Limitations and recommendations for measuring setting time, autogenous deformation, and chemical shr

来源 :The 14th International Congress on the Chemistry of Cement ( | 被引量 : 0次 | 上传用户:saialmaster
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  Traditionally, setting time of cement paste is measured using the Vicat setting time test method.However, the rate of hydration and time of initial and final set is affected by the temperature of the paste.Current specifications for the Vicat setting time allows a range.of conditioning temperatures during testing.Small changes in temperature can have a significant effect on the time of initial and final set.It is important to know a more exact time of final set, particularly in studies of autogenous deformation.Chemical shrinkage and autogenous deformation are of equal magnitude until rigidity in the paste structure occurs and internal strains can be developed.Adequate rigidity occurs at the time of final set and, at this time, a separation of chemical and autogenous shrinkage can be observed.This study examined the effects of temperature variations in the Vicat setting time test on final set to determine the initiation of autogenous shrinkage measurements.Setting time,autogenous deformation, and chemical shrinkage of portland cement pastes with a w/c =0.35 were measured.Setting time was measured according to the Vicat method.Volumetric measurements using the membrane method were used for determining autogenous deformation, and an automated dilatometry method per ASTM C 1608 was used for chemical shrinkage measurements.Surface temperature of the paste sample was measured during the Vicat test.Variations in final setting time of cement pastes of up to 1.5 h were observed and resulted in variations of up to 30% in the magnitude of autogenous deformation.These variations were caused by inconsistent temperature control for setting time.Recommendations for the three test methods to accurately determine when autogenous deformation measurements should be initiated in the laboratory are presented.
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