Efecte de l'addició d'àrids lleugers a morters de protecció passiva contra el foc formulats amb subproductes de magnesi

En aquest estudi es pretén contribuir a la millora de la formulació dels morters de protecció passiva del foc (PPF) formulats amb subproductes de magnesi, prèviament desenvolupats pel grup de recerca en el que s’emmarca aquest treball. Aquesta millora es realitza mitjançant l’addició d’àrids lleugers com la vermiculita i la perlita. Aquests àrids lleugers pretenen disminuir la densitat del morter resultant, per permetre el seu possible ús com a morters projectats. Un aspecte molt important a tenir en compte a part de la densitat, és el relacionat amb les propietats mecàniques. Tot i que no cal un elevat valor de resistència mecànica és d’interès avaluar l’efecte que els àrids lleugers produeixen sobre aquestes propietats, així com sobre el comportament al foc dels morters. Aquest estudi es divideix en 3 grans blocs. La primera part correspon als antecedents sobre la formulació de morters amb subproductes de magnesi. La segona part consisteix en la caracterització de tots els components de la formulació dels morters, per poder entendre el comportament final del morter de PPF. I la tercera part, principalment experimental, consisteix en la preparació i anàlisi de provetes de morters amb subproductes, que incorporen diferents percentatges dels àrids lleugers. S’ha analitzat el comportament al foc de mostres de morters amb diferents percentatges d’addició d’àrids lleugers. Això ha permès establir l’àrid lleuger que presenta millors resultats i la millor proporció d’addició. La incorporació d’àrids lleugers ha resultat ser eficaç, reduint notablement la densitat dels morters, i obtenint un bon compromís pel que fa al comportament a elevades temperatures i a les propietats mecàniques

Thermal degradation and fire behaviour of thermal insulation materials based on food crop by-products

Natural thermal insulation materials developed from renewable crop by-products and natural binders are analysed in terms of their thermal degradation and fire behaviour. A Pyrolysis Combustion Flow Calorimetre (PCFC) is used to characterise some kinds of crop by-products, including rice husk, corn pith and barley straw. This technique is complemented with a TG analysis. Six thermal insulation materials, formulated with such crop by-products and two kind of natural binders, corn starch and sodium alginate, are developed and analysed. PCFC results show an improvement when sodium alginate is incorporated, especially in the corn pith composite. Fire reaction tests are also performed that yield results which are in qualitative agreement with the small-scale tests

Granular material development applied in an experimental section for civil engineering purposes

In this study, a granular material (GM) derived from wastes generated in waste-to-energy plants was developed. Weathered bottom ash (WBA) and air pollution control (APC) ashes obtained from municipal solid waste incineration (MSWI) were used as raw materials. A mortar (M) with 50 wt. % of APC and 50 wt. % of Ordinary Portland Cement (OPC) CEM-I was prepared. The GM formulation was 20 wt. % M and 80 wt. % WBA. At the laboratory scale, WBA, APC, M, and crushed GM were evaluated by means of dynamic leaching (EN 12457-4) tests, and WBA, M, and crushed GM by percolation column (CEN/TS 16637) tests. The metal(loid)s analyzed were below the non-hazardous limits, regarding the requirement of the metal(loid)s released for waste revalorization. In order to simulate a road subbase real scenario, the crushed GM was tested in an experimental section (10 × 20 × 0.2 m). During a 600-day period, the leachates generated by the percolation of rainwater were collected. This research shows outstanding results regarding the metal(loid)s released for both the 'accumulated' and 'punctual' leachates collected. An accomplishment in the immobilization of metal(loid)s from APC residues was achieved because of the encapsulation effect of the cement. The GM formulation from both MSWI wastes can be considered an environmentally safe procedure for revalorizing APC residues

Stabilization study of a contaminated soil with metal(loid)s adding different low-grade MgO degrees

