REPAIR
OF
LEAKING CR ACKS IN wALLS
OF
L IQUID
CoNTAINMENT ST RUCTURES
Keywords: chemical grout; concrete repair; crack injection; epoxy; leak; repair; rout and seal; wall; water tank.
Introduction
Nonprestressed reinforced concrete liquid contain­
ment structures-in particular, noncircular tanks-often
exhibit vertical and diagonal cracks that are aestheti­
cally objectionable. More importantly, cracks could
result in loss of stored liquids, leakage of hazardous
materials, concrete deterioration, and corrosion of rein­
forcing bars. Such cracks, however, are seldom indica­
tive of structural failure. This TechNote reviews the
methodology of repair in liquid containment structures.
Question
What are the typical causes of, and best practices to
repair, vertical and diagonal cracks in liquid contain­
ment structures?
Answer
Fig. 1-Vertical cracking at the walls of a liquid containment
tank.
Vertical and diagonal cracks in liquid containment
structures are usually the result of restrained movement of concrete due to shrinkage, differential thermal expansion, and contraction from moisture and tempera­
ture gradients over the wall height.
In the absence of corrosion, dormant but leaking cracks are typically repaired by pressure injection of epoxy
or chemical grout, vacuum injection, or routing and sealing on the interior or exterior wall surfaces, or both.
Active cracks are repaired by pressure injection with chemical grouts; by routing and sealing with a flexible
sealant on the interior or exterior wall surfaces, or both; or by application of a flexible barrier membrane on the
liquid retention side of the wall. ACI Concrete Terminology (ACI CT-13) defines an active crack as one whose
width changes with time, and a dormant crack as the opposite-one whose width does not change with time.
Not all cracks require repair. Refer to ACI 224R, Table 4.1, for crack widths that require repair or remediation.
Discussion
Liquid containment structures, such as large rectangular tanks, often exhibit vertical and diagonal cracks that
are usually the result of restrained concrete shrinkage and thermal contraction, typically spaced 4 to 10 ft (1.2
to 3 m) apart (Fig. 1). These cracks generally have an insignificant effect on the structural integrity. Cracking,
however, can affect the performance, serviceability, or both, of a structure, making repairs necessary to assure
liquid-tightness and long-term durability (ACI 350). Liquid containment concrete structures could have concrete
roof slabs that should be kept liquid-tight to prevent contamination of the contents by exterior exposure. In
these cases, differential shrinkage and thermal deformation of the concrete could result in significant wall and
roof cracking if the appropriate expansion or contraction (movement joints) are not provided. Structures with
movement joints in the walls and without matching joints in the base slab are prone to crack development,
not only in the walls adjacent to the joint, but in the base slab below the movement joint. The cracks typically
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REPAIR OF LEAKING CRACKS IN WALLS OF LIQUID CONTAINMENT STRUCTURES (ACI364.12T-15)
extend diagonally, vertically, or both, and occur on both sides of
the movement joints, resulting from the restraint of the base slab.
The width and spacing of cracks depends on concrete shrinkage
and creep, the size and spacing of horizontal reinforcement, wall
thickness, height and length of each placement (distance between
vertical construction joints), and length between movement joints,
member restraints, and the concrete mixture.
Crack widths can be controlled with appropriate reinforcement
and detailing that result in tight cracks that do not leak. In liquid­
retaining structures, the internal sides of walls should be consid­
ered in repair selection and design.
For more concrete repair guidance, refer to ACI 562, ACI 546R,
ACI 224.1R, and ICRI Guideline No. 340.1. Refer to ACI 224. 1R for
an assessment of the intrinsic nature of cracks. Before selecting a
repair methodology, the licensed design professional should deter­
mine the cause of the cracks-if they are active or dormant and if
corrosion is active in cracked areas. Because shrinkage of concrete
continues over an extended period of time, resulting cracks should
be considered active, especially if the structure is subjected to
cycles of wet and dry periods. Dormant cracks usually result from
an event of limited duration, such as temporary overload condi­
tions during construction.
For dormant cracks, injecting a rigid epoxy product restores the
structural integrity of the member (ACI 503.7; RAP-1; ASTM C881/
CM881).
Fig. 2-Example of an active crack improperly
repaired.
Conversely, except where it is needed for load-transfer purposes, rigid epoxy products should not be used in
active cracks (Fig. 2). If the conditions that cracked the wall initially are not, or cannot, be changed, the wall will
crack again near the same location if the wall is structurally bonded back together. A repair technique incorpo­
rating flexibility across the crack is the correct approach for this type of condition (ACI 224.1R). Crack injection
should not be used to repair cracks caused by corrosion of steel reinforcement unless supplemental means are
used to mitigate the cause of the cracks and corrosion.
