Integrity Evaluation of Construction Materials in Bridge Engineering
View this Special IssueResearch Article  Open Access
Xiao Lei, Rui Wang, Hanwan Jiang, Faxiang Xie, Yanni Bao, "Effect of Internal Curing with Superabsorbent Polymers on Bond Behavior of HighStrength Concrete", Advances in Materials Science and Engineering, vol. 2020, Article ID 6651452, 13 pages, 2020. https://doi.org/10.1155/2020/6651452
Effect of Internal Curing with Superabsorbent Polymers on Bond Behavior of HighStrength Concrete
Abstract
Highstrength concrete (HSC) is widely used in engineering due to its high strength and durability. However, because of its low watertocement ratio, external curing water hardly enters the dense internal structure of HSC so that high selfdesiccation shrinkage often takes place. As a result, superabsorbent polymers (SAP) are added as an internal curing material to effectively reduce the shrinkage of highperformance concrete. Meanwhile, the bond performance between reinforcing steel and SAP HSC concrete remains unknown. In this paper, the bond performance of HSC mixed with SAP is studied by pullout tests, and the results were obtained as follows: (1) the bond strength of HSC mixed with SAP increased first and then decreased with the increase of SAP content; (2) the slip at ultimate bond strength of HSC with SAP decreased with the increase of compressive strength; (3) a prediction model of the stressslip relationship between steel rebars and HSC was established.
1. Introduction
Highstrength concrete has higher strength and durability than conventional concrete due to its low watertocement ratio, denser internal structure, and low permeability [1]. However, autogenous shrinkage may take place when the watertocement ratio is below the critical level, resulting in cracking and reduction of the structure’s serviceability [2–5]. Hence, internal curing has been employed to prevent autogenous shrinkage in highstrength concrete by replacing a percentage of normalweight aggregates with lightweightweight aggregates [6, 7], superabsorbent polymer (SAP), or other expansive materials [8, 9]. SAP has been extensively studied due to its advantages of being able to mitigate autogenous shrinkage and prevent selfdesiccation [10–15]. Multiple studies have proved that SAP can effectively reduce the selfshrinkage of HSC [16–18] while there is no consensus on the influence of SAP on the compressive strength of HSC. Some tests found that SAP would reduce the compressive strength of HSC [19–22], but some other tests found that SAP would increase the compressive strength of HSC [23–26]. It is reported that SAP content is one of the factors that affect HSC’s compressive strength [27]. While there are many factors that influence compressive strength of HSC such as the amount of compensated water, type and SAP particle size, the absorption, desorption kinetic of SAPs, and the interfacial properties between cement matrix and SAPs, the authors only focus on the effect of SAP content on compressive strength of HSC in this study.
Meanwhile, as a key parameter for structural design, bond strength for HSC with SAP added has not been studied yet. Although there were many studies published on the bond strength of normal reinforced concrete [28–36] as well as highstrength concrete [37–42], the law of bond strength and the stressslip relationship between HSC mixed with SAP and reinforcing steel remain unclear. The stressslip relationship of concrete is usually obtained from pullout tests. Various stressslip models for normal concrete and highperformance concrete have been developed in many studies [41–51]. However, the stressslip response for highstrength concrete mixed with SAP is still unknown. In this paper, an experimental study has been carried out aimed at establishing SAP content and compressive strength relationship, SAP content and HSC bond strength relationship, and the stressslip model for HSC with SAP.
2. Experimental Investigation
2.1. Material Properties
The cement used in this test is P.O. 42.5 Portland cement with chemical composition shown in Table 1. Medium coarse sand and 5–16 mm continuous graded gravel were mixed with the cement to create concrete with a compression strength of 50 MPa. High efficiency polycarboxylate superplasticizer was added as a water reducing agent. Drying and absorbing states of SAP are shown in Figure 1. Standard structural rebars are 16 mm in diameter, shown in Figure 2. In Theory, the internal curing water should be the same for same watertocement ratio. However, when SAP is added, water is partially absorbed such that more water is needed in addition to that for internal curing. Therefore, the internal curing water is set to be 20 times of the SAP content.

(a)
(b)
The mixture proportions of concrete used in the test are shown in Table 2.
 
“S” in the serial number stands for SAP content. 
