Previously, the traditional concrete used in the construction industry for many years had much room for improvement. The construction industry always needed a high-performance concrete which has the ability to flow easily around formwork and into complex shapes without the need for vibration. With designers creating structures with more heavily reinforced concrete members and increasingly complex formwork, an ongoing concern is honeycombing or exposed reinforcement in the columns and structural walls of these structures.
In the mid-1980’s, a Japanese professor conceptualised the idea self-consolidating concrete at a time when skilled labour was limited which caused many challenges in concrete-related industries. Consequently, self-consolidating concrete was introduced which is a highly flowable type of concrete that has the ability to spread into complex formwork without requiring mechanical vibration. This type of concrete is not only non-segregating and placed by means of its own weight, but it also maintains traditional concrete’s durability, stability, and other characteristics. The addition of superplasticisers and viscosity modifiers to the concrete mix results in reduced bleeding and segregation.
By using mineral fillers or fines along with special admixtures, self-consolidating concrete creates resistance to segregation. Self-consolidating concrete has high flowability to pass through highly reinforced areas, is required to fill special forms under its own weight, and has the capacity to prevent aggregate segregation. SCC must be placed at a higher velocity than traditional concrete and can be placed at heights taller than five metres without aggregate segregation. In addition, SCC using a similar water cement ratio will generally have a higher strength when compared with regular vibrated concrete as the lack of vibration provides an improved interface between the hardened paste and aggregate.
SCC is an excellent choice for architectural concrete which is permanently exposed to view and requires special care in in the selection of concrete materials, forming, placing, and finishing. Such examples of structures that use SCC are buildings and transportation structures such as bridges and highway sound/barrier walls. It’s paramount that these structures achieve superior surface characteristics through consolidation of fresh concrete and thoroughly filled formwork. Considering that SCC is a durable material, any water, precipitation, and aggressive chemicals are shed by the surface skin.
A notable project that used self-compacting concrete is the Akashi-Kaikyo Suspension bridge where the SCC was mixed on-site and pumped 200 metres to the specified point. The project’s timeframe was reduced from 2.5 years to 2 years. Other applications for the use of SCC include:
- Earth retaining systems
- Drilled shafts
- Structures with a large amount of rebar and pipes/conduits
Advantages of using SCC
SCC offers advantages aboveconventional concrete in all aspects of sustainable development – social, economic, and environmental. The uniformity of SCC decreases permeability and increases the overall durability of the concrete, which results in an expanded lifespan that reduces the environmental footprint when compared with traditional concrete.
As SCC eliminates the need for vibration, labour requirements are also reduced and this has resulted in a large number of precast operations adopting SCC. In addition, the energy consumption used for vibration is removed and the formwork is no longer subject to the stresses of these vibrations, reducing formwork and maintenance costs. With SCC eliminating the need for vibration, an added benefit of using this material is noise reduction which not only enhances safety in the working environment but also allows for extended operating hours in highly dense residential and commercial areas.
Some additional advantages of using SCC include the following:
- Labour reduction
- Improved structural integrity
- Improved constructability
- Accelerates project timeframes
- Reduces equipment wear
- Increases bond to reinforcing steel
- Superior surface finishes
- Increased durability and compressive strength
- Easier pumping procedures
- Faster placement without the need for vibration
- Enables innovative architectural features
Due to the myriad of advantages of using SCC along with the addition of superplasticisers and admixtures, the costs are slightly increased when compared with traditional concrete. Some other considerations when using SCC include:
- Hot weather
- On-site delays can affect the performance of the concrete mix design
- Long haul distances can reduce the flowability of SCC
- On-site water addition does not equate to increased flowability and can cause stability problems
With the increased complexity of structural designs in today’s construction, self-consolidating concrete is an ideal material due to a reduction in costs along with a superior final product. If you have any questions relating to self-consolidating concrete or its use in the construction industry, get in touch with the experts at Uni-Span by phoning 1300 882 825.