Hairline crack in concrete




Hairline cracks are observed in freshly placed concrete and that creates plastic shrinkage.
The causes for these cracks to show up can be due to the variations in air temperature, concrete temperature, relative humidity and wind velocity at the surface of the concrete. These factors can cause high rates of evaporation in either hot or cold weather.

Other factors for hairline cracks are water loss due to absorption by subgrade, formwork or aggregate, bleeding and sedimentation, poor workmanship and negligence, alkali-aggregate reactions, type and content of Portland cement and supplementary cementitious materials (fly ash, silica fume,etc.), type and dosage rate of chemical admixtures, construction operations like screeding and finishing operations.

There are ways to prevent hairline cracks such as use of fog nozzles to saturate the air above the surface, use the plastic to cover the surface between final finishing operations, use of wind breakers to reduce the windvelocity, sunshades to reduce the surface temperature are also helpful, use of microfibers in the concrete mixture toincrease the tensile capacity of the plastic concrete.
In repair procedure, Inspection of the crack is done and if any oil or stains have penetrated the crack and have discoloured the concrete, the stains will have to be addressed before repairing the crack.The sealant is a filler material that is penetrated into the crack. The ideal sealant must have low surface tension and low viscosity. Crack repair materials for concrete are often polymer-modified cement grouts, silicone or latex caulking, or epoxies. 

The selected sealer is applied on the substrate by using a squeegee and/or in combination with a roller. Proper curing must be ensured to complete hardening of sealant. The warmer the temperature, faster the curing, lower the temperature, the longer it will take.

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Blog written by

Shruti Doshi
Technical Officer – Sanghi Cement & Blogger
shruti.doshi@sanghicement.com
shrutidoshi.1492@gmail.com

Blog Managed by

Nirav Pandya
Digital Marketing Officer – Sanghi Cement
nirav.pandya@sanghicement.com




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