If there's one topic least likely to spark animated dinner party conversation, it's the bits and pieces of civil engineering that one sees while driving along a nation's road networks. These tend to be taken so much for granted that they may as well be invisible unless they're something spectacular like a suspension bridge or annoying like a road being resurfaced.

However mundane that these may seem, they are the product of some very complex and serious engineering design and serve very real and vital functions that many people don't appreciate until the road in front of them is washed away or a ramp collapses.

One of these is what is called a headwall, which is a retaining structure with a hole in it that's placed at the mouth of a drain or culvert. Its purpose is to anchor a culvert or similar and to prevent the fill around it from being scoured away by running water. In addition, it can also provide structural support to attached bridges and roadways as well as controlling the flow of water.

It's a very old bit of civil engineering but Cambrdige put a new spin on one installed on the A30 in Cornwall by constructing it onsite using a robotic 3D printer arm laying down layers of quick-setting concrete that hardened in only an hour. Again, not very new. What is new is that as the headwall was printed, a lidar unit made precise scans of the structure, building up a digital virtual twin against which the real thing can be compared.

Also, wireless sensors were placed in the wet concrete to transmit data on temperature, strain, pressure, humidity, electrical resistivity, and electrochemical potential.

Temperature was of particular interest because fast-setting concrete generates a lot of heat, which could damage the headwall as it hardens and cures. This is important because another innovation in the new structure is that it doesn't use the conventional steel reinforcement skeleton. Instead, it relies on its own geometry for strength, which isn't easy for something with a hollow, curving, interior wall.