Concrete, Its Properties, Uses and Defects
Concrete is human made material which is widely used for construction. Concrete is the best material used for construction of bridges, buildings, roads and dams. Concrete is strong in compression and weak in tension. Due to weakness in tension, reinforcement is used with concrete to support it in tension. Basically, concrete is composed of certain materials like cement, aggregates and water. Curing is necessary up to 28 days to get strength. There are many properties of concrete such as durability, strength and workability and setting time. Basically, these properties are affected by the handling, placing and transporting of concrete. Water cement ratio also plays an essential role in the strength of concrete.
Concrete is the crucial material for improper construction, handling, and setting can cause damage to the structure as well.
To increase the setting time of concrete, certain admixtures are used. Plasticizers are also used to improve the properties of concrete. In the construction industry, different grades of concrete are used like M10, M15, M20, M25, and M30. M30 indicates that compressive strength required for construction is 30MPA.
In construction industry concrete is prepared in different proportions w.r.t to cement. Practically there are two types of concrete mixes which is used in the construction industry one is nominal mix, and other is design mix.
The fundamental difference between two mixes is that nominal mix is used in normal construction like for small residential buildings. The proportion used in nominal mix is 1:2:4. Design mix is concrete is prepared and finalized after testing of cubes and cylinders for compressive strength.
This whole procedure is known as mix design. The primary purpose of all these tests is to find the exact ratio based on available materials to get perfect strength according to structural design. First of all when the mix design is known than all the materials like cement, aggregates and water are mixed according to ratio. In construction industry there are two methods of mixing one is tradition method hand mixing and other is machine mixing.
Now the method of mixing depends upon the quality and quantity. In traditional method of hand mixing all the materials are first placed on ground and then water is added then mixed. In machine method of mixing there are different of machines used simply cement aggregates and water is added and we get fresh concrete.
After all the procedure of mix design, proportion and mixing when concrete is ready then it is transported to the site and poured. After the pouring of concrete of concrete it is left for gaining strength and after one day formwork is removed and curing process is done and there are many methods for curing as well. Curing is done for the hydration process and for the moisture loss due to evaporation. Practically in construction industries curing is done for 7 days.
Generally there are two types of construction
Plain Concrete Construction
second reinforced construction
In plain concrete construction there is no use of any reinforcement and this type of construction is done where structural members are also subject to compressive force not bending. But when structural members are under tensile forces then reinforcement is used because concrete has 10% strength in tension. Now a day’s reinforced concrete is used construct residential houses, dams, roads, buildings and bridges. The famous structure which are made with only concrete are Hoover dam and Panama Canal. If concrete is not placed, cured and transported properly then defects occur after construction like honey combing and cracks. Bleeding is a problem occurs due to the excess use of water while mixing of concrete. Bleeding is a phenomenon in which free water is pushed upward and aggregates settle down. Honey combing also the problem and it occur due to poor grading of aggregates because we want uniform grading in concrete mix. Cracks are also developed after the construction because of excess evaporation of water mixed in concrete. Ready mix concrete is also used where we want rapid construction or due to weather affects. If there are site issue and there is no proper site for preparation of concrete then ready mix concrete is ordered. Portland cement is the common type of cement used for the preparation of concrete
Concrete is very good material in construction if we use it in a proper way by doing compaction, transport and mixing correctly. If all the process from mix design ratio till curing if we any mistake are made then it affects the strength of concrete. During mixing of concrete we should take care of time and it should not exceed the initial setting time of 30 minutes. Water cement ratio is very important for the strength of concrete so it must be taken under consideration. Curing is also necessary for the strength of concrete and the surface of concrete should be cured for 24 hours up to the seven from lying of concrete. In winter if the temperature is below 4.5 centigrade then construction is not possible. Retarders and admixtures are used to change the setting time of concrete for example concrete is going on concrete is ready and weather is rainy then admixture is used to change the setting time. In underwater concrete early strength concrete is used. In concrete there are other binding material is also used in place of cement like lime for lime concrete and bitumen for asphalt concrete.