| Substandard fly ash and byproduct limestone screenings are both plentiful materials in Tennessee and the Southeast region. Utilization of these materials, therefore, may result in both economic and environmental benefits.;Tennessee Department of Transportation (TDOT) Specification 312 for Aggregate-Lime-Fly Ash Stabilized Base Course includes hydrated lime, fly ash, and TDOT Grading C limestone. This specification was used to determine if substandard fly ash and byproduct limestone screenings could be used effectively. Two different fly ashes were obtained: the control was Cumberland City Class F fly ash with an LOI of 1.6%, the variable was from a Tennessee Valley Authority (TVA) plant in Northern Alabama with an LOI of 8%. The aggregate was utilized in two parts: the first used a blend of No. 57 stone with limestone screenings to produce a TDOT Grading C limestone, the second used only limestone screenings.;The specification requires an average compressive strength of 950-psi for three specimens, with no individual compressive strength less than 800-psi, after 28 days of curing at 100° F. Twenty-four Standard Proctor specimens were made for each set of materials. The aggregate blend specimens yielded an average compressive strength and coefficient of variation of 1,263-psi and 5.8% for the control and 1,219-psi and 3.0% for the variable, respectively. The limestone screenings specimens yielded an average compressive strength and coefficient of variation of 1,416-psi and 4.9% for the control and 966-psi and 3.2% for the variable, respectively. Each individual specimen met the minimum required compressive strength; however, the average compressive strength for three specimens was not met with sets from the limestone screenings specimens. Sixteen modulus of elasticity specimens were also made for each set of materials. The aggregate blend specimens yielded an average static modulus of elasticity of 3,000-ksi and 2,294-ksi for the control and variable, respectively. The limestone screenings specimens yielded an average static modulus of elasticity of 2,650-ksi and 1,400-ksi for the control and variable, respectively.;Analysis of these results indicates that a high LOI fly ash can be useful as a stabilizing agent when used in combination with hydrated lime. These results also suggest that limestone screenings can be used effectively as a significant amount of the aggregate for an Aggregate-Lime-Fly Ash Stabilized Base Course, but not, necessarily, as full replacement of the aggregate. |
