Materials Science and Engineering A 527 (2010) 3936–3941 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Study of hydrated phases present in calcined paper sludge (metakaolinite)/saturated CaO dissolution system cured at 40 ◦ C and 28 days of reaction Rosario García a,∗ , Raquel Vigil de la Villa a , Olga Rodríguez b , Moisés Frías b a Departamento de Geología y Geoquímica, Facultad de Ciencias, Universidad Autónoma, C/Francisco Tomás y Valiente 7, 28049 Madrid, Spain b Eduardo Torroja Institute (CSIC), c/Serrano Galvache 4, 28033 Madrid, Spain article info Article history: Received 8 January 2010 Received in revised form 24 February 2010 Accepted 25 February 2010 Keywords: Paper sludge Metakaolinite Stratlingite C-S-H gel Tobermorite Hydrotalcite abstract The present research is a part of an experimental study about obtaining recycled metakaolinite from a Spanish paper sludge waste as complementary cementing material. The mineral phases formation from paper sludge calcined at different temperatures (700, 750 and 800 ◦ C) and two times of stay in the furnace (2 and 5 h) mixed with saturated lime dissolution are obtained mineral phases: C-S-H gel, stratlingite, tobermorite, hydrotalcite. The C-S-H gels generated in the first stages lose crystallinity and filled the existing holes between stratlingite and hydrotalcite. The different mineral evolves according to their stability fields toward crystalline aggregates more compact where the gels fill hollow. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The generated residues during cellulose and paper manufacture process are classified in the European waste catalogue (EWC) as not dangerous. The current paper residues production is used in ceram- ics industry, agricultural, compost and is all catalogued as clean. The utilization of any by-product, tailing, etc. until formed during an industrial process has, nowadays, high-priority character. One way of recycling these materials is to seek concrete applications of compatible use with their characteristics. Mineral admixtures will inevitably increase over the next few decades, to provide greater sustainability in construction, and there will therefore be pressures to maximize their effectiveness with regard to cost, environmental impact, durability and performance [1]. The cement industry has been the first in recycling and valu- ing industrial by-products and wastes as well as natural materials, incorporating them to the different production stages of the man- ufacture of blended cements [2,3]. In recent years, there has been a growing interest in the use of metakaolinite (MK) obtained from natural kaolinite, as a mineral admixture to enhance the strength and durability of concretes [4–9]. The paper sludge from paper industry is characterized because its composition has high organic matter content (cellulose) and ∗ Corresponding author. Tel.: +34 914974819; fax: +34 914974900. E-mail address: rosario.garcia@uam.es (R. García). inorganic compounds, as clays, calcium carbonate, that under a con- trolled calcination transform the clayey materials, mainly kaolinite, into calcined products, metakaolinite [10,11], through the thermal activation and achieving high pozzolanic properties. It is reported the high pozzolanic activity of these calcined paper sludge from other industrial pozzolanic by-products used normally in cements like fly ashes, silica fume, blast-furnace slag, e.g. [12–14]. The optimal conditions to get maximum pozzolanic activity of paper sludge are 700 ◦ C and 2 h of stay in furnace in the range studied (700–800 ◦ C) [15–19]. The aim of the present work is study the formation of hydrated mineral phases formed by reactions in the metakaolinite (MK)/saturated CaO dissolution system cured at 40 ◦ C and 28 days of reaction, when the MK comes from paper sludge calcination at different temperatures and stays of furnace. The present research is a part of an experimental study about obtaining recycled metakaolinite from a Spanish paper sludge waste as complementary cementing material. 2. Experimental procedures 2.1. Preparation of the samples The starting materials were recycled metakaolinite (MK) that come from calcined paper sludge (CPS) at 700, 750 and 800 ◦ C and two times of stay in furnace (2 and 5 h). These temperatures were selected according to the pioneer studies carried out by Pera et 0921-5093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2010.02.075