Hot-Mix Asphalt That Contains Nickel Slag Aggregate Laboratory Evaluation of Use in Highway Construction George Wang, Russell G. Thompson, and Yuhong Wang tions (Figure 1). This air cooling results in some fragmentation into sizes conveniently suitable for riprap, armor stone, and gabion stone use. The fragmented AC nickel slag can be crushed and screened for a variety of construction aggregate purposes, as engineered fill, granular base and subbase, and hot-mix asphalt (HMA) coarse and fine aggregate. The purpose of this laboratory evaluation program was to fully assess the suitability of the nickel slag for use in construction and provide quantified data to support further, potential use of AC nickel slag in highway construction.
Air-cooled (AC) nickel slag is evaluated for highway construction applications as an aggregate in hot-mix asphalt (HMA). The AC nickel slag is a liquid coproduct of nickel production that is solidified under ambient conditions. The laboratory evaluation program, which was carried out to determine the characteristics of the AC nickel slag, included physical and mechanical properties testing, petrographic examinations, and HMA mixture designs. Accelerated laboratory testing was completed on the mixtures by using an asphalt pavement analyzer to assess their performance characteristics. Additional testing included autoclave disruption tests for free lime and free magnesia, chemical and mineralogical analyses, polished stone value, and aggregate abrasion value. This study indicated that suitably processed nickel slag was environmentally, mineralogically, and physically stable. From the accelerated laboratory testing that was completed, it was concluded that the AC nickel slag was suitable for use as coarse and fine aggregates in HMA. The use of nickel slag in a highway construction is also presented.
LABORATORY EVALUATION PROGRAM Two nickel slags, which were based on different cooling processes [i.e., AC slag and emergency pit (EP) slag] were selected for this study. The laboratory work consisted of sample preparation, crushing, and blending of large, bulk samples of AC nickel slag. Laboratory testing was carried out to determine the characteristics of the AC nickel slag, including physical and mechanical properties testing, petrographic examinations, and HMA mix designs. Accelerated laboratory testing was completed on the Marshall and Superpave® HMA mixtures with the use of an asphalt pavement analyzer (APA) to further assess their performance characteristics. Additional testing included autoclave disruption tests for free lime and free magnesia, chemical and mineralogical analyses, and determination of the polished stone value (PSV) and aggregate abrasion value (AAV). Experience and studies had indicated that the subject AC nickel slag was chemically stable and therefore had no leachate parameters of potential environmental concern when used in construction applications. As such, this evaluation program focused on the physical properties and mineral composition, with no supplementary environmental testing conducted. Composite samples of AC slag and EP slag were obtained after they were crushed by using laboratory jaw crushers. The gradations of coarse and fine AC and EP slags after crushing are summarized in Table 1. The gradation analyses were carried out in accordance with the ASTM C136 test method for sieve analysis of fine and coarse aggregate.
Laboratory studies and increased use of ferrous and nonferrous slags in civil and highway construction have been conducted by researchers around the world (1–4). Quantification work in laboratory evaluation of a specific slag is critical to ensure its appropriate use in highway construction (5). There are substantial environmental and economic benefits from using nickel slag in road construction. Because nickel slag is a molten coproduct of ferronickel production, its use in highway construction reduces the need to use natural materials and results in less exploitation of natural aggregate deposits. Use of nickel slag also reduces the need for its disposal and lowers the cost of producing new aggregate materials. A laboratory evaluation of the use of air-cooled (AC) nickel slag was conducted on the basis of the nickel slag produced at the Falcondo facility in Bonao, Dominican Republic. Nickel slag is a coproduct of ferronickel production that is solidified under ambient atmospheric conditions. Laterite ore is open-pit mined and then processed through a preparation, reduction, and electric-furnace melting process. Molten slag is removed from one end of the furnace, and ferronickel is removed from the other end, for refining and shipment. The liquid nickel slag is transported by rail to a stockpile area, where it is discharged and allowed to cool and solidify under ambient condi-
TEST RESULTS
G. Wang and Y. Wang, East Carolina University, Greenville, NC 27858. R. G. Thompson, Institute of Transport Studies, Monash University, Clayton, Victoria 3800, Australia. Corresponding author: G. Wang,
[email protected].
Physical Properties
Transportation Research Record: Journal of the Transportation Research Board, No. 2208, Transportation Research Board of the National Academies, Washington, D.C., 2011, pp. 1–8. DOI: 10.3141/2208-01
The following physical properties tests were completed by using the composite samples of AC slag and EP slag: bulk relative density (BRD) and absorption testing of the coarse aggregate (retained 1
2
Transportation Research Record 2208
(a)
(b)
FIGURE 1 Ferronickel slag: (a) dumped, molten fragmented by thermal shock during ambient cooling in the slag storage area and (b) fragmented sized, crushed, and screened to a wide range of gradations for highway construction uses.
