The mold you are referring to is for grout cubes ( cement and water ).

A more standardized reference is the 4 inch diameter, 8 inch long

cylinders for concrete,

Of course you could do both, and compare results of the compressive tests.

The 4 x 8 inch molds are used for smaller aggregates, while the 6 x 12

inch molds are used for larger aggregates. in an extension of this,

24 inch x 48 inch cylinders are made for dams with very large aggregates,

and they even can go up to 36 inch by 72 inch for even larger aggregates.

There are only two machines in the world that can crush concrete cylinders

this large, one is at the Federal Center in Lakewood , Colorado, USA.

The Bang when the cylinders crush is so great, that they have to notify

the Earthquake recording center in Boulder Colorado, USA prior to

loading the concrete cylinders to failure.

I didn't use any aggregate in the mix. I just use binder with sand maximum particle size is 0.5mm. Sol in this case can we behave this concrete mix as mortar. isn't it?

Then you can use the smallest concrete cylinders that are considered to

be and ASTM Standard where the height of the cylinders is twice the

diameter of the cylinders. If you do not use a Standard, your work will

not be considered as valid, especially as concrete under compression

breaks in conic sections, and not cubic sections. The cubes are not

round, and the cubes are not twice as high.

Ususally, in order to get a valid data, standard model was recommended. Height shoud be twice of the height if cylinders were grouted. Besides, if cubes were used, the wideth of model should be three times of the maximum diameter of aggregates to mitigate the size effect. So, theoretically speaking, the model you use is acceptable, yet you have no idea how to convert the data to standarized model.

Utilization of 50 mm cube samples for determination of the compressive strength of grout is a common practice and widely acceptable among the researchers.

For testing mortar you can use 50mm cubes. Check with euro British standard

Mohammed, for what it is worth!! You talk about high strength concrete, There are not recognized standards for using High strengths in design of structures. And If I am not mistaken most of the work in High strengths are for comparison of materials. So in that case using 50 mm cubes are in order I presume. In your case you have a very fine material as base. so I would use ISO bar prisms that they use in Europe to classify Cement strengths where you have a 160 X 40 X40 mm prism and you first test it in bending (MOR) and then you test the two halves in a special compression rig This gives you three MOR and six Compresive strength points for each mix. The argument about Cylinders and Cubes is not solved yet and a lot of Countries still use Cubes as quality control. And even here the original standard of using 6 inch (for the Americans) and 150 mm for the rest of the world is changed to 100 mm (4 inch) because of the incorporation of 80 mpa max in the design codes and most of the site cube crushers can not crush the bigger cubes. About the coment on the size of aggregate and size of mould, again different countries have different specs, We use 3 times for cover of shutter to reingforcing and 4 times for aggregate size and mould size. to eliminate "ANY' bridging in dryer mixes. But to keep in spec and publish your findings you have to use ASTM, EN or Australian or wherever you from's spec. 

usually 150X150X150mm cubes are used to find the cubic strength fck and 150mm dia cylender  is used to find the cylendrical strength fy . For all the practical purposes it is required to have fck and fy. moreover, nocylendrical mould is availble for 50 mm dia .

Hi Seshadri, You right but the Countries that use the BS 8110 to design structures use Cylindrical strengths as their Characteristic strength and the have a conversion factor from cube to cylinder, which is unfortunately not 100% correct because the difference in strength is a material factor more then a size factor. The 50 mm cubes were used to test the cement strengths before it was replaced by the 160 X 40 X 40 mm prisms.

For comparison purpose we may use 50 mm cube, but 150 mm cube is ideal.

It is an acceptable test for mortar but take care that the result you get is only for the 50mm cubes. This value is not similar to the standard value obtained by the 150mm cubes. The size of specimen has an effect on the standard strength. You can make your own modification factor by testing some 50mm and 150mm cubes and plot the strength results of both to get the modification factor (the higher the number of samples, the better prediction interval you can get)

I do support Hisham Qasrawi and Derek Mostert

Since you have not coarse aggregate, you are not testing concrete. it is mortar mix and follow the testing standards for compressive strength of mortar. 50mm cube testing is appropriate.

not used ( I noticed that the word ‘used‘ was missing in my response)

No

The cube mold is for grout only ( sand and portland cement )

Cylinder molds are for testing concrete. The bigger the aggregate, the

bigger the cylinder mold. In Lakewood Colorado they have a machine that can

create 5 million pounds of vertical force. They test large diameter concrete

cylinders there in the 2 foot diameter to 3 foot diameter range. But first they

have to notify the Earth quake center in Boulder Colorado as the energy released when the cylinder breaks generates detectable earth quakes about 50 miles away.

