ity control (3)(4)(5)(6)(7)(8)(9). Whether utilized to model hydrologic, hydraulic, or filtration phenomenon, k is of interest throughout the functional life of porous pavement and PFCs.To increase the permeability, porous asphalts with voids (porosity) up to 25% to 30% are produced (10). Higher porosities are commonly not recommended because of structural considerations. Other authors indicate that typically PFCs are designed with a porosity ranging from 18% to 22% (5).To measure k, both laboratory and field permeameters are available. In the laboratory, the measurements required for determination of k are performed on pavement cores or on samples prepared ex situ with a mix design either before or after construction. In the field, the measurements required for determination of k are performed directly on the in situ pavement. Although permeameters are generally classified as constant head or falling head, or as either laboratory or field tests, there is a wide spectrum of permeameters within these classifications (11,12). A major consideration for the choice of permeameter is the anisotropy of the porous matrix and the choice of a separate determination for vertical (k v ) and horizontal (k h ) hydraulic conductivity. These separate determinations are more readily facilitated with laboratory permeameters but not always possible with field permeameters that do not allow a separate measure of k v and k h (11,13).The variability of results for k can be attributable to many factors. For example, results for k can be attributable to the different ranges of the applied hydraulic heads (Δh) or the degree of saturation in a specimen (13-15). Compaction modalities of the mixes also are a challenging issue (4). Moreover, tests have demonstrated that the k of the same porous mix measured in the field and in the laboratory can yield different results (11,16). Field determinations of k are commonly based on falling-head permeameters. Falling-head permeameters have been preferred because such methods are more practical, simpler, and rapid. For laboratory determination of k, aside from selecting a permeameter method that is based on the range of k, the constant-head permeameters are preferred, given that constant-head permeameters allow better control of the flow (12, 15).Whether the determination of k is through constant-or falling-head permeameters or through laboratory or field methods, the goal is determination of k that is accurate and universal. This can be useful for quality control during and after construction and for modeling the flow for prediction and design purposes. Recently research efforts have produced several models of flow for designing porous pavement and PFC that will improve the safety of drivers and control of the hydrologic response, PM, and PM-based chemicals (3,6,(15)(16)(17)(18). Development of these models is based on an accurate determination of k.This study reviews and examines methods and protocols for determination of k whether in the field or laboratory. The role of an accurate determination o...
