There's something about HDR and concrete that rather appeals to me. I'm not sure if it's the increase in texture you seem to be able to achieve or if it's something else. This first shot, taken under a new overbridge, certainly has a much more gritty appearance after processing in Photomatix Pro. I suppose the clouds in the background give a more foreboding appearance also.
The second shot was taken landscape in an attempt to get more of the sweeping curve of the bridge into the shot. I was quite taken by the variation in height of the supports. Not sure which shot I prefer, but they both look better when enlarged so please click on the images to get a bigger view.