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Pozzolanic reaction of volcanic ash with hydrated lime is thought to dominate the cementing fabric and durability of 2000-year-old Roman harbor concrete. Pliny the Elder, however, in first century CE emphasized rock-like cementitious processes involving volcanic ash (pulvis) \"that as soon as it comes into contact with the waves of the sea and is submerged becomes a single stone mass (fierem unum lapidem), impregnable to the waves and every day stronger\" (Naturalis Historia 35.166). Pozzolanic crystallization of Al-tobermorite, a rare, hydrothermal, calcium-silicate-hydrate mineral with cation exchange capabilities, has been previously recognized in relict lime clasts of the concrete. Synchrotron-based X-ray microdiffraction maps of cementitious microstructures in Baianus Sinus and Portus Neronis submarine breakwaters and a Portus Cosanus subaerial pier now reveal that Al-tobermorite also occurs in the leached perimeters of feldspar fragments, zeolitized pumice vesicles, and in situ phillipsite fabrics in relict pores. Production of alkaline pore fluids through dissolution-precipitation, cation-exchange and/or carbonation reactions with Campi Flegrei ash components, similar to processes in altered trachytic and basaltic tuffs, created multiple pathways to post-pozzolanic phillipsite and Al-tobermorite crystallization at ambient seawater and surface temperatures. Long-term chemical resilience of the concrete evidently relied on water-rock interactions, as Pliny the Elder inferred. Raman spectroscopic analyses of Baianus Sinus Al-tobermorite in diverse microstructural environments indicate a cross-linked structure with Al3+ substitution for Si4+ in Q3 tetrahedral sites, and suggest coupled [Al3++Na+] substitution and potential for cation exchange. The mineral fabrics provide a geoarchaeological prototype for developing cementitious processes through low-temperature rock-fluid interactions, subsequent to an initial phase of reaction with lime that defines the activity of natural pozzolans. These processes have relevance to carbonation reactions in storage reservoirs for CO2 in pyroclastic rocks, production of alkali-activated mineral cements in maritime concretes, and regenerative cementitious resilience in waste encapsulations using natural volcanic pozzolans.

The pyroclastic aggregate concrete of Trajan’s Markets (110 CE), now Museo Fori Imperiali in Rome, has absorbed energy from seismic ground shaking and long-term foundation settlement for nearly two millenia while remaining largely intact at the structural scale. The scientific basis of this exceptional service record is explored through computed tomography of fracture surfaces and synchroton X-ray microdiffraction analyses of a reproduction of the standardized hydrated lime–volcanic ash mortar that binds decimeter-sized tuff and brick aggregate in the conglomeratic concrete. The mortar reproduction gains fracture toughness over 180 d through progressive coalescence of calcium–aluminum-silicate–hydrate (C-A-S-H) cementing binder with Ca/(Si+Al) ≈ 0.8–0.9 and crystallization of sträätlingite and siliceous hydrogarnet (katoite) at ≥90 d, after pozzolanic consumption of hydrated lime was complete. Platey strääätlingite crystals toughen interfacial zones along scoria perimeters and impede macroscale propagation of crack segments. In the 1,900-y-old mortar, C-A-S-H has low Ca/(Si+Al) ≈ 0.45–0.75. Dense clusters of 2- to 30-µm sträääätlingite plates further reinforce interfacial zones, the weakest link of modern cement-based concrete, and the cementitious matrix. These crystals formed during long-term autogeneous reaction of dissolved calcite from lime and the alkali-rich scoriae groundmass, clay mineral (halloysite), and zeolite (phillipsite and chabazite) surface textures from the Pozzolane Rosse pyroclastic flow, erupted from the nearby Alban Hills volcano. The clast-supported conglomeratic fabric of the concrete presents further resistance to fracture propagation at the structural scale. Significance A volcanic ash–lime mortar has been regarded for centuries as the principal material constituent that provides long-term durability to ancient Roman architectural concrete. A reproduction of Imperial-age mortar based on Trajan’s Markets (110 CE) wall concrete resists microcracking through cohesion of calcium–aluminum–silicate–hydrate cementing binder and in situ crystallization of platey strätlingite, a durable calcium-aluminosilicate mineral that reinforces interfacial zones and the cementitious matrix. In the 1,900-y-old mortar dense intergrowths of the platey crystals obstruct crack propagation and preserve cohesion at the micron scale. Trajanic concrete provides a proven prototype for environmentally friendly conglomeratic concretes that contain ∼88 vol % volcanic rock yet maintain their chemical resilience and structural integrity in seismically active environments at the millenial scale.

