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The effect of polypropylene fibers on the properties of fresh and hardened lightweight self-compacting concrete
Construction and Building Materials 25 (2011) 351–358
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The effect of polypropylene fibers on the properties of fresh and hardened lightweight self-compacting concrete H. Mazaheripour a,*, S. Ghanbarpour b, S.H. Mirmoradi a, I. Hosseinpour a a b
Department of Civil Engineering, Mazandaran University of Science and Technology, Babol, Iran Department of Civil Engineering, Babol University of Technology, Babol, Iran
a r t i c l e
i n f o
Article history: Received 28 May 2009 Received in revised form 1 June 2010 Accepted 7 June 2010 Available online 16 July 2010 Keywords: Light Expanded Clay Aggregate (LECA), Polypropylene fibers Lightweight Self-Compacting Concrete (SCC)
a b s t r a c t This paper evaluates the LECA Lightweight Self-Compacting Concrete (LLSCC) manufactured by Nan-Su, of which the Packing Factor (PF) of its design mixing method has been modified and improved. The study analyzes the impact of polypropylene fibers on LLSCC performance at its fresh condition as well as its mechanical properties at the hardened condition. The evaluation of Fiber Reinforced LLSCC (FR-LLSCC) fluidity has been conducted per the standard of second class rating of JSCE, by three categories of flowability, segregation resistance ability and filling ability of fresh concrete. For the mechanical properties of LLSCC, the study has been conducted as follows: compressive strength with elapsed age, splitting tensile strength, elastic modulus and flexural strength, all of which were measured after the sample being cured for 28 days. When self-compacting concretes were lightened to 75% of their normal weight, their fresh properties are affected immensely. Applying 0.3% volume fractions of polypropylene fiber to the LLSCC resulted in 40% reduction in the slump flow (from 720 mm to 430 mm). In general, the rate of slump flow over Super Plasticizer (SP) volume percentage reduced with the use of polypropylene fibers in the FR-LLSC. Polypropylene fibers did not influence the compressive strength and elastic modulus of LLSCC, however applying these fibers at their maximum percentage volume determined through this study, increased the tensile strength by 14.4% in the splitting tensile strength test, and 10.7% in the flexural strength. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Self-Compacting Concrete (SCC), a new kind of High Performance Concrete (HPC) with excellent deformability and segregation resistance, was first developed in Japan in 1986. It is a special kind concrete that can flow through and fill the gaps of reinforcement and corners of molds without any need for vibration and compaction during the placing process [1,2]. Self-compacting concretes are made using an innovative world renowned technology widely used in the vast field of construction. The increasingly extensive developments in the construction industry throughout the world along with the need for the application of concretes with such qualities as of the SCC, has lead to many studies on such types of concretes. One of the most crucial factors in the design and construction of structures is the considerable amount of weight of dead-load mainly due to the ceiling and the separating walls. Thus, it is evident that using lightweight materials in the beams, columns and * Corresponding author. Tel.: +98 9122957412. E-mail address: [email protected] (H. Mazaheripour). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.06.018
other structure components considerably reduces the dead-load, which could result in a cost-effective construction plan. It is also evident that applying lightweight concretes in many such structures as bridges with long spans, results in the decrease of the area of the bridge section. Lightweight concrete is known with its advantage of reducing the self-weight of the structures, reducing the areas of sectional members as well as making the construction convenient [3,4]. Thus, the construction cost can be saved when applied to structures such as long span bridge and high rise buildings [5]. The lightweight concrete requires specific mix design method that is quite different from conventional concrete. Using conventional mix design method would give rise the material segregation as well as lower the strength by the reduced weight of the aggregate. To avoid such problems, it is recommended to apply the mix design method of high performance self-compacting concrete for the lightweight concrete [5]. Excellent in segregation resistance ability and its flowability at its fresh condition, self-compacting concrete is generally known as the concrete capable of filling up the given structure only using its self-weight without an additional compaction. It was first
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developed in Japan during 1986, with further mix design method introduced by professor Okamura of Tokyo university in 1993 [6,7]. The most popular mix design method used for the self-compacting concrete is introduced by professor Okamura. His method conducts the cement paste and mortar test before moving onto evaluating properties of the superplasticizer, cement, fine aggregate and pozzolanic material for saving the process from the redundancy of unnecessary testing, although its complicated procedure makes it difficult to apply to companies which manufacture the ready-mixed concrete. Overcoming such obstacle, Taiwanbased Nan-Su suggested a new mix design method that is more convenient. Apart from its simplicity, Nan-Su’s new method has some problems with the fluctuating range of Packing Factor (PF), which is the most important variable [8,9]. This study introduces a production of lightweight self-compacting concrete by utilizing PF-modified and improved version of Nan-Su’s mix design method of self-compacting concrete. Lightweight concrete application has recently became conventional in different forms including lightweight aggregate concrete, fine aggregate concrete and bubbled air concrete that has been replaced with ordinary concrete. Lightening process of ordinary concretes has been done in different cases and with various shapes. Thus, self-compacting concretes are new generation of lightened concretes in concrete industry. Light Expanded Clay Aggregates (LECA) has been used to lighten in this study. Various mixed projects of the lightweight materials are made by coarse aggregates and the natural fine aggregates to lighten the concretes weight. Through a series of test mixes conducted during the study, the quality of the concrete at its fresh condition has been evaluated with the second class rating standards of self-compacting concrete published by Japan Society of Civil Engineers (JSCE), especially focused in its flowability, segregation resistance ability and filling ability [10]. The use of Fiber Reinforced Concretes (FRC) has increased in building structures because the reinforced fibers in concrete may improve the toughness, flexural strength, tensile strength, impact strength as well as the failure mode of the concrete. It has also been known that addition of fibers in concrete has little or no effect on the compressive strength and the modulus of elasticity [11]. Use of fibers into SCC mixes has been presented by many researchers [12–14]. Depending on many parameters such as maximum aggregate size, fiber volume, fiber type, fiber geometry, and fiber aspect ratio, fiber inclusion to concrete reduces the workability of concrete.
In this article also, polypropylene fibers are used, and the effect of this fiber inclusion on the workability of LECA Lightweight SelfCompacting Concrete (LLSCC) studied. Slump flow, V-funnel, and U-box tests are performed to assess workability. Moreover, the mechanical properties, namely the compressive, splitting tensile strength, elastic modulus and Flexural strength of lightweight self-compacting concrete mixtures (its density is 1700–2000 kg/ m3) that contain polypropylene fibers are also determined at 28th ages.
2. Experimental outline 2.1. Materials In this study, the coarse and fine aggregates were acquired from the mines of Amol. The maximum size of coarse aggregates used was 10 mm (a 3/8 in mesh was applied and the residue was sieved with a No. 4 mesh) where the smallest particles used as fine aggregate were 0–4.75 mm. All the natural aggregates used for this study were in the dry form. In this research, lightweight LECA aggregates were used to decrease the overall weight of the final self-compacting concrete. LECA aggregates are constructed from clay. They are produced during a synthetic process under known temperatures in a factory. They are characterized as spongy and very light; and highly water absorbent. LECA is an aggregate made of expanded clay produced in rotary kilns at temperatures of about 1200 °C. The LECA aggregates were used in Saturated Surface-Dry (SSD) form. The physical and chemical properties of these aggregates are shown in Tables 1 and 2, respectively. In this study Type II cement produced at Neka factory was used with a 3.15 g/ cm3 density and a Blaine fineness of 3498 cm2/g along with silica fume (GS = 2.1) and limestone (GL = 2.7) to produce self-compacting concrete. During the course of this research, 12 mm long polypropylene fibers manufactured by Vand Shimi were used. Some of the physical properties of these polypropylene fibers are shown in Table 3. 2.2. Mix design procedure Concrete mix design in this study has been modified and improved according to Nan-Su’s method. In other words, PF value was obtained through the pretest to solve the obscurity in assumption of PF value that is a main factor within Nan-Su’s method. Calculation principles of mixing procedure are based on Nan-Su’s procedure [8,9]. Determination of appropriate PF value has saved significant amount of time and efforts during the pretesting phase, and is designed to obtain the proper concrete mix. Based on the Yun Wang Choi method, a percentile volume of natural aggregates were replaced with the same percentile volume of LECA lightweight aggregate in the mixtures. The Yan Wang Choi method is in fact a modification of Nan-Su mix method. First of all, PF was calculated using Eq. (1) in which the coarse and fine aggregates in both compacted and loosely filled stage were implemented [5]:
Table 1 Physical properties of LECA aggregates.
a
Components
Natural coarse (NC)
Natural fine (NF)
LECA coarse (LC)
LECA fine (LF)
Density (kg/m3) Bulk density (kg/m3) Absorption (%)
2690 1440 0.7
2590 1400 2.6
530 ± 20 385 ± 30 30 ± 2a
690 ± 20 485 ± 30 30 ± 2a
More than 1 h.
