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An experimental approach to design self-consolidating concrete
Construction and Building Materials 229 (2019) 116939
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An experimental approach to design self-consolidating concrete Augusto M. Gil a, Kamal H. Khayat b, Bernardo F. Tutikian c,d,⇑ a
Michigan State University, 428 S. Shaw Lane, East Lansing, MI 48824, USA Missouri University of Science and Technology, 224 Engineering Research Lab, Rolla, MO 65409, USA c Unisinos University, Av. Unisinos 950, F01, São Leopoldo, RS 93.022-750, Brazil d Universidad de la Costa, Departamento de Civil y Ambiental, Barranquilla, Colombia b
h i g h l i g h t s It was possible to develop a self-consolidating concrete with local materials. The nomograms combine three relationships and allowing the comparison of properties. The use of two types of coarse aggregates resulted in greater properties. The use of the approach based on aggregate packing led to greater SCC performance.
a r t i c l e
i n f o
Article history: Received 19 August 2019 Received in revised form 8 September 2019 Accepted 10 September 2019
Keywords: Mixture design model Packing density Self-consolidating concrete
a b s t r a c t This paper presents the analysis of an experimental mixture design approach for self-consolidating concrete (SCC) based on two design parameters to optimize mechanical properties and durability. The first approach is based on an empirical determination of the self-consolidation ability of mixtures with a fixed mortar content, while the second approach is based on enhancing the aggregate packing. The proposed procedures enable the establishment of a mixture design nomogram that can correlate the materials’ composition and properties. The effect of mixture design parameters on hardened properties of investigated mixtures developed using each of the proposed approaches was compared in terms of compressive strength to secure a given modulus of elasticity, ultrasound wave propagation velocity and rapid chloride ion penetration. The modulus of elasticity and ultrasound wave propagation velocity of the designed SCC mixtures are found to be, respectively, almost 50% and 8% higher than those of conventional concrete, even at SCC mixtures with lower compressive strength values. Lower modulus of elasticity and ultrasound wave propagation velocity were obtained for SCC mixtures than conventional concrete with compressive strength between 50 and 60 MPa. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction The workability of concrete has a marked effect on the performance of the hardened concrete, including strength and durability. Self-consolidating concrete (SCC) is featured in the fresh state by its higher flowability and higher ability to self-consolidate [1]. These properties are influenced by the mixture design process, which involves not only high deformability of the paste, but also resistance to segregation between coarse aggregate and mortar, as well as its ability to flow readily through confined areas and ensure high filling capacity of reinforced structures [2,3]. The use of an appropriate model to design SCC mixtures is essential to ⇑ Corresponding author. E-mail addresses: [email protected] (A.M. Gil), [email protected] (K.H. Khayat), [email protected] (B.F. Tutikian). https://doi.org/10.1016/j.conbuildmat.2019.116939 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
ensure successful deformability, passing ability, filling capacity, and stability [2,4]. Several efforts have been made to develop mixture design methods, as describe in [5,6] that summarizes mixture-design methods for different types of material and properties from around the world [6]. However, it is agreed that there is no single universal approach for the mixture design of SCC, instead several approaches that can secure satisfactory performance can be employed [6,7]. Besides the selection of raw materials, their compositions, and the incorporation of different types of admixtures and supplementary cementitious materials, such as fly ash, the mixture design methods for SCC have achieved significant improvement in terms of rheology, strength development, and durability [8–10]. In the design of conventional concrete mixtures, the water-to-cement ratio (w/c) is usually fixed to secure a required strength level. However, in the design of SCC mixtures, the workability characteristics,
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which are related to the rheological properties, are adjusted with the incorporation of superplasticizer and in some cases viscosityenhancing admixtures, and the use of relatively high content of fine materials, resulting in relatively low w/c values [3]. Some of the mixture design methods address the determination of the dosage superplasticizer and w/c by conducting tests on the paste phase to predict the flow behavior of the SCC, considering the concrete as a solid aggregate phase in a liquid paste phase. Nevertheless, there is a lack of information regarding the principle involved in the relationship between paste or mortar properties and SCC workability [11]. Mixture design methods for SCC can be classified in different categories depending on the design principle, including (1) empirical approach, (2) compressive strength development approach, (3) securing high aggregate packing, (4) establishing statistical factorial design models for performance prediction, and (5) rheology of paste model approach [6]. The first mixture design method for SCC proposed by Okamura and Osaka [12] was an empirical approach based on author’s experience. It consisted in achieving self-compactability by the adjustment of water-to-powder ratio and superplasticizer dosage using the use slump-flow, V-funnel and U-box tests for concrete mixtures with fixed fine and coarse aggregate contents [3,12,13]. Despite the fact that this approach is simple, empirical design methods allow little flexibility in optimizing the granular skeleton due to predefined steps and require intensive laboratory testing. Besides, it results in higher portions of paste, since some of design parameters are almost constant and does not consider the properties of the aggregate [14]. Based on this method, other empirical design approaches aiming to reduce paste volume were proposed. The main idea of these methods was to increase the ratio between fine aggregate and mortar as well as the volume of coarse aggregate, where the adjustment of materials is made by trial mixing using the V-funnel test [4,15,16]. Compressive strength methods determine the content of each component based on required compressive strength [17]. As an example, the ACI 211.1 [18] method for proportioning conventional concrete considers the aggregate gradation and the contribution of mineral components, which can minimize the need of trial mixtures, but requires adjustments to all components to achieve the best proportioning. The widely used close-toaggregate packing method determines the mixture proportioning by securing the minimum void content based on the aggregate’s packing and filling these voids with paste, most of them using computational devices [19–21]. Statistical factorial models seek to optimize and predict the effects of different key mixture parameters on workability and compressive strength of SCC, in which reasonable ranges are established [22–25]. Lastly, the rheology of paste model approach uses the rheological properties of the paste to predict SCC workability and segregation for a specified particle size distribution and volume of aggregate in the mixture [26,27]. The present study proposes a new mixture design approach for portland cement SCC based on two design parameters to secure a given compressive strength. This procedure refers to design methods for conventional concrete and results in a mixture design diagram that correlates materials’ composition and properties. In order to validate the proposed approach, two types of coarse aggregates and two types of fine materials were tested.
composition is necessary to achieve the required durability parameters at a competitive cost is required. This proposed mixture proportioning methodology should be of interest in the application of SCC in precast plants, cast-in-place construction and rehabilitation projects where SCC can be used to facilitate construction operations and reduce construction time and labor cost. 3. Mixture design procedures of proposed approach The proposed approach is based on the mixture design procedure developed by Monteiro, Helene and Kang [28] for the design of conventional concrete to determined compressive strength, elastic modulus and fracture energy. In this approach, the dry mortar ratio (a) is determined experimentally for the selected materials in an intermediate amount of aggregates (At), where cement consumption is not considered too high or too low, as follows:
a¼
C þ Af C þ At
At ¼ Af þ Ac
ð1Þ ð2Þ
where C, Af and Ac are the masses of cement, sand, and coarse aggregate, respectively. Once a is determined, two mixtures are tested with smaller and higher values of aggregate contents, maintaining the same a value and resulting in different values of cement consumption. The w/c is determined experimentally for the intermediate aggregate content mixture to achieve the desired workability using the standard slump test. In order to maintain the same workability for the smaller and higher aggregate content mixtures, the w/c is established by maintaining the same water-to-dry materials ratio (H) expressed in percentage, as indicated in Eq. (3):
H ð%Þ ¼
w=c ð1 þ AtÞ
ð3Þ
The results obtained in compressive strength tests from the three mixtures prepared with three different aggregate contents and the same a value are plotted in the nomogram shown in
2. Research significance The use of SCC can provide significant benefits in the construction industry. Despite the increase of information regarding the influence of material’s composition on SCC properties, the mixture design methods are still being developed to find proper solution for each application. An appropriate method to determine material’s
Fig. 1. Mixture design nomogram with compressive strength as design criterion [28].
