4D Early Age Cement Hydration Analysis by Ptychographic X-ray Computed Tomography and Machine Learning Segmentation

Cement manufacturing is responsible for ~7% of the anthropogenic CO2 emissions and hence, decreasing the CO2 footprint, in a sustainable, safe and cost-effective way, is a top priority. To fully understand the binder main properties and to decrease their CO2 footprints, a sound description of their spatially resolved mineralogy is necessary. Developing this knowledge is very challenging as about half of the volume of hydrated cement is a nanocrystalline component, calcium silicate hydrate (C-S-H) gel. Furthermore, other poorly crystalline phases (e.g. iron siliceous hydrogarnet or silica oxide) coexist. Here, we have used ptychographic X-ray computed tomography (PXCT) for understanding the first days of cement hydration with the final goal to improve the mechanical strength performances of low-CO2 cements

2D Corrugated Magnesium Carboxyphosphonate Materials: Topotactic Transformations and Interlayer “Decoration” with Ammonia

In this paper we report the synthesis and structural characterization of the 2D layered coordination polymer Mg(BPMGLY)(H2O)2 (BPMGLY = bis-phosphonomethylglycine, (HO3PCH2)2N(H)COO2−). The Mg ion is found in a slightly distorted octahedral environment formed by four phosphonate oxygens and two water molecules. The carboxylate group is deprotonated but noncoordinated. This compound is a useful starting material for a number of topotactic transformations. Upon heating at 140 °C one (of the two) Mg-coordinated water molecule is lost, with the archetype 2D structure maintaining itself. However, the octahedral Mg in Mg(BPMGLY)(H2O)2 is now converted to trigonal bipyramidal in Mg(BPMGLY)(H2O). Upon exposure of the monohydrate Mg(BPMGLY)(H2O) compound to ammonia, one molecule of ammonia is inserted into the interlayer space and stabilized by hydrogen bonding. The 2D layered structure of the product Mg(BPMGLY)(H2O)(NH3) is still maintained, with Mg now acquiring a pseudo-octahedral environment. All of these topotactic transformations are also accompanied by changes in hydrogen bonding between the layers.Proyecto nacional MAT2010-1517

Structural Mapping and Framework Interconversions in 1D, 2D, and 3D Divalent Metal R,S-Hydroxyphosphonoacetate Hybrids

Reactions of divalent cations (Mg2þ, Co2þ, Ni2þ, and Zn2þ) with R,S-hydroxyphosphonoacetic acid (HPAA) in aqueous solutions (pH values ranging 1.0-4.0) yielded a range of crystalline hydrated M-HPAA hybrids. Onedimensional (1D) chain compounds were formed at room temperature whereas reactions conducted under hydrothermal conditions resulted in two-dimensional (2D) layered frameworks or, in some cases, three-dimensional (3D) networks incorporating various alkaline cations. 1D phases with compositions [M{HO3PCH(OH)CO2}(H2O)2]· 2H2O (M = Mg, Co, and Zn) were isolated. These compounds were dehydrated in liquid water to yield the corresponding [M{HO3PCH(OH)CO2}(H2O)2] compounds lacking the lattice water between the 1D chains. [M{HO3PCH(OH)CO2}(H2O)2] (M = Mg, Ni, Co, Zn) compounds were formed by crystallization at room temperature (at higher pH values) or also by partial dehydration of 1D compounds with higher hydration degrees. Complete dehydration of these 1D solids at 240-270 ºC led to 3D phases, [M{HO3PCH(OH)CO2}]. The 2D layered compound [Mg{HO3PCH(OH)CO2}(H2O)2] was obtained under hydrothermal conditions. For both synthesis methods, addition of alkali metal hydroxides to adjust the pH usually led to mixed phase materials, whereas direct reactions between the metal oxides and the hydroxyphosphonoacetic acid gave single phase materials. On the other hand, adjusting the pH with acetate salts and increasing the ratio M2þ/HPAA and/or the Aþ/M2þ ratio (A = Na, K) resulted in 3D networks, where the alkali cations were incorporated within the frameworks for charge compensation. The crystal structures of eight new M(II)-HPAA hybrids are reported herein and the thermal behavior related to dehydration/rehydration of some compounds are studied in detail.Proyecto nacional MAT2006-11080-C02-0

