Which characteristic makes masonry materials suited for fire resistance?

Masonry materials are well-known for their fire resistance, and one key characteristic that contributes to this property is low thermal conductivity. This means that masonry materials do not easily conduct heat, allowing them to resist the penetration of heat and flame from a fire. Therefore, when subjected to high temperatures, these materials will not allow heat to pass through quickly, which reduces the likelihood of ignition or damage to the structure's integrity.

While high melting points, high density, and low expansion rates are also beneficial properties, they do not primarily account for the fire resistance feature. High melting points can contribute to a material's ability to withstand extreme heat, but it does not necessarily define how well the material handles the heat transfer during a fire. High density can contribute to structural stability and durability but does not directly relate to fire resistance in terms of heat transfer. Low expansion rates can help materials maintain their shape and reduce the risk of cracking due to heat; however, again, it does not directly impact their ability to resist fire.

Ultimately, the primary characteristic that enhances masonry materials' fire resistance is their low thermal conductivity, which effectively decreases the transfer of heat through the material in fire situations.