Workability tests and rheological parameters in self-compacting concrete

Transcription

1 Materials and Structures (29) 42: DOI /s ORIGINAL ARTICLE Workability tests and rheological parameters in self-compacting concrete R. Zerbino Æ B. Barragán Æ T. Garcia Æ L. Agulló Æ R. Gettu Received: 26 October 27 / Accepted: 3 September 28 / Published online: 11 October 28 Ó RILEM 28 Abstract The characterization of the behaviour in the fresh state is critical for self compacting concrete (SCC), and it is usually performed through tests such as the slump flow or the V-funnel. A better description of SCC behaviour can be performed by using viscometers. It has been recognized that in SCC an adequate combination of the rheological parameters (yield stress and plastic viscosity) is required to obtain a mix with enough mobility but avoiding risks of segregation. This paper analyses the relationship between the engineering tests results and the rheological parameters. The experimental data corresponds to an extensive research program, where the effects of the mixing energy, time, concrete temperature and environmental exposure conditions on the rheological behaviour of SCC were studied. Simultaneous measurements with a BML viscometer, the slump flow and the V-funnel tests were carried out on different types of SCC. Relationships between the slump flow and the yield stress, and between the plastic viscosity and the flow times have been found for the same component R. Zerbino (&) LEMIT-CONICET, Fac. Ing. UNLP, 52 y 121, 19 La Plata, Argentina zerbino@ing.unlp.edu.ar B. Barragán T. Garcia L. Agulló Universitat Politècnica de Catalunya, Barcelona, Spain R. Gettu Indian Institute of Technology Madras, Chennai, India materials. In addition, typical ranges of yield stress and plastic viscosity for each class of SCC have been identified. Keywords Rheology Temperature Workability Self compacting concrete 1 Introduction The characterization and control of fresh concrete properties are more critical for self compacting concrete (SCC) than for normal concrete considering that for SCC, the final quality of the structure will strongly depend on such properties. Similar to conventional concrete, simple engineering tests such as the slump flow and the V-funnel tests have been developed for mix design and quality control of SCC. A few standards and several recommendations have been developed in many countries [1, 2] for design, production, control and application of SCC. Moreover, different SCC classes have been recently proposed based on these engineering tests [3]. It has been observed that it is not possible to perform a complete characterization of fresh SCC by using only one engineering test [4]. For instance, concretes that behave in a similar way in quasi static conditions (slump test) can show very different responses when they are pumped. Two types of SCC with the same V-funnel flow time can substantially differ in their rheological properties. It was

