Date of Graduation

5-2019

Document Type

Thesis

Degree Name

Bachelor of Science in Civil Engineering

Degree Level

Undergraduate

Department

Civil Engineering

Advisor/Mentor

Braham, Andrew F.

Committee Member

Hall, Kevin D.

Second Committee Member

Murray, Cameron

Abstract

Despite its economic and environmental benefits, the widespread use of Cold In-Place Recycling (CIR) is currently inhibited, to some degree, by a lack of laboratory testing and evaluation, specifically in the areas of compactability and workability of the reclaimed mixture stabilized with asphalt emulsion. The purpose of this study was to explore the influence of admixtures in CIR using modified Superpave Gyratory Compactor (SGC) compaction metrics. The primary stabilization technique considered in this research was asphalt emulsion, an application in which asphalt binder is suspended in water, allowing it to be stored and applied at ambient temperature, rather than the traditional, energy inefficient hot mix asphalt binder. This study explored multiple component binder (MCB) systems, meaning asphalt emulsion as well as an admixture were used to bind CIR samples. A MCB approach allows strength, compactability, and workability characteristics to be balanced, rather than having an excess of one characteristic. The two admixtures considered in this research were Portland cement and Type C fly ash. Fly ash is a cementitious admixture with similar characteristics to Portland cement created as a byproduct in coal burning power plants. In addition to the influence of admixtures, two different asphalt emulsions were considered, one fabricated in an industry laboratory (proprietary) and one on a lab-scale mill at the University of Arkansas (commodity).

Compactability and workability are quantified by values such as workability energy index (CIR-WEI), compactability energy index (CIR-CEI), compaction densification index (CIR-CDI), and traffic densification index (CIR-TDI). CIR-WEI values indicate the energy required to compact a sample to 76% Gmm, or N76. CIR-WEI values are inversely related to the energy required to compact a sample.

Independent of the source of asphalt emulsion, proprietary or commodity, Portland cement and fly ash introduced characteristics consistent with those exhibited in concrete mixtures. It was noted samples containing Portland cement produced the lowest CIR-WEI values. Samples containing fly ash had marginally decreased CIR-WEI values. Samples that contained asphalt emulsion alone had the highest CIR-WEI values.

Further exploration is required, but based upon these preliminary results, the presence of SCM’s had no significant impact on workability and shear strength. Further exploration of the effects of admixtures, such as Portland cement and fly ash, on the compactability and workability of MCB CIR will contribute to the growing body of knowledge surrounding CIR.

Keywords

Cold In-place recycling; compactability; workability; emulsified asphalt; applied sciences; pavements

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