scholarly journals Design of rapid hardening engineered cementitious composites for sustainable construction

2017 ◽  
Vol 12 (2) ◽  
pp. 107-112
Author(s):  
Uliana Marushchak ◽  
Myroslav Sanytsky ◽  
Nazar Sydor
Keyword(s):  
Resistance Coefficient ◽  
Sustainable Construction ◽  
Cement Matrix ◽  
Rapid Hardening ◽  
Fine Grain ◽  
Mineral Additives ◽  
Polycarboxylate Ether ◽  
Calcium Hydrosilicate ◽  
Nanoscale Level

Abstract This paper deals with design of environmentally friendly Rapid Hardening Engineered Cementitious Composite (RHECC) nanomodified with ultrafine mineral additives, polycarboxylate ether based superplasticizer, calcium hydrosilicate nanoparticles and dispersal reinforced by fibers. The incremental coefficient of surface activity was proposed in order to estimation of ultrafine supplementary materials (fly ash, methakaolin, microsilica) efficiency. A characterization of RHECC’s compressive and flexural properties at different ages is reported in this paper. Early compressive strength of ECC is 45-50 MPa, standard strength – 84-95 MPa and parameter Rc2/Rc28 – 65–70%. The microstructure of the cement matrix and RHECC was investigated. The use of ultrafine mineral supplementary materials provides reinforcement of structure on micro- and nanoscale level (cementing matrix) due to formation of sub-microreinforcing hydrate phase as AFt- and C-S-H phases in unclinker part of cement matrix, resulting in the phenomena of “self-reinforcement” on the microstructure level. Designed RHECC may be regarded as lower brittle since the crack resistance coefficient is higher comparison to conventional fine grain concrete.

scholarly journals Mineralogical and Geochemical Characterization of Gold Mining Tailings and Their Potential to Generate Acid Mine Drainage (Minas Gerais, Brazil)

Minerals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 39
Author(s):  
Mariana Lemos ◽  
Teresa Valente ◽  
Paula Marinho Reis ◽  
Rita Fonseca ◽  
Itamar Delbem ◽  
...  
Keyword(s):  
Acid Mine Drainage ◽  
Mine Drainage ◽  
Minas Gerais ◽  
Acid Mine ◽  
Fine Grain ◽  
Mineralogical Characteristics ◽  
Tailing Dams ◽  
The One ◽  
And Control

For more than 30 years, sulfide gold ores were treated in metallurgic plants located in Nova Lima, Minas Gerais, Brazil, and accumulated in the Cocoruto tailings dam. Both flotation and leaching tailings from a deactivated circuit, as well as roasted and leaching tailings from an ongoing plant, were studied for their acid mine drainage potential and elements’ mobility. Detailed characterization of both tailings types indicates the presence of fine-grain size material hosting substantial amounts of sulfides that exhibit distinct geochemical and mineralogical characteristics. The samples from the ongoing plant show high grades of Fe in the form of oxides, cyanide, and sulfates. Differently, samples from the old circuit shave higher average concentrations of Al (0.88%), Ca (2.4%), Mg (0.96%), and Mn (0.17%), present as silicates and carbonates. These samples also show relics of preserved sulfides, such as pyrite and pyrrhotite. Concentrations of Zn, Cu, Au, and As are higher in the tailings of the ongoing circuit, while Cr and Hg stand out in the tailings of the deactivated circuit. Although the obtained results show that the sulfide wastes do not tend to generate acid mine drainage, leaching tests indicate the possibility of mobilization of toxic elements, namely As and Mn in the old circuit, and Sb, As, Fe, Ni, and Se in the tailings of the plant that still works. This work highlights the need for proper management and control of tailing dams even in alkaline drainage environments such as the one of the Cocoruto dam. Furthermore, strong knowledge of the tailings’ dynamics in terms of geochemistry and mineralogy would be pivotal to support long-term decisions on wastes management and disposal.

Influence of the Residue of Casting by Lost Wax in the Modulus of Elasticity and Porosity of Concretes

2014 ◽  
Vol 805 ◽  
pp. 343-349
Author(s):  
Carine F. Machado ◽  
Weber G. Moravia
Keyword(s):  
Construction Industry ◽  
Modulus Of Elasticity ◽  
Chemical Characterization ◽  
Microstructural Characterization ◽  
Cement Matrix ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hardened State ◽  
Material Powder

This work evaluated the influence of additions of the ceramic shell residue (CSR), from the industries of Lost Wax Casting, in the modulus of elasticity and porosity of concrete. The CSR was ground and underwent a physical, chemical, and microstructural characterization. It was also analyzed, the environmental risk of the residue. In the physical characterization of the residue were analyzed, the surface area, and particle size distribution. In chemical characterization, the material powder was subjected to testing of X-ray fluorescence (XRF). Microstructural characterization was performed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The residue was utilized like addition by substitution of cement in concrete in the percentages of 10% and 15% by weight of Portland cement. It was evaluated properties of concrete in the fresh and hardened state, such as compressive strength, modulus of elasticity, absorption of water by total immersion and by capillarity. The results showed that the residue can be used in cement matrix and improve some properties of concrete. Thus, the CSR may contribute to improved sustainability and benefit the construction industry.

scholarly journals Reología, comportamiento físico-mecánicos y de durabilidad de hormigones con nanosílice.

