- Engineered cementitious composite
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- Zijl, G. P. A. G. van
- Concrete Plant Precast Technology
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Engineered cementitious composite
Alternate Sources. Save to Library. Create Alert. Share This Paper. Figures and Tables from this paper. Figures and Tables. Citations Publications citing this paper. Anchorage mechanisms of novel geometrical hooked-end steel fibres Sadoon Abdallah , Mizi Fan. Three specimens from each type of concrete mix were tested in direct tensile tests.
For the cracked specimens, six specimens from SHCC and two from each mortar type were used. The manual load was applied by tightening the bolts at both ends of the specimens as shown in Figure 1 b. Note that, all the specimens were loaded without measuring the load up to a certain deformation level. Figure 1 c shows the uncracked specimens under corrosion test.
Few cracks were also observed away from the middle portion of the specimens. About 3. The investigation is limited only to the corrosion potential and depassivation breaking of the protective thin film made from different oxides on the steel surface of steel bar in both SHCC, M1 and M2. For measuring the corrosion potential from the specimens, one ERE20 reference electrode was placed inside each specimen mould next to the embedded steel before the casting of concrete see Figure 1 a. It was placed in a stainless steel case and with a membrane of cement mortar ensuring good affinity with the concrete.
The potential was collected automatically by connecting the electrode on the cathode side and the steel bar on anode side to the data logger. For the ER test, one beam same size as for corrosion specimen from each type of concrete was cast. ER values were calculated in the dry and wet states of the specimens using Equation 2.
Dry ER values were measured directly after collecting the specimens by drilling. ER was also measured at the wet state of the specimen to study the influence of moisture on the specimens. Five faces of the specimens were sealed tightly with rubber strips and glued with silicon so that no leakage occurs between the specimen surface and the rubber strip as shown in Figure 2 c. Mass loss of the specimens was determined from the scaled materials obtained at 7, 14, 28 and 42 freeze-thaw cycles.
Equation 3 was used to calculate the total amount of mass loss of the specimen. Different slump values were obtained for the different batches of mixes. However, the average slump flow was not varied significantly one from another. Table 3 shows that SHCC has the highest air content, and this can be attributed to the inclusion of fibres in the mix thereby creating more voids compared to the M1 and M2 specimens.
Besides, M1 has lower air content compared to M2. It should be noted that mortar mix M2 has almost 3 times the sand content of M1, hence higher air content. A significant increase in sand content has been acknowledged to increase the air content of concrete mix Portland Cement Association, The mechanical properties of the specimens show that M2 has the highest ultimate compressive f uc and tensile f ut strength than the two other mixes.
Therefore, for the same cement matrix, the presence of fibres leads to increased flexural and tensile strength compared with the matrix without fibres. The strain was also measured during the tensile test to confirm the strain hardening behaviour of SHCC. It was found that the SHCC used in this study has approximately 1. Note that, because of the brittle behaviour of M1 and M2, the strain capacities of these specimens could not be measured.
Note that the ultimate tensile strength and strain of SHCC depends on its mix design and optimum fibre content Boshoff, ; Li et al. Table 4 shows the crack properties of the different cracked and uncracked specimens tested. These cracks were measured at the loaded state of the specimens. The applied load and deformations are already described in Section 2.
Zijl, G. P. A. G. van
Nevertheless, the major focus is the relation of the corrosion of the embedded steel bar to the crack properties. The photo image showing the crack width is then analysed and measured by the software attached to the camera depending on the image resolution chosen. This response is understandably based on the lower strain value obtained in the tensile test of the SHCC specimen. Table 4 shows the number of cracks, the average crack width, the maximum crack width and the corrosion potential in the cracked SHCC, M1 and M2.
It is interesting to see that the smaller crack widths total and maximum in the SHCC specimens lead to lower corrosion potential and at higher crack widths, the potential response is higher. For M1 and M2, the trend is not quite clear. However, it is known that the position of the anode and cathode in the corroded steel bar is dependent on the movement of ions, which is related to the density of concrete Broomfield, Therefore, the electrochemical process in the different matrices or for different crack patterns may vary, and as a result, different corrosion potentials can be observed.
Figure 4 shows the corrosion potential reading found in the different cracked and uncracked SHCC, M1 and M2 at different periods. Cracked specimens show significantly higher potential values soon after the application of chloride. These potential values are more than the recommended values given by ASTM C for predicting the probability of steel corrosion in concrete. It should be noted that corrosion is an electrochemical process. As the chloride solution comes in contact with the steel bar, the potential value changes significantly even though no major corrosion activity has occurred in the steel bar.
Furthermore, the high potential value can also be attributed to the lack of sufficient oxygen at the steel surface in the concrete. In this regard, the matrix composition plays an important role since the denser the matrix, the lesser the availability of oxygen in the matrix. It can, therefore, be said that a high negative potential in concrete specimens with a denser microstructure due to the addition of a large amount of binder cement, FA, ground granulated blast-furnace slag exposed to aggressive media does not necessarily portend higher corrosion.
In this case, other corrosion measurement methods such as polarisation resistance technique, electrochemical impedance spectroscopy, and galvanostatic pulse technique may be more suitable than half-cell potential method. Currently, there is limited research result available which correlate crack properties with the corrosion of steel bars in SHCC. Except in M2, the depassivation period in the cracked specimens is not clear since significantly higher potential values were found just after the application of chloride solution.
