Browsing by Author "Makkonen, Toni"

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  • Frost resistance of high-strength concrete with low air content
    (2019-10-21) Makkonen, Toni
     Insinööritieteiden korkeakoulu | Master's thesis
    Frost resistance is essential part of durability and service life of concrete structures especially in the Scandinavian countries. Frost resistance of concrete is mainly dependent on water to cement ratio (w/c) and air content. Low w/c-ratio provides more strength, whereas entrained air provides frost protection, but too high air content will also significantly decrease the strength and other mechanical properties of concrete. In this thesis, the effects of air entraining on the frost resistance properties of concrete were studied. Main objective was to investigate what level of air content would be enough to provide sufficient frost resistance with low w/c-ratios. Research included a compact literature review and experimental testing in laboratory. Total of 12 concrete mixes with varying w/c-ratios and air contents were designed and produced. W/c-ratios and air contents were chosen to be relatively low compared to typical concrete production. Both direct and indirect test methods were used to evaluate the frost resistance of the test concretes. Testing was focused on pure frost attack without de-icing solutions. Based on the experiments, it was concluded that use of air entraining seems justified when producing frost resistant concrete, at least when water to cement ratio is 0.35 or higher. All the air entrained concretes performed well in the freeze-thaw tests, which indicates that the required level of air entraining to reach adequate frost resistance is relatively low. Concretes with w/c of 0.35 performed somewhat better in the freeze-thaw tests even without air entraining, but they also had the highest initial air contents. Increasing air content due to air entraining affects the mechanical properties of similar concrete mixes rather consistently. In these tests one additional percent of air decreased the compressive strength of concrete by approximately 5% in all cases. Indirect test methods, such as thin section analysis seemed to predict the results of freeze-thaw tests quite accurately, especially with well air-entrained concretes. Indirect testing could be used as accepting criteria for frost resistance, but in some cases concrete performed well in direct frost exposure even though indirect results indicated the opposite. Freezing dilation results seemed to be more connected to w/c-ratio than air content, which was inconsistent with the results of other freeze-thaw tests. The results indicate that the present requirements for air content and w/c-ratio are still sensible when it comes to the frost resistance of concrete. F-factor works well as a design tool, but the equation could be revised for very low w/c-ratios and air contents.
  • Modeling Carbon 13-Migration in ASDEX Upgrade with OEDGE
    (2010) Makkonen, Toni
     School of Science | Master's thesis
    Selecting suitable wall materials and controlling impurities is a crucial issue for future fusion power plants. Ideally, the fusion plasma would involve only deuterium and tritium, or whatever fuel mixture is being used. The presence of other atomic species, called impurities, is unfortunately unavoidable. At the very least, helium ash from the DT fusion reaction will be present. Another challenge is impurities eroded from the walls. Impurities in the core plasma lower fusion performance. Long term material migration and the related co deposition of radioactive tritium with eroded carbon is also a serious issue. In order to study impurity transport, trace element experiments have been carried out. In these experiments, a fixed amount of isotopically labelled methane (13CH4) is puffed into the tokamak in known conditions. A set of wall tiles is subsequently removed and the carbon-13 deposition measured. The puffed methane is broken up in the plasma and the carbon-13 ions transported to the walls by various processes. The key forces controlling parallel (along the magnetic field lines) impurity transport are the friction force due to the flowing plasma and the ion temperature gradient force. Scrape off layer physics is still an active research area and perpendicular transport is best described by an ad hoc diffusive model. The correct charge state of the impurities is important meaning that atomic reactions have to be well accounted for. This work simulated the 2007 carbon-13 injection experiment at ASDEX Upgrade with the objective of replicating and interpreting the experimental results. Also, the validity of the used simulation method was critically reviewed. The simulations were carried out using the OEDGE program. The atomic reaction rate coefficients are taken from the ADAS database. The plasma background was acquired using a built-in solver in the code called the onion skin model 22. The main conclusions from this work were that (1) generating a realistic plasma background was more challenging than modelling impurity transport, (2) simulations with a realistic background seem to able to reproduce the experimental results, and (3) the perpendicular transport time for the impurity ions is important. The obvious point of improvement is the background generation. Experimentally, this work would strongly suggest removing just a few more additional tiles for measurement.
  • Pölynhallinta korjausrakentamisessa
    (2017-04-27) Makkonen, Toni
     Insinööritieteiden korkeakoulu | Bachelor's thesis