Microchim Acta (2008) 162: 325–331 DOI 10.1007/s00604-007-0927-4 Printed in The Netherlands Original Paper Chemical characterization of Cretan clays for the design of restoration mortars Meral Budak 1 , Pagona Maravelaki-Kalaitzaki 2 , Nikolaos Kallithrakas-Kontos 3 1 Mechanical Engineering Department, Izmir Institute of Technology, Izmir, Turkey 2 Ministry of Culture, 25th Ephorate of Prehistoric and Classical Antiquities, Chania, Greece 3 Analytical and Environmental Chemistry Lab, Technical University of Crete, Chania, Greece Received 31 December 2006; Accepted 6 December 2007; Published online 17 March 2008 # Springer-Verlag 2008 Abstract. Three clays and a marly-limestone from the West of Chania, Crete, fired at temperatures ranging from 200 to 1200  C, were characterized by XRD, FTIR, EDXRF and wet chemical analyses. The aim of this study was to assess the pozzolanic and hydraulic properties of these materials for potential use as bind- ers in the design of restoration mortars. The mineral- ogical composition of the clays is quartz, illite, calcite, plagioclase, kaolinite and hematite. The identification of larnite and gehlenite in the calcined marly-limestone established it as potential cementious binder. Among the clays, one with low amount of calcite and consid- erable kaolinite content exhibited the best pozzolanic activity upon heating at 600  C. Therefore, it can be considered as an appropriate material for restoration purposes. It is deduced that the pozzolanic activity of fired clays is greatly dependent on the firing tempera- ture and is enhanced in clays containing low calcite and high kaolinite amounts. Keywords: Clays and marly-limestone; FTIR; EDXRF; calcina- tion; pozzolanic activity Mortar is a material resulting from the intimate mix- ture of binder, aggregates and water. The properties and characteristics of mortars mainly depend on the nature of the binder component [1]. The binder of the lime mortars is calcium hydroxide (portlandite), which is transformed in calcium carbonate upon reaction with carbon dioxide. The binders can be classified as non-hydraulic and hydraulic; hydraulic binders are mainly composed of calcium silicates, calcium alumi- nates and calcium hydroxide [1, 2]. The aggregates used in lime mortars include sands, gravels and crush- ed materials, as well as pozzolanic materials introduc- ing a degree of chemical set to the mortar [3]. Pozzolanic materials are natural substances or in- dustrial by-products having partially crystalline struc- ture formed by silica, siliceous aluminous compounds or a combination of both. Natural pozzolans include materials such as diatomaceous earths, opaline cherts and shales, tuffs and volcanic ashes. The artificial pozzolans are obtained by heat treatment of natural materials such as clays, shales and pulverized fuel ash [4]. Pozzolans do not harden when mixed with water; in the presence of water, when pozzolans are finely powdered, are able to react with lime at ambient temperature, to form hydrated calcium silicates and to develop suitable mechanical strengths for mortar. The term pozzolanic activity denotes the ability of a Correspondence: Nikolaos Kallithrakas-Kontos, Analytical and Environmental Chemistry Lab, Technical University of Crete, 73100 Chania, Greece e-mail: kalli@mred.tuc.gr