Preparation for Concrete Placing
All water, wood scraps, and other debris shall be removed from areas where concrete is to be placed and the areas thoroughly cleaned to ensure proper placement and bonding of the concrete. Forms shall be oiled and sub-grades damp, but not wet, when concrete is placed. When fresh concrete is to be placed on set concrete, a 1.0 cm thick layer of mortar shall be applied by brush on the dry surface before the fresh concrete is placed. The mortar shall contain the same proportions of sand and cement as the concrete mix.
At construction joints, the concrete surface shall be roughened by air-water jet, after it has reached its final set but not more than 12 hours after its placing was completed, so as to expose the aggregate. All equipment and materials required for the proper placing, vibrating, finishing and curing of the concrete shall be at hand prior to the placing of concrete. The Contractor shall notify the owner when all preparations, as specified above, have been completed and are ready for inspection. No concrete shall be placed without the prior approval of the owner.
Transportation of Concrete
The Contractor shall provide equipment for conveying concrete from the mixer to the forms without segregation or loss of ingredients and in an acceptable condition of workability. The conveying equipment shall have sufficient capacity to complete the work within the established schedule. Transportation by truck mixers shall be permitted only when the mixers and their operation are such that the concrete is uniform in consistency and grading throughout the mixing batch. Any concrete retained in truck mixers requiring additional water to permit satisfactory placing shall not be used.
In principle, transportation time of fresh concrete, which include the mixing time and placing, shall be less than 1.5 hours. Transportation time is not more than one hour when outside atmospheric temperature exceeds 25 degrees centigrade without any cooling measures.
[We propose that transportation time of fresh concrete, which include the mixing time and placing, shall not be more than 1.5 hours when outside atmospheric temperature exceeds 25 degrees centigrade]