ASTM C39, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, specifies that the loading rate fall within 0.14 to 0.34 MPa/sec (20 to 50 psi/sec). On average, the compressive strength of cylinders tested at the high load rate limit will be 3% greater than cylinders tested at the low load rate limit. A 20% increase in compressive strength of high-strength concrete is possible when loading rates exceed the above ASTM C39 limits.

for example 0.20 MPa/sec = 12 MPa/min = 122 kg/cm2/min

(0.14 to 0.34 MPa/sec = 86 to 208 kg/cm2/min)

According to this: https://law.resource.org/pub/in/bis/S03/is.516.1959.pdf

the rate for IN IS 516 is 140 kg/cm2/min, not 7!

In testing, machines can be calibrated to provide the required rate for compression.

In IS 516.1959 Section 8.3.1 test procedure for flexural strength of beam. pace rate given as 7 kg/sqcm/min. 

8.3.1 Plac1'Kg the Specimen in ~he Testmg J\lacltine --- The bearing sur..

faces of the supporting and loading rollers -hall be wiped cit an, and any

loose sand or other material removed from the surfaces of the specimen

where they are to make contact witt. the rollers. The specimen shall then

be placed in the machine in such a manner that the load ,hC\11 be applied to

the uppermost surface as cast in the mould, a}clng two luu« spaced 20·0 or

13·3 ern apart. The axis of the specimen shall be carefullv aligned with

the axis of the loading device. No packing shall be used between the

bearing surfaces of the specimen and the rollers, The load shall be applied

without shock and increasing continuously at a rate such that the extreme

fibre stress increases at approximately 7 kg/sq cn.rmm. that is, at a

rate of loading of 400 kg/min for the 15·0 em specimen- and at a rate of

180 k~/min for the 10·0 em specimens, The load shall be increased until

the specimen fails, and the maximum load applied to the -perrrnen during

the test shall be recorded. The appearance of the fractured faces of concrete

and any unusual features in the type of failure shall be noted.

Hi again Bhupesh,

You are right! you are talking about the flexure test, while I thought that it was a simple compression test. Anyway, it is still simple. I made the calculations for you and you can see how from max stress rate = 7 kg/cm2/min you end up with force rate = 400 kg/min. Please see the attached PDF file, I hope it will be clear for you, although it was hand-written and done quickly!

Note that according to the specific code, the length of the beam (for 15*15 section) is 60 cm and there are 2 loads applied at 20 cm (L/3) and 40 cm (2L/3). The sum of the 2 point loads is the external load that is provided by the machine.

Vagelis