The influence of calcium carbonate on the mechanical properties and durability of ultra-high-performance concrete with varying silica fume content

Ultra-high-performance concrete (UHPC) is recognized as one of the most advanced concrete materials used in the construction and execution of concrete structures and precast components in civil engineering. These types of concrete, characterized by very high compressive strength and exceptional durability properties, are primarily utilized to fabricate precast parts in bridges and buildings. One of the main challenges associated with these concretes is the high consumption of cement, which this research addresses. In this study, nine mix designs were defined, incorporating 0%, 5%, and 10% calcium carbonate (CaCO3) as a partial substitute for cement, alongside 15%, 20%, and 25% silica fume also as a replacement for cement, to investigate the effects of these two additives on the properties of UHPC. Compression and electrical resistance tests were conducted at ages 7, 28, and 90 days, revealing the optimal percentages of 20% silica fume and 5% CaCO3. Additionally, tests for final water absorption and accelerated chloride ion penetration demonstrated a reduction in the permeability of these concretes with an increase in the silica fume content by up to 25%.