Flow characteristics and acceptance criteria of fiber-reinforced self-compacted concrete (FR-SCC)

Construction and Building Materials 27 (2012) 585–596

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Flow characteristics and acceptance criteria of fiber-reinforced self-compacted concrete (FR-SCC) A.S. El-Dieb a,⇑, M.M. Reda Taha b a b

Faculty of Engineering, Civil & Environmental Engineering Department, UAE University, P.O. Box 17555, Al Ain, United Arab Emirates Department of Civil Engineering, The University of New Mexico, USA

a r t i c l e

i n f o

Article history: Received 29 April 2008 Received in revised form 4 July 2010 Accepted 6 July 2011 Available online 10 August 2011 Keywords: Fiber-reinforced self-compacting concrete (FR-SCC) Flow characteristics Slump flow Filling box V-funnel

a b s t r a c t Self-compacting concrete (SCC) possesses exceptional flowability characteristics in its fresh state. While fibers are specified for their ability to limit concrete shrinkage cracks at early age and to enhance some of the concrete properties, inclusion of such fibers is expected to affect the flowability characteristics of SCC. This study investigates how the inclusion of fibrillated polypropylene fibers with different fiber content and the inclusion of steel fiber types with different aspect ratio and volume content affect the flowability of SCC. The flow characteristics were assessed by considering the slump flow test, V-funnel test and filling box test. It was found that it is quite possible to achieve self-compacting properties while using fiber reinforcement. While the mix composition and fiber type can greatly influence concrete flowability, there exists a maximum fiber content that could be used to produce fiber reinforced self-compacting concrete (FR-SCC). Moreover, our observations were used to develop a new acceptance criterion for FR-SCC. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The term ‘‘self-compacting concrete’’ (SCC) identifies a category of concrete that can be cast into a framework and fill it completely under its own weight without the need of any type of compacting or external vibration. SCC also has a great resistance to segregation and a high ability to flow around obstacles such as reinforcements or narrow sections. Since its development in the mid 1980s, various investigations have been carried out and this type of concrete has been used in several structures worldwide, culminating in the establishment of international guidelines [1–4]. SCC offers many benefits and advantages over conventional concrete. Such advantages include an improved concrete quality, fast rate of construction and low overall cost. Most of the hardened concrete properties of SCC are similar to those of conventional concrete, and most of the structural design requirements were reported to be unchanged [5]. Because SCC mixes usually have low water to cement ratio, SCC tends to be stronger, less permeable and eventually more durable compared with normal vibrated concrete. Such characteristics make it possible to produce durable structures when using SCC independent of on-site conditions relating to the quality of labor, casting and compacting systems available.

⇑ Corresponding author. Tel.: +971 3 7133042; fax: +971 3 7623154. E-mail addresses: [email protected] (A.S. El-Dieb), [email protected] (M.M. Reda Taha). 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.07.004

The inclusion of fibers in SCC will extend its benefits. Fibers bridge cracks and retard their propagation and thus improve the tensile and flexural strength and fracture toughness of hardened concrete. Therefore, the use of fibers may extend the possible fields of application of SCC. However, fibers are also known to affect the workability and flow characteristics of fresh concrete. The degree to which workability decreases depends on the type and content of fibers used and on the matrix and its constituents in which they are embedded. A good fiber distribution, however, is necessary in order to achieve optimum benefits of the fibers. Ultimately, a compromise between acceptable workability of fresh concrete and improved performance of hardened concrete has to be made. Moreover, it is well understood that the reduction of workability due to the addition of fibers is mainly dependent on the type, shape and amount of fibers used. The content of fibers that can be used while the mix is still workable depends entirely on the mixture composition and the type of fiber. Because fibers are known to affect the workability of concrete, the question arises whether the fibers are detrimental to the workability of SCC and whether it is possible to maintain the high workability of SCC while using fiber reinforcement in the mixture. Recently, several investigations were carried out to examine the ability of incorporating fibers into SCC mixtures [6–16]. It was generally concluded that including fibers will extend the technical benefits and the application possibilities of SCC [6,9,13,15]. Moreover, it was concluded that the flow characteristics of fiberreinforced self-compacting concrete (FR-SCC) differ from that of

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Table 1 Chemical analysis of cement and silica fume. Compound

CaO SiO2 Al2O3 MgO Fe2O3 SO3 Equiv. Na2O Loss on Ignition Insoluble Residue

Table 2 Properties of fibrillated polypropylene fibers.

