Residual tensile strength of dry and impregnated reinforcement fibres after exposure to alkaline environments

Fibrous materials have been extensively used in forms of Fibre Reinforced Polymers (FRP) as strengthening composites for civil construction. In the last years a new generation of inorganic-based fibrous strengthening systems are ongoing to be investigated all over the world, under the names of Fibre/Fabric Reinforced Cementitious Mortars/Matrix (FRCM) or Textile Reinforced Mortars (TRM), which indicate the same family of materials. In this new systems generally long dry fibres, in forms of soft nets are put in direct contact with a cementitious or lime-based matrix. In some other cases the reinforcement is represented by a pre-cured FRP grid, inserted within the inorganic plaster. The fibres that are used may vary from glass, basalt, aramid, carbon to steel. The presence of a matrix with high alkaline content may generate durability problems for the fibrous reinforcement, especially in those cases in which glass or basalt fibres are recommended and used. The experimental study presented herein reports and discusses the residual mechanical tensile properties of different dry and impregnated fibres, after exposure to four different ageing protocols in alkaline solutions. SEM microscopy images are also illustrated to show the damage at fibre level that was observed in the cases of vulnerable fibres. Important recommendation are provided for future research, also addressed to possible future design guidelines and acceptance criteria of new FRCM/TRM strengthening systems.