2 948 Materials and Structures (29) 42: found that concretes with the same slump flow prepared with different combinations of cements, mineral and chemical admixtures showed rheological responses, with significantly different thixotropy levels [5]. The use of rheometers or viscometers lead to a better characterization of conventional concrete and SCC [6], however their use is usually more expensive and difficult in field applications. Progress is being made to address this issue and some portable equipments have been recently developed [7, 8]. This paper analyses the rheological parameters of SCC and its relationship with the results of slump flow and V-funnel tests. The experimental data is the result of an extensive study on the factors affecting self-compactability, where the type of mixer, concrete temperature, time after mixing and the environmental conditions are included as variables [9]. The use of a combination of engineering tests is discussed. In addition, typical values of yield stress and plastic viscosity for different classes of SCC are identified. 2 Studies on the rheological parameters A complete description of fresh concrete behaviour can be performed by the use of viscometers. Concrete workability is commonly characterized using the Bingham or Herschel-Buckley rheological models. In the Bingham model the concrete mix follows the relationship s = s? lc, where c is the shear rate. The yield value (s ) represents the flow resistance while the plastic viscosity (l) is a measure of the resistance of the material to an increase in the rate of flow [1]. It is generally agreed that SCC has a very low yield stress (close to zero) while the plastic viscosity can vary significantly. It has been recognized that in SCC, cooperation between the rheological parameters is required to obtain a mix with adequate mobility and stability, avoiding risks of segregation [11]. Some authors indicate that SCC is better represented by the Herschel-Buckley model since negative values of yield stress can appear using the Bingham model. It must be noted that, in normal concrete, the yield stress can vary between very low values and 1, Pa or more, while the plastic viscosity (measured by a BML viscometer) only varies between 15 and 114 Pa.s. It has also been observed that the slump test is related to the yield stress [12, 13]. These observations are in accordance with the opinions of many authors summarized in a recent paper [14] where it is concluded that the slump test follows a negative potential law with the yield stress but independent of the viscosity. Regarding SCC, a relationship between the yield stress and the slump flow diameter was observed by Pedersen and Smeplass [15], though with significant dispersion. Studies on SCC with similar slump flow, showed no correlations between the plastic viscosity or the yield stress with the measures from the V-funnel or the U-box [16]. Using a BML viscometer, Nielsson and Wallevik [11] suggest a SCC zone in the yield stress plastic viscosity domain. Comparing different SCC, the authors showed that the yield stress increases as the water content decreases, reducing the filling capacity. Contrarily, an enhancement of the filling capacity was observed by increasing the fine material content or the superplasticizer dosages. In addition, a good relationship between the time to achieve a slump flow of 5 mm (T 5 ) and the plastic viscosity, was indicated. A similar tendency was observed in the case of the V-funnel passing time (T V ) or the Orimet test flow time. Though a correlation between yield stress and slump flow diameter was indicated, it is mentioned that it is not possible to qualify a SCC based on just the measure of the slump flow. Analyzing the correspondence between engineering tests and the rheological parameters obtained from a BML viscometer, a relationship between the yield stress and the slump flow has been found [17]. In this study SCC with similar slump flow but different yield stress or plastic viscosity values were obtained; this was attributed to the used of different types of superplasticizers. An acceptable relationship between the plastic viscosity and the T 5 or T V was also found when using similar component materials. Some relationships among the results of the slump flow (D f,t 5 ) or the V-funnel times (T V ) and the rheological parameters (BML viscometer) have been found for SCC prepared with different contents of filler, water, chemical admixtures, and aggregates [18], nevertheless these correlations are variable. It was indicated that if the slump flow diameter is below about 65 mm there is some relation between the yield stress and D f, but this does not occur for spread diameters higher than 65 mm. It was also observed

3 Materials and Structures (29) 42: that viscosity is related to T 5 and V-funnel times, but no correlation with the slump flow diameter was found. Finally, self-compactability zones in the yield stress plastic viscosity domain were indicated. Other authors propose self-compactability zones based on engineering test results such as the V-funnel and the slump flow [19]. A study on the effect of component materials in SCC [2] using engineering tests and a BML viscometer shows that, as the air content increases the paste content, the slump flow diameter increases and the V-funnel time decreases. At the same time, the yield stress remains constant while the plastic viscosity decreases. It must be noted that although the air content mainly affects the viscosity, the slump flow also changes, implying that the slump flow diameter is not solely dependent on the yield stress. It was also observed that when the microsilica content increases, the slump flow decreases and T V remains constant; the yield stress increases but the plastic viscosity only increases marginally. Finally, the authors indicate that the effect of aggregate type (specially the finest fraction 2 mm) was greater on the V-funnel time than on the slump flow diameter and also more significant on the plastic viscosity than on the yield stress [2]. 3 Test program An extensive research program was performed on two types of SCC that demonstrate an acceptable behaviour in practice. The factors affecting the variability of SCC during production as mixer type, temperature, time after mixing and environmental conditions have been considered. In this paper the simultaneous measurements of the rheological properties and results of the slump flow and the V-funnel are compared. 3.1 Test methods A coaxial cylinder ConTec BML Viscometer 3 was used for the evaluation of the rheological behaviour (Fig. 1). The torque produced on a stationary cylinder is recorded for various rotational speeds of an outer cylinder (container) when mobilizing a volume of approximately 2 l. The yield stress (s ) and the Fig. 1 Coaxial cylinder ConTec BML Viscometer 3 used for the evaluation of the rheological behaviour plastic viscosity (l) are calculated assuming that the concrete mix behaves like a Bingham fluid. The slump-flow and the V-funnel were selected as engineering tests to evaluate self-compactability. In the first, in addition to the measurement of the final diameter (D f ), the time to reach a 5 mm diameter (T 5 ) was measured and related to the viscosity by indicating the rate of flow. In a similar way, the concrete viscosity can be quantified by the V-funnel time (T V ). Test procedures have been extensively documented [1 3]. The slump flow, which will usually be specified for all SCC, describes the flowability of fresh concrete in unconfined conditions. Recently, typical slump-flow classes for a range of applications of SCC were presented [3]. Such classes are summarized in Table 1 including the range of values, the target values for conformity criteria and some examples of application. As it was mentioned above, viscosity can be assessed from the T 5 value obtained during the slump-flow test or by the V-funnel flow time. The cited Guidelines [3] also include different viscosity classes for SCC based on T 5 or T V values (see Table 2). According to these Guidelines, passing ability, viscosity and segregation resistance will affect in-situ properties of the hardened SCC but they should only be specified if specifically needed.

