<p>This paper investigates the mechanical properties and microstructural characteristics of Controlled Low-Strength Material (CLSM) modified with Alkali Activated Solution (AAS), synthesized by combining NaOH and Na₂SiO₃ in a 1:3.29 weight ratio. The study evaluates the flowability, compressive strength, elastic modulus, and tensile strength of conventional CLSM mixes across different water-to-cementitious material ratios (w/cm), humidity levels, and curing periods. These properties are then compared with modified CLSM mixes produced by partially substituting cement in the mix with AAS. The results indicate that AAS modification enhances flowability and significantly improves both early and long-term compressive strength compared to unmodified mixes. The authors performed Scanning Electron Microscopy analysis to evaluate the microstructural characteristics of both control and modified mixes. Microscopic analysis reveals the formation of unique tubular crystal zeolitic structures in modified mixes, contributing to their improved mechanical properties. However, the study also highlights challenges associated with shrinkage and cracking, particularly under low relative humidity curing conditions. These findings provide valuable insights into the efficacy of AAS modification for enhancing the performance of CLSM mixes and underscore the importance of considering both mechanical and microstructural aspects in the mix design.</p>