Concrete is the combination of three materials like cement, sand, aggregate with water. But in some cases, different types of admixture and chemicals are used to change the required amount of chemical as well as physical properties of concrete.
As the concrete is prepared, its physical, as well as chemical properties, begins to change according to age, temperature, humidity, materials used in the concrete, and load applied on it.
Generally, we design concrete to get its strength in 28 days, but the strength of concrete continues to increase up to a number of years. Here, I have described six properties of concrete according to IS CODE 456-2000.
There are different properties of concrete but here I am going to describe some important properties of concrete like thermal properties of concrete.
Some other properties of Concrete
1) Increase of strength with age
After 28 days concrete normally gains its strength. The strength of concrete depends upon the grade of cement, environmental condition, and proper curing.
2) Tensile Strength of concrete
The flexural and splitting tensile strength of concrete can be taken from IS 516 and IS 5816 respectively.
If a civil engineer requires to calculate the tensile strength of concrete from the given value of compressive strength then they can use the formula given below,
Fck is the characteristic cube compressive strength of concrete in N/mm2.
3) Elastic deformation
The elastic properties of concrete are mainly influenced by the elastic properties of aggregate used in the construction of the different structures.
However, the elastic properties of concrete also depend on curing, age of concrete, grade of concrete, and types of cement used. The modulus of concrete is normally related to the compressive strength of concrete.
The modulus elasticity of concrete can be assumed by the formula below,
Ec is the short term static modulus of elasticity in N/mm2
But, the measured value may be different by 20% above or 20% below from the value given by the formula above.
4) Shrinkage in concrete
The decrease in the volume of concrete after the setting time is known as shrinkage.
The shrinkage of concrete depends upon the size of structural members, environmental conditions, size of aggregate, and somewhat on types of cement.
The shrinkage of concrete highly depends on the water-cement ratio of concrete i.e ratio of water and cement used at the time of mixing.
The detailed information about the shrinkage of concrete you can refer to IS 1343.
But, if there is no actual data available for design and analysis, then the approximate value of total shrinkage strain can be taken as 0.0003.
5) Creep of Concrete
Creep is the deformation of concrete due to continuous and long-term load. It depends upon the grade of concrete, the amount of load applied on it and the duration of load applied on the concrete structure.
So, if possible, the stress in concrete should not be exceeded one-third of its characteristics compressive strength.
In the absence of experimental data and detailed information on the effect of the variable, the ultimate creep strain may be estimated from the following values of creep coefficient that is ultimate creep strain/elastic strain at the age of loading) for long-span structure, it is advisable to determine actual creep strain, likely to take place.
Age of loading – Creep Coefficient
7 days – 2.2
28 days – 1.6
1 year – 1.1
6) Thermal properties of concrete
The expansion or contraction of concrete members due to an increase in temperature is known as thermal expansion. It highly depends on the nature of aggregate used for the construction of different structural members and somewhat depends on the types of cement, relative humidity, etc.
The value of the coefficient of thermal expansion for concrete with different aggregates may be taken as below,
|S.N||Types of Aggregate||Coefficient of Thermal Expansion for concrete/Degree Celsius|
|1||Quartzite||1.2 to 1.3 x 10-5|
|2||Sandstone||0.9 to 1.2 x 10-5|
|3||Granite||0.7 to 0.95 x 10-5|
|4||Basalt||0.8 to 0.95 x 10-5|
|5||Limestone||0.6 to 0.9 x 10-5|
The average value of aggregate can be taken as 1 x 10-5
If the length of the member is 45 meters = 45000 mm
The difference in maximum and minimum temperature of the environment is 20 degrees Celcius.
Then thermal expansion in concrete = Coefficient of thermal expansion x Length of the members x Temperature difference
or, Then thermal expansion in concrete = 1 x 10-5 x 45000 x 20
or, Then thermal expansion in concrete = 900000 x 10-5 = 9 mm
Hence, 9 mm gap is required.
Some Question and answer regarding thermal properties of concrete
Q) What is the effect of thermal expansion in concrete?
Ans:- We know that concrete is strong in compression and weak in tension. So, whenever there is exerted compressive force then they can bear as per design but when there is exerted tension force, then concrete members begin to crack which are restrained with other concrete members.
7) Durability of Concrete
I hope this article on “Thermal properties of concrete” remains helpful for you.
Happy Learning – Civil Concept