HepCem
Heritage
The calcined clay used today as a supplementary cementitious material originates from this established manufacturing expertise. Within clay pipe production, calcined clay is produced and utilised as a carefully controlled feedstock to optimise firing behaviour, dimensional stability, and final product performance.
Through this process, Hepworth has developed extensive experience in:
Clay mineral selection and preparation
Thermal activation of clays through controlled calcination
Fine grinding and particle size optimisation
Consistent mineral processing at industrial scale
This heritage provides a unique foundation for the development of Hepworth Calcined Clay as a high-quality pozzolanic material for concrete.
Hepworth Calcined Clay is manufactured from carefully selected clay sources and processed through controlled calcination and grinding, ensuring consistent mineral composition and pozzolanic activity.
This controlled production process provides:
Reliable quality and consistent performance
Optimised particle size distribution for cement systems
Predictable reactivity in concrete mixes
Compatibility with modern admixture technologies
The material is particularly suited for infrastructure and structural concrete where durability, long service life and carbon reduction are critical requirements.
Through partial replacement of Portland cement, Hepworth Calcined Clay enables significant reductions in clinker content, supporting industry efforts to deliver lower carbon construction and net-zero aligned infrastructure.
Hepworth Calcined Clay is a reactive calcined clay pozzolana designed for use as a supplementary cementitious material (SCM) in concrete and cement systems.
Manufactured through the controlled calcination of selected clay minerals, the material provides a highly reactive aluminosilicate phase that reacts with calcium hydroxide produced during cement hydration. This pozzolanic reaction contributes to the formation of additional calcium silicate hydrates (C-S-H), improving both strength and durability of the concrete matrix.
The product is designed for use in low-clinker cement formulations and blended concrete systems, supporting the production of lower-carbon concrete while maintaining compliance with UK construction standards.
Hepworth Calcined Clay replaces a portion of Portland cement in concrete mixes, reducing clinker content and lowering CO₂ emissions by up to 30–40%, depending on mix design and substitution level.
Hepworth Calcined Clay can typically replace 20–35% of Portland cement in many concrete mix designs, depending on performance requirements and cement classification.
Hepworth Calcined Clay is produced from carefully selected clay minerals processed under controlled conditions, ensuring:
This consistency allows concrete producers to design mixes with confidence and repeatability.
Calcined clay contributes to improved long-term durability through:
These characteristics support longer service life in demanding environments such as infrastructure and marine structures.
Hepworth Calcined Clay is particularly well suited for ternary and quaternary blended cement systems, including combinations with limestone, ground granulated blast furnace slag (GGBS), pulverised fuel ash (PFA) or other supplementary materials.
These systems enable significant clinker reduction while maintaining performance.
The material can be incorporated into concrete formulations aligned with BS 8500 cement combination designations, supporting the development of compliant blended cements and low-carbon concrete mixes.
Hepworth Calcined Clay is a natural calcined pozzolanic material produced through controlled thermal activation of selected clay minerals. During calcination, clay minerals such as kaolinite are transformed into reactive aluminosilicate phases capable of reacting with calcium hydroxide generated during cement hydration.
The material is finely ground to produce a cement-compatible particle size distribution, ensuring efficient dispersion within concrete mixes and consistent pozzolanic performance.
Unlike materials derived from recycled fired bricks, Hepworth Calcined Clay originates from purpose-produced calcined clay manufactured under controlled industrial conditions, resulting in reliable mineral composition and predictable reactivity.
Hepworth Calcined Clay is certified to BS 8615-1:2019+A1:2026 for use as a pozzolanic material with Portland cement in concrete, mortar and grout.
Calcined clay exhibits a chemical composition suitable for pozzolanic reactivity, including:
These characteristics contribute to the formation of additional cementitious hydrates during hydration, improving concrete durability and microstructure.
