Benefits of Precast
The considerable advantages of precast construction are combined with the inherent benefits of concrete to provide a superior construction product.
These include:
- Inherent Fire Properties - Concrete has its own inbuilt fire resistance which is present during all construction phases. Fire resistance is typically achieved without the application of additional sprays or linings. This is an important inherent advantage over steel and timber solutions. Precast frames are generally designed for one hour inbuilt fire rating. This either totally eliminates or greatly reduces the need for additional fire protection and the associated costs.
- Economies are generated through reduced requirements for formwork, access scaffolding and less reliance on wet trades. Reduced on-site supervision by the main contractor is also a saving. Compared to cast in situ concrete, the following savings can be expected:
- Formwork 75% less
- Scaffolding 75% to 90% less
- Wet Concrete 90% less
- Health & Safety - Once precast floor slabs are installed, they provide a safe working platform for site operatives. Simultaneously installing precast stairs offers safe and easy access between floors.
- Reduced Construction Programme, due to speed of construction, gives earlier return on investment, freeing up the project critical path and allowing earlier completion. It is estimated that a precast structure takes up to 20% less time to construct than a similar cast in situ structure.
- Greater Project Control from a completion/project management perspective and from a costing perspective.
- Factory Production ensures increased accuracy and quality of finish and decreases weather dependency. Compared with cast in situ structures, site labour is reduced by between 50% and 80% using precast. Work for following trades is reduced by between 30% and 50% depending on finishes.
- Buildability - Precast frames can greatly improve buildability because sensitive parts of the operation can be moved from the site to the factory.
- Larger Clear Spans - Reducing the number of columns is critically important in developments such as sports stadia and car parks. Longer spans and shallower construction depths can be obtained by using prestressed concrete beams and floors.
- Proven Designs and Methodologies - Precast frame design incorporates proven designs and methodologies which have been developed over many years.
- Sound Resistance - Precast structures meet the highest standards for resistance to sound transmission. Test figures show the airborne sound insulation of a 150mm concrete floor is 50 db.
- Composite Action - Prestressed precast elements act compositely with an in situ structural screed (topping), combining the benefits of precast and in situ construction.
- Less Wastage - Precast systems significantly reduce the amount of waste materials produced on site.
- Loose Reinforcement - The amount of loose reinforcement on site is reduced by between 80% and 90%.
- Airtightness - Air infiltration in precast buildings is minimal because of the relatively small number of joints in the construction. This factor combined with the thermal mass of concrete gives excellent thermal performance.
- A Complete Service from design to manufacture to installation is available.
Health & Safety
IPCA members have developed a standard approach to facilitate the implementation of the highest Health & Safety standards. Member companies are now in a position to supply customers with standard procedures, outlining systems of work and the responsibilities of each party.
Safe and successful precast installation requires teamwork. This means close co-operation and co-ordination of all participants, including the client, architect, engineer, precaster and the contractor. To achieve the desired schedule and results, the basic working relationship between these parties must be established at an early stage.
To achieve this end, the Irish Precast Concrete Association has published a Precast Model Risk Assessment manual as part of the Irish Concrete Federation’s Health & Safety Manual.
The manual identifies potential risks and suitable controls during the manufacture, transport and erection of precast products. The Responsibilities Check List identifies the Health & Safety requirements in relation to the precast concrete elements.
A typical Responsibilities Check List sets out suggested responsibility for managing each item either to the Contractor (the purchaser of the precast concrete product) or the Precaster (the supplier and erector of the precast components).
The Precast Model Risk Assessment is intended for use to assist all those involved in the manufacture, design, specification, use and erection of precast floors. The IPCA is currently working with the Health & Safety Authority to produce a code of practice for the installation of load-bearing structures.
The installation of precast units should only be undertaken by specialists who are trained, competent, and experienced in this work. IPCA members provide Health & Safety training to all personnel in the safe erection of precast units and associated areas such as Safe Pass, Working at Heights, Slinger/Banksman, Mobile Elevated Platforms, Hoist, Crane, Power Tool, Manual Handling, Forklift, Abrasive Wheels, Role of the Supervisor, etc.
