Life cycle greenhouse gas emissions of blended cement concrete including carbonation and durability

The final publication is available at Springer via http://dx.doi.org/10.1007/s11367-013-0614-0Purpose 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 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 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 (35%FA), and BFS blended cements (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 CEMII/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, 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. 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.This research was financially supported by the Spanish Ministry of Science and Innovation (research project BIA2011-23602). The authors thank the anonymous reviewers for their constructive comments and useful suggestions. 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Stability of feature selection methods ::a study of metrics across different gene expression datasets

Analysis of gene-expression data often requires that a gene (feature) subset is selected and many feature selection (FS) methods have been devised. However, FS methods often generate different lists of features for the same dataset and users then have to choose which list to use. One approach to support this choice is to apply stability metrics on the generated lists and selecting lists on that base. The aim of this study is to investigate the behavior of stability metrics applied to feature subsets generated by FS methods. The experiments in this work explore a plethora of gene expression datasets, FS methods, and expected number of features to compare several stability metrics. The stability metrics have been used to compare five feature selection methods (SVM, SAM, ReliefF, RFE + RF and LIMMA) on gene expression datasets from the EBI repository. Results show that the studied stability metrics display a high amount of variability. The reason behind this is not clear yet and is being further investigated. The final objective of the research, that is to define how to select a FS method, is an ongoing work whose partial findings are reported herein