The effects of different temperatures on stone are mainly manifested in the following aspects:
1. Thermal expansion and contraction effect:
- Stone, as a porous material, will expand and contract when the temperature changes. When the stone is heated, the volume will expand; when it is cooled, the volume will shrink. This volume change will cause stress inside the stone. If the stress exceeds the tolerance of the stone, it will cause the stone to crack.
2. Internal pressure caused by water evaporation:
- The water in the stone may evaporate at high temperatures, causing the internal pressure to increase, thus causing the stone to crack, especially when there is water on the surface or inside the stone.
3. The influence of mineral composition:
- The mineral composition of stone is sensitive to temperature to different degrees. Some stones will undergo phase changes or chemical reactions after being heated, resulting in changes in the stone structure, causing cracking and weathering.
4. Changes in strength and deformation characteristics:
- Under high temperature, the strength and deformation characteristics of the stone will change. For example, the mechanical properties of marble do not change much from room temperature to high temperature of 200℃; but between 400℃ and 800℃, its peak strength, elastic modulus and deformation modulus decrease with increasing temperature, while the peak strain increases.
5. Changes in bulk density and pore properties:
- After high-temperature treatment, the bulk density and pore properties of rocks of different lithologies will change. For example, the magnitude of change in pore properties of sandstone and shale after high-temperature treatment will vary depending on the rock type. Shale has more pore space due to the combustion of organic matter, resulting in more obvious changes in its pore properties.
6. Changes in acoustic properties and dynamic elastic parameters:
- As the temperature increases, the attenuation coefficient of the rock continues to increase, and other acoustic parameters continue to decrease. At the same time, all dynamic elastic parameters except Poisson's ratio show a downward trend, especially for shale that is more severely damaged by heat.
7. Differences in refractoriness:
- Different stones have different refractoriness, and some stones will undergo chemical decomposition under high temperature. For example, gypsum decomposes at temperatures above 107°C, limestone and marble decompose at temperatures above 910°C, and granite cracks at 600°C due to uneven heating of its constituent minerals.
In summary, temperature has many effects on stone, including changes in physical properties, reduction in mechanical properties, and structural damage. These changes are of great significance to the protection and use of stone.
