The degradation of reinforced concrete (spalling) requires repair work that is not merely cosmetic but restores the element's monolithic integrity and original load-bearing capacity, ensuring mechanical compatibility between old and new.
Standard EN 1504-3 classifies mortars by strength (from R1 to R4). For structural interventions (R3 and R4), it is essential that the mortar's elastic modulus be compatible with that of the existing concrete (typically 20-25 GPa): a mortar that is too rigid or too deformable produces lethal shear stresses at the interface under thermal variations and dynamic loads, causing clean detachment of the repair.
To rebuild edges or the underside of beams without formwork, these mortars are thixotropic: they behave like a fluid under the action of the trowel but freeze their shape instantly at rest. Furthermore, the inclusion of expansive agents counteracts hygrometric shrinkage during setting (compensated shrinkage), eliminating the risk of surface cracking.
Standards
European and international references applicable.
Physical properties
Usage environment
Mandatory substrate preparation: mechanical scarification or hydrodemolition to achieve at least 5 mm surface roughness, followed by water saturation (SSD condition) before application. Without this, even the best mortar will delaminate.