Know the importance of materials in Concrete mixes

Material science has a simple law, know the importance of each material and add it into the recipe in specific amount. It applies everywhere either you are cooking food or pouring concrete.  For cooking the delicious food item you have to add the right portion of required ingredients in recipe. Same as food item, quality concrete mixes should be prepared knowing the importance of all constituents in the concrete.

There are 4 main ingredients required to produce the concrete;

•           Binding material i.e. Cement
•          Course Aggregates or jelly
•           Fine Aggregates
•           Water

(Image courtesy of cbenjasuwan /FreeDigitalPhotos.net)

Cement – Binders 

As we all know, cement is a binder material made of 4 base elements lime, silica, alumina and iron oxide, then form clinker to fine powder. It is mainly used as binding material in construction.

In contact with water reacts chemically to form cement paste, this reaction is called hydration. Hydration process is slow and takes longer period even after hardening of concrete.

Sand – Fine aggregates

In Construction work sand is used as an inert material in the mortar and concrete. It is naturally obtained from the river and water stream beds. Also, sand can be obtained artificially by crushing stone.

Sand serves the following purpose in concrete mixes

• Sand divides the paste of binding material into the thin film which allow binder to spread and stick to it
• It helps to reduce the cost of binder material like cement and increase the volume of binding material.
• It helps to fill up the gap between two jelly blocks and spread the binder.
• Sand is more important material which helps in preventing shrinkage of binder material i.e. cement.

Gravel/Stone – Course aggregates

Gravel and stone are the main materials used as jelly or aggregates in concrete mixes. Stone form the granular structure, which make the concrete stronger.  Stone can be obtained naturally and artificially using the various techniques such as crushing them using the mechanical equipments.

The size of course aggregates should not be greater than 80 mm and less than 4.75 mm as per IS standards. Further, Course aggregates should take approximate 70 to 80% weight of total volume of concrete.

Water

Water is an important element which helps cement in hydration process. As per the rule of thumb 25 to 30 % of water (by weight) is required to hydrate the cement. Water used in concrete should be free of oil, paint and other chemicals. You can also read more on the importance of water for construction in my previous post.

Concrete Mixes

As I discussed above, concrete is a mix of cement, course aggregates, fine aggregates and water. It can be mixed by various methods;

•           Hand Mixing
•          Concrete Mixer
•           Ready mix concrete

Specification of concrete mixes as per IS Standards

Grade  of Concrete	Portion ( Cement : Fine Aggregates : Course Aggregates)	Uses
M15	1:2:4	For PCC, non reinforcement work and mass concrete
M20	1:1.5:3	For RCC flooring and structural work relatively less load bearing
M25	1:1:2	For heavy and industrial structural work
Above M30	Obtain by Mix design	For heavy and special type of construction purpose

*M stands for mix and numerical value refers to the compressive strength of cement concrete in 28 days.