17.3
Causes of Cracks
·
Structural Crack
1) Crack
due to incorrect procedures in designing process, for instance; fault in given
design criterions and computation, or incorrect reinforcement detail.
2) Crack
due to utilizing substandard material i.e. poor quality of aggregate, impure
sand and aggregate, contaminated water or mix design is not proportionally
implemented and presence of rusted reinforcement.
3) Crack
due to substandard construction procedures i.e. mixing, transportation,
placing, precipitately removes shoring, inadequacy of curing or utilizing
deformed formwork.
·
Non Structural Crack
A. Shrinkage
of concrete
B. Settlement
of concrete
C. Heat
D. Others
These can be
simply categorized by basing on time before and after concrete is hardened as
illustrated in Figure 17.3 with examples of Structural and Non Structural Crack
as illustrated in Figure 17.4 (See in Excel file 17.4)
- Generally, feature of cracks that resulted from swelling, bending, dislocation of formwork due to self-expansion and nails or fastening equipment are not firmly secured, can not be precisely determined its characteristic.
- Generally, feature of cracks that resulted from underground settlement, particularly during the hardening phase resulting a subsequent settlement, can not be precisely determined its characteristic.
- Cracks that exist on top of steel reinforcement will result settlement of concrete, in which introduction of greater strength concrete as well as reinforcing the supporting base can be helpful to this case.
- Excessive quantity of cement added, insufficient curing or self-expansion of sand grains or poor treated cement, among of these aspects, they can result occurrences of crazing on the concrete surface.
- Cracks that appear before concrete reaches complete hardening are due to rapid loss of water from evaporation or water is drawn down to the ground beneath.
- Cracks that induced from corrosion along with expansion of concrete can be protected by providing sufficient concrete covering and placing adhesive material. This therefore will eliminate ambient humidity to penetrate through the concrete.
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