Ultra-high performance alkali activated material with silica fume and nanosilica

Based on the principles of ultra-high performance concrete a cement free, alkali-activated system was optimized in order to enhance the strength and durability. This system is based on a ground granulated blast furnace slag and the activator is a combination of potassium water-glass and potassium hydroxide. Furthermore, inorganic fines were used for enhancing the packing density. As aggregates, quartz sand (0-2 mm) and quartz powder are added. The rheological properties could be improved by adding a certain amount of silica fume. A water/binder ratio of 0.25 was realized using a certain mixing procedure on a high-intensity mixer. The compressive strength reaches 150 MPa after 14 days, which lies in the range of an ultra-high performance concrete. The rheology was measured by using a rotation rheometer depending on time and silica fume content. Different silica fumes were tested in order to vary the grain sized distribution and the chemical composition. Beneath silica fume with a d50-value of 2 µm also nanosilica with a d50 value of 0.2 µm was tested in terms of gaining higher strength and durability and as well in terms to enhance the rheological properties. The silica fume could be substituted by nanosilica, which proofs that the improving rheology is not only due to the ball bearing effect of silica fume. The microstructure of the hardened AAM was investigated using SEM, FTIR, XRD and MIP. Please click Additional Files below to see the full abstract

Determination of Suitable Imaging Techniques for the Investigation of the Bonding Zones of Asphalt Layers

The material behavior of asphalt depends on its composition of aggregate, bitumen, and air voids. Asphalt pavements consist of multiple layers, making the interaction of the materials at the layer boundary important so that any stresses that occur can be relieved. The material behavior at the layer boundary is not yet understood in detail, as further methods of analysis are lacking in addition to mechanical methods. For this reason, the layer boundary of asphalt structures was analyzed using imaging methods. The aim of this research was to find an imaging method that allows a detailed analysis of the bonding zone of asphalt layers. Two different imaging techniques were used for this purpose. One is a 2-D imaging technique (asphalt petrology) and the other is a 3-D imaging technique (high-resolution computed tomography). Image analysis is a widely used technique in materials science that allows to analyze the material behavior and their composition. In this research, attention was paid to the analysis of the position of the bitumen emulsion, because the contained bitumen is supposed to bond the layers together. It was found that the application of 2-D imaging (asphalt petrology) lacked the precision for a detailed analysis of the individual materials at the layer boundary. With high-resolution computed tomography, a detailed view is possible to visualize the individual materials at the layer boundary in 3D. However, it is difficult to differentiate the materials because there are no gradations in the gray values due to the identical densities. However, it is possible to differentiate between the bitumen from the asphalt and from the emulsion if a high-density tracer is added to the bitumen emulsion for the CT studies. The results of the investigations are presented in this article

Synthetic Determination of Specific Density, Specific Surface Area and Particle Size Distribution of Cementitious Powder Materials

The use of cementitious materials for construction of buildings and structures started during ancient civilization. Science of modifying physical and chemical properties of cementitious materials is a continual process which is because of a need to increase reactivity and improve strength and durability properties of binders. Due to increasing demand of modern infrastructures and continual depleting of binder sources the scientist, engineers and researchers work hard on improving binding properties of cementitious materials for construction of low cost and durable structures. Among of the factors which affect binding properties of cementitious properties are densities, surface areas and particle size distribution. Several methods and procedures have been developed to determine these physical properties on which other require huge capital investment and others takes long time to complete a test which hinders further investigation and improvement of alternative binders.This study investigated that there exist an ‘S’ curve similar to particle size distribution curve when time air flow against weights of sample measured using Blaine apparatus is drawn. The gradients of lower and middle lines of the curve and values at turning points were synthesized to determine specific densities, specific surface areas and particle size distribution of powder materials. The approach is time saving and the equipment is affordable by many researchers. In order to have accurate results the approach can be automated

Dissolution of β-C₂S Cement Clinker: Part 2 Atomistic Kinetic Monte Carlo (KMC) Upscaling Approach

Cement clinkers containing mainly belite (β-C₂S as a model crystal), replacing alite, offer a promising solution for the development of environmentally friendly solutions to reduce the high level of CO₂ emissions in the production of Portland cement. However, the much lower reactivity of belite compared to alite limits the widespread use of belite cements. Therefore, this work presents a fundamental atomistic computational approach for comprehending and quantifying the mesoscopic forward dissolution rate of β-C₂S, applied to two reactive crystal facets of (100) and (1¯00). For this, an atomistic kinetic Monte Carlo (KMC) upscaling approach for cement clinker was developed. It was based on the calculated activation energies (ΔG*) under far-from-equilibrium conditions obtained by a molecular dynamic simulation using the combined approach of ReaxFF and metadynamics, as described in the Part 1 paper in this Special Issue. Thus, the individual atomistic dissolution rates were used as input parameters for implementing the KMC upscaling approach coded in MATLAB to study the dissolution time and morphology changes at the mesoscopic scale. Four different cases and 21 event scenarios were considered for the dissolution of calcium atoms (Ca) and silicate monomers. For this purpose, the (100) and (1¯00) facets of a β-C₂S crystal were considered using periodic boundary conditions (PBCs). In order to demonstrate the statistical nature of the KMC approach, 40 numerical realizations were presented. The major findings showed a striking layer-by-layer dissolution mechanism in the case of an ideal crystal, where the total dissolution rate was limited by the much slower dissolution of the silicate monomer compared to Ca. The introduction of crystal defects, namely cutting the edges at two crystal boundaries, increased the overall average dissolution rate by a factor of 519

Dissolution of β-C₂S Cement Clinker: Part 1 Molecular Dynamics (MD) Approach for Different Crystal Facets

