Environmental Engineering Reference
In-Depth Information
shows the response trace plots for compressive strength, water absorption,
shrinkage, density and leaching concentration of lead and cadmium
respectively in the s/s sintered jarosite waste-cay-PCCRs composite products.
Each figure consists of 3 overlaid plots, one for each constituent namely
jarosite, clay and PCCRs. For a given constituent, the fitted value of the
response is plotted as the constituent is varied from its low to high setting in
the constrained region, while the other components are held in the same
relative ratio as a specified reference mixture, here the centroid. The plot
shows the ―effect‖ of changing each component on compressive strength. As
expected, increasing the amount of water decreased strength, while increasing
the amount of jarosite increased strength. Jarosite had the largest effect with its
higher amounts yielding higher strength. Addition of PCCRs decreased the
compressive strength.
Further, it is to note here that the compressive strength is decreasing with
increasing water absorption, which is obvious in clay based products. PCCRs
is a resultant by product of coal combustion at about 1500C and hence further
sintering did not influence in increasing the strength. However, under solid-
state reaction, the presence of silica and alumina significantly contributed
complexing in silicate matrix in formation of new crystallite phases (Al-Si
spinel and mullite) thus toxic substance/ elements were detoxified
immobilized. Whereas addition of clay increased the compressive strength up
to a certain level and further decrease in compressive strength at higher
concentrations in the jarosite composite. This confirms that due to high
plasticity soil / clay alone cannot be very good materials in making good
quality bricks.
The response contour plots for compressive strength, water absorption,
shrinkage, density and leaching concentration of lead and cadmium are shown
in Figure 12, 15, 18, 21, 24 and 27 respectively in the s/s sintered jarosite
waste-clay-PCCRs composite products. Whereas addition of clay increased the
compressive strength up to a certain level, with a slight decrease in
compressive strength at higher concentrations. Figures . 13, 16, 19, 22, 25, and
28 show the response 3 D graphs for compressive strength, water absorption,
shrinkage, density leaching of lead and cadmium respectively. The response
contour plots and 3D graph show the change in responses (compressive
strength, water absorption, shrinkage and density) with change in brick
constituents. It is to be noted here that the compressive strength is decreasing
with increasing water absorption, which is obvious in clay based products.
Since, PCCRs had already incinerated at very high temperature and hence
further sintering did not influence the properties. However, under solid-state
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