Towards a new salt crystallisation test: Comparison of salt contamination procedure

The RILEM TC 271-ASC is currently developing a new ageing test to assess the
resistance of porous building materials to salt crystallisation. The new test consists of two phases: salt accumulation and damage propagation. This paper focuses on the salt accumulation phase; this phase should promote salt crystallisation close to the evaporative surface of the substrates (common situation onsite) without leading to salt efflorescence or damage. Damage should take place in the propagation phase, which is not addressed in this paper. This work compares the effectiveness of three contamination procedures for salt accumulation: P1) salt contamination by capillary absorption of salt solution, followed by drying; P2) continuous capillary absorption of salt solution; P3) placement of salt crystals on the surface of the materials followed by the conditioning of the specimens at high relative humidity until complete dissolution of the salts. The results of P1 and P2 procedures presented in this paper are detailed in a separate publication, while this paper focuses on P3 procedure and compares the results. The effectiveness of each procedure has been evaluated by assessing the salt distribution in the specimen using ion chromatography and scanning electron microscopy. The results show that P3 is technically the least complicated to set up and does not entail the risk of development of salt efflorescence or damage. However, it can lead to salt migration within the specimens to a greater depth, hence future research is proposed to counteract this effect.