0100-2*
ISBN 0-626-10153-0*This standard references other standards Edition 2
1992
(As amended 1994)
SOUTH AFRICAN STANDARD
Code of practice
The structural use of concrete
Part 2: Materials and execution of work
Reprint 1994
(As amended 1994)
SOUTH AFRICAN BUREAU OF STANDARDS
CODE OF PRACTICE
THE STRUCTURAL USE OF CONCRETE
PART 2: MATERIALS AND EXECUTION OF WORK
Obtainable from the
South African Bureau of Standards Private Bag X191
Pretoria
Republic of South Africa 0001 Telephone : (012) 428-7911 Fax : (012) 344-1568 E-mail : [email protected] Website : http://www.sabs.co.za COPYRIGHT RESERVED
Printed in the Republic of South Africa by the South African Bureau of Standards
Notice
This part of SABS 0100 was approved in accordance with SABS procedures on 20 February 1992.
NOTE 1 In terms of the Standards Act, 1993 (Act 29 of 1993), no person shall claim or declare that he or any other person complied with an SABS standard unless
a) such claim or declaration is true and accurate in all material respects, and
b) the identity of the person on whose authority such claim or declaration is made, is clear.
NOTE 2 It is recommended that authorities who wish to incorporate any part of this standard into any legislation in the manner intended by section 31 of the Act consult the SABS regarding the implications.
This part of SABS 0100 will be revised when necessary in order to keep abreast of progress. Comment will be welcome and will be considered when this part of SABS 0100 is revised.
Foreword
This second edition (first revision) cancels and replaces SABS 0100-2:1980.
Annex A (Concrete subjected to wet conditions - aggressiveness of the water, and countermeasures) forms an integral part of this part of SABS 0100. Annex B (Curing), annex C (Technical data for prestressed structural elements required in a contract), annex D (Recommended specialist literature on massive concrete) and annex E (Bibliography) are for information only.
Reprint incorporating Amendment No. 1: 12 September 1994
Attention is drawn to the normative references given in clause 2 of this standard. These references are indispensable for the application of this standard.
Contents
Page Notice . . . ii Foreword . . . ii Committee . . . x 1 Scope . . . . 1 2 Normative references . . . . 1 3 Definitions . . . . 2 3.1 General . . . 3 3.2 Weather . . . 3 3.3 Conditions of exposure . . . 33.4 Concrete, general characteristics . . . 4
3.5 Concrete, strength characteristics . . . 5
3.6 Prestressing . . . 5
4 Materials for concrete . . . . 6
4.1 Cement . . . 6
4.1.1 General . . . . 6
4.1.2 Properties of concrete made with a blend of cement and cement extenders . . . 7
4.2 Water . . . 7
4.3 Aggregates . . . 7
4.3.1 Aggregate classification . . . . 7
4.3.2 Natural aggregates covered by SABS 1083 . . . . 7
4.3.3 Aggregates not covered by SABS 1083 . . . . 8
4.3.4 Nominal maximum size . . . . 8
4.3.5 Aggregates for high-strength concrete . . . . 8
4.3.6 Aggregates and fire resistance . . . . 8
4.3.7 Aggregates and concrete density . . . . 8
4.3.8 Use of "plums" . . . . 8 4.3.9 Storage . . . . 9 4.4 Admixtures . . . 9 4.4.1 General . . . . 9 4.4.2 Air-entraining agents . . . . 10 4.4.3 Storage . . . . 10 4.5 Deteriorated material . . . 10
5 Plant for concrete . . . . 10
5.1 General . . . 10
5.2 Batching plant . . . 10
5.3 Mixing plant . . . 10
(As amended 1994) 6 Proportioning . . . . 11 6.1 Quality of concrete . . . 11 6.1.1 General . . . 11 6.1.2 Strength . . . 11 6.1.3 Density of concrete . . . 11 6.1.4 Consistence . . . 12 6.1.5 Workability . . . 12 6.1.6 Bleeding . . . 12 6.1.7 Chloride content . . . 12 6.1.8 Sulfates in concrete . . . 13 6.1.9 Alkali-silica reaction . . . 13 6.1.10 Drying shrinkage . . . 13 6.2 Durability . . . 14 6.2.1 General . . . 14
6.2.2 Exposure to freezing and thawing . . . 14
6.2.3 Exposure to aggressive chemicals . . . 15
Amdt 1, 6.2.4 Exposure to salt-laden air . . . . 16
Sept. 1994 6.2.5 Exposure to corrosive fumes . . . . 17
6.2.6 Exposure to polluted air . . . 17
6.3 Mix proportions . . . 17
6.3.1 High cement content . . . 17
6.3.2 Concrete exposed only to mild conditions . . . 17
6.3.3 Deleted by Amendment No. 1 . . . 17
6.3.4 Deleted by Amendment No. 1 . . . 17
7 Production of concrete . . . . 18 7.1 Batching . . . 18 7.1.1 Cement . . . 18 7.1.2 Water . . . 18 7.1.3 Aggregates . . . 18 7.1.4 Admixtures . . . 18 7.2 Mixing . . . 18 7.2.1 Mixing on site . . . 18 7.2.2 Ready-mixed concrete . . . 20 7.3 Transportation . . . 20 8 Reinforcement . . . . 21 8.1 General . . . 21 8.2 Cover to reinforcement . . . 21 8.3 Bending . . . 22 8.3.1 General . . . 22
8.3.2 Preheating prior to bending or straightening . . . 22
8.4 Fixing . . . 22
8.4.1 Steel reinforcement . . . 22
8.4.2 Zinc-coated (galvanized) reinforcement . . . 24
8.4.3 Epoxy-coated reinforcement . . . 24
8.5 Welding . . . 24
8.5.1 General . . . 24
8.5.2 Use of welding . . . 24
8.5.3 Types of welding . . . 24
8.5.4 Location of welded joints . . . 25
8.5.5 Strength of structural welded joints . . . 25
9 Formwork . . . . 25
9.1 General . . . 25
9.2 Design and construction of formwork . . . 26
9.2.1 Loads . . . . 26 9.2.2 Deflection . . . . 26 9.2.3 Form accessories . . . . 26 9.2.4 Temporary openings . . . . 26 9.3 Preparation of formwork . . . 26 9.4 Re-use of formwork . . . 26 9.5 Removal of formwork . . . 27 9.5.1 General . . . . 27
9.5.2 Formwork removal time for cast-in-situ concrete . . . . 27
9.5.3 Reshoring . . . . 28
10 Placing and protection of concrete . . . . 29
10.1 General . . . 29 10.2 Placing . . . 29 10.3 Compaction . . . 30 10.4 Construction joints . . . 31 10.4.1 General . . . . 31 10.4.2 Location . . . . 31 10.4.3 Bonding . . . . 31 10.4.4 Reinforcement . . . . 32 10.4.5 Construction . . . . 32 10.5 Embedded items . . . 33 10.5.1 General . . . . 33 10.5.2 Waterstops . . . . 33
10.5.3 Pipes and conduits . . . . 33
10.6 Concrete for water-retaining structures . . . 34
10.7 Concrete in saturated ground . . . 34
10.8 Protection and curing of concrete . . . 34
10.8.1 General . . . . 34
10.8.2 Concreting in hot weather or in windy conditions . . . . 35
