The name itself provides information about the types of properties that cause cracking. These are the physical properties or behavior of the material or concrete. The physical reasons for cracks can be divided into three main categories.
- Shrinkable aggregates
- Dry shrinkage
- Fine cracks
Shrinkable aggregates – causes of cracking
The failure of structures is due to the instability of the aggregates. Aggregates subject to excessive dimensional changes as the concrete dries and ages cause such failures. For more information, see the articles on this topic.
Drying shrinkage – reasons for cracking
Dry shrinkage occurs due to capillary water loss in hardened concrete. This increases tensile stresses and causes the concrete to contract, which leads to cracks. Dry shrinkage occurs due to internal and external inhibitions. If there is no inhibition, cracking will occur. But there are often inhibitions that cannot be avoided. Therefore, necessary measures must be taken to control them. Dry shrinkage can be controlled using the following methods.
- Use a low water content. Try to reduce the volume of the cement paste; this can be achieved by increasing the aggregate volume.
- Use water-reducing additives
- Concrete hardening
- Crack control reinforcement could be provided considering, at the design stage,
Fine cracks in concrete – reasons for crack formation
Hairline cracks are the formation of a random network of fine cracks on the surface. They can occur due to changes in volume or shrinkage of the concrete close to the surface. These cracks occur on the surface and can be up to 0.3 mm deep. These cracks are sometimes called surface cracks or pattern cracks. Furthermore, these cracks do not affect structural properties and rarely affect durability or surface wear. Fine cracks can have the following causes
- Weak or insufficient healing
- Use of a very wet mix with a very high concentration of cement paste and fines on the surface
- Finish if water appears on the surface
- Sprinkle cement on the surface to dry the water from the blood on the surface.
The following measures can be taken to minimize cracking
- Start healing ASAP
- Using moderate drops in the range of 75mm to 125mm is more appropriate
- Do not use dry cement, as cement mixed with sand can cause the concrete surface to dry out.
- Do not finish the concrete surface until the bleeding stops
The following figure shows the crack pattern that can be observed during tearing.
