Climate Change, Materials And Materials Use, Winter 2007-08

Climate change

materials and materials use Sébastien Dupray and Jonathan Simm from HR Wallingford look at how climate change is affecting materials and their structures

Climate change is now a recognised phenomenon that will significantly affect the coastal environment. It is not exactly clear, however, how this phenomenon and materials in the coastal environment relate to one another, in particular the effects of sea level rise, changing storm severity and changes in water temperature on materials. What is known is that material properties and behaviours are influenced strongly by the form of structures in which they are embodied.

Structures Structures taken in a broad sense, ie artificial structures such as sea defences or natural structures such as beaches, may be looked at by the function for which they are designed or they naturally display. The primary functions of sea defence, coast protection or beach, for example, might include limitation or control of overtopping, protection from the aggressiveness of the sea, along with environmental and amenity functions. As a consequence, their position, their geometry, their components and their materials deserve specific consideration since they control the stability and the performance of the existing or planned structure. The anticipated material deterioration rates are an important consideration, especially in situations where normal deterioration rates may be affected by

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The edge Winter 2008

climate change. There will also be impacts of climate change on the structures themselves in terms of their future stability and performance.

Selecting the most appropriate maintenance strategy The concept of performance-based asset management (widely supported at HR Wallingford) means that selecting the most appropriate maintenance strategy is strongly emphasised. • The ‘do nothing’ option critically relies on the hypothesis made regarding long term material properties and deterioration. • The ‘repair’ option may be required to ensure further deterioration of the material does not occur, but would generally require detailed consideration of material compatibilities especially when older structures are repaired with products of a newer generation. The composition of cementitious product, for example, has dramatically changed over the centuries and the use of recent repair products should be considered with care. • The ‘upgrade’ or ‘demolish and build new’ option would in some cases be an option to address sea level rise in particular in low lying coastal areas. Due to the, sometimes intensive, use of space in coastal areas, many works would be limited to the footprint of the previous structure. This may require the use of innovative forms of construction, as well as material types such as composites. In addition, combination of soft and hard types of approaches would certainly be increasingly frequent to limit the use of the scarcer materials to places where it is the only alternative.

Materials in the coastal environment The relationship between structure and material is complex and has been attracting the attention of coastal engineers and materials specialists for years. The following key considerations for materials in the coastal environment with regards to climate change might be considered: availability, impacts of transport, durability, buildability, adaptability, environmental balance. These considerations may apply both to natural coastal material (such as sand/pebble/cobbles on beaches or from dredging), to raw conventional construction materials (such as natural quarried rock, timber, concrete, steel, binders) as well as to recycled/ secondary materials.

The effect of climate change on materials Climate change will directly affect materials. The increase in air and water temperature will definitely modify bacteriological and chemical reaction processes leading to increased deterioration of some rock minerals, corrosion of steel, alteration of concrete, for example. It would also modify the biological environment of these materials, allowing populations of marine borers to develop in new areas where previously they presented no threat for timber structures. Although these trends have been identified, the challenge is now to assess their degree and geographical extent.

The impact of materials on climate change As important as the impact of climate change is on materials, materials

use during extraction, design and construction also has an impact on climate change. For both artificial and natural structures, there is concern about the availability of suitable materials to allow structures stability and performance. A large number of glacial relic beaches around the UK coasts, for example, are made of stone sizes which are no longer available from marine sources. The sustainability of maintaining these beaches as defences should be studied with reference to various scenarios of sourcing including the use of dredged materials, raw or recycled/secondary materials. Shortages of beach sand/pebble can be overcome by using local quarried stone or even local stabilised wastes, such as glass cullet or tyre balls, instead of further exploiting marine sediments.

This may require designers to consider supply-based design approaches rather than more conventional demand-based design approaches. Northern Europe has shown that such approaches are possible, but this may require innovative design approaches for some coastal structures. A possible drawback is that local or recycled materials may be of poorer durability. Deterioration rates and anticipated changes of properties with time will therefore need to be considered in the design as well as in the asset management scheme to allow for regular and easy repair.

While carbon dioxide (CO2) emissions are associated with materials production, studies have shown that the majority of emissions associated with construction relate to the transport of materials to the site. A hierarchy of sourcing (available/reclaimed or recycled/primary) and transport (on site/locally sourced/transported from further afield by train, ship or road) options is generally used to compare supply scenarios.

Location, location, location

Dr Sébastien Dupray is senior civil engineer of the French Institute for Maritime and Fluvial Works (CETMEF), currently seconded as a project manager to HR Wallingford.

Jonathan Simm is Technical Director for Engineering at HR Wallingford.

In many cases, poor durability of structures is due, not to the material quality itself, but to inadequate consideration of the aggressive nature of the dynamic coastal environment in which structures are to be built and maintained. Early consideration of buildability during design is essential to ensure that materials will be placed and used in conditions that allow them to perform at their best. The risks of structure/material degradation

associated with climate change (or not) would then be limited, also limiting the amount of repairs. The environmental balance of the material in use, as well as its use in construction, has now become an indicator as part of the decision making process, in particular with reference to CO2 emissions. The awareness of the industry as well as its efforts to reduce the CO2 footprint of material production and construction have been increasing although better understanding of these issues is still needed.

Conclusion Climate change will affect structures and materials. Some anticipated effects on material deterioration have already been identified although further research is still required to define them in engineering terms. More challenging is without doubt the need to consider in more depth, the material aspects of construction during the design. In particular, the holistic study of materials should grow and take into account availability, impacts of transport, durability, buildability, adaptability and environmental balance aspects.

HR Wallingford provides analysis, advice and support in engineering and environmental hydraulics and in the management of water and the water environment. The edge Winter 2008

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