10.8.3 Concreting in cold weather . . . . 36
10.8.4 Concreting during rainfall . . . . 36
10.9 Surface finish of concrete . . . 36
10.9.1 Upper surfaces of concrete . . . . 36
10.9.2 Concrete surfaces cast against forms . . . . 36
10.9.3 Repair of surface defects . . . . 37
10.10 Records . . . . 37
11 Massive concrete . . . . 37
12 Prestressing . . . . 38
12.1 Prestressing tendons . . . 38
12.1.1 General . . . . 38
12.1.2 Handling and storage . . . . 38
12.1.3 Surface condition . . . . 38
12.1.4 Straightness . . . . 39
12.1.5 Cutting . . . . 39
12.1.6 Formwork . . . . 39
12.2 Tensioning . . . 40 12.2.1 General . . . . 40 12.2.2 Safety precautions . . . . 40 12.2.3 Tensioning apparatus . . . . 40 12.2.4 Pre-tensioning . . . . 41 12.2.5 Post-tensioning . . . . 41
12.3 Positioning of tendons and sheathing . . . 42
12.4 Tensioning procedure . . . 43
12.5 Grouting of prestressing tendons . . . 44
12.5.1 General . . . . 44 12.5.2 Grouting equipment . . . . 44 12.5.3 Materials . . . . 44 12.5.4 Ducts . . . . 45 12.5.5 Mixing . . . . 45 12.5.6 Strength of grout . . . . 45 12.5.7 Injection of grout . . . . 45
12.5.8 Grouting during cold weather . . . . 46
12.5.9 Protection and bond of prestressing tendons . . . . 46
13 Precast concrete . . . . 47
13.1 General . . . 47
13.2 Permissible deviations . . . 47
13.3 Prestressed units . . . 48
13.4 Handling and erection of precast concrete units . . . 48
13.4.1 Lifting equipment . . . . 48
13.4.2 Handling and transportation . . . . 48
13.4.3 Assembly and erection . . . . 49
13.4.4 Temporary supports during construction . . . . 49
13.4.5 Forming structural connection . . . . 49
13.4.6 Protection . . . . 51
14 Testing and acceptance of concrete . . . . 51
14.1 General . . . 51
14.2 Testing services . . . 51
14.2.1 Basic testing services . . . . 51
14.2.2 Testing services required by the engineer . . . . 51
14.2.3 Additional services when required . . . . 52
14.2.4 Test reports . . . . 52
14.2.5 Responsibilities and duties of the contractor . . . . 52
14.3 Strength tests of concrete during construction . . . 52
14.3.1 General procedures . . . . 52
14.3.2 Evaluation of strength test results . . . . 53
14.3.3 Acceptance criteria for strength test results . . . . 53
14.4 Strength tests of concrete in place . . . 54
14.4.1 Non-destructive testing . . . . 54
14.4.2 Core tests . . . . 54
(As amended 1994)
15 Load tests . . . 55
15.1 Individual precast units . . . 55
15.1.1 General . . . 55
15.1.2 Non-destructive test . . . 55
15.1.3 Destructive test . . . 55
15.1.4 Special test . . . 55
15.2 Structures and parts of structures . . . 55
15.2.1 General . . . 55
15.2.2 Age at test . . . 55
15.2.3 Test loads . . . 56
15.2.4 Measurements during the tests . . . 56
15.2.5 Assessment of results . . . 56
16 Procedure in the event of failure . . . . 57
Tables 1 Limits of chloride content of concrete . . . 13
2 Total air content for various sizes of coarse aggregate for normal-density concrete . . . . 14
3 Cement/water ratio and cement content for normal-density reinforced concrete and low-density reinforced concrete . . . 17
4 Cement/water ratio and cement content for normal-density unreinforced concrete . . . 17
5 Minimum cover for various conditions of exposure and cement/water ratios for normal-density concrete . . . 21
6 Minimum cover for various conditions of exposure and cement/water ratios for low-density concrete . . . 21
7 Removal of formwork: minimum time in days . . . 28
8 Permitted tolerance in the location of tendons and sheathing . . . 42
Annexes A Concrete subjected to wet conditions - aggressiveness of the water, and countermeasures . . . 58
A.1 General . . . . 58
A.2 Analytical tests required . . . . 58
A.3 Assessment of the aggressiveness of water, using the Basson Index (BI) . . . . 59
A.4 Recommended anti-corrosion measures . . . . 61
Tables A.1 Ionic characteristics . . . . 58
A.2 Calculation of water properties indices . . . . 59
A.3 Calculation of environmental indices . . . . 60
A.4 Classification of water in terms of Basson Index BI . . . . 60
A.5 Countermeasures against leaching corrosion . . . . 61
A.6 Countermeasures against spalling corrosion . . . . 63
A.7 Countermeasures against chloride corrosion . . . . 63
A.8 Concretes for aggressive chemical environments . . . . 64 Amdt 1, A.9 Cements recommended for the making of concretes for aggressive waters . 65 Sept. 1994 A.10 Coatings for concretes in aggressive waters . . . . 66
B Curing . . . 67
B.1 General . . . 67
B.2 Strength of concrete . . . 67
B.3 Distortion and cracking . . . 67
B.4 Durability and appearance . . . 68
C Technical data for prestressed structural elements required in a contract . . . . 69
C.1 Data for pre-tensioned elements . . . 69
C.2 Data for post-tensioned elements . . . 70
D Recommended specialist literature on massive concrete . . . . 72
Committee
South African Bureau of Standards . . . VJ Woodlock (Chairman) I Jablonski (Standards writer) E Coetzee (Committee clerk) CSIR
Division of Building Technology . . . BG Lunt Portland Cement Institute . . . BJ Addis
South African Federation of Civil Engineering Contractors . . . HH Meier The South African Association of Consulting Engineers . . . GJ de Ridder
CODE OF PRACTICE
SABS 0100-2
Edition 2
The structural use of concrete
Part 2:
Materials and execution of work
1 Scope
1.1
This part of SABS 0100 covers the materials and execution of work related to the structural use of concrete in buildings and structures where the design of reinforced, prestressed and precast concrete is entrusted to appropriately qualified structural or civil engineers and the execution of the work is carried out under the direction of appropriately qualified supervisors.1.2
This part of SABS 0100 does not cover the structural use of concrete made with high-alumina cement.2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part of SABS 0100. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of SABS 0100 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Information on currently valid national and international standards may be obtained from the South African Bureau of Standards.
