In this blog post, we will highlight the Signs of Bad concrete pour and the methods which should be used to treat the defects of the concrete.
Concrete is one of the most widely used building materials in our construction industry. Concrete must be pulled into the mould with proper precaution and care otherwise, we will not get the desired strength of concrete.
What Is Concrete?
Concrete is a uniform mixture of cement, sand, aggregate, and water in the prescribed proportion which sets and hardens and acquired the desired strength over a certain period.
Uses of Concrete
Concrete has various uses in the construction sectors which are as follows.
- Concrete is generally used in the construction of roads and bridges.
- Concrete is used in the construction of electric poles.
- Concrete is widely used in the construction of high-rise buildings.
- It is also used in various types of flooring.
- Concrete is used in the construction of sidewalks and driveways.
- Concrete is a very important building material that is used for the construction of various residential as well as commercial projects.
Signs of Bad Concrete Pour
The signs of bad concrete pour are classified into mainly two types.
- Signs of Bad Concrete Pour during concreting
- Signs of Bad Concrete Pour after Hardening of concrete
Signs of Bad Concrete Pour During Concreting
The list of Bad concrete signs time of pour during the concrete are as follows.
- Bleeding.
- Segregation.
- Spalling of Concrete.
- Cracking of concrete.
- Scaling of Concrete.
- Honeycombing of concrete.
- Alkali Aggregate Reactions in Concrete.
- Crazing.
- Delamination of Concrete.
- Dusting.
1. Bleeding
The Bleeding of concrete is a Phenomenon in which free water in the concrete mix rises up or comes on the surface of the concrete layer of cement slurry.
Bleeding is accepted at a certain limit, but excessive bleeding in the concrete can reduce the strength of the concrete. The bleeding in the concrete occurs when the coarse aggregates present in the concrete get to settle down and the free water present in the concrete comes to the surface of the concrete.
One of the main reasons which cause bleeding in concrete is an improper water-cement ratio. The greater water-cement ratio leads to excessive bleeding in the concrete.
Due to the bleeding concrete loses its strength and homogeneity. Bleeding causes permeability in the concrete. In the process of bleeding the water gets accumulated and it develops air voids in the concrete which reduces the bond between cement and aggregate.
The bleeding will not cause major harm if the rate of evaporation of the water is equal to the rate of bleeding in the concrete. Normal bleeding is quite good property of the concrete because it will improve its workability.
Methods to Reduce Bleeding in Concrete
The following method should be used during concreting to reduce bleeding in concrete.
- Add a very less amount of water content in the mix of the concrete or use chemical admixtures to show that demand for water gets reduced and required workability is also achieved.
- Design the concrete mix properly and add more amount of cement to the concrete mix.
- Proper measures and methods of mixing should be used to reduce bleeding in the concrete.
2. Segregation
Segregation of concrete is defined as the separation of the cement paste from the aggregate during the placing and handling of the concrete on the construction site.
Segregation occurs when the concrete is over vibrated or compacted during concreting work. Segregation will affects the strength and the durability of the concrete.
The cause of the segregation of concrete is due to the use of a high water-cement ratio in the mixing of concrete. Excessive vibration during concreting can also lead to the problem of segregation.
The primary cause of segregation in concrete is due to the variation in the specific gravity of different materials used in the manufacturing of concrete.
When the concreting operation is done from a larger height in the case of underground foundations, it will need to the secretion of concrete which is a bad sign of concrete pour.
Segregation of the concrete must be prevented to achieve the desired strength and quality of the concrete in the construction of the structure. During the concreting, the depth should not be more than 1.5 m.
The segregation of the concrete can be also minimised by adding air-entraining agents and admixtures in the concrete and maintaining proper proportioning of the design mix. Signs of bad concrete poor after Hardening of the concrete.
3. Spalling of Concrete
Spalling is the phenomenon in which an area of concrete gets cracked and delaminated from the substrate. spalling of the concrete leaves the concrete surface patchy and exposed aggregate.
Spalling in the concrete when a large area of the concrete separates or removes from the concrete member. The spalling defect is very similar to the scaling of the concrete in which flakes break loose from the concrete.
The effect of Spalling on the concrete is categorized into various forms as per its intensity.
- Light: When the detected area of the concrete measures less than 150 mm in any direction or less than 25 mm in depth. This will be considered as a light spalling of concrete.