4 95 Materials and Structures (29) 42: Table 1 SCC classes for a range of applications, based on the slump-flow test [3] Class Range (mm) Conformity criteria (mm) Applications SF Housing slabs, tunnel linings, piles and deep foundations SF Walls, columns SF Very congested structures Table 2 Viscosity SCC classes based on T 5 ot v values [3] Class T 5 (s) Conformity criteria (s) T V (s) Conformity criteria (s) Applications VS1/VF1 \2 \8 \8 \1 Very congested structures, better surface finishing, risk of bleeding or segregation VS2/VF2 [ Improve segregation resistance 3.2 Materials and SCC mixes The data analyzed in this paper was obtained from 4 batches of SCC prepared in different seasons using various mixing equipments. Two types of SCC varying the maximum size of coarse aggregate were considered: (12 mm) and SCC-2 (2 mm). Most mixes were prepared using crushed gravel and sand, cement type CEM I 42.5 R, calcareous filler and ether polycarboxylated based superplasticizer. Mix proportions are summarised in Table 3. Both types of concretes ( and SCC-2) demonstrated a good behaviour, without segregation and passing ability values higher than.8 in the L-Box test. In addition, one SCC prepared with CEM I 32.5 R and setting retarding admixture, and a series of five SCC prepared with CEM I 52.5 R with incorporation of zeolites (sodium aluminous silicates 12SiO 2 6Al 2 O 3 6Na 2 O 27H 2 O, mean particle size = 5 lm) as filler material was analyzed. The coarse and fine aggregates and the type of superplasticizer were not modified in any case. The rheological parameters determined by the BML viscometer and the slump flow and V-funnel test results were simultaneously obtained for each concrete during the first 1 min after mixing Table 3 Mix proportions (kg/m 3 ) of concretes type and SCC-2 Main program Complementary mixtures, SCC-2 Concrete type: SCC-2 #35 #36 #37 #38 #39 #4 Cement type: 42.5 R 32.5 R 52.5 R Cement Filler Zeolite Water Superplasticizer 6.2 or 9 a 5.7 or 8 a Set retarding admixture 5.7 Sand 2 mm Sand 5 mm Gravel 5 12 mm Gravel mm Paste volume (%) Coarse/total aggregate content (%) a Increase of superplasticizer content was required in winter time

