Calcined clay cement scales up as Holcim opens a new line in the Czech Republic

Holcim has launched a calcined clay production line at its Čížkovice cement plant in the Czech Republic, which the company says is the first line of its kind in the country. It has capacity for more than 115,000 tonnes of calcined clay a year from Holcim's local quarry, supporting the supply of 580,000 tonnes a year of the company's ECOPlanet lower-carbon cement.

The Čížkovice line follows earlier Holcim calcined clay lines elsewhere. Holcim opened a calcined clay line at Saint-Pierre-la-Cour in France in 2023 and commissioned a new line in Guayaquil, Ecuador in 2025. In Australia, universities and concrete producers have spent several years testing local clays, and the first trial pours are now in the ground.

Project at a glance

What calcined clay actually is

Ordinary cement gets its strength from clinker, which is made by burning limestone and other raw materials at between 1,400 and 1,500°C. Most of the carbon dioxide in conventional cement comes from making clinker, so the less clinker in a bag of cement, the lower its footprint.

Calcined clay is clay, typically a low-grade kaolinitic clay, that has been heated to about 800°C. That gentler burn turns the clay into a reactive material that can stand in for part of the clinker. The useful mineral is kaolinite, and suitable clays need far less of it than the kaolin used for ceramics or paper, so deposits are widespread.

The best-known recipe is LC3, or limestone calcined clay cement, developed by the LC3 Project based at EPFL, the Swiss federal technology institute in Lausanne, which has had support from the Swiss Agency for Development and Cooperation since 2014. LC3 blends clinker with calcined clay, limestone (typically around 15%) and a little gypsum. According to the LC3 Project, the clay and limestone react together to produce a less porous material, which is how the blend reaches performance similar to ordinary Portland cement with roughly half the clinker.

The LC3 Project says the blend can cut CO2 emissions by up to 40% compared with ordinary Portland cement, and that production costs can be up to 25% lower. It also says LC3 does not need capital-intensive changes to existing cement plants.

Why it matters as fly ash runs short

For decades, concrete producers have trimmed clinker by adding fly ash from coal-fired power stations and slag from steelmaking. UNSW notes that fly ash is the most common of these supplementary materials in Australia, and that the decline of coal-fired power raises the prospect of having to import it in large volumes. Boral makes the same point, describing global supplies of slag and fly ash as limited and expected to decline. Clay, by contrast, is abundant.

The Australian picture

Researchers at UNSW Sydney and the University of Melbourne have been collecting and calcining clays from around the country to find the ones best suited to concrete, and testing whether LC3 is viable here. Boral says its research centre with UTS identified several suitable Australian clay sources.

In February 2026 Boral announced it had completed product development of a low-carbon concrete using Australian calcined clay, in binary and triple-blend versions, following trials at its Maldon cement operations. Feasibility work began in 2024 with UTS, Transport for NSW and Calix, supported by SmartCrete CRC, building on preliminary studies by Boral and UTS from 2020. In August 2024 Boral reported that a first batch of its clay had been calcined using Calix's renewably powered electric calcination technology. Boral has also completed an on-site trial with the John Holland–Gamuda JV on the M1 Pacific Motorway extension between Tomago and Raymond Terrace, where Boral says the concrete placed and finished well.

In Victoria, Boral supplied a mix for a North East Link test slab with the University of Melbourne, using clay recycled from soil excavated on the same site. On the Suburban Connect project, ACCIONA reported that more than 250 cubic metres of calcined clay concrete were poured on project sites in Clarinda and Monash in early 2026, in mixes suited to non-structural uses, using clay sourced from Ballarat.

On standards, Australia already has a home for the material: AS 3582.4:2022, the standard for manufactured pozzolans, under which calcined clay is classified. The standard sets two grades that differ mainly in reactivity.

What's next

Holcim says it is scaling calcined clay worldwide under its NextGen Growth 2030 strategy, and Čížkovice now joins France and Ecuador as a working example. In Australia, Boral says it is developing a range of blends and has industry interest in further trials.

Published 6 November 2026 · Updated 27 October 2026