Calcined Clay for low carbon concrete

Product information

LKAB Minerals’ ground natural calcined clay pozzolana is an advanced supplementary cementitious material (SCM) designed to reduce the environmental impact of concrete without compromising its strength or durability. It is produced by recycling damaged fired bricks, originally part of the UK clay brick manufacturing process, that are finely ground to create a reactive pozzolanic powder. The use of this clay-based material aligns with UK concrete standards for blended cements and provides a low-carbon alternative for cement replacement in concrete.

This is the first Calcined Clay product of its kind to be produced in the UK, contributing to shorter supply chains, local circular economy practices, and significant embodied carbon savings.

Features and key benefits

Replaces up to 35% of Portland cement
Calcined Clay can substitute between 6-35% of cement in concrete mixes, depending on application and mix design. This reduction in cement use significantly lowers embodied carbon and supports low-clinker concrete formulations.

Reduces embodied carbon in concrete mixes
With Portland cement being the most carbon-intensive material in concrete, replacing a portion with Calcined Clay can cut CO₂ emissions by up to 30–40%, depending on the percentage used and the mix design.

Enhances sulphate and chloride resistance
When used in accordance with BS 8500, Calcined Clay helps protect structures from aggressive environments, improving resistance to sulphate and chloride attack. This makes it ideal for marine, coastal, or chemically exposed structures.

British-sourced from circular clay waste
The product is made from fired bricks that did not meet commercial standards. Rather than sending them to a landfill, LKAB processes this waste into a high-value construction material, contributing to a circular economy.

Supports BS 8500-compliant cement designs (CEM II)
Calcined Clay can be used to produce blended cements (CEM II/A-Q, CEM II/B-Q, CEM II/B-Q+SR) and ternary blended cements (CEM II/A-M, CEM II/B-M) with limestone. These are fully compliant with British Standards, allowing use in regulated commercial projects.

Extends setting time – ideal for large pours in warm conditions
The product slightly slows the hydration process, allowing longer working time and reducing the risk of cold joints. This is particularly beneficial for mass concrete pours, hot weather concreting, or large-scale infrastructure.

First UK-produced Calcined Clay available to market
This is the first product of its kind to be sourced, processed, and supplied entirely within the UK, making it a practical and lower-carbon choice for British construction.

Technical information

Calcined Clay from LKAB Minerals is a natural calcined pozzolanic material derived from fired clay bricks rejected during quality checks in brick manufacturing. These bricks are fired at high temperatures (typically above 800°C) and undergo calcination, a process that transforms kaolinite and other clay minerals into a reactive form suitable for cement replacement.

Once fired, the material is crushed and finely ground to achieve a consistent, cement-compatible particle size distribution.

Key mineral properties:

• High silica (SiO₂) and alumina (Al₂O₃) content: Essential for pozzolanic reactivity.
• Low levels of free lime (CaO), chlorides, and TOC (Total Organic Carbon): Improves long-term stability and safety.
• Low loss on ignition (LOI).
• Fine particle size (45μm fineness at 27.0%) for optimal dispersion in concrete mixes.
• Compliant with BS 8500 concrete standards for the following designations:
  • CEM II/A-Q
  • CEM II/A-M (with limestone)
  • CEM II/B-M (with limestone)
  • CEM II/B-Q
  • CEM II/B-Q +SR (sulfate resistance)

Typical chemical composition of LKAB Minerals ground natural calcined pozzolana (Calcined Clay): 

LOI = 1.40% 

Chloride = 0.01% 

Typical physical characteristics of LKAB Minerals ground natural calcined pozzolana (Calcined Clay):

Using our Calcined Clay as a cement replacement 

LKAB sells Calcined Clay as a separate product, but it can be added at the concrete batching plant along with cement, aggregates, water and admixture as a direct replacement for cement. Due to the slower strength development, total powder contents may need to be increased with higher addition levels where 28-day strength is a requirement. Typically, 25-30% cement replacement levels can be achieved in most applications, although they can be higher with the use of specialist admixtures. 

Applications

Calcined Clay is suitable for a number of applications where environmental impact, durability, and performance are all essential considerations:

Ready-mixed concrete

• Ideal for general construction projects looking to reduce carbon footprint while maintaining structural performance.

Precast components

• Used in modular and off-site construction, calcined clay helps reduce shrinkage and thermal cracking in factory-made elements.

Large-scale pours

• The extended setting time and reduced heat of hydration make it suitable for mass pours such as basements, bridges, or foundations where temperature gradients must be controlled.

Infrastructure and civil engineering

• Roads, tunnels, railways, and public sector infrastructure benefit from the long-term durability and low carbon profile of the material.

Blended cements (BS 8500 compliant)

Calcined clay supports combinations such as:

• CEM II/A-Q
• CEM II/A-M (ternary blend with limestone)
• CEM II/B-Q
• CEM II/B-M (ternary blend with limestone)

These cement combinations provide more environmentally responsible alternatives to traditional CEM I.

Environmental information

Diverted from landfill
The material is produced from surplus clay bricks that would otherwise be classified as waste, contributing to reduced landfill dependency.

UK manufactured
Production takes place entirely in the UK, supporting local industry and minimising emissions associated with international transport and logistics.

No virgin mineral extraction
Calcined clay is a recovered material, meaning no new quarrying or mining is needed, preserving natural resources.

Supports circular economy
Through material reuse and value recovery, the product embodies circular construction principles. It gives a second life to industrial waste that is chemically suited to cementitious performance.

Contributes to low clinker, low carbon cement
Ideal for formulations targeting low clinker ratios and environmental performance as per BS 8500 and government net-zero guidelines.

Helps meet UK carbon reduction and net-zero targets
Construction teams can contribute to PAS 2080-aligned carbon reporting and reduce embodied carbon in concrete-intensive developments.