China is building a 315-metre dam that could become the world’s tallest. 27 mirrors are helping engineers finish it

China is building the 315-metre Shuangjiangkou dam in Sichuan, which could become the world’s tallest completed dam. Engineers are using 27 sun-tracking mirrors to direct concentrated sunlight onto its clay core, raising temperatures by about 3°C and extending construction hours in the freezing mountain environment, helping overcome difficult winter conditions.