- Email: [email protected]
Workability of hybrid fiber reinforced self-compacting concrete
ARTICLE IN PRESS
Building and Environment 40 (2005) 1672–1677 www.elsevier.com/locate/buildenv
Workability of hybrid fiber reinforced self-compacting concrete Mustafa Sahmaran, Alperen Yurtseven, I. Ozgur Yaman Department of Civil Engineering, Middle East Technical University, 06531 Ankara, Turkey Received 24 March 2004; received in revised form 9 December 2004; accepted 14 December 2004
Abstract Compared to fiber reinforced concrete (FRC), self-compacting concrete (SCC) is a relatively new type of concrete with high flowability and good cohesiveness. It offers very attractive economical and technical benefits, which can be further extended when combined with FRC. In this article two different types of steel fibers were used, in combination, and the effects of fiber inclusion on the workability of hybrid fiber reinforced self-compacting concrete (HFR-SCC) is studied. The effects of fibers are quantified based on the fiber volume, length, and aspect ratios of the fibers. It was concluded that in addition to the above-mentioned quantifiable three properties, other properties of fibers such as shape and surface roughness are also found to be important but they cannot be quantified at this stage. r 2005 Elsevier Ltd. All rights reserved. Keywords: Concrete; Workability; Self-compacting concrete; Hybrid fiber reinforcement
1. Introduction Self-compacting concrete (SCC) can be considered as a concrete which has little resistance to flow so that it can be placed and compacted under its own weight with little or no vibration effort, yet possesses enough viscosity to be handled without segregation or bleeding. SCC was developed in Japan in the late 1980s as a solution to achieve durable concrete structures independent of the quality of construction work [1]. In designing a SCC usually new generation polycarboxylic-based super-plasticizers are utilized together with either some chemical or mineral admixtures that provides the necessary viscosity. The fresh mechanical properties of SCC are often determined through the use of rheometers, which measures the viscosity and the yield strength of concrete when it is in plastic state. However, this equipment is lab-oriented and is not usually practical for field-use. Therefore, other field-oriented Corresponding author. Tel.: +90 312 210 5473; fax: +90 312 210 1262. E-mail address: [email protected] (I. Ozgur Yaman).
0360-1323/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2004.12.014
test methods are used in quantifying the fresh properties and workability of SCC both in the lab and field. The term fiber reinforced concrete (FRC) can be defined as a concrete containing dispersed randomly oriented fibers. Inherently concrete is brittle under tensile loading and mechanical properties of concrete may be improved by randomly oriented discrete fibers which prevent or control initiation, propagation, or coalescence of cracks [2]. The character and performance of FRC changes, depending on the properties of concrete and the fibers. The properties of fibers that are usually of interest are fiber concentration, fiber geometry, fiber orientation, and fiber distribution. Moreover, using a single type of fiber may improve the properties of FRC to a limited level. However the concept of hybridization, adding two or more types of fiber into concrete, can offer more attractive engineering properties as the presence of one fiber enables the more efficient utilization of the potential properties of the other fiber [3,4]. Use of fibers into SCC mixes has been presented by many researchers [5,6]. Depending on many parameters such as maximum aggregate size, fiber volume, fiber
ARTICLE IN PRESS M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
type, fiber geometry, and fiber aspect ratio, fiber inclusion to concrete reduces the workability of concrete. Reduction of workability in FRC is a handicap for on-site applications. However, the combination of hybrid FRC and SCC together can provide a way of producing a hybrid fiber reinforced self-compacting concrete (HFR-SCC) with superior properties in not only hardened state but also fresh state. In this article, two different types of steel fibers (Dramix ZP-305 and OL-6/16) are used, in combination, and the effect of fiber inclusion on the workability of HFR-SCC is studied. Slump flow, V-funnel, and J-ring tests are performed to assess workability. Moreover, the mechanical properties, namely the compressive and tensile strengths, and the ultrasonic pulse velocities of HFR-SCC mixtures are also determined at various ages.
2. Experimental program The experimental program consisted of batching six mixtures of HFR-SCC, a plain control mix and five fiber reinforced mixes with a total fiber content of 60 kg/m3.
