Feasibility of sulfur concrete for martian constructions

A significant step in space exploration during the 21st century will be the human settlement on Mars. Instead of transporting all the construction materials from Earth to the red planet with incredibly high cost, using Martian soil to construct a site on Mars is a superior choice. Mars has long been considered a “sulfur-rich planet”. Studies of Martian meteorites suggest elevated sulfur concentrations in the interior, and Martian surface deposits contain high levels of sulfur (SO3 up to ~37 wt%, average ~6 wt%), likely in the form of sulfate salts1. To let the thoughts become facts, a new construction material using simulated Martian soil and molten sulfur is developed. In fact, sulfur concrete is not a new concept. The utilization of sulfur as a molten bonding agent can be traced back to prehistoric times2. Sulfur concretes are being produced by first hot-mixing sulfur (or modified sulfur) and aggregates, which allows the sulfur binder crystalize as monoclinic sulfur (Sβ), then letting the mixture cool down while sulfur transform to the stable orthorhombic polymorph (Sα) to achieve a reliable building material. In addition to the raw material availability, the utilization of sulfur concrete has many advantages compared to conventional Portland cement concrete. The strength reaches similar levels while the fatigue life, low temperature sustainability, and the curing time are superior, a minimum of 70-80 % of the ultimate compressive strength is reached within 24 hours

Cohesive crack analysis of size effect for samples with blunt notches and generalized size effect curve for quasi-brittle materials

This paper deals with the study of size effect on structural strength for quasi-brittle materials under mode I fracture conditions. By using a linear cohesive crack model, accurate numerical simulations were performed to compute the size effect curves for two test configurations – namely, the three-point bending test with span-to-depth ratio equal to 3 and the center crack panel test – featuring sharp notches and blunt notches whose width is also scaled with the specimen dimension. The analysis of the results shows that, as the specimen size tends to infinity, the asymptotic behavior depends on the type of notch. For sharp notches the size effect curve tends asymptotically to Bažant's Size Effect Law. On the contrary, for blunt notches the size effect curve tends to a horizontal asymptote corresponding to the elastic limit. The elastic limit can be calculated by the tensile strength reduced by the stress concentration factor at the tip of the blunt notch and it depends on the geometry of the specimen. Furthermore, the numerical results were utilized to derive the expression of a Generalized Cohesive Size Effect Curve (GCSEC) which agrees well with Bažant's Universal Size Effect Law (USEL) and with some experimental data gathered from the literature

Modelling of autogenous healing for regular concrete via a discrete model

In this paper a numerical model for autogenous healing of normal strength concrete is presented in detail, along with preliminary results of its validation, which is planned to be achieved by comparing the results of numerical analyses with those of a dedicated experimental campaign. Recently the SMM (Solidification-Microprestress-Microplane model M4) model for concrete, which makes use of a modified microplane model M4 and the solidification-microprestress theory, has been extended to incorporate the autogenous healing effects. The moisture and heat fields, as well as the hydration degree, are obtained from the solution of a hygro-thermo-chemical problem, which is coupled with the SMM model. The updated model can also simulate the effects of cracking on the permeability and the restoring effect of the self-healing on the mechanical constitutive laws, i.e. the microplane model. In this work, the same approach is introduced into a discrete model, namely the Lattice Discrete Particle Model (LDPM). A numerical example is presented to validate the proposed computational model employing experimental data from a recent test series undertaken at Politecnico di Milano

Calibration and comparison of concrete models with respect to experimental data

At the beginning of the 21st century, civil engineers more than ever face the often-contradictory demands for designing larger, safer and more durable structures at a lower cost and in shorter time. Concrete has been used for many centuries as a safe and durable building material. Two of the main advantages of concrete are its high compressive strength and that it can be cast on the construction site into a variety of shapes and sizes. Many different constitutive models have been developed to fulfill the above mentioned requirements and describe/predict the behavior and failure of concrete. The never ending challenge for engineers is to choose and set up the appropriate material model for the modeling of structures or structural elements. Therefore, the primary objective of the present research is to calibrate, validate and compare different constitutive models with respect to an extensive set of experimental data. Depending on the application and availability of data, the expected prediction quality of the available models may vary significantly. The studied material models include the microplane models M4 and M7, the damage plasticity models available in commercial (ATENA) or open source (OOFEM) finite element codes, e.g. the Grassl-Jirasek material model. Moreover, the Lattice-Discrete-Particle- Model (LDPM), implemented in the solver MARS, is utilized. We present a comparison of these models with regard to the number of input parameters, their physical meaning, the ease of calibration and their predictive capabilities by utilizing a large set of experimental data derived from specimens, cast from the same batch. All models are calibrated using three mean value nominal stress-strain curves obtained from a notched three-point bending, uniaxial compression and compression under passive confinement test. The calibrated numerical models are then used to predict the results of the remaining experiments, i.e. 3-point bending tests of 4 sizes with various notch depths, splitting tests of 5 sizes, direct tensions tests and torsion tests. These data then serve to assess the prediction quality of the models