PCI. TM 9.28.
SABS 82:1976, Bending dimensions of bars for concrete reinforcement.
SABS 471:1971, Portland cement (ordinary, rapid-hardening and sulphate-resisting).
SABS 626:1971, Portland blastfurnace cement.
SABS 831:1971, Portland cement 15 (ordinary and rapid-hardening).
SABS 878:1983, Ready-mixed concrete.
SABS 1024:1974, Welded steel fabric for concrete reinforcement. SABS 1083:1976, Aggregates from natural sources.
SABS 1200 G:1982, Standardized specification for civil engineering construction: Concrete (structural). SABS 1466:1988, Portland fly ash cement.
SABS 1491-1:1989, Portland cement extenders - Part 1: Ground granulated blastfurnace slag. SABS 1491-2:1989, Portland cement extenders - Part 2: Fly ash.
SABS 1491-3:1989, Portland cement extenders - Part 3: Condensed silica fume. SABS 0100-1:1980, Structural use of concrete - Part 1: Design.
SABS 0109:1969, Floor finishes on concrete.
SABS 0144:1978, Detailing of steel reinforcement for concrete. SABS 0155:1980, Accuracy in buildings.
SABS method 11:1990, Water - pH value.
SABS method 202:1983, Chloride content of water.
SABS method 212:1971, Sulphate content of water.
SABS method 213:1990, Water - Dissolved solids content. SABS method 216:1990, Water - Calcium content.
SABS method 217:1990, Water - Free and saline ammonia content. SABS method 218:1971, Albuminoid ammonia content of water.
SABS method 856:1976, Bulking of fine aggregates.
SABS method 861:1976, Sampling of freshly mixed concrete.
SABS method 862:1976, Slump of freshly mixed concrete.
SABS method 863:1976, Compressive strength of concrete (including making and curing of the test cubes).
SABS method 865:1982, The drilling, preparation, and testing of concrete cores.
SABS method 1071:1990, Water - Magnesium content.
SABS method 1085:1985, Initial drying shrinkage and wetting expansion of concrete.
3 Definitions
3.1 General
3.1.1 acceptable/approved: Acceptable to/approved by the engineer.
3.1.2 cement: Portland cement; blends of portland cement and portland cement extenders as covered
in SABS 1491.
3.1.3 concrete cover: The thickness of concrete between the face of the concrete, as cast, and the
outer face of reinforcing steel, prestressing steel, steel used for binding the reinforcing, or any embedded steel.
3.1.4 contractor: The individual who, or the organization that, has entered into an agreement to carry
out the work specified.
3.1.5 engineer: The representative appointed by the owner to administer the requirements of a
project specification for specific concrete work.
3.1.6 formwork: All the temporary aids and material required to support, and to provide the shape
of, the concrete in a structure (while the concrete is in the fresh state).
3.1.7 ready-mixed concrete: Concrete that complies with the relevant requirements of the project
specification and as further defined in SABS 878.
3.2 Weather
3.2.1 adverse weather: Cold weather or a combination of a high ambient temperature, low relative
humidity and high wind velocity, which may tend to impair the quality of fresh or hardening concrete or otherwise cause hardened concrete to have undesirable properties.
3.2.2 cold weather: Weather in which the ambient temperature is 5 °C or less.
3.2.3 cool weather: Weather in which the ambient temperature exceeds 5 °C but does not exceed 15 °C.
3.2.4 hot weather: Weather in which the ambient temperature exceeds 32 °C.
3.2.5 normal weather: Weather in which the ambient temperature exceeds 15 °C but does not exceed 32 °C.
3.3 Conditions of exposure
NOTE - For the definitions of- non-aggressive to mildly aggressive water, - mildly to fairly aggressive water, and - highly aggressive water,
see table A.4 of annex A, and for an explanation of wet conditions, see the commentary below.
3.3.1 mild conditions: The concrete is exposed generally to unpolluted air.
- indoors (but not including industrial areas); or - out of doors in arid rural areas (Karoo).
3.3.2 moderate conditions: The concrete is
a) sheltered from severe rain;
b) buried in non-aggressive soil; or
c) subject to polluted air (but not corrosive fumes). For example:
- indoors in industrial areas; or - out of doors in rural Highveld areas.
3.3.3 severe conditions: The concrete is exposed to
a) wet conditions in which the water is mildly to fairly aggressive;
b) corrosive fumes; or
c) salt-laden air. For example:
- out of doors in industrial areas;
- out of doors in marine atmospheric conditions (i.e. up to 15 km from the sea); or - out of doors in the Cape winter-rainfall area.
3.3.4 very severe conditions: The concrete is exposed to
a) wet conditions in which the water is mildly to fairly aggressive;
b) abrasive action under any wet conditions; or c) highly corrosive fumes.
3.3.5 extreme conditions: The concrete is exposed to wet conditions in which the water is highly
aggressive.
COMMENTARY - Conditions are considered wet if the concrete is exposed to water continuously or intermittently. The effect on the concrete of exposure to water depends on the aggressiveness of the water, the period of time during which the concrete is wet, and the frequency of the wet-dry cycling. It is not possible to propose definite limits in this regard. However, it should be kept in mind that highly aggressive water can have a seriously detrimental effect on concrete even if the period of time during which the concrete is exposed to such water is short.
3.4 Concrete, general characteristics
3.4.1 consistence: The extent (usually measured by the slump test) to which fresh concrete flows
(As amended 1994)
3.4.2 grade of concrete: An identifying number for a particular concrete, which is numerically equal
to the characteristic strength at 28 d, expressed in megapascals.
3.4.3 high-density concrete: Concrete made of a high-density aggregate complying with SABS 1083
and that usually has a density in the range 2 500 kg/m3 to 3 600 kg/m3. Amdt 1,
Sept. 1994
3.4.4 low-density concrete: Concrete intentionally made to have low density by the use of
low-density aggregate or a mixture of low-density and normal-density aggregates, and usually required to have an air-dry density not exceeding 2 000 kg/m3.
3.4.5 normal-density concrete: Concrete made with aggregates complying with SABS 1083 and that
usually has a density in the range 2 200 kg/m3 to 2 500 kg/m3.
3.4.6 precast concrete: Concrete that consists of units cast and cured in a position other than their
final position, and placed in position to form an integral part of the structure.
3.4.7 prescribed-mix concrete: Concrete for which the engineer has prescribed the mix proportions.
