The concrete pavilion, one year on

Last September we poured a small pavilion on the campus lawn, using a concrete mix that replaces most of the cement with clay and recycled aggregates. It cut the carbon of the material by more than half. The question was whether it would last outside.

After twelve months, the answer so far is yes. Sensors inside the walls have recorded 41 frost nights and a summer peak of 38 degrees on the roof. The cores we drilled in August are as strong as the samples we kept indoors, and the surface has weathered evenly, without the cracking we saw in earlier mixes.

The pavilion will stay up for at least four more years. Next spring we start on a second one, built with a construction company in Basel, to see whether the mix works at the scale of a real site.