SELECTION OF CONCRETE COVER THICKNESS

Concrete cover thickness of steel rebar can be determined by calculating of cracking limit state and crack width under the impact of external forces. In case of no calculation, we can refer the following standards: 

A/ Regarding Reinforced concrete structures in normal conditions:

Standard TCXDVN 356 : 2005 CONCRETE AND REINFORCED CONCRETE STRUCTURES – DESIGN STANDARD

I/ Regarding the axial reinforcing steel bar (non pre-stressed, pre-stressed), the concrete cover thickness are not smaller the diameter of steel bar or strand and not smaller than:

• In slab and wall have the thickness
  • 100 mm and thinner                           10 mm (15mm)
  • Above 100 mm                                     15mm (20mm)
• In beams and spandrel with height:
  • Lower than 250mm                             15mm (20mm)
  • Equal or higher 250 mm                     20mm (25mm)
• In columns:                                                         20mm (25mm)
• In foundation beams                                         30 mm
• In foundation:
  • Precast footings                                           30mm
  • Cast-in-place on bedding concrete:         35mm
  • Cast-in-place without bedding concrete: 70mm

NOTE:

1. Values in parentheses (…) to be applied for the outdoor structures or those in humid places 
2. In the structures made of light concrete and hollow concrete grade B7.5 or lower, the concrete cover thickness needs not smaller than 20mm and regarding the outside panel (without plaster), the cover will not smaller than 25mm.
3. Regarding one-layer structure made of honey concrete, concrete cover thickness must not be smaller than 25mm  in all cases.

II/ Regarding stirrups, distribution and constructive reinforcement, the concrete cover thickness  are not smaller than diameters of these steel bars and not smaller than:

- if the height of structure smaller than 250 mm:          ......10mm (15 mm)

- if the height of structure equal or greater than 250 mm:.15 mm (20 mm)

NOTE:

1. Values in parentheses (…) to be applied for the outdoor structures or those in humid places.
2. In the structures made of light concrete or hollow concrete grade B7.5 or lower and made of honey concrete, concrete cover thickness of cross reinforcement is not smaller than 15mm, regardless of height of the structures.

III/ Concrete cover thickness of at the end of pre-stressed structures along the length of stress transmission must be not smaller than:

-       with steel bar class CIV, A-IV, A-IIIB:.... 2d

-       with steel bar class A-V, A-VI, AT-VII:.... 3d

-       with steel strand:..................................... 2d

(where d is nominal diameter of steel bar, in milimeter)

In addition, the thickness of concrete cover mentioned-above must be not smaller than 40mm for all kind of steel rebar and not smaller than 30mm for steel strand.

B/ Regarding Reinforced concrete structures of Hydraulic works

I. Standard TCVN 4116:1985 HYDRAULIC CONCRETE AND REINFORCED CONCRETE STRUCTURES- DESIGN STANDARD

a/ Concrete cover thickness of the reinforced concrete structures in hydraulic works:  

• Not smaller than 30mm with load bearing steel rebars and 20mm with distribution/constructive rebars in the beams and slabs, which have their heights up to 1m, and the columns that its shorter side are up to 1m wide.
• Not smaller than 60mm and not smaller than the diameter of the load bearing and distribution rebars in the mass structures, which have the minimum cross dimension greater than 1m.

b/ Concrete cover thickness of the reinforced concrete structures in hydaulic works at sea must not smaller than:

              70mm – with load bearing wire steel rebar in bundle.

              50mm - with load bearing steel rebar;

               30mm – with distribution rebar and stirrups;

c/ With precast reinforced concrete structures that concrete strength equal or greater 200 kg/cm2, concrete cover thickness can be reduced 10mm in comparision with the values mentioned-above.

d/ In case that reinforced concrete structures are placed in aggressive environment, the concrete cover thickness must be specified according to the particular standards.

II. Standard  TCVN 9139:2012 HYDRAULIC WORK- CONCRETE/REINFORCED CONCRETE STRUCTURES IN LITTORAL AREA- TECHNICAL REQUIREMENTS

Table 1 – Technical requirements in design of the concrete and reinforced concrete structures of hydraulic work in the saline areas

Table 2 – Technical requirements in design of the concrete and reinforced concrete structures of hydraulic work in the acidic alum areas

C/ Regarding Reinforced concrete structures in marine environment:

Standard TCVN 9346:2012 CONCRETE AND REINFORCED CONCRETE STRUCTURES- REQUIREMENTS OF CORROSION RESISTANCE IN MARINE ENVIRONMENT