Concrete, one of the most common building materials, is also an excellent fire-resistant material. It is noncombustible and has low thermal conductivity, meaning that it takes a long time for fire to affect its structural, load-bearing ability, and it protects from the spread of fire. It's actually significantly more fire-resistant than steel, and often used to reinforce and protect steel from fire.
However, it's important to note that not all concrete is created equal. It consists of cement and aggregate, and the particular kinds of aggregate materials used can vary, as well as the amount used. Aggregate can make up 60 to 80 percent of the concrete's volume. The exact fire-resistance properties change depending on the type and amount of aggregate used. Natural aggregates tend not to perform as well. Moisture in the aggregate can expand when heated, causing concrete to sinter after long exposure.
Concrete is often listed as among the best fire-resistant roofing materials, too. And you shouldn't overlook the roof as essential in fire-protection, since it's extremely vulnerable to sparks blown from wildland fire.