If corrosion is present, it should be evaluated before making repairs. This TechNote does not cover repair of
cracks resulting from steel corrosion. There are various methods to mitigate, prevent, and control corrosion of
reinforcing steel in concrete (ACI 222R).
Active cracks can be repaired by: 1) pressure injecting of chemical grouts; 2) routing and sealing of cracks;
and 3) installing a flexible barrier system (ACI 224.1R). These methods are considered serviceability repairs and
not structural.
1) Chemical grout injection -Flexible hydrophobic polyurethane foam grout material is often used for the
crack repair in containment structures. Polyurethane foam retains most of its volume after curing, even if the
surrounding concrete should become dry, which is advantageous for repairing active cracks (Fig. 3 and 4).
Hydrophilic grouts tend to shrink when allowed to dry out and lose volume, resulting in active leaking when the
liquid is reintroduced at a later time. Note that some of these grouts might not re-swell sufficiently upon rewet­
ting to fully prevent future leakage. Both types of chemical grouts can be used to mitigate leaking cracks with
injection performed from the exterior side of a liquid containment structure so the tanks need not be emptied.
Interior injection can also be accomplished without draining the tank by experienced divers performing the
work underwater. Some excavation could be required to access cracks below grade. For extensive cracking
below grade, the application of a waterproofing system might be necessary.
There are conditions, however, where injection from the inside wall face is recommended to prevent liquid
exfiltration, which could require the tank be emptied. Injection from the inside, however, provides access for
crack repair below grade for buried or partially buried structures without excavation.
The proper climatic condition is crucial for successful crack injection, especially if polyurethane chemical
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REPAIR OF LEAKING CRACKS IN WALLS OF LIQUID CONTAINMENT STRUCTURES (ACI364.12T-15)
3
grout is used. In cold climates, it is best to complete
work in the spring or fall. Injection in the summer, when
cracks are the narrowest, should be avoided. Repairing
cracks in the winter, when they are the most open, is
beneficial but costly OCR! Guideline No. 340.1). Special
heated enclosures could be required to facilitate proper
injection and setting of the injection material. In all
cases, temperature at the time of application should be
within the limits recommended by the injection mate­
rial's manufacturer.
When leakage is present, injection using a water­
activated resin is recommended. The leakage of water
will be slowed down, and possibly stopped, during the
injection process. For tanks containing potable water,
chemical grouts and other repair products directly
exposed to the water must comply with NSF/ANSI 61
requirements for use in potable water ( Vrignaud et a!.
2003).
Injection penetration can be assessed by extracting
core samples that intercept the repaired cracks, as
described in Fig. 46 of ICRI Guideline No. 21 0. 1. Usually,
one or two cores taken at random locations for every
100 ft (30 m) of injection is adequate. Typically, penetra­
tion is considered adequate if 90 percent of the crack is
filled with injection grout. Although some nondestruc­
tive acoustic test methods may be used in some circum­
stances for testing epoxy adhesive injection repairs,
it is not recommended to use these methods for flex­
ible injection materials because the presence of low­
modulus materials in cracks and voids do not signifi­
cantly change the acoustic response from the structure.
Fig. 3-/njecting hydrophobic polyurethane chemicals to
repair active cracks in a liquid containment structure.
Fig. 4-Core sample taken from crack and injected with
polyurethane chemical grout provides information on the
Another method for crack repair is actual depth of penetration and effectiveness in filling the
routing and sealing cracks with a flexible sealant, incor­ entire crack width.
porating details that permit some movement. Because
routing and sealing are performed on the liquid side of the containment structure for tank leakage, the structure
should be emptied. In some cases, routing and sealing cracks on the exterior side can be used to reduce the
potential for contaminants penetrating the containment structure.
2) Rout and seal
-
3) Flexible barrier system-A flexible barrier system can also prevent containment structures from leaking. This
method may be preferred if there is a large quantity of leaking cracks. One should completely empty the contain­
ment for an extended length of time to allow the tank to dry before application of the barrier system. The construc­
tion details for active cracks or joints should be reviewed and confirmed by a lining product manufacturer.
Considerations for tanks containing aggressive m aterials When chemicals such as acids, alkalis, or process
contaminants are present in the liquid contained by the structure, the materials used to inject the cracks should
be carefully selected for compatibility (ACI 503. 7R) and chemical resistance (EPA 9090A). The sensitivity of mate­
rials to acid- and alkali-driven chemical attack depends on their composition, the containment chemistry (ACI 350;
515 .2R), and the severity of exposure conditions, such as concentration and temperature. Repair materials are
prone to deterioration by permeation if solvents in the tank are close to the solubility of the repair material. The
lower the molecular weight of the solvent, the more rapidly it diffuses into the repair material. Crack repair mate­
rial should be resistant to chemical attacks and other detrimental effects to avoid corrosion. Testing, consultation
with the material supplier, or both, is recommended to address chemical compatibility and chemical resistance.