2.2. Required Internal Curing Water
In order to ensure that the cement can reach the maximum hydration level, the internal curing water amount can be calculated according to the following equation [52]：where is internal curing water mass required for complete hydration of cement; is the cement mass (kg/m^{3}); is the shrinkage of cement when it reaches 100% hydration; for general cement, it is 0.07; and is the maximum hydration degree when all water in SAP is used for cement hydration without evaporation loss; generally, it is [W/C]/0.36 (when W/C ≤ 0.36).
According to the theoretical calculation, the internal curing water amount is 33.12 kg/m^{3}, but considering that different SAP contents were designed in the test, the final internal curing water amount of S0, S1, S2, S3, and S8 was determined to be 0, 10.2, 20.4, 30.6, and 81.6 kg/m^{3}, respectively.
2.3. Concrete Preparation for Compressive Strength and PullOut Test
A total of 6 specimens for pullout test were made as shown in Figure 3. The rebar was embedded centrically in the 150 mm × 150 mm × 150 mm concrete cube. The standard 28day strength of the concrete is 50 MPa. The embedment length of the rebar in the concrete block is 3 times of rebar diameter (48 mm). The rebar was sheathed with PVC pipes for debonding on both ends of the concrete block at a length of 34 mm and 68 mm, respectively. A shorter bond length 3 times rebar diameter instead of typically used 5 times rebar diameter [53] was adopted in order to obtain a complete stressslip curve and prevent splitting.
Three 150 mm concrete cubes were set for the compressive strength test. The concrete mixing is followed in a sequence. First of all, cement, coarse and fine aggregate, and dry SAP were put together and mixed for 30 s; then half of the water and the water reducing agent were added and mixed for another 2 min; after that, the remaining half of the water and the water reducing agent were poured and mixed for additional 2 min. Once the mixing was completed, the mixture was immediately poured into molds. The specimens have been cured for 28 days to achieve desirable strength.
2.4. Experimental Process
A hydraulic universal testing machine was used for the test, and an LVDT sensor was set on the specimen to measure the relative slip of steel bar and concrete, as shown in Figure 4(a). The test was controlled by displacement, and the loading rate was 0.3 mm/min. The test ended when the steel bar was pulled out or broken, the concrete specimen was damaged or reaches the specified displacement. Dynamic data collection was used to record the load value and the reading of the LVDT. The failure mode of all tests is deemed to be split failure from the visual inspection shown in Figure 4(b).
(a)
(b)
3. Experiment Results
3.1. Effect of SAP on Compressive Strength of HSC
The compressive strength of HSC with different content of SAP is shown in Figure 5. It indicates that a small amount of SAP can increase the compressive strength of HSC, but when the content exceeded the peak value, the compressive strength was reduced. When the SAP content was 0.1% of cement mass, the compressive strength of concrete increases by 4.55%; when the SAP content was 0.2%, 0.3%, and 0.8% of cement mass, the compressive strength of concrete decreased by 9.84%, 20.91%, and 33.33%, respectively. The amount of SAP needed to achieve maximum compressive strength is a tradeoff analysis. SAP reduces the shrinkage in concrete and improves cement hydration which helps increase the compressive strength. Meanwhile, the addition of SAP increases water diversion and porosity and therefore results in decreased compressive strength. This experiment showed that the peak of compressive strength had been achieved with 0.1% SAP addition.
The following equation was created to best fit the data points in Figure 5 with the goodness of fit R^{2} = 0.99:where is the compressive strength of SAP concrete, MPa; is the 28day compressive strength of ordinary concrete, MPa; is the SAP content, %.
The calculated and measured compressive strength of SAP concrete are listed in Table 3. It shows that the differences between the calculated and measured values are minimal so that equation (2) can be adopted to represent the SAP contentcompressive relationship.

3.2. Effect of SAP on Bond Strength of HSC
The equation for calculating the bond strength is simply to use the pullout force divided by the contact area around the rebar as shown in the following equation:where is the bond strength, MPa; is the pullout force, N; is the diameter of the steel bar, mm; and is the bond length, mm.
The bond strength for HSC with different SAP content is tested and shown in Table 4. It can be seen from the table that a small amount of SAP could increase the bond strength of HSC, but if adding more than 0.1% of SAP, the bond strength was reduced. When the SAP content was 0.1% of the cement mass, the bond strength of concrete increased by 8.92%; when the SAP content was 0.2%, 0.3%, and 0.8% of the cement mass, the bond strength of concrete decreased by 5.98%, 14.55%, and 25.24%, respectively.