3.4.8 strength concrete: Concrete designed primarily for strength considerations and designated by
its characteristic strength in conjunction with the maximum nominal size of stone used in its manufacture, e.g. 30 MPa/19 mm.
3.4.9 target slump: The average value for the slump of concrete aimed for to ensure compliance with
the slump required.
3.4.10 workability: The property of fresh concrete that determines the ease of placing and
compacting the concrete without segregation of its constituent materials.
3.5 Concrete, strength characteristics
3.5.1 characteristic strength: The value for the compressive strength of concrete, below which not
more than 5 % of the valid test results obtained on cubes of concrete of the same grade fall.
3.5.2 specified strength: The characteristic strength required by the engineer.
3.5.3 target strength: An average value of the strength of concrete that is higher than the specified
strength, and that is aimed for to ensure that the characteristic strength is attained.
3.5.4 valid test result: The average result obtained from three test cubes of concrete that have been
tested in accordance with SABS method 863, with the additional requirement that curing water be maintained at a temperature between 22 °C and 25 °C.
3.6 Prestressing
3.6.1 anchorage: A device used to anchor a tendon to the concrete member.
3.6.2 bonded tendon: A prestressing tendon that is bonded to the concrete throughout its effective
length, either directly (by being cast into the concrete) or by grouting.
3.6.3 coating: Material applied to unbonded tendons to protect them from corrosion, or material
3.6.4 coupler: A device designed to transfer the prestressing force from one tendon to another.
3.6.5 sheathing: An enclosure in which tendons intended to be post-tensioned are encased, to
prevent bonding during concrete placement (e.g. a paper or plastics jacket for unbonded tendons, or metal conduit for bonded tendons).
3.6.6 tendon: An assemblage of steel elements (e.g. wire, bar or strand) used to impart prestress to
concrete when the assemblage is tensioned.
3.6.7 unbonded tendon: A tendon that is not bonded to the concrete.
4 Materials for concrete
4.1 Cement
4.1.1 General
4.1.1.1 SABS specifications cover the following:
a) portland cements: these cements shall comply with SABS 471, Portland cement (ordinary, rapid-hardening, and sulphate-resisting);
b) cements containing ground granulated blastfurnace slag or fly ash: these cements shall comply with the applicable of the following specifications:
- SABS 831, Portland cement 15 (ordinary and rapid-hardening); - SABS 626, Portland blastfurnace cement; or
- SABS 1466, Portland fly ash cement.
NOTE - Any type of cement other than those referred to in 4.1.1.1 may be used when so required in terms of the project specification or when specifically authorized by the engineer.
4.1.1.2 Cement extenders shall comply with the applicable of the following specifications:
- SABS 1491-1, Ground granulated blastfurnace slag (GGBS); - SABS 1491-2, Fly ash (FA); or
- SABS 1491-3, Condensed silica fume (CSF).
NOTE - It is recommended that users of cement extenders consult producers of the extender or appropriate publications of recognized institutions (Portland Cement Institute or CSIR).
4.1.1.3 Cements for sulfate-resisting concrete shall be chosen in accordance with the procedures
given in annex A, taking into account the factors described in 6.2.3. Sulfate-resisting cements may have a lower resistance to chloride-ion migration than other cements.
4.1.1.4 For particular regions, or where it is suspected that alkali-silica reaction may occur, it may be
necessary to use cement of low alkali content (Na2O + 0,658 K2O) or aggregate of low potential
alkali-silica reactivity.
4.1.1.5 The type of cement to be used in each part of the structure shall be specified by the engineer,
and the cement used in the structure shall correspond to that specified. The type and source of cement may not be changed during the duration of a contract without the approval of the engineer.
4.1.1.6 Separate storage facilities shall be provided on the site for each type of cement used, and
cement shall be stored in weatherproof conditions. Storage of cement in bulk is permissible provided that the cement drawn for use is measured by mass and not by volume. Provision shall be made to ensure that different types of cement are stored in suitable silos. Cement shall be stored in such a manner that the oldest cement is used first.
Cement extender on its own or masonry cement shall not be used as cement for concrete works.
4.1.2 Properties of concrete made with a blend of portland cement and cement extenders
4.1.2.1 Strength
28 d strengths (under standard curing conditions) of GGBS or FA or CSF cement concretes comparable with 28 d strengths of ordinary portland cement concretes can be obtained in many cases, although adjustments in the concrete mix proportions may be necessary. Generally, as the cement extender content is increased, the early rate of strength development is reduced, particularly at lower temperatures. At ages exceeding 28 d, water-cured GGBS, FA and CSF concretes show an increase in strength over ordinary portland cement concretes of equivalent 28 d strengths.
4.1.2.2 Other properties
Provided sufficient GGBS or FA or CSF is incorporated and the concrete is properly cured, there is likely to be increased resistance to some forms of chemical attack and reduction of early heat of hydration.
4.2 Water
4.2.1 Water shall be clean and free from injurious amounts of acids, alkalis, chlorides, organic matter and other substances that could impair the strength or durability of concrete or metal embedded in the concrete. (It should be noted that sea water contains injurious amounts of chlorides and alkalis.)
4.2.2 Should the suitability of water be in doubt, particularly in remote areas or where water is derived from sources not normally utilized for domestic purposes, such water shall be tested.
4.3 Aggregates
4.3.1 Aggregate classification
Aggregates can be classified in terms of their density, as follows:
a) normal density: aggregates that have a particle density exceeding 2 000 kg/m3 but not exceeding
3 000 kg/m3;
b) low density: aggregates that have a porous structure and a particle density not exceeding 2 000 kg/m3;
c) high density: aggregates that have a particle density exceeding 3 000 kg/m3.
4.3.2 Natural aggregates covered by SABS 1083
4.3.2.1 Normally, both coarse aggregate (stone) and fine aggregate (sand) should comply with the
4.3.2.2 Acceptable variations to the requirements of SABS 1083 in the project specifications shall be
clearly specified.
4.3.2.3 Appendices to SABS 1083 identify characteristics of certain fine and coarse aggregates that
are normally not acceptable but are nonetheless suitable for use in particular circumstances and may be preferred on the grounds of economy. Such aggregates shall be clearly specified, and may only be used after tests have verified their particular characteristics and if guidance for their use is provided.
4.3.2.4 SABS 1083 specifies additional optional requirements for aggregates to be used for specific
purposes or where specific properties such as resistance to alkali-silica reaction, fire resistance, low shrinkage, or general durability are of significant importance.
4.3.3 Aggregates not covered by SABS 1083
Where aggregates other than those covered by SABS 1083 are to be used, such aggregates and requirements for their quality shall be clearly specified.
4.3.4 Nominal maximum size
The preferred nominal maximum sizes of coarse aggregate are 37,5 mm; 26,5 mm; 19 mm; 13,2 mm and 9,5 mm.
