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南非土木工程施工标准 CC2部分：混凝土工程（小型工程） 英文原文节选 20100079 2-4 |
4.7.4 Batching
4.7.4.1 Cement
The mass of cement supplied in a standard bag shall be assumed to be the mass indicated on the
bag. All cement taken from bulk storage containers and from partly used bags shall be batched by
mass to an accuracy of within 2 % of the mass required.
4.7.4.2 Water
The mixing water for each batch shall be measured. The amount of water measured shall be
adjusted to allow for the moisture content of the aggregates.
4.7.4.3 Aggregates
4.7.4.3.1 Sand and stone aggregates for site mixes shall be measured volumetrically in buckets or
wheelbarrows of known volume, or in suitable measuring boxes.
4.7.4.3.2 The fine and the coarse aggregates shall be measured separately in suitable measuring
boxes of known volume and of such capacity that the quantities of aggregate for each batch are
suitable for direct transfer into the mixer.
4.7.5 Mixing
4.7.5.1 Mixing at construction site
4.7.5.1.1 Hand mixing of concrete shall be undertaken on a surface which is free of contaminants.
The sand shall be thoroughly mixed with the cement before adding the water and stone. The
addition of water to the mix shall be controlled and shall be such that the resulting concrete can be
readily compacted into the corners of formwork and around reinforcement without segregation of
the materials or excessive bleeding of free water at the surface.
4.7.5.1.2 The following requirements shall apply to the mixing of concrete by means of a concrete
mixer at the construction site:
a) The total volume of material per batch shall not exceed the rated capacity of the mixer.
b) Before any concrete is mixed, the inner surfaces of the mixer shall be cleaned and all hardened
concrete shall be removed. Immediately before the mixer is charged with materials at the
SANS 2001-CC2:2007
Edition 1
13
commencement of each concrete production run, a slurry of cement, sand and water that
contains cement and sand in the ratio 1:2 and in sufficient quantities to cover the entire inside
surface of the mixer shall be produced in the clean mixer and discharged.
c) 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 requirements of (d), the mixing period for
each batch of 1,5 m3 or less shall be at least 1,5 min and at least 1 min for drum-type and pantype
mixers, respectively, and shall be increased by 20 s and 15 s, respectively, for each
additional cubic metre or part thereof. During this period, the drum or pan shall be rotated at the
speed recommended by the manufacturer of the mixer. The maximum continuous mixing times
at the recommended mixing speeds shall not exceed 10 min and 6 min per batch for drum-type
and pan-type mixers, respectively.
d) Discharge shall be so carried out that there is no segregation of the materials in the mix. The
mixer shall be emptied completely before it is recharged. If the mixer has been out of use for
longer than 30 min, it shall be thoroughly cleaned out, and particular attention shall be paid to the
removal of any build-up of materials in the drum, in the loading pan and around the blades or
paddles.
4.7.5.1.3 Concrete shall only be mixed in the quantities required for immediate use. Concrete that
has set shall be discarded.
4.7.5.2 Ready-mixed concrete
Ready-mixed concrete shall be mixed in accordance with the requirements of SANS 878.
4.7.5.3 No-fines concrete
4.7.5.3.1 No-fines concrete shall be composed of coarse aggregate of a specified single size,
cement and water. The cement and aggregate shall be mixed in a suitable mechanical mixer with
just enough water to form a smooth grout that will completely coat each particle of aggregate and
will be fluid enough to flow together to form a fillet at each point of contact of the aggregate
particles. Not more than 20 L of water per 50 kg of cement shall be used.
4.7.5.3.2 The aggregate shall, in addition to complying with the applicable requirements of
SANS 1083, be of a nominal size not greater than 20 % of the thickness of the no-fines concrete to
be placed and shall be measured by volume in suitable measuring boxes. The proportions of
aggregate and cement binder shall be 9 parts stone aggregate of the specified nominal single size
to 1 part of cement.
4.7.5.3.3 No-fines concrete shall be placed within 30 min of mixing. It shall be so worked that it fills
the space to be concreted and that adjacent particles are in contact with each other. No-fines
concrete shall not be vibrated.
4.7.5.3.4 The removal of formwork for no-fines concrete shall comply with 4.3.7, but the minimum
curing period shall be 2 d longer than that required at the applicable ambient temperature in terms
of 4.7.10.4.
4.7.6 Transportation of concrete
Mixed concrete shall be discharged from the mixer and transported to its final position in such a
manner that segregation, loss of ingredients and adulteration are prevented, and that the mix is of
the required workability at the point and time of placing.原件下载： 
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