What is Plastic Shrinkage Cracking?

Plastic shrinkage cracking refers to the cracks formed when concrete has not yet set. It occurs when the concrete is in the form of plastic only. The main cause behind crack formation is the rapid drying process. Cracks can be seen the next day after the finishing operations. Plastic shrinkage cracks can form randomly or can be roughly parallel to each other. Concrete Brisbane gets weak due to these cracks and therefore expand.

What Causes Plastic Shrinkage Cracks?

The basic reason behind the occurrence of cracks is the higher rate of evaporation of moisture from the surface. When the evaporation rate exceeds the moisture supplied to the concrete, cracks are formed. The concrete surface dries out because of the lack of moisture on the surface and hence it cracks.

Water is lost in the following two ways:

  1. Drying from the top: During the placement process, moisture seems to evaporate from the top surface of the concrete, which is also known as bleeding.
  2. Drying from the base: Water can get absorbed in the ground below the concrete slab. This increases the risk of cracking and also the settlement of concrete and mesh reinforcement Brisbane.

There are various environmental factors that affect the rate of evaporation from the surface of concrete, such as wind speed, temperature, and humidity. A combination of all these factors leads to cracking even in cold weather conditions. Also, the concrete mixtures which have a reduced rate of bleeding are prone to plastic shrinkage cracking. Any factor that contributes to a delay in the setting process, leads to cracking.

How to Control Plastic Shrinkage Cracking?

Mentioned below are the tips that will help you in minimising plastic shrinkage cracking in your concrete:

  • Dampen the surface of concrete frequently.
  • During hot weather, mix water with crushed ice or use chilled water.
  • Use windbreaks to reduce the velocity of wind that is coming on the surface of the concrete.
  • Use product substitutes that reduce the rate of evaporation from the surface.
  • Start the curing regime immediately after finishing.
  • Use synthetic or steel fibers to prevent cracking.
  • Accelerate the setting time of concrete.
  • Use fog sprays in dry periods to discharge a fine mist into the air. Fog sprays reduce the rate of evaporation from the surface of mini concrete Brisbane and should be used until curing is applied to the concrete.
  • Cover the concrete with moisture-retaining coverings like polyethylene or building paper sheets.

Reocrete is the leading supplier of concrete and steel reinforcing mesh in Brisbane. We deliver the right grade and consistency of concrete to your worksite at the exact time and day you need. We understand how much of a difference just a 30-minute delay in the compaction of concrete can cause. So, we practice what we preach and deliver exactly what you need!

6 Different Types of Cracks in Concrete

Concrete is easily one of the strongest and most reliable construction materials. From temperature changes and structural errors to tree roots and reinforcing mesh Brisbane, many things lead to cracks in concrete. Unlike the common perception, not all concrete cracks are the same. In fact, identifying the correct type can actually help you in properly correcting the cracks.

Let’s take a look at the six most common types of concrete cracks you might encounter:

1. Plastic Shrinkage Crack

Before the concrete hardens, it is considered plastic and contains a significant amount of water. Sometimes puddles of water, upon drying, leave behind voids within the slab. Such voids make the structure of the slab prone to cracks when subject to pressure. Unless prominently visible, plastic shrinkage cracks pose no threat to the structure of the slabs.

2. Expansion Crack

When subject to heat, concrete slabs tend to expand outwards. Lack of space to expand causes slabs to develop cracks. However, expansion cracks are mostly dealt with during the planning and concrete delivery Brisbane stage of the structure. Expansion joints are inserted between slabs that can absorb pressure from expansion and thus pre-empt and avoid cracks.

3. Heaving Crack

Another crack that occurs due to temperature are heaving cracks. Heaving cracks develop due to being exposed to extreme cold weather, which causes the slab to condense. When the temperature returns to normal, the slab also expands back to its normal shape. However, this change in shape often leads to the development of heaving cracks.

4. Settling Cracks

The structural weakness of the underlying ground can lead to settling cracks. For instance, when a large tree is removed, its roots decay and leave large voids behind which soften the ground. A weak ground gives poor support to the concrete slab above and the steel bar Brisbane surrounding it, causing settling cracks.

5. Cracks due to overloading

Premix concrete Brisbane comes with their own strength (measured in PSI or pounds per square inch), which indicates the maximum pressure they can take before being crushed. However, overloading of slabs occurs quite often in residential areas – this is not what actually causes the cracks. In cases where the underlying ground has become soft (like after heavy rain), it might enable a section of the slab to be pushed downwards. Heavy vehicle parking spots are most likely to see such cracks.

6. Premature Drying

When a concrete slab (or its top layer, to be specific) loses moisture quickly, it can lead to cracks. Crazing cracks appear when the top layer of the slab quickly loses moisture naturally, resembling a spider-web. Crusting cracks appear during the stamping process when the top layer is dried for embedding patterns. Both these types might look unappealing, but they are largely harmless for the structural strength of the slab.

As you saw, different causes lead to different types of concrete cracks. Understanding the specific types allows us to identify the root cause behind these cracks and take appropriate steps.