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Integrated development of treatment and management technologies of asbestos containing materials

Valouma Aikaterini

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Summary

This dissertation aims to develop a new technology concerning the detoxification and management of asbestos containing waste (ACW). Asbestos minerals were extensively used as raw materials in the construction sector, rendering asbestos containing materials (ACM) an increasingly hazardous waste stream, mainly due to renovation and demolition waste.The purpose of this thesis is to manage asbestos cement (AC) corrugated sheets. The AC corrugated sheets are cementitious materials reinforced with asbestos fibers. They are subjected to long term deterioration due to weathering in the natural environment. Since they are roofing materials, rain, humidity, acid rain and temperature variation cause weakening of their composites.Initially, the effect of different concentrations of the moderate organic acid, oxalic acid, on the detoxification of AC corrugated sheets is investigated. Oxalic acid is able to achieve dissolution of chrysotile fibers. AC was added to oxalic acid solutions of different concentrations in order to investigate the ability of asbestos fibers to react with oxalic acid in the presence of cement. Then, the use of tetraethyl orthosilicate (TEOS) on the simultaneous effect of asbestos cement detoxification and transformation of silica matrix into silica network is studied. This research is focused on the development of a nontoxic sol-gel. The gel is a product of ACW mixing in an aquatic solution of oxalic acid and TEOS addition, under stirring, in room temperature. The selection of the reagents of the combined treatments is based primarily on the oxalic acid’s ability to destruct the fibers of chrysotile, while it is also used as acid catalyst in sol-gel processes. Furthermore, treatment with the same reagents is conducted under microwave irradiation. A combined treatment of oxalic acid and potassium silicate also achieved the transformation of ACW into harmless material.Characterization analyses of asbestos minerals, cementitious and amorphous phases of AC, as well as newly-formed phases of treated samples, are performed with XRD, FTIR, XRF and TG-DTG. The results indicated that the combined treatment with TEOS achieves the full detoxification and transformation of AC structure. Specifically, during the treatment, calcium oxalate monohydrate is yielded, due to oxalic acid reaction with cementitious phases, and high production of silica of amorphous phase up to 90 %wt.Pozzolanic reactivity determination is evaluated based on an accelerated method (NF P 18 - 513) that determines lime-pozzolan reaction and quantifies the pozzolanic reaction measuring Ca(OH)2 reduction in the presence of pozzolans. This method is a fast and accurate way to determine the pozzolanic reactivity of a material. The long-term pozzolanic reactivity of the material, as supplementary cementitious material in mortar specimens is evaluated via Strength Activity Index (EN 450-1).Subsequently, the possibility of recycling the treated material as secondary raw material with pozzolanic properties to produce building elements with advantageous characteristics is studied. Two commercial types of cement, CEMI 42.5N and CEMII/A-LL 42.5N, standard sand as aggregate and silica fume (for comparison reasons) as additive, are used for the production of the mortars. The effect of the partial cement substitution (1.5-5 %wt.) by the artificial pozzolan is investigated.

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