E-Publication DOI

Sodium chloride damage to porous building materials

Lubelli, Barbara Antonietta

Jahr: 2006

Datei zum Herunterladen: PDF (174 pages, 54,89 MB)

Beschreibung:
This thesis starts with a short introduction into the behaviour of salt-water systems and salt solution transport in porous materials. Then the mechanisms most often addressed as causes of the damage are critically discussed with respect to the decay due to sodium chloride (chapter 2). The literature review identifies the still unsolved questions, points out the limits of the most diffused theories and indicates the hypotheses that need to be further studied: it constitutes therefore the starting point of the research developed in this work. From the literature review, the necessity of verifying the theories in practice emerges. For this reason, an approach starting from the study of the salt decay in the field is adopted in this research.
The investigation of several case-studies (chapter 3) points out the parameters influencing the type and the severity of the decay due to NaCl and evaluates their relative importance. This leads to the identification of the factors of risk for the occurrence of the decay in different circumstances, and sets therefore the basis for a correct intervention. The relevance of the environmental conditions, and in particular of the RH changes, for the development of damage due to NaCl is demonstrated. A case study is presented in which the combined monitoring of the damage (quantified as debris falling from a wall) and of the environmental conditions (temperature and RH) allows explaining the damage process (chapter 4).
The results obtained from the in-situ investigation give indications on the parameters to be adopted in the laboratory crystallization test and on their realistic range of variation. Chapter 5 deals with the development of an accelerated crystallization test for sodium chloride. At first the effects of the environmental conditions (high temperature, low RH, air flow and cycles of temperature and RH) on the damage are investigated. The obtained results are then applied in the set up of an accelerated crystallization test. The new developed procedure is tested on three materials and its reliability and degree of acceleration are evaluated with respect to both existing weathering tests and practice situations.
In chapter 6 the damage mechanism due to NaCl crystallization is investigated. The effects of the presence of NaCl on the hygric and hydric behaviour and on the related dilation of a limecement mortar are studied in detail. The hypothesis that damage may develop from the differential dilation of salt contaminated and not contaminated areas of a material is considered. Systematic experiments are performed in order to definitively assert the relevance of this mechanism for the occurrence of the damage. The behaviour of specimens contaminated with different salts (NaCl, NaNO3, KCl and Na2 SO4) is investigated to define whether this phenomenon is restricted to NaCl or common to more salts. On the basis of the results of the dilation experiments and the outcomes of the ESEM observations on cross sections of the specimens, a new hypothesis on the damage mechanism is proposed.

Zitation:
Lubelli, Barbara Antonietta:
Sodium chloride damage to porous building materials. Technische Universität Delft 2006
doi:10.5165/hawk-hhg/173