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and properties, allowing fast prediction of key fresh and hardened properties of concrete, such as slump and compressive strength. The nomogram is based on three classical concepts employed in concrete mixture design, comparing the influence of w/c, aggregate-to-cement ratio, and cement content, on the material’s compressive strength, as detailed below. 1. ‘Abram’s Law’ for hardened concrete: consists in the relationship between w/c and compressive strength; 2. ‘Lyse’s Law’ for fresh concrete: relates the volume of water and volume of consolidated fresh concrete, being able to maintain the same consistency for mixtures with different properties and proportions; 3. ‘Molinari’s Law’ for cement content: correlates the cement content with the aggregate-to-cement ratio. Based on this mixture design principle, two approaches were developed in this study. The first one is based on a fixed mortar content, an empirical model similar to previous studies. The other one is based on the principle of maximum compaction between solid materials to achieve desirable flowability with higher resistance to segregation. The procedure established for these approaches are presented below.
Fig. 2. Mixture design procedure of proposed approach based on fixed mortar content.
3.1. Approach based on a fixed mortar content (a) This mixture design procedure is shown in Fig. 2. Taking advantage of previous investigations [28], three conventional concrete mixtures are empirically designed with the same mortar ratio. In this step of the procedure, fine materials and superplasticizer are not employed in the mixture. The established mortar content obtained is maintained constant until the end of the mixture design process. The concrete becomes self-consolidating by the simultaneous incorporation of superplasticizer and fine materials (cement, pozzolanic or non-pozzolanic mineral additions). The superplasticizer is added until the concrete reaches the desired spread diameter in the slump-flow test, despite some segregation of coarse aggregate at high dosage rates of superplasticizer. Segregation is eliminated by the addition of fine materials, which is performed by partial replacement of sand aggregate by nonpozzolanic fine materials or the cement by pozzolanic materials, respectively. It is also possible to avoid segregation with the incorporation of a viscosity-modifying admixture. After the mixture reaches a satisfactory flow behavior in the slump-flow test, all fresh state characterization tests are performed, and samples are taken for compressive strength testing. The results obtained in the characterization and proportioning tests of the mixture (w/c, aggregate content and cement consumption) can enable the establishment of a nomogram similar to that of Fig. 1 for SCC mixtures.
Fig. 3. Mixture design procedure based on aggregate packing.
Fig. 1, used for conventional concretes with compressive strength ranging between 20 and 50 MPa and slump ranging between 0 and 20 cm. The nomogram correlates the concrete composition
Table 1 Determination of the compacted bulk density, specific gravity and volume of voids of two hypothetical materials A and B. Material A (%)
Material B (%)
Combined mass (kg)
Bulk density (kg/m3)
Specific gravity of mixture (kg/m3)
Voids (%)
100 90 80 70 60 50 40 30 20 10 0
0 10 20 30 40 50 60 70 80 90 100
38.36 39.45 42.45 43.12 45.10 44.70 43.00 41.89 39.23 38.11 37.23
2243 2307 2482 2522 2637 2614 2515 2450 2294 2229 2177
2880 2850 2820 2790 2760 2730 2700 2670 2640 2610 2580
28.4 23.5 13.6 10.6 4.6 4.4 7.4 9.0 15.1 17.1 18.5
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Fig. 4. Outline of experimental program.
Table 2 Properties of investigate materials. Sieve diameter (mm)
Passing (%) Fine aggregates
19.0 12.5 9.5 6.3 4.75 2.36 1.18 0.600 0.300 0.150 Fineness modulus Maximum diameter
Coarse aggregates
Fine Sand
Regular Sand
Coarse Type I
Coarse Type II
100 100 100 100 100 100 100 100 84 7 1.09 0.6
100 100 100 100 97 88 71 46 13 2 2.83 4.75
100 100 99 47 13 1 0 0 0 0 5.87 9.5
99 56 19 4 1 0 0 0 0 0 6.81 19
Table 3 Specific gravity and bulk density of raw materials. Material
Cement
Fly ash
Fine Sand
Regular Sand
Coarse Type I
Coarse Type II
Specific gravity (kg/dm3) Bulk density (kg/dm3)
2.92 –
1.92 –
2.65 1.57
2.64 1.53
2.82 1.50
2.82 1.42
3.2. Approach based on aggregate packing
Table 4 X-ray fluorescence of cement and fly ash. Chemical data
Cement (%)
Fly ash (%)
Calcium oxide (CaO) Silicon dioxide (SiO2) Ferric oxide (Fe2O3) Aluminum oxide (Al2O3) Sulphur trioxide (SO3) Magnesium oxide (MgO) Potassium oxide (K2O) Titanium dioxide (TiO2) Strontium oxide (SrO) Phosphorus pentoxide (P2O5) Manganese oxide (MnO)
65.71 17.15 4.93 4.54 3.88 1.44 1.33 0.58 0.27 0.12 0.05
3.02 65.92 7.54 18.71 0.25 0.29 2.88 1.35 – 0.05 –
Table 5 Gradation of cement and fly ash. Diameter (%)
Cement (lm)
Fly ash (lm)
<10% <50% <90% Medium
1.16 9.15 25.41 11.61
5.22 39.91 128.15 56.54
The procedures of this approach can be summarized in the steps presented in Fig. 3. The main consideration of this approach is to fill the voids between solid components with cement paste to achieve the desirable flowability and ensure greater stability, based on an aggregate packing model. By packing the aggregates, it is possible to determine the proportion of each material that will result in the least amount of voids to be filled by cement paste. It is recommended the use of the method proposed by O’Reilly [29], which consists in the packaging of components two by two in order of particle diameter until the smaller component is packed, except for the cement powder. Fine pozzolanic materials, such as fly ash, is packed after the sand fraction and are considered as fine aggregate in this approach. For the compaction tests, a container with a diameter at least five times larger than the average particle diameter shall be used. Table 1 shows the packing procedures for two hypothetical materials labeled A and B having specific gravity of 2880 and 2580 kg/m3, respectively. Using a container of 17.10 dm3, the combined mass is determined experimentally by the increase in 10% of one component in a dry mixture, starting from 0 until it is the only
Table 6 Mixture proportioning and results of fresh state properties. Mixture
a(%)
Conventional 1:3.0 1:4.0 1:5.0 1:6.0 1:7.0
concrete 53.0 53.0 53.0 53.0 53.0
Cement (kg/m3)
Fly ash (kg/m3)
Fine sand (kg/m3)
Regular sand (kg/m3)
Coarse Type I (kg/m3)
Coarse Type II (kg/m3)
w/c
H (%)
SP (%)
Slump-flow (mm)
V-Funnel (s)
L-box (l2/l1)
2420 2408 2367 2343 2312
553 443 364 309 265
– – – – –
– – – – –
620 731 794 836 859
– – – – –
1040 1042 1027 1015 997
0.37 0.43 0.50 0.59 0.72
9.35 8.64 8.37 8.49 9.01
– – – – –
100* 100* 100* 100* 100*
– – – – –
– – – – –
SCC – Fixed mortar ratio with fine sand 1:3.0 53.0 2446 1:4.0 53.0 2430 1:5.0 53.0 2406 1:6.0 53.0 2362 1:7.0 53.0 2347
561 449 371 310 270
– – – – –
253 297 323 335 352
376 445 486 505 525
– – – – –
1055 1056 1046 1020 1017
0.36 0.41 0.48 0.62 0.68
8.93 8.14 8.08 8.86 8.46
0.47 0.47 0.47 0.47 0.47
680 700 690 680 660
9 9 8 10 9
1.00 1.00 0.95 0.90 0.90
SCC – Fixed mortar ratio with fly ash 1:3.0 53.0 2387 1:4.0 53.0 2369 1:5.0 53.0 2363 1:6.0 53.0 2349 1:7.0 53.0 2346 1:8.0 53.0 2302
549 438 363 309 270 236
121 145 160 167 176 177
– – – – – –
494 578 632 670 701 711
– – – – – –
1032 1029 1024 1016 1017 997
0.35 0.41 0.50 0.61 0.67 0.77
8.68 8.16 8.42 8.66 8.41 8.57
0.47 0.47 0.47 0.47 0.47 0.47
720 680 680 690 700 680
8 10 11 9 9 10
0.90 1.00 0.90 0.85 0.90 1.00
SCC – Aggregates packed with coarse aggregate Type II and fine sand 1:3.0 62.8 2401 550 – 1:4.3 59.8 2382 411 – 1:5.7 58.0 2336 322 – 1:7.0 56.7 2301 262 –
165 177 184 183
671 720 738 744
– – – –
819 880 903 909
0.37 0.46 0.59 0.79
9.15 8.69 8.80 9.84
0.47 0.47 0.47 0.47
710 740 710 680
8 8 7 9
0.90 1.00 0.95 0.95
SCC – Aggregates packed with coarse aggregate type II and fly-ash 1:3.0 60.7 2353 540 81 1:4.7 57.0 2335 381 88 1:6.3 54.9 2323 292 93 1:8.0 53.6 2310 236 94
– – – –
691 757 792 808
– – – –
847 925 967 988
0.36 0.48 0.62 0.78
8.98 8.41 8.50 8.64