The nominal maximum size of coarse aggregate should not exceed
a) one-quarter of the minimum thickness of the concrete cross-section, and b) the cover of reinforcement specified.
In elements with closely spaced reinforcement, the use of a nominal maximum size of 9,5 mm or 13,2 mm should be considered.
4.3.5 Aggregates for high-strength concrete
Where high-strength concrete is required, both the source and the type of aggregate may need careful selection, based on results of previous use or of trial mixes.
4.3.6 Aggregates and fire resistance
It may be necessary to use an aggregate that behaves satisfactorily when exposed to high temperatures, e.g. low-density aggregates or limestone.
4.3.7 Aggregates and concrete density
The density of the aggregates used influences the density of the concrete. If a high-density concrete is required, a high-density aggregate (see 4.3.1) may need to be specified. If a low-density concrete (see 3.4.4) is required, a low-density aggregate (see 4.3.1) may need to be specified.
4.3.8 Use of "plums"
In plain concrete of thickness at least 300 mm, hard, clean, stone "plums" of mass 15 kg to 55 kg may, if approved, be used to displace concrete to a maximum of 20 % of the volume of the concrete, provided that
b) no plum has a dimension exceeding 300 mm or one-third of the smallest dimension of the concrete element, whichever is less,
c) each plum is surrounded by at least 80 mm of concrete, and
d) the strength of the rock that makes up the plums (as indicated by the aggregate crushing value or the 10 % fines aggregate crushing test) is at least that specified for coarse aggregate in SABS 1083.
4.3.9 Storage
4.3.9.1 Aggregates of different nominal sizes shall be stored separately and in such a way that
a) segregation of particles of the same size is minimized,
b) contamination by foreign matter is prevented, and c) intermixing of aggregates is minimized.
4.3.9.2 Where aggregates of different chloride content are stockpiled on the same site, strict control
shall be exercised over their use in different classes of concrete.
4.3.9.3 Stockpiles of natural or manufactured sand shall be free-draining to ensure a relatively uniform
moisture content throughout the stockpile.
4.4 Admixtures
4.4.1 General
4.4.1.1 Admixtures are added to a concrete mix to change certain properties of concrete by their
chemical effect or physical effect (or both). In changing certain properties, an admixture can significantly affect other properties.
4.4.1.2 Admixtures that may impair the durability of the concrete, or combine with the ingredients to
form harmful compounds, or increase the risk of corrosion of the reinforcement shall not be used. When an admixture is used in concrete that is made with any type of cement and that is to contain prestressing tendons, reinforcement and embedded metal, the chloride content of the admixture, expressed as chloride ions (by mass), should not exceed 2 % (m/m) of the admixture or 0,03 % (m/m) of the cement.
4.4.1.3 Admixtures shall not be used without the approval of the engineer, who may require tests to
be conducted before admixtures are used. To facilitate approval, the following information should be available:
a) the trade name of the admixture, its source and the manufacturer's recommended method of use; b) typical dosages and possible detrimental effects of underdosages and overdosages;
c) whether compounds likely to cause corrosion of the reinforcement or deterioration of the concrete (such as those containing chloride in any form as an active ingredient) are present and, if so, the chloride content of admixtures, expressed as chloride ions (by mass) or expressed as equivalent anhydrous calcium chloride (by mass); and
d) the average expected air content of freshly mixed concrete containing an admixture that causes air to be entrained (see 4.4.2) when the admixture is used at the manufacturer's recommended dosage.
4.4.1.4 If two or more admixtures are to be used simultaneously in the same concrete mix, all available
data should be used to assess the interaction of the admixtures and to ensure their compatibility.
4.4.1.5 Admixtures used in the work shall be of the same composition as those used in establishing
the concrete mix proportions.
4.4.1.6 The effect of an admixture can be highly specific to the combination of ingredients in the mix.
It is therefore important that trial mixes be made before an admixture is used in concrete for construction and if any mix ingredient is changed during the course of the project.
4.4.2 Air-entraining agents
An air-entraining admixture shall be of such a type and the dosage of sufficient quantity that the air content (see table 2) is maintained at the point of placing. When another admixture (or cement extender) is present in the concrete mix, a different dosage of the air-entraining admixture may be required. The entrainment of air tends to reduce the strength of concrete. Trial mixes should be made to determine the extent of strength reduction, and mix proportions adjusted if necessary.
4.4.3 Storage
Admixtures shall be stored in a manner that will prevent contamination, evaporation or damage. For admixtures used in the form of suspensions or non-stable solutions, agitating equipment shall be provided to ensure thorough distribution of the ingredients. Liquid admixtures shall be protected from temperature changes that would adversely affect their characteristics.
4.5 Deteriorated material
Cement or any other material that has deteriorated or that has been contaminated or otherwise damaged shall not be used in concrete and shall be removed from the site without delay.
5 Plant for concrete
5.1 General
All plant shall be maintained in good working order.
5.2 Batching plant
5.2.1 Regular examination, calibration and tests shall be carried out at frequencies that will ensure that the batching system functions effectively and accurately and that hoppers and cement containers are kept dry and clean.
5.2.2 The batching plant shall be such that the batching accuracy complies with 7.1.
5.2.3 In the case of an automatic plant, the mass batching scales shall be so interlocked that a new batch of materials cannot be delivered until the hoppers have been completely emptied of the previous batch and the scales are in balance. Where discharge of materials from the hoppers is manually controlled, a method of signalling shall be employed to ensure that ingredients are not omitted, or added more than once, when a batch of concrete is being made up.
5.3 Mixing plant
5.3.1 The type and capacity of mixing machines shall be such that the rate of output of concrete is suitable for the rate of concreting. Each machine shall be capable of producing a uniform distribution
of the ingredients throughout the batch within the time specified by the manufacturer. Worn or bent blades and paddles shall be replaced. The inner surfaces of the mixer shall be clean and shall have no hardened concrete adhering to them.
5.3.2 It is recommended that an agreement be reached between the contractor and the engineer if the mixer to be used
a) has unusual mixing characteristics, or
b) it is claimed that effective mixing can be consistently achieved in mixing periods shorter than those specified in 7.2.1.
5.4 Vibrators
Where compaction by vibration is specified, vibrators shall be capable of fully compacting each layer of concrete. It is recommended that at least one standby vibrator be available for every three (or lesser number of) vibrators necessary to maintain the rate of placing.
6 Proportioning
6.1 Quality of concrete
6.1.1 General
Concrete for all parts of the work shall be of the specified quality and capable of being placed and compacted without excessive segregation. When hardened, concrete should have developed all the properties required by this part of SABS 0100 and by the project specification.
The engineer shall ensure that samples of the constituent materials of the concrete, together with evidence that they comply with the provisions of clause 4, are supplied for approval in good time before concreting of the works commences.
