Why is concrete fire resistant?

建築材料には階層があるようです。木と花崗岩が最も人気があり、ガラスとアルミニウムが最もトレンディで、大理石が最高級です。そして、コンクリートがあります...貧しい、愛されないコンクリート。私たちはその上を歩き、その上を運転し、さらにはその上にガムを吐き出します。いくつかの敬意。ブロック住宅、駐車場、そして世界のほとんどの刑務所を私たちに与えてくれる素材を愛するのはとても難しいです。しかし、建築の醜いアヒルの子のために状況が変化している可能性があります。住宅建設にコンクリートを採用するという新しい傾向があります。これは主に、コンクリートが建築材料の中で最も強力で耐久性のあるものの1つであるためです。それはまた、それを家のための安全な賭けにする火に対して信じられないほど耐性があります。

コンクリートの難燃性はかなりわかりやすいです。コンクリートの成分（セメント（石灰石、粘土、石膏）および骨材）は化学的に不活性であるため、実質的に不燃性です。コンクリートはまた、熱伝達の速度が遅いため、家のコンクリート壁は防火シールドとして機能し、隣接する部屋を炎から保護し、激しい熱にさらされても構造の完全性を維持します[出典：コンクリートセンター]。

How do the properties of concrete make it so impervious to flames? Fire resistance refers to a material's ability to stand firm in a fire while everything around it burns. Determining a building material's fire resistance takes into account the rate of heat transfer and combustibility of that material under variable conditions such as the temperature of the fire, ventilation, and fuel sources within the building [source: Portland Cement Association]. While concrete walls can generally withstand up to four hours of extreme fire pressure, most wood-framed walls would fall in less than an hour [source: International Association of Certified Home Inspectors]. It's also important to note that when concrete does burn, it doesn't emit toxic fumes, produce smoke, or drip molten particles.

The fire resistant qualities of a material are very important in residential construction, as they determine how well the structural integrity of the home will be maintained when exposed to intense heat and flames. This is called fire performance, and we consider a few examples in the next section, including a comparison of concrete and wood.

If you're fortunate enough to have something to say about the choice of framing material in your home, you might consider concrete over wood. Homebuilders have been turning to concrete as a framing material in recent years for a variety of reasons, not the least of which is its fire resistant properties.

Concrete is generally considered to be a good value in home building when it comes to fire performance, as it holds up much better than wood in intense heat [source: The Concrete Center]. This is partly because concrete allows for compartmentalization (i.e. containment) of fire. For an example of compartmentalization, let's take a look at the burning of the World Trade Center (WTC) Towers on Sept. 11, 2001 .

その運命的な9月の朝に飛行機がWTCの建物に衝突したときのジェット燃料の燃焼の激しい熱にもかかわらず、タワーの各フロア間の4インチ（10センチメートル）のコンクリートスラブは、少なくとも火の広がりを制限することができました。しばらくの間。ただし、塔の壁はコンクリートではなく、鋼やその他の材料で縁取られていました。火の熱が華氏800度（摂氏427度）を超えると、塔の支持する鉄骨構造が弱まり、崩壊し始めました[出典：ScientificAmerican ]。それでも、ほとんどのエンジニアは、9月11日のWTCビルの火災性能が印象的だったことに同意しています。これは主に、熱と炎の区画化により、ビルが倒れる前に何千人もの人々が逃げる機会が与えられたためです。

As a building material, concrete also stands up well in the face of other hazards such as hurricanes , tornadoes , and floods , and provides better soundproofing and energy efficiency than wood [source: International Association of Certified Home Inspectors]. However, despite these qualities, it does have some drawbacks. One is its significant carbon footprint. Generally speaking, for every ton of concrete produced, there is a ton of CO₂ released into the atmosphere [source: Chemistry World]. The carbon footprint of other materials (for instance, steel) may be the same or worse, but since there is much more use of concrete in the world, the footprint seems bigger. Concrete factories are becoming more efficient all the time, but there is no denying this material's enormous environmental impact.

Nevertheless, if concrete is so fire-resistant, why is it not used in all homes? We'll explore that in the next section.

All things considered, concrete holds a great deal of promise for homes of the future. Currently, approximately 17 percent of new homes built in the U.S. are framed in concrete [source: International Association of Certified Home Inspectors]. According to Omar Garcia, President of SOGA Construction in Washington, D.C., a home made of concrete is going to last much longer than a wood-framed home.

"There would probably be many more homes made of concrete in the U.S. if they weren't so expensive to build," he says. The Portland Cement Association, the national concrete industry's trade group, estimates that the cost of a new house built using insulating concrete forms (the most common type of cement construction) costs 4 to 7 percent more than a similar house with a wood frame.

"There is a substantial jump in price based on the cost of material when you frame in concrete," says Garcia. "But the real increase comes when you factor in the additional labor hours for the installation of steel reinforcement and forming and for pouring the concrete."

However, with a concrete house, you do experience savings in the form of lower heating and cooling bills and lower home insurance policies.

"Considering how vulnerable wood is to rot, fire , and termite infestation , it's surprising how long wood has persisted as the dominant structural material of homes," Garcia says. "If the cost of building a home in concrete continues to decline, it makes sense that consumers would embrace it as the material of choice."

It seems likely that, in time, concrete will probably shed its image as a second-rate building material. There is no denying its durability, and few materials compare to its incredibly fire resistance. Perhaps concrete just needs a good PR campaign to bring it on par with much-loved materials such as wood, stone, and marble.

When I received the assignment to write about the fire resistance of concrete, I immediately recalled the many conversations I've had on the subject with my husband, who is both an engineer and builder. Being from Mexico, where most homes are made of concrete, he often comments on Americans' fascination with wood as a building material. As we've pointed out in the article, concrete is much stronger and more hazard-resistant than wood. But the fact is that many Americans cling to wood in an emotional way, perhaps because it was once a living thing...a tree standing proudly in a forest somewhere. It's also quite beautiful, and sometimes that trumps practicality.

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