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Some neglected areas of industrial chemistry in construction materials

asbestos

18 Dec 2012

Following the announcement of new studentships in 'neglected science', thanks to the legacy of Dr Sydney Andrew FRS, the Construction Materials Group has come up with a list of chemicals which tend to be neglected.

Asphalt, bitumen, cement and concrete are important areas of industrial chemistry that get overlooked. While these are complex materials, they are often not regarded as ‘proper chemical entities’.

Asbestos is also neglected, especially in finding good methods of disposal. More research and development is undoubtedly required for finding better ways of dealing with these materials in the future. These challenges are likely to take in both science and engineering aspects.

Some notes on these important materials follow:

Asphalt and Bitumen

  • These two construction materials are mostly interchangeable in their nomenclature, unless aggregates are present, when the term asphalt concrete is commonly employed; the name bitumen is used for the black, sticky material of highly viscous liquid or else for the partially-solid petroleum product.
  • Long ago in ancient Babylon sticky, bituminous material oozed out from the desert terrain and did have some uses at that time in conjunction with the available limes.
  • Natural bitumen today is also called crude bitumen or asphalt that has similar viscosity to what is given by cold molasses.
  • In modern times considerable natural deposits of asphalt/bitumen (from Trinidad, for example) have been utilised, and refined products (often also called pitch or tar) are regularly involved in road construction.
  • Such bitumen products include refined residues from distillation of carefully-selected crude oils by fractional distillation (boiling point ca. 525ºC).
  • These materials are very useful for waterproofing and for manufacturing roofing-felt and flat-roofs of buildings, plus asphalt concretes containing aggregates for major construction works.

Cement and Concrete

  • Cements are materials that bind other materials together with water:
  • Mortars are cement + fine aggregate (like sand or gravel) + water;
  • Concretes are cement + fine aggregate (like sand or gravel) + coarse aggregate (such as sand and rocks) + water.
  • There are many types of cements available nowadays, viz. Portland, high alumina, slag, pozzolanic, hydrophobic, coloured, masonry, oil-well, decorative, natural, other chemical cements etc, which enable structures of different kinds and, usefully, more choices for mortars and concretes to be manufactured.
  • Portland cements are still in the vanguard for utilisation in modern building work.
  • There is at present increased employment of composite cements, mortars and concretes in the preparations thereof for usage by scientists and engineers.

Asbestos Minerals

  • Vast numbers of buildings and structures of many different kinds throughout the world are still in use, where asbestos materials are integral to their fabric.
  • Most of those arose prior to the recognition of serious health and safety hazards.
  • In the UK many schools and universities contain asbestos.
  • The National Union of Teachers has a board member dealing with current problems of asbestos-related diseases from teachers who have been exposed to asbestos in their work at school.
  • Unfortunately there is no equivalent body dealing with universities!
  • Individual surveys are the keys to understanding the full extent of what happens.
  • Asbestos may well be sealed off and as such present only limited concern.
  • Methods of sealing off to prevent air contamination may be an option.
  • Controlled demolition is clearly the most testing scenario.
  • Individual surveys are key to understanding the full extent of difficulties found.
  • Supersonic aircraft need asbestos linings because of the high heat levels generated, because, unfortunately, no other materials can yet match the extensive diversity of performance from asbestos minerals.
  • There is a significant lack of up-to-date research for using modern instrumental techniques, such as the latest types of X-ray diffraction, X-ray crystallography and nuclear magnetic resonance, for experimentation.
  • Contemporary methods would also offer a greater detail on the biochemical and medical nature of these techniques and possibly lead to safer usage.

John Bensted, Construction Materials Group

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