Multiscale understanding of tricalcium silicate hydration reactions

Tricalcium silicate, the main constituent of Portland cement, hydrates to produce crystalline calcium hydroxide and calcium-silicate-hydrates (C-S-H) nanocrystalline gel. This hydration reaction is poorly understood at the nanoscale. The understanding of atomic arrangement in nanocrystalline phases is intrinsically complicated and this challenge is exacerbated by the presence of additional crystalline phase(s). Here, we use calorimetry and synchrotron X-ray powder diffraction to quantitatively follow tricalcium silicate hydration process: i) its dissolution, ii) portlandite crystallization and iii) C-S-H gel precipitation. Chiefly, synchrotron pair distribution function (PDF) allows to identify a defective clinotobermorite, Ca11Si9O28(OH)2.8.5H2O, as the nanocrystalline component of C-S-H. Furthermore, PDF analysis also indicates that C-S-H gel contains monolayer calcium hydroxide which is stretched as recently predicted by first principles calculations. These outcomes, plus additional laboratory characterization, yielded a multiscale picture for C-S-H nanocomposite gel which explains the observed densities and Ca/Si atomic ratios at the nano- and meso- scales.This work has been supported by Spanish MINECO through BIA2014-57658-C2-2-R, which is co-funded by FEDER, BIA2014-57658-C2-1-R and I3 (IEDI-2016-0079) grants. We also thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beam time at BL04-MSPD beamline

Quantitative analysis of cementitious materials by X-ray ptychographic nanotomography

Cement manufacturing is responsible for ~7% of the anthropogenic CO2 emissions and hence, decreasing the CO2 footprint, in a sustainable, safe, and cost-effective way, is a top priority. It is also key to develop more durable binders as the estimated world concrete stock is 315 Gt which currently results in ~0.3 Gt/yr of concrete demolition waste (CDW). Moreover, models under development predict a skyrocketing increase of CDW to 20–40 Gt/yr by 2100. This amount could not be easily reprocessed as aggregates for new concretes as such volumes would be more than two times the predicted need. Furthermore, concretes have very complex hierarchical microstructures. The largest components are coarse aggregates with dimensions bigger than a few centimetres and the smallest ones are amorphous components and the calcium silicate hydrate gel with nanoparticle sizes smaller than a few nanometres. To fully understand the properties of current and new cement binders and to optimize their performances, a sound description of their spatially-resolved contents is compulsory. However, there is not a tomographic technique that can cover the spatial range of heterogeneity and features of concretes and mortars. This can only be attained within a multitechnique approach overlapping the spatial scales in order to build an accurate picture of the different microstructural features. Here, we have employed far-field and near-field synchrotron X-ray ptychographic nanotomographies to gain a deeper insight into the submicrometer microstructures of Portland cement binders. With these techniques, the available fields of view range from 40 to 300 um with a true spatial resolution evolving between ~50to~300 nm. It is explicitly acknowledged here that other techniques like X-ray synchrotron microtomography are necessary to develop the whole picture accessing to larger fields of view albeit with poorer spatial resolution and without the quantitativeness in the reconstructed electron densities

Crystal engineering in confined spaces. A novel method to grow crystalline metal phosphonates in alginate gel systems

In this paper we report a crystal growth method for metal phosphonate frameworks in alginate gels. It consists of a metalcontaining alginate gel, in which a solution of phosphonate ligand is slowly diffused. Crystals of metal phosphonate products are formed inside the gel. We have applied this for a variety of metal ions (alkaline-earth metals, transition metals and lanthanides) and a number of polyphosphonic acid and mixed carboxy/phosphonic acid ligands.Proyecto nacional MAT2010-1517