These values are consistent with high-reactivity pozzolanic materials suitable for cement replacement.
| SiO₂ | Reactive SiO₂ | Al₂O₃ | Fe₂O₃ | Total | CaO | MgO | SO₃ | Na₂Oeq | LOI | Chloride |
|---|---|---|---|---|---|---|---|---|---|---|
| 60.62% | 42.98% | 23.31% | 6.18% | 90.11% | 0.89% | 0.87% | 0.14% | 1.60% | 1.87% | 0.01% |
| Component | Value |
|---|---|
| SiO₂ | 60.62% |
| Reactive SiO₂ | 42.98% |
| Al₂O₃ | 23.31% |
| Fe₂O₃ | 6.18% |
| Total (SiO₂ + Al₂O₃ + Fe₂O₃) | 90.11% |
| CaO | 0.89% |
| MgO | 0.87% |
| SO₃ | 0.14% |
| Na₂Oeq | 1.60% |
| Loss on Ignition | 1.87% |
| Chloride | 0.01% |
The fine particle size and controlled density allow the material to disperse effectively within cementitious systems
| Property | Value |
|---|---|
| Relative density | 2.68 Mg/m³ |
| Fineness (45 µm residue) | 10.6% |
| Initial setting time | 103 minutes |
| Water requirement | 104% of control |
The pozzolanic activity of Hepworth Calcined Clay has been evaluated in accordance with BS EN 196-1 activity index testing, achieving a 28-day strength activity index of 80%, exceeding the minimum activity requirements for calcined clay pozzolans and demonstrating effective reactivity with Portland cement systems. Hepworth Calcined Clay is now independently certified to BS 8615-1:2019+A1:2026.
Hepworth Calcined Clay is certified to BS 8615-1:2019+A1:2026, with independent assessment confirming conformity with the requirements for calcined pozzolana for use with Portland cement. Ongoing surveillance, autocontrol testing and audit testing remain in place as part of the certification scheme.
Hepworth Calcined Clay is suitable for a wide range of concrete applications where low embodied carbon, durability and reliable performance are required. Its consistent mineral composition and pozzolanic reactivity make it well-suited to modern concrete designs used in structural, precast and infrastructure construction.
In precast manufacturing, calcined clay can contribute to improved durability and dimensional stability while supporting lower-carbon concrete production. It can be used in a variety of factory-produced elements including structural units, drainage products and modular construction components.
Infrastructure projects often require concrete with enhanced durability and long service life. Calcined clay can improve resistance to aggressive environments such as chloride exposure and sulphate attack, making it suitable for transport infrastructure, bridges, tunnels and public works.
Calcined clay can contribute to reduced heat generation during cement hydration, which helps control temperature rise and thermal gradients in large concrete pours such as foundations, retaining structures and bridge piers.
Hepworth Calcined Clay can be used in the production of binary and ternary cement systems, including CEM II and limestone–calcined clay blends. These systems enable significant clinker reduction while maintaining the strength and durability required for modern concrete construction.
The material supports projects seeking to reduce embodied carbon and meet sustainability targets, including those aligned with net-zero construction strategies, PAS 2080 carbon management frameworks and low-carbon infrastructure programs.
Hepworth Calcined Clay supports the production of lower-carbon concrete by partially replacing Portland cement clinker, the most carbon-intensive component of concrete.
Through clinker substitution, calcined clay enables significant reductions in the embodied carbon of concrete while maintaining durability and long-term performance.
Preliminary carbon modelling has been undertaken based on plant-derived process data from trial production, incorporating verified UK Emissions Trading Scheme (UK ETS) fuel intensity factors and estimated electricity allocation across the raw materials process.
Under current trial conditions, this modelling places the embodied carbon of Hepworth Calcined Clay within the mid-range of the current UK benchmark values for calcined clay published by the Mineral Products Association (MPA).
This equates to approximately: ~200 kg CO₂e per tonne (A1–A3)
It is important to note that these figures are based on trial production conditions. Process parameters including blend composition, calcination temperature and plant throughput are still being refined.
A formal Life Cycle Assessment (LCA) compliant with EN 15804 will be undertaken once steady-state production conditions are established. This will support the development of a third-party verified Environmental Product Declaration (EPD).
Calcined clay is a key component in modern low-clinker cement systems, including ternary blends with limestone and emerging limestone–calcined clay cement (LC³) technologies.
These binder systems can significantly reduce clinker demand while maintaining mechanical performance and durability in concrete structures.
Hepworth Calcined Clay is produced within the UK, supporting local supply chains and reduced transport emissions associated with imported supplementary cementitious materials.
Calcined clay utilises abundant clay minerals, enabling sustainable use of widely available resources for cementitious applications.
The use of calcined clay in concrete can contribute to project carbon reduction strategies aligned with:
Hepworth Calcined Clay can be incorporated into cement systems as a natural calcined pozzolana (Q) in accordance with BS EN 197 and BS 8500 concrete standards.
