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Materials 2019, 12(23), 4000; https://doi.org/10.3390/ma12234000

Article
Experimental Investigation on the Impact Resistance of Carbon Fibers Reinforced Coral Concrete
1
College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China
2
Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education, Nanning 530004, China
*
Authors to whom correspondence should be addressed.
Received: 25 October 2019 / Accepted: 29 November 2019 / Published: 2 December 2019

Abstract

:
In this study, the impact resistance of coral concrete with different carbon fiber (CF) dosages subjected to drop-weight impact test was investigated. For this purpose, three concrete strength grades (C20, C30, C40) and six CF dosages (0.0%, 0.3%, 0.6%, 1.0%, 1.5%, and 2.0% by weight of the binder) were considered, and a total of 18 groups of carbon fibers reinforced coral concrete (CFRCC) were cast. For each group, eight specimens were tested following the drop-weight impact test suggested by CECS 13. Then, the two-parameter Weibull distribution theory was adopted to statistically analyze the variations in experimental results. The results indicated that the addition of CFs could transform the failure pattern from obvious brittleness to relatively good ductility and improve the impact resistance of coral concrete. Moreover, the impact resistance of CFRCC increases with the CF dosage increasing. The statistical analysis showed that the probability distribution of the blow numbers at the initial crack and final failure of CFRCC approximately follows the two-parameter Weibull distribution.
Keywords:
coral concrete; carbon fibers; impact resistance; drop-weight impact test; Weibull distribution

1. Introduction

The ocean is an essential space for the sustainable development of whole humans due to its abundant resources [1]. Recently, with the rapid development of society, the development and utilization of marine resources and the development of marine industry have received extensive attention [2,3]. Therefore, there are more and more island construction projects, which have led to a significant increase in demand for marine concrete [4,5]. In addition, the utilization of locally available resources on islands as materials to mix concrete has essential practical significance because it can solve the shortage of construction materials problem, shorten the construction period, and reduce costs for distant island reef construction projects [1,6,7].
On the tropic islands, there are abundant coral reef resources [8]. Thus, the coral reef is a desired material for mixing marine concrete. Extensive researches have shown that it is feasible to use coral as the raw material of marine concrete [4,6,9,10,11]. Researchers call this concrete, which uses coral as aggregates, coral concrete [4,6,12]. Many researchers have conducted research on the various properties of coral concrete, such as the compressive strength [13,14,15], the tensile strength [3,5,16], the elastic modulus [17,18,19], the durability [12,18,20], etc. However, the impact performance of coral concrete under impact loading has been rarely studied [21].
The impact resistance is recognized today as one of the significant properties of concrete used for civil engineering [22]. Many concrete elements may be subjected to low-velocity impact loads such as road pavements, breakwater, and precast concrete piles [21,23]. Therefore, it is especially important to understand and improve the impact resistance performance of coral concrete. Some studies indicated that the addition of fibers (such as steel fibers, polypropylene fibers, carbon fibers) could improve the impact resistance of concrete [24,25,26,27]. For example, Mastali et al. [27] found that, when incorporating carbon fibers (CFs) with a length of 30 mm and a volume fraction of 2.0%, the impact resistance of concrete at initial crack and ultimate crack can be increased to 3 and 5 times that of the reference specimen, respectively. Recently, the application of CFs in concrete is more and more extensive due to its high corrosion resistance, low density, high tensile strength, and high elastic modulus [28,29,30,31]. Thus, in the present study, CFs are chosen as the enhancement material to enhance the impact resistance of coral concrete.
Several test methods, including explosive test, projectile test, Charpy pendulum test, split Hopkinson pressure bar (SHPB) test, and drop-weight impact test, have been suggested to study the impact resistance performance of fibers reinforced concrete [24,32,33,34,35]. Among them, the explosive test and projectile test are usually used for high-velocity impact test; the Charpy pendulum test, split Hopkinson pressure bar (SHPB) test, and drop-weight impact test can be used for low-velocity impact test, but the test devices for Charpy pendulum test and SHPB test are expensive, and the test steps are also complicated; the device for drop-weight impact test is not expensive and the test steps are also simple. Thus, the drop-weight impact test method has been widely adopted to low-velocity impact experiments by many researchers [24,26,36]. Thus, the drop-weight impact test method is also selected as the test method for studying the impact resistance performance of carbon fibers reinforced coral concrete (CFRCC) in this study.
The purpose of the present study is to investigate the impact resistance performance of CFRCC under impact loading. For this purpose, a total of eighteen CFRCC mixtures with three strength grades (C20, C30, C40) and six CF dosages (0.0%, 0.3%, 0.6%, 1.0%, 1.5%, 2.0% by weight of the binder) were designed. Through the drop-weight impact test, the failure patterns, the blow numbers and impact energy at the initial crack and final failure of CFRCC were obtained. Based on the experimental results, the effect of CFs and concrete strength grade on the impact resistance of CFRCC was analyzed. Moreover, a statistical analysis was conducted to analyze the experimental results by the two-parameter Weibull distribution theory. The results of this study help extend the use of CFRCC and further understanding of the nature of the impact behavior of coral concrete.

2. Materials and Methods

2.1. Raw Materials

The binder was GB175 [37] Ordinary Portland P.O. 42.5 cement. Coral sand with a fineness modulus of 3.0 was used as the fine aggregates (Figure 1), while crushed coral stones (Figure 2) were used as coarse aggregates. Table 1 and Table 2 showed the physical properties of those aggregates tested according to the code GB/T 17431 [38] (similar to the code of ASTM C330) and JGJ 52 [39] (similar to the code of ASTM C33), respectively. The chopped CFs (Figure 3) with a length of 10 mm and a diameter of 7.3 μm were used in this study, which have an elastic modulus of 231 GPa, a tensile strength of 4558 MPa, an elongation at break of 2.05%, and a density of 1820 kg/m3. In order to obtain a good dispersion of CFs in the mixtures, hydroxypropyl methylcellulose (HPMC) and AGITAN P803 were used as dispersing agent and antifoaming agent, respectively. A QS-8020H Polycarboxylate Superplasticizer (SP) was used to enhance the workability. The mixing water was seawater taken from the sea in Guangxi Beibu Gulf.

