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Research on anti-chloride ion penetration property of crumb rubber concrete at different ambient temperatures
Construction and Building Materials 189 (2018) 42–53
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Research on anti-chloride ion penetration property of crumb rubber concrete at different ambient temperatures Han Zhu a, Jian Liang a,b, Jie Xu a,⇑, Mingxuan Bo a, Jianju Li c, Bing Tang c a
School of Civil Engineering/Key Laboratory of Coast Civil Structure Safety of China Ministry of Education, Tianjin University, Tianjin 300072, China Huaiwei Water Conservancy Science Research Institute, Anhui 230088, China c China Aviation Ninth Engineering Brigade, Sichuan 611430, China b
h i g h l i g h t s Crumb rubber concrete (CRC) has high resistance to chloride-ion erosion. High resistance when the temperature is lower than 20 °C. Concrete ductility factor of CRC is higher than that of ordinary concrete. CRC has a better energy-absorption property. CRC has a different durability with the test environment temperature.
a r t i c l e
i n f o
Article history: Received 11 March 2018 Received in revised form 22 August 2018 Accepted 28 August 2018
Keywords: Crumb rubber concrete Durability Resistance to chloride-ion penetration Corrosion of steel bar
a b s t r a c t The corrosion of steel bars in concrete is one of the most important factors that affect the durability of concrete structures, which can be caused by several factors, including marine environments, deicing salt environments, saline and alkaline land, and saline pollution in industrial environments. Research has shown that the addition of crumb rubber can increase the capillary saturation of concrete and reduce the corrosion degree of steel bars in concrete, and with the increase of crumb rubber content, the weight-loss rate of steel bars decreases. The effects of temperature on its resistance to chloride-ion erosion and the durability of crumb rubber concrete are analyzed based on concrete-accelerated corrosion tests by controlling the ambient temperature. The results showed that crumb rubber concrete has high resistance to chloride-ion erosion, especially when the temperature is lower than 20 °C. The concrete ductility factor of crumb rubber concrete with chloride-ion corrosion at different temperatures is generally higher than that of ordinary concrete, indicating that crumb rubber concrete has a better energyabsorption property. It is shown that the crumb rubber concrete has a different durability with the test environment temperature, and can provide a reference for the application of crumb rubber concrete in anti-chloride ion penetration. Ó 2018 Elsevier Ltd. All rights reserved.
1. Research background Different types of concrete have been widely used in construction and water conservancy projects because of their different strengths, shapes, and generally good performance. However, the corrosion of reinforced concrete owing to marine environments, ice salt environments, saline alkali land, and brine pollution in some industrial environments is the greatest threat to the durability of concrete structures. These kinds of widespread diseases can cause significant direct and indirect losses. Studies have shown ⇑ Corresponding author. E-mail address: [email protected] (J. Xu). https://doi.org/10.1016/j.conbuildmat.2018.08.193 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
that the corrosion rate of reinforced concrete is affected by the saturation of fine holes in the concrete. The addition of rubber aggregate can improve the saturation of fine holes in the concrete and reduce the degree of corrosion of the steel in concrete; further, with an increase of the rubber content, there is an increased reduction of the weight-loss rate of the steel bar [1]. The capillary saturation of concrete is influenced by temperature, and the test results of the test often vary in test environments at different temperatures. The corrosion rate of steel bars in the actual project varies with the temperature. Feng and Xing [2] investigated the Seaport Wharf used over different years in North China. Investigations have shown that concrete structures in the superstructures of the northern seaport are damaged owing to the different degrees of
H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
corrosion of the reinforcement, but the corrosion of the superstructure of the North China harbor wharf is less than that in Southeastern China. It is necessary to understand whether the degree of corrosion is related to the temperature distribution. As shown in Figs. 1 and 2, the sea temperature is different in different seasons, so it is necessary to study the resistance of concrete to chloride ions under different ambient temperatures. Zaccardi et al. [3] researched the corrosion of reinforced concrete that was exposed to the seaside environment for 60 months. Hu et al. [4] researched the combined effect of chloride ion and carbonation using the open-circuit potential method of reinforced concrete at 25 °C, 35 °C, and 45 °C. Chen et al. [5] researched the influence of temperatures of 5–60 °C on the passivation behavior of steel bars using scanning-electron microscopy (SEM) observations and electrochemical measurements. Xu et al. [6] studied the effect of temperature on the release of bound chlorides. Shao et al. [7] simulated the influence of exposure temperature on chloride diffusion into reinforced concrete pipe piles that are exposed to the atmosphere using salt spray test. Nguyen and Amiri [8] studied the distribution of chlorine ions in concrete in dry and wet cycles. Medeiros et al. [9] studied the effect of chloride ions on the life of reinforced concrete structures in a global warming environment. Yang et al. [10] studied the effect of temperature on the diffusion properties of chloride ions in concrete. Xu et al. [11] studied the effect of temperature on the resistance to the chloride-ion erosion of marine concrete and the prediction of life. Liu et al. [12] studied the chloride permeability of concrete in environments with different temperatures in brine. Han [13] studied the effect of thermal fatigue on the strength and permeability of high-performance concrete. This study is based on the work of these predecessors, and was conducted to study the corrosion resistance of crumb rubber concrete at different temperatures. There have been many studies by researchers to improve the strength of concrete. With an increased strength, defects of the
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corresponding concrete brittleness become increasingly prominent. In the past few decades, scholars have begun to use rubber particles as building materials in the field of concrete because it not only improves many of the defects present in concrete materials, such as large self-weight and brittleness, but also expands the application field of waste rubber, and rationally carries out the recycling of resources. Concrete mixed with waste rubber particles is made of concrete as the base material, mixed with rubber powder or crumb rubber made of composite materials. Rubber, which is a kind of super-elastic material, can improve the internal structure of concrete through physical action without changing the chemical properties of each component in concrete. The elastic modulus of rubber is almost negligible compared with that of concrete. In this case, the rubber particles can be considered as elastic pores when the rubber particles replace some of the aggregate, and are evenly distributed into the concrete. Elastic pores can be considered as a constraint, and can prevent the production and development of internal microcracks in the concrete, and become the deformation center to absorb strain energy. Many scholars have studied the physical and mechanical properties of crumb rubber concrete, and found that rubber particles can clearly improve the crack resistance and ductility of concrete. At the same time, the crumb rubber concrete will not experience. In addition, rubber particles play an active role in improving concrete frost resistance and resisting chloride-ion migration. Pelisser et al. [14] studies showed that the density of crumb rubber concrete is 13% lower than that of ordinary concrete. Yilmaz et al. [15] studies showed that the flexural strength of the concrete increased by 20% after adding the rubber with the form of fiber, after the addition, the bending strength shows a downward trend, and the ordinary concrete presents brittle fracture, and the rubber concrete is ductile fracture. Kang et al. [16] reported that the concrete specimens containing rubber particles will produce obvious plastic deformation during the bending process, and will not produce plastic fractures when subjected to
Fig. 1. Annual average temperature distribution of the ocean in January.
