Monitoring the variability of cement compressive strength using Multivariate Exponentially Weighted Moving Covariance Matrix (MEWMC) control chart

Cement quality plays an important role in ensuring the infrastructure development of a nation. PT "X" is a business entity engaged in cement production. The high demand for cement has driven PT "X" to constantly improve the quality under the established standards. In general, the quality of cement is determined by the compressive strength of cement measure on the 3^rd, 7^th, and 28^th days. In this paper, the MEWMC control chart is used to monitor the compressive strength of cement. MEWMC is an exponentially weighted control chart for monitoring the stability of the covariance matrix of a process. Using the optimum weighting value λ is 0.1 in phase two, the monitoring results show that the cement quality has been statistically controlled or there is no process shift.