In this blog, I will tell you about the essential points of concrete which will be beneficial to students, engineers, or any person who is about to construct there house.
Concrete is a building material generally formed by mixing various binding elements.
So now cement concrete is used in every stage in construction from start to finish. Generally they are used in the foundation as a base and also in Lintel, window sill, and slab.
Generally, they are also used in airports, rigid pavements, highways, tunnel lining traffic tunnels, and ropeway base.
They are also used in the lining of canals, tunnels and reservoirs, concrete dams, water treatment plants, water storage tanks, tube wells, and water-conducting tunnels.
They are also used as a coating material for waterproofing, fireproofing, soundproofing, as well as as shielding against radiations in X-ray plants and atomic power plants.
Let us understand the essential points in details:
- Preparation Of Concrete
- Grades Of Concrete
- Requirements Of Concrete
- Types Of Concrete With Uses
- Advantages And Disadvantages
Preparation Of Concrete
Method of Mixing
1. Hand mixing
Generally for small and important works mixing of concrete is done by hand.
In particular, hand mixing should be done on a hard, clean, watertight surface like a hard floor or a metal tray. Also hand mixing requires about 10% more of cement than what is required in machine mixing
Firstly the measured quantity of sand should be spread on the surface evenly. Then the quantity measured in cement is dumped and mixed well by shovel until the mixture appears to be a uniform color.
In addition the measured quantity of coarse aggregate is added and mixed by shoveling from the center to the side and from the side to the center. Then prepare a heap at the center and take a dip in the center of heap. Afterward pour half of the total quantity of water required.
Then mix the material and water by shovel. Now add remaining water and finally mix it properly till the whole mass appears to have the same color and consistency.
The mixing should be done continuously instead of intermittently. Lastly the surfaces of coarse and fine aggregates should be completely covered with the cement-water paste.
2. Machine mixing
Generally in terms of quality machine mixes very well. Also, the mixing is faster by the use of machines.
Since rotary mixers have a cylindrical drum which rotates about a horizontal axis. So it is fed from a hopper and mixed material is collected in a discharge chute.
Also, the tilting mixers have a conical or bowl-shaped drum which rotates about an inclined axis. So the mixed material is discharged by tilting the drum.
Then the drum of the mixer should be emptied. They should be cleaned perfectly as a result it avoids sticking and hardening of material in blades and drums of mixer.
Types of Concrete Mixer
- Rotary mixer
- Tilting mixer
Form work in Concrete Work
Since it is getting held after it’s poured in a timber or steel cover for a certain period. This cover is known as shuttering, centering, formwork, or mold and it is far to be removed only after when it has hardened sufficiently to carry its weight.
Although form work can be used over and over again or for other purposes, after it is removed.
So ultimately only skilled and experienced labor is required to provide proper formwork to get the desired shape and finishing surface of concrete work.
Grade Of Concrete
It is designated in following grades:
Since as it has low tensile strength. So generally in the construction of beams and slabs where tensile forces and tensile loads are involved, there is always a risk of failure.
Meanwhile drawback of it can be overcome by using steel with it- R.C.C. steel has high tensile strength.
Requirements Of Concrete
- When one extra of one extra liter of water is added to one bag of cement will reduce its strength by about 15 kg/cm. As a result, the water-cement ratio should be marked with care.
- The material of it should be thoroughly mixed, at least three times in dry condition and then water is added.
- Moreover, the mix which is prepared by adding water should be used within 50 minutes.
- The mix must be treated and moved from one place to another and in such a way that there is no segregation of the aggregates.
- Generally depositing of it must be in small quantities.
- It should be prepared generally on-site as near as practicable to its final position.
- An affordable height should be determined and then it should be placed vertically.
- It should be placed on the formwork as soon as possible within 30 minutes of its preparation.
- In any case, water should not come upon the surface of the mix.
- On balance, Coarse aggregates should not settle down at the bottom of the mix.
