Recommendations for the European prestandard for concrete repair

The paper analyses some of the proposals given in EN 1504, the European Prestandard for concrete repair with respect to specification of basic repair material properties. A total of ninety repair material characteristics are listed in the standard but this papers concentrates on the three properties considered important for efficient long term performance (elastic modulus, shrinkage and creep). Optimum limits for these properties are presented which will lead to satisfactory repair material performance upon compliance. The recommendations are based on findings from repairs to actual highway structures which were monitored over a long period of time. The results show that an efficient long term performance is assured when the elastic modulus of the repair material (Erm) is approximately 30% greater than that of the substrate concrete (Esub). Low shrinkage is desirable but higher shrinkage will not necessarily result in shrinkage cracking if the modular ratio, m (= Erm/Esub), is sufficiently high. Tensile creep helps reduce tension due to the restraint to shrinkage provided by the substrate concrete and steel reinforcement, especially in the early ages, when Erm is developing. The limits proposed for these properties are recommended for inclusion in the working version of the European Standard for concrete repair.