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Multiobjective optimization of post-tensioned concrete box-girder road bridges considering cost, CO2 emissions, and safety

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Abstract:聽This paper presents a multiobjective optimization of post-tensioned concrete road bridges in terms of cost, CO2 emissions, and overall safety factor. A computer tool links the optimization modulus with a set of modules for the finite-element analysis and limit states verification. This is applied for the case study of a three-span continuous post-tensioned box-girder road bridge, located in a coastal region. A multiobjective harmony search is used to automatically search a set of optimum structural solutions regarding the geometry, concrete strength, reinforcing and post-tensioned steel. Diversification strategies are combined with intensification strategies to improve solution quality. Results indicate that cost and CO2 emissions are close to each other for any safety range. A one-euro reduction, involves a 2.34聽kg CO2 emissions reduction. Output identifies the best variables to improve safety and the critical limit states. This tool also provides bridge managers with a set of trade-off optimum solutions, which balance their preferences most closely, and meet the requirements previously defined.

Keywords

  • Multiobjective optimization;
  • CO2 emissions;
  • Safety;
  • Post-tensioned concrete;
  • Box-girder bridge;
  • Multiobjective harmony search

Highlights

  • A multiobjective optimization of post-tensioned concrete road bridges is presented.
  • A computer tool combines finite-element analysis and limit states verification.
  • Output provides a trade-off between cost, CO2 emissions, and overall safety factor.
  • Near the optima, a one-euro reduction represents a 2.34聽kg CO2 emissions reduction.
  • Results show the cheapest and most eco-friendly variables for improving safety.

Reference:

GARC脥A-SEGURA, T.; YEPES, V. (2016). Multiobjective optimization of post-tensioned concrete box-girder road bridges considering cost, CO2 emissions, and safety. Engineering Structures, 125:325-336.聽DOI: 10.1016/j.engstruct.2016.07.012.

11 Agosto, 2016
 
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Life-cycle greenhouse gas emissions of blended cement concrete including carbonation and durability

Emisiones de gases de efecto invernadero a lo largo del ciclo de vida de hormigones con cementos con adiciones considerando la carbonataci贸n y la durabilidad

GARC脥A-SEGURA, T.; YEPES, V.; ALCAL脕, J. (2014).聽Life-cycle greenhouse gas emissions of blended cement concrete including carbonation and durability.The International Journal of Life Cycle Assessment, 19(1):3-12. DOI 10.1007/s11367-013-0614-0

carbonataci贸n

Carbonataci贸n del hormig贸n, que al bajar el Ph del hormig贸n, puede llevar a la corrosi贸n de la armadura

Los cementos con adiciones utilizan ciertos subproductos de desecho para reemplazar el cemento Portland, el principal contribuyente a las emisiones de CO2 en la fabricaci贸n de hormig贸n. El objetivo de este estudio es determinar si la reducci贸n de la durabilidad y la reducci贸n de la carbonataci贸n de los hormigones con cementos con adiciones compensan las menores emisiones en su producci贸n. Este estudio eval煤a las emisiones y la captura de CO2 en una columna de hormig贸n armado durante su vida 煤til y despu茅s de su demolici贸n y reutilizaci贸n como grava de relleno. El deterioro del hormig贸n debido a la carbonataci贸n y la inevitable corrosi贸n de las armaduras, terminan con la vida 煤til de la estructura. Sin embargo, la carbonataci贸n contin煤a incluso despu茅s de la demolici贸n, debido a la mayor superficie expuesta del material reciclado. Los resultados indican que los hormigones fabricados con cemento Portland, con adiciones de cenizas volantes sil铆ceas (35% FA) y con escoria sider煤rgicas granuladas de alto horno (80% BFS), capturan un 47, 41 y 20%, respectivamente, de las emisiones de CO2. La vida de servicio de cementos con altas cantidades de adiciones, como CEM III/A (50 % BFS), CEM III/B (80 % BFS), y CEM II/BV (35 % FA), es聽aproximadamente un 10 % m谩s corta, debido al mayor coeficiente de velocidad de carbonataci贸n. En comparaci贸n con el cemento Portland, y a pesar de una menor captura de CO2 y de vida 煤til, el CEM III/B emite un 20 % menos de CO2 al a帽o. Se concluye que la adici贸n de FA al cemento Portland, en lugar de BFS, conduce a menores emisiones, pues FA necesita menos procesamiento despu茅s de ser recogido, y las distancias de transporte son generalmente m谩s cortas. Sin embargo, las mayores reducciones se lograron usando BFS, debido a que se puede reemplazar una cantidad mayor de cemento. Los cementos con adiciones emiten menos CO2 al a帽o durante el ciclo de vida de una estructura, a pesar de que dicha adici贸n reduce notablemente la vida 煤til. Si el hormig贸n se recicla como grava en relleno, la carbonataci贸n puede reducir las emisiones de CO2 a la mitad. El caso estudiado demuestra c贸mo se pueden utilizar los resultados obtenidos.

