Time resolved analysis of water drainage in porous asphalt concrete using neutron radiography L.D. Poulikakos a,n , M. Sedighi Gilani b , D. Derome b , I. Jerjen c , P. Vontobel d a Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Road Engineering/Sealing Components. ¨ Uberlandstrasse 129, CH-8600 D¨ ubendorf, Switzerland b Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Building Physics, ¨ Uberlandstrasse 129, CH-8600 D¨ ubendorf, Switzerland c Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Electronics/Metrology/Reliability, ¨ Uberlandstrasse 129, CH-8600 D¨ ubendorf, Switzerland d Peter Vontobel, Department of Spallation Neutron Source (ASQ), Paul Scherrer Institute, CH-5232 Villigen, Switzerland HIGHLIGHTS c The water drainage process in porous asphalt was studied using neutron radiography. c Despite similar mix designs, different processes of water transport were established. c Water transport within porous asphalt showed filled dead end pores and water islands. article info Article history: Received 23 August 2012 Received in revised form 29 January 2013 Accepted 29 January 2013 Available online 18 February 2013 Keywords: Porous asphalt concrete Liquid drainage Pore distribution Neutron radiography X-ray tomography Spallation neutron source abstract Porous asphalt as a road surface layer controls aquaplaning as rain water can drain through its highly porous structure. The process of water drainage through this permeable layer is studied using neutron radiography. Time-resolved water configuration and distribution within the porous structure are reported. It is shown that radiography depicts the process of liquid water transport within the complex geometry of porous asphalt, capturing water films, filled dead end pores and water islands. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction In this paper, the process of water drainage in porous asphalt is studied using neutron radiography (NR). Asphalt concrete is a composite road material that consists of fine and coarse aggre- gates, a bituminous binder and air voids. Porous asphalt (PA) or open-graded asphalt concrete has a porosity of about 20%. The high proportion of coarse aggregates and lower sand content lead to the formation of a complex network of voids of different sizes, as shown at macro- and micro-scales in Fig. 1. In wet weather, the use of PA as the first pavement layer allows water to drain from the road surface, preventing aquaplaning and improving visibility. Fig. 2, taken at a Swiss motorway, demonstrates these advantages of PA in comparison to dense asphalt concrete on a rainy day. In addition, PA is an environmentally friendly road material due to its noise reduction properties. As the performance of porous asphalt is dependent not only on its mechanical loads, but also on its environmental loading, and as moisture is known to have a detrimental effect on mechanical properties of asphalt concrete and especially PA, exposure to moisture is of fundamental concern. Water residing in these mixtures may affect in the long term binder cohesion and adhesion between binder and aggregates, resulting in accelerated distress (Partl et al., 2008; Poulikakos and Partl, 2009). The ability of the material to dry after exposure to water affects its function- ality and durability. Furthermore, given the large surface area of PA due to the high void content that is exposed to water, a better knowledge of the wetting and drying processes at play in PA Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2013.01.040 n Corresponding author. Tel.: þ41 58 765 4479; fax: þ41 58 765 6244. E-mail addresses: lily.poulikakos@empa.ch (L.D. Poulikakos), marjan.gilani@empa.ch (M. Sedighi Gilani), dominique.derome@empa.ch (D. Derome), iwan.jerjen@empa.ch (I. Jerjen), Peter.Vontobel@psi.ch (P. Vontobel). Applied Radiation and Isotopes 77 (2013) 5–13