Z. Agioutantis

A numerical investigation of the effect of the interfacial zone in concrete mixtures under uniaxial compression: The case of the dilute limit

A two-dimensional numerical investigation concerning the effects of the interfacial transition zone (ITZ) on the mechanical behavior of concrete is presented in this paper. The ITZ lies between the cement paste and the aggregates. Considering elastic two-dimensional models of the cement paste, the aggregate material and the ITZ, which is modeled as a thin band around each grain of aggregate, the response of the composite material was calculated using the finite element method. A parametric analysis was conducted for different model geometries as well as varying model parameters for the dilute limit, i.e. when the aggregate volume fraction is very small. Results indicate that the maximum tensile stresses which could lead to the development of microcracks, as well as larger displacements, tend to develop mainly in the ITZ. The distribution of stresses and displacements along appropriate sections of these models are also presented.

The potential of district heating using geothermal energy. A case study, Greece

The purpose of this study is to investigate the possibility of using low-enthalpy geothermal energy from the geothermal field of Sousaki in the province of Korinthos, Greece, to cover the thermal needs of the nearby town of Ag. Theodori. The possibility of developing a system of district heating was examined based on a proposed town model. Total thermal demands were calculated on the basis of a model dwelling and prevailing weather conditions in the area. Subsequently, a heat transfer circuit is proposed, including the distribution network, the heat exchanger, the production and reinjection pumps, and the pumping station. Finally, energy indices are presented, such as demand in tons of equivalent oil and CO2 emissions.

Pressure stimulated electrical emissions from cement mortar used as failure predictors

The electrical signals emitted during the application of uniaxial compressive mechanical stress upon cement mortar specimens are observed and discussed in this paper. This work discusses the electrical signals that are detected when the specimens are excited by a stepwise uniaxial stress increase from a low level (σL) to a higher level (σH) at a fast or slow rate and consequently remain at a high pressure regime for a long time. When maintaining constant mechanical stress for a long time, creep phenomena are evident in the specimen and the corresponding electrical emissions are recorded and analyzed. The characteristics of the electrical signal give clear information regarding the breaking stress (σF) of the material. The electrical emission recordings are of great interest when the applied σH is located in the vicinity of the failure stress; the emitted electrical current increases greatly due to the sequential formation and propagation of cracks that occurs in this stress region. Thus, by correlating the strain rate variations to the electrical emissions this methodology can be used to predict failure due to compressive stress in cement mortars.

Numerical simulation of the mechanical behaviour of epoxy based mortars under compressive loads

According to current Greek and international regulations regarding repair of damage in concrete structures or masonry, epoxy based mortars can be used for these applications. In this paper, the mechanical behaviour of epoxy based mortars under typical laboratory testing conditions such as uniaxial compression, was simulated by means of finite element analysis of two-dimensional models. The analysis was performed in the elastic domain for the aggregates and the elastoplastic domain for the resin. Four elementary models were created and material model values were based on laboratory data. Comparative diagrams of stresses and displacements are presented and compared. The prominent failure mechanism is identified as plastic deformation of the resin material.

Recent developments in the application of the influence function method for ground movement predictions in the U.S.

Abstract The influence function method has been applied to calculate ground deformations caused by underground mining. A bell-shaped Gaussian function was utilized to develop two formulations one for regular and one for irregular excavation parcels, which can calculate various deformation indices including subsidence, horizontal displacements, horizontal strains, slope and curvature. Empirical subsidence parameters have been developed to facilitate the application of the method to various mining and geological conditions, although site-specific parameters can also be utilized. Comparisons between measured and predicted subsidence and strain values are presented for different case studies, and demonstrate the applicability of the influence function formulation for predicting surface deformations in U.S. coalfields.