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Table 1 Physical, mechanical, and chemical properties of Portland cement Properties
%
Chemical Insoluble residue SiO2 Al2O3 Fe2O3 CaO Free CaO MgO SO3 Loss on ignition Na2O K2O
0.38 18.85 5.58 2.5 63.27 0.88 2.82 2.93 2.44 0.19 1.04
Physical and mechanical Specific gravity (g/cm3) Fineness (Blaine) (cm2/g) Initial setting time (min) Final setting time (min) Comp. strength (MPa), 1 day 7 days 28 days
3.11 3020 188 240 18.7 29.5 42.4
2.1. Materials The properties of materials used in producing HFRSCC are as follows:
The cement used in all mixes was normal Portland cement, which corresponds to ASTM Type I cement. Chemical composition, physical and mechanical properties of the cement are given in Table 1. Limestone powder (LP) was used as a mineral viscosity enhancing admixture. LP was a by-product of marble extraction with a CaCO3 content of 98% and a specific gravity of 2.70. As for the aggregates, crushed limestone and crushed sand from the same local source were used. As can be seen from the gradation of the aggregates presented in Table 2, the maximum aggregate size was 19 mm. The coarse and fine aggregate each had a specific gravity of 2.70, and water absorptions of 0.5% and 1.2%, respectively. Two cylindrical steel fiber types, one with hooked ends (Dramix ZP 305) and one straight type (Dramix OL 6/16), were used. Their specific gravities were 7.85 and 7.17, respectively. The straight fiber (OL 6/16) was made of high strength steel with a brass coating, which provides it with a relatively smooth surface. The length and aspect ratio of the ZP 305 was 30 mm and 55, respectively, compared to 6 mm and 37.5 of OL 6/16. The fiber content was kept constant at 60 kg/ m3 for all the mixtures. A novel polycarboxylic ether type superplasticizer (SP) produced by a local manufacturer was used in all
Table 2 Grading of coarse and fine aggregate Sieve size (mm)
Fine (% passing)
Coarse (% passing)
19 12.7 9.5 4.75 2.36 1.18 0.6 0.3 0.15
100 100 100 96.9 85.5 68.3 42.3 17.4 3.7
100 58.6 35.8 0 — — — — —
concrete mixtures. The chemical and physical properties of SP are shown in Table 3. The SP used in this study had a significant price advantage over other commercially available superplasticizers. Thus from an engineering point of view, the use of this SP and investigation of its performance in SCC are found to be valuable.
2.2. Mixture proportions Six were Table fibers
mixtures, one control and five fiber reinforced, prepared. Mixture proportions are given in 4. As seen from the table, except for the steel all ingredients were kept constant. For the
ARTICLE IN PRESS M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
1674 Table 3 Properties of the superplasticizer Specific gravity
pH
Solid content (%)
Recommended amount (% cement weight)
Main component
1.08
5.7
40
0.5–2.5
Polycarboxylic ether
Table 4 Mixture proportions Mixture no
1 2 3 4 5 6
w/ca
0.4 0.4 0.4 0.4 0.4 0.4 a
Water (kg/m3)
200 200 200 200 200 200
Cement (kg/m3)
500 500 500 500 500 500
LP (kg/m3)
70 70 70 70 70 70
Aggregate (kg/m3)
Steel fiber (kg/m3)
Fine
Coarse
ZP 305
OL 6/16
990 977 977 977 977 977
586 578 578 578 578 578
0 60 42 30 18 0
0 0 18 30 42 60
SP (kg/m3)
9.5 9.5 9.5 9.5 9.5 9.5
w/c : water cement ratio.
mixtures with steel fibers, the fiber ratio of ZP305 to total fiber content was changed from 100, 70, 50, 30, and 0%. For all the mixes, the water/powder ratio by volume was kept constant as 1.07 and is in the range of SCC (0.80–1.10) given by the European Federation for Specialist Construction Chemicals and Concrete Systems (EFNARC) [7] as shown in Table 4. The fine and coarse aggregate together with fibers was initially dry mixed for about 30 s. This was followed by the addition of cement, limestone powder and 1/3 of total mixing water. After 1.5 min of mixing, the rest of the mixing water together with the SP was added. All batches were mixed for a total mixing time of 5 min. Specimens for the testing of the hardened properties were prepared by direct pouring of concrete into molds without compaction. For each mixture, six 150 mm cubes and three 150 300 mm cylinder specimens were cast. Cubes were used for the determination of compressive strengths and ultrasonic pulse velocities at 28 and 56 days, whereas cylinders were used for the determination of split tensile strength at 56 days. The specimens were demolded after one day and then placed in a curing room with 90% RH and 20–23 1C temperature until the testing day.
2.3. Test procedures The workability methods used in this study are given and standardized by the Self-Compacting-Concrete Committee of EFNARC [7] and measure the free and restricted deformability (slump flow and J-ring) and stability (V-funnel and slump flow) of an SCC mix [8]. These three test procedures are briefly described below:
The slump flow is used to evaluate the horizontal free flow (deformability) of SCC in the absence of obstructions. The test method is very similar to the test method for determining the slump of concrete. The difference is that, instead of the loss in height, the diameter of the spread concrete is measured in two perpendicular directions and recorded as slump flow (Fig. 1a ). The higher the slump flow, the greater the concrete’s ability to fill formworks. During the slump flow test, the time required for the concrete to reach a diameter of 500 mm is also measured and recorded as t500. This parameter is an indication of the viscosity of concrete and indicates how stable the concrete is. A lower time points to a greater flowability. J-ring test is used to determine the passing ability of the concrete. It is an extension of the slump flow test in which a ring apparatus (Fig. 1b ) is used and the difference in height between the concrete inside and that just outside of the ring is measured. This gives an indication of the passing ability, restricted deformability, of concrete. The V-funnel test is used to determine the flowability or viscosity of concrete. The funnel (Fig. 1c) is filled with about 12 l of concrete and the time it takes for the concrete to flow through the apparatus is measured. Good flowable and stable concrete would consume a short time to flow out.