- By the time proper curing of it should be carefully carried out for a defined period.
- It should possess proper compressive strength and also should be hard like a stone after the curing period.
- They should also properly cover the reinforcement used to avoid exposure to climate and to get resistance to corrosion. Also, the mix should be consolidated properly by ramming, tamping, spreading, and slicing with suitable tools.
- Above all the water-cement ratio of concrete plays a major role in deciding the strength and quality.
Types Of Concrete With Uses
- Plain cement concrete (PCC)
- Reinforced cement concrete (RCC)
- Precast concrete (PC)
- Prestressed concrete (PSC)
Concrete manufactured on site is termed as “in-situ-concrete
PCC is a mixture of cement, fine aggregates, coarse aggregates, and water.PCC has very less tensile strength; Hence it is not used for flexural member
Generally it is used in leveling course over plinth or below the footing and in lean concrete mixes used to fill columns of the terrace.
PCC is reinforced with a tensile material using round or square type of reinforcement steel bars to increase tensile strength.
Steel is added to PCC to make RCC. RCC caters for tensile and compressive. The general RCC work in buildings are beams, columns, slabs, stairs, lintels, weather sheds, machine foundations, arches etc.
Precast is used at a time of mass work which is needed for massive and fast production work. In this type of situation, They’re prepared in RMC plant in industries and transported to the location of pouring.
The precast solid and hollow blocks of desired shapes and sizes are made and afterward, it is shifted to the location of the site.
Precast is used as beams, columns, slabs, water tanks, compound wall poles, electricity poles, ornamental structures, RCC pipes, bridge girders, bridge piers, etc.
Prestressed is reinforced concrete in which it is subjected to compressive stresses, before the external loads are applied. So by including tensile stresses in the reinforcement it will counteract tensile stresses caused in it by external loads.
Since hydraulic jacks are placed to impart the prestressing force.
As it weakness in tension will be removed by using this method.
Generally, P.S.C. provides crack free members with excellent fire resistance and corrosion resistance. So they are used to prepare girders for bridges, beams for large spans, railway sleepers, electric poles, etc.
Advantages And Disadvantages
- It possesses a high compressive strength.
- Compared to steel it is more economical
- It is not subjected to corrosive wreathing and such effects
- High compressive strength possessed by it is an important advantage.
- It is a versatile material in building construction. For this reason, generally, it finds application from foundations to topmost storey’s in structures.
- Also, they are hard and durable material.
- On the positive side, it has water tightness and strength.
- It is a product obtained by mixing of cement, aggregates, and water in a planned definite proportion. Thus, the strength of it is governed by the properties of constituents and their quantities and the process of mixing them.
- It has a poor tensile strength and is liable to be cracked when subjected to tension.
- They also develop shrinkage stresses.
- Moreover, it work requires skill and supervision by technical persons.
- So surface cracks may occur and strength of it comes down, whenever it is allowed to dry too quickly by exposure to wind and sun.
- As repairing of this material work is difficult, as a result, old concrete and fresh concrete cannot bond easily.
- Since the Curing time of it is more. So as per the type of work, min 14 to 28 days is required for curing. Till that duration, the next step of construction cannot be started.
So it is necessary to maintain the newly placed concrete moist for several days
Generally speaking, it has attained the status of a major building material in the construction field; lime concrete and cement concrete are likely used as mass works for various structures of the building.
They can also be readily molded into durable structural items of various sizes and shapes. Also, they are strong and durable. Overall Concrete in building construction covers about 30% of the total cost. Generally, it is prepared at the project site under supervision and fabricated.
Since there are many technical reasons behind but the most common reason is shrinkage.
Generally the density is about 2400 kg per cubic meter.
Yes it can get burn but generally it does not catch fire as concrete is inflammable material.
IS: 456 (2000) Plain and Reinforced concrete at the present time is the official Indian standard code for it.