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At least 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Prehydration of calcium sulfoaluminate (CSA) clinker at different relative humidities

The use of CSA cement in practice has been hindered by its unstable performance and short shelf-life caused by the prehydration of CSA clinker. In this study, the effect of ambient humidity on the prehydration rate and process of CSA clinker was investigated. The prehydration degree, ageing progress, and the dynamic change of mineral composition of CSA clinker exposed to five different relative humidities (ranging from 23% to 98%) for up to 180 days were studied. Experiments revealed that the ambient humidity of 60% RH can be considered a threshold value for storage of CSA clinker. Exposure of CSA clinker to RH higher than 60% will not only result in a significant decrease of hydraulic reactivity, but also in agglomeration of the clinker. Although the exposure of CSA clinker to RH lower than 60% has little effect on the hydraulic reactivity, the main hydration peak was found to be slightly delayed with the increase of RH.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Hinderance of C-S-H sheet piling during first drying using a shrinkage reducing agent: A SAXS study

The role of a shrinkage reducing agent (SRA) in the hardened cement paste during a first desorption process was investigated by measuring the small-angle X-ray scattering (SAXS). Fractal disc analysis and Guinier approximation were adopted to interpret the SAXS profiles. We experimentally confirmed that the presence of SRA molecules mitigated the piling of calcium-silicate hydrate (C-S-H) sheets, which could be monitored by the increase in the thickness of the disc, representing the agglomeration of C-S-H sheets. In addition, the basal spacing of C-S-H did not change during the drying. By contrast, the diameter of the discs monotonically decreased and showed a similar trend to that of samples lacking SRA. Based on these findings, we concluded that SRA molecules were on the surface of the C-S-H sheets and mitigated the piling, facilitating water removal from the C-S-H agglomeration in the RH range of 80–40%.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multi-scale investigation on mechanical behavior and microstructural alteration of C-S-H in carbonated Alite paste

Carbonation treatment is a promising option to enhance recycled concrete aggregate (RCA) quality and eventually improve concrete performance. This study investigated the multi-scale mechanical properties of calcium silicate hydrates (C-S-H) in a mature alite paste subjected to accelerated carbonation treatment by testing macro compressive strength, microhardness and nanoindentation. The results show that, carbonation treatment resulted in a heterogeneous distribution of carbonation products in the alite sample. Reinforcement of C-S-H by the randomly precipitated calcite and vaterite crystals prevailed over the nano-structural and compositional alteration of C-S-H induced by carbonation, leading to an increase of nano-indentation modulus at the edge of the sample. Also, the microhardness at the edge zone was markedly higher than that at the core of the carbonated sample. The carbonated peripheral zone with improved nano-scale modulus and microhardness was likely serving as a “hard shell”, contributing to the improved macro compressive strength. The new insights into the multi-scale mechanical properties of carbonated C-S-H contribute to further understanding of the enhanced properties of RCA after carbonation treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The effects of calcium hydroxide and activator chemistry on alkali-activated metakaolin pastes

The impact of calcium hydroxide as an additive in sodium hydroxide- and silicate-activated metakaolin pastes is presented with a primary aim to ascertain the specific effects of calcium on the reaction kinetics and phase formation. FTIR and XRD are employed to understand the interaction of calcium hydroxide (10 wt% replacement of metakaolin) in 1, 5 and 10 M NaOH-activated pastes (and equivalent molarity Na{sub 2}SiO{sub 3}-activated pastes), with a focus on its impact on the nanoscale properties of the sodium-alumino-silicate-hydrate (N-A-S-(H)) gel. In situ FTIR and ICC are used to assess the impact of calcium hydroxide on the reaction kinetics, including the rate of metakaolin dissolution and associated rate of N-A-S-(H) gel growth. It is found that calcium hydroxide is effective at accelerating the reaction kinetics of 5 M Na{sub 2}SiO{sub 3}-activated metakaolin due to the formation of an initial calcium-rich gel that promotes additional metakaolin dissolution and enhances N-A-S-(H) gel formation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A parametric study of accelerated carbonation in alkali-activated slag