Synchrotron X-ray diffraction images are increasingly used to characterize not only structural and microstructural features of polycrystalline materials, but also crystal preferred orientation distributions. Diffraction data can be analyzed quantitatively and efficiently with the Rietveld method and here the detailed procedure is reported from the experiment to the calibration of the two-dimensional detector and full analysis of the sample. In particular, we emphasize the advantage of doing the calibration inside the Rietveld least-squares fitting instead of a preliminary graphical calibration. Then the procedure is described to quantify crystal preferred orientations with the Rietveld method implemented in software “Materials Analysis Using Diffraction”. The process is illustrated for a US “nickel” coin, a 75 at.% copper 25 at.% nickel alloy with face-centered cubic structure and a strong cube texture.

Slates transform from shales at relatively low-grade metamorphic conditions. They often reveal highly anisotropic microstructures and very strong crystal alignment that must be considered in seismic modeling and engineering construction. In this paper, we investigate nine slate samples from four regions in northern China: Fangshan, Beijing; Xushui, Hebei; Damao Qi, Inner Mongolia; and Zhengxiangbai Qi, Inner Mongolia. The microstructural characteristics were analyzed with scanning electron microscopy and explored with digital crystal size distribution analysis. Preferred crystal orientation characteristics of slate minerals were investigated with high-energy synchrotron X-ray diffraction and subsequent Rietveld refinement. This research shows that the main components of slates in this study are quartz, muscovite, chlorite, and minor orthoclase. In terms of morphology, muscovite, chlorite, and quartz are strongly elongated and oriented. The crystallographic orientation of sheet silicates is very strong, exceeding 100 multiples of random distribution for chlorite from Fangshan. However, quartz with a preferred strong shape orientation has a crystallographic preferred orientation close to random. The preferred orientation characteristics of minerals serve as a basis for calculating elastic properties and anisotropies of the Chinese slate samples that contribute significantly to seismic anisotropy documented in northern China.

The study of orientation variant selection helps to reveal the mechanism and dynamic process of martensitic transformations driven by temperature or pressure/stress. This is challenging due to the multiple variants which may coexist. While effects of temperature and microstructure in many martensitic transformations have been studied in detail, effects of stress and pressure are much less understood. Here, an in situ variant selection study of Mn₂O₃ across the cubic-to-orthorhombic martensitic transformation explores orientation variants at pressures up to 51.5 GPa and stresses up to 5.5 GPa, using diamond anvil cells in radial geometry with synchrotron X-ray diffraction. The diamonds not only exert pressure but also impose stress and cause plastic deformation and texture development. The crystal orientation changes were followed in situ and a {110} c 〈001〉 c //(100)ₒ 〈010〉ₒ relationship was observed. Only the {110} c plane perpendicular to the stress direction was selected to become (100)ₒ, resulting in a very strong texture of the orthorhombic phase. Contrary to most other martensitic transformations, this study reveals a clear and simple variant selection that is attributed to structural distortions under pressure and stress.

