What is meant by the common term 'cold joint?"
A cold joint is a plane of weakness in concrete caused by an interruption or delay in the concreting operations. It occurs when the first batch of concrete has begun to set before the next batch is added, so that the two batches do not intermix. Sometimes cold joints occur because of emergency interruptions and delays and sometimes because of the work stoppage at the end of the day, but they can 'also occur from poor consolidation. To prevent cold joints in walls, beams and other structural components it is necessary to place concrete in layers about 18 inches deep and intermix each layer with the previous one by using a vibrator. Placement of concrete should begin in the corners and work toward the center. When slabs are placed the concrete should be placed against the preceding batch and not dumped in an individual pile. On sloping grades the work should proceed uphill. In hot weather a retarding admixture may be needed to slow the setting time.