Properties of Concrete
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Properties of Concrete
After learning briefly about the history of concrete, let us focus upon the properties of concrete. Concrete is an artificial building material whose production differs from application to application. Amongst general properties of concrete, we must understand that concrete should possess certain physical and chemical properties, tensile strength, low-level of permeability to avoid moisture and retain chemical and volume stability.
Concrete essentially has a high level of compressional strength, while the tensile strength of concrete is relatively very weak. As concrete can crack under its own weight, it needs to be reinforced. It is generally reinforced using steel bars or fiber and iron mesh. To reduce the tensile strength of concrete, it is also pre-stressed with the use of steel cables. The deciding factor for strength is also inherently related to the proportion and ratio of water and cement, the type of cement used and the strength of used aggregate.
Generally, concrete made using lower water-cement ratio makes a stronger concrete than when higher ratios are used. It is noticed that concrete made out of rough broken rock pieces is much stronger than concrete made using smooth pebbles. The reason is that the material should not result into more surface bondage area as this will increase the quantity of bondage, which is cement, resulting in weaker concrete. It is known that limestone possesses higher bonding properties than conventionally used gravel.
Normally, a 28-day compressive strength testing is done to achieve desired workability. The 28-day test for compressive strength is achieved by determining the right quantity of cement required in water cement ratio. In structures like arches, vaults where shapes and structures with internal forces require concrete.
Workability of concrete means the ability of a concrete to fill the mould appropriately, producing the desired work without plummeting the quality of concrete. Concrete workability is achieved with the water ratio, shape and size of aggregate and the level of hydration. It is observed that workability can be considerably improved by increasing the quantity of water, or with usage of plasticizer. More water content can lead to bleeding and segregation, which can result in poor quality concrete formation.
Curing is a process that keeps the concrete intact by providing an appropriate environment. It is considered that good curing ensures a moist environment for hydration. This steady hydration results in low level of permeability, thus increasing concrete’s strength and quality. Concrete also needs to be protected from shrinkage. As concrete has low thermal expansion co-eficient, which means that it cannot handle repetitive expansion and shrinkage. If there is no external force used for expansion, it can result in sizeable force acting against it, resulting in shrinkage and cracking of structure. As concrete grows older, it goes on shrinking due to internal forces caused within the material.
Cracking of concrete begins at micro level. Normally, concrete is kept in a wet state to allow easy moulding when required. Hydration and hardening of concrete can lead to shrinkage and cracking when it has not yet developed the tensile strength. It is important to reduce stress before curing. Freezing of concrete before the curing is complete can seriously hamper the process of hydration. This can also decrease the concrete strength and weaken and damage the concrete.
Creeping is described as constant deformation of a material owing to internal stress taking place in the material. The amount of reinforcement of concrete structures ensures minimal shrinkage, creep and cracking.
These general concrete properties of concrete are taken care of during building of concrete. Depending upon the end application, concrete is accordingly treated for maximum strength and durability.
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