1. Senior Lecturer, Division of Civil Engineering, Univ. of Dundee, Dundee DD1 4HN, U.K. (corresponding author).
2. Technical Director, Geolabs Limited, Bucknalls Lane, Garston, Watford WD25 9XX, U.K.; formerly Associate Director, Building Technology Group, Building Research Establishment, Garston, Watford WD25 9XX, U.K.