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There are several methods of concrete crack repair such equally epoxy injection, routing and sealing, grouting, stitching, drilling and plugging, gravity filling of cracks in concrete. Details of these methods for the option of suitable methods for different types of cracks in concrete are discussed.

Contents:

  • How to Select Suitable Method of Concrete Crack Repair?
  • Methods of Concrete Crack Repair
    • Epoxy injection
    • Routing and Sealing of Cracks
    • Physical Crack Repair by Stitching
    • Additional Reinforcement for Crack Repair
    • Drilling and Plugging Method
    • Gravity Filling Method
    • Grouting Method of Crack Repair
    • Overlay and Surface Treatments of Cracks

How to Select Suitable Method of Concrete Crack Repair?

Suitable method for repair of cracks in physical can exist selected based on evaluation of the crack in structure for its causes. Once the cause is known and type of crack is established, then suitable method can be selected. For example, if the cracking was primarily due to drying shrinkage, then information technology is likely that after a period of time the cracks will stabilize. On the other mitt, if the cracks are due to a continuing foundation settlement, repair will exist of no employ until the settlement problem is corrected.

Methods of Concrete Cleft Repair

Epoxy injection

Epoxy injection method is used for cracks every bit narrow as 0.002 inch (0.05 mm). The technique mostly consists of establishing entry and venting ports at close intervals forth the cracks, sealing the cleft on exposed surfaces, and injecting the epoxy under force per unit area. Epoxy injection has been successfully used in the repair of cracks in buildings, bridges, dams, and other types of concrete structures (ACI 503R). However, unless the cause of the cracking has been corrected, information technology volition probably recur near the original cleft. If the cause of the cracks cannot be removed, then two options are available. One is to rout and seal the crack, thus treating it equally a joint, or, establish a joint that volition accommodate the movement so inject the crack with epoxy or other suitable material. With the exception of certain moisture tolerant epoxies, this technique is non applicative if the cracks are actively leaking and cannot be dried out. Wet cracks can be injected using moisture tolerant materials, but contaminants in the cracks (including silt and h2o) tin can reduce the effectiveness of the epoxy to structurally repair the cracks. The employ of a depression-modulus, flexible adhesive in a crack will non allow significant movement of the concrete structure. The effective modulus of elasticity of a flexible adhesive in a crack is essentially the same as that of a rigid adhesive because of the thin layer of material and high lateral restraint imposed by the surrounding concrete. Epoxy injection requires a loftier degree of skill for satisfactory execution, and application of the technique may be limited by the ambient temperature.

Epoxy injection Procedure

Clean the cracks The first step is to clean the cracks that have been contaminated; to the extent this is possible and practical. Contaminants such equally oil, grease, dirt, or fine particles of concrete prevent epoxy penetration and bonding, and reduce the effectiveness of repairs. Preferably, contamination should be removed by vacuuming or flushing with water or other specially effective cleaning solutions. Seal the surfaces Surface cracks should be sealed to keep the epoxy from leaking out before it has gelatinous. Where the scissure face cannot be reached, but where there is backfill, or where a slab-on-grade is being repaired, the backfill textile or sub base material is sometimes an adequate seal. A surface tin be sealed by applying an epoxy, polyester, or other advisable sealing material to the surface of the crack and allowing information technology to harden. If a permanent sleeky appearance along the crack is objectionable and if high injection force per unit area is not required, a strippable plastic surface sealer may be applied along the face up of the scissure. When the job is completed, the surface sealer can exist stripped away to expose the gloss-free surface. Cementitious seals can also be used where appearance of the completed work is important. If extremely high injection pressures are needed, the crack can exist cut out to a depth of 1/ii in. (13 mm) and width of about 3/4 in. (20 mm) in a Five-shape, filled with an epoxy, and struck off flush with the surface. Install the entry and venting ports: Three methods are used:

  1. Fittings inserted into drilled holes: This method was the starting time to exist used, and is often used in conjunction with V-grooving of the cracks. The method entails drilling a hole into the crack, approximately three/4 in. (twenty mm) in diameter and 1/2 to one in. (xiii to 25 mm) below the apex of the V grooved section.
  2. Bonded flush plumbing fixtures: When the cracks are non Five grooved , a method ofttimes used to provide an entry port is to bond a plumbing equipment affluent with the physical confront over the crack. The affluent fitting has an opening at the top for the agglutinative to enter and a flange at the lesser that is bonded to the physical.
  3. Interruption in seal: Some other organization of providing entry is to omit the seal from a portion of the crack. This method can be used when special gasket devices are bachelor that cover the unsealed portion of the fissure and allow injection of the agglutinative straight into the crevice without leaking.

