Use of Ash and Slag Waste from Thermal Power Plants as an Active Component of Building Materials (original) (raw)
Related papers
Materials
The article considered the issues of the modification of gypsum stone to improve its performance properties. The influence of mineral additives on the physical and mechanical characteristics of the modified gypsum composition is described. The composition of the gypsum mixture included slaked lime and an aluminosilicate additive in the form of ash microspheres. It was isolated from ash and slag waste from fuel power plants as a result of their enrichment. This made it possible to reduce the carbon content in the additive to 3%. Modified compositions of the gypsum composition are proposed. The binder was replaced with an aluminosilicate microsphere. Hydrated lime was used to activate it. Its content varied: 0, 2, 4, 6, 8 and 10% of the weight of the gypsum binder. Replacing the binder with an aluminosilicate product for the enrichment of ash and slag mixtures made it possible to improve the structure of the stone and increase its operational properties. The compressive strength of th...
Shrinkage and Related Properties of Alkali-Activated Binders Based on High MgO Blast Furnace Slag
Doctoral thesis, 2019
Concrete is the second most used material in the world just after water. A drawback is that it is mostly based on Portland cement, which has an extremely high carbon footprint reaching a staggering 900 kg/tonne. The carbon dioxide emissions related to the production of the Portland cement accounts for nearly 8 % of the global total. Consequently, the construction sector is engaged in an active search for sustainable alternatives. Over the past few decades, alkali-activated materials (AAMs) emerged as one alternative and attracted strong scientific and commercial interests. Many industrial by-products produced in large volumes can be used as precursors for the AAMs system. The most common include blast furnace slag, fly ash, mine tailings, metallurgical slags, and bauxite residues. So far, products based on ground granulated blast furnace slag (GGBFS) showed the best price/performance ratio. Still, there are a number of unresolved issues, which must be addressed to ensure the economical and safe full-scale utilisation of that material. The research work presented in this thesis focuses on alkali-activated concretes based on Swedish water-cooled high-MgO ground granulated blast furnace slag. The objective of this work was to identify experimentally factors that are controlling the shrinkage and the creep of concretes made with this type of GGBFS and to understand their influence on various physical and chemical properties of fresh and solidified systems. Liquid sodium silicate, powder sodium carbonate and a combination of both were used to activate the binder chemically. Two curing procedures were followed; laboratory curing and heat curing at 65°C applied for 24 hours. Various properties were determined including workability, setting time, hydration heat development, shrinkage, creep, efflorescence, carbonation, compressive strength, microstructure and phase composition. Additionally, the effects of the activator type, dose, binder fines, binder composition and curing regime were investigated. The results revealed that the particle size distribution of the binder as well as the activator type and its dosage have strong effects on the produced materials. Increasing the activator amount or decreasing the alkali modulus of the used sodium silicate activator improved the early-age compressive strength and accelerated the hydration reaction. Alkali-activated high-MgO slag concrete showed higher autogenous and drying shrinkage, as well as higher creep in comparison to the Portland cement-based reference concrete. The sodium silicate increased the slump, shortened the setting time, increased the compressive strength and shrinkage but lowered the creep in comparison with the sodium carbonate-activated mixes. Replacing 20% of the slag with fly ash and decreasing the alkali modulus of the sodium silicate activator increased the autogenous shrinkage but decreased the ultimate drying shrinkage. Application of a heat treatment produced in general a higher early age compressive strength, a lower VI later strength development, a more porous microstructure and a decreased ultimate measured shrinkage. Sealed curing decreased the ultimate shrinkage by up to 50%. Some of the produced mixes showed strong efflorescence. Two years of curing in laboratory conditions resulted in an extensive carbonation of some of the mixes. This weakened the silicate binding of the gel and produced a coarser porosity due to the decalcification of C-(A)-S-H. The heat-cured samples activated with sodium silicate were the most affected. Many mixes showed an extensive microcracking of the binder matrix. However, the within this study newly developed mixes were substantially less effected. These optimised mixes were based on a combination of sodium silicate and sodium carbonate activators, combined with a heat treatment and partial replacement of the slag with fly ash. The main hydration phase that formed was C-(A)-S-H, with gaylussite, calcite, nahcolite and hydrotalcite as secondary phases. The partial replacement of slag with fly ash resulted in a dominant formation of N-(A)-S-H and C-(A)-S-H
Materials, 2019
The effects of fines and chemical composition of three types of ground granulated blast furnace slag (GGBFS) on various concrete properties were studied. Those studied were alkali activated by liquid sodium silicate (SS) and sodium carbonate (SC). Flowability, setting times, compressive strength, efflorescence, and carbonation resistance and shrinkage were tested. The chemical composition and microstructure of the solidified matrixes were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) coupled with EDX analyser. The results showed that the particle size distribution of the slags and the activator type had significantly stronger effects on all measured properties than their chemical composition. The highest compressive strength values were obtained for the finest slag, which having also the lowest MgO content. SC-activated mortar produced nearly the same compressive strength values independently of the used slag. The most intensive efflorescence and the lowest carbonation resistance developed on mortars based on slag containing 12% of MgO and the lowest fineness. The slag with the highest specific surface area and the lowest MgO content developed a homogenous microstructure, highest reaction temperature and lowest drying shrinkage. Thermogravimetric analysis indicated the presence of C-(A)-S-H, hydrotalcite HT, and carbonate like-phases in all studied mortars.
