Experimental Characterization of Solid Clay Bricks: Correlations Among Mechanical Properties

Strengthening interventions on existing structures, especially in the case of Architectural Heritage, require an in-depth knowledge of construction techniques, geometry and materials for an optimal design aiming at the minimum intervention approach ideal. Nonetheless, conservative values of material properties, often derived from codes or literature, might hinder the effectiveness of the design approach. Non-Destructive Tests (NDT) and Minor Destructive Tests (MDT) are fundamental tools for the characterization of existing materials with a minimum or no impact. The paper presents an experimental study that investigated the possibility of defining empirical correlations among the main mechanical properties of solid clay bricks, which are one of the most common unit for masonry load-bearing members. Extruded bricks, typical of modern constructions, and soft-mud bricks, resembling historical units, were tested to cover for the ample variability of solid clay bricks. The examined mechanical properties were compressive, bending, splitting and pull-off strengths. The dataset of mechanical properties allowed calibrating linear correlations expressing one property as a function of another, thus giving the possibility of estimating a set of strengths based on the results of the MDT pull-off test. An innovative aspect consisted in performing the four tests on the same unit, so that the calibrated linear correlations are based on punctual data instead of average values. A practical application can consist in the on-site execution of pull-off tests, which are minor destructive and can be easily performed on a wall surface, for estimating the compressive strength of clay units.