1. PUAN NOORLI ISMAIL

2. CONTENTS Introduction Types and Causes of Concrete Crack
Method of Crack Repairing

3. Introduction
It is important to understand the different types of cracks before applying the proper remedy to it i.e. source, causes, etc.
If the cracks are due to a continuing foundation settlement, repair will not useful until the settlement problem is corrected.

4. Types and Causes Of Concrete Crack
Crazing
Plastic Shrinkage Cracking
Drying Shrinkage
Alkali-aggregate Reaction
Thermal Cracks
Corrosion
Weathering
Construction overloads
Error in design and detailing
Poor construction practices
Settlement cracking

5. Crazing
a pattern of fine cracks that do not penetrate much below the surface and are usually a cosmetic problem only
they are barely visible, except when the concrete is drying after the surface has been wet

6. Plastic Shrinkage Cracking
when water evaporates from the surface of freshly placed concrete faster than it is replaced by bleed water, the surface concrete shrinks
due to the restraint provided by the concrete below the drying surface layer, tensile stresses develop in the weak, stiffening plastic concrete, resulting in shallow cracks of varying depth
these cracks are often fairly wide at the surface

7. Drying Shrinkage
almost all concrete is mixed with more water than is needed to hydrate the cement, much of the remaining water evaporates, causing the concrete to shrink
restraint to shrinkage, provided by the subgrade, reinforcement, or another part of the structure, causes tensile stresses to develop in the hardened concrete – restraint to drying shrinkage is the most common cause of concrete cracking

8. Alkali-aggregate Reaction
the reactivity is a type of concrete deterioration that occurs when the active mineral constituents of some aggregates react with the alkali hydroxides in the concrete
alkali-aggregate reactivity occurs in two forms—alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR)
indications of the presence of alkali-aggregate reactivity may be a network of cracks, closed or spalling joints, or displacement of different portions of a structure.

9. Thermal Cracks
Temperature rise (especially significant in mass concrete) results from the heat of hydration of cementitious materials
As the interior concrete increases in temperature and expands, the surface concrete may be cooling and contracting – causes tensile stresses
Result in thermal cracks at the surface if the temperature differential between the surface and center is too great
The width and depth of cracks depends upon the temperature differential, physical properties of the concrete, and the reinforcing steel

10. Corrosion
corrosion of reinforcing steel and other embedded metals is one of the leading causes of deterioration of concrete
when steel corrodes, the resulting rust occupies a greater volume than steel – the expansion creates tensile stresses in the concrete, which can eventually cause cracking and spalling

11. METHOD OF CRACK REPAIRING
Epoxy injection
Routing and Sealing
Stitching
Concreting
Conventional Reinforcement
Pre-stressing
Drilling and Plugging
Gravity Filling
Portland Cement Grouting
Dry Packing

12. EPOXY INJECTION
Epoxy injection is one of the popular approach when it comes to cracks repair.
This method will weld the cracks but not repairing the cause of cracking.
Cracks as narrow as in. (0.05 mm) can be bonded by the injection of epoxy.
The process involved before injecting the epoxy;
1. Clean the cracks that have been contaminated from oil, grease, dirt, or fine particles. It can to increase the effectiveness of repairs and the bonding between epoxy penetration and surface will be better. It should be removed by vacuuming or flushing with water or other specially effective cleaning solutions.

13. 2. Surface cracks should be sealed to keep the epoxy from leaking out before it has gelled. A surface can be sealed by applying an epoxy, polyester, or other appropriate sealing material to the surface of the crack and allowing it to harden. If high injection pressure is not required, a strippable plastic surface sealer may be applied along the face of the crack. The surface sealer can be stripped away to expose the gloss-free surface. If extremely high injection pressures are needed, the crack can be cut out to a certain depth. Before that need to install the entry and venting ports.Three methods can be applied;

14. i. Fittings inserted into drilled holes.
-This method was the first to be used, and is often used in conjunction with V-grooving of the cracks.
-Drilling a hole into the crack, approximately 20 mm in diameter and 13 to 25 mm below the V grooved section.
ii. Bonded flush fitting.
-When the cracks are not V grooved, a method frequently used to provide an entry port is to bond a fitting flush with the concrete face over the crack.
-The flush fitting has an opening at the top for the adhesive to enter and a flange at the bottom that is bonded to the concrete.
iii. Interruption in seal.
-Provide an entry which is to omit the seal from a portion of the crack.
-Can be used when special gasket devices are available. It will cover the unsealed portion of the crack and allow injection of the adhesive directly into the crack without leaking.