Evidence shall be in the form of either
a) a statement, from an approved laboratory, of the results of tests, or
b) an authoritative and acceptable report or record of previous use of, and experience with, the material concerned.
6.1.2 Strength
6.1.2.1 Compressive strength
The specified compressive strength of concrete should be based on the 28 d characteristic compressive strength fcu, unless a different test age is specified.
6.1.2.2 Maximum cement content
Cement content should normally not exceed 550 kg per cubic metre of concrete.
6.1.3 Density of concrete
For certain purposes, e.g. to provide radiation shielding, a high-density concrete may have to be specified. In other cases, e.g. to provide thermal insulation, a low-density concrete may have to be specified. These densities are normally achieved by selecting suitable aggregates (see 4.3.7).
(As amended 1994)
6.1.4 Consistence
Unless otherwise dictated by the general workability of the concrete, the method of transportation or conditions of placement, or unless otherwise specified by the engineer, slump values for different types of construction should normally not exceed 150 mm for hand-placed concrete and 100 mm for vibrated concrete.
6.1.5 Workability
The concrete shall be of such workability that it can be readily compacted into the corners of the formwork and around reinforcement without the materials in the mix segregating.
6.1.6 Bleeding
The concrete shall be so proportioned with suitable materials that bleeding (i.e. the upward migration of water in compacted fresh concrete) is not excessive.
It is not possible to put quantitative limits to bleeding. To assess the bleeding behaviour of concrete, the consequences of bleeding should be borne in mind. Note that initially, bleeding is accompanied by the settlement of solid particles (i.e. cement and aggregates). Where this settlement is prevented by reinforcement or by changes in cross-section, differential settlement occurs and cracks and voids are formed in the concrete. This phenomenon is especially troublesome in columns, in T and I beams, and in beams and slabs with top reinforcement.
On the other hand, a film of bleed water on the surface of an element such as a slab will prevent or retard plastic shrinkage of the concrete and is therefore beneficial.
Methods of dealing with the detrimental consequences of bleeding and settlement are discussed in 10.3.8.
Amdt 1, 6.1.7 Chloride content Sept. 1994
The presence of chloride ions in concrete increases the risk of corrosion of embedded metal. Chlorides could be present in concrete as a result of inclusion in the raw materials; or they could become present at a later stage by ingress, especially via cracks and when the concrete is highly absorbent or permeable.
To reduce the likelihood of corrosion of embedded metal owing to the ingress of chlorides from an external source, it is essential to ensure adequate cover to reinforcement (see table 5), an appropriate cement/water ratio (minimum class 2 of table A.8 (see annex A)), good compaction and thorough curing of the concrete.
In particularly severe exposure conditions, alternative methods of reinforcement protection such as the use of surface coatings or more resistant reinforcement may be necessary.
(As amended 1994)
To minimize the chloride content in reinforced or prestressed concrete: Amdt 1,
Sept. 1994
a) the chloride content of the mixing water shall not exceed 500 mg/L (sea water shall not be permitted as mixing water);
b) calcium chloride and chemical admixtures that contain chlorides shall not be permitted; and
c) the chloride content of fine aggregate obtained from river estuaries, the sea or other sources likely to be contaminated by chlorides shall not exceed the limiting values given in SABS 1083.
Table 1 - Deleted by Amendment No. 1.
6.1.8 Sulfates in concrete
Although sulfates are present in most cements and in some aggregates, excessive amounts of sulfate in mix constituents can cause expansion and disruption of concrete. To prevent this, the total water-soluble sulfate content of the concrete mix, expressed as SO3, should not exceed 4 % (m/m), of the cement in the
mix. The sulfate content shall be calculated as the total from the various constituents of the mix.
6.1.9 Alkali-silica reaction
6.1.9.1 Some aggregates containing particular varieties of silica may be susceptible to attack by alkalis
(Na2O and K2O) originating from the cement or other sources, producing an expansive reaction that can
cause cracking and disruption of concrete. This is likely to happen only when all the following are present together:
a) a high moisture level within the concrete;
b) a cement that has a high alkali content, or another source of alkali; and
c) aggregate containing an alkali-reactive constituent.
6.1.9.2 When the materials are unknown and precautions based on the preceding three conditions are
judged to be necessary, these can take the following form:
a) limiting the alkali content of the concrete mix to 2,1 kg per cubic metre of Na2O equivalent; or
b) use of GGBS or FA or CSF as composite cements or replacement materials in order that at least 40 % of GGBS or 20 % of FA or 10 % of CSF, by mass, of the combined material is introduced in the mix.
6.1.10 Drying shrinkage
All concretes shrink when they dry out after the cessation of moist curing. Where this shrinkage is restrained, tensile stresses develop and may cause cracking. Factors in the proportioning of concrete that influence shrinkage are: water content, paste content, and elastic properties of aggregates.
6.2 Durability
6.2.1 General
A concrete element is durable if, when subjected to potentially destructive exposure (other than wear or loading), it protects the embedded metal from corrosion and performs satisfactorily for the life-time of the structure.
6.2.1.1 Impermeability
One of the main characteristics that enhances the durability of any concrete is its impermeability. Suitable impermeability is achieved with normal-density aggregates if there is a sufficiently high cement/water ratio (see 6.3), complete compaction of the concrete, and sufficient hydration of the cement through proper curing methods.
6.2.1.2 Cement content
The cement in the concrete is the component most vulnerable to attack by aggressive substances and thus the cement type and the cement content of the concrete will determine the degree of resistance of the concrete to attack by such substances.
6.2.1.3 Detailing
Since many processes of deterioration of concrete occur only in the presence of free water, the details of shape and design of exposed structural elements shall be such as to promote good drainage of water and to prevent standing pools. Minimum covers to reinforcement to meet the durability requirements for normal-density concrete and low-density concrete are given in 8.2.
6.2.2 Exposure to freezing and thawing
6.2.2.1 Normal-density concrete that is likely to be subjected to freezing-and-thawing action under wet
conditions should contain entrained air and should conform to the air-content limits given in table 2.
Table 2 - Total air content for various sizes of coarse aggregate for normal-density concrete
1 2
Nominal maximum size of coarse aggregate
mm
Total air content
% (V/V) 9,5 13,2 19 37,5 6-10 5-9 4-8 3-6
The cement/water ratio shall be at least 1,9 by mass.
6.2.2.2 Low-density concrete that is likely to be subjected to such freezing-and-thawing action shall
contain 6 % ± 2 % total air when the nominal maximum size of aggregate exceeds 9,5 mm, or 7 % ± 2 % total air when the nominal maximum size is 9,5 mm or less. Proportions shall be so selected that a characteristic strength fcu of 20 MPa or more is attained.
