What is Lightweight Concrete?

Lightweight concrete mixture is made with a lightweight coarse aggregate and sometimes a portion or entire fine aggregates may be lightweight instead of normal aggregates. Structural lightweight concrete has an in-place density
(unit weight) on the order of 90 to 115 lb / ft³ (1440 to 1840 kg/m³).
Normal weight concrete a density in the range of 140 to 150 lb/ft³ (2240 to 2400 kg/m³). For structural applications the concrete strength should be greater than 2500 psi (17.0 MPa).
Lightweight aggregates used in structural lightweight concrete are typically expanded shale, clay or slate materials that have been fired in a rotary kiln to develop a porous structure. Other products such as air-cooled blast furnace slag are also used.
There are other classes of non-structural LWC with lower density made with other aggregate materials and higher air voids in the cement paste matrix, such as in cellular concrete.

Classification of Lightweight Concrete


It is convenient to classify the various types of lightweight concrete by their method of production. These are:
1.       *By using porous lightweight aggregate of low apparent specific gravity, i.e. lower than 2.6. This type of concrete is known as lightweight aggregate concrete.
2.      *By introducing large voids within the concrete or mortar mass; these voids should be clearly distinguished from the extremely fine voids produced by air entrainment. This types of concrete is variously knows as aerated, cellular, foamed or gas concrete.
3.      *By omitting the fine aggregate from the mix so that a large number of interstitial voids is present; normal weight coarse aggregate is generally used. This concrete as no-fines concrete.

LWC can also be classified according to the purpose for which it is to be used: it can distinguish between structural lightweight concrete (ASTM C 330-82a), concrete used in masonry units (ASTM C 331-81), and insulating concrete (ASTM C 332-83).
This classification of structural lightweight concrete is based on a minimum strength: according to ASTM C 330-82a, the 28-day cylinder compressive strength should not be less than 17 MPa (2500 psi).
The density (unit weight) of such concrete (determined in the dry state) should not exceed 1840 kg/m³ (115 lb/ft³), and is usually between 1400 and 1800 kg/m³ (85 and 110 lb/ft³). On the other hand, masonry concrete generally has a density between 500 and 800 kg/m³ (30 and 50 lb/ft³) and a strength between 7 and 14 MPa (1000 and 2000 psi).





                                                 



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