A comparative study of modified fall cone method and semi-adiabatic calorimetry for measurement of setting time of cement based materials

Abstract Setting time is a critical parameter that limits the workability of cement-based materials and is generally determined using a Vicat needle test for cement paste, or by measuring the penetration resistance for mortar and concrete. The Vicat needle and penetration tests, however, are either adequate for cement paste or mortars, instead of all types of cementitious materials. Therefore, a modified fall cone method (FCM) was developed to serve as a unified test protocol for measuring the setting time of both cement paste and mortars while the semi-adiabatic calorimetry (SAC) was employed for a comparative study. Mortar samples with various mix proportions and aggregate sizes were tested by both methods. Two models were established to fit the FCM and SAC data, and the initial and final setting times were obtained by taking extremums from the derivatives. Test results indicated that the setting time measured by the FCM were consistently shorter than those measured by the SAC and such discrepancy gradually decreased with the increase of cement/sand ratio (wc/ws) and finally disappeared when pure cement paste was achieved. The discrepancy of the setting time measured from different methods is attributed to the mixing of aggregates, which significantly enhances the penetration resistance of mortar but only has a moderate effect on heat evolution at early-age hydration.