Sustainable inorganic Binders and Their Applications in Building Engineering: A Green Alternative to Ordinary Portland Cement

In the last decades, the building materials and construction industry has been contributing to a great extent to generate a high impact on our environment. As it has been considered one of the key areas in which to operate to significantly reduce our footprint on environment, there has been widespread belief that particular attention now has to be paid and specific measures have to be taken to limit the use of non-renewable resources.The aim of this thesis is therefore to study and evaluate sustainable alternatives to commonly used building materials, mainly based on ordinary Portland Cement, and find a supportable path to reduce CO2 emissions and promote the re-use of waste materials. More specifically, this research explores different solutions for replacing cementitious binders in distinct application fields, particularly where special and more restricting requirements are needed, such as restoration and conservation of architectural heritage. Emphasis was thus placed on aspects and implications more closely related to the concept of non-invasivity and environmental sustainability. A first part of the research was addressed to the study and development of sustainable inorganic matrices, based on lime putty, for the pre-impregnation and on-site binding of continuous carbon fiber fabrics for structural rehabilitation and heritage restoration. Moreover, with the aim to further limit the exploitation of non-renewable resources, the synthesis of chemically activated silico-aluminate materials, as metakaolin, ladle slag or fly ash, was thus successfully achieved. New sustainable binders were hence proposed as novel building materials, suitable to be used as primary component for construction and repair mortars, as bulk materials in high-temperature applications or as matrices for high-toughness fiber reinforced composites

Lightweight insulating geopolymer material based on expanded perlite

Expanded perlite, owing to its lightweight and excellent thermal insulating properties, has been extensively used in different industrial sectors to produce self-standing insulating boards bonded with various organic polymers or calcium-silicates. In order to improve the high temperature behavior and mechanical performances of such materials inorganic binders, such as geopolymers, can be regarded as a promising alternative. Please click Additional Files below to see the full abstract

Geopolymer oxygen carriers for chemical-looping combustion

One of the best alternatives to reduce the economic cost of CO2 capture is represented by the chemical looping combustion (CLC). This technology accomplishes indirect fuel combustion by use of a solid oxygen carrier (OC), generally a metal oxide having the capability of transporting the oxygen needed for the combustion from an air reactor to a fuel reactor, usually designed as two coupled fluidized beds. The combustion takes place in the fuel reactor through the reaction between the fuel and the solid OC, which is consequently reduced to a lower oxidation state. The reduced OC is then transferred to the air reactor, where it is regenerated by oxidation in air at high temperature. Therefore, the CLC process enables the inherent separation of the produced CO2, the stream exiting the fuel reactor being only composed of CO2 and H2O, easily separable by water condensation. Please click Additional Files below to see the full abstract

A Preliminary Laboratory Evaluation of Artificial Aggregates from Alkali-Activated Basalt Powder

The widespread use of natural aggregates is one of the main causes of the depletion of natural resources, as aggregates are constituents of several construction materials. Alternatively, it is, today, proven to be feasible to use mining tailings, either natural or recycled materials, to produce artificial aggregates through specific processes. A possible way to produce artificial aggregate is through the alkali activation of the powdered material in a process called geopolymerization. This study proposes to use a basalt powder and two different metakaolins as precursors for the production of an alkali-activated artificial aggregate, with a specific shape and size achieved by using 3Dprinted molds. The experimental aggregates were evaluated using traditional tests for natural aggregates, such as resistance to compression, specific density and resistance to abrasion and fragmentation. Furthermore, the material was chemically analyzed in order to evaluate the geopolymerization process promoted by the two adopted metakaolins. The physical tests showed that artificial aggregates do not perform well in terms of resistance to wear and fragmentation, which can be improved. However, they revealed promising results in terms of skid, polishing and micro-texture

Chemical Looping Combustion in a Bed of Iron Loaded Geopolymers

Abstract The chemical looping combustion allows for inherent CO 2 separation when burning fossil fuels in presence of a suitable oxygen carrier. The choice of the material to be used should take into account not only chemical/physical properties but also economical, environmental, and safety concerns, addressing for more common materials, like Fe oxides. In this research a geopolymeric oxygen carrier, based on Fe 2 O 3 , was tested for the first time in a laboratory CLC plant operated at high temperature for the combustion of a CO rich gas from char gasification in CO 2 . The CLC plant reliably performed in repeated cycles without decay of the CO conversion during the chemical looping combustion. The maximum CO content in the flue gas was around 1% vol. and carbon monoxide conversion achieved 97%. The calculated oxygen transport capacity was 0.66%. The plant results were confirmed by the XRD analysis that proved the presence of reduced phases in samples after chemical looping stage and by significant peaks obtained during H 2 reduction in TPR equipment

Pressurized Steam Conversion of Biomass Residues for Liquid Hydrocarbons Generation