Weight (%) Portland cement

Silica fume

61.5 21.0 6.1 3.8 3.0 2.5 0.59 1.6 0.9

1.0 90.0 1.0 1.5 1.5 0.2 1.46 – –

Color Fiber length (mm) Fiber diameter (lm) Specific gravity Young’s modulus (MPa)

Table 3 Characteristics of used steel fibers.

L (mm) D (mm) L/D

plain SCC [6,10,14] and the flow ability is impaired when fiber volume and/or aspect ratio increases [16]. Several factors were found to affect the amount of fibers that could be included without affecting the flow characteristics of SCC, such as original mix composition, fiber type, and fiber geometry (i.e. length and aspect ratio) [6,9–14]. Other factors were also identified but could not be quantified such as fiber shape and surface roughness [12]. It was also shown that some common testing techniques used for assessing plain SCC might not be suitable for FR-SCC [14]. Also, the flow through restricted space of SCC including fibers is considered more important than just judging its unrestricted flow. This might lead to increasing the free bar spacing compared with plain SCC in order to avoid blocking [6,11]. Therefore, the inclusion of fibers needs to be carefully optimized and the flow characteristics of the FR-SCC shall be properly evaluated. While all investigations examined the effect of different types of fibers on SCC, there is very limited information about the maximum fiber content to be used without affecting fundamental SCC flow characteristics (flowability, viscosity, filling capacity and passing ability). This study investigates and quantifies how the inclusion of different types of fibers affects the flow characteristics of selfcompacting concrete (SCC). It was also aimed to determine the maximum fiber content that can be used without affecting the flowability of SCC. Workability for FR-SCC was evaluated from all aspects; flowability, viscosity, filling capacity and passing ability through reinforcement (i.e. risk for blocking). Experimental investigations were carried out on several concrete mixes in order to map the dependence of the workability of SCC on mix composition, type and amount of fibers. Two types of fibers were used in this

White 18 18 0.9 360

Type (1)

Type (2)

Type (3)

8 0.16 50

13 0.16 80

30 0.5 60

Table 4 Mix proportions and characteristics of SCC reference mixes. Mix composition

M1

M2

M3

Cement content (kg/m3) Silica fume (kg/m3) W/B Ratio Sand (kg/m3) Gravel (kg/m3) Admixture (kg/m3) Sand/gravel ratio Paste volume (l/m3) Mortar volume (l/m3)

350 42 0.45 736 1104 7 40/60 314 569

400 40 0.4 720 1080 8 40/60 329 578

500 40 0.32 687 1030 10 40/60 359 597

study; fibrillated polypropylene fibers and steel fibers with various aspect ratios. A new acceptance criterion for FR-SCC is suggested. The effect of mix composition on the maximum fiber volume of each fiber type is also identified. 2. Experimental plan 2.1. Materials Cement used in this study was ordinary Portland cement (ASTM Type I). Standard silica fume was used as mineral additive; it had a specific gravity of 2.2. Chemical composition of used cement and silica fume is given in Table 1. The specific surface of the silica fume was 15.2 m2/gm. The coarse aggregate was natural siliceous gravel of nominal size of 19 mm, a specific gravity of 2.63, absorption% of 0.9%, and Los Angeles value of 14.3%. The sand used was natural siliceous sand with

Fig. 1. Experimental program of the study.

