Alkali-Activated Concrete: Evidence for Project Specification

Specify alkali-activated concrete only when the proposed mix has an acceptable project approval route, verified mechanical and durability performance for the exposure, and a supply and curing plan that reproduces the tested material. Carbon savings need a comparable environmental assessment. High recycled content or a successful demonstration elsewhere cannot establish structural suitability for a new project.

Project requirements and defined concrete mixes

Begin with the element and its conditions of service: loads, exposure, design life, reinforcement, geometry and construction programme. These determine the evidence needed from a supplier. A precast component cured under controlled factory conditions and an exposed cast-in-place structure are different applications. The environmental objective belongs alongside the structural and construction requirements. It should not replace them, because a lower production footprint has little value if the specified durability or build sequence cannot be achieved.

Alkali-activated concrete is a family of materials. Precursors such as slag, fly ash or calcined clay react with an activating system, and their chemistry influences the resulting binder. Rossi and colleagues’ assessment of alkali-activated concrete connects the diversity of formulations with the need to characterise performance by material type. Its analysis also identifies limitations in applying mechanical-property relationships across the whole family. The procurement object should therefore be a defined mix and production process, with controlled ranges for its constituents, rather than an unrestricted category labelled geopolymer or green concrete.

Compressive strength is one part of the evidence. The designer may also need elastic modulus, tensile behaviour, shrinkage, creep, reinforcement bond and other properties relevant to the element. Verify the specimen geometry, curing, test age and production conditions behind the figures. A result obtained after laboratory heat curing cannot be assigned unchanged to concrete placed in cold weather. Where familiar design relationships are used, establish that they suit the particular material rather than inferring their validity from matching a single strength value.

Exposure durability and site curing

Durability must address the actual exposure. Chloride ingress, carbonation, reinforcement corrosion, freezing, chemical attack and fire can matter in different combinations. The GeopolyConc project’s final report links binder chemistry and microstructure with durability and reinforcement protection. That research supports evaluating the underlying mechanisms; it does not certify a supplier’s mix. The testing and interpretation should be appropriate to its binder chemistry, supported where possible by relevant exposure history. A favourable test for one degradation mechanism cannot settle the service life under all the others.

Construction trials need to reproduce the intended delivery and placement. Demonstrate workability retention, pumping or compaction, finishing, setting and curing with the proposed equipment and weather envelope. Include the activator’s handling arrangements and the crew’s working method, especially when the system differs from familiar mixes. Define what happens when delivery is delayed or constituent variability changes setting. Acceptance specimens and production records should remain traceable to the batches placed, so the finished structure can be connected with the evidence used to approve it.

Comparable carbon evidence and supply assurance

The carbon comparison should use equivalent performance and compatible assessment boundaries. Habert and Ouellet-Plamondon’s environmental assessment examines how constituent choices affect geopolymer impacts. For a procurement comparison, inspect the declared mix, activator production, precursor processing, allocation of burdens to by-products, transport and any curing energy. Check which life-cycle stages an environmental product declaration covers. Recycled content is a separate quantity from greenhouse-gas impact, and neither is evidence of structural acceptance. Keep any offsets distinct from reductions in the production footprint.

For an illustrative project using 400 m³ of functionally equivalent concrete, a verified reduction from 300 to 180 kg CO2e per m³ would save 48 tonnes CO2e within the stated common boundary. That is a 40% reduction, not a generic saving attributable to all alkali-activated mixes. The calculation needs revision if the alternative changes required concrete volume, curing energy or service-life assumptions. Procurement should compare with a suitable available low-carbon conventional option as well as the original reference, since the choice is rarely limited to one clinker-rich baseline.

Confirm the applicable acceptance route and the scope of supporting certificates or assessments with the project’s responsible specification team before purchase. Published research and other projects provide useful evidence, but do not confer approval in every jurisdiction or application. Supply assurance is equally material: identify precursor sources, lot checks, blending controls and change-notification requirements, with a plan for interruptions. A credible specification combines the approved material envelope, site execution requirements, evidence for the service environment and a traceable carbon comparison. The supplier must be able to reproduce all four throughout the project.