Table 2 Chemical compositions of LECA aggregates (wt.%). Components
SiO2
Al2O
Fe2O3
MgO
K2O
NaO2
SO3
TiO2
CaO
LoI
MnO
P2O5
LECA
66.05
16.57
7.10
1.99
2.69
0.69
0.03
0.78
2.46
0.84
0.09
0.21
Table 3 Physical properties of polypropylene fibers [1]. Properties
Length of fibers (mm)
Tensile strength (MPa)
Density
Melting point
Appearance
Polypropylene
12
350
900 kg/m3
160 °C
White color fibers
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Unit weight of coarse aggregateðcompacted stageÞ S 1 Unit weight of coarse aggregateðloosely filled stageÞ a Unit weight of coarse aggregateðcompacted stageÞ S þ¼ Unit weight of coarse aggregateðloosely filled stageÞ a
2.3. Mixture proportions of concrete
PF ¼
ð1Þ
where aS is the volume ratio of fine aggregate to the total aggregate. Fig. 1 shows the steps for determining the PF value through measuring the unit weight of fine and coarse aggregates. After specifying the value of PF, the following stages of the calculation method are based on Yan Wang Choi. As already mentioned, the quantity of lightweight material is also calculated as percentile volume of the mixed natural material. So that a natural fine aggregate is replaced by 0– 3 mm fine LECA aggregate and natural coarse aggregate it is replaced by percentile volume of 3–10 mm coarse LECA aggregate (after meshing). Fig. 2 shows a schematic flowchart of the SCC mixed design method. As shown in this figure, for the slump flow values 650–750 mm, further tests including V-funnel and filling height of U-box (mm) have been conducted. When all of the above fresh tests are approved, the mixing design will be recognized as an appropriate workable self-compacting concrete project.
PF is initially assumed to be 1.14 and aS (the volume ratio of fine aggregate to the total aggregates) is assumed to be 60% (S=a ¼ 0:6). The appropriate mix design is then achieved through various experiments using different PF and aS values. Table 4 shows the mixture proportion of concrete as its categories of group A, B, C, D, E, F, G, H, I, J are divided per use of LECA fine and coarse aggregate. E–J mixes has appropriate flow, but separated mix design has not been seen. Mix designs of A– G contain a proportion of LECA fine aggregate as well as a proportion of natural aggregates. However, mix designs of H–J contain a proportion of LECA fine and coarse aggregates added a proportion of natural fine aggregates and without any coarse aggregate included. In Table 4, natural fine and natural coarse aggregate were abbreviated to NF and NC respectively. Beyond that, LF and LC were stated LECA Fine and LECA Coarse aggregates. To evaluate the flow properties of lightweight self-compacting concrete, slump flow test, the time required to reach 500 mm of slump flow, V-funnel and filling height of U-box test was conducted immediately after mixing the concrete, the range values was borrowed from testing methods for the self-compact concrete published by JSCE, and its standards are shown in Table 5.
Fig. 1. Step of determining the PF value [5].
Fig. 2. Flowchart of the SCC mix design method.
Table 4 Mixture proportions of concrete (kg/m3). Mix code
A B C D E F G H I J
PF
1.14 1.12 1.10 1.10 1.10 1.08 1.06 1.06 1.06 1.06
S/a (%)
60 60 65 70 80 80 80 65 65 65
Natural aggregates
LECA aggregates
NF
NC
LF
LC
287 282 300 323 370 363 355 963 772 626
657 645 554 475 317 311 305 – – –
179 175 187 201 230 226 221 – 64 90
– – – – – – – 105 105 105
Cement
Silica fume
Limestone
Water
Super plasticizer
Density
500 500 500 500 500 500 500 500 500 500
33 39 40 38 38 41 47 48 48 48
100 123 150 152 150 175 200 201 201 201
160 160 160 160 160 160 160 160 160 160
19.02 16.55 17.25 17.24 17.20 17.91 17.18 17.23 17.23 17.23
1989 1994 1965 1927 1850 1861 1872 2026 1868 1805
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Table 5 Specification of SCC proposed by JSCE [10]. Class of filling ability of concrete Construction condition
Minimum gap between reinforcement (mm) Amount of reinforcement (kg/m3)
Filling height of U-box test (mm) Absolute volume of coarse aggregates per unit volume of SCC (m3/m3) Flow ability Segregation resistance ability
Slump flow (mm) Time required to flow through V-funnel (s) Time required to reach 500 mm of slump flow (s)
1
2
3
30–60 P350 P300 0.28–0.30 650–750 10–20 5–25
60–200 100–350 P300 0.30–0.33 600–700 7–20 3–15
P200 6100 P300 0.30–0.36 500–650 7–20 3–15
Table 6 Mixture proportions of lightweight self-compacting concrete containing polypropylene fibers (in kg/m3). Mix code
GP0.1 GP0.2 GP0.3 IP0.1 IP0.2 IP0.3
Natural aggregates
LECA aggregates
NF
NC
LF
LC
355 355 355 722 722 722
305 305 305 0 0 0
221 221 221 64 64 64
0 0 0 105 105 105
Cement
Silica fume
Limestone
Water
Super plasticizer
Polypropylene
500 500 500 500 500 500
47 47 47 48 48 48
200 200 200 200 200 200
160 160 160 160 160 160
17.20 18.68 18.68 17.20 18.68 18.68
0.9 1.8 2.7 0.9 1.8 2.7
Both G and I mixing designs were selected among others for testing and are based on first class of JSCE; both mix designs are utilized to study the impact of polypropylene fibers. Table 6 shows mixture proportions of LLSCC containing polypropylene fibers.
2.4. Mixing project First of all, coarse aggregate material, and if available, 3–10 mm LECA, and then 0–3 mm fine aggregate and 0–3 mm LECA are poured into the mixer, They are mixed for 1–1.5 min. Then, cement, silica fume and limestone are mixed with 30% of the mixing water and is poured into the mixer to be mixed for 2 min. Then, water with super plasticizer are added to the mixer gradually, then the mixer is revolved for 1 min when the fresh concrete undergoes workability test. Applied polypropylene of the mixed materials are mixed with a little of mixed water inside the mixer at the final process.
2.5. Samples and maintenance procedure Specimen for concrete testing has been manufactured without the compacting. Its mold was taken out after 48 h followed by standard curing until the next test. Compressive strength of the concrete was tested on 7th, 14th and 28th days, while splitting tensile strength, elastic module and flexural strength were measured after 28 days of curing. The compressive strength was obtained for a cube of 100 100 100 mm in dimension. Specimens were demolded 2 days after casting and then cured in water at approximately 20 °C until testing was carried out at 7, 14 and 28 days’ age. Six specimens of each mixture were tested on the 28th and the mean value was reported. The splitting tensile strength was determined on Day 28 on cylinders measuring 150-mm diameter and 300 mm height and cured in water until the date of test according the ASTM C496 [15]. Three specimens of each mixture were tested and the mean value was reported.
The modulus of elasticity was determined according to ASTM C469 [16]. End capped Ø150 300 cylinder specimens were cured in water and tested at ages of 4–13 months for different mixtures. The flexural strength was determined according to ASTM C78 [17]. End capped Ø500 100 100 cylinder specimens were cured in water and tested at ages of 28 days for different mixtures. Three specimens of each mixture were tested and the mean value was reported.
3. Results and discussion 3.1. Properties of fresh concrete 3.1.1. LLSCC without fibers Test results of the fresh LLSCC are summarized in Table 7. In the last column of this table during the slump flow test, resistance towards mix segregation has been compared visually in order to specify three states of bad, good, and very good. Better test results are obtained when limestone is being added to the mix. Namely, increased viscosity of the mix is directly linked to the amount of limestone and super plasticizer, mix materials are less separated, and segregation is being superior. Utilization of more than 2.5% of super plasticizer in the mixes would induce too many air bubbles into the mix. Fig. 3 shows slump flow changes for various mix designs. As indicated in the figure, slump flow for mix A was less than 500 mm and for mixes B and C were not high enough. Slump flow for mix D was slightly less than the allowable range. Mix designs E–J are in the allowable first class of JSCE Standard. With increased amount of limestone in the mix and increased viscosity, slump
Table 7 Test results of the fresh lightweight self-compacting concrete. Mix code
PF
Powder (kg/m3)
Slump flow (mm)
T50 (s)
V-funnel (s)
U-Box (mm)
Segregation
A B C D E F G H I J
1.14 1.12 1.10 1.10 1.10 1.08 1.06 1.06 1.06 1.06
634 662 690 690 688 716 747 749 749 749
<500 530 550 630 660 670 720 690 745 750
– 5 5 6 7 9 10 5 7 11
– – 12 14 15 17 20 15 18 23
– – – 290 310 320 325 310 300 295
Bad Bad Bad Good Very good Very good Very good Very good Very good Very good
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Slump flow (mm)
800
745
750
720
700
660
650
690
670
630
600
550
550 530
500
G Series
700
750
Slump flow (mm)
800
I Series
600 500 400 300 200
(2.3 %)
(2.5%)
(2.5%)
0.10%
0.20%
0.30%
(2.3%)
100
450
0
400 A
B
C
D
E
F
G
H
I
0.00%
J
Percentage Volume of the fibers (% of SP)
Mix code
Fig. 6. Slump flow changes of self-compacting concrete when percentages of polypropylene fibers are increased.
