Issue 23/24

Concrete bridges were built originally to have a cost-effective maintenance -free life of 120 years, but work in the UK and USA shows that substantial maintenance is required after 20 to 30 years. This paper presents the description and results of an acoustic emission (AE) monitoring exercise on concrete bridge beams in situ, as part of a larger project aimed to develop an Advice Note on the use of AE to evaluate the structural conditions of concrete bridges. The fieldwork focussed on the concrete beams on Boghall Bridge, which is located in the Scottish Borders, south of Carfraemill on the A697. The AE processing described in this paper includes location of the AE sources in terms of the recorded energy and a b-value analysis. From the results one is able to distinguish between the different structural behaviour of the beams – thus showing that the AE method is a promising way to evaluate the condition of an in-situ structure. Ing. S. Colombo Prof. M. C. Forde, PhD, FREng, CEng, FICE, FIEE Both University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JN, Scotland, UK Prof. I. G. Main, BSc, MSc, PhD School of GeoSciences, The University of Edinburgh, The King’s Buildings, Edinburgh Scotland Jack Halliday, CEng, MICE The Highways Agency, St. Christopher House, Southwark Street, London SE1 0TE, UK

A review of the background to the deletion of high-alumina cement (HAC) from structural codes in 1975 is followed by consideration of the present state of pre-1975 structures, including their strength and durability. The attempts at re-introducing HAC into structural codes are discussed, and an argument against such a change is presented. It is suggested that recent changes in Building Regulations have resulted in a satisfactory solution in that designers may use HAC but only when they have demonstrated at the outset of construction that changes in properties of the materials with time will not detract from the performance of the building. Adam Neville, CBE, DSc(Eng), FIStructE, FREng, FRSE A & M Neville Engineering, London