Desenvolupament de ciments de fosfat formulats amb subproducte de magnesi que incorporen materials de canvi de fase

Els ciments químics de fosfat, altrament coneguts com a Chemically Bonded Phosphate Ceramics (CBPC), s’obtenen a partir de la reacció àcid-base en medi aquós, entre un òxid metàl·lic i un fosfat àcid. Es tracta d’una reacció espontània molt exotèrmica que permet un enduriment molt ràpid del material. La seva principal desavantatge respecte d’altres ciments és l’elevat cost de les matèries primes que el composen. És per aquest motiu que en el present projecte s’utilitza un subproducte (òxid metàl·lic de baixa llei), subministrat per l’empresa Magnesitas Navarras, S.A., amb la finalitat d’abaratir el preu final dels CBPC formulats. Aquest subproducte conté material inert que no reacciona durant el forjat i que actua com a reforç del ciment, fet que permet considerar el material com a morter. L’investigació que es presenta a continuació consisteix en l’estudi de diferents formulacions de CBPC amb subproductes de magnesi que incorporen un additiu airejant amb el fi d’incrementar la porositat del material. Posteriorment s’avalua la resposta de la formulació òptima en introduir diferents percentatges de materials de canvi de fase, també coneguts com a Phase Changing Materials (PCM), per tal de millorar les propietats tèrmiques del material per actuar com a sistema passiu d’acumulació d’energia en l’habitatge. Els resultats finals mostren que es possible formular CBPC que incorporen materials de canvi de fase per actuar com a sistema passiu d’emmagatzematge tèrmic, ja que la calor en la formació dels ciments no degrada els PCM i presenten un bon comportament tèrmic. Es demostra que l’augment del contingut de PCM incrementa notablement la inèrcia tèrmica dels CBPC degut al calor latent. També redueix la conductivitat tèrmica ja que, juntament amb l’additiu, ajuda a incrementar la porositat del material. Es verifica que l’ús d’aquest subproducte de magnesi abarateix el cost final dels CBPC, enfront l’utilització de MgO pur. A més, les formulacions amb PCM podrien tenir un impacte econòmic i mediambiental positiu, ajudant a reduir l’ús d’aparells artificials de calefacció i refrigeració als edificis

Estudi tèrmic i mecànic de la incorporació de materials de canvi de fase en ciments químics de fosfat formulats amb subproducte de magnesi.

Treballs Finals de Grau d'Enginyeria de Materials, Facultat de Química, Universitat de Barcelona, Any: 2015, Tutor: Dr. Joan Formosa MitjansMagnesium Phosphate Cements (KMgPO4·6H2O; k-struvite), that are known as MPC, part of the family of Chemically Bonded Phosphate Ceramics (CBPC), widely used in the field of biomaterials. These cements are obtained from the acid-base reaction on an aqueous medium between pure MgO and mono-potassium phosphate. It is a spontaneous and highly exothermic reaction that leads to a very fast setting of the material. The main disadvantage of these cements compared with others such as Portland is the high cost of raw materials that are necessary to elaborate the MPC. In the present study we use a by-product called LG-MgO (low magnesium oxide), supplied by the company Magnesitas Navarras, S.A., with the aim to reduce the final cost of MPC and promote aspects such as sustainability and green environment as a consequence of the reduction of the pure MgO mining activity. The research presented here consists in the exhaustive characterization of different dosages of MPC elaborated with magnesium by-product that incorporate air entraining additive and Phase Changing Materials (PCM) to improve the thermal behavior of material when there are thermal oscillations, and thus reduce the use of cooling and heating systems helping to the decrease of CO2 emissions and increasing energy efficiency on the buildings. Moreover, mechanical properties such as elastic modulus, compressive strength and flexural strength are analyzed to test the feasibility of the use of these cements as a passive cooling and heating system. Finally, the degradation of MPC when subjected to thermal cycles is analyzed (thermal durability). Results show that k-struvite is the major product formed in the MPC, although there are also inert phases of magnesium by-product that act as reinforcement. It is verified that the increase of PCM and additive in the content reduces the mechanical properties due to their contribution to increase the porosity and decrease the density. Moreover, we demonstrated that MPC and PCM do not suffer degradation after 750 thermal cycles equivalent to a year

