Testing superabsorbent polymer (SAP) sorption properties prior to implementation in concrete: results of a RILEM Round-Robin Test

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, ionmediated 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

Comprehensive tissue-specific proteome analysis of drought stress responses in Pennisetum glaucum (L.) R. Br. (Pearl millet)

Pearl millet is the fifth most important cereal crop worldwide and cultivated especially by small holder farmers in arid and semi-arid regions because of its drought and salt tolerance. The molecular mechanisms of drought stress tolerance in Pennisetum remain elusive. We have used a shotgun proteomics approach to investigate protein signatures from different tissues under drought and control conditions. Drought stressed plants showed significant changes in stomatal conductance and increased root growth compared to the control plants. Root, leaf and seed tissues were harvested and 2281 proteins were identified and quantified in total. Leaf tissue showed the largest number of significant changes (120), followed by roots (25) and seeds (10). Increased levels of root proteins involved in cell wall-, lipid-, secondary- and signaling metabolism and the concomitantly observed increased root length point to an impaired shoot–root communication under drought stress. The harvest index (HI) showed a significant reduction under drought stress. Proteins with a high correlation to the HI were identified using sparse partial least square (sPLS) analysis. Considering the importance of Pearl millet as a stress tolerant food crop, this study provides a first reference data set for future investigations of the underlying molecular mechanisms

Textile-reinforced concrete to realise ultra high durability concrete (UHDC) in the framework of the EU H2020 project "ReSHEALience"

The EU H2020 project “ReSHEALience” (rethinking coastal defence and green-energy service infrastructures through enhanced-durability high-performance cement-based materials) focuses on a holistic approach to create ultra-high durability concrete (UHDC) encompassing the concept and development of advanced materials and tailored design approaches to provide innovative structural solutions. One kind of cement-based composites to realise UHDC structures is textile-reinforced concrete (TRC), in which multiple layers of carbon multifilament yarns composed to a fabric serve as the reinforcement. TRC exhibits multiple micro-crack formation upon tensile loading with fairly small individual crack opening widths, below about 100 µm under service conditions. This characteristic in conjunction with functional admixtures is expected to reach a pronounced self-healing propensity of the cement-based matrix even under very harsh XS exposure conditions. Subsequent to durability-related laboratory experiments regarding sea water as the aggressive medium, two real-scale demonstration projects will be implemented, specifically a breakwater on the Irish west coast and the restoration of a historic water reservoir tower in Malta. This paper presents the concept of TRC development towards a UHDC, outlines the characteristics of the two demonstrators and some preliminary laboratory result

The effect of the capillary forces on the desorption of hydrogels in contact with a porous cementitious material

This paper examines the desorption of hydrogels in contact with porous cementitious materials to aid in understanding the mechanisms of water release from superabsorbent polymers (SAP) into cementitious materials. The dependence of hydrogel desorption on the microstructure of cementitious materials and relative humidity was studied. It was shown that the capillary adhesion developed at the interface between the hydrogel and cementitious materials increased the desorption of the hydrogels. The size of hydrogels was shown to influence desorption, beyond the known size dependence of bulk diffusion, through debonding from the cementitious matrix, thereby decreasing the effect of the Laplace pressure on desorption. Microscopic examination highlighted a stark contrast in the desorption morphology of hydrogels with different chemical compositions