International Association of Scientific Innovation and Research (IASIR) (An Association Unifying the Sciences, Engineering, and Applied Research) International Journal of Emerging Technologies in Computational and Applied Sciences (IJETCAS) www.iasir.net IJETCAS 13-612; © 2013, IJETCAS All Rights Reserved Page 346 ISSN (Print): 2279-0047 ISSN (Online): 2279-0055 A Comparative Experimental Study on the Hydraulic Conductivity of Treated and Untreated Open-Graded Base Courses Abdul A. Koroma 1 , Victor S. Kamara 2 1 Department of Civil and Environmental Engineering, Michigan Technological University, Michigan, 2 Department of Civil and Environmental Engineering, Namibia University of Science and Technology, Windhoek, Namibia Abstract: An experimental program was conducted to determine the coefficient of hydraulic conductivity of both treated and untreated open-graded base samples made from four different gradations, three aggregate types and two binder types. For the same gradation, dolomite samples have the highest K value, followed by natural gravel and recycled concrete aggregate respectively. Treated open-graded samples have K values in excess of an order of magnitude while the difference in K value between the asphalt-treated open-grade samples was less than an order magnitude Keywords: Base course, hydraulic, c conductivity, open-graded, aggregates I. Introduction The provision of adequate subsurface drainage in pavements in order to prevent or minimize moisture induced distresses is an important design consideration in pavement design. This is largely due to the pioneering work of Cedergren and others. Cedergren, through extensive research had shown that adequate subsurface drainage underneath pavements can drastically reduce the life cycle cost of pavements (Cedergren 1974). Premature failure of the pavement system due to a malfunction of the subsurface drainage feature can be costly, but if the permeability and stability of the drainable bases can be maintained, pavement design life and significant lower life cycle cost would be realized. In an effort to produce non-erodible and drainable base layer, many state highway agencies have moved from the traditional dense graded base course gradation specifications to more open graded base course specifications that allow for greater drainage in the pavement sub-layers. One major reason for this transition is due to the fact that dense gradations, even though they offer stiffer bases with good constructability have serious long term stability problems as a result of prolonged saturation of the pavement structural section leading to a reduction in 3 the stiffness as the pavement ages. As a result of this, open-gradation specifications like the 4G and 5G aggregate specifications used in Michigan have been developed in order to allow for greater permeability and lower field saturation levels in subsurface pavement layers (Mayrberger and Hodek 2007). There has been a marked increase in the use of open-graded base courses by many highway agencies in an effort to provide an effective and durable subsurface drainage system. This has led to many research opportunities in order to characterize the drainage characteristics of these free draining materials. The aggregate materials used for this purpose have different maximum size gradation, binder types and content, and as such are expected to have different hydraulic, mechanical and durability properties. The practical and economic combinations of these materials have resulted in different types of subsurface design options available to pavement designers. II. Experiment Programme The experimental program was designed to determine the coefficient of hydraulic conductivity of each aggregate type and how it varies within certain gradation limits and under varying environmental constraints Aggregate Base Materials Three aggregate base materials were investigated consisting of two natural aggregates and one recycled aggregate. The natural aggregates were Natural Gravel and Dolomite while the recycled material was Recycled Crushed Concrete. Figure1: Photo showing crushed surfaces of the three aggregate types Limestone Recycled Concrete