5　Freezing and Thawing Action

5.1　General

5.1.1　For concrete dam and other hydraulic structures affected by weathering and freezing-thawing action，the class of concrete frost resistance shall be clearly defined and the seepage control and drainage design of concrete structures shall be properly made.

5.1.2　Concrete frost resistance is divided into six classes:F400，F300，F200，F150，F100 and F50，which shall be determined by the test methods specified in DL/T 5150.For hydraulic structures in sea or salty lake area，the water sampled from the area where the hydraulic structures actually locate shall be used in the concrete frost resistance test.For thin-walled reinforced concrete structures，relative dynamic elastic modulus of concrete shall not be less than 80% after required freeze-thaw cycles.

5.1.3　For mass concrete，the zoning depth for frost resistance shall be deeper than the maximum frost depth where the structure located and the zoning depth should not be smaller than 2m.

5.1.4　For hydraulic concrete，the class of frost resistance shall meet the requirements in DL/T 5057 and DL/T 5082.