The experimental results show that the bond strength variations with SAP content in HSC is similar to that of compressive strength. It is worth noting that the addition of SAP made the bond strength of concrete increase more than compressive strength (Figure 6). For example, adding 0.1% of SAP caused 4.55% increase in compressive strength and 8.92% in bond strength. Similarly, adding 0.2%, 0.3%, and 0.8% SAP caused 9.84%, 20.91%, and 33.33% drawdown in compressive strength and 5.98%, 14.55%, and 25.24% decrease in bond strength. The correlation between bond strength and compressive strength is discussed in Section 3.3.
3.3. Relationship between Compressive Strength and Bond Strength of Concrete Mixed with SAP
There have been a number of studies carried out on the relationship between bond strength and compressive strength of concrete and rebar. In these studies, bond strength is expressed in terms of the exponent of compressive strength [29, 33–35, 39–42]:where is the bond strength in MPa, is the cylinder compressive strength in MPa, and and are the constants.
The authors of the literature [29, 33] studied the relationship between cylinder compressive strength and bond strength accounting for factors such as the minimum thickness of protective layer, diameter of steel bars, and bond length of steel bars. The empirical equation and value for parameters a and b were given:where is the minimum thickness of protective layer, mm; is the diameter of steel bars, mm; is the bond length, mm; and , , and are the constants.
The research results of literature [29, 33] are shown in Table 5.
In literature [34, 35, 39], the relationship between cylinder compressive strength and bond strength under the influence of minimum thickness of protective layer, maximum thickness of protective layer, diameter of steel bars, bond length of steel bars, and area of steel bars was studied; a different function and value for a and b were derived and shown in the following equations:where is the bond length, mm; is the minimum thickness of protective layer, mm; is the diameter of steel bars, mm; is the area of steel bars; is the maximum thickness of protective layer, mm; and and are the constants.
The research results of literature [34, 35, 39] are shown in Table 6.
In literature [39], experimental studies were conducted on concrete specimens with strength up to 90 MPa, and the expressions of and values were obtained as shown below:
In literature [41], bond strength of highstrength concrete was studied, and the expressions of and values obtained are shown in the following equation:
According to literature [44], the ratio of compressive strength of the 150 mm cube to that of the standard cylinder is 0.8, so the cylinder compressive strength of the concrete with 0, 0.1%, 0.2%, 0.3%, and 0.8% SAP content in this test is 39.42, 41.21, 35.54, 31.18, and 26.28 MPa, respectively.
The relationship between the cylinder compressive strength and bond strength obtained from the above calculation results and this test is shown in Figure 7.
As seen in Figure 7, the models from the listed literatures are not consistent with testing data for concrete mixed with SAP. Equation (4) was used to best fit the data, and the values for a and b were obtained (=2.03, = 0.8) with R^{2} = 0.97. Hence, the bond strength and the cylinder compressive strength relationship of SAP concrete can be expressed aswhere is the bond strength, MPa; is the cylinder compressive strength, MPa.
The calculated and measured bond strengths for concrete specimens with various SAP content are shown in Table 7. Since the difference between the two is within 5%, equation (9) is suitable for bond strength evaluation.

Substituting equation (2) into equation (9), the bond strength can be written aswhere is the bond strength, MPa; is the 28day compressive strength of ordinary concrete (MPa); and is the SAP content, %. The factor of 0.8 in the bracket is to convert cylinder strength to cube strength.
3.4. Slip and Compressive Strength Relationship
Shen et al. [42] proposed a nonlinear relationship between slip at ultimate bond stress and compressive strength based on their test data. Similar trend was observed in the experiment with SAP concrete. Hence, the nonlinear model in literature [42] is adopted in this study as shown below:where is the slip at ultimate bond stress, mm; is the cylinder compressive strength, MPa; and are the constants.
The slip at ultimate bond stress of concrete mixed with SAP in this test is shown in Figure 8. The factors of m and n in equation (11) were found to be = 48.74 and = 16.79 through data fitting with goodness of fit R^{2} = 0.93. Then the relationship between the slip at ultimate bond stress and cylinder compressive strength can be written as
Then the tested and theoretical slip from equation (12) at ultimate bond stress for HSC with various SAP contents are listed and compared in Table 8.

