Interactions between Wastes and Binders - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 163

7.2.5 E FFECTS OF W ASTES

The literature contains a large number and variety of case studies concerning S/S
treatment of a wide variety of industrial wastes. In fact, the MONOLITH database
of cement-based product properties 59 (available from http://www.civeng.ucl.ac.uk/
?ID=210) includes 3333 products containing real industrial wastes (as of March
2001). Aside from portland cement, which was the most common binder, and water,
these products contain 20 other binders or additives, and 230 different waste types.
The diversity of formulations makes it difficult to observe trends in the effects of
waste on cement, aside from the general fact that industrial wastes usually have a
deleterious effect on cement. However, refinement of this data set into data subsets
with common elements was attempted as part of a European project. 60 It was found
that the most common waste types were municipal solid waste incinerator (MSWI)
ash (European Waste Catalogue Codes 19 01 00, 19 01 01, and 19 01 03), plating
sludges (EWC Codes 11 01 03 and 19 02 01), and steel industry dusts (EWC Codes
10 02 03 and 10 09 04). Overall, there were 540 products from 74 references
composed of portland cement and these most common waste types. Elimination of
products with missing data resulted in 253 products from 18 references, which were
used to construct neural network models of UCS as a function of mix composition. 61
As expected, substantial decreases in UCS were caused by all wastes (Figure 7.1). 62
The effect was nonlinear to varying degrees, depending on the waste type, with the
greatest decrease caused initially by approximately 12% plating sludge, 40% foundry
dust, 58% other ash, and 72% MSWI fly ash by mass of dry product. It seems likely
that the maximum waste additions used in modelling are the practical limits of waste
addition to portland cement, i.e., 50% plating sludge or electric arc furnace dust,
64% foundry dust, 92% other ash, and 85% MSWI fly ash by mass of dry product.
As has been discussed in Chapter 4, blended cements may respond differently
to waste addition than portland cement. For instance, it has been shown that increas-
ing electric arc furnace dust concentrations retarded the setting of alkali-activated
slag cement more severely than the setting of portland cement. 63

7.3 CONTAMINANT IMMOBILIZATION

7.3.1 I NTRODUCTION

A cement-based S/S product provides a dense physical matrix of low permeability,
which constitutes a physical barrier to leaching. In addition, the matrix is composed
of highly alkaline crystalline and amorphous phases (Chapter 4) that maintain a high
pH in the pore solution (Chapter 10). Contaminants, particularly metals, may be
immobilized as precipitates under these alkaline conditions, or can also be taken up
into cement hydration products, or sorbed onto their surfaces, or onto admixtures
added for this purpose.
Thus, contaminant immobilization will be discussed in the following sections
under three headings: