# What are the possible implications of the heating of the structural stonework of Notre-Dame cathedral during the fire?

Yesterday, Notre Dame cathedral caught fire. The roof and the central spire were destroyed and some of the stonework was subjected to high temperatures for an extended period.

What are the likely implications for the strength of the individual stones, the walls and other structures?

• How hot did the stones get? Were they heated to an even temperature all the way through? Does rapid cooling have an effect? – Solar Mike Apr 16 '19 at 15:46
• I guess the peak temperature depends on their location with respect to the hottest part of the fire. I think wood-fired kilns and furnaces can get up to 1200C and are lined with firebrick. I guess duration of the exposure would have an effect too. I hadn't thought about rapid cooling, but presumably it must have happened in some areas that were being sprayed with water – Dave Gremlin Apr 16 '19 at 15:53

There is a specific temperature range that causes calcination of limestone.

$$\text{CaCO}_3 + \text{Heat} = \text{CaO} + \text{CO}_2$$

The temperature range of reaction is 840°C-900°C and is used for creating cement in a kiln. Adding oxygen and sulphur dioxide causes limestone to become gypsum... which is structurally significantly weaker than limestone from which the old cathedral is built. Above 900°C the carbon dioxide emissions accelerate beyond permissible emissions levels.

Effectively, superheating limestone causes chemical reactions that result in physical changes of the structural material blocks. Exfoliation is a likely result with degradation of surfaces reaction to other chemical compounds in the fire itself. If sulphur compounds were present then there is a risk that the stone may have been changed into another type of rock to varying depths.

Add water to carbon dioxide and it creates carbolic acid which may attack limestone.

Carbonic acid, hydrochloric acid and acetic acid are some acids that react with limestone, causing it to dissolve. Each of these acids reacts with limestone in different ways. Limestone is made up mainly of calcite that is the chemical compound calcium carbonate.

Carbonic acid, which is a weak acid, forms when rainwater and carbon dioxide in the air react with one another. When carbonic acid comes into contact with limestone or calcium carbonate, it can cause it to dissolve over a long period of time. In nature, this reaction leads to the formation of caves.

• So did the walls get that hot? – Solar Mike Apr 17 '19 at 6:03
• It's possible considering the colour of the flames and the height but not uniformly – Rhodie Apr 17 '19 at 6:53
• +1 I didn't realise that it was built of limestone. Presumably, since it is so porous, you'd also get the potential for spalling due to water turning to steam? – Dave Gremlin Apr 17 '19 at 8:16
• Quite possibly. Only once structural testing is done will they know by very much doubt it will become public knowledge – Rhodie Apr 18 '19 at 22:20
• Irreversible mechanical damage occurs at temperatures well below calcination temperatures. – blacksmith37 Apr 19 '19 at 15:20

Concrete can be significantly damaged at 600F but specifics are highly variable according to the Portland Cement association. It depends on the ratio of cement to aggregate , sizes of aggregate, composition of the aggregate, heating/cooling rate, duration, etc. Specific information on sandstone and limestone is even more difficult to find. Rock can even crack during the fire depending on moisture content and how fast it is heated. I expect it will be many weeks or months before objective information is available.

• I don't believe Portland cement was used back in the 14th century... – Rhodie Apr 18 '19 at 22:19

Two factors that are positive.

• Masonry, grout, concrete are some of the best fire resistant materials.
• Exposure to the hottest flames has been avoided by the fact that geometry of the building and its long hallways mostly acted as a ventilation manifold to feed the flames with fresh oxygen, and kept the walls awash with cool air.
• They have some of the best experts in preservation and rehab of these world heritage structures.
• It's incredible and offensive even why safety measures, fire sprinklers, alarms were not installed especially during the construction or failed to work.
• Back in the 11th and 12th centuries the fire alarms etc did not exist "during construction" but if you mean during the refurbishment... – Solar Mike Apr 16 '19 at 19:02
• You have to balance risk and reward. A sprinkler system that operates when not required could cause irreparable damage to the decoration of the building. comparable with a fire. Not to mention the potential damage and visual intrusion caused by installing such a system. – alephzero Apr 16 '19 at 19:08
• … there is also the challenge of installing such a system. For example, nobody has yet worked out how the spire of Salisbury Cathedral (the tallest in the UK) was built at all, given the technology available at the time. By the logic of modern structural engineering there must have been a temporary supporting structure that was later removed, but there is no historical record of what it was. This has been a puzzle for a long time - the first person who attempted to solve it (and failed) was Sir Christopher Wren, the architect of St Paul's Cathedral and a contemporary of Isaac Newton. – alephzero Apr 16 '19 at 19:13
• I was there 6 months ago and noticed latest safety and fire protection measures, in Pantheon in the Louvre museum, many other places, Sacre Coeur . Paris is a just a expansive museum with life streaming through it. In louver they have automatic dropping glass cages to protect Mona Lisa from water damage and arson.They make billions off tourists each year. they got to have measures in place, for every possibility. It was a great loss to world culture. – kamran Apr 16 '19 at 19:41