2.2. Mix Proportions and Specimen Preparation

The designed strength grades of CFRCC without CF addition were C20, C30, and C40, respectively. The basic mix proportions were designed according to JGJ 51 [40] and presented in Table 3. The CFs dosage were 0.0%, 0.3%, 0.6%, 1.0%, 1.5%, 2.0% by weight of the binder (cement). The usage of HPMC and P803 was 0.4% and 0.15% by weight of the binder, respectively. Some studies [13,41,42] pointed out that preparation of coral concrete with pre-wetted coral coarse aggregates is beneficial for improving the compressive strength, improving the workability, reducing the self-shrinkage and dry shrinkage of coral concrete. Thus, the coral coarse aggregates have been pre-wetted before mixing. The procedure of mixing CRFCC is illustrated in Figure 4. After the uniform mixture was obtained, the stirred mixture was cast in molds and vibrated for about 30 s on a vibration table. For each mixture, three 100 mm × 100 mm × 100 mm cubes and two 150 mm × 300 mm cylinders were cast. All cast specimens were cured at room temperature for 24 h, then demolded and cured in a marine environment curing cabinet for 28 d. The marine environment curing cabinet has a seawater spray device and several related sensors that can simulate the humidity of the real marine environment. Then, cube specimens conducted the cube compressive strength test following the code GB/T50081 [43] (similar to the code of ASTM C33, but the specimen used is cube specimen instead of cylindrical specimen) to obtain the cube compressive strength of each CFRCC mixtures (see Table 4), and each cylindrical specimen was cut into four discs of 150 mm × (63 ± 2) mm for the drop-weight impact test.

2.3. Impact Tests

The impact test was conducted following the China CECS 13 [34] drop-weight impact test that was modified from the ACI 544 [44] suggested method. The details of the drop-weight impact test setup are illustrated in Figure 5. As shown in Figure 5, a steel hammer with a mass of 4.5 kg drops from a height of 500 mm on a steel ball with a diameter of 63 mm located on the central surface of the disc specimens. The number of blows causing the first visible crack was recorded as the initial crack resistance factor (N1), and the number of blows until the pieces of specimen touching three of the four steel lugs was recorded as the final failure resistance factor (N2). For each mixture, eight discs were tested, and the impact resistance was represented based on the average of eight specimens. The impact energy at initial crack and final failure were calculated by using the following equation:
W i = N i × 1 2 × m × v 2 = N i m g h ,
where W i is the impact energy (J); N i is the number of blows; m is the weight of steel hammer with a mass of 4.5 kg; v is the velocity of the steel hammer (m/s); g is the acceleration of gravity (9.81 m/s2); h is the falling height of the steel hammer (500 mm); and i = 1, 2 is representing the initial crack and final failure, respectively.

3. Results and Discussion

3.1. Failure Patterns under Impact

After drop-weight impact tests, the failure patterns of part of the specimens with and without CFs are shown in Figure 6. As expected, for all the specimens without CFs, when the first visible crack appears, the specimens suddenly broke down into two pieces and showed an obviously brittle failure behavior. For the specimens with CFs at a low level, its failure pattern is similar to the specimens without CFs, but some specimens broke down into three pieces (Figure 6b). For the specimens with CFs at a high level, after the first visible crack appears, the specimen can continue to bear the impact loads, and finally break into two or three or four pieces (Figure 6c,d). It is worth noting that no matter whether the dosage of CFs is high or low, the specimens will eventually be wholly separated into several parts, which is similar to the basalt fibers reinforced concrete [45] but different from the impact failure phenomenon—the specimen still remains intact—of steel fibers reinforced concrete, macro polypropylene fibers reinforced concrete, NiTi-SMA fibers reinforced concrete, and polypropylene fibers reinforced concrete [21,36,46]. The reason is that the diameter of CFs is only 7.3 μm, and the elongation at the break of CFs is no greater than 2.05%; when CFs are added into coral concrete, there are tens of millions of micro CFs that exist in the coral concrete matrix, and almost all the microcracks have micro CFs, which can restrain the microcracks propagation and hence enhance the impact performance of CFRCC at the microcrack stage, but many CFs have been broken or pulled out at macrocracks stage, so the CFs mainly act in the microcrack stage, and have less hindrance effect on large cracks. Moreover, with the strength grade and CF dosage increasing, a more profound impact pit and more debris were observed at the central surface of the specimen when the specimen fails.
Figure 7 shows the fracture surface of part of the specimens after repeated drop-weight impact tests. It can be seen that, when the concrete strength grade is C20, there is a small amount of coral coarse aggregates broken (see Figure 7a), but almost all coral coarse aggregates broke (see Figure 7c) when the concrete strength grade is raised to C40. It can be concluded that the fracture rate of coral aggregates on the fracture surface increases with the increase of concrete strength grade. This phenomenon can be attributed to the relatively low strength of the coral coarse aggregates and the excellent bonding properties between the coral coarse aggregates and the cement matrix due to the rough surface morphology of the coral coarse aggregates [47].

