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INORGANIC GEOPOLYMERS SYNTHESIZED USING BLACK CLAY AS PRECURSORS BASED ON KAOLINITE SYSTEM
E. Bonet-Martínez, L. Pérez-Villarejo , D. Eliche-Quesada
Keywords: Geopolymers, Alkali-activation, Black clay, mechanical properties 1. Introduction
Inorganic polymers, or geopolymers, constitute a new class of materials synthesized from materials of aluminosilicate nature (clays and kaolin) and an alkaline activator. The geopolymers can be used in multiple applications, ranging from their use as a cementitious material (Sturm et al., 2016) to their use as a catalytic support (Azeer et al., 2016), and even as a reinforcing matrix for composite materials with fibers (Alshaaer et al., 2017).
Geopolymers are inorganic aluminosilicate polymers synthesized by alkali activation of Si- and Al-rich materials at near-ambient temperatures (Komnitsas et al., 2007).
For the synthesis of geopolymers, the chemical reaction between amorphous silica and alumina in combination with a highly alkaline environment at or slightly elevated temperature is used to form a three-dimensional polymer gel of Si-O-Al-O-Si (Hwang et al., 2015).
The objective of this research is to produce metakaolin and black clay-based geopolymeric materials for alkaline activation, using waterglass and sodium hydroxide.
2. Material and methods
The geopolymeric materials were prepared using metakaolin (MK), provided by the Caobar, S.A. located in Taracena (Guadalajara, Spain) and black clay (AN) obtained from clay quarries located in Bailén.
For alkaline activation, a mixture of hydrated sodium silicate (Panreac S.A.; 8,9 wt. % Na2O, 29,2 wt. % SiO2 and 61,9 wt. % H2O) and NaOH (reactive grade, 98 wt. %, Panreac S.A) was used. The NaOH solution was prepared in distilled water (8 M).
The geopolymers were prepared with five different compositions: pure MK ( 100 % MK, Si/Al=1.63) and four other compositions, such as MK-25BC (75% MK, 25% BC with a ratio Si/Al = 1.90), MK-50BC (50% MK, 50% BC, Si/Al = 2.29), MK-75BC (25% MK, 75% BC, Si/Al = 2.91) and 100BC (0% MK, 100% BC, Si/Al = 4.06). The synthesis was carried out by mixing the raw materials for 10 minutes. Subsequently, the activating solution was added and stirred for 10 minutes and, then, the generated slurry was transferred to plastic molds. The samples were cured under controlled conditions (70 oC) for 24 h and curing for 7 days at room temperature.
Geopolymers were characterized by XRD, ATR-FTIR. Microstructural analysis and FTIR scanning were used to examine the progress of the geopolymer reaction during the curing stage.
The bulk density (kg/m3) was determined by Archimedes method. Water absorption capacity (wt.%) was determined according to the standard procedure UNE 772-21:2011 from weight
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