Fig. 3. Slump flow.
35
25
G Series
V-funnel time (sec)
Time required to reach 500mm slump flow (s)
30
20
15
10
C
5
D
F E H
25 20 15 10 5
J
G
I Series
0
(2.3%)
(2.3%)
0.00%
0.10%
(2.5%)
(2.5%)
0.15%
0.20%
0.30%
Percentage Volume of the fibers (% of SP)
I
Fig. 7. Impact of fibers percentage volume on the V-funnel time.
0 5
10
15
20
25
30
35
Filling height of U-box test (mm)
0
V-funnel time (sec)
Filling height of U-box test (mm)
Fig. 4. Relationship of time required to flow through V-funnel and to reach 500 mm of slump flow.
400 310 320
300
300
325 310
290
295
350 330
G Series
310
I Series
290 270 250 230 210 190
(2.3%)
(2.3%)
0.00%
0.10%
(2.5%)
170 150
0.20%
0.30%
Percentage Volume of the fibers (% of SP)
200
Fig. 8. Impact of fibers percentage volume on filling height of U-box test.
100
flow is enhanced, its degree being directly linked to the rate of utilized limestone. According to Fig. 4, for mixes B–G, increased T50 time of the mix results in V-funnel time increase, (except for unaccomplished A mix in V-funnel). In fact T50 and V-funnel time have been increased
0 A
B
C
D
E
F
G
H
I
J
Mix code Fig. 5. Filling height of U-box test.
Table 8 Test results of the fresh lightweight self-compacting concrete containing fibers. Mix code
PF
Powder (kg/m3)
Slump flow (mm)
T50 (s)
V-funnel (s)
U-box (mm)
Fibers (%)
Super plasticizer (%)
GP0.0 GP0.1 GP0.2 GP0.3 IP0.0 IP0.1 IP0.2 IP0.3
1.06 1.06 1.06 1.06 1.06 1.06 1.06 1.06
747 747 747 747 749 747 747 747
720 680 560 430 745 650 530 410
10 12 15 – 7 10 12 –
20 21 23 – 18 24 30 –
325 290 255 – 300 285 260 –
0.0 0.1 0.2 0.3 0.0 0.1 0.2 0.3
2.3 2.3 2.5 2.5 2.3 2.3 2.5 2.5
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when powder amount and viscosity were increased. Again, weight is increased in mix design H where T50 time is reduced. But, increased light LECA material in mix designs I and J again T50 time and V-tunnel time are increased. Fig. 5 illustrates the result of filling height of U-box test (mm) for the filling ability of lightweight self-compacting concrete. Results of U-box test were just within the range 290–325 mm and there were fluctuations. The result of filling height of U-box for mixes A, B and C have not reported in order to have bad segregation. Mixes J and D are reported to be slightly lower than the allowable range. 3.1.2. LLSCC with fibers Test results of fresh LLSCC with percentages of different fibers are shown in Table 8. As shown, they reduce slump flow remarkably. Consequently, it could be concluded that it influences other fresh properties, too. Fig. 6 shows percentage comparison of different polypropylene fibers as well as the slump flow changes for two mix projects. Test results for V-funnel and filling height of U-box test are shown in Figs. 7 and 8, respectively. Time increase for Vfunnel test is remarkable when polypropylene is added, unless the volume percentage of polypropylene fibers is about 0.15% for both group of mixes GP and IP. Contrarily, the V-funnel time is decreased by the added percentage of the fibers. 0.15% of polypropylene fibers seems somewhat improving the filling ability of Fiber Reinforced LECA Lightweight Self-Compacting Concrete (FRLLSCC). Filling height of U-Box test results are more discouraging than those for other tests; there is a blockage phenomenon in the test. As shown in Fig. 8, when the volume percentages of polypropylene fibers were increased, passing ability of FR-LLSCC declined.
850
GP0.0 GP0.2 IP0.0 IP0.2 G Series I Series
750 700 650 600 550 500 450 400
1.8
1.9
2
2.1
2.2
2.3
2.4
2.5
2.6
Volume Percentage of SP (%) Fig. 9. The difference in the rate of slump flow over SP volume percentage for LLSCC and FR-LLSCC.
In fact, the packing theory of Fuller and Thompson [18] represents a special case of the more general packing equations derived by Andreasen and Andersen [19]. According to their theory, optimum packing can be achieved when the cumulative Particle Size Distribution (PSD) obeys the following equation [20]:
PðDÞ ¼
D Dmax
q ð2Þ
where P is the fraction that can pass through a sieve with opening diameter D; Dmax is maximum particle size of the mix. The parameter q has a value between 0 and 1, Andreasen and Andersen [19] have found that optimum packing is obtained when q = 0.37. The grading by Fuller is obtained when q = 0.5 [20]. PSD curve of some of the mixtures used in this research has been compared with the Fuller and A&A optimized PSD curve, shown in Fig. 10. As shown, the more the PSD curve of the mixtures approaches the Fuller curve (q = 0.5) the more the results for the fresh LLSCC tests and segregation resistance of the mixes are improved. 3.3. Test results for hardened concrete 3.3.1. Compressive strength Compressive strength test results for LECA content light selfcompressing concrete for 7, 14 and 28 day old samples are shown in Fig. 11. As shown here, day 7 strength of ordinary coarse aggregate design (without LECA coarse aggregate) is 7% more than average amounts of the second group mixes (H, I, J). Whereas, the proportion of water/cement has been the same for all designs. In addition, according to the figure, it is concluded that, increasing LECA coarse aggregates instead of ordinary coarse aggregates would reduce compressive strength.
30
100
% Cumulative finer (M/M)
3.2. Grading
90
A&A [5] - q=0.37
80
Fuller [4] - q=0.5
70
MIX A
60
MIX D MIX G
50
MIX H
40
MIX I
30 20 10 0 0.1
1
10
100
Particle size (D) [mm] Fig. 10. Analysis of actual PSD of aggregates used with Andreasen and Andersen [19], Fuller model [18].
Compressive strength at days (MPa)
Slump flow (mm)
800
Although there was a fluctuation in test results of U-box for LLSCC mixes, the filling height of U-box fell dramatically for FR-LLSCC. Meanwhile, when the volume percentage of polypropylene fibers is about 0.3%, blocking behavior was observed, Therefore, the result has omitted. Fig. 9 compares the increase in the rate of slump flow over the SP volume percentage for four different mix designs of GP0.0, GP0.2, IP0.0 and IP0.2. As shown in Fig. 9, for GP0.0 and IP0.0, in absence of polypropylene fibers, the slump flow increases sharply with the increase of the percentage of super plasticizer in the mix, whilst the rate is much less steep for GP0.2 and IP0.2 where 0.2% of polypropylene fiber were applied.
25 20
days 28 days 14
17% 21%
14%
17%
15% 14%
19%
days 7
13% 12%
8%
30%
32%
60%
58%
60%
H
I
J
15% 27%
15 10
68%
65%
67%
68%
5 0
D
E
F
G Mix Code
Fig. 11. Compressive strength at days.
