A Study on the Shrinkage Control of Fiber Reinforced Concrete

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Procedia Engineering 14 (2011) 2815–2822

The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction

A Study on the Shrinkage Control of Fiber Reinforced Concrete Pavement S. Y. CHOI*, J. S. PARK, W. T. JUNG Structure Engineering & Bridges Research Division, Korea Institute of Construction Technology (KICT), South Korea

Abstract Cement concrete pavement provides durable service life and remarkable applicability for heavy traffic. Its purchase being easier than asphalt, cement concrete pavement offers excellent advantages in terms of durability and economic efficiency. However, adequate repair of this pavement is harder than asphalt concrete in case of degradation or damage. Cracking in the concrete pavement is the major cause of such disadvantages and the demand of repair on road sites is growing every day. This emphasizes the urgency to secure technologies for the control of early and longterm cracking. Accordingly, this study evaluates the drying and autogenous shrinkage strains regard to fiber reinforcement in order to reduce cracking of the concrete pavement mix so as to control the damage of the pavement by means of fiber reinforcement. The results show that the drying shrinkage strain can be significantly reduced to about 1/4 through the admixing of 0.2% volume ratio of NY fiber compared to the non-reinforced plain concrete, and that the hybrid fiber reinforcement mix H-N1-ST1 can realize remarkable reduction of the autogenous shrinkage.

© 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection Keywords: Fiber Reinforced Concrete, Macro Fiber, shrinkage, Pavement, Hybrid

* Corresponding author and Presenter Email: [email protected]

1877–7058 © 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2011.07.354

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S.Y. CHOI et al. / Procedia Engineering 14 (2011) 2815–2822

1. Introduction Two techniques are generally used for road pavement: the asphalt concrete pavement that is ductile pavement and the cement concrete pavement that is rigid pavement. Cement concrete asphalt offers longterm service life and excellent applicability for heavy traffic. Its purchase being easier than asphalt, this pavement technique presents remarkable cost-effectiveness and durability. However, adequate repair of the cement concrete pavement is more difficult than the asphalt pavement in case of degradation or damage and demands works with a larger scale (Yang 2000; Um 2000). The typical causes of cracks in concrete pavement are the hydration cracking at early hydration state of concrete, the plastic shrinkage cracking, the environmental cracking caused by thermal changes at the top of the pavement, the drying shrinkage cracking according to the hardening of concrete, and the cracking caused by the long-term process of alkali-silica reaction. The Korean research community has and is developing various solutions for the control of cracks. The fundamental cause of the occurrence of cracks in concrete pavement is the poor resistance of the concrete pavement to bending, tension and cracking. Fiber reinforcement is a representative method for supplementing the bending tensile performance of concrete. To date, research on fiber reinforcement has been steadily conducted. The recent trend of research on fiber reinforcement focuses on studies dedicated to the plastic shrinkage cracking of fiber reinforced concrete with hybrid type of fibers and the tensile strength performance of steel fiber reinforced concrete (Won 2004; Kim 2005). Research devoted to fiber reinforcement focuses mainly on the evaluation of the change of the mechanical performances according to the content and type of fibers in ordinary concrete and high strength concrete. However, poor interest is given to the fiber reinforcement effect with respect to the mix proportions of concrete. Especially, the quasi-absence of thorough study on the fiber reinforcement effect on concrete pavement of which the mix proportion is limited to a specific weight and is prescribed to adopt coarse aggregates with granulometry different to that of concrete pavement is noteworthy. Accordingly, this study intends to evaluate the drying shrinkage and autogenous shrinkage strains with respect to the fiber reinforcement in order to reduce cracking of the concrete pavement mix. Fiber reinforced concrete specimens are fabricated with the type and content of fiber chosen as test variable to select the type and quantity of fiber effective for shrinkage control. To that goal, the shrinkage strain of concrete is measured. Three types of macro fibers with length longer than 30 mm and small aspect ratio together with micro nylon fibers with length of 12 mm and aspect ratio larger than 1000 are selected for the tests. Both reinforcement with a single type of fiber and hybrid reinforcement involving micro and macro fibers were executed, and the fiber volume ratio was set to 0.2 to 0.3% of the concrete pavement mix. Using the so-fabricated specimens, the change of the length caused by drying shrinkage and autogenous shrinkage of concrete is analyzed comparatively. 2. Test 2.1. Test planning and test variables The detailed mix proportions of the concrete pavement in this study are listed in Table 1. Fig. 1 describes the designation of the variables, and Table 2 presents the test variables and their explanation. Table 3 arranges the experimental setup. In the tests on fresh concrete, the slump was measured in compliance with KS F 2402, the air content was measured according to the specifications of KS F 2421, and the change of length by drying shrinkage and autogenous shrinkage was measured in compliance with the stipulations of KS F 2424 and KS F 2586.

