Abstract

High temperatures affecting buildings during fires have a potential of impact on the material’s performance. A variety of thermal effects may take place on natural stones in historic buildings, and their investigation in laboratory simulations may be effective to support a reliable diagnosis of fire damage in order to select proper conservation measures. To this aim, this study reports on the high temperature effects on a highly porous calcareous stone. Analytical and microscopic techniques (X-Ray Diffractometry, Thermogravimetry and Differential Scanning Calorimetry, optical microscopy and SEM), were combined in a systematic investigation of chemical-mineralogical and microstructural modifications affecting the stone under increasing temperatures, up to 700 °C. Non-destructive ultrasonic velocity propagation (UPV) test and quantitative evaluations of colour changes and physical parameters relating to the stone microstructure were also performed. The overall findings highlight that thermal effects mainly compromised the aesthetic features of the investigated stone, through colour changes relating to chemical-mineralogical transitions. The damage to the stone microstructure due to thermal dilatations was limited, likely because of the high presence of pore spaces. Fissuring was observed microscopically, and also recorded through porosimetric changes and UPV decreases, but it led to negligible increases of both the open porosity and water uptake.

摘要

火灾期间影响建筑物的高温可能会影响材料的性能。历史建筑中的天然石材可能会发生各种热效应，在实验室模拟中对它们的研究可能有助于支持对火灾损害的可靠诊断，从而选择适当的保护措施。为此，本研究报告了高温对高度多孔钙质石头的影响。分析和显微技术（X 射线衍射、热重和差示扫描量热法、光学显微镜和 SEM）相结合，系统地研究在温度升高（最高 700 °C）下影响石头的化学矿物学和微观结构变化。还进行了无损超声速度传播 (UPV) 测试以及与石材微观结构相关的颜色变化和物理参数的定量评估。总体研究结果强调，热效应主要通过与化学-矿物学转变相关的颜色变化而损害了所研究石头的美学特征。由于热膨胀对石材微观结构的破坏是有限的，这可能是因为孔隙空间的存在。在显微镜下观察到裂缝，并通过孔隙率变化和UPV降低记录，但它导致开孔率和吸水率的增加可以忽略不计。总体研究结果强调，热效应主要通过与化学-矿物学转变相关的颜色变化而损害了所研究石头的美学特征。由于热膨胀对石材微观结构的破坏是有限的，这可能是因为孔隙空间的存在。在显微镜下观察到裂缝，并通过孔隙率变化和UPV降低记录，但它导致开孔率和吸水率的增加可以忽略不计。总体研究结果强调，热效应主要通过与化学-矿物学转变相关的颜色变化而损害了所研究石头的美学特征。由于热膨胀对石材微观结构的破坏是有限的，这可能是因为孔隙空间的存在。在显微镜下观察到裂缝，并通过孔隙率变化和UPV降低记录，但它导致开孔率和吸水率的增加可以忽略不计。