Design and construction of a post-tensioned arch footbridge that reuses cut blocks of cast-in-place concrete walls

The Structural Xploration Lab is exploring the potential of an alternative circular pathway in which obsolete reinforced concrete is cut with diamond-saws and/or dismembered with high-pressure water-jet, before being reused as fully operational load-bearing members.

Reinforced concrete is a wonderful construction material, enabler of the many technical feats that led to the creation of the built environment as we know it. Yet, cement is today responsible for about 9% of all man-made greenhouse gas emissions and concrete constitutes a major portion of waste. Urban densification worldwide leads to the premature demolition of too many reinforced concrete buildings that have yet to reach their design service life. Today, obsolete concrete parts are, at best, crushed and recycled into new concrete, which requires new cement production.

The RE:CRETE footbridge is a prototype serving as a proof-of-concept. Funded by an ENAC Innovation Seed Grant, it uses 25 concrete blocks that were cut from a cast-in-place building currently under renovation in the region. The blocks were then assembled on a centering and with mortar in-between, in order to counteract with the wide variability in the block dimensions, which is characteristic of the reuse approach when compared with traditional manufacturing. Before removal of the centering, the thrust in the 10-m long arch was further increased with two post-tensioning cables running through the blocks centroids.

In terms of life-cycle assessment, the resulting arch provides a new lower-bound of global warming potential, far below any variant made of new material (concrete, steel, or even timber). The prototype also demonstrates that large amounts of concrete waste can be avoided by leveraging its load-bearing capabilities, while achieving a similar structural quality as a newly-produced concrete arch. This prototype opens up new directions to build with reinforced concrete… without pouring concrete.

Read the research story: Building out of concrete, but without pouring concrete.