Recent Developments with High Alumina Cement and Risk Management

A joint meeting of the Construction Materials Group, the Concrete Society London & South East Club and the Cementitious Materials Group of the Institute of Materials, Minerals and Mining was held at SCI International Headquarters, 14/15 Belgrave Square, London SW1X 8PS, UK on 22 January 2009. There were two technical presentations:

Risk management is becoming increasingly important in managing construction projects. Innovation and invention are very prevalent in the construction sector, particularly relating to new products. New markets are created, resulting in improved performance and value. However, before a new product enters the market it is preceded by product development that may result in pre-production prototypes. These prototypes may be regarded as original models from which improved types can be made. Changes may still be made resulting from experience in use or when subjected to trials. Manufacturers often seek endorsement of their innovative products by Agrément, product conformity certification, affidavits technical reports etc. There has to be a balance between the intent and the actuality, which can cause problems if the product cannot be used because it has not been fully assessed and cannot be fully assessed until it is used! Common sense and suitable risk management assessment need to prevail.

Extensive engineering and scientific studies have been carried out in more recent years, following three building collapses in the UK in the 1970s that led to the banning of HAC in structures. The collapses were primarily due to poor design work and conversion of the initially formed hydrates into a dense hydrogarnet phase that led to increased permeability and structural weakening. The Concrete Society had published their Technical Report in 1997, which reassessed the situation. This reassessment led to the blanket ban on HAC in structures being lifted subject to numerous safeguards in the light of more technical information being available, such as the water/cement ratio being limited to 0.40 in mortars and concretes. More was learnt about the chemistry, like the importance of the ferrite phase in ameliorating compressive strength and durability in dark grey/black HAC. The message should get across that HAC is a good speciality product if used properly, and not a simple replacement for Portland cement.

These talks generated considerable technical discussion among the engineers and scientists present. One discussion included a ‘link’ between the two talks on ostensibly different presentations. When some years back there was a large fire in the Channel Tunnel which caused considerable damage, this damage could have been ameliorated had HAC (with high fire resistance) been used instead of Portland cement during construction of the tunnel. At the time the tunnel was well over budget and nobody would have considered using the more expensive HAC, since talk of a likely fire would not have been believed! With benefit of hindsight, risk management would have been a consideration here, but, if it had been suggested in advance, the possibility of a such fire would have been rejected straightaway as being nonsensical!

A larger than expected audience of 24 on a cold January evening clearly enjoyed these two  thought-provoking presentations with plenty of high quality discussion.

John Bensted

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