History and story of RAAC

[Mike4]

I've been trying to look up what exactly what RAAC is. No not what the acronym is for, but how and why it was developed, how it is made and the technical details of why it is a problem now. Also is it still in use and for what?

Trouble is, every link I find seems to lead into how to find out if your child's skool has it, why the government seem to have done nothing about it and how awful it all is.

So can any of our building professionals here tell us the back story of RAAC as a building material, or bung up any links please? Much obliged

[monabri]

https://www.concrete.org.uk/fingertips- ... ay&id=1068

"Reinforced Autoclaved Aerated Concrete (RAAC) panels are widely used in mainland Europe and less so in the UK.

These panels consist of autoclaved aerated concrete (sometimes called Aerated concrete) reinforced to form structural precast units. This form of concrete (really an aerated silica product) provides little protection to the corrosion of embedded metal and therefore a bituminous or cement latex coating is applied to the reinforcement as protection. It is typically used for walls, floor planks and roof planks.

Pre-1980 RAAC roof planks are now past their expected service life, there have been some failures and a safety alert has been issued by the Collaborative Reporting for Safer Structures (CROSS)"


Probably the selling point was that, being aerated, it needed less raw material, not as heavy, and provided some insulation.


https://www.lboro.ac.uk/news-events/new ... rete-raac/

Lots of pictures

https://www.google.co.uk/search?sca_esv ... =941&dpr=1

And from Wiki, the pros and cons of using it.

https://en.wikipedia.org/wiki/Autoclave ... resistance.

Pros

"- Improved thermal efficiency reduces the heating and cooling load in buildings.
-Porous structure gives superior fire resistance.
-Workability allows accurate cutting, which minimizes the generation of solid waste during use.
-Eco-friendly in nature not producing pollution in the environment and contributes to LEED rating green building material.[1]
-Resource efficiency gives it lower environmental impact in all phases from the processing of raw materials to the ultimate disposal of waste.
-Being lighter in weight the blocks can be handled easily. The lighter weight saves cost and energy in transportation, labour expenses, and increases chances of survival during seismic activity.
-Larger size blocks lead to faster masonry work.
-Reduces project cost for large constructions.
-Fire-resistant: AAC, like other concretes, is fire-resistant.
-Good ventilation: This material is very airy and allows the diffusion of water, reducing humidity inside the building. AAC absorbs moisture and releases humidity, helping to prevent condensation and other problems related to mildew.
-Non-toxic: There are no toxic gases or other toxic substances in autoclaved aerated concrete. It does not attract rodents or other pests, and cannot be damaged by them.
-Accuracy: Panels and blocks made of autoclaved aerated concrete are produced to the exact sizes needed before leaving the factory. There is less need for on-site trimming. Since the blocks and panels fit so well together, there is less use of finishing materials such as mortar.
-Long-lasting: The life of this material is longer because it is not affected by harsh climates or extreme weather changes, and will not degrade under normal climate changes."

Cons
The process of using AAC is somewhat complex, so builders have to undergo special training.
-Non-structural shrinkage cracks may appear in AAC blocks after installation in rainy weather or humid environments. This is more likely in poor-quality blocks that have not been properly steam cured. However, most AAC block manufacturers are certified and their blocks are tested in certified labs, so poor-quality blocks are rare.
-Has some brittle nature: requires more care than clay bricks to avoid breakage during handling and transporting.
-Fixings: the somewhat brittle nature of the blocks requires longer, thinner screws when fitting cabinets and wall hangings. Special wall fasteners (screw wall plug anchors) designed for autoclaved aerated concrete including gypsum board and plaster tiles are available at a higher cost than standard expandable wall plugs, including special safety-relevant anchors for high load bearing;[30][31][32] It's recommended to drill fixing holes using HSS drill bits on a steady constant speed without hammer-action.[30][31] Masonry drill bits and standard expandable wall plugs are not suitable for use with AAC blocks.[31]
- Using AAC blocks alone would require very dense walls to achieve the insulation levels demanded by newer building codes in Northern Europe

[88V8]

The process of using AAC is somewhat complex, so builders have to undergo special training.