A major concern in the modern cement industry is considering how to minimize the CO₂ footprint. Thus, cements based on belite, an impure clinker mineral (CaO)₂SiO₂ (C₂S in cement chemistry notation), which forms at lower temperatures, is a promising solution to develop eco-efficient and sustainable cement-based materials, used in enormous quantities. The slow reactivity of belite plays a critical role, but the dissolution mechanisms and kinetic rates at the atomistic scale are not known completely yet. This work aims to understand the dissolution behavior of different facets of β-C₂S providing missing input data and an upscaling modeling approach to connect the atomistic scale to the sub-micro scale. First, a combined ReaxFF and metadynamics-based molecular dynamic approach are applied to compute the atomistic forward reaction rates (RD) of calcium (Ca) and silicate species of (100) facet of β-C₂S considering the influence of crystal facets and crystal defects. To minimize the huge number of atomistic events possibilities, a generalized approach is proposed, based on the systematic removal of nearest neighbors’ crystal sites. This enables us to tabulate data on the forward reaction rates of most important atomistic scenarios, which are needed as input parameters to implement the Kinetic Monte Carlo (KMC) computational upscaling approach. The reason for the higher reactivity of the (100) facet compared to the (010) is explained

Comparative environmental footprint analysis of ultra-high-performance concrete using Portland cement and alkali-activated materials

Considering the ambitious greenhouse gas emission reduction and efficient use of resource targets set by the Sustainable Development Goals and the importance of concrete structures to achieve these goals, there is an increasing need to study the environmental performance of different concrete production alternatives. Cement is one of the main building materials that contribute significantly to global warming; therefore, studying the environmental performance of innovative binders that can substitute the use of cement is highly recommended. This article investigates the climate, material, energy, and water footprints of four innovative mixtures of ultra-high-performance concrete (UHPC) with a binder made of alkali-activated materials in comparison with the one made of Portland cement. Footprint analysis is carried out within cradle-to-grave life cycle assessment boundaries. Within the life cycle assessment, the functional unit defines the quantification of the final product or service. The functional units of the UHPC were adapted for the comparability of concrete mixtures with different compressive strengths. The results show that UHPC made with an alkali-activated material has 32%–45% better performance in terms of a climate footprint and 19%–33% better performance in terms of material footprints, whereas a trade-off can be seen regarding 44%–83% higher energy footprints and 75%–146% higher water footprints. The disadvantages in energy and water footprints are caused by waterglass. When allocation is considered, mixtures with high silica fume content have higher environmental footprints

Re-assessing the diversity of negative strand RNA viruses in insects.

The spectrum of viruses in insects is important for subjects as diverse as public health, veterinary medicine, food production, and biodiversity conservation. The traditional interest in vector-borne diseases of humans and livestock has drawn the attention of virus studies to hematophagous insect species. However, these represent only a tiny fraction of the broad diversity of Hexapoda, the most speciose group of animals. Here, we systematically probed the diversity of negative strand RNA viruses in the largest and most representative collection of insect transcriptomes from samples representing all 34 extant orders of Hexapoda and 3 orders of Entognatha, as well as outgroups, altogether representing 1243 species. Based on profile hidden Markov models we detected 488 viral RNA-directed RNA polymerase (RdRp) sequences with similarity to negative strand RNA viruses. These were identified in members of 324 arthropod species. Selection for length, quality, and uniqueness left 234 sequences for analyses, showing similarity to genomes of viruses classified in Bunyavirales (n = 86), Articulavirales (n = 54), and several orders within Haploviricotina (n = 94). Coding-complete genomes or nearly-complete subgenomic assemblies were obtained in 61 cases. Based on phylogenetic topology and the availability of coding-complete genomes we estimate that at least 20 novel viral genera in seven families need to be defined, only two of them monospecific. Seven additional viral clades emerge when adding sequences from the present study to formerly monospecific lineages, potentially requiring up to seven additional genera. One long sequence may indicate a novel family. For segmented viruses, cophylogenies between genome segments were generally improved by the inclusion of viruses from the present study, suggesting that in silico misassembly of segmented genomes is rare or absent. Contrary to previous assessments, significant virus-host codivergence was identified in major phylogenetic lineages based on two different approaches of codivergence analysis in a hypotheses testing framework. In spite of these additions to the known spectrum of viruses in insects, we caution that basing taxonomic decisions on genome information alone is challenging due to technical uncertainties, such as the inability to prove integrity of complete genome assemblies of segmented viruses

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

The IceCube Neutrino Observatory, the Pierre Auger Observatory and the Telescope Array: Joint Contribution to the 34th International Cosmic Ray Conference (ICRC 2015)

We have conducted three searches for correlations between ultra-high energy cosmic rays detected by the Telescope Array and the Pierre Auger Observatory, and high-energy neutrino candidate events from IceCube. Two cross-correlation analyses with UHECRs are done: one with 39 cascades from the IceCube `high-energy starting events' sample and the other with 16 high-energy `track events'. The angular separation between the arrival directions of neutrinos and UHECRs is scanned over. The same events are also used in a separate search using a maximum likelihood approach, after the neutrino arrival directions are stacked. To estimate the significance we assume UHECR magnetic deflections to be inversely proportional to their energy, with values $3^\circ$, $6^\circ$ and $9^\circ$ at 100 EeV to allow for the uncertainties on the magnetic field strength and UHECR charge. A similar analysis is performed on stacked UHECR arrival directions and the IceCube sample of through-going muon track events which were optimized for neutrino point-source searches.Comment: one proceeding, the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands; will appear in PoS(ICRC2015