2.4. Fresh and hardened properties Basic workability requirements for successful casting of SCC are summarized by Khayat [8] as excellent
ARTICLE IN PRESS M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
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Table 5 Tests on fresh concrete Mixture no.
1 2 3 4 5 6
Slump flow D (mm)
t500 (s)
745 620 695 615 660 675
4.2 4.3 4.5 4.1 2.8 2.6
V-funnel time (s)
¯ (mm) J-ring DH
13.8 17.6 16.4 15.1 14.0 9.2
10.0 10.0 10.0 11.3 7.5 15.0
in Table 5. In addition to the above properties, visual inspection of fresh concrete did not dictate any segregation or considerable bleeding in any of the mixtures. All mixtures were tested for compressive strength at 28 and 56 days, and split tensile strength at 56 days in accordance with the related ASTM standards. The density of hardened concrete at 28 days and the ultrasonic pulse velocities were also measured for all mixes at 28 and 56 days. The average of three specimen properties at a particular age was considered as its property and presented in Table 6.
3. Results and discussion
Fig. 1. Workability tests and apparatus: (a) Slump flow, (b) J-ring, (c) V-funnel.
deformability, good stability and low risk of blockage. In this experimental program these three properties are measured, respectively, by slump flow, V-funnel and Jring tests. The measured fresh properties are presented
As can be seen from Table 5, slump flow test results show that all mixes had enough deformability under their own weight, despite the fiber inclusion, and had a moderate viscosity, which is necessary to avoid segregation. V-funnel measurements of some mixes exceeded the upper limit suggested by EFNARC (Table 7); however it should be kept in mind that limits suggested by EFNARC are designated for plain SCC. As mentioned earlier, the viscosity of the HFR-SCC, as dictated by the t500 measurements of the slump flow test and V-funnel test, seemed to be affected by the fiber inclusion, giving shorter slump flow (t500) and V-funnel test measurements and pointing out to a better flowing concrete. As presented in Fig. 2, as the volume fraction (Vf) of OL 6/16 fibers increased, the viscosity decreased as dictated by the reduction in the slump flow (t500) and V-funnel tests. On the other hand, both the slump flow (D) and J-ring test results did not show any effect of fiber inclusion as seen in Fig. 3. To quantify the effects of ZP305 and OL6/16 on the viscosity of HFR-SCC, regression analysis is performed. In FRC, the parameter Vfl/d, named fiber factor, which is the volume fraction of fibers times the aspect ratio of the fiber, is used to identify the effects of fibers. Assuming the fiber factor as the single parameter to affect the properties of HRF-SCC, single-variate regression analyses are performed with respect to slump flow
ARTICLE IN PRESS M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
1676 Table 6 Tests on hardened concrete Density (kg/m3) (28 days)
Mix. no.
1 2 3 4 5 6
2327 2389 2387 2362 2311 2349
Compressive strength (MPa) (28 days)
(56 days)
50.9 49.5 44.4 56.3 55.2 58.9
53.0 52.7 54.8 61.5 61.0 63.2
4.3 4.6 4.8 5.1 3.7 3.6
Unit
Slump flow t500 Slump flow J-ring V-funnel
Min
Max
Normalized Measurement
(56 days)
4823 4790 4690 4755 4742 4754
4886 4873 4876 4772 4752 4790
650 2 0 6
800 5 10 12
ðR2 ¼ 0:10Þ,
Slump flow t500 ðsÞ ¼ 3:85 0:32V f l=d
ðR2 ¼ 0:01Þ:
As can be seen from the low correlation coefficients of the above regression equations, the fiber factor is not the only parameter affecting HFR-SCC properties. Since the fibers had different geometry and surface roughness, they have to be treated differently and multivariate regression analyses should be performed using the fiber factor parameter as the variable. The following relationships and R2 were obtained after such analyses.
1.50
V funnelðsÞ ¼ 13:8 þ 11:2V f l=d ZP305 10:8V f l=d OL6=16
ðR2 ¼ 0:90Þ,
Slump flow t500 ðsÞ ¼ 4:20 þ 1:16V f l=d ZP305 4:99V f l=d OL6=16
1.25 1.00 0.75 0.50 t500 - Slump Flow V-funnel
0.25 0.00 0.0
0.2
0.4
0.6
0.8
1.0
Vf,OL6/16 / (Vf,OL6/16 + Vf,ZP305) Fig. 2. Tests for stability (viscosity) of HFR-SCC.
1.50 Normalized Measurement
(28 days)
V-funnelðsÞ ¼ 12:5 þ 5:89V f l=d
Typical range values
mm s mm s
Ultrasonic pulse velocity (m/s)
(t500) and V-funnel tests and the following relationships and correlation coefficients (R2) were obtained.
