Ultra-High-Performance Concrete (UHPC) is traditionally produced with binder contents exceeding 800 kg/m³ and very low water-to-binder (w/b) ratios. While this approach ensures dense microstructures, it severely limits binder hydration, leaving substantial amounts of unhydrated cement merely as inert filler. This not only raises material costs but also intensifies environmental impact. This study focuses on developing while maintaining both fresh-state rheology and hardened-state performance. Rheological behavior was evaluated by rotational rheometry, and hydration was assessed through isothermal calorimetry, thermogravimetric analysis, and scanning electron microscopy (SEM). We introduce the Hydration–Porosity Performance (HPP) model to explain the relationship between hydration and strength in dense cementitious systems, relating compressive strength to the ratio of hydrate volume to the square of porosity (Φₕ/Φₚ²). Importantly, HPP enables the prediction of concrete mechanical performance directly from paste-level hydration and porosity measurements, thereby reducing experimental complexity and enabling scalable mix design development. Results show that strengths above 120 MPa can be achieved even with reduced binder consumption, ranging from 1,013 kg/m³ to 372 kg/m³. Overall, this work seeks to balance mix-design parameters, rheology, and hydration efficiency to enable the development of ultra–low-binder UHPC, moving beyond a packing-dominated approach toward a more holistic and eco-efficient design framework.
Mesquita et al. (Tue,) studied this question.