The primary reasons for the cracking are rate of heat transfer and thermal expansion. This applies especially to brick,masonry and concrete which are quite brittle when put under tension.Heat transfer refers to how fast heat moves through a material and thermal expansion is the principle that most materials expand when heated and contract when cooled. In a wall if the materials are essentially locked into place and not able to freely expand the resulting changes in size can cause destuction of the wall. A more familiar example of this is in concrete highways and sidewalks. These materials are constructed with expansion joints to allow for the expansion and contraction to occur without the concrete being damaged.
In materials such as brick heat moves slowly through the material. Thus when hot water is poured onto the brick the surface becomes relatively hot compared to the remainder of the brick. This means the surface will want to expand more than the underlying brick and result in cracking.
likewise, if the surface is cooled quickly, it will contract compared to the underlying material and again cracking can occur.
No comments:
Post a Comment