Articles

Contribution to the Study of the Chemical and Microstructural Quality of Reinforcing Bars in DR. Congo “Case of the City of Lubumbashi”

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: This research highlights the contribution to the study of the microstructural quality of reinforcing bars on the Lubumbashi market including bars imported from South Africa (FA), Zambia (FZ) and those produced locally ( FC) by the only steel industry, in the former province of Katanga, the iron processing company SOTRAFER, in acronym.

The samples of the locally produced reinforcement bars (FC) were collected at SOTRAFER at the end of production, while the samples of the FA and FZ reinforcement bars were taken randomly on the Lushois market in a hardware store specializing in sales to avoid errors.Microstructural analysis of all bars revealed a similar microstructure consisting of a ferrite (light areas) and pearlite (dark areas) matrix and a ferrito-pearlitic structure. This microstructure, as predicted by the Fe-C equilibrium diagram, could be justified by the carbon content (lower than the eutectoid point content); the results prove that all bars are hypoeutectoid steels (%C ≤ 0.77). They can also be assimilated to the category of mild steels (0.1 ≤ %C ≤ 0.25). This also shows that all the bars have not undergone a particular heat treatment and have been cooled very slowly in order to allow the diffusion of atoms and reach equilibrium conditions. The results obtained from the variance analyses of different materials of dimensions of 10, 12 and 16 mm revealed that at the level of chemical and mechanical analyses, there was no significant difference on all the parameters studied and that all the reinforcement bars could perfectly be used in construction. Finally, the survey reveals that FA is reputed to be of better quality among consumers, for several reasons including the psychological one although its price is lower than that produced locally.

Study of the Genetic Formation of New Formations during the Hardening of Pozzolanic Cement with a High Content of Ash and Slag Waste of Dry Selection

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The results of physical and chemical studies of the processes of hydration and structure formation during hardening of pozzolanic cements containing dry–selection ash and slag waste from the Angren TPP as an active mineral additive are presented. It has been established that, despite the replacement of up to 50% of the clinker part, the experimental cements acquire high hydraulic activity, which ensures their grade 400–500, which is facilitated by the presence of active silica, alumina and low–basic calcium silicates in the composition of the additive, which in the process of chemical interaction with hydration products clinker minerals are involved in the formation of a dense microstructure of the cement composite.

A Review of the Failure and Damage Forms of Metals under Cyclic Loading

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The studies related to metals damage under cyclic loading as the dominant form of structural failure is reviewed. The early approaches including stress-based and strain-based as well as the later approaches of energy-based, critical plane-based and damage mechanics-based are briefed on. Recent methods including thermography, finite element, and microstructural are summarized and explained. Different phenomenon occurring under cyclic loading are explained including fatigue crack initiation, crack propagation, fretting, and buckling. This review provides insight on the underlying mechanisms of different fatigue damage types and related proposed models. In addition, it explains the different aspects of each model along with their methodology