Page 232 - Materials Chemistry, Second Edition

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Recycling of Municipal Solid Waste Rejects
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Abrasive wear is the natural consequence of the shearing of junctions
between surfaces caused by the introduction of abrasive particles from out-
side; by using soft plastics, the abrasive particles will sink below the surface
resulting in no further harm (Cordon, 1979). Thus, increasing the polymeric
content on behalf of the filler reduces abrasive wear and seizure can be com-
pletely avoided. Moreover, when there is a weak adhesive bond between the
filler and the polymeric matrix, fillers will increase the rate of wear of the
material due to the ease with which the filler gets separated from the matrix.
Hence, increasing the sand content will decrease the resistance to abrasion.
Regardless of the differences encountered in the average thickness loss
between the mixes, the highest value of 0.24 mm for mix 12 (60% sand, sieve
2, and temperature 240°C) was 70% lower than the Egyptian standard limit
for cement tiles, and 92% lower than the ASTM standard limit for solid con-
crete interlocking paving units. Hence, all mixes reveal an excellent abrasion
resistance.

Density and water absorption
The density of all the prepared mixes was determined using procedure A of the
ASTM standard test method D 792-91 (1998). The relative rate of absorption of
water for all mixes was evaluated by the 24 hour immersion procedure of the
ASTM standard test method D 570-95 (1998) for water absorption of plastics.
The average density and water absorption results of the different mixes
investigated are shown in Table 6.4. All mixes resulted in low densities
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ranging between 1.12 and 1.68 g/cm . The increase in the sand content is
due to the high density of sand as opposed to that of a polymeric material.
Table 6.5 lists the maximum water absorption percentages entitled by the
ASTM and the Egyptian standards for various types of bricks, tiles, and paving

TABLE 6.4
Average Densities and Water Absorption Results of Prepared Mixes
(Abou Khatwa et al., 2005)
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Mix no. Density (g/cm ) Water absorption (%)
Mix 1 1.12 1.6
Mix 2 1.27 0.71
Mix 3 1.63 1.51
Mix 4 1.13 0.7
Mix 5 1.29 0.94
Mix 6 1.59 1.1
Mix 7 1.12 1.04
Mix 8 1.39 0.64
Mix 9 1.59 1.29
Mix 10 1.16 0.98
Mix 11 1.41 0.83
Mix 12 1.68 0.85