Journal of Advanced Concrete Technology
Online ISSN : 1347-3913
ISSN-L : 1346-8014
Volume 18, Issue 8
Displaying 1-3 of 3 articles from this issue
Scientific paper
  • Kiyofumi Kurumisawa, Ole Mejlhede Jensen
    2020 Volume 18 Issue 8 Pages 456-462
    Published: August 12, 2020
    Released on J-STAGE: August 12, 2020

    In this study, thermoporometry by differential scanning calorimetry and proton NMR measurements of hardened cement paste equilibrated under different humidity conditions were carried out, and the results of both measurements were compared. The results reveal that thermoporometry by low temperature DSC measurement cannot detect the water present in samples equilibrated at low relative humidity. On the other hand, it is possible to detect a signal at low relative humidity by proton NMR measurement. It is clarified that water strongly bound to the surface, which cannot be detected by low temperature DSC, exists at a relative humidity of 33% or less. If it is relevant to detect tightly held water, such as water present in the fine gel pores, it is recommended to apply proton NMR measurements. This paper is an extended English version of the authors’ previous work [Kurumisawa, K. and Jensen, O. M., (2020). “Measurement of cement paste at different humidities by thermoporometry and proton NMR.” Proceedings of the Japan Concrete Institute, 42, 347-352. (in Japanese)].

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  • Daisuke Yamazaki, Mitsuyasu Iwanami, Masaaki Isa
    2020 Volume 18 Issue 8 Pages 463-472
    Published: August 28, 2020
    Released on J-STAGE: August 28, 2020

    The steel-plate bonding method used to reinforce concrete slabs in bridges has a long record of adoption, and has played an important role for many years. Favorable conditions have been observed with this method in periodic inspections; however, as part of durability tests, decreases in strength of the epoxy resin adhesive (which is one of its component materials) have been observed following over time outdoor exposure under standard environmental conditions. Investigations into the causes of decreased strength of epoxy resin adhesive are useful for increasing long-term durability in future infrastructure maintenance. The estimation of environmental factors that incorporate exposure conditions and the results of conducting accelerated tests revealed that the performance of epoxy resin adhesive was influenced by humidity. Additionally, decreases in strength accompanying reaction progress of epoxy resin were also observed. These results indicate that the degradation due to water absorption and the generation of internal stress due to the progress of the curing reaction of the epoxy resin are the causes of the decrease in the strength of the epoxy resin.

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  • Nuttawut Intaboot
    2020 Volume 18 Issue 8 Pages 473-480
    Published: August 27, 2020
    Released on J-STAGE: August 27, 2020

    This study involved the application of natural materials to produce interlocking blocks for thermal conductivity and sound absorption by mixing rice straw and rice husk ash. The ratios of soil, cement and sand used in the mix was 5:1:1. The mixing ratios of rice straw were zero, 1, 2 and 3% and those of rice husk ash were 10, 20 and 30% of the weight of cement. The test included the measure of compressive strength, unit weight, water absorption, porosity, thermal conductivity and sound absorption using blocks at the age of 28 days. The results showed that the addition of rice straw caused the compressive strength to reduce, while porosity and water absorption were increased. The addition of rice husk ash helps to improve the compressive strength and unit weight. All of these qualities passed the Thai Industrial Standard TIS 58-2533 (TIS 1990). The increasing of rice straw and rice husk ash resulted in low thermal conductivity and better sound absorption. Therefore, rice straw and rice husk ash are interesting materials in the production of energy-saving building materials.

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