Table 7 EFNARC suggested workability limits Method
Split tensile strength (MPa) (56 days)
1.25 1.00 0.75 0.50 Slump Flow - D J-ring
0.25 0.00 0.0
0.2
0.4
0.6
0.8
Vf,OL6/16 / (Vf,OL6/16 + Vf,ZP305) Fig. 3. Tests for deformability of HFR-SCC.
1.0
ðR2 ¼ 0:79Þ.
As can be seen from the high correlation coefficients, these equations tend to represent the original data quite well. This could be explained by the OL 6/16 fibers being smaller then ZP 305 fibers, thus having less potential to prevent the movement of aggregates. In addition, OL 6/ 16 fibers are coated with brass and have very smooth surfaces, which reduces the energy loss during the movement of particles. On the other hand, ZP 305 fibers have hooked ends, and relatively larger dimensions thus cause blocking of particles during flow. In addition to the fresh properties, some hardened properties of the HFR-SCC are also determined. These include the compressive, tensile, and ultrasonic pulse velocity of concrete at various ages. As seen in Fig. 4, an increase in compressive strengths was observed as the OL 6/16 content was increased in all mixes. Compared with the mix having only ZP305, when only OL6/16 was used both 28 and 56 day strengths increased on the order of 20%. This trend can be attributed to the relatively small dimensions of OL 6/16 fibers, which delay and to a certain extent prevent the formation and propagation of micro-cracks in the concrete matrix. As for the tensile strength, which is determined by the split tension test, the split tensile strength seemed to be affected by the fibers and the effect of fiber hybridization can be observed on the obtained test results. Highest split tensile strength occurred in mix 4 in which fibers were proportioned equally. On the other hand,
ARTICLE IN PRESS
Normalized Measurement
M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
1.25 1.20 1.15
f'c,28 f'c,56 ft,56
1.10 1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.0
0.2
0.4
0.6
0.8
1.0
Vf,OL6/16 / (Vf,OL6/16 + Vf,ZP305) Fig. 4. Tests for strength properties of HFR-SCC.
ultrasonic pulse velocities did not seem to be affected by the amount of fibers used in this article. The negligible variation in the ultrasonic pulse velocity test results can be considered as an indication of the uniformity of concrete matrix in all mixes.
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invaluable data for the purpose of producing HFRSCC. In order to retain high level workability with fiber reinforcement, the amount of paste in the mix should be increased to provide better dispersion of fibers. Increasing cement content, increasing fine aggregate content or using pozzolanic admixtures can be alternative solutions to this problem, and these alternatives will be investigated through the progress of this experimental program. As for the hardened properties, only the effects of the strengthening component of fiber reinforcement were observed. The mix reinforced with only OL 6/16 fibers had the highest compressive strength values at both 28 and 56 days, whereas mix containing equal amounts of ZP305 and OL 6/16 fibers gave the highest splitting tensile strength value. The effects of the toughening component of fiber reinforcement and fiber hybridization shall be observed and a clearer view shall be attained with the results of the toughness tests, which are yet to be obtained.
References 4. Conclusions This paper discusses the preliminary results of an ongoing experimental program carried out to investigate the effects of fiber inclusion on the flow characteristics of HFR-SCC and mechanical properties in the hardened state. Two different types of steel fibers were used in combination and tests were performed in both fresh and hardened states. It was observed that it is possible to achieve selfcompaction with considerable fiber inclusion (60 kg/m3). Although results obtained from some of the mixes exceeded the upper limits suggested by EFNARC, all mixes had good flowability and possessed self-compaction characteristics. SP with the commercial name Smartflow was successfully employed and proved to be efficient in the production of an economical SCC without the use of any viscosity enhancing chemical admixtures. The results of this study yielded raw but
[1] Okamura H, Ouchi M. Self-compacting concrete. Journal of Advanced Concrete Technology 2003;1(1):5–15. [2] Hannant DJ. Fiber cements and fiber concrete. Chichester, UK: Wiley; 1987. [3] Bentur A, Mindess S. Fiber reinforced cementitious composites. London: Elsevier; 1990. [4] Mobasher B, Li CY. Mechanical properties of hybrid cementbased composites. ACI Materials Journal 1996;93(3):284–92. [5] Khayat KH, Roussel Y. Testing and performance of fiberreinforced, self-consolidating concrete. In: Skarendahl A, Petersson O, editors. Proceedings of the first international RILEM symposium on self-compacting concrete. Stockholm, Sweden: September 13–14, 1999. p. 509–21. [6] Groth P, Nemegeer D. The use of steel fibres in self-compacting concrete. In: Skarendahl A, Petersson O, editors. Proceedings of the first international RILEM symposium on self-compacting concrete. Stockholm, Sweden: 13–14 September: 1999. p. 497–507. [7] EFNARC. Specification & guidelines for self-compacting concrete. English ed. Norfolk, UK: European Federation for Specialist Construction Chemicals and Concrete Systems; 2002. [8] Khayat KH. Workability, testing and performance of selfconsolidating concrete. ACI Materials Journal 1999;96(3):346–53.
