In modern construction, increasing the sustainability of materials without sacrificing performance is crucial. Ultra-High-Performance Concrete (UHPC) is known for its exceptional strength and durability. However, incorporating waste and optimizing the mix is still a key focus. The main goal of this article is to evaluate the enhancement of the mechanical properties of UHPC by replacing silica sand with steel slag at various percentages (25%, 50%, 75%, and 100%). With this purpose, we measured the compressive, tensile, and flexural strengths, as well as relative density and water absorption. It was found that the best mechanical performance of UHPC occurs at 50% replacement, exhibiting a maximum compressive strength of 126 MPa (+13.5%), a bending strength of 11.6 MPa (+20.8%), and a tensile strength of 7.2 MPa (+6.5%). Moreover, for the same steel slag replacement, 5.1% decrease in the CO₂ eq. emissions was found. However, exceeding the 50% threshold led to a deterioration of UHPC’s mechanical properties, and the SEM images revealed that this was mainly caused by the weakened bond between the cement matrix and the aggregates. Thus, it was concluded that the use of steel slag may significantly improve the structural integrity of UHPC when the adequate replacement percentage is adopted (around 50%), being a viable alternative to traditional aggregates that also has environmental advantages (e.g., reduced carbon emissions).

This study presents a comprehensive comparative analysis of seismic resilience and sustainability between steel and reinforced concrete structures. With growing demand for environmentally responsible and disaster-resilient infrastructure, evaluating the life cycle performance of construction materials has become critical. Three building typologies—10-, 20-, and 30-story residential structures—are analyzed using a life cycle assessment (LCA), life cycle costing (LCC), and incremental dynamic analysis (IDA) to assess environmental, economic, and seismic performance. The results reveal that reinforced concrete structures tend to exert greater environmental impacts, particularly in categories such as carcinogenic emissions, ecotoxicity, and acidification, primarily due to cement production. Steel structures, while associated with higher energy consumption and mineral resource depletion, demonstrated superior seismic performance across all building heights, characterized by a greater level of ductility and collapse capacity. For instance, the 30-story reinforced concrete structure generated approximately 6.93 million kg CO₂ eq, compared to 6.79 million kg CO₂ eq for its steel counterpart. Steel structures, while associated with higher energy consumption and mineral resource depletion, demonstrated superior seismic performance across all building heights, sustaining up to a 15% greater spectral acceleration before collapse. Additionally, the LCC analysis showed that reinforced concrete is more cost-effective in high-rise construction, especially during the construction stage. These findings offer valuable insights for engineers and decision makers aiming to balance sustainability and structural performance in urban development.

This study investigates environmentally friendly high-performance concrete (HPC) by partially replacing cement and silica sand with zeolite powder. The replacement levels included 10%, 20%, and 30% for cement and up to 50% for silica sand. The optimal mix achieved 85 MPa compressive strength, 6 MPa tensile strength, and 7.8 MPa flexural strength with a 30% cement replacement, reducing the carbon footprint to approximately 659.72 kg CO₂/m³. These findings demonstrate the potential of zeolite powder to enhance sustainability in HPC without compromising essential mechanical properties, promoting eco-friendly practices in construction.