Microsoft Word - CET--006.docx


 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 59, 2017 

A publication of 

 

The Italian Association 
of Chemical Engineering 
Online at www.aidic.it/cet 

Guest Editors: Zhuo Yang, Junjie Ba, Jing Pan 
Copyright © 2017, AIDIC Servizi S.r.l. 

ISBN 978-88-95608- 49-5; ISSN 2283-9216 

Analysis on the Anti-cracking and Anti-permeability 

Performance of Polypropylene Fiber-Reinforced Concrete in 

Subway Retaining Structure  

Xianchun Liu 

Anhui Technical College of Water Resources and Hydroelectric Power, Hefei 231603, China  

2754875063@qq.com 

In this paper, regarding the problems of subway and tunnel retaining structures such as cracking and 

seepage, we study the stress, strain and temperature changes of the new polypropylene fiber-reinforced 

concrete (PFRC) through laboratory test and engineering measurement. The results show that mixing 

polypropylene crude and fine fiber into concrete can greatly improve the tensile strain and deformation 

performance of basic concrete. The amount of polypropylene fiber added has something to do with the 

aggregate composition of the concrete, and polypropylene fiber has little effect on the tensile modulus of the 

concrete. Compared with the purely crude fiber and fine fiber concrete, the blended fiber-reinforced concrete 

has the greatest increase in the tensile strength over the basic concrete. The results show that, after crude 

and fine fiber is added into the ordinary concrete, cracks on the concrete surface are greatly reduced and the 

width of the cracks is also within the standard, which is in accordance with the intended anti-cracking and anti-

permeability target. Concrete is mostly likely to have cracks 1 week after being placed, so the internal 

temperature of concrete must be strictly controlled. 

1. Introduction 

The cracking and seepage problems of subway station and tunnel retaining structures have become great 

challenges in subway construction. With the increase in the buried depth of subway tunnels, the difficulty in 

groundwater seepage prevention for subway construction is also increased. Therefore, it is of great practical 

significance to study how to prevent cracking and seepage of subway retaining structures. 

The main building material for subway interior is concrete structures. In the process of pouring, it is avoidable 

that concrete will have natural pores, bubbles and cracks. After the concrete is put into service, these original 

minor defects will gradually become large cracks, and with the opening of these cracks, the bearing capacity 

of the concrete will be reduced, and groundwater will seep into subway tunnels and stations. The anti-seepage 

performance of concrete is also known as impermeability. In recent years, it has been found that the addition 

of fibers into concrete can significantly improve its anti-cracking and anti-permeability performance.  

At present, in subway engineering, there are two common types of fiber-reinforced concrete materials - steel 

fiber and non-steel fiber. The former is widely applied in construction, but it is also costly; the latter is being 

rapidly developed in recent years. Currently, there are two kinds - high-elastic and low elastic fiber. Synthetic 

fiber, as a representative of low-elastic fiber, has the advantages of corrosion resistance, high strength and 

low cost, and thus it has been extensively applied (Altoubat and Lange, 2001; Banthia and Nandakumar, 

2003; Bentur and Kovler, 2003; Song et al., 2005; Wang et al., 2001; Usman et al., 2016). Regarding the 

addition of synthetic fiber into concrete, through continuous lab analysis and engineering applications, there 

have been several development stages – fine synthetic fiber (Choi and Yuan, 2005; Gopalaratnam et al., 

1991), steel synthetic fiber (Najm and Balaguru, 2002), polypropylene fiber-reinforced concrete (Oh et al., 

2007; Bui, Voigt and Shah, 2004; Feng et al, 2016), polypropylene crude fiber-reinforced concrete (Malmgren, 

2007; Ladanchuk and Nehdi, 2004) and polypropylene blended fiber-reinforced concrete (Ding et al., 2009; 

Qian and Stroeven, 2000), producing a number of research results.  

                               
 
 

 

 
   

                                                  
DOI: 10.3303/CET1759057

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Xianchun Liu, 2017, Analysis on the anti-cracking and anti-permeability performance of polypropylene fiber-
reinforced concrete in subway retaining structure, Chemical Engineering Transactions, 59, 337-342  DOI:10.3303/CET1759057   

337



In this paper, regarding the problems of subway and tunnel retaining structures such as cracking and 

seepage, we study the stress, strain and temperature changes of the new PFRC through laboratory test and 

engineering measurement. 

