CO2-absorbing type of soda straw in cement-grouting tunnels at
Wujiangdu Hydropower Station of Guizhou, China.
These soda straws were formed in 12 years, and the maximum length is 126cm. Due to the quick absorption of CO2 from the surrounding atmosphere, the CO2 content as low as 150 ppmv was measured in some places, such as in the small holes for water-leading and decompression in the figure. This low CO2 content, compared to the local atmospheric CO2 concentration (350 ppmv), indicates that there is an important CO2 sink during the formation of the special speleothems.