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H. Mazaheripour et al. / Construction and Building Materials 25 (2011) 351–358 Table 9 Hardened FR-LLSCC test results, standard deviation (s) and coefficient of variation (COV%) for. Hardened self-compacting concrete property
Number of specimen tested for each mixture
Standard deviation-r/mean (COV%) GP0.0
GP0.1
GP0.2
GP0.3
IP0.0
IP0.1
IP0.2
IP0.3
28 days Compressive strength (MPa) 28 days Splitting tensile strength (MPa) 28 days Flexural strength (MPa) 28 days Elastic module (GPa)
6
1.38/25.3 (5.4) 0.14/2.77 (5.3) 0.29/4.86 (5.9) 1.00/23.9 (4.2)
2.76/24.6 (11.2) 0.06/2.98 (2.2) 0.22/5.10 (4.4) 1.02/24.8 (4.1)
1.29/26.3 (4.9) 0.09/3.02 (3.0) 0.06/5.28 (1.1) 1.31/24.1 (5.4)
3.00/24.6 (12.2) 0.09/3.17 (2.8) 0.18/5.38 (3.3) 1.31/24.0 (5.4)
2.12/21.5 (9.9) 0.14/2.32 (6.0) 0.36/4.36 (8.2) 0.59/22.1 (2.7)
2.31/21.7 (10.7) 0.20/2.34 (8.4) 0.09/4.52 (2.1) 0.73/21.6 (3.4)
2.40/22.7 (10.6) 0.23/2.62 (8.7) 0.04/4.69 (0.9) 0.71/22.0 (3.2)
3.14/22.8 (13.8) 0.14/2.65 (5.1) 0.15/4.74 (3.2) 0.74/22.4 (3.3)
3 3
Table 9 illustrates the main mix results containing polypropylene fibers. Also, Fig. 9 is an indication of two different mixed projects. According to some articles [21,22] and the test results, polypropylene fibers do not have any impact on compressive strength of the material. LECA aggregates result in concrete breakage. Mainly, LECA aggregates do not enhance the strength of concrete when a high compressive force is applied. It will not enhance the strength of LECA aggregate; it will detach the cement joint and break it. Thus, the LECA aggregates are just a lightweight material replaced with heavy stone materials but their compressive strength is low and they cannot tolerate considerable forces. Fig. 12 shows the impact comparison of compressive strength for FR-LLSCC. For mix design G; where coarse aggregates are used in absence of LECA coarse aggregate, compressive strength rate is higher than that of mix design I. Generally, the amount of compressive strength by increasing volume percentage of fibers was fluctuated for both mixes G and I. 3.3.2. Tensile strength The test was conducted just to demonstrate the differences of the mixes containing polypropylene fibers with those without it (where the percentage is zero). The test results are shown in Table 9. Three samples were tested on 28th day. When 0.2% and 0.3% samples containing polypropylene were tested the maximum force cracked the cylinder, it split down, i.e. polypropylene fibers prevented the cylinder from rupturing. When polypropylene fibers are added to the SCC concrete mix, they become viscid, thus LECA aggregates in SCC mix are modified when they are added to the mix, because they are evenly distributed throughout the mix, although workability of concrete is reduced, Test results for split cylinder are compared in Fig. 13. The maximum rate of tensile strength in the mix of G series for 0.3% polypropylene containing SCC is 14.4% and in I series with 0.3% polypropylene fibers, the maximum tensile strength is 14.2%. The results demonstrate that added polypropylene fibers can increase tensile strength of SCC
2.75 2.5 2.25 (2.3%)
(2.3%)
(2.5%)
(2.5%)
0.00%
0.10%
0.20%
0.30%
Fig. 13. Impact of increased volume percentage of polypropylene fibers on tensile strength.
concrete by as much as 14%, when the rate is enhanced based on the volume percentage of the fabrics.
3.3.3. Flexural strength According to the study, all of the samples ruptured at two points. The test results of the maximum force on the sample and the calculated stage of rupture is named rupture module (R) and are shown in Table 9. As shown in Fig. 14 rupture module change shows an ascending trend when the volume percentage of polypropylene fibers is increased and for the maximum increase of the fibers by 0.3% for the mixed project of the G and I series, rupture modules are 10.7% and 8.7%, respectively, depending on the maximum increase of applied polypropylene. Bending strength test results for SCC samples (the values of rupturing module) are shown for the mixed project and the obtained results are compared in the two G and I series. The properties increase as the volume percentage is increased. For the 0.1%, 0.2% and 0.3% increase in volume percentage of the G series, the properties are increased by 4.9%, 5.5
G Series
I Series
23 21 19
15
3
Volume Percentage of the fibers (% of SP)
G Series
25
17
G Series I Series
3.25
2
(2.5%) (2.3%)
0.00%
(2.5%)
(2.3%)
0.10%
0.20%
0.30%
Volume percent of the fibers (% of SP)
Flexural strength (MPa)
Compressive strength (MPa)
27
3.5
Tensile strength (MPa)
3
I Series
5.25 5 4.75 4.5 4.25 4
(2.3%) 0.00%
(2.3%) 0.10%
(2.5%)
(2.5%)
0.20%
0.30%
Volume percentage of the fibers (% of SP) Fig. 12. Impact comparison of compressive strength of the samples containing fibers.
Fig. 14. Impact of fibers’ volume percentage on the rupture module.
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H. Mazaheripour et al. / Construction and Building Materials 25 (2011) 351–358 26
G Series I Series
Elastic moduli (GPa)
25 24 23 22 21 (2.3%) 20
0.00%
(2.3%) 0.10%
(2.5%)
(2.5%)
0.20%
0.30%
Percentage Volume of the fibers (% of SP) Fig. 15. Impact of volume percentage of the fabrics on elastic module.
8.6% and 10.7%; they are 3.7%, 7.6% and 8.7% for I series, respectively. 3.3.4. Elastic module The test is to specify elastic module of SCC lightweight concretes with fibers. Samples of the cylinder splitting tensile strength were tested on 28th day. Compressive tension is increased by 30% for the mix cube samples to obtain tension strength and the value of displacement change. It is possible to obtain elastic module of the concrete when a compressive force is applied. According to the obtained function, polypropylene fibers do not impact on these concretes and the changes are slight. As shown in Table 9, when the fibers are increased in LECA mixes, the increased rates or decrease rates are negligible. For mixes G where the LECA coarse aggregate is not used, the rate of elastic module is higher than that of mix design I. These results for G and I mixes are compared in Fig. 15. 4. Conclusion Based on the results presented in this paper, the following conclusions can be drawn: (1) When self-compacting concretes were lightened to 75% of their normal weight, their fresh properties are affected immensely. (2) Based on the results of the experiment done on fresh LLSCC, lightening of the concrete mainly impacted the permeability and flow rates obtained from U-box and V-funnel tests. (3) When a percentile volume of natural aggregates are replaced with the same percentile volume of LECA lightweight aggregates in the mixtures. With respect to the properties and grading of the substituted LECA aggregates, the PSD of the LLSCC is disoriented. Thus, more limestone and filler is needed to regain the fresh properties of an SCC. In addition, in order to compensate for the afore-mentioned flaw, the cement portion needs to be increased in order to enhance the compressive strength of the LLSCC. (4) The presence of polypropylene fibers in LLSCC greatly decreases the slump flow, where 0.3% of these fibers in the concrete (G series) reduces the flowability from 720 mm to 430 mm. The reduced slump flow for 0.1% and 0.2% of fiber usage is 680 mm, and 560 mm, respectively. (5) When polypropylene fibers are used, the time of the V-funnel test is increased, except for 0.15% fiber usage where the time of the test is slightly decreased.
(6) Increasing the volume percentage of polypropylene fibers in LLSCC reduces the filling height in U-box test. (7) Polypropylene fibers do not have an impact on the compressive strength and elastic module of LLSCCs. The changes in both qualities are irregular and insignificant as the volume percentage of polypropylene fibers is increased. (8) Splitting tensile strength is increased as volume percentage of polypropylene fibers in LLSCC is increased. In I and G mix series, the splitting tensile strength is increased by 14.2% and 14.1%, respectively for maximum volume percentage of the fibers (0.3%). (9) Flexural strength is increased when volume percentage of polypropylene fibers in LLSCC are increased. In I and G mix series, the flexural strength is increased by 8.7% and 10.7%, respectively for maximum volume percentage of the fibers (0.3%).
