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Question on High Alumina Cement (HAC)

My building may contain High Alumina Cement concrete. How can I tell and what should I do if it does?

Answer

High Alumina Cement (HAC) differs from Portland cement, being composed calcium aluminates rather than calcium silicates. Its rapid strength development made HAC popular from 1950 to 1970. However, mineralogical ´conversion´ sometimes caused reductions in concrete strength and increased vulnerability to chemical attack. HAC is also known as Calcium Aluminate Cement (CAC).

HAC concrete was effectively banned for use in new structural concrete in the UK following a few well publicised collapses in the 1970s. Time and experience have shown that the primary causes of these collapses were poor construction details or chemical attack, rather than problems with the concrete itself. Most HAC concrete in the UK went into precast beams. Up to 50,000 buildings with similar beams continue to remain successfully in service today in the UK. The beams can be found in public and industrial buildings such as schools, flats and business units

If the presence of HAC is suspected, confirmation requires chemical or laboratory testing of samples. If the presence of HAC is confirmed, professional advice on its condition may be required. It is important to remember, however, that the majority of these buildings are performing perfectly adequately.


Acknowledgement: The Concrete Society


Other references:BRE Information Paper IP11/98, Assessing carbonation depth in ageing HAC concrete, June 1998.
BRE Digest 392: Assessment of existing high alumina cement concrete construction in the UK
BRE Report ´Durability of ageing high alumina cement (HAC) concrete: A literature review and summary of BRE research findings´
BRE Information Paper IP 8/00, March 2000,The durability of pre-cast HAC concrete in buildings.
BRE Special Digest SD3, Nov 2002 HAC concrete in the UK