0.47 0.47 0.47 0.47
750 720 740 730
7 7 7 8
1.00 1.00 0.95 0.95
SCC – Aggregates packed with coarse aggregate Types I and II and fine sand 1:3.0 64.0 2381 546 – 327 1:4.0 61.6 2367 437 – 349 1:5.0 60.0 2354 360 – 360 1:6.0 58.9 2342 304 – 364 1:7.0 58.0 2338 267 – 373
524 559 579 583 597
431 463 475 480 493
355 375 389 395 403
0.36 0.42 0.53 0.71 0.77
9.10 8.44 8.92 10.19 9.61
0.47 0.47 0.47 0.47 0.47
680 690 680 660 670
9 9 10 11 10
0.90 0.95 0.90 0.90 1.00
SCC – Aggregates packed with coarse aggregate Types I and II and fly ash 1:3.0 59.5 2343 535 161 – 1:4.0 56.8 2333 430 172 – 1:5.0 54.9 2330 358 179 – 1:6.0 53.7 2323 306 183 – 1:7.0 52.8 2304 266 186 – 1:8.0 52.0 2301 237 189 –
578 619 644 660 671 682
476 511 533 544 554 564
391 417 437 446 452 459
0.38 0.43 0.51 0.60 0.66 0.72
9.45 8.62 8.50 8.57 8.21 7.97
0.46 0.46 0.46 0.46 0.46 0.46
750 730 710 700 710 700
7 6 8 8 9 9
1.00 1.00 0.95 0.90 0.95 0.85
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Specific gravity (kg/m3)
*Slump test for conventional concrete.
5
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component in the mixture, or 100%. With the combined mass and container volume, it is possible to determine the mixture’s bulk density. Each mixture’s specific density and voids percentage are determined as follows:
SGðABÞ ¼ VðABÞ ¼
ðSGðAÞ %AÞ þ ðSGðBÞ %BÞ 100
SGðABÞ BDðABÞ 100 SGðABÞ
ð4Þ ð5Þ
where SG(A), SG(B) and SG(AB) are the specific gravity values of components A, B and their combination, respectively; and V(AB) and BD(AB) are the void contents and bulk densities of the mixture combining components A and B, respectively. In this example, the optimal mixture would be the combination 50%-50% of both materials, which results in the lowest volume of voids: 4.4%, although this mixture does not present the highest bulk density. When the smallest volume of voids of a mixture is not 5% lower than of the volume of voids of the mixture immediately under or above it, the mixture with the smallest amount of aggregate having the smallest particle size should be used so that less water is required by the fresh concrete. In the example above, as material A has a larger particle size than material B, the choice would be to use the 60–40% combination, which has a volume of voids less than 5% higher of the 50–50% combination, even though a mixture of particles with larger diameter would be used. At this point, the granular skeleton of the mixture has then been established and if the selected materials are suitable for the production of SCC, no segregation and no excess of fine material are expected. With reference to the former model, at least three mixtures containing different aggregate contents are chosen. The recommended values usually vary from 3.5 to 6.5. For each aggregate content, the same proportion between all components are maintained, resulting in mixtures with different values of dry mortar ratio. All the compositions within a family can be then be calculated without the need for adjustments in the mixer. The w/c or superplasticizer content is determined before the compositions’ mixture. The user can then decide whether to pin the w/c or admixture content based on durability consideration. At this point, the intermediate mixture will be used to prepare the experimental mixture and confirm if the w/c is correct, as well as determine the dosage rate of the superplasticizer experimentally. Workability tests are carried out to confirm the admixture concentration. Water is added to maintain the same workability for the smaller and higher aggregate contents for a fixed admixture concentration. Specimens of each mixture are molded to determine compressive strength at the age of interest, which will be used to draw the require nomogram.
aggregates with nominal maximum aggregate sizes of 9.5 and 19 mm were used. Particle size distribution of both types of fine and coarse aggregates determined according to ASTM C136 [30] is presented in Table 2. The specific gravity and bulk density, determined according to ASTM C127 [31] and ASTM C29 [32], respectively, of the investigated materials are presented in Table 3. The properties of portland cement and fly-ash are presented in Table 4 and Table 5. The oxide composition was determined using x-ray fluorescence and gradation by laser granulometry. Polycarboxylate-based superplasticizer (SP) with 40% of solid content was used. 4.2. Mixture composition and preparation The concrete was mixed using a planetary shaft mixer in batches of 60 L. The following mixing protocol as adopted: coarse aggregate and cement were placed together with water in a planetary mixer and mixed for 2 min. Sand and fine aggregates were introduced and mixed for 1 min. Lastly, the superplasticizer was added, and mixing was resumed for 3 min. The results obtained in the proportioning of the mixtures according to the proposed approaches as well as the results of fresh state properties are shown in Table 6. The conventional concrete with the specified materials resulted in an ideal a of 53%, which is defined experimentally by increasing the dry mortar ratio (a) until good finishing is obtained by levelling the sample with a trowel. This value was the same as that used in the composition of the SCC mixtures. To cover the entire range of the desired strength without a large gap between two adjacent values, at least five aggregate contents were adopted for each mixture: 3, 4, 5, 6 and 7. The aggregate content represents the sum of coarse in fine aggregate masses in relation to the mass of cement. For mixtures containing fly ash, an additional aggregate content (8) was used, due to the probable higher resistance obtained by the use of this material. The superplasticizer was adjusted experimentally at 0.47%, by mass of cement for all mixtures. The water was added experimentally until the mixtures achieved the desired workability. For conventional concrete, the targeted slump was 100 mm, while a slump flow of 700 mm was targeted for the SCC mixtures. The w/c values remained consistent according to the aggregate content.
4. Experimental program The experimental program outlined in Fig. 4 demonstrates the application of the two proposed approaches. The influence of two mixture design parameters was investigated using the same combination of raw materials. A conventional concrete was adopted as a reference for the comparative analysis of SCC mixtures. Besides regular sand for each SCC mixture, two types of fine materials were tested: fine sand and fly ash. For the approach based on the aggregate packing, a combination of two coarse aggregate gradations was used. 4.1. Materials Two types of continuously graded natural sands with fineness moduli of 1.09 and 2.83, as well as two types of crushed basalt
Fig. 5. Conventional concrete mixture design nomogram.
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The mass replacement ratio between fly ash and fine sand was determined experimentally for the intermediate aggregate content mixtures (1:5), which resulted in 40% fly ash and 20% fine sand, respectively, for all mixtures designed by the fixed mortar content approach. Using the aggregate packing procedure presented in Section 3.2, the packing of aggregates was carried out for aggregate combination made with and without coarse aggregate having a
(a) SCC - Fixed
– fine sand
nominal maximum size of 9.5 mm. The first compaction test was performed between the Type II coarse aggregate and the regular sand, which was then packed with the fine sand, resulting in a combination of 10%, 40% and 50% of each of the three materials, respectively, to obtain the granular combination with a relatively low void index. Using coarse aggregate Type I, the compaction was carried out between coarse aggregate Type II and coarse
(b) SCC - Fixed
– fly ash
(c) SCC – Aggregates packed – Coarse aggregate (d) SCC – Aggregates packed - Coarse aggregate Type II and fine sand Type II and fly ash
(e) SCC – Aggregates packed - Coarse aggregate Types I, II and fine sand
(f) SCC – Aggregates packed - Coarse aggregate Types I, II and fly ash
Fig. 6. SCC mixture design nomograms.