3.5. The Prediction Model of StressSlip Relationship between Steel Bars and HSC Mixed with SAP
Various stressslip models have been developed in the past two decades [41–51] showing that there is a clear relationship between bond stress and slip. In this study, the BPE model [51] was used:
It can also be expressed aswhere is the bond stress value, MPa; is the slip corresponding to bond stress, mm; is the ultimate bond strength, MPa; is the slip at ultimate bond strength, mm; and is a constant.
Performing best fitting analysis, values for SAP content of 0, 0.1%, 0.2%, 0.3%, and 0.8% were found to be 0.2477, 0.1367, 0.19, 0.2101, and 0.1615, respectively, as shown in Figure 9. Then the mean of the five numbers 0.1892 was taken for the finalized stressslip relationship of SAP concrete as shown in the following equation:
(a)
(b)
(c)
(d)
(e)
Combined with equation (2), equation (9), equation (10), and equation (13), bonding performance of UPC with SAP can be expressed as follows:where is the compressive strength of SAP concrete, MPa; is the 28day compressive strength of ordinary concrete, MPa; is the SAP content, %; is the cylinder compressive strength, MPa; is the bond strength, MPa; is the slip at ultimate bond strength, mm; is the bond stress value, MPa; and is the slip corresponding to bond stress, mm.
The comparison between the theoretical value calculated according to formula (14) and the actual value in the test is shown in Figure 10.
4. Conclusions
In this paper, through relevant tests and theoretical derivation, the bond behavior of concrete mixed with SAP was systematically studied, and the following conclusions were obtained:(1)The compressive strength of HSC mixed with SAP first increases and then decreases with the increase of SAP content. The compressive strength of concrete with SAP content of 0, 0.1%, 0.2%, 0.3%, and 0.8% is 49.27, 51.51, 44.42, 38.97, and 32.85 MPa, respectively.(2)With the increase of SAP content, the bond strength of HSC with SAP content first increases and then decreases. The bond strength of concrete with SAP content of 0, 0.1%, 0.2%, 0.3%, and 0.8% are, respectively, 36.76, 40.04, 34.56, 31.41, and 27.48 MPa.(3)The bond strength of HSC mixed with SAP increases with the increase of its compressive strength, and a prediction model of the bond strength of SAP concrete is established.(4)The slip corresponding to bond strength of HSC mixed with SAP decreases with the increase of compressive strength, and the prediction model of slip corresponding to bond strength of concrete mixed with SAP is established.(5)A prediction model of stressslip relationship between steel bars and HSC mixed with SAP was established, which was in good agreement with the experimental data and could be used to estimate the stressslip relationship of HSC mixed with different SAP content.
5. Future Work
In this paper, compression and bond strength for HSC with various SAP content were determined from pullout tests. The results presented can be utilized for determining the amount of SAP addition in engineering applications. Also, the slipstress relationship developed in this study can be incorporated into the finite element analysis for structures. In addition, the slipstress curve was developed for 50 MPa compression strength HSC. The reason of not being able to obtain the descending portion after the ultimate bonding stress can be attributed to the high bond strength between HSC and the rebar. In the future, the bond strength for normal strength concrete should be compared with this study.
Data Availability
The research data used to support the findings of this study are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
References
 ACI Committee 363, 363R10 Report on HighStrength Concrete, American Concrete Institute, Indianapolis, IN, USA, 2010.
