The real temperature distribution within 24 h of the main beam in a single-tower hybrid beam cable-stayed bridge is analysed according to its actual section and material parameters, as well as other factors of local atmospheric temperature, geographical environment, and solar intensity. The results show that the internal temperature distribution in the steel–concrete composite beam is uneven, and the temperature of the steel is higher than that at the surface of the concrete slab. Then, a finite element model of the whole bridge is established using the thermal–mechanical sequential coupling function in ABAQUS to acquire the structural response under the action of a 24-h temperature field. The results show that the vertical temperature gradients have a great influence on the longitudinal stress in the lower flange of the steel I-beam, with a maximum compressive stress of 11.9 MPa in the daytime and a maximum tensile stress of 13.36 MPa at midnight. The temperature rise leads to a downward deflection of the main span, and the maximum deflection occurs at the 1/4 main span. There was an obvious temperature gradient in the concrete slab, with a difference between the maximum and minimum value of 14 °C. Similarly, the longitudinal compressive stress of the concrete slab increases with increasing temperature in the daytime, but the peak time is obviously inconsistent with that of the steel beam.

The cement industry’s intricate production process, including kiln heating and fossil fuel use, contributes 5–8% of global CO₂ emissions, marking it as a significant carbon emitter in construction. This study focuses on quantifying CO₂ capture potential in blended cement systems through the utilisation of phenolphthalein and thermalgravimetric methodologies. Its primary objective is to assess the CO₂ absorption capacity of these blended systems’ pastes. Initial evaluation involves calculating the carbon capture capacity within the paste, subsequently extended to estimate CO₂ content in the resultant concrete products. The findings indicate that incorporating ground granulated blast-furnace slag (GGBS) or an ettringite-based expansive agent did not notably elevate carbonation depth, irrespective of their fineness. Conversely, the introduction of fly ash (FA) notably augmented the carbonation depth, leading to a substantial 36.4% rise in captured CO₂ content. The observed distinctions in carbonation behaviour primarily stem from variances in pore structure, attributable to distinct hydration characteristics between GGBS and FA. Thermal analysis confirms the increased stabilisation of CO₂ in FA blends, highlighting the crucial influence of material composition on carbonation and emission reduction. Incorporating both GGBS and FA notably diminishes binder emissions, constituting almost half of PC-concrete emissions. Initially, 60% GGBS shows lower emissions than 50% FA, but when considering CO₂ capture, this emission dynamic significantly changes, emphasising the intricate influence of additives on emission patterns. This underscores the complexity of evaluating carbonation-induced emissions in cementitious systems.