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A.S. El-Dieb, M.M. Reda Taha / Construction and Building Materials 27 (2012) 585–596 fineness modulus of 2.59, a specific gravity of 2.6 and fine materials of 1.9% by weight. A modified polycarboxylate type superplasticizer was used in the study; it complies with ASTM C 494 Types F and G. The specific gravity of the admixture was 1.1 kg/l. Two types of fibers were used in the investigation; fibrillated polypropylene and straight steel fibers. Properties of the polypropylene fibers are given in Table 2. The steel fibers used were straight fibers with circular cross section; three types with different aspect ratios were used in the study. Table 3 provides the aspect ratio, the length and the diameter for the different steel fibers used. The steel fibers had specific gravity of 7.85.

Table 6 Steel fiber mixes including SCC reference mixes M1, M2 and M3. Cement content (kg/m3)

Mix ID

Fiber factor (Vf  L/D)

350

M1 SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 SF9 SF10 SF11 SF12

0 25 50 100 150 30 60 90 120 40 80 120 160

400

M2 SF13 SF14 SF15 SF16 SF17 SF18 SF19 SF20 SF21 SF22 SF23 SF24

0 25 50 100 150 30 60 90 120 40 80 120 160

500

M3 SF25 SF26 SF27 SF28 SF29 SF30 SF31 SF32 SF33 SF34 SF35 SF36

0 25 50 100 150 30 60 90 120 40 80 120 160

2.2. Program and mixtures proportions The effects of different mix compositions on SCC flow characteristics were investigated in an earlier study in order to optimize the SCC mix proportions [17]. The SCC reference mix proportions used in this study were selected from these investigations. Three reference mixes were selected in order to have different mix proportions; primarily total cement content, total cementitious materials, paste volume, mortar volume and water to binder ratio (W/B). The reference mixes are denoted M1, M2 and M3, incorporating cement content of 350, 400 and 500 kg/m3 as presented in Table 4. Five fiber contents for the fibrillated polypropylene fibers were used for each of the SCC reference mixes. The fiber contents used in the study were 600, 900, 1200, 1500 and 1800 gm/m3. For the steel fibers, four fiber volumes (Vf) were used for each fiber type and for each SCC reference mix. The fiber volumes used for steel fiber Type (1) were 0.5%, 1.0%, 2.0% and 3.0%, while steel fiber volumes for Type (2) and Type (3) were 0.5%, 1.0%, 1.5% and 2.0%. Fig. 1 shows the experimental program of the investigation. A total of 54 mixes were examined in the study (3 control mixes, 15 mixes including polypropylene fibers and 36 mixes including steel fibers). Tables 5 and 6 present the parameters for the polypropylene fiber and steel fiber mixes respectively.

2.3. Evaluation methods Several tests were carried out in order to properly evaluate the different flow characteristics of FR-SCC as recommended by many researchers [3,4,6,18]. The properties that determine the quality of SCC are flowability, plastic viscosity, filling capacity and passing ability through reinforcement (i.e. resistance to blocking). The slump flow test characterizes the flowability of the SCC, the V-funnel gives an indication of the viscosity and the increase of resistance to flow caused by the fibers, while the filling box with reinforcement bars gives an indication of the filling capacity and passing ability through reinforcement. Table 7 gives the acceptance criteria values for SCC for the different workability tests [3]. Care shall be considered when implementing these specifications to avoid possible deposition of concrete due to the very short time specified (less than 12 s). The V-funnel test was used to evaluate the facility of aggregate particles, fibers and mortar to change their flowing paths and spread through a restricted area without blockage. Fig. 2 shows the V-funnel apparatus used in the study and its dimensions. The filling box test was used to determine the ability of concrete to deform readily among closely spaced reinforcement. Fig. 3 shows a schematic diagram of the used apparatus. The filling capacity was calculated as the ratio between the areas filled by concrete to the total area of the compartment as shown in Fig. 3.

