Miles Robert William Judd

Masonry structures predominantly work under compression; elasticity in constituent materials is therefore typically characterised during uniaxial compression tests via load and deformation measurements. In most practical applications, deformation measurements can only be conducted at the surface of the sample. To understand the influence of this restriction on characterisation results, this study conducts in-situ load tests on hydraulic lime mortar samples with both surface and volumetric imaging, using stereo cameras and synchrotron X-rays. The imaging data is processed with Digital Image and Volume Correlation algorithms (local and global) to obtain full-field displacements and strains. Deformation measurements are then used to conduct surface characterisation with the Virtual Fields Method (VFM) and volumetric characterisation with Finite Element Model Updating (FEMU). Since the inverse models indicate limited identifiability for Poisson’s ratio, only the Young’s moduli are compared. Results indicate that accurate Young’s moduli can be obtained from surface measurements, provided that through-thickness load gradients are considered by averaging VFM results from front and back faces of the sample. In addition, it is shown that a surface characterisation domain away from contacts needs to be chosen to ensure that surface strains are representative of bulk behaviour. Finally, a systematic reduction of elastic moduli with increasing loads is observed, suggesting damage development at relatively low stress levels in hydraulic lime mortars.

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.

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 amplitude. 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 microcracking and may be 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 nonlinearity of hydraulic lime mortar constitutive behaviour at small strains and indicate the need for standardised procedures.