- Email: [email protected]
Second international conference on cryogenic concrete
Conference reports
duced in the USA in the 1940s, formed the theme of another paper. In fibre form, these fibres have some 4 0 - 5 0 % of AI203 and 5 0 - 6 0 % of SiO2 with fibre lengths of 40 2 5 0 m m and fibre diameter 3-181~m. They are available as fibres, blankets, felts and textile products. Known as fibrefrax, the fibres have high temperature stability, light weight, shock resistance, chemical stability and electrical resistivity. It was clear from the papers presented that many developments w e r e still in their early stages, but that they had a w i d e range of potential and ability to replace asbestos. There w a s no clear answer, however, as to the nature of their long term durability, nor was there any unmistakable evidence as to their freedom from health hazards. Obviously a lot more research needs to be undertaken, but the development of asbestos replacement material is well in hand; however, the question as to w h e t h e r asbestos can be totally replaced remains unanswered.
Second International Conference on Cryogenic Concrete, Amsterdam, The Netherlands, 4 7 October, 1983 Attendance by nearly 200 delegates from 17 countries must have gratified the organisers of this conference, the Concrete Societies of the Netherlands and the UK. Drawn from designers, builders, purchasers, users, government and academia, the delegates' presence accorded recognition to the importance of the subject. With the first three days being allocated to the formal presentation of papers (and often lively discussion) and the accompanying exhibition, the conference opened with a keynote session on the liquefied gas storage for the Fife ethylene project at Mossmorran in Scotland. There then followed in sequence ten sessions on design philosophy, research on reinforcing bars, earthquakes, research on properties of concrete, aspects of analysis, tank proiects, blast, research on prestressing steel, extreme thermal loads, and liquid impact The apparent structural simplicity of the tanks built to date, under construction or contemplated belies the complexity of the problerns involved. In the main used to store hazardous liquids (such as liquefied gaseous hydrocarbons like methane natural gas), they incur additional penalties because of the low temperatures of refrigeration used to reduce the gas volume by liquefaction (by a factor of 1/600. say. but at around -165°C for methane). Added to the problems inherent in this are the need to guard against hazard caused by tank failure, for example, or by threat as from an adjacent fire or impact from a Boeing 747 aircraft. Observation and experiment are rendered particularly difficult because of the temperature and can be dangerous because of the stored materials Such questions were discussed at varying length and at times very comprehen sively due to the variety of ~nterests represented. Summary of the 45 or so papers in a short space is impossible, of course, but a flavour may be obtained by rearranging the content Inevitably there is some overlap but there is a degree of Iogl(: ~n considering the headings of research, design (embracing analysis and load estimation)
124
and construction. It ought to be remembered too that the conference was intended to provide an update on the highly successful first conference held in Newcastle upon Tyne in 1981.
RESEARCH Normal reinforcement is generally considered unsuitable for cryogenic use due to its brittleness, consequently special reinforcing steels have been produced. Depending on the design load conditions, various requirements are made of the manufacturer whose viewpoint was given. These requirements include: minimum yield strength, minimum elongation and minimum elongation after rupture on notched tensile specimens (all at the design temperature) for static load conditions; adequate yield strength, minimum yield strength after rupture and high impact resistance (Charpy) where dynamic load also is expected. Relatively conventional tests give appropriate results but, at least in Spain and Japan, fracture toughness assessment is being essayed to seek more meaningful values than from say, Charpy tests. Bond is currently being studied in Belgium. Prestressing steels present fewer problems. However, tendon-anchorage assemblies must be demonstrably acceptable, as indicated in work in Germany and Spain: in the latter examination was also reported of temperature distribution in specimens under test. Reinforcing and prestressing steels are also discussed in a paper from the UK. Research on concrete properties drew the largest number of contributions to any single session (eight papers with a further brief communication from the floor). They included the conference's sole consideration of marine applications. Particular attention was also paid in the UK contributions to the relation of concrete behaviour to design and to permeability. Thermal deformation also received 'plural' attention as did certain features of testing. To select various conclusions at random may be unfair but it might give some flavour of the session: marine applications are feasible, moisture content is important, there is a greater scatter of results at low temperatures, concrete impermeable to methane can be produced, lightweight concrete is more impermeable, thermal deformation under load differs from that in its absence, temperature cycling need not be detrimental with appropriate design, water/ cement ratio is very important and must be kept low. DESIGN Within the broad definition of design given above a wide variety of papers was presented. From the Netherlands came a review of the vital question of safety, emphasising the need for agreement on loads (both normal and disastrous) and the need for specification of calculation procedures (including materials properties to be adopted) i.e. design methods. There was a specific design case in the Netherlands discussed succeeded by Japanese in-ground and Spanish overground examples. Grossly over-simplifying, there are two main applications for concrete: in the actual refrigerated gas containment (i.e. in the principal structure) and in the outer protective wall (whether the principal structure is of steel or concrete) i.e. as secondary
Conference reports
containment in the event of rupture of the primary containers. One almost controversial area seems still to be whether or not the connection between wall and base slab should be rigid. Analysis of structures is essential to their design. For superficially simple structures such as storage tanks static analysis is straightforward. However, dynamic analysis is a great deal more complex and difficult and depends very largely on successful modelling of loads and structural response. In the present case there is the added complication of such factors as liquid sloshing, degree of interaction between inner and outer tanks or walls and between structure and foundation (whether piled or not), and the role of interstitial insulation. These topics were covered in various papers concerned with analysis, seismic loading, blast (from explosion) and liquid impact (due to inner tank failure). General conclusions are impossible in such limited space other than to remark that various criteria were defined and techniques described ranging from basic initial simple assumptions to highly sophisticated calculations. Aggravating the situation are the extreme temperatures involved and their consequences. Clearly very low temperatures must be taken into 'global' account but so must local effects due to, say, accidental spillage or insulation damage. It is easy too to visualise the possibility of fire although the consideration may be more appropriate to safety walls (if a storage tank ignites then it may be sacrificed resulting in radiation on adjacent structures). At any rate closer study is warranted of a group of papers
presenting a number of aspects.
