Engineering properties, phase evolution and microstructure of the iron-rich aluminosilicates-cement based composites: Cleaner production of energy efficient and sustainable materials

This paper investigates the direct transformation of laterites (natural iron-rich aluminosilicates) to cementitious composites with principal mineral phases being Gismondine and Stratlingite. The effects of particles size distribution and cement content (2 to 8 wt%) on the mechanical properties and microstructure of laterite-cement composites are assessed. Four grades of granulometry with various percentages of fine and coarse particles were considered. The Environment Scanning Electron Microscopy (ESEM), Mercury Intrusion Porosimetry (MIP), Fourier Transformed Infrared Spectroscopy (FT-IR) and X-ray Powder Diffractometry (XRD) were performed after 1, 90 and 365 days, to assess the phase's evolution, mechanical performance and the microstructure of the laterite-cement composites. It is found that fines particles, essentially pozzolanic and amorphous, are responsible for the bonding strength while coarse particles improve the compressive strength. Dense and compact microstructure, water absorption under 18% and flexural strength above 6 MPa (compressive strength > 30 MPa) could be achieved as from 4 wt% of cement making the laterite-cement composite appropriate as building and construction materials. The choice of a highly corroded class of laterite and the selection of the particle size distribution allows the production of optimum composite that is presented as energy-efficient and sustainable. Thus, corroded or indurated laterites are considered as “green metakaolins” which do not require any energy for their transformation unlike clayey materials

Refractory ceramics bonds from potassium-based inorganic polymer for advanced applications: Crystalline phase changes and descriptive microstructure

Understanding the structural and meso-scale properties of alkali activated matrices subjected to high temperature treatment, provides useful information on the stability of their self-life service or, fire resistance in extreme environments. The current project focuses on the transformation of phase and structural bonds within kyanite-reinforced refractory geopolymer. After being exposed to temperatures ranging from 1050 °C to 1250 °C, the micro-structural and macro-scale properties of the resulting matrices were evaluated using X-ray diffraction, chemical bond analysis, SEM-EDS, and resistance to flexural strengths. The fineness of the kyanite powder played an important role in the geopolymer composites' bonding system, as well as the crystallization of the cordierite phase during the sintering process. Further decomposition of kyanite minerals limited the thermal expansion to less than 0.8%, suggesting the formation of new and stronger bonds between the particles, which result in the formation of crystalline phases such as: cordierite, mullite, leucite and enstatite. These phases render the matrices compact and dense. Based on the findings, kyanite particles were discovered to be refractory components and fillers in the formation of refractory alkali-bonds ceramics, with environmental and eco-friendly benefits

Innovative porous ceramic matrices from inorganic polymer composites (IPCs): Microstructure and mechanical properties

The thermal performance of pegmatite-based geopolymer composites is investigated. Dense and compact matrix was prepared replacing metakaolin with pegmatite in the range of 70\u201385 wt% and activate with sodium hydroxide/sodium silicate solution in 1:1 vol ratio. The products of geopolymerization, cured at room temperature for 28 days, were heated at 100, 200, 400, 600, 800, 900, 1000 and 1100 \ub0C with 2 h soaking time. The high values of flexural strength (46\u201351 MPa) were observed at 1000 \ub0C as the consequences of low porosity (173 mm3/g) and water absorption (4.50\u20135.62%). The increase of the vitrification at 1100 \ub0C enhanced the liquid phase and develop porosities responsible for reduction of strength. The mechanical properties, microstructural evolution and pore size distribution were found to be influenced by the amount of fine powder of pegmatite (solid solution)