This document discusses high density concrete, which has a density of at least 3360-3840kg/m3 compared to the 2400kg/m3 density of conventional concrete. High density concrete uses heavy aggregates like magnetite, iron ore, or manufactured aggregates like iron or lead shot. It has properties suitable for radiation shielding and strength even at high temperatures. While it provides more shielding and strength in less space, high density concrete also has disadvantages like increased costs and risk of aggregate segregation during mixing.