Civil Engineering Reference
In-Depth Information
C-S-H phase/sulfoaluminate hydrate and Ca(OH)
2
respectively. The poly-
mer impregnated paste
B
shows several endothermal and exothermal
effects. The exothermal peaks also occur in pure polymers, hence this effect
may be ascribed to the oxidation of the polymer. There is also an indication
that the Ca(OH)
2
peak in the impregnated samples is decreased in intensity.
This decrease in intensity could be due to the masking effect of the
exothermal peak occurring at about the same temperature and a dilution
effect. Curve
C-1
refers to a mechanical mix of the polymer and cement
paste. Both
B-1
and
C-1
are similar in terms of exo- and endothermal
effects, except the sharp endothermal effects at 230-270°C and 250-350°C
are not apparent in sample
C-1
. This may be due to the masking effect of the
endotherm of portland cement paste. Other experimental evidence suggests
that the emergence of new thermal effects in the polymer-impregnated
cement paste are not due to Ca(OH)
2
-polymer interaction during impregna-
tion. It is rather due to complex interaction that occurs between hydrated
cement decomposition products and PMMA during heating in the DTA
apparatus. In samples exposed to N
2
only, endotherms result.
The effect of polymers on the fly ash concrete has also been studied
by thermal methods. The amount of lime formed in mixes containing
cement, fly ash, and a non-ionic polymer (Versicol) and cured for 1 to 90
days has been determined by thermal analysis.
[95]
At all curing times, the
amount of lime formed in the cement-fly ash-polymer mixtures was higher,
especially at a w/c ratio of 0.25. It was concluded that the polymer interacts
preferentially with the silica and alumina of the fly ash rather than with lime
produced in the reaction.
Stabilized laterite soils have been applied in highways, dams, and
foundations. Laterites consist of quartz, hematite, gibbsite, etc. It has been
found that heating laterite to about 800°C and curing with cement produces
a strong body with good durability characteristics. By replacing cement
with 20% laterite, the 28 day strength reaches a value of 80% of that of the
reference.
[96]
DTA studies indicate that in laterite-cement mixes the amount
of lime produced is decreased due to the pozzolanic reaction, and the
amount of the C-S-H phase is increased. Other phases, such as C
2
ASH
8
and
C
4
AH
13
, were also identified.
Red mud is a by-product derived from the aluminum industry and
consists mainly of Si, Al, Fe, Ca, and compounds kaolinite and gibbsite.
Pera and Momtazi
[97]
evaluated the pozzolanic activity of red mud by
heating it at different temperatures in the range 600° to 800°C. The cement
was mixed with 30-50% red mud and cured for different times in water. The
products were subjected to DTA and XRD studies. Lime was completely