When liquids being contained are corrosive and chemical deterioration of the crack repair materials is expected,
additional barrier linings may be required to assure long-term performance of the repair.
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4
REPAIR OF LEAKING CRACKS IN WALLS OF LIQUID CONTAINMENT STRUCTURES (ACI364.12T-15)
Summary
Treatment of vertical and diagonal nonstructural cracks often found in ordinary reinforced concrete liquid
containment structures depends on if they are active or dormant. Dormant but leaking cracks are typically
repaired with a rigid material, either by pressure injection or routing. Active cracks are repaired by pressure
injection with chemical grouts, by routing and sealing with a flexible sealant on the interior or exterior wall
surface, or both, or by application of a flexible barrier membrane on the liquid retention side of the wall.
References
American Concrete Institute (ACI)
ACI 222R-01(1 0)-Protection of Metals in Concrete Against Corrosion
ACI 224.1R-07-Causes, Evaluation, and Repair of Cracks in Concrete Structures
ACI 224R-01-Control of Cracking in Concrete Structures
ACI 350-06-Code Requirements for Environmental Engineering Concrete Structures and Commentary
ACI 503. 7- 07-Specification for Crack Repair by Epoxy Injection
ACI 515.2R-13-Guide to Selecting Protective Treatments for Concrete
ACI 546R-14-Guide to Concrete Repair
ACI 562-13-Concrete Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings and
Commentary
ACI RAP-1-Structural Crack Repair by Epoxy Injection
ACI CT-13-ACI Concrete Terminology (web access)
ASTM International
ASTM C881/C881M-10-Standard Specification for Epoxy-Resin-Base Bonding Systems for Concrete
International Concrete Repair Institute
Guideline No. 21 0.1-1998-Guide for Verifying Field Performance of Epoxy Injection of Concrete Crack (formerly
No. 03734)
Guideline No. 340.1-2006-Guide for the Selection of Grouts to Control Leakage in Concrete Structures
(formerly No. 03738)
NSF International/American National Standards Institute
NSF/ANSI 61-13-Drinking Water System Components-Health Effects
United States Environmental Protection Agency
EPA 9090A-Compatibility Test for Waste and Membrane Liners (Rev. 1, 1 992)
Authored documents
Vrignaud, J. P.; Ballivy, G.; Perret, S.; and Fernagu, E., 2003, "Selection Criteria of Polyurethane Resins to Seal
Concrete Joints in Underwater Road Tunnels in the Montreal Area," Grouting and Ground Treatment, Third Inter­
national Conference on Grouting and Ground Treatment, New Orleans, LA., Feb. 1 0-12, pp. 1338-1346.
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REPAIR OF LEAKING CRACKS IN WALLS OF LIQUID CONTAINMENT STRUCTURES (ACI364.12T-15)
5
Reported by ACI Committee 364
Marjorie M. Lynch, Secretary
David A. VanOcker, Chair
Randal M. Beard
Kal R. Hindo
Alexander M. Vaysburd
Benoit Bissonnette
Charles J. Hookham
James Warner
Christopher D. Brown
Ashok M. Kakade
David W. Whitmore
Ryan Alexander Carris
Keith E. Kesner
Larry D. Church
Erick N. Larson
Bruce A. Collins
John S. Lund
Consulting Members
Boris Dragunsky
Pritpal S. Mangat
Robert V. Gevecker
Paul E. Gaudette
Surendra K. Manjrekar
Stephen A. Johanson
Timothy R. W. Gillespie
James E. McDonald
Emory L. Kemp
Fred R. Goodwin
Jay H. Paul
Howard H. Newlon Jr.
Zareth B. Gregorian
Murat B. Seyidoglu
Weilan Song
Pawan R. Gupta
K. Nam Shiu
DeJa Tharmabala
John L. Hausfeld
Thomas E. Spencer
Robert Tracy
Robert L. Henry
Valery Tokar
William F. Wescott
ACI TechNotes are intended for reference for the design and construction of concrete structures. This document is intended for the use of
individuals who are competent to evaluate the significance and limitations of its content and who will accept responsibility for the appli­
cation of the information it contains. The American Concrete Institute disclaims any and all responsibility for the accuracy of the content
and shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents.
ACI 364.12T-15 was adopted and published October 2015.
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