Benefits of internal curing on service life and life-cycle cost of high-performance concrete bridge decks – A case study

This paper investigates the impact of internal curing on the service life of high-performance concrete (HPC) bridge decks by using analytical models to predict the times to onset of corrosion, onset of corrosion-induced damage, and failure of decks. Three bridge deck design options were compared: (i) normal concrete deck; (ii) HPC deck with supplementary cementing materials (SCM); and (iii) HPC deck with SCM and internal curing. It was found that the use of internal curing can extend the service life of high-performance concrete bridge decks by more than 20 years, which is mainly due to a significant reduction in the rate of penetration of chlorides in concrete as a result of reduced early-age shrinkage cracking and reduced chloride diffusion. Compared to normal concrete, HPC with SCM and internal curing was predicted to add more than 40 years to the service life of bridge decks in severe environmental conditions. Life-cycle cost reductions of 40% and 63% were estimated when conventional HPC and internally-cured HPC were used in bridge decks instead of normal concrete, respectively, despite the fact that the in-place unit cost of internally-cured HPC can be 4% higher than that of conventionally-cured HPC, which in turn can be up to 33% higher than that of normal concrete. This is due to a longer service life and less frequent maintenance activities offered by low-permeability HPC bridge decks.     

Observation of intrinsic size effects in the optical response of individual gold nanoparticles

The photothermal heterodyne imaging method is used to study for the first time the absorption spectra of individual gold nanoparticles with diameters down to 5 nm. Intrinsic size effects that result in a broadening of the surface plasmon resonance are unambiguously observed. Dispersions in the peak energies and homogeneous widths of the single-particle resonances are revealed. The experimental results are analyzed within the frame of Mie theory.     

Punctual versus continuous auction coordination for multi-robot and multi-task topological navigation

This paper addresses the interest of using punctual versus continuous coordination for mobile multi-robot systems where robots use auction sales to allocate tasks between them and to compute their policies in a distributed way. In continuous coordination, one task at a time is assigned and performed per robot. In punctual coordination, all the tasks are distributed in Rendezvous phases during the mission execution. However, tasks allocation problem grows exponentially with the number of tasks. The proposed approach consists in two aspects: (1) a control architecture based on topological representation of the environment which reduces the planning complexity and (2) a protocol based on sequential simultaneous auctions (SSA) to coordinate Robots’ policies. The policies are individually computed using Markov Decision Processes oriented by several goal-task positions to reach. Experimental results on both real robots and simulation describe an evaluation of the proposed robot architecture coupled wih the SSA protocol. The efficiency of missions’ execution is empirically evaluated regarding continuous planning.     

Replicated Case Studies for Investigating Quality Factors in Object-Oriented Designs

Thispaper aims at empirically exploring the relationships betweenmost of the existing design coupling, cohesion, and inheritancemeasures for object-oriented (OO) systems, and the fault-pronenessof OO system classes. The underlying goal of this study is tobetter understand the relationship between existing design measurementin OO systems and the quality of the software developed. in addition,we aim at assessing whether such relationships, once modeled,can be used to effectively drive and focus inspections or testing.The study described here is a replication of an analogous studyconducted in a university environment with systems developedby students. In order to draw more general conclusions and to(dis)confirm the results obtained there, we now replicated thestudy using data collected on an industrial system developedby professionals. Results show that many of our findings areconsistent across systems, despite the very disparate natureof the systems under study. Some of the strong dimensions capturedby the measures in each data set are visible in both the universityand industrial case study. For example, the frequency of methodinvocations appears to be the main driving factor of fault-pronenessin all systems. However, there are also differences across studies,which illustrate the fact that, although many principles andtechniques can be reused, quality does not follow universal lawsand quality models must be developed locally, wherever needed.     

