This method describes the making of concrete test cubes for testing for compressive strength.
Required equipment
- Mould of cast iron or steel, with removable base plate. The depth of the mould and the distance between the two pairs of opposite internal side faces, shall be the nominal size of 100 ± 0.15 mm or 150 ± 0.15 mm.
- Scoop
- Vibrating table or steel compacting bar weighing 1.8 kg, 380 mm long and having a ramming face 25 mm square.
- Plasterer’s steel float
- Sampling tray
- Shovel
Mixing
- Air-dry the aggregate to be used and bring it to temperature preferably about 25 °C. Mix the cement thoroughly and bring it to a temperature preferably about 25 °C. Portion the material by mass to the nearest 0.5 %.
- Mix the concrete in a mixing machine. Load the mixing drum with coarse aggregate, fine aggregate, cement and add water slowly. Continue mixing until the concrete is uniform in appearance, but not for less than 2 minutes after all material is in the drum.
Sampling
- Obtain a sample of fresh concrete either from the laboratory made batch or from a mix at a building site. The sample shall be thoroughly mixed just before it is moulded.
- From each sample of fresh concrete there shall be made a minimum of 2 test cubes specimens.
Moulding
- Place the moulds on a rigid horizontal surface or on the vibrating table. Fill with concrete in layers of approximately 50 mm deep and compact each layer by the compacting bar or the vibrating table.
- When compacting with a compacting bar, distribute the strokes evenly over the cross-section of the mould without penetrating any previous layer significantly. Use 35 strokes per layer for 150 mm cubes or 25 strokes per layer for 100 mm cubes.
- When using a vibrating table, compact until the surface of the concrete becomes relatively smooth and has aglazed appearance.
Curing
- Cover the test cubes (in the moulds) with an impervious sheet and store them in a place free from vibrations. The room shall have a relative humidity preferably of min. 90 % and a temperature preferably about 25 °C.
- After an initial curing period of 24 hours, mark each cube so that it can clearly be identified, and remove it carefully from the mould.
- Submerge the cubes immediately in water at a temperature preferably of about 25 °C