5 Materials and Structures (29) 42: ( initial measures). In addition, other measurements were performed within the first two hours in order to analyze the effects of the environmental conditions on the loss of self-compactability. As expected, many concretes lost the SCC characteristics with time, especially when they were exposed to high environmental temperatures. Nevertheless these data was also included in this paper, to discuss the relationship between engineering tests and rheological parameters. Test results are presented in Table 4. Batches of 2 l (#1 1) were prepared in summer time (initial temperature 27 ± 1 C). After initial measurements three 4 l samples of each concrete were exposed to different environmental conditions (temperature in the range of 2 4 C and relatively humidity equal to 5 or 8%). Two samples remained in static condition and were tested after 3 and 6 min; the third sample was periodically remixed and tested after approximately 45 min. Other set of results corresponds to batches of 25 l of where the temperature of the component materials was intentionally modified. Batches #11 2 were prepared during the summer, the initial temperatures ranged between 12 and 38 C, while batches #21 26 were prepared at moderate temperatures (between 9 and 2 C). Many of these SCC were also tested after remaining in static condition during a lapse of time. A 15 l batch of (#27) prepared at 19 C and exposed to different environmental conditions is also included. Finally, 25 l batches of SCC-2 varying the temperature of the component materials (#28 34), a SCC-2 prepared in a drum mixer (#35), and SCC-2 including different contents of zeolites (#36 4) were also selected to discuss the relationship between engineering tests and the rheological behaviour of SCC. 4 Analysis of the results The results of s, l, D f, T 5, and T V obtained simultaneously on each concrete are given in Table 4. As it was mentioned, SCC with similar composition were prepared at different temperatures and exposed to different environmental conditions. In SCC prepared the same day with the same proportions of component materials, a greater slump flow diameter was observed at intermediate temperatures, near 2 C, than in concretes prepared with cold water or with materials at temperatures higher than 3 C (mixtures #11 13, 14 16, 21 23, 24 26, 28 3). It was also found that SCC that was periodically remixed showed lower viscosity values and higher yield stresses than SCC remaining in static condition. Finally, for a same SCC mixture composition, the rheological properties also depend on the imparted mixing energy. 4.1 Rheological parameters in SCC Figure 2 presents the initial yield stress vs. plastic viscosity of all SCC, together with the self-compactability zone proposed by Nielsson and Wallevik [11] using a BML viscometer. As it can be seen, most data points fall into the suggested area. Some points outside the borders of the zone correspond to concrete mixes prepared at extreme temperatures. The shape of the self-compactability zone reflects the need of cooperation between the yield stress and the plastic viscosity. Segregation is prevented when both properties are appropriately balanced. High viscosity concretes usually require a very low yield stress (near zero), while a greater yield stress is recommended in low viscosity SCC. If both parameters (s and l) are very low, the risk of segregation increases. It is interesting to mention that some SCC (batches #1 1) with good performance in practice, showed values of s and l below the self-compactability area immediately after mixing but increased both rheological parameters during the first 3 min after remixing. Concerning the effect of the mixing (see Table 4) it is interesting to note that the values of s increase with continuous mixing compared with the results of the concrete without agitation, but the contrary occurs in the case of the plastic viscosity (l). These facts can be appreciated comparing the evolution with time of batches #2 4 and 7 9. The reduction in l can be associated to the breakage of particle links. 4.2 Rheological parameters and engineering test results Regarding the relationship between engineering test results and rheological measurements, which is the main interest of this analysis, it can be seen from

6 952 Materials and Structures (29) 42: Table 4 Test results Batch Exposure conditions SCC type Viscometer Slump flow V-funnel Time after mixing (min) Temp (8C) RH (%) s (Pa) l (Pa.s) D f (mm) T 5 (s) T V (s) Observations Initial 2 l batches prepared in summer and exposed at different environmental conditions with (*) and without continuous Initial agitation (*) Initial (*) Initial (*) Initial 6 SCC Initial Initial (*) Initial (*) Initial (*) Initial Batch Concrete initial temperature (8C) SCC type Viscometer Slump flow V-funnel Time after mixing (min) s (Pa) l (Pa.s) D f (mm) T 5 (s) T V (s) Observations Initial Small batches prepared at different temperatures Initial

7 Materials and Structures (29) 42: Table 4 continued Batch Concrete initial temperature (8C) SCC type Viscometer Slump flow V-funnel Time after mixing (min) s (Pa) l (Pa.s) D f (mm) T 5 (s) T V (s) Observations Initial Small batches prepared at different temperatures Initial Initial Initial Initial Initial Initial Initial Initial Initial Initial Initial Initial Initial Batch Exposure conditions SCC type Viscometer Slump flow V-funnel Time after Observations mixing (min) Temp (8C) RH (%) s (Pa) l (Pa.s) D f (mm) T 5 (s) T V (s) Initial 15 l batch prepared at 198C and exposed at different environmental conditions

