What type of surface should the slump mold be placed on?

The slump mold should be placed on a rigid and flat surface that is moist and non-absorbent to ensure accurate test results. A rigid surface is essential because it provides stability during the test, preventing any deformation of the mold that could affect the slump measurement. If the surface were soft and uneven, it could lead to errors in the slump reading as the mold might shift or settle during the measurement process.

Additionally, placing the mold on a moist and non-absorbent surface helps to prevent excessive moisture loss from the concrete mix, which could also impact the consistency and, subsequently, the slump result. An absorbent surface might draw moisture away from the concrete, resulting in a false or misleading slump measurement.

By ensuring that the mold is on the correct surface, technicians can achieve reliable and accurate measurements of the concrete's workability, which is a critical factor in the quality of the final product.