Brian W. Randolph

Analysis of Resilient Modulus of Dense- and Open-Graded Aggregates

The results of analyses of laboratory resilient modulus testing conducted on dense-graded and open-graded aggregates are presented. The testing program included three different aggregate materials (crushed limestone, natural stone, and slag), five different gradation specifications, and three different moisture conditions (dry, moist, and saturated). In addition to the five aggregate specifications, test specimens were prepared so that they would satisfy the lower, central, and upper bounds for the gradations. Resilient modulus tests were conducted as closely as possible according to Strategic Highway Research Program Protocol P-46 (AASHTO T 294-92 I). The test results were analyzed using log-linear regression analysis with two-parameter (bulk stress) and three-parameter (bulk stress and octahedral shear stress) expressions for resilient modulus. The results of the testing indicate that the resilient modulus of aggregates and regression constants vary significantly depending on the type of material and va...

LABORATORY STUDY OF HYDRAULIC CONDUCTIVITY FOR COARSE AGGREGATE BASES

Inadequate drainage of pavement structures has been identified as a primary cause of pavement distress. Hydraulic conductivity is the most important factor controlling drainage capability. Coarse grained materials have high values of hydraulic conductivity. ASTM and AASHTO standard test methods are limited for coarse materials used in pavement bases and subbases because of their high permeability and large particle sizes and the horizontal flow in the field conditions. A large scale horizontal permeameter and a testing procedure were developed and the range of hydraulic conductivities of six base and subbase specifications made up of three material types provided by the Ohio Department of Transportation were evaluated. A horizontal permeameter (305 X 305 X 457 mm) and a testing procedure were developed to reduce errors produced by sidewall leakage, partial saturation, measurement of small head differences, and interpretation of turbulent flow as laminar flow. Fifty-four samples were tested, including vari...

In Situ Test for Hydraulic Conductivity of Drainable Bases

The development and use of an in situ hydraulic conductivity test for drainable bases under existing pavements is presented. Six highway test sections were constructed by the Ohio Department of Transportation to test the drainage characteristics and durability of four unbound and two stabilized base materials. The in situ test was then used to determine the field hydraulic conductivity of the highway test section bases. This test uses an approach to Darcys law called the direct velocity technique. A standpipe is placed in a cored hole in the pavement to establish steady-state horizontal flow through the base toward the edge drains. Two probes along a radial flow line measure differential pressure and electrical resistance in the water. An electrolytic solution injected at the standpipe is used to determine the water velocity as the median resistance is noted at each probe. The in situ hydraulic conductivity is calculated by dividing the discharge velocity by the hydraulic gradient. The in situ test provided results that compare favorably with published values from carefully controlled laboratory tests. It proved to work well for high-hydraulic-conductivity drainable bases, and it has the potential to be a valuable tool for condition assessment of bases under existing pavements.