8 954 Materials and Structures (29) 42: Table 4 continued Batch Concrete initial temperature (8C) SCC type Viscometer Slump flow V-funnel Time after mixing (min) s (Pa) l (Pa.s) D f (mm) T 5 (s) T V (s) Observations SCC Initial Small batches Initial prepared at different Initial temperatures Initial Initial Initial Initial Initial Mixer truck SCC-2 series Initial 2 l batches with zeolites Initial Initial Small batches Initial Initial batches #1 1 that the initial values of T V tend to be higher in SCC-2 than in. It can also be observed that the yield stress and the plastic viscosity are slightly higher in SCC-2 than in. This is in accordance with recent papers [11, 2] that indicate a reduction of the passing ability and an increase in plastic viscosity when larger maximum size aggregate is used. In general, the variations of the engineering tests results (D f, T 5 and T V ) are consistent with the changes in the rheological parameters. Nevertheless, in other cases, for example when varying the mixing equipment, changes in the rheological parameters took place, while some engineering test results were not significantly modified. Figure 3 represents the obtained results of the slump-flow (D f,t 5 ) and V-funnel (T V ) tests as a function of the yield stress or the plastic viscosity. The plotted data includes the measures taken immediately after mixing together with the test results obtained during the first hours. As it was expected some concretes loss their self-compactability properties during this time, these data is also included in the figure for the analysis of the relationships between engineering tests and rheological parameters. It can be observed that there is a clear relationship between the slump-flow diameter and the yield stress (Fig. 3a), and between the plastic viscosity and the flowing times T 5 and T V, Fig. 3e and f. Some isolated points can be related to possible experimental errors or segregation. Figure 3a, e, and f also include the corresponding correlation curves, where continuous lines correspond to all points and discontinuous lines either to (short dashes) or SCC-2 (long dashes). On the contrary, it does not seem to be clear relationships neither between D f and l, nor between T 5 or T V and s (Fig. 3b, c, and d). This shows that a SCC with a certain viscosity can present very different values of yield stress. Also, that SCC mixes of different viscosity can be included into a same SCC class defined by the slump-flow diameter (D f ). Considering the yield stress vs. slump flow diameter relationship plotted in Fig. 3a, results:

9 Materials and Structures (29) 42: s ¼ :46ð649 D f Þ R 2 ¼ :77 ð1þ Equation 1 is very similar to the expression: s ¼ðdensity g=1174þð88 D f Þ ð2þ proposed by Sedran and de Larrard [21]. The differences can be attributed to the component materials or types of SCC used. It is interesting to note that if only the set of results where T 5 was measured are considered, i.e. D f [ 5 mm, the fitting of the correlation becomes worse, signifying that the relationship between D f and s might be better in normal concrete than in SCC. Considering the relationship between the plastic viscosity and the V-funnel flow time (T V ), the best fit was obtained using the following equation (Fig. 3f): l ¼ lnðt V =3:4Þ=:13 R 2 ¼ :84 ð3þ Carrying out the analysis for each type of SCC, it comes out that: l ¼ lnðt V =2:95Þ=:13 R 2 ¼ :72 for SCC Fig. 2 Comparison between the rheological parameters measured immediately after mixing, and the self-compacting zone suggested by Nielsson and Wallevik [11] ð4þ l ¼ lnðt V =2:93Þ=:17 R 2 ¼ :69 for SCC-2 ð5þ In concretes where T 5 was measured (D f [ 5 mm) the yield stress was usually smaller than 6 Pa, but the plastic viscosity values significantly varied. In this case, the obtained correlation is: l ¼ lnðt 5 =:68Þ=:19 R 2 ¼ :76 ð6þ No differences in the correlations were found when considering or SCC-2 types separately. Thus, it can be assumed that while T 5 mainly depends on the viscosity of SCC, T V is also affected by the passing ability (blocking); the later is influenced by the ratio between the maximum size of the aggregate and the dimension of the bottom opening of the V-funnel. This fact can cause a higher estimation of the plastic viscosity for larger coarse aggregate, which should be taken into consideration in practice since it may result in a poor field performance of a SCC (segregation) a priori classified as appropriate for a given application. Moreover, Sedran and de Larrard [21] have shown that the time to reach a 5 mm diameter spread is related to the plastic viscosity by: l ¼ðdensity g=1þð:26d f 2:39 T 5 Þ ð7þ In these experiences the best fit (continuous line in Fig. 3) was obtained using: l ¼ðdensity g=1þð:21d f 1:68 T 5 Þ ð8þ which is very similar to Eq. 7. To contribute to the discussion of the relationship between rheological parameters and engineering test results, Fig. 4a represents the experimental data in the yield stress plastic viscosity domain, for different ranges of slump flow diameter (D f ). As it can be seen, practically all points where D f is smaller than 54 mm are placed outside of the self-compactability zone. The fact that SCC with similar slump-flow diameters fit into the yield stress plastic viscosity region, strengthens the ability of the slump-flow test to classify SCC. In a similar manner, Fig. 4b represents the test results for different ranges of T V. The points are