Resistance to carbonation is one important attribute that low-CO{sub 2} cement alternatives must possess, and is particularly crucial for cement alternatives subjected to aggressive CO{sub 2} concentrations such as those used in construction of oil wells and wells for below ground carbon sequestration. Here, a parametric study of alkali-activated slag (AAS) carbonation in aggressive environments has been conducted to examine (i) calcium carbonate polymorphism using X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy, and (ii) the extent of calcium carbonate formation and CO{sub 2} adsorption using thermogravimetric analysis (TGA). A range of AASs have been studied by varying the magnesium content of the slag, the activator type (sodium hydroxide and sodium silicate), the activator concentration, and the curing time prior to carbonation. It was uncovered that both (i) magnesium from the slag and (ii) silica from the activating solution are needed to reduce the propensity for the sodium-containing calcium-alumino-silicate-hydrate gel to undergo decalcification.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Development and characteristics of ultra high-performance lightweight cementitious composites (UHP-LCCs)

Highlights: • An ultra high-performance lightweight cementitious composite (UHP-LCC) was designed. • The UHP-LCCs had ultra high strength (>120 MPa) and very low density (3 ). • The UHP-LCCs had high structural efficiency, good functional properties and superior durability. • The strategies and mechanisms on achieving UHP-LCCs with excellent performance were proposed. High strength and light weight are two recent opposite development trends of concrete. This study proposed a design concept of an ultra high-performance lightweight cementitious composite (UHP-LCC), which had a compressive strength of higher than 120 MPa and an air-dried density down to around 1800 kg/m{sup 3}. The UHP-LCCs were innovatively developed by incorporating micro-sized hollow particles with a high strength shell (hollow glass microspheres, HGM) into an ultra-high performance cementitious composite (UHPC). The roles of HGM in the UHP-LCCs were investigated by evaluating the reactivity of the HGM and the mechanisms on achieving the excellent mechanical properties, low density and superior durability were revealed. The Chapelle test results showed that the HGM exhibited some pozzolanic reactivity, which facilitated the reaction between the shell of HGM and the alkali hydration products of the paste matrix. This chemical reaction was conducive to improving the HGM-paste interface and enhancing the mechanical properties. With the use of microspheres with a high stiff shell, the fundamental properties of the UHP-LCCs including thermal insulation, sound absorption, resistance to water ingress and electrical resistivity were improved significantly. The strategies for preparing the UHP-LCCs with high structural efficiency and great performance were proposed. The results of this study provide a new approach for designing and producing a lightweight UHPC, which would be a promising material for long-span structures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The crystal structure of a new calcium aluminate phase containing formate

A new calcium aluminate phase containing formate ions was synthesized and its crystal structure determined. This new phase is indicated as M-phase and was firstly observed in Portland cement pastes hydrated in presence of Ca-formate and in excess of water. The crystal structure of the M-phase was successfully solved in the R-3 space group of the trigonal system on the basis of synchrotron X-ray single crystal diffraction data. The structural model was confirmed by Rietveld refinement of the powder diffraction data acquired on the synthesized pure sample. The crystal structure of the M-phase is similar to that of ettringite, being characterized by columns of AlO{sub 6} octahedra alternating with groups of three edge-sharing CaO{sub 7} polyhedra. The formate ions (HCOO){sup −} share two oxygens with Ca polyhedra and are located in the interspace between the columns. The crystal structure of the M-phase testifies the strong interaction occurring between small organic molecules as formate and the calcium aluminate components of Portland cement.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Screening candidate supplementary cementitious materials under standard and accelerated curing through time-series surface resistivity measurements and change-point detection

Time-series surface resistivity (SR) measurements are evaluated as an indicator of pozzolanicity in concretes containing 13 materials of both known and unknown pozzolanicity, under standard and accelerated curing conditions, and the results were validated against portlandite consumption obtained through thermogravimetric analysis. Change-point detection (CPD) analysis is applied to the data to provide a rigorous indicator of hydration age of the onset and rate of the pozzolanic reaction, if occurring. The SR measurements were able to capture the onset of the pozzolanic reactions in concretes curing at elevated temperature regimes, which allows determination of pozzolanicity weeks earlier than at standard curing temperatures. Using CPD along with slope analysis allows a comprehensive analysis of a material's reactivity and determination of pozzolanicity in as quickly as two days. Time-series SR measurements at elevated curing conditions, along with limits on material composition, are recommended for determination of pozzolanic reactivity in novel or variable materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Limestone calcined clay cement and concrete: A state-of-the-art review

This article reviews the rapidly developing state-of-the-art literature available on the subject of the recently developed limestone calcined clay cement (LC{sup 3}). An introduction to the background leading to the development of LC{sup 3} is first discussed. The chemistry of LC{sup 3} hydration and its production are detailed. The influence of the properties of the raw materials and production conditions are discussed. The mixture design of concrete using LC{sup 3} and the mechanical and durability properties of LC{sup 3} cement and concrete are then compared with other cements. At the end the economic and environmental aspects of the production and use of LC{sup 3} are discussed. The paper ends with suggestions on subjects on which further research is required.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Physical-chemical-mechanical quantitative assessment of the microstructural evolution in Portland-limestone cement pastes exposed to magnesium sulfate attack at low temperature

