Microstructure and engineering properties of Fe2O3(FeO)-Al2O3-SiO2 based geopolymer composites
Introduction
Laterites and lateritic soils, described as Fe2O3(FeO)–Al2O3–SiO2–H2O matrices, are made from kaolinite in which a high proportion of Al3+ is replaced by Fe2+ or Fe3+ (Lyon Associates, Inc., 1971; Kamseu et al., 2013a, Kamseu et al., 2013b, Obonyo et al., 2014). These materials are available in tropical and sub-tropical areas of the world, with nearly 67% found in the Cameroonian territory (Mbumbia et al., 2000). The replacement of aluminium by iron atoms in kaolinite structure affects their crystallinity with consequent increase of amorphous content and enhance their vulnerability to chemical attack (Obonyo et al., 2014; Pignatelli et al., 2014; Kaze et al., 2017). Geopolymers produce from natural iron-rich aluminosilicate (laterites) without treatment should be eco-friendly and more greener in comparison of metakaolin based geopolymer which requires an energy for the thermal treatment in the range of 700–800 °C (Kamseu et al., 2012; Elimbi et al., 2014, Kamseu et al., 2014, Tchakouté et al., 2016). The use of laterites as raw materials for the development of geopolymers might be considered as the way for the reduction of amount of CO2 emitted from cement industries and also the energy used to activate the clay materials. As reported by Kamseu et al., 2013a, Kamseu et al., 2013b and Obonyo et al. (2014), it is easier in tropical areas to have laterites, generally at the surface, than struggle for clays for which exploitation will be detrimental for the environment because they are covered in most cases by laterites or various types of soils. Therefore a sustainable materials from activated laterites locally sourced, with negligible transport costs and environmental impact, will present thermal efficiency, financial viability and low energy required in the manufacturing process as mentioned by Duxson et al. (2007).
This paper is the second in a series of articles describing the use of laterite for the development of geopolymer composites. It explores the engineering properties of two laterites, with similar degree of laterisation (∼35 wt% of FeO(Fe2O3)) used for the preparation of alkali activated materials, hereafter indicated as geopolymer composites, with addition of rice husk ash under different curing conditions.
Physical and chemical properties of laterites based geopolymers were described in the first paper (Kaze et al., 2017). We observed that, the values of flexural strength of laterites based geopolymers are similar to those of standard metakaolin based geopolymers and decrease with the thermal activation of solid precursors above 500 °C (Kaze et al., 2017). The setting time and the water absorption also decreased with thermal treatment of laterite. Their microstructure appeared coarse and more inhomogeneous with the increase of the calcined temperature above 500 °C. In recent times these soils were valorised as potential candidate for the development of geopolymer cements (Cristiane et al., 2010, Kamseu et al., 2013a, Kamseu et al., 2013b, Obonyo et al., 2014; Ninla et al., 2014; Lassinantti et al., 2015, Ab Aziz et al., 2015, Kaze et al., 2017) while others preferred mixtures with cement (Jayasinghe and Mallawaarachchi, 2009). The most used of traditional precursor materials for geopolymers are like metakaolinite (Fe2O3 content of 2–5%), fly ash (Fe2O3 content of 10%), volcanic scoria (10–15%) and blast furnace slag (Fe2O3 content of 0.5%). Nevertheless, recent studies have shown that precursors with iron content higher than the usually found in fly ashes and volcanic scoria may be activated in alkaline environment (Kaze et al., 2017, Gomes et al., 2007, Kamseu et al., 2013a, Kamseu et al., 2013b, Obonyo et al., 2014; Ninla et al., 2014) with potential applications in engineering. Gomes et al. (2007) observed that, the alkaline activation of raw material with high iron and low aluminium content produced the geopolymer with compressive strength ranging from 20 to 80 MPa. Obonyo et al. (2014) reported that the addition of calcined low iron content laterite (up to 30% mass) to poorly reactive natural laterite in alkaline medium, led to geopolymers with improved 28 days physical and mechanical properties. The detailed microstructure of products of the geopolymerization of laterites revealed low level of homogeneity and phase distribution although the relative good mechanical strength in comparison with standard geopolymer cements. The presence of some large capillary pores also affect the final properties of products of geopolymerization of laterites. In our point of view the poor homogeneity and larger and non-homogeneous porosity are due to alumina and iron-rich oligomers that remain unbounded to the geopolymer system after geopolymerization. This study aims to investigate the possibility of using rice husk ash (RHA) as SiO2 source for the improvement of the strength and stability of Fe2O3(FeO)-Al2O3-SiO2 systems, sustainable inorganic polymers materials (geopolymers). We plan the experimental design so that sufficient amount of soluble silica added to the laterite-based geopolymer composites will combine all the residual Al and Fe-oligomers that do not react effectively in laterites. The soluble silica provides Si-based oligomers to develop more bending phases. The three-point flexural strength was used as an indicator for the bending bonds development. The microstructural analysis of geopolymer composites was done through Environment Scanning Electron Microscope (ESEM) analysis to understand the features of the composites. The Mercury Intrusion Porosity (MIP) and water absorption were also studied to evaluate and appreciate the pore sizes distribution within specimens. The main factors that govern our investigations include percentages of RHA (SiO2 source) and curing process.
