Clay-Based Materials in Geopolymer Technology

Abstract

The term "geopolymer" was introduced by Davidovits in the 1970s. The prefix "geo" was selected to symbolize the constitutive relationship of the binders to geological materials, natural stone and/or minerals. Geopolymer is mineral polymers of inorganic polymer glasses with structure resembling natural zeolitic materials. Previously, geopolymer formation used source materials such as clay (e.g. kaolin and calcined kaolin) or industrial by-product (e.g. slag and fly ash). The precursor material plays an important role in the formation of geopolymer. The source material provides silicon (Si) and aluminum (Al) for reaction by an alkali activator solution. The Si and Al contents in the source materials dissolve in the alkaline activator solution and then polymerize to form a polymeric Si-O-Al-O framework which becomes the binder. Geopolymeric materials are attractive because of their excellent mechanical properties; durability and thermal stability can also be achieved. Owing to their low calcium content, they are more resistant to acid attack than materials based on Portland cement. In addition, they are of great interest because of the reduced energy requirement for their manufacture and the higher sustainability. Recently the search for alternative low cost and easily available materials led among others to Clay. Clay generally consists of a mixture of different clay minerals and associated minerals, which are strongly affected by the nature of the parent rocks. These materials are extensively distributed over the surface of the world and may show certain reactivity after a thermal activation process shows a great potential to be utilized in geopolymer technology. This article presents the potential of different types of clay as the source materials for geopolymerization reaction in terms of morphological properties. Moreover, the mechanical and microstructural properties of geopolymer made with various kinds of clay and its potential application are also presented.The aluminosilicate sources are materials rich in alumina and silica content (e.g. ashes [11][12][13][14], clays [15,16] or slag [17,18]). Some other natural and artificial silicoaluminates such as zeolite [19] and magnesium-contained minerals [20] have also been used as an important source of Si 4+ and Al 4+ ions in the geopolymer binding system. Normally, the total composition of Al 2 O 3 and SiO 2 is more than 70%, preferable in reactive amorphous phase [3,21]. In this book chapter, the utilization of clay or clay minerals in geopolymer formation is discussed. Kaolin/kaoliniteKaolinite is the most common clay mineral used in geopolymer synthesis. It has 1:1 uncharged dioctahedral layer structure (Figure 2a) whereby the layers are (Si 2 O 5 ) n 2− sheet and the Al(OH) 3 (gibbsite) sheet linked by sharing oxygen atoms. The layers are held together by weak van der waals and hydrogen bonds leading to the layered structure (Figure 2b). Figure 2. Structure of kaolinite (above) and microstructure of kaolinite (below) [22]. Clay-Based Materials in Geopolymer ...

Alkaline Activation of Kaolin Group Minerals

“…The results are shown in Figure 7. Generally, the strength achieved by geopolymers based on clay minerals is relatively low compared to materials based on fly ash or blast furnace waste [20]. In the case of this work, these values did not exceed 12 MPa.…”

Clayey soils from Boulgou (North Cameroon): geotechnical, mineralogical, chemical characteristics and properties of their fired products

“…Above this temperature, firing shrinkage values were beyond the industrial limits for brick production [30]. The bulk density values increased from 1.7 to 2.3 g/cm 3 (at 1200 °C), confirming the mineralogical transformations that occurred such as mullite formation originating from the melting of feldspar. However, and according to [4,30] the presence of smectite, mineralization may limit the extent of densification at temperature less than 1000 °C, due to the fact that its dehydroxylation is followed by expansion of the crystal network.…”

“…contributes to the development of the local economy (creation of local jobs that cannot be relocated). Many researchers are focusing their works on clayey soils in engineering applications such as geopolymers for road and building materials [3], ceramic application for fired bricks and porcelains [4][5][6][7] and materials for backfill and core of earth fill dams [2,[8][9][10][11]. In North Cameroon, clayey soils at Boulgou are extracted by the local population for pottery, plastering walls of houses and the production of construction materials (adobes and fired bricks using clamp kilns).…”

Low-Grade Clay as an Alkali-Activated Material

“…All of the mortar specimens showed an increase in crystalline content, suggesting the presence of zeolites rather than an amorphous geopolymeric phase [56,57]. It is hypothesized that the growth of zeolite crystalline phases is supported by the high water content and the employed high curing temperature [58].…”

“…The peak at 470 cm −1 could be due to the Si-O in-place bending vibration or Fe-O-T stretching. The band at 540 cm −1 is due to the Si-O-Al (VI) bending vibrations from the kaolinite and illite [54,57,64].…”