Placing a load on standard concrete causes it to break when the applied stress exceeds 1361kg / in^2. This knowledge allows you to calculate whether a given slab of concrete will fracture under a specific load. According to the Portland Cement Association, concrete roughly has a composition of air (6 per cent), cement (11 per cent), gravel (41 per cent), sand (26 per cent), and water (16 per cent). The cement is composed mostly of lime and silica (85 per cent) and other ingredients which include calcium, silicon, aluminium, iron and gypsum.

Measure the length and the width in inches of the rectangular area on the concrete's surface to which the load will be applied. As an example, say that the length equals 10 inches and the width equals 20 inches.

Calculate the area of the section of concrete in^2 by multiplying length times width. In the example, you have 10 inches x 20 inches = 200 in^2.

Determine the weight of the load in pounds by utilising a scale. For the example, say you have a 3,000-pound block of steel.

Calculate the stress on the concrete by dividing the weight by the area. The stress for the example problem is 1361kg / 200 in^2 which equals a stress of 6.8kg / in^2. This stress is well under the limit of 1361kg / in^2, so the concrete will not break.

### Things you need

- tape measure
- pencil
- paper

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