Flexible formwork

Can the type of concrete used for a project affect the formwork needed to ensure its success?

Can the type of concrete used for a project affect the formwork needed to ensure its success? Construction Week investigates the effects of self-compacting concrete on formwork.

One of the latest developments in the concrete industry is that of self-compacting concrete (SCC). When used correctly, the product does not need mechanical vibration and will simply flow into the areas that have been created by the formwork to meet the structural design.

Shorter on-site times and higher quality finishes are among the benefits cited for SCC, but how does its use impact the formwork applied to contain it on a project? And how are the formwork manufacturers overcoming these issues?

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Concrete choices
When a contractor opts to use SCC on a project there will be an immediate impact on the type of formwork system that can be used. This is primarily due to the higher pressures that will occur during the casting period.

“If SCC is to be utilised this will generally negate the option for the contractor to use traditional hand-built timber and plywood columns or walls as is sometimes still seen on sites,” reports Aluma Systems Middle East Abu Dhabi area manager Daniel Taylor.

“Due to the considerably higher design pressures created when SCC, as opposed to traditional concrete, is poured into vertical forms, the contractor is advised to use high quality system formwork,” adds Taylor.

Specially designed formwork may be necessary in some cases. “Some of the ready-made panel formworks might not be able to withstand the higher concrete pressure generated by SCC depending on the shutter height,” explains Peri technical manager UAE and Oman, Oliver Weiss.

MFE Formwork Technology design manager Michael Allen agrees: “The choice of SCC will affect our formwork supply if the design calls for areas to prevent the rise of the concrete post-pour. We will also need to look at the wall/column formwork design.

“SCC obviously flows better into any features, negating the need for vibration and giving a better finish to the concrete. This leaves extra pressure on the formwork self generated compactions, but gives sharp edges on all columns and beams,” adds Allen.

Factors to consider
By far the biggest issue of SCC for formwork providers is the increased pressure, however, other factors such as costs and time must also be taken into account when designing a system.

“The biggest factor when designing formwork for SCC is the consideration of higher design pressures for the vertical forms such as columns and walls,” explains Taylor.

“For conventional concrete, the design pressures are lower due to the lower slump flow and quicker setting times, meaning that primary beams, joists and tie-rod spacing in our adjustable Aluma Vertical systems can all be spaced farther apart.