Cracks in concrete can be structural and reduce safety, or non-structural and caused by factors like moisture or temperature changes. Cracks are categorized by their width and can be caused by things like shrinkage, foundation issues, or earthquakes. The document discusses various methods for repairing cracks in concrete, such as epoxy injection, routing and sealing, stitching, drilling and plugging, or gravity filling cracks with low viscosity resins.

1. k.pratyusha
assst.prof,NEC

2. • A crack is a complete or incomplete separation of concrete into two or more
parts produced by breaking or fracturing
• Cracks are one kind of universal problems of concrete construction as it
affects the building artistic and it also destroys the wall’s integrity, affects
the structure safety and even reduce the durability of structure
Dangers & affects of cracks:
• Carbon dioxide penetrates into the concrete through the cracks and speed up
carbonation around the cracks, thus shortening the structure usage.
• The cracks in the concrete wall would cause the leakage of the building; it
reduces the stiffness, durability and seismic performance of buildings.
• Cracks on the wall surface damage to the later rendering, will affect to the
appearance.

3. I. Structural Cracks: These cracks occur due to incorrect design, faulty
construction or overloading and these may endanger the safety of a
building.
II. Non-Structural Cracks: They are due to internal forces developed in
materials due to moisture variations, temperature variation, crazing,
effects of gases, liquids etc.
III. Based On Width:
a) Thin - less than 1mm in width
b) Medium - 1 to 2mm in width
c) Wide - more than 2mm in width

4. Causes & Preventive measures:
A. Elastic Deformation
B. Thermal Movement
C. Chemical Reaction
D. Shrinkage
E. Foundation Movement and Settlement of Soil
F. Earthquake
G. Vegetation
H. Poor Construction practices

5. i. Epoxy injection:
• Cracks as narrow as 0.002 in. (0.05 mm) can be bonded by the
injection of epoxy.
• The technique generally consists of establishing entry and venting
ports at close intervals along the cracks, sealing the crack on exposed
surfaces and injecting the epoxy under pressure.
• However, unless the cause of the cracking has been corrected, it will
probably recur near the original crack.

6. ii. Routing and sealing:
• This method involves enlarging the crack along its exposed face and
filling and sealing it with a suitable joint sealant. The procedure is
most applicable to approximately flat horizontal surfaces such as
floors and pavements.
• However, routing and sealing can be accomplished on curved
surfaces (pipes, piles and pole).

7. iii. Stitching:
• 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 non shrink grout or an epoxy resin-based bonding
system.
• Stitching may be used when tensile strength must be re-established
across major cracks.

8. iv. Drilling and plugging :
• Drilling and plugging a crack consists of drilling down the length of
the crack and grouting it to form a key.
• 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.

9. v. Gravity Filling:
• Low viscosity monomers and resins can be used to seal cracks with
surface widths of 0.001 to 0.08 in. (0.03 to 2 mm) by gravity filling.
• High-molecular- weight methacrylate, urethanes, and some low
viscosity epoxies have been used successfully.
• The lower the viscosity, the finer the cracks that can be filled.
• Wet surfaces should be permitted to dry several days to obtain the
best crack filling.