Building and Environment 40 (2005) 1672–1677 www.elsevier.com/locate/buildenv
Workability of hybrid fiber reinforced self-compacting concrete Mustafa Sahmaran, Alperen Yurtseven, I. Ozgur Yaman Department of Civil Engineering, Middle East Technical University, 06531 Ankara, Turkey Received 24 March 2004; received in revised form 9 December 2004; accepted 14 December 2004
Abstract Compared to fiber reinforced concrete (FRC), self-compacting concrete (SCC) is a relatively new type of concrete with high flowability and good cohesiveness. It offers very attractive economical and technical benefits, which can be further extended when combined with FRC. In this article two different types of steel fibers were used, in combination, and the effects of fiber inclusion on the workability of hybrid fiber reinforced self-compacting concrete (HFR-SCC) is studied. The effects of fibers are quantified based on the fiber volume, length, and aspect ratios of the fibers. It was concluded that in addition to the above-mentioned quantifiable three properties, other properties of fibers such as shape and surface roughness are also found to be important but they cannot be quantified at this stage. r 2005 Elsevier Ltd. All rights reserved. Keywords: Concrete; Workability; Self-compacting concrete; Hybrid fiber reinforcement
1. Introduction Self-compacting concrete (SCC) can be considered as a concrete which has little resistance to flow so that it can be placed and compacted under its own weight with little or no vibration effort, yet possesses enough viscosity to be handled without segregation or bleeding. SCC was developed in Japan in the late 1980s as a solution to achieve durable concrete structures independent of the quality of construction work [1]. In designing a SCC usually new generation polycarboxylic-based super-plasticizers are utilized together with either some chemical or mineral admixtures that provides the necessary viscosity. The fresh mechanical properties of SCC are often determined through the use of rheometers, which measures the viscosity and the yield strength of concrete when it is in plastic state. However, this equipment is lab-oriented and is not usually practical for field-use. Therefore, other field-oriented Corresponding author. Tel.: +90 312 210 5473; fax: +90 312 210 1262. E-mail address: [email protected] (I. Ozgur Yaman).
0360-1323/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2004.12.014
test methods are used in quantifying the fresh properties and workability of SCC both in the lab and field. The term fiber reinforced concrete (FRC) can be defined as a concrete containing dispersed randomly oriented fibers. Inherently concrete is brittle under tensile loading and mechanical properties of concrete may be improved by randomly oriented discrete fibers which prevent or control initiation, propagation, or coalescence of cracks [2]. The character and performance of FRC changes, depending on the properties of concrete and the fibers. The properties of fibers that are usually of interest are fiber concentration, fiber geometry, fiber orientation, and fiber distribution. Moreover, using a single type of fiber may improve the properties of FRC to a limited level. However the concept of hybridization, adding two or more types of fiber into concrete, can offer more attractive engineering properties as the presence of one fiber enables the more efficient utilization of the potential properties of the other fiber [3,4]. Use of fibers into SCC mixes has been presented by many researchers [5,6]. Depending on many parameters such as maximum aggregate size, fiber volume, fiber
ARTICLE IN PRESS M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
type, fiber geometry, and fiber aspect ratio, fiber inclusion to concrete reduces the workability of concrete. Reduction of workability in FRC is a handicap for on-site applications. However, the combination of hybrid FRC and SCC together can provide a way of producing a hybrid fiber reinforced self-compacting concrete (HFR-SCC) with superior properties in not only hardened state but also fresh state. In this article, two different types of steel fibers (Dramix ZP-305 and OL-6/16) are used, in combination, and the effect of fiber inclusion on the workability of HFR-SCC is studied. Slump flow, V-funnel, and J-ring tests are performed to assess workability. Moreover, the mechanical properties, namely the compressive and tensile strengths, and the ultrasonic pulse velocities of HFR-SCC mixtures are also determined at various ages.
2. Experimental program The experimental program consisted of batching six mixtures of HFR-SCC, a plain control mix and five fiber reinforced mixes with a total fiber content of 60 kg/m3.