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Table 1: Mixture proportions of concrete Volume mixing (Ɛ/m3)

Type

W/C (%)

S/a (%)

AE/C (%)

SP/C (%)

W (kg/m3)

Max. coarse aggregate size (mm)

C

S

G

Pavement

42.3

39

0.02

0.28

150

32

113

270

422

Table 2: Parameter and fiber volume fraction Fiber dosage (%)

Specimen

Mixture

Plain

Pavement concrete

Nylon

PP

PVA

ST -

-

-

-

S-N2-00

0.2

-

-

-

S-00-PP2

-

0.2

-

-

-

-

0.2

-

S-00-PV2

Single fiber

-

-

-

0.2

H-N1-PP1

S-00-ST2

0.1

0.1

-

-

H-N1-PV1

0.1

-

0.1

-

H-N1-ST1

0.1

-

-

0.1 -

H-N13-PP07

0.133

0.066

-

H-N07-PV13

0.066

-

0.133

-

H-N07-ST13

0.066

-

-

0.133

H-N2-PP1

0.2

0.1

-

-

H-N1-PV2

0.1

-

0.2

-

H-N1-ST2

0.1

-

-

0.2

Figure 1: Specimen description Table 3: Experimental plan Factors

Experiments

Levels Fresh concrete

3

ɁSlump ɁAir content ɁConsistency (Vebe test)

Hardened concrete

2

ɁDrying Shrinkage length variation (1, 7, 14, 28, 56 days) ɁAutogenous Shrinkage length variation (1,2,3......28 days)

2.2. Materials and test methods Table 4: Physical properties of Ordinary Portland Cement

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Density (g/cm3)

Blaine (cm2/g)

Soundness (%)

3.15

3 165

0.18

Setting time (min) Ini. Fin. 235

Compressive strength (MPa) 3 days 7 days 28 days

320

20.4

29.4

38.7

Table 5: Physical properties of aggregates

Density (g/cm3) 2.65 2.50 2.71 2.70

Type River sand Crushed sand Coarse agg. 20 mm Coarse agg. 32 mm

Fineness modules 2.86 2.62 7.01 6.88

Absorption ratio (%) 2.63 1.42 1.18 0.58

Table 6: Physical properties of fiber Property

NY 3

PP

PVA

ST 7.86

Density (g/cm )

1.16

0.91

1.30

Aspect ratio

1000

75~100

45

65

Length (mm)

12

30

30

35

Diameter (mm)

0.012

0.3~0.4

0.66

0.54

Tensile strength (MPa)

896

250~1000

900~1600

1200

Modulus of elasticity (GPa)

3.9~4.9

3~30

23~41

200

2.3. Test Results 2.3.1. Variation of length by drying shrinkage

k GzGsG} T] OXW P

100

P lain S -N Y2-00 S -00-P P2 S -00-P V2 S -00-S T 2

0 -100 -200 -300 -400 -500 -600

0

7

14

21

28

35

42

49

56

h O k P Figure 2: Drying shrinkage of fiber reinforced concrete

Fig. 2 plots the variation of length by drying shrinkage with respect to the age per single fiber type. First, plain specimen experiences a strain of about –400u10–6 at 56 days, while concrete reinforced with a

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single type of fiber shows a change of length smaller than plain at all levels. Especially, the micro NY fiber reinforcement provides the most remarkable shrinkage control effect with a very small strain below –100u10–6. Among the macro fibers, S-00-PV2 offers the most effective performance with a drying shrinkage ratio of –200u10–6.

k GzGsG} T] OXW P

100

Plain H-N1-PV1 H-N07-PV13 H-N1-PV2 H-N1-ST1 H-N07-ST13 H-N1-ST2 H-N1-PP1 H-N13-PP07 H-N2-PP1

0 -100 -200 -300 -400 -500 -600

0

7

14

21

28

35

42

49

56

h Ok P

Figure 3: Drying shrinkage of hybrid fiber reinforced concrete

-600

k GzGsG} T] OXW P

56 Day -500

-400

-300

-200

-100

0

Plain

H-N1-PT1

H-N1-PV1

H-N1-ST1

H-N13-PT07 H-N07-PV13 H-N07-ST13

H-N2-PT1

H-N1-PV2

H-N1-ST2

mG

Figure 4: Variation of drying shrinkage strain of hybrid fiber reinforced concrete at 56 days

Fig. 3 plots the variation of length by drying shrinkage with respect to the age per hybrid fiber type. The variation of length is reduced by more than 2 times at all reinforcement levels compared to the nonreinforced plain specimen when hybrid fiber reinforcement is adopted. Mix H-N1-ST1 shows the smallest strain. As shown in Fig. 4, the effect of the variation of the fiber content by 0.2~0.3 is practically nonexistent. Compared to the results for the 0.2% volume reinforcement ratio by NY fiber, the mix H-N2PP1 with hybrid reinforcement by NY fiber at 0.2% and macro fiber at 0.1% exhibits much larger drying

