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cement ratio on the fresh and hardened properties of self-compacting concrete
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Building and Environment 42 (2007) 1795–1802 www.elsevier.com/locate/buildenv
Effect of water/cement ratio on the fresh and hardened properties of self-compacting concrete Burak Felekog˘lu, Selc- uk Tu¨rkel, Bu¨lent Baradan Department of Civil Engineering, Dokuz Eylul University, 35160 Izmir, Turkey Received 10 June 2005; received in revised form 15 December 2005; accepted 23 January 2006
Abstract The use of self-compacting concrete (SCC) with its improving production techniques is increasing every day in concrete production. However, mix design methods and testing procedures are still developing. Mix design criterions are mostly focused on the type and mixture proportions of the constituents. Adjustment of the water/cement ratio and superplasticizer dosage is one of the main key properties in proportioning of SCC mixtures. In this study, five mixtures with different combinations of water/cement ratio and superplasticizer dosage levels were investigated. Several tests such as slump flow, V-funnel, L-box were carried out to determine optimum parameters for the self-compactibility of mixtures. Compressive strength development, modulus of elasticity and splitting tensile strength of mixtures were also studied. r 2006 Elsevier Ltd. All rights reserved. Keywords: Admixture; Elastic modulus; Fresh concrete; Self-compacting concrete; Strength
1. Introduction Self-compacting concrete (SCC), requiring no consolidation work at site or concrete plants, has been developed in Japan to improve the reliability and uniformity of concrete in 1988 [1]. However, to design a proper SCC mixture is not a simple task. Various investigations have been carried out in order to obtain rational SCC mix-design methods. The establishment of methods for the quantitative evaluation of the degree of self-compactibility is a key issue in establishing the mix design system [2]. Okamura and Ozawa [1] have proposed a simple mixture proportioning system. In this method, the coarse and fine aggregate contents are kept constant so that self-compactibility can be achieved easily by adjusting the water/cement ratio and superplasticizer dosage only. Water/powder ratio is usually accepted between 0.9 and 1.0 in volume, depending on the properties of the powder Corresponding author. Tel.: +90 232 453 10 08 x 1041; fax: +90 232 453 11 91. E-mail address: [email protected] (B. Felekog˘lu).
0360-1323/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2006.01.012
[2,3]. In Sweden, Petersson and Billberg [4] developed an alternative method for mix design including the criterion of blocking, void and paste volume as well as the test results derived from paste rheology studies. Many other investigators have also dealt with the mix-proportioning problems of SCC [3,5,6]. Some design guidelines have been prepared from the acceptable test methods [7]. In the mix-proportioning of traditional concrete, the water/cement ratio is kept constant in order to obtain the required strength and durability. However, with SCC, the water/powder ratio has to be chosen by taking selfcompactibility into account, since self-compactibility is very sensitive to this ratio [1]. Many different test methods have been developed in attempts to characterize the properties of SCC. So far no single method or combination of methods has achieved universal approval and most of them have their adherents. Similarly no single method has been found which characterizes all the relevant workability aspects so each mix design should be tested by more than one test method in order to obtain different workability parameters [7]. For site quality control, two test methods are generally sufficient to monitor production quality of SCC. Typical
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combinations are slump flow and V-funnel or slump flow and J-ring. However, filling and passing ability cannot be evaluated sufficiently by a slump-flow test alone [2]. Both L-box and U-box tests may be used as a passing ability indicator [7]. Another mixture design parameter is resistance to segregation which is more difficult to detect in the laboratory [4]. In order to detect segregation resistance of SCC, GTM screen stability, penetration, settlement column, Munich sedimentation tests were developed and successfully used [7–10]. From a rheological point of view, a successful SCC is characterized by low yield stress necessary for high capacity of deformation and moderate viscosity to ensure uniform suspension of solid particles during casting. Reducing the free water content and increasing the concentration of fine particles can enhance the cohesion and viscosity, and hence the stability of SCC. Free water is the total water minus water that is physically and chemically retained by aggregate and powder materials as well as any water bound by chemical admixtures. In general, the approach of minimizing free water content to enhance stability can result in SCC mixtures with a low yield stress and moderate-to-high viscosity levels. The low water content requires a relatively high dosage of highrange water reducers to obtain the required deformability especially with the lower binder contents [11]. In this study, five different mixtures with the same cement dosage (377 kg/m3) were produced by reducing the free water content (from 227 to 140 l/m3) and at the same time increasing the superplasticizer dosage (from 3.7 to 13.0 l/m3) in order to obtain a slump-flow value in the range of 65–80 cm. A wide range of potentially SCC mixtures with different rheological properties can be produced by changing the mixing water amount and plasticizer dosage. The self-compacting ability depends on the concreting case. There was no clear relation yet between the characteristics obtained in laboratory tests (slump flow and funnel test, if the Japanese method is used, or plastic viscosity and yield stress, if a viscometer is used) and various conditions at the building site (density of reinforcement, casting height, temperature, distance to concrete producing plant). For an application the most appropriate mixture had to be specially developed [12]. This study aims to propose a method for selecting the appropriate mix design. The self-compactibility and mechanical performance of these mixtures were investigated by various test methods. 2. Experimental studies 2.1. Materials
dust (limestone powder) was used in order to enhance viscosity. Its specific gravity and Blaine fineness were 2.58 and 4403 m2/kg, respectively. The superplasticizer was a ‘‘polycarboxylic-acid’’ based admixture, commercially branded as HS100. It is an F-type high-range water reducer, in conformity with ASTM C 494 [13]. The solid content, pH and specific gravity were 35.7%, 6.5 and 1.11, respectively. The coarse aggregate (crushed limestone) had a 15 mm maximum size. The maximum aggregate size was selected 15 mm in order to avoid the blocking effect in the L-box. The gap between rebars in L-box test was 35 mm. As fine aggregate, a mix of crushed 0–5 mm limestone and natural river sand was used. The grading curve of the aggregate mix is illustrated in Fig. 1. 2.2. Mixture proportions Five SCC mixtures were designed in order to obtain different fresh-state properties. The water content has been reduced and superplasticizer dosage has been increased at the same time to obtain the target slump-flow values. It should be noted that in particular the flowability of mixtures with low water/cement ratios was achieved by abnormally increasing the superplasticizer dosage and ignoring the water to fines ratio criterion [2,3]. Cement content and aggregate grading were kept constant in all mixtures (Fig. 1). The compositions of mixtures are presented in Table 1. 2.3. Fresh concrete tests A 100 dm3 batch has been prepared for all mixtures. The mixing sequence consisted of homogenizing the sand, the coarse aggregate, limestone powder and cement in a free fall non-tilting horizontal axis type laboratory mixer. After incorporation of water, superplasticizer was finally introduced to the wet mixture. Initial mixing time is more critical for polycarboxylate based admixtures due to their dispersing mechanism. In order to sustain the equilibrium viscosity, longer mixing times are required. Optimum mixing time and order should be examined at pre-tests 100
100 Cumulative passing %
1796
80
79 62
60 44
40 26
20
14
7
An ordinary Type-I Portland Cement (PC 42.5) was used in all compositions. Its specific gravity, specific surface area by Blaine, and 28 days compressive strength were 3.12, 369 m2/kg, and 48.5 MPa respectively. A quarry filtration
100
0 0.25
0.5
1
2
4
8
16
Sieve size (mm) Fig. 1. Aggregate grading of SCC mixtures.
