Investigation of unbound granular materials in flexible pavement

The factors that affect the engineering properties of unbound granular materials in flexible pavements include water content, material gradation, and dry density of the granular materials. Another important factor is stress condition, which is influenced by wheel load and base layer thickness, etc. Most state highway agencies have requirements or limitations on these influencing factors. Possible relaxation of some of the limitations may be desirable in terms of construction quality and cost and further study of the factors is warranted.; The objective of this research is to investigate the effect of GAB gradation and layer thickness on engineering properties and performance of unbound GAB materials. The influence of water content is also evaluated. In situ GAB stiffness was measured in full-scale laboratory pit tests (static plate tests and Soil Stiffness Gauge tests) and in field test sections (Falling Weight Deflectometer and Soil Stiffness Gauge tests). Resistance to permanent deformation was measured by full-scale cyclic plate load.; A linear program was developed to backcalculate the GAB modulus from static plate load test results. The GAB modulus inferred from plate load tests were compared with the SSG measured modulus. Permanent deformation resistance of the GAB materials was evaluated using laboratory cyclic plate load tests. In the field sections, FWD tests results were analyzed using EVERCALC programs. The backcalculated moduli were compared with field SSG measurements.; Test results and analysis indicate that the influence of water content on the performance of the GAB materials is pronounced. Cyclic plate load test results suggest that, for the GAB materials tested in this study, percent passing No. 4 sieve alone is not a determinable factor for material rutting resistance. An examination of gradation uniformity of the GAB materials shows that poorly-graded materials tend to have lower rutting resistance than well-graded materials. Static plate load test and soil stiffness gauge test results indicate that modified GAB materials have higher modulus values than unmodified materials. Generally, the changes in moduli of GAB materials are relatively insignificant in the range of base layer thickness of 6 in. and 12 in.