General requirements

034 PRECAST CONCRETE

0341 DEFINITION

Precast units shall be understood as plain or reinforced concrete units set in moulds, cured and fixed in position as detailed on drawings.

0342 GENERAL REQUIREMENT

Comply with the general requirements, and products section of the following.

Cast in place concrete Section 031

Concrete formwork " 032

Reinforcement " 033
0343 EXECUTION
03431 Samples of Precast Units

Before fabrication in bulk, specimen samples of the precast units shall be submitted for approval, with which further deliveries or castings shall be compared for uniformity of colour and finish.

03432 Casting

Precast concrete shall be concrete as specified and shall be thoroughly compacted by vibration in the moulds and shall not be removed from them until seven days after placing the concrete. The sides may be removed after three days provided that the moulds are such that the sides are easily removable without damaging the concrete.

Precast work shall be cast under sheds and shall remain three days in the moulds and a further seven days after removal from the moulds. During the whole of this period the concrete shall be shielded by sacking or other approved material kept wet. It shall then be removed from the sheds and stacked in the open for at least seven days to cure.
Unless specific dimension are given, precast work shall be cast in lengths convenient for handling. The precast units shall have adequate strength to resist over stressing and damage during handling and erection. Care shall be taken to ensure that the units are not chipped or damaged.
Architectural, structural and services drawings shall be examined to determine dimension and location of holes.
Permission to form holes in precast units after casting shall not normally be given, but in exceptional cases where the structural soundness of the perforated unit and its visual acceptability is satisfactory such permission may be given by the Engineer in writing.
Precast units shall be clearly marked immediately after casting or demolishing, showing the identification of the unit and, if necessary erection instruction. The marking is to be such as to be invisible after erection.
03433 Erection

Precast units shall be hoisted placed in proper position and tied in such a way as to avoid over stressing or damaging the units nor causing damage to previously erected structure. Where shown the units shall be laid on thin bed of cement in order to even out irregularities of supporting members.