Thesis supervisor: Éva Eszter Majorosné Lublóy
Location of studies (in Hungarian): Department of Construction Materials and Technologies Abbreviation of location of studies: EOEM
Description of the research topic:
Several studies have already investigated the fire resistance of fiber-reinforced concretes. It was found that the compressive strength and toughness of steel fiber-reinforced concrete were higher after heat exposure than those of the reference concrete (which is why they are advantageous in the shotcrete structures of tunnels). It was observed that cracks appeared at the interface of the steel fibers and the cement stone after a thermal load of 400 °C in the case of steel fiber-reinforced concrete, which gradually increased with the temperature. Due to the formation of cracks, the adhesion of fibers to concrete deteriorates, but at the same time, a pore system forms, which prevents the explosive spalling of the concrete surface.
Due to increasing temperature (between 150-250 °C), plastic fibers soften and melt. Subsequently, with further temperature increase, plastic fibers decompose, and a capillary system is formed in their place within the concrete. This fact is very important because many researchers have confirmed that the layered delamination of the concrete surface during a fire can be explained by the high pore pressure that develops. The steam generated by the thermal load can escape from the concrete through the capillary system formed, thus effectively reducing the risk of explosive detachment of the concrete surface (so-called spalling).
In addition to the quantity and material of the fibers, the geometric characteristics of the fibers also significantly influence the fire resistance of fiber-reinforced concretes. However, the question is, for what strength of concrete, exactly what type and quantity of fibers with what geometry are optimal?
The aim of this research is to clarify the effect of fiber geometry and material on the fire resistance of structures.
Before starting the measurements, the candidate must review the relevant literature and determine the parameters of the laboratory tests based on this.
To clarify the question, the candidate needs to perform laboratory tests, which, in addition to strength testing, include macro (visual inspection, optical microscope) and microstructure (SEM) examinations, as well as the realization of engineering relationships.
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