1673
Table 1 Physical, mechanical, and chemical properties of Portland cement Properties
%
Chemical Insoluble residue SiO2 Al2O3 Fe2O3 CaO Free CaO MgO SO3 Loss on ignition Na2O K2O
0.38 18.85 5.58 2.5 63.27 0.88 2.82 2.93 2.44 0.19 1.04
Physical and mechanical Specific gravity (g/cm3) Fineness (Blaine) (cm2/g) Initial setting time (min) Final setting time (min) Comp. strength (MPa), 1 day 7 days 28 days
3.11 3020 188 240 18.7 29.5 42.4
2.1. Materials The properties of materials used in producing HFRSCC are as follows:
The cement used in all mixes was normal Portland cement, which corresponds to ASTM Type I cement. Chemical composition, physical and mechanical properties of the cement are given in Table 1. Limestone powder (LP) was used as a mineral viscosity enhancing admixture. LP was a by-product of marble extraction with a CaCO3 content of 98% and a specific gravity of 2.70. As for the aggregates, crushed limestone and crushed sand from the same local source were used. As can be seen from the gradation of the aggregates presented in Table 2, the maximum aggregate size was 19 mm. The coarse and fine aggregate each had a specific gravity of 2.70, and water absorptions of 0.5% and 1.2%, respectively. Two cylindrical steel fiber types, one with hooked ends (Dramix ZP 305) and one straight type (Dramix OL 6/16), were used. Their specific gravities were 7.85 and 7.17, respectively. The straight fiber (OL 6/16) was made of high strength steel with a brass coating, which provides it with a relatively smooth surface. The length and aspect ratio of the ZP 305 was 30 mm and 55, respectively, compared to 6 mm and 37.5 of OL 6/16. The fiber content was kept constant at 60 kg/ m3 for all the mixtures. A novel polycarboxylic ether type superplasticizer (SP) produced by a local manufacturer was used in all
Table 2 Grading of coarse and fine aggregate Sieve size (mm)
Fine (% passing)
Coarse (% passing)
19 12.7 9.5 4.75 2.36 1.18 0.6 0.3 0.15
100 100 100 96.9 85.5 68.3 42.3 17.4 3.7
100 58.6 35.8 0 — — — — —
concrete mixtures. The chemical and physical properties of SP are shown in Table 3. The SP used in this study had a significant price advantage over other commercially available superplasticizers. Thus from an engineering point of view, the use of this SP and investigation of its performance in SCC are found to be valuable.
2.2. Mixture proportions Six were Table fibers
mixtures, one control and five fiber reinforced, prepared. Mixture proportions are given in 4. As seen from the table, except for the steel all ingredients were kept constant. For the
ARTICLE IN PRESS M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
1674 Table 3 Properties of the superplasticizer Specific gravity
pH
Solid content (%)
Recommended amount (% cement weight)
Main component
1.08
5.7
40
0.5–2.5
Polycarboxylic ether
Table 4 Mixture proportions Mixture no
1 2 3 4 5 6
w/ca
0.4 0.4 0.4 0.4 0.4 0.4 a
Water (kg/m3)
200 200 200 200 200 200
Cement (kg/m3)
500 500 500 500 500 500
LP (kg/m3)
70 70 70 70 70 70
Aggregate (kg/m3)
Steel fiber (kg/m3)
Fine
Coarse
ZP 305
OL 6/16
990 977 977 977 977 977
586 578 578 578 578 578
0 60 42 30 18 0
0 0 18 30 42 60
SP (kg/m3)
9.5 9.5 9.5 9.5 9.5 9.5
w/c : water cement ratio.
mixtures with steel fibers, the fiber ratio of ZP305 to total fiber content was changed from 100, 70, 50, 30, and 0%. For all the mixes, the water/powder ratio by volume was kept constant as 1.07 and is in the range of SCC (0.80–1.10) given by the European Federation for Specialist Construction Chemicals and Concrete Systems (EFNARC) [7] as shown in Table 4. The fine and coarse aggregate together with fibers was initially dry mixed for about 30 s. This was followed by the addition of cement, limestone powder and 1/3 of total mixing water. After 1.5 min of mixing, the rest of the mixing water together with the SP was added. All batches were mixed for a total mixing time of 5 min. Specimens for the testing of the hardened properties were prepared by direct pouring of concrete into molds without compaction. For each mixture, six 150 mm cubes and three 150 300 mm cylinder specimens were cast. Cubes were used for the determination of compressive strengths and ultrasonic pulse velocities at 28 and 56 days, whereas cylinders were used for the determination of split tensile strength at 56 days. The specimens were demolded after one day and then placed in a curing room with 90% RH and 20–23 1C temperature until the testing day.
2.3. Test procedures The workability methods used in this study are given and standardized by the Self-Compacting-Concrete Committee of EFNARC [7] and measure the free and restricted deformability (slump flow and J-ring) and stability (V-funnel and slump flow) of an SCC mix [8]. These three test procedures are briefly described below:
The slump flow is used to evaluate the horizontal free flow (deformability) of SCC in the absence of obstructions. The test method is very similar to the test method for determining the slump of concrete. The difference is that, instead of the loss in height, the diameter of the spread concrete is measured in two perpendicular directions and recorded as slump flow (Fig. 1a ). The higher the slump flow, the greater the concrete’s ability to fill formworks. During the slump flow test, the time required for the concrete to reach a diameter of 500 mm is also measured and recorded as t500. This parameter is an indication of the viscosity of concrete and indicates how stable the concrete is. A lower time points to a greater flowability. J-ring test is used to determine the passing ability of the concrete. It is an extension of the slump flow test in which a ring apparatus (Fig. 1b ) is used and the difference in height between the concrete inside and that just outside of the ring is measured. This gives an indication of the passing ability, restricted deformability, of concrete. The V-funnel test is used to determine the flowability or viscosity of concrete. The funnel (Fig. 1c) is filled with about 12 l of concrete and the time it takes for the concrete to flow through the apparatus is measured. Good flowable and stable concrete would consume a short time to flow out.
