Producing sustainable building materials from volcanic ash and rocks

When a volcano erupts, people living nearby face the threat of damage to property, loss of life and even the destruction of entire towns. Now, researchers from the Italian city of Catania, Sicily, have found a way to recycle ash produced during an eruption as a building material.

On the eastern side of the island of Sicily stands Europe’s most volatile volcano – Etna, or Muncibeḍḍu, as the locals know it – which began erupting again in February 2021 and is still sending ash, smoke and sparks into the sky. When that ash falls to earth, it must be cleared away and sent to landfill sites. But if it could be recycled, scientists think it could become a new source of renewable raw materials.

From destruction to sustainable construction

This recent round of volcanic activity is tame by comparison with past events. Some 8,000 years ago, a massive eruption at Etna caused a landslide and an avalanche that triggered a tsunami bigger than a 10-story building. It “spread across the entire Mediterranean Sea, slamming into the shores of three continents in only a few hours,” according to Live Science, which cites work carried out by Italy’s National Institute of Geophysics and Volcanology.

A team from the University of Catania, the city built almost in the shadow of the volcano, has identified a way to recycle ash from Etna's eruptions. Potential uses for the recovered ash include road surfaces and construction.

The properties of the ash make it well suited to construction. High numbers of tiny holes inside the rocks give them thermal insulation, for example, so they could be used to good effect in thermal blocks or insulating panels.

The Romans already knew about the characteristics of volcanic ash, which they mixed with other materials to build walls. Scientists analyzing the composition of ancient Roman sea walls, which have withstood the test of time, have detected a strengthening substance called aluminium tobermorite, which crystallized when the ash mixture was exposed to seawater.

Boosting construction’s eco-friendliness

There are two key benefits of recycling debris from volcanic eruptions. It reduces the need for raw materials to manufacture new products - in this case, blocks, bricks and insulation - making their production more sustainable. It also means finding a productive use for something that would otherwise have to be collected and disposed of.

In 2019, the buildings and construction sector was connected to 38% of total global energy related CO2 emissions, according to the United Nations Environment Programme (UNEP). And, there’s significant work to be done. In April 2021, UNEP warned that the sector is ‘not on track’ to reach the targets of the Paris Agreement.

And there are more specific concerns too. Demand for concrete - and the sand that goes into it - has risen. A 2018 WWF report suggests that aggregate (sand and gravel) is the most mined material in the world - all with implications for the environment and our planet. Indeed, a 2017 perspective in the journal Science suggests that overexploitation of sand is not just damaging to the environment, but also endangers communities and risks violent conflict.