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Mathematical modelling of transport phenomena in concrete matrix  [PDF]
Ple?a? I.,Dimovi? S.
Facta Universitatis Series : Physics, Chemistry and Technology , 2011, DOI: 10.2298/fupct1101021p
Abstract: Two fundamental concerns must be addressed when attempting to isolate low-level waste in a disposal facility on land. The first concern is isolating the waste from water, or hydrologic isolation. The second is preventing movement of the radionuclides out of the disposal facility, or radionuclide migration. Particularly, we have investigated the latter modified scenario. To assess the safety for disposal of radioactive waste-concrete composition, the leakage of 60Co from a waste composite into a surrounding fluid has been studied. Leakage tests were carried out by original method, developed in Vinca Institute. Transport phenomena involved in the leaching of a radioactive material from a cement composite matrix are investigated using three methods based on theoretical equations. These are: the diffusion equation for a plane source an equation for diffusion coupled to a first-order equation, and an empirical method employing a polynomial equation. The results presented in this paper are from a 25-year mortar and concrete testing project that will influence the design choices for radioactive waste packaging for a future Serbian radioactive waste disposal center.
Effect of Pour Size on Concrete Placing Productivity in Nigeria  [cached]
Olaoluwa Olatunde,Ojo Stephen Okunlola,Adesanya David Abiodun
Research Journal of Applied Sciences, Engineering and Technology , 2012,
Abstract: Pour size as one of the site factors affecting concreting was examined to determine its effects on concreting productivity. A total of 167 separate concrete pours were observed on 25 building construction sites in Lagos, Nigeria,comprising 35 pours placed by crane and skip; 26 pours placed by dumper; 58 pours placed by wheelbarrow; 37 pours placed by head pan; and 11 pours placed jointly by pump, wheelbarrow and head pan. Data collected from the daily concrete pours were analyzed to determine operational productivity rates. The relationship between concreting productivity and pour size was examined using regression analyses to develop a model relating productivity to pour size. The results showed that irrespective of placing method, productivity generally increased by 1.1 m3/h for every 10 m3 increase in pour size. It was recommended that the obtained index of productivity increase per pour size be standardised for use in improving on-site productivity in the Nigerian construction industry.
MODERN ROUTES TO EXPLORE CONCRETE’S COMPLEX PORE SPACE  [cached]
Piet Stroeven,Zhanqi Guo
Image Analysis and Stereology , 2006, DOI: 10.5566/ias.v25.p75-86
Abstract: This paper concentrates on discrete element computer-simulation of concrete. It is argued on the basis of stochastic heterogeneity theory that modern concurrent-algorithm-based systems should be employed for the assessment of pore characteristics underlying durability performance of cementitious materials. The SPACE system was developed at Delft University of Technology for producing realistic schematizations of realcrete for a wide range of other particle packing problems, involving aggregate and fresh cement, and for the purpose of exploring characteristics in the hardened state of concrete, including of the pore network structure because of obvious durability problems. Since structure-sensitive properties are involved, schematization of reality should explicitly deal with the configuration of the cement particles in the fresh state. The paper concentrates on the stereological and mathematical morphology operations executed to acquire information on particle size, global porosity, and on distribution of porosity and of the connected pore fraction as a result of the near neighbourhood of aggregate grains. Goal is to provide information obtained along different exploration routes of concrete's pore space for setting up a pore network modelling approach. This type of methodological papers is scarce in concrete technology, if not missing at all. Technical publications that report on obtained results in our investigations are systematically referred to.
On the Mathematical Modelling of Microbial Growth
Svetoslav M. Markov
International Journal Bioautomation , 2010,
Abstract: We propose a new approach to mathematical modelling of microbial growth different to the approaches used in Jacob-Monod type models. Such an approach may be useful in the modelling of biotechnological processes, where microorganisms are used for various biodegradation purposes and are often put under extreme unfavourable conditions, such as prolonged depletion or excess of nutrients.
