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.
Highlights
Investigations in the field of alkali activated materials had an exponential increase starting from 1978 after the research results of the French author Davidovits, who developed and patented binders obtained from the alkali-activation of metakaolin and named them after with the term “geopolymer”.Synthesis of geopolymers is based on the reaction of aluminosilicate materials with an alkali metal hydroxide and an alkali metal salt and their transformation into a three-dimensional inorganic amorphous structure [1]
The chemical composition of the raw materials was obtained, according to the following procedure: they were first calcined at 550 °C for 2 h, a weighted amount of the dry samples was subjected to digestion, under microwave-induced heating (Perkin-Elmer Multiwave 3000 oven) in a
Considering the aluminum release, calcined clay release. This could be explained by the fact that that static test did not provide any stirring of the sediments showed the higher percentage, metakaolin showed composition the higher Si leaching solutions and so release the results are more whereas affected by the initial chemical of release
Summary
Investigations in the field of alkali activated materials had an exponential increase starting from 1978 after the research results of the French author Davidovits, who developed and patented binders obtained from the alkali-activation of metakaolin and named them after with the term “geopolymer”. There thereisis aa lack lack of of data data concerning concerning the the behavior behavior in in alkaline alkaline media secondary raw rawmaterials, materials,often oftenproposed proposed a precursor of geopolymers an industrial media of secondary as as a precursor of geopolymers at anatindustrial scale. It is extremely interesting focusing scientific on the individuation of a it is extremely interesting focusing scientific studiesstudies on the individuation of a method method thatevaluate could evaluate the “geopolymerising”.
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