Measurement of Hydraulic Conductivity in Porous Mixes

In the past two decades, runoff-permeable porous pavement and porous friction courses of pavement systems have been implemented more frequently, first in Europe and subsequently in the United States. Consequently, research and case studies are increasing, with a commensurate increase in the knowledge base for these drainable pavement matrices and systems. The main distinguishing parameter of these porous matrices is the hydraulic conductivity (k), as compared with traditional impervious pavements. Equipment and standards for measuring k vary widely. This variability includes laboratory and field permeameters, constant-head and falling-head permeameters, and methods based on differing equipment and differing protocols. In many cases, such variability generates results that are either difficult to compare or not comparable. As a result, the value of k that is generated from different methods and different equipment is uncertain. The disparate methods and measurement of k as a parameter challenge the researcher and the practitioner. During the development and specifying phase, the researcher and the designer require a representative value of k to ensure proper predictive models and design. During and after construction, the engineer and the practitioner require k for quality control. This paper illustrates and summarizes the available methods for measuring the k of pavement porous mixes. Some case studies are examined to verify the differences between methods and equipment used for determination of k. The European Standard UNI EN 12697-19 is examined through an experimental study. Theoretical and practical results help explain the measurement of k for pavements as a primary parameter of porous runoff-permeable mixes.