What is the required accuracy class for a CTM in a typical lab?

Class 1 is generally required for most testing labs, with a permissible error of ± 1.0% of the indicated load (Table 1).

How often should a Compression Testing Machine be calibrated?

At intervals not exceeding 12 months, after being moved, or after any repairs that may affect its accuracy (Clause 8.1.1).

What is the minimum hardness required for the machine platens?

The bearing surfaces of the platens must not be less than 55 HRC (Rockwell Hardness) according to Clause 5.5.1.

Does the CTM need to control the loading speed?

Yes, the machine must be capable of applying load at specified rates with an accuracy of ±10%, a feature known as 'pacing' (Clause 7).

IS 14858

: 2000

Requirements for compression testing machine used for testing of concrete and mortar

CurrentFrequently UsedSpecificationMaterials Science · Cement, Concrete, Aggregates and RCC

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This standard specifies the requirements for compression testing machines (CTMs) used for determining the compressive strength of concrete and mortar specimens. It covers the machine's load frame, load indication system, accuracy, platen characteristics, and calibration procedures to ensure reliable and consistent test results.

Requirements for compression testing machine used for testing of concrete and mortar

Quick Reference Values

Permissible error for Class 1 machine± 1.0 % of indicated load

Platen hardness (Rockwell)Not less than 55 HRC

Platen flatness tolerance0.03 mm

Minimum vertical clearance between platens340 mm

Loading rate (pacing) accuracy± 10 %

Repeatability of force indication (Class 1)1.0 % of indicated load

Practical Notes

Ensure the machine is calibrated at least annually, or after relocation, using a proving device traceable to national standards as per Clause 8.

The rate of loading is critical for accurate results. The machine must have a pacing system, and the operator must adhere to the rate specified in the relevant test standard (e.g., IS 516).

Regularly check the condition of the machine platens for flatness and any damage, as this directly affects the stress distribution on the specimen and the final strength value.