this is the blog give some basic information about quality aspects for civil engineering materials
Monday, June 6, 2011
Comparision between light weight concrete and conventional concrete
Light weight concrete
One of the main advantages of conventional concrete is the self weight of concrete. Density of normal concrete is of the order of 2200 to 2600. This self weight will make it to some extend an uneconomical structural material.
Self weight of light weight concrete varies from 300 to 1850 kg/m3.
It helps reduce the dead load, increase the progress of building and lowers the hauling and handling cost.
The weight of building on foundation is an important factor in the design , particularly in case of weak soil and tall structures. In framed structure , the beam and column have to carry load of wall and floor. If these wall and floor are made of light weight concrete it will result in considerable economy.
Light weight concrete have low thermal conductivity.( In extreme climatic condition where air condition is to installed the use of light weight concrete with low thermal conductivity is advantageous from the point of thermal comfort and low power consumption.
Only method for making concrete light by inclusion of air. This is achieved by a) replacing original mineral aggregate by light weight aggregate, b) By introducing gas or air bubble in mortar c) By omitting sand fraction from concrete. This is called no – fine concrete.
Light weight aggregate include pumice, saw dust rice husk, thermocole beads, formed slag. Etc
Light weight concrete aggregate exhibit high fire resistance.
Structural lightweight aggregate’s cellular structure provides internal curing through water entrainment which is especially beneficial for high-performance concrete
9. lightweight aggregate has better thermal properties, better fire ratings, reduced shrinkage, excellent freezing and thawing durability, improved contact between aggregate and cement matrix, less micro-cracking as a result of better elastic compatibility, more blast resistant, and has better shock and sound absorption, High-Performance lightweight aggregate concrete also has less cracking, improved skid resistance and is readily placed by the concrete pumping method
Aerated concrete is made by introducing air or gas into a slurry composed of Portland cement.
No fine concrete is made up of only coarse aggregate , cement and water.These type of concrete is used for load bearing cast in situ external walls for building. They are also used for temporary structures because of low initial cost and can be reused as aggregate.
High density concrete
The density of high density concrete varies from 3360 kg/m3 to 3840 kg/m3.They can however be produced with density upto 5820 kg/m3 using iron as both fine and coarse aggregate.
2. Heavyweight concrete uses heavy natural aggregates such as barites or magnetite or manufactured aggregates such as iron or lead shot. The density achieved will depend on the type of aggregate used. Typically using barites the density will be in the region of 3,500kg/m3, which is 45% greater than that of normal concrete, while with magnetite the density will be 3,900kg/m3, or 60% greater than normal concrete. Very heavy concretes can be achieved with iron or lead shot as aggregate, is 5,900kg/m3 and 8,900kg/m3 respectively.
They are mainly used in the construction of radiation shields (medical or nuclear). Offshore, heavyweight concrete is used for ballasting for pipelines and similar structures
The ideal property of normal and high density concrete are high modulus of elasticity , low thermal expansion , and creep deformation
Because of high density of concrete there will be tendency for segregation. To avoid this pre placed aggregate method of concreting is adopted.
High Modulus of Elasticity, Low thermal Expansion ,Low elasticity and creep deformation are ideal properties.
The high density. Concrete is used in construction of radiation shields. They are effective and economic construction material for permanent shielding purpose.
Most of the aggregate specific gravity is more than 3.5