3.2. Effect of CFs on the Impact Resistance

Table 5 summarizes the drop-weight impact test results for all the CFRCC mixtures (the detailed results of each specimen see Appendix A Table A1) where an increase in the number of post-first crack blow (INPB) is introduced, and the INPB is calculated as follows:
I N P B = N 2 N 1 ,
where N1 and N2 are representing the number of blows at initial crack and final failure, respectively.
For the specimens of CC20C00, the first crack impact energy (W1) equals the failure impact energy (W2). For the specimens of CC30C00 and CC40C00, the failure impact energy (W2) is only 2 J and 6 J more than the first crack impact energy (W1). That is to say, when the first visible crack appears, the final failure of the specimen will occur at the same time, and the specimens without CFs show distinct brittle behavior.
Figure 8 shows the effect of CFs dosage on the impact energy at first crack (W1) and final failure (W2) of CFRCC of three strength grades. It is easily found from the Figure 8 that adding CFs in coral concrete can improve the first impact energy and the final failure impact energy, and further improvement was recorded for the final failure impact energy, as compared to the first impact energy. With the increasing of additional CFs in coral concrete, the increase percentage of W1 and W2 is also increasing. In other words, the addition of CFs in coral concrete can improve both the initial crack and ultimate failure impact resistances of CFRCC, and its improvement increases with the increase of CF dosage.
Figure 9 exhibits the effect of CFs dosage on the INPB and INPB/N1 of three strength grades’ CFRCC. In Figure 9, there is a clear trend of INPB and INPB/N1 increasing with the increasing of CFs dosage. With the increasing of concrete strength grade, the INPB is also increasing while the INPB/N1 decreases. It must be noted that, even with a CF dosage of 2.0%, INPB is also small, only 3.3, 4.8, and 6.1 for C20, C30, and C40, respectively, and the INPB/N1 for all the mixture is no more than 14%. Mastali et al. [27] conducted the drop-weight impact test on CF reinforced self-compacting concrete and obtained similar results. That is to say, the improvement effect of CFs on the impact resistance of specimens after cracking is not apparent, which is obviously different from the test results of steel fibers reinforced concrete and macro PP fibers reinforced concrete obtained by Zhang, Rahmani, Ding, and Murali et al. [36,48,49,50]. The explanation for this is that the steel fibers are macro fibers (the diameter is generally higher than 0.4 mm) and have a relatively large elongation at break (more than 3.5%), so the steel fibers can play an excellent bridging role in macrocracks after the first visible crack appeared of specimens. However, the CFs have a diameter of only 7.3 μm and an elongation at break of only 2.05%, so the CFs mainly play a positive role in microcracks and a less positive role in macrocracks under the drop-weight impact test. The previous research data [26,50,51] also clearly indicated that, in the drop-weight impact test, the larger the diameter of fiber and elongation at break is, the larger the INPB will be, when other conditions are the same.

3.3. Effect of Concrete Strength Grade on the Impact Resistance

As shown in Figure 10, the impact energy at first crack (W1) and final failure (W2) and strength grade is approximately in a linear relationship, which indicates that, for CFRCC, the higher the concrete strength grade is, the higher the impact resistance will be. For polypropylene fibers reinforced coral concrete, Wang et al. [21] also reached a similar conclusion.

3.4. Correlation between Cube Compressive Strength, CFs Dosage, and Impact Energy

After regression analysis, it is found that the effect of CFs dosage and cube compressive strength on the impact resistance of CFRCC can be illustrated by Equation (3):
W 1 ( W 2 ) = ( a + b   f c u 1.5 ) ( c + d   ρ c 1.2 ) ,
where W1 and W2 are the impact energy at the first visible crack and final failure, respectively (J); fcu is the cube compressive strength (MPa); ρc is the CFs dosage (%); a, b, c, and d are fitting parameters.
The fitting results of Equation (3) to test data are presented in Table 6, Figure 11, and Figure 12. It can be seen that the standardized residuals of most of the points are in the range of −2 to 2, and the Adjusted R2 are 0.995 and 0.996 for W1 and W2, respectively, which indicates that Equation (3) fits the experimental data well. Moreover, Figure 11c and Figure 12c also indicate that the fitting values are very close to the experimental values.

