Hydraulic mortars for joining archaeological stone fragments – A methodological approach

Abstract

A methodological approach, followed for the development of compatible repair mortars, for joining archaeological stone fragments of marl limestones, is presented. The development of compatible mortars for joining archaeological stone fragments requires an in-depth study of mechanical and microstructural properties of both stone substrate and mortar mixtures. Therefore, this work focuses on the evaluation of the stone-repair mortar interface, based on the interpretation of mechanical properties of both individual stone and mortar specimens as well as, of joined stone specimens with different types of adhesive mortar mixtures. The cementing material used in the different repair mixtures was: white cement, natural hydraulic lime and lime-metakaolin mixed binder. The binders were further modified with metakaolin to adjust hydraulicity and mechanical strength. The evaluation of adhesion strength and compatibility parameters was based on unconfined compression, three-point flexural bending and four point bending tests. It was shown that mechanical properties of join mortars can be adjusted by modifying the binder chemistry. Moreover, it was proved that adhesion strength is more relevant to the total surface area and porosity of the binder rather than compressive strength of the mortar.