Strain-level dependency in static and dynamic Young’s moduli characterisation of hydraulic lime mortars

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Abstract
Young’s modulus is commonly estimated using dynamic tests or from load and deformation measurements under static loading. However, these methods may yield different results due to variations in strain levels where characterisation is conducted. Existing studies reported discrepancies between static and dynamic Young’s moduli of hydraulic lime mortar. This paper examines the role that strain amplitudes and testing configurations play during Young’s moduli characterisation of prismatic samples to understand the root causes for these differences. Dynamic characterisation is conducted using standard impulse excitation of vibration tests while static characterisation is done with three-point bending and uniaxial compression tests. A tailored loading regime is used to examine the evolution of Young’s modulus at different strain levels. Repeated IEV measurements reveal progressive decay with increasing strain amplitudes. A similar trend is observed for static moduli, although decay magnitudes are notably higher and depend on the adopted test configuration. Reductions in Young’s moduli are associated with microscale damage processes and were observed at strain levels as low as 100 με. They become notably pronounced at compressive loads corresponding to ~30% of material compressive strength, which is typically used for static elasticity characterisation. The results highlight the small-strain nonlinearity of hydraulic lime mortar and indicate the need for improved characterisation procedures to describe the constitutive behaviour of this material.

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