In this work, the possibility of reusing ashes issued by an oxyfuel combustion process (OC) as a source of material in the production of belite calcium sulfoaluminate BCSA cements has been investigated.OF process is one of the most promising combustion technologies for CO2 reduction from power plants.Combustion tests were carried out in an oxyfuel bubbling fluidized bed pilot plant.Four BCSA clinker-generating raw mixes were heated in a laboratory electric oven in the temperatures range 1150°-1350°C: one included only natural materials (limestone, clay, bauxite and gypsum), the others contained OC ashes as total substitute for clay.X-ray diffraction (XRD) analysis on the burning products showed high conversion of reactants toward the main BCSA clinker components (C2S and C4A3$), especially at 1200° or 1250°C.Moreover, physical-mechanical tests associated with XRD and differential thermal-thermogravimetric analyses accomplished on all the cements (obtained by adding natural gypsum to the clinkers produced at the best synthesis temperatures) generally displayed a similar hydration behaviour.

48 49 The paper represents "a state of the art" on sustainability in construction materials. In Part 50 1 of the paper, issues related to production, microstructures, chemical nature, engineering 51 properties and durability of mixtures based on binders alternative to Portland cement were 52 presented. This second part of the paper concerns use of traditional and innovative Portland- 53 free lime-based mortars in conservation of cultural heritage and recycling and management 54 of wastes to reduce consumption of natural resources in production of construction 55 materials. The latter is one of the main concern in terms of sustainability since nowadays 56 more the 75% of wastes are disposed in landfills. 57 58

gives an example for synergistically coupling two different processes both aimed at 41 CO2 reduction, to convey in a scheme for which savings in the consumption of natural 42 materials/fuels and in the flue gas/ash environmental impact can be achieved as well. 43 44 45

Oxyfuel combustion represents one of the most interesting processes aimed at CO2 capture and storage to mitigate greenhouse effects ascribable to the process industry.In a different technical area, searching for new processes aimed at producing low-CO2 cements has comparable relevance, due to the huge generation of greenhouse gases related to cement production.This paper proposes an integration of these two aspects, with an approach new in the pertinent literature.The possibility of reusing ashes, issued by a pilot plant fluidized bed oxyfuel combustion process, as a source of material in the production of low-CO2 cements is investigated.Ashes were tested as substitutes for natural pozzolan in blended cements.They were mixed with an industrial Portland clinker and natural gypsum in order to evaluate their hydraulic behavior at different curing temperatures (20-40°C) and times (2-28 days).Pozzolanicity tests together with differential thermal-thermogravimetric and X-ray diffraction analyses were employed to explore the hydration behavior of oxyfuel ashes-based blended cements.

In this paper, it is investigated the possibility of reusing ashes, issued by an oxyfuel combustion process aimed at mitigating CO2 emission, as substitutes for natural pozzolan in the production of low-CO2 blended cements. To this end, the oxyfuel plant (a 95 kWth pilot-scale fluidized bed reactor) was operated under controlled conditions by feeding blends of anthracite or lignite and biomass corn stover. Characterization of fly and bottom ashes revealed that the latter showed properties able to make them considerable for obtaining blended cements by mixing them with Portland clinker and natural gypsum. The cements were subjected to pozzolanicity and hydration tests for curing times ranging from 2 to 28d at 20° and 40°C. X-ray fluorescence and diffraction, differential thermal–thermogravimetric analyses and scanning electron microscopy were employed as characterization techniques. With reference to a standard blended cement, and with particular eye on the blended cement containing bottom ashes obtained from the lignite–biomass mixture combustion, it was observed a good similarity in the ability of the silico-aluminous fraction to react with Ca(OH)2 produced by Portland clinker hydration, to yield the desired calcium silicate hydrates among the hydration products.

In 2014 about four billion tonnes of cement were produced [CEMBUREAU, 2014].The use of industrial by-products, as a source of raw materials in the manufacture of portland and blended cements, is a research theme of significant relevance to the construction industry.Such industrial byproducts can be employed as constituents of the final product or components of the raw feed in a cement kiln.Due to their hydraulic and/or pozzolanic activity, industrial by-products are utilized worldwide.Such by-products also increase durability and reduce costs for producing blended cements.The use of such by-products as raw mixture component for the cement production has received comparatively little attention by researchers and engineers.There is currently an increasing interest towards searching for new categories of by-products, which would be able to provide reactive calcium, silicon, aluminum, and/or iron oxides, for portland cement clinker manufacture.In this regard, construction and demolition waste (C&DW) is worthy of consideration because, when obtained from a properly selective demolition process, they could be employed as alternative raw material for portland clinker production.The present study deals with the use of two different kinds of C&DW, namely concrete waste (CW) and masonry waste (MW).In this study, C&DW is proposed to be employed as partial or total substitute for limestone and clay, respectively, in the portland clinker generating raw mixture.Four ternary mixtures containing limestone, as well as CW and MW, were subjected to laboratory tests in order to evaluate the clinker raw mixture produced and the performance of the related portland cement.A binary mixture, composed of limestone and clay, was used as a reference.All of these different cements displayed similar hydration behavior.Detailed results are presented and discussed.