Quality & Accuracy
Precast concrete units are manufactured in factory conditions where strict manufacturing controls apply. This ensures that reinforcement bars are accurately located and that clients receive high quality products manufactured to controlled dimensional tolerances. Precast delivers a high performance product with a quality appearance.
Speed of Construction & Buildability
Speed of construction and tight construction programmes are primary considerations in most building projects and this is where precast concrete excels. To maximise the advantage of precast, two critical factors should be taken into consideration:
- Design the building layout to maximise repetition of precast units
- Design construction details to maximise the number of standardised components
The importance of these two factors cannot be over emphasised. Adherence to good design practice will speed up the manufacturing process and make construction faster. Maximum efficiency can be achieved by rationalising designs in consultation with precast concrete frame manufacturers.
Choosing a Construction Method – Comparative Costs
In making cost comparisons between alternative systems, it is imperative that total like for like costs are considered. There are substantial savings to be made using precast construction which are not evident when a direct elemental cost comparison is made with alternative construction methods. To get an accurate like for like cost, whole building costs must be estimated. To accurately assess whole building cost, each of the advantages of precast as listed in section 1.2 (pages 4 & 5) must be accurately costed.
Savings through factors such as earlier completion dates, inbuilt fireproofing, reduced formwork, scaffolding, reduced wet trades and increased budget control can be significant. Also, fast-track procurement and construction may minimise capital costs by reducing financing costs and securing earlier rental income. The precast frame package typically includes columns, beams, floors, wall panels, stairs, landings, balconies etc., all of which have an inbuilt minimum one-hour fire protection.
Specialist precast frame producers will assist design teams in evaluating the scope for standardised precast components for a particular project. Budget costings and erection programmes can be prepared by the precaster on receipt of outline drawings and a list of performance criteria.
Sustainability
Most of the sustainable developments throughout Europe use concrete as the primary construction material. Concrete is long lasting and requires virtually no maintenance or replacement and does not require the application of toxic paints or preservatives. Even highly exposed precast concrete units (such as box culverts) are virtually maintenance free and have a design life of 120 years.
Precast maximises the sustainable potential of concrete by reducing the amount of construction waste on site to almost zero. IPCA manufacturing plants are monitored on an ongoing basis by a qualified Planning and Environmental Engineer to ensure that each IPCA member implements an ongoing environmental programme.
Because of its inherent fire and soundproofing properties, concrete (and particularly precast) lends itself to multi-storey, high density developments which greatly contribute to a sustainable use of land and justifies investment in quality public transport. These types of precast concrete developments offer a sustainable and viable alternative to urban sprawl type housing.
Concrete is 100% recyclable and is generally supplied (in Ireland) within a 30 mile radius, with the resultant savings in transport costs and fossil fuels.
Thermal Capacity
The thermal capacity, particularly of exposed concrete, offers considerable energy savings.
Modern buildings have a tendency to overheat throughout the year. Ventilation and air conditioning equipment is sometimes used as an expensive high energy solution to this problem. Using the inherent thermal capacity of concrete, particularly in combination with other passive systems, can either reduce or eliminate the capital and running cost of air conditioning.
Exposed concrete acts like a storage heater in absorbing heat. Daytime temperatures are reduced by 3°C to 4°C and peaks in temperature are delayed by up to six hours. The exposed soffits of floor slabs and other concrete elements including beams and columns act as a passive system providing an effective cooling capacity of up to 25W/m2 of surface area, which is more than adequate for the average commercial building. This principle is utilised by architects and engineers to bring about considerable energy savings.
Concrete has excellent sustainability credentials allowing for a reduction in the use of fossil fuels and greenhouse gases. By using concrete as a passive moderator, there are enormous potential savings as 90% of the energy consumed in the life cycle of the building is attributable to heating and cooling.
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