Common Structural Features in Calcium Hydroxyphosphonoacetates. A High-Throughput Screening

R,S-Hydroxyphosphonoacetic acid (H3HPA) is an inexpensive multidentate organic ligand widely used for the preparation of organo-inorganic hybrid materials. There are reports of several crystal structures and the variability of the resulting frameworks is strikingly high, in contrast with the simplicity of the ligand. In an attempt to investigate and rationalize some salient structural features of the crystal structures, we have carried out a systematic high-throughput study of the reaction of H3HPA with Ca2þ in aqueous solutions (pH values ranging 1.0-7.5) at room temperature and hydrothermally at 180 ºC. The tested synthetic conditions yielded five crystalline singlephase Ca-H3HPA hybrids: Ca3(O3PCHOHCOO)2 · 14H2O (1), Ca(HO3PCHOHCOO) · 3H2O (2), Ca5(O3PCHOHCOO)2(HO3PCHOHCOO)2 · 6H2O (3), CaLi(O3PCHOHCOO) (4), and Ca2Na(O3PCHOHCOO (HO3PCHOHCOO) ·1.5H2O(5). Four new crystal structures, 2-5, are reported (three frompowder diffraction data and one from single-crystal data), which allowed us to unravel some key common structural features. The Ca-H3HPA hybrids without an extra alkaline cation, 1-3, contain a common structural motif, which has been identified as a linear Ca-H3HPA-Ca-H3HPA-Ca trimer. This inorganic motif has a central Ca2+ in a distorted octahedral environment, whereas the two side Ca2+ cations are in an eight-coordinated oxygen-rich environment. The H3HPA ligands are chelating the central Ca2+ through two pairs of carboxylate and phosphonate oxygen atoms forming six-membered rings, Ca-O-C-C-P-O-Ca. This coordination mode allows the peripheral Ca(II) ions to bind the ligand through the -OH group and the other carboxylate oxygen, forming a fivemembered ring, Ca-O-C-C-O-Ca. The presence of alkaline cations, Li+ and Na+, disrupt this common structural feature leading to highly dense frameworks. Finally, similarities (and differences) between Ca-H3HPA and Cd-H3HPA hybrids are also discussed.Proyectos nacionales MAT2009-07016 y MAT2010-15175 (MICINN, España

High Proton Conductivity in a Flexible, Cross-Linked, Ultramicroporous Magnesium Tetraphosphonate Hybrid Framework

Multifunctional materials, especially those combining two or more properties of interest, are attracting immense attention due to their potential applications. MOFs, metal organic frameworks, can be regarded as multifunctional materials if they show another useful property in addition to the adsorption behavior. Here, we report a new multifunctional light hybrid, MgH6ODTMP·2H2O(DMF)0.5 (1), which has been synthesized using the tetraphosphonic acid H8ODTMP, octamethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic acid), by highthroughput methodology. Its crystal structure, solved by Patterson-function direct methods from synchrotron powder Xray diffraction, was characterized by a 3D pillared open framework containing cross-linked 1D channels filled with water and DMF. Upon H2O and DMF removal and subsequent rehydration, MgH6ODTMP·2H2O (2) and MgH6ODTMP·6H2O (3) can be formed. These processes take place through crystalline−quasi-amorphous−crystalline transformations, during which the integrity of the framework is maintained. A water adsorption study, at constant temperature, showed that this magnesium tetraphosphonate hybrid reversibly equilibrates its lattice water content as a function of the water partial pressure. Combination of the structural study and gas adsorption characterization (N2, CO2, and CH4) indicates an ultramicroporous framework. High-pressure CO2 adsorption data are also reported. Finally, impedance data indicates that 3 has high proton conductivity σ = 1.6 × 10−3 S cm−1 at T = 292 K at ∼100% relative humidity with an activation energy of 0.31 eV.Proyecto nacional MAT2010-15175 (MICINN, España

