Strength Test

The strength of cement can not be determined directly on cement. Instead the strength of cement is indirectly determined on cement-mortar of 1:3, and the compressive strength of this mortar is the strength of cement at a specific period.

For this test, 555 g of standard sand and 185 g of cement is mixed with water quantity P/4 + 3% of the combined weight of the cement and sand mixture. These are mixed thoroughly within 3–4 minutes. The mixed paste is filled in a cube mould of size 7.06 mm, which has a face area of 50 sq cm. The mortar is compacted by a tamping rod or in a vibrator. The moulds have to be kept in a room with a controlled temperature of 27 ± 2°C and at least 90% humidity. If this facility is not available, the moulds are kept under a wet gunny bag to simulate 90% relative humidity. The cubes are removed from the mould after 24 hours and kept immersed in clean water till taken out for testing.

Three cubes are tested for compressive strength after a specific period (viz., 3, 7 or 28 days). The period is being reckoned from the completion of vibration. The average compressive strength of the three cubes gives the strength of cement at the specific period.