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Scientists assess the firing conditions of old fired-clay bricks to find the most suitable restoration materials

Date: 20/10/2017

Sample T (a) and U5 (b) Sample T (a) and U5 (b) Optical microscope image in cross-polarised light of sample T (a) and U5 (b) in thin section

A research team around Alberto Viani from the Institute of Theoretical and Applied Mechanics in the Czech Republic performed a study to find the correlation between the structure of old fired-clay bricks and their firing temperature during the manufacturing process, in order to help in the replacement of damaged bricks for restoring some objects of our priceless cultural heritage.

Fired-clay bricks have been one of the most widespread construction materials in Europe. Their use flourished in the 19th century, when they were employed in the construction of a huge number of buildings. Most of them still survive but have endured a number of different environmental conditions over the years. The preservation of these often culturally important buildings is therefore a challenge. A widely accepted approach in cultural heritage restoration is to use the best compatible materials. To this end, the structural characterization of the original bricks is important in order to choose the best replacement material and prevent further damage to buildings. The results of this study were recently published in the Journal of Materials Characterization and in Brick and Block Masonry – Trends, Innovations and Challenges.

The research team investigated a number of bricks from two historical production sites in the Czech Republic, made at different firing temperatures for different purposes (masonry and chimney bricks). In addition to common mineralogical analysis methods such as electron microscopy, X-ray diffraction and porosimetry, they used the small angle neutron scattering (SANS) technique.

Since neutrons can penetrate deeply into matter, they are an ideal tool for the investigation of a dense porous system, such as fired bricks, ceramics and metals. SANS performed at the CERIC Hungarian facility, the Budapest Neutron Centre, therefore enabled characterization of the micro and nanostructure of bricks and information to be obtained about both their surface and their inner structure.

As a result of the study, the scientists could show that the amount of hematite – a mineral that is formed during the burning process – may be an indicator of the firing temperature used during the production process. Moreover, at the 16th International Brick and Block Masonry Conference in Padova (Italy), they showed the existence of an empirical relationship between the surface area per unit volume of pores obtained by SANS and the firing temperature. SANS was used in combination with a number of other standard techniques for the study of historical fired-clay bricks, confirming that it is a very effective tool for their characterization. Thanks to its efficiency, it greatly reduces the number of methods necessary to analyze old bricks and it may help in finding and/or producing suitable replacement materials for the preservation of valuable objects of the cultural heritage.

Original Publications

A. Viani, K. Sotiriadis, A. Len, P. Šašek, R. Ševčík
Assessment of firing conditions in old fired-clay bricks: The contribution of X-ray powder diffraction with the Rietveld method and small angle neutron scattering
Materials Characterization, 116, 22-43 (2016)

A. Viani, K. Sotiriadis, P. Šašek, R. Ševčík, A. Len
Characterization of historical fired clay bricks with small angle neutron scattering
Proceedings of the 16th International Brick and Block Masonry Conference, Modena C., da Porto F., Valluzzi M.R. (eds.), Padova, Italy, June 26th-30th, 2016, Taylor & Francis Publications, Milton Park, 2016.

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