Low-grade magnesium oxide (LG-MgO) was proposed as ordinary Portland cement (OPC) or lime substitute (CaO) for metal(loid)s remediation in contaminated soils. Some metal(loid)s precipitate at pH ≈ 9 in insoluble hydroxide form thus avoiding their leaching. LG-MgO avoids the re-dissolution of certain metal(loid)s at 9.0 < pH < 11.0 (pH-dependents), whose solubility depends on the pH. A highly contaminated soil with heavy metal(loid)s was stabilized using different LG-MgO by-products sources as stabilizing agents. Two of the three studied LG-MgOs were selected for the stabilization, by mixing 5, 10, and 15 wt.%. The effect of using LG-MgO not only depends on the size of the particles, but also on those impurities that are present in the LG-MgO samples. Particle size distribution, X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis, citric acid test, specific surface, bulk density, acid neutralization capacity, batch leaching tests (BLTs), and percolation column tests (PCTs) were techniques used to deeply characterize the different LG-MgO and the contaminated and remediated soils. The remediation's results efficacy indicated that when the medium pH was between 9.0 and 11.0, the concentration of pH-dependent metal(loid)s decreases significantly. Although around 15 wt.% of a stabilizing agent was appropriate for the soil remediation to ensure an alkali reservoir that maintains optimal stabilization conditions for a long period, 5 wt.% of LG-MgO was enough to remedy the contaminated soil. When evaluating a polluted and decontaminated soil, both BLTs and PCTs should be complementary procedures

Epsomite as flame retardant treatment for wood: Preliminary study

The effect of epsomite as flame retardant for wood has been investigated and compared with a commercial boron salt. Both flame retardants have been introduced into wood samples by vacuum impregnation. Epsomite is a hydrated sulphate salt with a water solubility of 731 g L-1 at room temperature. Thanks to this high solubility it was possible to obtain elevated epsomite loadings in comparison with the borax salt. Flame retardancy was evaluated by means of the limiting oxygen index, the dripping test and the exposition to a direct flame (Bunsen test). The results showed that the addition of epsomite increases the limiting oxygen index, delays the time to ignition and the evolution of the temperatures trough the wood. © 2016 Elsevier LtdPeer ReviewedPostprint (author's final draft

Structural characterisation and reactivity measurement of chemically activated kaolinite

This study examines the structural evaluation of differently activated kaolins for potential use as supplementary cementitious materials (SCM) or as precursor for alternative cementitious materials (ACM). Chemical activation involved amorphizing the kaolinite structure using varying phosphoric acid concentrations, reaction times, and temperatures. Metakaolin obtained via thermal activation served as a comparison. Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) characterization of the activating solutions revealed phosphoric acid activation leading to dealumination in kaolinite structures, with temperature emerging as the most significant parameter. X-ray diffraction (XRD) confirmed amorphization, attributed to the dealumination process causing Al loss and creating new Si–O–Si interlayered bonds, as monitored by 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) tracking the change from Q3 to Q4 environments. Furthermore, pozzolanic activity was assessed through Ca(OH)2 consumption and reaction heat release via modified Chapelle and R3 tests, respectively. Kaolinite subjected to intensive chemical activation exhibited high reactivity and increased specific surface area, indicating its potential as a pozzolanic material. Keywords: Kaolin; Chemical activation; Supplementary cementitious materials; Alternative cementitious materials; Dealumination; Pozzolanic reactivity

APC fly ash recycling: development of a granular material from laboratory to a pilot scale

The aim of this article is to present the research carried out over a 10 year period to develop an environmentally safe method for recycling Air Pollution Control (APC) residues. The initial studies aimed to formulate a mixture of Weathered Bottom Ash (WBA), APC residues and Portland Cement (PC) to be used as a sub-base in road constructions. Mechanical performance was subsequently enhanced by preparing a mortar prior to mixing it with WBA in order to obtain a granular material. After testing different formulations, the optimum mortar consisted of 50% APC residues and 50% PC. The evaluation was carried out based on the concentration release of the heavy metals and metalloids included in the Catalan legislation for revalorization of residues. After the applicability of the granular material was successfully demonstrated at laboratory scale from an environmental and mechanical point of view, a pilot scale plant was designed in order to assess its performance in a real scenario during four month. Thus, three roads were built: two containing 100% granular material and a third containing 100% WBA. The results showed that the immobilisation of all toxic species from APC residues is accomplished by the pozzolanic effect of the cement. The WBA, APC, and PC proportions show to be the most appropriate for compliance with regard to environmental and mechanics requirements

Characterisation and partition of valuable metals from WEEE in weathered municipal solid waste incineration bottom ash, with a view to recovering

