1. Concrete Protective Layer The concrete cover refers to the distance from the outer edge of stressed bars to the concrete surface, which shall not only meet the requirements specified in Table 1-1 and also not be less than the nominal diameter d of the steel bar. Minimum Thickness of the Concrete Cover of Longitudinal Stressed Bar (mm) Table 1-1 Environment type Slab, wall Beam Column ≤C20 C25~C45 ≥C50 ≤C20 C25~C45 ≥C50 ≤C20 C25~C45 ≥C50 I 20 15 15 30 25 25 30 30 30 II a — 20 20 — 30 30 — 30 30 b — 25 20 — 35 30 — 35 30 III — 30 25 — 40 35 — 40 35 Notes: 1. The thickness of concrete cover for the longitudinal stressed bar in the foundation shall not be less than 40mm and shall not be less than 70mm where there is no cushion layer. 2. The thickness of the protective cover for the steel bars distributed in slab and wall shall not be less than the corresponding value in table minus 10mm, and shall not be less than 10mm; the thickness of protective cover for stirrups and constructional bars in beams and columns shall not be less than 15mm. 3. Where the thickness of concrete cover for longitudinal stressed bar in the beam and column is greater than 40mm, effective anti-cracking constructional measures shall be taken for the protective cover; As for the projecting slab in Type II and Type III environment, effective protection measures shall be taken for its surface. 4. As for the buildings with fire resistance requirement, the concrete cover shall also meet the requirements of relevant current national standards. Environment Type of Concrete Structures Table 1-2 Environment type Conditions I Indoor normal environment II a Indoor humid environment; outdoor environment in non-severe cold and non-cold regions, and environment having direct contact with non-aggressive water or soil b Outdoor environment in severe cold and cold regions, and environment having direct contact with non-aggressive water or soil III Environment using deicing salt; environment in severe cold and cold regions where water level changes in winter; outdoor environment at coast IV Seawater environment V Environment affected by human action or natural corrosive substance