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Fig. 7. Modulus of elasticity variation versus compressive strength.
Fig. 8. Variations in ultrasound wave propagation velocity with compressive strength.
aggregate Type I, which was then packed with the regular sand and finally with the fine sand, resulting in the proportion of 21.7%, 26.3%, 32% and 20% of each of these materials, respectively. 4.3. Test methods For testing the SCC in the fresh state, the slump flow was determined in compliance with ASTM C1611 [33]. Passing ability was evaluated by the use of two typical test methods for SCC: the Vfunnel and L-box tests. The V-funnel is 600 mm high with an outflow opening of 65 75 mm. The L-box used in the test is equipped with three reinforcing bars, and the blocking ratio (H2/H1) was determined by the measurement of concrete height at the end of the horizontal chamber. Cylindrical test specimens measuring 100 mm in diameter and 200 mm in height were cast to determine mechanical properties. Specimens were demolded one day after casting and cured in a standard moist-curing room until the age of testing. Mechanical
tests were carried out to determine the compressive strength (f’c) and modulus of elasticity according (E’c) to ASTM C39 [34] and ASTM C469 [35], respectively. The durability was estimated using the rapid chloride ion permeability test (RCPT) (ASTM C1202 [36]) and ultrasound wave propagation test methods. 5. Results and discussion 5.1. Mixture design nomogram Mixture design nomograms for conventional concrete and SCC are presented in Figs. 5 and 6, respectively. The nomograms were adapted from the original proposed approach [28] to include the dry mortar ratio (a). For each mixture composition, f’c was determined at 1, 7, 28 and 91 days. As highlighted in red lines on Fig. 5, for a given f’c of 40 MPa, it is possible to determine the mixture composition that can attend the required workability parameters.
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9
Fig. 9. Variation in penetration of chloride ions with compressive strength.
5.2. Properties for specific 28-day strength The hardened properties of the investigated mixtures are compared in terms of f’c to secure a given E’c, ultrasound wave propagation and RCPT. Based on the nomograms, these properties were calculated for five compressive strength values of 25, 30, 40, 50 and 60 MPa. As expected, the E’c values in Fig. 7 are shown to increase with the increase in f’c. Conventional concrete presented the lowest E’c for the mixtures with f’c of 25 MPa and the highest E’c for the concrete mixtures with f’c 60 MPa. The mixtures containing fine sand can develop greater E’c for higher f’c values since the sand modulus of elasticity is higher than that of the cement paste containing fly ash. No clear relation, however, was found between design criteria, although SCC designed through the approach based on a fixed a presented greater E’c for the mixture with f’c of 60 MPa. Ultrasound wave propagation results are presented in Fig. 8. The Ultrasound wave propagation velocities are similar to those of the E’c with the conventional concrete presenting the lowest value for f’c 25 MPa and the highest value for concrete with f’c 60 MPa. Although no clear relation was found between the design criteria and the modulus of elasticity, an inverse behavior was observed where the SCC mixture proportioned with fly ash presented higher values for the same f’c than the SCC made with fine sand. As expected, the mixtures containing fly ash shown in Fig. 9 had lower RCPT values compared to the other mixtures given the pozzolanic activity of the fly ash that can lead to pore refinement. SCC mixtures designed with a fixed a presented lower RCPT values. Despite the optimized granular packing density, the SCC made with coarse aggregate Types I, II and fine sand did not follow the expected behavior, once concrete with f’c lower than 40 MPa presented the highest RCPT. 6. Conclusions In this paper, two simple approaches for the mixture design of SCC have been presented and assessed in comparison with analogously designed conventional concrete. The proposed approaches enabled the development of mixture design nomograms that combine three relationships and allowing the comparison of key properties of SCC prepared for different mixture proportions. The first
approach is based on an empirical determination of selfcompactability of mixtures with a fixed mortar content. The second approach is based on aggregates packing, which results in different mortar contents for each mixture. Both models proved to be efficient in the design of SCC mixtures with selected filling ability and passing ability properties, employing different types of fine materials and coarse aggregate. The effect of mixture design parameters on mechanical and durability characteristics were assessed. Based on the results presented, the following conclusions can be drawn: 1. SCC mixtures designed through the proposed approach that is based on a fixed a presented greater E’c, greater ultrasound wave velocity and lower RCPT penetration of chloride ions for mixtures with f’c of 60 MPa. 2. The use of two types of coarse aggregates that can secure high packing density resulted in greater E’c, greater ultrasound wave velocity and lower RCPT when compared to mixtures designed by the same approach. 3. In general, the use of the approach based on aggregate packing led to greater SCC performance.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] B. Vakhshouri, S. Nejadi, Mix design of light-weight self-compacting concrete, Case Stud. Constr. Mater. 4 (2016) 1–14. [2] H. Okamura, M. Ouchi, Self-compacting concrete, J. Adv. Concr. Technol. 1 (1) (2003) 5–15. [3] C.I. Goodier, Development of self-compacting concrete, Struct. Build. 156 (4) (2003) 405–414. [4] Y. Edamatsu, N. Nishida, M.A. Ouchi, Rational mix-design method for selfcompacting concrete considering interaction between coarse aggregate and mortar particles, in: Proceedings of the First International RILEM Symposium on Self-compacting Concrete, Stockholm. Sweden; 1999. [5] S. Klippel-Filho, G.L. Prager, P.E. Mezzomo da Silva, F.L. Bolina, B.F. Tutikian, Comparative study of the fire resistance and acoustic performance of ceramic brick walls in concern to NBR 15575 in residencial buildings in Brazil, Dyna 85 (2018) 53–58.
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[6] C. Shi, Z. Wu, K. Lv, L. Wu, A review on mixture design methods for selfcompacting concrete, Constr. Build. Mater. 84 (2015) 387–398. [7] M.S.C. Nepomuceno, L.A. Pereira-de-Oliveira, S.M.R. Lopes, Methodology for the mix design of self-compacting concrete using different mineral additions in binary blends of powders, Constr. Build. Mater. 64 (2014) 82–94. [8] B. Esmaeilkhanian, K.H. Khayat, A. Yahia, D. Feys, Effects of mix design parameters and rheological properties on dynamic stability of selfconsolidating concrete, Cem. Concr. Compos. 54 (2014) 21–28. [9] R. Siddique, P. Aggarwal, Y. Aggarwal, Mechanical and durability properties of self-compacting concrete containing fly ash and bottom ash, J. Sustain. Cem. Based Mater. 1 (3) (2012) 67–82. [10] X.H. Wang, K.J. Wang, P. Taylor, G. Morcous, Assessing particle packing based selfconsolidating concrete mix design method, Constr. Build. Mater. 70 (2014) 439–452. [11] Q. Wu, X. An, Development of a mix design method for SCC based on the rheological characteristics of paste, Constr. Build. Mater. 53 (2014) 642–651. [12] H. Okamura, K. Ozawa, Mix design for self-compacting concrete, Concr. Lib. JSCE 25 (1995) 107–120. [13] H. Okamura, Self-compacting high-performance concrete, Concr. Int. Design Constr. 19 (7) (1997) 50–54. [14] T. Sedran, F. Larrard, Optimization of self-compacting concrete thanks to packing model. In: 1st International RILEM symposium on SCC. Sweden; September 1999. p. 321–332. [15] Y. Edamatsu, T. Sugamata, M. Ouchi, A mix-design method for self-compacting concrete based on mortar flow and funnel tests, in: International RILEM Symposium on Self Compacting Concrete. RILEM Publications SARL; 2003. [16] P. Domone, Proportioning of self-compacting concrete – the UCL method. 2009. [17] G.F. Kheder, R.S. Al Jadiri, New method for proportioning self-consolidating concrete based on compressive strength requirements, ACI Mater J 107 (5) (2010). [18] Institute A.C., Standard practice for selecting proportions for normal, heavyweight and mass concrete (ACI 211.1-91), A. Committee, A. Committee Editors; 1991. p. 33. [19] C. Hwang, C. Tsai, The effect of aggregate packing types on engineering properties of self-consolidating concrete, in: Zhiwu Yu, et al., (Eds.), SCC’2005China: 1st International Symposium on Design, Performance and Use of Selfconsolidating Concrete. RILEM Publications SARL, 2005. [20] Sedran T., De Larrard F. Optimization of self-compacting concrete thanks to packing model, in: Proceedings 1st SCC Symp, CBI Sweden, RILEM PRO7; 1999.
