Unreacted Cement Content in Macro-Defect-Free Composites: Impact on Processing-Structure-Property Relations.
Unreacted Cement Content in Macro-Defect-Free
Composites: Impact on Processing-Structure-Property
Desai, P. G.; Lewis, J. A.; Bentz, D. P.
Journal of Materials Science, Vol. 29, 6445-6452, 1994.
building technology; cements; composite materials;
flexural strength; interphase; macrodetect free;
moisture absorption; percolation
The effect of unreacted cement content on the
processing, structure, and properties of
macro-defect-free (MDF) composites fabricated from
calcium aluminate cement (CAC), A-ALUMINA (Al2O3), and
polyvinyl alcohol-acetate (PVAA) has been investigated.
Three systems were formed with initial CAL:Al2O3 ratios
of 50:50, 35:65, and 25:75 by volume in their respective
formulations. The amount of unreacted cement was
reduced from 68.1 vol% which is present in standard
(100% CAC) MDF cement, to 14.9 vol% for composites with
an initial CAC:Al2O3 ratio of 25:75, while the hydration
product content was reduced from 18.1 vol% to 11.4 vol%
for these respective systems. A hard core/soft shell
continuum percolation model was used to determine that
alumina substitution did not significantly affect the
percolative nature of the interphase and bulk polymer
regions. However, experiments showed that the reduction
in unreacted cement content through Al2O3 substitution
affected both the processing and microstructural
features of these composites. The moisture absorption
kinetics and flexural strength of composites exposed to
100% relative humidity were also evaluated, and it was
found that their moisture sensitivity improved with
decreasing unreacted cement content. A hypothesis is
presented to explain the role of unreacted cement on the
moisture sensitivity of these materials.