4. Distribution of Impact Resistance Factors

Over the past few decades, several statistical models have been employed for analysis of the variations in impact test results of concrete [36,46,49,50,52,53,54,55,56]. Among them, the normal distribution model is widely used. However, many researchers [54,56] pointed out that the impact test results exhibited poor fitness with normal distribution at a 95% confidence level. By contrast, the two-parameter Weibull distribution has been proved by some researchers [36,46,50] that it is appropriate to evaluate the impact performance of concrete under impact. Therefore, for analyzing the variations in the impact resistance of CFRCC under drop-weight impact test, the two-parameter Weibull distribution is employed in this study.
According to [46], the expression of the cumulative distribution function F(x) of two-parameter Weibull probability law is as follows:
F ( x ) = 1 exp [ ( x x 0 λ ) k ] ,
where x is the impact life of the concrete; k is the shape parameter; λ is the scale parameter; x0 is the minimum impact life of concrete and assumed to be 0 in this study.
The function F(x) denotes the failure probability of concrete under impact loading. Thus, the probability estimator L(x) may be defined as:
L ( x ) = 1 F ( x ) = exp [ ( x x 0 λ ) k ] ,
Take x0 = 0 and the natural logarithm twice on both sides of Equation (5) to get:
ln ln 1 L ( x ) = k ln x k ln λ .
Thus, Equation (6) can be used to verify whether the impact resistance factors (N1, and N2) of CFRCC follow the two-parameter Weibull distribution. Since Equation (6) represents a linear relationship between ln ln (1/L(x)) and ln x, if an appropriately linear relationship between ln ln (1/L(x)) and ln x is observed from the test results, the conclusion that using two-parameter Weibull distribution to characterize the statistical distribution of impact test results of CFRCC is feasible can be conducted. In order to verify whether there is an appropriately linear relationship between ln (1/L(x)) and ln x, first, the impact results (N1, and N2) are arranged in an descending order, and then the probability estimator is assumed and the linear regression analysis is performed.
Many probability estimators have been used in previous studies and Murali et al. [50] summarized twenty probability estimators used in previous papers. It can be seen from the summaries of Murali [50] that there are two expression forms of the probability estimator:
L ( x ) = j + α n + β ,
L ( x ) = 1 j + α n + β ,
where j is the sequence number of the impact failure specimen; n is the total number of the impact specimens for each mixture; α and β are constants.
After trial calculating the test results with Equations (7) and (8), Equation (7) is chosen as the recommended probability estimator in this study, and the values of α and β are −0.6, and 0.9, respectively. Figure 13 shows the distribution of the impact resistance factor (N1, and N2) of each CFRCC mixture and the corresponding fitted curves, and Table 7 gives the detailed linear regression results. Rahmani et al. [49] pointed out that a R2 of 0.7 or higher is sufficient for establishing a reasonable reliability model. Since the appropriately linear relationship plot in Figure 13 and all the impact test results have Adjusted R2 equal to or higher than 0.837, the two-parameter Weibull distribution is considered suitable for establishing the statistical distribution of impact test data of coral concrete incorporating CFs. These developed reliability curves are highly suitable as a useful tool to quickly investigate the impact resistance of CFRCC, thereby eliminating the necessity of time-consuming impact testing process. Some previous studies [36,46,49,50] have drawn similar conclusions for other types of fibers reinforced concrete.
According to Equations (5) and (6), the number of blows (N1, N2) of CFRCC at the corresponding failure probability P can be derived as follows:
N = x = 1 k ln ln 1 1 P + ln λ ,
where P is the failure probability.
Figure 14 shows the N2 of CFRCC acquired by reliability analysis at different failure probability. It is easy to note that the impact resistance performance of CFRCC increases approximately linearly with the CF dosage increasing at the same failure probability.
As an example of verifying whether the two-parameter Weibull distribution recommended in this study is also suitable to evaluate the impact performance of other fibers reinforced concrete, the test results of Ding et al. [36] for macro polypropylene fibers and steel fibers reinforced concrete are also analyzed by using Equations (6) and (7), and the regression analysis results are given in Table 8. From Table 8, it can be seen that the Adjusted R2 of each mixture is no less than 0.833, which indicates that the two-parameter Weibull distribution recommended in this study is also suitable to evaluate the impact performance of other types of fibers reinforced concrete.

5. Conclusions

In this study, the impact resistance of CFRCC under impact loading was investigated by conducting the drop-weight impact test. Based on the experimental results and regression analysis, the main conclusions can be drawn as follows:
(1)
The addition of CFs into coral concrete changed the failure pattern of coral concrete specimens under impact loading from obvious brittleness to relatively good ductility.
(2)
CF addition can improve the impact resistance at initial crack and final failure of coral concrete. Still, the improvement of the impact resistance after initial cracking due to the addition of CFs is not as significant as steel fibers.
(3)
The impact resistance of CFRCC increases with the increase of CF dosage and concrete strength grade.
(4)
The impact energy (W1, and W2) of CFRCC can be evaluated by the cube compressive strength and CFs dosage using Equation (3).
(5)
The two-parameter Weibull distribution theory is proved capable of adequately representing the impact test results, and these developed reliability curves through the two-parameter Weibull distribution theory can be considered a useful tool to investigate the impact resistance of CFRCC quickly.

Author Contributions

B.L. and Z.D. designed the research; B.L., J.Z., X.W., J.G., and X.Z. performed the research; B.L. analyzed the data and wrote the paper; Z.D. and H.W. performed review and editing. All authors read and approved the final manuscript.

Funding

This research was funded by the National Natural Science Foundation of China, Grant Nos. 51868005, 51478126; the Guangxi Natural Science Foundation Program, Grant No. 2018GXNSFAA050133; the “College Students Innovation and Entrepreneurship Training Program” of Guangxi University, Grant No. 201910593161, the Innovation Project of Guangxi Graduate Education.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

Table A1. The detail drop-weight impact test results of each specimen.
Table A1. The detail drop-weight impact test results of each specimen.
No.12345678MeanStandard DeviationCoefficient of Variation
CC20C00 N 1 111216111614111313.02.140.16
N 2 111216111614111313.02.140.16
I N P B 000000000.00.000.00
CC20C03 N 1 161116161212141514.02.070.15
N 2 161117171213141614.52.330.16
I N P B 001101010.50.791.59
CC20C06 N 1 131715201515151816.02.200.14
N 2 131816201616161916.82.190.13
I N P B 011011110.80.450.60
CC20C10 N 1 131717192121211618.12.900.16
N 2 141918202222221819.42.770.14
I N P B 121111121.30.340.27
CC20C15 N 1 181818191727302020.94.850.23
N 2 202020211830332323.15.410.23
I N P B 222213332.31.260.56
CC20C20 N 1 222619252023263124.03.850.16
N 2 252921282427303427.33.990.15
I N P B 332344433.30.840.26
CC30C00 N 1 322830252523262626.92.950.11
N 2 322830252623262627.02.880.11
I N P B 000010000.10.282.26
CC30C03 N 1 332926223030412129.06.370.22
N 2 342927243030422129.66.390.22
I N P B 101200100.60.771.22
CC30C06 N 1 284232362927314734.07.170.21
N 2 294332372927324834.67.460.22
I N P B 110100110.60.811.29
CC30C10 N 1 334237444338373939.13.680.09
N 2 354338464442394241.13.560.09
I N P B 211214232.00.950.48
CC30C15 N 1 393838585440534846.08.230.18
N 2 424142625743555049.08.180.17
I N P B 334433223.00.700.23
CC30C20 N 1 514438674663674752.911.260.21
N 2 535141725071705357.611.710.20
I N P B 273548364.82.580.54
CC40C00 N 1 363832425241343739.06.210.16
N 2 363833425242343739.36.110.16
I N P B 001001000.30.361.46
CC40C03 N 1 483054404948303641.99.200.22
N 2 483254414949303642.48.930.21
I N P B 020101000.50.480.96
CC40C06 N 1 285551494155555849.09.990.20
N 2 285752504256575950.110.470.21
I N P B 021111211.11.121.00
CC40C10 N 1 725855536460495257.97.430.13
N 2 735959566663525260.07.170.12
I N P B 114323302.11.090.51
CC40C15 N 1 745172817470656569.08.940.13
N 2 785475847974687172.99.080.12
I N P B 433354363.91.260.33
CC40C20 N 1 928367878590965581.913.880.17
N 2 9991739391961025988.014.590.17
I N P B 786666646.11.830.30

