Having special properties of hardened concrete is the key reason to use the concrete as a construction material in the majority of structures.
Hardened concrete shows special features that can be gained other using any other materials.
Concrete is a very special invention by mankind that enabled the construction industry to move to the next level.
Let’s discuss them in detail.
Properties of Hardened Concrete
Out of many properties, we are discussing the special properties of the concrete. All the structural engineers and construction engineers shall be aware of these.
It will engage the quality control and quality assurance process easier.
Mechanical Strength
There is two component of the mechanical strength of the concrete and having these properties is the key reason to use the concrete as a construction material widely.
Concrete is very strong in compression and weak in tension. In general, the tensile strength of the concrete is about 10th of its compressive strength.
The type of strengths is as follows.
- Compressive Strength
The most important and widely used concrete is because it is having higher compressive strength. The strength of the concrete is represented by the concrete grade. Starting from C15, C20, C25, C30… there are many other concrete grades.
The concrete grade is defined by the design and it is called the characteristic strength of concrete.
Different compressive strength of the concrete is achieved by the concrete mix design. Change in the mix proportions is the key to having different characteristic strengths.
The followings are some of the key reasons that create concretes having different strengths.
-
- Water Cement Ratio – here the increase in the cement content directly affect the strength of the concrete.
- Fine aggregate content
- Fine aggregate gradation
- Course aggregate content
- Course aggregate gradation
- Tensile Strength of Concrete
The tensile strength of concrete is not generally considered in the structural design, especially in the normal reinforced concrete structures.
However, when designing prestress and post tension structures, we considered the tensile strength of the concrete for the design. Since the grade of the concrete of the prestress/post tension constructions is higher, we can have a reasonable tensile strength though it is one-10th of its compressive strength. Therefore, the tensile strength of concrete can be considered one of the good properties of hardened concrete.
Some more factors affect the strength of concrete.
- Curing of concrete
- Compaction of the concrete
- Testing method- errors and omissions
- Use of admixtures – there could be an indirect effect.
Durability of Concrete
The durability of concrete is a kind of property of hardened concrete.
There are many facts related to the durability of concrete. If the durability of concrete is the key to holding the structure for its design life.
Some of the properties of concrete connected with durability are as follows.
- Ultraviolet resistance
- Chemical Resistance
- Seawater exposure
- Chloride resistance and steel corrosion
- Sulfate resistance
- Resistance to Alkali-silica reaction (ASR)
- Abrasion Resistance
- Resistance to freezing and Thawing
Porosity and Density of Concrete
Porosity and the density of the concrete are interconnected. Higher the porosity of the concrete lesser the density of the concrete.
Depending on the grade of the concrete, there is a range of densities. It shall be made sure to have the required density. In addition, conditions or the density of the aggregate used for the concrete also affect the density of the concrete.
On the other hand, higher the porosity of the concrete could lead to the durability issues such as higher absorption of water, an increase in the concrete dampness, etc.
There is concrete made with voids or air which is called air-entrained concrete. They are made for a purpose. However, if the porosity of the concrete increases without a reason, it will create issues.
Fire Resistance of Concrete
The fire rating of the concrete is taken into account at the initial stage of the structural design. Whether the structure stands for one hour or two hours or any other will be considered when selecting the grade of the concrete and the cover to the reinforcement, etc.
Concrete has higher fire resistance compared to other structural materials such as structural steel. Structural steel is weak on fire. Its temperature increases rapidly.
Thermal Properties of Concrete
The thermal response of the concrete is very good when compared to the other material. However, when the concrete gets heated, it takes time to cool down.
Concrete can acts as an insulator. Further, in roof slabs, we place insulations that have higher heat resistance to control the heat.
Concrete thermal properties are connected with the durability of the structure. If it can not bear the seasonal temperature variations, it could deteriorate faster.
Other Properties of Hardened Concrete
The following properties of hardened concrete can also be considered as important as above mentioned properties.
- Impact resistance
- Abrasion resistance
- Creep of Concrete
- Shrinkage properties of hardened concrete
- Modulus of Elasticity
- Permeability
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