Steve Webb of Webb Yates Engineers on the role that natural stone can play in the drive to carbon-free construction. The carbon released in the manufacturing of building materials is a major part of the global warming problem. As a nation the UK has been keen to boast of gains in driving down locally produced carbon, while effectively pushing carbon release elsewhere by, for example, importing low cost coal made steel.
The EU and UK are set to impose border taxes on carbon intensive imports in an attempt to level the playing field for lower carbon products. If the UK actually follows through with this, locally produced alternatives and low carbon products for export will be in demand.
While the UK building sector remains highly reliant on high-carbon concrete and steel, the use of CLT (solid timber panels) was growing steadily until recently and offsetting significant amounts of carbon both through being a lightweight low energy product, but also through promotion of tree planting for forestry.
Sadly this growth has slowed of late because of legislation against the use of flammable materials resulting from the Grenfell tower fire. In addition to legislative barriers, issues related to insurance cost rises, not only because of fire but because of durability problems, have further dampened the timber revolution.
The time is ripe for the invention of a new low carbon material, or rather the reinvention of an old one – stone.
Stone has been relegated to an expensive and fussy decoration of buildings since the emergence of steel and concrete and largely forgotten about as a noble structural material but there is very little that cannot be built with stone.
Stone is very low carbon compared to other materials, while mostly stones are more than double the strength and long term stiffness of a standard concrete mix. With an average carbon content of 0.06kg/kg, however, it has about 1/3 of the carbon footprint of concrete.
While steel and cement production are unlikely to be decarbonised by a long-talked-about hydrogen revolution, quarries can easily be run on electricity. The stone supply is almost inexhaustible. If everyone on the planet built a new house out of stone we’d need a volume of stone equivalent to a quarry 40km square and 20m deep: a pinprick in geological terms.
Quarrying can be clean and when they’re exhausted they can be backfilled with waste or left open as nature reserves.
But what can we make with stone?
Let’s consider a few possibilities:
Foundations can be stone. Vibro stone column piles offer a cheap alternative to concrete piles while blocks of stone can act as spread footings.
Our addiction to fired brickwork has a huge carbon cost. Many quarries are setting up brick lines to use waste or unwanted stone to create brick sized modules that have around 40% of the carbon footprint of clay ceramics.
Floor slabs can be replaced by reinforced stone slabs. Drilling holes through stone blocks, passing cables through and tensioning those cables would produce a floor slab with about 10% of the carbon cost of an ordinary reinforced slab.
Steel beams can be replaced by stone beams, again drilling holes through stone blocks and post tensioning can produce a stone beam a similar size to the steel equivalent with around 1/15th of the carbon footprint.
All of these elements can be produced anywhere in the world on the quarry side with very minimal plant investment compared to the astronomical cost of other decarbonising measures like nuclear power.
While there is a dire need of codification and supply standards for strength it is still possible to build in this way today. Webb Yates Engineers have significant advances with collaborators such The Stone Masonry Company and Amin Taha with innovative projects such as Formby, 15 Clerkenwell Close or Provost Rd. There is nothing to stop others from doing the same and right now there is a great opportunity for the stone sector to start to supply simple beam and slab components and start to carve out a market for these products here in the UK and maybe the world.
