Purpose Blended cements use waste products to replace Portland cement, the main contributor to CO 2 emissions in concrete manufacture. Using blended cements reduces the embodied greenhouse gas (GHG) emissions; however, little attention has been paid to the reduction in CO 2 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 CO 2 capture.Methods This study evaluates CO 2 emissions and CO 2 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 CO 2 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). 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. Results and discussionRecommendations and perspectives Blended cements emit less CO 2 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 CO 2 emissions by half. A case study is presented in this paper demonstrating how the results may be utilized.

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This paper describes one approach to a methodology to design reinforced concrete cantilever retaining walls for road construction, using a hybrid multistart optimization strategic method based on a variable neighborhood search threshold acceptance strategy (VNS-MTAR) algorithm. This algorithm is applied to two objective functions: the embedded CO2 emissions and the economic cost of reinforced concrete walls at different stages of materials production, transportation and construction. The problem involved 20 design variables: four geometric variables (thickness of the stem and the base slab, as well as the toe and heel lengths), four material types, and 12 variables for the reinforcement set-up. Results first indicate that embedded emissions and cost are closely related, and that more environmentally-friendly solutions than the lowest cost solution are available at a cost increment of less than 1.28%. The analysis also indicated that reducing costs by one euro could save up to 2.28% kg in CO2 emissions.Finally, the cost-optimized walls require about 4.8% more concrete than the best environmental ones, which need 1.9% more steel.

ElsevierMartí Albiñana, JV.; Gonzalez Vidosa, F.; Yepes Piqueras, V.; Alcalá González, J. (2013 AbstractThis paper describes one approach to the analysis and design of prestressed concrete precast road bridges, with double U-shaped cross-section and isostatic spans. The procedure used to solve the combinatorial problem is a variant of simulated annealing with a neighborhood move based on the mutation operator from the genetic algorithms (SAMO). This algorithm is applied to the economic cost of these structures at different stages of manufacturing, transportation and construction. The problem involved 59 discrete design variables for the geometry of the beam and the slab, materials in the two elements, as well as active and passive reinforcement. The parametric study showed a good correlation for the cost, geometric and reinforcement characteristics with the span length, which can be useful for the day-to-day design of PC precast bridges. A cost sensitivity analysis first indicates that a maximum 20% rise in steel costs leads to an 11.82% increase in the cost, while a 20% rise in concrete costs increases the cost up to 4.20%, namely 2.8 times less. The analysis also indicated that the characteristics of the cost-optimized bridges are somewhat influenced by different economic scenarios for steel and concrete costs. Finally, there is a growth in the volume of concrete when the steel cost rises; surprisingly, the variation in the volume of concrete is almost insensitive to its rising price.