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CORRECT CONCRETE COVER TO REINFORCEMENT

Correct cover to reinforcing steel not only affects the durability of the concrete but also the extent and severity of cracking under working loads. In conditions of fire the amount of cover also governs the time scale before damage to the reinforced concrete elements occurs. Attention to correct detailing practices, which include making allowances for permissable tolerances of both reinforcing and formwork the maintenance of good construction practices and the specification and use of the correct number and type of reinforcing cover devices will ensure that the rebar can be placed and maintained in the position intended. Nominal cover required should be clearly shown on all relevant drawings. The amount of nominal cover is dependant upon the size and type of the structural member, the environmental conditions to which it will be exposed (including fire), the class of concrete and the type and size of reinforcing bar which will be used.
Actual cover obtained on site should never be less than the minimum nominal cover by the relevant authorities, nor more than the minimum, plus variations as specified. Positive tolerances on cover are as important as negative. To ignore them would invalidate design assumptions relating to effective depth and would also influence the width of surface cracks under design loads.

Correct Covers:
a. Ensures protection of the Rebar from the environment by providing a physical barrier
b. Ensures that concrete completely encircles Rebar allowing passivation
c. Ensures that concrete completely encircles Rebar allowing complete bond to develop
d. Allows the Rebar to assume position and act as designed
e. Prevents staining
g. Provides a time lag in cases of fire

The engineering and detailer should specify and schedule the correct number and type of cover devices required (SABS 0144)
  

EXAMPLE OF BAR SCHEDULING TO SABS 82: 1997

1 2 3 4 5 6 7 8 9 10 11 12 13
Member Reinforcement Bending dimensions for shape codes (SABS 82) Fixing and non-standard bending details
Mark, size & No. Of No. in each Type & size Bar mark Total No. Length¹ mm Shape Code A²
mm		 B²
mm		 C²
mm		 D²
mm		 E² or r² mm  
                       
  Masses Nom. size 6 8 10 40 Total

R=Mild steel bars (250 MPa) to SABS 920
Y= High yield steel bars (450 MPa) to SABS 920
Z= Cold drawn wire rod

1) Specified in multiples of 25 mm
2) Specified in multiples of 10 mm

This schedule complies with SABS 82

 Sheet title Project No. Schedule No.
M.S.             Project Ref. Drawing Revision suffix
H.T.                        
Total           Section Date Drawn Checked


SOME PRACTICAL COST SAVING HINTS

  • Every bend adds cost so keep it simple

  • Consider stock lengths as every offcut adds cost

  • Rework is costly so recheck the schedules

  • Transporting bars that were left off the schedules can be very costly indeed

  • Shortcuts taken in the drawing office can lead to delays and increased cost on site

  • Prefabrication can ease the programme and significantly reduce fixing costs.

  • Enlarged details of complicated sections can save time on site and reduce costs. Remember that a Y25 deformed bar needs a space of at least 32mm to pass through

  • If bending creep is deducted, ensure that the total length is sufficient to allow the bending machine to grip the bend

  • It would be beneficial for aspirant detailers to conclude their training by spending a few months cutting, bending and fixing steel. This would greatly enhance their ability to produce good detailing to produce good detailing during the rest of their careers.