2006 Fiscal Year Final Research Report Summary
Development of Shrinkage Crack Control Method due to Combined use of Inert Powder and Chemical Admixture
| Project/Area Number |
16360271
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Building structures/materials
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
NAWA Toyoharu Hokkaido Univ., Grad.School of Eng., Prof., 大学院工学研究科, 教授 (30292056)
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| Co-Investigator(Kenkyū-buntansha) |
IZUMO Kenji Hokkaido Univ., Grad.School of Eng., Inst., 大学院工学研究科, 助手 (10312381)
YUASA Noboru Nihon Univ., College of Ind.Tech., Asso.Prof., 生産工学部, 助教授 (00230607)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Inert inorganic powder / Organic admixture / Autogenous shrinkage / Drying shrinkage / Surface tension / Calcium sulfate / Restrained cracking test / Calcium silicate hydrate |
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| Research Abstract |
Prevent concrete from cracking is actually one of the key issues for the design of concrete. The purpose of this study is to develop control of shrinkage crack due to combination of inert powder and chemical admixture. Most important results are summarized as follows:
(1)When the inert inorganic additives such as slowly cooled blast furnace slag powder and limestone powder were added to the mortar with the organic admixtures which consist of polycarboxylate-based and polyoxyalkylene alcohol based polymer, autogenous shrinkage of mortar decreased markedly. However, the effect varied depending on the kind of organic admixture added. On the other hand, addition of fly ash also reduced significantly the autogenous shrinkage of cement mixes, but promoted to decrease their tensile strength. The opposite effects sometimes brought out a little tensile stress / tensile strength ratio, resulting in a low resistance of cracking. Hence, it was clear that to prevent crack due to autogenous and drying shrinkage, further development of sophisticated shrinkage reducing admixtures were required.
(2)The polyethyleneimine based shrinkage reducing admixture absorbed strongly on to cement, providing no reduction of surface tension of pore solution in cement paste. However, it had an effect to reduce autogenous shrinkage and drying shrinkage, and showed good development in strength. Further, the combined use of calcium sulfate enhanced to reduce shrinkage and increase in strength.
(3)The density of C-S-H in binary blends system could be calculated from data of Rietveld analysis, selective dissolution and mercury intrusion. As a result, the density of C-S-H became lower as increasing replacement ratio of fly ash. This implied that the volume of C-S-H gel due to fly ash hydration was larger than that of OPC hydration, providing elf-healing effect. Therefore, development of new method to prevent crack by this self-healing effect will be expected in future.
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Research Products
(33 results)