Influence of bed ash on the rheology and properties of gypsum building mixtures
E3S Web of Conferences
In the article, the influence of the aluminosilicate part of fuel bottom ash and slag mixtures on the water demand of gypsum raw materials of dry building mixtures is considered. It is shown that the aluminosilicate filler has a plasticizing effect. This is due to the presence of microspheres in the composition of the filler. They reduce the amount of water needed to achieve normal gypsum paste consistency. This is reflected in other physical, mechanical and structural characteristics of gypsum. The ash filler in the optimal ratio with the gypsum binder compacts the structure of the stone. does not participate in chemical transformations. To increase the efficiency of the ash filler, it is necessary to introduce additional components that activate the processes of structure formation in ash-gypsum binders.
Materiales de Construcción, 2013
This study assesses the viability of using an agro-industrial by-product, rice husk ash (RHA) from a Colombian rice company's combustion facility, as a total replacement for the commercial sodium silicate ordinarily used in alkaliactivated binders. Fly ash (FA), granulated blast furnace slag (GBFS) and binary 50FA:50GBFS blended pastes were activated with a mix of sodium hydroxide and either sodium silicate or one of two types of RHA. The pastes were characterised for strength, mineralogy and microstructure. The findings showed that the agro-industrial by-product can be used to yield alkali-activated materials with 7-day mechanical strengths on the order of 42 MPa. The study confirmed that both amorphous silica and part of the crystalline silica present in RHA participate in the alkaline activation process, providing the alkalinity is suitably adjusted.
Alkali silicate activated slag and class F fly ash-based binders are ambient curing, structural materials that are feasible replacements for ordinary Portland cement (OPC). They exhibit advantageous mechanical properties and less environmental impact than OPC. In this work, five sodium silicate activated slag-fly ash binder mixtures were developed and their compressive and flexural strengths were studied as a function of curing temperature and time. It was found that the strongest mixture sets at ambient temperature and had a Weibull average flexural strength of 5.7 AE 1.5 MPa and Weibull average compressive strength of 60 AE 8 MPa at 28 days. While increasing the slag/fly ash ratio accelerated the strength development, the cure time was decreased due to the formation of calcium silicate hydrate (C-S-H), calcium aluminum silicate hydrate (C-A-S-H), and (Ca,Na) based geopolymer. The density, microstructure, and phase evolution of ambient-cured, heat-cured, and heat-treated binders were studied using pycnometry, scanning electron microscopy, energy dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffraction (XRD). Heat-cured binders were more dense than ambient-cured binder. No new crystalline phases evolved through 28 days in ambient-or heat-cured binders.
2011
Hydrothermal reactions among lime, silica, alumina and calcium sulfate are of interest for the production of preformed building components, due to the generation of binding products such as calcium silicate hydrate (CSH) and ettringite (6CaO·Al2O3·3SO3·32H2O). Coal fly ash and flue gas desulfurization (FGD) gypsum can be used together with lime as suitable raw materials for the manufacturing process. A laboratory investigation on the hydration behaviour of two ternary systems containing 35% calcium hydroxide, 25% fly ash and 40% FGD gypsum or natural gypsum (as a reference material) was carried out using X-ray diffraction and differential thermal analyses as main characterization techniques. The amounts of the constituents of both mixtures were nearly stoichiometric for the formation of ettringite and a calcium silicate hydrate with a CaO/SiO2 molar ratio equal to 1.5. Water/solid mass ratio was 0.75. Curing temperatures and times were 55°, 70°, 85°C, and 1, 3, 7 days, respectively....
Mineralogical and microstructural characterisation of alkali-activated fly ash/slag pastes
2003
A mechanical, mineralogical and microstructural characterisation of the cement pastes obtained by alkaline activation of fly ash/ slag mixtures cured at different temperatures has been carried out. The pastes obtained were characterised by XRD, FTIR, MAS NMR, SEM/EDX, atomic absorption and ion chromatography, also the insoluble residue in HCl was determined. The results obtained have proved the existence of two different reaction products in those activated pastes. The average atomic ratios in the main reaction product were Ca=Si $ 0:8, Al=Ca $ 0:6, Si=Al $ 2-3. Such analysis corresponds to calcium silicate hydrate rich in Al, which includes Na in its structure. Other reaction product which was detected in the pastes as result of fly ash activation, was an alkaline aluminosilicate hydrate with a three-dimensional structure.
Sodium silicate activated slag-fly ash binders: Part III-Composition of soft gel and calorimetry
Sodium silicate activated, slag-fly ash binders are potential alternative binders to Portland cement. In this study, the early age properties of slag-fly ash binders namely, set time, and heats of reaction were investigated. Set time was investigated using a combination of two methods namely, the ASTM C403 penetration testing, and s-wave ultrasonic wave reflectometry (SUWR). The discrepancy in set time identified by these two methods suggested the presence of a soft gel which eventually hardened with time. The composition of this soft gel was analyzed by suspending the chemical reaction of the binder after the soft gel formed, but before it hardened. In order to analyze the composition of the soft gel, selective chemical extractions were performed on the binder. 29 Si Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR), and FTIR spectroscopy were performed on binders and extraction residues. The soft gel contained a modified calcium silicate hydrate gel (C-N-S-H where N=Na), with a short mean chain length and no observable Al incorporation. Orthosilicate units were also found to be present in relatively high proportions when compared to hardened binders at later ages.
Minerals
Numerous factors influence the complexity of environmental and waste management problems, and the most significant goal is the reuse of materials that have completed their “life cycle” and the reduction in the use of new resources. In order to reduce impact of waste slag on the environment, in the present study, waste slag, generated in heating plants after lignite combustion, was characterized in detail and tested for application as a replacement for cement in mortar or concrete production. For physical–chemical characterization of slag, different experimental and instrumental techniques were used such as chemical composition and determination of the content of heavy metals, investigation of morphological and textural properties, thermal analysis, X-ray, and infrared spectroscopy. Physical–mechanical characterization of slag was also performed and included determination of activity index, water requirement, setting time and soundness. A leaching test was also performed. Presented r...