Now-a-days there have a tendency to provide lighter structure with the development of concrete technology. The lighter the structure, the less earthquake impact the structure suffers. As ground acceleration comes from seismic waves, converts to force with the weight of structure. The structural engineers, who analyze structure for seismic load, know about seismic dead load. We will not go to that point. This tendency of production lighter concrete brings forth light weight concrete.
At first we will provide the ranges of density of lightweight concrete. A density ranging from (300-1859) kg/cum can be achieved by light weight concrete. There a relationship between density and strength of concrete.
So a very light concrete never produce a concrete to be act as structural member. Structural lightweight concrete should have density ranging from (1350-1900) kg/cum. The compressive strength of structural lightweight concrete should not less than 17 Mpa.
Weight reduction is done by using
1. Light weight aggregate
2. Foamed concrete
3. Autoclaved aerated concrete
We will first learn about light weight aggregate. We can collect this aggregate from both natural, artificial and sometimes from the by-product from industries. The sources of aggregate are from:
a. Natural sources:
b. Industrial by product:
1. Fly ash is the very common by-product of industry. As an example, Lytag has been using over 40 years as lightweight aggregate. It is light, strong, consistent and environmental friendly too. It complies with EN13055.
2. Slag is also a processed by-product of industry. Furnace Bottom Ash (FBA) is found from power stations that use coal as fuel. Its size may vary from fine grained sand to gravel.
c. Artificial or treated:
treated with temperature, clay, shale or slate can be used as light weight aggregate. Example: light expanded clay aggregate (LECA). This is formed by burning clay. It has numerous cavities filled with air. This makes it light and thermal insulator as well.
Dear reader we will publish posts regarding the lightweight aggregate in details. For learning foamed concrete and autoclaved aerated concrete, please read next few posts. In the very next post you will find important` information about LECA.