dc.description.abstract | In the past decades, a large amount of high-level waste (HLW) has been continuously produced. Nuclear power plants are nearing full capacity for the temporary disposal facilities for HLW. The geological disposal facility (GDF) concept is to build the final disposal site between 200 m and 1,200 m below the surface and is designed with the engineered barrier systems (EBS) as the central concept, which requires the construction of a large volume of cement matrix materials. Because ordinary cement materials have high alkalinity and high alkalinity solution, and it will affect the performance of bentonite as buffer material, the pH value of the pore solution of low pH cement materials used in the final disposal site must be less than 11.
There are a total of 15 mixed designs. The ratio of cement, silica fume, and fly ash for low pH of general concrete and low pH of self-compacting concrete are 5:4:1, while the ratio of low pH of shotcrete (sprayed concrete) is 4:2:4. Then there was the study of bentonite, using MX-80 and SPV 200. The effects of different pH on the expansion properties of the samples were investigated under normal temperature (23±1 ℃), medium temperature (50±1 ℃), and high temperature (80±1 ℃), in the range of 7 ~ 13.5. At the same time, the effect of low-pH concrete pore solution on bentonite was verified.
The results show that the additive amount of superplasticizer in these concrete needs to be between 1.3 % and 3.5 %. Exception of shotcrete (sprayed concrete), the pH of all concrete can drop below 11 at 90 days. The compressive strength develops completely in about 56 days, and the maximum compressive strength is about 62 MPa in 90 days. Their volume stability, sulfate resistance, and compactness are excellent. Among them, the ratio of PC-LB350-W45, SCC-LB300-W29, and SHC-LB330-W30 had the best comprehensive performance. The experimental results of bentonite show that pH value and temperature change have a significant effect on the expansion property of bentonite. It needs a pH value of less than 11 to ensure the stability of the expansion ability. Moreover, the use of low-pH concrete can significantly reduce the influence on the expansion of bentonite. | en_US |