Vitrified Clay for the Production of a Green Sustainable Ultra-High-Performance Fiber-Reinforced Concrete

As awareness of the impact of anthropogenic activities on climate change increases, the concepts of durability, resilience, and sustainability in concrete tend to be adopted more seriously in the concrete construction industry. In this sense, one of the concrete technologies that began in the 1980s and that significantly contributes to maximize the beneficial effect on all these concepts are the ultra-high-performance concretes, a very attractive technology because it presents ultra-high strength and durability performances far superior to those of conventional concretes, a performance that is leading to a permanent increased demand. However, the development of these concretes has been widely criticized due to their high ecological impact, which is mainly attributable to the high cement dosages required for their production (800-1000 kg/m³). To address this criticism in a comprehensive manner and thereby reduce the embodied carbon attributable exclusively to the material, this research was oriented to determine the effect of an industrial by-product of vitrified clay, as a partial or total substitution for cement, silica fume, and limestone aggregate, on the compressive strength, flexural toughness, and embodied CO₂. For the UHPC's evaluated in this work with a dosage of 2% by volume of steel micro-fibers, the results evidence the feasibility that the following substitutions by mass: 30% of the Portland cement, 100% of the silica fume, and 30% of the limestone aggregate and powder, do not detract the fresh stage, the compressive strength, the static modulus of elasticity, and the flexural strength, leading to significant reductions of the embodied CO₂.