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Redmond Lloyd – National R&D Manager

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Developments in low-carbon concrete

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Why low carbon concrete?

Concrete is an excellent (and irreplaceable) building material…

� Low cost, excellent performance

� Low / no toxicity

� No waste or byproducts during manufacture

� Very good durability and service life

� Good insulation properties and beneficial thermal mass

� Some (limited) ability to be beneficially recycled

But…

� Cement manufacture is responsible for 5-8% of anthropogenic CO2 emissions

� Burning limestone to make clinker produces the majority of CO2 emissions

� Consequently, there is a global trend to reduce clinker use

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Global trends to reduce Portland clinker use

Substitution and replacement depend on locally available materials

� Europe: high interest, but limited ash and slag availability

- Limestone � to 30%+

- Different clinker � high belite, sulfoaluminate

- Alternate SCM’s � limestone + metakaolin (+ activators)

� Australia: limestone, fly ash and slag prevalent

� US: don’t care at present, but starting to…

- Have good reserves of highly reactive ash

� Canada: limestone primarily, due to limited ash and slag

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Lower carbon clinkers: high belite cement

Clinker type Portland Belite rich

C3S 60% 10%

C2S 20% 65%

Other 20% 25%

CO2 emitted ~0.9 t/t ~0.65 t/t

0 5 10 15 20 25 30

Time (days)

Portland

High belite

Pro:↓ clinkering temperature↓ CO2

� Standard compliant

Cons:↓ early strength? CO2 saving limited

Just use fly ash…

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Lower carbon clinkers: sulfoaluminate clinkers

Clinker Portland Sulpho-aluminate

Lafarge‘Aether’

C3S 60%

C2S 20% 25% 55%

C4AF 20% 5% 20%

C4A3$ 70% 25%

CO2 emitted ~0.9 t/t ~0.7t/t

Pro:↓ clinkering temperature↓ CO2

↑ early strength

Cons:� Not standard compliant? CO2 saving limited

Niche use for precast?

0 5 10 15 20 25 30

Time (days)

Portland

Sulfoaluminate

Novel clinkers do not deliver enough

carbon benefit and are too costly for a

small market like Australia…

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Lower Carbon Cements: High Volume SCM Blends

Current practical limit is:

� ~60% (slag/ash & slag)

� ~40% ash only

� Not uncommon in Sydney:

Pros:

- Standards compliant, easy & practical, durable

Cons:

- Reduced early strength � limits use in a practical sense

Extended ‘high-volume replacement’ limits:

� ~80% slag – e.g. Masdar City

� ~50% ash – e.g. CANMET work

� Achieved through high Superplasticizer dosage � ‘sticky’, very difficult to pump, finish etc.

� Does not overcome reduced early strength development

� High volume SCM blends have reduced early strength: Compromise on construction

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Lower Carbon Cements: Geopolymers

Alkali-activated fly ash binders

Typical Composition:

� Binder is > 70% fly ash

� Activators include:

- Alkali hydroxides and carbonates

- Alkali silicates (solid and liquid)

Pros:

- ‘No cement’ system, very high ash use, reduced CO2

Cons:

- Hazardous, not standards compliant, ash variability, heat-curing often required, high carbon activators, conversion??

Current applications:

� Limited to controlled trials � mainly through Universities

� Likely end point � some precast and/or specialty products

� Geopolymers have many technical & practical hurdles which must be overcome

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Lower Carbon Cements: Alkali-activated slag

Alkali-activated Slag Binders

Typical Composition:

� Binder is > 50% slag

� Activators include:

- Alkali hydroxides and carbonates

- Alkali silicates (solid and liquid)

Pros:

- Very high SCM use, reduced CO2, room temperature curing, less hazardous than geopolymers

Cons:

- Still hazardous, not standards compliant, slag variability affects performance, high CO2 content in alkali and silicates (Cl2 by-products), carbonation a significant issue.

Current applications:

� Field trials and use by some commercial companies (Zeobond, Wagners)

� Likely end point � some precast and/or specialty products

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Lower Carbon Concretes: Ideal Product?

So…in a crowded landscape, what are the ideal product attributes?

� High cement replacement with SCMs

� Non-hazardous

� No compromise on early strength

� Standards compliant

� Highly durable

� Enough Ca2+ to limit carbonation to ‘acceptable’ rate

� Robust mix designs

� Compatibility with admixtures – retarders, accelerators, superplasticisers

No material will always meet all criteria

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Lower Carbon Concretes: Envisia®

High-volume cement replacement technology

� 20-40% OPC

� 60-80% slag + ash

� activator (soluble sulfate)

- Non-hazardous

- Not alkaline

Properties:

� Same reaction products as regular blend but strength development is faster

� Reaction products are calcium silicate hydrates � same as typical slag/OPC blends

� Improved ettringite formation and stabilisation

� No compromise on early strength

� Improved shrinkage and durability

� Standards compliant

� Enough Ca2+ to limit carbonation to ‘acceptable’ rate

� Robust mix designs, regular setting times, normal pumping/placing/finishing

� Compatibility with existing admixture technology – retarders, accelerators, superplasticisers.

� Part of the solution ���� allows increased SCMs where they couldn’t be before

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Future directions…

Boral is committed to…

1. Safety � zero harm

2. Meeting the market need for lower carbon concretes

… in that order

Current research…

� Concretes that are 50-100% stronger with the same cement content

� SCM’s that perform much better

� In future we will see concretes at higher strength grades and lower Portland contents:

- 50 - 120 MPa with 150 – 300 kg/m3 Portland cement

- 20 – 50 MPa with 50 – 100 kg/m3 Portland cement

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Boral Innovation Factory – CM&C

August 2014