 D. Shen, M. Wang, Y. Chen, W. Wang, and J. Zhang, “Prediction of internal relative humidity in concrete modified with super absorbent polymers at early age,” Construction and Building Materials, vol. 149, pp. 543–552, 2017. View at: Publisher Site  Google Scholar
 D. P. Bentz, M. A. Peltz, and J. Winpigler, “EarlyAge properties of cementbased materials. II: influence of watertocement ratio,” Journal of Materials in Civil Engineering, vol. 21, no. 9, pp. 512–517, 2009. View at: Publisher Site  Google Scholar
 D. Shen, J. Jiang, W. Wang, J. Shen, and G. Jiang, “Tensile creep and cracking resistance of concrete with different watertocement ratios at early age,” Construction and Building Materials, vol. 146, pp. 410–418, 2017. View at: Publisher Site  Google Scholar
 D. J. Shen, K. Q. Liu, Y. Ji, H. F. Shi, and J. Y. Zhang, “Early age residual stress and stress relaxation of fly ash highperformance concrete,” Magazine of Concrete Research, vol. 72, no. 2, 2017. View at: Google Scholar
 A. Bentur, S.I. Igarashi, and K. Kovler, “Prevention of autogenous shrinkage in highstrength concrete by internal curing using wet lightweight aggregates,” Cement and Concrete Research, vol. 31, no. 11, pp. 1587–1591, 2001. View at: Publisher Site  Google Scholar
 D. Shen, J. Jiang, Y. Jiao, J. Shen, and G. Jiang, “Earlyage tensile creep and cracking potential of concrete internally cured with prewetted lightweight aggregate,” Construction and Building Materials, vol. 135, pp. 420–429, 2017. View at: Publisher Site  Google Scholar
 J. Liu, C. Shi, X. Ma, K. H. Khayat, J. Zhang, and D. Wang, “An overview on the effect of internal curing on shrinkage of high performance cementbased materials,” Construction and Building Materials, vol. 146, pp. 702–712, 2017. View at: Publisher Site  Google Scholar
 T. J. Barrett, I. De la Varga, and W. J. Weiss, “Reducing cracking in concrete structures by using internal curing with high volumes of fly ash,” Structures Congress, vol. 46, pp. 699–707, 2012. View at: Google Scholar
 X.M. Kong, Z.L. Zhang, and Z.C. Lu, “Effect of presoaked superabsorbent polymer on shrinkage of highstrength concrete,” Materials and Structures, vol. 48, no. 9, pp. 2741–2758, 2015. View at: Publisher Site  Google Scholar
 D. Shen, J. Jiang, M. Zhang, P. Yao, and G. Jiang, “Tensile creep and cracking potential of high performance concrete internally cured with super absorbent polymers at early age,” Construction and Building Materials, vol. 165, pp. 451–461, 2018. View at: Publisher Site  Google Scholar
 J. Schlitter and T. J. Barrett, “Restrained shrinkage behavior due to combined autogenous and thermal effects in mortars containing super absorbent polymer (SAP),” in Proceedings of the International RILEM Conference on Use of Superabsorbent Polymers and Other New Additives in Concrete, pp. 233–242, Lyngby, Denmark, August 2010. View at: Google Scholar
 D. Shen, X. Wang, D. Cheng, J. Zhang, and G. Jiang, “Effect of internal curing with super absorbent polymers on autogenous shrinkage of concrete at early age,” Construction and Building Materials, vol. 106, pp. 512–522, 2016. View at: Publisher Site  Google Scholar
 L. Dudziak and V. Mechtcherine, “Enhancing earlyage resistance to cracking in highstrength cementbased materials by means of internal curing using super absorbent polymers. Additions improving properties of concrete,” RILEM Proceedings Pro, vol. 77, pp. 129–139, 2010. View at: Google Scholar
 O. M. Jensen and P. Lura, “Techniques and materials for internal water curing of concrete,” Materials and Structures, vol. 39, no. 9, pp. 817–825, 2006. View at: Publisher Site  Google Scholar
 O. M. Jensen and P. F. Hansen, “Waterentrained cementbased materials,” Cement and Concrete Research, vol. 31, no. 4, pp. 647–654, 2001. View at: Publisher Site  Google Scholar
 O. M. Jensen and P. F. Hansen, “Waterentrained cementbased materials,” Cement and Concrete Research, vol. 32, no. 6, pp. 973–978, 2002. View at: Publisher Site  Google Scholar