Table 7 Acceptance criteria for SCC [3]. Slump flow V-funnel Filling box

Minimum value of 600 mm Minimum 6 s and not more than 12 s Not less than 90%

3. Results and discussions Table 5 Polypropylene fiber mixes including SCC references mixes M1, M2 and M3. Cement content (kg/m3)

Mix ID

Fiber content (g/m3)

350

M1 P1 P2 P3 P4 P5

0 600 900 1200 1500 1800

400

M2 P6 P7 P8 P9 P10

0 600 900 1200 1500 1800

500

M3 P11 P12 P13 P14 P15

0 600 900 1200 1500 1800

For polypropylene fibers, the fiber volume is used to compare the fiber effect on the SCC flowability characteristics. For steel fibers a ‘‘fiber factor’’ (Vf  L/D) is used to compare the effect of fiber on SCC flowability. The use of the fiber factor (Vf  L/D) has been adopted by other researchers to examine the combined effect of fiber volume and aspect ratio on concrete characteristics [6]. Besides the quantitative measurements of the different flowability characteristics, the distribution of aggregate and fibers were observed for each mix. Possible clustering of fibers (fibers balling), especially for steel fibers, and non-homogeneous spread of cement mortar were used as criteria to judge segregation of the mix. 3.1. Effect of polypropylene fibers The inclusion of fibers has a direct effect on the flow characteristics of SCC. The flow characteristics decrease proportionally with increasing the fiber volume. Additionally, the degree to which the flow characteristics decrease depends on the cement content in the

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425 mm

490 mm

2

150 mm

1 Outlet Gate

75

65 mm

mm

Fig. 2. V-funnel used in the investigation.

Filling capacity = (A x100)/(220x350)

Concrete

A Width 300 mm 150 mm

7x50=350 = mm

Fig. 3. Schematic diagram of the filling-box apparatus.

750 C.C. 350

C.C. 350

C.C. 400

700

Slump Flow (mm)

220 mm

300 mm

Copper pipes 16 mm diameter

concrete mix. Figs. 4–6 show the effect of fiber content on the slump flow, V-funnel flow time and the filling capacity results, respectively. From the slump flow results (Fig. 4) it could be observed that the maximum fiber content that could be included in the mixes without affecting the SCC characteristics ranges from 1300 to 1400 g/m3 depending on the mixture composition mainly cement and mortar content. At fiber volume above 1200 g/m3 it could be noticed the effect of increasing the cement content and hence the paste and mortar volume on slump flow values. As the cement content increases it helps to better disperse the fibers in the mix and helps maintain mix flowability and stability [9,10,12,14,15]. Based on the flow time and filling capacity results (Figs. 5 and 6) the maximum fiber content that could be used without affecting the SCC characteristics ranges from 1000 to 1300 g/m3. This difference in the maximum fiber content obtained from the slump flow, flow time and filling capacity tests could be attributed to the difference in the flow characteristics that each test evaluates. The slump flow test measures the free deformability of the SCC, while the V-funnel and filling box tests measure the restricted deformability of the SCC. It is obvious that the slump flow is less affected by the inclusion of fibers compared with both the flowability and filling capacity measured by the V-funnel and filling box tests. This can be attributed to the significance of friction on the flowability time and filling capacity ratio as measured by the V-funnel and filling box tests. Furthermore, the relatively high surface area of the fibers, that is typically dry, consumes some water to get wet during concrete mixing. This might affect concrete workability and flowability. Both tests force the fresh concrete to flow through small cross sections and bounded space, and therefore the friction and interference exerted by the fibers are augmented leading to the reduction of the maximum fiber content that can be used to produce SCC. By comparing the slump flow, the V-funnel flow time and the filling capacity ratio, it can be observed that there is a difference between the slump flow and both the flow time and the filling capacity ratio. Fig. 7 compares the slump flow and the flow time as SCC acceptance criteria, while Fig. 8 compares the slump flow and the filling capacity as SCC acceptance criteria. From these two figures it can be observed that the mixes categorized as SCC by the slump flow are not necessary categorized as SCC by either

C.C. 500

650

Minimum Slump Flow for SCC

600

C.C. 500

550 C.C. 400

500 0

200

400

600

800

1000

1200

1400

1600

Polypropylene Fiber Content (gm/m3) Fig. 4. Effect of polypropylene fiber content on slump flow of SCC.