References [1] Okamura H. Self-compacting high performance concrete. Concr Int; 19(7): 50–4. [2] Okamura H, Maekawa K, Ozawa K. High performance concrete. Tokyo: Gihoudou Pub; 1993 [in Japanese]. [3] Yasar E, Atis CD, Kilic A, Gulsen H. Strength properties of lightweight concrete made with basaltic pumice and fly-ash. Mater Lett 2003;57:2267–70. [4] Rossignolo JA, Agnesini MVC, Morais JA. Properties of highperformance LWAC for precast structures with Brazilian lightweight aggregate. Cem Concr Compos 2003;25:77–82. [5] Choi Yun Wang, Kim Yong Jic, Shin Hwa Cheol, Moon Han Young. An experimental research on the fluidity and mechanical properties of high strength lightweight self-compacting concrete. Cem Concr Res 2006;36:1595–602. [6] Okamura H, Maekawa K, Ozawa K. High performance concrete. Tokyo: Gihoudou Pub; 1998. [7] Okamura H. Self-compacting high performance concrete. Tokyo: Social System Institute; 1999. [8] Su N, Miao B. A new method for the mix design of medium strength flowing concrete with low cement content. Cem Concr Compos 2003;25:215–22. [9] Su N, Hsu KC, Chai HW. A simple mix design method for self-compacting concrete. Cem Concr Res 2001;31:1799–807. [10] Japanese society of civil engineering. Guide to construction of high flowing concrete. Tokyo: Gihoudou Pub; 1998. [11] ACI Committee 544. Measurements of properties of fiber reinforced concrete. ACI Mater J 1988; 85(6): 583–93. [12] Khayat KH, Roussel Y. Testing and performance of fiber reinforced, selfconsolidating concrete. In: Skarendahl A, Petersson O, editors. Proceedings of the first international RILEM symposium on self-compacting concrete. Sweden: Stockholm, 1999 September 13–14. p. 509–21. [13] 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. Sweden: Stockholm, 1999 September 13–14. p. 497–507. [14] Sahmaran Mustafa, Yurtseven Alperen, Ozgur Yaman I. Workability of hybrid fiber reinforced self-compacting concrete. Build Environ 2005;40:1672–7. [15] ASTM C496-96, Standard test method for splitting tensile strength of cylindrical concrete specimens. Annual book ASTM standards, vol. 4(04.02); 2001. [16] ASTM C469-94, Standard test method for static modulus of elasticity and Poisson’s ratio of concrete in compression, Annual book ASTM standards, vol. 4 (04.02); 2001. [17] ASTM C78-00, Flexural strength of concrete (using simple beam with thirdpoint loading), Annual book ASTM standards, vol. 4 (04.02); 2001. [18] Fuller WB, Thompson SE. The laws of proportioning concrete. Trans Am Soc Civil Eng 1907;33:222–98. [19] Andreasen AHM, Andersen J. Ueber die Beziehung zwischen Kornabstufung und Zwischenraum in Produkten aus losen Körnern [Mit einigen Experimenten]. Kolloid-Zeitschrift 1930;50:217–28 [in German]. [20] Brouwers HJH, Radix HJ. Self-compacting concrete: theoretical and experimental study. Cem Concr Res 2005;35:2116–36. [21] Al-Tayyib AJ, Al-Zahrani MM, Rasheeduzzafar A, Al-Sulaimani GJ. Effect of polypropylene fiber reinforcement on the properties of fresh and hardened concrete in the Arabian gulf environment. Cem Concr Res 1988;18:561–70. [22] Alhozaimy AM, Soroushian P, Mirza F. Mechanical properties of polypropylene fiber reinforced concrete and the effect of pozzolanic materials. Cem Concr Compos 1996;18:85–92.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
The effect of polypropylene fibers on the properties of fresh and hardened lightweight self-compacting concrete H. Mazaheripour a,*, S. Ghanbarpour b, S.H. Mirmoradi a, I. Hosseinpour a a b
Department of Civil Engineering, Mazandaran University of Science and Technology, Babol, Iran Department of Civil Engineering, Babol University of Technology, Babol, Iran
a r t i c l e
i n f o
Article history: Received 28 May 2009 Received in revised form 1 June 2010 Accepted 7 June 2010 Available online 16 July 2010 Keywords: Light Expanded Clay Aggregate (LECA), Polypropylene fibers Lightweight Self-Compacting Concrete (SCC)
a b s t r a c t This paper evaluates the LECA Lightweight Self-Compacting Concrete (LLSCC) manufactured by Nan-Su, of which the Packing Factor (PF) of its design mixing method has been modified and improved. The study analyzes the impact of polypropylene fibers on LLSCC performance at its fresh condition as well as its mechanical properties at the hardened condition. The evaluation of Fiber Reinforced LLSCC (FR-LLSCC) fluidity has been conducted per the standard of second class rating of JSCE, by three categories of flowability, segregation resistance ability and filling ability of fresh concrete. For the mechanical properties of LLSCC, the study has been conducted as follows: compressive strength with elapsed age, splitting tensile strength, elastic modulus and flexural strength, all of which were measured after the sample being cured for 28 days. When self-compacting concretes were lightened to 75% of their normal weight, their fresh properties are affected immensely. Applying 0.3% volume fractions of polypropylene fiber to the LLSCC resulted in 40% reduction in the slump flow (from 720 mm to 430 mm). In general, the rate of slump flow over Super Plasticizer (SP) volume percentage reduced with the use of polypropylene fibers in the FR-LLSC. Polypropylene fibers did not influence the compressive strength and elastic modulus of LLSCC, however applying these fibers at their maximum percentage volume determined through this study, increased the tensile strength by 14.4% in the splitting tensile strength test, and 10.7% in the flexural strength. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Self-Compacting Concrete (SCC), a new kind of High Performance Concrete (HPC) with excellent deformability and segregation resistance, was first developed in Japan in 1986. It is a special kind concrete that can flow through and fill the gaps of reinforcement and corners of molds without any need for vibration and compaction during the placing process [1,2]. Self-compacting concretes are made using an innovative world renowned technology widely used in the vast field of construction. The increasingly extensive developments in the construction industry throughout the world along with the need for the application of concretes with such qualities as of the SCC, has lead to many studies on such types of concretes. One of the most crucial factors in the design and construction of structures is the considerable amount of weight of dead-load mainly due to the ceiling and the separating walls. Thus, it is evident that using lightweight materials in the beams, columns and * Corresponding author. Tel.: +98 9122957412. E-mail address: [email protected] (H. Mazaheripour). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.06.018
other structure components considerably reduces the dead-load, which could result in a cost-effective construction plan. It is also evident that applying lightweight concretes in many such structures as bridges with long spans, results in the decrease of the area of the bridge section. Lightweight concrete is known with its advantage of reducing the self-weight of the structures, reducing the areas of sectional members as well as making the construction convenient [3,4]. Thus, the construction cost can be saved when applied to structures such as long span bridge and high rise buildings [5]. The lightweight concrete requires specific mix design method that is quite different from conventional concrete. Using conventional mix design method would give rise the material segregation as well as lower the strength by the reduced weight of the aggregate. To avoid such problems, it is recommended to apply the mix design method of high performance self-compacting concrete for the lightweight concrete [5]. Excellent in segregation resistance ability and its flowability at its fresh condition, self-compacting concrete is generally known as the concrete capable of filling up the given structure only using its self-weight without an additional compaction. It was first
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developed in Japan during 1986, with further mix design method introduced by professor Okamura of Tokyo university in 1993 [6,7]. The most popular mix design method used for the self-compacting concrete is introduced by professor Okamura. His method conducts the cement paste and mortar test before moving onto evaluating properties of the superplasticizer, cement, fine aggregate and pozzolanic material for saving the process from the redundancy of unnecessary testing, although its complicated procedure makes it difficult to apply to companies which manufacture the ready-mixed concrete. Overcoming such obstacle, Taiwanbased Nan-Su suggested a new mix design method that is more convenient. Apart from its simplicity, Nan-Su’s new method has some problems with the fluctuating range of Packing Factor (PF), which is the most important variable [8,9]. This study introduces a production of lightweight self-compacting concrete by utilizing PF-modified and improved version of Nan-Su’s mix design method of self-compacting concrete. Lightweight concrete application has recently became conventional in different forms including lightweight aggregate concrete, fine aggregate concrete and bubbled air concrete that has been replaced with ordinary concrete. Lightening process of ordinary concretes has been done in different cases and with various shapes. Thus, self-compacting concretes are new generation of lightened concretes in concrete industry. Light Expanded Clay Aggregates (LECA) has been used to lighten in this study. Various mixed projects of the lightweight materials are made by coarse aggregates and the natural fine aggregates to lighten the concretes weight. Through a series of test mixes conducted during the study, the quality of the concrete at its fresh condition has been evaluated with the second class rating standards of self-compacting concrete published by Japan Society of Civil Engineers (JSCE), especially focused in its flowability, segregation resistance ability and filling ability [10]. The use of Fiber Reinforced Concretes (FRC) has increased in building structures because the reinforced fibers in concrete may improve the toughness, flexural strength, tensile strength, impact strength as well as the failure mode of the concrete. It has also been known that addition of fibers in concrete has little or no effect on the compressive strength and the modulus of elasticity [11]. Use of fibers into SCC mixes has been presented by many researchers [12–14]. Depending on many parameters such as maximum aggregate size, fiber volume, fiber type, fiber geometry, and fiber aspect ratio, fiber inclusion to concrete reduces the workability of concrete.
In this article also, polypropylene fibers are used, and the effect of this fiber inclusion on the workability of LECA Lightweight SelfCompacting Concrete (LLSCC) studied. Slump flow, V-funnel, and U-box tests are performed to assess workability. Moreover, the mechanical properties, namely the compressive, splitting tensile strength, elastic modulus and Flexural strength of lightweight self-compacting concrete mixtures (its density is 1700–2000 kg/ m3) that contain polypropylene fibers are also determined at 28th ages.
