Design and specification so that 21st century reinforced concrete structures won't corrode so soon

Design and specification so that 21st century reinforced concrete structures won't corrode so soo

Restoration of Partially Occluded Shapes of Faces using Neural Networks

One of the major difficulties encountered in the development of face image processing algorithms, is the possible presence of occlusions that hide part of the face images to be processed. Typical examples of facial occlusions include sunglasses, beards, hats and scarves. In our work we address the problem of restoring the overall shape of faces given only the shape presentation of a small part of the face. In the experiments described in this paper the shape of a face is defined by a series of landmarks located on the face outline and on the outline of different facial features. We describe the use of a number of methods including a method that utilizes a Hopfield neural network, a method that uses Multi-Layer Perceptron (MLP) neural network, a novel technique which combines Hopfield and MLP together, and a method based on associative search. We analyze comparative experiments in order to assess the performance of the four methods mentioned above. According to the experimental results it is possible to recover with reasonable accuracy the overall shape of faces even in the case that a substantial part of the shape of a given face is not visible. The techniques presented could form the basis for developing face image processing systems capable of dealing with occluded faces

Comparing different classifiers for automatic age estimation

We describe a quantitative evaluation of the performance of different classifiers in the task of automatic age estimation. In this context we generate a statistical model of facial appearance, which is subsequently used as the basis for obtaining a compact parametric description of face images. The aim of our work is to design classifiers that accept the model-based representation of unseen images and produce an estimate of the age of the person in the corresponding face image. For this application we have tested different classifiers: a classifier based on the use of quadratic functions for modeling the relationship between face model parameters and age, a shortest distance classifier and artificial neural network based classifiers. We also describe variations to the basic method where we use age-specific and/or appearance specific age estimation methods. In this context we use age estimation classifiers for each age group and/or classifiers for different clusters of subjects within our training set. In those cases part of the classification procedure is devoted to choosing the most appropriate classifier for the subject/age range in question, so that more accurate age estimates can be obtained. We also present comparative results concerning the performance of humans and computers in the task of age estimation. Our results indicate that machines can estimate the age of a person almost as reliably as humans

Long-term performance of hybrid anodes for cathodic protection of reinforced concrete

© 2018 The Authors, published by EDP Sciences. The long-term performance of hybrid anode corrosion protection systems (UK invention disclosed in Patent GB2426008B) was investigated on six bridge structures as part of a holistic approach to corrosion risk management, using the performance criteria in ISO BS EN 12696:2016. The aim of the study was to review the effectiveness of current design approaches to meet the residual service life when the anodes are operating in the galvanic phase. This was achieved by analysing data on the general condition of the structures, the ongoing performance of the installed hybrid anodes, and assessing the subsequent corrosion risk. It was found that the six structures were generally in good condition, 1 to 8 years after refurbishment works, with low associated corrosion risk in areas protected by the hybrid anode systems. This is a positive finding for the wider implementation of hybrid anode systems as an alternative corrosion management technique. The reinforcement in the protected areas remained predominately in a passive condition, with calculated corrosion rates below the ISO 12696:2016 recommended threshold of 2mA/m

Site performance of galvanic anodes in concrete repairs

Galvanic anodes can be used to limit the extent of concrete replacement and extend the service life of patch repairs to reinforced concrete (RC) structures. They respond to changes in environmental conditions and this attribute has been employed to extend their use. Traditionally, galvanic anodes are installed within the repair area itself. Although simple to install, this has certain limitations however, due primarily to the resistivity of the repair material. A recent alternative has been to install galvanic anodes in pre-drilled cavities in the parent concrete around the perimeter of the patch repair. This paper reviews and compares the performance of discrete galvanic anodes installed both within the repair area and parent concrete in full-scale RC structures. Results indicate that galvanic anodes installed within the parent concrete had a more profound effect on the polarisation of the steel around the perimeter of the patch repair. This provides the empirical basis for alternative designs incorporating galvanic anodes that will enable increased corrosion protection to the steel reinforcement around the patch repair, which is generally considered to be at the highest risk

