Feature: Temperature control, crack prevention at high-altitude hydropower station

BEIJING, Feb. 23 (Xinhua) -- On the upper reaches of the Jinsha River in southwest China, a high altitude hydropower station is under construction. Notably, the significant difficulty of temperature control and crack prevention during the concrete pouring process in such a cold and high-altitude area has been overcome by the construction team.

The Yebatan Hydropower Station is located at the junction of Baiyu County in southwest China's Sichuan Province and Konjo County in Xizang Autonomous Region, which is also in the southwest of China.

With a highest elevation of nearly 2,900 meters -- this hydropower station features a 217-meter-high arch dam and total installed capacity of 2.24 million kilowatts.

"Cracks are always troublesome for the pouring of concrete dams," said Du Guangyuan, an engineering management department director at Huadian Jinsha River Upstream Hydropower Development Co., Ltd. Even the tiniest cracks can have a negative impact on durability, thus shortening the service life of dams.

"Pouring a concrete dam is like baking a cake," said Du. After injecting raw material into the mold, constructors wait for the dam to take shape "but the former is far more complicated than the latter."

During pouring, the exterior of the concrete cools rapidly, while the interior heat continues to accumulate due to the hydration reaction of cement. This temperature difference generates internal stress.

If the stress exceeds the concrete's tolerance limit, cracks will slowly emerge -- weakening the structural strength of the dam and reducing its load-bearing capacity.

The harsh environment found in high-cold and high-altitude areas, with longer winters and shorter spring and autumn periods, increases the risk of cracks, and constructors had to bear this in mind at the Yebatan Hydropower Station. Building such a dam would clearly be a challenge given the weather conditions at its construction site.

"Old concrete cracking prevention methods were almost ineffective here," said Zhong Fulin, an assistant director with the engineering management department.

After countless trials and discussions, the construction team came up with an imaginative solution, building an "air-conditioned house" for the dam.

To maintain thermal insulation, they sprayed polyurethane on the upstream and downstream surfaces of the dam, and laid plastic film on the deck and transverse crest areas -- effectively maintaining a moist environment, Zhong explained.

Through such determined and skilled efforts, they managed to install three-layer insulated covers while adding heating facilities, such as air heaters, on the surface to ensure that the concrete maintained an appropriate temperature range after pouring.

In the end, the construction team succeeded in achieving year-round concrete dam pouring.

Currently, they are also applying intelligent systems to control the temperature of the dam in carrying out efficient grouting.

The intelligent temperature control system is capable of monitoring the internal temperature changes in real-time and with precision. It can respond swiftly if any abnormality is detected -- and is capable of automatically switching to either heating or cooling mode.

Construction of the main project of the hydropower station started in September 2018, with its first group of units expected to be put into operation by the end of 2025.

The hydropower station will be able to generate 10.2 billion kilowatt-hours of power annually, saving almost 4 million tonnes of coal and cutting carbon dioxide emissions by 7.37 million tonnes per year. ■