However, the same M2 specimens show a lower corrosion potential value than the other two. The half-cell potential measurements provide a classification of the corrosion activity of the steel and indicate locations where the steel is potentially corroding.
Therefore, it can be said that the corrosion potential does not show the real corrosion status in the specimen. This method may be a good indication of depassivation of a steel bar in concrete since the higher potential value towards more negative value defines higher possibility of corrosion activities Broomfield, ; Elsener et al. The above result can be described in two ways: first, there is the possibility that the inclusion of fibre in the matrix might have increased the chances of corrosion. Second, the current corrosion potential technique may need to be calibrated for a different type of matrix such as SHCC, which is showing higher corrosion potential reading though no real corrosion activity appears on the surface Figure 5 a.
The average capillary water absorption coefficient w was calculated to be 4. Note that, the w values were obtained from Figure 6 by applying Equation 1. This indicates that, for this particular type of SHCC matrix, the permeability can be high and promotes faster water and chloride penetration.
SHCC and M1 contain a large amount of binder cement and FA , and there is a possibility that hydration may not occur in all the binder with the mixed water. Therefore, further hydration process may occur in the un-hydrated binder particles FA when specimens were in contact with water during CWA test. It should be noted that the curing process for this test was different from other tests. In this case, air dry curing method was followed as per DIN However, in all cases, the dry specimens show higher ER than their wet counterparts as expected.
Also, the dense microstructure of concrete has higher resistance against the current flow, and the dense microstructure is often related to the material composition, particles grading, compaction and curing. Therefore, the ER value can differ for concrete and mortar having different material composition. Concrete resistivity is also related to the presence of moisture in concrete. This is because the electrical current through the concrete is conducted by ions in the moisture Neville, Lower ER values were found in all types of specimens in the wet stage.
It may be explained by the presence of water in the pores of wet specimens, which allowed more current to pass through the specimens.
Concrete Plant Precast Technology
Due to the changes in the applied frequency from 0. Conversely, this change was not significant in M2 specimens. The lower electrolyte resistance may be the reason for corrosion stain seen in cracked M2 specimens in Figure 5 c. The addition of blast furnace slag and silica fume in addition to Portland cement in concrete has also been reported to have some influence on the ER; ER is increased when they are used in concrete over Portland cement only Neville, After 42 cycles of freeze-thaw attacks, less than 0.
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On the other hand, just after 7 cycles, significant mass losses were found in both M1 and M2 specimens, but the loss in M2 was very high compared to M1. After 7 cycles, the mass loss in M1 was not significant, whereas almost double mass loss was found in M2 specimens from 7 to 14 cycles. Therefore, the denser matrix and lower air content in M1 than M2 may have been responsible for the better performance in CDF.
Therefore, increased strength of traditional mortar as in sample M2 may not offer increased resistance against freeze-thaw attack. Conversely, SHCC with similar water absorption capacity to M1 is still more stable because fibres bridge the matrix and increase the tensile force. Therefore, the tensile force generated by freezing of de-icing salt in concrete pores is not sufficient to create any damage in the SHCC specimen.
This research has focused on some important parameters such as corrosion, capillary water absorption, electrical resistivity and freeze-thaw attack, which are the key parameters of a design service-life modelling for reinforced concrete structures. From the outcome of this research, it can be said that, depending on the importance of a structure, SHCC may be used as a partial or full replacement in traditional concrete or mortar application.
From this research work, the following conclusions can be made. Therefore, in reinforced concrete, crack properties such as the number of cracks, average crack width, maximum crack width and total crack width must be considered in the corrosion activities. At the initial stage of capillary water absorption test, significantly higher water absorption was found in SHCC and M1 than in M2. However, the reason for this behaviour is not quite clear since only limited number of specimens was used in this research, and more future research is recommended in this regard.
Nevertheless, it is assumed that a large amount of un-hydrated binder FA in the matrix of SHCC and M1 may contribute faster absorption of water than the matrix with a lower binder of M2. SHCC has significantly higher resistance against freeze-thaw attack than M1 and M2 used in this research.
The first author would like to express his sincere thanks to the staff of the laboratory and workshop of BAM lab. The financial assistance provided by the German-South African year of science SPIN project towards this work is hereby acknowledged. You are free to: Share — copy and redistribute the material in any medium or format. Adapt — remix, transform, and build upon the material for any purpose, even commercially.
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Cite this article as:. Article Figures and tables References. Abstract Abstract The performance of strain hardening cement-based composite SHCC under various exposure conditions such as chloride-induced accelerated corrosion, capillary water absorption CWA , electrical resistivity ER , and freezing-thawing CDF tests is reported. Subjects Engineering Education Materials Science Civil, Environmental and Geotechnical Engineering Keywords Keywords corrosion potential strain hardening cement-based composite electrical resistivity water absorption and freeze-thaw.
Public Interest Statement The durability of reinforced concrete RC structures is a critical issue in the sustainability of these structures. Table 1. Table 2. Results and discussion 3. Table 3.
Ultimate strength of SHCC and mortars a compressive and b flexural strength. Table 4. Corrosion potential in cracked and un-cracked SHCC and mortar specimens. Electrical resistivity of un-cracked SHCC and mortars specimens at different frequencies.