Impact of Gypsum Addition on Portland Composite Cement (PCC)

Gypsum can serve as a substitute for clinker in Portland Composite Cement. It affects cement's compressive strength by regulating the hydration reaction speed to optimize the compressive strength obtained. Besides, it also slows down the cement's initial hardening and the final hardening. Other materials such as trass that have not previously been considered are also used in this study. It is a soft rock or soil layer derived from volcanic ash. It is known by the name pozzolana, which can be used in cement mixtures to increase compressive strength. This research aims to observe the effect of gypsum on the quality of Portland Composite Cement, such as compressive strength, setting time and SO3 content of mortar. They investigated clinker characteristics by adding some gypsum already done by several studies. However, the effect of SO3 content caused by gypsum added still needs more observation. The Samples were prepared with the addition of gypsum in the range of 0 - 5%. The clinker ratio was fixed at 75%, as other components, then limestone and trass were added with a fixed ratio of 1.2. Since a controlled variable, the fineness factor is kept in the range of 3850 ± 50 cm2/gr. The effect of adding gypsum to clinker was measured by performing a mortar compressive strength test and the binding time at the ages of 1, 3, 7, and 28 days. The results show that gypsum added as much as 3.5% improved properties of PCC of a 28-day cure binder: compressive strength of 348 kg/cm2, SO3 content is 1.7%, the initial setting time is 90, and the final setting time is maximum at 375 minutes.