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Fig. 2. Annual average temperature distribution of the ocean in July.
a maximum load, but undergo ductile failure after large plastic deformation. Thomas et al. [17] reported that the carbonization depth of the concrete mixed with rubber is smaller than that of ordinary concrete. Raghavan et al. [18] added 0.6% mass of rubber to the concrete. The results showed that the mass loss of the rubber concrete in the freeze–thaw test is the smallest. Oikonomou et al. [19] studied that the chloride permeability decreases with an increase in the amount of rubber. Gupta et al. [20] showed that the chloride concentration in all mixture ratios of rubber concrete was very low, indicating that the rubber aggregate concrete has a good chloride-ion permeability. Thomas et al. [17] reported that the chloride-ion penetration of concrete mixed with 10% of rubber was smaller than that of ordinary concrete. Thomas and Gupta [21] pointed out that the disposal of waste tire rubber has become a major environmental problem worldwide, and raw materials used in crumb rubber concrete mainly come from solid waste such as waste tires, etc. This is a very effective way of managing waste tires and protecting the increasingly tense land and rubber resources. At the same time, it has advantages in terms of cost because of the low cost of rubber aggregate. Therefore, the development of crumb rubber concrete has high economic and social benefits. However, in recent years, China’s annual production capacity of concrete is about 1.3 billion m3. With the expected further increase of China’s investment in infrastructure construction, it is foreseeable that the cement concrete production will be very large in future. If such a large amount of concrete is subjected to durability damage, the consequences will be severe. Therefore, it is necessary to find new solutions from the material science perspective. Crumb rubber concrete has attracted extensive attention and applications because of its outstanding performance in terms of its durability [22–24]. Therefore, the analysis and research into the durability and mechanism of crumb rubber concrete are important to solving the durability
problems, and ensuring the quality of engineering [25–28]. Hence, this current paper focuses on this perspective, and the concrete ductility factor of crumb rubber concrete with chloride-ion corrosion at different temperatures was investigated. 2. Experimental program 2.1. Material properties This research is a continuation of our previous study. The goal of the previous experiment was mainly to study the effect of the rubber content and water cement ratio on the corrosion of steel bars [29]. In this research, our attention is focused on the effect of the same mixture ratio at different temperatures. Details of the mixture ratio for the crumb rubber concrete and the ordinary concrete are listed in Table 1. Based on this mixed proportion, 12 specimens for crumb rubber concrete and 12 specimens for ordinary concrete with a size 100 mm 100 mm 515 mm [30] were simultaneously fabricated, and were cured in a standard curing room (temperature is 20 ± 3 °C and relative humidity is above 90%) for the 28 days. For each kind of concrete, four different test conditions (normal, 0 °C, 20 °C, and 45 °C) were considered, and there are three specimens for each condition. The crumb rubber was 40 mesh rubber powder, and the ingredients of the crumb rubber are listed in Table 2. 2.2. Test setup 2.2.1. Corrosion test The key to the design of the corrosion test is to form a corrosion current loop. At the same time, it is necessary to ensure the presence of oxygen, water, and chloride ions around the steel bar,
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53 Table 1 Design of mix proportion (kg/m3).
Crumb rubber concrete Ordinary concrete
P.O.42.5 cement
Sand
Coarse aggregate
Fine aggregate
Water
Rubber
Admixture
385 325
644 644
753 753
611 611
187 127
110 0
6 6
Table 2 Chemical ingredients of crumb rubber (mass fraction)/%. Rubber hydrocarbon
Carbon black
Acetone extract
Isoprene
Water
Ash content
Fiber content
Metal content
Others
45.2
25.8
14.2
12.1
0.8
0.9
0.5
0.08
0.42
which is the prerequisite for corrosion. Almusallam [31] studied the effect of the degree of corrosion of the steel bar on its mechanical properties by electric corrosion method. Lee and Cho [32] quantitatively studied the relationship between the degree of corrosion of steel bars and the mechanical properties of steel bars using the electric corrosion method. Zhang et al. [33] used the electrochemical method to study the corrosion of steel bars in a reinforced concrete plate, and then studied the static tensile and fatigue behavior of corroded steel bars. Wu and Yuan [34] studied the influence of two accelerated corrosion methods on the mechanical properties of corroded steel bars by performing the tensile test of corroded reinforced bar of reinforced concrete members subjected to corrosion by a simulated artificial climate environment and a constant current-accelerated corrosion. Based on the experience of a previous study on the accelerated corrosion of reinforced concrete, the accelerated test devices were designed as shown in Figs. 3 and 4. The device in Fig. 3 is used to control the temperature rise of the test solution, and the one in Fig. 4 is a cooling device for controlling the test solution. The temperature-control box is equipped with a temperature meter, which controls the accelerated corrosion environment temperature through the temperature control box, and to enable the analysis of the resistance to chloride-ion erosion. When
the corrosion environment temperature is lower than the ambient temperature, the heating pipe is used to heat the water temperature, as shown in Fig. 3. The temperature controller in the temperature control box is used to set the temperature. The temperature sensor is placed in the water tank to make the water temperature reach the set ambient temperature, whose accuracy is ±1 °C. Considering that water evaporates fast when the temperature is high, the water-replenishing device is designed to keep the water level constant. When the corrosion environment temperature is higher than the ambient temperature, the freezer is used to cool the water, as shown in Fig. 4. The temperature controller is used in the temperature-control box to set the temperature in order to make the water temperature reach the set ambient temperature. The power supply of the freezer is led by the temperaturecontrol box, where a temperature sensor is arranged, whose accuracy is ±1 °C. As the water is easy to freeze in a freezer less than 0 °C, a specific proportion of alcohol is added to water to reduce the freezing point of the solution. During the test, the water salinity is measured by a salinity meter. If the measured salinity is lower than the set salinity, the salt is added according to the salinity calculation value to keep the experimental environment constant. During the test period, the atmospheric temperature ranged from 5 °C to 14 °C. When corrosion ambient temperature
Fig. 3. Schematic diagram of high-temperature accelerated corrosion test device.