32
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for each type of plant and recipe. The results of pre-tests showed that a total mixing time of 5 min is enough to stabilize the slump flow and V-funnel flow values. Thirty percent of the batch was used for fresh concrete tests. The remaining part was used to prepare cylindirical specimens without any vibration in order to determine the mechanical properties. The specimens were cured in lime saturated water at 20 1C right up until the testing day. For determining the self-compactibility properties (slump flow, T50 time, V-flow time, L-box blocking ratio) tests were performed and air content of the mixtures was measured. All fresh test measurements were duplicated and the average of measurements was given. In order to reduce the effect of workability loss on variability of test results, the fresh-state properties of mixtures were determined in a period of 30 min after mixing. Before testing, fresh SCC was remixed for 30 s. The order of testing was: (a) (b) (c) (d)
Spread flow test and measurement of T50 time; V-flow test; L-box test; Measurement of air content,
Table 1 Mixture proportions Weight (kg/m3)
Materials
Mix I Mix II Mix III Mix IV Mix V Portland cement (C) Limestone powder (quarry dust) Free water (W) Coarse Aggregate (SSDa) Sand (SSDa) Superplasticizer (HS100) Total powder (P) by weight W/C (by weight) W/P (by weight) W/P (by volume) Unit weight (kg/m3) a
377 239 227 562 861 3.7 616 0.60 0.37 1.07 2269
376 246 203 577 886 6.5 622 0.54 0.33 0.95 2293
377 247 181 593 898 7.9 624 0.48 0.29 0.84 2303
376 263 158 609 932 9.0 639 0.42 0.25 0.71 2346
377 272 140 630 963 13.0 649 0.37 0.22 0.62 2394
Aggregates were used in saturated surface dry (SSD) condition.
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respectively. The tests were performed in accordance with EFNARC [7] standards. 2.4. Hardened concrete tests The compressive strength was obtained on cylinders of 100-mm diameter and 200-mm height. Specimens were demolded 1 day after casting and then cured in water at approximately 20 1C until testing was carried out at 1, 7 and 28 days’ age. Six specimens of each mixture were tested and the mean value was reported. The splitting tensile strength was determined at 28 days on cylinders measuring 150-mm diameter and 300-mm height and cured in water until the date of test according the BS 1881: Part 117 [14]. Three specimens of each mixture were tested and the mean value was reported. The modulus of elasticity was determined according to British Standard 1881, Testing concrete: Part 121: Method for determination of static modulus of elasticity in compression [15]. End capped f150 300 cylinder specimens were cured in water and tested at ages of 4–13 months for different mixtures. Average results obtained from five individual specimens for compressive strength and three for tensile strength and determination of modulus of elasticity from each concrete mixture was reported. In Table 2 the mean, standard deviation and coefficient of variation of test results are given. The lower coefficient of variation of test results can be attributed to the enhanced homogeneity of SCC mixes. 3. Test results and discussion 3.1. Fresh concrete test results The slump-flow values of the SCC mixtures were measured between 65 and 80 cm, which refers to the mean spread diameter of concrete following the removal of slump cone as specified by JSCE [2]. Dosages of admixture were adjusted in order to obtain initial slump-flow values
Table 2 Mean, standard deviation (s) and coefficient of variation (COV %) of hardened concrete test results Hardened concrete property
1 day compressive strength (MPa) 7 days compressive strength (MPa) 28 days compressive strength (MPa) 28 days splitting tensile strength (MPa) 28 days modulus of elasticity (GPa)
Number of specimen tested for each mixture
Standard deviation-s/Mean (COV %)
I
II
III
IV
V
5
1.51/22.10 (6.81)
1.65/20.80 (7.95)
0.94/15.50 (6.07)
1.05/16.00 (6.55)
0.75/12.30 (6.06)
5
2.31/46.80 (4.94)
1.74/40.70 (4.28)
1.48/30.40 (4.86)
0.86/30.20 (2.85)
0.29/19.30 (1.51)
5
2.97/56.10 (5.29)
3.22/49.70 (6.49)
2.24/46.80 (4.78)
1.31/42.80 (3.06)
1.11/36.30 (3.05)
3
0.10/4.60 (2.17)
0.29/3.80 (7.66)
0.25/3.50 (7.12)
0.47/3.70 (12.66)
0.21/3.40 (6.18)
3
0.44/37.30 (1.17)
0.85/34.80 (2.45)
1.70/33.80 (5.02)
0.62/35.30 (1.77)
2.23/25.60 (8.69)
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greater than 65 cm which is necessary for the production of a highly flowable SCC. The slump-flow test judges the capability of concrete to deform under its own weight against the friction of the surface with no external restraint present. Because of the viscous nature of some SCC mixtures, the slump-flow measurements were carried out there was no discernable movement of the concrete, approximately 60 s after the removal of the slump cone [16]. At the same time, the slump-flow time (T50) was measured when the concrete was slumping until it reached 500 mm of flow. The V-funnel and L-box tests were performed according to the procedure given by EFNARC Commitee [7]. From the rheological point of view, fresh concrete as a Bingham fluid can be defined by two parameters, yield stress and plastic viscosity, respectively. Slump flow, as a poor indicator of yield stress is not enough to characterize the fresh behavior of concrete exactly [17]. A typical example of this insufficiency has been observed in this study: Mix I (W =C ¼ 0:60, superplasticizer dosage: 0.60%) and Mix V had nearly the same slump-flow values with 69.0 and 69.5 cm, respectively. However, their behavior in fresh state was totally different having V-funnel times of 3 and 46 s, respectively. Also filling abilities were quite different with L-box ratio of 0.95 and 0.50, respectively. The effect of water/powder ratio and superplasticizer dosage, on slump flow and V-funnel time is presented in Fig. 2. With the reduction of free water content simultaneously, the increase in superplasticizer dosage is not sufficient to obtain similar V-funnel times in the range of permissible slump-flow values (65–80 cm). The effect of water reduction on V-funnel times, seems to be more dominant than the effect of superplasticizer dosage. Many researchers have used both the T50 and V-funnel times as indicators of viscosity of highly flowable concrete mixes. The relationship between these results is presented in Fig. 3. This figure shows that there is an acceptable relationship (R2 ¼ 0:85) between T50 and V-funnel times
for these SCC mixtures. It should not be forgotten that higher V-funnel of T50 times may reduce the acceptability of mixture for self compactibility. Experimental measurements related with L-box ratio indicate the filling and passing ability of each mixture. Lbox test is more sensitive to blocking. There is a risk of blocking of the mixture when the L-box blocking ratio is below 0.8 [18,19]. However, there are contraversory observations from full-scale trials. It was reported that Lbox ratio of 0.6 was found to be sufficient to obtain good filling ability [8,20]. The determined L-box ratios of five mixtures are presented in Fig. 4. It can be said that mixtures having a water/cement ratio greater than 0.48 have a L-box ratio greater than 0.8. However, this does not mean that one cannot prepare SCC with water/cement ratio lower than 0.48. If the concrete proportions are properly redesigned according to self-compactibility criteria, SCC can be produced at lower water/cement ratios. Air content tests were carried out by using a modified procedure of ASTM C231 [21] standard (pressurizing method). The molded fresh concrete was not compacted, it was poured into the air-meter mold and consolidated by 60 V-funnel flow time (sec)
Vft (s) = 2.83 [T50 (s)]2.05 R2 = 0.87
50 40 30 20 10 0
1
0
3
2
Fig. 3. Relationship between V-funnel and T50 time.