10 956 Materials and Structures (29) 42: Fig. 3 Relationship between engineering measurements and rheological parameters (a) Slump flow (mm) (c) Flow time T 5 (s) SCC (b) 9 Slump flow (mm) SCC (d) SCC-2 SCC Flow time T 5 (s) (e) Flow time T V (s) SCC-2 (f) Flow time T V (s) SCC scattered and it is not easy to associate a value of T V to the condition of SCC. However, a tendency to increase the passing times as viscosity increases can be observed. Note that in Fig. 4a the points corresponding to a same range are located very close while in Fig. 4b it is not possible to define a region for each group of passing times. Most concretes with T V lower than 6 s fall into the self-compactability zone, but high V-funnel times are also included in the same area. Though the V-funnel test has appropriated repeatability and reproducibility values for quality control of SCC; it seems possible that many other factors might as well affect the relationship between T V and the rheological parameters. One of the weak points of the tests based on time measurement, as the V-funnel, the T 5 in the slumpflow or the T 6 in the L-Box, is the lack of precision in the determination due to human eye estimation. Regarding T 5, it is not only the shortest time, but also its definition can be cause of uncertainty, since the actual instant when concrete makes contact with the circle of 5 mm is very operator-dependent. However, it is evident that exists a relationship between T V and T 5 for a same type of SCC, as both values are affected by the viscosity of concrete. Figure 4c compares the obtained results, a direct relationship can be observed especially for. On the other hand, SCC-2 show greater T v values, which can be explained considering the capacity of the V-funnel to evaluate the passing ability of SCC. It can also be observed that the distance between SCC- 12 and SCC-2 points increases with the concrete viscosity. Finally, Fig. 4d represents, similarly to Fig. 4a and b, the results in the yield stress plastic viscosity domain for different ranges of T 5. It can be seen that SCC with T 5 values between 2 and 4 s

