Diffusivity and micro-hardness of blended cement materials exposed to external sulfate attack

Many degradation processes in cement based materials include the diffusion of one or more chemical species into concrete and consequent chemical reactions which alter the chemical and physical nature of the microstructure. External sulfate attack is mostly described by a coupled diffusion-reaction mechanism which leads to the decomposition of hardened cement constituents and cracking of the paste. This paper discusses the significance of diffusion properties and chemical changes in external sulfate attack in blended cement based composites. A method based on Particle Induced X-ray Emission (PIXE) was developed to measure the diffusion properties in a non-destructive test method. Quantitative Energy Dispersive Spectrometry (EDS) and micro-hardness technique were also used to study the chemical and mechanical changes from sulfate attack. Diffusion coefficients and rates of reaction were determined for paste and mortar mixtures, showing higher diffusion rates and lower hardness values in mortar compared to paste for control mixtures. Partial replacement of cement with fly ash improved the transport properties and reduced the level of damage in exposure to sulfate attack.     

Thermodynamic equilibrium calculations in cementitious systems

This review paper aims at giving an overview of the different applications of thermodynamic equilibrium calculations in cementitious systems. They can help us to understand on a chemical level the consequences of different factors such as cement composition, hydration, leaching, or temperature on the composition and the properties of a hydrated cementitious system. Equilibrium calculations have been used successfully to compute the stable phase assemblages based on the solution composition as well as to model the stable phase assemblage in completely hydrated cements and thus to asses the influence of the chemical composition on the hydrate assemblage. Thermodynamic calculations can also, in combination with a dissolution model, be used to follow the changes during hydration or, in combination with transport models, to calculate the interactions of cementitious systems with the environment. In all these quite different applications, thermodynamic equilibrium calculations have been a valuable addition to experimental studies deepening our understanding of the processes that govern cementitious systems and interpreting experimental observations. It should be carried in mind that precipitation and dissolution processes can be slow so that thermodynamic equilibrium may not be reached; an approach that couples thermodynamics and kinetics would be preferable. However, as many of the kinetic data are not (yet) available, it is important to verify the results of thermodynamic calculations with appropriate experiments. Thermodynamic equilibrium calculations in its different forms have been applied mainly to Portland cement systems. The approach, however, is equally valid for blended systems or for cementitious systems based on supplementary cementitious materials and is expected to further the development of new cementitious materials and blends.     

Effect of rice-husk ash on durability of cementitious materials

In this paper the effects of partial replacements of Portland cement by rice-husk ash (RHA) on the durability of conventional and high performance cementitious materials are investigated. Different percentages of RHA replacement levels, two RHAs (amorphous and partially crystalline optimized by dry-milling) and several water–cementitious materials ratio are studied. The following durability aspects were tested: air permeability, chloride ion penetration, alkali-silica expansion, sulfate and acid resistance. The results were compared with those of cementitious materials without RHA. It is concluded from the tested properties that the incorporation of both RHAs in concretes show different behaviors for air permeability and chloride ion penetration depending on the water/cementitious materials ratio used; in mortars, it reduces the mass loss of specimens exposed to hydrochloric acid solution and decreases the expansion due to sulfate attack and the alkali-silica reaction. The results of durability aspects due to physical or pozzolanic effects after the addition of both RHAs, and its chemical composition, in general indicate an enhanced performance, proving the feasibility of its rational utilization as a supplementary cementing material.     

Nanoindentation and SEM/EDX characterization of the geopolymer-to-steel interfacial transition zone for a reactive porcelain enamel coating

The increasing use of alternative cementitious materials such as geopolymers as an environmentally-friendly alternative to traditional cements requires an improved understanding of the interfacial transition zone (ITZ) between the matrix and reinforcing steels. In this study, nanoindentation measurements were spatially coupled to images with scanning electron microscopy and chemical composition using energy dispersive X-ray microanalysis. The study focused on the microstructure and chemical composition of the interfacial transition zone (ITZ) for reinforcing steel embedded in a geopolymer mortar. The ITZ was analyzed for uncoated steel and steel coated with a reactive porcelain enamel that improves bonding and corrosion resistance. Results indicate that a more gradual transition of mechanical properties and chemical composition for the coated steel coupled with improved integration to the mortar correlates to increased bond strength measured in macroscale experiments.     