[21] N. Sebaibi, M. Benzerzour, S. Yahya, Composition of self-compacting concrete (SCC) using the compressible packing model, the Chinese method and the European standard, Constr. Build. Mater. 43 (2013) 382–388. [22] K.H. Khayat, A. Ghezal, M.S. Hadriche, Factorial design model for proportioning self-consolidating concrete, Mater. Struct. 32 (9) (1999) 679–686. [23] K.H. Khayat, A. Ghezal, M.S. Hadriche, Utility of statistical models in proportioning self-consolidating concrete, Mater. Struct. 33 (5) (2000) 338–344. [24] M. Sonebi, Medium strength self-compacting concrete containing fly ash: modelling using factorial experimental plans, Cem. Concr. Res. 34 (7) (2004) 1199–1208. [25] T. Bouziani, Assessment of fresh properties and compressive strength of selfcompacting concrete made with different sand types by mixture design modelling approach, Constr. Build. Mater. 49 (2013) 308–314. [26] A.W. Saak, H.M. Jennings, S.P. Shah, New methodology for designing selfcompacting concrete, ACI Mater. J. 98 (6) (2001) 429–439. [27] V.K. Bui, Y. Akkaya, S.P. Shah, Rheological model for self-consolidating concrete, ACI Mater. J. 99 (6) (2002) 549–559. [28] P.J.M. Monteiro, P. Helene, S.H. Kang, Designing concrete mixtures for strength, elastic modulus and fracture energy, RILEM Mater. Struct. 26 (162) (1993) 443–452. [29] V.D. O’Reilly, Método de dosagem de concreto de elevado desempenho, São Paulo, Pini, 1992. [30] ASTM C136, Standard test method for sieve analysis of fine and coarse aggregates, ASTM International, West Conshohocken, PA, 2014, 5 pp. [31] ASTM C127-04, Standard test method for density, relative density (specific gravity) and absorption of coarse aggregate, ASTM International, West Conshohocken, PA, 2004, 6 pp. [32] ASTM C29/C29M-09, Standard Test Method for Bulk Density (Unit Weight) and Voids in Aggregate, ASTM International, West Conshohocken, PA, 2012, 5 pp. [33] ASTM C1611/C1611M-14, Standard Test Method for Slump Flow of SelfConsolidating Concrete, ASTM International, West Conshohocken, PA, 2014, 6 pp. [34] ASTM C39/C39M-17b, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, ASTM International, West Conshohocken, PA, 2017, 8 pp. [35] ASTM C469/C469M-14, Standard Test Method for Static Modulus of Elasticity and Poisson’s Ratio of Concrete in Compression, ASTM International, West Conshohocken, PA, 2014, 5 pp. [36] ASTM C1202-17, Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration, ASTM International, West Conshohocken, PA, 2017, 7 pp.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
An experimental approach to design self-consolidating concrete Augusto M. Gil a, Kamal H. Khayat b, Bernardo F. Tutikian c,d,⇑ a
Michigan State University, 428 S. Shaw Lane, East Lansing, MI 48824, USA Missouri University of Science and Technology, 224 Engineering Research Lab, Rolla, MO 65409, USA c Unisinos University, Av. Unisinos 950, F01, São Leopoldo, RS 93.022-750, Brazil d Universidad de la Costa, Departamento de Civil y Ambiental, Barranquilla, Colombia b
h i g h l i g h t s It was possible to develop a self-consolidating concrete with local materials. The nomograms combine three relationships and allowing the comparison of properties. The use of two types of coarse aggregates resulted in greater properties. The use of the approach based on aggregate packing led to greater SCC performance.
a r t i c l e
i n f o
Article history: Received 19 August 2019 Received in revised form 8 September 2019 Accepted 10 September 2019
Keywords: Mixture design model Packing density Self-consolidating concrete
a b s t r a c t This paper presents the analysis of an experimental mixture design approach for self-consolidating concrete (SCC) based on two design parameters to optimize mechanical properties and durability. The first approach is based on an empirical determination of the self-consolidation ability of mixtures with a fixed mortar content, while the second approach is based on enhancing the aggregate packing. The proposed procedures enable the establishment of a mixture design nomogram that can correlate the materials’ composition and properties. The effect of mixture design parameters on hardened properties of investigated mixtures developed using each of the proposed approaches was compared in terms of compressive strength to secure a given modulus of elasticity, ultrasound wave propagation velocity and rapid chloride ion penetration. The modulus of elasticity and ultrasound wave propagation velocity of the designed SCC mixtures are found to be, respectively, almost 50% and 8% higher than those of conventional concrete, even at SCC mixtures with lower compressive strength values. Lower modulus of elasticity and ultrasound wave propagation velocity were obtained for SCC mixtures than conventional concrete with compressive strength between 50 and 60 MPa. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction The workability of concrete has a marked effect on the performance of the hardened concrete, including strength and durability. Self-consolidating concrete (SCC) is featured in the fresh state by its higher flowability and higher ability to self-consolidate [1]. These properties are influenced by the mixture design process, which involves not only high deformability of the paste, but also resistance to segregation between coarse aggregate and mortar, as well as its ability to flow readily through confined areas and ensure high filling capacity of reinforced structures [2,3]. The use of an appropriate model to design SCC mixtures is essential to ⇑ Corresponding author. E-mail addresses: [email protected] (A.M. Gil), [email protected] (K.H. Khayat), [email protected] (B.F. Tutikian). https://doi.org/10.1016/j.conbuildmat.2019.116939 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
ensure successful deformability, passing ability, filling capacity, and stability [2,4]. Several efforts have been made to develop mixture design methods, as describe in [5,6] that summarizes mixture-design methods for different types of material and properties from around the world [6]. However, it is agreed that there is no single universal approach for the mixture design of SCC, instead several approaches that can secure satisfactory performance can be employed [6,7]. Besides the selection of raw materials, their compositions, and the incorporation of different types of admixtures and supplementary cementitious materials, such as fly ash, the mixture design methods for SCC have achieved significant improvement in terms of rheology, strength development, and durability [8–10]. In the design of conventional concrete mixtures, the water-to-cement ratio (w/c) is usually fixed to secure a required strength level. However, in the design of SCC mixtures, the workability characteristics,
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which are related to the rheological properties, are adjusted with the incorporation of superplasticizer and in some cases viscosityenhancing admixtures, and the use of relatively high content of fine materials, resulting in relatively low w/c values [3]. Some of the mixture design methods address the determination of the dosage superplasticizer and w/c by conducting tests on the paste phase to predict the flow behavior of the SCC, considering the concrete as a solid aggregate phase in a liquid paste phase. Nevertheless, there is a lack of information regarding the principle involved in the relationship between paste or mortar properties and SCC workability [11]. Mixture design methods for SCC can be classified in different categories depending on the design principle, including (1) empirical approach, (2) compressive strength development approach, (3) securing high aggregate packing, (4) establishing statistical factorial design models for performance prediction, and (5) rheology of paste model approach [6]. The first mixture design method for SCC proposed by Okamura and Osaka [12] was an empirical approach based on author’s experience. It consisted in achieving self-compactability by the adjustment of water-to-powder ratio and superplasticizer dosage using the use slump-flow, V-funnel and U-box tests for concrete mixtures with fixed fine and coarse aggregate contents [3,12,13]. Despite the fact that this approach is simple, empirical design methods allow little flexibility in optimizing the granular skeleton due to predefined steps and require intensive laboratory testing. Besides, it results in higher portions of paste, since some of design parameters are almost constant and does not consider the properties of the aggregate [14]. Based on this method, other empirical design approaches aiming to reduce paste volume were proposed. The main idea of these methods was to increase the ratio between fine aggregate and mortar as well as the volume of coarse aggregate, where the adjustment of materials is made by trial mixing using the V-funnel test [4,15,16]. Compressive strength methods determine the content of each component based on required compressive strength [17]. As an example, the ACI 211.1 [18] method for proportioning conventional concrete considers the aggregate gradation and the contribution of mineral components, which can minimize the need of trial mixtures, but requires adjustments to all components to achieve the best proportioning. The widely used close-toaggregate packing method determines the mixture proportioning by securing the minimum void content based on the aggregate’s packing and filling these voids with paste, most of them using computational devices [19–21]. Statistical factorial models seek to optimize and predict the effects of different key mixture parameters on workability and compressive strength of SCC, in which reasonable ranges are established [22–25]. Lastly, the rheology of paste model approach uses the rheological properties of the paste to predict SCC workability and segregation for a specified particle size distribution and volume of aggregate in the mixture [26,27]. The present study proposes a new mixture design approach for portland cement SCC based on two design parameters to secure a given compressive strength. This procedure refers to design methods for conventional concrete and results in a mixture design diagram that correlates materials’ composition and properties. In order to validate the proposed approach, two types of coarse aggregates and two types of fine materials were tested.