2.4. Fresh and hardened properties Basic workability requirements for successful casting of SCC are summarized by Khayat [8] as excellent
ARTICLE IN PRESS M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
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Table 5 Tests on fresh concrete Mixture no.
1 2 3 4 5 6
Slump flow D (mm)
t500 (s)
745 620 695 615 660 675
4.2 4.3 4.5 4.1 2.8 2.6
V-funnel time (s)
¯ (mm) J-ring DH
13.8 17.6 16.4 15.1 14.0 9.2
10.0 10.0 10.0 11.3 7.5 15.0
in Table 5. In addition to the above properties, visual inspection of fresh concrete did not dictate any segregation or considerable bleeding in any of the mixtures. All mixtures were tested for compressive strength at 28 and 56 days, and split tensile strength at 56 days in accordance with the related ASTM standards. The density of hardened concrete at 28 days and the ultrasonic pulse velocities were also measured for all mixes at 28 and 56 days. The average of three specimen properties at a particular age was considered as its property and presented in Table 6.
3. Results and discussion
Fig. 1. Workability tests and apparatus: (a) Slump flow, (b) J-ring, (c) V-funnel.
deformability, good stability and low risk of blockage. In this experimental program these three properties are measured, respectively, by slump flow, V-funnel and Jring tests. The measured fresh properties are presented
As can be seen from Table 5, slump flow test results show that all mixes had enough deformability under their own weight, despite the fiber inclusion, and had a moderate viscosity, which is necessary to avoid segregation. V-funnel measurements of some mixes exceeded the upper limit suggested by EFNARC (Table 7); however it should be kept in mind that limits suggested by EFNARC are designated for plain SCC. As mentioned earlier, the viscosity of the HFR-SCC, as dictated by the t500 measurements of the slump flow test and V-funnel test, seemed to be affected by the fiber inclusion, giving shorter slump flow (t500) and V-funnel test measurements and pointing out to a better flowing concrete. As presented in Fig. 2, as the volume fraction (Vf) of OL 6/16 fibers increased, the viscosity decreased as dictated by the reduction in the slump flow (t500) and V-funnel tests. On the other hand, both the slump flow (D) and J-ring test results did not show any effect of fiber inclusion as seen in Fig. 3. To quantify the effects of ZP305 and OL6/16 on the viscosity of HFR-SCC, regression analysis is performed. In FRC, the parameter Vfl/d, named fiber factor, which is the volume fraction of fibers times the aspect ratio of the fiber, is used to identify the effects of fibers. Assuming the fiber factor as the single parameter to affect the properties of HRF-SCC, single-variate regression analyses are performed with respect to slump flow
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Mix. no.
1 2 3 4 5 6
2327 2389 2387 2362 2311 2349
Compressive strength (MPa) (28 days)
(56 days)
50.9 49.5 44.4 56.3 55.2 58.9
53.0 52.7 54.8 61.5 61.0 63.2
4.3 4.6 4.8 5.1 3.7 3.6
Unit
Slump flow t500 Slump flow J-ring V-funnel
Min
Max
Normalized Measurement
(56 days)
4823 4790 4690 4755 4742 4754
4886 4873 4876 4772 4752 4790
650 2 0 6
800 5 10 12
ðR2 ¼ 0:10Þ,
Slump flow t500 ðsÞ ¼ 3:85 0:32V f l=d
ðR2 ¼ 0:01Þ:
As can be seen from the low correlation coefficients of the above regression equations, the fiber factor is not the only parameter affecting HFR-SCC properties. Since the fibers had different geometry and surface roughness, they have to be treated differently and multivariate regression analyses should be performed using the fiber factor parameter as the variable. The following relationships and R2 were obtained after such analyses.
1.50
V funnelðsÞ ¼ 13:8 þ 11:2V f l=d ZP305 10:8V f l=d OL6=16
ðR2 ¼ 0:90Þ,
Slump flow t500 ðsÞ ¼ 4:20 þ 1:16V f l=d ZP305 4:99V f l=d OL6=16
1.25 1.00 0.75 0.50 t500 - Slump Flow V-funnel
0.25 0.00 0.0
0.2
0.4
0.6
0.8
1.0
Vf,OL6/16 / (Vf,OL6/16 + Vf,ZP305) Fig. 2. Tests for stability (viscosity) of HFR-SCC.
1.50 Normalized Measurement
(28 days)
V-funnelðsÞ ¼ 12:5 þ 5:89V f l=d
Typical range values
mm s mm s
Ultrasonic pulse velocity (m/s)
(t500) and V-funnel tests and the following relationships and correlation coefficients (R2) were obtained.
