LITERATURE STUDY ON

CRACKS by V.Chiranjeevi 13061AA011 v sem,s.a.r.c.a

INTRODUCTION. Majority of cracks occur when the building

or its components or the material of which the building is made up of its subjected to forces which are greaterthan those which it can withstand.

Cracks may also occur if the material used in the building is of poor quality and the construction is not carried out in accordance with relevant drawings , prescribed job specifications and In a work –man-like manner.

Cracks can be divided into two

categories STRUCTURAL CRACKS NON STRUCTURAL CRACKS

STRUCTURAL CRACKS. These cracks may arise due to various

reasons such as incorrect design, overloading of the structural components, overloading of soil on which the following building is constructed or other similar factors.

Structural cracks endanger the stability of the building and maybe difficult to be rectified.

Ectensive cracking of foundation walls, beams, columns or slab etc., are examples of structural cracks.

NON-STRUCTURAL CRACKS. These cracks are generally due to internal

forces developed in the building on account of changes in the size of building components due to moisture variation, temperature variation, the effect of gases, liquids and solids on the building components.

The non-structural cracks can be repaired provided the reasons for cracks are identified and suitable remedial measures are taken to prevent the re –occurrance.

CAUSES OF OCCURANCE OF CRACKS.

CRACKS DUE TO MOISTURE CHANGES. CRACKS DUE TO TEMPERATURE. CRACKS DUE TO VEGETATION. CRACKS DUE TO MOVEMENTS OF

GROUND. CRACKS DUE TO EFFECT OF CHEMICAL

REACTION. CRACKS DUE TO ELASTIC

DEFORMATION AND CREEP.

TYPES OF CRACKS.HORIZONTAL CRACK.VERTICAL CRACK.DIAGONAL CRACK.TOOTHED CRACK.IRREGULAR OR RANDOM

CRACKS.

EPOXY INJECTION Cracks are generally about 0.05mm width These can be generally over come by epoxy

injection process In this process is established by entry and

venting ports at close intervals along the cracks,sealing the crack on exposed surfaces,and injecting the epoxy under pressure

Epoxy injection has been successfully used in repair of cracks in buildings,dams,all other types of structures

If the cause of the crack cannot be removed

then 2 options are available One is to route and seal the crack ,thus

treating it as a joint And the other is to establish a joint that will

accommodate the movement and then inject the crack with epoxy or other suitable materials

o epoxy injection requires a high degree of skill for satisfactory excruciation of technique

CLEAN THE CRACKS This is to clean the cracks that have

been contaminated In the contaminants such as oil,

grease ,dirt, fine particles of concrete will prevent epoxy penetration and bonding and reduce the effectiveness of the repairs

These can be removed by vacuuming are flushing with water or other special effective cleaning solutions

sealing of surfaces A surface can be sealed applying an

epoxy ,polyester, or other appropriate sealing materials to the surface of the crack and allowing it to harden.

A strippable plastic surface sealer can be stripped away to expose the gloss-free surface.

For an extremely high injection pressure are needed , the crack can be cut out to a depth of ½ inch to 13mm and width of about ¾ inch or 20mm in a V shape , filled with a epoxy , and struck of flush with surface

GENERAL METHODS IN INSTALLING ENTRY AND VENTING PORTS 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. The method entails drilling a hole into the crack, approximately 3/4 in. (20 mm) in diameter and 1/2 to 1 in. (13 to 25 mm) below the apex of the V grooved section.

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.

Interruption in seal: Another

system of providing entry is to omit the seal from a portion of the crack. This method can be used when special gasket devices are available that cover the unsealed portion of the crack and allow injection of the adhesive directly into the crack without leaking.

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

 If the pressure can not be maintained, the epoxy is still flowing into unfilled portions or leaking out of the crack

Alternative procedure: For massive

structures, an alternate procedure consists of drilling a series of holes [usually 7/8 to 4-in. (20 to 100-mm) diameter] that intercepts the crack at a number of locations. Typically, holes are spaced at 5-ft (1.5-m) intervals. 

ROUTING AND SEALING The procedure consists of preparing a groove

at the surface ranging in depth, typically, from 1/4 to 1 in. (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

How to refill crack

CRACK IN BEAMS

Pre-stressing 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 be closed . 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 . shown in the above figure

Slab failre due to improper treatment and rain water de[position

CRACKS IN SLABS CAUSES DUE TO THE IMPROPER

MAINTANENCE OF CURING DUE TO SALTS THAT CORRODE THE

STEEL IN SLAB PREVENTION

Adding joints maybe necessary to reduce further slab cracking if the joints are omited in the original construction.

CRACKS IN COLUMNS

REASONS MANY OF THE TIMES IT BECOMES

NECESSARY TO INTRODUCE RCC COLUMNS IN A LOAD BEARING WALLS FOR SUPPORTING HEAVIER LOADS WITH PASSAGE OF TIME.

RCC COLUMS UNDERGO SOME SHORTENING DUE TO ELASTIC DEFORMATION AND CREEP RESULTING IN VERTICAL CRACKS.

THESE CAN BE APPEARED AT THE JUNCTION OF COLUMN WITH MASONRY

PREVENTION These types of cracks can be

prevented by ensuring adequate curing of R.C.C columns and by providing air gap between the masonry and column.

Besides this a groove in the plaster at the joints between the column and the masonry also helps in restricting crack within the groove.

Brick wall cracks. These are the some of the reasons

for the brick wall cracks.Cold weather.

Bad foundation.Too much weight.

Structural problem.Too much moisture.

Preventative stepsRemove protrusions or loose

debris.Tape holes and cracks.Fill voids and cover tape.Smooth the area.Finish the area.

Cracks in walls.

CRACKS ABOVE WINDOWS AND DOOR OPENINGS

These are common structural defects that show signs of movement which will need to be rectified

Diagonal stepped cracking often indicates that the lintel and supports the masonry above the openings has failed

Lintel failure often occurs upon the removal of hard wood windows that are originally designed to bear a substantial load with out distorting and are replaced with standard u-pvc windows which are non load bearing allowing the lintel to drop

Prevention Lintels can now be repaired using the twist fix

helical system by using their bed joint reinforcement which is effectively creates a new lintel within the existing masonry by removing the mortar within two bed joints above the lintel and inserting helical rods composed in grout to create a load bearing lintel which spreads the structural loads across the length of bars preventing further sagging of a lintel with the patented twist fix 9mm CD helical tie we are able to install 450mm long vertical ties through masonry in the lintel

Cracks above arches

Window seal level crack