Early stage cracking
Different types of early stage cracking can affect your concrete. So it’s helpful to know what they are, how they are caused and how to prevent them. Early stage cracking can be caught and prevented before and during the concrete pour. This post aims to help you identify them.
Plastic cracks are a type of early stage cracking that occur in the first few hours of concrete setting. These types of cracks include plastic settlement and plastic shrinkage cracks.
Plastic settlement cracks
Cause: Heavier aggregates go to the bottom of the concrete mixture. This pushes lighter material such as cement paste and water to the top. Thus causing concrete bleed, where there is a thin layer of water on top of the concrete.
Common locations: Around reinforcement beams, in deep sections, at the tops of columns and in slabs.
Time after placing: These cracks can be found between 10 minutes and 3 hours.
Preventative actions: Choose a mix with a low water cement ratio. Micro-fibres and plasticizers can reduce bleeding and plastic settlement cracks. Air entrainment admixtures also help to reduce these cracks. Curing your concrete correctly is one of most important things you can do. We have another blog post dedicated to this topic alone. We can help you choose the right mix for your job if further help is needed.
Corrective actions: If plastic settlement cracks occur, re-vibrate the surface of the concrete. If the cracks still show when the concrete hardened, dry brush cement powder over the surface. Plastic settlement cracks are not structural, so they don’t affect the integrity of the concrete structure.
Plastic shrinkage cracks
Cause: Rapid early drying caused by weather conditions. Not enough water to complete the chemical reaction between cement and water.
Common locations: Roads, slabs and reinforced concrete slabs.
Time after placing: These cracks can be found within 30 minutes and 6 hours.
Preventative actions: Ensure that the mix has enough water, especially in hot or windy conditions. Wind can cause evaporation even more than heat, so using wind guards or covers can prevent this.
Corrective actions: Good curing is important, it can keep moisture within the concrete.