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南非土木工程施工标准 CC1部分：混凝土结构工程 英文原文节选 20100079 2-3 |
4.7.10.9 Placing of concrete in an element that is supported shall not be commenced until the
concrete previously placed in supporting elements (columns, walls or beams) is no longer plastic
and has been in place for at least 2 h. When elements that are supported and supporting elements
are placed in one operation, the concrete in the vicinity of the junction between these elements shall
be revibrated shortly before it sets.
NOTE This procedure is necessary to eliminate defects such as cracks caused by the settlement of solids in
the fresh concrete. This is also relevant for horizontal reinforcement in deep sections and in slabs.
4.7.10.10 Unless otherwise specified in the specification data, the entire thickness of a bridge deck
shall be placed in one pass so as to avoid the layering of concrete. Fresh concrete shall not be
placed against concrete which has been in position for more than 30 min unless a construction joint
has been formed or unless a retarding additive has been used in the concrete.
4.7.10.11 In plain concrete with a thickness of not less than 300 mm, plums may, if permitted in terms
of the specification data, be included to displace concrete for up to 20 % of the total volume, provided
that
a) the plums are spread evenly throughout the concrete;
b) no plum laid shall have a dimension that exceeds one-third of the smallest dimension of the
concrete in any plane; and
c) each plum is surrounded by at least 75 mm of concrete.
4.7.10.12 When closed circuits are being concreted, work shall commence at one or more points in
the circuit and proceed in opposite directions at the same time so that, on completion of the circuit,
the junction or junctions are formed with freshly placed concrete.
4.7.10.13 Concrete shall not be placed under water unless permitted in terms of the specification
data. No concrete shall be placed in flowing water. When the placing of concrete under water is
permitted, it shall be placed by means of a tremie. During placing, the lower end of the tremie shall
be continuously immersed in the concrete being deposited so that the fresh concrete enters the
mass of previously placed concrete from within, causing water to be displaced with minimum
disturbance at the surface of the concrete. To maintain the desired properties of the concrete, the
quantity of cementitious binder in the concrete mix shall be increased by 20 %.
4.7.10.14 During and after concreting under water, pumping or dewatering operations in the
immediate vicinity shall be suspended should there be any danger that such operations will interfere
with the freshly placed concrete before it has set and gained sufficient strength.
4.7.10.15 Concrete may be placed by pumping if so permitted in terms of the specification data.
4.7.10.16 No-fines concrete shall be placed in its final position within 15 min of mixing.
4.7.10.17 Where sliding formwork is used, the following additional requirements shall apply:
a) All necessary measures to ensure the continuity of operations shall be taken, including the
provision of all the necessary lighting and standby equipment for mixing, hoisting, placing and
compacting and the availability of all the materials on site required for completing each structure
before casting commences.
b) Concrete shall be cast in uniform layers in the formwork so that the level of the top surface of the
concrete differs by no more than 250 mm between any two points in the formwork. In addition, the
top level of the concrete shall not be so low down in the formwork as to cause structural instability
in the formwork. The working platform shall be kept clean and no concrete which has dried out in
part shall be swept into the formwork.
SANS 2001-CC1:2007
Edition 1
31
c) The concrete shall be compacted during and immediately after placing. Care shall be taken not to
damage or disturb previously placed concrete. To ensure the proper bonding of successive layers,
not more than 1 h shall elapse between the placing of successive layers except where a suitable
retarding additive has been applied, in which case an appropriate delay is permissible.
4.7.11 Compaction
4.7.11.1 The concrete shall be fully compacted by suitable means during and immediately after
placing. It shall be thoroughly worked against the formwork and around reinforcement and other
embedded items without displacing them, and into corners of formwork to form a solid void-free
mass that has the required surface finish.
NOTE Internal vibrators should be capable of operating at more than 10 000 cycles per minute and external
vibrators at more than 3 000 cycles per minute. Sufficient standby vibrators should be kept available in case of
breakdowns.
4.7.11.2 The concrete shall be free from honeycombing and planes of weakness. Successive
layers of the same lift shall be thoroughly worked together. To achieve this, the compaction tool
shall penetrate through the new layer to the lower layer which shall still be sufficiently plastic to
permit interknitting.
4.7.11.3 Compaction shall be carried out by mechanical vibration or, if permitted in terms of the
specification data, by spading, rodding or forking. The concrete shall not be over-vibrated, which
results in segregation, surface laitance, or leakage, or any combination of these.
NOTE Vibration should be applied continuously during the placing of each batch of concrete until the
expulsion of air has virtually ceased. Immersion vibrators should be inserted vertically into the concrete to be
compacted, at regular intervals that do not exceed 0,6 m or 10 times the diameter of the vibrator, whichever is
the lesser. As soon as a water sheen is visible on the surface, the vibrator should be slowly withdrawn from the
concrete, care being taken to avoid the formation of voids.
4.7.11.4 Contact with reinforcement and formwork shall, as far as is practicable, be avoided when
internal vibrators are used.
4.7.11.5 When external vibrators are used, the design of formwork and the disposition of vibrators
shall be such as to ensure efficient compaction and to avoid surface blemishes.
4.7.11.6 No-fines concrete shall be worked sufficiently to ensure that it will completely fill the space
to be concreted and that adjacent aggregate particles are in contact with one another. Excessive
tamping shall be avoided and the no-fines concrete shall not, in any circumstances, be vibrated.
4.7.11.7 The rate of concrete placing shall be commensurate with the available compaction
equipment and only skilled operators shall undertake compaction by vibration. The number of
vibrators used shall be compatible with the rate at which concrete is placed. Standby vibrators shall
be made available.
4.7.11.8 Concrete shall not be subjected to disturbance by vibration within 4 h to 24 h of it having
been compacted.
NOTE Special attention should be given to the compaction of concrete in the anchorage zones and behind the
anchor plates, and in all places where high concentrations of reinforcing steel or cables occur.原件下载： 
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