Biomass residues are often considered as a resource if conveniently converted in fuel and alternative feedstock for chemical processes, and their conversion into valuable products may occur by different pathways. This work is focused on the thermochemical conversion at moderate temperature and in steam atmosphere, a mild process in comparison to hydrothermal liquefaction, followed by extraction of soluble products in a solvent. Such process has been already applied to various residues and here extended to the case of marc, the residual pomace from wine making, largely produced worldwide. A pressurized batch reactor was used for the quantitative determination of produced solid and liquid fractions, and their qualitative characterization was performed by instrumental analyses. The pressurized steam conversion of marc was effective, providing a yield in liquid fraction, upon extraction in solvent, up to 30% of the raw dried biomass. The use of polar and nonpolar solvent for the extraction of the liquid fraction was inspected. Applied operating conditions, namely residence time in the batch reactor and extraction modality, showed a significant influence on the process performance. In particular, long residence and extraction times and use of nonpolar solvent substantially improved the yield in liquid fraction

Production and characterization of geopolymer blocks based on hydroxyapatite rich biomass ashes

Vegetal and animal derived biomass ashes were selected to realize new sustainable chemically consolidated ceramics via acid or alkaline activation. Mixed biomass ashes are mainly based on calcium phosphate and secondly on aluminosilicate compounds ;they still represent an unexplored source material to be used in alternative ceramics production for building industry by low-cost manufacturing processes.Mixed biomass ashes were used to produce room-temperature hardened materials by chemical activation with solutions of phosphoric acid or potassium poly-silicate. Reactive mineral powders (metakaolin, magnesia and wollastonite) were also added to fasten the consolidation and the formation of a binding phase. The obtained formulations were finalized to maximize the amount of ashes disposed. Microstructural, physical and mechanical properties of the obtained materials were evaluated, along with their waterstability. Acid-activated samples, even in presence of secondary reactive precursors, maintained a crystalline structure,while alkali-activated ones were able to form a partially amorphous and wellc onsolidated matrix, with compressive strength of about 20 MPa

High temperature behaviour of ambient cured alkali-activated materials based on ladle slag

This paper investigates the thermal properties of alkali activated materials (AAMs) made from ladle slag, a by-product from electric arc furnaces. AAMs have the potential to exhibit improved durability in high temperature environments over conventionalmaterials such as ordinary Portland cement due to a reduced concentration of hydrated phases in their structure. A series of sampleswith varying compositional ratioswas synthesised from a combination of ladle slag and metakaolin or ladle slag and fly ash. Ambient cured AAMs ofmoderate compressive strengths (between 11 and 46 MPa) were achieved. Samples were exposed to temperatures up to 1000 °C and analysed for residual strength, thermal expansion, phase and microstructural changes. The ladle slag and fly ash based AAMs exhibited superior strength gains and better thermal stability than the ladle slag and metakaolin based AAMs believed to be due to unstable C–A–S–H phases formed in the latter group of samples

Nano-to-macroporous TiO 2 (anatase) by cold sintering process

Cold Sintering Process (CSP) was applied on commercial nanopowders to produce nanostructured TiO 2 anatase with nano-to-macro porosity. Nanoporous TiO 2 based materials were obtained by applying CSP at 150 °C and pressures up to 500 MPa on three TiO 2 nanopowders with different specific surface area (s.s.a. = 50, 90 and 370 m 2 /g), using water as transient aqueous environment. Although TiO 2 is insoluble in water, a density of 68% and s.s.a. = 117 m 2 /g were achieved from the powder with the highest specific surface area. A post annealing process at 500 °C increased the density up to 73% with a s.s.a. = 59 m 2 /g, and the crystallites dimensions passed from 110 Å in the powder to 130 Å in CSP material and 172 Å after post annealing. Finally, macroporosity was produced by using thermoplastic polymer beads as sacrificial templates within TiO 2 nanopowder during CSP, followed by a debonding at 500 °C

Porous Geopolymer Insulating Core from a Metakaolin/Biomass Ash Composite

Ashes derived from the combustion of vegetal and animal biomass still represent a mostly unexplored secondary raw material for the production of alkali-activated materials, given their peculiar chemical nature. In this work, calcium phosphate biomass ashes were successfully used as partially reactive fillers in a metakaolin-based geopolymer composite to produce, by direct foaming, sustainable and lightweight boards with thermal insulating properties. The investigated materials were obtained by activating a blend of metakaolin and biomass ash in a weight ratio of 1: 1 and foamed with the addition of H2O2 in measure of 5 wt. %, to maximize the volume of disposed ash and ensure adequate properties to the material at the same time. The obtained geopolymer composite was characterized by microstructural, chemical-physical, mechanical and thermal analysis: the obtained results showed that biomass ash and metakaolin well integrated in the microstructure of the final porous material, which was characterized by a density of about 310 kg/m3 and a thermal conductivity of 0.073 W/mK at a mean test temperature of 30 °C, coupled with an acceptable compressive strength of about 0.6 MPa. Dilatometric and thermogravimetric analysis, performed up to 1000 °C, highlighted the thermal stability of the composite, which could be regarded as a promising material for low-cost, self-bearing thermal insulating partitions or lightweight cores for thermostructural sandwich panels