Evaluation of mechanically activated kaolin as alkali-activated material precursor

Please click Additional Files below to see the full abstract

Alkali activated binders based on municipal solid waste Incineration bottom ash

Please click Additional Files below to see the full abstract

Fluidised-bed incineration bottom ash as the sole precursor of alkali-activated binders: A comparison with bottom ash from grate incinerators

The novel formulation of alkali-activated binders (AABs) using incineration bottom ash (IBA) from fluidised bed (FB) combustion technology as a sole precursor was assessed. In addition, IBA-FB was compared with IBA from moving grate (IBA-MG) combustion technology. The AABs formulated with IBA-FB (AAB-FB) and IBA-MG (AAB-MG) were also evaluated from a physicochemical, mechanical, and environmental perspective. The results revealed that specific surface area in IBA-FB hinders the retention of kneading water of fresh pastes, affecting the workability, consistency, porosity, and mechanical strength of AAB-FB. Moreover, the low calcium content of IBA-FB requires that the formulated AABs must be cured at higher curing temperatures to ensure the formation of (N,C) ASH gels, while the high calcium content of IBA-MG promotes the formation of CSH gels at room temperature. The compressive strength results demonstrated that AAB-MG (≈ 11 MPa) and AAB-FB (≈ 8 MPa) could be used for non-structural purposes

Municipal solid waste incineration bottom ash as alkali-activated cement precursor depending on particle size

Bottom Ash (BA) is the main by-product of municipal solid waste incineration (MSWI). It is stabilised outdoors to obtain weathered bottom ash (WBA) whose main application is in the construction sector as a secondary aggregate for road sub-base. Here, the aim of this work is to advance the study of the potential use of WBA as a precursor in the synthesis of new alkali-activated cements (AACs). An exhaustive physicochemical characterisation (X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, inductively coupled plasma - optical emission spectroscopy, and Inductively coupled plasma - mass spectroscopy) of WBA was provided depending on its particle size (<30, 30-16, 16-8, 8-4, 4-2 and 2-0 mm). The study reveals that WBA is composed mainly of the essential reactive phases to form AACs, which are SiO2, Al2O3, and CaO. It is demonstrated the larger the particle size, the higher the content of SiO2; and the smaller the particle size, the higher the heavy metal(loid) content. The availability of reactive phases was analysed through chemical attacks with HF and NaOH solutions of different concentrations (2M, 4M, and 8M). The results demonstrate the availability of reactive phases (including 150-250 g kg−1 of SiO2 and 50-65 g kg−1 of Al2O3) in all the particle size fractions studied. WBA potential will be of considerable use to formulate AACs, depending on the particle size fraction and the Si/Al ratio, both as the sole precursor and mixed with others

High-porosity alkali-activated binders based on glass and aluminium recycling industry waste

The potential as alkali-activated precursors of ceramic-stone-porcelain (CSP) and PAVAL, two residues derived from the optical separation of glass cullet and salt slag from secondary aluminium recycling, has been assessed. Alkali-activated CSP and PAVAL binders’ formulations were prepared using NaOH 4 M and 6 M as alkaline activator solutions. The effect of the Na2O/Al2O3 ratio and alkaline activator concentration was evaluated from a chemical, physical, mechanical, and environmental perspective. The results revealed the formation of secondary reaction products attributed to the formation of (C,N)-A-S-H gels. It also showed the influence of decreasing Na2O/Al2O3 ratio in the obtained binders, increasing porosity and affecting the mechanical performance. Besides, it was demonstrated that PAVAL acts as a precursor and pore-generator. Finally, the environmental characterisation showed a significant leaching concentration of heavy metal(loid)s such as As, Cr, Mo, Sb, and Se, which decreases with longer curing periods.This work is partially supported by the Grants PID2021-125810OB-C21 and TED2021-129718B-I00, funded by MCIN/AEI/https://doi.org/10.13039/501100011033 , by “ERDF A way of making Europe”, and by the “European Union NextGenerationEU/PRTR”, and the Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR) with the Grant 2021 SGR 00708. The authors would like to thank Daniel Rosas, S.A. for supplying the CSP, and Befesa Company for supplying the PAVAL. Mr Jofre Mañosa is grateful to the Government of Catalonia for its research Grant (FI-DGR 2020). Dr Teresa López-Montero is supported by the Spanish grant Juan de la Cierva Formación referenced as FJC-2018-035747-I.Peer ReviewedPostprint (published version

