What are Early age cracks?
Early-age concrete, within the first hours to months of casting, is susceptible to cracking due to temperature differences and stress development during hardening which can significantly impact its performance and durability.
These include:
Plastic Settlement Cracks:
Emerging within 30 minutes to 6 hours post-casting, these surface cracks, are formed due to the differential settlement of the freshly poured concrete around reinforcements or abrupt changes in the formwork's depth.
Typically, 1 mm wide, these often appear in deeper sections like walls and beams due to conditions and mix characteristics.
Plastic Shrinkage Cracks:
These cracks form while the concrete is fresh, during the first few hours after mixing, when excessive moisture loss causes the concrete to contract to a reduced volume and crack to relieve pressure where this movement is restrained. Often going unnoticed for days, these cracks can stretch up to 3 mm wide and 3 m long, running parallel at 45º angles to the casting direction.
Drying Shrinkage Cracks:
Drying shrinkage cracks are caused by the preferential loss of bound water from the surface of hardened concrete during the first few weeks of curing, creating of tensile stress between the concrete at the surface and the interior.
These cracks result from environmental factors like low humidity, high temperatures, and wind, alongside inadequate curing practices.
Depending on environmental curing conditions, these cracks may emerge months or years post-casting without a typical pattern but usually perpendicular to shrinkage restraints.
Thermal Cracks:
Thermal cracking is created due to large temperature gradients between the concrete surface and its interior, along a single cast element or when concrete is restrained when it tries to contract under rapid cooling.
When concrete hydration temperatures are high and ambient temperatures are low, the surface is being forced to contract and while interior is being forced to expand with cracks occurring to when this pressure become too great.
Each type of cracking has distinct characteristics influenced by the concrete mix, environmental conditions, and construction practices, highlighting the importance of understanding and mitigating these issues for long-term concrete durability.
How do Early age cracks damage concrete structures?
Early age cracks in concrete structures can undermine their long-term performance and appearance. These cracks facilitate the ingress of water and chemicals, accelerating reinforcement corrosion and material degradation, thus diminishing durability.
Although non-structural, such cracks can evolve under stress, potentially affecting the structure's load-bearing capabilities.
Aesthetically, cracks detract from the visual appeal of architectural surfaces, necessitating cosmetic repairs.
In water-retentive structures like pools or basements, they compromise water tightness, leading to leakage.
Mitigating these impacts requires addressing the root causes through careful design, mixing, and curing practices to enhance concrete's resilience against early age cracking.
What causes Early age cracks?
High heat of hydration.
Large thermal gradients between the core of the concrete and its surface.
Rapid moisture evaporation from the concrete surface that cannot be replaced by bleed water.
Rapid cooling of concrete elements.
How can I identify Early age cracks in concrete structures?
Visual survey | Non-destructive testing | Destructive testing |
How can I repair Early age cracks in concrete structures?