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This article presents the results of a round-robin test performed by 13 international research groups in the framework of the activities of the RILEM Technical Committee 260 RSC “Recommendations for use of superabsorbent polymers in concrete construction”. Two commercially available superabsorbent polymers (SAP) with different chemical compositions and gradings were tested in terms of their kinetics of absorption in different media; demineralized water, cement filtrate solution with a particular cement distributed to every participant and a local cement chosen by the participant. Two absorption test methods were considered; the tea-bag method and the filtration method. The absorption capacity was evaluated as a function of time. The results showed correspondence in behaviour of the SAPs among all participants, but also between the two test methods, even though high scatter was observed at early minutes of testing after immersion. The tea-bag method proved to be more practical in terms of time dependent study, whereby the filtration method showed less variation in the absorption capacity after 24 h. However, absorption followed by intrinsic, ion-mediated desorption of a specific SAP sample in the course of time was not detected by the filtration method. This SAP-specific characteristic was only displayed by the tea-bag method. This demonstrates the practical applicability of both test methods, each one having their own strengths and weaknesses at distinct testing times.

This communication explores the influence of boundary effects, embedded sensors and crack opening on high-temperature experiments of concrete as revealed by in situ neutron tomography. The hypotheses routinely taken about these experimental aspects in common practice are hereby reassessed in light of the insight given by noninvasive full-field measurements. Notably, we directly assess the heat and moisture insulation techniques and reveal the influence of temperature and gas pressure monitoring on the testing conditions, opening new perspectives toward their improvement.

New methods are proposed for the verification of the presence of superabsorbent polymers (SAP) in freshly mixed concrete and estimation of SAP quantity. The methods are in general based on flushing concrete with excess water. They allow separating the light, water-sorbed hydrogel particles from the mineral components in the fresh concrete and making these particles available for further tests. Two types of tests are proposed: Test 1 serves for a visual verification of the presence of SAP (qualitative test), while Test 2 enables quantifying the mass of the collected SAP as a proxy of their concentration in concrete (quantitative test). Different procedures are proposed for these two test methods and their performance is evaluated. The testing procedures were scrutinized in an interlaboratory study carried out by 14 participants from 12 countries. All participating groups detected the presence of SAP in the mix using the qualitative procedures (Test 1). Based on this outcome, we suggest that this method should be applied in the field. In contrast, while most participants obtained reasonably reliable results with the quantification procedure of Test 2, some participants reported large errors. Therefore, the quantification method needs to be further refined, starting from the experience gained in this interlaboratory study.

An emerging strategy to compensate for the greenhouse gas emissions of products is to incorporate carbonaceous materials obtained from removed atmospheric carbon dioxide, mainly obtained through biomass conversion. This approach can turn asphalt pavements into a functional carbon sink. In particular, biochar has been used as a bitumen modifier. However, due to performance limitations, carbonaceous materials were only added in small quantities to asphalt mixtures. An alternative approach is to produce lightweight aggregates to substitute a part of the mineral aggregates of the asphalt mixture. To this end, biochar is pelletised with a hydraulic binder and water in a cold-bonding process, forming spherical pellets labelled as carbon-rich lightweight aggregates (C-LWA). Like other lightweight aggregates, C-LWA showed a reduced mechanical strength compared to conventional mineral aggregates, adversely affecting the asphalt mixture performance. Cracking and rutting resistance almost linearly decreased with C-LWA content. The direct addition of biochar had a similar adverse influence on the mixture performance. Despite a reduced performance, adding biochar and C-LWA reduces the greenhouse gas emissions of asphalt mixtures. Net-zero emissions were estimated for the produced asphalt mixture by adding 5.5 ± 0.4% C-LWA or 3.0 ± 0.2% biochar obtained from the pyrolysis of landscape management wood. A wider range of C-LWA addition (1% to 35.1%) was estimated considering the greenhouse gas emission estimation variability of both asphalt and biochar production.