Environmental Engineering Reference
In-Depth Information
but varies with the applied stress. The test conditions are thus critical to ensure that
the results from different samples can be compared.
11.4.21
B IODEGRADABILITY
The biodegradability of a treated waste can be estimated from the total organic
content in the treated waste. It has been suggested that measurement of biodegrad-
ability is necessary only if the total organic content of the treated waste is over 10%,
and that ASTM G21-96 104 could be used for this purpose. 15
11.4.22
M ICROSTRUCTURAL E XAMINATION
Microstructural examination of S/S materials can be performed by several tech-
niques, as discussed in detail in Chapter 9. The most commonly used techniques
are scanning electron microscopy (SEM), usually with energy dispersive X-ray
analysis (EDX) or electron probe microanalysis (EPMA), and X-ray diffractometry
(XRD). These techniques allow better understanding of the mechanisms by which
contaminants are bound to the matrix and the effects of waste components on binder
hydration. However, S/S materials are heterogeneous at microscopic scale, so obtain-
ing representative samples is difficult. Thus, these techniques are more useful in
research, or for observing known features and comparing different samples, rather
than for general investigation.
11.5
PERFORMANCE CRITERIA
11.5.1
G ENERAL
Whereas it is possible to perform testing of S/S materials in order to obtain a
quantitative understanding of the material for evaluating technological options and
management scenarios, the results from testing are often compared to performance
criteria. Such performance criteria may be acceptance limits prescribed for a specific
management scenario, e.g., landfill disposal, or they may be derived from a site-
specific risk assessment. Conformity with performance criteria may be a regulatory
requirement, or simply a part of responsible practice by industry. Since environmen-
tal behavior of S/S materials is the subject of ongoing research, development of
performance criteria, and assessment of data in comparison with performance cri-
teria, are not usually a straightforward matter.
A recently established database incorporates 1506 literature references and prop-
erties of 7953 cement-based S/S materials containing impurities. 105 This database
represents a large proportion of information available in the literature and incorpo-
rates results of various physical and chemical tests, which have been measured for
various mix designs involving binders and wastes, tested over different time periods
and temperatures. The range of values for many of these properties has been com-
piled from the database and is given in Table 11.3. The figures show very wide
ranges of results, which emphasize the diverse nature of the materials tested and the
properties of the resulting S/S material, as well as differences among test methods.
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