What is the required precision (least count) for the dial gauge on the length comparator?

The dial gauge must have a least count of 0.002 mm (Clause 3.1).

What are the standard specimen sizes this apparatus is designed for?

The standard specifies moulds for prisms of 25 x 25 mm and 75 x 75 mm cross-sections, both with an effective gauge length of 250 mm (Clause 4.1.1).

What material should the reference bar be made of?

It should be made of Invar steel or another material with a coefficient of thermal expansion not exceeding 2 x 10⁻⁶ per degree Celsius (Clause 5.1).

IS 9459

: 1980

Specification for apparatus for use in measurement of length change of hardened cement paste, mortar and concrete

CurrentSpecializedSpecificationMaterials Science · Cement, Concrete, Aggregates and RCC

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This standard specifies the requirements for the apparatus used to measure the change in length of hardened specimens of cement paste, mortar, and concrete. It covers the detailed specifications for the length comparator, moulds for preparing specimens, gauge studs, and the reference bar used for calibration.

Specification for apparatus for use in measurement of length change of hardened cement paste, mortar and concrete

Quick Reference Values

Dial gauge least count0.002 mm

Standard gauge length250 mm

Gauge stud diameter6.5 ± 0.1 mm

Reference bar thermal expansion coefficient (max)2 x 10⁻⁶ per °C

Small mould internal dimensions25 x 25 x 282 mm

Large mould internal dimensions75 x 75 x 282 mm

Practical Notes

The accuracy of measurements is highly dependent on regular calibration of the length comparator with the Invar steel reference bar.

Ensure the contact points of the comparator and the gauge studs on the specimen are clean before each reading to avoid errors.

Handle specimens carefully during demoulding and measurement to prevent damage to the embedded gauge studs.