In the world of construction materials, hydraulic lime mortar has long been a favorite for its durability and eco-friendly properties. But a new study led by Marialuigia Sangirardi from the Department of Engineering Science at the University of Oxford is challenging our understanding of this material, with significant implications for the energy sector.
The research, published in the RILEM Technical Letters (translated from French as Materials and Structures Technical Letters), delves into the strain-level dependency of Young’s modulus in hydraulic lime mortar. Young’s modulus, a measure of a material’s stiffness, is crucial for understanding how materials will behave under different loads. Traditionally, it’s estimated using dynamic tests or static loading measurements. However, these methods can yield different results, and Sangirardi’s team wanted to understand why.
“We found that the strain amplitudes and testing configurations play a significant role in the characterisation of Young’s modulus,” Sangirardi explains. Her team conducted dynamic characterisation using standard impulse excitation of vibration tests and static characterisation with three-point bending and uniaxial compression tests. They used a tailored loading regime to examine the evolution of Young’s modulus at different strain levels.
The results were revealing. Repeated impulse excitation measurements showed a progressive decay in Young’s modulus with increasing strain amplitudes. A similar trend was observed for static moduli, although the decay magnitudes were notably higher and depended on the test configuration. “Reductions in Young’s moduli were associated with microscale damage processes and were observed at strain levels as low as 100 microstrain,” Sangirardi notes. These reductions became notably pronounced at compressive loads corresponding to about 30% of the material’s compressive strength, a level typically used for static elasticity characterisation.
So, what does this mean for the energy sector? Understanding the constitutive behavior of hydraulic lime mortar is crucial for its application in energy-efficient buildings. The small-strain nonlinearity highlighted in this study indicates a need for improved characterisation procedures. This could lead to more accurate modeling and design, ultimately enhancing the performance and durability of structures built with hydraulic lime mortar.
“This research underscores the importance of considering strain-level dependency in material characterisation,” Sangirardi concludes. As the construction industry continues to evolve, such insights will be invaluable in shaping future developments and ensuring the optimal use of materials in the energy sector.
The study, “Strain-level dependency in static and dynamic Young’s moduli characterisation of hydraulic lime mortars,” was published in the RILEM Technical Letters, offering a significant step forward in our understanding of this versatile material.