Tabla

Tabla

 

Resultados interesantes:

  • 聽La vida de servicio de cementos con altas cantidades de adiciones, como CEM III/A (50 % BFS), CEM III/B (80 % BFS), y CEM II/BV (35 % FA), es聽aproximadamente un 10 % m谩s corta, debido al mayor coeficiente de velocidad de carbonataci贸n.
  • CEM III/B emite un 20% menos de CO2 anual que el CEM Portland, a pesar de que tiene una vida 煤til menor y que recarbonata mucho menos. En valores de emisiones absolutas, CEM III/B emite un 28% menos que el CEM Portland. Tambi茅n es verdad que este cemento se recomienda en para hormig贸n en masa y armado de grandes vol煤menes, como presas de hormig贸n vibrado o cimentaciones de hormig贸n armado. No es utilizable para hormig贸n de alta resistencia, hormig贸n prefabricado u hormig贸n pretensado.
  • Si el hormig贸n se recicla como grava en relleno, la carbonataci贸n puede reducir las emisiones de CO2 a la mitad.

 

Grandes vol煤menes de hormig贸n vibrado

Abstract

Purpose Blended cements use waste products to replace Portland cement, the main contributor to CO2 emissions in concrete manufacture. Using blended cements reduces the embodied greenhouse gas (GHG) emissions; however, little attention has been paid to the reduction in CO2 capture (carbonation) and durability. The aim of this study is to determine if the reduction in production emissions of blended cements compensates for the reduced durability and CO2 capture.

Methods This study evaluates CO2 emissions and CO2 capture for a reinforced concrete (RC) column during its service life and after demolition and reuse as gravel filling material. Concrete depletion, due to carbonation and the unavoidable steel embedded corrosion, is studied, as this process consequently ends the concrete service life. Carbonation deepens progressively during service life and captures CO2 even after demolition due to the greater exposed surface area. In this study results are presented as a function of cement replaced by fly ash (FA) and blast furnace slag (BFS).

Results and discussion Concrete made with Portland cement, FA blended cement (35% FA) and BFS blended cement (80% BFS) captures 47%, 41% and 20% of CO2 emissions, respectively. The service life of blended cements with high amounts of cement replacement, like CEM III/A (50% BFS), CEM III/B (80% BFS) and CEM II/B-V (35% FA), was about 10% shorter given the higher carbonation rate coefficient. Compared to Portland cement and despite the reduced CO2 capture and service life, CEM III/B emitted 20% less CO2 per year.

Conclusions To obtain reliable results in a Life-cycle Assessment (LCA) it is crucial to consider carbonation during use and after demolition. Replacing Portland cement with FA, instead of BFS, leads to a lower material emission factor since FA needs less processing after being collected, and transport distances are usually shorter. However, greater reductions were achieved using BFS since a larger amount of cement can be replaced.

Recommendations and perspectives Blended cements emit less CO2 per year during the life-cycle of a structure, although a high cement replacement reduces the service life notably. If the demolished concrete is crushed and recycled as gravel filling material, carbonation can cut CO2 emissions by half. A case study is presented in this paper demonstrating how the results may be utilized.

Keywords

Life-Cycle, CO2 emission, blended cement, carbonation, durability, recycled concrete.

Link:http://link.springer.com/article/10.1007%2Fs11367-013-0614-0

4 Julio, 2013
 
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Optimization of high-performance concrete structures by variable neighborhood search

TORRES-MACH脥, C.; YEPES, V.; ALCALA, J.; PELLICER, E. (2013). Optimization of high-performance concrete structures by variable neighborhood search. International Journal of Civil Engineering, 11(2):90-99 .

Abstract

This paper describes a methodology in designing high-performance concrete for simply supported beams, using a hybrid聽optimization strategy based on a variable neighborhood search threshold acceptance algorithm. Three strategies have been聽applied to discrete optimization of reinforced concrete beams: Variable Neighborhood Descent (VND), Reduced Neighborhood聽Search (RNS) and Basic Variable Neighborhood Search (BVNS). The problem includes 14 variables: two geometrical; one聽material type; one mix design; and 10 variables for the reinforcement setups. The algorithms are applied to two objective聽functions: the economic cost and the embedded CO2 emissions. Firstly, this paper presents the application of these three different聽optimization strategies, which are evaluated by fitting the set of solutions obtained to a three-parameter Weibull distribution聽function. The Variable Neighborhood Descent with Threshold Accepting acceptance strategy algorithm (VND-TA) results as the聽most reliable method. Finally, the study presents a parametric study of the span length from 10 to 20 m in which it can be聽concluded that economic and ecological beams show a good parabolic correlation with the span length.

Keywords: Structural optimization, Reinforced concrete, Sustainable construction, CO2 emission, High-performance concrete,聽Heuristics.

Link:http://ijce.iust.ac.ir/browse.php?a_code=A-10-1013-1&slc_lang=en&sid=1&sw=Yepes

CO2-Optimization of PC precast bridges by hybrid heuristics

MART脥, J.V.; YEPES, V.; GONZ脕LEZ-VIDOSA, F.; ALCAL脕, J. (2012). CO2-Optimization of PC precast bridges by hybrid heuristics. SSCS 2012 Numerical Modeling. Strategies for Sustainable Concrete Structures, May 29-June 1, Aix-en-Provence, France.

1 Junio, 2012
 
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Universidad Politécnica de Valencia