1800

2000

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20 C.C. 350 C.C. 400

18

V-Funnel Flow Time (sec)

C.C. 500 C.C. 350

16 C.C. 400

14

C.C. 500 Maximum Flow Time for SCC

12

10

8

6 0

200

400

600

800

1000

1200

1400

1600

1800

2000

3

Polypropylene Fiber Content (gm/m ) Fig. 5. Effect of polypropylene fiber content on flow time of SCC.

105 C.C. 350 C.C. 400

Filling Capacity (%)

100

C.C. 500 C.C. 500 C.C. 400

95

C.C. 350

Minimum Filling Capacity for SCC

90

85

80 0

200

400

600

800

1000

1200

1400

1600

1800

2000

3

Polypropylene Fiber Content (gm/m ) Fig. 6. Effect of polypropylene fiber content on filling capacity of SCC.

the V-funnel flow time or filling capacity ratio criteria. On the other hand, Fig. 9 shows the results of comparing the flow time and the filling capacity ratio as SCC acceptance criteria. It is interesting to note that all the mixes categorized as SCC based on flow time are also categorized as SCC based on filling capacity ratio. Moreover, comparison between Figs. 7–9 shows that the mixes classified as SCC based on a combined flow time and filling capacity criteria in Fig. 9 are a subset of the mixes categorized as SCC in Figs. 7 and 8. It is therefore noted that the slump flow might not be consistent criteria for judging SCC with the inclusion of fibrillated polypropylene fibers. 3.2. Effect of steel fibers Similar to the polypropylene fibers, the inclusion of steel fibers has a significant impact on the flow time and the filling capacity of

SCC different in comparison to its effect on the slump flow. The V-funnel and the filling box were used to characterize this increase of resistance to flow. Figs. 10–12 show the effect of fiber factor (Vf  L/D) on the slump flow, V-funnel flow time and the filling capacity respectively. Observing the changes in the slump flow (Fig. 10) it can be noticed that the fiber factor that could be used without affecting the flow characteristics of the SCC ranges from 70 to 110. However, a smaller fiber factor ranging from 50 to 100 could be used without affecting the flow characteristics for SCC mixes considering the flow time and filling capacity criteria (Figs. 11 and 12). Similar to the effect of polypropylene fibers, by comparing the results from the different tests, it can be observed that a subset of the mixes categorized as SCC in Figs. 13 and 14 are also the mixes classified as SCC based on a combined flow time and filling capacity criteria in Fig. 15. We therefore argue that the slump flow test does not

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19 P5

18

V-Funnel Flow Time (sec)

17 16 P4

P10

15 P9 P15

14

P14

13

Minimum Slump Flow for SCC

590

C.C. 350 C.C. 400 C.C. 500

SCC Mixes Fulfilling Both Slump Flow and Flow Time Criteria P3 P8

Maximum Flow Time for SCC

12 11

P2

P13

P1

P12

10 P7

P6

9

P11

M1 M2

8 M3

7 500

550

600

650

700

750

Slump Flow (mm) Fig. 7. Relation between slump flow and flow time for SCC incorporating polypropylene fibers.