2012 ◽  
Vol 2 (2) ◽  
pp. 82-88
Author(s):  
E. Téllez Girón ◽  
A .N. Martín Acosta ◽  
A. Pérez Hernández ◽  
U. Verdecia Rodríguez
Keyword(s):  
Resistance Coefficient ◽  
Ultrasonic Pulse ◽  
Effective Porosity ◽  
Capillary Absorption ◽  
Water Absorption Coefficient ◽  
Characterization Methods ◽  
Natural Pozzolans ◽  
Chemical Admixtures ◽  
Microscopy Analysis

RESUMENLa nanosílice es una de las aplicaciones de la nanotecnologia en la construcción, a base de sílica amorfa nanométrica, que se emplea igual que la microsílice, pero con la ventaja que no produce contaminación al medio ambiente y la agresión a la salud por inhalación de ésta. Se dan los resultados de la caracterización física de dos compuestos de nanosílice comerciales mediante los métodos de la caracterización de aditivos y el empleo de la microscopia para la determinación de compuestos fundamentales, de sus actividades puzolánicas en morteros, así como la determinación de la absorción capilar, velocidad ultrasónica, masa volumétrica, coeficientes de resistencia a la penetración de agua, coeficiente de absorción de agua y porosidad efectiva en hormigones elaborados con los compuestos evaluados y en hormigones con aditivos superplastificantes y tobas zeolitizadas como patrones de comparación. Los valores demuestran un mejor comportamiento de durabilidad en los hormigones elaborados con nanosílice.Palabras Clave: nanotecnología; nanosílice; microsílice; aditivos químicos; adiciones.ABSTRACTNanosilice based in nanometric amorphous silica is one of the aplications of nanotechnology in the building industry, that has the same use than microsilica, but with the advantage that it does not produce environmental pollution or respiratory complains due to inhalation. We give the results of the physical characterization of two commercial nanosilice compounds by the admixtures characterization methods and electronic microscopy analysis to determine the fundamental compound, its pozzolanic activity in mortars, as well as its capillary absorption, ultrasonic pulse speed, volumetric mass, water penetration resistance coefficient, water absorption coefficient and effective porosity in concrete with nanosilice and in ordinary concrete with natural pozzolans and superplasticizer admixtures like comparative patterns. Results show a better behavior of durability in concretes with nanosilice.Keywords: nanotechnology; nanosilica; microsilica; chemical admixtures; additions.

Characterization of Polycarboxylate-Ether Based Superplasticizer on Cement Clinker Surfaces

2012 ◽  
Vol 95 (7) ◽  
pp. 2189-2195 ◽  
Author(s):  
Lucia Ferrari ◽  
Laetitia Bernard ◽  
Florian Deschner ◽  
Josef Kaufmann ◽  
Frank Winnefeld ◽  
...  
Keyword(s):  
Cement Clinker ◽  
Polycarboxylate Ether

FlakyLoc: Flakiness Localization for Reliable Test Suites in Web Applications

2020 ◽  
Author(s):  
Jesús Morán ◽  
Cristian Augusto ◽  
Antonia Bertolino ◽  
Claudio De La Riva ◽  
Javier Tuya
Keyword(s):  
Environmental Factors ◽  
Web Application ◽  
Web Applications ◽  
Test Case ◽  
Test Cases ◽  
Root Cause ◽  
Test Execution ◽  
Fine Grain ◽  
Asynchronous Communications

Web application testing is a great challenge due to the management of complex asynchronous communications, the concurrency between the clients-servers, and the heterogeneity of resources employed. It is difficult to ensure that a test case is re-running in the same conditions because it can be executed in undesirable ways according to several environmental factors that are not easy to fine-grain control such as network bottlenecks, memory issues or screen resolution. These environmental factors can cause flakiness, which occurs when the same test case sometimes obtains one test outcome and other times another outcome in the same application due to the execution of environmental factors. The tester usually stops relying on flaky test cases because their outcome varies during the re-executions. To fix and reduce the flakiness it is very important to locate and understand which environmental factors cause the flakiness. This paper is focused on the localization of the root cause of flakiness in web applications based on the characterization of the different environmental factors that are not controlled during testing. The root cause of flakiness is located by means of spectrum-based localization techniques that analyse the test execution under different combinations of the environmental factors that can trigger the flakiness. This technique is evaluated with an educational web platform called FullTeaching. As a result, our technique was able to locate automatically the root cause of flakiness and provide enough information to both understand it and fix it.

Preparation and Characterization of (1-x)BiScO3-xPbTiO3 Ceramics by Two-Step Sintering

2008 ◽  
Vol 368-372 ◽  
pp. 8-10 ◽  
Author(s):  
Ting Ting Zou ◽  
Xiao Hui Wang ◽  
Long Tu Li
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
High Performance ◽  
Piezoelectric Properties ◽  
Sintering Temperature ◽  
Sintering Aid ◽  
Potential Approach ◽  
Fine Grain ◽  
Sintering Method

High-performance fine-grain (1-x)BiScO3-xPbTiO3 ceramics were prepared by two-step sintering method. Influences of sintering temperature, holding time, and composition on the microstructure and properties were discussed. The BSPT ceramics obtained via two-step sintering reaches density higher than 95% at a low temperature of 800°C without any sintering aid, and the grain size of the ceramics is also effectively controlled. Excellent piezoelectric properties between the composition of x=0.63 and x=0.64 reveals a probable MPB in this range, suggesting a potential approach to pursue high performance BSPT ceramics.

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