Components of Asphalt Mixtures ...................................................................... 460 Asphalt Cement ...................................................................................... 460 Aggregate................................................................................................ 461 Proportioning of Mixture........................................................................ 462

Early Porous Asphalt Mixtures .......................................................................... 463 Development by the Franklin Institute, 1970-1972 .............................. 463 The Problem of Asphalt Drain-Down .................................................... 464 The University of Delaware Prototype, 1973 ........................................ 466

Contemporary Changes in Porous Asphalt Mixtures ........................................ 468 Construction of Porous Asphalt Pavement ........................................................ 471

Required Thickness ................................................................................ 473 Porous Asphalt Construction Cost...................................................................... 475

Cost without Stormwater Management .................................................. 475 Cost with Stormwater Management ...................................................... 476 Cost Tradeoffs in Practice ...................................................................... 477

Porous Asphalt Hydrology ................................................................................ 479 Decline of Infiltration Rate under Traffic Load .................................... 480 Decline of Infiltration Rate under Winter Sanding ................................ 481 Water-Quality Effects ............................................................................ 482

Porous Asphalt Maintenance and Rehabilitation .............................................. 483 Porous Asphalt Pavements in Practice .............................................................. 484

Quiet Waters Park, Annapolis, Maryland .............................................. 484 Siemens Office, Great Valley, Pennsylvania .......................................... 486 Walden Pond State Reservation, Concord, Massachusetts .................... 488 Morris Arboretum, Philadelphia, Pennsylvania...................................... 493 Residential Street, Luleå, Sweden.......................................................... 494 Rt. 87, Chandler, Arizona ...................................................................... 495

Porous Asphalt In Overlays ................................................................................ 496 The Development of Overlay Technology ............................................ 496 Effects of Porous Asphalt Overlays on Safety ...................................... 498 Effects of Porous Overlays on Noise .................................................... 499 Effects of Porous Overlays on Hydrology ............................................ 500 Cost of Porous Asphalt Overlays............................................................ 502

Recent Experience in Oregon ................................................................ 502 Recent Experience in Georgia ................................................................ 504

Acknowledgments .............................................................................................. 507 References .......................................................................................................... 507

“Asphalt” is an informal term for aggregate bound with asphalt cement, the technical term for which is asphalt concrete. This book follows the common informal convention of using the terms “asphalt” and “asphalt concrete” interchangeably. The aggregate can constitute 60 to 90 percent or more of the mixture’s volume; the asphalt cement is a semifluid binder between aggregate particles.