Minimum Slump Flow for SCC

100 98

Filling Capacity (%)

96 94 92 90

M3 M2 P11

M1 P6

P12 P1

P7 P2

P13

Minimum Filling Capacity for SCC P8 P14

88

P3 P4

86

P9

P10

84

C.C. 350

SCC Mixes Fulfilling Both Slump Flow and Filling Capacity Criteria

P15

C.C. 400 C.C. 500

P5

82 500

550

600

650

700

750

Slump Flow (mm) Fig. 8. Relation between slump flow and filling capacity for SCC incorporating polypropylene fibers.

seem to yield results consistent with other flowability test methods in classifying SCC with the incorporation of different types of fibers. Figs. 13–15 show that for the same data, acceptance of SCC is a challenging decision due to the use of multiple acceptance criteria that might not be easy to achieve all together. It is also interesting to note that most experimental results show a close to linear correlation between flow time and filling capacity ratio. An aggregated acceptance criterion based on flow time and filling capacity might provide a single consistent acceptance criterion for FR-SCC. 3.3. A new acceptance criterion for FR-SCC Based on the above observations, a new acceptance criterion of FR-SCC is suggested here. The new criterion fuses the observations

of V-funnel and filling box tests. The new flowability criterion denoted fSCC can be computed as

fSCC ¼

1 2

"

T T SCC

2

 þ

100  c 100  cSCC

2 # ð1Þ

where T is the flow time from the V-funnel test and TSCC is the acceptable flow time (considered as 12 s by the ENFRAC [3] and ACI [4]), c is the filling capacity ratio from the filling box test represented in percentage and cSCC is the acceptable filling capacity ratio (defined as 90% by the ENFRAC [3] and ACI [4]). Eq. (1) represents a classical interaction relationship where a single criterion is established to combine dual criteria requirements. Similar formulae are used in structural capacity analysis under two straining actions (e.g. torsion moment and shear forces). Eq. (1), therefore, provides

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100 M3

C.C. 350

98 M2

96

C.C. 400

SCC Mixes Fulfilling Both Flow Time and Filling Capacity Criteria

P11 M1

C.C. 500

P1 P12

92

P2

P7

90 88 86 84

Minimum Filling Capacity for SCC

P8

P13

Maximum Flow Time for SCC

Filling Capacity (%)

P6

94

P3 P14

P9 P4 P15 P10

P5

82 7

8

9

10

11

12

13

14

15

16

17

18

19

V-Funnel Flow Time (sec) Fig. 9. Relation between flow time and filling capacity for SCC incorporating polypropylene fibers.

750 C.C. 350 C.C. 400

Slump Flow (mm)

700

C.C. 500

650 C.C.500

Minimum Slump Flow for SCC

600

C.C. 400

550 C.C. 350

500

0

40

80

120

160

200

Fiber Factor (Vf * L/D) Fig. 10. Effect of fiber factor of steel fibers on slump flow of SCC.

a single acceptance criterion for SCC using V-funnel and the filling box criteria. Fiber reinforced concrete mixes with a flowability criterion fSCC 6 1.0 can be categorized as FR-SCC. Mixes with flowability criterion fSCC > 1.0 cannot be categorized as FR-SCC. Fig. 16 demonstrates the suggested acceptance criterion for FRSCC applied to all polypropylene fiber mixes. Fig. 17 shows the suggested acceptance criterion for FR-SCC applied to all steel fiber mixes. In both figures the acceptance criterion is represented by the contour line representing fSCC = 1.0. Mixes that lie inside the contour area can be categorized as FR-SCC. Mixes which lie outside the contour area cannot be categorized as FR-SCC. The suggested flowability criterion is less conservative than considering two independent criteria for flow time and filling capacity ratio as

considered in Figs. 7–9 for polypropylene fibers or Figs. 13–15 for steel fibers. The strong correlation between the flow time and filling capacity ratio observed in all experimental data downplays the effect of added area for the suggested flowability criterion (from a graphical representation point of view compared with the independent straight lines used to categorize FR-SCC mixes in Figs. 7–9 and 13–15) as no practical mixes will fall in the added area. All concrete mixes including polypropylene fiber classified as SCC in Fig. 9 are classified as SCC in Fig. 16. Moreover, all concrete mixes including steel fiber classified as SCC in Fig. 15 are classified as SCC in Fig. 17. This indicates that the proposed criterion agrees with the classification using the two independent criteria: flow time and filling capacity ratio.

