Jul 14, 2010 - It has a specific area of 0.35 m2/g (Blaine fine- ness), average ..... In: Kogel Jessica Elzea, Trivedi Nikhil C, Barker James M, editors. US; 2006.
Construction and Building Materials 25 (2011) 163–170
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of red mud addition on the rheological behaviour and on hardened state characteristics of cement mortars L. Senff a,*, D. Hotza b, J.A. Labrincha a a b
Department of Ceramics and Glass Engineering, Centre for Research in Ceramics and Composite Materials (CICECO), University of Aveiro, 3810-193 Aveiro, Portugal Department of Chemical Engineering (EQA), Federal University of Santa Catarina (UFSC), 88040-900 Florianópolis, SC, Brazil
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Article history: Received 6 April 2010 Received in revised form 7 May 2010 Accepted 19 June 2010 Available online 14 July 2010 Keywords: Red mud Mortars Rheology Flow table test Design of experiments
a b s t r a c t This paper reports on the use of red mud (RM) in mortars, applying design of experiments. Portland cement was replaced up to 50 wt.% RM, adjusting the relative amount of water (34–38 wt.%) in order to get mortars with suitable workability as defined by rheometry and flow table measurements. Temperature of hydration, compressive strength and water absorption were also determined. RM decreases the workability and increases the torque, but causes lower impact than water variation. The effect on initial yield stress depends on water content. Mortars with similar spread on table show different behaviour along the rheology test. Values of spread on table follow a quadratic model and RM exhibited an interactive effect with water. RM did not change the hydration process, but above 20% the maximum temperature decreases. The reduction of compressive strength is not constant and depends on the water added. Its variation also follows a quadratic model. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The use of solid wastes in the building industry can contribute to achieve the sustainable development of certain industrial activities, while it might help to reduce production costs. Selected wastes may be considered alternative/secondary raw materials, gaining an intrinsic value in the market while costs for disposal are eliminated. This apparently easier change requires however deep and careful studies to perspective viable reuse ways for wastes or by-products [1]. The red mud is a residue generated in large scale from the Bayer process used to produce alumina. Through this process, bauxite is digested in a concentrated caustic soda (NaOH) solution at high pressure and elevated temperatures (270 °C), in order to obtain the alumina trihydrate (Al2O33H2O) [2,3]. This process leads to the formation of insoluble hydroxides where the impurities are concentrated, after proper washing, settling, and filtration operations. Such is the case of the red mud, containing goethite (a-FeOOH), hematite (a-Fe2O3), bohemite (cAlO(OH)), quartz (SiO2), sodalite (Na4Al3SiO12Cl), and gypsum (CaSO42H2O) as major phases, and calcite (CaCO3), whewellite (CaC2O4H2O), gibbsite (Al(OH)3), and TiO2 as minor components [2]. Obviously, the exact composition of the mud depends on the origin of bauxite and also on processing details. Physically, the red mud particles are fine (
