GENERAL Measure batch and mix concrete materials in accordance with ASTM C94, Sections 8, 9, 10 and 11, with a manual, semi-automatic or automatic batching plant.
EQUIPMENT
Batching and mixing equipment shall be acceptable to Owner. Equipment shall be brought to the Site sufficiently in advance of its use to permit inspection and acceptance.
Batching and mixing equipment shall be acceptable to Owner. Equipment shall be brought to the Site sufficiently in advance of its use to permit inspection and acceptance.
The concrete shall be mixed in pan or drum type mixers and
the weight of materials used for each batch shall not exceed the manufacturer's
rated capacities for the machines. Other types of mixer shall be used only
after permission has been obtained from the Owner.
All mixing machines shall be kept clean, free from hard or
partially set concrete and well maintained in good working order.
Mixers and agitators shall be examined from the time to time
for changes in conditions due to the accumulation of hardened concrete or
mortar or through wear of the blades, and if found defective shall be corrected
by the Contractor at the Contractor's cost.
The materials used in concrete shall be measured solely by
weight, by means of an approved weight batching machine. Due allowance shall be
made for the water content of the aggregates.
Prior to delivering concrete, the plant shall be tested by
manufacturing several batches of concrete and perform uniformity tests on the
mixers in accordance with ASTM C94, Annex A1. The plant and mixer uniformity
tests shall be documented. The test batches of concrete may be used for
construction where determined suitable by the Owner.
Batching and mixing shall be carried out in plant approved
by the Owner.
The time allowed for mixing after all ingredients are in the
machine shall be not less than two minutes.
Small quantities of concrete less than half (0,5) cubic meter may be hand mixed on a clean water tight platform. The fine and coarse aggregate shall be thoroughly mixed together, cement then added, and the whole tuned over three times dry. The material shall be tuned over whilst adding water, then finally turned twice and worked to produce a mixture of uniform colour and consistency.
For hand mixing the specified quantities of cement shall be increased by 10 (ten) per cent without alteration in price.
Small quantities of concrete less than half (0,5) cubic meter may be hand mixed on a clean water tight platform. The fine and coarse aggregate shall be thoroughly mixed together, cement then added, and the whole tuned over three times dry. The material shall be tuned over whilst adding water, then finally turned twice and worked to produce a mixture of uniform colour and consistency.
For hand mixing the specified quantities of cement shall be increased by 10 (ten) per cent without alteration in price.
MEASURING
The Materials used in concrete shall be measured solely by weight, by means of an approved weight-batching machine. Due allowance shall be made for the water content of the aggregates.
Documentation shall be furnished on testing the metering devices. All measuring devices shall be accurate to within 1 % before any concrete is mixed, and at such other times as may be directed by the Owner.
The Materials used in concrete shall be measured solely by weight, by means of an approved weight-batching machine. Due allowance shall be made for the water content of the aggregates.
Documentation shall be furnished on testing the metering devices. All measuring devices shall be accurate to within 1 % before any concrete is mixed, and at such other times as may be directed by the Owner.
MIXING All concrete shall be mixed until there is a uniform distribution of material. All concrete shall be discharged completely before mixer is recharged. Production of concrete shall be in accordance with the applicable requirements of ACI 301 and ASTM C94.
The time allowed for mixing after all the materials have
been placed in the mixer, shall be sufficient for thorough mixing to take
place, but segregation of the consistituent materials shall not occur. When
uniformity tests in accordance with ASTM C94 are not performed, a minimum
mixing time of 1 1/2 minutes for drum type mixers shall be allowed or such
other time as the Owner shall direct. For batches larger than one cubic meter,
mixing time shall be increased 15 seconds for each additional cubic meter or
fraction thereof.
Cement when contained in bags, shall be used in such a way
that each batch of concrete required no part bags to be used. If the cement is
stored in bulk, the measuring device shall be approved by the Owner before use.
The water quantity for each batch shall be accurately
measured and discharged to the mixer while the later is being charged.
Concrete shall have the minimum water cement ratio practical
and shall be of such a consistency that if can be really worked into corners
and angles of the formwork, and around the reinforcement without segregation of
the materials or bleeding of the free water at the surface. On striking the
formwork, it shall present a face which is uniform, free from honeycombing,
surface crazing on excessive dusting. The water cement ratio used shall be
approved by the owner.
Ready - mixed concrete may be used if written consent is
obtained from the Owner and shall be mixed and delivered in accordance with
applicable requirements of ASTM C94, except that only trucks equipped with a
rotary drum or agitator shall be used, and concrete shall be deposited within
the time limits specified in Clause. The Contractor shall have adequate plant
to produce the required output, and have satisfactory control of the mix
proportions and the mixing of the concrete. The Owner shall have access to all
parts of the plant during working hours.
It shall be the contractor’s responsibility to design the
concrete mixes, using the constituent materials specified, to comply with the
requirements of the various grades of concrete.
The contractor shall, as soon as possible after the contract
has been placed, obtain representative samples of water and fine and coarse
aggregates in sufficient quantities for testing as directed by the Owner. Tests
so designated by the Owner shall be in accordance with the provisions of the
appropriate standards by the Owner.