Low-Carbon Cement Replacement
Clinker replacement through calcined clay and synthetic pozzolan blending — targeting 25–50% reduction in embodied CO2 vs OPC baseline across the GX product range. This is a carbon reduction pathway we design into every formulation, not a greenwash claim appended to marketing copy. The numbers on this page are design targets with explicit disclaimers; the EPD data will follow the development programme.
Supplementary cementitious materials strategy
Portland cement clinker production accounts for approximately 85–90% of the embodied CO2 in a standard ready-mix concrete. The clinker is the irreducible carbon cost of calcium silicate chemistry — it requires high-temperature calcination of limestone. Every percentage of clinker replaced with a pozzolanic or latent hydraulic SCM reduces the embodied CO2 in direct proportion to the replacement rate.
GX formulations are designed to incorporate blends of synthetic pozzolans and calcined clays as the primary SCM system. Unlike fly ash or slag — which depend on industrial co-product supply chains with variable quality and declining availability — calcined clays can be produced from widely available kaolinite clay deposits with controlled composition.
GX low-carbon mortars are designed to target compliance with ASTM C618 requirements for fly ash use in concrete, adapted for the calcined clay SCM system. This is a design and compliance-targeting objective — GX materials are not currently certified to ASTM C618.
All values are indicative design targets. Not based on EPD-certified measurements. See our Sustainability page for full framing.
| Formulation | Clinker Replacement Rate | Target CO2 Reduction vs OPC | SCM System |
|---|---|---|---|
| OPC baseline (reference) | 0% | — | Portland cement only |
| GX-30 | ~30% | Targeting ~25–30% reduction | Calcined clay + synthetic pozzolan |
| GX-40 | ~40% | Targeting ~35–40% reduction | LC3-type calcined clay blend |
| GX-50 | ~50% | Targeting ~45–50% reduction | High-replacement LC3 + microsilica |
LC3 = limestone calcined clay cement — a clinker reduction technology developed in academic materials science research. GX formulations adapt these approaches for the US supply chain and ASTM compliance framework.
Design-to-standard framing
GX materials are designed to contribute to LEED v4 MR credit categories related to building product disclosure and optimization, specifically EPD and sourcing credits. This is a contribution language — GX does not hold a LEED certification, and no project automatically earns LEED points by specifying GX materials.
For ASTM compliance, GX formulations are designed to target the following standards as design objectives:
| Standard | Relevance | GX Design Intent |
|---|---|---|
| ASTM C618 | Fly ash and natural pozzolans for cement blending | Designed to target Class N pozzolan requirements for the calcined clay component |
| ASTM C1240 | Silica fume used in cementitious mixtures | GX-50 microsilica component targeted to meet C1240 reactivity requirements |
| ASTM C94 | Ready-mixed concrete | GX Concrete Series designed to be batched as a standard C94 ready-mix with GX additive |
| ASTM C270 | Mortar for unit masonry | GX Mortar Series designed to target Type S and Type N property compliance |
Important disclaimer: All CO2 reduction figures on this page are design targets and aspirational goals for the GX formulation program. They are not based on Environmental Product Declaration (EPD) data or third-party certified lifecycle assessment results. Gelmedix is in the process of preparing EPD documentation for GX product lines. Specifiers should use project-specific EPDs from their ready-mix supplier for LEED documentation purposes.