Nowadays most of the buildings are RCC framed structure. And concrete is the backbone of RCC framed structure buildings. But defects in concrete make a building unusable or unsafe to use.
See the image below:
That is a crack in the roof slab through which water penetrates. It made the room unusable for dwellers.
There are many defects can arise in concrete structures. Most of the defects in concrete happen due to the lack of supervision in the process of concrete construction.
In this post, I’m going to discuss some defects in concrete that you can minimize with proper inspection.
5 Defects In Concrete That Can Be Minimized With Proper Inspection
These defects happen due to faulty construction process of concrete. So, if you inspect the construction process – before concreting, during pouring concrete, and after pouring concrete – you’ll be able to build structures without any defects in concrete.
So, let’s begin the discussion without further ado…
1. Concrete Cracking
One thing is sure that whatever you do, no matter, concrete will crack.
A certain level of concrete cracks is acceptable. You can’t avoid it.
But excessive cracks is harmful to concrete members. You need to reduce cracks with proper supervision. So that it doesn’t affect the quality of the structure.
Let’s see various reasons for concrete crack and how to control it with proper inspection.
Reason For Concrete Cracks:
Reason #1: Using excess water in the mix
We use water in the concrete mix for the chemical reaction of cement. It is called hydration.
For the hydration process, we actually don’t need much water.
But we need to take care of the workability of concrete.
The workability is the thing which makes the concrete easy to work with.
The more workable the concrete, the more it is easy to pour and place concrete into the form.
And it takes less manpower to work with more workable concrete.
It is the reason concrete workers tend to mix more water to the concrete mix to make it more workable.
But mixing more water to concrete reduces the strength of it.
As the excess water evaporates, the concrete shrinks that cause cracks in concrete.
Concrete slabs can shrink as much as ½” per hundred square feet.
But more water in the concrete mix can make concrete members shrinks more which can cause for wider concrete cracks.
What To Inspect?
- Know the allowable water content for the concrete. It is normally described as the water-cement ratio in the mix design.
- Check the workability of concrete by the slump test. Take at least one slump for every twenty cubic meters of concrete.
- Don’t allow excess water in the concrete mix.
Reason #2: Rapid drying of concrete
As we know concrete requires water for the hydration process. This hydration continues to occur for days, even weeks, after pouring concrete.
If the concrete doesn’t get enough water for hydration, it tends to form cracks.
What To Inspect:
You need to inspect proper curing is being done after pouring.
Related: Method of curing concrete
Honeycombs are hollow spaces or cavities on surfaces or inside concrete members.
The honeycomb affected area of an RCC member is weak in strength.
The steel bars of the honeycomb affected member can get affected by corrosion as there is a possibility to penetrate water through the honeycombs.
Reason For Honeycombs:
Common reasons for honeycomb in concrete are –
- Improper vibration
- Penetrating cement slurry through formwork
- Using very stiff concrete
- Less concrete cover to reinforcing bar
- Using more bigger size aggregate
What To Inspect:
To reduce honeycomb in concrete carefully inspect the following things –
- Inspect the vibrating process properly. Enlist experienced workers to vibrate concrete.
- Check the concrete formwork properly before start pouring concrete. There shouldn’t be any gap in the formwork.
- Maintain the workability of concrete.
- Check the concrete clear cover for reinforcing bar.
- Make sure concrete mix design is being followed while batching.
You might have seen something on a concrete surface like the image below:
Those are crazing.
It actually a network fine random cracks.
Crazing sometimes referred to as map cracking or pattern cracking or shallow map.
The craze generally develops at an early age and are visible the day after placement or by the end of the first week.
Reasons for Concrete Crazing:
- Inadequate concrete curing
- Using a too wet concrete mix
- Concrete finishing performed while bleed water on the surface
- Sprinkling cement on the concrete surface to dry up bleed water
- Spraying water on the concrete surface during finishing work
What To Inspect To Reduce Concrete Crazing:
Taking care of the following things will reduce concrete crazing to a certain level –
- Make sure curing starts as soon as possible.
- Avoid alternate drying and wetting of concrete surface at an early stage.
- Use moderate concrete slump to prevent excessive bleeding.
- Never sprinkle dry cement to absorb bleed water.
- Don’t spray water on the surface during concrete finishing.
- Don’t perform any finishing operation while bleed-water present on the surface. Let it dry naturally first.
Curling normally happens in concrete slabs.
When a concrete slab is distorted into a curve shape by upward or downward movement of edges that is called curling.
Note that curling can be downward or upward.
When the bottom surface of the concrete slab is dried and shrunk before the top surface of the slab then downward curling takes place.
If the top surface is shrunk faster than the bottom surface then upward curling happens.
Reason For Slab Curling:
- The primary reason for slab curling is the drying shrinkage of concrete.
- The temperature difference between the top and bottom of the slab.
What To Inspect To Reduce Drying Shrinkage:
Although you can’t completely eliminate drying shrinkage (which is the main cause for curling), you can control it to prevent slab curling.
You need to inspect factors that can lead to slab curing that include –
- Using concrete with the lowest possible water content and highest possible coarse aggregate content.
Avoid using aggregates in the concrete mix that increases shrinkage.
- Prevent excessive bleeding of concrete.
- Find a way to balance the temperature between the top and bottom of the slab.
Have you ever seen the existence of powdery particle on the hardened concrete surface?
That is dusting. It’s also called chalking.
Reasons For Dusting:
- Presence of excess water content in the mix
- Spraying water during concrete finishing
- Sprinkling dry cement during finishing
- Exposure to rainfall while finishing
- Inadequate concrete curing.
What To Inspect To Prevent Dusting?
- Use low slump concrete mix
- Don’t use water and dry cement while finishing the concrete
- Don’t start concrete finishing before removing bleed water.
- Take protective action for rainfall
- Cure the concrete properly.
It is possible to keep defects in concrete to an acceptable rage with proper inspection techniques.
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