Apart from 'spalling' of concrete which occurs at high temperatures (in the fire condition), are there any other effects that the temperature or gases can have on concrete beams or columns?
Yes. Carbonation and other "lowering" of the pH. This can be checked by using a freshly broken piece of concrete and applying a phenolphthalien solution to it. Good concrete will turn purple.
Carbonation "softens" the concrete. It will ultimately become friable where carbonation occurs. If carbonation exceeds about 1/4 inch, treatment (removal and resurfacing) is necessary to protect the rebar.
Also, long term fire exposure (more than a couple of hours) will cause the chemical compounds achieve through hydration to begin to break down. While the result is usually deterioration and lower strength, it is not always easy to predict the extent.
Hey Ron,
What do you think about concrete exposed to salt water, particularly where reinforcement has deteriorated? I'm refering to the lowering of the pH and strength of the concrete. I am aware that the detiorating reinforcement
is a serious problem.
nbryan...the effect is a bit different. Lowering the pH by exposure to water (saline or otherwise) tends to promote more deterioration of the concrete than a loss of strength. Similar carbonation issues exist, though in the presence of water, there is a tendency for crystal growth to occur in the concrete pores (can be beneficial or detrimental...depends on chemistry)that does not occur from fire event. Further, the presence of water, even saline, promotes continued hydration of cement and long term strength gain. The absence of moisture (fire event), actually reduces concrete strength.
concman...amorphous compounds are those without definite shape or form. Generally this refers to gelatinous inclusions or reactivity that may result from alkali-silica reactivity or other forms of reactivity; however, it also depends upon whether the reference is to microscopic amorphous compounds or macroscopic amorphous inclusions. It can also refer to hydration products that do not produce distinct compounds or structural bonds.
Sirs, Please be so kind as to answer one simple question: My
family's home, built around 1900, was recently gutted in a fire. Ironically, my grandfather built it out of concrete
because of his fear of fire. Is the strength of the concrete
compromised? I am asking for your opinion (I know you can only guess at the temperature reached, composition of the
concrete, etc.).
Sincerely, Carl Vermandere
cvermandere@juno.com
Sirs, Please be so kind as to answer one simple question: My
family's home, built around 1900, was recently gutted in a fire. Ironically, my grandfather built it out of concrete
because of his fear of fire. Is the strength of the concrete
compromised? I am asking for your opinion (I know you can only guess at the temperature reached, composition of the
concrete, etc.).
Sincerely, Carl Vermandere
cvermandere@juno.com
Carl,
Using a screwdriver, scratch the concrete with moderate force. If the gouge is more than about 1/16-inch deep, you might have a concrete problem. Compare you gouge to an area where you know the concrete to be good.
Usually house fires do not last long enough to do much damage to concrete, other than thermal cracking and sudden shrinkage when the fire is extinguished. Localized spalling is to be expected. To compromise the strength, the fire has to exceed about 600F for several hours. Concrete is a good insulator from fire and usually fairs quite well. Your grandfather knew what he was doing!
