What happens when there is a large air void in concrete?
Air void :- “The ratio of the volume of air space to the total volume of voids in a Soil mass”.
In HCC , a void is an empty space, other than a crack, in the cement paste that contains nothing but air. The type, size, shape, arrangement and abundance of the goods are factors controlling many important properties such as comprehensive strength, resistance to destruction by freezing and thawing and resistance to chemical attack on the reinforcement steel and the cement paste.
(The percentage of air voids volume is generally specified by the design of mixture.)
- A large number of very small air voids are desired so that an appropriate amount of air cn be distributed throughout the HCC in such a way that the distance between voids is very short and the paste is protected bfrom freezing and thawing.
- A ratio of air void voulme to paste volume that exceeds the specified range weakens the HCC and many create channelways for the permeation and circulation of deleterious substance.
- In Concrete design and quality control, strength is the property generally specified.
- This is beacuse , compare to most other properties, testing strength is relatively easy. Also the High Strength Concrete (HSC) is a part of concrete series.
- Designed to provide several benefits in the construction of concrete structures that can not always be better achieved routinely using conventional ingredients, normal mixing and curing practices furthermore, other properties of concrete, such as elastic modulus, water tightness or impermeability.
- Freeze thaw cycle and resistance to weather agents including aggressive waters, are directly related to strength and can therefore be deduced from the strength data.
“The presence of capillary pores and air voids influences concrete permeability to a large extent”.
- Concrete desnity is inversely proportional to its porosity. The ingress of aggressive agents into the pore structure is responsible to a large extent for various durability problems in concrete structures. Therefore, a durable concrete should have low permeability.
Permeability of concrete increases with the increase in porosity in concrete structures. Therefore, a durable concrete should have a low permeability.
- Permet of concrete increases with the increase in porosity of concrete and in same time toward the damages and degraded the concrete structures.
Generally four types of air voids are to be found :-
Capillary air voids
Entrained air voids
Entrapped air voids
I am attaching some pics below related the air voids in concrete.You can see them and observe for study.
Image 1. Air voids in Concrete Surface
In the above pic i tried to show you that when the air voids exists or created in the concrete than the amount of water pass through like that.
Image 2. Air voids ( small /Big) at the surface of concrete.