Simulation of Bulk Solids Blending in Longitudinal Stockpiles

A bulk solid blending simulator for longitudinal stockpiles has been developed using the Visual Basic development platform for Windows®. The program can be applied to optimizing blending in stockyards of mines, coal-fired power plants or cement industries. Input to the simulator consists of the average value, the standard deviation and the autocorrelation of the property for which blending is attempted. The program initially creates a time series of property values for the material delivered to the stockyard. Then, this input sequence is rearranged by simulating the operation of the stacking and reclaiming equipment. The output sequence of property values reflects the quality fluctuation of the material as it is delivered to the customer.

Sustainable Development Criteria and Indicators for the Assessment of Rare Earth Element Mining Projects

Abstract Rare earth elements (REEs) are recognized globally as being strategic and critical minerals. Therefore, assessment of the sustainability of REE mining projects is of particular interest to many stakeholders. Currently, there is a lack of information regarding the assessment of REE mining projects from a sustainability point of view. The best method to assess REE mining projects is to use measurable qualitative and/or quantitative indicators. Rare earth element mining projects are characterized by specific particularities as well as the potential presence of radiation. Thus, there is a need for a set of REE-specific criteria and indicators to supplement Global Reporting Initiative–based indicators. This chapter identifies existing indicator sets and lays out the importance of effective communication in estimating a mines contribution to sustainable development and gaining the social license to operate. Then, 31 criteria and indicators are proposed to support a decision on the sustainability of REE mining projects. The proposed and selected criteria and indicators can be used by stakeholders and assist decision and policy makers, and can also be used to estimate baseline conditions for social, economic, environmental, geopolitical, and technological aspects for REE development.

The optimal location of the distribution point of the belt conveyor system in continuous surface mining operations

Continuous surface mining projects are dynamic and quite complex. They are characterized by geological and spatial variability and several stochastic parameters that affect initial planning and final design. In strategic mine planning and operations management of such projects, the location of the distribution point of the belt conveyor system (BCDP) is of high importance as it directly influences mine development and the production schedule. In addition, the spatial location of the BCDP directly affects project cash flow including investment and operating costs and, as a result, the economic viability of the mining project. Therefore, the problem of the optimal location of BCDP could be defined as an economic optimization problem focusing on the material transportation cost. In this paper a model for the optimal location of BCDP in continuous surface mines is formulated based on the minimization of the transportation cost within the lifetime of the mine. A computer model was developed based on a methodological approach and was verified utilizing an actual lignite deposit which was simplified in terms of geometry and geology. Simulation results compare well with actual data available for the specific lignite mine.

Contribution of electrical tomography methods in geotechnical investigations at Mavropigi lignite open pit mine, Northern Greece

In this paper, the application of 2D and 3D electrical resistivity methods in geotechnical investigations is explored through a case study in Northern Greece. These two methods were employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonate formations near the southern limits of the pit, as well as to estimate the thickness of the carbonate rocks on top of the Schist formations to evaluate the stability of the southern slopes. Synthetic data were initially generated to help plan an efficient electrical tomography survey, in a region with complex geology and irregular terrain. Three configurations (Wenner–Schlumberger and dipole–dipole or pole–dipole) proved essential in such conditions and helped improving the resolution of the resistivity section. The sections were then calibrated by boreholes. Finally, the geophysical survey provided invaluable data regarding the geometry of the bedrock and possible faults, which was essential for the slope stability calculations.

Numerical Simulation of the Cracked Brazilian Disc under Diametral Compression

This paper focuses on the diametral compression of a disc with an “almost mathematical” central crack (Centrally Cracked Brazilian Disc - CCBD). A 2D finite element methodology is used to study the stress field and the Stress Intensity Factors KI and KII at the tips of the crack for different values of the crack length, 2L and the crack inclination angle, ϕ. By changing the crack inclination angle the mode of fracture was varied from mode I (tensile) to mixed mode (tension-shear and compression-shear). The dimensions of the models fitted those of the specimens (as suggested by the international standards), in order to check the numerical results by standardized experiments that are planned in the future