11 Materials and Structures (29) 42: Fig. 4 a (left, up) Results of slump-flow diameter (D f ) in the yield stress plastic viscosity domain. b (right, up) Results of V-funnel time (T V ) in the yield stress plastic viscosity domain. c (left, down) Relationship between T 5 and T V. d (right, down) Results of T 5 time in the yield stress plastic viscosity domain (a) > 7 mm 66-7 mm mm mm mm < 54 mm (b) s 6-9 s 9-12 s s > 15 s (c) T V (s) (d) < 1 s > 1 a 2 s > 2 a 3 s > 3 a 4 s > 4 s SCC T 5 (s) adjust to the self-compactability zone. In SCC where both the yield stress and the viscosity are low, T 5 values are equal or lower than 1 s. 4.3 Engineering tests and the definition of SCC Self-compactability zones based on engineering test results (initial conditions), as the slump flow diameter and the V-funnel time, have also been proposed [19]. Figure 5a plots all data points (initial, showed in Fig. 2, and the later measurements) in the yield stress plastic viscosity domain, indicating as SCC the points inside the zone suggested by Nielsson and Wallevik [11], NC the points above the zone (usually D f \ 5 mm), and as S? the concrete with segregation risk with simultaneous low values of plastic viscosity and yield stress were measured. Representing the same test results in the slump flow diameter V-funnel time domain (Fig. 5b) it can be seen that most SCC are placed into the grey zone, the S? mixes below it and the NC mixes on the left. Note that T V values are always higher than 3 s. Then, it is evident that there is a segregation risk for very short T V, but is not easy to define an upper limit for T V. However, some NC and S? points remain in the grey zone; these limit points have been identified with a circle lim both in Fig. 5a and b. As it can be seen in Fig. 5a, these limit points are placed in the surroundings of the suggested SCC zone. Finally, three points with T V higher than 1 s, defined as HV, were differentiated. These points are clearly located within the proposed zone in Fig. 5a but far from the grey zone in Fig. 5b; these points probably correspond to other SCC class. The definition of SCC zones based on these engineering tests results (D f T V ) has interest for practical applications. A study developed to investigate the segregation tendency when vibrating highly fluid concretes, including SCC [22], showed that the V-funnel time is an important tool to describe segregation tendency. Therein, a vibration-susceptibility

12 958 Materials and Structures (29) 42: (a) (b) T V (s) Slump flow (mm) graph was proposed in the slump-flow vs. V-funnel time domain for concretes of different workability. Three regions where indicated for the different mixes; mixes that accept vibration freely, mixes that require a controlled vibration and mixes that require a certain dosage of viscosity enhancing admixture before vibration. It must be noted that the regions coincide with the zone found in this study. 4.4 Rheological parameters for different classes of SCC SCC NC S? lim HV SCC NC S? lim HV Fig. 5 a All data in the plastic viscosity yield stress domain. b All data in Slump flow diameter V-funnel time domain The same as it occurs with the general concept of workability in normal concrete, the idea of SCC must be associated to a specific type of structure or application [23]. As it was indicated in Sect. 3.1 (Tables 1 and 2) three slump-flow classes for a range of applications and two viscosity classes of SCC based on T 5 or T V values have been established [3]. In this section, the obtained data is analyzed considering combinations of each slump flow class (SF1, SF2, and SF3) and viscosity class (VF1/VS1 and VF2/VS2). Six possible groups are identified: SCC1a, SCC1b, SCC2a, SCC2b, SCC3a, SCC3b, where 1, 2 or 3 refers to the SF type and a or b indicates low or high viscosity class, respectively. As the target values of the different tests are superimposed, some SCC can be included in two groups. Figure 6 presents the obtained test results identified according to the class they belong in the yield stress vs. plastic viscosity plane. It can be seen that classes SCC2 and SCC3 have yield stresses smaller than 2 Pa, while in SCC1 yield stresses up to 6 Pa were measured. The plastic viscosity is usually below 8 Pa.s in VF1/VS1 while values of 1 Pa.s or higher where measured in class VF2/VS2. Although most data adjust to the self-compactability zone suggested by Nielsson and Wallevik [11], it appears that mixes with yield stresses near 4 Pa and plastic viscosity ranging between 4 and 1 Pa.s could also be included. Nevertheless, it should be kept in mind that a combination of a high yield stress and high viscosity can redound in a SCC exhibiting low self-compactability (flowability and blocking resistance) which, depending on the application, can be of concern, i.e. might be adequate for elements such as ramps and piles but inadequate for beams and slabs. Finally, mixes with simultaneous low values of yield stress and plastic viscosity, apparently correspond to SCC of class SF SCC3a SCC2a SCC2b SCC1a SCC1b Fig. 6 Rheological parameters corresponding to different SCC Classes. Dashed line: SCC zone suggested by Nielsson and Wallevik [11]

