Lightweight concrete or leca blocks are made with lightweight coarse aggregate clay with a portion of fine aggregates. The lightweight concrete has an in-place density on the order of 90 to 115lb/ft3. On the other hand, normal weight concrete has a density range of 140 to 150lb/ft3.
In order to use these blocks in construction, the concrete strength should be greater than 2500 psi. Usually, the lightweight aggregates is used in lightweight concrete which are typically expanded shale, clay or slate materials. These materials have been fired in a rotary kiln in order to develop a porous structure. Other products are also used like an air-cooled blast furnace slag.
Classification of Lightweight Concrete
It is easy to classify the various types of lightweight concrete by their method of production. There are:
In order to use the porous lightweight aggregate of a low apparent specific gravity of lower than 2.6 then this type of concrete is known as lightweight aggregate concrete.
The voids should be clearly distinguished from the extremely fine voids produced by air entertainment. This type of concrete is known as aerated or gas concrete.
Last but not the least is the no-fine concrete which is omitted by fine aggregate from the mix so that a large number of interstitial voids is present where normal weight coarse aggregate is generally used.
Lightweight concrete can also be classified according to the purpose for which it will be used. It can generally distinguish between structural lightweight concrete or concrete used in masonry units or insulating concrete.
Types of Lightweight Concrete
Lightweight Aggregate Concrete
In the 1950s, the use of lightweight concrete blocks was accepted in the UK for load bearing inner leaf of cavity walls. After that, the development and production of new types of artificial lightweight aggregate made it possible to introduce lightweight concrete of high strength that is suitable for structural work.
While the advancement encouraged the structural use of lightweight concrete, probably to that places where the need to reduce weight in a structure was in a structure was an important consideration for design or for the economy.
Here is the list of different types of lightweight aggregates that are suitable for structural reinforced concrete.
Pumice
This is used for reinforced concrete roof slab, usually in industrial roofs.
Foamed Slag
This was the first lightweight aggregate which was suitable for reinforced concrete that was produced in large quantity.
Expanded Clays and Shales
These are capable of achieving sufficiently high strength for prestressed concrete. This concrete was established under the names of Aglite and LECA, Haydite, Rocklite, Gravelite, and Aglite.
Sintered Pulverised
This was basically fuel ash aggregate which was being used for a variety of structural purposes and is being marketed under the trade name of Lytag.
Aerated Concrete
This type of concrete has the lowest density, thermal conductivity, and strength. Moreover, it can be sawn, screwed, and even nailed like timber. In order to make it for work in-situ, the usual methods of aeration are by mixing in stabilized foam or by whipping air in with the aid of an air entraining agent.
However, the precast products from aerated concrete are usually made by the addition of about 0.2% of aluminum powder to the mix. This reacts with the alkaline substance in the binder forming hydrogen bubbles.
Aerated concrete is usually light in weight and is made of cellular material consisting of cement or lime and sand or other siliceous materials. It is made by a physical method or a chemical process during which either air or gas is introduced into a slurry which contains no coarse material.
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