Towards arresting reinforced concrete corrosion-a review

© 2018 The Authors, published by EDP Sciences. This work reviews developments in the understanding of chloride induced corrosion of steel in concrete from both a kinetic and thermodynamic perspective. Corrosion damage is at least in part attributed to the production of acid at sites of corrosion initiation. Solid phase inhibitors provide a reservoir of hydroxyl ions to inhibit damage. Pit re-alkalisation is identified as an important protective effect in electrochemical treatments used to arrest corrosion. A process like pit re-alkalisation is achieved more easily by impressing current from sacrificial anodes using a power supply which may then be followed by low maintenance galvanic protection to prevent local acidification. Methods for monitoring the steel corrosion rate in electrochemically treated reinforced concrete have been developed and used to assess corrosion risk. Some of these concepts have been adopted in the recent international standard on cathodic protection, ISO 12696:2016, some of the amendments of which are considered in the work presented here

Discussion: Hybrid anode concrete corrosion protection - independent study

Discussion: Hybrid anode concrete corrosion protection - independent stud

Cathodic protection on the UK’s Midland Links motorway viaducts

The Midland Links motorway viaducts (MLMV) are a series of reinforced concrete structures comprising 21 km of elevated motorway around the outer circumference of Birmingham. Deterioration was identified early in their serviceable life due to chloride induced corrosion of the steel reinforcement. An electrochemical treatment utilising an impressed current cathodic protection (ICCP) was successfully trialled in 1987 with the first large-scale commercial application of the treatment on the network in 1991. Since then it has been the principal corrosion management strategy for the MLMV, with 740 structures currently protected by ICCP. The aim of this paper is to offer a brief historical review of the MLMV network, discuss the deterioration mechanisms and review the historical developments of ICCP together with its overall performance as a corrosion-management method. Recent developments in cathodic protection technology and secondary beneficial effects of the ICCP previously not recognised are also discussed on how they can potentially result in significant cost savings for maintenance agencies for this and other similarly protected structures

A trade-off concept for lightweight concrete in chloride environments

The aim of this study was to investigate the influence of supplementary cementing materials (SCM’s) on the initial surface absorption (ISA), sorptivity and chloride penetrability to ASTM C1202 and NT Build 492 of lightweight aggregate based concretes (LWAC), and to compare these properties to those of normal-weight aggregate based concretes (NWAC). The lightweight aggregate (LWA) was Lytag, a fly ash based aggregate, which was pelletised during manufacture. Three normal-weight aggregates (NWA) were investigated, including, natural river gravel, jurassic oolitic limestone and crushed dolomitic limestone. The SCM’s used were fly ash (FA), ground granulated blastfurnace slag (GGBS), limestone (LS), silica fume (SF), and metakaolin (MK). CEM I replacement was undertaken on a percentage mass basis. Experimental work focused on concrete mixes with a fixed water/binder ratio of 0.50 and a constant total binder content of 330kg/m3. 28-day results indicate that with respect to aggregate influence, for CEM I only concrete, reduced concrete performance is obtained when replacing normal-weight aggregate with lightweight on a like-for-like basis. These negative effects can be reduced however, by good cement addition specification, as was found in the majority of the concretes in this study. These benefits include, to varying degrees, enhanced compressive strength, and increased resistance to water permeation and chloride ion penetration. A trade-off between aggregate type and binder combination is therefore desirable, to enable enhanced concrete chloride ion resistance

The antigenic switching network of Plasmodium falciparum and its implications for the immuno-epidemiology of malaria

Published onlineJournal ArticleResearch Support, Non-U.S. Gov'tAntigenic variation in the human malaria parasite Plasmodium falciparum involves sequential and mutually exclusive expression of members of the var multi-gene family and appears to follow a non-random pattern. In this study, using a detailed in vitro gene transcription analysis of the culture-adapted HB3 strain of P. falciparum, we show that antigenic switching is governed by a global activation hierarchy favouring short and highly diverse genes in central chromosomal location. Longer and more conserved genes, which have previously been associated with severe infection in immunologically naive hosts, are rarely activated, however, implying an in vivo fitness advantage possibly through adhesion-dependent survival rates. We further show that a gene's activation rate is positively associated sequence diversity, which could offer important new insights into the evolution and maintenance of antigenic diversity in P. falciparum malaria. DOI:http://dx.doi.org/10.7554/eLife.01074.001.The work was funded by the Wellcome Trust (Grant No. 082130/Z/07/Z to CN), the Biotechnology and Biological Sciences Research Council (studentship to RN) and the Royal Society (University Research Fellowship to MR)