<p>This study investigates the energy dissipation and stiffness degradation behaviour of three geopolymer concrete (GPC) grades- M40, M50 and M60. Using cyclic compression test data, the relationships between plastic strain, stiffness loss, envelope strain and energy dissipation are examined. Empirical expressions are developed to estimate the energy dissipation ratio (E_d) for each grade based on the observed experimental results. The results show that both energy dissipation and stiffness degradation in GPC exhibit a bilinear pattern, where the early stage is dominated by elastic strain accumulation, followed by a second phase with a steeper rise in E_d as loading continues. The transition between these two regions allows the identification of elastic limits for each grade through their respective stress-envelope strain ratios. The results also indicate that GPC strength plays a significant role in its cyclic behaviour: higher-strength mixes display a more stable, linear stress–strain response with reduced conversion of strain energy into crack formation, whereas lower-strength mixes experience faster deterioration under comparatively lower strains and higher stresses.</p>