A study of the influence of aggregate grading on concrete penetrability

Concrete is generally perceived as being an inherently durable material. However, many concrete structures need substantial repairs and maintenance during their service life, with the resultant costs to the economy reaching 3-5 % of GNP in some countries. Durability is therefore key in concrete design and specification. Aggregates constitute between 60 and 80 %, by volume, of typical concretes and have a profound influence on the physical properties of hardened concrete. The aggregate particle size distribution is usually selected so as to achieve a particle packing density that is equal to or near the maximum, which is seen as optimal for strength and durability. However, the influence of aggregate grading on durability apart from that which it has through its effect on particle packing density is not understood. Alternative mechanisms through which grading may effect durability include tortuosity and the porosity of the interfacial transition zone. This research aimed to determine the extent of the influence that aggregate grading has on concrete durability independently of particle packing density and to determine whether fineness modulus (FM) is a suitable and sufficient parameter for the characterisation of aggregate particle size distribution with regard to the performance based specification of concrete where durability is the concern. The coefficient of uniformity (Cu) and the use of gap or continuous grading were two further factors considered

The power of purpose – lessons in agility from the Ventilator Challenge

Purpose: COVID-19 has shaken views of what is normal and what is possible, raising questions about conventional norms, ways of working and our understanding of agility. This paper aims to respond to calls for empirical research of supply chain capacities in times of crisis and offer a unique perspective on agile procurement and supply chain management from a case study of the Ventilator Challenge. Design/methodology/approach: A descriptive case study was undertaken, adopting an inductive approach. Interviews were conducted with the major stakeholders tasked with the design, sourcing and assembly of ventilators. Findings: Findings are delivered across four key areas: context; procurement and supply chain management; technology and culture; and environment. Key challenges and enablers are discussed, highlighting the critical roles of trust, empowerment and enabling technologies in the construction of an entirely new ventilator supply chain, from scratch, in five weeks. Originality/value: This paper delivers contributions for both academic research and practice. The case study offers rich new insights relating to procurement in times of crisis, contributing to efforts to advance beyond outdated approaches for resilience in literature. Practical contributions arise in highlighting the significance of adapted sourcing and recruitment, technology, collaboration, people and power of purpose in enabling agility and achieving the impossible

The Red Sea under the Caliphal Dynasties, c. 639–1171

Students of world history will be familiar with the Red Sea as a strategic communications corridor linking the Mediterranean to the Indian Ocean. This paper examines the Red Sea region between the seventh and twelfth centuries, when it was ruled by a succession of Islamic caliphal dynasties, namely, the Umayyads, ʿAbbāsids, and Fāṭimids. It first sets out a sketch of the political history of the Red Sea and its constituent hinterland polities, including particularly Egypt, Sudan, al‐Ḥijāz, and Yemen, drawing attention to episodes and processes in which the Red Sea was significant. A section on Africa and Arabia explores the Red Sea as a zone of economic and social interaction; another section deals with the historic shift of Indian Ocean trade from the ʿAbbāsid Persian Gulf to the Fāṭimid Red Sea. Finally, the impact of the Red Sea on its constituent hinterland polities and the wider sweep of Islamic history is considered

Nothing Lasts Forever: Environmental Discourses on the Collapse of Past Societies

The study of the collapse of past societies raises many questions for the theory and practice of archaeology. Interest in collapse extends as well into the natural sciences and environmental and sustainability policy. Despite a range of approaches to collapse, the predominant paradigm is environmental collapse, which I argue obscures recognition of the dynamic role of social processes that lie at the heart of human communities. These environmental discourses, together with confusion over terminology and the concepts of collapse, have created widespread aporia about collapse and resulted in the creation of mixed messages about complex historical and social processes

Réseau éphémère : la disparition des villes antiques britanniques et ses implications continentales

This paper discusses the rapid disappearance of the entire urban network in Britain in the decades around 400. The textual evidence is extremely limited, but the archaeology indicates that this was one feature of a wider social breakdown which occurred at the end of Roman rule, after a period of gradual urban decline in the fourth century. The cities were very largely abandoned. Although a few individual sites show signs of occupation, these are exceptional, and there is nothing to distinguish them from rural settlements. The situation in post-Roman Gaul is very different ; here cities retained a variety of functions and the urban network underwent only gradual evolution. But this impression of stability owes much to texts ; the archaeology of late antique and early medieval Gallic cities suggests that it is more indicative of the persistence of urban-based institutions than of classical urbanism. This helps to explain the contrast with Britain, where post-Roman societies had no particular use or need for cities.Cet article montre la disparition rapide de l'ensemble du réseau urbain britannique autour de 400 ap. J.-C. Les textes sont très rares à ce sujet, mais l'archéologie indique qu'il s'agit là d'un des aspects d'une importante cassure sociale à la fin de la domination romaine, après un déclin progressif des villes durant le IVe s. : les cités furent largement abandonnées. Bien que quelques rares sites présentent des traces d'occupation, ils sont exceptionnels et rien ne les distingue des installations rurales. La situation en Gaule post-romaine est très différente, où les cités conservent une activité très diversifiée et où le tissu urbain connaît une évolution progressive. Toutefois, cette impression de stabilité doit plus aux textes qu'à l'archéologie, qui suggère que les villes dans l'Antiquité tardive et au haut Moyen Âge sont davantage le reflet de la persistance des institutions civiques que d'un urbanisme classique. Ceci contribue à expliquer le contraste avec la Bretagne où la société post-romaine n'a ni l'usage ni le besoin de cités.Loseby Simon T. Réseau éphémère : la disparition des villes antiques britanniques et ses implications continentales. In: Capitales éphémères. Des Capitales de cités perdent leur statut dans l’Antiquité tardive, Actes du colloque Tours 6-8 mars 2003. Tours : Fédération pour l'édition de la Revue archéologique du Centre de la France, 2004. pp. 255-267. (Supplément à la Revue archéologique du centre de la France, 25

L'ajustement de l'offre et de la demande sur les marchés des produits agricoles de la C.E.E. : le cas du secteur laitier

[eng] The problems of assessing both the extent and the cost of market imbalance are discussed, and the difficulties of reconciling national and Communauty policy objectives noted. With reference to the dairy industry, it is suggested that, in the absence of harmonization of economic policies in areas other than agriculture, measures to restrict supply should take into account the particular problems arising for countries where consumption exceeds production. Certain measures are proposed, which might be implemented in the context of a policy aiming to gradually reduce the level of public support in agriculture. [fre] La mesure de l'ampleur et du coût des déséquilibres sur les marchés est difficile et fait apparaître les contradictions entre objectifs politiques nationaux et communautaires. Dans le cas du secteur laitier, l'absence d'harmonisation dans les politiques économiques non agricoles conduit à recommander que les restrictions quantitatives tiennent compte des problèmes particuliers des pays où la production ne couvre pas les besoins. Un certain nombre de mesures sont proposées. Elles pourraient. s'insérer dans des politiques visant à réduire progressivement les dépenses publiques pour le secteur agricole.

Marseille in late antiquity and the early Middle Ages

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