Research paper Valorization of pozzolanicity of Algerian clay: Optimization of the heat treatment and mechanical characteristics of the involved cement mortars Siline Mohammed a,b , Ghorbel Elhem b, ⁎, Bibi Mekki a a University of M'sila, Algeria b L2MGC, University of Cergy Pontoise, 5 Mail Gay Lussac, Neuville Sur Oise 95031, France abstract article info Article history: Received 30 March 2016 Received in revised form 26 August 2016 Accepted 27 August 2016 Available online xxxx The aim of this study is to optimize the pozzolanicity of Algerian clay deposits that are essentially composed by calcite, dolomite, and illite/muscovite. The heat treatment cycles were applied to these raw materials deposits by varying target temperature and the holding time. The evaluation of dehydroxylation degrees is determined by different techniques such as thermal gravimetric (TG) analysis, differential scanning calorimetric (DSC) analysis and Fourier transform infrared spectroscopy (FTIR). Results show that the optimal pozzolanicity was obtained, if the clay is calcined at 700 °C for 5 h. Moreover, adding 10% of the heat-treated clay deposit to 85% of clinker and to 5% of gypsum by weight leads to manufacturing blended cements with the highest mechanical characteristics. Mortars elaborated with the blended cements were studied and their compressive strengths after exposure to high temperature up to 1000 °C were investigated through compressive test up to the age of 90 days. It appears that adding heat-treated clay to clinker enhances strengths of normalized mortars at early age by comparison to those elaborated with CEM I. However, opposite effects were observed for ages up to 28 days except for blended cements with clay treated at 700 °C-5 h. This was related to the presence of new cementitious compounds (NCC) highlighted by TG analysis. The behavior of mortars after exposure to high temperatures is not affected signifi- cantly when blended cements are used. The optimum blended cement is elaborated with deposit clay calcined at 700 °C for 5 h. Concretes manufactured with this blended cement exhibit quite similar compressive strengths than the control one. © 2016 Elsevier B.V. All rights reserved. Keywords: Cement Thermal treatment Pozzolanicity Calcined clay Dehydroxylation High temperatures 1. Introduction The Portland cement is made of ground clinker and calcium sulfate. Its production is one of the world's largest CO 2 sources with emissions amounted to 29.4 Tg CO 2 6(Emad et al., 2012). The release of CO 2 from the cement takes place at two stages: during the combustion of fossil fuels related to the production of the clinker and by chemical reac- tions that convert limestone into calcium oxide and carbon dioxide. The partial substitution of the clinker by some additions leading to a blended Portland cement CEM II is among the solutions proposed to re- duce the level of CO 2 emissions from cement production. The additions may be inert such as limestone or active like slag, fly ash and pozzolan used to improve some characteristics of concretes and mortars as the strength (Kadri et al., 2011), the durability (Siddique and Klaus, 2009) or the transfer properties (Paiva et al., 2012). The enhancement of these properties, when active additions are incorporated, is linked to the pozzolanic reaction that produces, in presence of water, new ce- mentitious compounds (NCC) by fixing the portlandite released during Portland cement hydration: calcium silicate hydrates (C \\ S \\ H), calci- um aluminate hydrates (CAH), and calcium alumino-silicate hydrates (CASH) (reaction (1)). Pozzolan þ Portlandite þ H 2 O → NCCðC\S\H; CAH; CASHÞ ð1Þ The pozzolanic additions have been widely used because of their binding properties. They might be natural, as volcanic rocks, or artificial, like fly ash and heat-treated clays, which composed essentially of kao- linite that becomes metakaolin after an adequate heating, which allowed to release all water chemically bounds. Such additions are the subject of the NF P18 513 standard and many studies (Bich et al., 2009; Grilo et al., 2014; Mansour et al., 2011; Ramezanianpour and Jovein, 2012; San Nicolas et al., 2013; Tironi et al., 2012). It follows that the kaolinite heat treated between 600 and 850 °C develops pozzalanic properties so that when added at 10–30% in cement, it en- hances significantly physical and mechanical performances of mortars. Other clays and clay minerals as montmorillonite (Changling et al., Applied Clay Science xxx (2016) xxx–xxx ⁎ Corresponding author. E-mail addresses: silinemohammed@gmail.com (S. Mohammed), Elhem.ghorbel@u-cergy.fr (G. Elhem), bibi_mekki@yahoo.fr (B. Mekki). CLAY-03964; No of Pages 11 http://dx.doi.org/10.1016/j.clay.2016.08.027 0169-1317/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Please cite this article as: Mohammed, S., et al., Valorization of pozzolanicity of Algerian clay: Optimization of the heat treatment and mechanical characteristics of the involved ..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.08.027