The steel–concrete interface

Although the steel–concrete interface (SCI) is widely recognized to influence the durability of reinforced concrete, a systematic overview and detailed documentation of the various aspects of the SCI are lacking. In this paper, we compiled a comprehensive list of possible local characteristics at the SCI and reviewed available information regarding their properties as well as their occurrence in engineering structures and in the laboratory. Given the complexity of the SCI, we suggested a systematic approach to describe it in terms of local characteristics and their physical and chemical properties. It was found that the SCI exhibits significant spatial inhomogeneity along and around as well as perpendicular to the reinforcing steel. The SCI can differ strongly between different engineering structures and also between different members within a structure; particular differences are expected between structures built before and after the 1970/1980s. A single SCI representing all on-site conditions does not exist. Additionally, SCIs in common laboratory-made specimens exhibit significant differences compared to engineering structures. Thus, results from laboratory studies and from practical experience should be applied to engineering structures with caution. Finally, recommendations for further research are made

Assessment of the invasive German wasp, Vespula germanica, in South Africa

Thesis (MSc)--Stellenbosch University, 2015.ENGLISH ABSTRACT: The invasive social wasp, Vespula germanica (Fabricius, 1793) (Hymenoptera: Vespidae), stands out as a remarkably successful insect invader worldwide. It flourishes in newly invaded ecosystems, where it has become a major problem in urban settings due to its close association with humans. The wasp is characterised by its devastating economic, social and environmental impact. Since its initial discovery in 1974 in Cape Town, all aspects of the wasp’s invasion throughout South Africa have been poorly documented. The wasp’s occurrence in the Cape Floristic Region (CFR) in the Western Cape Province (WCP), an area highly valued for its unique biodiversity, is of great concern due to the possible detrimental environmental effect of the wasp on this vulnerable biome. In this study, the present distribution of V. germanica was determined. Results indicate V. germanica’s distributional range is presently restricted within a small region of the WCP and it is thought that the Cape Fold Mountain range has acted as a natural barrier limiting the range expansion of the wasp. Field trials were conducted to determine V. germanica’s bait preference (protein versus carbohydrate) under local conditions and identify the best method in trapping the wasp. Fresh meats (lean smoked ham and minced beef) were overall the most preferred bait in both 2013 and 2014. Future studies should consider investigating the use of volatile meat extracts instead of fresh meat baits, as it could be as attractive but more practical for use in the field. Heptyl butyrate showed the most promising result of the artificial lures and warrants further investigation. Other lures (heptyl butyrate + acetic acid, isobutanol, isobutanol + acetic acid) were highly unattractive and possible reasons explaining this phenomenon, are discussed. A questionnaire survey was used during face-to-face interviews to explore the perspectives of forty farmers with regard to V. germanica occurring on their property. The current impact of the wasp in the agricultural context in the WCP was also determined. The majority of the respondents presented a negative view of the wasp and eradication seems to be a high priority for them. V. germanica is presently more of a social than an economic pest. Although indications are that with an increase in its density and distributional range, agro-economic problems and an increasing negative impact on local biodiversity can be expected. Management efforts should focus on its peripheral distribution, in order to curb further natural spread. The wasp’s distribution should also continue to be monitored, to enable early detection and rapid response, in the event that it succeeds in establishing itself in a new location. Further investigations into the suitability of a monitoring tool, including bait preferences, as well as continuing studies on the wasp’s overall impact, are recommended.AFRIKAANSE OPSOMMING: Die sosiale perdeby, Vespula germanica (Fabricius, 1793) (Hymenoptera: Vespidae), is ‘n merkwaardig suksesvolle indringerinsek wêreldwyd. Dit floreer in ekosisteme waar dit aanland en het in stedelike gebiede in ‘n groot probleem ontaard weens die insek se noue verbintenis met die mens. Die perdeby word geassosieer met verwoestende ekonomiese-, maatskaplike- en omgewingsimpakte. Dit is in 1974 in Kaapstad ontdek, maar sedertdien is die insek se verspreiding in Suid-Afrika swak gedokumenteer. Die perdeby se teenwoordigheid in die Kaapse-blommestreek (geleë in die Wes-Kaap provinsie), 'n hoogs bedreigde area bekend vir sy unieke biodiversiteit, is kommerwekkend weens die moontlike nadelige omgewingsimpakte van die perdeby op hierdie kwesbare bioom. In hierdie studie word V. germanica se verspreiding ondersoek. Die resultate dui daarop dat dit tans beperk is tot ‘n klein gebied in die Wes-Kaap. Daar word vermoed dat die Kaapse-plooiberge as 'n natuurlike versperring optree om die verdere verspreiding van die spesie te voorkom. Veldproewe is gedoen om die lokmiddel-voorkeure (proteïene vs. koolhidrate) van V. germanica te bepaal om sodoende die beste metode om die perdebye te lok en te vang te identifiseer. Vars vleis (ham en gemaalde bees) het voorkeur geniet in beide 2013 en 2014. Toekomstige studies kan vlugtige vleisaftreksels as lokmiddel oorweeg, aangesien dit ewe aantreklik as vars vleis kan wees, maar meer prakties is. Daar is bevind dat heptiel-butyraat die mees belowende kunsmatige lokmiddel is, en verdere ondersoeke hiermee word dus aangemoedig. Daarteenoor was V. germanica geensins tot enige van die ander kunsmatige lokmiddels (heptiel-butyraat + asynsuur, isobutanol, isobutanol + asynsuur) aangetrokke nie. Moontlike redes hiervoor word volledig bespreek. Die sosio-ekonomiese impakte van V. germanica is ondersoek deur onderhoude te voer met veertig Wes-Kaapse boere op wie se eiendom die perdeby voorkom. Waardevolle insig vanuit ‘n landbou-perspektief kon ingewin word. Die meerderheid van respondente het ‘n negatiewe siening van V. germanica en was van mening dat dit in hul belang sal wees om die perdebye uit te roei. V. germanica is tans meer van 'n sosiale as 'n ekonomiese pes. Indien hul digtheid of verspreiding egter sou toeneem, kan dit agri-ekonomiese probleme sowel as ‘n toenemende negatiewe impak op inheemse biodiversiteit tot gevolg hê. Pogings om die perdebypopulasie te beheer moet fokus op die perifere van die verspreiding, ten einde hul verdere natuurlike verspreiding te bekamp. Monitering van die verspreiding word aanbeveel om te verseker dat nuut-gevestigde populasies dadelik opgespoor en verwyder kan word. Verdere navorsing oor die lokmiddel-voorkeure as ‘n moniteringsmeganisme en die algehele negatiewe impakte van die perdebye kan bepaal word