The changes in structural integrity and microstructure of Portland-limestone cement pastes were investigated in the course of magnesium sulfate attack at low temperature. A deterioration front, consisting of three distinct layers (brucite, gypsum, leached cement matrix), swelled in time due to the expansive nature of the deterioration products, generating cracks and subsequently detaching from the sound cement matrix, continuously promoting the process. Gypsum and thaumasite characterized the leached matrix, which experienced extensive cross-linking of the aluminosilicate structures, as a result of decalcification and dealumination of the calcium silicate hydrates (C(A)SH), impairing the overall mechanical performance. CSH of low packing density was most severely affected by the process, as confirmed by the significant drop in nano-mechanical properties. The increased rate of deterioration with limestone content was tentatively attributed to the prevalent morphology of the CSH phase. Results were validated by thermodynamic simulations, indicating that the real systems did not reach equilibrium.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Time-dependent water vapor desorption isotherm model of hardened cement paste

Highlights: • Short-term and long-term desorption isotherms of hardened cement paste are reviewed. • Water content at RH depends on both thermodynamic and microstructural equilibria. • An extended GAB equation is proposed to fit the cavitation drop during desorption. • A dynamic time-dependent sorption isotherm model is shown and used for simulations. • Numerical results capture anomalous drying in the same RH as seen experimentally. This study aims to enhance moisture transport modeling by elucidating the so-called anomalous water diffusion in cementitious materials. Water desorption isotherms are measured from samples at various drying stages using techniques with different durations to quantify the impact of the drying duration on the water sorption ability. A single water sorption isotherm does not solely give a relationship between the water content and relative humidity but also represents the state of microstructure. The continuous evolution of a desorption isotherm due to drying-induced microstructural rearrangement is demonstrated. For numerical modeling, the microstructural alteration can be explicitly considered through a dynamic desorption isotherm model, which governs the local thermodynamic equilibrium at the capillary meniscus. This approach is implemented into a multiphase transport code, whose ability to predict drying is validated using literature data. Finally, the effect of prolonged drying on the colloidal nature of the calcium-silicate-hydrate gel is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Advances in imaging, scattering, spectroscopy, and machine learning-aided approaches for multiscale characterization of cementitious systems

Recent progress in methods used in the multiscale characterization of cementitious systems is reviewed, focusing on advances in imaging, scattering, and spectroscopy. The review includes relevant applications and developments in machine learning and other data analytics approaches to enhance characterization. Developments in imaging using light and electron microscopy as well as x-ray (i.e., from synchrotron) methods are summarized. Updates include scanning electron microscopy (SEM), transmission electron microscopy (TEM), tomography, and holography. A critical overview of spectroscopy (e.g., MAS NMR, Raman) and scattering (e.g., neutron, x-ray, synchrotron x-ray) methods is provided, and the intersection of these with imaging is developed (e.g., Raman imaging). Additionally, the paper summarizes recent developments in and implementations of state-of-the-art machine-learning algorithms and data analytics methods for automated, systematic, and/or quantitative analyses of image data sets. The review considers but is not limited to the application of these methods for investigating the hydration and microstructure development of cement phases, low-carbon-footprint cements (e.g., limestone calcined clay cements, LC3), environmental interactions (e.g., ASR) and model systems. Finally, the present work provides a critical presentation of advances in characterization methods that link together the composition and multiscale structure of cementitious materials.

42 ENGINEERING↗
DOE OSTI2025

Intrinsic mechanical properties and seeding effect of tobermorite synthesized in supercritical water

This publication reports for the first time the physiochemical, the intrinsic mechanical properties and the seed effect of anomalous Al-substituted 11 Å tobermorite synthesized via the innovative supercritical hydrothermal flow process at 400 °C and 25 MPa. This approach allows synthesizing highly crystalline tobermorite fibers in only 8 s, with characteristics very close to the natural tobermorite. The anomalous 11 Å tobermorite exhibits aluminosilicate chains with a high polymerisation degree and a less defective structure compared to materials produced via the conventional hydrothermal method. Furthermore, the intrinsic mechanical properties of Al-tobermorite synthesized in supercritical water are investigated for the first time by High-Pressure XRD. This Al-substituted 11 Å tobermorite is characterised by higher incompressibility along the b-axis and bulk modulus K0 in comparison with what is commonly observed for other synthetic tobermorite. The tobermorite acts as nucleation points to trigger the quick formation of the hydration product in Portland cement paste.

Calcium silicate hydrate↗
DOE OSTI2020

Oxygen Affinity: The Missing Link Enabling Prediction of Proton Conductivities in Doped Barium Zirconates

Proton-conducting oxides, specifically doped barium zirconates, have garnered much attention as electrolytes for solid-state electrochemical devices operable at intermediate temperatures (400–600 °C). In chemical terms, hydration energy, E hyd , and proton–dopant association energy, E as , are two key parameters that determine whether an oxide exhibits fast proton conduction, but to date ab initio studies have for the most part studied each parameter separately, with no clear correlation with proton conductivity identified in either case. Here, we demonstrate that the oxygen affinity, E O.dopant , defined as the energy released when an oxide ion enters an oxygen vacancy close to a dopant atom, is the missing link between these two parameters and correlates well with experimental proton conductivities in doped barium zirconates. Ab initio calculations of point defects and their complexes in Sc-, In-, Lu-, Er-, Y-, Gd-, and Eu-doped barium zirconates are used to determine E hyd , E as , E O.dopant , and the hydrogen affinity, E H.host , of each system. These four energy terms are related by E hyd = E O.dopant + 2E H.host + 2E as . Complementary impedance spectroscopy measurements reveal that the stronger the calculated oxygen affinity of a system, the higher the proton conductivity at 350 °C. Although the proton trapping site is also an important factor, the results show that oxygen affinity is an excellent predictor of proton conductivity in these materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Enthalpy of Uranium Adsorption onto Hematite

The influence of temperature on the adsorption of metal-ions at the solid-water interface is often overlooked, despite the important role that adsorption plays in metal ion fate and transport in the natural environment where temperatures vary widely. Herein, we examine the temperature-dependent adsorption of uranium, a widespread radioactive contaminant, onto the ubiquitous iron oxide, hematite. The multi-temperature batch adsorption data and surface complexation models indicate that adsorption of uranium, as the hexavalent uranyl (UO 2 2+ ) ion, increases significantly with increasing temperature, with an adsorption enthalpy (ΔH ads ) of +71 kJ mol –1 . We suggest that this endothermic, entropically-driven adsorption behavior is linked to reorganization of the uranyl-ion-hydration and interfacial water structures upon U VI adsorption at the hematite surface. Altogether, this work provides fundamental insight into the thermodynamics driving metal-ion adsorption reactions and provides the specific enthalpy value necessary for improved predictive geochemical modeling of U VI adsorption in the environment.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Low-Energy Isomers of the Magic Number H + (H 2 O) 21 Cluster

Electronic structure calculations are used to characterize low-energy isomers of H + (H 2 O) 21 . Eleven different classes of isomers, based on the (H 2 O) 20 pentagonal dodecahedron with the excess proton localized on the surface (as a hydrated hydronium ion) and the “extra” water molecule located in the interior of the cluster, are characterized. In 10 of these classes, the internal water molecule is engaged in six 5-membered rings, but in the remaining class, which is predicted to start at only 0.6 kcal/mol above the global minimum, the internal water is engaged in a 4- membered ring, an additional 6-membered ring, and four 5- membered rings. In addition, isomers with two 4-membered rings and two 6-membered rings on the cluster surface are predicted to start at only ∼1.3 kcal/mol above the lowest-energy dodecahedralbased structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Moving beyond the Solvent-Tip Approximation to Determine Site-Specific Variations of Interfacial Water Structure through 3D Force Microscopy

Although interfacial solution structure impacts environmental, biological, and technological phenomena, including colloidal stability, protein assembly, heterogeneous nucleation, and water desalination, its molecular details remain poorly understood. Here, we visualize the three-dimensional (3D) hydration structure at the boehmite(010)-water interface using fast force mapping (FFM). Using a self-consistent scheme to decouple long-range tip-sample interactions from short-range solvation forces, we obtain the solution structure with lattice resolution. The results are benchmarked against molecular dynamics simulations that explicitly include the effects of the tip with different levels of approximation and systematically account for tip size, chemistry, and confinement effects. We find four laterally structured water layers within 1 nm of the surface, with the highest water densities at sites adjacent to hydroxyl groups. The key features beyond the first two layers can only be predicted using a full-scale simulation of the boehmite-water-silica system. Our findings further reveal a complex relationship between site-specific chemistry, water density, and long-range particle interactions; and present important advances toward quantitative data interpretation in 3D FFM.

36 MATERIALS SCIENCE↗