 S. Mönning and P. Lura, “Superabsorbent polymers–an additive to increase the freezethaw resistance of high strength concrete,” in Advances in Construction Materials, C. U. Grosse, Ed., pp. 351–358, Springer, Berlin, Germany, 2007. View at: Google Scholar
 L. Faping and L. Jiesheng, “Study on the properties and mechanism of mortars modified by super absorbent polymers,” Journal of Testing and Evaluation, vol. 47, no. 2, pp. 1516–1532, 2019. View at: Publisher Site  Google Scholar
 H. AzariJafari, A. Kazemian, M. Rahimi, and A. Yahia, “Effects of presoaked super absorbent polymers on fresh and hardened properties of selfconsolidating lightweight concrete,” Construction and Building Materials, vol. 113, pp. 215–220, 2016. View at: Publisher Site  Google Scholar
 A. Mignon, D. Snoeck, D. Schaubroeck et al., “pHresponsive superabsorbent polymers: a pathway to selfhealing of mortar,” Reactive and Functional Polymers, vol. 93, pp. 68–76, 2015. View at: Publisher Site  Google Scholar
 D. Snoeck, D. Schaubroeck, P. Dubruel, and N. De Belie, “Effect of high amounts of superabsorbent polymers and additional water on the workability, microstructure and strength of mortars with a watertocement ratio of 0.50,” Construction and Building Materials, vol. 72, pp. 148–157, 2014. View at: Publisher Site  Google Scholar
 S. AlHubboubi, T. alAttar, H. AlBadry, S. Abood, R. Mohammed, and B. Haddhood, “Performance of superabsorbent polymer as an internal curing agent for selfcompacting concrete,” MATEC Web of Conferences, vol. 162, Article ID 02023, 2018. View at: Publisher Site  Google Scholar
 A. J. Klemm and K. S. Sikora, “The effect of superabsorbent polymers (SAP) on microstructure and mechanical properties of fly ash cementitious mortarsfly ash cementitious mortars,” Construction and Building Materials, vol. 49, pp. 134–143, 2013. View at: Publisher Site  Google Scholar
 X. Bian, L. Zeng, Y. Deng, and X. Li, “The role of superabsorbent polymer on strength and microstructure development in cemented dredged clay with high water content,” Polymers, vol. 10, no. 10, p. 1069, 2018. View at: Publisher Site  Google Scholar
 P. Lura, O. M. Jensen, and S.I. Igarashi, “Experimental observation of internal water curing of concrete,” Materials and Structures, vol. 40, no. 2, pp. 211–220, 2007. View at: Publisher Site  Google Scholar
 H. Zhu, Z. Wang, J. Xu, and Q. Han, “Microporous structures and compressive strength of highperformance rubber concrete with internal curing agent,” Construction and Building Materials, vol. 215, pp. 128–134, 2019. View at: Publisher Site  Google Scholar
 B. P. Hughes and C. Videla, “Design criteria for earlyage bond strength in reinforced concrete,” Materials and Structures, vol. 25, no. 8, pp. 445–463, 1992. View at: Publisher Site  Google Scholar
 R. A. Chapman and S. P. Shah, “Earlyage bond strength in reinforced concrete,” ACI Materials Journal, vol. 84, no. 6, pp. 501–510, 1988. View at: Google Scholar
 X. Song, Y. Wu, X. Gu, and C. Chen, “Bond behaviour of reinforcing steel bars in early age concrete,” Construction and Building Materials, vol. 94, pp. 209–217, 2015. View at: Publisher Site  Google Scholar
 X. L. Tang, Y. H. Qin, and W. J. Qu, “Experimental study on timevarying regularity of compressive and bond strength of concrete at earlyage,” Journal of Building Materials and Structures, vol. 30, no. 4, pp. 145–150, 2009. View at: Google Scholar
 X. Fu and D. D. L. Chung, “Decrease of the bond strength between steel rebar and concrete with increasing curing age 11 Communicated by D.M. Roy,” Cement and Concrete Research, vol. 28, no. 2, pp. 167–169, 1998. View at: Publisher Site  Google Scholar
 C. O. Orangun, J. O. Jirsa, and J. E. Breen, “A revaluation of test data on development length and splices,” Journal of ACI, vol. 74, no. 3, pp. 114–122, 1977. View at: Google Scholar
 D. Darwin, M. L. Tholen, E. K. Idun, and J. Zuo, “Splice strength of high relative rib area reinforcing bars,” American Concrete Institute Structural Journal., vol. 93, no. 1, pp. 95–107, 1996. View at: Google Scholar
 ACI Committee 408, Bond and Development of Straight Reinforcing Bars in Tension, ACI 408R03, American Concrete Institute, Indianapolis, IN, USA, 2003.