50
90 80
Slump flow V-funnel time
40
slump flow (cm)
70 60
30
50 40
20
30 20
10
10 0
0 1.07 (0.60)
0.95 (0.90)
0.84 (1.27)
4
T50 (sec)
0.71 (1.41)
0.62 (2.00)
W/P ratio by volume (admixture dosage % by weight of cement) Fig. 2. Effect of W/P ratio and admixture dosage on slump-flow value and V-funnel time.
V-funnel time (sec)
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5
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1
5
3.2. Hardened concrete test results
0.8
4
0.6
3
0.4
2
Compressive strength tests were carried out at 1, 7 and 28 days. Modulus of elasticity and splitting tensile strengths of specimens were determined at 28 days. Although the mixtures IV and V were rejected at fresh state measurements, the characteristics of all mixtures at hardened state has been investigated since all mixtures were molded without any compaction. Compressive strength development of mixtures up to 28 days has been presented in Fig. 5. It is clear that a rapid strength development can be obtained by reducing the free water content and thereby W/C. When the strength development is in question, water reduction is more dominant than the retardation effect of superplasticizer at higher dosages. Modulus of elasticity of concrete is mainly related with its compressive strength. Normal weight aggregate has a higher modulus of elasticity than hydrated cement paste, a higher content of a given aggregate results in a higher modulus of elasticity of concrete of a given compressive strength. There are many expressions for traditional concrete, in order to predict the modulus of elasticity which is mainly related to compressive strength and density of concrete [24,25]. As a different material SCC may exhibit different stress–strain behavior relationship since SCC mixtures have a lower amount of coarse aggregate. Various studies on modulus of elasticity of SCC resulted with conflicting conclusions. According to Persson [26,27] elastic modulus of SCC coincided well with the same properties of traditional concrete when strength was held constant. Erik and Pentti [28] found similar findings. On the other hand, the experimental study made by Dehn et al. [29] showed that the modulus of elasticity for the SCC is lower than for traditional concrete; so the SCC is ‘‘softer’’. Jacobs and Hunkeler [30] found that at a given strength the modulus of elasticity of SCC is lower than that of a common concrete. This is due to the smaller maximum grain size of SCC and the higher amount of cement paste of SCC. From these investigations it may be concluded that it is not easy to compare the modulus of elasticity with traditional concrete. These contradictory results may possibly be explained by the fact that the constituents
1 blocking ratio
air content %
0
0 0.6
0.54
0.48
0.42
0.37
W/C ratio Fig. 4. Effect of W/C ratio on filling ability and air content of concrete.
its own weight. The relationship between air content and W/P ratio is presented graphically in Fig. 4. Reducing free water while increasing the superplasticizer dosage resulted in an increase of viscosity. As can be observed from Fig. 4 increased air percentage can be attributed to the entrapped air bubbles that could not rise and escape from the surface due to high viscosity. Also superplasticizers caused the air trapping during mixing as a side effect. The fresh unit weight of mixtures varies between 2250 and 2400 kg/m3 and the testing temperature was between 24 and 30 1C. In order to achieve self-compactible highly flowable mixtures, acceptance criteria can be summarized in three steps. Step 1: Mixtures with a slump flow value between 65 and 80 cm were accepted. According to this criteria mixtures I–V fulfilled this requirement. Step 2: Mixtures with a V-funnel time below 20 s. were accepted. According to this criteria mixtures IV and V were rejected. The mixtures having V-funnel times higher than the upper limit tend to entrap air due to the high viscosity. This means that self-compactibility cannot be maintained. On the other hand, the lower limit of V-funnel time (in the range of 8–10 s) has been proposed by many researchers. It is considered that a mixture having a V-funnel time below this limit has a potential of stability loss. Conversely, in this experimental study no visual stability loss has been observed at mixtures I and II having V-funnel times of 3 and 5 s, respectively. The same limitations for T50 time exist in some technical literature. However, it was reported that in France successful SCC mixtures were prepared with T50 time of 1 s without any segregation and bleeding [22]. Static segregation stability of fresh mixtures was detected by visual stability index [23]. All mixtures were in the rate of 0 and 1. Step 3: Mixtures with a L-box ratio below 0.6 were rejected. The same mixtures (IV, V) also could not fulfill this requirement. The mixtures having L-box blocking ratio below 0.6 may have a tendency of blockage between reinforcement due to the high viscosity.
60 Compressive strength (MPa)
0.2
Air content (%)
Blocking ratio
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1day
7days
28 days
50 40 30 20 10 0 0.37
0.42
0.48 0.54 W/C (by weight)
0.60
Fig. 5. Compressive strength development of concrete mixtures.