2. Experimental outline 2.1. Materials In this study, the coarse and fine aggregates were acquired from the mines of Amol. The maximum size of coarse aggregates used was 10 mm (a 3/8 in mesh was applied and the residue was sieved with a No. 4 mesh) where the smallest particles used as fine aggregate were 0–4.75 mm. All the natural aggregates used for this study were in the dry form. In this research, lightweight LECA aggregates were used to decrease the overall weight of the final self-compacting concrete. LECA aggregates are constructed from clay. They are produced during a synthetic process under known temperatures in a factory. They are characterized as spongy and very light; and highly water absorbent. LECA is an aggregate made of expanded clay produced in rotary kilns at temperatures of about 1200 °C. The LECA aggregates were used in Saturated Surface-Dry (SSD) form. The physical and chemical properties of these aggregates are shown in Tables 1 and 2, respectively. In this study Type II cement produced at Neka factory was used with a 3.15 g/ cm3 density and a Blaine fineness of 3498 cm2/g along with silica fume (GS = 2.1) and limestone (GL = 2.7) to produce self-compacting concrete. During the course of this research, 12 mm long polypropylene fibers manufactured by Vand Shimi were used. Some of the physical properties of these polypropylene fibers are shown in Table 3. 2.2. Mix design procedure Concrete mix design in this study has been modified and improved according to Nan-Su’s method. In other words, PF value was obtained through the pretest to solve the obscurity in assumption of PF value that is a main factor within Nan-Su’s method. Calculation principles of mixing procedure are based on Nan-Su’s procedure [8,9]. Determination of appropriate PF value has saved significant amount of time and efforts during the pretesting phase, and is designed to obtain the proper concrete mix. Based on the Yun Wang Choi method, a percentile volume of natural aggregates were replaced with the same percentile volume of LECA lightweight aggregate in the mixtures. The Yan Wang Choi method is in fact a modification of Nan-Su mix method. First of all, PF was calculated using Eq. (1) in which the coarse and fine aggregates in both compacted and loosely filled stage were implemented [5]:
Table 1 Physical properties of LECA aggregates.
a
Components
Natural coarse (NC)
Natural fine (NF)
LECA coarse (LC)
LECA fine (LF)
Density (kg/m3) Bulk density (kg/m3) Absorption (%)
2690 1440 0.7
2590 1400 2.6
530 ± 20 385 ± 30 30 ± 2a
690 ± 20 485 ± 30 30 ± 2a
More than 1 h.
Table 2 Chemical compositions of LECA aggregates (wt.%). Components
SiO2
Al2O
Fe2O3
MgO
K2O
NaO2
SO3
TiO2
CaO
LoI
MnO
P2O5
LECA
66.05
16.57
7.10
1.99
2.69
0.69
0.03
0.78
2.46
0.84
0.09
0.21
Table 3 Physical properties of polypropylene fibers [1]. Properties
Length of fibers (mm)
Tensile strength (MPa)
Density
Melting point
Appearance
Polypropylene
12
350
900 kg/m3
160 °C
White color fibers
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Unit weight of coarse aggregateðcompacted stageÞ S 1 Unit weight of coarse aggregateðloosely filled stageÞ a Unit weight of coarse aggregateðcompacted stageÞ S þ¼ Unit weight of coarse aggregateðloosely filled stageÞ a
2.3. Mixture proportions of concrete
PF ¼
ð1Þ
where aS is the volume ratio of fine aggregate to the total aggregate. Fig. 1 shows the steps for determining the PF value through measuring the unit weight of fine and coarse aggregates. After specifying the value of PF, the following stages of the calculation method are based on Yan Wang Choi. As already mentioned, the quantity of lightweight material is also calculated as percentile volume of the mixed natural material. So that a natural fine aggregate is replaced by 0– 3 mm fine LECA aggregate and natural coarse aggregate it is replaced by percentile volume of 3–10 mm coarse LECA aggregate (after meshing). Fig. 2 shows a schematic flowchart of the SCC mixed design method. As shown in this figure, for the slump flow values 650–750 mm, further tests including V-funnel and filling height of U-box (mm) have been conducted. When all of the above fresh tests are approved, the mixing design will be recognized as an appropriate workable self-compacting concrete project.
PF is initially assumed to be 1.14 and aS (the volume ratio of fine aggregate to the total aggregates) is assumed to be 60% (S=a ¼ 0:6). The appropriate mix design is then achieved through various experiments using different PF and aS values. Table 4 shows the mixture proportion of concrete as its categories of group A, B, C, D, E, F, G, H, I, J are divided per use of LECA fine and coarse aggregate. E–J mixes has appropriate flow, but separated mix design has not been seen. Mix designs of A– G contain a proportion of LECA fine aggregate as well as a proportion of natural aggregates. However, mix designs of H–J contain a proportion of LECA fine and coarse aggregates added a proportion of natural fine aggregates and without any coarse aggregate included. In Table 4, natural fine and natural coarse aggregate were abbreviated to NF and NC respectively. Beyond that, LF and LC were stated LECA Fine and LECA Coarse aggregates. To evaluate the flow properties of lightweight self-compacting concrete, slump flow test, the time required to reach 500 mm of slump flow, V-funnel and filling height of U-box test was conducted immediately after mixing the concrete, the range values was borrowed from testing methods for the self-compact concrete published by JSCE, and its standards are shown in Table 5.
Fig. 1. Step of determining the PF value [5].
Fig. 2. Flowchart of the SCC mix design method.
Table 4 Mixture proportions of concrete (kg/m3). Mix code
A B C D E F G H I J
PF
1.14 1.12 1.10 1.10 1.10 1.08 1.06 1.06 1.06 1.06
S/a (%)
60 60 65 70 80 80 80 65 65 65
Natural aggregates
LECA aggregates
NF
NC
LF
LC
287 282 300 323 370 363 355 963 772 626
657 645 554 475 317 311 305 – – –
179 175 187 201 230 226 221 – 64 90
– – – – – – – 105 105 105
Cement
Silica fume
Limestone
Water
Super plasticizer
Density
500 500 500 500 500 500 500 500 500 500
33 39 40 38 38 41 47 48 48 48
100 123 150 152 150 175 200 201 201 201
160 160 160 160 160 160 160 160 160 160
19.02 16.55 17.25 17.24 17.20 17.91 17.18 17.23 17.23 17.23
1989 1994 1965 1927 1850 1861 1872 2026 1868 1805
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Table 5 Specification of SCC proposed by JSCE [10]. Class of filling ability of concrete Construction condition
Minimum gap between reinforcement (mm) Amount of reinforcement (kg/m3)
Filling height of U-box test (mm) Absolute volume of coarse aggregates per unit volume of SCC (m3/m3) Flow ability Segregation resistance ability
Slump flow (mm) Time required to flow through V-funnel (s) Time required to reach 500 mm of slump flow (s)
1
2
3
30–60 P350 P300 0.28–0.30 650–750 10–20 5–25
60–200 100–350 P300 0.30–0.33 600–700 7–20 3–15
P200 6100 P300 0.30–0.36 500–650 7–20 3–15
Table 6 Mixture proportions of lightweight self-compacting concrete containing polypropylene fibers (in kg/m3). Mix code
GP0.1 GP0.2 GP0.3 IP0.1 IP0.2 IP0.3
Natural aggregates
LECA aggregates
NF
NC
LF
LC
355 355 355 722 722 722
305 305 305 0 0 0
221 221 221 64 64 64
0 0 0 105 105 105
Cement
Silica fume
Limestone
Water
Super plasticizer
Polypropylene
500 500 500 500 500 500
47 47 47 48 48 48
200 200 200 200 200 200
160 160 160 160 160 160
17.20 18.68 18.68 17.20 18.68 18.68
0.9 1.8 2.7 0.9 1.8 2.7
Both G and I mixing designs were selected among others for testing and are based on first class of JSCE; both mix designs are utilized to study the impact of polypropylene fibers. Table 6 shows mixture proportions of LLSCC containing polypropylene fibers.
2.4. Mixing project First of all, coarse aggregate material, and if available, 3–10 mm LECA, and then 0–3 mm fine aggregate and 0–3 mm LECA are poured into the mixer, They are mixed for 1–1.5 min. Then, cement, silica fume and limestone are mixed with 30% of the mixing water and is poured into the mixer to be mixed for 2 min. Then, water with super plasticizer are added to the mixer gradually, then the mixer is revolved for 1 min when the fresh concrete undergoes workability test. Applied polypropylene of the mixed materials are mixed with a little of mixed water inside the mixer at the final process.
2.5. Samples and maintenance procedure Specimen for concrete testing has been manufactured without the compacting. Its mold was taken out after 48 h followed by standard curing until the next test. Compressive strength of the concrete was tested on 7th, 14th and 28th days, while splitting tensile strength, elastic module and flexural strength were measured after 28 days of curing. The compressive strength was obtained for a cube of 100 100 100 mm in dimension. Specimens were demolded 2 days after casting and then cured in water at approximately 20 °C until testing was carried out at 7, 14 and 28 days’ age. Six specimens of each mixture were tested on the 28th and the mean value was reported. The splitting tensile strength was determined on Day 28 on cylinders measuring 150-mm diameter and 300 mm height and cured in water until the date of test according the ASTM C496 [15]. Three specimens of each mixture were tested and the mean value was reported.