Cement paste or Mortar (cement and sand) testing cube 50mm

Or concrete cylinder 150 mm diameter x 300 mm height

Or 200mm diameter x 200 height

Equivalent concrete testing cube 100mm or 150mm

ASTM C109 / C109M - 20b

Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50 mm] Cube Specimens)

ASTM C39 / C39M - 20

Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens

Good luck

What is the purpose of compressive strength on mortar? if it is to develop the mix composition, then 50mm cube could be used if you are unable to test according to your local standard. British standard (currently European standard) allows to use cubes and cylinders. If you are using cylinder then it has be capped before testing, which is not easily done with high strength mortar.

If the compressive strength measurement is done for compliance testing then you have to follow the standard requirements including test specimen size and shape and test procedures.

Since the size of the aggregate is sand, and the sand is vastly smaller than the

50 x 50 x 50 cube, then it should work. The key to testing concrete in cubes or cylinders is that the maximum sized aggregate be far smaller than the diameter of the cylinder, or, the cross-section of the cube.

To cross check, do both cylinders, and cubes, and compare the results obtained from each method. Remember cylinders are always twice as tall as the diameter

of the cylinder. 6 inch ( 150 mm ) diameter cylinders are 12 inches ( 300 mm ) tall. 2 foot diameter cylinders are 4 foot tall, and 3 foot diameter cylinders are 6 foot tall. They stopped crushing the 3 foot diameter cylinders as it approached the 5 million pound rating of the machine. The machine was cast by the Baldwin Locomotive Works, and they are now out of business, so, they can not get replacement parts if the machine breaks.

When I was in college ( a long time ago ), one of the research students built a machine to do uni-axial, bi-axial, and tri-axial compression of concrete cubes to see how concrete broke in different ways under different applied loads.

Uni-axial breaks are the norm for cylinders.

MWC

Yes, I think you can use it. By using the equivalent mortar mixes of the high strength concrete. I have done it, and find the strength results of the equivalent mortar mixes were similar to the that of their equivalen concrete strengths.equivalent

Mortar Cubes give you the results of the strength of the Mortar. They do not give you the combined strength of the aggregate, Mortar, and the bond between the aggregates and the mortar. You could have bad or dirty aggregate that does not bond well to the mortar.

Use the correct tests to get the correct results. Cylinders were designed by testing to be twice as tall as their diameter so that fracture patterns could be studied.

You can use it if your aggregate size is fine. I can also send to you one of my papers about UHPC and using 50*50*50 mm cubic size.

best luck

It depends on the reason for testing. For mix design, 50mm cubes could be used if the maximum aggregate size is 10mm. However, standard 100mm cubes are needed to satisfy the specification requirements. Variability of the test results is found to have affected by the specimen size.

The test method is very much dependent upon the size of the aggregate used in the concrete. In the upper limit, when cores from dams were being tested, the cores were 3 feet in diameter, and 6 feet long. The test machine was capable of creating 5 million pounds of force to crush these cylinders. Since it was manufactured by a company that made giant castings for trains, it has been de-rated so they only test cylinders 2 feet in diameter by 4 feet in length any more.

The company that made the castings is no longer in business.

Before testing, they would contact the national earth quake center in Boulder Colorado to tell them of the test as it registers as a small earth quake when the cylinders break.

Most Concrete is now tested using 4 inch diameter X 6 inch long cylinders.

Maximum sized aggregates have diminished over the years, so the 6 inch by 12 inch cylinders are not used very much any more.

Make sure that your test methods reflect the maximum sized aggregate that you will be using in your finished concrete.

Cement mortar is often used to test the behavior of the additive material when added to cement materials. For example, if you have added nanomaterials or any waste material, you will see whether this added material enhanced the properties you aim to improve.

Using of cube 50 mm to determine the compressive strength of mortar is well known among the authors. Best regards.

I used a cube of 50 mm for finding the compressive strength of reactive powder concrete as there is no coarse aggregate in this type of concrete

using of 100X100X100mm or 150X150X150mm are in practice for finding the fck

In UHPC very less variation you can see by changing the mould size.. i have used 100*100*100 cube size for M200 UHPC. For more info read the following paper -

Cube size and it’s impact on compressive strength

https://www.bau.uni-siegen.de/subdomains/massivbau/publikationen/download/effect_of_specimen_size_on_the_compressive_strength_of_ultra-high_performance_concrete.pdf

Yes, ... you might can