Another supplementary cementitious material has reached the market, and this one comes out of a clay pipe works. HepCem, a calcined clay that can replace 20% to 35% of Portland cement in concrete, launched Oct. 22 at the Precast and Masonry Expo in the UK, according to New Civil Engineer and Global Cement.
Hepworth Clay makes it at its Crow Edge site near Sheffield. CemBlend, a powder blending specialist, will distribute it at scale and sell blended products that include it. Neither company has said how many tonnes a year Crow Edge can produce or what HepCem costs.
How the calcined clay replaces clinker
HepCem is a pozzolan: purpose-selected clay fired under controlled conditions so it reacts with the calcium hydroxide that cement hydration produces. Every tonne of it that goes into a mix is a tonne of clinker that doesn’t, and clinker is where most of cement’s carbon comes from.
The certification is the part producers will care about. Construction Products Certification has confirmed the material conforms to BS 8615-1, the British standard for pozzolanic materials in concrete, with ongoing factory production control surveillance and sample testing at Crow Edge. It can be added at the batching plant under BS 8500 and used in ternary and quaternary blends with limestone, ground granulated blast-furnace slag or fly ash.
Hepworth also claims lower permeability, better resistance to chloride ingress and sulfate attack, and mitigation of alkali-silica reaction. The company’s own caveat is that those outcomes depend on mix design and exposure conditions. Specifiers should ask for test data on their mix before they count on any of it.
Why SCM supply is the real story
CemBlend director Simon Boulter pitched HepCem as “an alternative to increasingly constrained supplies of traditional SCMs.” That’s the market problem. Fly ash comes from coal plants, and Britain shut its last one in 2024. Slag depends on blast furnaces, which are closing as steelmakers move to electric arc furnaces. The two materials that did most of concrete’s carbon-cutting for decades are both tied to industries that are shrinking.
Clay doesn’t have that problem. It’s abundant, and a pipe maker with a century of kiln experience already knows how to fire it consistently. “This isn’t a product that’s still on the drawing board,” Boulter said.
What it means for U.S. concrete producers
The same squeeze is playing out here. U.S. producers have been chasing new SCM sources, from Ozinga’s 1-million-ton slag cement mill in East Chicago to Urban Mining’s ground-glass pozzolan. In the U.S., calcined clays generally qualify as Class N natural pozzolans under ASTM C618, so the code path exists.
What HepCem hasn’t published is the number buyers will ask first: embodied carbon per tonne of the finished product, including the energy to fire the clay. Calcining runs far cooler than a clinker kiln, but it isn’t free. Until Hepworth puts out an EPD, the 35% replacement figure is a ceiling, not a carbon claim.