Plutonic Rocks as Protection Layers to Concrete Exposed to Ultra-High Temperature

Our plain-English summary of Plutonic Rocks as Protection Layers to Concrete Exposed to Ultra-High Temperature, by F.F. de Mendonça Filho, C. Romero Rodriguez, E. Schlangen, et al (Materials, 2022).

The study

• Authors: F.F. de Mendonça Filho, C. Romero Rodriguez, E. Schlangen, O. Çopuroğlu
• Journal: Materials
• Published: 2022;15(10)
• Read it: PubMed · Publisher · Free full text

Abstract

Concrete structures perform poorly when withstanding thermal shock events, usually requiring repair or replacement after one single instance. In certain industries (such as petrol, metallurgic and ceramics), these events are not only likely but frequent, which represents a considerable financial burden. One option to solve this issue would be to decrease the heating rate imposed onto the concrete material through the use of a protective surface layer. In this work, the suitability of dunite and microgabbro as protective materials is explored through X-ray diffraction, thermal dilation, optical microscopy, X-ray microtomography, thermo-gravimetric analysis and a compressive test. Further, the thermal dilation was used as an input to simulate a composite concrete-rock wall and the respective stresses caused by a thermal shock event. The dehydration of chrysotile in dunite and the decomposition of analcime, chamosite and pumpellyite in microgabbro were both favourable for the performance of the stones in the desired application. The thermal stability and deformation were found in the range of what can be applied directly on concrete; however, it was clear that pre-heating treatment results in a far more durable system in a cyclic thermal load situation.

In plain English

This was a laboratory materials study, not a health study. The authors tested whether two rocks mined in Turkey, dunite and microgabbro, could serve as a protective surface layer for concrete exposed to very hot industrial spills such as molten slag. Half the samples were pre-heated to 900 °C for one hour. The authors used X-ray diffraction, thermogravimetric analysis, optical microscopy, X-ray microtomography, thermal expansion tests, compressive strength tests and a computer simulation of a concrete wall with a stone layer. X-ray diffraction found trace amounts of a serpentine mineral in the dunite, which the article mostly calls chrysotile. Its peaks were absent after heating, which the authors explained as dehydration. Dunite's compressive strength rose 77% after heating, from 84 to 149 MPa. Microgabbro's strength fell 14%, from 193 to 166 MPa. In the simulation, the concrete layer stayed below 100 °C. The authors concluded that both rocks have fitting properties for this use, but that pre-heating gives a far more durable system under repeated heating. The study did not examine health effects or fiber release.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory materials-testing study of rock samples (mineral analysis, imaging, thermal and mechanical tests) combined with a finite element computer simulation of a concrete wall with a stone overlay
• Who was studied: Rock samples, not people: dunite mined from the Orhaneli ophiolite south of Bursa, Turkey, and microgabbro mined from the Alanya Massif, Turkey. Three 40 mm cubes of each rock were used for compressive strength, in natural and pre-heated states.
• Exposure: Heat: half the samples were pre-heated to 900 °C for one hour. Thin-section plates were exposed to 40 g of molten slag at 1530 °C. The dunite contained trace amounts of a serpentine mineral, printed as 'chrysolite' in the X-ray diffraction section and 'chrysotile' elsewhere.
• Main results:
  • In dunite, X-ray diffraction found trace amounts of the serpentine mineral. Its peaks were absent in the heated dunite sample, which the authors took as confirmation that it had dehydrated.
  • In CT segmentation of dunite, the chrysotile phase made up 11.53% of volume before heating and 9.33% after heating. The authors stated that the dark phases remaining after heating are silica and fluid produced by the conversion of the serpentine.
  • Dunite compressive strength was 84 MPa in natural state and 149 MPa after heating, an increase of 77%.
  • Microgabbro compressive strength was 193 MPa in natural state and 166 MPa after heating, a decrease of 14%. The authors considered this negligible because strength stayed above 160 MPa.
  • Above 100 °C, non-heated dunite expanded on average 10% more than pre-heated dunite.
  • In the computer simulation of a hot spill on a concrete wall with a stone layer, the concrete layer stayed below 100 °C. Its maximum temperature occurred about 50 minutes after exposure.
  • In the simulation, pre-heated dunite gave the lowest principal stresses in the concrete.
• The authors' conclusion: The authors concluded that both rocks have properties suited to use as a protection layer in industrial applications, but that pre-heating results in a far more durable system under cyclic thermal loading.
• Limitations the authors state:
  • The authors stated that the increase in dunite strength after heating had not been reported before and requires further investigation.
  • In microtomography of microgabbro, analcime could not be told apart from albite, so it could not be analysed. Pumpellyite and chamosite also could not be separated.

Topics

Medical terms in this study, explained in our Lexicon: Dunite, X-Ray Diffraction (XRD), Chrysotile, Thermal Stability.

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