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Fig. 4. Schematic diagram of low-temperature accelerated corrosion test device.
is 20 °C and 45 °C, the heating-temperature accelerated corrosion test device control in Fig. 3 is used; when the corrosion ambient temperature is 0 °C, the low-temperature accelerated corrosion test device control in Fig. 4 is used. The voltage output range of the steady voltage and steady current power supply used in the test is 0–30 V, the maximum output current is 5 A, and the temperature-control box can vary the temperature from 0 to 100 °C. During the test, half of the beam specimen was submerged in the 3.5% NaCl solution, and it was equipped with two 10-mm diameter steel bars in the part above water. As the anode, the steel was connected with the positive pole of the power supply. The cathode was a stainless rope arranged at the lower part of the specimen. In series resistance in the loop, the measured resistance is 10.8 X, and is used to measure the current in the loop. After the specimen was cured for 28 days, the corrosion is accelerated and the corrosion period will be 10 days. The corrosion temperature was controlled at 0 °C, 20 °C, and 45 °C, respectively. As shown in Fig. 5, accelerated corrosion was performed on two sets (3 2) simultaneously. Each steel bar is connected to one resistance and then connected in parallel. The voltage of the test is 12 V and remains constant. The current of the steel bar varies with the resistance of the closed circuit. The voltage at the two ends of the series resistance is measured every 6 h, and the current magnitude of the reinforcing bar in the beam is calculated. According to Faraday’s law, the corrosion of the reinforcement depends on the amount of electricity that passes through the steel bar, and then the corrosion of each test beam is estimated. The electric flux that is applied to the steel bar is measured, and the potential reflecting the corrosion degree of rebar. Then, the salinity of the environmental solution in the process is controlled in order to observe the cracks of the concrete caused by the corrosion of the steel rein-
Fig. 5. Corrosion test setup.
forced bar and the size of the cracks is measured at the end of the test. The different parameters of crumb rubber concrete and ordinary concrete are compared to take the result as the standard of the permeability performance of crumb rubber concrete and ordinary concrete. 2.2.2. Four-point bending test On this basis of the corrosion test, the four-point bending test of the reinforced concrete beam was carried out, and the stress–strain curve of the reinforced concrete beam, the mid-span deflection of the beam, and the final fracture crack were measured to determine the mechanical properties of the corroded steel bar of the crumb rubber concrete and ordinary concrete. As shown in Fig. 6, the test was carried out on a WE-30 universal testing machine with a maximum load of 100 kN. The loading speed was set at 0.3 cm/s, and
H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
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Fig. 6. Four-point bending test device (unit: mm).
the data were collected every 1 kN. A micrometer was used to measure the mid-span deflection of the beam. 3. Test results and discussion 3.1. Accelerated corrosion test results After the corrosion, crumb rubber concrete and ordinary concrete specimens at different temperatures are shown in Figs. 7 and 8, respectively. It can be seen that the surface rust of the two kinds of concrete increases markedly with the increase of temperature, indicating that the temperature significantly influences the corrosion of the reinforced bar in the concrete. The reason is mainly owing to the increase of the saturation of the fine holes in the concrete as the temperature rises, and it also makes the current through the concrete increase. 3.1.1. Potential change The current and potential changes for two kinds of concrete with time at different temperatures are shown in Figs. 9–11. The potential change at three temperatures for two kinds of concrete is shown in Figs. 12 and 13, and the trend of the average potential and current in the last 24 h of accelerated corrosion is shown in Fig. 14. The figure shows that the potential change of crumb rubber concrete and ordinary concrete decreases with an
Fig. 8. Corrosion of ordinary concrete beams under: (a) normal condition; (b) 0 °C; (c) 20 °C; and (d) 45 °C.
Fig. 9. Diagram of concrete potential and current at 0 °C.
Fig. 7. Corrosion of crumb rubber concrete beams under: (a) normal condition; (b) 0 °C; (c) 20 °C; and (d) 45 °C.
increase of temperature. The lower the temperature, the more obvious is the performance of crumb rubber concrete antichloride ion erosion. The corrosion rate of steel is mainly influenced by the concentration of chloride ions in the concrete hole solution. The higher
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Fig. 10. Diagram of concrete potential and current at 20 °C. Fig. 13. Potential change diagram of ordinary concrete.
Fig. 11. Diagram of concrete potential and current at 45 °C. Fig. 14. Average value for last 24 h of accelerated corrosion.
reduces the extraction effect of the fine hole to the liquid phase, and then the saturation of the fine hole of the concrete is reduced. In this condition, the content of the chloride ion in the fine hole is reduced, and the degree of corrosion of the steel bar is inevitably reduced. The results show that the current density of the steel rises gradually as the temperature varies, and in the middle-temperature environment, it is basically constant with ordinary concrete. This shows that the crumb rubber concrete is still conductive with the pore solution, and the rubber aggregate itself is not involved in chloride ion in mixed concrete during the process of electro migration.
Fig. 12. Potential change diagram of crumb rubber concrete.
the ambient temperature of concrete accelerated corrosion, the higher the capillary saturation of concrete around the reinforced concrete, the higher the content of chloride ion in the liquid phase, the quicker the process of rebar blunt to form corrosion, and vice versa. Temperature plays a critical role in the control of chloride ion in concrete pore solution. The steel bar in the concrete is near the water surface, and the liquid permeation is completely controlled by the fine pore pressure. The contact-angle effect of the rubber aggregate (as explained in Fig. 15) [1,2] significantly
3.1.2. Mass loss The degree of corrosion of steel is expressed by the weight loss, and there are two methods of theoretical calculation and actual measurement. According to Faraday’s law, the weight loss of steel corrosion can be calculated by the weight of the steel that is oxidized by the charge of the steel bar [12]:
W loss
EW ¼ TC ¼ F
( n X Ij þ Ij1 j¼1
2
tj tj1
)
EW F
ð1Þ
where Wloss is the total weight loss for the steel bar (g), TC is the total electricity (C), and Ew is the equivalent molar weight, which refers to the molar mass of the metal (g/mol). The equivalent weight
H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
(a) Without rubber
49
(b) With rubber
Fig. 15. Schematic diagram of the liquid surface of a fine hole.
can be expressed as Ew = W/n, where W is the atomic weight of the element, and n is the element of the atomic price. For carbon steel, Ew is 27.93 g/mol, F is the Faraday constant, F = 96494 (A s/mol), and Ij is the current through the steel bar (A) at tj (s). As shown in Fig. 16 and Table 3, the theoretical weightlessness rate of the steel bar is inconsistent with the weight-loss rate of the measured reinforcement, and is higher than the measured value. It
is believed that the reasons for this analysis are affected by the chloride-ion concentration of the concrete capillary solution. The higher the temperature of the ambient solution, the higher is the capillary saturation in the concrete around the steel, the higher the chloride content in the liquid phase, and the part of the electric energy forms the loop through the pore solution. The difference between the measured weight and the theoretical weight increases
Fig. 16. Mass-loss diagram.