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and rheological behavior of SCC are quite different from the traditional concrete. Neither aggregate content and maximum size nor cement paste properties are the same. Some specifications gave the properties of reference (normal) concrete for SCC. Modulus of elasticity of standard cured high fluidity concrete specimens at 28 days tested in accordance with draft JIS (Method of Static Modulus of Elasticity) should not be less than 20 GPa or not less than 90% of that reference concrete incorporating the same aggregate. Reference concrete should be made of normal Portland cement with a water/cement ratio of 0.50, slump of 18 cm, air content of 3–6%, unit water content of 175–185 kg/m3 and bulk volume of coarse aggregate of 0.62–0.63 m3/m3 [31]. The relationship between compressive strength and modulus of elasticity of SCC mixtures is presented in Fig. 6; additionally the correlation between compressive strength and modulus of elasticity for SCC with different powder ingredients (fly ash, limestone powder, quartz powder, silica fume, GGBS) or viscosity modifying chemical admixtures and standard vibrated traditional concrete for normal construction purposes according to other researchers and committees are shown [29,32,33]. As can be seen from the figure SCC mixtures have lower elastic modulus when compared with traditional concrete standard limits. This general tendency of SCC mixtures can be attributed to the lower amount of coarse aggregate and increased paste content. The relationship between the compressive strength (fc) and modulus of elasticity (E) for the tested mixtures has been determined by the
following equation: E ¼ 1:57f 0:8 c
½EðGPaÞ; f c ðMPaÞ. (1) pffiffiffiffiffi In Fig. 7, the E= f c ratios are compared. The ratios derived from experimental study were similar with the ACI 318 recommendations. The variability of this ratio with different SCC’s can be attributed to two reasons. First the strength grade of tested SCC’s are not the same. Second the powder ingredients of SCC’s prepared by researchers are all different. The reactivity or inert nature of filler may change the strength characteristics and stress strain relations of mixtures. The relationship between the splitting tensile strength (ft) and compressive strength for the SCC mixtures and also the results obtained by other researchers and committees are presented in Fig. 8 [32–34]. For the tested mixtures the tensile strength can be calculated by using the
ACI 318 [24] Felekoglu et al. (exp.) Persson [30] König [33] Turcry [32] Dehn et al. [29] 0
2
3
4
5
6
E/ (fc)1/2
pffiffiffiffiffi Fig. 7. E= f c ratios of different researchers and ACI 318.
König [33] Dehn et al. [29] Turcry [32] Felekoglu et al. (experimental) ACI 318 [24] CEB FIB 90 upper limit [25] CEB FIB 90 lower limit [25] Felekoglu et al. (model)
König [33] Turcry [32] Bosiljkov [34] Felekoglu et al. (experimental) ACI 318 [24] CEB FIB 90 upper limit [25] CEB FIB 90 lower limit [25] Felekoglu et al. (model)
60
7 28 days indirect tensile strength (MPa)
28 days modulus of elasticity (GPa)
1
50
40
30
20
10
6 5 4 3 2 1 0
0 0
40 60 20 28 days compressive strength (MPa)
80
Fig. 6. Relationship between modulus of elasticity and compressive strength of traditional concrete and SCC.
0
20
40
60
80
28 days compressive strength (MPa) Fig. 8. Relationship between splitting tensile strength and compressive strength of traditional concrete and SCC.
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following equation: ft ¼
0:43f 0:6 c .
(2)
Sonebi and Bartos [18] found that splitting tensile strength of SCC at 28 days is higher than that of traditional concrete. But the strength grades of SCC and traditional concrete at 28 days are different. The results derived from Fig. 8 showed that the splitting tensile strength of SCC mixtures are usually higher than traditional concrete due to better homogeneity coming from vibration free production. 4. Conclusions Based on the results presented in this paper, the following conclusions can be drawn: 1. Optimum water/cement ratio for producing SCC is in the range of 0.84–1.07 by volume. The ratios above and below this range may cause blocking or segregation of the mixture, respectively. 2. Self-compactibility test method stipulations are not universally accepted rules. Degree of toleration depends on the engineering judgement, material type and variety. Proper concrete mixtures can be produced by trial and error method. Successful design and production stipulations may not be in the limits suggested by different committees and researchers due to the facts listed above. 3. In the scope of this study higher splitting tensile strength and lower modulus of elasticities are obtained from SCC mixtures when compared with normal vibrated concrete. Further research is necessary to establish proper relationships between mechanical properties of SCCs at different strength grades and including different constituent materials. References [1] Okamura H, Ouchi M. Self-compacting concrete. Development, present use and future. First International RILEM symposium on self-compacting concrete. Rilem Publications s.a.r.l., 1999. p. 3–14. [2] Noor MA, Uomoto T. Three-dimensional discrete element simulation of rheology tests of self-compacting concrete. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 35–46. [3] Sedran T, De Larrard F. Optimization of self-compacting concrete thanks to packing model, First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 321–332. [4] Emborg M. Rheology tests for self-compacting concrete—how useful are they for the design of concrete mix for full-scale production? First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 95–108. [5] Bui VK, Montgomery D. Mixture proportioning method for selfcompacting high performance concrete with minimum paste volume. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 373–384. [6] Roshavelov TT. Concrete mixture proportioning with optimal dry packing. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 385–396. [7] EFNARC, Specification and guidelines for self-compacting concrete. UK, 2002. pp.32, ISBN 0953973344.
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[8] Petersson O¨. Brite-EuRam project: rational production and improved working environment through using self-compacting concrete. Final report: Task-2, workability, Swedish Cement and Concrete Research Institute, 1999. 56pp. [9] Cussigh F, Sonebi M, Schatter G. Project tests SCC-segregation test methods. Third international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 2003. p. 311–22. [10] Lowke D, Wiegrink K-H, Schiessl P. A simple and significant segregation test for SCC. Third international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 2003. p. 356–66. [11] Khayat KH, Hu C, Monty H. Stability of self-consolidating concrete, advantages, and potential applications. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 143–52. [12] Walraven J. Structural aspects of SCC. Third international RILEM symposium on self-compacting concrete, Ed: Rilem Publications s.a.r.l., 2003. 15–22. [13] ASTM C 494-99a. Standard specification for chemical admixtures for concrete. Annual book of ASTM Standards, 2002. [14] BS 1881 part 117. Method for determination of tensile splitting strength. 1983. [15] BS 1881 part 121. Method for determination of static modulus of elasticity in compression. 1983. [16] Sonebi M, Bartos PJM. Hardened SCC and its bond with reinforcement. First international RILEM symposium on selfcompacting concrete, Rilem Publications s.a.r.l., 1999. p. 275–90. [17] Utsi S, Emborg M, Carlsward J. Relation between workability and rheological parameters. Third international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 2003. p. 311–22. [18] Petersson O¨, Billberg P. Investigation on blocking of self-compacting concrete with different maximum aggregate size and use of viscosity agent instead of filler. First international RILEM symposium on selfcompacting concrete, Rilem Publications s.a.r.l., 1999. p. 333–44. [19] Tviksta LG. Brite Euram Project: rational production and improved working environment through using self compacting concrete. Final report: Task 8.4, quality control, NCC AB, 2000. 28pp. [20] Bernabeu M, Laborde, Brite-EuRam project: rational production and improved working environment through using self-compacting concrete, Final report: Task-8.3, Production System for Civil Engineering, GTM Construction, 2000. 40pp. [21] ASTM C231-91b Test for air content of freshly mixed concrete by the pressure method. Annual book of ASTM standards, 2002. [22] So¨derland L, Claeson C. Brite-EuRam project rational production and improved working environment through using self-compacting concrete. Final report: Task-8.2, Production system for housing, GTM Construction, 2000 51pp. [23] Daczko JA, Stability of Self-consolidating concrete, assumed or ensured? Conference proceedings of first North American conference on the design and use of self-consolidating concrete, ACMB, 2002 p. 245–51. [24] ACI Building Code 318–99. Buıldıng code requirements for structural concrete (ACI 318-99) and commentary (ACI 318R–99). Reported by ACI Commıttee 318, 1999. 392pp. [25] CEB – FIB – 90. Model code for prediction of elastic modulus. 1990. [26] Persson B, Creep, shrinkage and elastic modulus of self-compacting concrete. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 239–50. [27] Persson B. A comparison between mechanical properties of selfcompacting concrete and the corresponding properties of normal concrete. Cement and Concrete Research 2001;31:193–8. [28] H.E. Gram, P. Piiparinen, Properties of SCC-especially early age and long term shrinkage and salt frost resistance. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999 p. 211–26. [29] Dehn F, Holschemacher K, WeiXe D. Self-compacting concrete time development of the material properties and the bond behavior. The Leipzig annual civil engineering report., Germany LACER No. 5, ISSN 1432-6590, 2000. p. 115–24.