As the demand for critical and valuable metals increases due to industrial developments, especially in electronics and high-technology industries, the search for novel and sustainable sources grows in significance. Incinerated municipal solid waste (MSW) is a potential source of valuable metals, since a lot of waste from electrical and electronic equipment (WEEE) is not recycled properly and are is managed together with the refuse fraction of MSW, which is often landfilled or incinerated. Bottom Ash (BA) is the main by-product of incinerated MSW, which has been characterized to assess the potential recovery of valuable metals. The determination of the total amount of valuable metals (Ag, Al, Au, Be, Co, Cu, Ga, Ge, In, Ir, Li, Ni, Pd, Pt, Sb, Ta, and W) in seasonal samples of weather bottom ash (WBA) was performed by a total acid digestion followed by a chemical analysis. Besides, a sequential extraction procedure (SEP) is conducted to define their partition. The characterisation has shown that the content of valuable metals in the incineration WBA, which was highest in the 0-2mm fraction was much lower than in concentrated ores commonly used as primary sources. Moreover, the SEP showed little potential for the valorisation of most of the metals, as they are embedded in or bound to a silicic matrix or sintered metal oxides, and so their extraction requires strong-acid digestion or a highly oxidizing environment. This work contributes to the use of residual sources as secondary resources and to the correct management of the end-of-life electrical and electronic equipment

Thermal activation of kaolinite through potassium acetate intercalation: A structural and reactivity study

Calcined clays have emerged as a suitable alternative to partially replace conventional cement due to their highpozzolanic activity. This study explores a novel activation methodology for kaolinite, aiming to obtain metakaolinat lower temperatures than conventional thermal activation. This methodology involves a prior intercalationstage with potassium acetate (KAc) before thermal activation. The effectiveness of KAc intercalation wasassessed through X-ray diffraction (XRD), indicating an intercalation ratio of approximately 90%. Severalcalcined temperatures were tested in accordance with the thermal behaviour analyzed through thermogravimetricanalysis (TGA). Once calcined, the intercalated kaolinites exhibited enhanced reactivity compared toconventional calcined clays in the range between 400 ◦C to 550 ◦C, as demonstrated by modified Chapelle andSi/Al availability tests. A comprehensive structural characterization was conducted to facilitate a better understandingof the novel KAc-based metakaolin reactivity through various techniques (XRD, 27Al - 1H MAS NMR,and TGA). This focused on the crystalline changes in the kaolinite structure, the evolution of Al atoms conformation,and the OH behaviour at different thermal activation temperatures. Overall, this study highlights thepotential of KAc intercalation as a strategy to obtain higher metakaolin content at lower temperatures thanthrough conventional thermal treatments, offering insights into the development of its potential use as supplementarycementitious materials or alternative cementitious materials precursor

Municipal solid waste incineration bottom ash as sole precursor in the alkali-activated binder formulation

The concern about the large amount of weathered bottom ash (WBA) produced in waste-to-energy plants (WtE) has caused an increased search for alternatives to reduce their environmental impact. The present study aims to provide an added value through the WBA valorization from municipal solid waste incineration (MSWI) for its use as a sole precursor for developing alkali-activated binders (AABs). Alkali-activated weathered bottom ash binders (AA-WBA) were formulated with a liquid-to-solid ratio of 1.0 and using sodium silicate (80 wt.%) and NaOH (20 wt.%) at different concentrations (2, 4, 6, and 8M) as alkali-activator solutions. AA-WBA were cured at room temperature to extend their applicability. The effect of the alkali-activator solution molarity on the final properties of the AA-WBA was evaluated. The physicochemical characterization by XRD, FTIR, and SEM evidenced the presence of the typical phases (calcium silicate hydrate and gehlenite) of C-(A)-S-H gel. Leaching concentrations of As, Cu, and Mo exceed the acceptance in landfills for inert waste, while the leaching concentration of Sb exceeds the one for non-hazardous waste. The structure of the binders depends on the alkalinity of the activator, obtaining better results using NaOH 6M in terms of microstructure and compressive strength (6.7 MPa). The present study revealed that AA-WBA for non-structural purposes can be obtained. The AA-WBA formulation contributes to the WBA valorization and development of low-carbon cements; therefore, it is an encouraged alternative to ordinary Portland cement (OPC). Considering the amounts and costs of the WBA, sodium silicate, NaOH, and wat