Orthophosphates of langbeinite structure for immobilization of alkali metal cations of salt wastes from pyrochemical processes

Mixtures of alkali metal chlorides used as electrolytes in pyrochemical processes for nuclear fuel production and spent nuclear fuel reprocessing were subjected to conversion into orthophosphate ceramic materials based on langbeinite mineral. The results of the solid-state synthesis of the phosphates are described. The phase and chemical composition, chemical stability, and heat resistance of the orthophosphates were studied by X-ray phase analysis, X-ray spectrum microanalysis, emission spectrum analysis, and scanning electron microscopy. Quantitative incorporation of alkali metal cations, including Cs, into such materials was proved. The use of a binder (89% Bi₂O₃ + 11% NaF mixture) considerably increases the density of the ceramic prepared and substantially enhances its chemical stability.     

The effect of the capillary forces on the desorption of hydrogels in contact with a porous cementitious material

This paper examines the desorption of hydrogels in contact with porous cementitious materials to aid in understanding the mechanisms of water release from superabsorbent polymers (SAP) into cementitious materials. The dependence of hydrogel desorption on the microstructure of cementitious materials and relative humidity was studied. It was shown that the capillary adhesion developed at the interface between the hydrogel and cementitious materials increased the desorption of the hydrogels. The size of hydrogels was shown to influence desorption, beyond the known size dependence of bulk diffusion, through debonding from the cementitious matrix, thereby decreasing the effect of the Laplace pressure on desorption. Microscopic examination highlighted a stark contrast in the desorption morphology of hydrogels with different chemical compositions.     

Autonomous bioremediation of a microbial protein (bioremediase) in Pozzolana cementitious composite

The self-bioremediation in cementitious composite material is one of the most interesting avenues relating to damage management and self-life of constructions, which needs to be cogitated. The self-bioremediation of a microbial protein-impregnated cementitious material has been explored in this work. The bioremediase protein was isolated from a hot spring bacterium (BKH1) and incorporated at three different concentrations into commercial Pozzolana cements that are widely used for mortar sample preparation. Artificial cracks were generated within the mortar samples by applying partial breaking load (50 %) and the samples were cured under water for different days. Image analysis by Crackscope and microstructure analysis by field emission scanning electron microscope ascertained the formation of irregular crystalline healing material within the cracks of the test samples. X-ray diffractometer and energy dispersive spectra analyses confirmed that the irregular crystalline structures were due to the deposition of new silicate phase (Gehlenite) within the cracks. Increase of ultrasonic pulse velocity and compressive strength, augmentation of sulphate resistance, decrease of chloride permeability and water absorption capacity revealed that there were overall improvement of mechanical properties and durability of the protein-incorporated mortar samples compared to the control (without protein incorporation) mortar samples. This cost effective and eco-friendly self-bioremediation phenomenon observed in mortar is evolved due to the biosilicification activity of bioremediase protein when amended in mortar samples. The exceptional potential of the microbial bioremediase protein for self-bioremediation attribute may add a new dimension in self-healing construction technology in near future.     

A combined SPM/NI/EDS method to quantify properties of inner and outer C-S-H in OPC and slag-blended cement pastes

To identify the distinct microstructural features and to provide insight into the mechanism by which the phases in hardened paste possess, this study adopts the coupled techniques of quantitative modulus mapping in the form of Scanning Probe Microscopy (SPM) images, nanoindentation (NI), and energy-dispersive X-ray spectroscopy (EDS) for comprehensive investigation on the chemical-mechanical-morphological properties of C-S-H gel in both ordinary Portland cement (OPC) and slag-blended cement pastes. The thickness of the inner C-S-H (IP) layer is precisely measured for the first time by modulus mapping, it varies with the types of unreacted cores as well as the addition of the supplementary cementitious materials. An interface transition zone (ITZ) is found between the unreacted C₃S grain and the surrounding inner C-S-H layer. The mechanical properties of the five types of C-S-H in OPC and the slag-blended pastes are not significantly affected by their chemical compositions. A good correlation between the storage modulus and the indentation modulus of the individual phases is found. The results indicate the significance of SPM-based modulus mapping technique as a powerful tool to characterize the phase in cementitious materials with more attractive features of higher spatial resolution.     

镍基钎料的相组成及其显微组织

采用光学显微镜、X射线衍射仪、电子探针及其能谱仪等仪器对五种不同化学成分的铸态镍基钎料的相组成和显微组织进行了分析。结果表明：五种镍基钎料的相组成和显微组织在一定程度上存在差异，但均为镍固溶体＋化合物共晶组织。     

Comparative study on the corrosion behavior of Ti-Nb and TMA alloys for dental application in various artificial solutions