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[30] Jacobs F, Hunkeler F. Design of self-compacting concrete for durable concrete structures. First international RILEM symposium on selfcompacting concrete, Rilem Publications s.a.r.l., 1999. p. 397–410. [31] Tomasawa F, Masuda Y, Izumi I, Hayakawa M. AIJ recommended practice for high-fluidity concrete for building construction. First international RILEM symposium on self-compacting concrete. Rilem Publications s.a.r.l., 1999. p. 775–86. [32] Turcry P, Loukili A, Haidar K. Mechanical properties, plastic shrinkage and free deformations of self-consolidating concrete. First
North American conference on the design and use of self-consolidating concrete, ACBM, 2002. p. 335–40. [33] Ko¨ning G, Holschemacher K, Dehn F, WeiXe D. Self-compacting concrete -time development of material properties and bond behaviour. Second international RILEM symposium on self compacting Concrete, COMS Engineering Corporation, 2001. p. 507–16. [34] Bosiljkov VB. SCC mixes with poorly graded aggregate and high volume of limestone filler. Cement Concrete Research 2003;33: 1279–86.
Building and Environment 42 (2007) 1795–1802 www.elsevier.com/locate/buildenv
Effect of water/cement ratio on the fresh and hardened properties of self-compacting concrete Burak Felekog˘lu, Selc- uk Tu¨rkel, Bu¨lent Baradan Department of Civil Engineering, Dokuz Eylul University, 35160 Izmir, Turkey Received 10 June 2005; received in revised form 15 December 2005; accepted 23 January 2006
Abstract The use of self-compacting concrete (SCC) with its improving production techniques is increasing every day in concrete production. However, mix design methods and testing procedures are still developing. Mix design criterions are mostly focused on the type and mixture proportions of the constituents. Adjustment of the water/cement ratio and superplasticizer dosage is one of the main key properties in proportioning of SCC mixtures. In this study, five mixtures with different combinations of water/cement ratio and superplasticizer dosage levels were investigated. Several tests such as slump flow, V-funnel, L-box were carried out to determine optimum parameters for the self-compactibility of mixtures. Compressive strength development, modulus of elasticity and splitting tensile strength of mixtures were also studied. r 2006 Elsevier Ltd. All rights reserved. Keywords: Admixture; Elastic modulus; Fresh concrete; Self-compacting concrete; Strength
1. Introduction Self-compacting concrete (SCC), requiring no consolidation work at site or concrete plants, has been developed in Japan to improve the reliability and uniformity of concrete in 1988 [1]. However, to design a proper SCC mixture is not a simple task. Various investigations have been carried out in order to obtain rational SCC mix-design methods. The establishment of methods for the quantitative evaluation of the degree of self-compactibility is a key issue in establishing the mix design system [2]. Okamura and Ozawa [1] have proposed a simple mixture proportioning system. In this method, the coarse and fine aggregate contents are kept constant so that self-compactibility can be achieved easily by adjusting the water/cement ratio and superplasticizer dosage only. Water/powder ratio is usually accepted between 0.9 and 1.0 in volume, depending on the properties of the powder Corresponding author. Tel.: +90 232 453 10 08 x 1041; fax: +90 232 453 11 91. E-mail address: [email protected] (B. Felekog˘lu).
0360-1323/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2006.01.012
[2,3]. In Sweden, Petersson and Billberg [4] developed an alternative method for mix design including the criterion of blocking, void and paste volume as well as the test results derived from paste rheology studies. Many other investigators have also dealt with the mix-proportioning problems of SCC [3,5,6]. Some design guidelines have been prepared from the acceptable test methods [7]. In the mix-proportioning of traditional concrete, the water/cement ratio is kept constant in order to obtain the required strength and durability. However, with SCC, the water/powder ratio has to be chosen by taking selfcompactibility into account, since self-compactibility is very sensitive to this ratio [1]. Many different test methods have been developed in attempts to characterize the properties of SCC. So far no single method or combination of methods has achieved universal approval and most of them have their adherents. Similarly no single method has been found which characterizes all the relevant workability aspects so each mix design should be tested by more than one test method in order to obtain different workability parameters [7]. For site quality control, two test methods are generally sufficient to monitor production quality of SCC. Typical
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combinations are slump flow and V-funnel or slump flow and J-ring. However, filling and passing ability cannot be evaluated sufficiently by a slump-flow test alone [2]. Both L-box and U-box tests may be used as a passing ability indicator [7]. Another mixture design parameter is resistance to segregation which is more difficult to detect in the laboratory [4]. In order to detect segregation resistance of SCC, GTM screen stability, penetration, settlement column, Munich sedimentation tests were developed and successfully used [7–10]. From a rheological point of view, a successful SCC is characterized by low yield stress necessary for high capacity of deformation and moderate viscosity to ensure uniform suspension of solid particles during casting. Reducing the free water content and increasing the concentration of fine particles can enhance the cohesion and viscosity, and hence the stability of SCC. Free water is the total water minus water that is physically and chemically retained by aggregate and powder materials as well as any water bound by chemical admixtures. In general, the approach of minimizing free water content to enhance stability can result in SCC mixtures with a low yield stress and moderate-to-high viscosity levels. The low water content requires a relatively high dosage of highrange water reducers to obtain the required deformability especially with the lower binder contents [11]. In this study, five different mixtures with the same cement dosage (377 kg/m3) were produced by reducing the free water content (from 227 to 140 l/m3) and at the same time increasing the superplasticizer dosage (from 3.7 to 13.0 l/m3) in order to obtain a slump-flow value in the range of 65–80 cm. A wide range of potentially SCC mixtures with different rheological properties can be produced by changing the mixing water amount and plasticizer dosage. The self-compacting ability depends on the concreting case. There was no clear relation yet between the characteristics obtained in laboratory tests (slump flow and funnel test, if the Japanese method is used, or plastic viscosity and yield stress, if a viscometer is used) and various conditions at the building site (density of reinforcement, casting height, temperature, distance to concrete producing plant). For an application the most appropriate mixture had to be specially developed [12]. This study aims to propose a method for selecting the appropriate mix design. The self-compactibility and mechanical performance of these mixtures were investigated by various test methods. 2. Experimental studies 2.1. Materials
