http://hdl.handle.net/10366/166812 2026-04-22T02:24:27Z http://hdl.handle.net/10366/167392 [EN]This work was carried out on fresh samples of silicified sandstone and white conglomerate quarry from Zamora, Spain. The stones were treated with conservation treatments (H224, RC70, and RC80) and/or processes of freeze/thaw aging (similar to that of cold areas). The values obtained for the chromatic coordinates (L*, a*, b*) and the ultrasound propagation speed of the samples studied were analyzed and a statistical design was created. In addition, a multivariate technique (Canonical Biplot) was applied to determine the effectiveness of the treatments and the durability of the fresh and treated stones. In most of the cases studied, the ultrasonic propagation speed decreased in both the untreated samples and those treated with the conservation products after carrying out the aging process. Moreover, it was found that the ultrasonic propagation speed was lower with respect to the treated samples. Our results indicate that the treated samples are more durable than the untreated fresh samples and that the most severe changes can be appreciated when the untreated (fresh) samples are compared with their corresponding treated samples. For these samples, the ultrasonic propagation speed increased showing the effectiveness of each of the conservation products. The most effective consolidating treatment used was RC80. Also, the chromatic coordinates of the treated samples, in general, were darker (↓L *), redder (↑a *), and more yellow (↑b *) with respect to the fresh, untreated quarry samples, except in sample Z1 treated with RC80, where redness (↓a *) and yellowness (↓b *) decrease. 2021-01-01T00:00:00Z http://hdl.handle.net/10366/167376 [EN]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. 2022-01-01T00:00:00Z http://hdl.handle.net/10366/167375 [EN]In the present work we determined the chromatic coordinates (L*, a*, b*) for three building stones used in the heritage city of ´Avila, Spain (World GraniteHeritage City, 1988). The stones came from quarries and were subjected to90 cycles of three types of accelerated ageing processes: (a) freezing/thawingtogether with cooling/heating (T1); (b) salt crystallisation (T2); and(c) freezing/thawing together with cooling/heating + salt crystallisation (T3).A three-way mixed MANOVA (multivariate analysis of variance) was appliedto the data obtained. Significant variations in the three chromatic coordinates(L*, a*, b*) were observed between the three types of accelerated artificial age-ing processes compared to the data obtained from the quarry samples, with atendency towards darkness (#L*), redness ("a*) and much less intensitytowards yellowing ("b*). 2024-01-01T00:00:00Z