Using control flow concrete for tunnel linings

/ concrete / ready-mix

Concrete linings are a fundamental part of ensuring the structural integrity of tunnels, but pumping and placing the concrete for these jobs is a cumbersome process. Numerous challenges can arise. For example:

• Access within the tunnel is very limited, so concrete with very good flow is critical. 
• Conventional concrete is not ideal for this application since it does not flow well and it can cause an obstruction in the pump, resulting in costly delays. 

Why self-consolidating concrete is not ideal for tunnel linings

Some contractors have tackled these challenges by using self-consolidating concrete, due to its high flow and workability. However, there can be some difficulties involved with using this type of concrete.

• Self-consolidating concrete generally requires a specialized mix design, which adds to the cost.
• Producing self-consolidating concrete is a fine balancing act that requires on-site quality control, which gets expensive, particularly given the labor shortages in the construction industry.

Control flow concrete – a solution to these challenges 

Control flow concrete was created to bridge the gap between conventional concrete and self-consolidating concrete. The compressive strengths of control flow concrete and conventional concrete are equivalent. However, control flow concrete offers higher flow at a lower cost than self-consolidating concrete, and it is also segregation resistant, making it a good solution for concrete tunnel linings. 

• Concrete discharges quickly, pumps easily and can be placed with minimal energy. This can result in a faster construction schedule with the same or higher quality concrete. 
• Using control flow concrete can also help contractors run a leaner operation, since handling the higher flowing concrete requires much less manual labor. 
• Control flow concrete is handy in confined spaces like tunnels. It has a wider slump flow range than conventional concrete. It flows well to easily fill the form, creating a smooth, strong tunnel lining.

Concrete admixtures under the CONCERA® brand enable the production of segregation resistant concrete with a flow range of 16-25” (410-635mm) using conventional mix designs.