| Summary: | 碩士 === 國立中央大學 === 土木工程學系 === 84 === The hydration of cement has a great influence on the
workability of high performance concrete (H.P.C.) as well
as its setting, such as strength and durability. Therefore,
it''s very important to understand and control the dynamic
properties and hardening rate of cement during hydration. In
applying materials, high performance concrete has to add
chemical admixtures like superplasticizer in order
to improve the workability, rheological behavior,
lowering the amount of water and decreasing
microstructure air void of concrete. At present there are many
brands of superplasticizer, among which the ingredients,
characteristics and moculer weight are widely different,
Further, cement is composed of four main clinker, each
of which has different and sophisticated mechanism of
hydration. When these materials are combined to be HPC, it will
affect with each other. Consequently, by measuring
concentration of pore solution,heat evolution of
hydration, the change of setting time, matching experiments
like adsorption behavior and X ray diffractrometry analysis to
examine the influence of superplasticizer to hydration of C3A
and cement materials, in order to have a better imformation
of the application strategy of every materials.
The result of this research shows that obviously C3A affects the
early hydration and setting of concrete; the amount of gypsum
also affects the hydration of C3A. Adding superplasticizer
cement will delay the process of hydration because of SP
adsorption. Besides, slowing phenomenon is more apparent
along with the increasing of dosage. As a result, the best
dosage is about 1~2% weight as many of cement. C3A and cement
adsorb superplasticizer''s adsorption equilibrium time is
different, but its tendency is similar; the curves of isothermal
adsorption all belong to monolayer adsorption. In C3A
system, the amount of SP adsorption is dependent on the
amount of gypsum, while in cement system, it depends of the
amount of C3A and sulfate. The amount of gypsum determines
the morphology of C3A hydrated; adding
superplasticizer will also delaying hydration of C3A and the
producing rate of hydrate.
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