1、 1 ACI 364.12T-15TechNoteRepaiR of Leaking CRaCks in WaLLs of Liquid Containment stRuCtuResKeywords: chemical grout; concrete repair; crack injection; epoxy; leak; repair; rout and seal; wall; water tank.IntroductionNonprestressed reinforced concrete liquid contain-ment structuresin particular, nonc
2、ircular tanksoften 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
3、structural failure. This TechNote reviews the methodology of repair in liquid containment structures.QuestionWhat are the typical causes of, and best practices to repair, vertical and diagonal cracks in liquid contain-ment structures?AnswerVertical and diagonal cracks in liquid containment structure
4、s are usually the result of restrained move-ment 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 o
5、r 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 o
6、f 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 oppositeone whose width does not change with time.Not all cracks require repair. Refer to ACI 224R, Ta
7、ble 4.1, for crack widths that require repair or remediation.DiscussionLiquid 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
8、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 con
9、crete 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 expansi
10、on 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 Fig. 1Verti
11、cal cracking at the walls of a liquid containment tank.American Concrete Institute Copyrighted Material www.concrete.org2 REPAIR OF LEAKING CRACKS IN WALLS OF LIQUID CONTAINMENT STRUCTURES (ACI 364.12T-15)extend diagonally, vertically, or both, and occur on both sides of the movement joints, resulti
12、ng 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,
13、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 rep
14、air 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 cracksif they are active or dormant
15、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 durati
16、on, 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).Conversely, except where it is needed for load-transfer purposes, rigid epoxy products should not be
17、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
18、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 Tec
19、hNote 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)
20、 installing a flexible barrier system (ACI 224.1R). These methods are considered serviceability repairs and not structural.1) Chemical grout injectionFlexible hydrophobic polyurethane foam grout material is often used for the crack repair in containment structures. Polyurethane foam retains most of
21、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
22、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
23、 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, h
24、owever, 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
25、condition is crucial for successful crack injection, especially if polyurethane chemical Fig. 2Example of an active crack improperly repaired.American Concrete Institute Copyrighted Material www.concrete.orgREPAIR OF LEAKING CRACKS IN WALLS OF LIQUID CONTAINMENT STRUCTURES (ACI 364.12T-15) 3grout is
26、 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 (ICRI Guideline No. 340.1). Special heated enclosures could be
27、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-rials manufacturer.When leakage is present, injection using a water-activated resin is recommended. The le
28、akage 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 al. 2003).Injection pene
29、tration can be assessed by extracting core samples that intercept the repaired cracks, as described in Fig. 46 of ICRI Guideline No. 210.1. 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 perce
30、nt 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 materi
31、als in cracks and voids do not signifi-cantly change the acoustic response from the structure.2) Rout and sealAnother method for crack repair is routing and sealing cracks with a flexible sealant, incor-porating details that permit some movement. Because routing and sealing are performed on the liqu
32、id 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.3) Flexible barrier systemA flexible barrier system can al
33、so 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 ac
34、tive cracks or joints should be reviewed and confirmed by a lining product manufacturer.Considerations for tanks containing aggressive materialsWhen chemicals such as acids, alkalis, or process contaminants are present in the liquid contained by the structure, the materials used to inject the cracks
35、 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 conce
36、ntration 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 resis
37、tant 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 ma
38、terials is expected, additional barrier linings may be required to assure long-term performance of the repair.Fig. 3Injecting hydrophobic polyurethane chemicals to repair active cracks in a liquid containment structure.Fig. 4Core sample taken from crack and injected with polyurethane chemical grout
39、provides information on the actual depth of penetration and effectiveness in filling the entire crack width.American Concrete Institute Copyrighted Material www.concrete.org4 REPAIR OF LEAKING CRACKS IN WALLS OF LIQUID CONTAINMENT STRUCTURES (ACI 364.12T-15)SummaryTreatment of vertical and diagonal
40、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
41、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.ReferencesAmerican Concrete Institute (ACI)ACI 222R-01(10)Protection of Metals in Concrete
42、 Against CorrosionACI 224.1R-07Causes, Evaluation, and Repair of Cracks in Concrete StructuresACI 224R-01Control of Cracking in Concrete StructuresACI 350-06Code Requirements for Environmental Engineering Concrete Structures and CommentaryACI 503.7-07Specification for Crack Repair by Epoxy Injection
43、ACI 515.2R-13Guide to Selecting Protective Treatments for ConcreteACI 546R-14Guide to Concrete RepairACI 562-13Concrete Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings and CommentaryACI RAP-1Structural Crack Repair by Epoxy InjectionACI CT-13ACI Concrete Terminology (we
44、b access)ASTM InternationalASTM C881/C881M-10Standard Specification for Epoxy-Resin-Base Bonding Systems for Concrete International Concrete Repair InstituteGuideline No. 210.1-1998Guide for Verifying Field Performance of Epoxy Injection of Concrete Crack (formerly No. 03734)Guideline No. 340.1-2006
45、Guide for the Selection of Grouts to Control Leakage in Concrete Structures (formerly No. 03738)NSF International/American National Standards InstituteNSF/ANSI 61-13Drinking Water System Components-Health EffectsUnited States Environmental Protection AgencyEPA 9090ACompatibility Test for Waste and M
46、embrane Liners (Rev. 1, 1992)Authored documentsVrignaud, 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 Grout
47、ing and Ground Treatment, New Orleans, LA., Feb. 10-12, pp. 1338-1346.American Concrete Institute Copyrighted Material www.concrete.orgREPAIR OF LEAKING CRACKS IN WALLS OF LIQUID CONTAINMENT STRUCTURES (ACI 364.12T-15) 5ACI TechNotes are intended for reference for the design and construction of conc
48、rete 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 responsibi
49、lity 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.Copyright 2015, American Concrete Institute.All rights reserved including the rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in an
