Not less than 35 cm. The third phase expansion project of Xi Xianyang International Airport is the airport reconstruction and expansion project with the largest investment, the largest building volume and the most complicated technology in the history of northwest civil aviation. There is a difference in runway thickness between international airports and local small airports. Large international airports need to take off and land Boeing 747 and other large passenger planes, and the runway thickness should not be less than 35 cm. As for the design strength, wear resistance, durability and workability of concrete, it must follow the industry standards of People's Republic of China (PRC) and China.