The Measurement of Hydraulic Conductivity in Porous Mixes

In the last two decades porous pavement and porous friction courses of pavement systems are implemented more frequently, first in Europe and for over the last decade in the United States. Research studies and case studies are also increasing as a consequence of this implementation 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 to traditional impervious pavements. There is a wide variability of equipment and standards that have developed for measuring k. This variability includes laboratory and field permeameters, constant and falling head permeameters, and methods that vary based on differing equipment and differing protocols. In many cases such variability generates results that are difficult to compare or simply not comparable. As a result there still is uncertainty as to the value of k that is generated from different methods and different equipment. This measurement of k as a parameter remains a challenge to the researcher and the practitioner. During the development and specifying phase the researcher and designer require k to ensure proper predictive models and design and during and after construction the practitioner requires k for quality control. The paper illustrates and summarizes the available methods for measuring the k of pavement porous mixes. Some case studies are examined in order to verify the differences between methods and equipment utilized for determination of k. From a European perspective, the European Standard UNI EN 12697-19 is examined through an experimental study. Theoretical and practical results are illustrated that help illuminate the measurement of k for pavements as a primary parameter of porous mixes