| Summary: | 碩士 === 國立臺灣師範大學 === 化學系 === 84 === Chemical admixture is one key component in forming high
performance concrete. This study has selected several
domestic chemical admixtures, namely sulfonated naphthalene-
formaldehyde condensates (N1, N2, N3, N4), sulfonated melamine-
formaldehyde condensates (M1), and sulfonated phenolic resin
(S1). The basic properties of these chemical admixtures were
determined through IR, UV, TGA and GPC measurements. The cement
pastes with or without chemical admixtures present were prepared
and tested at the curing age of 1, 3, 7, 28day. The degree of
hydration and the length of polysilicate of tested materials
were analyzed from Solid 29Si MAS NMR spectra; the amount of CH
and C3S of samples were examined by using a powder X-ray
diffractometer; the Vicat Needle was applied to determine the
setting time of cement pastes. Thus, the effects of admixtures
on the hydration behavior of cement pastes were investigated.
Moreover, the effect of admixtures on the material properties of
harden samples were also examined through fluidity, compressive
strength and porosity measurements. The results show that
different type of admixture presents different properties such
as appearance, solid content, UV spectrum and molecular weight
and distribution. Both the degree of hydration and the length of
polysilicate of cement pastes increases with curing age. Pastes
with W/C=0.4 become more hydrated than those with W/C=0.3.
Admixtures would lower the degree of cement hydration or prolong
the setting time; the retarding effect is in the order of N2 >S1
>N1 > M1. Besides, increase of admixture dosage also show more
retarding effect. As most chemical admixtures could enhance the
dispersion of cement particles; they will enhance the fluidity
of cement pastes, densify the microstructures, and increase the
compressive strength of the resulting materials. However, it is
noted that both N2 and S1 exhibit less reinforcement effect,
since they show more retarding effect on the cement hydration.
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