High alumina cement
High Alumina Cement (HAC), sometimes known as calcium aluminate cement (CAC) or aluminous cement, is composed of calcium aluminates, unlike Portland cement which is composed of calcium silicates. It is manufactured from limestone or chalk and bauxite (Special clay having extremely high alumina content).
HAC was first developed by Lafarge, the cement producer, and became available in the UK in 1925. It was used in particular for marine applications where it was considered to be resistant to chemical attack. It became popular in the 1950s, 60s and 70s, as it developed strength rapidly and so was relatively fast to manufacture. It was widely used in structural concrete such as pre-cast beams.
However, HAC was prone to a crystalline re-arrangement (or ‘conversion’), which could result in reduced strength and also vulnerability to chemical attack when exposed to water for long periods (perhaps as a result of poor detailing or poor manufacturing). This resulted in five high-profile structural failures of roof beams (where the presence of water is more likely) during the 1970s.
In 1975, MP for Sutton and Cheam, Neil Macfarlane, said “Those words—or the abbreviation "HAC"—are rapidly and relentlessly becoming a combination of misery, apprehension, worry and fear for thousands of people in the United Kingdom.”
HAC is no longer used in structural concrete in the UK, although it is still prevalent in buildings constructed in the 50s and 60s, and continues to be used for non-structural uses under the name Calcium Aluminate Cement (CAC).
In 1975, The Department of the Environment (DOE) Building Regulations Advisory Committee (BRAC) published guidance for design-check procedures for High Alumina Cement. Commonly known as the BRAC rules, this guidance remains the best advice available and continues to be used to assess the structural performance of buildings containing pre-cast HAC concrete beams.
It should be noted that many buildings that contain HAC components are entirely problem free, and the problems that have occurred have been traced back to manufacturing faults. However, If the presence of HAC is suspected, testing should be carried out, and if it is confirmed, HAC components should be assessed for strength and long-term durability. This is likely to require expert advice.
[edit] Related articles on Designing Buildings Wiki
- Aggregate.
- Asbestos.
- Brick.
- Cement.
- Coal ash.
- Concrete v steel.
- Defects in brickwork.
- Deleterious materials.
- Demolition.
- Ferro-cement.
- Hempcrete.
- How scientists solved the riddle of cement’s structure.
- Lime mortar.
- Portland cement.
- Pre-construction information.
- Research on novel cements to reduce CO2 emissions
- Screed.
- Sustainable materials.
- Types of cement.
[edit] External references
Featured articles and news
Designing sustainability and performance into buildings
Specifying and selecting sustainable resilient timber products.
Modifying wood to improve resistance to decay and movement.
A last minute, long look for built environment professionals.
The architecture of creative reuse. Book review.
Installing solar panels on listed structures.
Sustainable development global goals, history in progress?
"Unless we act now, the 2030 Agenda will become an epitaph for a world that might have been."
Mike Kagioglou FCIOB named CIOB President
'Sustainable Development Goals must be focus for construction'
BSRIA training; a look at what's on offer
From energy management to compliance training.
TESP video warns to beware of rogue trainers.
Highlighting the slippery tactics of non-approved providers.
New Building Safety Wiki launched
Boosting awareness and understanding of the new fire safety regime.
New playbook on AI in construction published by CIOB
How to get to grips with, and the best from AI.
Digital Construction Report NBS
BIM, cloud, off-site, immersive tech, AI, twins and sustainability.
ECA learning zone and industry focus video series
From updates and amendments to circular economy, emergency lighting and much more.
The Building People Communities Network
Celebrating and amplifying voices of the under-represented, this refugee week and pride month.
Pride of Place: queer heritage
Acknowledging and taking pride in LGBTQ histories.
A reminder of the five basic styles that determine columns.
Comments