En 12390-2:2019 Best: Bs

The concrete is placed in the molds in layers. The number of layers and the duration of vibration or number of tamps depend on the dimensions of the specimen and the workability of the mix. Over-vibration must be avoided as it can cause segregation, while under-compaction leads to voids that artificially lower the recorded strength. After compaction, the top surface is leveled using a trowel or float to create a smooth, flat finish. The Curing Process: A Critical Phase

| Equipment | Requirement | |-----------|-------------| | | Must be rigid, non-absorbent, and resistant to corrosion. Dimensional tolerance: ±0.5% of nominal size. Internal surfaces must have a roughness depth ≤ 3.2 µm. Moulds showing dents, warping, or wear beyond tolerance must be retired. | | Vibrating table | Frequency: 50 Hz ± 3 Hz; Amplitude: 0.5 mm ± 0.1 mm for cubes (0.8 mm for cylinders). Compliance must be verified annually. | | Compacting bar | Circular cross-section (e.g., 16 mm or 25 mm diameter depending on aggregate size), with a hemispherical tip. Mass and dimensions specified in the standard. | | Curing tank | Must maintain water temperature at 20°C ± 1°C (or ±2°C for lower grades). Water must be saturated with lime (to prevent leaching of calcium hydroxide from specimens). | | Humidity cabinet | For air curing: Must maintain 20°C ± 2°C and ≥95% relative humidity. | bs en 12390-2:2019

Plastic sheeting or damp burlap/hessian is typically used to cover specimens immediately after casting to prevent moisture loss during initial curing. Standard Overview The concrete is placed in the molds in layers