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Table 3 Theoretical and experimental values of mass loss (g). Temperature
0 °C
20 °C
45 °C
Theoretical value of crumb rubber concrete Theoretical value of ordinary concrete Measured value of crumb rubber concrete Measured value of ordinary concrete
3.11 6.09 0.74 2.76
8.17 10.06 3.91 5.60
13.42 12.56 8.95 7.10
with increasing temperature, and this problem can be reflected from the side. The mass loss – temperature and potential – temperature changes in the law are similar, but at 45 °C, they are different. In this paper, it is considered that the measurement method using the steel-corrosion instrument gives only the probabilistic response of corrosion, but it does not strictly represent the extent of steel corrosion. 3.2. Test results of bending performance after corrosion The damaged condition of the samples for the ordinary concrete and the crumb rubber concrete were respectively shown in Figs. 17 and 18. After being corroded, the concrete was destroyed at the four-point bending test, and the shear failure of the ordinary concrete and the crumb rubber concrete was produced. The diagonal cracks were generated along the support point to the loading point. For the ordinary concrete, as shown in Fig. 17, the steel bar was exposed due to the concrete crushed and dropped at the support; the crack occurs along the diagonal of the concrete, and develops in a short duration with no omen, which is brittle damage; When continuing to load after cracking, one could hear the damage caused by steel and concrete bond issued by the ‘‘Peng, Peng” sound. As shown in Fig. 18, the failure process of crumb rubber concrete is that a diagonal crack is formed in the abdomen at first, and some visible cracks appear in the pure bending section of the beam when loading is continued. The cracks develop to about 1/3 height along the normal section of the beam, and the number of cracks increases continuously. There is no bond failure between steel bar and concrete, and no concrete crushed and dropped occurs during the failure. The original rust expansion crack did not develop very much, and the failure process underwent large deformation, showing good ductility.
Fig. 17. Cracking temperatures.
of
ordinary
concrete
beams
under
different
Fig. 18. Cracking of crumb rubber concrete beams under different ambient temperatures.
3.2.1. Load–displacement curve The resulting load-span mid-displacement curve is shown in Figs. 19–24. The load–displacement curve shows that the load–displacement changes linearly at the initial stage of loading, and the slope decreases with the increase in the degree of corrosion. The slope reduction of crumb rubber concrete is smaller than that of ordinary concrete, which shows that the flexural rigidity of the crumb rubber concrete beam is lower than that of ordinary concrete after corrosion. After the linear segment, the load–displacement relationship has mutations, and the increase of the displacement is faster than the increase of the load, the curve becomes gentle, the concrete enters the work with a crack, and the point where the sudden change occurs is called the initial crack point. The displacement corresponding to this point is initial crack displacement. During the course of the test, the bearing capacity of the rubber aggregate concrete increased with the increase of the neutral axis and reinforced steel bar. During the process of long deformation, the concrete was broken owing to the crushing of the concrete in the compression zone, and it exhibited good ductility. After entering the nonlinear state, the bearing capacity was not significantly
ambient Fig. 19. Beam-load–displacement curve with no treatment.
H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Fig. 20. Beam-load–displacement curve after treatment at 0 °C.
Fig. 21. Beam-load–displacement curve after treatment at 20 °C.
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Fig. 23. Load–displacement curves of crumb rubber concrete beams under different ambient temperatures.
Fig. 24. Load–displacement curves of ordinary concrete beams under different ambient temperatures.
Fig. 22. Beam-load–displacement curve after treatment at 45 °C.
reduced, and it had a certain ability to change. The ductility was better, and some of the energy was absorbed by plastic deformation, and the seismic performance was enhanced. For ordinary concrete, the performance decreased abruptly after the maximum load, with it being in a brittle failure state. The failure load of rubber aggregate concrete after accelerated corrosion did not markedly decrease, and the failure load of ordinary concrete accelerated corrosion declined clearly.
Fig. 25. Load–displacement curves of concrete beams under different ambient temperatures.
3.2.2. Ductility performance As shown in Fig. 25, the displacement ductility coefficient of a component is the ratio of the limit displacement to the yield displacement. In this paper, the ductility coefficient of displacement
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
rubber concrete and ordinary concrete does not change regularly with the temperature.
Conflict of interest None.
Acknowledgment The writers of this paper would like to express their appreciation for the financial support given by the National Natural Science Foundation of China (No. 51408408).
References Fig. 26. Displacement ductility coefficient of concrete.
is used to indicate the ductility of beams, and the displacement ductility coefficient is expressed by the following formula:
lD ¼
Du Dc
ð2Þ
where lD is the displacement ductility coefficient, Du is the limit displacement, and Dc is the initial crack displacement. The displacement ductility coefficient of concrete is shown in Fig. 26. In general, the ductility coefficient of crumb rubber concrete specimens is better than that of ordinary concrete with the same degree of corrosion. 4. Conclusion The corrosion rate of steel bars is significantly affected by the ambient temperature. The main reason is that when the ambient temperature of concrete accelerated corrosion increases, the capillary saturation of the concrete around the steel increases, the chloride content in the liquid phase increases, and the effect of the ambient temperature range on the crumb rubber concrete is greater than that of ordinary concrete. The degree of corrosion of concrete in contact with chlorine salt is mainly affected by fine pore pressure. Owing to the effect of the contact angle, the addition of rubber aggregate can change the fine pore pressure of the concrete and then reduce the degree of corrosion of the inner steel. When the ambient temperature is low, the degree of corrosion of the steel bar can be reduced, and when the temperature of the environment is high, the degree of corrosion of the steel bar is increased. The anti-cracking performance of crumb rubber concrete is strong owing to the plastic deformation of the absorption of part of the energy. Compared with ordinary concrete, it has obvious advantages in that the carrying capacity is not significantly reduced, and it has a specific degree of deformation ability in the non-linear state; the measured weight loss of steel is generally less than the theoretical calculation. The surface rust area and the actual crack width of the crumb rubber concrete specimen are smaller than that of the ordinary concrete, and the crack characteristics of crumb rubber concrete are dispersed in the direction of the steel bar. Compared with the ordinary concrete perforation cracks, there are obvious differences. The failure load of crumb rubber concrete is lower than that of ordinary concrete, but the ductility coefficient of rubber aggregate concrete is generally higher than that of ordinary concrete, which indicates that the rubber aggregate concrete has better antiseismic performance. However, the ductility coefficient of crumb
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Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Research on anti-chloride ion penetration property of crumb rubber concrete at different ambient temperatures Han Zhu a, Jian Liang a,b, Jie Xu a,⇑, Mingxuan Bo a, Jianju Li c, Bing Tang c a
School of Civil Engineering/Key Laboratory of Coast Civil Structure Safety of China Ministry of Education, Tianjin University, Tianjin 300072, China Huaiwei Water Conservancy Science Research Institute, Anhui 230088, China c China Aviation Ninth Engineering Brigade, Sichuan 611430, China b
h i g h l i g h t s Crumb rubber concrete (CRC) has high resistance to chloride-ion erosion. High resistance when the temperature is lower than 20 °C. Concrete ductility factor of CRC is higher than that of ordinary concrete. CRC has a better energy-absorption property. CRC has a different durability with the test environment temperature.
