Abstract:
Modern structures are comparatively tall and slender, have thin
walls are designed for higher stresses and are built at a fast pace. These
structures are therefore, more prone to cracks as compared with old structures,
which used to be low, had thick walls, were lightly stressed and were built at
a slow pace. Moreover moisture can easily reach the inside of the modern
buildings due to the usage of thin walls. Thus measures for control of cracks
in buildings assume much greater importance than ever before.
Cracks result in applied forces greater than those which the
building or its part can withstand. These forces may have emerged externally to
the building or internally within the building or have been developed in the
materials of the building as a result of Chemical changes. There may be a
single force or a combination of forces having a single cause or several
causes.
Most cracks occur due to drying of construction water.
These are generally superficial Do not affect the serviceability of the
building
Can be easily repaired If cracks are more significant, repair work
may be repeated periodically.
Structural significance of the cracks tends to be exaggerated by a
natural reaction of the owner.
Many cracks do not have any effect on the stability of structure,
because of “high factor of safety”.
Cracking has adverse effects on appearance. Sometimes several
cracks go unnoticed for years which affect the performance of the structure.
Cracks must be repaired immediately when observed otherwise the
life of structure will reduce causing structural failure. They not only weaken
the building but spoil the beauty of walls also. This write up tells you about
repair of cracks in plaster, RCC member, Brick walls, Floor and Fine
Cracks.
The cracks can be prevented at the time of construction
PREVENTIONS OF CRACKS IN BUILDING
CHANGE IN MOISTURE
Excessive Water
Use minimum quantity of water required for mixing cement concrete
or cements mortar according to water cement ratio. Never allow cement concrete
work without mechanical mix and vibrator.
Quantity of Cement
Do not use excessive cement in the mortar mix.
Un-graded Aggregate
Use largest possible aggregate and ensure good grading of
materials. The use of water according to required workability has less
shrinkage because of reduction in the porosity of hardened concrete.
Curing
Proper curing should be started as soon as initial setting has
taken place and be continued for at least seven to ten days. When
hardening of concrete takes place under moist environment, the shrinkage due to
drying is comparatively less.
Excessive Fine materials
Do not use fine materials containing silt, clay and dust. Use
coarse sand/fine aggregate in cement concrete and cement mortar mix which has
silt and clay less than 4%. Use coarse aggregate and fine aggregate after
washing to reduce silt contents.
Thermal Movement
All materials expand on heat and contract on cool. Thermal
movement in components of structure creates cracks due to tensile of shear
stresses. It is one of the most potent causes of cracking in buildings and
needs attention.
Elastic Deformation
When the walls are unevenly loaded, due to variation in stresses
in different parts of wall the cracks are formed in walls. When two materials
having wide different elastic properties are built together under the effect of
load, different shear stresses in these materials create cracks at the
junction. Dead and live loads cause elastic deformation in structural
components of a building.
Chemical Reaction
Chemical reactions in building materials increase their volume and
internal stress causes cracks. The components of structure also weaken due to
chemical reactions. Some common instances of chemical reactions are
following.
Sulphate attack on cement products
Carbonation in cement based materials
Corrosion of reinforcement in concrete
Alkali aggregate reaction
Certain chemical reaction in building materials result is
appreciable change in volume of resulting products and internal stresses are
set up which may result in outward thrust and formation of cracks.
Download :
Download :