The material may be supplied as a separate component and added at the concrete batching plant alongside cement, aggregates, water and admixtures, allowing partial replacement of Portland cement in concrete mixes.
Typical replacement levels in many applications range from 20–35% of the cement content, depending on mix design and performance requirements.
As with other pozzolanic supplementary cementitious materials, calcined clay may exhibit slower early-age strength development, particularly at higher replacement levels. Where early strength or 28-day strength targets are required, adjustments to total powder content or the use of modern chemical admixtures may be used to optimise performance.
Calcined clay is also well suited to ternary cement systems, where it is combined with limestone or other SCMs to further reduce clinker content while maintaining durability and long-term strength.
In accordance with BS 8500-2, Hepworth Calcined Clay can be used as a natural calcined pozzolana (Q) within Portland composite cement systems defined in BS EN 197 and BS 8500. Now independently certified to BS 8615-1:2019+A1:2026, it can support partial replacement of Portland cement to reduce clinker content and embodied carbon in concrete.
Notes:
Ternary cement systems combine calcined clay with limestone to optimise clinker reduction while maintaining strength development and durability.
| Cement Type | Cement System Description | Minimum Calcined Clay | Maximum Calcined Clay |
|---|---|---|---|
| CEM II/A-Q | Portland cement with calcined clay | 6% | 20% |
| CEM II/B-Q | Portland cement with higher calcined clay content | 21% | 35% |
| CEM II/B-Q +SR | Sulphate-resisting Portland composite cement with calcined clay | 25% | 35% |
| CEM II/A-M (Q-L) | Ternary blend of Portland cement, calcined clay and limestone | 12% | 20% |
| CEM II/B-M (Q-L) | Ternary blend with higher calcined clay and limestone content | 21% | 35% |
Calcined clay can also be used as the primary pozzolanic component in pozzolanic cements (CEM IV), allowing significantly higher levels of clinker substitution.
| Cement Designation | Minimum Calcined Clay | Maximum Calcined Clay |
|---|---|---|
| CEM IV/A-Q | 36% | 55% |
| CEM IV/B-Q | 56% | 65% |
These cements enable very high clinker replacement levels and may be used where lower heat generation, improved durability and reduced embodied carbon are desired.
Calcined clay is particularly well suited to modern low-clinker cement systems, where it is combined with materials such as limestone or other supplementary cementitious materials.
Examples include:
| Cement System | Typical Clinker Reduction |
|---|---|
| CEM II/B-Q | 21–35% |
| CEM II/B-M (Q-L) | 21–35% |
| Limestone–Calcined Clay systems (LC³-type) | Up to ~50% |
| Multi-component low-clinker cements | Up to ~60% |
Hepworth Calcined Clay is a reactive calcined clay pozzolana designed for use as a supplementary cementitious material (SCM) in concrete and cement systems.
Manufactured through the controlled calcination of selected clay minerals, the material provides a highly reactive aluminosilicate phase that reacts with calcium hydroxide produced during cement hydration. This pozzolanic reaction contributes to the formation of additional calcium silicate hydrates (C-S-H), improving both strength and durability of the concrete matrix.
The product is designed for use in low-clinker cement formulations and blended concrete systems, supporting the production of lower-carbon concrete while maintaining compliance with UK construction standards.
Hepworth Calcined Clay replaces a portion of Portland cement in concrete mixes, reducing clinker content and lowering CO₂ emissions by up to 30–40%, depending on mix design and substitution level.
Hepworth Calcined Clay can typically replace 20–35% of Portland cement in many concrete mix designs, depending on performance requirements and cement classification.
Hepworth Calcined Clay is produced from carefully selected clay minerals processed under controlled conditions, ensuring:
This consistency allows concrete producers to design mixes with confidence and repeatability.
Calcined clay contributes to improved long-term durability through:
These characteristics support longer service life in demanding environments such as infrastructure and marine structures.
Hepworth Calcined Clay is particularly well suited for ternary and quaternary blended cement systems, including combinations with limestone, ground granulated blast furnace slag (GGBS), pulverised fuel ash (PFA) or other supplementary materials.
These systems enable significant clinker reduction while maintaining performance.
The material can be incorporated into concrete formulations aligned with BS 8500 cement combination designations, supporting the development of compliant blended cements and low-carbon concrete mixes.
