# Optimal Expansion Gap for Concrete Highway in Varying Temperatures

• liz_p88
In summary, the highway's concrete slabs have a coefficient of linear expansion of 12 (10^-6 K^-1) and a length of 15 m at 20.0°C. To prevent buckling, a gap of 1.08 cm should be left at 20.0°C when the temperature range is from -20.0°C to +40.0°C. At -20.0°C, the gap should be .72 cm. The calculation for the gap takes into account the expansion and contraction of the concrete slabs due to temperature changes.
liz_p88

## Homework Statement

A highway is made of concrete slabs that are 15 m long at 20.0°C. (a) If the temperature range at the location of the highway is from -20.0°C to +40.0°C, what size expansion gap should be left (at 20.0°C) to prevent buckling of the highway? (b) How large are the gaps at -20.0°C?

## Homework Equations

Coefficient of Linear Expansion for concrete is 12 (10^-6 K^-1)
Change in length = (coefficient of linear expansion)(initial length)(change in temp)

## The Attempt at a Solution

(a) I did {(12 x 10^-6 K^-1)(15m)(40C)} = .0072 m or .72 cm
{(12 x 10^-6 K^-1)(15m)(20C)} = .0036 m or .36 cm
.72 + .36 = 1.08 cm

(b) .72 cm

For (a), why did you add the length changes for 40C and 20C?

For (b), where did 0.72 cm come from?

I'm a bit confused. I added them thinking that the total expansion would vary, going up from 20 to 40 and down from 20 to -20. But what I'm thinking is that maybe when it heats up, it expands and when it cools down to -20, it contracts? I really have no idea what I'm doing and posted it on here for help.

Okay. The coefficient of expansion is positive, so the concrete will expand when heated, and contract when cooled.

The stated temperature for the initial length is 20C. If the temperature gets cooler than 20C then the slab will contract and the gap will widen -- no fear of crumpling if the gap gets wider. On the other hand, when the slab gets warmer than 20C it will expand, acting to close the gap. So it seems that if you pour the concrete at 20C you only need to make allowance for the +20C rise to 40C.

That makes sense. So would I only have to account for the temperature increase and disregard the contraction when solving for (a)? And did I calculate it correctly?

The value for the increase in length that you obtained looks good.

Awesome thank you for your input!

## What is the linear expansion of concrete?

The linear expansion of concrete refers to the increase in length or volume of concrete when it is exposed to high temperatures or changes in temperature.

## What causes linear expansion in concrete?

Linear expansion in concrete is mainly caused by the presence of water in the concrete mix. When the temperature increases, the water in the concrete heats up and expands, causing the concrete to expand as well.

## How does linear expansion affect the strength of concrete?

Linear expansion can cause cracking and deformation in concrete, which can weaken its structural integrity. This is especially important to consider in applications where concrete is exposed to high temperatures.

## Can linear expansion be prevented in concrete?

Linear expansion in concrete can be reduced or prevented by using low-heat cement, minimizing the amount of water in the concrete mix, and using expansion joints to allow for movement without causing damage.

## How is linear expansion of concrete measured?

The linear expansion of concrete is typically measured by calculating the coefficient of thermal expansion, which is the change in length or volume of the concrete per unit change in temperature. This can be expressed as a percentage or as a decimal value.

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