Table 7 EFNARC suggested workability limits Method
Split tensile strength (MPa) (56 days)
1.25 1.00 0.75 0.50 Slump Flow - D J-ring
0.25 0.00 0.0
0.2
0.4
0.6
0.8
Vf,OL6/16 / (Vf,OL6/16 + Vf,ZP305) Fig. 3. Tests for deformability of HFR-SCC.
1.0
ðR2 ¼ 0:79Þ.
As can be seen from the high correlation coefficients, these equations tend to represent the original data quite well. This could be explained by the OL 6/16 fibers being smaller then ZP 305 fibers, thus having less potential to prevent the movement of aggregates. In addition, OL 6/ 16 fibers are coated with brass and have very smooth surfaces, which reduces the energy loss during the movement of particles. On the other hand, ZP 305 fibers have hooked ends, and relatively larger dimensions thus cause blocking of particles during flow. In addition to the fresh properties, some hardened properties of the HFR-SCC are also determined. These include the compressive, tensile, and ultrasonic pulse velocity of concrete at various ages. As seen in Fig. 4, an increase in compressive strengths was observed as the OL 6/16 content was increased in all mixes. Compared with the mix having only ZP305, when only OL6/16 was used both 28 and 56 day strengths increased on the order of 20%. This trend can be attributed to the relatively small dimensions of OL 6/16 fibers, which delay and to a certain extent prevent the formation and propagation of micro-cracks in the concrete matrix. As for the tensile strength, which is determined by the split tension test, the split tensile strength seemed to be affected by the fibers and the effect of fiber hybridization can be observed on the obtained test results. Highest split tensile strength occurred in mix 4 in which fibers were proportioned equally. On the other hand,
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Normalized Measurement
M. Sahmaran et al. / Building and Environment 40 (2005) 1672–1677
1.25 1.20 1.15
f'c,28 f'c,56 ft,56
1.10 1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.0
0.2
0.4
0.6
0.8
1.0
Vf,OL6/16 / (Vf,OL6/16 + Vf,ZP305) Fig. 4. Tests for strength properties of HFR-SCC.
ultrasonic pulse velocities did not seem to be affected by the amount of fibers used in this article. The negligible variation in the ultrasonic pulse velocity test results can be considered as an indication of the uniformity of concrete matrix in all mixes.
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invaluable data for the purpose of producing HFRSCC. In order to retain high level workability with fiber reinforcement, the amount of paste in the mix should be increased to provide better dispersion of fibers. Increasing cement content, increasing fine aggregate content or using pozzolanic admixtures can be alternative solutions to this problem, and these alternatives will be investigated through the progress of this experimental program. As for the hardened properties, only the effects of the strengthening component of fiber reinforcement were observed. The mix reinforced with only OL 6/16 fibers had the highest compressive strength values at both 28 and 56 days, whereas mix containing equal amounts of ZP305 and OL 6/16 fibers gave the highest splitting tensile strength value. The effects of the toughening component of fiber reinforcement and fiber hybridization shall be observed and a clearer view shall be attained with the results of the toughness tests, which are yet to be obtained.
References 4. Conclusions This paper discusses the preliminary results of an ongoing experimental program carried out to investigate the effects of fiber inclusion on the flow characteristics of HFR-SCC and mechanical properties in the hardened state. Two different types of steel fibers were used in combination and tests were performed in both fresh and hardened states. It was observed that it is possible to achieve selfcompaction with considerable fiber inclusion (60 kg/m3). Although results obtained from some of the mixes exceeded the upper limits suggested by EFNARC, all mixes had good flowability and possessed self-compaction characteristics. SP with the commercial name Smartflow was successfully employed and proved to be efficient in the production of an economical SCC without the use of any viscosity enhancing chemical admixtures. The results of this study yielded raw but
[1] Okamura H, Ouchi M. Self-compacting concrete. Journal of Advanced Concrete Technology 2003;1(1):5–15. [2] Hannant DJ. Fiber cements and fiber concrete. Chichester, UK: Wiley; 1987. [3] Bentur A, Mindess S. Fiber reinforced cementitious composites. London: Elsevier; 1990. [4] Mobasher B, Li CY. Mechanical properties of hybrid cementbased composites. ACI Materials Journal 1996;93(3):284–92. [5] Khayat KH, Roussel Y. Testing and performance of fiberreinforced, self-consolidating concrete. In: Skarendahl A, Petersson O, editors. Proceedings of the first international RILEM symposium on self-compacting concrete. Stockholm, Sweden: September 13–14, 1999. p. 509–21. [6] Groth P, Nemegeer D. The use of steel fibres in self-compacting concrete. In: Skarendahl A, Petersson O, editors. Proceedings of the first international RILEM symposium on self-compacting concrete. Stockholm, Sweden: 13–14 September: 1999. p. 497–507. [7] EFNARC. Specification & guidelines for self-compacting concrete. English ed. Norfolk, UK: European Federation for Specialist Construction Chemicals and Concrete Systems; 2002. [8] Khayat KH. Workability, testing and performance of selfconsolidating concrete. ACI Materials Journal 1999;96(3):346–53.