Ž . Construction and Building Materials 14 2000 3546 Physico-chemical adhesion and cohesion bonds in joint mortars imparting durability to the historic structures A. Moropoulou  , A. Bakolas, K. Bisbikou Department of Chemical Engineering, Section of Materials Science and Engineering, National Technical Uni  ersity of Athens, 9 Iroon Polytechniou, 15780 Athens, Greece Received 14 April 1999; received in revised form 2 August 1999; accepted 25 August 1999 Abstract It is well known that even though historic mortars present low strength and elastic moduli they confer durability to the structures surviving today. The present work investigates the durability of historic mortars in relation to the production technologies employed. Thermal analysis allows for classification of historic mortars in both lime and hydraulic types. Mineralogical data, concerning fabrication and texture, along with thermal analysis provide criteria on specific classification, for: typical lime, crushed brick  lime, cementitious, rubble masonry, hot lime technology and gypsum mortars. The correlation of the Ž . measured tensile strength fmt, k with the estimated CO structurally bound water ratio, indicates direct proportionality to the 2 levels of the hydraulicity. Physico-chemical adhesion and cohesion bonds, studied by SEM-TEMEDX, developed at the matrix and at the binderaggregate interface, respectively, becomes the key factor in interpreting the considerable durability that the historic mortars confer to the structures as bearing elements.  2000 Elsevier Science Ltd All rights reserved. Keywords: Historic mortars; Adhesion and cohesion bonds; Durability of historic structures 1. Introduction Although mortars seem to be simple systems, in reality they are very complicated multi-phase compos- ites, comprised of crystalline and amorphous phases and containing inert as well as reactive aggregates. The presence of reactive additives can cause various chemi- cal reactions which make it difficult to differentiate  newly formed compounds from the older ones 1 . Historic composites concern ‘disturbed’ systems, as in ‘service’ for decades of centuries under severe me-  Corresponding author. National Technical University, Chemical Eng. Dept., Mater. Sci. & Section, Zograou Campus, 157 80 Zo- graou, Athens, Greece. Tel.: 30-1-772-3276; fax: 30-1-772-3215. Ž . E-mail address: amoropul@central.ntua.gr A. Moropoulou chanical and environmental loadings. Therefore, the characterization of such materials can be achieved by integrating properly the results of the various analyses, in order to understand the procedures employed to produce the final composites and the nature of the physico-chemical bonds developed among its con-   stituents 2  4 . It is obvious that the relatively low strength of old mortars does not explain their longevity. Historic structures can be considered as early con- crete structures, when cohesion and adhesion pheno- mena among binding material and active aggregates or   mortar and building units are established 3,5 8 . On the contrary, it has been found that weak adhesion bonds affect negatively the durability of the masonry, especially when physico-chemical phenomena, like dis- solution, transport and recrystallization of salts leading  to salt decay, occur 6 . 0950-061800$ - see front matter  2000 Elsevier Science Ltd All rights reserved. Ž . PII: S 0 9 5 0 - 0 6 1 8 99 00045-8