Toshikatsu Saito

MECHANICAL PROPERTIES OF FIBER-REINFORCED POROUS CONCRETES COMBINED USE OF VINYLON SHORT-FIBERS AND MICRO-FIBERS

The purpose of this study is to investigate the effect of combined use of vinylon short-fibers and micro-fibers on the mechanical properties of fiber-reinforced porous concretes. The fiber-reinforced porous concretes using vinylon short-fibers with the length of 40mm (F40) and micro-fibers with the length of 12mm (F12) are prepared with the F40 contents of 0, 0.3, 0.5, 0.7% and F12 contents in binder of 0, 0.4, 0.6, 1.2%. As a result, the flexural behavior of porous concrete are considerably improved by combined use of the vinylon short-fibers and micro-fibers with proper fiber contents.

QUESTIONNAIRE SURVEY TARGETED TO SUBCONTRACTORS ON THE ACTUAL STATE OF DEMOLITION WORK

Until now, demolition work has been upgraded about technical matters and qualification system. However, actual state of demolition work from Engineer and skilled worker’s standpoint has not been fully elucidated. Therefore, the purpose of this study is to investigate the actual state of demolition work by the questionnaire survey targeted to subcontractors. As a result, this paper showed the actual state of demolition work about preliminary survey, calculation, consciousness of accepting order and contract system, construction scheme, construction control and human materials.

EFFECT OF EMULSION TREATMENT FOR BAMBOO REINFORCEMENT ON FREEZING AND THAWING RESISTANCE OF BAMBOO-REINFORCED CEMENT MORTARS

The purpose of this study is to investigate the effect of emulsion treatment for bamboo reinforcement on the freezing and thawing resistance of bamboo-reinforced cement mortars. The bamboo elements and bamboo reinforcements are treated by the emulsion with the polymer coating ratio of 0, 10, 20 and 40 g/mm₂ and dried under 20℃ and 60％（RH） for 48h. The bamboo-reinforced cement mortar specimens using the emulsion treated bamboo reinforcements are prepared with the size of 20×100×400 mm and subjected to 1d-moist, 6d-water and 21d-dry cure. The emulsion treated bamboo elements are tested for the tensile properties. The bamboo-reinforced cements mortar specimens are subjected to the freezing and thawing resistance test. As a result, the tensile strength of the bamboo element is increased with an increase in the polymer coating ratio. However, the effect of the emulsion treatment on the modulus of elasticity of the bamboo element is hardly recognized. The reduction of the relative dynamic modulus of elasticity and mass of the bamboo-reinforced cement mortar during freezing and thawing cycles is inhibited with an increase in the polymer coating ratio of the bamboo reinforcements. The durability factor of the bamboo-reinforced cement mortar is also increased with an increase in the polymer coating ratio of the bamboo reinforcements. The freezing and thawing resistance of bamboo-reinforced cement mortars is improved by the emulsion treatment of the bamboo reinforcements.本研究では、竹素材及び竹補強材のエマルション処理による引張性状及び竹補強セメントモルタルの凍結融解抵抗性の改善効果について検討している。その結果、竹素材の引張強さはエマルション塗布量の増加に伴い、増大する傾向にあり、弾性係数は若干増大する。又、エマルション塗布量の多い竹補強材を用いた竹補強セメントモルタルほど凍結融解サイクル数の増加に伴う相対動弾性係数及び質量減少率の低下の程度は緩慢になり、耐久性指数は増大する。本研究の限りでは、竹補強材をエマルション処理することにより、竹補強セメントモルタルの凍結融解抵抗性は改善されることが明らかである。

EFFECT OF COMBINED USE OF VINYLON SHORT-FIBERS AND MICRO-FIBERS ON FREEZING AND THAWING RESISTANCE OF FIBER-REINFORCED POROUS CONCRETES