2. Performance analysis on multi-scale PFRC 

2.1 Testing materials and process 

The concrete strength is 42.5R; the fineness modulus of fine aggregate is 0.73; the coarse aggregate mainly 

consists of macadam, with a particle size of 7-18mm; the polypropylene fiber has a density of 0.9g/cm, an 

average elasticity modulus of 6.2GPa, a tensile strength of 569MPa, a fiber length of 32mm and a diameter of 

0.03-0.7mm; the design strength of concrete is C30; the ratio of cement: sand: stone: water = 405: 549: 1220: 

210. The fiber is added according to the testing and engineering experience.  

Concrete mixing process: put the sand, stones and polypropylene fiber into an agitator and stir the mixture 

well for 5min; add cement and stir it for 3min; pour water into the mixture and stir it for 2min. When 

polypropylene fiber is evenly distributed in the formed concrete, the mixing is completed.  

Prepare concrete specimens into cuboids with a size of 150mm×100mm×250mm. Fabricate 5 test pieces from 

each kind of concrete cuboid. Let them sit for 48h and maintain them in the curing room for 10d. Dry and 

polish the surfaces of the test pieces. 

2.2 Analysis on the tensile strain of PFRC 

The tensile stress-strain curves of ordinary concrete and PFRC are shown in Figure 1. Figure 1(a) shows the 

stress-strain comparison of fiber-free concrete and polypropylene fine fiber concrete. It can be seen from the 

figure that when fiber is not added in the concrete, the stress decreases very fast and the descending section 

of the curve is short. When the strain is 0.1, the stress is close to 0MPa, and the concrete exhibits obvious 

brittleness. When polypropylene fiber is added into concrete, the decrease in the stress-strain curve slows 

down obviously at 0.07, and a slow downward trend is shown, indicating that the addition of polypropylene 

fiber can obviously improve the brittleness of concrete. 

 

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

S
tr

e
ss

/M
P

a

Strain/%

 Without fiber

 Fine fiber

 
(a) Ordinary concrete and polypropylene fine concrete 

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0
0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

  Crude fiber

  Blended fiber

S
tr

e
ss

/M
P

a

Strain/%  
(b) Polypropylene crude and blended fiber concrete 

Figure 1: Stress-strain curve of multi-scale polypropylene fiber concrete 

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Figure 1 (b) shows the stress and strain curves of the crude fiber and blended fiber added to the concrete. 

When the test piece is cracked, the bearing capacity instantly decreases sharply from the highest value, but 

with the continued effect of the external load, the carrying capacity of the test piece rises after hitting the local 

minimum value, and when the external load is further applied to the test piece, breaking the fiber, the test 

piece gradually loses its bearing capacity, and the descending section of the curve of the test piece is long 

and gentle. It can also be seen from Figure 1(b) that the blended fiber concrete can better exert the tensile 

strength and fracture resistance of polypropylene fiber in different stress stages than the crude fiber concrete, 

and significantly improve the anti-cracking and anti-permeability capabilities and toughness of the concrete. 

There are natural defects like pores and bubbles inside the concrete. When an external load is applied, stress 

will be concentrated in the weak area of concrete. When the external load is greater than the tensile strength 

of the material, cracks will appear in the concrete and gradually expand. With the stress concentrated at the 

concrete defect increasing, microcracks develop slowly into macrocracks and rapidly expand, finally leading to 

concrete instability and damages. When polypropylene fiber is added into the concrete, fiber constrains the 

further expansion of microcracks and applies a stress field to the microcrack tips to offset the cracks, which in 

this way improves the tensile strength of the concrete. 

3. Analysis on the anti-cracking and anti-permeability performance of subway station 
retaining structures 

3.1 Addition of polypropylene fiber into concrete and field test 

Based on the laboratory analysis on PFRC in the above section, in this section, we further study the 

application of PFRC in actual engineering and analyze its anti-cracking and anti-permeability performance in 

subway tunnel and station retaining structures. In the field test, we select an actual subway section under 

construction. The main framework of the station consists of single-span, double-wall and double-box 

structures. The test section is divided into two parts – one part of the wall retaining structure is made of 

ordinary concrete and the other part is the concrete structure added with polypropylene fiber. The two parts 

are divided into five monitoring sections, where Section 1, 2 and 3 are in the PFRC structure while Section 4 

and 5 in the ordinary concrete structure. The detailed monitoring chart is shown in Figure 2. 

According to test analysis and engineering experience, the amount of polypropylene added into the concrete 

can be calculated according to formula 1: 

max D
t t     (1) 

Δtmax is the thermal limit for concrete; ΔtD is the damage limit temperature drop of concrete under the 

waterproof condition, expressed in the following formula:  

   0 0.8 1D wt t K H              (2) 

The strain gauges and thermometers are embedded in the concrete subway retaining structures. The 

temperature correction coefficient for the fiber-reinforced concrete is as follows: 

      0 0m k F b t k F F b t t              (3) 

εm is the strain of the concrete structure; α is the linear expansion coefficient; F0 is the measured strain value; 

t0 is the temperature reference value. 

