According to Caetano , adherence friction occurs after the breaking of the bonding adherence, that is, when the sliding of the bar begins to happen.
Concrete @ your Fingertips
This portion refers to the action of the frictional force between the steel and the concrete, which varies according to the surface coefficient bar. This factor can be harmed by the hot-dip galvanization, once the bar gets a zinc coating, making the rebar smoother. Regarding the influence of the friction adherence part of the ribbed bars, there is still some disagreement among authors, whether it influences or not.
According to Lutz and Gergely  and Cairins Du and Law  this part only exists in smooth bars, however for most of the latest research, the adherence provoked by friction also affects the ribbed bars. There is also the mechanical resistance, which in its turn is the most aggravating for a good adherence, being directly allied to the hardness of the material.
According to Fusco  and ACI , the rebars still suffer, in addition to these, three other efforts, which would be compressive and frictional forces on the ribs in addition to the friction on the body of the bar. These forces act in many ways, preventing the sliding of the bar. To simulate all these conditions and verify adherence between the concrete and steel without external protection and hot-dip galvanization, the method that most closely matches the real situation is the Beam Test proposed by Rilem .
In this experiment, the beam is subjected to bending with the contribution of other important factors on the steel-concrete adherence. Thus, the aim of this paper is to compare the adherence of steel bars of 8.
The test for adherence between steel and concrete is achieved through the Rilem  procedure that is the bending test on the concrete beams to identify adherence. Concrete mix was used for the beams, of mass to ensure the compressive strength of 25MPa, with a tolerance of 2. After the results, a statistical analysis to identify significant properties for this parameter was performed.
Materials and method. To scale the beams to be tested, it was followed the procedure of Rilem  according to the specifications of Table 2.
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This trait was set to achieve what was proposed by the Rilem  method, which provides the compressive strength of concrete at 28 days, at 25 MPa, with a tolerance of 2. For a better understanding of the growth curve of the concrete, the tests were performed in 7 and 28 days. The dosage method of the concrete was Ibracon Brazilian Institute of Concrete, . After defined the parameters of the beams and materials, three sets were molded for each studied diameter 8mm, Figure 2 illustrates one of the concretes and six molded sets.
After this, the sets were cured in a moist chamber for 28 days. The beams were instrumented at its ends, with digital dial indicators to measure the deformations of the bars that tend to slip during the test. Points 1 mm, 0. The principle used was the arithmetic mean of the results obtained at both ends, moments before the breaking of the beam. For the last reading 1mm it was considered the first load that reached this limit. The rate of the load application to the rods of 8.
After that, the beams were placed and subjected to the bending test being double supported and receiving the load application distributed on two points, as it can be seen in Figure 3. To analyze the test results of the beams, it was adopted the method of analysis of variance ANOVA , which seeks to verify the existence of significant differences, based on a statistical analysis between the obtained mean values.
In addition, the method checks whether the applied values influence the dependent variable. Results and considerations. The results of the 7 and 28 days of compressive strength of the concrete are shown in Table 3. It is observed that the concrete had compressive strength within the range recommended by Rilem , allowing the tests within the specified time. For each type of bar diameter 8mm, Figure 4 shows the load versus deflection curves for each diameter and provided with three measurements for each condition. It is noticeable that for beams with diameter of 8.
Galvanized Steel Reinforcement in Concrete
In beams with bars of For both bars, from 8mm to 12mm, the adherence between the concrete and steel was higher in beams with hot-dip galvanized reinforcements. The same performance was observed on the beams with 16mm bars, showing that for larger diameters, the adherence between the concrete and hot-dip galvanized steel was also higher. It is important to highlight that the parameters of the beams with 16mm bars is different from the earlier ones, according to the Rilem procedure Based on the collected data, it was calculated the values of adherence strength, expressed in Table 4.
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The results are shown in Table 5. If Fcal is higher than the tabulated value of F, the null hypothesis will be rejected. So that means there is significant difference between the group means and, consequently, the study variable influences the dependent variable.
Hot dip galvanised reinforcing steel for concrete structures - Specifier
In this way, it is noticeable that the kind of bar galvanized or not does not have a significant level, because P is greater than 0. Therefore, it is observed that the diameter of the bar influences the bond strength between the concrete and the steel, but whether the bar is hot-dip galvanized or not, it does not affect the final adherence to the results obtained in this paper.
Finally, Figure 5 shows the values of the arithmetic mean among the three results of bond strength for each type and diameter of the bar. Therefore, the zinc layer which protects the reinforcement against corrosion did not damage the adherence between the steel and the concrete, and there may even be a small gain in certain situations. After the experimental work, it is possible to conclude that:. Therefore, for these materials under these conditions, it is possible to specify the hot-dip galvanized steel without concerning for adherence strength between the concrete and the steel.
Essai per flexion 7-IID. Recommendation Provisoires. Paris, v. NBR , Rio de Janeiro, In fact, hot dip galvanized reinforcing was the corrosion protection chosen by the designers of the massive The Baha'i Temple at Qutub Minar near Delhi in the s, which has an anticipated design life of years. Hot Dip Galvanized coatings are extremely tough and damage resistant, making then an excellent alternative to epoxy coatings when the potential for damage to the epoxy is a concern or where extended UV exposure is unavoidable.
Because HDG is UV stable, it can to be stored outside and uncovered at the job site for extended periods of time with no damage. Also, reinforcing that has been Hot Dip Galvanized can be handled in the same manner as conventional A or A uncoated bar, with no need to employ special slings and pads. Hot Dip Galvanized reinforcing can also be installed at the jobsite in the same manner as 'black' bar, eliminating special placing sequences and worries about damage to already installed product.
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