Effect of Artificial Freeze/Thaw and Thermal Shock Ageing, Combined or Not with Salt Crystallisation on the Colour of Zamora Building Stones (Spain)

Abstract

After subjecting Zamora building stones to accelerated ageing tests, colour changes were studied, namely: (a) freezing/thawing and thermal shock (gelifraction and thermoclasty), and (b) combination of freezing/thawing plus thermal shock and salt crystallisation (sulphates or phosphates) (gelifraction, thermoclasty and haloclasty). Zamora building stones are silicified conglomerates (silcretes) from the Cretaceous that show marked colour changes due to the remobilisation of iron oxyhydroxides. In this work, four varieties were: white stone; ochreous stone; white and red stone; and purple stone Their micromorphological characterization (skeleton, weathering plasma and porosity/cutan) is formed of grains and fragments of quartz and quartzite as well as by accesory minerals muscovite and feldspar (more or less altered), and some opaque. Quartz, feldspar and illite/mica were part of the skeleton; kaolinite, iron oxyhydroxides, and CT opal were part of the weathering plasma or cutans; their porosity were 11.7–8.7%. Their chromatic data have been statistically analysed (MANOVA-Biplot). They showed higher variations in ΔE*, ΔL*, Δa* and Δb*on combined freezing/thawing plus thermal shock and sulphates crystallisation leading to rapid alteration of the building stones. Chromatic differences between the other two artificial ageing tests were less evident and were not detected in all samples. The global effect of ageing on the Zamora building stones darkened them and reduced their yellowing. The ochreous stone suffered the least variation and the purple stone the most. This study of the colour by statistical analyse may be of interest for the evaluation and monitoring of stone decay, which is an inexpensive, simple, easy and non-destructive technique.

A Themed Issue in Honor of Prof. Dr. Vicente Rives

“…This Special Issue has received eighteen contributions, six review papers [1][2][3][4][5][6], and twelve research papers [7][8][9][10][11][12][13][14][15][16][17][18]. Most of the papers originated from groups who have previously worked with Prof. Rives, but five of the contributions came from authors who had not previously worked with him [6,7,13,17,18].…”

“…Other materials included Ni-based catalysts [1], g-C 3 N 4 [5], mesoporous silica [6], MOFs [7], carbons [8,9], AlPO 4 [12], acid-modified clays [13], and porous aluminosilicates [17]. Finally, one of the papers was devoted to the study of cultural heritage conservation [14].…”

“…In an area more related to biological applications, Golubeva et al studied the adsorption and hemolytic behavior of porous aluminosilicates in a simulated body fluid [18]. On the other hand, related to cultural heritage conservation, García-Talegón et al reported on the ageing of Spanish building stones under different physical agents, mainly studied by the evolution of their color [14].…”