CONSTRUCTION Several papers (classed as 'tank projects') describe actual construction and techniques adopted in practice. Perhaps not quite so esoteric as some of what is described above, nevertheless it is an important subject. Even so elementary a consideration as access to the interior of a tank during construction can cause serious problems. Continuity of prestressing for externally wrapped tanks must clearly be assured. Materials actually used must be tested and monitored for their cryogenic performance. All these raise issues discussed in a group of five papers which form an essential component of a comprehensive coverage of the subject. It is difficult to do justice to such a conference in such a space. Certainly it was a worthy successor to its progenitor in Newcastle. There is no doubt that its proceedings when published will form essential reading for anyone concerned with concrete structures for refrigerated gas storage. Not just that, however, because it has relevance to low temperature concrete structures more generally. As to the future and its relevance particularly to this journal, there are indications that lightweight concrete could have a significant role and fibre reinforcement has its part to play. As yet this is at a research level and work has been, is being and will be done to explore its possibilities. In the classic words of advertising, watch this space!
125
duced in the USA in the 1940s, formed the theme of another paper. In fibre form, these fibres have some 4 0 - 5 0 % of AI203 and 5 0 - 6 0 % of SiO2 with fibre lengths of 40 2 5 0 m m and fibre diameter 3-181~m. They are available as fibres, blankets, felts and textile products. Known as fibrefrax, the fibres have high temperature stability, light weight, shock resistance, chemical stability and electrical resistivity. It was clear from the papers presented that many developments w e r e still in their early stages, but that they had a w i d e range of potential and ability to replace asbestos. There w a s no clear answer, however, as to the nature of their long term durability, nor was there any unmistakable evidence as to their freedom from health hazards. Obviously a lot more research needs to be undertaken, but the development of asbestos replacement material is well in hand; however, the question as to w h e t h e r asbestos can be totally replaced remains unanswered.
Second International Conference on Cryogenic Concrete, Amsterdam, The Netherlands, 4 7 October, 1983 Attendance by nearly 200 delegates from 17 countries must have gratified the organisers of this conference, the Concrete Societies of the Netherlands and the UK. Drawn from designers, builders, purchasers, users, government and academia, the delegates' presence accorded recognition to the importance of the subject. With the first three days being allocated to the formal presentation of papers (and often lively discussion) and the accompanying exhibition, the conference opened with a keynote session on the liquefied gas storage for the Fife ethylene project at Mossmorran in Scotland. There then followed in sequence ten sessions on design philosophy, research on reinforcing bars, earthquakes, research on properties of concrete, aspects of analysis, tank proiects, blast, research on prestressing steel, extreme thermal loads, and liquid impact The apparent structural simplicity of the tanks built to date, under construction or contemplated belies the complexity of the problerns involved. In the main used to store hazardous liquids (such as liquefied gaseous hydrocarbons like methane natural gas), they incur additional penalties because of the low temperatures of refrigeration used to reduce the gas volume by liquefaction (by a factor of 1/600. say. but at around -165°C for methane). Added to the problems inherent in this are the need to guard against hazard caused by tank failure, for example, or by threat as from an adjacent fire or impact from a Boeing 747 aircraft. Observation and experiment are rendered particularly difficult because of the temperature and can be dangerous because of the stored materials Such questions were discussed at varying length and at times very comprehen sively due to the variety of ~nterests represented. Summary of the 45 or so papers in a short space is impossible, of course, but a flavour may be obtained by rearranging the content Inevitably there is some overlap but there is a degree of Iogl(: ~n considering the headings of research, design (embracing analysis and load estimation)
124
and construction. It ought to be remembered too that the conference was intended to provide an update on the highly successful first conference held in Newcastle upon Tyne in 1981.
