Abstract:The extent of the dissolution of aluminosilicate compounds is crucial, since the amount of Si and Al initially dissolved is essential for the following polycondensation and can strongly influence physical and mechanical performances of the final product. In order to set up a method to test the ability of a material to react in alkaline media, different aluminosilicate sources have been selected: a mineral resource (a zeolitized tuff), an industrial by product (silt from washing process of construction and demolition wastes), a heat treated clay sediment and a calcined clay (metakaolin). Two test methods, static and dynamic, have been applied to evaluate the attitude of a silicoaluminate precursor to give a geopolymerization reaction. In particular, a fixed amount of precursor was put into contact with a alkaline solution under continuous stirring or in static conditions at 60 • C for fixed times. The dynamic test method seems to be more suitable, since it is faster and requires lower amounts of reactants (solution). Moreover, the dynamic test provides a reactivity sequence (ordered from the more to the less reactive precursor) metakaolin > treated clay sediment > zeolitized tuff ≈ silt both for Si and Al release, which is coherent with the performances of geopolymers obtained by using the above precursors.
The awareness of environmental protection, with the conservation of resources and the efficient use of industrial waste, has attracted the attention in recent decades as both the overexploitation of natural resources and the disposal of industrial waste have a negative impact on the environment and sustainability [1]. Under such circumstances, replacing ordinary Portland cement (OPC) with industrial waste has been shown as a sustainable and practical way to reduce the use of natural resources, as well as landfill waste and pollution [2]. The discussion of this issue is part of a path, which sees as its starting point the design of a hydraulic pipeline prototype (Figure 1) made of geopolymer mortar instead of conventional concrete pipes. The environmental sustainability of geopolymer mortars was demonstrated through the Life Cycle Assessment (LCA) methodology. Analysis results indicate that the use of eco-friendly materials contributes to minimizing the environmental impact of new technologies for engineering sector.
Incineration is considered one of the most convenient treatment of urban solid waste (MSW) as it allows a significant volume reduction and an energy enhancement of the waste itself. However, it cannot be considered a final treatment solution because of the formation of solid residues, mainly composed of two groups of ash, bottom ash (BA) and fly ash (FA). Their characteristics depend on the type of incoming waste and on the combustion methods. BA are considered non-hazardous waste, while FA, due to their high content of heavy metals, alkali chlorides and soluble metal salts, have the characteristics of hazardous waste. Among the various recovery possibilities is the use of FA for the production of artificial lightweight aggregates (LWA), used for the production of lightweight concrete (LWC). This article aims to highlight how the use of FA granules as aggregates in LWC can give good results in terms of compressive strength, rupture and elastic modulus. In fact, the particle size distribution and chemical composition of the FA, as well as the generally spherical shape and low cost, make this type of ash an ideal material for this use.
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