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19 18

V-Funnel Flow Time (sec)

17 C.C. 350

16 15 14 13

Maximum Flow Time for SCC

12 11 10

C.C. 500

9

C.C. 400

C.C. 350

8

C.C. 400

7

C.C. 500

6 5 0

40

80

120

160

200

Fiber Factor (Vf * L/D) Fig. 11. Effect of fiber factor of steel fibers on flow time of SCC.

105 C.C. 350 C.C. 400

100

Filling Capacity (%)

C.C. 500

95

Minimum Filling Capacity for SCC

90

C.C. 400

85

C.C. 350

80

C.C. 500

75 0

40

80

120

160

200

Fiber Factor (Vf * L/D) Fig. 12. Effect of polypropylene fiber content on filling capacity of SCC.

The proposed acceptance criterion shall provide an individual performance index to easily categorize SCC mixes incorporating fibers. The use of individual acceptance criterion shall enable using different types of fibers while maintaining SCC performance. Finally, it is important to note that given the proposed acceptance criterion, the maximum polypropylene fiber content of 1000, 1200 and 1300 g/m3 and a maximum steel fiber factor of 50, 90 and 100 can be used to produce SCC for the three control mixes of interest M1, M2 and M3 respectively. 3.4. Effect of mixture composition The flowability characteristics of the FR-SCC were not only affected by the fiber volume and fiber type but also by the mixture

composition [6,7,10,12]. The maximum fiber volume to be incorporated in the mixture was found to depend on the mixture composition; mainly its paste and mortar volume fractions. Fig. 18 shows the maximum fibrillated polypropylene fiber content and the maximum steel fiber factor (Vf  L/D) for different cement contents that could be incorporated into the mixtures to produce FR-SCC based on flow time and filling capacity test results. As the paste and mortar volume fractions increase, the mixture could accommodate higher fibrillated polypropylene fiber volume and higher steel fiber factor (i.e. either higher fiber volume for the same aspect ratio or higher aspect ratio for the same fiber volume). This could be attributed to the better flowability of the mix as increasing the cement paste volume makes it possible to increase the fiber content and still produces SCC mixes with acceptable flowability limits.

593

18 SF12

17

SF4 SF11

16 SF8 SF24

V-Funnel Flow Time (sec)

15

SF3

SF7

SF36 SF28

SF16

14

SF10

SF23

C.C. 350 C.C. 400 C.C. 500 SCC Mixes Fulfilling Both Slump Flow and Flow Time Criteria

SF35 SF32 SF20 SF15 SF27

13 12

Minimum Slump Flow for SCC

A.S. El-Dieb, M.M. Reda Taha / Construction and Building Materials 27 (2012) 585–596

SF6 SF31

Maximum Flow Time for SCC

SF19

SF18 SF34 SF9 SF2 SF30

SF22

11

SF14 SF26

SF5

10

SF21

SF17

SF1

9

SF13

SF33

M1

SF25

SF29

M3

8

M2

7 500

550

600

650

700

750

Slump Flow (mm) Fig. 13. Relation between slump flow and flow time for SCC incorporating different steel fibers.

Minimum Slump Flow for SCC

105

Filling Capacity (%)

100

95

M2 SF13

SF26 SF21

M3 SF29 SF33

M1

SF30 SF18

SF14

SF19 SF22

Minimum Filling Capacity for SCC

SF25

SF17

90

SF2

SF1

SF5 SF34 SF9

SF31 SF20 SF23

SF27 SF6

SF15

C.C. 350

SF10

85

SF16

SF8 SF4

80

SF7

SF35

C.C. 400

SCC Mixes Fulfilling Both Slump Flow and Filling Capacity Criteria

SF32

SF24 SF3 SF28

C.C. 500

SF36 SF11

SF12

75 500

550

600

650

700

750

Slump Flow (mm) Fig. 14. Relation between slump flow and filling capacity for SCC incorporating different steel fibers.

