Design Mixes For Asphalt Using 1Inch And 1/2 Inch Steel Slag
Asphalt concrete can be produced and the pavement constructed readily in Oregon when crushed steel slag is used as a portion of the aggregate. If the unit cost of steel slag modified mixes is the same as conventional dense graded mixes, overall project costs may increase because of the decrease in coverage by the heavier steel slag mix. For the test section hot mix asphalt concrete (HMAC) constructed with 30% steel slag, the coverage was 15% less than a conventional “B” mix. Reported increased resistance to rutting and improved skid resistance was not measured during the five years the pavements have been monitored. The differences between the two sections may not be measurable because only 30% steel slag with dimension of 1-inch (25.4 mm) … 1/2-inch (12.7 mm) was used in the test mix and the slag was finer than the conventional ½ – ¼” (12.7 to 6.3 mm) material it replaced. To date, both the control and test sections are performing satisfactorily.
1.1 Background Of The Study
In September 1994, steel slag test and control sections were constructed in Oregon to evaluate the use of steel slag in hot mix asphalt concrete (HMAC). Steel slag, a by-product of the steel- making process, is readily available in the Portland Metropolitan area. If unused, the slag material could end up in landfills, costing Oregon taxpayers money as disposal facilities reach capacity and new landfills are required. One way to utilize the steel slag is to incorporate it into hot mix asphalt concrete (HMAC). This process has been used successfully in the midwest and eastern United States with reported improved pavement performance (Ramirez 1992). Prior to this study, Oregon had no experience in handling, testing, or constructing steel slag pavements.
1.2 Objectives Of The Project
The primary objective of this study is to evaluate the use of steel slag in hot mix asphalt concrete. All aspects of using this material in a pavement will be evaluated, including:
- Steel slag sampling methods and laboratory tests,
- Asphalt concrete mix design and testing,
- Constructability, and
- Performance characteristics.
Other objectives include determining appropriate revisions to mix design procedures for the addition of steel slag.
1.3 Scope And Significance Of Work
Steel slag has been used to construct pavements for nearly one hundred years. Since it was discovered that the residue from the manufacture of steel could be crushed and processed into a product that looked like crushed rock, other testing was performed to determine the usefulness of this “waste” product.
It was discovered that the highly angular, rough textured, vesicular, pitted surfaces provide the particle interlock, and if properly compacted, the high stability required for good serviceable pavements. The slag is usually added as part of the coarse aggregate fraction of the mixture at a percentage of 20% to 100%, depending on the application of the mixture.
Addition of steel slag may enhance the performance characteristics of the pavement. Since the slag is rough, the material improves the skid resistance of the pavement. Also, because of the high specific gravity and angular, interlocking features of the crushed steel slag, the resulting HMAC is more stable and resistant to rutting (Ramirez 1992, Noureldin and McDaniel 1990, Lemass 1992).
Currently there are two steel mills producing steel slag in Oregon, both in the Portland area: Cascade and Oregon Steel. Cascade currently produces about 60,000 to 70,000 tons/year (54,000 to 63,000 Mg/year) of steel slag. Oregon Steel produces about 100,000 tons/year (90,000 Mg), and currently has about 300,000 tons (270,000 Mg) on hand. This slag would normally be placed in a landfill if it was not crushed and used for construction material.
1.4 Benefits Of The Project
Steel slag may be an appropriate addition to asphalt concrete. The current specifications do not exclude the use of steel slag. The overall benefit of the research will be an understanding of the properties of steel slag hot mix asphalt concrete and the applicability to future projects.
Typical aggregate used for HMAC in the Portland area includes crushed gravel. Pavements with the crushed gravel are typically not as stable as mixes without gravel and are often susceptible to rutting. The addition of steel slag may provide a viable alternative to the crushed gravel, as it reportedly increases the stability of the mix materials, thus reducing the rutting potential.
If steel slag used as an aggregate is determined to be an appropriate addition with benefits to asphalt concrete, then additional HMAC pavements may be constructed with steel slag. The agency may also encourage the use of steel slag in some pavements by providing incentives.
Other benefits of using steel slag in asphalt concrete include the recycling of a waste product, thus reducing the volume of material placed in Oregon landfills.
1.5 Project Organisation
The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.
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