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The possibility of crack development in different structural concrete elements can be reduced by adopting various design and construction measures. These methods can help reduce or eliminate the causes responsible for the formation of cracks.
Common types of cracks in concrete are plastic settlement cracks, plastic shrinkage cracks, thermal contraction cracks, long-term drying shrinkage cracks, cracks due to reinforcement corrosion and alkali-aggregate reactions, and crazing.
One can prevent shrinkage and settlement cracks in plastic concrete through the use of shrinkage-compensating admixture, sufficient concrete cover, controlled rate of evaporation, etc. Moreover, cracks due to thermal contractions and long-term drying shrinkage can be controlled by the proper distribution of steel bars, provision of expansion joints, etc.
The quality of concrete constituent materials, concrete placement, compaction, and curing play a crucial role in reducing the occurrence of crack developments.
Table-1: Types of Cracks in Concrete and their Preventive Measures
|Plastic settlement cracks
|• Use a high-quality concrete mix containing shrinkage compensating admixture.
• Compact poured concrete adequately.
• Use sufficient concrete cover thickness to avoid the development of surface cracks.
• Use adequately rigid forms for slabs.
• Start concrete placement from deep sections to decrease surface crack development.
• Wet soil before concreting of footings to prevent water loss from the base of concrete.
|Plastic shrinkage cracks
|• Wet substrate and formwork and remove excess water before pouring concrete.
• Use synthetic steel fibers in concrete to offset the influence of plastic shrinkage.
• Employ chilled water or ice to lower fresh concrete temperature in hot weather conditions.
• Provide wind barriers.
• Apply aliphatic alcohol over concrete surface after screening to control the evaporation of bleed water.
|Early thermal contraction cracks
|• Reduce heat of hydration by cooling concrete before placement.
• Provide expansion joints early on, if applicable, to allow concrete expansion.
• Insulate concrete to decrease thermal gradients.
Place reinforcements at suitable spacing to control crack width.
|Long term drying shrinkage cracks
|• Provide suitable spacing between steel bars to control crack width.
• Decrease water content to enhance concrete curing.
• Consider low workability for concrete.
• Use water-reducing admixtures.
• Prevent the use of admixture containing calcium chloride because it increases drying shrinkage.
• Utilize shrinkage compensating admixtures to decline the rate of drying shrinkage cracks.
• Use rigid aggregate in concrete to lower cement content to reduce shrinkage because hard aggregates create restraints.
• Provide expansion joints to eliminate external restraints.
|• Begin concrete curing as soon as possible as it prevents the appearance of craze cracks later on.
• Keep concrete surface wet for at least three days.
• Excessive segregation and bleeding create a low-strength concrete surface layer, which encourages crazing. So, consider low slump concrete or entrained concrete to prevent excessive segregation and bleeding.
• Prevent large moisture differences between the concrete surface and its interiors.
• Avoid any finishing work while bleed water is on the concrete surface.
|Cracks due reinforcement corrosion
|• Adequately compact concrete around steel bars.
• Make sure bar spacings are according to applicable codes such as ACI 318-19 to permit both, easy flow of fresh concrete and adequate compaction.
• Use clean steel bars to create a good bond at the concrete-steel interface.
• A good bond ensures the transfer of tensile stresses to steel bars and hence reduces crack width. Reduce concrete permeability to make it withstand the penetration of harmful agents.
• A low w/c ratio, adequate compaction, and curing would yield low permeable concrete.
• Apply a protective coating system to the concrete surface to improve the resistance of concrete against the ingression of harmful substances.
|Cracks due to alkali-aggregate reaction
|• Use low-alkali Portland cement to produce concrete.
• Prevent the use of aggregate that is susceptible to alkali-carbonate reaction.
• Consider pozzolans as cement replacement material because they decrease the alkalinity in concrete.
• Utilize protective coating and joint sealing to protect concrete structures.
Common types of cracks in concrete are plastic settlement cracks, plastic shrinkage cracks, thermal contraction cracks, long term drying shrinkage cracks, cracks due to reinforcement corrosion, alkali-aggregate reactions, and crazing. Read more about it here.
1. Permeability of concrete
2. Thermal movement
3. Creep movement
4. Corrosion of reinforcement
5. Moisture movement
6. Poor construction practices
7. Improper structural design and specifications
8. Poor maintenance
9. Movement due to chemical reactions
Read more about it here.
There are several methods of concrete crack repair such as epoxy injection, routing and sealing, grouting, stitching, drilling and plugging, gravity filling of cracks in concrete. Read more about it here.
Use a high-quality concrete, compact adequately, provide sufficient concrete cover, use rigid forms, start concreting from deep sections of the concrete element, and wet soil before pouring concrete for the footing.