References

  1. Lyu, B.; Wang, A.; Zhang, Z.; Liu, K.; Xu, H.; Shi, L.; Sun, D. Coral aggregate concrete: Numerical description of physical, chemical and morphological properties of coral aggregate. Cem. Concr. Compos. 2019, 100, 25–34. [Google Scholar] [CrossRef]
  2. Yang, S.; Yang, C.; Huang, M.; Liu, Y.; Jiang, J.; Fan, G. Study on bond performance between frp bars and seawater coral aggregate concrete. Constr. Build. Mater. 2018, 173, 272–288. [Google Scholar] [CrossRef]
  3. Wang, Q.; Li, P.; Tian, Y.; Chen, W.; Su, C. Mechanical properties and microstructure of portland cement concrete prepared with coral reef sand. J. Wuhan Univ. Technol. Mat. Sci. Ed. 2016, 31, 996–1001. [Google Scholar] [CrossRef]
  4. Ma, L.; Li, Z.; Liu, J.; Duan, L.; Wu, J. Mechanical properties of coral concrete subjected to uniaxial dynamic compression. Constr. Build. Mater. 2019, 199, 244–255. [Google Scholar] [CrossRef]
  5. Wang, Y.; Zhang, S.; Niu, D.; Su, L.; Luo, D. Effects of silica fume and blast furnace slag on the mechanical properties and chloride ion distribution of coral aggregate concrete. Constr. Build. Mater. 2019, 214, 648–658. [Google Scholar] [CrossRef]
  6. Ehlert, R. Coral Concrete at Bikini Atoll. Concr. Int. 1991, 13, 19–24. [Google Scholar]
  7. Tang, J.; Cheng, H.; Zhang, Q.; Chen, W.; Li, Q. Development of properties and microstructure of concrete with coral reef sand under sulphate attack and drying-wetting cycles. Constr. Build. Mater. 2018, 165, 647–654. [Google Scholar] [CrossRef]
  8. Wang, Y.; Shui, Z.; Gao, X.; Huang, Y.; Yu, R.; Li, X.; Yang, R. Utilizing coral waste and metakaolin to produce eco-friendly marine mortar: Hydration, mechanical properties and durability. J. Clean. Prod. 2019, 219, 763–774. [Google Scholar] [CrossRef]
  9. Liu, J.; Ou, Z.; Peng, W.; Guo, T.; Deng, W.; Chen, Y. Literature review of coral concrete. Arab. J. Sci. Eng. 2018, 43, 1529–1541. [Google Scholar] [CrossRef]
  10. Howdyshell, P.A. The Use of Coral as an Aggregate for Portland Cement Concrete Structures; No. CERL-TR-M-88; Construction Engineering Research Lab (Army): Champaign, IL, USA, June 1974. [Google Scholar]
  11. Dempsey, G. Coral and salt water as concrete materials. J. Proc. 1951, 48, 157–166. [Google Scholar]
  12. Da, B.; Yu, H.; Ma, H.; Tan, Y.; Mi, R.; Dou, X. Chloride diffusion study of coral concrete in a marine environment. Constr. Build. Mater. 2016, 123, 47–58. [Google Scholar] [CrossRef]
  13. Arumugam, R.A.; Ramamurthy, K. Study of compressive strength characteristics of coral aggregate concrete. Mag. Concr. Res. 1996, 48, 141–148. [Google Scholar] [CrossRef]
  14. Shen, J. Experimental study on compressive strength of coral aggregate concrete mixed with seawater. Soil Eng. Found. 2016, 30, 524–526. [Google Scholar]
  15. Wei, Z.; Li, Z.; Shen, J. Research on the influencing factors of performance of coral concrete and its early mechanical property. Ind. Constr. 2017, 47, 130–136. [Google Scholar]
  16. Mi, R.J.; Yu, H.F.; Ma, H.Y.; Da, B.; Yuan, Y.F.; Zhang, X.P.; Zhu, H.W.; Dou, X.M. Study on the mechanical property of coral concrete. Ocean Eng. 2016, 34, 47–54. [Google Scholar]
  17. Da, B.; Yu, H.; Ma, H.; Tan, Y.; Mi, R.; Dou, X. Experimental investigation of whole stress-strain curves of coral concrete. Constr. Build. Mater. 2016, 122, 81–89. [Google Scholar] [CrossRef]
  18. Li, Y.; Zhou, L.; Zhang, Y.; Cui, J.; Shao, J. Study on long-term performance of concrete based on seawater, sea sand and coral sand. Adv. Mater. Res. 2013, 706, 512–515. [Google Scholar] [CrossRef]
  19. Lei, W.; Zujing, X.; Cunkeng, L.; Quanlong, L. Mechanical property tests of coral concrete with polypropylene fiber. Concrete 2014, 7, 96–99. [Google Scholar]
  20. Cheng, S.; Shui, Z.; Sun, T.; Yu, R.; Zhang, G. Durability and microstructure of coral sand concrete incorporating supplementary cementitious materials. Constr. Build. Mater. 2018, 171, 44–53. [Google Scholar] [CrossRef]
  21. Gold, E.; Chao, L.; Lei, W. Experimental study on shock resistance of polypropylene fiber reinforced coral concrete. Sci. Technol. Eng. 2019, 19, 244–248. [Google Scholar]
  22. Zhang, M.H.; Li, L.; Paramasivam, P. Flexural toughness and impact resistance of steel-fibre-reinforced lightweight concrete. Mag. Concr. Res. 2004, 56, 251–262. [Google Scholar] [CrossRef]
  23. Agostinacchio, M.; Ciampa, D.; Olita, S. The vibrations induced by surface irregularities in road pavements—A matlab ® approach. Eur. Transp. Res. Rev. 2014, 6, 267–275. [Google Scholar] [CrossRef]
  24. Naraganti, S.R.; Pannem, R.M.R.; Putta, J. Impact resistance of hybrid fibre reinforced concrete containing sisal fibres. Ain Shams Eng. J. 2019, 10, 297–305. [Google Scholar] [CrossRef]
