When concrete is used for construction in cold-temperature regions, cold-resistant accelerators based on calcium nitrite (Ca(NO2)2) and calcium nitrate (Ca(NO3)2) are added to prevent early freezing damage. Although cold-resistant accelerators increase the early compressive strength and prevent early freezing damage by promoting cement hydration, the strength enhancement effect owing to the formation of such hydrates has not been evaluated quantitatively thus far. This study covers various types of analysis to understand the relationship between cement hydrate formation behavior and strength development upon the addition of varying amounts of nitrite-based accelerator. We find that the early compressive strength is enhanced by the addition of nitrite-based accelerator via the promotion of the relative production of monosulfate and C-S-H in the early age. However, the development of compressive strength decreases with an increase in the curing age. Furthermore, we find that the promotion of hydration reactions at an early age with the addition of nitrite-based accelerator can affect the formation ratio of each hydrate at a late age. We believe our findings can significantly contribute to developments in concrete application and allied fields.
Feasibility of starfish bone to be a source material for apatite bone substitute was investigated in the present study because starfish bone is known to be porous calcium carbonate. Starfish bone was assembly of Mg containing calcite granules. And the calcite granules had fully interconnected porous structure with approximately 20 µm of pore size. After the hydrothermal treatment of the calcite granules in Na2HPO4 aqueous solution, the granules were gradually transformed to apatite. Therefore, starfish derived calcium carbonate would be a candidate of a source material for carbonate apatite bone substitute.
You end up observing mirrored images of graphic signs when you watch light‐emitting glass tubes from back. So our research group proposed the passive light‐emitting aero signage display which is floating in the air and enables to make transparent view from back side to avoid observing mirrored images in 2020. But this signage display has a defect that it emits no light itself and you cannot observe its signage in the dark night without another light source for illuminating surfaces of the signage display. This paper shows a one‐way observable display for aero signage which enables to make transparent from back side and emits light itself using a lighting guide tube. The authors utilize a cylindrical long transparent acrylic stick as the lighting guide. Our proposed light‐emitting and color generating mechanism realize the one‐way observable imaging which enables to make invisible from back side. You may use connectable or jointable lighting guide blocks instead of the long, unbroken and jointless lighting guide tube such as a cylindrical transparent acrylic stick. This paper also describes a one‐way observable display for aero signage which enables to joint pixel modules having optical lighting guide block and emits light itself using this lighting guide. The connectable lighting guide blocks reconstruct the unidirectional imaging which enables to emit lights and make invisible from back.
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