Living with AAR: An Engineer’s Perspective

Director, Structural Studies & Design Ltd. Chiddingfold UK

^* Corresponding author: jonathan@ss-design.demon.co.uk

Abstract

In the 1980s some unexpected cases of AAR cracking developed in the UK. There was no guidance on its effects on structures. In Devon many bridges, a car park and the 400 bed Exeter hospital had severe cracking and it was growing. Innovations in testing and analysis on these structures and their concrete led to the development of the IStructE Guidance on Structural Effects of AAR. The severity of damage to the hospital led to its replacement. Other buildings and bridges throughout the UK have benefited from this engineering approach to their management. It has provided a basis for RILEM international guidance. Expansion to date can be determined from surface cracking or loss of stiffness of cores. Well detailed reinforcement, to contain expansion in 3-dimensions, retains strength. Cracking leading to failure can develop where there is no reinforcement aligned to contain it. Petrography can diagnose AAR, even when it is trivial, but cannot quantify its severity. Most structures can live safely with an AAR diagnosis, but the containment provided by the reinforcement must be checked and augmented if necessary. Controlling moisture can slow the reaction, but this is not possible below ground where the worst problems occur.