Dear Allyn,

if you would like to have an explanation of why a different geometry produces a different strength, you can read the following paper by me:

https://www.researchgate.net/publication/235998938_Shape-Effect_in_the_Effective_Laws_of_Plain_and_Rubberized_Concrete

Best regards.

Article Shape-Effect in the Effective Laws of Plain and Rubberized Concrete

I see no problem using a strength specified using cubes translated into strength for cylinders for design purposes.  However, I believe one should never use a translated strength, going either way, for concrete acceptance.

EN-206 standard allows the use of cubic and cylindrical samples. Cylinders 300x150 mm and 150 mm cubes. The ratio between the strength test on cubic and cylindrical samples is 0.8 / 1.25.

Best Regards, Wojtek Kubissa

Dear Allyn,

if you would like to have an explanation of why a different geometry produces a different strength, you can read the following paper by me:

https://www.researchgate.net/publication/235998938_Shape-Effect_in_the_Effective_Laws_of_Plain_and_Rubberized_Concrete

Best regards.

Article Shape-Effect in the Effective Laws of Plain and Rubberized Concrete

According to the EN 206 , exist the ratio between the cube(150mm) and cylindrical sample(150x300 mm).

Using the direct results from cylindrical samples or using the ratio from cube samples is same for the calculations.

In China, the compressive strength tested by the cube(150mm or 100mm), and the ratio between the strength test on cubic sample is 1.0/0.95。 Acooriding to our experimental, the stength of cube is about less 10MPa than that of cylindrical sample.  

The relationship between concrete strength measured using cubes and cylinders depends on the effect of shape of specimens. cylinders is slender compared to cubes. the ratio of h/d of cylinders is 2 while that of cubes is 1. This is one of the causes.    

From my own experience and experimentation, I found the cube/cylinder strength ratio decreases by the increase in concrete strength. A ratio of 1.15 to 1.25 is expected for normal concrete (25  to 50MPa cube strength), while this value reaches 1.1 for high strength concrete (55 to 85MPa cube strength). In my opinion, while these values provide some estimates for design, they cannot be accepted for compliance criteria.

Dear Hisham Qasrawi,

I can not agree with You. According to European standards both cylindrical and cubic samples are used to assess compliance for many years. Cubic samples are used commonly while cylindrical occasionally. The ratio between the strength test on cubic and cylindrical samples is 0.8 / 1.25.

Best Regards, Wojtek Kubissa

The ratio between the strength test on cubic and cylindrical sample is 1.25

Dear Wojciech Kubissa

Thank for your response. I understood that you are pointing to BS EN 206-1, which we teach in our concrete technology courses. However, even in this table you will find that the ratio of cyl/cube increases for strength grades above 70 and reaches 0.87 for grade 100.

Moreover, there are lots of researches in this respect.Some reported similar results to those I found in my studies. For example, Neville (in Properties of Concrete) reported values of cyl/cube strength increasing with strength. This ratio reaches values above 0.9 for high strength concrete.

On the other hand, practically, it is much easier  to use the simple standard 0.8 ratio.

Please remember that my opinion I mentioned early is based on my experience and is not meant to replace standards. For better understanding of the topic, it is better to refer to various research in this respect.

Dear Hisham Qasrawi,

I know that there are many publications on the coefficient we are talking about.

I agree with that for HPC is different coefficient .

What I mean is that the cubic samples are in Poland and other countries commonly used for evaluation of conformity of concrete. For this reason, I can not agree with: "They can not be accepted for compliance criteria".

On the atached jpg table of coefficients for the different shapes and sizes of  samples (small F - cubic big F - cylindrical).

Best Regards, Wojtek Kubissa

Thank you Wojciech Kubissa. Our opinions are close now.

The strength of cylinder with diameter of 15cm and 30cm tall can be approximated as 0.84 of the strength of a 15x15x15 cm cube  according to Eurocodes. This ratio can be variable indeed, 0.84 is a lower limit, I generally find values close to 0.9 and 0.95 using stronger concretes.

Thank you gentlemen for your information.  

+What I need to know is how do you use the translated strengths?  Is there a problem for design if a strength were specified in terms of cubes and translated  to cylinder strength?  Would there be a problem if strength measured from a cube were translated for quality assurance?  If a project were specified in for cylinders, would translated cube tests be acceptable?

European standards, in strength classification, use both cylinder and cube strength: C 25/30, 30/37, 35/45 and so on. In structure design, cylinder strength is used.

Cylinder strength is lower because height to diameter ratio is 2 and at cube height to side ratio is 1. Also, friction at upper and lower plane of specimen with plates is different so that influences too. There are probably more factors but cannot remember them, sorry.

