Moulding new path for self-compacting concrete

Self-compacting concrete holds a variety of advantages over traditional methods of concrete compaction, including speed, reduced labour and improved surface finishes. However, until now, it has not been suitable for use in the construction of thin structures, limiting its application in the construction sector.

Concrete is a composite material comprising a mix of fine and coarse aggregates, which are bonded together using liquid cement. The concrete composition can then be shaped, typically by pouring it into a mould. The moulded concrete is then cured to harden it. Prior to curing, it is usually necessary to encourage residual water and air to rise to the surface through compaction, which is achieved through a process of vibration. An alternative method however is to create a concrete composition that is able to flow under its own weight, known as ‘self-compaction’.

Such self-compacting concrete compositions are made by adding a plasticiser, which helps the material to flow and enhances its stability. The self-compacting concrete then flows to fill the formwork, providing a smooth and solid finish. The hardened concrete produced is dense, homogeneous and has the same engineering properties and durability as traditional vibrated concrete.

Self-compacting concrete also produces fewer surface imperfections, such as pin holes, as well as reducing labour and equipment costs by omitting the vibration process.

Traditionally, is has been difficult to form thin structures, such as paving slabs, using self-compacting concrete because the mass of the moulded concrete composition for such structures is not sufficient. However, Marshalls Mono Ltd, a company specialising in the manufacture of concrete items for gardens and other landscapes, has recently been granted a UK patent (GB2564129B), for an innovative self-compacting concrete composition that can be used to produce thin slabs.

The patent covers the aggregate content and particle size distribution of the concrete composition. This is expressed as a percentage of the total weight of the aggregate particles that can pass through a specified set of sieves.

Sieve size, mm	% by weight of aggregate passing through the sieve
6.3	90 to 100
2.8	60 to 66
2.0	52 to 58
1.0	43 to 47
0.5	34 to 38
0.25	26 to 28
0.125 (and/or 0.063)	21 (17 to 19)

 

Marshalls’ self-compacting concrete composition is especially suited for use in the formation of thin slabs. When creating such articles, it is important that the concrete does not set too quickly to preclude further moulding into the desired shape. Specifically, the composition has a ‘workability retention’ of at least 42 minutes. ’Workability retention’ refers to the time at which the self-compacting concrete composition remains within the limits set in the slump-flow test defined in British Standard EN 12350-8:2010.

With a granted patent for its invention, Marshalls is able to prevent competitors from manufacturing, importing and even marketing concrete compositions that fall within its scope of protection. This gives the company a market monopoly for its self-compacting concrete composition and a strong competitive advantage over its competitors. The patent also enables the company to benefit from tax relief on profits generated by sale of products manufactured using the composition through the Government’s Patent Box scheme.

Self-compacting concrete has the potential to bring positive changes for the construction industry by speeding up labour processes and reducing costs. With quality levels matching that of traditional methods, there is no reason not to explore its potential further.

Mark Sugden is a patent attorney specialising in the construction sector at European intellectual property firm, Withers & Rogers.  

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