RESEARCH Normal reinforcement is generally considered unsuitable for cryogenic use due to its brittleness, consequently special reinforcing steels have been produced. Depending on the design load conditions, various requirements are made of the manufacturer whose viewpoint was given. These requirements include: minimum yield strength, minimum elongation and minimum elongation after rupture on notched tensile specimens (all at the design temperature) for static load conditions; adequate yield strength, minimum yield strength after rupture and high impact resistance (Charpy) where dynamic load also is expected. Relatively conventional tests give appropriate results but, at least in Spain and Japan, fracture toughness assessment is being essayed to seek more meaningful values than from say, Charpy tests. Bond is currently being studied in Belgium. Prestressing steels present fewer problems. However, tendon-anchorage assemblies must be demonstrably acceptable, as indicated in work in Germany and Spain: in the latter examination was also reported of temperature distribution in specimens under test. Reinforcing and prestressing steels are also discussed in a paper from the UK. Research on concrete properties drew the largest number of contributions to any single session (eight papers with a further brief communication from the floor). They included the conference's sole consideration of marine applications. Particular attention was also paid in the UK contributions to the relation of concrete behaviour to design and to permeability. Thermal deformation also received 'plural' attention as did certain features of testing. To select various conclusions at random may be unfair but it might give some flavour of the session: marine applications are feasible, moisture content is important, there is a greater scatter of results at low temperatures, concrete impermeable to methane can be produced, lightweight concrete is more impermeable, thermal deformation under load differs from that in its absence, temperature cycling need not be detrimental with appropriate design, water/ cement ratio is very important and must be kept low. DESIGN Within the broad definition of design given above a wide variety of papers was presented. From the Netherlands came a review of the vital question of safety, emphasising the need for agreement on loads (both normal and disastrous) and the need for specification of calculation procedures (including materials properties to be adopted) i.e. design methods. There was a specific design case in the Netherlands discussed succeeded by Japanese in-ground and Spanish overground examples. Grossly over-simplifying, there are two main applications for concrete: in the actual refrigerated gas containment (i.e. in the principal structure) and in the outer protective wall (whether the principal structure is of steel or concrete) i.e. as secondary
Conference reports
containment in the event of rupture of the primary containers. One almost controversial area seems still to be whether or not the connection between wall and base slab should be rigid. Analysis of structures is essential to their design. For superficially simple structures such as storage tanks static analysis is straightforward. However, dynamic analysis is a great deal more complex and difficult and depends very largely on successful modelling of loads and structural response. In the present case there is the added complication of such factors as liquid sloshing, degree of interaction between inner and outer tanks or walls and between structure and foundation (whether piled or not), and the role of interstitial insulation. These topics were covered in various papers concerned with analysis, seismic loading, blast (from explosion) and liquid impact (due to inner tank failure). General conclusions are impossible in such limited space other than to remark that various criteria were defined and techniques described ranging from basic initial simple assumptions to highly sophisticated calculations. Aggravating the situation are the extreme temperatures involved and their consequences. Clearly very low temperatures must be taken into 'global' account but so must local effects due to, say, accidental spillage or insulation damage. It is easy too to visualise the possibility of fire although the consideration may be more appropriate to safety walls (if a storage tank ignites then it may be sacrificed resulting in radiation on adjacent structures). At any rate closer study is warranted of a group of papers
presenting a number of aspects.
CONSTRUCTION Several papers (classed as 'tank projects') describe actual construction and techniques adopted in practice. Perhaps not quite so esoteric as some of what is described above, nevertheless it is an important subject. Even so elementary a consideration as access to the interior of a tank during construction can cause serious problems. Continuity of prestressing for externally wrapped tanks must clearly be assured. Materials actually used must be tested and monitored for their cryogenic performance. All these raise issues discussed in a group of five papers which form an essential component of a comprehensive coverage of the subject. It is difficult to do justice to such a conference in such a space. Certainly it was a worthy successor to its progenitor in Newcastle. There is no doubt that its proceedings when published will form essential reading for anyone concerned with concrete structures for refrigerated gas storage. Not just that, however, because it has relevance to low temperature concrete structures more generally. As to the future and its relevance particularly to this journal, there are indications that lightweight concrete could have a significant role and fibre reinforcement has its part to play. As yet this is at a research level and work has been, is being and will be done to explore its possibilities. In the classic words of advertising, watch this space!
125