Fly ash based AAC to IS 2185 Part 3 - roughly a quarter the weight of concrete, with far better thermal performance.
AAC is fly ash, lime, cement and an aerating agent, steam-cured under pressure into a closed-cell block. The result weighs about a quarter of dense concrete, insulates roughly eight times better, and can be cut and drilled on site with hand tools.
For a high-rise frame the dead load saving alone often pays for the switch.