3.16
Precast Concrete
Precast concrete is any piece of concrete which is cast in a mould or location which is not its final intended location. For the most part this is manufactured off-site in the factory of a specialist precast producer.
Precast concrete differs in some important aspects from in-situ concrete construction:
- Collaboration is required between project designer and precast producer (preferably at an early stage) as the producer usually is responsible for structural design of the individual units (e.g. loads, spans, opes, fire resistance, durability etc.). The producer usually chooses the concrete mix to meet these needs, as well as early handling requirements. The project designer should specify / agree with the precast producer the type of surface finish that is required.
- Collaboration is also required with the builder to ensure dimensions and levels, erection sequences, building stability during construction, requirements for temporary supports, craneage, storage areas, etc. are all known and agreed.
- Many precast elements arrive on site as finished units ; however, some precast elements may require in-situ finishing of joints, overlay screeds, etc.
Designer
- Initial sizing of members
- Communication of general layouts and loading scenarios and other technical requirements to precast producer
- Inclusion of precast details on general drawings where required
- Consideration of overall structural integrity of structure
- Consideration of structural connections
- Consideration / inclusion of aesthetic / architectural details in technical specifications
- Communication with precast producer on the inspection regime
- Awareness of temporary stability requirements
- Approval of design
Builder
- Awareness of temporary stability requirements
- Knowledge of who has responsibility for erection of precast elements
- Knowledge of who has responsibility for temporary works
- Responsibility for back-propping?
- Lay down areas / suitable access and egress
- Craneage requirements
- Precast specific tolerances, including minimum bearings
- Responsibility for design and installation of anchors / fixings?
- Agreed procedures for openings for services and other site alterations
Precast Producer
- Knowledge of Product harmonized standards (hENs) relevant to precast elements
- Awareness of CE marking requirements for products produced to harmonised standards
- Obtain all relevant design information from designer
- Carry out element design, where applicable
- Communications on alterations to prescribed design
- Product quality control procedures
- Pre-installation / site check arrangements
- Pre-delivery procedures for compliance of units
- Erection arrangements: whose responsibility is this?; are there specific procedures required?
