SITELIVE 
Where the rest of the world has got to
Portland-limestone cement stopped being an alternative in North America and became the default. Manufactured to ASTM C595 or AASHTO M 240 and designated "IL", it contains 5 to 15 per cent blended or interground limestone; the Federal Highway Administration's TechNote on the material states it is engineered to deliver 28-day performance equivalent to ordinary portland cement at 1:1 replacement while reducing global warming potential by 8.3 per cent on average, with suppliers typically landing on 10 to 12 per cent limestone because that blend gives the cleanest one-for-one substitution. Type IL entered the blended-cement specifications in 2012. FHWA is candid that adoption has not been frictionless: agencies and contractors have reported implementation challenges arising from limited field experience, which is why the TechNote exists at all.
Europe went considerably further. EN 197-5:2021 created two cement families outside EN 197-1: Portland-composite cement CEM II/C-M, with clinker at 50 to 64 per cent and other main constituents at 36 to 50 per cent, and composite cement CEM VI, with clinker at just 35 to 49 per cent. These are binders in which clinker is a minority constituent, which is the only structural route to large reductions given that around 60 per cent of cement's emissions come from the calcination chemistry itself, not the fuel. At the other end of the effort curve, Heidelberg Materials opened the cement industry's first industrial-scale carbon capture and storage facility at Brevik in Norway on 18 June 2025, capturing about 400,000 tonnes of CO2 a year — roughly half that plant's emissions — with transport and offshore storage handled by Northern Lights under Norway's state-backed Longship programme. The resulting evoZero cement began reaching European customers in October 2025. Both approaches are real; only one of them is cheap.
Australia's cap, and the reason it exists
AS 3972-2010 permits up to 7.5 per cent limestone as a mineral addition in general-purpose cement, with Type GL general-purpose limestone cement (8 to 20 per cent) and Type GB blended cements as the declared alternatives. The Cement Industry Federation has argued that lifting the general-purpose allowance to 12 per cent would not materially affect performance, would cut around 250,000 tonnes of CO2 a year — about 5 per cent of the industry's emissions — and would bring Australia closer to North American practice, where up to 15 per cent is used routinely. Austroads tested that proposition and published the answer in 2019 (AP-T346-19). Compressive strength was comparable between concretes made with 2.9 per cent and 12 per cent limestone cement, but the 12 per cent concrete was inferior on drying shrinkage, modulus of elasticity and creep, and significantly worse on carbonation and chloride ingress resistance — particularly where concrete was steam-cured at 80 °C, which also degraded sulfate resistance and resistance to delayed ettringite formation. Austroads concluded it would be highly inadvisable to replace current general-purpose cement wholesale unless cements at 7.5 per cent or below remained available to the market. The finding that matters most for practice is the one in the middle of the report: those durability gaps narrowed when the cement was blended with 25 per cent fly ash or 65 per cent slag. The durable path to less clinker runs through supplementary cementitious materials, not through more filler.
The supply question underneath the debate
Which raises the problem nobody specifying concrete in Australia can avoid. The NSW Government's own guidance on supplementary cementitious materials sets out the trade plainly: fly ash mitigates alkali-silica reaction at minimum 20 to 25 per cent replacement, improves chloride resistance and reduces heat of hydration and early-age thermal cracking risk, at the cost of slower setting and slower strength development, with additional cover flagged above 35 per cent replacement where carbonation is a risk. Queensland's Department of Transport and Main Roads mandates 20 to 25 per cent fly ash in most of its concrete — while the eight coal-fired power stations that supply that ash retire under the state's emissions plan. The NACOE-funded review welcomed by the Ash Development Association of Australia puts fresh fly ash supply as viable to around 2040, and identifies harvested ponded ash from Queensland ash dams — an estimated 250-plus years of current consumption — as the most feasible long-term alternative, subject to investment in processing and, critically, standardisation. Clinker substitution in Australia is therefore a supply-chain and standards programme with a decade-long lead time, not a mix-design tweak.
What to do before the comment period closes
AS 3972-2010 is listed by Standards Australia as pending revision, and the redlined draft DR AS 3972:2026 is open for public comment under committee BD-010 until 7 September 2026 — alongside DR AS 3600:2026, the redlined concrete structures standard, which closes on 19 August. For anyone who specifies, supplies, places or certifies concrete in this country, that is a narrow window in which the binder rules are actually movable, and industry bodies including CCAA and the CIF have already put the case for shifting AS 3972 toward performance-based rather than prescriptive composition limits. Separately, prepare the site for binders that behave differently: lower-clinker mixes change strength gain and therefore formwork stripping and post-tensioning timing, they change curing discipline and its consequences for carbonation and cover, and — per the Austroads work — they behave worst under aggressive steam-curing regimes, which is a direct warning to precast. The practical defence is evidence: trial mixes against your own exposure classes and early-age strength requirements, and a pour-by-pour record of mix, placement conditions and curing that lets a new binder be accepted on data rather than defended after the fact.