• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.3
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• pp.72-83
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• 2022

This paper studied the effect on the microstructure, electrical properties, and compressive strength of cement mortar containing carbon fiber (CF) and steel fiber (SF), which are conductive materials. The resistivity of conductive fiber-reinforced cement mortar (FRCM) was measured using the 4-probe method, and the compressive strength was measured based on the compression test. Their performance was compared and reviewed with plain mortar (PM). Furthermore, the surface shape and composition of the fracture surface of the conductive FRCM were analyzed using a scanning electron microscope (SEM) and an energy disperse X-ray spectrometer (EDS). The results showed that the resistivity gradually increased as the curing time increased in all specimens, whereas the resistivity decreased significantly as the fiber volume fraction increased. Adding steel fibers up to 1.25% did not affect the resistivity of cement mortar considerably. On the contrast, the resistivity of carbon fiber was somewhat decreased even at low contents (ie, 0.1 to 0.3%), and thereafter, it was significantly decreased. The percolation threshold of the conductive CFRCM containing CF used in this experiment was 0.4%, and it is judged to be the optimum carbon fiber dosage to maximize the conductive effect while maintaining the compressive strength performance as much as possible. For the surface shape and composition analysis of conductive FRCM, the fracture surface was observed through SEM-EDS. These results are considered to be very useful in establishing the microstructure mechanism of reinforcing fibers in cement mortars.

• Corrosion Science and Technology
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• v.8 no.2
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• pp.74-80
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• 2009

The high alkaline property in the concrete pore solution protects the embedded steel in concrete from corrosion due to aggressive ions attack. However, a continuous supply of those ions, in particular, chlorides altogether with a pH fall in electrochemical reaction on the steel surface eventually depassivate the steel to corrode. To mitigate chloride-induced corrosion in concrete structures, finely grained mineral admixtures, for example, pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS) and silica fume (SF) have been often advised to replace ordinary Portland cement (OPC) partially as binder. A consistent assessment of those partial replacements has been rarely performed with respect to the resistance of each binder to corrosion, although the studies for each binder were extensively looked into in a way of measuring the corrosion rate, influence of microstructure or chemistry of chlorides ions with cement hydrations. The paper studies the behavior of steel corrosion, chloride transport, pore structure and buffering capacity of those cementitious binders. The corrosion rate of steel in mortars of OPC, 30% PFA, 60% GGBS and 10% SF respectively, with chloride in cast ranging from 0.0 to 3.0% by weight of binder was measured at 7, 28 and 150 days to determine the chloride threshold level and the rate of corrosion propagation, using the anodic polarization technique. Mercury intrusion porosimetry was also applied to cement pastes of each binder at 7 and 28 days to ensure the development of pore structure. Finally, the release rate of bound chlorides (i.e. buffering capacity) was measured at 150 days. The chloride threshold level was determined assuming that the corrosion rate is beyond 1-2 mA/$m^3$ at corrosion and the order of the level was OPC > 10% SF > 60% GGBS > 30% PFA. Mercury intrusion porosimetry showed that 10% SF paste produced the most dense pore structure, followed by 60% GGBS, 30% PFA and OPC pastes, respectively. It was found that OPC itself is beneficial in resisting to corrosion initiation, but use of pozzolanic materials as binders shows more resistance to chloride transport into concrete, thus delay the onset of corrosion.