- Medium: When the defected area concrete measures between 150mm to 300mm in any direction or between 25mm and 50mm in depth. This will be considered as a medium spalling of concrete.
- Severe: When the defected area of concrete measures between 300mm to 600mm in any direction or between 50mm and 100mm in depth. It will be considered as severe spalling of concrete.
- Very severe: When the defected area of the concrete is more than 600 mm in any direction or greater than 100 mm in depth. This will be considered as the very severe spalling of concrete.
4. Cracking of Concrete
Cracking is one of the most commonly observed and major defects occurred in the concrete. A crack in concrete is a fine fracture that extends partly or completely through the member.
The Tensile stresses which are developed in the concrete members are one of the major reason which causes cracking in the concrete.
5. Scaling of Concrete
The scaling of concrete generally occurs when the loss of the surface portion of the concrete due to freezing or deterioration of concrete. The scaling of concrete is generally observed in air-entrained concrete.
The scaling of concrete mainly occurs on the poorly finished surface of the concrete. Scaling is a bad sign of concrete that affects the appearance of the surface of the concrete.
The range of scaling of the concrete categorized is as follows.
- Light: The light scaling of the concrete occurs When there is a Loss of surface mortar up to 5mm depth without any exposure of coarse aggregates.
- Medium: The medium scaling of the concrete occurs When there is a Loss of surface mortar up to 6 to 10 mm depth with exposure of some coarse aggregates.
- Severe: The severe scaling of the concrete occurs when there is a loss of surface mortar up to 11 mm to 20 mm with aggregate particles standing out from the concrete.
- Very Severe: The very severe scaling of the concrete occurs when there is a loss of mortar and aggregate particles to a depth greater than 20 mm.
6. Honeycombing of Concrete
Honeycombing of the concrete sign of bad concrete generally occurs due to the improper compaction for vibration of the concrete during placing and compacting the concrete on the construction site.
The honeycombing of the concrete develops voids in the concrete due to which the concrete loses its compressive strength.
Honeycombing of Concrete is measured in a different range which is as follows.
- Light: The honeycombing of the concrete up to a depth of less than 25mm.
- Medium: Honeycombing of the concrete ranges to a depth between 25mm and 50mm.
- Severe: Honeycombing of a concrete range to a depth between 50 mm and 100 mm.
- Very Severe: Honeycombing of the concrete to a depth greater than 100 mm.
7. Alkali Aggregate Reactions in Concrete
A chemical attack on concrete can occur if aggregates are alkaline and chemically reactive. concrete can be attacked by different chemically active matters like acids, some alkalis, various salt solutions, and organics such as sugars, and animal oils, especially if they contain free acids.
Aggregates present in the concrete are alkaline and chemically reactive, it will cause an alkali-aggregate reaction in concrete. The alkali-aggregate reaction will affect the durability and appearance of the concrete
To prevent the alkali-aggregate reaction use low alkali cement in the concrete and also reduce the moisture and maintained the concrete in a dry state.
8. Crazing
Crazing is a defect that occurs on the surface of the concrete and forms a map pattern of fine cracks. The cracks extend only through the surface layer. This is due to minor surface shrinkage as a result of dry conditions.
The problem of creating can be prevented by proper finishing and curing of the concrete as soon as possible. These types of cracks do not harm the concrete structure. It will affect the appearance of the structure.
9. Delamination of Concrete
The delamination of the concrete is the separation of the concrete surface into a layer that is substantially separated but not completely detached from the concrete element.
Delamination of the concrete will affect the durability of the structure. The performance of the concrete gets reduced gradually due to the delamination of the concrete.
The delamination of the concrete can be prevented by finishing the surface of the slab after the process of bleeding starts.
10. Dusting
Dusting is the surface defect that appears as a fine powder on the surface of the concrete. The fine powder will come off when the brushed surface of the concrete. The dusting is due to the finishing of the concrete before bleed water has dried out.
Dusting can also cause due to inadequate curing of the concrete. It can be repaired by applying a chemical floor hardener or a bonded topping.
Conclusion of Signs of Bad Concrete
The spalling of concrete, Honeycombing, cracking of the concrete surface, bleeding, crazing, dusting, scaling of the concrete and delamination of concrete are the signs of bad concrete pour.
All the defects must be treated properly otherwise they will cause major harm to the structures and affects the durability of the concrete.
Source: civiljungle
