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This article belongs to the Special Issue Green Deal in Construction and Building Materials., Solar energy is an energy intermittent source that faces a substantial challenge for its power dispatchability. Hence, concentrating solar power (CSP) plants and solar process heat (SPH) applications employ thermal energy storage (TES) technologies as a link between power generation and optimal load distribution. Ordinary Portland cement (OPC)-based materials are widely used in sensible TES, but their use is limited to operation temperatures below 400 to 500 °C because of thermal degradation processes. This work proposes a geopolymer (GEO)-based concrete as a suitable alternative to OPC concrete for TES that withstands high running temperatures, higher than 500 °C. To this end, thermophysical properties of a geopolymer-based concrete sample were initially measured experimentally; later, energy storage capacity and thermal behavior of the GEO sample were modeled numerically. In fact, different thermal scenarios were modeled, revealing that GEO-based concrete can be a sound choice due to its thermal energy storage capacity, high thermal diffusivity and capability to work at high temperature regimes., This work was born under the umbrella of the project “Energy storage solutions based on concrete (E-CRETE)” (RTI2018-098554-B-I00) funded by MCIN/AEI/10.13039/501100011033 (Program I+D+i RETOS INVESTIGACIÓN 2018). Mohammad Rahjoo acknowledges the grant PRE2019-087676 funded by MCIN/AEI/ 10.13039/501100011033 and co-financed by the European Social Fund under the 2019 call for grants for predoctoral contracts for the training of doctors contemplated in the State Training Subprogram of the State Program for the Promotion of Talent and its Employability in R&D&I, within the framework of the State Plan for Scientific and Technical Research and Innovation 2017–2020. Besides, the economic support from POVAZSKA is also acknowledged.

This article belongs to the Topic Thermal Energy Transfer and Storage., Thermal energy storage (TES) systems are dependent on materials capable of operating at elevated temperatures for their performance and for prevailing as an integral part of industries. High-temperature TES assists in increasing the dispatchability of present power plants as well as increasing the efficiency in heat industry applications. Ordinary Portland cement (OPC)-based concretes are widely used as a sensible TES material in different applications. However, their performance is limited to operation temperatures below 400 °C due to the thermal degradation processes in its structure. In the present work, the performance and heat storage capacity of geopolymer-based concrete (GEO) have been studied experimentally and a comparison was carried out with OPC-based materials. Two thermal scenarios were examined, and results indicate that GEO withstand high running temperatures, higher than 500 °C, revealing higher thermal storage capacity than OPC-based materials. The high thermal energy storage, along with the high thermal diffusion coefficient at high temperatures, makes GEO a potential material that has good competitive properties compared with OPC-based TES. Experiments show the ability of geopolymer-based concrete for thermal energy storage applications, especially in industries that require feasible material for operation at high temperatures., This work was born under the umbrella of the project “Energy storage solutions based on concrete (E-CRETE)” (RTI2018-098554-B-I00) funded by MCIN/AEI/10.13039/501100011033 (Program I+D+i RETOS INVESTIGACIÓN 2018). Mohammad Rahjoo acknowledges the grant PRE2019-087676 funded by MCIN/AEI/10.13039/501100011033 and co-financed by the European Social Fund under the 2019 call for grants for predoctoral contracts for the training of doctors contemplated in the State Training Subprogram of the State Program for the Promotion of Talent and its Employability in R&D&I, within the framework of the State Plan for Scientific and Technical Research and Innovation 2017–2020. In addition, the economic support from POVAZSKA is acknowledged. Jorge S. Dolado acknowledges the funding from the Gobierno Vasco UPV/EHU (project no. IT1569-22).

