Reusing concrete elements

Reusing complete structures is not the only route to a circular economy. Emily Halliwell explains how extracting and repurposing concrete components can open up a world of possibilities

A circular economy is one in which resources are kept at their highest value for as long as possible. For concrete frames, reusing them in-situ will typically result in the lowest carbon emissions. There are many examples of concrete buildings being adapted and repurposed, with changes of use and layout, enabling the frame to be used for many more years.

This is not always feasible – for example, where there are very low ceiling heights or constrained layouts. In these cases, the default option is demolition, though not usually landfill: in the UK, nearly all concrete from demolished buildings is recycled, often used as aggregate in new concrete or hardcore. However, recent research has demonstrated an alternative, with the potential to keep concrete resources at a higher value for longer: reusing concrete elements in new structures.


Across Europe, a number of projects have used reclaimed concrete elements in new structures, including Återbruket in Gothenburg, Sweden, a housing project where 50-year old hollowcore slabs from a demolished IKEA store will make up 80% of the loadbearing floors. Barriers do exist to the wider use of this approach, with concerns about cost and feasibility. To help resolve these, and to show the potential cost and carbon savings, researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL) have developed three prototype structures.

These include a footbridge (Re:Crete), an office floor (FLO:RE) and a community pavilion (rebuiLT). Each prototype uses different types of elements, from 1200 x 400mm blocks to 3D assemblies of columns and slabs, extracted using saw-cutting from existing buildings – referred to as “donor structures”.

Donor structures

Identifying suitable donor structures is key to enabling wider reclamation of concrete elements. Efficiencies can be achieved by using them on the same site. When developing a scheme, designers may have the opportunity to assess existing structures to identify whether they can be reused in-situ.

One outcome of this assessment might be that the existing frame does need to be demolished, but could be a source of components for the new building. This minimises travel distances, and maximises embodied carbon savings.

A lifecycle analysis of the FLO:RE prototype found that, compared to an equivalent in-situ 220mm- thick reinforced concrete slab, there were carbon savings of 80% when the structure was built within 140km of the donor structure. This increased to 92% if it was built within a 20km radius, and 94% if it was built on the same site.

As with in-situ reuse, assessment and testing are important for determining the condition of a structure. As-built information can assist with identifying the best way to reuse existing elements, particularly if the reinforcement within the concrete is to be used as part of the new structural scheme.

There is a wide range of testing techniques available, and reusing structural elements may enable greater use of destructive testing than is possible in cases where the structure is reused in-situ. Designers can find further guidance in the second generation Eurocode 2, which includes an annex on the assessment of existing concrete structures.

Consideration should also be given to how best to use the donor structure. For the FLO:RE prototype, elements were cut from a continuous slab and used as a simply supported slab. This meant that the critical section was at mid-span, where the largest bending moment was located. As the reinforcement within the concrete is determined by whatever is in the donor structure, the span was limited to 3m in the new structure, approximately 75% of the donor slab span.

Careful planning can result in cost and programme savings, and enable more of the existing structure to be reused. The 3D structural elements in the rebuiLT pavilion came from a donor structure that also supplied three other projects. A total of 137 reinforced concrete elements were extracted, allowing for optimisation of the sawing pattern used for deconstruction.

New structures

In principle, reclaimed concrete elements can be used in much the same way as precast elements. Connections are key in precast concrete structures – particular consideration needs to be given to tying, to ensure the robustness of the frame and prevent disproportionate collapse.

To achieve this, precast concrete connections often rely on in-situ toppings or grouting. On EPFL’s FLO:RE scheme, dry connections (without concrete or grout) are used so that the structure is fully demountable, facilitating further reuse in the future. While this approach works for the prototype, larger schemes would need to consider vertical tying and fire protection requirements.

Laing O’Rourke’s D-Frame is a fully demountable and reusable precast concrete system, designed to suit the typical loading and layout of an office building. Working with Imperial College, the company developed innovative jointing methods to achieve the required robustness. The system uses bolted connections, allowing for quick assembly and disassembly with minimal extra cost. Low-strength grout is included where necessary – for example, for diaphragm action.

Testing has shown that this may be removed easily through hydrodemolition: using low-strength grout enables the grout to be removed without damage to the higher- strength concrete. It also showed that disassembly of the D-frame by unstitching is significantly safer, quicker and cheaper than traditional demolition techniques, as well as enabling reuse of the concrete frame elements.

A similar approach has been adopted for Circle House in Denmark (CQ 278), a housing scheme made of precast components that can be reconfigured in different ways. The development will include two and three-storey terraced houses, and five-storey tower blocks.

Similar to the D-frame, the system is connected using bolts and screws with a lime-based mortar for durability, acoustic and fire requirements. This may be removed using a pressure hose, enabling the easy disassembly of the units for reuse in a different location or configuration.

Emily Halliwell is senior structural engineer at The Concrete Centre