Hugh Wang

C4AF Reactivity—Chemistry and Hydration of Industrial Cement

The study described in this paper involved a close examination of one of the least-researched cement phases, 4CaO•Al(2)O(3)•Fe(2)O(3) (C(4)AF or ferrite). The two ferrite materials used in this program were: (1) extracted from an industrial clinker free of 3CaO•Al(2)O(3) (C(3)A or aluminate); and (2) a laboratory-synthesized C(4)AF compound. Both ferrite materials were initially characterized using optical microscopy, x-ray diffraction (XRD), and Raman spectroscopy. The hydration kinetics and reactivity of both materials were studied with a calorimetric technique. Similar to aluminate, ferrite also demonstrated a strong early hydration rate. An adequate amount of sulfate (SO(3)) was needed to regulate the ferrite hydration rate. Based on this work, an equivalent aluminate content, C(3)A(eq), is proposed. The hydration of C(3)A(eq) needs to be properly controlled with the appropriate amount of sulfate. The concept, based on equivalent aluminate content for cement sulfate optimization, ensures proper early hydration behavior from both C(3)A and C(4)AF and avoids potential cement-admixture incompatibility probems, especially for the cements containing little or no C(3)A content.

Use of Isothermal Conduction Calorimetric Method for Measuring the Heat of Hydration of Cement

In the present study, an extensive test program is conducted to measure and compare the heat of hydration obtained from both calorimeter and ASTM C186-05 test methods. A statistical analysis is performed to evaluate the variations of the test data. The results indicate that the isothermal conduction calorimeter method is a more reliable, less time-consuming, and less labor-intensive method than the ASTM C186-05 test method. The heat of hydration at 3 days showed the least variation in all calorimeter tests. These suggest that ASTM shall consider adopting the isothermal conduction calorimeter method for measuring the heat of hydration of cement. The 3-day heat of hydration value can be used for specifying the limit of heat release for type II cements.