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Showing 6 results for Cement
Taftan Pozzolan-Based Geopolymer Cement
A. Allahverdi, K. Mehrpour , E. Najafi Kani,
Volume 19, Issue 3 (7-2008)
Abstract

  Abstract: In recent years, many research works have been done to investigate the possibility of utilizing a broad range of materials as raw materials in the production of geopolymer cements. The use of artificial pozzolans or aluminosilicate-type industrial waste materials such as granulated blast-furnace slag and fly ash has been reported in many research works. Natural pozzolans are also aluminosilicate-type materials which can be activated with solutions of NaOH and Na2SiO3. Using a pumice-type natural pozzolan from Taftan Mountain located at the south east of Iran and different alkali-activators based on combinations of Na2SiO3 and NaOH, a number of natural-pozzolan-based geopolymer cement systems were designed and prepared. Final setting time, workability, and 28-day compressive strength of the systems were studied. The results obtained reveal that Taftan pozzolan can be activated using a proportioned mixture of Na2SiO3 and NaOH resulting in the formation of a geopolymer cement system exhibiting suitable workability and relatively high 28-day compressive strengths up to 63 MPa.


Formation Mechanism of Silicon Modified Aluminide Coating on a Ni-Base Superalloy
S. Rastegari, Z. Salehpour , Bakhshi , H. Arabi,
Volume 19, Issue 5 (7-2008)
Abstract

Formation mechanism of silicon modified aluminide coating applied on a nickel base super alloy IN-738 LC by pack cementation process was the subject of investigation in this research. Study of the microstructure and compositions of the coating was carried out, using optical and scanning electron microscopes, EDS and X-ray diffraction (XRD) techniques. The results showed that due to low partial pressure of silicon halide in Pack process, the amount of soluble silicon in the coating can not exceed 1 wt % of the total coating composition, although the Si content of the particles present within the outer coating sub-layer could reach as far as 5 wt%. Thus, the small amount of soluble Si within the coating could not provide the necessary conditions for formation of any intermetallic and it seems that the formation and growth behavior of various sub-layers in Si-modified aluminide coating is similar to that of simple aluminide coating. Three sub-layers were detected in the coating structure after being subjected to diffusion heat treatment. They were an outer Ni-rich NiAl sub-layer a middle Ni-rich NiAl and an inter diffusion sub-layers. The details of formations and growth mechanism of these sub-layers has been discussed in this research.


Design a Relief Transportation Model with Uncertain Demand and Shortage Penalty: Solving with Meta-Heuristic Algorithms
Reza Ramezanian, Soleiman Jani,
Volume 32, Issue 3 (9-2021)
Abstract
In this paper, a fuzzy multi-objective optimization model in the logistics of relief chain for response phase planning is addressed. The objectives of the model are: minimizing the costs, minimizing unresponsive demand, and maximizing the level of distribution and fair relief. A multi-objective integer programming model is developed to formulate the problem in fuzzy conditions and transformed to the deterministic model using Jime'nez approach. To solve the exact multi-objective model, the ε-constraint method is used. The resolved results for this method have shown that this method is only able to find the solution for problems with very small sizes. Therefore, in order to solve the problems with medium and large sizes, multi-objective cuckoo search optimization algorithm (MOCSOA) is implemented and its results are compared with the NSGA-II. The results showed that MOCSOA in all cases has the higher ability to produce higher quality and higher-dispersion solutions than NSGA-II.
 
