Reinforcement

Reinforcement should comply with the relevant requirements of SABS 82, SABS 920 and SABS 1024.

NOTE - See also the relevant section of SABS 0100-1.

8.2 Cover to reinforcement

The minimum cover to reinforcement for normal-density concrete and low-density concrete is given in Amdt 1,

table 5 for various conditions of exposure (see 3.3). Sept. 1994

Detailing of reinforcement shall allow for fire resistance (see SABS 0100-1), dimensional tolerances in cutting, bending and fixing of reinforcement (see 4.13 and 5.1.5 of SABS 0144:1978), and permissible deviations in dimensions of concrete work (see SABS 0155).

Table 5 — Minimum cover for normal-density and low-density

concrete for various conditions of exposure Amdt 1,

Sept. 1994

1 2 3 4 5 6

Concrete

Minimum cover mm

Conditions of exposure

Mild Moderate Severe Very severe Extreme Normal-density

concrete

20 30 40 50 60

Low-density concrete

20 40 50 60 70

NOTE - This table should be used in conjunction with table A.8 of annex A.

Table 6 — Deleted by Amendment No. 1.

8.3 Bending

The following provisions shall apply:

a) all reinforcement shall be bent to the dimensions shown on the drawings and in accordance with the requirements of SABS 82;

b) all reinforcement shall be bent cold unless otherwise permitted (see 8.3.2);

c) bending shall be carried out slowly, using a steady, even pressure without jerk or impact;

d) it is permissible to bend grade 250 reinforcement protruding from concrete elements, provided that care is taken to ensure that the radius of bend is not less than that specified in SABS 82. 450 MPa bars shall not be bent, rebent or straightened without the engineer's approval;

e) where it is necessary to reshape steel previously bent, this shall only be done with the engineer's approval and each bar shall be inspected for signs of fracture.

8.3.2 Preheating prior to bending or straightening

Provided that the bars do not depend on cold working for their strength, they may be bent or straightened hot, in accordance with the following provisions:

a) the preheating procedure shall be such as not to harm the bar material (or to cause damage to the concrete in the case of bars already cast-in);

b) the preheat shall be applied to a length of bar equal to at least five bar diameters in each direction from the centre of the bend. The temperature of the bar at the concrete interface shall not exceed 260 °C;

c) the preheat temperature shall not exceed 650 °C;

d) the preheat temperature shall be maintained until bending or straightening is complete;

e) heated bars shall be cooled slowly in air. (Hot bars shall not be quenched with water.)

8.4 Fixing

The grade of accuracy for cover over reinforcement shall comply with the requirements of SABS 1200 G.

Reinforcement shall not be subjected to mechanical damage, rough handling, dropping from a height, or shock loading.

8.4.1 Steel reinforcement

8.4.1.1 All reinforcement, at the time of placing of the concrete, shall be free from rust, scale, oil and other coating that may reduce the bond between the steel and surrounding concrete, or initiate corrosion of the reinforcement. The reinforcement shall not be contaminated by any substance used as a release agent for the formwork.

All reinforcement shall be well and cleanly rolled. Rust, seams, surface irregularities and mill scale shall not be cause for rejection, provided that the mass per metre, dimensions, cross-sectional area and tensile properties of a test specimen comply with the applicable requirements for the specified bar.

8.4.1.2 Reinforcement shall be placed as shown on the drawings and shall be maintained in that position within the specified tolerances. Reinforcement shall be tied with annealed wire of diameter 1,6 mm or 1,25 mm or by acceptable clips, at sufficient intersections to avoid displacement of bars. It may also similarly be secured by welding if permitted by the engineer. Reinforcement shall be supported in its correct position by hangers or saddles, and aligned by means of chairs and spacers of approved design.

Spacers of such materials and designs shall be durable, shall not lead to corrosion of the reinforcement and shall not cause spalling of the concrete cover. Spacer blocks made from cement and sand shall be made of the cement and sand used for the surrounding concrete. Proportions shall be 1 volume of cement (loose), 1 volume of sand (dry and loose) and sufficient water to produce a mix that can be thoroughly compacted. Spacer blocks shall be cured in water for at least 14 d before being used. Concrete spacer blocks made on the construction site shall not be used unless they are made under strictly controlled conditions. Spacers and chairs shall be placed at the spacing recommended in 5.2.2 of SABS 0144:1978.

8.4.1.3 The clear distance between reinforcing bars shall be determined in accordance with 3.11 of SABS 0100-1:1980.

8.4.1.4 In the detailing and dimensioning of bars (in particular bends, hooks and stirrups), the designer should take into account the diameters of all the bars intersecting at any point, the sweep or curve of bends, the need for the use of ties to fix steel, the shuttering and reinforcement tolerances, the cover specified for various exposure conditions and the tolerances permitted for the fabrication of reinforcement and erection of formwork. The concrete cover specified is equally applicable to the upper layer of reinforcing steel in floors and slabs. For any slab, cognizance shall be taken of the specified concrete cover, and the detail dimensions and diagrams of the reinforcing bars to which the steel is to be bent shall be such that the specified concrete cover can be achieved.