The corrosion behavior of Ti-Nb dental alloy in artificial saliva with and without the addition of lactic acid and sodium fluoride was investigated by electrochemical techniques, with the commercial Titanium-molybdenum alloy (TMA) as a comparison. The chemical composition, microstructure and constitutional phase were characterized via energy dispersive spectrometry, optical microscope and X-ray diffraction, meanwhile the open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization measurements were carried out to study the corrosion resistance of experimental alloys, with the corroded surface being further characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that the corrosion behavior of Ti-Nb alloy was similar to those TMA alloy samples in both artificial and acidified saliva solutions, whereas statistical analysis of the electrochemical impedance spectroscopy and polarization parameters showed Ti-Nb alloy exhibited better corrosion resistance in fluoridated saliva and fluoridated acidified saliva. SEM observation indicated that TMA alloy corroded heavily than Ti-Nb alloy in fluoride containing saliva. XPS surface analysis suggested that Nb₂O₅ played an important role in anti-corrosion from the attack of fluoride ion. Based on the above finding, Ti-Nb alloy is believed to be suitable for the usage in certain fluoride treated dental works with excellent corrosion resistance in fluoride-containing oral media.     

一类新型碱激发胶凝材料催化剂的研究进展

碱激发固体铝硅酸盐胶凝材料是先进无机非金属材料的前瞻性研究领域之一, 本文对碱激发铝硅酸盐胶凝材料的分类、制备工艺、形成机理以及潜在的应用前景进行了综述; 详尽地论述了碱激发胶凝材料基新型催化剂的最新研究进展, 综合分析了碱激发胶凝材料作为结构材料研究的局限性, 展望了该材料作为新型催化材料的发展动态。     

Surface Roughness in Plasma-Etched $hbox{As}_{bf 2}hbox{S}_{bf 3}$ Films: Its Origin and Improvement

We describe the microstructure of As₂S₃ films and its effect on the morphology of plasma-etched surfaces. The Raman spectroscopy and X-ray photoelectron spectroscopy demonstrated that the observed grainy morphology of etched As₂S₃ surfaces comes from differential chemical attack between different phases within the film. Two approaches were found to be effective for improving the smoothness of etched surfaces: a change in the plasma chemistry from CF₄-O₂ to CHF₃-O₂ and the application of a thin-conformal coating onto structures already patterned using CF₄-O₂ plasma.     

Diffusivity evolution under decalcification: influence of aggregate natures and cement type

Since the decalcification of cement paste has been largely reviewed, we focus our studies on the influence of aggregate nature on this phenomenon in relation to the type of cement used, Ordinary Portland Cement or blended cement with fly ash and slag. Some characteristics of similar mortar mixtures where only aggregate nature differs (lime and siliceous sand) are therefore compared for the two types of cement before and after chemical decalcification induced by ammonium nitrate attack: mechanical strength, microstructure (porosity observed by mercury intrusion and profiles of oxide content trough degraded and sound zones determined by electronic microprobe analysis), transport properties (chloride ions diffusivity, gas and water permeabilities). The characterization of sound mortars underlines that siliceous aggregates promote less porous cementitious matrix. The duplication of ammonium nitrate attacks on same material allows testing the experimental parameters governing the degradation. The flows of calcium leached, the microstructure and the evolution of transport properties with decalcification suggest that limestone aggregates are not inert material. Consequently, for the mortars incorporating siliceous sand, the cementitious matrix is more decalcified and this leads to an amplification of ionic transports, especially through blended cement paste.     

Microstructural characterisation of a glass and a glass-ceramic obtained from municipal incinerator fly ash

Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analyses were used to characterise the microstructure and chemical composition of a glass and a glass-ceramic material obtained from incinerator filter fly ash. Although the as-quenched material (vitrified fly ash) was amorphous under the detection limits of XRD, a dispersion of droplets indicating glass-in-glass phase separation was observed. In the glass-ceramic material (crystallised vitrified fly ash), crystals belonging to the pyroxene group and spinels were identified. The microstructure of the glass-ceramic consisted of crystals embedded in an amorphous glassy phase. The crystalline phases contain a higher amount of metallic elements (e.g. Al, Cr, Fe, Ni and Zn and most probably also other heavy metals) than the residual glassy phase. A change of composition of the residual glass phase in the glass-ceramic product, in comparison with the parent glass, is considered to explain, in comparative terms, the higher toxic potential of the glass-ceramic over the glass. The present results demonstrate that for an accurate assessment of the correlation between toxicity, release of hazardous compounds and microstructure, high-resolution characterisation techniques must be employed. In this context, the effect of crystallisation on the chemical durability of the products remains as an important area for further research.     