Response Surfaces for Fresh and Hardened Properties of Concrete with E-Waste (HIPS)  [PDF]
K. Senthil Kumar,K. Baskar
Journal of Waste Management , 2014, DOI: 10.1155/2014/517219
Abstract: The fresh and hardened properties of concrete with E-waste plastic, that is, high impact polystyrene (HIPS), as a partial replacement for coarse aggregate were analyzed using response surface methodology (RSM). Face-centred central composite response surface design was used in this study. The statistical models were developed between the factors (HIPS and water cement ratio) and their response variables (slump, fresh density, dry density, compressive strength, spilt tensile strength, and flexural strength). The Design-Expert 9.0.3 software package was used to analyze the experimental values. The relationships were established and final mathematical models in terms of coded factors from predicted responses were developed. The effects of factors on properties for all variables were seen visually from the response surface and contour plot. Validation of experiments has shown that the experimental value closely agreed with the predicted value, which validates the calculated response surface models with desirability?=?1. The HIPS replacement influenced all the properties of concrete than water cement ratio. Even though all properties show the decline trend, the experimented values and predicted values give a hope that the E-waste plastic (HIPS) can be used as coarse aggregate up to certain percentage of replacement in concrete which successively reduces the hazardous solid waste problem and conserves the natural resources from exhaustion. 1. Introduction Generation of solid waste and its safe disposal have become a challenging task for developing and developed countries. Among the solid waste, electronic waste (E-waste) shows an alarming growth. For the past few decades, the developed and developing countries totally ignored this waste. The major reasons are complexity of waste, lack of recycling infrastructure, recycling in informal sector, lack of awareness among people, and so forth. Now, the E-waste generation receives the attention of the developed countries but their way of recycling the E-waste is different; that is, they have started exporting this harm to developing countries as shown in Figure 1 [1, 2]. E-waste comprises many toxic substances like mercury, lead, cadmium, brominated flame-retardants, beryllium, polyvinyl chloride, printed circuit boards, plastic casings, cathode ray tubes, batteries, and cable sheathing, and so forth, which are harmful to human health and environment if not handled properly [3–5]. In developing countries, after recovering the precious metals and useful materials from the E-waste in informal manner, the waste is
Mixture design approach to evaluate fresh properties of SCC made with various sands
Tayeb Bouziani, Madani Bédérina, Zoubir Makhloufi, Mourad Hadjoudja
Journal of Building Materials and Structures ,
Abstract: The aim of the present paper is to provide a mixture design modelling to evaluate the effect of different sand types on fresh properties of self-compacting concrete (SCC). A statistical approach was used to highlight the effect of river sand (RS), crushed sand (CS) and dune sand (DS) as proportions in binary and ternary systems in SCC composition. The responses of the derived statistical models are sand packing density (SPD), T500 and J-ring. The resulting mathematical models are used to illustrate the variation of different responses in ternary contours plots with respect to the proportions of RS, CS and DS. This offers flexibility to optimize RS, CS and DS blends with tailor-made of a given property that suit a particular recommendations. Results indicate that SPD of RS can be enhanced by a 40% of CS and 30% of DS proportions. Moreover, it is shown that flowability, measured by J-ring, can be improved by the increase of CS and DS in RS-CS and RS-DS binary systems. Results also indicate that passing ability measured with T500 decreased with the increase of CS proportion and increased with the increase of DS proportion in binary and ternary systems.
Cast in place temperature 5 influence on fresh concrete made with limestone filler and blended cement
Soria, E. A.,Rahhal, V.F.
Materiales de Construccion , 2003,
Abstract: Properties of fresh concrete play a relevant role on placing and consolidation; and its design strength and durability depends on them. It is well known too that the concrete temperature during placing affects all its properties in different ways and extent. This paper presents the influence of placing temperature of concretes made with portland cement, limestone filer cement and blended cement, commercially available, on slump, slump loss, setting time and bleeding. The results show that generally when concrete temperature rises, the bleeding and slump fall down and the slump loss and setting time are accelerated. However, regardless of the strength class the type of cement affects the value of these variations Las propiedades de los hormigones en estado fresco desempe an un papel fundamental durante las operaciones de colocación y compactación de los mismos y de ellas depende, en gran medida, que se alcance en el estado endurecido la resistencia y la durabilidad de dise o. Es sabido, además, que la temperatura que alcanza un hormigón durante dichas operaciones, afecta en mayor o menor grado a todas sus propiedades, de manera diferente. En el presente trabajo se analizó la influencia de la temperatura de colocación sobre el asentamiento, la pérdida del asentamiento en el tiempo, los tiempos de fraguado y la exudación, en hormigones elaborados con cemento portland normal, fillerizado y compuesto, de procedencia comercial. Los resultados han mostrado, en general, que con el aumento de la temperatura de colocación disminuyen la exudación y el asentamiento; mientras que la pérdida de asentamiento y los tiempos de fraguado se aceleran. Sin embargo, las magnitudes de dichas variaciones resultan a su vez muy influenciadas por el tipo de cemento utilizado, aun siendo de la misma clase resistente.
Computational modelling of failure mechanisms in reinforced concrete structures  [PDF]
Mark Peter,Bender Michél
Facta Universitatis Series : Architecture and Civil Engineering , 2010, DOI: 10.2298/fuace1001001m
Abstract: A modelling approach for macroscopic reinforced concrete (RC) structures and structural elements under static loading conditions is presented. It uses the embedded modelling technique to separately account for concrete volumes and single longitudinal bars or stirrups. The material equations of the 3D elasto-plastic damage model for concrete are derived assuming isotropic damage, stiffness recovery and loss due to crack closing and reopening and a non-associated flow rule. Suitable material functions and material parameters as well as a regularisation by energy criteria are given. The approach is applied to shear beam tests illustrating numerical results compared to corresponding experimental data.
On the mathematical modelling of measurement  [PDF]
Jonathan Barzilai
Mathematics , 2006,
Abstract: The operations of linear algebra, calculus, and statistics are routinely applied to measurement scales but certain mathematical conditions must be satisfied in order for these operations to be applicable. We call attention to the conditions that lead to construction of measurement scales that enable these operations.
Mathematical modelling of the cardiovascular system  [PDF]
Alfio Quarteroni
Mathematics , 2003,
Abstract: In this paper we will address the problem of developing mathematical models for the numerical simulation of the human circulatory system. In particular, we will focus our attention on the problem of haemodynamics in large human arteries.
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