Segregation in concrete is generally due to excessive water in the matrix but can also be caused by over compaction (vibration), dropping the concrete from a height or simply through inappropriate mix design. If the mix looses its cohesion, excess water will naturally attempt to escape at the path of least resistance, upwards at the form face. Once a path of escape is achieved more excess water will find this path and a sand run will be created. Sand runs are also exacerbated