Thermal Expansion Concrete Problem

In summary, the conversation discusses the need for an expansion gap in a highway made of concrete slabs to prevent buckling due to temperature changes. The correct size for the gap at 20.0 degrees Celsius is 3.6 mm. It is also mentioned that the concrete contracts when temperature is lowered, so a gap is not needed in that case.
  • #1
Mr. Goosemahn
24
0

Homework Statement


A highway is made of concrete slabs that are 15 m long at 20.0 degrees Celsius.

(a) If the temperature range at the location of the highway is from -20.0degrees Celsius to +40.0degrees Celsius, what size expansion gap should be left (at 20.0degrees Celsius) to prevent buckling of the highway?

1. 3.8 mm
2. 1.6 mm
3. 3.6 mm
4. 4.2 mm
5. 2.6 mm

(b) How large are the gaps at -20.0 degrees Celsius?

1. 9.5 mm
2. 11.7 mm
3. 11.0 mm
4. 12.7 mm
5. 10.8 mm

Homework Equations


L=L0*a*T

The Attempt at a Solution


I plugged in the values I have and I got:

L=15*(12*10-6)*40 and got .0072 meters, or 7.2 millimeters, but that isn't one of the options.

I can't do 'B' until I have A.

Am I plugging in the values incorrectly?

Help?
 
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  • #2
Anybody?
 
  • #3
I tried the problem again and still get 7.2 millimeters. Does anybody know what exactly I'm doing wrong?
 
  • #4
Do I have to divide the 7.2 by 2? That's the only possible relation that I see between what I'm getting and the possible answers, being 3.6.
 
  • #5
Why did you use 40 for the temperature difference? The hottest it gets is 40 degrees, so the maximum possible temperature difference is 20 degrees.
 
  • #6
ideasrule said:
Why did you use 40 for the temperature difference? The hottest it gets is 40 degrees, so the maximum possible temperature difference is 20 degrees.

But wouldn't it be 40 since the difference between -20 and 20 is 40?
 
  • #7
But the concrete contracts when temperature is lowered, so you wouldn't need to leave a gap. You'd need to leave a gap when it expands.
 
  • #8
ideasrule said:
But the concrete contracts when temperature is lowered, so you wouldn't need to leave a gap. You'd need to leave a gap when it expands.

Ooohhhh, that makes sense. Yeah, 3.6 worked. Thanks for the help, I really appreciate it.
 

Related to Thermal Expansion Concrete Problem

1. What is thermal expansion and how does it affect concrete?

Thermal expansion is the tendency of a material to expand when exposed to heat. In the case of concrete, when it is heated, it expands and when it cools down, it contracts. This expansion and contraction can cause stress and potential cracking in concrete structures.

2. What are the main causes of thermal expansion in concrete?

The main causes of thermal expansion in concrete are changes in temperature, exposure to sunlight, and moisture content. When concrete is heated, the water inside the concrete evaporates and causes the concrete to expand. Additionally, external heat sources such as the sun can also cause concrete to expand.

3. How can thermal expansion be prevented in concrete?

To prevent thermal expansion in concrete, proper joint spacing and reinforcement should be used to allow for expansion and contraction. Additionally, using low shrinkage concrete mixtures and incorporating insulation can help reduce the effects of thermal expansion.

4. What are the consequences of not addressing thermal expansion in concrete?

If thermal expansion in concrete is not addressed, it can lead to cracking, spalling, and other forms of damage. This can compromise the structural integrity of the concrete and potentially lead to costly repairs or even failure of the structure.

5. Can thermal expansion in concrete be repaired?

In some cases, thermal expansion damage in concrete can be repaired by filling in cracks and reinforcing the structure. However, prevention is always the best approach when it comes to thermal expansion in concrete as repairs can be costly and may not fully restore the strength of the structure.

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