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Article

Influence of NaCl Freeze–Thaw Cycles on the Mechanical Strength of Reactive Powder Concrete with the Assembly Unit of Sulphoaluminate Cement and Ordinary Portland Cement

by
Zhangjie Cai
1 and
Hui Wang
2,3,*
1
Civil Engineering Department, Yancheng Institute of Technology, Yancheng 224051, China
2
School of Civil and Environmental Engineering, Ningbo University, Ningbo 315000, China
3
State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Nanjing 210000, China
*
Author to whom correspondence should be addressed.
Coatings 2021, 11(10), 1238; https://doi.org/10.3390/coatings11101238
Submission received: 13 July 2021 / Revised: 28 September 2021 / Accepted: 1 October 2021 / Published: 12 October 2021
(This article belongs to the Special Issue Interface and Surface Modification for Durable Concretes)
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Abstract

:
The influence of sulphoaluminate cement and the dosage of polypropylene fibers on the basic mechanical strengths (compressive and flexural strengths) of reactive powder concrete (RPC) cured for 1 d, 3 d, 7 d, 14 d and 28 d is studied in this research. The content of sulphoaluminate cement ranges from 0% to 100% and the dosages of polypropylene fibers are 0%~3.5%, respectively. Moreover, the mechanical properties (compressive and flexural strengths), the relative dynamic elastic modulus (RDEM) and the chloride permeability of specimens with 50% sulphoaluminate cement and different dosages of polypropylene fibers are determined after the specimens are exposed to different NaCl freeze–thaw cycles. The water–binder ratio in this study is 0.25, and the sand-to-binder ratio is 1.25. Results show that the relationship between the mechanical strengths of RPC at early curing ages (lower than 7 d) and the sulphoaluminate cement content is a linear function with a positive correlation. However, when the curing age reaches 14 d, the compressive and flexural strengths decrease in the form of a linear function with the addition of sulphoaluminate cement. The correlation between the mechanical strengths and polypropylene fiber volume is a positive quadratic function. However, the mass loss rate and flexural strength loss rate increased in the form of a quadratic function, and RDEM shows a negative quadratic function with the freeze–thaw cycles. Moreover, the compressive strength loss rate increases linearly with the freeze–thaw cycle. The addition of polypropylene fibers can effectively improve the freeze–thaw resistance of cement mortar with an assembly unit of ordinary cement and sulphoaluminate cement.

1. Introduction

Nowadays, large-scale marine concrete constructs (like Hangzhou Bay Bridge, Jiaozhou Bay Bridge, and Hong Kong-Zhuhai-Macao Bridge etc.) have been widely used in China’s civil engineering construction projects. However, when the concrete structure has been put to use in a coastal environment over a long period, the concrete materials can be seriously damaged due to the complex chloride corrosion from seawater [1]. In order to solve these problems, the damaged concrete structures need to be repaired routinely. Additionally, some important traffic structures in coastal cities, such as sea crossing bridges and highways, are frequently damaged due to the marine environment. The damages to concrete construction should be repaired quickly so as to prevent further deterioration, traffic jams and other problems [2]. In response to these problems, fast-hardening, high-performance, cement-based materials are needed.
Conventional pavement repairing materials cannot be put into use until they have been cured for more than 3 days. Therefore, the traffic cannot pass until the strength reaches a higher value. Sulphoaluminate cement is a kind of cement with a fast setting speed which has been used as a kind of rapid repairing material for several years. Additionally, a smaller amount of carbon dioxide is produced during the productive process of sulphoaluminate cement [3]. Some researchers [4] have found that the flexural and compressive strengths of sulphoaluminate cement-based materials with a dosage of steel fibers higher than or equal to 1.5% are higher than 17 MPa and 37.5 MPa, respectively, after curing for 5 h. It can be summarized from some studies that sulphoaluminate cement-based materials possess high early strength (cured for less than 1 day). However, the mechanical strength is lower than that of Portland cement-based materials, and the cost of sulphoaluminate cement-based material is very high [5]. Therefore, it is necessary to decrease the manufacturing cost of rapid repairing cement-based materials. However, little attention to this has been reported. The use of the assembly unit of ordinary Portland cement and sulphoaluminate cement mixed with an early strength agent on rapid repairing cement-based materials could prove a good idea.
Ultra-high performance concrete (UHPC) with high strength and durability was first invented by an Aalborg cement researcher (Bache) in the 1980s. Reactive powder concrete (RPC) is a kind of ultra-high performance concrete which was first invented by the Bouygues Company in the 1990s. RPC is produced according to the maximum density theory. Due to high compactness, RPC shows excellent mechanical strength and durability. As pointed out by some researchers [6,7,8,9], the addition of carbon nanofibers and stainless steel fibers can improve the mechanical strength and the functional properties of RPC. Additionally, RPC reinforced with stainless steel fibers performs with excellent durability when the specimens are exposed to NaCl freeze–thaw cycles and NaCl dry–wet alternations [10]. Although, RPC with carbon nanofibers and stainless steel fibers shows excellent properties, the cost of the two kinds of fibers is expensive [11,12,13]. On the other hand, while the mechanical and durable performances of RPC have been investigated for many years, little attention has been paid to the mechanical properties and durability of RPC manufactured by the assembly unit of sulphoaluminate cement and ordinary Portland cement.
Polypropylene fiber is a kind of flexible fiber which has been applied in cement concrete for several years. This kind of fiber can effectively improve the mechanical strength of cement-based materials. Unlike steel fibers, polypropylene fibers may exhibit good corrosion resistance to chloride environments. Moreover, polypropylene fibers show better dispersion than basalt fibers and carbon fibers in a cement matrix. Therefore, this kind of fiber is suited to act as reinforcement fibers for cement concrete applied in marine environments [14,15]. The addition of sulphoaluminate cement can increase the mechanical and durable properties of RPC at an early curing age. Yet, the mechanical and durable properties may decay at late curing ages. The RPC manufactured by the assembly unit of sulphoaluminate cement and ordinary Portland cement may overcome this difficulty [16,17]. However, little research about RPC with the assembly unit of sulphoaluminate cement and ordinary Portland cement reinforced with polypropylene fibers has been reported.
In this study, the influence of sulphoaluminate cement and polypropylene fibers on the mechanical strengths (flexural strength and compressive strength) of RPC is studied. Moreover, the mechanical strengths and chloride ion permeability of polypropylene fibers and RPC mixed with the assembly unit of sulphoaluminate cement (SAC) and ordinary Portland cement are researched. This research study could provide a new kind of rapid repairing cement-based material in the future.

2. Experimental Materials and Methods

2.1. Raw Materials

Polypropylene fibers (PPFs) showing a density of 0.91 g/cm3, length of 10–13 mm, diameter of 18–48 μm and aspect ratio of 208–722 supplied by Hongyu Engineering Materials COBIT Co., Ltd., Jinan, China, were used in this study. The polypropylene fibers presented a tensile strength of 710 MPa, and the average elastic modulus of polypropylene fibers is higher than 3850 MPa. This type of fiber possesses excellent acid and alkali resistance. Rapid hardening sulphoaluminate cement (RSAC; manufactured by Tangshan Polar Bear Building Materials Co., Ltd., Tangshan, China) and ordinary Portland cement (produced by Zhejiang Ningbo conch Co., Ltd. Ningbo, China), whose strength grade is 42.5 MPa, were applied in this study. Silica fume (SF) with a specific surface area of 15 m2/g, density of 2.2 g/cm3 and more than 98% SiO2 was used in this study. Granulated blast furnace slag powder (GGBS) possessing a density of 2.9 g/cm3, a specific surface area of 436 m2/g and a loss on ignition of 2.3% was used as another cementitious material which can increase the activity of cement. The particle size distribution and the chemical composition of the cementitious materials are presented in Table 1 and Table 2, respectively. The silica fume and granulated blast furnace slag powder were produced by Lingshou Aihong mineral products Co., Ltd., Lingshou, China. Lithium sulfate and calcium formate with a purity of higher than 99.9% produced by Yingshan New Material Technology Co., Ltd., Shanghai China, are used as early strength agents in the sulphoaluminate cement and ordinary Portland cement, respectively. Tartaric acid with higher than 99.9% purity and polycarboxylate superplasticizer with a 40% water reduction rate provided by Yingshan New Material Technology Co., Ltd. (Shanghai, China) were used to adjust the setting time of concrete. The quartz sand provided by Lingshou Aihong mineral products Co., Ltd., Lingshou, China with three sieving sizes of 1−0.71 mm, 0.59−0.35 mm and 0.15−0.297 mm are used as aggregate in this study. The mass ratio of the three sieving sizes is 1:1.5:0.8. In this study, the composition of the quartz sand is 99.6% SiO2, 0.02% Fe2O3 and other ingredients. The binder–sand ratio of the RPC in this study is 1.25. The SAC contents in this study are 0%, 25%, 50%, 75% and 100%. While the content of SAC is 50%, the dosages of polypropylene fibers are 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0% and 3.5% by volume of sulphoaluminate cement reactive powder concrete (SAC-RPC). For all specimens, the lithium sulfate and calcium formate in this study are 0.15% and 0.7% by mass of cementitious materials, respectively. The binder–water ratio in the mix proportions of SAC-RPC is 0.2. Table 3 shows the mix proportions of SAC-RPC. To manufacture RPC with the assembly unit of sulphoaluminate cement and Portland cement, the following steps should be carried out:
Firstly, all powder admixtures including sulphoaluminate cement, ordinary Portland cement (OPC), silica fume (SF), ground granulated blast furnace slag (GGBS) and quartz sand are first mixed in UJZ-15 mortar mixer Hebei Daoneng Construction Engineering Co., Ltd., Cangzhou, China, for 30 s, then polypropylene fiber is added and mixed for another 120 s. Finally, the water reducing agent is added and stirred into the mixture for the last 5.5 min. The slump flow of fresh RPC paste is adjusted to 210~230 mm by the water-reducing agent. DF-04 polyether surfactant with a density of 0.4 g/cm3 and a pH of 7.0~7.5 produced by Yingshan New Material Technology Co., Ltd. (Shanghai, China) is used to eliminate air bubbles in the RPC. The mechanical strengths of specimens with a size of 40 mm × 40 mm × 160 mm are determined after they have been cured in a standard curing environment (temperature of 20 ± 2 °C and relative humidity of above 95%) for 1 d, 3 d, 7 d, 14 d and 28 d, respectively. In the NaCl experiment, the mechanical strengths loss and the chloride migration coefficient (CMC) are determined with the specimens of size 40 mm × 40 mm × 160 mm and Φ100 mm × 50 mm, and specimens with dimensions of 100 mm × 100 mm × 400 mm were used for experiments on mass loss and relative dynamic modulus of elasticity during freeze–thaw cycles. Three specimens were prepared for each experiment. Prior to the experiments, all specimens were cured in a standard curing environment for 24 days. Finally, all specimens were immersed in a 3% NaCl solution for 4 d prior to the freeze–thaw cycle after curing for 24 d.

2.2. Measurement Methods

The YAW-300 microcomputer full-automatic universal tester with the maximum testing force of 300 kN manufactured by Henruijin Co., Ltd., Jinan, China was used to measure the mechanical strengths of the RPC according to the GB/T 17671-1999 Chinese standard [18]. A rapid freeze–thaw concrete testing machine with temperatures ranging from −15 °C to 8 °C was utilized for the NaCl freeze–thaw experiment according to the Chinese Standard GB/T 50082-2009 [19]. Before freeze–thaw cycles, each specimen was placed in a stainless steel sealed casing filled with 3% NaCl solution. The mechanical strengths (flexural and compressive strengths), the mass and the CMC were determined after 0, 50, 100, 150, 200, 250 and 300 freeze–thaw cycles. The mechanical strengths loss and the mass loss were calculated. The CMC experiment after different NaCl freeze–thaw cycles is described as follows: First, the NaCl solution on the surface of the cylinders (Φ100 mm × 50 mm) was wiped out, and then the specimens were immersed in 3% NaCl solution in the concrete intelligent vacuum water saturator vacuum desiccator for the 3% NaCl solution treatment. After that, the sides of the treated specimen are sealed by silica gel. Finally, the specimens were settled in the chloride ion diffusion coefficient tester. The DT-20 dynamic elastic modulus tester produced by Cangzhou Huaheng Test Instrument Co., Ltd., Cangzhou, China was used to determine the relative dynamic modulus of the elasticity of SAC-RPC. The water or NaCl solution was wiped off with a wrung wet cloth. The test frequency of the experiment ranges from 100 to 20,000 Hz. Figure 1 shows the testing process of the relative dynamic modulus of elasticity. The details for these experiments refer to the Chinese Standard GB/T 50082-2009.

3. Results and Discussion

3.1. Mechanical Strengths

Figure 2 shows the mechanical strengths (flexural and compressive strengths) of RPC mixed with different dosage of SAC. Table 4 shows the fitting results for the mechanical strengths and the mass ratio (V) of SAC. It can be observed from Figure 2 and Table 4 that the flexural and compressive strengths of RPC at early curing ages (no more than 3 days) increase in the form of a linear function with the mass ratio of SAC. However, when the curing age reaches 7 days, the flexural and compressive strengths decrease linearly with the mass ratio of SAC. This is attributed to the fact that the addition of SAC can effectively improve the early mechanical properties of RPC. Therefore, the flexural and compressive strengths of RPC an early curing age increase with the addition of SAC. However, the mechanical strengths of SAC-based materials are lower than that of ordinary Portland cement when the curing age reaches 7 days [20,21,22]. Therefore, the flexural and compressive strengths of RPC are reduced by the addition of SAC when the curing age is equal to or higher than 7 days. Finally, the mechanical strengths of RPC cured for equal to or higher than 7 days are obviously higher than that of RPC cured for 1 day and 3 days. Meanwhile, the mechanical strengths of RPC cured for 1 day and 3 days are similar. Additionally, the mechanical strengths of RPC cured for 7 days and 14 days are close to that of specimens cured for 28 days. This is attributed to the fact that the mechanical strengths of RPC with a certain amount of SAC and early strength agent approach the maximum value, therefore, the mechanical strengths of RPC cured for 7 days and 14 days are close to that of specimens cured for 28 days [23,24,25].
Figure 3 shows the relationship between mechanical strengths and the curing time of RPC with different dosage of SAC. Table 5 shows the fitting results of the mechanical strengths (flexural strength and compressive strength) and the curing time of RPC with different SAC. It can be observed from Figure 3 that the relationship between mechanical strengths and the curing time conforms to the quadratic function. It can be observed from Table 5 that the fitting degrees of compressive strength are higher than those of flexural strength.
Figure 4 shows the mechanical strengths (flexural and compressive strengths) of RPC mixed with 50% SAC. Table 6 shows the fitting results of mechanical strengths and the volume ratio (V) of PPFs. The dosage of polypropylene fibers in this study ranges from 0 to 3.5%. As can be observed from Figure 4 and Table 6, the flexural strength firstly increases and then decreases in the form of a quadratic function with the volume of polypropylene fibers. Moreover, as shown in Figure 4, the flexural strength of RPC with 3.0% polypropylene fibers is the highest. However, the compressive strength of RPC increases in the form of quadratic function with the volume of polypropylene fibers. This is attributed to the fact that the polypropylene fibers can bridge the cracks in RPC, thus improving the mechanical properties [26,27,28]. However, the dispersion efficiency of polypropylene fibers is decreased by the increasing dosage of polypropylene fibers. Therefore, the mechanical strengths remain unchanged after growing to a stable value [29,30,31].
Figure 5 shows the relationship between the mechanical strengths and the curing time of RPC with different dosage of PPFs. Table 7 presents the fitting results of the mechanical strengths (flexural strength and compressive strength) and the curing time of SAC-RPC with different PPFs. As can be observed from Figure 5, the relationship between mechanical strengths and the curing time fits well with the quadratic function. As can be observed in Table 7, the compressive strength possesses higher fitting degrees than that of flexural strength.

3.2. Mass Loss of RPC during NaCl Freeze-Thaw Cycles

Figure 6 shows the mass loss of RPC during NaCl freeze–thaw cycles. Table 8 shows the fitting results of mass loss rate and the number of freeze–thaw cycles (N). As depicted in Figure 6 and Table 8, the mass loss ratio increases in the form of a quadratic function. This is attributed to the fact that the frost heave stress can lead to the spalling of RPC specimens [32,33]. Consequently, the mass of RPC decreases with the number of NaCl freeze–thaw cycles. Moreover, as illustrated in Figure 6, the mass loss of RPC is decreased by the increasing dosage of polypropylene fibers due to the fact that the polypropylene fibers can bridge the cracks in RPC during NaCl freeze–thaw cycles, thus preventing the spalling of concrete [34,35]. Therefore, the polypropylene fibers demonstrate a positive effect on the integrity of RPC, leading eventually to decreasing the mass loss ratio of RPC.

3.3. Mechanical Strengths Loss Rate of RPC during NaCl Freeze-Thaw Cycles

Figure 7 and Figure 8 show the flexural and compressive strengths loss rate of RPC. Table 9 shows the fitting results of the mechanical strengths loss and the number of freeze–thaw cycles (N). As can be observed from Figure 7 and Figure 8 and Table 9, the flexural strength loss rate increases in the form of a quadratic function, while the compressive strength loss rate increases in the form of linear function. This is attributed to the fact that the NaCl freeze–thaw cycles can lead to the inner damage of RPC [36,37]. Therefore, the mechanical strengths decrease with the number of NaCl freeze–thaw cycles. Meanwhile, the increasing dosage of polypropylene fibers is able to bridge the cracks caused by NaCl freeze–thaw cycles, thus improving the NaCl freeze–thaw resistance and decreasing the mechanical strengths loss of RPC.
Figure 9 shows the relative dynamic elastic modulus (RDEM) values of RPC specimens during NaCl freeze–thaw cycles. Table 10 shows the fitting results of the RDEM and the number of freeze–thaw cycles (N). As can be observed from Figure 9 and Table 10, the RDEM decreases in the form of a quadratic function with successive NaCl freeze–thaw cycles. This is attributed to the fact that the NaCl freeze–thaw cycles lead to inner cracks in RPC. The cracks can block the propagation of testing sound waves, thus demonstrating a negative effect on the relative dynamic elastic modulus (RDEM) [38].

3.4. Chloride Migration Coefficient during Freeze–Thaw Cycles

Figure 10 shows the chloride migration coefficient (CMC) of RPC during NaCl freeze–thaw cycles. Table 11 shows the fitting results of the CMC and the number of freeze-thaw cycles (N). As can be observed from Figure 8, the chloride migration coefficient of RPC increased in the form of a quadratic function. This is attributed to the fact that the cracks in the RPC increase and widen during NaCl freeze–thaw cycles, thus increasing the NaCl permeability of RPC [39]. The increasing dosage of polypropylene fibers can bridge the cracks in RPC, thus improving the NaCl permeability.

4. Conclusions

In this study, the mechanical performances and durability of RPC with the assembly unit of sulphoaluminate cement and ordinary Portland cement with polypropylene fibers are investigated. The conclusions are summarized as follows:
The correlation between the mechanical strengths and the mass loss ratio of sulphoaluminate cement follows a linear function and depends on the curing time. Before 7 d of curing, the correlation is positive; however, after 7 d of curing, it changes to negative.
The mechanical strengths exhibit a positive quadratic relationship as a function of polypropylene fiber volume. Specifically, the strengths increase markedly with the increasing dosage of polypropylene fibers and then reach a plateau when the polypropylene fiber volume is over 3.4%.
The mass loss rate and flexural strength loss rate demonstrate a positive quadratic correlation, while the relative dynamic elastic modulus exhibits a negative quadratic function with NaCl freeze–thaw cycles. The compressive strength loss rate increases linearly with freeze–thaw cycles with the addition of polypropylene fibers. With an increase in the fiber contents, the strength loss rate becomes less pronounced, i.e., features an improved freeze–thaw resistance.

Author Contributions

Conceptualization, H.W. and Z.C.; methodology, Z.C.; validation, H.W. and Z.C.; formal analysis, H.W.; investigation, Z.C.; resources, H.W.; data curation, Z.C.; writing—original draft preparation, H.W.; writing—review and editing, H.W.; visualization, Z.C.; supervision, H.W.; project administration, Z.C.; funding acquisition, H.W. All authors have read and agreed to the published version of the manuscript.

Funding

This work is sponsored by the National Natural Science Foundation of China [No. 51808300].

Data Availability Statement

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

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Coatings 11 01238 g001 550
Figure 1. The testing process of the relative dynamic modulus of elasticity.
Figure 1. The testing process of the relative dynamic modulus of elasticity.
Coatings 11 01238 g001
Coatings 11 01238 g002 550
Figure 2. The mechanical strengths of RPC with different dosage of SAC. (a) Flexural strength (ft), (b) compressive strength (fcu).
Figure 2. The mechanical strengths of RPC with different dosage of SAC. (a) Flexural strength (ft), (b) compressive strength (fcu).
Coatings 11 01238 g002
Coatings 11 01238 g003 550
Figure 3. The relationship between mechanical strengths and the curing time of RPC with different dosage of SAC. (a) Flexural strength (ft), (b) compressive strength (fcu).
Figure 3. The relationship between mechanical strengths and the curing time of RPC with different dosage of SAC. (a) Flexural strength (ft), (b) compressive strength (fcu).
Coatings 11 01238 g003
Coatings 11 01238 g004 550
Figure 4. The mechanical strengths of RPC with different dosage of polypropylene fibers. (a) Flexural strength, (b) compressive strength.
Figure 4. The mechanical strengths of RPC with different dosage of polypropylene fibers. (a) Flexural strength, (b) compressive strength.
Coatings 11 01238 g004
Coatings 11 01238 g005 550
Figure 5. The relationship between the mechanical strengths and the curing time of SAC-RPC with different dosage of PPFs. (a) Flexural strength (ft), (b) compressive strength (fcu).
Figure 5. The relationship between the mechanical strengths and the curing time of SAC-RPC with different dosage of PPFs. (a) Flexural strength (ft), (b) compressive strength (fcu).
Coatings 11 01238 g005
Coatings 11 01238 g006 550
Figure 6. The mass loss of RPC during NaCl freeze–thaw cycles.
Figure 6. The mass loss of RPC during NaCl freeze–thaw cycles.
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Coatings 11 01238 g007 550
Figure 7. The flexural strength loss rate of RPC during NaCl freeze–thaw cycles.
Figure 7. The flexural strength loss rate of RPC during NaCl freeze–thaw cycles.
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Coatings 11 01238 g008 550
Figure 8. The compressive strength loss rate of RPC during NaCl freeze–thaw cycles.
Figure 8. The compressive strength loss rate of RPC during NaCl freeze–thaw cycles.
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Coatings 11 01238 g009 550
Figure 9. The RDEM during NaCl freeze–thaw cycles.
Figure 9. The RDEM during NaCl freeze–thaw cycles.
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Coatings 11 01238 g010 550
Figure 10. The chloride migration coefficient (CMC) during NaCl freeze–thaw cycles.
Figure 10. The chloride migration coefficient (CMC) during NaCl freeze–thaw cycles.
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Table
Table 1. Particle passing percentage of the cementitious materials/%.
Table 1. Particle passing percentage of the cementitious materials/%.
TypesParticle Size/μm
0.30.614864360
SAC00.351.9216.3530.1295.15100
P·O cement00.332.6615.0128.7793.59100
Slag power0.0250.13.5119.6335.0197.9100
Silica fume31.258.382.3100100100100
Table
Table 2. Chemical composition of the cementitious materials/%.
Table 2. Chemical composition of the cementitious materials/%.
TypesSiO2Al2O3Fe2O3MgOCaOSO3Ti2O
SAC13.9522.462.672.9239.3914.341.66
P·O cement20.865.473.941.7362.232.66/
Slag power34.0614.740.239.7335.930.233.51
Silica fume900.20.60.20.407.4
Table
Table 3. Mix proportions of SAC-RPC per one cubic meter (kg).
Table 3. Mix proportions of SAC-RPC per one cubic meter (kg).
WaterOPCSACSFGGBSQuartz SandWater-ReducerPPFsLi2SO4Tartaric
Acid		Calcium Formate
244.4740.70370.3111.1977.916.30005.2
244.4555.5185.2370.3111.1977.916.301.30.33.9
244.4370.4370.4370.3111.1977.916.302.60.62.6
244.4185.2555.5370.3111.1977.916.303.90.81.3
244.40740.7370.3111.1977.916.305.21.10
244.4370.4370.4370.3111.1977.916.302.60.62.6
244.4370.4370.4370.3111.1977.916.30.462.60.62.6
244.4370.4370.4370.3111.1977.916.30.912.60.62.6
244.4370.4370.4370.3111.1977.916.31.372.60.62.6
244.4370.4370.4370.3111.1977.916.31.822.60.62.6
244.4370.4370.4370.3111.1977.916.32.282.60.62.6
244.4370.4370.4370.3111.1977.916.32.732.60.62.6
244.4370.4370.4370.3111.1977.916.33.192.60.62.6
Table
Table 4. The fitting results of mechanical strengths and the mass ratio (V) of SAC.
Table 4. The fitting results of mechanical strengths and the mass ratio (V) of SAC.
EquationCuring Time/dabR2
f t = a V + b 10.1362.990.994
30.1115.370.957
7−0.013517.900.950
14−0.017918.510.967
28−0.016818.630.953
f c u = a V + b 10.3799.740.900
30.14730.840.980
7−0.072452.40.946
14−0.20565.740.918
28−0.28978.140.879
Table
Table 5. The fitting results of the mechanical strengths (flexural strength and compressive strength) and the curing time (t) of RPC with different SAC.
Table 5. The fitting results of the mechanical strengths (flexural strength and compressive strength) and the curing time (t) of RPC with different SAC.
Equation SAC Content/%abcR2
f t = a t 2 + b t + c 0−0.0562.1651.6060.785
25−0.04401.7174.460.780
50−0.02891.1358.3870.762
75−0.01030.41313.710.836
100−0.0006120.045316.3070.962
f c u = a t 2 + b t + c 0−0.1476.7727.3320.931
25−0.1104.80916.7800.901
50−0.04512.26733.0350.985
75−0.004530.76540.1490.959
100−0.001760.28343.7020.953
Table
Table 6. The fitting results of mechanical strengths and the volume ratio (V) of PPFs.
Table 6. The fitting results of mechanical strengths and the volume ratio (V) of PPFs.
EquationCuring Age/dabcR2
f t = a V 2 + b V + c 1−0.8955.9848.2650.952
3−0.8465.04711.0760.996
7−0.4722.58216.1190.940
14−0.06161.51316.9040.854
28−0.07141.7530.8470.847
f c u = a V 2 + b V + c 13.9813.98135.4830.983
30.4080.408138.5790.992
71.8051.80548.3420.988
140.3440.344155.5790.981
280.9930.99361.2250.998
Table
Table 7. The fitting results of the mechanical strengths (flexural strength and compressive strength) and the curing time (t) of RPC of different dosage of PPFs.
Table 7. The fitting results of the mechanical strengths (flexural strength and compressive strength) and the curing time (t) of RPC of different dosage of PPFs.
EquationPPFs
Content/%		abcR2
f t = a t 2 + b t + c 0−0.02160.9439.0950.879
0.5−0.02120.89010.3170.793
1−0.01470.63013.3570.833
1.5−0.01060.45215.6210.827
2−0.004840.29516.9550.877
2.50.002640.088518.0930.938
3−0.009730.48117.3870.995
3.5−0.005420.31717.5280.950
f c u = a t 2 + b t + c 0−0.04512.26733.0350.985
0.5−0.04322.16634.8760.970
1−0.04382.18235.5590.961
1.5−0.04022.04137.3920.964
2−0.03891.99738.7290.994
2.5−0.03811.95540.2050.997
3−0.04312.08541.4890.984
3.5−0.05122.33742.0730.942
Table
Table 8. The fitting results of mass loss rate and the number of freeze–thaw cycles (N).
Table 8. The fitting results of mass loss rate and the number of freeze–thaw cycles (N).
EquationPPFs
Content/%		abcR2
Δ m m = a N 2 + b N + c 0.5−6.76 × 10−50.0430.4480.968
1.0−6.62 × 10−50.04120.3330.975
1.5−5.07 × 10−50.03580.3440.971
2.0−4.91 × 10−50.03430.2820.979
2.5−4.69 × 10−50.03280.2260.979
Table
Table 9. The fitting results of the mechanical strengths loss and the number of freeze–thaw cycles (N).
Table 9. The fitting results of the mechanical strengths loss and the number of freeze–thaw cycles (N).
EquationPPFs
Content/%		abcR2
Δ f t f t = a N 2 + b N + c 01.56 × 10−40.009420.6400.954
11.37 × 10−40.009120.3130.967
21.02 × 10−40.01150.1330.957
31.12 × 10−40.004790.2060.953
47.90 × 10−50.009410.09740.935
Δ f c u f c u = a N + b 00.0395−0.806/0.983
10.0356−0.695/0.992
20.0340−0.698/0.988
30.0329−0.759/0.981
40.0301−0.600/0.998
Table
Table 10. The fitting results of the RDEM and the number of freeze–thaw cycles (N).
Table 10. The fitting results of the RDEM and the number of freeze–thaw cycles (N).
Equation PPFs
Content/%		abcR2
R D E M = a N 2 + b N + c 05.90 × 10−5−0.08485100.2870.992
16.98 × 10−5−0.0680199.8270.984
24.30 × 10−5−0.05075100.0930.951
3−4.33 × 10−5−0.03131100.0700.979
4−3.97 × 10−5−0.01466100.0400.997
Table
Table 11. The fitting results of the CMC and the number of freeze–thaw cycles (N).
Table 11. The fitting results of the CMC and the number of freeze–thaw cycles (N).
Equation PPFs
Content/%		abcR2
C M C = a N 2 + b N + c 0−2.52 × 10−50.02812.0670.999
1−2.10 × 10−50.02701.6740.997
2−2.72 × 10−50.02691.4110.998
3−1.61 × 10−50.02331.3380.995
4−1.77 × 10−50.02321.0290.998
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Cai, Z.; Wang, H. Influence of NaCl Freeze–Thaw Cycles on the Mechanical Strength of Reactive Powder Concrete with the Assembly Unit of Sulphoaluminate Cement and Ordinary Portland Cement. Coatings 2021, 11, 1238. https://doi.org/10.3390/coatings11101238

AMA Style

Cai Z, Wang H. Influence of NaCl Freeze–Thaw Cycles on the Mechanical Strength of Reactive Powder Concrete with the Assembly Unit of Sulphoaluminate Cement and Ordinary Portland Cement. Coatings. 2021; 11(10):1238. https://doi.org/10.3390/coatings11101238

Chicago/Turabian Style

Cai, Zhangjie, and Hui Wang. 2021. "Influence of NaCl Freeze–Thaw Cycles on the Mechanical Strength of Reactive Powder Concrete with the Assembly Unit of Sulphoaluminate Cement and Ordinary Portland Cement" Coatings 11, no. 10: 1238. https://doi.org/10.3390/coatings11101238

APA Style

Cai, Z., & Wang, H. (2021). Influence of NaCl Freeze–Thaw Cycles on the Mechanical Strength of Reactive Powder Concrete with the Assembly Unit of Sulphoaluminate Cement and Ordinary Portland Cement. Coatings, 11(10), 1238. https://doi.org/10.3390/coatings11101238

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