Comparison study of microstructure, chemical composition and optical properties between resistive heating and electron beam evaporated LaF3 thin films

LaF₃ thin films were deposited by electron beam (EB) and resistive heating (RH) evaporation, respectively. Properties such as microstructure, chemical composition, surface morphology and optical constants of the LaF₃ thin films were characterized by measurements of X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and spectrophotometer, then comparison was made between this two deposition methods. It's found that the microstructure properties of the LaF₃ films deposited by these two methods were different, and slight content of oxyfluoride films was formed during deposition according to the result of chemical composition analysis. The microstructure of LaF₃ bulk materials after interaction with electron beam and resistive heating was also characterized to analyze how the two deposition processes affect the formation of LaF₃ thin films and their microstructure properties. When it was for the laser resistance of the films, although the EB evaporated LaF₃ thin films occupied lower absorption and optical loss than those of the RH films, they showed slightly smaller laser induced damage thresholds at 355 nm, which was thought to be related to their much more rougher surface and higher tensile stress.     

用交流阻抗法研究碳纤维混凝土导电性

随着水泥基材料的发展 ,人们对水泥基材料提出的更新的要求 ,其中水泥基导电复合材料的研究引起了广泛的兴趣。制备水泥基导电复合材料的方法是在水泥基材料中掺入各种导电组分 ,目前较常用的是掺入碳纤维 ,它不仅可以大幅度提高水泥基复合材料的电导率 ,还能够改善水泥基材料的力学性能、增加其韧性。本研究主要通过对碳纤维混凝土的交流阻抗谱进行分析 ,研究其导电性能与内部微结构的关系。     

Development and Characterization of Cr3C2–NiCr Coated Superalloy by Novel Cold Spray Process

The coating deposition by cold spray process depends upon the mechanical properties of both the coating and substrate materials. This results in variation of the coating microstructure for different coating–substrate system materials. In this study cold sprayed 75%Cr₃C₂–25%(Ni–20%Cr) coating–superalloy system is developed. The microstructure of the coating obtained is suitable for restricting the penetration of corrosive species toward the substrate. The techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX), and elemental X-ray analysis were used for characterization of the newly developed cold spray coated superalloy.     

水热法制备CuAlO_2粉末

以CuO、Cu、Al2O3和NaOH粉末作为反应原料,通过水热法制备了CuAlO2粉末。用X射线衍射(XRD),扫描电子显微镜(SEM),X射线光电子能谱(XPS),红外光谱对产物进行表征。XRD和SEM分析结果表明,反应时间、反应温度对产物的结晶程度和晶粒大小有着重要的影响。随着反应时间的增加,样品晶粒的粒径增大,而且晶粒变得均匀。XPS分析结果表明,当反应温度达到360℃,反应时间为12小时,反应产物中只有CuAlO相。     

TiO2/bone composite materials for the separation of heavy metal impurities from waste water solutions

Pure bone material obtained from cow meat, as apatite-rich material, and TiO₂-bone composite materials are prepared and studied to be used for heavy metal ions separation from waste water solutions. Meat wastes are chemically and thermally treated to control their microstructure in order to prepare the composite materials that fulfill all the requirements to be used as selective membranes with high performance, stability and mechanical strength. The prepared materials are analyzed using Hg-porosimetry for surface characterization, energy dispersive X-ray spectroscopy (EDAX) for elemental analysis and Fourier transform infrared spectroscopy (FTIR) for chemical composition investigation. Structural studies are performed using X-ray diffraction (XRD). Microstructural properties are studied using scanning electron microscopy (SEM) and specific surface area studies are performed using Brunauer-Emmet-Teller (BET) method. XRD studies show that multiphase structures are obtained as a result of 1h sintering at 700?C1200 °C for both pure bone and TiO₂-bone composite materials. The factors affecting the transport of different heavy metal ions through the selected membranes are determined from permeation flux measurements. It is found that membrane pore size, membrane surface roughness and membrane surface charge are the key parameters that control the transport or rejection of heavy metal ions through the selected membranes.     

Influence of cement type on transport properties and chemical degradation: Application to nuclear waste storage

The geological repository of nuclear waste in concrete containers is a possible storage method explored by ANDRA (Agence Nationale pour la gestion des Déchets RadioActifs). The concrete must display a high confinement capacity for long periods, characterized by low transport properties and by the acido-basic buffer of hydrated cement. During service life, these properties can be endangered by chemical attack of underground water. The cement type has an important influence on the concrete's performances. Then, it is essential to establish appropriate mixtures with accurate components. In this work an ordinary Portland cement and a fly ash and blast furnace slag blended cement are compared. To determine confinement capacities, transfer properties and mortars microstructure were investigated. To predict the long term behaviour, an ammonium nitrate test has been developed to enhance decalcification and to accelerate hydrolysis of cementitious materials. Measurement of degraded depth with time regarding calcium content was carried out. Impact of decalcification on transport properties was evaluated. Fly ash and blast furnace slag provide better properties for native mortars, and more particularly diffusion properties, but not as much as necessary to limit leaching in degraded material by chemical attack.