4.3　Materials of Concrete Components

Ⅰ　Concrete

4.3.1　The concrete strength classes should not be lower than the specifications in the Table 4.3.1 below.

4.3.2　Enhanced strength，that is known to exist for concrete as a material of construction at low temperature，is normally not used in determining the ultimate strength of concrete sections.However，when adequate testing data is available，the low temperature properties may be utilized.

4.3.3　Admixtures of certain ratio may be considered appropriate for concrete.

4.3.4　Where air entraining agents are used，they may be resin based to ensure the concrete mix may contain up to 5% entrained air；however，the metal-based agents should not be used.

4.3.5　Concrete material should be Portland cement with low heat of hydration，ground granulated blast furnace slag or pulverized fuel ash may be used in combination with Portland cement.However，the designer shall be aware that there may be a slower strength gain.

4.3.6　The low temperature concrete mixing proportion shall be determined by laboratory testing.

4.3.7　For corrosive environment，the concrete shall also be in accordance with the current national standard Standard for corrosion protection design for industrial constructions GB 50046.

Ⅱ　Steels

4.3.8　Typical yield strength of reinforcing steel for concrete tank may be selected from Table 4.3.8.

4.3.9　2.0×105N/mm2 may be taken as the modulus of elasticity of reinforcing steel.

4.3.10　The reinforcing steel shall comply with the following requirements：

1　When the service temperature is not below-20℃，the reinforcing steel shall be in accordance the current national standard Standard of concrete structure design GB 50010.

2　When the service temperature falls below-20℃，the connectors shall be subject to tensile tests at low temperature，and the result difference of these tests shall be within 5% of those specified at ambient temperature.

4.3.11　In addition to the requirements specified in Table 4.3.8 of this code，the low temperature resistant steel in the interior wall of the pre-stressed wall shall also comply with the ductility requirements at low temperatures specified in Attachment D of this code.If the low temperature steel fails to satisfy the ductility requirements specified in Attachment D of this code，the following alternatives may be considered：

1　Carbon-manganese steel，9% nickel steel or austenitic stainless steel.

2　Reducing allowable tensile stress of reinforcing or pre-stressing steel.

4.3.12　Pre-stressing steel shall comply with the following requirements：

1　Pre-stressing steel should be low-relaxation steel stands and shall have proper ductility，and its physical and mechanical properties shall comply with the current national standard Steel strand for prestressed concrete GB/T 5224，the typical ultimate strength should be 1860N/mm2，jacking stress should not exceed 80% of typical ultimate strength of the pre-stressing steel，and the stress relaxation after jacking for 1000h shall not be higher than 2.5%.

2　The modulus of elasticity of pre-stressing steel may be taken as 1.95×105N/mm2.

3　Pre-stressing steel shall be less sensitive to stress corrosion.

4　Pre-stressing steel should not be welded，and only the weld joints before pre-stressing are allowed for the single stranded wires in the steel strands.

4.3.13　Anchorage，grips and couplers for pre-stressing steel shall satisfy the strength，elongation and fatigue-resistant design requirements，and their specifications shall conform to the current national standard Anchorage，grip and coupler for pre-stressing tendons GB/T 14370.The anchorage shall have sufficient strength to permit the stress of pre-stressing steel to be transmitted to the concrete and shall properly work in case of cracking in the anchorage zone，and the anchorage shall not be located in high stress zone.

4.3.14　When the design temperature is lower than-20℃，special testing shall be carried out for the pre-stressing steel and anchorage.

4.3.15　Steel wires may also be used as the pre-stressing steel；however，they shall comply with the current national standard Steel wires for the pre-stressed of concrete GB/T 5223.