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•Red mud was used as the main filling material to prepare magnesium cement building materials.•The compressive strength and water resistance of magnesium cement were enhanced by red ...mud.•More red mud was used compared with other recovery methods.•Soluble salt in red mud was solidificated by magnesium cement.
In this paper, influences of red mud on the properties of magnesium oxychloride cement (MOC) and magnesium oxysulfate cement (MOS) were studied with a 200 day time scale.The results showed that the addition of red mud greatly enhanced the 28d water resistance of MOC cement from 0.84 to 1.10, of MOC cement, significantly increased the compressive strength of MOS cement from 24.12 MPa to 33.31 MPa and water resistance from 0.48 to 0.68. At 200d, the addition of red mud had little effect on MOC cement but greatly increased compressive strength and water resistance of MOS cement. The red mud and magnesium cement produced an amorphous gel, which made the matrix more compact.Meanwhile, magnesium cement played the role of solidification soluble salt in red mud and only slight frosting appeared.The research results show the potential of red mud as a modifier of magnesium cement and its application potential as a building material.
Cement industry is one of the six energy intensive industries in Iran accounting for 15% of total energy consumption in the industrial sector. The sudden reform of energy prices in Iran is expected ...to have a great impact on production and energy consumption in this industry. In this paper, we present a system dynamics model to analyze energy consumption and CO2 emission in Iranian cement industry under various production and export scenarios. We consider new energy prices to estimate possible energy demand by this industry over next 20 years. The model includes demand for cement, production, energy consumption and CO2 emission in an integrated framework with emphasis on direct natural gas consumption. Producing blended cement, production using waste materials as alternative fuel, and wasted heat recovery for electricity generation in cement industry are three main corrective policies simulated and discussed herein. Simulation result show that complete removal of energy subsidy and implementation of corrective policies in the cement industry could potentially lead to reductions of 29% and 21%, respectively in natural gas and electricity consumptions and 22% reduction in CO2 emission.
► We have developed a system dynamics model to analyze the demand, production, energy consumption and CO2 emission of cement industry in Iran. ► Various production and export scenarios have been simulated to project the energy demand of Iranian cement industry over next 20 years. ► A causal structure is used to show how subsidy reform would affect energy consumption in the cement industry over the long term. ► Producing blended cement, using waste materials as an alternative fuel and recycling wasted heat for electricity generation are the main corrective policies discussed herein.
Abstract
The Calcium Silicate Hydrate (C-S-H) nucleation is a crucial step during cement hydration and determines to a great extent the rheology, microstructure, and properties of the cement paste. ...Recent evidence indicates that the C-S-H nucleation involves at least two steps, yet the underlying atomic scale mechanism, the nature of the primary particles and their stability, or how they merge/aggregate to form larger structures is unknown. In this work, we use atomistic simulation methods, specifically DFT, evolutionary algorithms (EA), and Molecular Dynamics (MD), to investigate the structure and formation of C-S-H primary particles (PPs) from the ions in solution, and then discuss a possible formation pathway for the C-S-H nucleation. Our simulations indicate that even for small sizes the most stable clusters encode C-S-H structural motifs, and we identified a C
4
S
4
H
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cluster candidate to be the C-S-H basic building block. We suggest a formation path in which small clusters formed by silicate dimers merge into large elongated aggregates. Upon dehydration, the C-S-H basic building blocks can be formed within the aggregates, and eventually crystallize.
This paper explores the energy-intensive cement industry, focusing on a plant in Greece and its mill and kiln unit. The data utilized include manipulated, non-manipulated, and uncontrolled variables. ...The non-manipulated variables are computed based on the machine learning (ML) models and selected by the minimum value of the normalized root mean square error (
) across nine (9) methods. In case the distribution of the data displayed in the user interface changes, the user should trigger the retrain of the AI models to ensure their accuracy and robustness. To form the objective function, the expert user should define the desired weight for each manipulated or non-manipulated variable through the user interface (UI), along with its corresponding constraints or target value. The user selects the variables involved in the objective function based on the optimization strategy, and the evaluation is based on the comparison of the optimized and the active value of the objective function. The differential evolution (DE) method optimizes the objective function that is formed by the linear combination of the selected variables. The results indicate that using DE improves the operation of both the cement mill and kiln, yielding a lower objective function value compared to the current values.
This paper reports on a comparative study of the mechanical performance at different temperatures of a commercial Portland cement, used as a control, and a new cementitious material made from an ...8M‐NaOH activated fly ash and containing no OPC. Two types of mechanical tests were conducted: (i) high temperature mechanical tests, to determine the strength and fracture toughness of the two materials between 25° and 600°C, and (ii) post‐thermal treatment tests, to evaluate the residual strength after 1 h of exposure to different temperatures (200°, 400°, 600°, 800°, and 1000°C). In both cases, the results showed that the new cementitious material performed significantly better at high temperatures than the Portland cement control. Differential thermogravimetry (DTG)/TG, Fourier transform infrared (FTIR), and X‐ray diffraction analyses were also conducted to analyze the mineralogical and microstructural variations taking place in the material as a result of high temperature exposure. The results of these tests were correlated with the mechanical behaviour observed.
