# Size of specimen and compressive strength of concrete

• ichabodgrant
In summary, the compressive strength of concrete is often tested using 150 mm x 150 mm x 150 mm cubes in some countries, but in others, 100 mm x 100 mm x 100 mm cubes may also be used depending on the designed strength of the concrete. This is because the applied load of a compression machine is a fixed value, and using a smaller cube size can result in a higher stress and a more accurate measurement of strength. However, some people argue that using a smaller cube size may result in slightly lower compressive strength. Standards allow for both sizes to be used as long as more than one cylinder is tested to account for variability. Correction factors may also be applied for different geometries.
ichabodgrant
Hello everyone.
I have a question about compressive strength of concrete. It is said that (in my country) 150 mm x 150 mm x 150 mm concrete cube is used for concrete testing. Someone asks me why 100 mm x 100 mm x 100 mm is not used. In fact, I know that sometimes it is allowed or even preferred to use 100 mm one instead of 150 mm one. I have looked up some research papers and they mention that it depends of the designed compressive strength of concrete.

One explanation says the applied load of a compression machine is often a definite value, let's say 2000 kN. If the concrete produced is of a designed compressive strength 60 MPa, then 150 mm cube is sufficient for the test. If a higher strength concrete is produced, then a 100 mm cube is more suitable. (As stress = Force/Area, same force smaller area can give a higher stress)

My question is that what will happen if I make a 100 mm cube from the same concrete mixture and put it onto the compression machine? Is the resulting compressive strength higher or lower than that of a 150 mm cube? Some people say it should be slightly lower. What is the reasoning?

I've always specified 6 inch diameter by 12 inch cylinders(150 mm x 300 mm) although the smaller size 100 mm x 200 mm cylinders are allowed by Standards as long as aggregate size is smaller than about 3 cm. There isn't much difference in results as long as more than one cylinder is tested to allow for variability. The smaller size as you mentioned requires less test load and is more suitable for the higher strength concretes I suppose, but being old school I like the larger ones.

## What is the relationship between the size of a specimen and its compressive strength?

The size of a specimen does not necessarily determine its compressive strength. Other factors such as the type and quality of materials, mixing and curing processes, and environmental conditions can also impact the strength of concrete.

## Does increasing the size of a specimen always result in a higher compressive strength?

No, increasing the size of a specimen may or may not result in a higher compressive strength. The strength of concrete depends on a variety of factors and increasing the size may not be the most significant factor.

## How does the size of a specimen affect the testing process for compressive strength?

The size of a specimen can affect the testing process for compressive strength in terms of sample preparation and equipment used. Larger specimens may require specialized equipment and longer testing times compared to smaller specimens.

## Can the compressive strength of a concrete specimen be accurately predicted based on its size?

No, the compressive strength of a concrete specimen cannot be accurately predicted based on its size alone. Other factors such as the composition of materials, curing process, and testing methodology must also be considered.

## Are there any standard sizes for concrete specimens used in compressive strength testing?

Yes, there are standard sizes for concrete specimens used in compressive strength testing. The most commonly used sizes are cylinders with a diameter of 6 inches and a height of 12 inches, and cubes with a side length of 6 inches. However, other sizes may also be used depending on the specific testing requirements.

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