composition is necessary to achieve the required durability parameters at a competitive cost is required. This proposed mixture proportioning methodology should be of interest in the application of SCC in precast plants, cast-in-place construction and rehabilitation projects where SCC can be used to facilitate construction operations and reduce construction time and labor cost. 3. Mixture design procedures of proposed approach The proposed approach is based on the mixture design procedure developed by Monteiro, Helene and Kang [28] for the design of conventional concrete to determined compressive strength, elastic modulus and fracture energy. In this approach, the dry mortar ratio (a) is determined experimentally for the selected materials in an intermediate amount of aggregates (At), where cement consumption is not considered too high or too low, as follows:
a¼
C þ Af C þ At
At ¼ Af þ Ac
ð1Þ ð2Þ
where C, Af and Ac are the masses of cement, sand, and coarse aggregate, respectively. Once a is determined, two mixtures are tested with smaller and higher values of aggregate contents, maintaining the same a value and resulting in different values of cement consumption. The w/c is determined experimentally for the intermediate aggregate content mixture to achieve the desired workability using the standard slump test. In order to maintain the same workability for the smaller and higher aggregate content mixtures, the w/c is established by maintaining the same water-to-dry materials ratio (H) expressed in percentage, as indicated in Eq. (3):
H ð%Þ ¼
w=c ð1 þ AtÞ
ð3Þ
The results obtained in compressive strength tests from the three mixtures prepared with three different aggregate contents and the same a value are plotted in the nomogram shown in
2. Research significance The use of SCC can provide significant benefits in the construction industry. Despite the increase of information regarding the influence of material’s composition on SCC properties, the mixture design methods are still being developed to find proper solution for each application. An appropriate method to determine material’s
Fig. 1. Mixture design nomogram with compressive strength as design criterion [28].
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and properties, allowing fast prediction of key fresh and hardened properties of concrete, such as slump and compressive strength. The nomogram is based on three classical concepts employed in concrete mixture design, comparing the influence of w/c, aggregate-to-cement ratio, and cement content, on the material’s compressive strength, as detailed below. 1. ‘Abram’s Law’ for hardened concrete: consists in the relationship between w/c and compressive strength; 2. ‘Lyse’s Law’ for fresh concrete: relates the volume of water and volume of consolidated fresh concrete, being able to maintain the same consistency for mixtures with different properties and proportions; 3. ‘Molinari’s Law’ for cement content: correlates the cement content with the aggregate-to-cement ratio. Based on this mixture design principle, two approaches were developed in this study. The first one is based on a fixed mortar content, an empirical model similar to previous studies. The other one is based on the principle of maximum compaction between solid materials to achieve desirable flowability with higher resistance to segregation. The procedure established for these approaches are presented below.
Fig. 2. Mixture design procedure of proposed approach based on fixed mortar content.
3.1. Approach based on a fixed mortar content (a) This mixture design procedure is shown in Fig. 2. Taking advantage of previous investigations [28], three conventional concrete mixtures are empirically designed with the same mortar ratio. In this step of the procedure, fine materials and superplasticizer are not employed in the mixture. The established mortar content obtained is maintained constant until the end of the mixture design process. The concrete becomes self-consolidating by the simultaneous incorporation of superplasticizer and fine materials (cement, pozzolanic or non-pozzolanic mineral additions). The superplasticizer is added until the concrete reaches the desired spread diameter in the slump-flow test, despite some segregation of coarse aggregate at high dosage rates of superplasticizer. Segregation is eliminated by the addition of fine materials, which is performed by partial replacement of sand aggregate by nonpozzolanic fine materials or the cement by pozzolanic materials, respectively. It is also possible to avoid segregation with the incorporation of a viscosity-modifying admixture. After the mixture reaches a satisfactory flow behavior in the slump-flow test, all fresh state characterization tests are performed, and samples are taken for compressive strength testing. The results obtained in the characterization and proportioning tests of the mixture (w/c, aggregate content and cement consumption) can enable the establishment of a nomogram similar to that of Fig. 1 for SCC mixtures.
Fig. 3. Mixture design procedure based on aggregate packing.
Fig. 1, used for conventional concretes with compressive strength ranging between 20 and 50 MPa and slump ranging between 0 and 20 cm. The nomogram correlates the concrete composition
Table 1 Determination of the compacted bulk density, specific gravity and volume of voids of two hypothetical materials A and B. Material A (%)
Material B (%)
Combined mass (kg)
Bulk density (kg/m3)
Specific gravity of mixture (kg/m3)
Voids (%)
100 90 80 70 60 50 40 30 20 10 0
0 10 20 30 40 50 60 70 80 90 100
38.36 39.45 42.45 43.12 45.10 44.70 43.00 41.89 39.23 38.11 37.23
2243 2307 2482 2522 2637 2614 2515 2450 2294 2229 2177
2880 2850 2820 2790 2760 2730 2700 2670 2640 2610 2580
28.4 23.5 13.6 10.6 4.6 4.4 7.4 9.0 15.1 17.1 18.5
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Fig. 4. Outline of experimental program.