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shrinkage, which reveals that synergy of both micro and macro fibers did not apply in the reduction of the drying shrinkage. For a small fiber content of about 0.2~0.3%, NY fiber provides the most remarkable shrinkage reduction effect. 2.3.2. Variation of length by autogenous shrinkage

hGzGsG} OXWT ]P

40

Plain S-NY2-00 S-00-PP2 S-00-PV2 S-00-ST2

20 0 -20 -40 -60 -80 -100 -120 -140 -160

7

14

21

28

hOk P

Figure 5: Autogenous shrinkage of fiber reinforced concrete

hGzGsG} T] OXW P

40

Plain H-N1-PV1 H-N07-PV13 H-N1-PV2 H-N1-ST1 H-N07-ST13 H-N1-ST2 H-N1-PP1 H-N13-PP07 H-N2-PP1

20 0 -20 -40 -60 -80 -100 -120 -140 -160

7

14

21

28

h Ok P

Figure 6: Autogenous shrinkage of hybrid fiber reinforced concrete

Fig. 5 plots the variation of length by autogenous shrinkage with respect to the age per single fiber type. The plain mix experiences an autogenous shrinkage strain of about 100u10–6 at 28 days. For the fiber reinforced mixes, specimen S-N2-00 tends to show large autogenous shrinkage at early age but, at later age, the

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autogenous shrinkage becomes nearly identical to that of plain and S-00-PP2. Specimen S-N2-00, which developed the most remarkable performance during the evaluation of the drying shrinkage, provides performance similar to plain in the evaluation of the autogenous shrinkage. This means that the improvement of the performance brought by NY fiber reinforcement cannot be developed for the autogenous shrinkage. The most effective mix in reducing the autogenous shrinkage is S-00-PV2, which reveals the largest autogenous reducing effect of PVA fiber.

hGzGsG} T] OXW P

-140

28 Day

-120 -100 -80 -60 -40 -20 0

Plain

H-N1-PT1

H-N1-PV1

H-N1-ST1

H-N13-PT07 H-N07-PV13 H-N07-ST13

H-N2-PT1

H-N1-PV2

H-N1-ST2

mG

Figure 7: Variation of autogenous shrinkage strain of hybrid fiber reinforced concrete at 28 days

Fig. 6 plots the variation of length by autogenous shrinkage with respect to the age per hybrid fiber type. The plain mix shows an autogenous shrinkage strain of about 100u10–6. The variation of the shrinkage is sensitive to the change of the fibers. Specimen H-N2-PP1 presents the largest autogenous shrinkage of approximately –130u10–6 while mixes H-N1-ST1 and H-N-PP1 shows the smallest shrinkage strains with value of about –70u10–6. Fig. 7 compares the autogenous shrinkage at 28 days. The mix proportions with fiber content of 0.2% shows shrinkage reducing effect generally equivalent or superior to the mixes with fiber content of 0.3%. The most remarkable fiber ratio is 1:1. 3. Conclusions This study analyzed comparatively the shrinkage performance of concrete pavement according to fiber reinforcement. It was seen that mix S-N2-00 with single fiber reinforcement provides the largest reduction of the drying shrinkage while mix H-N1-ST1 with hybrid fiber reinforcement developed the smallest shrinkage. The most remarkable performance for the autogenous shrinkage was provided by specimen S-00-PV2 with single fiber reinforcement and mixes H-N1-ST1 and H-N1-PP1 with hybrid fiber reinforcement. References [1]

Yang SC, Park GH, Kwon SM(2000). Construction Trends of Korea Concrete Pavement. Korean Society of Road Engineers, Vol. 2, No. 3, pp.11-23.

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[2]

UM JY(2000). Methodology for Constraining Asphalt Concrete Oerlay Against Reflection Cracking, Research Paper, Korea

[3]

Won JP, Hwang KS, Park CG, Park HG(2004). Evaluation of Crack Control and Permeability of Hydrophilic PVA Fiber

[4]

Kim MH, Kim JH, Kim YR, Kim YD(2005). An Experimental Study on the Mechanical Properties of HPFRCCs Reinforced

[5]

Sivakumar A, Manu Santhanam(2007). A quantitative study on the plastic shrinkage cracking in high strength hybrid fibre

[6]

Olivito RS, Zuccarello FA(2010). An experimental study on the tensile strength of steel fiber reinforced concrete. Cement &

[7]

Li VV and Stang H(1997). Interface property characterization and strengthening mechanisms in fiber reinforced cement

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