Eduardo de Moraes Rego Fairbairn

Cement replacement by sugar cane bagasse ash: CO2 emissions reduction and potential for carbon credits.

This paper presents a study of cement replacement by sugar cane bagasse ash (SCBA) in industrial scale aiming to reduce the CO(2) emissions into the atmosphere. SCBA is a by-product of the sugar/ethanol agro-industry abundantly available in some regions of the world and has cementitious properties indicating that it can be used together with cement. Recent comprehensive research developed at the Federal University of Rio de Janeiro/Brazil has demonstrated that SCBA maintains, or even improves, the mechanical and durability properties of cement-based materials such as mortars and concretes. Brazil is the worlds largest sugar cane producer and being a developing country can claim carbon credits. A simulation was carried out to estimate the potential of CO(2) emission reductions and the viability to issue certified emission reduction (CER) credits. The simulation was developed within the framework of the methodology established by the United Nations Framework Convention on Climate Change (UNFCCC) for the Clean Development Mechanism (CDM). The State of São Paulo (Brazil) was chosen for this case study because it concentrates about 60% of the national sugar cane and ash production together with an important concentration of cement factories. Since one of the key variables to estimate the CO(2) emissions is the average distance between sugar cane/ethanol factories and the cement plants, a genetic algorithm was developed to solve this optimization problem. The results indicated that SCBA blended cement reduces CO(2) emissions, which qualifies this product for CDM projects.

Use of Ultra-Fine Sugar Cane Bagasse Ash as Mineral Admixture for Concrete

Alcohol factories and sugar boilers generate a combustion byproduct known as sugar cane bagasse ash (SCBA). SCBA is composed mainly of silica and can be used as a concrete mineral admixture. Residual ultra-fine SCBA (9, 10, 15 and 20%) were used to produce conventional and high-performance concretes (CCs and HPCs, respectively) as a cement replacement (in mass) in this investigation. Tests performed for these concretes consisted of adiabatic calorimetric, durability, mechanical, and rheological. That concrete mechanical properties were not significantly changed through SCBA use at all replacement levels was indicated by results. When compared with the reference mixtures, there was superior rapid chloride-ion permeability, water sorption capillary, and rheological test performance by the ultra-fine SCBA concretes. Replacing 15% of cement with ultra-fine SCBA substantially decreased (11%) the maximum CC adiabatic temperature rise.

Steel–concrete interface: revisiting constitutive and numerical modeling

Abstract This paper presents a new modeling of bond-slip phenomena at steel–concrete interface concerning both constitutive and numerical modeling. The constitutive modeling is set up within a nearly standard thermodynamic approach which considers the interface as a surface of discontinuity. In the numerical modeling, we take into account in an explicit way the relative displacement at the interface. Assuming isotropic plastic behavior, standard continuous plasticity is extended to the interface to account for bond deterioration. A return mapping algorithm is used for the integration of relative plastic displacement. The formulation has been applied to truss elements and implemented in a finite element program.

Determination of probabilistic parameters of concrete: solving the inverse problem by using artificial neural networks

Abstract The probabilistic approach, based on the Monte Carlo method, has been recently introduced to simulate cracking of concrete in the framework of a finite element analysis [Rossi P, Wu X, le Maou F, Belloc A. Mater Struct 1994;27(172):437–44; Rossi P, Ulm F-J, Hachi F. J Engng Mech ASCE 1996;122(11):1038–43; Rossi P, Richer S. Mater Struct 1987;20(119):334–7; Rossi P, Ulm F-J. Mater Struct 1997;30(198):210–6; Fairbairn EMR, Paz CNM, Alves JLD, Silva RCC. Proceedings of XVIII CILAMCE-Iberian Latin American Congress on Computational Methods in Engineering, Brasilia, vol. 2, 1997;709–15]. If the uncertainties of the material parameters are assumed to vary spatially following a normal distribution, the samples corresponding to a simulation are function of the mean and the standard deviation that define the Gauss density function. The problem is that these statistical moments are not known, a priori, for the characteristic volume of the finite elements. In this paper, neural networks are used to evaluate the parameters characterizing the statistical distribution for a given response of the structure following an inverse analysis procedure. It is shown that this procedure improves a recently proposed algorithm [Fairbairn EMR, Guedes QM, Ulm F-J. Mater Struct 1999;32(215):9–13], which is able to solve the problem, but is very hard to operate. Finally, the procedure presented in this paper is used to identify the probabilistic parameters of a beam tested at TU-Delft.

Ultrafine sugar cane bagasse ash: high potential pozzolanic material for tropical countries

Abstract Resumo This work describes the characterization of sugar cane bagasse ashes produced by controlled burning and ultrafine grinding. Initially, the optimum burning conditions of the bagasse were determined aiming the maximum pozzolanic activity. In sequence, an ultrafine sugar cane bagasse ash was produced in vibratory mill. Finally, the influence of use of ultrafine sugarcane bagasse ash (10, 15 and 20% of cement replace-ment, in mass) in properties of high-performance concretes was studied. Rheology (BTRHEOM rheometer), compressive strength (7, 28, 90, and 180 days) and rapid chloride penetrability were investigated. The results indicated that the addition of sugarcane bagasse ash improved the durability characteristics, and did not change the rheological and mechanical properties.Keywords: sugar cane bagasse ash, pozzolan, concrete, grinding, calcination. Este trabalho descreve a caracterizacao de cinzas do bagaco de cana-de-acucar produzidas a partir de queima controlada e moagem ultrafina. Inicialmente, as condicoes otimas de queima do bagaco foram determinadas com o objetivo de alcancar a maxima atividade pozolânica. Em seguida, uma cinza ultrafina de elevada reatividade foi produzida em moinho vibratorio. Por fim, estudou-se a influencia do emprego de cinza ultrafina do bagaco de cana-de-acucar (10, 15 e 20% de substituicao de cimento, em massa) nas propriedades de concretos de alto desempenho. Foram avaliadas a reologia (reometro BTRHEOM), a resistencia a compressao (7, 28, 90 e 180 dias) e a penetracao acelerada de ions cloro. Os resultados indicaram que a cinza do bagaco nao altera as propriedades reologicas e mecânicas e possibilita a obtencao de concretos mais duraveis.Palavras-chave:

Influence of initial CaO/SiO2 ratio on the hydration of rice husk ash-Ca(OH)2 and sugar cane bagasse ash-Ca(OH)2 pastes

This work presents the results of a study on the hydration of pastes containing calcium hydroxide and either rice husk ash (RHA) or sugar cane bagasse ash (SCBA) in various initial CaO/SiO2 molar ratios. The products of the reactions were characterized by thermal analyses X-ray diffraction, and scanning electron microscopy. In the case of the RHA pastes, the product was composed of CaO-SiO2-H2O (type I C-S-H) or CaO-SiO2-H2O (type II C-S-H) according to the CaO/SiO2 ratio of the mixture. In contrast, in the case of the SBCA pastes, the product was composed primarily of CaO-SiO2-H2O that differed from both the previous types; the product also contained inclusions of calcium aluminate hydrates.

A study of the carbonation profile of cement pastes by thermogravimetry and its effect on the compressive strength

In a previous work, the authors have carbonated totally high initial strength and sulfate-resistant Portland cement pastes. In order to solve the mechanical problems caused by the intense carbonation that occurred during those experiments, new carbonation conditions were applied in this study. The obtained products were analyzed with respect to the carbonation reactions by thermogravimetry and compressive mechanical strength. Comparative analysis with reference pastes obtained without carbonation at the same age shows that CO2 capture increases with carbonation time. However, there is an optimum time, up to which the carbonation treatment does not affect the mechanical properties of the paste. Below this time, the lower is the carbonation time the higher is the increase of compressive strength, when compared to that of the reference pastes processed at same operating conditions without carbonation.

Influence of local raw materials on the mechanical behaviour and fracture process of PVA-SHCC

This paper addresses the results of an investigation on the influence of the Brazilian raw materials on the mechanical performance of Strain Hardening Cementitious Composites (SHCC). The mixtures were produced with variations of fly ash/cement and sand/cement proportions and with different maximum sand particle. Mechanical properties were evaluated by direct tension, bending and compression tests. Crack formation under direct tension and bending loads was also investigated. The results indicate that the use of high quantities of fly ash with low quantities of fine sand is the ideal combination to obtain strain hardening composites with tensile strain capacity superior to 3% using local materials. The increase in the sand content and particle size affects the behavior of the composites and tended to reduce the strain capacity of the specimens by up to 30%. Keeping constant the fly ash/cement and sand/cement rates it was found that the crack density and width measured under direct tension are only affected by the diameter of the sand for tensile strains in the range of 2%. The same general trends were observed for specimens submitted to compressive and bending loads.

Use of neural networks for fitting of FE probabilistic scaling model parameters

The probabilistic crack approach, based on the Monte Carlo method, was recently developed for finite element analysis of concrete cracking and related size effects. In this approach the heterogeneity of the material is taken into account by considering the material properties (tensile strength, Young modulus, etc.) to vary spatially following a normal distribution. N samples of the vector of random variables are generated from a specific probability density function, and the N samples corresponding to a simulation are functions of the mean value and of the standard deviation that define the Gauss density function. The problem is that these statistical moments are not known, a priori, for the characteristic volume of the finite elements used in the analysis. The paper proposes an inverse finite element analysis using neural networks for the determination of the statistical distribution parameters (e.g., for a normal distribution, the mean and the standard deviation) from a given response of the structure (for instance, an average load-displacement curve). From FE-analysis of 4-point bending beam tests, it is shown that the backanalysis technique developed in this paper is a powerful tool to determine the probabilistic distribution functions at the material level from structural tests for material volumes which are generally not accessible to direct testing.

Durability under thermal loads of polyvinyl alcohol fibers

In the present paper, the thermal durability of polyvinyl alcohol fibers (PVA) was studied after fiber samples had been subjected to temperatures ranging from 90°C to 250°C. Residual mechanical properties, such as tensile strength, elastic modulus and elongation at break, and physical properties, such as density were determined. Weibull statistics were used to quantify the degree of variability in fiber strength, at the different temperature. In addition, thermal analysis of PVA fibers were carried out employing thermogravimetry and differential scanning calorimetry up to the temperature of 800°C. SEM analysis of heated and unheated samples had been carried out in order to allow the identification of the changes in the microstructure of the fibers. The degradation process of PVA fibers manifests itself in a significant loss of mass, stiffness and strength of the fibers, which is progressive with increasing temperature. Thermal analysis has shown that the melting point of PVA fibers begins at approximately 200°C and thermal degradation initiates at about 239oC. However, progressive loss in tensile strength and elastic modulus was observed starting at a temperature as low as 90°C, due to glass transition temperature of PVA fibers at approximately 66°C. At 220°C, the elastic modulus and strength were reduced at about 45% and 52%, respectively, when compared with respective values of unheated samples. With regards to Weibull modulus, the statistical parameter did not exhibit significant influence on temperature for samples heated up to 145°C, which ranged from 23.4 to 28.8. However, samples heated to 220°C showed a sudden reduction in Weibull modulus to 8.6, indicating that a significant change occurred in the populations of fracture inducing flaws at this temperature level, which clearly affect the tensile strength and Weibull modulus.