Self-Compacting Concrete - Why Use It?

The areas in which self-compacting concrete is used have increased considerably since it was developed in earthquake zones throughout Asia where structural columns attached to tall buildings were heavily congested with steel reinforcement. Self-compacting concrete was designed to flow around this type of reinforcement and provide a fully-compacted, durable concrete to work in conjunction with steel.

Since 2000, Sika has been among companies leading the development of self-compacting concrete in the UK. Its growth in this country is predominately due to its use in ground floor housing slabs. Before its introduction, conventional concrete made this type of application machine and labour intensive. For instance, concrete poured in the traditional way and is tacky and stiff in consistency, would normally require up to six installers to screed an area. This method also requires the use of mechanical vibration to rid the freshly-poured concrete of entrapped air to ensure its suitability and long-term performance. And that's not all. Upon installation, concrete applied the ‘old-fashioned way' needs to be power-floated to give the slab a smooth, polished finish. Concreting an area the same size using self-compacting material requires at least half the manpower to complete in half the time, with its speed and ease of placement being key to its improved management and distribution.

Easy placement

Laying self-compacting concrete is like laying liquid as opposed to treacle - it's that easy. It also eliminates the need for power-floating as it naturally provides a polished, high-quality finish. The secret of this substance's success can be found in admixtures such as Sika ViscoFlow®, which brings much-needed flexibility to the most challenging concreting application. Infused with graded aggregate, the high-performance admixture extends the concrete's plasticity, with its two-hour retention property allowing time for site transportation and placement. Sika ViscoFlow® technology also ensures target consistency in a concrete mix in high or low temperature climates in new-build and refurbishment projects.

Preparation is vital to successful self-compacting concrete placement. Admixture/aggregate ratios should be tailored to the precise needs of the project's size and scope. A slip membrane should also be used in conjunction with all self-compacting applications. Again, this method negates the need for mechanical vibration processes, therefore increasing on-site health and safety and resulting in a time and cost-effective installation with a material that is stronger and more durable than traditional placement techniques.

Fibres

Another important development in self-compacting concrete is the availability of fibres which new NHBC regulations state should be incorporated within certain applications. From January 2018, the authority decreed steel, micro or macro fibres or steel mesh should be used - where appropriate - as reinforcement to concrete toppings above suspended beam and block floors. Sika is already ahead of the curve on that score by providing a range of fibres which allow concrete mix designs to meet NHBC specifications.

In terms of the future, it's my wish to see self-compacting concrete be used more architecturally in building columns and facias. Its flexibility certainly allows for a more design-led approach to its application, which could be enhanced by the availability of pigmented self-compacting solutions. Compatibility with watertight admixtures would also advance self-compacting concrete's use whilst eliminating the risk of lack of compaction – one of the biggest threats to its long-term performance.

Whatever tomorrow holds, the one thing we can be sure of today is self-compacting concrete's status as an easy-to-apply, durable alternative to conventional concrete, with its superb flexibility being without detriment to its proven, long-term strength.

By Peter Cowan, Regional Sales Manager at Sika Concrete & Waterproofing

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