Sodium silicate activated slag‐fly ash binders: Part I – Processing,microstructure, and mechanical properties

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 ± 1.5 MPa and Weibull average compressive strength of 60 ± 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.     

Temperature stability of a pure metakaolin based K-geopolymer: Part 2. Variations in the mesoporous network and its rehydration stability

The thermal behavior of a model MK-based K-geopolymer was investigated between room temperature and 1400°C in order to evaluate its potentiality for high-temperature applications. The purpose of our study was to monitor the behavior of a geopolymer during a temperature rise in order to better understand its variations with respect to temperature. The works from the present paper focus only changes in the porous network; it follows a first part devoted to variations in the mineral matrix. The results obtained here show that the geopolymer material preserves its porous integrity up to 800°C, while maintaining the reversibility of water exchanges corresponding to about 25 weight percent. Together with the results of part 1, the findings of this study allow us to affirm that geopolymer materials are only very little affected by temperatures up to 800°C, or even 900°C (keeping its mesoporous amorphous structure).     

Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network

The thermal behavior of a model MK based K-geopolymer (Si/Al = 1.38 and K/Al = 0.68; obtained by alkaline activation of a very pure metakaolin) was investigated between room temperature and 1400°C in order to evaluate its potentiality for high-temperature applications. The purpose of our study was to monitor the behavior of a geopolymer during a temperature rise in order to better understand its variations with respect to temperature. The works from the present paper focus only variations in the internal structure of the mineral matrix. The results presented here show that the amorphous mineral matrix is preserved up to 900°C. The results also show that there is a densification of the internal structure of tetrahedral network during heating, due to changes in the Q³ environments in fully-connected Q⁴ for both silicates and aluminates. Thus, our work provides a new more precise vision of the 3D geopolymeric mineral matrix for which the silicoaluminous network is not exclusively composed of Q⁴ entities, contrary to what is frequently encountered in the literature before.     

聚合MDI粘合剂在人造板工业中的应用

聚合MDI作为粘合剂应用于人造板加工业的起源、发展、特点、工业化中尚存在的一些问题及解决方法     

Pore solution in alkali-activated slag cement pastes. Relation to the composition and structure of calcium silicate hydrate

In this work, the relationship between the composition of pore solution in alkali-activated slag cement (AAS) pastes activated with different alkaline activator, and the composition and structure of the main reaction products, has been studied. Pore solution was extracted from hardened AAS pastes. The analysis of the liquids was performed through different techniques: Na, Mg and Al by atomic absorption (AA), Ca ions by ionic chromatography (IC) and Si by colorimetry; pH was also determined. The solid phases were analysed by XRD, FTIR, solid-state ²⁹Si and ²⁷Al NMR and BSE/EDX.The most significant changes in the ionic composition of the pore solution of the AAS pastes activated with waterglass take place between 3 and 24 h of reaction. These changes are due to the decrease of the Na content and mainly to the Si content. Results of ²⁹Si MAS NMR and FTIR confirm that the activation process takes place with more intensity after 3 h (although at this age, Q² units already exist). The pore solution of the AAS pastes activated with NaOH shows a different evolution to this of pastes activated with waterglass. The decrease of Na and Si contents progresses with time.The nature of the alkaline activator influences the structure and composition of the calcium silicate hydrate formed as a consequence of the alkaline activation of the slag. The characteristic of calcium silicate hydrate in AAS pastes activated with waterglass is characterised by a low structural order with a low Ca/Si ratio. Besides, in this paste, Q³ units are detected. The calcium silicate hydrate formed in the pastes activated with NaOH has a higher structural order (higher crystallinity) and contains more Al in its structure and a higher Ca/Si ratio than those obtained with waterglass.     

Dip-coating technique for the manufacture of alumina microfilters using PVA and Na-CMC as binders: a comparative study

α-Alumina microfiltration flat-membranes have been prepared using the dip-coating procedure. The effect of slip concentration (<30 wt.%), coating time and binder type (PVA and Na-CMC) on the thickness, porosity, roughness and effective pore diameter of the membrane layers has been investigated. A new method for the characterization of the membrane layer based on gas permeation has been presented and the pertaining equations derived. The method is applicable if permeability measurements embrace both Knudsen and Poiseuille flow regimes.     

