The use of cement alternatives to reduce carbon footprint – some considerations

Recent publicity over Chatham House’s research underlining the need for drastic changes in the production and use of concrete, due to the high levels of CO2 produced through the production of its key ingredient – cement, has prompted Triton’s Alan Sleigh to remind us that, although cement replacements are already used in a limited way, those with extremely low carbon footprints are still not easy to specify and use due to difficulties with standard compliance and costs.

He said, “The use of cement replacement materials in concrete has been well established for many years. As well as delivering a reduced carbon footprint, they also offer a range of benefits including increased durability of the final concrete in place. This durability can be enhanced further by the addition of appropriate waterproof admixtures such as Triton TT Admix https://www.tritonsystems.co.uk/product/triton-tt-admix/ as, by keeping moisture out of the concrete, other damaging materials such as chlorides and sulphates can also be excluded, thereby creating a more durable and sustainable concrete for constructions such as basements and other below ground level projects.

The cement most commonly used is Ordinary Portland Cement (OPC) and its key replacement material is currently Ground Granulated Blast Furnace Slag (GGBS). This typically replaces up to 30% to 70% of the OPC in the concrete mix when needed, therefore reducing the embedded carbon. In essence this material is the waste clinker from steel production (with an extremely low waste product carbon footprint) that is then ground to a fine powder and will be readily available in volume as long as steel is being produced.

In spite of the concerns over CO2 emissions from the production of cement, we seem to be a long way off moving to a high-volume based alternative construction material that can provide similar properties to concrete, and attempts to use more sustainable alternatives, with even lower embedded carbon properties, are often hampered by commercial considerations, if not initially at design stage, certainly at later costing stages.

A strong government initiative to genuinely support alternatives to OPC cement via financial incentives (zero tax rates / R&D grants etc) would certainly be welcomed as there are some very good options already out there ready for further investment and development, which would in turn lead to their wider industry adoption, lower production cost and and specification.

Complying with existing industry standards is also a big hurdle as most concrete related standards are in place to measure existing cementitious materials. Before their adoption, any new innovative materials would preferably require a fast-track standards process to be measured by, not the years of painstaking processes that are currently used and which have contributed to some lack of industry adoption of cement alternatives such AACM’s (Alkali Activated Cementitious Materials) that are currently being considered under PAS 8820:2016 as they don’t fit the current standards’ profiles.

There are a number of other good alternatives currently and painfully going through the process of firstly establishing a standard and then being measured by it – but we are a long way off completion.

I believe it’s currently a big ask for designers to reconsider the use of concrete, particularly with little commercial benefit linked to the currently available alternatives that have no chance of complying with the current non-relevant standards. Whose PI Insurance would cover these?!

 

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