Improving energy efficiency is a highly effective policy for protecting the environment and preserving resources. Previous studies have measured energy efficiency in the industrial sector. We further ...contribute to understanding the factors that affect energy efficiency changes. This study measures energy efficiency based on plant-level data in Japan's paper/pulp and cement industries as representative energy intensive sectors. We analyze the relationship between the industrial agglomeration effect and the energy efficiency of each studied industry. Our results reflect several important findings. First, energy efficiency has improved in the paper and pulp industry as well as the cement industry between 2000 and 2010. However, the factors for improving energy efficiency differ between the industries. Second, industrial agglomeration affects energy efficiency. In the paper and pulp industry, the same industry agglomerations contribute to improvements in energy efficiency. However, the agglomeration effect is negative for energy efficiency in the cement industry. Our results indicate that one must consider regional circumstances more carefully when seeking to improve energy efficiency.
•This study measures energy efficiency in Japan’ paper/pulp and cement industry.•We then focus on the industry agglomeration effect on energy efficiency.•Our results imply that regional characteristics affect energy efficiency.
The drying of cement-based materials is intimately related to their durability, which has significant economic, social and environmental repercussions. The evolution of the saturation of the pore ...network and the associated drying shrinkage are in fact leading causes of cracking and of the ensuing penetration of aggressive chemicals.
This process is highly heterogeneous, due to the thermo-hydric spatial gradients developing in the material from the exposed surfaces to its core and because of local effects, driven by the intrinsically heterogeneous micro-structure (e.g., by the distribution of pores and aggregates). It follows that macroscopic, sample-scale measurements cannot fully disclose the complexity of the underlying processes. In the last few decades, significant advances in full-field techniques have allowed an unprecedented insight into these local processes. For cement-based materials, x-ray and neutron tomography lend themselves as ideal, and highly complementary, tools for the study of their thermo-hydro-mechanical behavior. Notably, the high sensitivity to density variations of x-ray imaging gives access to the developments of fractures, in 4D (3D + time). On the other hand, neutron tomography allows the study of the evolution of the moisture field in 4D, thanks to its high hydrogen sensitivity. The combination of these two techniques provides a unique insight in thermo-hydro-mechanical couplings, e.g., the effect of cracks on the water content field.
This contribution presents novel 5D datasets (3D tomographies along time, plus truly simultaneous x-ray and Neutron rapid acquisitions) in-operando of a cement paste and of a concrete sample heated at moderate temperatures (up to 140∘C).
The analysis of this 5D data-set (once aligned in time and across modalities) allows for example a quantification of the 4D moisture profiles which were found to predict an overall water loss at hydric equilibrium coherent with the corresponding analytical analysis. In the cement paste sample, the x-ray dataset captures the evolution of an extensive cracking network, opening and propagation toward the core of the sample. A novel analysis procedure is here proposed which allows the extraction of these fractures and the analysis of their interplay with local drying as captured through neutron imaging. This for example reveals the depth of penetration of drying in the vicinity of the fractures along time, which is essential for the assessment and calibration of hydro-mechanical coupled models.
The macroscale mechanical properties of cement-stabilized soil have been widely reported, but the microscale behavior remains largely unexplored. This paper presents the first attempt to reveal the ...microscale strengthening mechanisms in a cement-stabilized kaolinite via big data cross-scale nanoindentation coupled with X-ray diffraction, scanning electron macroscopy, and upscaling analyses. A high-purity kaolinite clay was treated by 15 wt% Portland cement, and the 28-day-cured specimens were investigated to unravel the primary hydration of the cement, secondary reactions between cement and kaolinite, and the resulting constituents and microstructure of the solidified composite. Massive depth-dependent Young’s modulus data, obtained by statistical nanoindentation with continuous stiffness measurements, were processed by three different deconvolution techniques including probability density function, cumulative distribution function, and Gaussian mixture modeling. Results from compositional, microstructural, and micromechanical analyses show that two mechanically distinct phases exist in the final composite: a relatively homogeneous fine-grained matrix consisting of solidified cement hydrates–kaolinite mixture, and relatively stronger, coarse-grained inclusions as fillers that are made of pure, cement hydrate aggregates randomly distributed within the fine-grained matrix. Furthermore, the cement hydrates function as two distinct roles in strengthening the kaolinite: (1) bonding the platy kaolinite particles at the edge surfaces and (2) forming the stronger constituents as aggregates embedded in the matrix. Upscaling analysis based on four micromechanical models further validates the above nanoindentation results and inclusion–matrix microstructure. Such an improved understanding of the strengthening mechanisms is expected to shed light on the practical applications of cement stabilization for soft clays.
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