 

Ordinary concrete test section

Section 5 Section 4

Anti-permeability test section

Induced joint B

Section 3 Section 2

Induced joint A

Section 1

 

Figure 2: Layout chart for anti-permeability testing of concrete  

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3.2 Test results and analysis 

We observe the concrete structures in the two parts for a long time. The temperature and strain results of the 

concrete in the two parts are shown in Figure 3. It can be seen from the temperature curves of ordinary 

concrete and PFRC in Figure 3(a) that the PFRC structure reaches the maximum temperature of 49℃ after 

100-120h, which is much higher than the ambient temperature, because the concrete releases heat after 

hydration, significantly increasing the internal temperature of the structure. When the temperature reaches the 

maximum value, the temperature curve shows a decreasing trend with fluctuations. After 800-1000h, the 

temperature inside the concrete decreases to the ambient temperature - 20-25℃. The temperature changes of 

ordinary concrete are similar to that of PFRC. The general temperature curve trend is also a rapid rise within a 

short period of time and then a decline in oscillation and the final temperature also drops to the ambient 

temperature. 

 

0 200 400 600 800 1000
10

15

20

25

30

35

40

45

50

t/
C

Duration time/h

 Anti-permeability

 Ordinary concrete

 
(a) Test section temperature 

0 200 400 600 800 1000
-6

-4

-2

0

2

4

6

8

 Anti-permeability

 Ordinary concrete



1
0

-5

Duration time/h  
(b) Test section strain 

Figure 3: Curve of concrete temperature and strain versus time 

From the strain curves of PFRC and ordinary concrete in Figure 3(b), it can be seen that the maximum strain 

of PFRC is compressive strain, which is 4.8×10-5. When the temperature inside the concrete gradually 

increases, the concrete at the test point suffers from thermal expansion and is pressed due to the stress 

concentration around it. When the temperature inside the concrete gradually decreases, the concrete at the 

test point shrinks, and the tensile stress occurs at the test point. From the figure, we can see that the 

maximum tensile strain is 2.7×10-5. When the temperature further decreases, the tensile strain inside the fiber-

reinforced concrete also decreases, and finally to 1.95×10-5 after 1000h. And the closer it is to the concrete 

surface, the greater drop there is in the tensile strain. For ordinary concrete, the maximum compressive strain 

is 2.03×10-5, while the tensile strain is up to 7.9×10-5, much higher than that of the PFRC. The concrete is 

more susceptible to tensile damage, so when the tensile strain exceeds the ultimate tensile strain of concrete, 

cracks will occur. Therefore, the addition of polypropylene fiber into the concrete can effectively prevent 

concrete cracking and avoid water seepage caused by concrete cracking. 

Figure 4 shows the wall surface cracks of PFRC and ordinary concrete. As can be seen from the figure, there 

are two wall cracks in the PFRC wall, while there are 6 in the ordinary concrete wall. According to onsite 

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construction experience, cracks mainly occur within 1 week after the concrete pouring. Table 1 shows the 

average width of the cracks in PFRC and ordinary concrete. As can be seen from the table, the maximum 

width of the cracks in PFRC is 0.16mm, and the average width of the two cracks is only 0.12mm, while in the 

ordinary concrete, the maximum width of cracks is 0.57mm, and the average width of the six cracks is 

0.33mm. According to relevant subway design specifications, the maximum allowable width of concrete cracks 

is 0.2mm. The surface crack width of the ordinary concrete is much greater than this specification, while that 

of PFRC is within the allowable range. 

Table 1: Average crack width of anti-permeability and ordinary concrete (mm) 

 1 2 3 4 5 6 

Ordinary concrete 0.47 0.19 0.36 0.57 0.15 0.24 

Anti-permeability concrete 0.16 0.08     

 

Ordinary concrete test section

1
2

3 4
5 6

1
2

Anti-permeability test section

4
0
0
0

4
0
0
0

8000 3800 12200

5500 11900 6600

Unit: mm
 

Figure 4: Crack distribution of different test concrete 

4. Conclusions 

In this paper, regarding the problems of subway and tunnel retaining structures such as cracking and 

seepage, we study the stress, strain and temperature changes of the new polypropylene fiber-reinforced 

concrete (PFRC) through laboratory test and engineering measurement. And the research conclusions are as 

follows: 

(1) Mixing polypropylene crude and fine fiber into concrete can greatly improve the tensile strain and 

deformation performance of basic concrete. The amount of polypropylene fiber added has something to do 

with the aggregate composition of the concrete, and polypropylene fiber has little effect on the tensile modulus 

of the concrete. Compared with the purely crude fiber and fine fiber concrete, the blended fiber-reinforced 

concrete has the greatest increase in the tensile strength over the basic concrete. 

