Available online at www.sciencedirect.com Journal of the European Ceramic Society 29 (2009) 3121–3128 Durability of clay rooﬁng tiles: the inﬂuence of microstructural and compositional variables M. Raimondo a,∗ , C. Ceroni b , M. Dondi a , G. Guarini a , M. Marsigli c , I. Venturi a , C. Zanelli a a CNR – Institute of Science and Technology for Ceramics, Via Granarolo, 64, 48018 Faenza, Italy b Department of Applied Chemistry and Material Science, Engineering Faculty, University of Bologna, via Terracini, 28, 40138 Bologna, Italy c CertiMaC, S.r.l., via Ravegnana, 186, 48018 Faenza, RA, Italy Received 5 February 2009; received in revised form 14 May 2009; accepted 10 June 2009 Abstract The frost behaviour of 13 industrially manufactured rooﬁng tiles was assessed through a double approach: performing severe freeze/thaw testing (EN 539-2) and calculating durability indices, according to models present in the literature. The products microstructure was fully investigated in terms of physical, technological and compositional parameters, and the results correlated with the frost resistance of rooﬁng tiles. No prediction model was able to reliably foresee the product performances; in particular, the correspondence with the excellent experimental behaviour of the most resistant samples is lacking. Coupling microstructural with compositional variables, new indications came out concerning the design and production of rooﬁng tiles able to withstand adverse climatic conditions. If, once again, bulk density can be considered as the most inﬂuent parameter (highest values involve an improved durability), the production of rooﬁng tiles with excellent frost resistance involves also the evaluation of an increased number of product (i.e. raw materials composition, microstructure and phase composition) and processing (i.e. ﬁring temperature) variables. © 2009 Elsevier Ltd. All rights reserved. Keywords: Frost resistance; Traditional ceramics; Structural ceramics; Porosity; Microstructure-ﬁnal 1. Introduction Nowadays, clay rooﬁng tiles are widely used as exterior build- ing components and their durability, intended as the ability to withstand adverse climatic conditions, is one of the most impor- tant requirements to be considered in the structural design of modern buildings. 1,2 The deterioration of construction mate- rials may be due to several factors; among them, design and construction techniques, environmental conditions and material properties may be, in most cases, considered predominant over other causes. 3 In particular, in cold climates, the service lifetime of clay-based components is heavily affected by frost action and salt crystallization. 4,5 Frost action is produced when the temperature falls below 0 ◦ C and the water included in the material porous structure starts freezing; the density change at the liquid–solid water tran- sition implies the development of an internal pressure, leading ∗ Corresponding author. Tel.: +39 0546 699718; fax: +39 0546 46381. E-mail address: mariarosa.raimondo@istec.cnr.it (M. Raimondo). to the formation of micro-cracks whose extent can overcome the mechanical resistance of the material, hence promoting inescapable damages. 6 The extent of these damages will be strictly dependent on the exposed surface area, as well as on the number and size of pores 7–9 and the saturation degree of the material. 9,10 For pore dimensions greater than a critical value and/or for a low saturation degree, the pressure developed, and hence damages, will be negligible since the free space within pores accommodates the expansion of the freezing water. On the opposite, when unfavourable climatic conditions are cou- pled with the presence of a high volume of capillary pores, the material ability to absorb water is increased 11 and severe structural damages, varying from surface scaling to complete disintegration, may occur. Owing to these circumstances, the material characteristics, which in turn depend on the raw mate- rial formulations, 12 the shaping process and the ﬁring cycle, 13–15 become a key factor in the evaluation of the deterioration risk connected with frost action. 16–18 Many papers in the ﬁeld of civil engineering have anal- ysed the factors affecting the durability of some construction materials (e.g. concrete), while freezing and thawing of 0955-2219/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2009.06.004