The feasibility of some widespread zeolite-rich tuffs to act as pozzolanic material for manufacturing blended cements was evaluated by chemical and mechanical characterization. Two different methods were used: (a) Fratini’s test, that allowed to evaluate the ability of the pozzolanic material to combine with Ca(OH)2 in a blended cement; (b) Saturated Lime Test, where the pozzolanic behaviour was directly evaluated in a lime saturated solution.Mechanical characterization was carried out by measuring compressive strength of blend mortars, after 28-day curing. The good pozzolanic behaviour proved by all the tuffs, coupled with their low cost, makes very promising the use of zeolitic tuffs for the production of eco-sustainable blended cements.

The present work studies the hydration process and microstructural features of five calcium sulfoaluminate (CSA) cements and a ternary mixture including also ordinary Portland cement (OPC). The pastes were studied with simultaneous differential thermal-thermogravimetric (DTA-TG) analysis, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and expansion/shrinkage tests. The DTA-TG analysis confirmed the role of the hydration reactions involving the main CSA clinker constituent, tetracalcium trialuminate sulfate, which produced (i) ettringite when combined with lime and calcium sulfate, (ii) ettringite and aluminum hydroxide in the presence of calcium sulfate alone, and (iii) monosulfate and aluminum hydroxide in the absence of both lime and calcium sulfate. The MIP and SEM were able to discriminate between expansive (ternary mixture and CSA cement containing 50% gypsum) and non-expansive cements. Expansive cement pastes had (i) a nearly unimodal pore size distribution shifted toward higher radii and (ii) ettringite crystals smaller in size during the first day of curing. In a SEM image of a hardened paste of the CSA cement containing 50% gypsum, a stellate ettringite cluster was observed.

Within the curing period 4 hours90 days, a dimensionally stable calcium sulfoaluminate (CSA) cement, consisting of 83% CSA clinker and 17% natural gypsum by mass, and an expansive cementitious blend (MIX), composed by 40% CSA clinker, 40% CEM Iclass 52.5 R ordinary Portland cement (OPC) and 20% natural gypsum by mass, were submitted to shrinkage and compressive strength tests as well as differential thermal-thermogravimetric analysis (DTA-TG) and mercury intrusion porosimetry (MIP). OPC was also used as a reference term. The early and late mechanical strengths were respectively highest for CSA cement and lowest for MIX cement which, furthermore, showed the minimum shrinkage. These phenomena were attributed to (i) the faster reaction rate of CSA and MIX cements, and (ii) the non-expansive/expansive nature of ettringite respectively formed. Each investigated cement exhibited peculiar features in terms of pore size distribution modalities and threshold pore widths.

Calcium sulphoaluminate cements, mainly composed by 4CaO·3Al2O3·SO3 and 2CaO·SiO2, are special hydraulic binders which require limestone, bauxite and gypsum as natural raw materials for their manufacture. In order to save bauxite and natural gypsum, it has been explored the possibility of using, among the raw mix components, FBC waste together with pulverised coal fly ash or anodization mud and, when necessary, flue gas desulphurization gypsum. Mixtures containing limestone (29–39%), FBC waste (30–44%), pulverised coal fly ash (0–13%) or anodization mud (0–32%), bauxite (0–18%) and flue gas desulphurization gypsum (0–8%) were heated for 2 hours in a laboratory electric oven at temperatures ranging from 1150° to 1300°C. The X-ray diffraction patterns on the burnt products generally showed a good conversion of the reactants and a high selectivity degree towards 4CaO·3Al2O3·SO3, particularly at 1250°C.

The properties of a hydrated high-performance calcium sulfoaluminate (CSA) cement were investigated by means of XRD, DTA-TGA, SEM analyses and mercury porosimetry The early hydration behaviour was strongly influenced by the high (0.78) stoichiometric water-solid mass ratio required by the reaction of C(4)A(3)(S) over bar with calcium sulfate and water towards ettringite and aluminium hydroxide. The high rate of this reaction resulted into a rapid depletion of water within a relatively short curing period and both full consumption of reactants and hydration of other CSA cement components were hindered. However, C(4)A(3)(S) over bar conversion degrees of 0.60 and 0.87 were obtained at 3 hours and 28 days respectively, for CSA cement pastes cured with a water-cement ratio equal to 0.45. Both the fast formation of ettringite and the rapid establishment of prevailing low-porosity regions can play a very important role in regulating the technical behaviour of high-performance CSA cements.

