Stones and concrete may lose small portions of their surface when heated, a condition called _______.

• A. Cracking
• B. Spalling
• C. Chipping
• D. Erosion

Answer: (B)

This is about surface material loss caused by heat, known as spalling. When concrete or stone is heated, moisture inside the pores turns to steam and builds up pressure. The surface layer also experiences rapid temperature change and tensile stresses. If the surface can’t restrain or accommodate that stress, small chunks peel off or flake away from the rest of the material. That shedding of thin surface pieces is what we call spalling.

Cracking is a general break in the material and doesn’t necessarily involve surface flakes. Chipping usually refers to damage from impact or mechanical action, not heat. Erosion is wearing away by a flowing substance like wind or water. So the heat-induced peeling of surface pieces fits spalling best.