 R. Eligehausen, E. P. Popov, and V. V. Bertero, Local Bond Stress–Slip Relationships of Deformed Bars under Generalized Excitations, University of California, Berkeley, CL, USA, 1983.
 M. R. Esfahani and B. V. Rangan, “Bond between normal strength and high strength concrete (HSC) and reinforcing bars in splices in beams,” ACI Structural.Journal, vol. 95, no. 3, pp. 272–280, 1998. View at: Google Scholar
 M. N. S. Hadi, “Bond of high strength concrete with high strength reinforcing steel∼!20080724∼!20081028∼!20081126∼!,” The Open Civil Engineering Journal, vol. 2, no. 1, pp. 143–147, 2008. View at: Publisher Site  Google Scholar
 J. Zuo and D. Darwin, “Splice strength of conventional and high relative rib area bars in normal and highstrength concrete,” ACI Structural Journal, vol. 97, no. 4, pp. 630–641, 2000. View at: Google Scholar
 J.Y. Lee, T.Y. Kim, T.J. Kim et al., “Interfacial bond strength of glass fiber reinforced polymer bars in highstrength concrete,” Composites Part B: Engineering, vol. 39, no. 2, pp. 258–270, 2008. View at: Publisher Site  Google Scholar
 R. Okelo and L. R. Yuan, “Bond strength of fiber reinforced polymer rebars in normal strength concrete,” Journal of Composites for Construction, vol. 9, no. 3, pp. 203–213, 2014. View at: Google Scholar
 D. Shen, X. Shi, H. Zhang, X. Duan, and G. Jiang, “Experimental study of earlyage bond behavior between high strength concrete and steel bars using a pullout test,” Construction and Building Materials, vol. 113, pp. 653–663, 2016. View at: Publisher Site  Google Scholar
 Comité EuroInternational du Béton (CEBFIP), in CEBFIP Model Code 2010, in First Completed Draft, , Comité EuroInternational du Béton, Lausanne, Switzerland, 2010.
 China Ministry of Construction, Chinese Standard GB 500102010, Code for Design of Concrete Structures, China Ministry of Construction, Beijing, China, 2010.
 M. H. Harajli, M. Hout, and W. Jalkh, “Local bond stress–slip behavior of reinforcing bars embedded in plain and fiber concrete,” ACI Materials Journal, vol. 92, no. 4, pp. 343–353, 1995. View at: Google Scholar
 M. Harajli, B. Hamad, and K. Karam, “Bondslip response of reinforcing bars embedded in plain and fiber concrete,” Journal of Materials in Civil Engineering, vol. 14, no. 6, pp. 503–511, 2002. View at: Publisher Site  Google Scholar
 Y. L. Xu and W. D. Shen, “Experimental study of bond behavior of reinforced concrete,” Journal of Building Materials and Structures, vol. 15, no. 3, pp. 26–37, 1994. View at: Google Scholar
 J. M. Alsiwat and M. Saatcioglu, “Reinforcement anchorage slip under monotonic loading,” Journal of Structural Engineering, vol. 118, no. 9, pp. 2421–2438, 1992. View at: Publisher Site  Google Scholar
 E. Cosenza, G. Manfredi, and R. Reallfonzo, “Analytical modeling of bond between FRP reinforcing bars and concrete,” in Proceedings of the 2nd International RILEMS Ymposium, pp. 164–171, London, UK, August 1995. View at: Google Scholar
 B. Tighiouart, B. Benmokrane, and D. Gao, “Investigation of bond in concrete member with fibre reinforced polymer (FRP) bars,” Construction and Building Materials, vol. 12, no. 8, pp. 453–462, 1998. View at: Publisher Site  Google Scholar
 J. Y. Lee, C. K. Yi, Y. G. Cheong, and B. I. Kim, “Bond stressslip behaviour of two common GFRP rebar types with pullout failure,” Magazine of Concrete Research, vol. 64, no. 7, pp. 575–591, 2012. View at: Publisher Site  Google Scholar
 ASTM, Standard Specification for Lightweight Aggregate for Internal Curing of Concrete, ASTM International, West Conshohocken ,PA, USA, 2013.
 RILEM/CEB/FIP, Recommendations on Reinforcement Steel for Reinforced Concrete, CEB News, Lausanne, Switzerland, 1983.
Copyright
Copyright © 2020 Xiao Lei et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.