Therefore, concrete will settle more when
1) Slump of the concrete is too high or the concrete has too low sand content or too much water content. Bleeding will occur concurrently will the settlement.
2) Using to dry aggregates to produce concrete. If the aggregates are still absorbing water after the concrete has been placed, settlement of the concrete may occur.
3) Consolidation off the concrete is not sufficiently done. Insufficient consolidation may leave many entrapped air voids in the concrete. The evacuation of those air voids from the concrete results in settlement. However, over-consolidation causing segregation of the concrete must be avoided too.
4) Water absorption of the formwork is high.
5) Curing of concrete is not properly done so that water can evaporate much form the surface of the concrete or the concrete or the covering materials for curing concrete can absorb large amount of water from the concrete.
6) Relative humidity of the environment is low.
7) Deformation and movement of the formwork is excessive.
2.1.3 Possible Location of Settlement Cracks
1) Top surface of concrete beams or slabs above the reinforcements in the direction along the reinforcement. In addition to the cracks, voids can be formed under the reinforcements, usually under the top bars, too.
2) Side faces of columns along the tied bars.
3) Top surface of the shallower sections of concrete slabs when there are deeper sections beside.
4) Side faces of columns or walls that are in contact with the formwork.
2.1.4 Time of Occurrence of Settlement Cracks
Settlement cracks can start to appear from a few minutes after placing until before final setting time.