The modulus of elasticity was determined according to ASTM C469 [16]. End capped Ø150 300 cylinder specimens were cured in water and tested at ages of 4–13 months for different mixtures. The flexural strength was determined according to ASTM C78 [17]. End capped Ø500 100 100 cylinder specimens were cured in water and tested at ages of 28 days for different mixtures. Three specimens of each mixture were tested and the mean value was reported.
3. Results and discussion 3.1. Properties of fresh concrete 3.1.1. LLSCC without fibers Test results of the fresh LLSCC are summarized in Table 7. In the last column of this table during the slump flow test, resistance towards mix segregation has been compared visually in order to specify three states of bad, good, and very good. Better test results are obtained when limestone is being added to the mix. Namely, increased viscosity of the mix is directly linked to the amount of limestone and super plasticizer, mix materials are less separated, and segregation is being superior. Utilization of more than 2.5% of super plasticizer in the mixes would induce too many air bubbles into the mix. Fig. 3 shows slump flow changes for various mix designs. As indicated in the figure, slump flow for mix A was less than 500 mm and for mixes B and C were not high enough. Slump flow for mix D was slightly less than the allowable range. Mix designs E–J are in the allowable first class of JSCE Standard. With increased amount of limestone in the mix and increased viscosity, slump
Table 7 Test results of the fresh lightweight self-compacting concrete. Mix code
PF
Powder (kg/m3)
Slump flow (mm)
T50 (s)
V-funnel (s)
U-Box (mm)
Segregation
A B C D E F G H I J
1.14 1.12 1.10 1.10 1.10 1.08 1.06 1.06 1.06 1.06
634 662 690 690 688 716 747 749 749 749
<500 530 550 630 660 670 720 690 745 750
– 5 5 6 7 9 10 5 7 11
– – 12 14 15 17 20 15 18 23
– – – 290 310 320 325 310 300 295
Bad Bad Bad Good Very good Very good Very good Very good Very good Very good
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Slump flow (mm)
800
745
750
720
700
660
650
690
670
630
600
550
550 530
500
G Series
700
750
Slump flow (mm)
800
I Series
600 500 400 300 200
(2.3 %)
(2.5%)
(2.5%)
0.10%
0.20%
0.30%
(2.3%)
100
450
0
400 A
B
C
D
E
F
G
H
I
0.00%
J
Percentage Volume of the fibers (% of SP)
Mix code
Fig. 6. Slump flow changes of self-compacting concrete when percentages of polypropylene fibers are increased.
Fig. 3. Slump flow.
35
25
G Series
V-funnel time (sec)
Time required to reach 500mm slump flow (s)
30
20
15
10
C
5
D
F E H
25 20 15 10 5
J
G
I Series
0
(2.3%)
(2.3%)
0.00%
0.10%
(2.5%)
(2.5%)
0.15%
0.20%
0.30%
Percentage Volume of the fibers (% of SP)
I
Fig. 7. Impact of fibers percentage volume on the V-funnel time.
0 5
10
15
20
25
30
35
Filling height of U-box test (mm)
0
V-funnel time (sec)
Filling height of U-box test (mm)
Fig. 4. Relationship of time required to flow through V-funnel and to reach 500 mm of slump flow.
400 310 320
300
300
325 310
290
295
350 330
G Series
310
I Series
290 270 250 230 210 190
(2.3%)
(2.3%)
0.00%
0.10%
(2.5%)
170 150
0.20%
0.30%
Percentage Volume of the fibers (% of SP)
200
Fig. 8. Impact of fibers percentage volume on filling height of U-box test.
100
flow is enhanced, its degree being directly linked to the rate of utilized limestone. According to Fig. 4, for mixes B–G, increased T50 time of the mix results in V-funnel time increase, (except for unaccomplished A mix in V-funnel). In fact T50 and V-funnel time have been increased
0 A
B
C
D
E
F
G
H
I
J
Mix code Fig. 5. Filling height of U-box test.
Table 8 Test results of the fresh lightweight self-compacting concrete containing fibers. Mix code
PF
Powder (kg/m3)
Slump flow (mm)
T50 (s)
V-funnel (s)
U-box (mm)
Fibers (%)
Super plasticizer (%)
GP0.0 GP0.1 GP0.2 GP0.3 IP0.0 IP0.1 IP0.2 IP0.3
1.06 1.06 1.06 1.06 1.06 1.06 1.06 1.06
747 747 747 747 749 747 747 747
720 680 560 430 745 650 530 410
10 12 15 – 7 10 12 –
20 21 23 – 18 24 30 –
325 290 255 – 300 285 260 –
0.0 0.1 0.2 0.3 0.0 0.1 0.2 0.3
2.3 2.3 2.5 2.5 2.3 2.3 2.5 2.5
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when powder amount and viscosity were increased. Again, weight is increased in mix design H where T50 time is reduced. But, increased light LECA material in mix designs I and J again T50 time and V-tunnel time are increased. Fig. 5 illustrates the result of filling height of U-box test (mm) for the filling ability of lightweight self-compacting concrete. Results of U-box test were just within the range 290–325 mm and there were fluctuations. The result of filling height of U-box for mixes A, B and C have not reported in order to have bad segregation. Mixes J and D are reported to be slightly lower than the allowable range. 3.1.2. LLSCC with fibers Test results of fresh LLSCC with percentages of different fibers are shown in Table 8. As shown, they reduce slump flow remarkably. Consequently, it could be concluded that it influences other fresh properties, too. Fig. 6 shows percentage comparison of different polypropylene fibers as well as the slump flow changes for two mix projects. Test results for V-funnel and filling height of U-box test are shown in Figs. 7 and 8, respectively. Time increase for Vfunnel test is remarkable when polypropylene is added, unless the volume percentage of polypropylene fibers is about 0.15% for both group of mixes GP and IP. Contrarily, the V-funnel time is decreased by the added percentage of the fibers. 0.15% of polypropylene fibers seems somewhat improving the filling ability of Fiber Reinforced LECA Lightweight Self-Compacting Concrete (FRLLSCC). Filling height of U-Box test results are more discouraging than those for other tests; there is a blockage phenomenon in the test. As shown in Fig. 8, when the volume percentages of polypropylene fibers were increased, passing ability of FR-LLSCC declined.
850
GP0.0 GP0.2 IP0.0 IP0.2 G Series I Series
750 700 650 600 550 500 450 400
1.8
1.9
2
2.1
2.2
2.3
2.4
2.5
2.6
Volume Percentage of SP (%) Fig. 9. The difference in the rate of slump flow over SP volume percentage for LLSCC and FR-LLSCC.
In fact, the packing theory of Fuller and Thompson [18] represents a special case of the more general packing equations derived by Andreasen and Andersen [19]. According to their theory, optimum packing can be achieved when the cumulative Particle Size Distribution (PSD) obeys the following equation [20]:
PðDÞ ¼
D Dmax
q ð2Þ
where P is the fraction that can pass through a sieve with opening diameter D; Dmax is maximum particle size of the mix. The parameter q has a value between 0 and 1, Andreasen and Andersen [19] have found that optimum packing is obtained when q = 0.37. The grading by Fuller is obtained when q = 0.5 [20]. PSD curve of some of the mixtures used in this research has been compared with the Fuller and A&A optimized PSD curve, shown in Fig. 10. As shown, the more the PSD curve of the mixtures approaches the Fuller curve (q = 0.5) the more the results for the fresh LLSCC tests and segregation resistance of the mixes are improved. 3.3. Test results for hardened concrete 3.3.1. Compressive strength Compressive strength test results for LECA content light selfcompressing concrete for 7, 14 and 28 day old samples are shown in Fig. 11. As shown here, day 7 strength of ordinary coarse aggregate design (without LECA coarse aggregate) is 7% more than average amounts of the second group mixes (H, I, J). Whereas, the proportion of water/cement has been the same for all designs. In addition, according to the figure, it is concluded that, increasing LECA coarse aggregates instead of ordinary coarse aggregates would reduce compressive strength.
30
100
% Cumulative finer (M/M)
3.2. Grading
90
A&A [5] - q=0.37
80
Fuller [4] - q=0.5
70
MIX A
60
MIX D MIX G
50
MIX H
40
MIX I
30 20 10 0 0.1
1
10
100
Particle size (D) [mm] Fig. 10. Analysis of actual PSD of aggregates used with Andreasen and Andersen [19], Fuller model [18].
Compressive strength at days (MPa)
Slump flow (mm)
800
Although there was a fluctuation in test results of U-box for LLSCC mixes, the filling height of U-box fell dramatically for FR-LLSCC. Meanwhile, when the volume percentage of polypropylene fibers is about 0.3%, blocking behavior was observed, Therefore, the result has omitted. Fig. 9 compares the increase in the rate of slump flow over the SP volume percentage for four different mix designs of GP0.0, GP0.2, IP0.0 and IP0.2. As shown in Fig. 9, for GP0.0 and IP0.0, in absence of polypropylene fibers, the slump flow increases sharply with the increase of the percentage of super plasticizer in the mix, whilst the rate is much less steep for GP0.2 and IP0.2 where 0.2% of polypropylene fiber were applied.
