26 January 2010

Durability of monumental stones (2009)

Title: Durability of monumental stones treated with siloxane-based water repellents
Author: Ana Bogdana Simionescu
University: University of Bologna (Italy)
Year: 2009
Type of document: PhD thesis
Download: http://amsdottorato.cib.unibo.it/... (pdf, 76 Mb)

The thesis investigates the effect of siloxane-based water repellents on the durability of monumental stones. Laspra, a micritic limestone typical for the Spanish region of Asturias, and Repedea, an oolitic limestone from Moldavia, Romania were selected for the present study, due to their regional / national significance and level of usage. As for the siloxane-based water repellents, three worldwide used products, namely Lotexan-N, Silres® BS 290 and Tegosivin HL 100 and a newly synthesized nanocomposite material, TMSPMA, obtained starting from the 3(trimethoxysilyl)propyl methacrylate as a precursor were investigated. The limestones and the water repellents were thoroughly characterized using specific techniques. The coating of the two monumental stones with the mentioned products and the investigation of coating efficiency yielded to the conclusion that all treatments induce good water repellent properties. The treated limestones were afterwards submitted to different artificially accelerated ageing tests – resistance against UV irradiation, resistance to salt mist action and resistance to SO2 action in the presence of humidity –, the results being analyzed according to standardized evaluation methods. The durability of the treated stones was proved to depend on both stone characteristics and water repellent chemical structure. All four water repellents induced a good protection against UV irradiation, no significant differences among them being noticed. As far as the resistance to salt mist action is concerned, the product that afforded the best results when applied on Laspra was TMSPMA, and on Repedea, Silres® BS 290 or / and TMSPMA showed the highest efficiency. The best resistance to SO2 action in the presence of humidity was conferred by Tegosivin HL 100 and TMSPMA when applied on Laspra, while Silres® BS 290 and TMSPMA afforded better results in the case of Repedea.

Table of contents (compact version):

I. Introduction. State of the art
II. Objectives

III. Methods
III.1. Microscopic and instrumental techniques
III.2. Chemical composition
III.3. Determination of the velocity of propagation of ultrasonic waves
III.4. Pore space structure
III.5. Hydraulic properties
III.6. Color measurements
III.7. Chemical characterization of water repellent treatments as liquids and films
III.8. Thermal stability and properties of water repellent treatments
III.9. Swelling and solubility test of the polymeric films
III.10. Contact angle measurements
III.11. Artificially accelerated ageing tests

IV. Stones selection and sampling
IV.1. Laspra
IV.2. Repedea

V. Stones characterization
V.1. Introduction
V.2. Macro and micro observation
V.3. Chemical composition
V.4. Velocity of propagation of the ultrasonic waves
V.5. Pore space structure
V.6. Hydraulic properties
V.7. Color measurements

VI. Water repellent treatments
VI.1. Introduction
VI.2. Characterization of three selected worldwide used water repellent products (Lotexan-N, Silres® BS 290, Tegosivin HL 100)
VI.3. Synthesis and characterization of a new water repellent product
VI.4. Conclusions

VII. Treated stones characterization
VII.1. Introduction
VII.2. Characterization of the treated stones
VII.3. Conclusions

VIII. Artificially accelerated ageing
VIII.1. Introduction
VIII.2. Artificially accelerated ageing under UV irradiation
VIII.3. Resistance to salt mist action 192 iv
VIII.4. Resistance to SO2 action in the presence of humidity 212

IX. Conclusions
X. Annex 1, Annex 2
XI. Acknowledgements
XII. References

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