Hybrid control charts for active control and monitoring of concrete strength

Concrete is the most widely used material in construction industries. Therefore, it is necessary to understand and when possible, improve the efficiency of a concrete production process. Statistical process control is generally applied to gain information about variation in the manufacturing process. Control charts can be implemented to monitor the various processes involved in the production, the delivery and construction of concrete. When historical data are available on various projects, better insight into operational procedures can be obtained through the use of control charts. This paper studies a series of statistical analysis procedures to analyze the compressive strength of concrete. The proposed method is based on combining the cumulative sum (CUSUM) control chart and a run chart (CUSUM-run chart) for early detection of shifts in the process mean. The combined charts address both the consumers' and the producers' perspectives. The CUSUM-run chart can aid the consumer in making decisions about accepting or rejecting a strength test. In addition, the producers (concrete manufacturers) can use the chart to determine if the monitored process is out-of-control and subsequently attempt to identify the possible causes for the out-of-control situation. By identifying assignable causes of the out-of-control process, the producer can then improve the manufacturing process by reducing product variation, unnecessary waste, or over-designed concrete mixtures. The CUSUM-run chart is also beneficial in that it can often indicate when the strength of mixture is less than the minimum acceptable level very quickly. The delay in detecting an unacceptable strength can result in more penalties, project delays and increased associated costs.