Fig. 1. Vertical casting of floor panel
Fig. 2. Erecting a wall panel
Published by permission of the Tropical Division, Building Research Station, UK, this article deals with the site precasting of internal wall and floor units for multi-storey blocks
DURING recent years Britain's Build- ing Research Station has studied various methods used in the construc- tion of multi-storey flats. These in- clude fully in situ, partially precast and fully precast methods, and a num- ber of proprietary techniques.
The studies showed that the great- est potential economy in the construc- tion of tall blocks of flats lay in re- ducing formwork, wet trades and scaffolding, and making most use of ground-level prefabrication, whether off- or on-site. For the structural frame in particular, the precasting of large panels makes possible consider- able savings on formwork and plas- tering, which together represent ap- proximately 50 per cent of the cost of an in situ wall.
Although some reduction in cost can be made by replacing in situ with precast units of average accuracy and finish, and proceeding with all the finishing trades as before, this is not enough. It is necessary to exploit all the potentialities of precasting by do- ing most of the fixing, services and finishes on each element before erec- tion.
Most of the concrete units required to be precast for flats, in particular, will be internal walls and floors, which are intrinsically simple. Con- duit for electrical wiring is the only service likely to be cast into some of the units, and most of the grounds or fixings will be required at perimeters where they can be readily located. Large units of this kind can therefore be precast on site, with a production
44
BATTERY-CAST CONCRETE
UNITS
line serving the needs of each block. involving minimal capital expenditure and little or no transport costs.
As the internal wall and floor units are simple, both may be cast vertical- ly, a most important advantage. Ver- tical casting, using the battery method enables the units to be precast on a considerably smaller ground area than that required for horizontal casting, assuming equivalent output speeds; and on many sites this could be a de- termining factor. A further advant- age of vertical casting is that the operations of screeding and trowel- ling-off in horizontal casting are eliminated, and man-hours are reduc- ed. With careful mix control and correct vibration, plane smooth sur- faces can be produced on both sides of the cast units, so that plastering and floor screeds may be omitted.
At present, the vertical casting of concrete cladding panels cannot be generally recommended. Each of the various types of external finish, to- gether with the need for insulation and the profiles, usually more com- plex than found with internal walls, make for difficulties with both bat- tery and individual vertical casting. Because of the need for raking props, no space savings accrue from indivi- dual vertical castings, therefore such units are best cast flat. Scope exists
for considerable rationalisation of horizontal casting and, if space per- mits, site precasting of these units may well be satisfactory. We are concern- ed here, however, with vertical bat- tery casting for internal wall and floor units.
Precasting Method
The aim of this development was to evolve a method of vertical casting which could provide accurate units with minimal capital expenditure. The principle adopted was to cast two initial panels horizontally with consi- derable accuracy, and then to use these as formers for vertical casting to reproduce similar units. The ad- vantages of using concrete as form- work are that after curing has taken place, it is almost inert, not subject to serious shrinkage movements or twist- ing, and it can produce good surfaces. That is, accurate and plane units. which will not require plastering, can be produced.
The wall surfaces may be finished by direct painting, lining and painting.
Far East Architect & Builder August, 1966