Property Analysis of Slag Composite Concrete Using a Kinetic–Thermodynamic Hydration Model

Slag is increasingly unitized for the production of sustainable concrete. This paper presents a procedure with which to analyze the property development of slag composite concrete. Experimental studies of the hydration heat and compressive strength development and simulation studies using a kinetic hydration model and a thermodynamic model were performed. First, we performed an experimental study of the isothermal hydration heat of cement–slag blends. Based on the results of the experimental study on cumulative hydration heat, the reaction degree of slag was determined. We found that the reaction degree of slag decreased as the slag content increased. Second, the reaction degree of slag and cement were used as the input parameters for the Gibbs energy minimization (GEM) thermodynamic equilibrium model. Moreover, the phase assemblage of hydrating cement–slag was determined. The trends of calcium silicate hydrate (CSH) are similar to those of strength. Based on the CSH content, the strength of hardening cement–slag blends was determined. In addition, the calcium hydroxide (CH) content resulting from the thermodynamic model shows good agreement with the experimental results. In summary, the integrated kinetic–thermodynamic model is useful for analyzing the properties of cement–slag blends.

Reactivity Effect of Calcium Carbonate on the Formation of Carboaluminate Phases in Ground Granulated Blast Furnace Slag Blended Cements

The reactivity effect of calcium carbonate, present in ground oyster shells and limestone filler, on the formation of carboaluminate phases in ground granulated blast furnace slag blended cement pastes was reported in this paper. Six different binary and ternary blended cement pastes were prepared using ground granulated blast furnace slag, ground oyster shells and limestone filler with different replacement levels (from 5 to 35%). The carboaluminate formation was assessed and quantified directly using X-ray diffraction (XRD), and indirectly by following the aluminate phase’s reaction (heat flow) and consumed calcium carbonate using Isothermal Calorimetry (IC) and Thermogravimetric Analysis (TGA), respectively. Further, the overall reaction degree calculated based on TGA results and the compressive strength were determined to support the findings obtained. The results revealed that the calcium carbonate present in ground oyster shells is more reactive when compared to that present in limestone filler, where more formed hemi- and monocarboaluminate phases were observed in mixtures containing ground oyster shells. An enhancement in compressive strength and overall reaction degree was observed by adding 5% ground oyster shells as cement replacement.

Synthesis, characterization and applications of chitosan based metallic nanoparticles: A review

Chitosan as a natural biopolymer has been produced to be the important host for the preparation of metallic nanoparticles (MNPs) because of its excellent characteristics like:- good stabilizing and capping ability, biocompatibility, biodegradability, eco-friendly and non-toxicity properties. Chitosan can play a very important role for synthesis of metallic nanoparticles, as chitosan is a cationic polymer. It attracts metal ions and reduces them and also Capps and stabilizes. So basically chitosan can be responsible for the controlled synthesis of metallic nanoparticle. Chitosan has a very good chelating property. This property is due to its –NH2 and –OH functional groups. Size and shape of metallic nanoparticles are much affected by chitosan concentration, molecular weight, time of reaction, degree of acetylation of chitosan, pH of the medium, method of synthesis and type of derivative of chitosan etc. Metallic nanoparticles`s properties and applications are much associated with their size and shape. Optimization of the metallic nanoparticle size and shape has been the subject of curiosity for nanotechnology scientist. Chitosan can solve this problem by applying the optimization conditions. But a very little work is reported about: - how chitosan can affect the size and shape of metallic nanoparticles and how can it reduce metal salts to prepare metallic nanoparticle, stablilized in chitosan metrics. This is very first report as a review article highlighting the effect of chitosan on synthesis of metallic nanoparticles and optimization conditions. This review will also be beneficial for scientist working on food sensing application of nanoparticles. Various synthesis methods and applications of chitosan based metallic nanoparticles have also been reported in details.