Hepworth Calcined Clay is a natural calcined pozzolanic material produced through controlled thermal activation of selected clay minerals. During calcination, clay minerals such as kaolinite are transformed into reactive aluminosilicate phases capable of reacting with calcium hydroxide generated during cement hydration.
The material is finely ground to produce a cement-compatible particle size distribution, ensuring efficient dispersion within concrete mixes and consistent pozzolanic performance.
Unlike materials derived from recycled fired bricks, Hepworth Calcined Clay originates from purpose-produced calcined clay manufactured under controlled industrial conditions, resulting in reliable mineral composition and predictable reactivity.
The material has been tested in accordance with BS 8615-1:2019 for natural pozzolanas used as additions in concrete.
Calcined clay exhibits a chemical composition suitable for pozzolanic reactivity, including:
These characteristics contribute to the formation of additional cementitious hydrates during hydration, improving concrete durability and microstructure.
These values are consistent with high-reactivity pozzolanic materials suitable for cement replacement.
| SiO₂ | Reactive SiO₂ | Al₂O₃ | Fe₂O₃ | Total | CaO | MgO | SO₃ | Na₂Oeq | LOI | Chloride |
|---|---|---|---|---|---|---|---|---|---|---|
| 60.62% | 42.98% | 23.31% | 6.18% | 90.11% | 0.89% | 0.87% | 0.14% | 1.60% | 1.87% | 0.01% |
| Component | Value |
|---|---|
| SiO₂ | 60.62% |
| Reactive SiO₂ | 42.98% |
| Al₂O₃ | 23.31% |
| Fe₂O₃ | 6.18% |
| Total (SiO₂ + Al₂O₃ + Fe₂O₃) | 90.11% |
| CaO | 0.89% |
| MgO | 0.87% |
| SO₃ | 0.14% |
| Na₂Oeq | 1.60% |
| Loss on Ignition | 1.87% |
| Chloride | 0.01% |
The fine particle size and controlled density allow the material to disperse effectively within cementitious systems
| Property | Value |
|---|---|
| Relative density | 2.68 Mg/m³ |
| Fineness (45 µm residue) | 10.6% |
| Initial setting time | 103 minutes |
| Water requirement | 104% of control |
The pozzolanic activity of Hepworth Calcined Clay has been evaluated in accordance with BS EN 196-1 activity index testing with a 28-day strength activity index of 80%, which exceeds the minimum activity requirements defined for calcined clay pozzolans, demonstrating effective reactivity with Portland cement systems.
Hepworth calcined clay has been tested in accordance with BS 8615-1. Results obtained to date meet the specified limits for natural clay pozzolans. A programme of ongoing testing is in place to establish statistical conformity.
Hepworth Calcined Clay is suitable for a wide range of concrete applications where low embodied carbon, durability and reliable performance are required. Its consistent mineral composition and pozzolanic reactivity make it well-suited to modern concrete designs used in structural, precast and infrastructure construction.
In precast manufacturing, calcined clay can contribute to improved durability and dimensional stability while supporting lower-carbon concrete production. It can be used in a variety of factory-produced elements including structural units, drainage products and modular construction components.
Infrastructure projects often require concrete with enhanced durability and long service life. Calcined clay can improve resistance to aggressive environments such as chloride exposure and sulphate attack, making it suitable for transport infrastructure, bridges, tunnels and public works.
Calcined clay can contribute to reduced heat generation during cement hydration, which helps control temperature rise and thermal gradients in large concrete pours such as foundations, retaining structures and bridge piers.
Hepworth Calcined Clay can be used in the production of binary and ternary cement systems, including CEM II and limestone–calcined clay blends. These systems enable significant clinker reduction while maintaining the strength and durability required for modern concrete construction.
The material supports projects seeking to reduce embodied carbon and meet sustainability targets, including those aligned with net-zero construction strategies, PAS 2080 carbon management frameworks and low-carbon infrastructure programs.
Hepworth Calcined Clay supports the production of lower-carbon concrete by partially replacing Portland cement clinker, the most carbon-intensive component of concrete.
Through clinker substitution, calcined clay enables significant reductions in the embodied carbon of concrete while maintaining durability and long-term performance.
Preliminary carbon modelling has been undertaken based on plant-derived process data from trial production, incorporating verified UK Emissions Trading Scheme (UK ETS) fuel intensity factors and estimated electricity allocation across the raw materials process.
