Sustainable iron-rich cements: Raw material sources and binder types

The bulk of the cement industry's environmental burden is from the calcareous source. Calcium is mostly available naturally as limestone (CaCO3), where almost half of the mass is eventually released as CO2 during clinker manufacture. Iron (Fe) is the fourth most common element in the Earth's crust surpassed only by oxygen, silicon, and aluminium; therefore, potential raw materials for alternative cements can contain significant amounts of iron. This review paper discusses in detail the most abundantly available Fe-rich natural resources and industrial by-products and residues, establishing symbiotic supply chains from various sectors. The discussion then focusses on the impact of high iron content in clinker and on ferrite (thermo)chemistry, as well as the importance of iron speciation on its involvement in the reactions as supplementary cementitious material or alkali-activated materials, and the technical quality that can be achieved from sustainable Fe-rich cements

Influence of the chemical and mineralogical composition on the reactivity of volcanic ashes during alkali activation

The influence of chemical and mineralogical compositions on alkali activation of four natural volcanic ashes was investigated. NaOH was used as the sole alkaline activator. The reactivity of the systems was studied with Differential Scanning Calorimetry. The X-ray spectra of reacted materials showed a mixture of amorphous and crystalline phases. The SEM micrographs showed that the dissolution of larger particles is incomplete while smaller particles dissolved in the activating solution forming the glassy aluminosilicate matrix. The infrared spectra showed a broad absorbance at 820-1250 cm-1and 480-600 cm-1 assigned to internal vibration of Si3O3Si and Si3O3Al in both raw volcanic ash and resulting inorganic polymers. The reactivity of the volcanic ashes was found to correlate with their amorphous fraction. The dry compressive strength of synthesized products from all the ashes were in the range 14-63 MPa, suggesting their possible utilization as building materials. However, the strength was found to decrease (1-28 MPa) after specimens' immersion overnight in water, but was partly or totally recovered after overnight drying at 90 C. © 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Influence of the activating solution composition on the stability and thermo-mechanical properties of inorganic polymers (geopolymers) from volcanic ash

The influence of the activating solution composition on the stability and thermo-mechanical properties of geopolymers made from a Cameroonian volcanic ash is investigated. NaOH, KOH solutions and silicate solutions with low modulus were tested. The samples are cured at 90 C and the mechanical strength increases up to 21 days. With NaOH the strength development is faster, with a dry and wet compressive strength respectively around 40 MPa and 20 MPa at 21 days. The largest particles only act as reactive filler while smaller particles dissolve in the activating solution as seen by SEM. Pure volcanic ash and synthesized materials consisted of mostly X-ray amorphous material with some newly formed crystalline phases. KOH specimens were found to be thermally more stable, shrinking less than 3% after heating till 1000 C. The obtained results suggest the possible use of the synthesized materials for building applications and low temperature refractories up to 700-800 C. © 2013 Elsevier Ltd. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Influence of the processing temperature on the compressive strength of Na activated lateritic soil for building applications

The present study investigates the suitability of alkali activation of a lateritic soil for building applications. Lateritic soil was found to contain kaolinite, associated with quartz and hematite minerals. Both the processing temperatures and the amount of NaOH used were found to influence the development of compressive strength which was in the range of 12-51 MPa and 2-23 MPa respectively for dry and wet specimens. The synthesized products were thermally more stable, containing crystalline and amorphous phases mainly resulting from the dissolution of kaolinite. The XRD, FTIR, SEM and TG/DTA analyses showed an incomplete dissolution of the starting minerals. © 2014 Elsevier Ltd. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Cleaner production of the lightweight insulating composites: Microstructure, pore network and thermal conductivity

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Effect of nano-clay on mechanical and thermal properties of geopolymer

The effect of nano-clay platelets (Cloisite 30B) on the mechanical and thermal properties of fly ash geopolymer has been investigated in this paper. The nano-clay platelets are added to reinforce the geopolymer at loadings of 1.0%, 2.0%, and 3.0% by weight. The phase composition and microstructure of geopolymer nano-composites are also investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) techniques. Results show that the mechanical properties of geopolymer nano-composites are improved due to addition of nano-clay. It is found that the addition of 2.0 wt% nano-clay decreases the porosity and increases the nano-composite's resistance to water absorption significantly. The optimum 2.0 wt% nano-clay addition exhibited the highest flexural and compressive strengths, flexural modulus and hardness. The microstructural analysis results indicate that the nano-clay behaves not only as a filler to improve the microstructure, but also as an activator to facilitate the geopolymeric reaction. The geopolymer nano-composite also exhibited better thermal stability than its counterpart pure geopolymer