Surface blemishes on power-trowelled concrete floors due to aggregate particles at the surface

摘要

Three types of surface blemish can occasionally occur on power-trowelled floors: aggregate transparency, black spots, and rocking aggregate particles. These are a direct result of unusually high numbers of coarse aggregate particles at or very close to the surface of the slab during finishing. Various factors are thought to influence the risk of aggregate particles at or near the surface, i.e. harsh mixes, poor coarse aggregate grading, poor compaction, incomplete mixing and segregation. In practice, it is likely that a combination of two or more of these factors will be involved in a particular case. To reduce the risk, all factors likely to influence the risk of poor aggregate packing must be considered in the specification, design and production of the concrete and in the construction of the slab.rnThe concrete supplier should make certain that the concrete is well mixed and not harsh or stony. The contractors should themselves check on site that the concrete is well mixed before discharge and sufficiently cohesive. The contractor must use construction methods so the concrete does not segregate and is well-compacted.