Characterization of concrete failure behavior: a comprehensive experimental database for the calibration and validation of concrete models

Concrete is undoubtedly the most important and widely used construction material of the late twentieth century. Yet, mathematical models that can accurately capture the particular material behavior under all loading conditions of significance are scarce at best. Although concepts and suitable models have existed for quite a while, their practical significance is low due to the limited attention to calibration and validation requirements and the scarcity of robust, transparent and comprehensive methods to perform such tasks. In addition, issues such as computational cost, difficulties associated with calculating the response of highly nonlinear systems, and, most importantly, lack of comprehensive experimental data sets have hampered progress in this area. This paper attempts to promote the use of advanced concrete models by (a) providing an overview of required tests and data preparation techniques; and (b) making a comprehensive set of concrete test data, cast from the same batch, available for model development, calibration, and validation. Data included in the database ‘http://www.baunat.boku.ac.at/cd-labor/downloads/versuchsdaten’ comprise flexure tests of four sizes, direct tension tests, confined and unconfined compression tests, Brazilian splitting tests of five sizes, and loading and unloading data. For all specimen sets the nominal stress–strain curves and crack patterns are provided.Austria. Ministry of Environment, Youth and FamilyAustria. National Foundation for Research, Technology and DevelopmentUnited States. Dept. of Transportation (Grant No. 20778

Developing alternative SCDDP implementations for hydro-thermal scheduling in New Zealand.

In a hydro-dominated system, such as New Zealand, the continual improvement and development of effective optimization and simulation software to inform decision making is necessary for effective resource management. Stochastic Constructive Dual Dynamic Programming (SCDDP) is a technique which has been effectively applied to the New Zealand system for optimization and simulation. This variant of Dynamic Programming (DP) allows optimization to occur in the dual space reducing the computational complexity and allows solutions from a single run to be formed as price signal surfaces and trajectories. However, any application of this method suffers from issues with computational tractability for higher reservoir numbers. Furthermore, New Zealand specific applications currently provide limited information on the system as they all use the same two-reservoir approximation of the New Zealand system. This limitation is of increasing importance with the decentralization of the New Zealand electricity sector. In this thesis we develop this theory with respect to two key goals: • To advance the theory surrounding SCDDP to be generalizable to higher reservoir numbers through the application of the point-wise algorithm explored in R. A. Read, Dye, S. & Read, E.G. (2012) to the stochastic case. • To develop at least two new and distinct two-reservoir SCDDP representations of the New Zealand system to provide a theoretical basis for greater flexibility in simulation and optimization of hydro-thermal scheduling in the New Zealand context

Structural Characterization of Doped GaSb Single Crystals by X-ray Topography

We characterized GaSb single crystals containing different dopants (Al, Cd and Te), grown by the Czochralski method, by x-ray topography and high angular resolution x-ray diffraction. Lang topography revealed dislocations parallel and perpendicular to the crystal's surface. Double-crystal GaSb 333 x-ray topography shows dislocations and vertical stripes than can be associated with circular growth bands. We compared our high-angular resolution x-ray diffraction measurements (rocking curves) with the findings predicted by the dynamical theory of x-ray diffraction. These measurements show that our GaSb single crystals have a relative variation in the lattice parameter ({Delta}d/d) on the order of 10{sup -5}. This means that they can be used as electronic devices (detectors, for example) and as x-ray monochromators

Drug transporters: recent advances concerning BCRP and tyrosine kinase inhibitors

Multidrug resistance is often associated with the (over)expression of drug efflux transporters of the ATP-binding cassette (ABC) protein family. This minireview discusses the role of one selected ABC-transporter family member, the breast cancer resistance protein (BCRP/ABCG2), in the (pre)clinical efficacy of novel experimental anticancer drugs, in particular tyrosine kinase inhibitors

Biomarkers of clinical benefit for anti-epidermal growth factor receptor agents in patients with non-small-cell lung cancer

Non-small-cell lung cancer (NSCLC) remains by far the major cause of cancer-related death in the Western world in both men and women. The majority of patients will be diagnosed with metastatic disease, and chemotherapy doublets remain the cornerstone of treatment for these patients. However, chemotherapy has a minimal impact on long-term survival and prognosis remains poor for these patients. Further improvement in treatment is likely to require incorporation of novel targeted therapies. Among these agents, inhibitors of the epidermal growth factor receptor (EGFR) have demonstrated significant activity in the first-, second- or third-line treatment of NSCLC. The purpose of current paper is to present the evidence for using several proposed molecular biomarkers as a tool for selection of NSCLC patients for anti-EGFR treatment. According to current data, EGFR mutation status appears to be the strongest predictor for the selection of NSCLC patients to first-line treatment with EGFR tyrosine kinase inhibitors vs chemotherapy. Use of other biomarkers remains investigational