Exploring Structural Evolution of Portland Cement Blended with Supplementary Cementitious Materials in Seawater

The present study investigated the structural evolution of Portland cement (PC) incorporating supplementary cementitious materials (SCMs) exposed to seawater. The samples were made with replacing Portland cement with 10 mass-% silica fume, metakaolin or glass powder. The reaction degree of SCMs estimated by the portlandite consumption shows that metakaolin has the highest reaction degree, thus metakaolin-blended PC exhibits the highest strength. The control exposed to seawater exhibited 14.82% and 12.14% higher compressive strengths compared to those cured in tap water at 7 and 28 days. The samples incorporating metakaolin showed the highest compressive strength of 76.60 MPa at 90 days tap water curing and this was 17% higher than that of the control. Exposure to seawater is found to retard the rate of hydration in all SCM-incorporating systems, while the strength development of the neat PC system is enhanced. The main reaction product that forms during exposure to seawater is Cl-AFm and brucite, while it is predicted by the thermodynamic modelling that a significant amount of M-S-H, calcite and hydrotalcite is to form at an extended period of exposure time.

Electron-Interfered Field-Effect Transistors as Sensor Platform for Detecting a Delicate Surface Chemical Reaction

We introduce a new electron-interfered field-effect transistor (EIFET) device using a modified organic charge-modulated FET (OCMFET) structure and demonstrate its ability to detect the surface chemical reaction degree (or rate)....

Investigations Into Aerodynamic Performance of Turbine Stages With Flexible Shroud Seals

The present paper utilizes a numerical method to investigate the effect of flexible shroud seals, including the forward bending flexible seals and backward bending flexible seals, on aerodynamic performance of high pressure steam turbine stages. At first, the wear performance of flexible seal is analyzed with the Finite Element Analysis method. It shows that wear in flexible strip is so small that only the installation clearance needs to be considered in operation process. Then, by replacing the labyrinth shroud seals with flexible shroud seals, the aerodynamic efficiency, outlet flow angle distributions, and reaction degree distributions in two-stages are obtained. At three installation clearances, interactions between leakage flow and main flow, as well as the flow patterns in flexible shroud seals, are visualized and also compared with the original design case. The numerical results indicate that turbine stages configured with forward bending flexible shroud seals have a very close aerodynamic performance to those configured with conventional labyrinth shroud seals at the same clearance, whereas the turbine stages configured with backward bending flexible seals have lower total-total isentropic efficiency than those with conventional labyrinth shroud seals. By replacing the conventional labyrinth shroud seals with forward bending flexible shroud seals (at the same clearance), the aerodynamic efficiency, outlet flow angles, limiting streamlines, secondary flow patterns in shroud region and reaction degree distributions in stages are almost not affected. Since the forward bending flexible seal allows relatively smaller installation clearance than the conventional labyrinth seal, application of this kind of seal in rotor blade tip gap is much beneficial to achieve lower leakage rate and higher aerodynamic performance in large power steam turbine stages.

Usage of supplementary cementitious materials: advantages and limitations

It is well known that cement production is not neutral for natural environment among others due to high CO2 emission. Different strategies of mitigation of negative environmental impact of its production are developed. One of the ways is utilization of supplementary cementitious materials (SCMs) in the manufacture of cement and concrete. Introduction of aluminosilicate SCMs into binding mixture makes that more amount of so-called C–A–S–H phase appears in hydration products, affecting microstructure and properties of final hardened composite. The aim of this work is to discuss the possibilities of utilization of selected SCMs in different binding mixtures including some advantages and limitations. Literature review on the subject was carried out. Some of our own research results were also presented. In the Part I of this review, some information about history of ancient binding materials and the possibilities of inspiring modern engineers with ancient constructions in the aspect of using SCMs in modern concrete were presented. Using pozzolanic aluminosilicate SCMs in relation to their influence on formed products, microstructure and mechanical properties of hardened material were discussed. Some problems with possibilities of study of SCMs reaction degree were identified. Emphasis was put on the usefulness of isothermal calorimetry and thermal analysis for investigations of hydration process and identification of hydrated products as well as evaluation of degree of reaction of SCMs.