a r t i c l e
i n f o
Article history: Received 11 March 2018 Received in revised form 22 August 2018 Accepted 28 August 2018
Keywords: Crumb rubber concrete Durability Resistance to chloride-ion penetration Corrosion of steel bar
a b s t r a c t The corrosion of steel bars in concrete is one of the most important factors that affect the durability of concrete structures, which can be caused by several factors, including marine environments, deicing salt environments, saline and alkaline land, and saline pollution in industrial environments. Research has shown that the addition of crumb rubber can increase the capillary saturation of concrete and reduce the corrosion degree of steel bars in concrete, and with the increase of crumb rubber content, the weight-loss rate of steel bars decreases. The effects of temperature on its resistance to chloride-ion erosion and the durability of crumb rubber concrete are analyzed based on concrete-accelerated corrosion tests by controlling the ambient temperature. The results showed that crumb rubber concrete has high resistance to chloride-ion erosion, especially when the temperature is lower than 20 °C. The concrete ductility factor of crumb rubber concrete with chloride-ion corrosion at different temperatures is generally higher than that of ordinary concrete, indicating that crumb rubber concrete has a better energyabsorption property. It is shown that the crumb rubber concrete has a different durability with the test environment temperature, and can provide a reference for the application of crumb rubber concrete in anti-chloride ion penetration. Ó 2018 Elsevier Ltd. All rights reserved.
1. Research background Different types of concrete have been widely used in construction and water conservancy projects because of their different strengths, shapes, and generally good performance. However, the corrosion of reinforced concrete owing to marine environments, ice salt environments, saline alkali land, and brine pollution in some industrial environments is the greatest threat to the durability of concrete structures. These kinds of widespread diseases can cause significant direct and indirect losses. Studies have shown ⇑ Corresponding author. E-mail address: [email protected] (J. Xu). https://doi.org/10.1016/j.conbuildmat.2018.08.193 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
that the corrosion rate of reinforced concrete is affected by the saturation of fine holes in the concrete. The addition of rubber aggregate can improve the saturation of fine holes in the concrete and reduce the degree of corrosion of the steel in concrete; further, with an increase of the rubber content, there is an increased reduction of the weight-loss rate of the steel bar [1]. The capillary saturation of concrete is influenced by temperature, and the test results of the test often vary in test environments at different temperatures. The corrosion rate of steel bars in the actual project varies with the temperature. Feng and Xing [2] investigated the Seaport Wharf used over different years in North China. Investigations have shown that concrete structures in the superstructures of the northern seaport are damaged owing to the different degrees of
H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
corrosion of the reinforcement, but the corrosion of the superstructure of the North China harbor wharf is less than that in Southeastern China. It is necessary to understand whether the degree of corrosion is related to the temperature distribution. As shown in Figs. 1 and 2, the sea temperature is different in different seasons, so it is necessary to study the resistance of concrete to chloride ions under different ambient temperatures. Zaccardi et al. [3] researched the corrosion of reinforced concrete that was exposed to the seaside environment for 60 months. Hu et al. [4] researched the combined effect of chloride ion and carbonation using the open-circuit potential method of reinforced concrete at 25 °C, 35 °C, and 45 °C. Chen et al. [5] researched the influence of temperatures of 5–60 °C on the passivation behavior of steel bars using scanning-electron microscopy (SEM) observations and electrochemical measurements. Xu et al. [6] studied the effect of temperature on the release of bound chlorides. Shao et al. [7] simulated the influence of exposure temperature on chloride diffusion into reinforced concrete pipe piles that are exposed to the atmosphere using salt spray test. Nguyen and Amiri [8] studied the distribution of chlorine ions in concrete in dry and wet cycles. Medeiros et al. [9] studied the effect of chloride ions on the life of reinforced concrete structures in a global warming environment. Yang et al. [10] studied the effect of temperature on the diffusion properties of chloride ions in concrete. Xu et al. [11] studied the effect of temperature on the resistance to the chloride-ion erosion of marine concrete and the prediction of life. Liu et al. [12] studied the chloride permeability of concrete in environments with different temperatures in brine. Han [13] studied the effect of thermal fatigue on the strength and permeability of high-performance concrete. This study is based on the work of these predecessors, and was conducted to study the corrosion resistance of crumb rubber concrete at different temperatures. There have been many studies by researchers to improve the strength of concrete. With an increased strength, defects of the
43
corresponding concrete brittleness become increasingly prominent. In the past few decades, scholars have begun to use rubber particles as building materials in the field of concrete because it not only improves many of the defects present in concrete materials, such as large self-weight and brittleness, but also expands the application field of waste rubber, and rationally carries out the recycling of resources. Concrete mixed with waste rubber particles is made of concrete as the base material, mixed with rubber powder or crumb rubber made of composite materials. Rubber, which is a kind of super-elastic material, can improve the internal structure of concrete through physical action without changing the chemical properties of each component in concrete. The elastic modulus of rubber is almost negligible compared with that of concrete. In this case, the rubber particles can be considered as elastic pores when the rubber particles replace some of the aggregate, and are evenly distributed into the concrete. Elastic pores can be considered as a constraint, and can prevent the production and development of internal microcracks in the concrete, and become the deformation center to absorb strain energy. Many scholars have studied the physical and mechanical properties of crumb rubber concrete, and found that rubber particles can clearly improve the crack resistance and ductility of concrete. At the same time, the crumb rubber concrete will not experience. In addition, rubber particles play an active role in improving concrete frost resistance and resisting chloride-ion migration. Pelisser et al. [14] studies showed that the density of crumb rubber concrete is 13% lower than that of ordinary concrete. Yilmaz et al. [15] studies showed that the flexural strength of the concrete increased by 20% after adding the rubber with the form of fiber, after the addition, the bending strength shows a downward trend, and the ordinary concrete presents brittle fracture, and the rubber concrete is ductile fracture. Kang et al. [16] reported that the concrete specimens containing rubber particles will produce obvious plastic deformation during the bending process, and will not produce plastic fractures when subjected to
Fig. 1. Annual average temperature distribution of the ocean in January.