4.75 mm or No. 4 sieve) completed in accordance with the ASTM C127 test method, with the fine aggregate (passing 4.75 mm) tested by using the ASTM C128 method; flat or elongated particles coarse aggregate testing, carried out in accordance with the ASTM D4791 test method (for both 3:1 and 5:1 aspect ratios); microdeval abrasion testing in accordance with the Ministry of Transportation Ontario, Canada, (MTO) LS-618 and LS-619 test procedures for coarse and fine aggregate, respectively; Los Angeles abrasion tests completed in accordance with ASTM C131 (use of Grading B); and equivalent tests completed by following the ASTM D2419 and AASHTO T176 test methods. Uncompacted voids tests were carried out in accordance with the AASHTO T304 procedure. Plasticity index testing was performed in accordance with the ASTM D4318 test method. Organic impurities testing of the fine aggregate was carried out in accordance with the ASTM C40 method. Table 2 presents the physical properties of the coarse and fine AC nickel slag samples. It can be seen that the BRD of the slag is some-
what higher than that of natural aggregate. The BRD value itself, however, did not affect the final binder content.
Chemical Composition Analysis The chemical analysis results indicated that the chemical compositions of AC and EP slags were close. The subject cooling regimes had little influence on the chemical compositions of the two slags. The main chemical compositions of the slags were silicon dioxide (SiO2), iron oxide (FeO), and magnesium oxide (MgO) (Table 3). The main mineral components of the AC and EP slags were ferromagnesium silicate minerals, which had the following molecular composition: (Mg, Fe)2SiO4. It is the solid solution of forsterite (2MgO䡠SiO2) and fayalite (2FeO䡠SiO2). No uncombined MgO monomers were observed in the AC or EP slag samples.
Scanning of Electron Microscope Analysis TABLE 1
Gradations of Nickel Slag Aggregate
Sieve Size 11⁄2 in. (37.5 mm) 1 in. (25.0 mm) 3 ⁄4 in. (19 mm) 1 ⁄2 in. (12.5 mm) 3 ⁄8 in. (9.5 mm) 6.3 mm No. 4 (4.75 mm) No. 8 (2.36 mm) No. 16 (1.18 mm) No. 30 (600 μm) No. 50 (300 μm) No. 100 (150 μm) No. 200 (75 μm) a
Not required.
Passing, % (coarse)
Passing, % (fine)
AC Slag
EP Slag
AC Slag
EP Slag
100.0 97.8 90.1 66.2 43.9 25.8 19.3 10.3 6.3 4.1 2.8 1.9 1.3
100.0 98.0 83.3 52.9 37.1 24.3 19.6 11.8 7.7 5.2 3.4 2.1 1.1
— — 100 97.1 81.9
— — — — 100
a
a
37.0 18.4 10.6 6.9 4.7 3.2 2.3
98.7 71.4 50.6 38.3 29.3 21.7 14.6
A secondary imaging analysis method was used to observe FeO, SiO2, and MgO; back-reflection imaging was used to observe minerals that contained light metals, such as nickel, cobalt, and tungsten (Figure 2). The results of the scanning electron microscope analysis showed that the minerals were main block and long strip in shape.
Volumetric Expansion Testing Volumetric expansion testing, carried out in accordance with the ASTM D4792 test method, indicated that the vertical volume expansions were 0.73% and 0.43% at 7 days for AC and EP slags, respectively. At these expansion values, both the AC and EP slag were well within the 2% limit typically specified for use in HMA applications.
PSV and AAV PSV and AAV tests were carried out in accordance with the British Standards test method (BS 812) on samples of the AC and EP slags.
Wang, Thompson, and Wang
3
TABLE 2
Physical Properties of Nickel Slag Aggregate
Test BRD Absorption (%) Flat or elongated particles (%) 3:1 aspect ratio 4:1 aspect ratio 5:1 aspect ratio Unconfined freeze–thaw, % loss Crushed content, one face, % Microdeval abrasion, % loss Los Angeles abrasion, % loss Magnesium sulfate soundness, % loss Sand equivalent
Test Results (coarse)
Test Results (fine)
AC Slag
EP Slag
AC Slag
3.157 1.11
3.192 1.00
4.5 1.1 0.5 0.8 100 3.7 13.3 0.5
16.7 9.5 1.5 0.2 100 7.7 22.0 1.2 —
—
EP Slag
3.182 1.25
3.306 0.73
34.6 22.8 9.0 49.8 98.2 — Not plastic 1.5
31.8 19.8 6.1 48.3 89.0 — Not plastic 7.7
98
98
NOTE: — = not tested.
TABLE 3
Chemical Compositions of Slag Samples
Sample
FeO
Fe2O3
SiO2
MgO
CaO
Free CaO
AC slag EP slag
15.20 15.40
5.80 5.30
50.20 50.50
26.70 26.00
1.80 2.20