The size of nanocrystals provides a limitation on dislocation activity and associated stress-induced deformation. Dislocation-mediated plastic deformation is expected to become inactive below a critical particle size, which has been proposed to be between 10 and 30 nanometers according to computer simulations and transmission electron microscopy analysis. However, deformation experiments at high pressure on polycrystalline nickel suggest that dislocation activity is still operative in 3-nanometer crystals. Substantial texturing is observed at pressures above 3.0 gigapascals for 500-nanometer nickel and at greater than 11.0 gigapascals for 20-nanometer nickel. Surprisingly, texturing is also seen in 3-nanometer nickel when compressed above 18.5 gigapascals. The observations of pressure-promoted texturing indicate that under high external pressures, dislocation activity can be extended down to a few-nanometers-length scale.

Synchrotron X-ray diffraction images are increasingly used to characterize crystallographic preferred orientation distributions (texture) of fine-grained polyphase materials. Diffraction images can be analyzed quantitatively with the Rietveld method as implemented in the software package Materials Analysis Using Diffraction. Here we describe the analysis procedure for diffraction images collected with high energy X-rays for a complex, multiphase shale, and for those collected in situ in diamond anvil cells at high pressure and anisotropic stress.

Crystallographic preferred orientation (CPO) of post-perovskite (Mg,Fe)SiO 3 (pPv) has been believed to be one potential source of the seismic anisotropic layer at the bottom of the lower mantle (D″ layer). However, the natural CPO of pPv remains ambiguous in the D″ layer. Here we have carried out the deformation experiments of pPv-(Mg 0.75 ,Fe 0.25 )SiO 3 using synchrotron radial X-ray diffraction in a membrane-driven laser-heated diamond anvil cell from 135 GPa and 2,500 K to 154 GPa and 3,000 K. Our results show that the intrinsic texture of pPv-(Mg 0.75 ,Fe 0.25 )SiO 3 should be (001) at realistic P – T conditions of the D″ layer, which can produce a shear wave splitting anisotropy of ∼3.7% with V SH > V SV . Considering the combined effect of both pPv and ferropericlase, we suggest that 50% or less of deformation is sufficient to explain the origin of the shear wave anisotropy observed seismically in the D″ layer beneath the circum-Pacific rim. The source of the anisotropic layer (D'' layer) at the bottom of the lower mantle remains unclear. Here, using high pressure and temperature experiments, the authors find that seismic anisotropy observed at the D'' layer is caused by 50% deformation of the minerals post-perovskite and ferropericlase.

Serpentine minerals have received a lot of attention because of their unique crystal structures, their wide occurrence in orogenic belts and their potential role in contributing seismic anisotropy in subducting slabs. Several studies have investigated crystal preferred orientation (CPO) in high temperature antigorite serpentinites from Japan, the Alps, Spain, Cuba and Tibet, documenting significant crystal alignment. However, only a limited number of lower grade serpentines have been explored to date. Mainly because of submicroscopic microstructural heterogeneities CPO cannot be measured with conventional methods such as optical microscopy and EBSD. In this study 15 serpentinites from different tectonic settings in California, the Central Alps and Northern Spain have been investigated, mainly with high energy synchrotron X-ray diffraction, to quantify bulk crystal alignment. We find that CPO is strong on sheared surfaces of fractured blocks and secondary veins but the bulk of most serpentinite samples, except high-grade recrystallized antigorite serpentinite, show only weak crystal alignment. Correspondingly calculated seismic anisotropy based on CPO is not very significant. This is supported by very heterogeneous microstructures as documented with SEM and TEM analyses.

Clinopyroxene and plagioclase (andesine) microlites in an obsidian flow from Glass Mountain (NE California, USA) display strong alignment. Synchrotron X-ray diffraction, coupled with Rietveld analysis, was used to quantify crystallographic-preferred orientation (CPO). Clinopyroxene, with a rod-shaped morphology, shows a strong alignment of [001] in the flow direction and (010) aligned parallel to the inferred flow plane. Andesine, with a platy morphology, displays an alignment of (010) platelets in the flow plane. Some pole densities exceed 90 multiples of random distribution. Applying a model of rigid ellipsoidal inclusions in a viscous matrix, the local pure shear strains are between 2 and 3.