13 Materials and Structures (29) 42: Conclusions This paper has analysed the relationship between the rheological parameters of Self-compacting Concrete (SCC) and the corresponding engineering test results. The study was based on simultaneous determinations of the yield stress and the plastic viscosity using a BML viscometer, and the results obtained from the slump flow and V-funnel tests. The main conclusions are presented as follows. It was verified that SCC has yield stress close to zero. Most values of the rheological parameters measured with the BML viscometer adjust to the self-compactability zone proposed by Nielsson and Wallevik [11], where the yield stress and plastic viscosity ranged between to 6 Pa and 2 to 12 Pa.s, respectively. Nevertheless, SCC mixes with yield stresses near 4 Pa and plastic viscosities between 4 and 1 Pa.s may also be included since, even if practically leading to little flowability and blocking resistance, can be suitable for applications requiring low self-compactability, i.e. ramps. On the other hand, SCC mixes with simultaneously low values of yield stress and plastic viscosity showed satisfactory performance in practical applications, therefore, might also considered. Typical values of the rheological parameters were found for each class of SCC according to [3]; classes SF2 and SF3 usually have yield stresses smaller than 2 Pa, while in class SF1 yield stresses up to 6 Pa were measured. At the same time, in SCC type VF1/VS1 the plastic viscosity is usually below 8 Pa.s, while in class VF2/VS2 values of 1 Pa.s or higher were measured. SCC prepared with similar types of component materials showed direct relationships between the slump flow diameter and the yield stress and also between the plastic viscosity and the flow times (T 5 or T V ), even when the concrete temperature, the mixing energy, the environmental conditions or the time after mixing was varied. It was observed that as the maximum aggregate size increases SCC tend to show greater viscosity and passing time through the V-funnel. In mixes where the slump flow diameter was greater than 5 mm (T 5 ) the measured yield stress was always lower than 6 Pa, but the plastic viscosity varied significantly. The V-funnel times (T V ) were always greater than 3 s but the upper limit of this parameter is not clear. At the same time, T 5 values varied between 2 and 4 s. In this sense, the specification of a lower limit for T 5 could guarantee a minimum level of viscosity to avoid segregation. It is evident that engineering tests have limited capacity to compare SCC prepared with different component materials and are mainly oriented to quality control in field applications; the use of rheometers or viscometers constitutes a more powerful tool to evaluate the SCC performance. Nevertheless, from the results of this study it appears that the combined use of the slump flow and V-funnel tests constitutes an alternative for the definition of selfcompactability zones for different classes of SCC, and its corresponding field control. Acknowledgements Funding from the Spanish Ministry of Education and Science, through grants MAT23-553, BIA C2-1 and PSE (PS ): HABITAT 23, is greatly appreciated. The first author received financial support from Programme Alban, the European Union Programme of High Level Scholarships for Latin America, scholarship No. E4E47473AR. References 1. EFNARC (22) Specifications and guidelines for selfcompacting concrete. SCC.PDF. Accessed Feb Concrete Society (25) Self-compacting concrete a review. Technical Report No. 62, CCIP-1, Camberley, UK 3. EPG (25) The European guidelines for self-compacting concrete specification production and use. efnarc.org/pdf/sccguidelinesmay25.pdf. Accessed May Bartos PJM (25) Assessment of key characteristics of fresh selfcompacting concrete: European approach to standardisation of tests. In: Shah SP (ed) Second North American conference on the design and use of self-consolidating concrete (SCC) and fourth international RILEM symposium on self-compacting concrete, Hanley Wood Publications, Addison, pp Assaad J, Khayat KH, Mesbah H (23) Assessment of thixotropy of flowable and self-consolidating concrete. ACI Mater J 1(2): Ferraris C, de Larrard F, Martys N (1998) Fresh concrete rheology: recent developments. In: Skalny J, Mindess S (eds) Materials science of concrete V. American Ceramic Society, USA, pp Koehler EP, Fowler DW (25) A portable rheometer for self-consolidating concrete. In: Shah SP (ed) Second North American conference on the design and use of self-consolidating concrete (SCC) and fourth international RILEM symposium on self-compacting concrete. Hanley Wood Publications, Addison, IL, USA, pp

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