4. Conclusions Experimental investigations of SCC including fiber reinforcement have showed that it is possible to maintain self-compacting flow characteristics while using fiber reinforcement. The maximum fiber content that can be used without affecting the

flowability characteristics of SCC has been determined. It is evident that the mix compositions mainly paste and mortar volume and the fiber type greatly influence the maximum possible fiber content. The experimental investigations have also shown that the use of the slump flow test might not yield consistent results in evaluating

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105 C.C. 350

100

SCC Mixes Fulfilling Both Flow Time and Filling Capacity Criteria

M2

C.C. 400 C.C. 500

SF25 SF13 M3

SF17 SF21

SF26

SF33

SF14 SF1

SF5

SF18 SF30 SF34 SF9

SF19 SF31

SF22

90

85

80

Minimum Filling Capacity for SCC

SF20

SF6

SF2

Maximum Flow Time for SCC

Filling Capacity (%)

SF30 M1

95

SF23

SF27 SF15

SF10 SF35

SF16 SF7

SF32

SF8

SF28 SF3 SF24

SF11 SF4

SF36

SF12

75 7

8

9

10

11

12

13

14

15

16

17

18

V-Funnel Flow Time (sec) Fig. 15. Relation between flow time and filling capacity for SCC incorporating different steel fibers.

Fig. 16. Proposed acceptance criterion applied to polypropylene fiber mixes showing mixes classified as FR-SCC laying inside the SCC contour (fSCC = 1.0).

the flowability of FR-SCC. This can be attributed to the test method, which only evaluates free deformability of the SCC and cannot efficiently evaluate the restricted deformability, which is important in the case of FR-SCC. V-funnel and filling box tests should be used to assess workability and blockage resistance. These two tests have showed consistent results and can be used to identify the suitable fiber content for FR-SCC. Therefore, combination of test devices can be regarded as an appropriate means to describe and evaluate flow characteristics of FR-SCC. New aggregated acceptance criteria based on flow time from the V-funnel test and the filling capacity ratio from the filling box test is suggested. The suggested criterion, while being less conservative, yields consistent results with the two independent

acceptance criteria (flow time and filling capacity ratio) and can thus be used to identify the maximum fiber content to produce FR-SCC. For polypropylene fibers, the maximum fiber content that could be used to produce FR-SCC is 1000, 1200 and 1300 g/m3 for SCC mixtures with cement content 350, 400 and 500 kg/m3 respectively. While for steel fibers, the maximum fiber factor (Vf  L/D) that could be used is 50, 90 and 100 for SCC mixtures with cement content 350, 400 and 500 kg/m3 respectively. The above investigation was limited to straight fibers. Other types of steel fibers, especially those with corrugated/crimped shape and bent edges, need to be examined in order to establish their maximum fiber content to produce FR-SCC.

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Fig. 17. Proposed acceptance criterion applied to steel fiber mixes showing mixes classified as FR-SCC laying inside the SCC contour (fSCC = 1.0).

1400

120 1300 1200

100

Steel Fibers

100 90

1000

1000 80 800 60 600

50

40 400

Steel Fiber Factor (Vf * L/D)

Polypropylene Fiber Content (gm/m3)

Polyp. Fibers

1200

20

200

0

0 350

400

500

Cement Content (kg/m3) Fig. 18. Maximum polypropylene fiber content and steel fiber factor to produce FR-SCC.

Acknowledgment The authors would like to acknowledge the help by Mrs. E. Khattab in performing experiments of reference mixes. The financial support by home institutions for both authors is greatly acknowledged. References [1] Okamura H, Ouchi M. Self-compacting concrete. J Adv Concr Technol 2003;1(1):5–15. [2] Okamura H. Self-compacting high-performance concrete. Concr Int 1997;19(7):50–4.

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