  25. Mahakavi, P.; Chithra, R. Impact resistance, microstructures and digital image processing on self-compacting concrete with hooked end and crimped steel fiber. Constr. Build. Mater. 2019, 220, 651–666. [Google Scholar] [CrossRef]
  26. Feng, J.; Sun, W.; Zhai, H.; Wang, L.; Dong, H.; Wu, Q. Experimental study on hybrid effect evaluation of fiber reinforced concrete subjected to drop weight impacts. Materials 2018, 11, 2563. [Google Scholar] [CrossRef]
  27. Mastali, M.; Dalvand, A.; Sattarifard, A. The impact resistance and mechanical properties of the reinforced self-compacting concrete incorporating recycled cfrp fiber with different lengths and dosages. Compos. Part B Eng. 2017, 112, 74–92. [Google Scholar] [CrossRef]
  28. Han, B.; Zhang, L.; Zhang, C.; Wang, Y.; Yu, X.; Ou, J. Reinforcement effect and mechanism of carbon fibers to mechanical and electrically conductive properties of cement-based materials. Constr. Build. Mater. 2016, 125, 479–489. [Google Scholar] [CrossRef]
  29. Rodin, H.I.; Rangelov, M.; Nassiri, S.; Englund, K. Enhancing mechanical properties of pervious concrete using carbon fiber composite reinforcement. J. Mater. Civ. Eng. 2018, 30, 040180123. [Google Scholar] [CrossRef]
  30. Li, M.; Yang, Y.; Liu, M.; Guo, X.; Zhou, S. Hybrid effect of calcium carbonate whisker and carbon fiber on the mechanical properties and microstructure of oil well cement. Constr. Build. Mater. 2015, 93, 995–1002. [Google Scholar] [CrossRef]
  31. Han, B.; Wang, Y.; Dong, S.; Zhang, L.; Ding, S.; Yu, X.; Ou, J. Smart concretes and structures: A review. J. Intell. Mater. Syst. Struct. 2015, 26, 1303–1345. [Google Scholar] [CrossRef]
  32. Bentur, A.; Mindess, S. Fibre Reinforced Cementitious Composites; CRC Press: Boca Raton, FL, USA, 2006. [Google Scholar]
  33. Banyhussan, Q.S.; Yıldırım, G.; Anıl, Ö.; Erdem, R.T.; Ashour, A.; Şahmaran, M. Impact resistance of deflection-hardening fiber reinforced concretes with different mixture parameters. Struct. Concr. 2019, 20, 1036–1050. [Google Scholar] [CrossRef]
  34. Standardization, C.A.F.E. Standard Test Methods for Fiber Reinforced Concrete; China Planning Press: Beijing, China, 2009. [Google Scholar]
  35. Pu, W.; Zhen, H.; Dai, Z.; Dong, W.X.; Chang, Z. Impact mechanical properties of concrete reinforced with hybrid carbon fibers. J. Vib. Shock 2012, 31, 14–18. [Google Scholar]
  36. Ding, Y.; Li, D.; Zhang, Y.; Azevedo, C. Experimental investigation on the composite effect of steel rebars and macro fibers on the impact behavior of high performance self-compacting concrete. Constr. Build. Mater. 2017, 136, 495–505. [Google Scholar] [CrossRef]
  37. China, S.A.O.T. Common Portland Cement; China Architecture& Building Press: Beijing, China, 2007. [Google Scholar]
  38. China, S.A.O.T. Lightweight Aggregates and its Test methods—Part 2: Test Methods for Lightweight Aggregates; China Architecture& Building Press: Beijing, China, 2010. [Google Scholar]
  39. China, M.O.C.O. Standard for Technical Requirements and Test Method of Sand and Crushed Stone (or Gravel) for Ordinary Concrete; China Architecture& Building Press: Beijing, China, 2006. [Google Scholar]
  40. China, M.O.C.O. Technical Specification for Lightweight Aggregate Concrete; China Architecture& Building Press: Beijing, China, 2002. [Google Scholar]
  41. Cheng, S.; Shui, Z.; Yu, R.; Sun, T.; Zhang, X. Multiple influences of internal curing and supplementary cementitious materials on the shrinkage and microstructure development of reefs aggregate concrete. Constr. Build. Mater. 2017, 155, 522–530. [Google Scholar] [CrossRef]
  42. Chen, F.; Zhang, G.; Ding, S.; Qing, M. Half-dry coral sand concrete preparation technology under natural conditions. China Harb. Eng. 2017, 37, 68–72. [Google Scholar]
  43. China, M.O.C.O. Standard for Test Method of Mechanical Properties on Ordinary Concrete; China Architecture& Building Press: Beijing, China, 2002. [Google Scholar]
  44. ACI Committee 544. Measurement of Properties of Fiber Reinforced Concrete. Materials Journal 1988, 85, 583–593.
  45. Li, D.; Tao, J.; Jia, B. Experimental study on the effect of impact resistance of basalt fiber reinforced concrete. New Build. Mater. 2012, 39, 47–51. [Google Scholar]
  46. Ali, M.A.E.M.; Soliman, A.M.; Nehdi, M.L. Hybrid-fiber reinforced engineered cementitious composite under tensile and impact loading. Mater. Des. 2017, 117, 139–149. [Google Scholar] [CrossRef]
  47. Wang, J.; Feng, P.; Hao, T.; Yue, Q. Axial compressive behavior of seawater coral aggregate concrete-filled FRP tubes. Constr. Build. Mater. 2017, 147, 272–285. [Google Scholar] [CrossRef]
  48. Zhang, W.; Chen, S.; Liu, Y. Effect of weight and drop height of hammer on the flexural impact performance of fiber-reinforced concrete. Constr. Build. Mater. 2017, 140, 31–35. [Google Scholar] [CrossRef]
  49. Rahmani, T.; Kiani, B.; Shekarchi, M.; Safari, A. Statistical and experimental analysis on the behavior of fiber reinforced concretes subjected to drop weight test. Constr. Build. Mater. 2012, 37, 360–369. [Google Scholar] [CrossRef]
  50. Murali, G.; Asrani, N.P.; Ramkumar, V.R.; Siva, A.; Haridharan, M.K. Impact resistance and strength reliability of novel two-stage fibre-reinforced concrete. Arab. J. Sci. Eng. 2019, 44, 4477–4490. [Google Scholar] [CrossRef]
  51. AbdelAleem, B.H.; Ismail, M.K.; Hassan, A.A.A. The combined effect of crumb rubber and synthetic fibers on impact resistance of self-consolidating concrete. Constr. Build. Mater. 2018, 162, 816–829. [Google Scholar] [CrossRef]
  52. Chen, X.Y.; Ding, Y.N.; Azevedo, C. Combined effect of steel fibres and steel rebars on impact resistance of high performance concrete. J. Cent. South Univ. 2011, 18, 1677–1684. [Google Scholar] [CrossRef]
  53. Arora, S.; Singh, S.P. Analysis of flexural fatigue failure of concrete made with 100% coarse recycled concrete aggregates. Constr. Build. Mater. 2016, 102, 782–791. [Google Scholar] [CrossRef]
  54. Nataraja, M.C.; Dhang, N.; Gupta, A.P. Statistical variations in impact resistance of steel fiber-reinforced concrete subjected to drop weight test. Cem. Concr. Res. 1999, 29, 989–995. [Google Scholar] [CrossRef]
  55. Song, P.S.; Wu, J.C.; Hwang, S.; Sheu, B.C. Assessment of statistical variations in impact resistance of high-strength concrete and high-strength steel fiber-reinforced concrete. Cem. Concr. Res. 2005, 35, 393–399. [Google Scholar] [CrossRef]
  56. Badr, A.; Ashour, A.F.; Platten, A.K. Statistical variations in impact resistance of polypropylene fibre-reinforced concrete. Int. J. Impact Eng. 2006, 32, 1907–1920. [Google Scholar] [CrossRef]
Figure 1. Coral fine aggregates: (a) appearance; (b) grading curve.
Figure 1. Coral fine aggregates: (a) appearance; (b) grading curve.
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Figure 2. Coral coarse aggregates: (a) appearance; (b) grading curve.
Figure 2. Coral coarse aggregates: (a) appearance; (b) grading curve.
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Figure 3. Chopped carbon fibers.
Figure 3. Chopped carbon fibers.
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Figure 4. The process of the mixing method
Figure 4. The process of the mixing method
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Figure 5. The details of the drop-weight impact test setup.
Figure 5. The details of the drop-weight impact test setup.
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Figure 6. The failure patterns of part of specimens: (a) CC30C00; (b) CC30C06; (c) CC30C15; (d) CC20C20.
Figure 6. The failure patterns of part of specimens: (a) CC30C00; (b) CC30C06; (c) CC30C15; (d) CC20C20.
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Figure 7. The fracture surface of part of specimens: (a) C20; (b) C30; (c) C40.
Figure 7. The fracture surface of part of specimens: (a) C20; (b) C30; (c) C40.
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Figure 8. The impact energy at first crack and final failure of specimens with different CFs: (a) C20; (b) C30; (c) C40.
Figure 8. The impact energy at first crack and final failure of specimens with different CFs: (a) C20; (b) C30; (c) C40.
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Figure 9. The INPB of specimens with different CFs: (a) C20; (b) C30; (c) C40.
Figure 9. The INPB of specimens with different CFs: (a) C20; (b) C30; (c) C40.
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Figure 10. Comparison of test value and predicted value of splitting tensile strength: (a) W1; (b) W2.
Figure 10. Comparison of test value and predicted value of splitting tensile strength: (a) W1; (b) W2.
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Figure 11. The fitting results of W1: (a) Standardized Residuals vs. fcu; (b) Standardized Residuals vs. ρc; (c) comparison of test and fitting.
Figure 11. The fitting results of W1: (a) Standardized Residuals vs. fcu; (b) Standardized Residuals vs. ρc; (c) comparison of test and fitting.
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Figure 12. The fitting results of W2: (a) Standardized Residuals vs. fcu; (b) Standardized Residuals vs. ρc; (c) comparison of test and fitting.
Figure 12. The fitting results of W2: (a) Standardized Residuals vs. fcu; (b) Standardized Residuals vs. ρc; (c) comparison of test and fitting.
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Figure 13. Linear regression of N1 and N2 in Weibull distribution: (a) N1; (b) N2.
Figure 13. Linear regression of N1 and N2 in Weibull distribution: (a) N1; (b) N2.
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Figure 14. N2 vs. ρc based on reliability analysis with different failure probability: (a) P = 5%; (b) P = 15%; (c) P = 30%.
Figure 14. N2 vs. ρc based on reliability analysis with different failure probability: (a) P = 5%; (b) P = 15%; (c) P = 30%.
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Table 1. Physical properties of coral coarse aggregates.
Table 1. Physical properties of coral coarse aggregates.
Bulk Density
(kg/m3)
Apparent Density
(kg/m3)
Void Content
(%)
Water   Absorption / % Water Content
(%)
Tube Compressive Strength
(MPa)
Dust Content
(%)
Particle Shape Factor
1 h24 h
9151841508.511.02.63.12.92.4
Table 2. Physical properties of coral fine aggregates.
Table 2. Physical properties of coral fine aggregates.
Bulk Density
(kg/m3)
Apparent Density
(kg/m3)
GraduationFineness ModulusWater
Content   ( % )
Water   Absorption   ( % ) Dust Content
12962707II3.02.93.70.5
Table 3. Coral concrete mix proportions
Table 3. Coral concrete mix proportions
Strength GradeCement
(kg)
Net W/C1Net Water
(kg)
Additional Water
(kg)
Coral Coarse Aggregates (kg)Coral Sand (kg)
CC20C003800.532005.8774674
CC30C004800.381805.8774674
CC40C006500.281805.8774674
1 Net W/C= Net water/Cement.
Table 4. Cube compressive strength.
Table 4. Cube compressive strength.
No.Average
(MPa)
Standard DeviationCoefficient of Variation
CC20C0021.03.080.15
CC20C0321.71.830.08
CC20C0622.91.340.06
CC20C1023.02.020.09
CC20C1524.52.120.09
CC20C2024.70.420.02
CC30C0033.40.910.03
CC30C0333.92.520.07
CC30C0635.23.560.10
CC30C1035.31.560.04
CC30C1536.41.390.04
CC30C2036.64.690.13
CC40C0042.74.910.11
CC40C0344.32.160.05
CC40C0644.71.040.02
CC40C1045.12.030.05
CC40C1546.42.770.06
CC40C2047.52.590.05
Table 5. The drop-weight impact tests results.
Table 5. The drop-weight impact tests results.
No.Average Number of BlowsStandard DeviationCoefficient of Variation W 1 ( J ) W 2 ( J )
N 1 N 2 I N P B σ N 1 σ N 2 σ I N P B C V N 1 C V N 2 C V I N P B
CC20C0013.013.00.02.142.140.000.160.160.00287287
CC20C0314.014.50.52.072.330.790.150.161.59309320
CC20C0616.016.80.82.202.190.450.140.130.60353371
CC20C1018.119.41.32.902.770.340.160.140.27400428
CC20C1520.923.12.34.855.411.260.230.230.56461510
CC20C2024.027.33.33.853.990.840.160.150.26530603
CC30C0026.927.00.12.952.880.280.110.112.26594596
CC30C0329.029.60.66.376.390.770.220.221.22640653
CC30C0634.034.60.67.177.460.810.210.221.29750764
CC30C1039.141.12.03.683.560.950.090.090.48863907
CC30C1546.049.03.08.238.180.700.180.170.2310151082
CC30C2052.957.64.811.2611.712.580.210.200.5411681271
CC40C0039.039.30.36.216.110.360.160.161.46861867
CC40C0341.942.40.59.208.930.480.220.210.96925936
CC40C0649.050.11.19.9910.471.120.200.211.0010821106
CC40C1057.960.02.17.437.171.090.130.120.5112781324
CC40C1569.072.93.98.949.081.260.130.120.3315231609
CC40C2081.988.06.113.8814.591.830.170.170.3018081942
Table 6. Fitting results.
Table 6. Fitting results.
Dependent VariableabcdAdjusted R2
W 1 −32.0351.3062.6010.8480.995
W 2 −26.7911.3262.5100.9750.996
Table 7. Linear regression results of impact resistance in Weibull distribution.
Table 7. Linear regression results of impact resistance in Weibull distribution.
Specimen No.N1N2
kλAdjusted R2 k λ Adjusted R2
CC20C005.382 13.420 0.853 5.382 13.420 0.853
CC20C035.723 14.437 0.874 5.375 14.964 0.926
CC20C066.468 16.454 0.865 6.514 17.227 0.864
CC20C105.190 18.730 0.884 5.593 20.001 0.841
CC20C153.971 21.779 0.881 3.910 23.983 0.894
CC20C205.736 24.720 0.962 6.196 28.027 0.982
CC30C008.318 27.497 0.924 8.507 27.615 0.919
CC30C034.173 30.040 0.946 4.302 30.667 0.950
CC30C064.410 35.203 0.888 4.298 35.869 0.885
CC30C109.444 39.945 0.940 10.241 41.929 0.956
CC30C154.874 47.590 0.849 5.302 50.598 0.858
CC30C204.179 54.810 0.912 4.259 59.766 0.869
CC40C005.878 40.164 0.895 5.954 40.420 0.871
CC40C033.862 43.493 0.908 4.071 43.957 0.927
CC40C065.112 50.648 0.902 4.783 51.757 0.897
CC40C107.251 59.354 0.942 7.689 61.472 0.938
CC40C156.201 71.067 0.848 6.363 75.026 0.837
CC40C204.503 84.860 0.902 4.579 91.076 0.885
Table 8. Linear regression results of impact resistance of Ding et al.’s [36] results in Weibull distribution.
Table 8. Linear regression results of impact resistance of Ding et al.’s [36] results in Weibull distribution.
Specimen No.N1N2
kλAdjusted R2λkAdjusted R2
NC1.24311.6740.9271.24311.6740.927
PP42.18715.1090.7122.72630.8330.865
PP66.89221.9140.9585.35738.4560.952
SF201.13422.0160.9431.35241.7120.958
SF350.86019.9370.9881.38945.2080.899
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