Table 2 Properties of investigate materials. Sieve diameter (mm)
Passing (%) Fine aggregates
19.0 12.5 9.5 6.3 4.75 2.36 1.18 0.600 0.300 0.150 Fineness modulus Maximum diameter
Coarse aggregates
Fine Sand
Regular Sand
Coarse Type I
Coarse Type II
100 100 100 100 100 100 100 100 84 7 1.09 0.6
100 100 100 100 97 88 71 46 13 2 2.83 4.75
100 100 99 47 13 1 0 0 0 0 5.87 9.5
99 56 19 4 1 0 0 0 0 0 6.81 19
Table 3 Specific gravity and bulk density of raw materials. Material
Cement
Fly ash
Fine Sand
Regular Sand
Coarse Type I
Coarse Type II
Specific gravity (kg/dm3) Bulk density (kg/dm3)
2.92 –
1.92 –
2.65 1.57
2.64 1.53
2.82 1.50
2.82 1.42
3.2. Approach based on aggregate packing
Table 4 X-ray fluorescence of cement and fly ash. Chemical data
Cement (%)
Fly ash (%)
Calcium oxide (CaO) Silicon dioxide (SiO2) Ferric oxide (Fe2O3) Aluminum oxide (Al2O3) Sulphur trioxide (SO3) Magnesium oxide (MgO) Potassium oxide (K2O) Titanium dioxide (TiO2) Strontium oxide (SrO) Phosphorus pentoxide (P2O5) Manganese oxide (MnO)
65.71 17.15 4.93 4.54 3.88 1.44 1.33 0.58 0.27 0.12 0.05
3.02 65.92 7.54 18.71 0.25 0.29 2.88 1.35 – 0.05 –
Table 5 Gradation of cement and fly ash. Diameter (%)
Cement (lm)
Fly ash (lm)
<10% <50% <90% Medium
1.16 9.15 25.41 11.61
5.22 39.91 128.15 56.54
The procedures of this approach can be summarized in the steps presented in Fig. 3. The main consideration of this approach is to fill the voids between solid components with cement paste to achieve the desirable flowability and ensure greater stability, based on an aggregate packing model. By packing the aggregates, it is possible to determine the proportion of each material that will result in the least amount of voids to be filled by cement paste. It is recommended the use of the method proposed by O’Reilly [29], which consists in the packaging of components two by two in order of particle diameter until the smaller component is packed, except for the cement powder. Fine pozzolanic materials, such as fly ash, is packed after the sand fraction and are considered as fine aggregate in this approach. For the compaction tests, a container with a diameter at least five times larger than the average particle diameter shall be used. Table 1 shows the packing procedures for two hypothetical materials labeled A and B having specific gravity of 2880 and 2580 kg/m3, respectively. Using a container of 17.10 dm3, the combined mass is determined experimentally by the increase in 10% of one component in a dry mixture, starting from 0 until it is the only
Table 6 Mixture proportioning and results of fresh state properties. Mixture
a(%)
Conventional 1:3.0 1:4.0 1:5.0 1:6.0 1:7.0
concrete 53.0 53.0 53.0 53.0 53.0
Cement (kg/m3)
Fly ash (kg/m3)
Fine sand (kg/m3)
Regular sand (kg/m3)
Coarse Type I (kg/m3)
Coarse Type II (kg/m3)
w/c
H (%)
SP (%)
Slump-flow (mm)
V-Funnel (s)
L-box (l2/l1)
2420 2408 2367 2343 2312
553 443 364 309 265
– – – – –
– – – – –
620 731 794 836 859
– – – – –
1040 1042 1027 1015 997
0.37 0.43 0.50 0.59 0.72
9.35 8.64 8.37 8.49 9.01
– – – – –
100* 100* 100* 100* 100*
– – – – –
– – – – –
SCC – Fixed mortar ratio with fine sand 1:3.0 53.0 2446 1:4.0 53.0 2430 1:5.0 53.0 2406 1:6.0 53.0 2362 1:7.0 53.0 2347
561 449 371 310 270
– – – – –
253 297 323 335 352
376 445 486 505 525
– – – – –
1055 1056 1046 1020 1017
0.36 0.41 0.48 0.62 0.68
8.93 8.14 8.08 8.86 8.46
0.47 0.47 0.47 0.47 0.47
680 700 690 680 660
9 9 8 10 9
1.00 1.00 0.95 0.90 0.90
SCC – Fixed mortar ratio with fly ash 1:3.0 53.0 2387 1:4.0 53.0 2369 1:5.0 53.0 2363 1:6.0 53.0 2349 1:7.0 53.0 2346 1:8.0 53.0 2302
549 438 363 309 270 236
121 145 160 167 176 177
– – – – – –
494 578 632 670 701 711
– – – – – –
1032 1029 1024 1016 1017 997
0.35 0.41 0.50 0.61 0.67 0.77
8.68 8.16 8.42 8.66 8.41 8.57
0.47 0.47 0.47 0.47 0.47 0.47
720 680 680 690 700 680
8 10 11 9 9 10
0.90 1.00 0.90 0.85 0.90 1.00
SCC – Aggregates packed with coarse aggregate Type II and fine sand 1:3.0 62.8 2401 550 – 1:4.3 59.8 2382 411 – 1:5.7 58.0 2336 322 – 1:7.0 56.7 2301 262 –
165 177 184 183
671 720 738 744
– – – –
819 880 903 909
0.37 0.46 0.59 0.79
9.15 8.69 8.80 9.84
0.47 0.47 0.47 0.47
710 740 710 680
8 8 7 9
0.90 1.00 0.95 0.95
SCC – Aggregates packed with coarse aggregate type II and fly-ash 1:3.0 60.7 2353 540 81 1:4.7 57.0 2335 381 88 1:6.3 54.9 2323 292 93 1:8.0 53.6 2310 236 94
– – – –
691 757 792 808
– – – –
847 925 967 988
0.36 0.48 0.62 0.78
8.98 8.41 8.50 8.64
0.47 0.47 0.47 0.47
750 720 740 730
7 7 7 8
1.00 1.00 0.95 0.95
SCC – Aggregates packed with coarse aggregate Types I and II and fine sand 1:3.0 64.0 2381 546 – 327 1:4.0 61.6 2367 437 – 349 1:5.0 60.0 2354 360 – 360 1:6.0 58.9 2342 304 – 364 1:7.0 58.0 2338 267 – 373
524 559 579 583 597
431 463 475 480 493
355 375 389 395 403
0.36 0.42 0.53 0.71 0.77
9.10 8.44 8.92 10.19 9.61
0.47 0.47 0.47 0.47 0.47
680 690 680 660 670
9 9 10 11 10
0.90 0.95 0.90 0.90 1.00
SCC – Aggregates packed with coarse aggregate Types I and II and fly ash 1:3.0 59.5 2343 535 161 – 1:4.0 56.8 2333 430 172 – 1:5.0 54.9 2330 358 179 – 1:6.0 53.7 2323 306 183 – 1:7.0 52.8 2304 266 186 – 1:8.0 52.0 2301 237 189 –
578 619 644 660 671 682
476 511 533 544 554 564
391 417 437 446 452 459
0.38 0.43 0.51 0.60 0.66 0.72
9.45 8.62 8.50 8.57 8.21 7.97
0.46 0.46 0.46 0.46 0.46 0.46
750 730 710 700 710 700
7 6 8 8 9 9
1.00 1.00 0.95 0.90 0.95 0.85
A.M. Gil et al. / Construction and Building Materials 229 (2019) 116939
Specific gravity (kg/m3)
*Slump test for conventional concrete.
5
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component in the mixture, or 100%. With the combined mass and container volume, it is possible to determine the mixture’s bulk density. Each mixture’s specific density and voids percentage are determined as follows:
SGðABÞ ¼ VðABÞ ¼
ðSGðAÞ %AÞ þ ðSGðBÞ %BÞ 100
SGðABÞ BDðABÞ 100 SGðABÞ
ð4Þ ð5Þ
where SG(A), SG(B) and SG(AB) are the specific gravity values of components A, B and their combination, respectively; and V(AB) and BD(AB) are the void contents and bulk densities of the mixture combining components A and B, respectively. In this example, the optimal mixture would be the combination 50%-50% of both materials, which results in the lowest volume of voids: 4.4%, although this mixture does not present the highest bulk density. When the smallest volume of voids of a mixture is not 5% lower than of the volume of voids of the mixture immediately under or above it, the mixture with the smallest amount of aggregate having the smallest particle size should be used so that less water is required by the fresh concrete. In the example above, as material A has a larger particle size than material B, the choice would be to use the 60–40% combination, which has a volume of voids less than 5% higher of the 50–50% combination, even though a mixture of particles with larger diameter would be used. At this point, the granular skeleton of the mixture has then been established and if the selected materials are suitable for the production of SCC, no segregation and no excess of fine material are expected. With reference to the former model, at least three mixtures containing different aggregate contents are chosen. The recommended values usually vary from 3.5 to 6.5. For each aggregate content, the same proportion between all components are maintained, resulting in mixtures with different values of dry mortar ratio. All the compositions within a family can be then be calculated without the need for adjustments in the mixer. The w/c or superplasticizer content is determined before the compositions’ mixture. The user can then decide whether to pin the w/c or admixture content based on durability consideration. At this point, the intermediate mixture will be used to prepare the experimental mixture and confirm if the w/c is correct, as well as determine the dosage rate of the superplasticizer experimentally. Workability tests are carried out to confirm the admixture concentration. Water is added to maintain the same workability for the smaller and higher aggregate contents for a fixed admixture concentration. Specimens of each mixture are molded to determine compressive strength at the age of interest, which will be used to draw the require nomogram.