Under current trial conditions, this modelling places the embodied carbon of Hepworth Calcined Clay within the mid-range of the current UK benchmark values for calcined clay published by the Mineral Products Association (MPA).
This equates to approximately: ~200 kg CO₂e per tonne (A1–A3)
It is important to note that these figures are based on trial production conditions. Process parameters including blend composition, calcination temperature and plant throughput are still being refined.
A formal Life Cycle Assessment (LCA) compliant with EN 15804 will be undertaken once steady-state production conditions are established. This will support the development of a third-party verified Environmental Product Declaration (EPD).
Calcined clay is a key component in modern low-clinker cement systems, including ternary blends with limestone and emerging limestone–calcined clay cement (LC³) technologies.
These binder systems can significantly reduce clinker demand while maintaining mechanical performance and durability in concrete structures.
Hepworth Calcined Clay is produced within the UK, supporting local supply chains and reduced transport emissions associated with imported supplementary cementitious materials.
Calcined clay utilises abundant clay minerals, enabling sustainable use of widely available resources for cementitious applications.
The use of calcined clay in concrete can contribute to project carbon reduction strategies aligned with:
Hepworth Calcined Clay can be incorporated into cement systems as a natural calcined pozzolana (Q) in accordance with BS EN 197 and BS 8500 concrete standards.
The material may be supplied as a separate component and added at the concrete batching plant alongside cement, aggregates, water and admixtures, allowing partial replacement of Portland cement in concrete mixes.
Typical replacement levels in many applications range from 20–35% of the cement content, depending on mix design and performance requirements.
As with other pozzolanic supplementary cementitious materials, calcined clay may exhibit slower early-age strength development, particularly at higher replacement levels. Where early strength or 28-day strength targets are required, adjustments to total powder content or the use of modern chemical admixtures may be used to optimise performance.
Calcined clay is also well suited to ternary cement systems, where it is combined with limestone or other SCMs to further reduce clinker content while maintaining durability and long-term strength.
In accordance with BS 8500-2 - Hepworth Calcined Clay can be used as a natural calcined pozzolana (Q) within Portland composite cement systems defined in BS EN 197 and BS 8500. These systems allow partial replacement of Portland cement to reduce clinker content and embodied carbon in concrete.
Notes:
Ternary cement systems combine calcined clay with limestone to optimise clinker reduction while maintaining strength development and durability.
| Cement Type | Cement System Description | Minimum Calcined Clay | Maximum Calcined Clay |
|---|---|---|---|
| CEM II/A-Q | Portland cement with calcined clay | 6% | 20% |
| CEM II/B-Q | Portland cement with higher calcined clay content | 21% | 35% |
| CEM II/B-Q +SR | Sulphate-resisting Portland composite cement with calcined clay | 25% | 35% |
| CEM II/A-M (Q-L) | Ternary blend of Portland cement, calcined clay and limestone | 12% | 20% |
| CEM II/B-M (Q-L) | Ternary blend with higher calcined clay and limestone content | 21% | 35% |
Calcined clay can also be used as the primary pozzolanic component in pozzolanic cements (CEM IV), allowing significantly higher levels of clinker substitution.
| Cement Designation | Minimum Calcined Clay | Maximum Calcined Clay |
|---|---|---|
| CEM IV/A-Q | 36% | 55% |
| CEM IV/B-Q | 56% | 65% |
These cements enable very high clinker replacement levels and may be used where lower heat generation, improved durability and reduced embodied carbon are desired.
Calcined clay is particularly well suited to modern low-clinker cement systems, where it is combined with materials such as limestone or other supplementary cementitious materials.
Examples include:
| Cement System | Typical Clinker Reduction |
|---|---|
| CEM II/B-Q | 21–35% |
| CEM II/B-M (Q-L) | 21–35% |
| Limestone–Calcined Clay systems (LC³-type) | Up to ~50% |
| Multi-component low-clinker cements | Up to ~60% |
We support customers during material testing and mix development by providing representative samples for laboratory validation and plant-scale trials. All sample requests are managed in coordination with our technical team to ensure appropriate material selection and performance alignment.
To request a sample of HepCem, please contact the Hepworth team with details of your intended application, required volumes, and testing requirements. We will respond promptly to discuss logistics, technical documentation, and next steps.
