Abstract
The effects of simultaneous carbonation and chloride ion attack on mechanical characteristics and durability of concrete containing silica fume have been investigated through an accelerated test method. Specimens containing different amounts of silica fume were maintained in an apparatus in which carbon dioxide pressure and concentration and relative humidity were kept constant, and wetting and drying cycles in saline water were applied. Surface resistivity, sorptivity, CO2consumption, and carbonation and chloride ion ingress depths measurements were taken. Phase change due to carbonation and chloride ion attack was monitored by XRD analysis, and microstructures and interfacial transition zones were studied by implementing SEM as well as mercury intrusion porosimetry. It was expected to have a synergistic effect in the tidal zone where simultaneous carbonation and chloride ion attack happen. However, the observed reduced surface resistivity, compared to specimens maintained in CO2gas, could be due to the moisture that is available near the surface, hindering CO2from penetrating into the pores of the specimens. Moreover, the porosity analysis of the specimens showed that the sample containing silica fume cured in the tidal zone had 50.1% less total porosity than the plain cement paste cured in the same condition.
Highlights
Deterioration of exposed structures, especially the ones made with concrete, may occur due to freezing and thawing cycles, sulfate attack, carbonation, and chloride ion attack [1]
In the same way, carbonated specimens have a higher SR value; specimens maintained in the tidal zone did not have a high value of surface resistivity which could be due to the moisture available at the surface of specimens during the simulation of four tide cycles of six hours per day
Extensive experimentation was carried out to determine the effect of an accelerated test method of simultaneous carbonation and chloride ion attack on mechanical properties and the durability of concrete containing silica fume
Summary
Deterioration of exposed structures, especially the ones made with concrete, may occur due to freezing and thawing cycles, sulfate attack, carbonation, and chloride ion attack [1]. If Friedel’s salt gets carbonated, some chloride ions bound by it may dissolute into the pore solution, and an increase in chloride ions may lead to a higher chloride ion ingress rate. Such ions reach the reinforcement bars, and according to the following reaction, this causes corrosion: Fe2+ + 2Cl− → FeCl2. In order to evaluate the durability of silica fume concrete under simultaneous carbonation and chloride ion attack, measurements of water penetration, surface resistivity, sorptivity, CO2 consumption, carbonation, and chloride ion ingress depths were taken. TEM analysis, and CO2 consumption, as well as SEM analysis, were thoroughly discussed in the previous paper [22], this paper will mostly consider the durability aspects; for a comprehensive discussion of durability properties, some data from the previous paper has been used
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