The salt attack of Fired Clay Bricks (FCBs) causes surface damage that is aesthetically displeasing and eventually leads to structural damage. Methods for determining the resistances of FCBs to salt weathering have mainly tried to simulate the process by using accelerating aging tests. Most research in this area has concentrated on the types of salt that can cause damage and the damage that occurs during accelerated aging tests. This approach has lead to the use of accelerated aging tests as standard methods for determining resistance. Recently, it has been acknowledged that are not the most reliable way to determine salt attack resistance for all FCBs in all environments. Few researchers have examined FCBs with the aim of determining which material and mechanical properties make a FCB resistant to salt attack. The aim of this study was to identify the properties that were significant to the resistance of FCBs to salt attack. In doing so, this study aids in the development of a better test method to assess the resistance of FCBs to salt attack. The current Australian Standard accelerated aging test was used to measure the resistance of eight FCBs to salt attack using sodium sulfate and sodium chloride. The results of these tests were compared to the water absorption properties and the total porosity of FCBs. An empirical relationship was developed between the twenty-four-hour water absorption value and the number of cycles to failure from sodium sulfate tests. The volume of sodium chloride solution was found to be proportional to the total porosity of FCBs in this study. A phenomenological discussion of results led to a new mechanism being presented to explain the derivation of stress during salt crystallisation of anhydrous and hydratable salts. The mechanical properties of FCBs were measured using compression tests. FCBs were analysed as cellular materials to find that the elastic modules of FCBs was equivalent for extruded FCBs that had been fired a similar temperatures and time. Two samples were found to have significantly different elastic moduli of the solid microstructure. One of these samples was a pressed brick that was stiffer due to the extra bond that is obtained during sintering a closely packed structure. The other sample was an extruded brick that had more firing temperature and time compared with the other samples in this study. A non-destructive method was used to measure the indentation hardness and indentation stress-strain properties of FCBs. The indentation hardness of FCBs was found to be proportional to the uniaxial compression strength. In addition, the indentation hardness had a better linear correlation to the total porosity of FCBs except for those samples that had different elastic moduli of the solid microstructure. Fractography of exfoliated particles during salt cycle tests and compression tests showed there was a similar pattern of fracture during each failure. The results indicate there were inherent properties of a FCB that determines the size and shape of fractured particles during salt attack. The microstructural variables that determined the fracture properties of FCBs were shown to be important variables to include in future models that attempt to estimate the resistance of FCBs to salt attack.

There are still research gaps regarding the effects of key parameters such as water-to-cementitious materials ratio (w/cm), type of binder and pore structure characteristics on the response of concrete to special forms of sulfate attack: physical salt attack (PSA) and thaumasite sulfate attack (TSA). Hence, this study aims at developing an innovative type of concrete: nano-modified fly ash concrete, incorporating various dosages of nano-silica (NS) or nano-alumina (NA) and fly ash, and explores its efficiency in resisting various forms of sulfate attack.

This thesis is unique in that it investigated two completely different forms of concrete deterioration: physical sulfate attack and the alkali-silica reaction (ASR). Research was undertaken to better understand physical sulfate attack in order to provide much needed guidance on how to prevent durable this form of deterioration. A testing regime was designed to evaluate and analyze different concrete mixtures with varying water to cementitious material ratios (w/cm), cement types (Type I and V), and use of supplementary cementing materials (SCMs) in accelerated laboratory exposure and outdoor exposure testing. The accelerated laboratory testing evaluated the performance of concrete cylinder segments fully submerged in 30% (by mass of solution) sodium sulfate solution exposed to a temperature and humidity cycle that would promote cycles of alternative conversion between anhydrous sodium sulfate (thenardite) and decahydrate sodium sulfate (mirabilite). In the outdoor exposure site, two different sized concrete cylinders per mixture proportion were partially submerged in 5% (33,000 ppm) sodium sulfate solution and exposed to alternative wetting and drying conditions, along with, temperature fluctuations that would promote conversion between thenardite (Na2SO4) and mirabilite (Na2SO4∙10H2O). With regard to ASR test methods, it has been shown with past research that it is not possible to evaluate “job mixtures” or determine alkali thresholds using ASTM C 1293 (Concrete Prism Test) with evaluating aggregates and concrete mixture proportions for the susceptibility of ASR when testing job mixtures. The most commonly cited issue with the concrete prism test is excessive leaching of alkalis during the course of the test, which may not be a major issue when using the standard, high-alkali concrete mixtures as per ASTM C 1293 but is clearly an issue when testing lower-alkali concrete mixtures. For low-alkali mixtures, alkali leaching can reduce the internal alkali content below the threshold that triggers expansion for a given aggregate. A comprehensive study was initiated that evaluated various modifications to ASTM C 1293, with the intention of developing a testing regime better suited to testing “job mixes” and/or low-alkali concrete mixtures. / text