Segmental and Conventional Precast Prestressed Concrete I-Bridge Girders

Conventional precast I-girder bridge systems are widely used in North America for short and medium spans, up to 45 m. Spliced standard precast I-girder segments made continuous by longitudinal posttensioning have been used for spans of up to 75 m, making them far more competitive with the steel plate girder and concrete box girder alternatives. The span and∕or girder spacing capabilities of the standard I-sections of Nebraska University, Florida, American Association of State Highway and Transportation Officials-Precast∕Prestressed Concrete Institute (AASHTO-PCI), and Canadian Prestressed Concrete Institute (CPCI) are determined for both spliced posttensioned and conventional pretensioned girder systems. This investigation shows that the Florida and Nebraska University I-sections are the most efficient girders for spliced posttensioned and conventional pretensioned bridges, respectively. Using a nonlinear optimization program, the optimum girder shape is found to be a bulb-tee for spliced posttensioned girders and a quasi-symmetrical I-section for conventional pretensioned girders. A new set of five I-sections that achieve a balanced efficiency for both spliced posttensioned and conventional pretensioned bridge girder systems are proposed. Three examples of alternative preliminary bridge designs using both the existing standard and the newly proposed I-sections illustrate the practicality of the presented results.     

Influence of Catalyst Composition on NOX Trap Performances

In the present work the influence of the type of noble metals present in NO_X storage catalysts was investigated regarding the NO oxidation, NO_X storage and NO reduction performances. Monolith samples with combinations of platinum, palladium and rhodium were tested in a flow-reactor. From this study, it was concluded that platinum is necessary for NO oxidation while palladium shows a better ability to oxidize NO to NO₂ at high temperature. The presence of Rh on Pt/Rh and Pt/Pd/Rh was found to have a negative effect on NO oxidation reaction. Results suggest also that the storage capacity is partially linked to the oxidation function: Surface area developed by the storage material and the Pt–Ba interaction have an important influence on NO_X storage function. The rich step was not efficient to purge completely the trap and leads to accumulation of NO_X and so to performances degradation which was assigned to accumulation of NO_X after each cycle and storage on of Ba-bulk sites. In presence of Rh, a high oxygen storage capacity leads to high exothermic process between reducing agent and stored oxygen which improves the ability of catalyst to release NO_X.     

Prediction of Onset of Corrosion in Concrete Bridge Decks Using Neural Networks and Case-Based Reasoning

Abstract:   This article proposes a methodology for predicting the time to onset of corrosion of reinforcing steel in concrete bridge decks while incorporating parameter uncertainty. It is based on the integration of artificial neural network (ANN), case-based reasoning (CBR), mechanistic model, and Monte Carlo simulation (MCS). A probabilistic mechanistic model is used to generate the distribution of the time to corrosion initiation based on statistical models of the governing parameters obtained from field data. The proposed ANN and CBR models act as universal functional mapping tools to approximate the relationship between the input and output of the mechanistic model. These tools are integrated with the MCS technique to generate the distribution of the corrosion initiation time using the distributions of the governing parameters. The proposed methodology is applied to predict the time to corrosion initiation of the top reinforcing steel in the concrete deck of the Dickson Bridge in Montreal. This study demonstrates the feasibility, adequate reliability, and computational efficiency of the proposed integrated ANN-MCS and CBR-MCS approaches for preliminary project-level and also network-level analyses.     

Electroextraction of Pb ions from diluted solutions by a process combining ion-exchange textiles and membranes

The extraction of Pb²⁺ ions from diluted solutions was achieved using a hybrid process combining cation exchange textiles, ion-exchange membranes and electric current. Two methods were investigated: an electroextraction process in two steps where the fixation of Pb²⁺ ions was followed by electroregeneration of the cation-exchange textiles; the second one a continuous electroextraction process where the ion exchange and regeneration take place simultaneously. For these electroextraction processes, the cation-exchange textile is introduced into an electrodialysis cell and compressed between two cation-exchange membranes. Under an applied current, the Pb²⁺ ions are substituted by regenerating ions coming from the anodic compartment and are transferred into a receiver compartment at the cathodic side where they are concentrated. Cation-exchange textiles having strong or weak acid functional groups, sulfonic (SCET) and carboxylic (CCET), respectively, were used. Different regenerating ions, H⁺, Na⁺, K⁺ and NH₄⁺ were investigated under various current densities. Electroregeneration ratios between 85% and 100% were obtained with sulfonic and carboxylic textiles previously loaded with Pb²⁺ ions. In the continuous electroextraction, removal efficiencies higher than 95% were obtained with a 10 ppm Pb²⁺ feed solution giving an outlet concentration of less than 1 ppm. The efficiency of the two textiles was compared in terms of mass transfer and energy consumption.