Paper by HAARDT KLEISER HILSDORF from ISCR 5th 1986 Aachen Germany
The surfaces of concrete carriageways are subject to continuous wear due to the action of traffic and also to that of frost and the application of de-icing salts. The deteriorative damage affecting the concrete can range from mere surface wear by abrasion to loosening oi the structure of the material at greater depths. An economical and reliable method of reconditioning surface-damaged concrete carriageways consists in the application of a cement-bound repair mortar which bonds durably to the undamaged old concrete eve~ ~hen such mortar is applied in thin layers. The requ~s~te material characteristics of the repair mortar, the choice of suitable bondins agents at the interface, and efficient working methods have been the subject of theoretical and experimental investigations. A layered composite system is obtained as a result of the firm bonding of the repair layer to the old concrete. However, because of the different material characteristics of the repair mortar and the old concrete, internally induced stresses (due to internal restraint) develop in the composite system. These stresses are due chiefly to differential shrinkage or to temperature gradients. Their magnitude in the contact zone and in the repair layer (the resurfacing) is substant ially determined by the material characteristics and the geometric relationships. The stresses occurring in the composite system were analysed in a parameter study with the aid of a closedform mathematical solution and finite-element analysis, taking account of non-linear material properties and the effect of creep. Various bonding agents were experimentally applied on a section of a Federal German motorway which was being resurfaced with a cement-bound repair laver. The bond strength achieved by this layer was determined at regular intervals of time. The first tests were performed directly after the motorway had been reopened to traffic, followed by further tests six months later, after the winter season.