Concrete drop during vertical placement shall not exceed 2.5m. For heights greater than 2.5m, the Contractor shall pour concrete through enclose chutes or access hatches, details of which shall be approved by the Engineer.
This must comply with four main requirements, namely:
- It must be rapid so that the concrete does not dry out, lose its workability or plasticity between mixing and placing.
- To avoid non-uniform concrete, segregation must be reduced to a minimum, and any loss in fine material or cement and water prevented.
- Organise transport to avoid delays during placing of any particular lift or section. These delays cause the formation of pour planes, cold joints, or poor construction joints.
- When using open vehicles in hot or wet weather, protect the concrete from the effects of sun, rain and wind, and wind-borne dirt.
Concrete shall be transported as quickly as possibles from mixer to its final position, and in no case shall the time interval between the addition of water and placing exceed 30 minutes.
All placing and compacting shall be carried out by experienced workmen and under the the direct supervision of a competent staff.
Gangways for concrete transporter and foot traffic, shall not be permitted to bear on the fixed reinforcement. They will be supported clear of the reinforcement on chairs or stools designed for the purpose.
Concrete shall remain in sufficiently plastic condition for adequate compaction when placed. Concrete shall be placed as near as possible to its final position, and shall be placed square against the forms. Concrete shall not be moved into position by means of vibrators.
In walls, the concrete shall be placed in approximately horizontal layers. The concrete shall be placed in one continuous operation, rising uniformly in the formwork at a rate not less than 2.00m per hour. The concrete shall not be handled in any manner that may cause segregation.
A competent steel fixer shall be in continuous attendance during concreting to adjust and correct the position of any reinforcement which may be displaced.
Concreting operation must cease during rain and the Engineer will decide whether work can be done under light drizzle. The Contractor shall carry ut concreting in such sequence as to minimize the effects on the permanent works of temporary stoppage of concreting due to rain. The Contractor shall also provide adequate cover and protection from inclement weather for permanent works.