Cement paste leaching and concomitant decalcification is a common cause of concrete structure deterioration. Such alterations entail microstructural changes that condition concrete durability. This study analysed those changes in cement pastes exposed to accelerated decalcification, layer-by-layer, from the surface in contact with the leaching agent, 6 M NH4NO3, to the unaltered area. The microstructural changes were analysed with BSEM, MIP and BET whilst the mineralogical and nanostructural alterations in each layer were assessed with XRD, FTIR, 29Si and 27Al MAS NMR and BSD. Decalcification affected not only portlandite and CSH gel, but also the anhydrous clinker and ettringite, inducing major micro- and nano-structural changes, particularly in the two layers closest to the leaching agent. CSH gel decalcification was more intense in the outer layers where long chain gels co-existed with silicon rich gels. BDS, in turn, revealed differences between the amount of bound water in the surface interfacing with the leaching agent and in the leaching front. More specifically, larger numbers of water molecules were tightly bound to silanol groups in the outer, whereas hydroxyl group distribution was more orderly in the inner layers., This study was funded by the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement No. 760858. Funding was also received from the Regional Government of Madrid, (S2018/NMT-4372 TOP Heritage-CM Programme).

Calcium silicate hydrates are members of a large family of minerals with layered structures containing pendant CaOH and SiOH groups that interact with confined water molecules. To rationalize the impact of the local chemical environment on the dynamics of water, SiOH- and CaOH-rich model nanocrystals were synthesized by using the continuous supercritical hydrothermal method and then systematically studied by a combination of spectroscopic techniques. In our comprehensive analysis, the ultrafast relaxation dynamics of hanging hydroxy groups can be univocally assigned to CaOH or SiOH environments, and the local chemical environment largely affects the H-bond network of the solvation water. Interestingly, the ordered “ice-like” solvation water found in the SiOH-rich environments is converted to a disordered “liquid-like” distribution in the CaOH-rich environment. This refined picture of the dynamics of confined water and hydroxy groups in calcium silicate hydrates can also be applied to other water-containing materials, with a significant impact in many fields of materials science., This research was carried out under the umbrella of the Bordeaux-Euskampus Euro-regional Campus of International Excellence initiative and supported by the International Doctoral Program developed between the University of Bordeaux (UB) and the University of the Basque Country (UPV/EHU). Valentina Musumeci is grateful to the Initiative of Excellence (IdEX) of the University of Bordeaux for financial support. The authors also acknowledge CNRS, Bordeaux INP and Région Nouvelle-Aquitaine for their financial support. This work is partially supported by the Gobierno Vasco-UPV/EHU project IT1246-19 and the Spanish Ministry of Science, Innovation and Universities projects PCI2019-103657 and RTI2018-098554-B-I00.

This article belongs to the Special Issue Modeling of Cementitious Materials and Structures., To find materials with an appropriate response to THz radiation is key for the incoming THz technology revolution. Unfortunately, this region of the electromagnetic spectra remains largely unexplored in most materials. The present work aims at unveiling the most significant THz fingerprints of cement-based materials. To this end transmission experiments have been carried out over Ordinary Portland Cement (OPC) and geopolymer (GEO) binder cement pastes in combination with atomistic simulations. These simulations have calculated for the first time, the dielectric response of C-S-H and N-A-S-H gels, the most important hydration products of OPC and GEO cement pastes respectively. Interestingly both the experiments and simulations reveal that both varieties of cement pastes exhibit three main characteristic peaks at frequencies around ~0.6 THz, ~1.05 THz and ~1.35 THz, whose origin is governed by the complex dynamic of their water content, and two extra signals at ~1.95 THz and ~2.75 THz which are likely related to modes involving floppy parts of the dried skeleton., This work is partially supported by the Gobierno Vasco-UPV/EHU project IT1246-19 and the Spanish Ministry of Science, Innovation and Universities projects PCI2019-103657 and RTI2018-098554-B-I00. Besides, the economic support from POVAZSKA and SKKC foundation is also acknowledged.

This article belongs to the Special Issue Energy in Construction and Building Materials., Understanding the mechanisms that govern the conductive properties of multifunctional cement-materials is fundamental for the development of the new applications proposed to enhance the energy efficiency, safety and structural properties of smart buildings and infrastructures. Many fillers have been suggested to increase the electrical conduction in concretes; however, the processes involved are still not entirely known. In the present work, we investigated the effect of graphene nanoplatelets (1 wt% on the electrical properties of cement composites (OPC/GNPs). We found a decrease of the bulk resistivity in the composite associated to the enhancement of the charge transport properties in the sample. Moreover, the study of the dielectric properties suggests that the main contribution to conduction is given by water diffusion through the porous network resulting in ion conductivity. Finally, the results support that the increase of direct current in OPC/GNPs is due to pore refinement induced by graphene nanoplatelets., This work is partially supported by the Gobierno Vasco-UPV/EHU project IT1246-19 and the Spanish Ministry of Science, Innovation and Universities projects PCI2019-103657 and RTI2018-098554-B-I00. The project is co-funded by EUSKAMPUS FUNDAZIOA.