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Fig. 2. Annual average temperature distribution of the ocean in July.
a maximum load, but undergo ductile failure after large plastic deformation. Thomas et al. [17] reported that the carbonization depth of the concrete mixed with rubber is smaller than that of ordinary concrete. Raghavan et al. [18] added 0.6% mass of rubber to the concrete. The results showed that the mass loss of the rubber concrete in the freeze–thaw test is the smallest. Oikonomou et al. [19] studied that the chloride permeability decreases with an increase in the amount of rubber. Gupta et al. [20] showed that the chloride concentration in all mixture ratios of rubber concrete was very low, indicating that the rubber aggregate concrete has a good chloride-ion permeability. Thomas et al. [17] reported that the chloride-ion penetration of concrete mixed with 10% of rubber was smaller than that of ordinary concrete. Thomas and Gupta [21] pointed out that the disposal of waste tire rubber has become a major environmental problem worldwide, and raw materials used in crumb rubber concrete mainly come from solid waste such as waste tires, etc. This is a very effective way of managing waste tires and protecting the increasingly tense land and rubber resources. At the same time, it has advantages in terms of cost because of the low cost of rubber aggregate. Therefore, the development of crumb rubber concrete has high economic and social benefits. However, in recent years, China’s annual production capacity of concrete is about 1.3 billion m3. With the expected further increase of China’s investment in infrastructure construction, it is foreseeable that the cement concrete production will be very large in future. If such a large amount of concrete is subjected to durability damage, the consequences will be severe. Therefore, it is necessary to find new solutions from the material science perspective. Crumb rubber concrete has attracted extensive attention and applications because of its outstanding performance in terms of its durability [22–24]. Therefore, the analysis and research into the durability and mechanism of crumb rubber concrete are important to solving the durability
problems, and ensuring the quality of engineering [25–28]. Hence, this current paper focuses on this perspective, and the concrete ductility factor of crumb rubber concrete with chloride-ion corrosion at different temperatures was investigated. 2. Experimental program 2.1. Material properties This research is a continuation of our previous study. The goal of the previous experiment was mainly to study the effect of the rubber content and water cement ratio on the corrosion of steel bars [29]. In this research, our attention is focused on the effect of the same mixture ratio at different temperatures. Details of the mixture ratio for the crumb rubber concrete and the ordinary concrete are listed in Table 1. Based on this mixed proportion, 12 specimens for crumb rubber concrete and 12 specimens for ordinary concrete with a size 100 mm 100 mm 515 mm [30] were simultaneously fabricated, and were cured in a standard curing room (temperature is 20 ± 3 °C and relative humidity is above 90%) for the 28 days. For each kind of concrete, four different test conditions (normal, 0 °C, 20 °C, and 45 °C) were considered, and there are three specimens for each condition. The crumb rubber was 40 mesh rubber powder, and the ingredients of the crumb rubber are listed in Table 2. 2.2. Test setup 2.2.1. Corrosion test The key to the design of the corrosion test is to form a corrosion current loop. At the same time, it is necessary to ensure the presence of oxygen, water, and chloride ions around the steel bar,
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53 Table 1 Design of mix proportion (kg/m3).
Crumb rubber concrete Ordinary concrete
P.O.42.5 cement
Sand
Coarse aggregate
Fine aggregate
Water
Rubber
Admixture
385 325
644 644
753 753
611 611
187 127
110 0
6 6
Table 2 Chemical ingredients of crumb rubber (mass fraction)/%. Rubber hydrocarbon
Carbon black
Acetone extract
Isoprene
Water
Ash content
Fiber content
Metal content
Others
45.2
25.8
14.2
12.1
0.8
0.9
0.5
0.08
0.42
which is the prerequisite for corrosion. Almusallam [31] studied the effect of the degree of corrosion of the steel bar on its mechanical properties by electric corrosion method. Lee and Cho [32] quantitatively studied the relationship between the degree of corrosion of steel bars and the mechanical properties of steel bars using the electric corrosion method. Zhang et al. [33] used the electrochemical method to study the corrosion of steel bars in a reinforced concrete plate, and then studied the static tensile and fatigue behavior of corroded steel bars. Wu and Yuan [34] studied the influence of two accelerated corrosion methods on the mechanical properties of corroded steel bars by performing the tensile test of corroded reinforced bar of reinforced concrete members subjected to corrosion by a simulated artificial climate environment and a constant current-accelerated corrosion. Based on the experience of a previous study on the accelerated corrosion of reinforced concrete, the accelerated test devices were designed as shown in Figs. 3 and 4. The device in Fig. 3 is used to control the temperature rise of the test solution, and the one in Fig. 4 is a cooling device for controlling the test solution. The temperature-control box is equipped with a temperature meter, which controls the accelerated corrosion environment temperature through the temperature control box, and to enable the analysis of the resistance to chloride-ion erosion. When
the corrosion environment temperature is lower than the ambient temperature, the heating pipe is used to heat the water temperature, as shown in Fig. 3. The temperature controller in the temperature control box is used to set the temperature. The temperature sensor is placed in the water tank to make the water temperature reach the set ambient temperature, whose accuracy is ±1 °C. Considering that water evaporates fast when the temperature is high, the water-replenishing device is designed to keep the water level constant. When the corrosion environment temperature is higher than the ambient temperature, the freezer is used to cool the water, as shown in Fig. 4. The temperature controller is used in the temperature-control box to set the temperature in order to make the water temperature reach the set ambient temperature. The power supply of the freezer is led by the temperaturecontrol box, where a temperature sensor is arranged, whose accuracy is ±1 °C. As the water is easy to freeze in a freezer less than 0 °C, a specific proportion of alcohol is added to water to reduce the freezing point of the solution. During the test, the water salinity is measured by a salinity meter. If the measured salinity is lower than the set salinity, the salt is added according to the salinity calculation value to keep the experimental environment constant. During the test period, the atmospheric temperature ranged from 5 °C to 14 °C. When corrosion ambient temperature
Fig. 3. Schematic diagram of high-temperature accelerated corrosion test device.
