Abstract
Recycling geopolymer waste, by reusing it as a raw material for manufacturing new geopolymer binding matrices, is an interesting asset that can add to the many technical, technological and environmental advantages of this family of materials in the construction field. This can promote them as promising alternatives to traditional materials, such as Portland cements, which are not so environmentally friendly. Recent studies have shown that the partial replacement of reactive aluminosilicates (metakaolin and fly ash) up to a mass rate of 50% by geopolymer waste does not significantly affect the compressive strength of the new product. In line with these findings, this paper investigates the effects of aggressive environments, i.e., high temperatures (up to 1000 °C) and acid attacks (pH = 2), on the characteristics of these new matrices. Different techniques were used to understand these evolutions: mineralogical analysis by X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TGA-DTA), mechanical characterization and scanning electron Microscopy (SEM) observations. The results are very satisfactory: in the exposure temperature range explored, the new matrices containing geopolymer waste suffered losses in compressive strength similar to those of the matrices without waste (considered as materials reference). On the other hand, the new matrices exhibited good chemical stability in acid media. These results confirm that the reuse of geopolymer waste is a promising recycling solution in the construction sector.
Highlights
In the building and civil engineering sectors, geopolymers are considered a promising alternative to conventional materials based on Portland cements [1,2]
In a recent study [24], we investigated the possibility of partially replacing fly-ash (FA) or metakaolin (MK) with Fly-ash-based Recycled Geopolymer (FARG) and Metakaolin-based Recycled Geopolymer (MKRG) wastes in order to manufacture new geopolymer matrices that consume less raw materials
thermogravimetrydifferential thermal analysis (TGA-Differential thermal analysis (DTA)) thermal analyses are suitable techniques for determining the various phenomena that occur in a material subjected to the action of heat
Summary
In the building and civil engineering sectors, geopolymers are considered a promising alternative to conventional materials based on Portland cements [1,2]. These environmentally friendly materials are characterized by a simple implementation protocol at temperatures below 100 ◦C (meaning a low carbon footprint), great diversity and availability of raw materials, good properties in the fresh state, excellent mechanical resistance in the hardened state, high fire resistance, good resistance to acids and sulphates [3–8] and excellent immobilization capability of toxic and radioactive elements [9–11] These inorganic materials with amorphous behavior under X-ray have a microstructure made up of a three-dimensional stack of aluminate (AlO4) and silicate (SiO4) tetrahedra, with the insertion of alkaline or alkaline-earth cations (generally Na+, K+ and Ca2+) compensating charges. The second part is dedicated to the evaluation of the characteristics of these new binders subjected for 28 days to the chemical action of acid media After these various treatments, the residual compressive strengths were measured, microstructural analyses by X-ray diffraction and observations by optical microscopy and by scanning electron microscopy were performed
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