Dear Allyn,

Look: http://www.en206-1.com/index.php?id=33&desc=About+EN+206-1

Best Regards,

Wojtek Kubissa

You ask about experience using a cube strength in place of a cylinder, and if anyone would use a "translated" cube strength specification for design and cube strength in place of a cylinder test for acceptance.

For the massive concrete gravity structures placed in the North Sea (for oil exploration),  since the mid 70th, the strength of 100x100x100 mm cubes were used both for acceptance and to derive the design strength. With the great amount of testing required in conjunction with large scale concrete production, the small 100 mm cubes are far easier to use than the 150 x 300 mm cylinders.

The design standard used till a few years back, was the Norwegian NS 3473. Since adopting the Eurocodes, the Norwegian material standard NS-EN 206-1 (with a national Norwegian annex) allows testing of the concrete using either cylinders, or 100 mm or 150 mm cubes (which are considered equivalent).

The ratio between cylinder and cube strength is typically taken equal to 0.8 at lower to medium grades, and increasing up to 0.87 for cylinder strength of 90 MPa.

Possibly this was of some use to you.

For quality assurance, either of the cube test or cylinder test can be performed. roughly we take 0.8 times of cube strength equivalent to cylindrical strength for lower to medium grade of concrete.

As per A. M Neville, he wrote in his book "Properties of Concrete" that strength of two different shape of concrete cant be compared, not for the lower grade or higher grade, for the support of this he use ref. of RILEM.

But piratically i also observed that for M40 Grade of concrete this Cylindrical to cubical strength is coming around 0.85 to 0.87.

 0.8 times of cube strength equivalent to cylindrical strength for  medium grade of concrete. is ok.

European standards, in strength classification, use both cylinder and cube strength: C 25/30, 30/37, 35/45 and so on. In structure design, cylinder strength is used.

Cylinder strength is lower because height to diameter ratio is 2 and at cube height to side ratio is 1. The crushed mode of cube and cylinder is one of the most effective factors which have impact in this factor.

Also for higher class of concrete the factor is smaller 

What is the relationship between concrete strength measured.... Available from: https://www.researchgate.net/post/What_is_the_relationship_between_concrete_strength_measured_using_cubes_and_cylinders?view=598f084393553bcb184fb602 [accessed Aug 12, 2017].

I test some cube and cylinder specimen of same grade (M30) in our lab, we experience  the ratio between cylinder to cube vary in range of 0.78 to 0.82. we tested about 5 sets

How can I convert cubic resistance of 800-900 to cylinder?

My concrete cubes and cylinders are 100x100x100mm and 150x300mm. The compressive strength results indicated a cylinder/cube ratio of the range 0.74 to 0.81.

I made an evaluation between concrete cubes (150mmx150mmx150mm) and cylinders (150mmx300mm) for concrete strength from 15 MPa to 100 MPa using 680 samples and found out a conversion factor (fc,cyl/fc,cu) with mean value of 0.84 and an associated variation coefficient of 0.095. A detailed evaluation can be found in the following paper:

Article Uncertainties of concrete parameters in shear capacity calcu...

Best regards,

Ngoc Linh Tran

Does anybody have the conversion factors for GROUTING MORTAR specimens?

I am looking for the conversion factors of strength from cubic or prismatical specimens of GROUTING MORTARS to cylindrical specimens.

Great answer.

compressive strength of cylinder 150x300mm= 0.8xcomp strength of cube 150x150x150mm.

This is due to platen restraint.essentially saint varnants principle.

Cube gives more strength as compared to cylinders because of difference of areas. Cube has less area and hence during computing compressive stresses of cubes, one can get more stresses as area is in denominator. Cylinder will give less value of stresses because of more area. Remember this answer in only for standard sizes of cubes and cylinders.

The main difference between cyllinder & cube testing procedures is Capping. Cylinder ends are not plane or parallel enough to mate properly with platens of compression testing machines, and thus must be capped with sulphur, neoprene, or other sutiable material for proper distribution of the load. Cube however are not capped but cast in rigid molds with sides that are plane & parallel. When tested they are flipped on their sides so that machine platens mate properly with cube surfaces. Factor affecting the cylinder/cube strength ratio are 1) Casting,curing & testing procedure, 2) Specimen Geometry, 3 ) level of strength, 4) direction of loading & machine characteristics, 5 ) aggregate grading. Past efforts to determine emperical conversion relationships & conversion factors have shown that it is difficult ( if not impossible ) to predict relationships between cylinders & cube stregths. past research has shown the cylinder/ cube strength ratio to be between about 0.65 to 0.90.