dust (limestone powder) was used in order to enhance viscosity. Its specific gravity and Blaine fineness were 2.58 and 4403 m2/kg, respectively. The superplasticizer was a ‘‘polycarboxylic-acid’’ based admixture, commercially branded as HS100. It is an F-type high-range water reducer, in conformity with ASTM C 494 [13]. The solid content, pH and specific gravity were 35.7%, 6.5 and 1.11, respectively. The coarse aggregate (crushed limestone) had a 15 mm maximum size. The maximum aggregate size was selected 15 mm in order to avoid the blocking effect in the L-box. The gap between rebars in L-box test was 35 mm. As fine aggregate, a mix of crushed 0–5 mm limestone and natural river sand was used. The grading curve of the aggregate mix is illustrated in Fig. 1. 2.2. Mixture proportions Five SCC mixtures were designed in order to obtain different fresh-state properties. The water content has been reduced and superplasticizer dosage has been increased at the same time to obtain the target slump-flow values. It should be noted that in particular the flowability of mixtures with low water/cement ratios was achieved by abnormally increasing the superplasticizer dosage and ignoring the water to fines ratio criterion [2,3]. Cement content and aggregate grading were kept constant in all mixtures (Fig. 1). The compositions of mixtures are presented in Table 1. 2.3. Fresh concrete tests A 100 dm3 batch has been prepared for all mixtures. The mixing sequence consisted of homogenizing the sand, the coarse aggregate, limestone powder and cement in a free fall non-tilting horizontal axis type laboratory mixer. After incorporation of water, superplasticizer was finally introduced to the wet mixture. Initial mixing time is more critical for polycarboxylate based admixtures due to their dispersing mechanism. In order to sustain the equilibrium viscosity, longer mixing times are required. Optimum mixing time and order should be examined at pre-tests 100
100 Cumulative passing %
1796
80
79 62
60 44
40 26
20
14
7
An ordinary Type-I Portland Cement (PC 42.5) was used in all compositions. Its specific gravity, specific surface area by Blaine, and 28 days compressive strength were 3.12, 369 m2/kg, and 48.5 MPa respectively. A quarry filtration
100
0 0.25
0.5
1
2
4
8
16
Sieve size (mm) Fig. 1. Aggregate grading of SCC mixtures.
32
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for each type of plant and recipe. The results of pre-tests showed that a total mixing time of 5 min is enough to stabilize the slump flow and V-funnel flow values. Thirty percent of the batch was used for fresh concrete tests. The remaining part was used to prepare cylindirical specimens without any vibration in order to determine the mechanical properties. The specimens were cured in lime saturated water at 20 1C right up until the testing day. For determining the self-compactibility properties (slump flow, T50 time, V-flow time, L-box blocking ratio) tests were performed and air content of the mixtures was measured. All fresh test measurements were duplicated and the average of measurements was given. In order to reduce the effect of workability loss on variability of test results, the fresh-state properties of mixtures were determined in a period of 30 min after mixing. Before testing, fresh SCC was remixed for 30 s. The order of testing was: (a) (b) (c) (d)
Spread flow test and measurement of T50 time; V-flow test; L-box test; Measurement of air content,
Table 1 Mixture proportions Weight (kg/m3)
Materials
Mix I Mix II Mix III Mix IV Mix V Portland cement (C) Limestone powder (quarry dust) Free water (W) Coarse Aggregate (SSDa) Sand (SSDa) Superplasticizer (HS100) Total powder (P) by weight W/C (by weight) W/P (by weight) W/P (by volume) Unit weight (kg/m3) a
377 239 227 562 861 3.7 616 0.60 0.37 1.07 2269
376 246 203 577 886 6.5 622 0.54 0.33 0.95 2293
377 247 181 593 898 7.9 624 0.48 0.29 0.84 2303
376 263 158 609 932 9.0 639 0.42 0.25 0.71 2346
377 272 140 630 963 13.0 649 0.37 0.22 0.62 2394
Aggregates were used in saturated surface dry (SSD) condition.
1797
respectively. The tests were performed in accordance with EFNARC [7] standards. 2.4. Hardened concrete tests The compressive strength was obtained on cylinders of 100-mm diameter and 200-mm height. Specimens were demolded 1 day after casting and then cured in water at approximately 20 1C until testing was carried out at 1, 7 and 28 days’ age. Six specimens of each mixture were tested and the mean value was reported. The splitting tensile strength was determined at 28 days on cylinders measuring 150-mm diameter and 300-mm height and cured in water until the date of test according the BS 1881: Part 117 [14]. Three specimens of each mixture were tested and the mean value was reported. The modulus of elasticity was determined according to British Standard 1881, Testing concrete: Part 121: Method for determination of static modulus of elasticity in compression [15]. End capped f150 300 cylinder specimens were cured in water and tested at ages of 4–13 months for different mixtures. Average results obtained from five individual specimens for compressive strength and three for tensile strength and determination of modulus of elasticity from each concrete mixture was reported. In Table 2 the mean, standard deviation and coefficient of variation of test results are given. The lower coefficient of variation of test results can be attributed to the enhanced homogeneity of SCC mixes. 3. Test results and discussion 3.1. Fresh concrete test results The slump-flow values of the SCC mixtures were measured between 65 and 80 cm, which refers to the mean spread diameter of concrete following the removal of slump cone as specified by JSCE [2]. Dosages of admixture were adjusted in order to obtain initial slump-flow values
Table 2 Mean, standard deviation (s) and coefficient of variation (COV %) of hardened concrete test results Hardened concrete property
1 day compressive strength (MPa) 7 days compressive strength (MPa) 28 days compressive strength (MPa) 28 days splitting tensile strength (MPa) 28 days modulus of elasticity (GPa)
Number of specimen tested for each mixture
Standard deviation-s/Mean (COV %)