The peculiar chemical and mineralogical composition of fluidized bed combustion (FBC) waste complicates its landfill disposal and/or utilization in the ordinary cement and concrete industry [1]: upon hydration, exothermal and expansive phenomena occur and the ash pozzolanic activity is poor due to its reduced glass content associated with the relatively low combustion temperature. Recent papers [2,3] have shown that special cements based on calcium sulphoaluminate, 4CaO3Al2O3SO3 ( S A C 3 4 , according to the cement chemistry notation under which C=CaO; A=Al2O3;S=SO3, S=SiO2 and H=H2O), can be successfully synthesized at a laboratory scale from raw mixes containing limestone, bauxite, FBC bottom and/or fly ash heated at 1200°1300°C. The key-component of calcium sulphoaluminate (CSA) cement, S A C 3 4 , and dicalcium silicate, C2S, are easily obtained by reactions in which limestone and bauxite act as primary sources of CaO and Al2O3, respectively, while FBC waste gives substantially SiO2 and sulphate toghether with significant additional amounts of lime and alumina. The Al2O3 content of FBC waste enables a reduction of concentration of an expensive natural material like bauxite in the raw mix generating CSA clinker, but it is relatively low and additional cheap sources of alumina are required in order to obtain a more significant saving of bauxite. To this end in a previous paper [3] the possibility of using, as raw mix component, a lowquality fly ash with a high loss in ignition, generated in a traditional pulverized coal-fired plant, has been investigated. A flue gas desulphurization (FGD) gypsum, coming from the same power plant, was also utilized as supplementary source of sulphate: very satisfactory results were obtained in terms of conversion and selectivity towards the desired hydraulic compounds, S A C 3 4 and C2S. The bauxite saving increased to 28%. In this work the hydration behaviour of two CSA cements, prepared by addition of FGD gypsum to clinkers obtained from raw mixes basically containing limestone, bauxite, pulverized coal fly ash, FBC bottom and/or fly ash, was investigated using differential thermal-thermogravimetric analysis (DTA-TGA), scanning electron microscopy (SEM) and mercury porosimetry as main characterization techniques.

Through laboratory burnability tests and industrial runs carried out for 1 month in a dry processcement kiln it has been found that an oil well-derived drilling waste and an electric arc furnace (EAF) slag generated in a steel plant are suitable partial substitutes for both limestone and clay in the kiln feed.Drilling waste was available in two streams: the one, muddy and argillaceous; the other, rocky and calcareous. Both gave satisfactory burnability indexes (BI) and high percentages of replacement of limestone (up to 38%) and clay (up to 72%).EAF slag was introduced in the kiln feed at a lesser degree (20%), but promoted a better raw mix burttability: furthermore, being a non-carbonated source of lime, it allows a reduction of both thermal requirement and emission of COZ, gas responsible for the greenhouse effect.The manufacturing process of waste-based clinkers was environmentally compatible and the related cements were similar in performance to common hydraulic binders. (c) 2007 Published by Elsevier B.V.

In this paper coal–fuel oil ash has been characterized in terms of leaching behaviour and reactivity against lime and gypsum in hydratory systems for the manufacture of building materials. Its behaviour was also compared to that of coal ash. Metal release was measured in a dynamic leaching test with duration up to 16 days. The results have shown that coal–fuel oil ash behaves very similarly to coal ash. The reactivity of coal–fuel oil ash against lime and gypsum was measured in mixtures containing only lime and in mixtures containing both lime and gypsum. These systems were hydrated at 25 and 40 °C under 100% R.H. The results have shown that the main hydration products are the same as those that are usually formed in similar coal ash-based systems. That is, calcium silicate hydrate in coal–fuel oil ash/lime systems and calcium silicate hydrate plus calcium trisulphoaluminate hydrate in coal–fuel oil ash/lime/gypsum systems. From the quantitative point of view, hydration runs showed that the amounts of both chemically combined water and reacted lime measured in the case under investigation are very similar to those found in similar coal ash-based systems. Finally, the measurement of unconfined compressive strength proved that the systems have potentiality for the manufacture of pre-formed building blocks.

The hydration processes of mixtures containing calcined gypsum, blastfurnace slag or fly ash, portland cement and/or hydrated lime, able to generate calcium trisulphoaluminate and silicate hydrates, have been studied by means of differential thermal analysis. Samples were aged at 55°,70° and 85°C for 16, 24 and 48 hours, followed by a further curing at room temperature and humidity up to 28 days.

Wastes generated in a bench-scale atmospheric fluidized bed combustor, using two different coals and a high-lime limestone, sorbent, were employed as raw materials for the synthesis of calcium sulphoaluminate (4 CaO·3 Al2O3·SO3)-based cements, which can be utilized for a wide range of applications. Raw mixes containing the bed material were heated in an electric oven in the temperature range 1000°–1200°C. The best results in terms of reactants conversion, and selectivity towards 4 CaO·3 Al2O3·SO3 were obtained at 1200°C with the addition of an external source of alumina which was required to avoid melting phenomena or integrate the Al2O3 content, necessary for the 4 CaO·3 Al2O3·SO3 formation.