6.2.3 Exposure to aggressive chemicals
NOTE - See annex A for additional information.
Deterioration of concrete by chemical attack can occur by contact with gases or solutions of many chemicals, but is generally the result of exposure to acidic solutions or to solutions of sulfate salts. Concrete made with portland cement is not recommended in persistently acidic conditions (pH 5,5 or less).
Solutions of naturally occurring sulfates of sodium, potassium, calcium or magnesium, as may be present in some soils and groundwaters, can cause expansion and disruption of concrete.
In extreme conditions, some form of lining such as those listed in table A.10 of annex A should be used to prevent access by deleterious solutions.
Corrosive attack by water is one of the most serious conditions of exposure. All the materials found in concrete are to some extent soluble in water. The aggregates normally used are generally more resistant to attack than is the cementitious binder, which is the most vulnerable constituent owing to its greater chemical activity. (Steel reinforcement is also susceptible, if embedded in a pervious concrete or if corrosive attack on an initially impervious concrete has reached a relatively advanced stage and the corrosive agents have penetrated to the depth where reinforcement is embedded.)
The two properties of water that contribute most towards its high corrosiveness are the following: - water is an extremely effective solvent; and
- water is able to dissociate dissolved salts and enable them to participate in ion-exchange and ion-addition reactions.
The corrosiveness of water depends on the rate of dissolution of concrete in the water, which is influenced by the factors given in 6.2.3.1 to 6.2.3.7.
6.2.3.1 The concentration gradient between the solid phase (concrete) and the liquid phase (water)
In the case of concrete wetted by water, the concentration of calcium compounds in the concrete is usually many orders of magnitude higher than that of these compounds in the water. In the case of distilled or very soft water, the concentration of dissolved calcium salts in the water is almost zero and the concentration gradient becomes very large. The resultant dissolution rate can consequently be very high and rapid attack will take place. It is this mechanism that is responsible for the extremely aggressive behaviour of distilled water and very soft water towards concrete, which can result in the rapid leaching-out of the components of the concrete, especially calcium hydroxide, the presence of which is essential for maintaining the integrity of the binder. On the other hand, where water already contains a high concentration of the compounds present in the concrete, the concentration gradient is lower and can disappear when saturation of the aqueous phase is achieved.
6.2.3.2 The acidity of the water
The materials normally found in concrete have a higher solubility in acidic than in alkaline water.
6.2.3.3 The temperature of the water
(As amended 1994)
6.2.3.4 The movement of the water relative to the concrete
Corrosion rates proceed much more rapidly if the water is in motion and the interface layer is constantly replenished. (Thus wave movements in tidal zones or turbulent flow in pipelines are accelerating agents by virtue of their effective mixing action.)
6.2.3.5 The volatility of reaction products
Ammonium compounds present in the water in contact with the concrete, become part of the reaction products resultant from the corrosive attack on the concrete and may, under certain conditions, volatilize and be lost to the atmosphere as ammonia. The net result is the formation of voids in the concrete and a loss of alkalinity (rise in acidity) of the water, which then becomes even more corrosive.
6.2.3.6 The mobility of ions
The mobility of ions is an important factor in the control of the rate of penetration of the ions into the concrete.
6.2.3.7 The presence of dissolved gases
The presence of dissolved gases is required for certain corrosion reactions to proceed and the concentration of the gases in the water influences the corrosion rate.
In the case of many concrete structures in contact with water, the water level is variable and certain areas of the concrete are subjected to cycles of wet and dry conditions. The following factors can influence the corrosion rate in such areas:
a) enhanced concentration of dissolved salts: if the water level drops, previously wetted areas dry off as a result of evaporation of the surface layer of water. Any salts present in this layer become more and more concentrated as evaporation proceeds and eventually crystallize out of solution. A coat of variably concentrated salts can therefore be created, with all the implications that this may hold for the concrete;
b) exposure to gases present in the atmosphere: in heavily polluted industrial atmospheres, gases may be significant corrosion accelerators.
Amdt 1, 6.2.4 Exposure to salt-laden air Sept. 1994
In coastal environments, concrete structures are exposed to wind-driven, salt-laden air. When a critical concentration of free chlorides is reached, depassivation of the reinforcement could occur, leading to corrosion and to subsequent spalling of the concrete. Salts that enter the pore structure of the surface concrete could also crystallize on drying. This process sets up expansive forces which could cause the concrete to crack and spall, allowing the rate of chloride ingress to increase.
The degree of aggressiveness of coastal environment depends on the salt content of the air and the atmospheric relative humidity. In areas where the salt content and relative humidity of the air are high, it may be necessary to undertake protective measures similar to those for concretes in marine environments (see table A.8 of annex A).
(As amended 1994)
6.2.5 Exposure to corrosive fumes Amdt 1,
Sept. 1994
The deterioration of concrete as a result of exposure to corrosive fumes is usually associated with a high relative-humidity environment which presents a special case of concrete deterioration caused by aggressive water. Corrosive fumes are often characterized by a high concentration of corrodants, and special protection measures are usually required for the concrete.
Depending on the degree of aggressiveness of the fumes, protective measures could range from the provision of a high-strength, low-permeability concrete to the application of a chemically resistant barrier to isolate the concrete from the aggressive fumes. A careful assessment of the degree of aggressiveness of the fumes, together with specialist advice, is essential in determining the most effective protection method.
6.2.6 Exposure to polluted air Amdt 1,
Sept. 1994
The deterioration of concrete in heavily polluted industrial areas is caused by a number of mechanisms, depending on the nature of the atmospheric pollutant; for example, in areas around coal-burning power stations where emission of sulfates results in the precipitation of sulfuric acid, both acid attack and sulfate attack could cause concrete deterioration. The minimum requirements for concrete that is exposed to heavily polluted air are given in class 1 of table A.8 (see annex A).
6.3 Mix proportions
6.3.1 High cement content
A cement content in excess of 550 kg per cubic metre of concrete should normally not be used because such a cement content tends to make concrete sticky and difficult to handle, place and compact.
6.3.2 Concrete exposed only to mild conditions (see 3.3)
Specified strength shall be determined by structural design considerations. If the concrete is to include embedded metal, the characteristic strength shall not be less than 20 MPa. There is no requirement for minimum cement/water ratio or for minimum cement content.
6.3.3 Deleted by Amendment No. 1.
(As amended 1994)
7 Production of concrete
7.1 Batching
7.1.1 Cement
The mass of cement in a standard sack is 50 kg. All cement taken from bulk storage containers and from partially emptied bags shall be batched by mass to an accuracy of 2 % (or better) of the mass required.
7.1.2 Water
Mixing water for each batch shall be measured and the amount of water adjusted to allow for the moisture content of the aggregates (see 7.1.3). The true quantity shall be measured to an accuracy of 2 % (or better).
