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In respect of the alkali-activated concretes, the CO2 equivalent is already reduced by about 43 wt.-% for Concrete 1 with a mixing ratio of 1:3 (crushed concrete sand to metakaolin) with 118 kg CO2 eq/m³ of fresh concrete as against the reference mix design. An increase of the portion of crushed concrete sand to a ratio of 1:1.5 for Concrete 3 has a further positive effect on the CO2 equivalent to 106 kg CO2/m³ owing to a further reduction of the CO2-intensive metakaolin (423 kg CO2/t) [HEA 14] and thus resulting in a reduction compared to the reference of about 49 wt.-%.
7 Conclusion and outlook:
The investigations carried out as part of this research project demonstrate impressively that it is possible to produce alkali-activated concretes based an alternative binder consisting of metakaolin and crushed concrete sand, which in terms of workability and green strength satisfy the manufacturing requirements for the production of concrete blocks on large-scale plants.
However, the results also reveal that there is still need for optimization in view of the high requirements on compactability, compressive strength and splitting tensile strength. This, anyhow, should not obscure the fact that the alternative concretes developed here exhibit material properties that are relevant to construction practice and are comparable to conventional concretes, being used in building construction and civil engineering today. ...