15. 3. Mix the epoxy. It can be done by batch methods
3. Mix the epoxy. It can be done by batch methods. In batch mixing, the adhesive components are premixed according to the manufacturers instructions, usually with the use of a mechanical stirrer, like a paint mixing paddle. Care must be taken to mix only the amount of adhesive that can be used prior to commencement of gelling of the material.
4. 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 rate of injection. If the crack is vertical or inclined, the injection process should begin by pumping epoxy into the entry port at the lowest elevation until the epoxy level reaches the entry port above. For horizontal cracks, the injection should proceed from one end of the crack to the other in the same manner. The crack is full if the pressure can be maintained. If the pressure can not be maintained, the epoxy is still flowing into unfilled portions or leaking out of the crack.

16. Ekenel and Myers, 2006 said epoxy injection is one of the repair method of cracks in reinforced concrete (RC). It should be repaired if the crack is potential for durability related problems such as corrosion of reinforcing steel.
Filiatrault and Lebrun (1996) investigated the use of the epoxy pressure injection technique to rehabilitate reinforced concrete beam-column joints damaged by earthquakes. Two full-scale exterior beam-column joint specimens were submitted to reverse cyclic pseudo-static displacements.

17. The first specimen was typical of existing structures built in the 50’s and 60’s, in which the special seismic recommendations related to the spacing of lateral reinforcement in the beam, column and joint were ignored.
The second specimen was typical of new structures and incorporated full seismic details as prescribed in current building codes.
The specimens were then repaired with an epoxy pressure injection technique. The repaired specimens were subjected to the same displacement history as that imposed on the original specimens. The results indicate that epoxy pressure injection was effective in restoring the strength, stiffness, and energy dissipation capacity of the specimens.
For the specimen representing an older design, the strength and energy dissipation of the repaired assembly were increased as a result of the epoxy injection repair.

18. Basic equipments
Epoxy injection pump machine
Epoxy injection gun

19. A worker handling the injection device working on the infected area.
This is a common technique for crack treatment and is relatively simple in comparison to the procedures. The procedure is most applicable to approximately flat horizontal surfaces such as floors and pavements.

20. EXAMPLE OF WORKS

21. ROUTING AND SEALING
It can be used in conditions requiring remedial repair and where structural repair is not necessary.
This method involves enlarging the crack along its exposed face and filling and sealing it with a suitable joint sealant.
Proposed by Johnson,1965

22. However, routing and sealing can be accomplished on vertical surfaces (with a non-sag sealant) as well as on curved surfaces (pipes, piles and pole).

23. The procedure consists of preparing a groove at the surface ranging in depth, typically, from 6 to 25 mm. A concrete saw, hand tools or pneumatic tools may be used. The groove is then cleaned by air blasting, sandblasting, or water blasting, and dried. A sealant is placed into the dry groove and allowed 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.

24. The bond breaker may be a polyethylene strip or tape which will not bond to the sealant. Careful attention should be applied when detailing the joint so that its width to depth aspect ratio will accommodate anticipated movement.
Routing and sealing treatment reduces the ability of moisture to reach the reinforcing steel or pass through the concrete, causing surface stains or other problems.
The sealants can be any of several materials, including epoxies, urethanes, silicones, polysulfides, asphaltic materials, or polymer mortars.

25. EXAMPLE OF WORKS

26. STITCHING
The technique of repairing a crack by stitching can be performed by drilling holes on both sides of the crack and grouting a U-shaped steel stitch with epoxy (see Fig. la).
Stitching of concrete to arrest crack propagation is inexpensive and versatile (ACI, 1980). The use of stitches can be effective if guidelines for the designer have been provided (Hamoush and Ahmad, 1997).

28. Repair of crack by stitching (Johnson,1965)

29. 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 as shown in figure on page 25, with either a non shrink grout or an epoxy resin-based bonding system.

30. CONVENTIONAL REINFORCEMENT
Cracked reinforced concrete bridge girders have been successfully repaired by inserting reinforcing bars and bonding them in place with epoxy. This technique consists of sealing the crack, drilling holes that intersect the crack plane at approximately 90 deg, filling the hole and crack with injected epoxy and placing a reinforcing bar into the drilled hole.