8.4.1.5 The design of the laps and the lengths of main bars in vertical reinforcement shall be such as to suit the position of construction joints shown on the drawings or as specified. It is particularly important that where a kicker or starter stub for a wall is specified or shown on the drawings or will be permitted, that the lap in the vertical reinforcement start above the kicker. A lap shall not start below a joint at the top of a kicker and shall not finish above it.

8.4.1.6 Templates should be furnished for placement of all column dowels, unless otherwise permitted.

8.4.1.7 Welded wire fabric for slabs on grade shall extend to within 100 mm of the concrete edge. Welded wire fabric shall be adequately supported during placing of concrete, to assure proper positioning in the slab.

8.4.1.8 Where exposed-aggregate, ribbed or patterned finishes are to be achieved, the detail dimensions of reinforcing bars shall be such that the specified concrete cover can be maintained after the texture, ribbing or pattern is applied.

NOTE - The contractor cannot provide the specified cover unless the outside dimensions of reinforcement cages and the like provide for greater cover than would be provided for plain finishes of concrete.

8.4.1.9 Supporting steel should be included in the reinforcing schedule by the engineer. The use of other supporting materials is subject to the approval of the engineer.

8.4.1.10 Laps and joints of reinforcing bars shall be formed only as and where shown on the drawings or as approved by the engineer. Bars left exposed for bonding of future extensions to the structure shall be well protected from corrosion, using suitable means.

8.4.1.11 Reinforcement in elements cast on ground shall rest on precast concrete blocks at least 100 mm square, and having a compressive strength at least equal to the specified compressive strength of the concrete being placed. Other means of support may be used if approved by the engineer.

8.4.2 Zinc-coated (galvanized) reinforcement

Zinc-coated reinforcing bars supported away from formwork shall rest on zinc-coated wire bar-supports or on wire bar-supports made of dielectric material or other acceptable materials. All other reinforcement and embedded steel items in contact with zinc-coated reinforcing bars, or within a minimum clear distance of 50 mm from zinc-coated reinforcing bars, shall be zinc-coated, unless otherwise approved.

Zinc-coated reinforcing bars shall be fixed with zinc-coated tie wire or non-metallic-coated tie wire or other acceptable material.

8.4.3 Epoxy-coated reinforcement

Epoxy-coated reinforcing bars supported away from formwork shall rest on epoxy-coated wire bar-supports, or on bar-supports made of dielectric material or other acceptable materials. Wire bar supports shall be coated with dielectric material for a minimum distance of 50 mm from the point of contact with the epoxy-coated reinforcing bars. All reinforcing bars used as support bars or as spreader bars shall be epoxy-coated or coated with dielectric material.

Epoxy-coated reinforcing bars shall be fastened with nylon-coated, epoxy-coated or plastics-coated tie wire, or with other acceptable materials.

8.5 Welding

Generally, all welding should be carried out under controlled conditions in a factory or workshop and welding on site should be avoided if possible. Welding on site may be undertaken when required and permitted by the engineer, provided that suitable safeguards and techniques are employed and the types of steel (including high-yield steels to SABS 920) have the required welding properties. The competence of the operators shall be demonstrated prior to, and periodically during, welding operations.

8.5.2 Use of welding

Welding may be used for:

a) fixing in position; for example, by welding between crossing or lapping reinforcement, or between bars and other steel elements (metal-arc welding or electric resistance welding may be used on suitable steels); or

b) structural welds involving transfer of load between reinforcement or between bars and other steel elements.

Butt welds may be carried out by flash butt welding or metal-arc welding. For lapped joints, metal-arc welding or electric resistance welding may be used.

8.5.3 Types of welding

8.5.3.1 Flash butt welding

Flash butt welding shall be carried out with the correct combination of flashing, heating, upsetting and annealing, and with the use of only those machines that automatically control this cycle of operations.

8.5.3.2 Metal-arc welding

Metal-arc welding of reinforcement shall be carried out in accordance with the recommendations of the reinforcement manufacturer, as approved by the engineer.

8.5.3.3 Electric resistance welding

Electric resistance welding is done by the use of welding machines that can be adequately controlled but that require the correct preparation of the bars to be welded.

8.5.3.4 Other methods

Other methods of welding may be used, subject to their satisfactory performance in trial joints.

8.5.4 Location of welded joints

Structural welds shall not occur at bends in reinforcement. Unless otherwise agreed by the engineer, joints in parallel bars of the principal tensile reinforcement shall be staggered in the longitudinal direction.

For joints to be regarded as staggered, the distance between them shall be at least equal to the end anchorage length for the bar.

8.5.5 Strength of structural welded joints

The strength of all structural welded joints shall be assessed by means of testing trial joints.

8.5.6 Welded lapped joints

The length of run deposited in a single pass shall not exceed five times the diameter of the bar. If a longer length of weld is required, it shall be divided into sections and the space between runs shall be at least five times the diameter of the bar.

9 Formwork