Publisher's Synopsis
In Indiana, the steelmaking industries and power plants generate large quantities of steel slag, blast furnace slag and fly ash every year. The excess of these underutilized industrial by-products are stockpiled and eventually landfilled at disposal sites. Use of steel slag, fly ash and blast furnace slag in road applications, such as in subgrade stabilization projects, can be a cost-effective alternative to lime stabilization in some cases. In addition, use of large quantities of these underutilized industrial by-products in these types of applications helps to reduce the need for new disposal sites and to conserve natural resources. The main objectives of this research were to evaluate the feasibility of using soil-steel slag-Class-C fly ash and soil-steel slag-blast furnace slag mixtures in subgrade applications and to implement the selected mixture as a subgrade material in a road construction project of INDOT. In order to achieve these goals, in situ clayey soils, collected from a prospective implementation site, were characterized through a series of laboratory tests which included specific gravity, grain size distribution, Atterberg limits, compaction and unconfined compressive strength. Two types of steel slag mixtures were evaluated for use in subgrade stabilization applications: i) steel slag-Class-C fly ash mixtures and ii) steel slag-blast furnace slag mixtures. The mechanical properties of soil-5% steel slag-5% Class-C fly ash, soil-7% steel slag-3% Class-C fly ash, soil-8% steel slag-2% Class-C fly ash, and soil-7% steel slag-3% blast furnace slag mixtures were determined through compaction and unconfined compression tests. CBR swelling tests were also performed to assess the swelling potential of the mixtures. The optimum moisture content and maximum dry unit weight of the in situ clayey soil samples were 13% and 18.56 kN/m3 (118.2 pcf), respectively. Based on the results of the long-term CBR swelling tests, the maximum swelling strain of the compacted soil samples was approximately 0.41 %. The average unconfined compressive strength of the in situ soil samples was 282.9 kPa (41 psi). Unconfined compressive strength tests performed on various mixtures at different times indicated the occurrence of stronger cementitious reactions in the soil-steel slag-Class-C fly ash mixtures than in the soil-steel slag-blast furnace slag mixtures. The two-day and seven-day unconfined compressive strength of the compacted soil-7% steel slag-3% Class-C fly ash mixture were 820 kPa (119 psi) and 886 kPa (128 psi), respectively. The maximum 1-D swelling strain of the soil-7% steel slag-3% Class-C fly ash mixture was 0.13 %. The soil-7% steel slag-3% Class-C fly ash mixture was selected as the most suitable and cost-effective subgrade material for the implementation project. The implementation project for the soil-steel slag-Class-C fly ash mixture was located at the intersection of 109th Avenue and I-65, near Crown Point, Indiana. The pre-mixed 7% steel slag-3% Class-C fly ash mixture was used to stabilize the in situ subgrade soils of some sections of the I-65 ramps located in the SW and NW quadrants of the intersection of 109th Avenue and I-65. Field compaction quality control was done by performing DCPTs and nuclear gauge tests. Cracks or signs of distress were not observed on the subgrade before base course and concrete placement. The soil-steel slag-Class-C fly ash stabilized subgrade performed satisfactorily.