I
II
III
IV
V
5
1.51/22.10 (6.81)
1.65/20.80 (7.95)
0.94/15.50 (6.07)
1.05/16.00 (6.55)
0.75/12.30 (6.06)
5
2.31/46.80 (4.94)
1.74/40.70 (4.28)
1.48/30.40 (4.86)
0.86/30.20 (2.85)
0.29/19.30 (1.51)
5
2.97/56.10 (5.29)
3.22/49.70 (6.49)
2.24/46.80 (4.78)
1.31/42.80 (3.06)
1.11/36.30 (3.05)
3
0.10/4.60 (2.17)
0.29/3.80 (7.66)
0.25/3.50 (7.12)
0.47/3.70 (12.66)
0.21/3.40 (6.18)
3
0.44/37.30 (1.17)
0.85/34.80 (2.45)
1.70/33.80 (5.02)
0.62/35.30 (1.77)
2.23/25.60 (8.69)
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greater than 65 cm which is necessary for the production of a highly flowable SCC. The slump-flow test judges the capability of concrete to deform under its own weight against the friction of the surface with no external restraint present. Because of the viscous nature of some SCC mixtures, the slump-flow measurements were carried out there was no discernable movement of the concrete, approximately 60 s after the removal of the slump cone [16]. At the same time, the slump-flow time (T50) was measured when the concrete was slumping until it reached 500 mm of flow. The V-funnel and L-box tests were performed according to the procedure given by EFNARC Commitee [7]. From the rheological point of view, fresh concrete as a Bingham fluid can be defined by two parameters, yield stress and plastic viscosity, respectively. Slump flow, as a poor indicator of yield stress is not enough to characterize the fresh behavior of concrete exactly [17]. A typical example of this insufficiency has been observed in this study: Mix I (W =C ¼ 0:60, superplasticizer dosage: 0.60%) and Mix V had nearly the same slump-flow values with 69.0 and 69.5 cm, respectively. However, their behavior in fresh state was totally different having V-funnel times of 3 and 46 s, respectively. Also filling abilities were quite different with L-box ratio of 0.95 and 0.50, respectively. The effect of water/powder ratio and superplasticizer dosage, on slump flow and V-funnel time is presented in Fig. 2. With the reduction of free water content simultaneously, the increase in superplasticizer dosage is not sufficient to obtain similar V-funnel times in the range of permissible slump-flow values (65–80 cm). The effect of water reduction on V-funnel times, seems to be more dominant than the effect of superplasticizer dosage. Many researchers have used both the T50 and V-funnel times as indicators of viscosity of highly flowable concrete mixes. The relationship between these results is presented in Fig. 3. This figure shows that there is an acceptable relationship (R2 ¼ 0:85) between T50 and V-funnel times
for these SCC mixtures. It should not be forgotten that higher V-funnel of T50 times may reduce the acceptability of mixture for self compactibility. Experimental measurements related with L-box ratio indicate the filling and passing ability of each mixture. Lbox test is more sensitive to blocking. There is a risk of blocking of the mixture when the L-box blocking ratio is below 0.8 [18,19]. However, there are contraversory observations from full-scale trials. It was reported that Lbox ratio of 0.6 was found to be sufficient to obtain good filling ability [8,20]. The determined L-box ratios of five mixtures are presented in Fig. 4. It can be said that mixtures having a water/cement ratio greater than 0.48 have a L-box ratio greater than 0.8. However, this does not mean that one cannot prepare SCC with water/cement ratio lower than 0.48. If the concrete proportions are properly redesigned according to self-compactibility criteria, SCC can be produced at lower water/cement ratios. Air content tests were carried out by using a modified procedure of ASTM C231 [21] standard (pressurizing method). The molded fresh concrete was not compacted, it was poured into the air-meter mold and consolidated by 60 V-funnel flow time (sec)
Vft (s) = 2.83 [T50 (s)]2.05 R2 = 0.87
50 40 30 20 10 0
1
0
3
2
Fig. 3. Relationship between V-funnel and T50 time.
50
90 80
Slump flow V-funnel time
40
slump flow (cm)
70 60
30
50 40
20
30 20
10
10 0
0 1.07 (0.60)
0.95 (0.90)
0.84 (1.27)
4
T50 (sec)
0.71 (1.41)
0.62 (2.00)
W/P ratio by volume (admixture dosage % by weight of cement) Fig. 2. Effect of W/P ratio and admixture dosage on slump-flow value and V-funnel time.
V-funnel time (sec)
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5
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1
5
3.2. Hardened concrete test results
0.8
4
0.6
3
0.4
2
Compressive strength tests were carried out at 1, 7 and 28 days. Modulus of elasticity and splitting tensile strengths of specimens were determined at 28 days. Although the mixtures IV and V were rejected at fresh state measurements, the characteristics of all mixtures at hardened state has been investigated since all mixtures were molded without any compaction. Compressive strength development of mixtures up to 28 days has been presented in Fig. 5. It is clear that a rapid strength development can be obtained by reducing the free water content and thereby W/C. When the strength development is in question, water reduction is more dominant than the retardation effect of superplasticizer at higher dosages. Modulus of elasticity of concrete is mainly related with its compressive strength. Normal weight aggregate has a higher modulus of elasticity than hydrated cement paste, a higher content of a given aggregate results in a higher modulus of elasticity of concrete of a given compressive strength. There are many expressions for traditional concrete, in order to predict the modulus of elasticity which is mainly related to compressive strength and density of concrete [24,25]. As a different material SCC may exhibit different stress–strain behavior relationship since SCC mixtures have a lower amount of coarse aggregate. Various studies on modulus of elasticity of SCC resulted with conflicting conclusions. According to Persson [26,27] elastic modulus of SCC coincided well with the same properties of traditional concrete when strength was held constant. Erik and Pentti [28] found similar findings. On the other hand, the experimental study made by Dehn et al. [29] showed that the modulus of elasticity for the SCC is lower than for traditional concrete; so the SCC is ‘‘softer’’. Jacobs and Hunkeler [30] found that at a given strength the modulus of elasticity of SCC is lower than that of a common concrete. This is due to the smaller maximum grain size of SCC and the higher amount of cement paste of SCC. From these investigations it may be concluded that it is not easy to compare the modulus of elasticity with traditional concrete. These contradictory results may possibly be explained by the fact that the constituents
1 blocking ratio
air content %
0
0 0.6
0.54
0.48
0.42
0.37
W/C ratio Fig. 4. Effect of W/C ratio on filling ability and air content of concrete.
