Mechanical Performance of Alkali-Activated Cement Incorporating Lime Kiln Dust and High-Calcium Fly Ash under Ambient and Heat Curing Conditions

This study investigated the strength development of alkali-activated cements (AACs) synthesized from lime kiln dust (LKD) as a novel high-calcium precursor. The experimental program evaluated soft- and hard-burn LKDs, alone and blended with high-calcium fly ash (HCFA), under ambient and heat-curing conditions (50°C–70°C). X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses characterized the chemical composition and phase assemblages influencing strength evolution. Under ambient curing, soft-burn LKD exhibited higher reactivity and compressive strength ( ≈ 6 – 7 MPa at 28 days) than hard-burn LKD ( ≈ 0.2 – 0.6 MPa ). Optimum activation occurred at 8 M NaOH for soft-burn and 10 M for hard-burn LKD. Incorporating HCFA markedly enhanced performance, with a 30 ∶ 70 LKD-to-HCFA blend achieving ≈ 20 – 25 MPa , providing an effective balance between strength and sustainability. At 60°C—the optimal curing temperature—soft-burn and hard-burn LKD AACs attained 9–12 and 2.5–3 MPa, respectively, confirming the critical role of temperature in accelerating polymerization. The findings demonstrate that LKD-based AACs, particularly when combined with HCFA, offer a promising low-carbon binder for precast and accelerated construction applications.