content and expansion. Setting Time Cement paste setting time is affected by a number of items including cement fineness, water-cement ratio, chemical content especially gypsum content and admixtures. Setting tests are used to characterize how a particular cement paste sets. For construction purposes, the initial set must not be too soon and the final set must not be too late. Normally, two setting times are defined
Initial set. Occurs when the paste begins to stiffen considerably.
Final set. Occurs when the cement has hardened to the point at which it can sustain some load.
Setting is mainly caused by C3A and C3S and results in temperature rise in the cement paste.
False set No heat is evolved in a false set and the concrete can be remixed without adding water
Occures due to the conversion of unhydreous semihydrous gypsum to hydrous gypsum CaSO4.2H2O
Flash Set is due to absence of Gypsum. Specifically used for under water repair.
Strength Cement paste strength is typically defined in three ways compressive, tensile and flexural. These strengths can be affected by a number of items including water-cement ratio, cement-fine aggregate ratio, type and grading of fine aggregate, curing conditions, size and shape of specimen, loading conditions and age Duration of Testing Typically, Durations of testing are 1 day for high early strength cement
3 days, 7 days, 28 days and 90 days for monitoring strength progress