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*; *; Kubo, Hiroshi*; Uegaki, Yoshiaki*
JNC TJ8400 2002-039, 38 Pages, 2002/02
JNC-TJ8400-2002-039.pdf:4.01MB
A concept of radioactive waste repository in which both bentonite and cementitious materials exist in deep cavern as engineered barriers is proposed. It is pointed out that pore water of cement is approximately 12.0 to 13.0 of pH and that it maintains for a long period. Therefore alteration of bentonite and rocks should be studied. Mixing test upon some interaction between modeled cement water and bentonite and rocks have been carried out since 1995 as a part of TRU repository's study. And low alkalinity of cement has been studied as parallel to study on alteration of bentnite. HFSC which has high fly ash content and which shows approximately 10.5 to 11.0 of pH of pore water was developed. Cementitious materials are generally use as a combination with steel, since its tensile strength is low. The corrosion of steel in concrete becomes a big problem in case of decreasing pH of cement. There is little available reference, since low alkalinity cement is quite new and special ordered one. Accelerating test for corrosion in low alkalinity concrete were carried out in order to collect data of corrosion. Although alteration of bentonite by several types of modeled cement water was tested. Long term test by actual cement pore water has not carried out. The alteration in 360 days was investigated. Conclusion obtained in this study is following. [Corrosion of steel (re-bar)] (1)Re-bar in HFSC with 60% of W/C is significantly corroded. The corrosion rate is bigger than the rate of ordinary used cement. (2)Diffusivity of Cl
ion in HFSC is similar to it in OPC comparing by the same water powder ratio. (3)Corrosion rate of HFSC 30 is similar to OPC60. However corrosion is progressed in HFSC 30 without Cl ion due to lower alkalinity, but it isn't done in OPC within a certain amount of Cl ion. [Alteration of bentonite and rocks] (1)Although no secondary minerals was observed in HFSC, monmorironite is gradually lost by increasing calcite. (2)Secondary ...
Iriya, Keishiro*; *; Kubo, Hiroshi*; Uegaki, Yoshiaki*
JNC TJ8400 2002-038, 83 Pages, 2002/02
JNC-TJ8400-2002-038.pdf:24.9MB
A concept of radioactive waste repository in which both bentonite and cementitious materials exist in deep cavern as engineered barriers is proposed. It is pointed out that pore water of cement is approximately 12.0 to 13.0 of pH and that it maintains for a long period. Therefore alteration of bentonite and rocks should be studied. Mixing test upon some interaction between modeled cement water and bentonite and rocks have been carried out since 1995 as a part of TRU repository's study. And low alkalinity of cement has been studied as parallel to study on alteration of bentnite. HFSC which has high fly ash content and which shows approximately 10.5 to 11.0 of pH of pore water was developed. Cementitious materials are generally use as a combination with steel, since its tensile strength is low. The corrosion of steel in concrete becomes a big problem in case of decreasing pH of cement. There is little available reference, since low alkalinity cement is quite new and special ordered one. Accelerating test for corrosion in low alkalinity concrete were carried out in order to collect data of corrosion. Although alteration of bentonite by several types of modeled cement water was tested. Long term test by actual cement pore water has not carried out. The alteration in 360 days was investigated. Conclusion obtained in this study is following. [Corrosion of steel (re-bar)] (1)Re-bar in HFSC with 60% of W/C is signmcantly corroded. The corrosion rate is bigger than the rate of ordinary used cement. (2)Diffusivity of Cl ion in HFSC is similar to it in OPC comparing by the same water powder ratio. (3)Corrosion rate of HFSC 30 is similar to OPC60. However corrosion is progressed in HFSC 30 without Cl ion due to lower alkalinity, but it isn't done in OPC within a certain amount of Cl ion. [Alteration of bentonite and rocks] (1)Although no secondary minerals was observed in HFSC, monmorironite is gradually lost by increasing calcite. (2)Secondary ...
Iriya, Keishiro*; Mikami, Tetsuji*; Akiyoshi, Kenji*; Uegaki, Yoshiaki*
JNC TJ8400 2002-013, 87 Pages, 2002/02
JNC-TJ8400-2002-013.pdf:1.59MB
The underground research laboratory, which will be constructed in Horonobe, plays a role of demonstration of construction technique upon nuclear waste repositories. Low alkalinity cement is one of candidates for repositories as a cementitious material in order to prevent alteration of bentonite and rock by hyper alkaline solution. JNC has developed a low alkalinity cement (HFSC) which contains a lot of fly ash, and has studied the physical and chemical properties by laboratory test. However workability which is required for construction procedure of repositories has not been studied enough yet. This study shows if requirements in actual construction, such as shotcreting, self-compacting, and, grouting, are fulfilled, and if the workability is preferable for tunneling construction. It is demonstrated that HFSC is applicable for shotcreting by testing in a modeled tunnel. It is pointed out that re-bars have a possibility of corrosion in low alkalinity cement. In-site test for saline water which may accelerate corrosion is started by setting specimen made in last year. Analyzing and assessing will be done next year. Construction method of tunnel lining is investigated in case of applying pre-cast segments. Self-compacting concrete is adopted, since added silica-fume needs superplasticizer and its workability is very flowable. Two piece of segment were made for the section which designed for a ordinary urban tunnel. It is noted that pre-casting concrete can be made by HFSC. Super fine cement powder for grouting which indicate low alkalinity can be selected by combination of grinned lime stone powder and silica fume with grinned ordinary Portland cement. The items to be improved toward using in Horonobe construction are pointed out by results of this study and summarized a study plan is described. Major problem to be solved is delaying compressive strength generation of HFSC. It is recognized in shotcrete and self-compacting concrete. Selecting types of fly ash and ...
Iriya, Keishiro*; Mikami, Tetsuji*; *; Uegaki, Yoshiaki*
JNC TJ1400 2001-004, 150 Pages, 2001/05
no abstracts in English