Mix the epoxy This is done either past batch or continuous methods. In batch mixing, the adhesive components are premixed according to the manufacturer's instructions, usually with the utilise of a mechanical stirrer, like a paint mixing paddle. Care must be taken to mix only the amount of agglutinative that can exist used prior to beginning of gelling of the material. Inject the epoxy Hydraulic pumps, paint pressure pots, or air-actuated caulking guns may be used. The pressure used for injection must be selected carefully. Increased pressure often does little to accelerate the charge per unit of injection. If the crack is vertical or inclined, the injection process should begin past pumping epoxy into the entry port at the everyman elevation until the epoxy level reaches the entry port in a higher place. For horizontal cracks, the injection should keep from one finish of the crack to the other in the same manner. The crack is total if the pressure can be maintained. If the force per unit area tin non exist maintained, the epoxy is still flowing into unfilled portions or leaking out of the crack. Remove the surface seal Later on the injected epoxy has cured, the surface seal should be removed by grinding or other means every bit appropriate. Alternative procedure For massive structures, an alternating procedure consists of drilling a series of holes [ordinarily vii/8 to iv-in. (20 to 100-mm) diameter] that intercepts the crack at a number of locations. Typically, holes are spaced at 5-ft (1.5-yard) intervals. Another method recently being used is a vacuum or vacuum assist method. At that place are two techniques: one is to entirely enclose the cracked member with a bag and introduce the liquid agglutinative at the bottom and to apply a vacuum at the top. The other technique is to inject the cracks from one side and pull a vacuum from the other. Typically, epoxies are used; yet, acrylics and polyesters have proven successful.

Routing and Sealing of Cracks

Routing and sealing of cracks can be used in atmospheric condition requiring remedial repair and where structural repair is non necessary. This method involves enlarging the crack along its exposed face and filling and sealing it with a suitable joint sealant  (Fig.i). This is a mutual technique for crack treatment and is relatively simple in comparing to the procedures and the training required for epoxy injection. The procedure is most applicable to approximately flat horizontal surfaces such as floors and pavements. However, routing and sealing can exist achieved on vertical surfaces (with a non-sag sealant) also as on curved surfaces (pipes, piles and pole). Routing and sealing is used to treat both fine pattern cracks and larger, isolated cracks. A mutual and constructive use is for waterproofing past sealing cracks on the physical surface where water stands, or where hydrostatic pressure level is applied. This treatment reduces the ability of moisture to achieve the reinforcing steel or pass through the concrete, causing surface stains or other problems. The sealants may exist any of several materials, including epoxies, urethanes, silicones, polysulfides, asphaltic materials, or polymer mortars. Cement grouts should be avoided due to the likelihood of cracking. For floors, the sealant should be sufficiently rigid to support the anticipated traffic. Satisfactory sealants should be able to withstand cyclic deformations and should not be brittle. The procedure consists of preparing a groove at the surface ranging in depth, typically, from 1/4 to 1 inch (6 to 25 mm). A concrete saw, hand tools or pneumatic tools may exist used. The groove is so cleaned by air blasting, sandblasting, or waterblasting, and stale. A sealant is placed into the dry out groove and immune to cure. A bond breaker may be provided at the bottom of the groove to allow the sealant to change shape, without a concentration of stress on the bottom (Fig.2).

Fig.i: Routing and Sealing of Cracks in Physical

Fig.2: Concrete Cleft with Bond Breaker

The bail breaker may be a polyethylene strip or record which will not bond to the sealant. Conscientious attention should be practical when detailing the articulation so that its width to depth aspect ratio will suit predictable move (ACI 504R).

Concrete Fissure Repair by Stitching

Stitching involves drilling holes on both sides of the crack and grouting in    U-shaped metal units with brusque legs (staples or stitching dogs) that span the crack every bit shown in Fig.three. Stitching may be used when tensile strength must be reestablished across major cracks. The stitching procedure consists of drilling holes on both sides of the crack, cleaning the holes, and anchoring the legs of the staples in the holes, with either a not shrink grout or an epoxy resin-based bonding system. Concrete Crack Repair by Stitching

Fig.3: Concrete Crack Repair by Stitching

Additional Reinforcement for Crevice Repair

Conventional reinforcement

Cracked reinforced concrete bridge girders have been successfully repaired by inserting reinforcing confined and bonding them in place with epoxy. This technique consists of sealing the scissure, drilling holes that intersect the scissure plane at approximately 90 deg (Fig.4), filling the pigsty and fissure with injected epoxy and placing a reinforcing bar into the drilled pigsty. Typically, No. iv or v (10 G or 15 Thou) confined are used, extending at to the lowest degree 18 in. (0.v m) each side of the crevice. The reinforcing bars tin be spaced to accommodate the needs of the repair. They tin can be placed in any desired pattern, depending on the design criteria and the location of the in-place reinforcement.

Fig.4: Reinforcement bar orientation for scissure repair

Prestressing steel

Post-tensioning is often the desirable solution when a major portion of a member must be strengthened or when the cracks that have formed must exist airtight (Fig.5). This technique uses pre stressing strands or bars to apply a compressive forcefulness. Adequate anchorage must be provided for the prestressing steel, and care is needed and then that the problem will not merely migrate to some other part of the structure. Prestressing Steel for Crack Repair

Fig.v: Prestressing Steel for Fissure Repair

Drilling and Plugging Method

Drilling and plugging a crack consists of drilling down the length of the scissure and grouting it to form a key (Fig.6). Concrete Crack Repair by Drilling and Plugging

Fig.6: Concrete Scissure Repair by Drilling and Plugging

This technique is simply applicative when cracks run in reasonable straight lines and are accessible at one end. This method is nigh frequently used to repair vertical cracks in retaining walls. A hole [typically two to 3 in. (50 to 75 mm) in diameter] should exist drilled, centered on and post-obit the crack. The grout key prevents transverse movements of the sections of concrete adjacent to the crack. The key will likewise reduce heavy leakage through the crack and loss of soil from behind a leaking wall. If water-tightness is essential and structural load transfer is not, the drilled hole should be filled with a resilient material of low modulus in lieu of grout. If the keying result is essential, the resilient material can be placed in a second pigsty, the fiat existence grouted.