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Fig. 4. Schematic diagram of low-temperature accelerated corrosion test device.
is 20 °C and 45 °C, the heating-temperature accelerated corrosion test device control in Fig. 3 is used; when the corrosion ambient temperature is 0 °C, the low-temperature accelerated corrosion test device control in Fig. 4 is used. The voltage output range of the steady voltage and steady current power supply used in the test is 0–30 V, the maximum output current is 5 A, and the temperature-control box can vary the temperature from 0 to 100 °C. During the test, half of the beam specimen was submerged in the 3.5% NaCl solution, and it was equipped with two 10-mm diameter steel bars in the part above water. As the anode, the steel was connected with the positive pole of the power supply. The cathode was a stainless rope arranged at the lower part of the specimen. In series resistance in the loop, the measured resistance is 10.8 X, and is used to measure the current in the loop. After the specimen was cured for 28 days, the corrosion is accelerated and the corrosion period will be 10 days. The corrosion temperature was controlled at 0 °C, 20 °C, and 45 °C, respectively. As shown in Fig. 5, accelerated corrosion was performed on two sets (3 2) simultaneously. Each steel bar is connected to one resistance and then connected in parallel. The voltage of the test is 12 V and remains constant. The current of the steel bar varies with the resistance of the closed circuit. The voltage at the two ends of the series resistance is measured every 6 h, and the current magnitude of the reinforcing bar in the beam is calculated. According to Faraday’s law, the corrosion of the reinforcement depends on the amount of electricity that passes through the steel bar, and then the corrosion of each test beam is estimated. The electric flux that is applied to the steel bar is measured, and the potential reflecting the corrosion degree of rebar. Then, the salinity of the environmental solution in the process is controlled in order to observe the cracks of the concrete caused by the corrosion of the steel rein-
Fig. 5. Corrosion test setup.
forced bar and the size of the cracks is measured at the end of the test. The different parameters of crumb rubber concrete and ordinary concrete are compared to take the result as the standard of the permeability performance of crumb rubber concrete and ordinary concrete. 2.2.2. Four-point bending test On this basis of the corrosion test, the four-point bending test of the reinforced concrete beam was carried out, and the stress–strain curve of the reinforced concrete beam, the mid-span deflection of the beam, and the final fracture crack were measured to determine the mechanical properties of the corroded steel bar of the crumb rubber concrete and ordinary concrete. As shown in Fig. 6, the test was carried out on a WE-30 universal testing machine with a maximum load of 100 kN. The loading speed was set at 0.3 cm/s, and
H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
47
Fig. 6. Four-point bending test device (unit: mm).
the data were collected every 1 kN. A micrometer was used to measure the mid-span deflection of the beam. 3. Test results and discussion 3.1. Accelerated corrosion test results After the corrosion, crumb rubber concrete and ordinary concrete specimens at different temperatures are shown in Figs. 7 and 8, respectively. It can be seen that the surface rust of the two kinds of concrete increases markedly with the increase of temperature, indicating that the temperature significantly influences the corrosion of the reinforced bar in the concrete. The reason is mainly owing to the increase of the saturation of the fine holes in the concrete as the temperature rises, and it also makes the current through the concrete increase. 3.1.1. Potential change The current and potential changes for two kinds of concrete with time at different temperatures are shown in Figs. 9–11. The potential change at three temperatures for two kinds of concrete is shown in Figs. 12 and 13, and the trend of the average potential and current in the last 24 h of accelerated corrosion is shown in Fig. 14. The figure shows that the potential change of crumb rubber concrete and ordinary concrete decreases with an
Fig. 8. Corrosion of ordinary concrete beams under: (a) normal condition; (b) 0 °C; (c) 20 °C; and (d) 45 °C.
Fig. 9. Diagram of concrete potential and current at 0 °C.
Fig. 7. Corrosion of crumb rubber concrete beams under: (a) normal condition; (b) 0 °C; (c) 20 °C; and (d) 45 °C.
increase of temperature. The lower the temperature, the more obvious is the performance of crumb rubber concrete antichloride ion erosion. The corrosion rate of steel is mainly influenced by the concentration of chloride ions in the concrete hole solution. The higher
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Fig. 10. Diagram of concrete potential and current at 20 °C. Fig. 13. Potential change diagram of ordinary concrete.
Fig. 11. Diagram of concrete potential and current at 45 °C. Fig. 14. Average value for last 24 h of accelerated corrosion.
reduces the extraction effect of the fine hole to the liquid phase, and then the saturation of the fine hole of the concrete is reduced. In this condition, the content of the chloride ion in the fine hole is reduced, and the degree of corrosion of the steel bar is inevitably reduced. The results show that the current density of the steel rises gradually as the temperature varies, and in the middle-temperature environment, it is basically constant with ordinary concrete. This shows that the crumb rubber concrete is still conductive with the pore solution, and the rubber aggregate itself is not involved in chloride ion in mixed concrete during the process of electro migration.
Fig. 12. Potential change diagram of crumb rubber concrete.
the ambient temperature of concrete accelerated corrosion, the higher the capillary saturation of concrete around the reinforced concrete, the higher the content of chloride ion in the liquid phase, the quicker the process of rebar blunt to form corrosion, and vice versa. Temperature plays a critical role in the control of chloride ion in concrete pore solution. The steel bar in the concrete is near the water surface, and the liquid permeation is completely controlled by the fine pore pressure. The contact-angle effect of the rubber aggregate (as explained in Fig. 15) [1,2] significantly
3.1.2. Mass loss The degree of corrosion of steel is expressed by the weight loss, and there are two methods of theoretical calculation and actual measurement. According to Faraday’s law, the weight loss of steel corrosion can be calculated by the weight of the steel that is oxidized by the charge of the steel bar [12]:
W loss
EW ¼ TC ¼ F
( n X Ij þ Ij1 j¼1
2
tj tj1
)
EW F
ð1Þ
where Wloss is the total weight loss for the steel bar (g), TC is the total electricity (C), and Ew is the equivalent molar weight, which refers to the molar mass of the metal (g/mol). The equivalent weight
H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
(a) Without rubber
49
(b) With rubber
Fig. 15. Schematic diagram of the liquid surface of a fine hole.
can be expressed as Ew = W/n, where W is the atomic weight of the element, and n is the element of the atomic price. For carbon steel, Ew is 27.93 g/mol, F is the Faraday constant, F = 96494 (A s/mol), and Ij is the current through the steel bar (A) at tj (s). As shown in Fig. 16 and Table 3, the theoretical weightlessness rate of the steel bar is inconsistent with the weight-loss rate of the measured reinforcement, and is higher than the measured value. It
is believed that the reasons for this analysis are affected by the chloride-ion concentration of the concrete capillary solution. The higher the temperature of the ambient solution, the higher is the capillary saturation in the concrete around the steel, the higher the chloride content in the liquid phase, and the part of the electric energy forms the loop through the pore solution. The difference between the measured weight and the theoretical weight increases
Fig. 16. Mass-loss diagram.
