Investigating the Effect of Specimen Size on Compressive Strength in Ultrahigh-Performance Concrete

Ultrahigh-performance concrete (UHPC) has gained significant traction in civil and military applications due to its enhanced properties. The study investigates the compressive strength conversion factors for various UHPC specimen shapes and sizes, addressing the challenges posed by standard concrete compression tests such as the requirement for high-capacity testing machines and additional procedures, like cylinder testing surface preparation. Different lengths, dosages, and combinations of steel fibers, including short (6), long (13), and extra-long (25 mm) fibers, were tested. Conversion factors range from 0.95–1.09 for single fiber types and 0.95–1.04 for hybrid fibers in reference to 100 mm cube specimens. Conversion ratios from 100 mm diameter cylinders to cubes were 1.03 for the control sample (without fiber), with slight variations for different fiber dosages. The study established new compressive strength relationships for UHPC, differing from normal strength concrete. These findings aid construction companies, testing labs, research institutions, and standards organizations in standardizing testing, optimizing material use, and ensuring reliable strength measurements.