The purpose of this study is to investigate the effect of combined use of vinylon short-fibers and micro-fibers on the freezing and thawing resistance of fiber-reinforced porous concretes. The fiber-reinforced porous concretes using vinylon short-fibers with the length of 40mm（F40） and micro-fibers with the length of 12mm（F12）are prepared with the target voids of 20％, F40 contents of 0, 0.3, 0.5％ and F12 contents in binder of 0, 0.4, 0.6, 1.2％. The fiber-reinforced porous concrete specimens are cured under 20℃ moist for 24h, 70℃ hot water for 1d and 20℃ water for 1d, and subjected to the freezing and thawing resistance test. The relative dynamic modulus of elasticity and reduction in mass of the specimens are measured during the test. After the freezing and thawing test, the specimens are tested for flexural strength and flexural toughness. As a result, the fiber-reinforced porous concrete combined use of F40 with the content of 0.3％ and F12 with the content of 0.4％ gives superior freezing and thawing resistance by evaluating the relative dynamic modulus of elasticity. The flexural properties of the fiber-reinforced porous concrete after the freezing and thawing test are improved by combined use of F40 with the content of 0.5％ and F12 with the content up to 1.2％. The freezing and thawing resistance of porous concrete is considerably improved by combined use of the vinylon short-fibers and micro-fibers with the proper fiber contents.本研究では、粗骨材間を架橋する長さ40mmのビニロン短繊維（F40）及び結合材組織を補強する長さ12mmのビニロン微細繊維（F12）を複合使用した繊維補強ポーラスコンクリートの凍結融解抵抗性について検討している。その結果、相対動弾性係数を指標とした場合、F40混入率0.3％及びF12混入率0.4％としてF40及びF12を併用した繊維補強ポーラスコンクリートは、優れた凍結融解抵抗性を持つことが認められる。一方、凍結融解試験後の曲げ性状は、F40混入率0.5％としてF12を併用した場合に改善される。本研究の限りでは、繊維混入率を適度に調整して短繊維及び微細繊維を併用することで、ポーラスコンクリートの凍結融解抵抗性が改善されることが明らかである。

EFFECT OF COMBINED USE OF VINYLON FIBERS WITH DIFFERENT LENGTH ON COMPRESSIVE AND FLEXURAL BEHAVIOR OF FIBER-REINFORCED POROUS CONCRETES

The purpose of this study is to investigate the effect of combined use of vinylon fibers with different length on the compressive and flexural behavior of fiber-reinforced porous concretes. The fiber-reinfoced porous concretes using coarse aggregates with maximum size of 20mm are reinforced by the mixed vinylon fibers with the length of 30mm and 40mm. The fiber-reinforced porous concretes having target voids of 20％ are prepared with various fiber content and fiber mixture ratio, and cured under 70℃ hot water for 1d. The fiber-reinforced porous concrete specimens are subjected to compression and flexural tests. As a result, the effect of combined use of vinylon fibers with different length on the compressive strength of the fiber-reinforced porous concretes is hardly recognized. The modulus of elasticity, flexural strength and flexural toughness of the fiber-reinforced porous concretes with fiber content of 0.3 and 1.0％ is slightly improved by combined use of vinylon fibers with the length of 30mm and 40mm. The effectiveness of combined use of vinylon fibers with different length on the mechanical behavior of the fiber-reinforced porous concretes is affected by the particle size distribution of coarse aggregate, fiber content and content of cement mortar as binder.本研究では、粗骨材最大寸法を20mmとし、長さ30及び40mmのビニロン短繊維を併用した繊維補強ポーラスコンクリートの圧縮及び曲げ強度、静弾性係数並びに曲げタフネスについて検討している。その結果、短繊維の併用効果は圧縮強度についてはほとんど認められないが、その静弾性係数、曲げ強度及び曲げタフネスについては、繊維混入率0.3又は1.0％とした場合、若干認められる。本研究の限りでは、繊維補強ポーラスコンクリートの力学的性質に及ぼす、粗骨材間を架橋するほどの長さを持つビニロン短繊維の併用効果は、使用する粗骨材の粒度組成、繊維混入率、空隙率の変化に伴う結合材としてのセメントモルタル量に複雑に影響されることが示唆される。