Warranty cost models for a repairable multi-component product protected by Lemon laws with failure interaction
Fakhri Ikhwanul Alifin, Bermawi Priyatna Iskandar, Nadia Fasa, Fransisca Debora,
Volume 35, Issue 2 (6-2024)
Abstract
This study develops warranty cost models for repairable products subject to Lemon Laws, encompassing Critical and Non-Critical components forming a multi-component system. Failures can arise naturally or be induced by other components (i.e., failure interaction), defining a lemon if recurrent failures reach a threshold (k) during the warranty period. A lemon declaration triggers a refund or replacement by the manufacturer. Four warranty cost models are proposed from the manufacturer's standpoint, considering failure mechanisms. Increasing failure thresholds in the warranty scheme substantially decreases warranty cost rates. For instance, a threshold (k) of 5 in refund and replacement schemes yields the lowest cost rates of 33.7159 and 25.8249, respectively. Failure interactions escalate total warranty costs; for instance, in a refund scheme (k = 5), costs with failure interaction reach 31.0169 compared to 28.7603 without. Similar trends apply to replacement schemes. Moreover, a lower warranty cost rate will extend the period, indicating regulation fulfillment due to a closer warranty period to the Lemon period. Sensitivity analysis also underscores the role of higher reliability in reducing warranty costs and complying with Lemon Laws. Finally, maintenance strategies and product reliability are emphasized to fulfill Lemon Laws with minimal costs, i.e., fewer warranty claims.

Development and Optimization of Maintenance Using the Monte Carlo Method
Khamiss Cheikh, El Mostapha Boudi, Hamza Mokhliss, Rabi Rabi,
Volume 35, Issue 3 (9-2024)
Abstract
Maintenance plan efficacy traditionally prioritizes long-term predicted maintenance cost rates, emphasizing performance-centric approaches. However, such criteria often neglect the fluctuation in maintenance costs over renewal cycles, posing challenges from a risk management perspective. This study challenges conventional solutions by integrating both performance and robustness considerations to offer more suitable maintenance options.
The study evaluates two representative maintenance approaches: a block replacement strategy and a periodic inspection and replacement strategy. It introduces novel metrics to assess these approaches, including long-term expected maintenance cost rate as a performance metric and variance of maintenance cost per renewal cycle as a robustness metric.
Mathematical models based on the homogeneous Gamma degradation process and probability theory are employed to quantify these strategies. Comparative analysis reveals that while higher-performing strategies may demonstrate cost efficiency over the long term, they also entail greater risk due to potential cost variability across renewal cycles.
The study underscores the necessity for a comprehensive evaluation that balances performance and resilience in maintenance decision-making. By leveraging the Monte Carlo Method, this research offers a critical appraisal of maintenance strategies, aiming to enhance decision-making frameworks with insights that integrate performance and robustness considerations.

Cement supply chain distortion and its Shadow Market in Ethiopia
Alemayehu Derege,
Volume 36, Issue 2 (6-2025)
Abstract
The booming of construction sector, including cement factories, has been great success, however, the price of cement has been quadrupled. Among others, critical shortage of cement is observed throughout the country regardless of the success, demanding a critical investigation into its supply chain, governance and regulatory system. Mixed, qualitative and quantitative approaches are applied to investigate the value chain, its administration and regulatory framework. SEM was used to index the level of cement supply distortions in the country.  Samples are taken through referral technique from stratified target group across Ethiopian cement supply chain, starting from factory CEO to end-users, from purposively selected major factories. Multinomial logit model is used to analyze the determinant of cement supply distortion. The study found mis-management of regulation, high intervention with ineffective regulatory measure, opened up a room for bribery, favoritism, government interventionism and amplified the roles of intermediaries beyond the market requirement. Brokers are involved in about 85 percent of the country's total cement distribution. Besides, not only intermediaries but also the factories and their agents are contributing a lot in cement supply distortion. The supply chain distortion is observed in all market types, black, gray, and white respectively. The regulatory framework is ineffective and few regulatory bodies are fixed towards reactive measures. Majority of cement distribution is facilitated by brokers and factory agent. Hoarding and smuggling emerge as the most influential factors, with their increase being strongly and significantly linked to a rise in high and severe illegal cement distribution. Regulatory strength and administrative malpractice display complex patterns, indicating that having policies in place is not sufficient; effective enforcement is crucial. Strengthening regulatory, good governance and law enforcement system reduces the cement supply distortion while long run digitalization should be targeted along with supply side intervention.

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