How the admixtures industry can assist in low carbon concrete production

Innovative admixture technologies driving reductions in embodied carbon content for sustainable concrete

Author

Ian Ellis

Head of Technical Services Admixtures, UK & Ireland

The admixtures play a key role in reducing the embodied carbon content of concrete through innovative products such as Low Carbon Concrete Admixtures (LCCA). These formulations optimise hydration, enabling lower cement content or higher dosage of Supplementary Cementitious Materials (SCM) while maintaining high performance. The use of Mapecube 60W admixtures allows CO₂ reductions of up to 35%. Further strategies include using reclaimed aggregates, dry concrete recycling, and macro synthetic fibres. Together, these innovations support the construction sector’s path toward Net Zero by 2050.

The topic of low carbon construction and therefore low carbon concrete has been discussed many times over the last few years and there is no doubt that the construction industry is taking great strides to reduce it’s environmental impact despite the current challenging marketplace. The target of Net Zero by 2050 is often seen as being quite daunting and this paper highlights some of the strategies that can be employed to progress towards achieving that target.

Recent developments from the admixtures industry have included a new type of admixture with the unofficial title of Low Carbon Concrete Admixtures (LCCA). These new admixtures work in conjunction with a traditional High Range Water Reducing Admixture (HRWRA) to further increase the performance of the concrete by optimising the hydration process. The main focus for LCCA is to either further reduce the cementitious content, or to increase the % replacement of supplementary cementitious material (SCM), or a combination of both.

LCCA’s such as Mapei’s Mapecube 60W will have a small reduction in the free water content of the concrete, but not such that they detrimentally effect the concrete rheology. LCCA’s are not currently defined by any harmonised standard, so in order to provide them as a CE marked product they incorporate a small amount of water reduction to comply with the requirements of BS EN 934-2 Table 2 (water reducing admixture). A good example of innovation being ahead of standardisation.

In the examples below, the charts show both the strength development and embodied carbon content of the concrete ⁽¹⁾. In all the charts the reference mix (first data series) contains Dynamon Easy 31 (UK) @ 0.60%, the other mixes contain both Dynamon Easy 31 (UK) as the HRWRA at 0.6% dosage by weight of cement and Mapecube 60W @ 0.80% by weight of cement.

Figure 1. The chart illustrates strength development and embodied carbon content in concrete mixes using Dynamon Easy 31 alone and in combination with Mapecube 60W, as GGBS (Ground Granulated Blast Furnace Slag) replacement levels increase.

In the first example, a concrete mix with a 350kg/m³ CIIIA (40% GGBS replacement) was used as the reference mix, this was compared to 3 separate mixes incorporating Mapecube 60W @ 0.80% -:

320kg/m³ CIIIA with 40% GGBS replacement
350kg/m³ CIIIA with 50% GGBS replacement
350kg/m³ CIIIB with 70% GGBS replacement

As can be seen from the chart below, at 30kg/m³ reduced cement content we have 2.4N/mm² additional strength at 28 days but with a CO₂ saving of 16kg/m³, an 8% reduction compared to the reference. Maintaining the cement content at 350kg/m³ but increasing the GGBS replacement level to 50% gives 8.0N/mm² additional strength at 28 days, with a CO₂ saving of 22kg/m³, an 11% reduction compared to the reference. The 28 day strength increase obviously gives the potential for a further cement content reduction and shows the synergy between Mapecube 60W and higher GGBS levels. Increasing the GGBS replacement level to 70% further highlights this synergy, as at 28 days we have the same 7 & 28 day strengths as the reference mix, but with a CO₂ saving of 70kg/m³, a 35% reduction. There is some reduction in the 24 hour strengths for the reduced cement content & 70% GGBS replacement mixes, but this is quite small & can be compensated for by incorporating a small amount of chloride free accelerator into the concrete.

As a further point to consider when looking at how we can reduce the embodied carbon content of concrete, one of the potential barriers to achieving this is the use of minimum cement contents in areas such as exposure classes. Perhaps it’s time to review these levels and adopt a less conservative approach by having a base line minimum cement content of 280 - 300kg/m³ but still retain the original w/c ratios for durability & exposure. This would permit the modern admixtures to further reduce cement contents, potentially providing both an environmental & economic benefit.

The Re-Con Dry Reclaimer system was recently launched by Mapei.

Although this paper so far has focussed on the reduction of CO₂ by optimising the composition of the cementitious component of the concrete, we should not forget the contribution of the aggregate content.The admixtures industry already has products such as Re-Con AGG 100 that can permit the use of previously less desirable aggregate sources in concrete. This will permit the utilisation of more local sources and see a direct CO₂ benefit from reduced transport distances. It’s generally recognised that up to 5% of concrete produced globally is returned to the production plant unused. This places an immense challenge to the concrete producer on how to deal with this waste, traditional wet concrete reclaimers have been used for many years, however, although the aggregate fraction is easily reclaimed and re-used, the resulting cementitious and fine fines slurry has proved more challenging. It is not unusual to see a mothballed wet concrete reclaimer & filled in slurry pit at a concrete plant.

Mapei S.p.A have recently launched their new innovative & patented dry reclaiming system, Re-Con Dry Reclaimer, that, when used in conjunction with Re-Con Zero L/A, is able to convert fresh returned concrete, within minutes, into a totally re-usable earth dry granular material without utilising any water or giving rise to the production of any subsequent cementitious slurry. This granular material can be stored and re-used directly at the concrete plant as part of the coarse aggregate content of subsequent concrete, without any detriment to performance. This provides the opportunity for a concrete plant to produce near zero, d potentially zero concrete waste with the resultant environmental and economic benefits.

Fresh concrete after processing being discharged by Mapei Re-Con Dry Reclaimer.

Other aspects of construction can also be considered, for example, macro synthetic fibres (MSF) can also be utilised to reduce the embodied carbon content of concrete of industrial floor slabs. The article “The advantages of macro-synthetic fibres in concrete” mentions that by incorporating MSF instead of traditional steel fabric, while also eliminating contraction joints can provide an associated CO₂ reduction of up to 49.5%.

In conclusion, the admixtures industry has many tools and options available to the concrete and construction industry to help achieve the net zero target by 2050, or potentially earlier, some of these are already available within existing codes & standards, whereas some will require their review & ultimate revision.

^{(1) All CO₂e figures are based on the latest edition of MPA Fact Sheet 18 & are factory gate figures, for Dynamon Easy 31 (UK) the value is that defined by EFCA (EPD-EFC-20210198-IBG1-EN, for Mapecube 60W the value is defined by the Mapei EPD (EPD International AB S-P-09427). The numbers shown are only the sum of the cementitious content and any admixtures, no allowance for aggregate content contribution, energy or transport are included.}

^{This article was published in Concrete magazine, (October 2025) which we would like to thank.}

Author

Ian Ellis

Head of Technical Services Admixtures, UK & Ireland

Tag

#circulareconomy

Product Lines

Admixtures for concrete