We have combined X-ray diffraction, neutron diffraction with polarization analysis, small angle neutron scattering, differential scanning calorimetry, and broad band dielectric spectroscopy to investigate the structure and dynamics of binary mixtures of poly(2-(dimethylamino)ethyl methacrylate) with either water or tetrahydrofuran (THF) at different concentrations. Aqueous mixtures are characterized by a highly heterogeneous structure where water clusters coexist with an underlying nano-segregation of main chains and side groups of the polymeric matrix. THF molecules are homogeneously distributed among the polymeric nano-domains for concentrations of one THF molecule/monomer or lower. A more heterogeneous situation is found for higher THF amounts, but without evidences for solvent clusters. In THF-mixtures, we observe a remarkable reduction of the glass-transition temperature which is enhanced with increasing amount of solvent but seems to reach saturation at high THF concentrations. Adding THF markedly reduces the activation energy of the polymer β-relaxation. The presence of THF molecules seemingly hinders a slow component of this process which is active in the dry state. The aqueous mixtures present a strikingly broad glass-transition feature, revealing a highly heterogeneous behavior in agreement with the structural study. Regarding the solvent dynamics, deep in the glassy state all data can be described by an Arrhenius temperature dependence with a rather similar activation energy. However, the values of the characteristic times are about three orders of magnitude smaller for THF than for water. Water dynamics display a crossover toward increasingly higher apparent activation energies in the region of the onset of the glass transition, supporting its interpretation as a consequence of the freezing of the structural relaxation of the surrounding matrix. The absence of such a crossover (at least in the wide dynamic window here accessed) in THF is attributed to the lack of cooperativity effects in the relaxation of these molecules within the polymeric matrix., Financial support from the Projects Nos. MAT2012-31088 and MAT2015-63704-P (Spanish-MINECO and EU) and IT-654-13 (Basque Government) is acknowledged. This work is based on experiments performed at SANS-2 (SINQ, Paul Scherrer Institute, Villigen, Switzerland), and DNS-instrument JNSE (Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany) and has been supported by the European Commission under the 7th Framework Programme through the “Research Infrastructures” action of the “Capacities” Programme, NMI3-II Grant No. 283883.

We have investigated the dynamical processes-α-relaxation, local motions of the side-groups, and methyl group rotations-in poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) in the dry state and in mixtures (at 70 wt% polymer concentration) with tetrahydrofuran (THF) and water, to address the question as to how these polymer motions are affected by plasticizers interacting in different ways with the polymer. Differential scanning calorimetry, dielectric spectroscopy, and neutron scattering techniques on labeled samples (with deuterated solvents to isolate the signal of the polymer component) have been combined. The α-relaxation is drastically affected, with similar shifts of the glass-transition temperature for both solvents. Effects of compositional heterogeneities and reduction of the fragility are also observed. On the contrary, methyl-group dynamics are unaffected by the presence of solvent. Regarding side-group local motions (β-relaxation), two kinds of components-a slow and a fast one-could be identified in the dry state. On the basis of the spatial information provided by neutron scattering, a model for the geometry of the motions involved in the fast component has been proposed. Adding solvent, this process would remain essentially unaltered, but the population involved in the slower one would be reduced. With THF as solvent, this reduction would be complete, but with water it would be only partial. This could be attributed to rather heterogeneous distribution of water molecules in the polymer likely associated with the presence of water clusters. Such a scenario would also explain the much more pronounced broadening of the glass-transition region observed for the polymer in the aqueous mixture with respect to that induced by THF., Financial support from the Projects MAT2012-31088 (Spanish MINECO and EU) and IT-654-13 (Basque Government) is acknowledged. This work is based on experiments performed at FOCUS (SINQ, Paul Scherrer Institute, Villigen, Switzerland), and at TOFTOF and SPHERES (Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany), and has been supported by the European Commission under the seventh Framework Programme through the “Research Infrastructures” action of the “Capacities” Programme, NMI3-II Grant Number 283883.