7.1.3 Aggregates
If batching is by mass, the mass of the aggregates of each size shall be measured and a correction made for the moisture content of the aggregates. The true mass shall be measured to an accuracy of 3 % (or better). If batching is by volume, the fine and coarse aggregates shall be measured separately in suitable measuring boxes of known volume and of such capacity that the quantities of aggregates for each batch are suitable for direct transfer into the mixer. Bulking tests on the fine aggregate (or moisture determination if the relation between bulking and moisture content of the specific fine aggregate is known) shall be conducted at least daily (in accordance with SABS method 856) and the results used to adjust the batch volume of fine aggregate to give the true volume required. Additional tests for bulking shall be carried out after rain has fallen or if there has been any other reason for variation in the moisture content of the aggregate.
7.1.4 Admixtures
The amount of admixture to be used shall be measured to an accuracy of 2 % (or better). Daily calibration of the measuring device is imperative, and after each day's use, the measuring device shall be uncoupled from the supply and cleaned. The person responsible for batching shall be fully conversant with the effects of the admixture and the consequences of underdosage or overdosage.
Amdt 1, Sentence deleted by Amendment No. 1.
Sept. 1994
7.2 Mixing
7.2.1 Mixing on site
7.2.1.1 General
7.2.1.1.2 The total volume of material per batch shall not exceed the rated capacity of the mixer. 7.2.1.1.3 Concrete shall only be mixed in quantities required for immediate use. Concrete that has set
shall be discarded. In the event of delay in the concreting operations, concrete may be retained in the mixer for a maximum period of 2 h, provided that only just enough water is added to the mixer to maintain the target slump. During this time, the mixer shall be restarted and run for about 2 min every 15 min. The period of 2 h shall be reduced if the ambient temperature, or any other factor, tends to produce early setting.
7.2.1.1.4 At the commencement of each concrete production run and before any concrete is mixed, the
inner surfaces of the mixer shall be cleaned and all hardened concrete removed. Sand, cement and water, proportioned as for the concrete to be made, shall then be introduced into the cleaned mixer in sufficient quantity to cover the entire inside surface of the mixer. The mixer shall then be operated (to mix these materials and to coat the interior surfaces of the mixer with the mixture) and discharged immediately prior to charging of the mixer with the first batch.
7.2.1.1.5 Instructions for the sequence of charging the particular mixer shall be given before operations
commence. Control systems shall be introduced to ensure that the batch is not discharged until the required mixing time has elapsed. At least three-quarters of the required mixing time shall take place after the last of the mixing water has been added.
7.2.1.1.6 The period of mixing shall be measured from the time when all the materials are in the drum
or pan, to the commencement of discharge. Subject to the exception given in 7.2.1.1.7, mixing shall take place for at least 1,5 min or 1 min, for drum-type and pan-type mixers respectively, for each batch of 1,5 m3 or less, and the mixing time shall be increased by 20 s or 15 s respectively, for each additional
cubic metre or part of a cubic metre. During this period, the drum or pan shall be rotated at the speed recommended by the manufacturer of the mixer. To prevent attrition, continuous mixing periods shall not exceed 10 min or 6 min per batch, for drum-type and pan-type mixers respectively, at the recommended mixing speeds.
7.2.1.1.7 If a mixer of the type described in 5.3.2(b) is used, shorter mixing periods may be used if
approved by the engineer.
7.2.1.1.8 The mixed concrete shall be so discharged that there is no significant segregation of the
materials in the mix.
7.2.1.2 Control of admixtures
7.2.1.2.1 Air-entraining admixtures, calcium chloride and other chemical admixtures shall be charged into
the mixer as solutions, and shall be measured by means of an acceptable mechanical dispensing device, the liquid being considered a part of the mixing water. Admixtures that cannot be added in solution may be weighed or may be measured by volume if so recommended by the manufacturer.
7.2.1.2.2 If two or more admixtures are used in the concrete, they shall be added separately to avoid
possible interaction that could interfere with the effectiveness of either admixture or that could adversely affect the concrete.
7.2.1.2.3 Addition of retarding admixtures shall be completed within 1 min after addition of the water has
been completed, or prior to the beginning of the last three-quarters of the required mixing, whichever occurs first.
7.2.1.3 Tempering and control of mixing water
When concrete delivered at the place of operation has a slump below that suitable for placing, as indicated by the project specifications, water may be added, provided that the cement/water ratio is not reduced to below the minimum permissible for strength and durability and the maximum slump is not
exceeded. The water shall be incorporated by additional mixing equal to at least half of the total mixing time required. Any addition of water in excess of that permitted by the limitation on the cement/water ratio shall be accompanied by a quantity of cement sufficient to maintain the proper cement/water ratio. The approval of the engineer (or of his representative) for such addition shall be obtained before the water is added.
7.2.1.4 Adverse weather 7.2.1.4.1 Cold weather
The required concrete temperature from the time of mixing until the concrete has hardened (see 10.8.3) may be obtained in several ways, such as by:
a) heating the mixing water and the aggregate (if water or aggregate is heated above 60 °C, combine the water with the aggregate in the mixer before adding the cement. Cement shall not be mixed with water or mixtures of water and aggregate of temperatures exceeding 60 °C);
b) increasing the cement content in the mix;
c) using a cement that hardens more rapidly; or
d) incorporating an accelerator. (Chloride-free accelerators should be used when the concrete contains reinforcement or other embedded metal.)
NOTE - If insulation is used, its effect on the temperature of concrete should be taken into consideration.
7.2.1.4.2 Hot weather
When the temperature of the fresh concrete is likely to exceed the permissible maximum (see 10.8.2), the concrete can be cooled by
a) cooling the mixing water or substituting flaked or well-crushed ice for part or all of the mixing water; ice particles have to be small enough to melt completely during the mixing process;
b) cooling the aggregates, for example by shading the stockpiles and by wetting the stone to cause evaporative cooling; or
c) injecting liquid nitrogen into the mix during mixing.
7.2.2 Ready-mixed concrete
Where concrete is delivered to the site ready mixed, the requirements of SABS 878 shall apply.
7.3 Transportation
The mixed concrete shall be discharged from the mixer and transported as rapidly as practicable to its final position by means that will prevent segregation, adulteration, loss of ingredients and ingress of foreign matter or water and that will maintain the required workability at the point of placing.
Concrete may only be conveyed through pipes made with materials that are non-reactive with cement. Aluminium pipes shall be suitably protected.
The capacity of conveying equipment shall be sufficient to ensure that placed concrete does not set before adjacent concrete of the same pour is placed.
(As amended 1994)
8 Reinforcement
8.1 General
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.
8.3 Bending
8.3.1 General
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.