Advantageous features of sodium silicate as the plasticizer for low-cement refractory castables

The plasticizing effect of an aqueous sodium silicate solution of low concentration (0.3 – 0.4%) on the properties of a low-cement refractory castable is studied. The merits of using sodium silicate, rather than the conventional sodium tripolyphosphate, for plasticizing sintered refractory castables are emphasized.Translated from Novye Ogneupory, No. 9, pp. 48 – 51, September, 2004.     

Use of reservoir clay sediments as raw materials for geopolymer binders

Abstract

Abstract

Among low cost or readily available raw materials, reservoir clay sediments are of interest as potential precursors in geopolymer binder manufacture. These materials come from dredging of reservoirs because periodical sediment removal is necessary in order to keep a satisfactory level of functionality. In this paper, two sediments, coming from reservoirs located in Southern Italy, have undergone preliminary characterisation by X-ray diffraction, differential thermogravimetry and Fourier transformed infrared (FTIR) spectroscopy. Then, the sediments were submitted to 1 and 2 h calcination treatments at 650 and 750°C. The effects of calcination were evaluated by means of ²⁷Al magic angle spinning nuclear magnetic resonance and FTIR. The calcined samples were mixed with 5M NaOH solution, and the obtained mixtures were studied for reactivity by means of differential scanning calorimetry. Finally, cylindrical samples were prepared with the same mixtures and cured for 3 days at 60°C plus 4 and 25 days at room temperature. The obtained samples were subjected to unconfined compressive strength determinations in order to verify the actual occurrence of geopolymerisation. The results show that the calcined clay sediments can be suitable precursors in polycondensation reactions.     

Factors affecting the suitability of fly ash as source material for geopolymers

The suitability of fly ash stock piles for geopolymer manufacturing was studied. The results of chemical analyses, X-ray diffraction (XRD) and particle size distribution (PSD) of five sources of fly ash obtained from coal-fired power generating plants in the US are presented. Geopolymer paste and concrete specimens were prepared from each stock pile. The specimens were subjected to an array of chemical and mechanical tests including XRD, RAMAN spectroscopy, setting time and compressive strength. A correlation study was undertaken comparing the fly ash precursor chemical and crystallographic compositions as well as particle size distribution, with the mechanical and chemical characteristics of the resulting geopolymer. Factors inherent to the fly ash stockpile such as particle size distribution, degree of vitrification and location of the glass diffraction maximum were found to play an important role in the fresh and hardened properties of the resulting geopolymer.     

Cementitious mixtures containing industrial process wastes suitable for the manufacture of preformed building elements

Mixtures made from materials containing reactive oxides of calcium, aluminium, sulphur and silicon which are able, upon hydration, to generate calcium trisulphoaluminate and silicate hydrates, have been studied with a view to possible applications in the field of preformed building elements. The materials employed were natural gypsum, phosphogypsum, fly ash, blast furnace slag, Portland cement and hydrated lime. The samples were cured at 55, 70 and 85°C and 100% RH for 24 h, followed by further curing at ordinary temperatures and humidities (21°C, 67% RH) for up to 28 days. The cured samples were tested for compressive strength and shrinkage. It has been found that the most important effect on the strength is due to the pre-curing temperature, while the post-curing time has much less effect. In general, the optimum pre-curing temperature is 70°C. Satisfactory strength results were obtained even with systems containing up to 80% waste materials.     

Effect of Al2O3 addition on the thermal expansion of sodium alkaline-earth silicate glasses: A molecular dynamics study

Coefficient of thermal expansion (CTE) is an important property to consider when utilizing oxide glasses in thermal treatment processes to avoid thermal damage at the interfaces of the glasses with heterogeneous materials. It is thus important to know the effect of additives on CTE for designing glasses. The use of alumina efficiently improves chemical and mechanical durability of oxide glasses while maintaining the functionality and productivity; however, alumina-doping often induces nonlinear variation of CTE. In this work, we therefore tried to investigate the relationship between CTE and the microstructure of sodium alkaline-earth aluminosilicate glasses using classical molecular dynamics (MD) simulations. To accurately model the glasses, we extended a force-matching potential by optimizing the parameter sets for Ca–O, Mg–O, and Na–O pair interactions using Bayesian optimization. The MD simulations reproduced the nonlinear variation of CTE as a function of alumina content, and detailed structural analyses identified inhomogeneous expansion in the glasses. It was found that the nonuniform CTE change at the nanoscale was related to the formation of an alumina-rich region, in which more fivefold-coordinated aluminum exist, when alumina content exceeded Na₂O content. Accordingly, the microstructural change by alumina-doping was identified as the origin of the nonlinear variation in the CTE of the glasses.     

