This study investigates the microstructure, phase formation, and mechanical properties of LC3-50 based auto-claved aerated blocks. The microstructure and phase formation is studied using SEM-EDS and X-ray diffraction techniques. The fresh and hardened properties are determined using different methodologies. Three different densities (i.e.500,600,700 kg/m3) are designed by varying the aluminum powder dosage. The compressive strength and thermal conductivity depend on the density of the block. The primary hydration product formed during the autoclave process is katoite, and it is responsible for the strength development in LC3-50 based blocks to a certain extent. The autoclave process will help the carbonation of the block altogether, and portlandite is converted to calcite during the autoclave process. Secondary phases like ettringite, monosulfoaluminate and hemicarboaluminate were converted to anhydrite during the autoclave process. Excess lime changes the mechanism of the phase formation, and it initiates the formation of two significant phases: tobermorite and katoite. Significant clinker is present in the unhydrated form.