Section snippets
Materials and characterization
The iron-rich aluminosilicates (laterites), LATOD and LATEL, used in this study were extracted respectively at laterite deposit of Odza and Eloumden (Yaoundé town, Central Region of Cameroon). These materials are currently used in roads construction by the enterprise RAZEL Cameroon, Yaoundé, Cameroon as in earth fill dam and highway. The dried raw materials were ground with a grinder (model BULLI I. PIAMO, M.M.S., Modena, Italy) for 4 h (rpm = 1200) in order to have fine powders with particles
Effect of amorphous silica (RHA)
The geopolymerization products of laterite (35% FeO(Fe2O3)) have shown the flexural strength in the range of 4–6 MPa, with water absorption less than 13% and similar to the characteristic properties of metakaolin based geopolymer (Kaze et al., 2017). Despite these properties, the microstructure of laterite based geopolymer exhibited more cracks, large pores, with the poor distribution of grains into the matrix (Fig. 3). The thermal treatment of starting materials at temperature >500 °C (600 and
Discussion
The action of RHA in laterites based geopolymer composites yields better reactivity and more polycondensation together with the formation of more dense interpores spaces that in this case substitute the matrix. The laterites based geopolymer composites with high volume of RHA evidenced a fundamental difference for the standard curing at room temperature and the curing at temperatures around 90 °C. While the curing at room temperature gave the flexural strength that remained between 8 and
Conclusions
Two laterites with similar degree of laterisation and iron content (∼35 wt%) used in the present study as solid precursors were mixed with quartz sand, rice husk ash and alkaline solution for the production geopolymer composites under different curing conditions. The laterites based geopolymer composites appear more sustainable, low cost and environmentally-friendly. The solid precursors that do not need pretreatment appear ideal raw materials for the cleaner production of eco-friendly cements
Acknowledgments
The authors are grateful to Ingessil S.r.l., Verona, Italy, for providing sodium silicate used in this study. This project received the contribution of the Academic of Science for the Third World TWAS through the funding grant no. 15-079 RG/CHE/AF/AC_I to Dr. Elie Kamseu.
References (36)
- et al.
Thermal behavior and characteristics of fired geopolymers produced from local cameroonian metakaolin
Ceram. Int.
(2014) Iron silicate scale formation and inhibition at the salton sea geothermal field
Geothermics
(1989)- et al.
Characterization of geothermal scale deposits by Fe-57 mossbauer spectroscopy and complementary X-ray diffraction and infrared studies, geothermics
Geothermics
(1991) - et al.
Study on solids-to-liquid and alkaline activator ratios on kaolin-based geopolymers
- et al.
Flexural strength of compressed stabilized earth masonry materials
Mater. Des.
(2009) - et al.
Bulk composition and microstructure dependence of effective thermal conductivity of porous inorganic polymer cements
J. Eur. Ceram. Soc.
(2012) - et al.
Design of inorganic polymer cements: effects of matrix strengthening on microstructure
- et al.
Cement & concrete composites metakaolin-based inorganic polymer composite: effects of fine aggregate composition and structure on porosity evolution, microstructure and mechanical properties
- et al.
Substitution of sodium silicate with rice husk ash-NaOH solution in metakaolin based geopolymer cement concerning reduction in global warming
J. Clean. Prod.
(2017) - et al.
Applied clay science the corrosion of kaolinite by iron minerals and the effects on geopolymerization
Synthesis and characterization of geopolymer binders based on local materials from Burkina Faso Metakaolin and rice husk ash
Construct. Build. Mater.
Influence of compaction effort for laterite soil mix with geopolymer in designing soil liner
Electron. J. Geotech. Eng.
Natural ferrihydrites in surface deposits from Finland and their association with silica
Geochem. Cosmochim. Acta
Geopolymers of the first generation: SILIFACE-Process
Geopolymer Cement of the Calcium Ferro-aluminosilicate Polymer Type and Production Process
A study of the infrared absorption in the oxidation of magnetite to maghemite and hematite:mines branch
Inv. Rept
Geopolymer bonded steel plates
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