Processing and characterisation of calcium sulphoaluminate ecocements containing Microencapsulated Phase Change Materials

Calcium SulphoAluminate (CSA) cements can be considered as ecocements, since their production releases up to 40% less CO2 than Ordinary Portland Cement (OPC) [1]. In addition, Microencapsulated Phase Change Materials (MPCM) are receiving a growing attention in the last years for their capability of storing and releasing high energy (latent heat storage) at a narrow temperature range. Thus, the use of CSA ecocements blended with MPCM would let control the inner temperature of buildings. This would allow a double reduction of CO2 emissions due to the use of CSA rather than OPC, and the better reconditioning of houses, with the consequent social, economic and environmental benefits. This work is focused on the dispersion of MPCM in a CSA ecocement matrix and the further characterisation of the corresponding materials. All the important parameters evolved in the preparation of homogeneous CSA pastes and CSA+MPCM pastes were optimised (e.g. percentage of superplasticiser) through rheological studies. MPCM particles were well dispersed in the paste and were kept unaltered in the matrix. The thermal analysis confirmed the phase change properties of the blended cement pastes. In addition, a CSA paste was successfully coated by CSA+MPCM paste, supporting the technical viability of this type of coatings in buildings. Finally, the optimal thickness of a coating of CSA+PCM mortar adhered in a typical building located in Malaga (south of Spain) was theoretically calculated to avoid/minimise the use of air conditioning/heating, resulting in an economically viable project with a considerable reduction of CO2 emissions. [1] M.A.G. Aranda, A.G. De la Torre, Sulfoaluminate cement, in: F. Pacheco-Torgal, S. Jalali, J. Labrincha, V.M. John (Eds.), Eco-efficient concrete. Woodhead Publishing Limited, Cambridge, 2013.Universidad de Málaga. Campus de Excelencia Internacional Angalucía Tech

Tuning Proton Conductivity in Alkali Metal Phosphonocarboxylates by Cation Size-Induced and Water-Facilitated Proton Transfer Pathways

The structural and functional chemistry of a family of alkali-metal ions with racemic R,S-hydroxyphosphonoacetate (M-HPAA; M = Li, Na, K, Cs) are reported. Crystal structures were determined by X-ray data (Li+, powder diffraction following an ab initio methodology; Na+, K+, Cs+, single crystal). A gradual increase in dimensionality directly proportional to the alkali ionic radius was observed. [Li3(OOCCH(OH)PO3)-(H2O)4]·H2O (Li-HPAA) shows a 1D framework built up by Li-ligand “slabs” with Li+ in three different coordination environments (4-, 5-, and 6-coordinated). Na-HPAA, Na2(OOCCH(OH)PO3H)(H2O)4, exhibits a pillared layered “house of cards” structure, while K-HPAA, K2(OOCCH(OH)PO3H)(H2O)2, and Cs-HPAA, Cs(HOOCCH(OH)-PO3H), typically present intricate 3D frameworks. Strong hydrogen-bonded networks are created even if no water is present, as is the case in Cs-HPAA. As a result, all compounds show proton conductivity in the range 3.5 × 10−5 S cm−1 (Cs-HPAA) to 5.6 × 10−3 S cm−1 (Na-HPAA) at 98% RH and T = 24 °C. Differences in proton conduction mechanisms, Grothuss (Na+ and Cs+) or vehicular (Li+ and K+), are attributed to the different roles played by water molecules and/or proton transfer pathways between phosphonate and carboxylate groups of the ligand HPAA. Upon slow crystallization, partial enrichment in the S enantiomer of the ligand is observed for Na-HPAA, while the Cs-HPAA is a chiral compound containing only the S enantiomer.Proyectos nacionales MAT2010-15175 y MAT2013-41836-