Cristiana Nunes
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4 records found
1
Towards a new salt crystallisation test
Comparison of salt contamination procedure
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. ...
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.
The RILEM TC ASC-271 is developing a new laboratory test to assess the durability of porous building materials to salt crystallisation. The test encompasses two phases: salt accumulation and damage propagation. This paper focuses on designing a procedure for the accumulation phase; this is considered successful when salts crystallise at the material's evaporative surface (common situation observed on site) without the occurrence of damage. Two procedures were developed and tested on two limestones with different porosity: (1) capillary absorption of a salt solution followed by drying, and (2) continuous capillary absorption. Sodium chloride or sodium sulphate solutions were used. Several methods for assessing the salt distribution were employed: ultrasonic pulse velocity, drilling/scratching resistance, hygroscopic moisture content, ion chromatography, scanning electron microscopy, and micro X-ray fluorescence. The results enabled the selection of the most effective protocol for the salt accumulation phase.
State of Conservation of Concrete Heritage Buildings
A European Screening
The durability of building materials with respect to salt crystallization is commonly determined by accelerated weathering tests, carried out in the laboratory. An effective laboratory weathering test should assess the durability and, in the case of conservation of historic buildings, the compatibility of repair materials with those existing. Besides, the test should provide reliable results within a reasonable period of time, accelerating the deterioration process without however altering its mechanism. Despite several national and international standards, recommendations and guidelines, a commonly accepted testing protocol does not yet exist. Researchers often develop and apply their own procedure, a fact that complicates comparison between different studies. The RILEM Technical Committee 271 ASC has been set up with the scope of developing improved test procedures for the assessment of the behaviour of materials under the influence of salt crystallization, which should overcome the limitations of existing standards and recommendations. This paper constitutes one of the first results of the work of the Technical Committee. It critically reviews the literature on salt crystallization tests, identifies advantages and limitations of the several test protocols and provides new ideas for the development of improved salt crystallization procedures.