We have investigated a mixture of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and tetrahydrofuran (THF) (70 wt. % PDMAEMA/30 wt. % THF) by combining dielectric spectroscopy and quasielastic neutron scattering (QENS) on a labelled sample, focusing on the dynamics of the THF molecules. Two independent processes have been identified. The >fast> one has been qualified as due to an internal motion of the THF ring leading to hydrogen displacements of about 3 Å with rather broadly distributed activation energies. The >slow> process is characterized by an Arrhenius-like temperature dependence of the characteristic time which persists over more than 9 orders of magnitude in time. The QENS results evidence the confined nature of this process, determining a size of about 8 Å for the volume within which THF hydrogens' motions are restricted. In a complementary way, we have also investigated the structural features of the sample. This study suggests that THF molecules are well dispersed among side-groups nano-domains in the polymer matrix, ruling out a significant presence of clusters of solvent. Such a good dispersion, together with a rich mobility of the local environment, would prevent cooperativity effects to develop for the structural relaxation of solvent molecules, frustrating thereby the emergence of Vogel-Fulcher-like behavior, at least in the whole temperature interval investigated., Financial support from the Project Nos. MAT2012-31088 (Spanish-MINECO and EU) and IT-654-13 (Basque Government) is acknowledged. This work is based on experiments performed at TOFTOF and DNS (Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany) and has been supported by the European Commission under the 7th Framework Programme through the “Research Infrastructures” action of the “Capacities” Programme, NMI3-II Grant No. 283883.

The coherent excitations of DNA hydration water at 100 K have been investigated by neutron scattering spectroscopy to extract the excess signal of D(2)O-hydrated DNA with respect to dry DNA samples. A structural characterization of the sample, through the analysis of the static structure factor, has suggested that DNA hydration water is largely in an amorphous state up to high hydration degree, with only a small contribution coming from slightly deformed crystalline ice. To describe the inelastic spectra of DNA hydration water, we exploited a phenomenological model already applied in similar disordered systems, such as bulk water (Sacchetti et al. Phys. Rev. E2004, 69, 061203; Petrillo et al. Phys. Rev. E2000, 62, 3611-3618; Sette et al. Phys. Rev. Lett.1996, 77, 83-86) and protein hydration water (Orecchini et al. J. Am. Chem. Soc.2009, 131, 4664-4669). Over the low-energy range, the coherent dynamics of DNA hydration water is characterized by a branch at about 7.5 meV, a value slightly larger than that of bulk water. An additional mode in the energy range 20-35 meV is found, with a wavevector dependence seemingly connected with the structural features of amorphous ice. The ensemble of the results supports the glassy nature of DNA hydration water.

The pulpal reaction and the marginal sealing of in vivo restored samples using resin composite and Scotchbond Multi-Purpose adhesive system (3M Dental Products) were analyzed in this study.Twelve Class I non-exposed cavity preparations were placed on premolars to be removed for orthodontic reasons. They were restored and observed at 7 d and 28 d.The examination of the resin-dentin interface under the scanning electron microscope (SEM) revealed: 1) a gap-free attachment between adhesive resin and dentinal surface in 80% of the areas studied, 2) penetration of resin tags into the dentinal tubules, and 3) formation of a 3-5 micrometer thick acid-resistant hybrid layer. Microfissures measuring about 10 micrometers were observed in only 20a% of the areas studied; these were located along the walls of the cavities, especially near the enamel in zones where there was a lower concentration of dentinal tubules. The histological analysis, carried out 7 d after preparation of the restoration, did not show any alteration of the pulp. After 4 wk, reparative dentin was produced in the pulpal areas corresponding to the restored cavities.The quantity of newly formed dentin is correlated with the distance from the cavity to the pulp. The results indicate that acid-etching of vital dentin using 10% maleic acid does not impair pulpal healing in deep Class I cavities and that the Scotchbond Multi-Purpose adhesive system is able to preserve the morphological and biological integrity of the pulpo-dentinal complex.