1996 Fiscal Year Final Research Report Summary
Elucidation of Mechnisms of Deterioration of Concrete Caused by Chemical Attack of De-icing Salts and its Preventive Measures
| Project/Area Number |
07555134
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 試験 |
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| Research Field |
土木材料・力学一般
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| Research Institution | Kanazawa University |
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Principal Investigator |
KAWAMURA Mitsunori Kanazawa University, Graduate School of Natural Science and Technology, Professor, 自然科学研究科, 教授 (20019730)
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| Co-Investigator(Kenkyū-buntansha) |
TANIKAWA Shin Toagosei Co.Ltd., Chief Researcher, 主任研究員
IGARASHI Shinich Kanazawa University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (50168100)
TORII Kazuyuki Kanazawa University, Faculty of Engineering, Professor, 工学部, 教授 (50115250)
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| Project Period (FY) |
1995 – 1996
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| Keywords | De-icing salts / Mechanisms of Deterioration / Calcium Chloride Attack / Alkali-Aggregate Reaction / Mineral Admixtures / Preventive Measures / Surface Treatments |
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| Research Abstract |
With regard to the deterioration of concrete due to the chemical attack caused by de-icing salts, it was found that a high-concentration CaCl_2 was very aggressive towards Portland cement concrete, and its aggressivity became more severe at a low temperature than at a high temperature, while no sign of deterioration was observed in NaCl solution idependent of both the temperature and the concentration of solution. The deterioration caused by the ingress of CaCl_2 solution seemed to be attributed to the dissolution of calcium hydroxide and the formation of complex salts. In the mortars incorp orating mineral admixtures such as fly ash, blast-furnace slag and silica fume, the combined effect of a decrease in the content of calcium hydroxide and a reduced chloride ion permeability on the process of hydration of mineral admixtures effectively improved the resistance to calcium chloride attack. Furthermore, it was confirmed that the entrained air in concrete improved the resistance to the calcium chloride attack, but the reduced water : cement ratio had little influence at later stages of exposure time in a high-concentration CaCl_2 solution. Interestingly, a further deterioration accompanied by cracking was found to be caused by the repetitive drying and wetting in CaCl_2 solution.
With the regard to the deterioration of concrete due to alkali-silica reaction, in a reactive aggregate-bearing mortars with relatively low alkali contents, the promotion of their expansions in 1N NaCl solution was caused by a rise of OH^- ion concentration in pore solution. The increase in OH^- ion concentration in the pore solution was responsible for the intrusion of NaCl into the mortars containing a reactive aggregate.
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[Publications] Torii, K., Sasatani, T., Kawamura, M.: "Effects of Fly Ash, Blast-furnace Slag and Silica Fume on Resistance of Mortar to Calcium Chloride Attack" Proc.of 5th Intl.Conf.on Fly Ash, Silica fume, Slag, and Natural Pozzolans in Concrete, ACI SP-153. Vol.2. 931-949 (1995)
Description
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