31. The reinforcing bars can be spaced to suit the needs of the repair
The reinforcing bars can be spaced to suit the needs of the repair. They can be placed in any desired pattern, depending on the design criteria and the location of the in-place reinforcement.
Reinforcing bar orientation used to effect the repair – Stratton et.al1978

32. PRESTRESSING STEEL
It is often the desirable solution when a major portion of a member must be strengthened or when the cracks that have formed must be closed.
Examples of external prestressing

33. This technique uses pre stressing strands or bars to apply a compressive force. Adequate anchorage must be provided for the pre stressing steel and care is needed so that the problem will not merely migrate to another part of the structure.

34. DRILLING AND PLUGGING
Drilling and plugging a crack consists of drilling down the length of the crack and grouting it to form a key.

35. This technique is only applicable when cracks run in reasonable straight lines and are accessible at one end. This method is most often used to repair vertical cracks in retaining walls. A hole [typically 50 to 75 mm) in diameter should be drilled, centered on and following the crack.
The key will also reduce heavy leakage through the crack and loss of soil from behind a leaking wall.

36. GRAVITY FILLING
Low viscosity monomers and resins can be used to seal cracks with surface widths of 0.03 to 2 mm by 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 blasting and/or water blasting. Wet surfaces should be permitted to dry several days to obtain the best crack filling.

37. Water blasting followed by a drying time may be effective in cleaning and preparing these cracks. Cores taken at cracks can be used to evaluate the effectiveness of the crack filling.
The depth of penetration of the sealant can be measured. Shear (or tension) tests can be performed with the load applied in a direction parallel to the repaired cracks (as long as reinforcing steel is not present in the core in or near the failure area).

38. Camille and Pauls (2007) said the application of epoxy by gravity filling can be done in order to bond the crack and restore its structural integrity. The objective of study is to increase the compressive strength and stiffness of cracked concrete test cubes by gravity filling of cracks using a low viscosity gel-type epoxy resin system.
By penetrating and filling the cracks, the resin is able to form a polymer plug that seals the crack, keeping out water, chlorides, carbon dioxide, sulfates, and other aggressive liquids and gases.
This repair can only be applied to horizontal concrete elements such as bridge and parking decks, floor slabs, plaza decks, and similar surfaces. Gravity feed of resin is not effective for repairing moving cracks.

39. PORTLAND CEMENT GROUTING
Wide cracks, particularly in gravity dams and thick concrete walls, may be repaired by filling with Portland cement grout. This method is effective in stopping water leaks but it will not structurally bond cracked sections.
The procedure consists of cleaning the concrete along the crack, 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.

40. Grout mixtures may contain cement and water or cement plus sand and water, depending on the width of the crack.
For the small area

41. the water-cement ratio 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 should be used. After the crack is filled, the pressure should be maintained for several minutes to insure good penetration.
Can be applied to horizontal and vertical cracks.

42. DRY PACKING
The hand placement of a low water content mortar followed by tamping or ramming of the mortar into place, producing intimate contact between the mortar and the existing concrete. Because of the low water-cement ratio of the material, there is little shrinkage, and the patch remains tight and can have good quality with respect to durability, strength, and water tightness.

43. Dry pack can be used for filling narrow slots cut for the repair of dormant cracks. The use of dry pack is not advisable for filling or repairing active cracks.
Before a crack is repaired by dry packing, the portion adjacent to the surface should be widened to a slot about 25 mm wide and 25 mm deep. The slot should be undercut so that the base width is slightly greater than the surface width.

44. References
'Concrete Repair and Restoration', ACI Compilation, No. 5, American Concrete Institute, Detroit (1980) 118 (compiled from Concrete International Design and Construction 2 (9) (Sept. 1980).
Ekenel, M. and Myers, J. J., Durability performance of RC beams strengthened with epoxy injection and CFRP fabrics. Construction and Building Materials, Vol. 21, Issue 6, pp
Filiatrault, A. and Lebrun, I., Seismic rehabilitation of reinforced joints by epoxy pressure injection technique. Special Publication, Vol. 160, pp
Hamoush, S. and Ahmad, S. H., Concrete crack repair by stitches. Materials and Structures, Vol. 30, August-September 1997, pp

45. Camille A. Issa, Pauls Debs, Experimental study of epoxy repairing of cracks in concrete, Construction and Building Materials 21 (2007) 157–163

46. Extracted from http://www. askthebuilder
Extracted from on January 22, 2011 at 2130 hours.
Extracted from on January 22, 2011 at 2230 hours. [Portland Cement Association]
Extracted from on January 26, 2011 at 1400 hours.

47. thank you