United States Department of Transportation
i
Development of guidelines for proper selection of finer graded aggregate base for Georgia pavements - phase I.
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2014-09-01
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Abstract:In this study, the effects of No. 810 screening contents in GAB on pavement performance and GAB strength were investigated. One
Group I (013C) source and three Group II sources (028C, 048C, and 158C) were selected and specimens were prepared for Proctor Test,
CBR measurement, and morphological analysis. It showed that Proctor and CBR test results were influenced by morphological data and
particle size distribution. It was found that replacing 25% of GAB with No. 810 screening materials decreased the density and strength of
Group II assemblies while the opposite was true for Group I assemblies. Pavement performance with/without screening materials in GAB
was simulated using the MEPDG software based on the measured CBR. As a result, replacing GAB with 25% of screening materials
increased alligator cracking when Group II sources were used and decreased alligator cracking when Group I sources were used.
Nevertheless, most of the aggregate assemblies with 25% of screening materials didn’t meet the GDOT’s GAB gradation requirements.
Thus, further investigations including the permeability, plasticity index, resilient modulus, and life cycle cost analysis, may be needed
prior to the adoption of screening materials in GAB.
Additionally, a new methodology was developed to estimate the stress-strain relationship of unbound aggregate base using linear
viscoelastic theory. Aggregate specimens prepared from two different sources were subjected to CBR test and relaxation modulus test
thereafter. From the test data, the time-dependent stress due to a known strain rate was computed as a convolution integral of the strain.
The computed stress-strain relationship was compared with ones from the resilient modulus test. The results indicate that the stress-strain
relationships from the resilient modulus test and the convolution integral are quite comparable with nearly same slopes when horizontal
stress is assumed as approximately 45% of vertical stress. Given this agreement, the proposed methodology could be used to assist state
highway agencies to validate the resilient modulus test results for quality control and quality assurance of aggregate base materials for
pavement design and construction.
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