There are many benefits associated with the use of precast concrete components. Of course these require proper design, use of the correct materials and manufacturing processes with skilled and knowledgeable personnel. Benefits available include:
- Dimensional accuracy
- Tight tolerances
- Speed of construction
- Reduction of on-site labour
- Reduction of on-site activity, noise, and disturbance
- Reduction of on-site waste
- Low life cycle cost
- Minimal maintenance
- Non combustible
- Fire rated
- Not subject to rot
- Acoustic insulation
- Thermal inertia reduces lifetime energy costs
- Sandwich panels available for insulation
- Large spans available from pre-stressing
These impact on all parties providing benefits for the architect, engineer, builder, developer, and owner. The benefits are many, including financial gains from shorter construction times and earlier occupation.
Not all precast is created equal. Purchase of precast concrete components from a "Certified Plant" guarantees certain benefits.
Factory made precast concrete is manufactured under controlled conditions in a special purpose facility dedicated to efficient and economical production of quality components for delivery to the customer.
|FACTORY MANUFACTURED PRECAST
||CONCRETE CAST ON-SITE
|Concrete NZ Precast Sector Group "Certified Plant" guarantees benefits.
||Site produced precast is not from a dedicated plant and is not subject to the same level of independent inspection.
|Moulds designed and manufactured produced by experienced personnel.
||Unlikely to have the same level of specialist experience.
|Factory re use of moulds justifies the expense of high quality moulds.
|Moulds for site produced precast will be produced as economically as possible for just the one project.
|Precast factories employ full time specialists in precast production, finishing and handling.
||Site staff are unlikely to be full time precast workers with the same level of skills and experience.
|Precast factories are equipped with the most appropriate specialist equipment for production, finishing curing and handling.
|Building sites are unlikely to be as well equipped to produce quality precast.
|Factory made precast can be stored for delivery as required.
|Few building sites have adequate space for storage of precast components.
|Factories are familiar with storage methods to minimise problems.
|Incorrect storage can produce creep distortions, marking and damage.
|QC systems specifically designed for the plant dedicated solely to quality precast production.
|General QC systems not specifically tailored to production of precast concrete.
|Experience with handling and finishing high cement content and low water cement ratio concretes with appropriate admixtures to ensure quality finishes and high durability.
||Site and general concrete workers seldom have extensive experience of handling the special mixes that produce the best quality finished product.
|Quality assured dimensions of components.
|Factory facilities to accurately fix moulds to prevent movement while placing concrete may not be available on site.
|Quality assured location of fixings and inserts.
|The means, skills and experience to prevent inserts moving during placing and vibration of concrete may not be available.
|Full factory curing facilities are available including heated moulds.
|Curing is often not ideal due to lack of facilities.
|Concrete NZ Precast Sector Group "Certified Plant" provide an additional level of assurance.
||No equivalent level of assurance is available for site casting of concrete.
Precast plants have experience of handling a variety of special concretes. Lightweight aggregate can be used where weight is critical. Recycled aggregates can be used. Glass has been recycled for use as aggregate at a customer’s request.
Additives for high performance concrete include silica fume, fly ash, water reducing agents, plasticizers. Self compacting concrete can provide real benefits, particularly where there is congestion of reinforcing or difficult shapes to cast.
Special concrete mixtures for high strength, durability and exposure to different environments are available and Group members' plants have the special skills for handling them.
Marine environments are a particular concern. Modern materials, special additives, and tightly controlled production can add immense value by extending the economic life of very expensive infrastructure projects.
Precast components have been supplied with a 100 year design life for exposure to sub soil conditions.
A variety of finishes are available to suit the end use. Exposed aggregate finishes give non slip surfaces. Textured and patterned surfaces can provide pleasing appearances to enhance the environment.
Formliners, honing or polishing, chemically treating or acid etching, painting or other special coatings are all available as surface treatments whether for appearance, environmental or durability considerations.
Few other building materials have been shown to be as durable as concrete with examples existing from the Roman times.
Corrosion of reinforcing is the most common cause of premature failure of concrete components. The reasons are normally a combination of insufficient concrete cover, and inadequate quality of concrete protecting the reinforcing. Concrete quality problems may be due to porosity, excess water used to aid placing, poor compaction, inadequate curing or from use of an inappropriate concrete.
Factory produced precast is manufactured to tighter tolerances by experienced workers following established quality procedures using specifically designed concrete mixes.
More water in the concrete mix makes it easier to place, but it also reduces the quality and durability. Precast factories are experienced at handling low water content concretes and have the means to properly compact them. Once the concrete is compacted and finished, it is important to prevent water escaping from the surface as that compromises the quality of the surface layer of concrete.
Other common durability issues are a result of inadequate curing or premature drying of the surface. Poor curing can result in a lower strength, and premature drying of the surface produces a dusty less durable surface and poorer quality finish.
Precast factories have the appropriate curing facilities for the products they manufacture and means of protection where products are not manufactured under cover.
Group members are environmentally aware and plants are required to eliminate polluting discharges and comply with all resource management requirements.
Environmentally beneficial features of precast concrete include:
- Local materials are used to reduce environmental impact
- Precast concrete is produced from natural materials
- No toxic substances are involved in production or use of precast concrete
- Low energy input into production of precast concrete
- Concrete absorbs carbon dioxide from the atmosphere
- Precast concrete can be recycled without pollution or toxicity concerns
- Re use of forms reduces waste from disposal of formwork
- Factory production and in house manufacture reduces material waste
- Extreme durability where required reduces future use of resources for replacement