The fracture toughness of an Imperial Roman mortar

The vaulted concrete monuments of ancient Rome have an unreinforced concrete core of Pozzolanic mortar and decimeter-sized coarse aggregate. An assessment of the mechanical and fracture properties of a reproduced Trajanic-era (c. 100ad) mortar is the subject of the present work. Description of a newly developed arc-shaped three-point bending test, devised to optimize eventual testing of Trajanic-era concrete specimens with an unusual drill core geometry, is supplemented with details of the reproduced material composition and inverse data reduction procedures. Three ages of mortar are tested, with results suggesting a relatively long curing process that increases mechanical and fracture properties. The mortar cured longest (180 days) is found to have a Young’s modulus of 3.4 GPa, uniaxial tensile strength of 0.5 MPa, and mode-I tensile fracture energy of 55 J/m2. These measurements describe a relatively ductile cementitious material with respect to modern concretes.

► First published test results of the fracture properties of an ancient material. ► First published details of the mix design of Trajanic-era Roman mortar, a key part of history’s most durable concrete. ► First published details of a new test system to measure fracture properties, the arc-shaped three-point bend test.