its own weight. The relationship between air content and W/P ratio is presented graphically in Fig. 4. Reducing free water while increasing the superplasticizer dosage resulted in an increase of viscosity. As can be observed from Fig. 4 increased air percentage can be attributed to the entrapped air bubbles that could not rise and escape from the surface due to high viscosity. Also superplasticizers caused the air trapping during mixing as a side effect. The fresh unit weight of mixtures varies between 2250 and 2400 kg/m3 and the testing temperature was between 24 and 30 1C. In order to achieve self-compactible highly flowable mixtures, acceptance criteria can be summarized in three steps. Step 1: Mixtures with a slump flow value between 65 and 80 cm were accepted. According to this criteria mixtures I–V fulfilled this requirement. Step 2: Mixtures with a V-funnel time below 20 s. were accepted. According to this criteria mixtures IV and V were rejected. The mixtures having V-funnel times higher than the upper limit tend to entrap air due to the high viscosity. This means that self-compactibility cannot be maintained. On the other hand, the lower limit of V-funnel time (in the range of 8–10 s) has been proposed by many researchers. It is considered that a mixture having a V-funnel time below this limit has a potential of stability loss. Conversely, in this experimental study no visual stability loss has been observed at mixtures I and II having V-funnel times of 3 and 5 s, respectively. The same limitations for T50 time exist in some technical literature. However, it was reported that in France successful SCC mixtures were prepared with T50 time of 1 s without any segregation and bleeding [22]. Static segregation stability of fresh mixtures was detected by visual stability index [23]. All mixtures were in the rate of 0 and 1. Step 3: Mixtures with a L-box ratio below 0.6 were rejected. The same mixtures (IV, V) also could not fulfill this requirement. The mixtures having L-box blocking ratio below 0.6 may have a tendency of blockage between reinforcement due to the high viscosity.
60 Compressive strength (MPa)
0.2
Air content (%)
Blocking ratio
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1day
7days
28 days
50 40 30 20 10 0 0.37
0.42
0.48 0.54 W/C (by weight)
0.60
Fig. 5. Compressive strength development of concrete mixtures.
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1800
and rheological behavior of SCC are quite different from the traditional concrete. Neither aggregate content and maximum size nor cement paste properties are the same. Some specifications gave the properties of reference (normal) concrete for SCC. Modulus of elasticity of standard cured high fluidity concrete specimens at 28 days tested in accordance with draft JIS (Method of Static Modulus of Elasticity) should not be less than 20 GPa or not less than 90% of that reference concrete incorporating the same aggregate. Reference concrete should be made of normal Portland cement with a water/cement ratio of 0.50, slump of 18 cm, air content of 3–6%, unit water content of 175–185 kg/m3 and bulk volume of coarse aggregate of 0.62–0.63 m3/m3 [31]. The relationship between compressive strength and modulus of elasticity of SCC mixtures is presented in Fig. 6; additionally the correlation between compressive strength and modulus of elasticity for SCC with different powder ingredients (fly ash, limestone powder, quartz powder, silica fume, GGBS) or viscosity modifying chemical admixtures and standard vibrated traditional concrete for normal construction purposes according to other researchers and committees are shown [29,32,33]. As can be seen from the figure SCC mixtures have lower elastic modulus when compared with traditional concrete standard limits. This general tendency of SCC mixtures can be attributed to the lower amount of coarse aggregate and increased paste content. The relationship between the compressive strength (fc) and modulus of elasticity (E) for the tested mixtures has been determined by the
following equation: E ¼ 1:57f 0:8 c
½EðGPaÞ; f c ðMPaÞ. (1) pffiffiffiffiffi In Fig. 7, the E= f c ratios are compared. The ratios derived from experimental study were similar with the ACI 318 recommendations. The variability of this ratio with different SCC’s can be attributed to two reasons. First the strength grade of tested SCC’s are not the same. Second the powder ingredients of SCC’s prepared by researchers are all different. The reactivity or inert nature of filler may change the strength characteristics and stress strain relations of mixtures. The relationship between the splitting tensile strength (ft) and compressive strength for the SCC mixtures and also the results obtained by other researchers and committees are presented in Fig. 8 [32–34]. For the tested mixtures the tensile strength can be calculated by using the
ACI 318 [24] Felekoglu et al. (exp.) Persson [30] König [33] Turcry [32] Dehn et al. [29] 0
2
3
4
5
6
E/ (fc)1/2
pffiffiffiffiffi Fig. 7. E= f c ratios of different researchers and ACI 318.
König [33] Dehn et al. [29] Turcry [32] Felekoglu et al. (experimental) ACI 318 [24] CEB FIB 90 upper limit [25] CEB FIB 90 lower limit [25] Felekoglu et al. (model)
König [33] Turcry [32] Bosiljkov [34] Felekoglu et al. (experimental) ACI 318 [24] CEB FIB 90 upper limit [25] CEB FIB 90 lower limit [25] Felekoglu et al. (model)
60
7 28 days indirect tensile strength (MPa)
28 days modulus of elasticity (GPa)
1
50
40
30
20
10
6 5 4 3 2 1 0
0 0
40 60 20 28 days compressive strength (MPa)
80
Fig. 6. Relationship between modulus of elasticity and compressive strength of traditional concrete and SCC.
0
20
40
60
80
28 days compressive strength (MPa) Fig. 8. Relationship between splitting tensile strength and compressive strength of traditional concrete and SCC.
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following equation: ft ¼
0:43f 0:6 c .
(2)
Sonebi and Bartos [18] found that splitting tensile strength of SCC at 28 days is higher than that of traditional concrete. But the strength grades of SCC and traditional concrete at 28 days are different. The results derived from Fig. 8 showed that the splitting tensile strength of SCC mixtures are usually higher than traditional concrete due to better homogeneity coming from vibration free production. 4. Conclusions Based on the results presented in this paper, the following conclusions can be drawn: 1. Optimum water/cement ratio for producing SCC is in the range of 0.84–1.07 by volume. The ratios above and below this range may cause blocking or segregation of the mixture, respectively. 2. Self-compactibility test method stipulations are not universally accepted rules. Degree of toleration depends on the engineering judgement, material type and variety. Proper concrete mixtures can be produced by trial and error method. Successful design and production stipulations may not be in the limits suggested by different committees and researchers due to the facts listed above. 3. In the scope of this study higher splitting tensile strength and lower modulus of elasticities are obtained from SCC mixtures when compared with normal vibrated concrete. Further research is necessary to establish proper relationships between mechanical properties of SCCs at different strength grades and including different constituent materials. References [1] Okamura H, Ouchi M. Self-compacting concrete. Development, present use and future. First International RILEM symposium on self-compacting concrete. Rilem Publications s.a.r.l., 1999. p. 3–14. [2] Noor MA, Uomoto T. Three-dimensional discrete element simulation of rheology tests of self-compacting concrete. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 35–46. [3] Sedran T, De Larrard F. Optimization of self-compacting concrete thanks to packing model, First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 321–332. [4] Emborg M. Rheology tests for self-compacting concrete—how useful are they for the design of concrete mix for full-scale production? First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 95–108. [5] Bui VK, Montgomery D. Mixture proportioning method for selfcompacting high performance concrete with minimum paste volume. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 373–384. [6] Roshavelov TT. Concrete mixture proportioning with optimal dry packing. First international RILEM symposium on self-compacting concrete, Rilem Publications s.a.r.l., 1999. p. 385–396. [7] EFNARC, Specification and guidelines for self-compacting concrete. UK, 2002. pp.32, ISBN 0953973344.
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