© 2006 by Taylor & Francis Group, LLC

Blast Cleaning and Other Heavy Surface Pretreatments 71
4.2.3.1 Variations in Composition and Physical Properties
It should be noted that, because these abrasives are by-products of other industrial
processes, their chemical composition and physical properties can vary widely. As
a result, technical data reported can also vary widely for this class of abrasives. For
example, Bjorgum has reported that copper slag created more blasting debris than
nickel slag in trials done in conjunction with repainting of the Älvsborg bridge in
Gothenburg, Sweden [4]. This does not agree with the information reported by Keane
[1], which is shown in Table 4.1.
This contradiction in results almost certainly depends on differences in the
chemical composition, hardness, and particle size of different sources of the same
generic type of by-product abrasive.
Because of the very wide variations possible in chemical composition of these
slags, a cautionary note should perhaps be introduced when labeling these abrasives
as nontoxic. Depending on the source, the abrasive could contain small amounts of
toxic metals. Chemical analyses of copper slag and nickel slag used for the Älvsborg
bridge work have been reported by Bjorgum [4]. Eggen and Steinsmo have also
analyzed the composition of various blasting media [5]. The results of both studies
are compared in Table 4.2. Comparison of the lead levels in the nickel slags or of
the zinc levels in the copper slags clearly indicates that the amounts of an element
or compound can vary dramatically between batches and sources.
By-product abrasives are usually considered one-time abrasives, although there are
indications that at least some of them may be recyclable. In the repainting of the Älvsborg
bridge, Bjorgum found that, after one use, 80% of the particles were still larger than 250
µm; and concluded that the abrasive could be used between three and five times [4].
4.2.4 MANUFACTURED ABRASIVES
TABLE 4.1
Physical Data for By-Product Abrasives
Abrasive Degree of dusting Reuse
Boiler slag High Poor
Copper slag Low Good
Nickel slag High Poor
Modified from: Good Painting Practice, Vol. 1, J.D.
Keane, Ed.. Steel Structures Painting Council, Pittsburgh,
PA, 1982.
The iron and steel abrasives discussed in Section 4.2.1 are of course man-made. In
this section, however, we use the term “manufactured abrasives” to mean those
produced for specific physical properties, such as toughness, hardness, and shape.
The two abrasives discussed here are very heavy, extremely tough, and quite expensive.
Their physical properties allow them to cut very hard metals, such as titanium
© 2006 by Taylor & Francis Group, LLC