(2) The results show that, after crude and fine fiber is added into the ordinary concrete, cracks on the concrete 

surface are greatly reduced and the width of the cracks is also within the standard, which is in accordance with 

the intended anti-cracking and anti-permeability target. Concrete is mostly likely to have cracks 1 week after 

being placed, so the internal temperature of concrete must be strictly controlled, and at the same time, 

waterproof work must be strengthened at the concrete joints.  

Reference  

Altoubat S.A., Lange D.A., 2001, Creep, shrinkage, and cracking of restrained concrete at early age. Aci 

Materials Journal, 98(4), 323-331. DOI: 10.14359/10401. 

Banthia N., Nandakumar N., 2003, Crack growth resistance of hybrid fiber reinforced cement composites. 

Cement & Concrete Composites, 25(1), 3-9. DOI: 10.1016/s0958-9465(01)00043-9. 

Bentur A., Kovler K., 2003, Evaluation of early age cracking characteristics in cementitious systems. Materials 

and Structures, 36(3), 183-190. DOI: 10.1617/14014. 

Bui V.K., Voigt T., Shah S.P., 2004, Drying shrinkage of concrete reinforced with fibers and welded-wire fabric. 

Aci Materials Journal, 101(3), 233-241. DOI: 10.14359/13119. 

341

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http://dict.cnki.net/dict_result.aspx?searchword=%e5%88%86%e5%b8%83&tjType=sentence&style=&t=distribution


Choi Y., Yuan R.L., 2005, Experimental relationship between splitting tensile strength and compressive 

strength of gfrc and pfrc. Cement & Concrete Research, 35(8), 1587-1591. DOI: 

10.1016/j.cemconres.2004.09.010. 

Ding Y., Zhang Y., Thomas A., 2009, The investigation on strength and flexural toughness of fibre cocktail 

reinforced self-compacting high performance concrete. Construction & Building Materials, 23(1), 448-452. 

DOI: 10.1016/j.conbuildmat.2007.11.006. 

Feng H., Peng Y., Gong J., Yin F., 2016, Numerical simulation of two-dimensional large-amplitude acoustic 

oscillations. International Journal of Heat and Technology, 34(1), 143-150. DOI: 10.18280/ijht.340121. 

Gopalaratnam V.S., Shah S.P., Batson G.B., Criswell M.E., Ramakrishnan V., Wecharatana M., 1991, 

Fracture toughness of fiber reinforced concrete. Aci Materials Journal, 88, 4, 339-353. DOI: 

10.14359/1840. 

Ladanchuk J.D., Nehdi M., 2004, Fiber synergy in fiber-reinforced self-consolidating concrete. Aci Materials 

Journal, 101(6), 508-517. DOI: 10.14359/13490. 

Malmgren L., 2007, Strength, ductility and stiffness of fibre-reinforced shotcrete. Magazine of Concrete 

Research, 59(4), 287-296. DOI: 10.1680/macr.2007.59.4.287. 

Najm H., Balaguru P., 2002, Effect of large-diameter polymeric fibers on shrinkage cracking of cement 

composites. Aci Materials Journal, 99(4), 345-351. DOI: 10.14359/12216. 

Oh B.H., Ji C.K., Choi Y.C., 2007, Fracture behavior of concrete members reinforced with structural synthetic 

fibers. Engineering Fracture Mechanics, 74(1), 243-257. DOI: 10.1016/j.engfracmech.2006.01.032. 

Qian C., Stroeven P., 2000, Fracture properties of concrete reinforced with steel–polypropylene hybrid fibres. 

Cement & Concrete Composites, 22(5), 343-351. DOI: 10.1016/s0958-9465(00)00033-0. 

Song P.S., Hwang S., Sheu B.C., 2005, Strength properties of nylon- and polypropylene-fiber-reinforced 

concretes. Cement & Concrete Research, 35(8), 1546-1550. DOI: 10.1016/j.cemconres.2004.06.033. 

Usman, H., Mabood, F., & Lorenzini, G., 2016, Heat and mass transfer along vertical channel in porous 

medium with radiation effect and slip condition. International Journal of Heat and Technology, 34(1), 129-

136. DOI: 10.18280/ijht.340119. 

Wang K., Shah S.P., Phuaksuk P., 2001, Plastic shrinkage cracking in concrete materials-influence of fly ash 

and fibers. Aci Materials Journal, 98(6), 458-464. DOI: 10.14359/10846. 

 

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