Shrinkage in carbonatable binders: Are the cementitious standards applicable for non-hydraulic lime-cement systems?
Description
Recently approved regulations that aim to mitigate the release of greenhouse gases have been pushing the construction industry into reducing its carbon dioxide (CO2) footprint. Therefore, promoting new low-carbon cements and carbonatable binders have been some of the strategies adopted. Lime has been trending as a green binder because it consumes less energy during production and due to the CO2 capture during its hardening process. However, a new generation of binders demands a new generation of characterization standards. Given the absence of guidelines to measure the shrinkage of air lime-cement systems, the suitability of cementitious standards – ASTM C191:2021 (Vicat setting), ASTM C1698:2019 (autogenous shrinkage), and EN 12390-16:2019 (total shrinkage) – was addressed. Four mixtures were studied (C0L100, C33L67, C50L50, and C100L0). The first digit corresponds to the cement (CEM II/A-L 32.5R), and the second corresponds to the air lime (CL90S) content, both in the percentage of binder volume. Regarding the Vicat setting, the samples could be measured satisfactorily. On the autogenous shrinkage, the lack of interaction with CO2 prevented lime carbonation, meaning limited hardening for those samples. Therefore, ASTM C1698:2019 was not suitable for lime-based materials. For the total shrinkage, EN 12390-16:2019 was suitable but complementary tests are needed to distinguish individual contributions (chemical, autogenous, and carbonation) to the total shrinkage. The results showed expansion for the groups with lime (especially for lime-cement, where lime acted as a catalyst). The expansion was associated with the carbonation of the unbounded portlandite. Finally, future studies should investigate chemical and carbonation shrinkage at early ages since the autogenous method was not capable of monitoring the volume instability of lime-based mortars.
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01. ICCC2023_Full_paper_Munhoz_Ye.pdf
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