Calorimetric study of geopolymer binders based on natural pozzolan

This paper investigates the kinetics of geopolymerisation in an inorganic polymeric binder based on a natural pozzolan. The heat released by the exothermic geopolymerisation reaction process is monitored under isothermal temperature conditions, maintained in a differential scanning calorimeter using a water circulation cell. Calorimetric data are obtained isothermally at 65, 75, and 85 °C with various Na2O/Al2O3 and SiO2/Na2O molar ratios and in the presence and absence of small amounts of calcium aluminate cement (used as an efflorescence control admixture in these binder systems). The first stage of reaction, which is rapid and strongly exothermic, is shortened as the temperature increases. The total heat of reaction increases in the mixes containing calcium aluminate cement, but the apparent activation energy calculated using a pseudo-first-order reaction model is lower than without added calcium aluminate cement. At a constant overall SiO2/Na2O molar ratio, the apparent activation energy is decreased as the Na2O/Al2O3 molar ratio increases. Calcium aluminate cement, therefore, reduces the minimum energy required to initiate geopolymerisation reactions of this natural pozzolan and facilitates the progress of the reactions which lead to formation of a cementitious product

Development and characterization of aluminum alloy foam - cork hybrid structures

Cellular solids and porous materials have been considered as one of the most suitable lightweight multifunctional materials for a wide range of commercial and industrial applications, e.g. in medicine, military. Their use contributes to an immediate and significant weight reduction and material savings of the components but also to multifunctionality due to their 3D cellular structures (open-cells or closedcells). Herein, hybrid structures based on cellular materials are developed and studied by combining open-cell aluminum foam with cork. These hybrid structures were prepared by infiltrating a mixture containing polymer-coated cork powders into the open-cell foam. The samples are geometrically analyzed using X-ray microcomputed tomography to extract morphological and topological properties of the voids and the solid phase. The mechanical, thermal, acoustic, and fire retardancy properties of these aluminum foam-cork hybrid structures are evaluated and compared with their individual components (open-cell aluminum alloy foam and agglomerated cork).publishe