Advanced Minor Destructive Testing for the Assessment of Existing Masonry

This thesis focuses on minor-destructive testing (MDT) techniques for the mechanical characterisation of historical mortars, as it is a fundamental task for the assessment of existing masonries. In the first part, a novel in-situ MDT technique is investigated, based on the field vane shear test for soils. The instrumentation consists in a four-winged pin (X-Drill) and a torque wrench. This research presents the results of an experimental campaign based on the comparison between standard tests and X-Drill measurements on different types of mortars. The interpretation of the test provides a possible correlation between the measured torque and the compressive strength of the material. In the second part, the thesis focuses on the extraction of samples to be tested in the laboratory. Brazilian tests can be carried out on cores including a diametral mortar joint with a defined inclination with respect to its original horizontal position. A new integrated methodology is developed for the comprehensive mechanical characterization of historical mortar based on different types of experimental tests results. This task is carried out by means of a large set of experiments performed ex-novo on lime mortar masonry walls built in the laboratory. The processing of the results from Brazilian tests on cores with inclined diametral joint is complemented with the application of the double punch tests on mortar joints that may be also extracted through core drilling. The proposed experimental methodology is then compared with the results obtained from standard tests performed on the same materials, such as compression tests, flexural tests and shear tests on triplets. Finally, the parameters obtained are used as input parameters for 2D and 3D numerical analyses based on the Continuum Damage Mechanics constitutive model. The comparison between the experimental results and the numerical analyses confirms the good prediction capacity of the proposed techniques

Torque Penetrometric Test for the in-situ characterisation of historical mortars: fracture mechanics interpretation and experimental validation

The assessment of historical structures requires appropriate knowledge of the behaviour of the investigated materials. Concerning masonry, its mechanical characterisation is a challenging task, since its composite nature requires the careful evaluation of the behaviour of its material components. In particular, the experimental assessment of the strength of existing mortar in historical structures still encounters several difficulties. This study investigates a novel Minor Destructive Testing (MDT) technique virtually equivalent to the vane test used for soils. The instrumentation, called herein Torque Penetrometric Test (TPT), is composed of a steel nail with four protruding teeth and a torque wrench. The test consists in inserting the toothed nail into a mortar joint and then applying a torque by means of a dynamometric key, until reaching the failure of the material. This work presents a novel interpretation theory based on basic concepts of fracture mechanics and applied to the micro-mechanical analysis of the stress state induced by the instrument on the investigated mortar. The proposed interpretative theory is validated through the execution of experimental tests in the laboratory and in a historical masonry building. The test proves to be effective for a quick in-situ MDT evaluation of the strength of existing mortars.Peer ReviewedPostprint (author's final draft

Interpretation of experimental tests on small specimens of historical mortars

Postprint (published version

Evaluation of mortar strength in existing masonry structures through a Minor Destructive Technique

The mechanical characterization of material components in existing masonry structures has been the topic of several research studies. Most of them are currently focusing on mortar, the most difficult material component to characterize, trying to evaluate its strength. To achieve this aim, a good option is performing Minor-Destructive Testing (MDT). A novel MDT technique is investigated in this study, based on the field vane shear test for soils. The instrumentation consists in a four-winged pin (X-Drill) and a torque wrench. The testing procedure consists in inserting the pin in a mortar joint and applying a torque to the pin through the dynamometric key. The dynamometric key records the magnitude of the torque while the pin brings the material to failure. This research presents the results of an experimental campaign based on the comparison between standard tests and X-Drill measurements on different types of mortars.Postprint (published version

Evaluation of mortar strength in existing masonry structures through a Minor Destructive Technique

The mechanical characterization of material components in existing masonry structures has been the topic of several research studies. Most of them are currently focusing on mortar, the most difficult material component to characterize, trying to evaluate its strength. To achieve this aim, a good option is performing Minor-Destructive Testing (MDT). A novel MDT technique is investigated in this study, based on the field vane shear test for soils. The instrumentation consists in a four-winged pin (X-Drill) and a torque wrench. The testing procedure consists in inserting the pin in a mortar joint and applying a torque to the pin through the dynamometric key. The dynamometric key records the magnitude of the torque while the pin brings the material to failure. This research presents the results of an experimental campaign based on the comparison between standard tests and X-Drill measurements on different types of mortars

Torque Penetrometric Test for the in-situ characterisation of historical mortars: fracture mechanics interpretation and experimental validation

The assessment of historical structures requires appropriate knowledge of the behaviour of the investigated materials. Concerning masonry, its mechanical characterisation is a challenging task, since its composite nature requires the careful evaluation of the behaviour of its material components. In particular, the experimental assessment of the strength of existing mortar in historical structures still encounters several difficulties. This study investigates a novel Minor Destructive Testing (MDT) technique virtually equivalent to the vane test used for soils. The instrumentation, called herein Torque Penetrometric Test (TPT), is composed of a steel nail with four protruding teeth and a torque wrench. The test consists in inserting the toothed nail into a mortar joint and then applying a torque by means of a dynamometric key, until reaching the failure of the material. This work presents a novel interpretation theory based on basic concepts of fracture mechanics and applied to the micro-mechanical analysis of the stress state induced by the instrument on the investigated mortar. The proposed interpretative theory is validated through the execution of experimental tests in the laboratory and in a historical masonry building. The test proves to be effective for a quick in-situ MDT evaluation of the strength of existing mortars.Peer Reviewe