Rapid sintering of weathered municipal solid waste incinerator bottom ash and rice husk for lightweight aggregate manufacturing and product properties

This study assessed the technical feasibility of formulating lightweight aggregates (LWA) from municipal solid waste incinerator bottom ash (IBA) and residual biomass. Weathered IBA (WIBA) particles larger than 8 mm contain a mixture of calcium-rich compounds and other silicates mainly composed of glass and synthetic and natural ceramics, with low contents of heavy metals and soluble salts. Unfired LWA were formulated with the particle size fraction of WIBA larger than 8mm and rice husk (RH) used as the bloating agent. Rapid sintering of the unfired spherical pellets at 1,100°C for 5min produced some cohesive sintered LWA, whose porosity, apparent particle density, water absorption, and compressive strength directly correlated with the percentage of RH added. The fired LWA formulated with 5wt% of RH showed the highest bloating index (115%) and porosity (53%) and the lowest apparent particle density (0.61Mgm−3) and compressive strength (1.4MPa). The addition of more than 5wt% of RH increased the internal temperature of the sintered aggregates and decreased the viscosity of the molten glassy materials, resulting in the collapse of the inner structure. Consequently the porosity decreased and the apparent density of the particles increased, thereby shrinking the volume of the fired LWA. According to the standard leaching test (EN 12457-4), both the unfired precursor and the sintered aggregates showed concentrations of heavy metals and metalloids in the leachates that were well below the safety limits established for their reuse as secondary material

Alkali-activated binders using bottom ash from waste-to-energy plants and aluminium recycling waste

Alkali-activated binders (AABs) stand out as a promising alternative to replace ordinary Portland cement (OPC) due to the possibility of using by-products and wastes in their manufacturing. This paper assessed the potential of weathered bottom ash (WBA) from waste-to-energy plants and PAVAL® (PV), a secondary aluminium recycling process by-product, as precursors of AABs. WBA and PV were mixed at weight ratios of 98/2, 95/5, and 90/10. A mixture of waterglass (WG) and NaOH at different concentrations (4 and 6 M) was used as the alkaline activator solution. The effects of increasing NaOH concentration and PV content were evaluated. Alkali-activated WBA/PV (AA-WBA/PV) binders were obtained. Selective chemical extractions and physicochemical characterization revealed the formation of C-S-H, C-A-S-H, and (N,C)-A-S-H gels. Increasing the NaOH concentration and PV content increased porosity and reduced compressive strength (25.63 to 12.07 MPa). The leaching potential of As and Sb from AA-WBA/PV exceeded the threshold for acceptance in landfills for non-hazardous waste

Alkali-activated binders based on the coarse fraction of municipal solid waste incineration bottom ash

The potential of the least polluted fraction (from 8 to 30mm) of municipal solid waste incineration (MSWI) weathered bottom ash (WBA) as an alkali-activated cement precursor was evaluated. Alkali-activated WBA binders (AA-WBA) formulations were prepared through alkali-activation of WBA as sole precursor. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) mixtures with different pH's were used as alkali-activator solution. The effect of alkali-activator solution pH on the final properties was assessed. Results showed the hydrolytic stability of allformulations. The selective chemical extractions and physicochemical characterisation revealed the formation of the C-S-H, C-A-S-H, and (N,C)-A-S-H gels. The promising compressive strength results demonstrated the potential of AA-WBA binders. The increase of pH in the alkali-activated solution promotes the formation of gel reaction products and enhance mechanical properties. This investigation promotes the green cements manufacturing and the use of secondary resources to reduce the impact of natural resources extraction used for the ordinary Portland cement (OPC) production