Gravity Filling Method

Low viscosity monomers and resins tin be used to seal cracks with surface widths of 0.001 to 0.08 in. (0.03 to ii mm) past gravity filling. High-molecular- weight methacrylates, urethanes, and some low viscosity epoxies have been used successfully. The lower the viscosity, the finer the cracks that can be filled. The typical procedure is to clean the surface by air diggings and/or water blasting. Wet surfaces should be permitted to dry several days to obtain the best crack filling. H2o blasting followed by a drying time may be effective in cleaning and preparing these cracks. Cores taken at cracks tin be used to evaluate the effectiveness of the crack filling. The depth of penetration of the sealant can exist measured. Shear (or tension) tests tin exist performed with the load practical in a direction parallel to the repaired cracks (every bit long as reinforcing steel is not present in the cadre in or near the failure area). For some polymers the failure crack will occur outside the repaired crack.

Grouting Method of Scissure Repair

Portland cement grouting

Broad cracks, particularly in gravity dams and thick physical walls, may be repaired by filling with Portland cement grout. This method is effective in stopping water leaks, but information technology volition not structurally bond cracked sections. The procedure consists of cleaning the concrete along the crack; installing built-up seats (grout nipples) at intervals astride the crack (to provide a pressure tight connexion with the injection appliance); sealing the cleft between the seats with a cement paint, sealant, or grout; flushing the crack to clean it and examination 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 crevice. However, the water-cement ratio should be kept as low equally 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 should be used. Subsequently the fissure is filled, the force per unit area should be maintained for several minutes to insure good penetration.

Dry out packing

Dry packing is the hand placement of a depression water content mortar followed by tamping or ramming of the mortar into identify, producing intimate contact between the mortar and the existing concrete. Considering of the low water-cement ratio of the material, there is petty shrinkage, and the patch remains tight and can have proficient quality with respect to durability, strength, and water tightness. Dry pack tin can exist used for filling narrow slots cut for the repair of fallow cracks. The apply of dry pack is not advisable for filling or repairing active cracks. Before a scissure is repaired by dry out packing, the portion adjacent to the surface should be widened to a slot almost one in. (25 mm) wide and 1 in. (25 mm) deep. The slot should be undercut so that the base width is slightly greater than the surface width. To minimize shrinkage in place, the mortar should stand for one/2 60 minutes after mixing and and then should be remixed prior to use. The mortar should be placed in layers about three/8 in. (10 mm) thick. Each layer should be thoroughly compacted over the surface using a blunt stick or hammer, and each underlying layer should be scratched to facilitate bonding with the next layer. The repair should be cured by using either h2o or a curing compound. The simplest method of moist curing is to back up a strip of folded wet burlap forth the length of the crack.

Overlay and Surface Treatments of Cracks

Fine surface cracks in structural slabs and pavements may be repaired using either a bonded overlay or surface treatment if in that location volition not exist further meaning movement across the cracks. Unbonded overlays may be used to encompass, but not necessarily repair a slab. Overlays and surface treatments can be appropriate for cracks acquired by one-time occurrences and which do not completely penetrate the slab.

Surface treatments

Low solids and depression-viscosity resin-based systems have been used to seal the physical surfaces, including handling of very fine cracks. They are most suited for surfaces not field of study to significant wearable. Bridge decks and parking structure slabs, too as other interior slabs may exist coated effectively after cracks are treated by injecting with epoxy or past routing and sealing. Materials such as urethanes, epoxies, polyesters, and acrylics have been applied in thickness of 0.04 to 2.0 in. (1 to 50 mm), depending on the material and purpose of the treatment. Skid-resistant aggregates are oftentimes mixed into the material or broadcast onto the surface to ameliorate traction.

Overlays

Slabs containing find dormant cracks can be repaired by applying an overlay, such equally polymer modified Portland cement mortar or concrete, or by silica fume concrete. Slabs with working cracks can exist overlaid if joints are placed in the overlay straight over the working cracks. In highway span applications, an overlay thickness as low as 1-one/4 in. (30 mm) has been used successfully. Suitable polymers include styrene butadiene or acrylic latexes. The resin solids should be at least 15 percent by weight of the Portland cement, with 20 percent usually being optimum. Read More than: Methods for Repair of Small and Large Cracks in Concrete Reinforcements for Slabs-on-Ground Crack Width Control -As Per ACI Cement Grouting for Cracks in Concrete and Masonry Plastic Shrinkage Cracks in Physical and Its Prevention Epoxy Injection Grouting of Cracks in Structures