Concrete Construction Online is a really useful resource for concrete sculpture, mainly because of their large inventory of articles from back issues of Residential Concrete and Decorative Concrete magazines. The following link is for an article which gives a good overview of several artists' approaches to concrete sculpture. It was originally published in 2006 in Residential Concrete Magazine.

http://www.concreteconstructiononline.com/industry-news.asp?sectionID=715articleID=292505&artnum=1

Several other excellent articles about concrete sculpture are available as PDF downloads, by searching through the "news and articles" link on their menu bar using the word "sculpture." You'll find information about the artists as well as technical information such as mix design and process.