Lightweight foam concrete is an appealing thermal insulation material with great potential for decarbonizing the building sector, given that its superior thermal insulation and reduced material usage promote energy-efficient and low-carbon constructions. However, traditional foam concrete largely depends on carbon-intensive ordinary Portland cement (OPC) and costly foam stabilizers, e.g., nanomaterials. To address these issues, this study developed an eco-friendly foam concrete formula incorporating limestone calcined clay cement as a low-carbon cement substitute and used engine oil (UEO) as a foam stabilizer. The viability of this formula was confirmed by assessing foam stability performance of UEO-enhanced foam and crucial engineering performance – thermal conductivity and compressive strength – of foam concrete. Experiments demonstrate that 1 % UEO notably boosts foam stability, with prolonged stable time by 75 % and enhanced remaining foam fraction by 43 %. Additionally, 1 % UEO-containing foam concrete exhibits superior compressive strength of 3.2 MPa and reduced thermal conductivity of 0.162 W⋅m-1K-1, outperforming foam concrete without UEO. The mechanisms of macroscopic performance changes were revealed through scanning electron microscopy (SEM), which disclosed a uniformly established UEO-enhanced pore system and UEO-driven hydration process as the microscale origins. These findings provide waste-enhanced foam stabilizers and present an environmentally appealing alternative to traditional foam concrete, with implications for clean waste management and building decarbonization.