Lightweight aggregate (LWA) refers to porous, low-density materials used to replace conventional aggregates in concrete to reduce weight without significantly sacrificing strength. Types of LWA often include expanded clay, slate, shale, or slags. These materials are chosen for their ability to decrease the overall weight of concrete structures, enhance insulation properties, and improve fire resistance. LWA is particularly beneficial in applications where reduced weight can lead to lower costs in construction and enhanced structural integrity, such as in high-rise buildings or long-span bridge decks.