Journal of Advanced Concrete Technology
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Volume 13 , Issue 12
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Scientific paper
  • Mohammad Mahdi Raouffard, Minehiro Nishiyama
    Volume 13 (2015) Issue 12 Pages 554-563
    Released: December 15, 2015
    JOURNALS FREE ACCESS
    This paper describes the results of fire tests, which were carried out to study the behavior of moment-resisting reinforced concrete frame at elevated temperatures. The continuity of the beams with the columns generates considerable internal forces and rotation demands, which in turn could have detrimental (geometrical second order effect) and/or beneficial (increasing load bearing capacity) influences on the fire resistance of the global structure. In this paper, two 1/3 scale statically indeterminate RC frames, RCF1 and RCF2, under service loads were exposed to the ISO-834 fire. The target frame was a two-storey frame, in which the lower columns and middle beam were under fire attack. RCF1 was heated for 175 minutes until eventually its concrete beam failed from the excessive flexural cracks and deformations, whereas RCF2 was heated for 60 minutes until the temperature of the tensile reinforcements of its beam reached 550°C. The beam ends and the joints relatively attained lower internal temperatures owing to the unheated upper columns. The axial and moment restraints significantly increased the load bearing capacity of the fire-attacked beams without occurrence of any failure at the side columns and joints.
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  • Hai Yen Nguyen Thi, Hiroshi Yokota, Katsufumi Hashimoto
    Volume 13 (2015) Issue 12 Pages 564-582
    Released: December 23, 2015
    JOURNALS FREE ACCESS
    The adverse effects of the long term application of electrochemical chloride extraction on binding capacity of hydrated cement products are innegligible. In this study, the influences of electrochemical chloride extraction in the microstructural properties of hydrated cement products of cement pastes were investigated in paste specimens by using a modified migration cell that was conducted with the applied current density of 4.5 A/m2 and synthesized pore solutions as electrolytes for 8 weeks. Three types of cement pastes were used with the water-to-binder ratio of 0.4 including ordinary Portland cement (OPC), fly ash cement (FC) and ground granulated blast furnace slag cement (SC) pastes. Chloride source was supplied by adding 1.5% sodium chloride. After extraction, the acid-soluble and water-soluble chloride contents significantly reduced. Portlandite content increased proportionally with the time of extraction in OPC and FC pastes although the contribution of calcium ions in transferring the current is negligible. Some unsteady gel phases was obtained after a short time the extraction was stopped. Furthermore, the alteration and decomposition of C-S-H were inevitable with different rates depending on the type of cement.
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