moisture from the surface. f th e loss of moisture at the surfaceis greater than the rate that moisture can be replenished by
bleed water or capil1aryaction, tensile stress will develop in the
surface region. This phenomenon is related to the evaporation
rate, which in tum is influenced by the combined effects of
humidity, wind, and concrete and air temperatures. Detailed
discussions of the mechanism and preventative measures can
be found in ACI 305R, 308R, and 302 l R.
Settlement cracks typically occur directly above reinforcing
bars and ex tend to the bar. Settlemen t cracking is caused by
subsidence of fresh concrete, which can occur due to
improper consolida tion or, more commonly, from bleedin g.
Because crack s act as a avenue for the ent ry of water,
deicing chemicals, carbon dioxide, and aggressive chemicals,
the ir presence may lead to a reduc tion in the durability of the
concrete . The extent of the influence on durability will be
dependent on the width and. more importantly, the depth, of
the cracks . Cracks less than 5 mm 0.2 in.) deep may have a
negligible effec t. Cracks of greater dep th, however, increase
the penetrat ion of carbon dioxide, water, and deicing
chemicals, increasing the likelih ood of re inforcement
corrosion, damage due tu free zing and thawing, and AAR .
For nonreinforccd concrete not exposed to freezing and
thawing or aggressive chemicals, plastic shrinkage cracks may
be of little significance, other than for aesthetic considerations.
Crack s in fresh concrete can appear to be closed during the
finishing operations. The closure, however, may be only a
thin skin over the surface of the crack, and the crack may
subsequently reopen. I f such cracki ng occurs, actions should
be taken to prevent the continued occurrence of cracks
forming in the fresh concrete.
3 7 Summary[he strcngth and durability of concrete can be significantly
impaired by the use of improper placement, finishi ng, and
curing techniques while concrete is in the unhardened state.
Appropriately proportioned concrete mixtures that are properly
placed, consolidated, finished, cured. tested, and inspecte d
will help to ensure that the desired durability characteristics
are achieved.
CHAPTER 4 FREEZINGAND THAWINGOF CONCRETE
4 1 lntroduct lonDeterioration of concre te exposed to freezing conditions
can occur when there is sufficient internal moisture present
that can free ze at the given exposure conditions. The source
of moisture can beeither internal water already in the pores
of concrete that is redistributed by thermodynamic conditions
to provide a high enough degree of saturation at the point of
freezing to cause damage ) or external water entering the
concrete from an external source,such asrainfall).Dry concrete
generally below approximately 75 to 80 internal relative
humidity) is normally immune to damage from freezing.
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