A 50% volume replacement of natural coarse aggregate with the selected clay-based artificial lightweight aggregate (ALWA) produced the best strength-density balance within the tested matrix, reaching 24.19 MPa compressive strength, 7.12 MPa flexural strength, and 2210 kg/m³ concrete density at 28 days, corresponding to a 5.1% density reduction relative to the control. The ALWA was produced from 97% clay, 2% coconut fiber ash (CFA), and 1% rice husk ash (RHA) and evaluated under three thermal regimes: 500 °C, 900 °C, and two-stage sintering at 500 °C followed by 900 °C. Aggregate characterization included visual observation, oven-dry bulk specific gravity, water absorption, single-particle crushing strength, and qualitative X-ray diffraction (XRD). The two-stage C1-S3 aggregate showed fewer visible macroscopic defects than direct 900 °C firing and the highest mean C1 single-particle crushing strength (16.29 MPa), with an oven-dry bulk specific gravity of 1.62 and water absorption of 27.49%. Concrete containing 0%, 35%, 50%, and 100% ALWA was evaluated for density, compressive strength, and flexural strength. Although all ALWA mixtures exceeded the cited Indonesian compressive-strength threshold for structural lightweight concrete, their densities remained above 1850 kg/m³; the tested mixtures are therefore classified consistently as reduced-density concrete. The XRD interpretation is qualitative, and no SEM, quantitative phase analysis, or pore-size data are available. The high ALWA absorption is consequently treated as a principal constraint requiring controlled moisture conditioning, workability-retention verification, durability testing, and field-scale batch-water correction.