aggregates with nominal maximum aggregate sizes of 9.5 and 19 mm were used. Particle size distribution of both types of fine and coarse aggregates determined according to ASTM C136 [30] is presented in Table 2. The specific gravity and bulk density, determined according to ASTM C127 [31] and ASTM C29 [32], respectively, of the investigated materials are presented in Table 3. The properties of portland cement and fly-ash are presented in Table 4 and Table 5. The oxide composition was determined using x-ray fluorescence and gradation by laser granulometry. Polycarboxylate-based superplasticizer (SP) with 40% of solid content was used. 4.2. Mixture composition and preparation The concrete was mixed using a planetary shaft mixer in batches of 60 L. The following mixing protocol as adopted: coarse aggregate and cement were placed together with water in a planetary mixer and mixed for 2 min. Sand and fine aggregates were introduced and mixed for 1 min. Lastly, the superplasticizer was added, and mixing was resumed for 3 min. The results obtained in the proportioning of the mixtures according to the proposed approaches as well as the results of fresh state properties are shown in Table 6. The conventional concrete with the specified materials resulted in an ideal a of 53%, which is defined experimentally by increasing the dry mortar ratio (a) until good finishing is obtained by levelling the sample with a trowel. This value was the same as that used in the composition of the SCC mixtures. To cover the entire range of the desired strength without a large gap between two adjacent values, at least five aggregate contents were adopted for each mixture: 3, 4, 5, 6 and 7. The aggregate content represents the sum of coarse in fine aggregate masses in relation to the mass of cement. For mixtures containing fly ash, an additional aggregate content (8) was used, due to the probable higher resistance obtained by the use of this material. The superplasticizer was adjusted experimentally at 0.47%, by mass of cement for all mixtures. The water was added experimentally until the mixtures achieved the desired workability. For conventional concrete, the targeted slump was 100 mm, while a slump flow of 700 mm was targeted for the SCC mixtures. The w/c values remained consistent according to the aggregate content.
4. Experimental program The experimental program outlined in Fig. 4 demonstrates the application of the two proposed approaches. The influence of two mixture design parameters was investigated using the same combination of raw materials. A conventional concrete was adopted as a reference for the comparative analysis of SCC mixtures. Besides regular sand for each SCC mixture, two types of fine materials were tested: fine sand and fly ash. For the approach based on the aggregate packing, a combination of two coarse aggregate gradations was used. 4.1. Materials Two types of continuously graded natural sands with fineness moduli of 1.09 and 2.83, as well as two types of crushed basalt
Fig. 5. Conventional concrete mixture design nomogram.
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The mass replacement ratio between fly ash and fine sand was determined experimentally for the intermediate aggregate content mixtures (1:5), which resulted in 40% fly ash and 20% fine sand, respectively, for all mixtures designed by the fixed mortar content approach. Using the aggregate packing procedure presented in Section 3.2, the packing of aggregates was carried out for aggregate combination made with and without coarse aggregate having a
(a) SCC - Fixed
– fine sand
nominal maximum size of 9.5 mm. The first compaction test was performed between the Type II coarse aggregate and the regular sand, which was then packed with the fine sand, resulting in a combination of 10%, 40% and 50% of each of the three materials, respectively, to obtain the granular combination with a relatively low void index. Using coarse aggregate Type I, the compaction was carried out between coarse aggregate Type II and coarse
(b) SCC - Fixed
– fly ash
(c) SCC – Aggregates packed – Coarse aggregate (d) SCC – Aggregates packed - Coarse aggregate Type II and fine sand Type II and fly ash
(e) SCC – Aggregates packed - Coarse aggregate Types I, II and fine sand
(f) SCC – Aggregates packed - Coarse aggregate Types I, II and fly ash
Fig. 6. SCC mixture design nomograms.
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Fig. 7. Modulus of elasticity variation versus compressive strength.
Fig. 8. Variations in ultrasound wave propagation velocity with compressive strength.
aggregate Type I, which was then packed with the regular sand and finally with the fine sand, resulting in the proportion of 21.7%, 26.3%, 32% and 20% of each of these materials, respectively. 4.3. Test methods For testing the SCC in the fresh state, the slump flow was determined in compliance with ASTM C1611 [33]. Passing ability was evaluated by the use of two typical test methods for SCC: the Vfunnel and L-box tests. The V-funnel is 600 mm high with an outflow opening of 65 75 mm. The L-box used in the test is equipped with three reinforcing bars, and the blocking ratio (H2/H1) was determined by the measurement of concrete height at the end of the horizontal chamber. Cylindrical test specimens measuring 100 mm in diameter and 200 mm in height were cast to determine mechanical properties. Specimens were demolded one day after casting and cured in a standard moist-curing room until the age of testing. Mechanical
tests were carried out to determine the compressive strength (f’c) and modulus of elasticity according (E’c) to ASTM C39 [34] and ASTM C469 [35], respectively. The durability was estimated using the rapid chloride ion permeability test (RCPT) (ASTM C1202 [36]) and ultrasound wave propagation test methods. 5. Results and discussion 5.1. Mixture design nomogram Mixture design nomograms for conventional concrete and SCC are presented in Figs. 5 and 6, respectively. The nomograms were adapted from the original proposed approach [28] to include the dry mortar ratio (a). For each mixture composition, f’c was determined at 1, 7, 28 and 91 days. As highlighted in red lines on Fig. 5, for a given f’c of 40 MPa, it is possible to determine the mixture composition that can attend the required workability parameters.
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Fig. 9. Variation in penetration of chloride ions with compressive strength.
5.2. Properties for specific 28-day strength The hardened properties of the investigated mixtures are compared in terms of f’c to secure a given E’c, ultrasound wave propagation and RCPT. Based on the nomograms, these properties were calculated for five compressive strength values of 25, 30, 40, 50 and 60 MPa. As expected, the E’c values in Fig. 7 are shown to increase with the increase in f’c. Conventional concrete presented the lowest E’c for the mixtures with f’c of 25 MPa and the highest E’c for the concrete mixtures with f’c 60 MPa. The mixtures containing fine sand can develop greater E’c for higher f’c values since the sand modulus of elasticity is higher than that of the cement paste containing fly ash. No clear relation, however, was found between design criteria, although SCC designed through the approach based on a fixed a presented greater E’c for the mixture with f’c of 60 MPa. Ultrasound wave propagation results are presented in Fig. 8. The Ultrasound wave propagation velocities are similar to those of the E’c with the conventional concrete presenting the lowest value for f’c 25 MPa and the highest value for concrete with f’c 60 MPa. Although no clear relation was found between the design criteria and the modulus of elasticity, an inverse behavior was observed where the SCC mixture proportioned with fly ash presented higher values for the same f’c than the SCC made with fine sand. As expected, the mixtures containing fly ash shown in Fig. 9 had lower RCPT values compared to the other mixtures given the pozzolanic activity of the fly ash that can lead to pore refinement. SCC mixtures designed with a fixed a presented lower RCPT values. Despite the optimized granular packing density, the SCC made with coarse aggregate Types I, II and fine sand did not follow the expected behavior, once concrete with f’c lower than 40 MPa presented the highest RCPT. 6. Conclusions In this paper, two simple approaches for the mixture design of SCC have been presented and assessed in comparison with analogously designed conventional concrete. The proposed approaches enabled the development of mixture design nomograms that combine three relationships and allowing the comparison of key properties of SCC prepared for different mixture proportions. The first
approach is based on an empirical determination of selfcompactability of mixtures with a fixed mortar content. The second approach is based on aggregates packing, which results in different mortar contents for each mixture. Both models proved to be efficient in the design of SCC mixtures with selected filling ability and passing ability properties, employing different types of fine materials and coarse aggregate. The effect of mixture design parameters on mechanical and durability characteristics were assessed. Based on the results presented, the following conclusions can be drawn: 1. SCC mixtures designed through the proposed approach that is based on a fixed a presented greater E’c, greater ultrasound wave velocity and lower RCPT penetration of chloride ions for mixtures with f’c of 60 MPa. 2. The use of two types of coarse aggregates that can secure high packing density resulted in greater E’c, greater ultrasound wave velocity and lower RCPT when compared to mixtures designed by the same approach. 3. In general, the use of the approach based on aggregate packing led to greater SCC performance.
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