Light weight concrete 

Answer:-  Aerated or Foamed Concrete

This type of lightweight concrete is also known as gas concrete or foamed concrete, since it is developed by introducing large voids into the mortar mass or concrete. ... Aerated or foamed concrete does not require flattening, exhibits appropriate thermal insulation, and is self-compacting.

Structural lightweight concrete has an in-place density (unit weight) on the order of 90 to 115 lb/ ft3 (1440 to 1840 kg/m3) compared to normal weight concrete with a density in the range of 140 to 150 lb/ ft3 (2240 to 2400 kg/m3). It can be more reduced for non structural members. 

They generally have densities ranging from 560 to 1100 kg/m3 as per use of different aggregate 

The benefits of using lightweight aggregate concrete include:

Reduction in dead loads making savings in foundations and reinforcement.

Improved thermal properties.

Improved fire resistance.

Savings in transporting and handling precast units on site.

Reduction in formwork and propping.