25 20
days 28 days 14
17% 21%
14%
17%
15% 14%
19%
days 7
13% 12%
8%
30%
32%
60%
58%
60%
H
I
J
15% 27%
15 10
68%
65%
67%
68%
5 0
D
E
F
G Mix Code
Fig. 11. Compressive strength at days.
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H. Mazaheripour et al. / Construction and Building Materials 25 (2011) 351–358 Table 9 Hardened FR-LLSCC test results, standard deviation (s) and coefficient of variation (COV%) for. Hardened self-compacting concrete property
Number of specimen tested for each mixture
Standard deviation-r/mean (COV%) GP0.0
GP0.1
GP0.2
GP0.3
IP0.0
IP0.1
IP0.2
IP0.3
28 days Compressive strength (MPa) 28 days Splitting tensile strength (MPa) 28 days Flexural strength (MPa) 28 days Elastic module (GPa)
6
1.38/25.3 (5.4) 0.14/2.77 (5.3) 0.29/4.86 (5.9) 1.00/23.9 (4.2)
2.76/24.6 (11.2) 0.06/2.98 (2.2) 0.22/5.10 (4.4) 1.02/24.8 (4.1)
1.29/26.3 (4.9) 0.09/3.02 (3.0) 0.06/5.28 (1.1) 1.31/24.1 (5.4)
3.00/24.6 (12.2) 0.09/3.17 (2.8) 0.18/5.38 (3.3) 1.31/24.0 (5.4)
2.12/21.5 (9.9) 0.14/2.32 (6.0) 0.36/4.36 (8.2) 0.59/22.1 (2.7)
2.31/21.7 (10.7) 0.20/2.34 (8.4) 0.09/4.52 (2.1) 0.73/21.6 (3.4)
2.40/22.7 (10.6) 0.23/2.62 (8.7) 0.04/4.69 (0.9) 0.71/22.0 (3.2)
3.14/22.8 (13.8) 0.14/2.65 (5.1) 0.15/4.74 (3.2) 0.74/22.4 (3.3)
3 3
Table 9 illustrates the main mix results containing polypropylene fibers. Also, Fig. 9 is an indication of two different mixed projects. According to some articles [21,22] and the test results, polypropylene fibers do not have any impact on compressive strength of the material. LECA aggregates result in concrete breakage. Mainly, LECA aggregates do not enhance the strength of concrete when a high compressive force is applied. It will not enhance the strength of LECA aggregate; it will detach the cement joint and break it. Thus, the LECA aggregates are just a lightweight material replaced with heavy stone materials but their compressive strength is low and they cannot tolerate considerable forces. Fig. 12 shows the impact comparison of compressive strength for FR-LLSCC. For mix design G; where coarse aggregates are used in absence of LECA coarse aggregate, compressive strength rate is higher than that of mix design I. Generally, the amount of compressive strength by increasing volume percentage of fibers was fluctuated for both mixes G and I. 3.3.2. Tensile strength The test was conducted just to demonstrate the differences of the mixes containing polypropylene fibers with those without it (where the percentage is zero). The test results are shown in Table 9. Three samples were tested on 28th day. When 0.2% and 0.3% samples containing polypropylene were tested the maximum force cracked the cylinder, it split down, i.e. polypropylene fibers prevented the cylinder from rupturing. When polypropylene fibers are added to the SCC concrete mix, they become viscid, thus LECA aggregates in SCC mix are modified when they are added to the mix, because they are evenly distributed throughout the mix, although workability of concrete is reduced, Test results for split cylinder are compared in Fig. 13. The maximum rate of tensile strength in the mix of G series for 0.3% polypropylene containing SCC is 14.4% and in I series with 0.3% polypropylene fibers, the maximum tensile strength is 14.2%. The results demonstrate that added polypropylene fibers can increase tensile strength of SCC
2.75 2.5 2.25 (2.3%)
(2.3%)
(2.5%)
(2.5%)
0.00%
0.10%
0.20%
0.30%
Fig. 13. Impact of increased volume percentage of polypropylene fibers on tensile strength.
concrete by as much as 14%, when the rate is enhanced based on the volume percentage of the fabrics.
3.3.3. Flexural strength According to the study, all of the samples ruptured at two points. The test results of the maximum force on the sample and the calculated stage of rupture is named rupture module (R) and are shown in Table 9. As shown in Fig. 14 rupture module change shows an ascending trend when the volume percentage of polypropylene fibers is increased and for the maximum increase of the fibers by 0.3% for the mixed project of the G and I series, rupture modules are 10.7% and 8.7%, respectively, depending on the maximum increase of applied polypropylene. Bending strength test results for SCC samples (the values of rupturing module) are shown for the mixed project and the obtained results are compared in the two G and I series. The properties increase as the volume percentage is increased. For the 0.1%, 0.2% and 0.3% increase in volume percentage of the G series, the properties are increased by 4.9%, 5.5
G Series
I Series
23 21 19
15
3
Volume Percentage of the fibers (% of SP)
G Series
25
17
G Series I Series
3.25
2
(2.5%) (2.3%)
0.00%
(2.5%)
(2.3%)
0.10%
0.20%
0.30%
Volume percent of the fibers (% of SP)
Flexural strength (MPa)
Compressive strength (MPa)
27
3.5
Tensile strength (MPa)
3
I Series
5.25 5 4.75 4.5 4.25 4
(2.3%) 0.00%
(2.3%) 0.10%
(2.5%)
(2.5%)
0.20%
0.30%
Volume percentage of the fibers (% of SP) Fig. 12. Impact comparison of compressive strength of the samples containing fibers.
Fig. 14. Impact of fibers’ volume percentage on the rupture module.
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H. Mazaheripour et al. / Construction and Building Materials 25 (2011) 351–358 26
G Series I Series
Elastic moduli (GPa)
25 24 23 22 21 (2.3%) 20
0.00%
(2.3%) 0.10%
(2.5%)
(2.5%)
0.20%
0.30%
Percentage Volume of the fibers (% of SP) Fig. 15. Impact of volume percentage of the fabrics on elastic module.
8.6% and 10.7%; they are 3.7%, 7.6% and 8.7% for I series, respectively. 3.3.4. Elastic module The test is to specify elastic module of SCC lightweight concretes with fibers. Samples of the cylinder splitting tensile strength were tested on 28th day. Compressive tension is increased by 30% for the mix cube samples to obtain tension strength and the value of displacement change. It is possible to obtain elastic module of the concrete when a compressive force is applied. According to the obtained function, polypropylene fibers do not impact on these concretes and the changes are slight. As shown in Table 9, when the fibers are increased in LECA mixes, the increased rates or decrease rates are negligible. For mixes G where the LECA coarse aggregate is not used, the rate of elastic module is higher than that of mix design I. These results for G and I mixes are compared in Fig. 15. 4. Conclusion Based on the results presented in this paper, the following conclusions can be drawn: (1) When self-compacting concretes were lightened to 75% of their normal weight, their fresh properties are affected immensely. (2) Based on the results of the experiment done on fresh LLSCC, lightening of the concrete mainly impacted the permeability and flow rates obtained from U-box and V-funnel tests. (3) When a percentile volume of natural aggregates are replaced with the same percentile volume of LECA lightweight aggregates in the mixtures. With respect to the properties and grading of the substituted LECA aggregates, the PSD of the LLSCC is disoriented. Thus, more limestone and filler is needed to regain the fresh properties of an SCC. In addition, in order to compensate for the afore-mentioned flaw, the cement portion needs to be increased in order to enhance the compressive strength of the LLSCC. (4) The presence of polypropylene fibers in LLSCC greatly decreases the slump flow, where 0.3% of these fibers in the concrete (G series) reduces the flowability from 720 mm to 430 mm. The reduced slump flow for 0.1% and 0.2% of fiber usage is 680 mm, and 560 mm, respectively. (5) When polypropylene fibers are used, the time of the V-funnel test is increased, except for 0.15% fiber usage where the time of the test is slightly decreased.
(6) Increasing the volume percentage of polypropylene fibers in LLSCC reduces the filling height in U-box test. (7) Polypropylene fibers do not have an impact on the compressive strength and elastic module of LLSCCs. The changes in both qualities are irregular and insignificant as the volume percentage of polypropylene fibers is increased. (8) Splitting tensile strength is increased as volume percentage of polypropylene fibers in LLSCC is increased. In I and G mix series, the splitting tensile strength is increased by 14.2% and 14.1%, respectively for maximum volume percentage of the fibers (0.3%). (9) Flexural strength is increased when volume percentage of polypropylene fibers in LLSCC are increased. In I and G mix series, the flexural strength is increased by 8.7% and 10.7%, respectively for maximum volume percentage of the fibers (0.3%).
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