Coupling effect of size and strain rate on uniaxial compressive properties of coral reef limestone

• UCS and RCS of coral reef limestone decrease with increasing L/D ratio, while DIF of UCS linearly increases with log strain rate and is further enhanced by larger L/D ratios. • Elastic modulus increases with strain rate or L/D ratio, while Poisson's ratio remains constant at 0.24; failure strain increases with strain rate or decreasing L/D ratio. • High porosity and low mineral strength lead to high residual strength (16.7%–64.9% of UCS), low brittleness, and irregular fracture planes. • Failure mode transitions from shear-dominated to splitting-dominated with increasing strain rate or decreasing L/D ratio, governed by end friction and crack propagation; a predictive formula for UCS was established.