Anything that requires extra care from the building industry is doomed.

V8

[Mike4]

Hmmm the material itself bears a remarkable resemblance to Thermalite aerated building blocks.

[Dod101]

https://www.concrete.org.uk/fingertips-nuggets.asp?cmd=display&id=1068

"Reinforced Autoclaved Aerated Concrete (RAAC) panels are widely used in mainland Europe and less so in the UK.

These panels consist of autoclaved aerated concrete (sometimes called Aerated concrete) reinforced to form structural precast units. This form of concrete (really an aerated silica product) provides little protection to the corrosion of embedded metal and therefore a bituminous or cement latex coating is applied to the reinforcement as protection. It is typically used for walls, floor planks and roof planks.

Pre-1980 RAAC roof planks are now past their expected service life, there have been some failures and a safety alert has been issued by the Collaborative Reporting for Safer Structures (CROSS)"


Probably the selling point was that, being aerated, it needed less raw material, not as heavy, and provided some insulation.


https://www.lboro.ac.uk/news-events/new ... rete-raac/

Lots of pictures

https://www.google.co.uk/search?sca_esv ... =941&dpr=1

And from Wiki, the pros and cons of using it.

https://en.wikipedia.org/wiki/Autoclave ... resistance.

Pros

"- Improved thermal efficiency reduces the heating and cooling load in buildings.
-Porous structure gives superior fire resistance.
-Workability allows accurate cutting, which minimizes the generation of solid waste during use.
-Eco-friendly in nature not producing pollution in the environment and contributes to LEED rating green building material.[1]
-Resource efficiency gives it lower environmental impact in all phases from the processing of raw materials to the ultimate disposal of waste.
-Being lighter in weight the blocks can be handled easily. The lighter weight saves cost and energy in transportation, labour expenses, and increases chances of survival during seismic activity.
-Larger size blocks lead to faster masonry work.
-Reduces project cost for large constructions.
-Fire-resistant: AAC, like other concretes, is fire-resistant.
-Good ventilation: This material is very airy and allows the diffusion of water, reducing humidity inside the building. AAC absorbs moisture and releases humidity, helping to prevent condensation and other problems related to mildew.
-Non-toxic: There are no toxic gases or other toxic substances in autoclaved aerated concrete. It does not attract rodents or other pests, and cannot be damaged by them.
-Accuracy: Panels and blocks made of autoclaved aerated concrete are produced to the exact sizes needed before leaving the factory. There is less need for on-site trimming. Since the blocks and panels fit so well together, there is less use of finishing materials such as mortar.
-Long-lasting: The life of this material is longer because it is not affected by harsh climates or extreme weather changes, and will not degrade under normal climate changes."

Cons
The process of using AAC is somewhat complex, so builders have to undergo special training.
-Non-structural shrinkage cracks may appear in AAC blocks after installation in rainy weather or humid environments. This is more likely in poor-quality blocks that have not been properly steam cured. However, most AAC block manufacturers are certified and their blocks are tested in certified labs, so poor-quality blocks are rare.
-Has some brittle nature: requires more care than clay bricks to avoid breakage during handling and transporting.
-Fixings: the somewhat brittle nature of the blocks requires longer, thinner screws when fitting cabinets and wall hangings. Special wall fasteners (screw wall plug anchors) designed for autoclaved aerated concrete including gypsum board and plaster tiles are available at a higher cost than standard expandable wall plugs, including special safety-relevant anchors for high load bearing;[30][31][32] It's recommended to drill fixing holes using HSS drill bits on a steady constant speed without hammer-action.[30][31] Masonry drill bits and standard expandable wall plugs are not suitable for use with AAC blocks.[31]
- Using AAC blocks alone would require very dense walls to achieve the insulation levels demanded by newer building codes in Northern Europe

And I guess you could add a limited life span to the list of cons. That should be made clear; the point that it does not, this time, appear to be shoddy workmanship and there appears to be no 'scandal' involved. Unfortunate timing of the announcement though.

Dod