Environmental Tests

According to the United States Environmental Protection Agency (EPA) regulations, a waste is considered hazardous if it exhibits one or more of the hazardous characteristics of ignitability, corrosivity, reactivity, and toxicity. In order to assess the environmental effects of using steel slag in geotechnical applications, environmental tests were performed to assess the leaching and corrosion potential of both BOF and EAF(L) slag samples.

4.7.1. Corrosivity Tests

Corrosivity is a characteristic of a material (or of an environment) that indicates the likelihood of corrosion of a metal in contact with it. Metal structures such as rebars present in concrete used in highway structures, steel pipes used in drainage systems of retaining walls, steel water pipes or steel strips in reinforced earth walls are all susceptible to corrosion when the surrounding material has a corrosive nature.

In order to evaluate the corrosive nature of steel slag samples, parameters that are indicators of the corrosion potential - electrical resistivity (R) and pH - were determined.

The corrosion potential of BOF and EAF(L) slag were determined by evaluating these parameters.

Electrical Resistivity

The electrical resistivity test (popularly known as the soil resistivity test) is a common method used by geotechnical engineers to evaluate soil corrosivity. Corrosion of a metal is affected by the variation in potential that exist at different points or areas on the surface of a metal. Similarly, the electric resistance between opposite faces of a unit cube of a material can be obtained by measuring the potential drop between metal electrodes placed in the material. The electrical resistivity test uses this principle.

As-compacted and soaked samples from all batches of BOF and EAF(L) slag were tested for electrical resistivity according to ASTM G57-95a. Resistivity measurements were made using a Nilsson Model 400, 4-pin soil resistance meter (manufactured by Nilsson Electrical Laboratory Inc.) in a soil box of 3.8 cm x 22 cm x 3.1 cm in size with 4 insulated electrodes.

Steel slag samples were prepared at their optimum moisture content and compacted in the soil box by moist tamping until a compacted dry unit weight corresponding to 95% relative compaction was achieved. Special care was taken to level the top surface of the steel slag in the box; any voids present in the sample were filled.

Figure 4.27 shows a photograph taken at the time of compaction of a BOF slag sample in the soil box for resistivity testing. Following sample preparation, two of the electrodes were connected to the two outer sides of the soil box, and the remaining two were connected to the box through the holes available along the longer sides of the soil box.

All of the inner and outer electrodes were connected to the resistivity meter as shown (see Figure 4.28), and the resistivity of the as-compacted sample measured by the resistance meter was recorded (in ohm-centimeters). Then, the as-compacted sample was soaked in water for about 4 hrs to ensure full saturation, and the electrical resistivity of the soaked sample was measured following the same procedure.

Figure 4.27 BOF slag sample preparation in the soil box for resistivity testing

Figure 4.28 Electrical resistivity tests performed on (a) as-compacted BOF slag, and (b) as-compacted EAF(L) slag

400 Nilsson Model Resistance Meter

Soil box

(a) (b)

pH

The main objective of the pH tests was to supplement the electrical resistivity measurements in evaluating the corrosivity of the steel slag samples. In accordance with ASTM G 51, pH tests were performed on the saturated specimens of both BOF and EAF (L) slag in the soil box. The pH probe, connected to an electronic pH meter (manufactured by Corning Instruments), was inserted into the sample to take the pH measurement (refer to Figure 4.29). The pH measurements together with the resistivity measurements were considered in evaluating the corrosion potential of steel slag samples.

Figure 4.29 pH measurement on a soaked BOF-slag

4.7.2. Leaching Tests

Steel slag is typically classified as a solid waste based on EPA regulations. However, the possibility of leaching of heavy metals (arsenic, barium, cadmium, chromium, lead, etc.) into the groundwater should be evaluated when steel slag is used as a geo-material.

Typically, the Extraction Procedure (EP) Toxicity Test and the Toxicity Characteristic Leaching Analysis (TCLP) are performed to determine the concentrations of the contaminants identified by the EPA in the steel slag leachates. The TCLP test consists of two major steps: extracting the contaminants using an acetic acid solution and

pH probe pH-meter

determining the concentration of these contaminants. The TCLP test simulates the worst case scenario for leaching of contaminants from a landfill in acidic conditions. Many industrial wastes are not disposed in acidic conditions. Therefore, in some cases neutral leachate tests, such as the EP Water Tests (Indiana Water Leach Test), can provide a more realistic assessment of the leaching potential of wastes in the environment.

Fresh EAF(L) and BOF slag samples were tested for their leaching potential by the Severn Trent Laboratories, Inc. located in Valparaiso, IN. Representative steel slag samples were supplied to this laboratory by the slag processor companies. TCLP analysis was performed with an Inductively Coupled Argon Plasma (ICAP) in accordance with the test methods outlined in EPA 6010 B and EPA 7470 which are used to determine heavy metal contaminants in leachates. The other contaminant concentrations were determined by neutral leachate tests. Based on the TCLP analysis, steel slag samples were classified according to the Indiana Administrative Code Restricted Waste Site Type Criteria (Indiana Administrative Code, 329 IAC 2-9-3).