An improved basis for characterizing the suitability of fly ash as a cement replacement agent

Fly ash is a critical material for partial replacement of ordinary portland cement (OPC) in the binder fraction of a concrete mixture. However, significant compositional variability currently limits fly ash use. For example, the performance of OPC‐fly ash blends cannot be estimated a priori using current characterization standards (eg, ASTM C618). In this study, fly ashes spanning a wide compositional range are characterized in terms of glassy and crystalline phases using a combination of X‐ray fluorescence (XRF), X‐ray diffraction (XRD), and scanning electron microscopy with X‐ray energy‐dispersive spectroscopy (SEM‐EDS) techniques. The compositional data are distilled to a unitless parameter, the network ratio (N_r), which represents the network behavior of atoms that form alkali/alkaline earth‐aluminosilicate glasses that make up fly ashes. N_r is correlated with known composition‐dependent features, including the glass transition temperature and amorphous XRD peak (“hump”) position. Analysis of heat release data and compressive strengths are used to evaluate the impact of fly ash compositions on reaction kinetics and on the engineering properties of cement‐fly ash blends. It is shown that fly ashes hosting glasses with a high network ratio (ie, having a less stable glass structure) are more reactive than others.     

Enhancing fracture strength of ceramic core using sodium silicate as the binder

Ceramic cores used in the casting must exhibit high heat resistance because they come in direct contact with molten metals. Therefore, in this study, ceramic cores with high heat resistance and fracture strength were fabricated using sodium silicate as the binder instead of a commonly used organic binder. In addition, the prepared ceramic core was coated with Si and Si-Na precursors as the inorganic binder to improve the firing strength of the ceramic core. The thermal stability and firing strength of the sample were investigated. The results revealed that the firing strength of the ceramic core was significantly improved up to 15.2 MPa owing to the formation of a glass phase between the ceramic particles, which was formed by the reaction of sodium silicate and the inorganic binder precursor. In addition, the core was completely decomposed in an NaOH solution at a relatively low temperature of 60°C, indicating the excellent elution properties of the sample. These results indicate that the method proposed in this study is suitable for the preparation of ceramic cores with high fracture strength and excellent elution behavior.     

粉煤灰掺量及颗粒群分布与水泥浆体流变性的关系研究

研究了原状粉煤灰与磨细粉煤灰不同掺量和不同颗粒群分布与水泥浆流变性能的相互关系。结果发现:原状粉煤灰加入水泥后具有降低水泥浆的粘度与屈服值的作用,且随粉煤灰细度及掺量的增加而更明显;磨细粉煤灰加入水泥后具有提高水泥浆的粘度与屈服值的效应,且随粉煤灰细度及掺量的增加而更突出。用灰色关联分析原理证实了原状灰<10μm的颗粒含量与水泥浆的流变性呈负关联,即对改善水泥的流动性是有益的;而磨细灰<10μm的颗粒含量与水泥浆的流变性呈正关联,即对提高水泥的流动性是不利的。     

Use of fly ash as an admixture for electromagnetic interference shielding

The use of fly ash as an admixture results in enhancement of the electromagnetic interference (EMI) shielding effectiveness from 4 to 8 dB at 1 GHz, whereas the use of silica fume as an admixture results in negligible effect on the shielding effectiveness. The DC electrical resistivity is decreased slightly by silica fume, but is essentially not affected by fly ash. Both fly ash and silica fume cause slight increases in the reflectivity. The effectiveness of fly ash for shielding is attributed to the Fe₂O₃ component (15.4 wt.%) in the fly ash.     

Effect of magnesium aluminum silicate glass on the thermal shock resistance of BN matrix composite ceramics

The effects of magnesium aluminum silicate (MAS) glass on the thermal shock resistance and the oxidation behavior of h‐BN matrix composites were systematically investigated at temperature differences from 600°C up to 1400°C. The retained strength rate of the composites rose with the increasing content of MAS showing a maximum value at the 60 wt% MAS. Compared with the original strength, the retained strength of the specimen after thermal shock increased to 77% (ΔT=1000°C). The strengthening effect of MAS and the surface microstructural evolution of composites are responsible for the improved thermal shock resistance. Surface oxidation of the composites during the thermal shock process plays a positive role in enhancing the retained strength by self‐healing cracks and the appearance of the compressive stress. The oxide layer also acted as a thermal barrier to decelerate the actual thermal stress. Furthermore, this dense layer also improved the oxidation resistance of h‐BN matrix composites by prevent diffusion of oxygen. These results indicated that short‐term surface oxidation during thermal shock process is favorable to the enhancement of the thermal shock resistance of BN‐MAS composite ceramics.     

城市垃圾焚烧飞灰处理技术及其在水泥生产中资源化利用

分析了城市垃圾处理技术的现状和发展趋势;介绍了城市垃圾焚烧飞灰处理技术的发展和资源化利用的紧迫性;阐述了水泥生产中资源化利用垃圾焚烧飞灰的可行性和前景;回顾了国内外水泥生产协同处理固体废物技术的发展历程,并提出了目前亟需解决的一些关键技术。在广泛研究的基础上,明确指出了水泥生产中资源化利用垃圾焚烧飞灰是实现焚烧飞灰资源化利用和无害化处理的重要途径。     

Sucrose retards the reaction of non-calcium geopolymers: An implication for developing kinetics-controlling admixtures

For geopolymers (no or low calcium), the chemical admixtures designed for ordinary portland cement are either inefficient or ineffective. In this study, the effects of sucrose on the kinetics of geopolymerization (no calcium) were investigated. From calorimetry tests, we found sucrose retarded the geopolymerization of sodium silicate-activated metakaolin. This retardation is unlikely to be related to the dissolution of metakaolin, since sucrose also hindered the reaction of the synthetic gel (no metakaolin) as evidenced by the smaller particle sizes under microscopy. Further spectroscopy and total organic carbon (TOC) tests indicated that sucrose did not adsorb or chemically interact with the synthetic aluminosilicate gel and the intermediate (alumino)silicate species. In contrast, the retardation mechanism was found to be due to the interaction of sucrose with alkalis in the solution, partially based on the structural characterization of sucrose under alkaline condition. To the best of our knowledge, this work is the first of its type to explore and understand the reaction-controlling admixtures for non-calcium geopolymers.     

Thermal plasma vitrification process as an effective technology for fly ash and chromium‐rich sewage sludge utilization

The main goal of the vitrification process for environmental research is the destruction of hazardous waste. This study proposes the use of a thermal plasma treatment process to transform fly ash and chromium‐rich sewage sludge into glassy products called vitrificates that can be stored on the land without harmful environmental effects. This is achieved by: (i) decreasing the temperature and energy used to adjust process cost minimization; and (ii) stabilization of vitrificates for different compositions of waste mixture. The chemical stabilization of final products was examined by heavy metals leachability tests. Hardness tests were done to verify the physical stabilization of vitrificates. The most stable vitrificates were obtained from a sample consisting of 90 wt% fly ash and 10 wt% chromium sludge. The thermal plasma treatment is an effective method which can be used to convert hazardous waste mixtures into less toxic or inert glassy products. The chemical composition of raw materials influenced the chemical and physical properties of the vitrificates and determined their internal structures. Mixtures of two different hazardous wastes reduces the process cost without negative environmental impact, which is an innovation in thermal plasma treatment technology. © 2013 Society of Chemical Industry     

Stability and rheological study of sodium carboxymethyl cellulose and alginate suspensions as binders for lithium ion batteries

Currently, the most widely used binder in batteries is polyvinylidene fluoride with N‐methyl‐2‐pyrrolidone used as a solvent. This solvent is flammable and toxic. Here, we focus on the suitability of using water‐soluble sodium alginate (Na‐alginate) and sodium carboxymethyl cellulose (Na‐CMC) as alternative biobased binder materials for the anodes of lithium ion batteries. It reduces the environmental impact of current manufacturing processes. However, control of the rheological characteristics of the binder whilst containing active and conductive additives is key for optimized processing. Here, we perform stability and rheological measurements of Na‐alginate and Na‐CMC solutions containing varying amounts of graphite and carbon black used as active and conductive materials, respectively. Compared with the benchmark Na‐CMC, the degree of flocculation shows that for the same concentration of binder in water, Na‐alginate suspensions are more stable. The rheology measurements show that Na‐alginate slurries have a higher viscosity than Na‐CMC at a shear rate of 50 s^?1 with that for a 1.5% of Na‐alginate binder being 1.26 Pa s while for Na‐CMC it was for 0.20 Pa s. The loss factor was lower for Na‐Alginate, between 2 and 3 against between 2.9 and 3.3 for Na‐CMC, showing a more developed network structure. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46217.