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Table 3 Theoretical and experimental values of mass loss (g). Temperature
0 °C
20 °C
45 °C
Theoretical value of crumb rubber concrete Theoretical value of ordinary concrete Measured value of crumb rubber concrete Measured value of ordinary concrete
3.11 6.09 0.74 2.76
8.17 10.06 3.91 5.60
13.42 12.56 8.95 7.10
with increasing temperature, and this problem can be reflected from the side. The mass loss – temperature and potential – temperature changes in the law are similar, but at 45 °C, they are different. In this paper, it is considered that the measurement method using the steel-corrosion instrument gives only the probabilistic response of corrosion, but it does not strictly represent the extent of steel corrosion. 3.2. Test results of bending performance after corrosion The damaged condition of the samples for the ordinary concrete and the crumb rubber concrete were respectively shown in Figs. 17 and 18. After being corroded, the concrete was destroyed at the four-point bending test, and the shear failure of the ordinary concrete and the crumb rubber concrete was produced. The diagonal cracks were generated along the support point to the loading point. For the ordinary concrete, as shown in Fig. 17, the steel bar was exposed due to the concrete crushed and dropped at the support; the crack occurs along the diagonal of the concrete, and develops in a short duration with no omen, which is brittle damage; When continuing to load after cracking, one could hear the damage caused by steel and concrete bond issued by the ‘‘Peng, Peng” sound. As shown in Fig. 18, the failure process of crumb rubber concrete is that a diagonal crack is formed in the abdomen at first, and some visible cracks appear in the pure bending section of the beam when loading is continued. The cracks develop to about 1/3 height along the normal section of the beam, and the number of cracks increases continuously. There is no bond failure between steel bar and concrete, and no concrete crushed and dropped occurs during the failure. The original rust expansion crack did not develop very much, and the failure process underwent large deformation, showing good ductility.
Fig. 17. Cracking temperatures.
of
ordinary
concrete
beams
under
different
Fig. 18. Cracking of crumb rubber concrete beams under different ambient temperatures.
3.2.1. Load–displacement curve The resulting load-span mid-displacement curve is shown in Figs. 19–24. The load–displacement curve shows that the load–displacement changes linearly at the initial stage of loading, and the slope decreases with the increase in the degree of corrosion. The slope reduction of crumb rubber concrete is smaller than that of ordinary concrete, which shows that the flexural rigidity of the crumb rubber concrete beam is lower than that of ordinary concrete after corrosion. After the linear segment, the load–displacement relationship has mutations, and the increase of the displacement is faster than the increase of the load, the curve becomes gentle, the concrete enters the work with a crack, and the point where the sudden change occurs is called the initial crack point. The displacement corresponding to this point is initial crack displacement. During the course of the test, the bearing capacity of the rubber aggregate concrete increased with the increase of the neutral axis and reinforced steel bar. During the process of long deformation, the concrete was broken owing to the crushing of the concrete in the compression zone, and it exhibited good ductility. After entering the nonlinear state, the bearing capacity was not significantly
ambient Fig. 19. Beam-load–displacement curve with no treatment.
H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
Fig. 20. Beam-load–displacement curve after treatment at 0 °C.
Fig. 21. Beam-load–displacement curve after treatment at 20 °C.
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Fig. 23. Load–displacement curves of crumb rubber concrete beams under different ambient temperatures.
Fig. 24. Load–displacement curves of ordinary concrete beams under different ambient temperatures.
Fig. 22. Beam-load–displacement curve after treatment at 45 °C.
reduced, and it had a certain ability to change. The ductility was better, and some of the energy was absorbed by plastic deformation, and the seismic performance was enhanced. For ordinary concrete, the performance decreased abruptly after the maximum load, with it being in a brittle failure state. The failure load of rubber aggregate concrete after accelerated corrosion did not markedly decrease, and the failure load of ordinary concrete accelerated corrosion declined clearly.
Fig. 25. Load–displacement curves of concrete beams under different ambient temperatures.
3.2.2. Ductility performance As shown in Fig. 25, the displacement ductility coefficient of a component is the ratio of the limit displacement to the yield displacement. In this paper, the ductility coefficient of displacement
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H. Zhu et al. / Construction and Building Materials 189 (2018) 42–53
rubber concrete and ordinary concrete does not change regularly with the temperature.
Conflict of interest None.
Acknowledgment The writers of this paper would like to express their appreciation for the financial support given by the National Natural Science Foundation of China (No. 51408408).
References Fig. 26. Displacement ductility coefficient of concrete.
is used to indicate the ductility of beams, and the displacement ductility coefficient is expressed by the following formula:
lD ¼
Du Dc
ð2Þ
where lD is the displacement ductility coefficient, Du is the limit displacement, and Dc is the initial crack displacement. The displacement ductility coefficient of concrete is shown in Fig. 26. In general, the ductility coefficient of crumb rubber concrete specimens is better than that of ordinary concrete with the same degree of corrosion. 4. Conclusion The corrosion rate of steel bars is significantly affected by the ambient temperature. The main reason is that when the ambient temperature of concrete accelerated corrosion increases, the capillary saturation of the concrete around the steel increases, the chloride content in the liquid phase increases, and the effect of the ambient temperature range on the crumb rubber concrete is greater than that of ordinary concrete. The degree of corrosion of concrete in contact with chlorine salt is mainly affected by fine pore pressure. Owing to the effect of the contact angle, the addition of rubber aggregate can change the fine pore pressure of the concrete and then reduce the degree of corrosion of the inner steel. When the ambient temperature is low, the degree of corrosion of the steel bar can be reduced, and when the temperature of the environment is high, the degree of corrosion of the steel bar is increased. The anti-cracking performance of crumb rubber concrete is strong owing to the plastic deformation of the absorption of part of the energy. Compared with ordinary concrete, it has obvious advantages in that the carrying capacity is not significantly reduced, and it has a specific degree of deformation ability in the non-linear state; the measured weight loss of steel is generally less than the theoretical calculation. The surface rust area and the actual crack width of the crumb rubber concrete specimen are smaller than that of the ordinary concrete, and the crack characteristics of crumb rubber concrete are dispersed in the direction of the steel bar. Compared with the ordinary concrete perforation cracks, there are obvious differences. The failure load of crumb rubber concrete is lower than that of ordinary concrete, but the ductility coefficient of rubber aggregate concrete is generally higher than that of ordinary concrete, which indicates that the rubber aggregate concrete has better antiseismic performance. However, the ductility coefficient of crumb
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