Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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Energy dissipation in self-compacting concrete with or without fibers in compression

Farhad Aslani1, Shami Nejadi1, and Bijan Samali1

1 Centre for Built Infrastructure Research, School of Civil and Environmental Engineering, University of

Technology Sydney, Australia

Email: Farhad.Aslani@uts.edu.au

ABSTRACT: Fiber-reinforced self-compacting concrete (FRSCC) is an advanced high-performance construction material that

combines features of fresh properties of the self-compacting concrete (SCC) with improved characteristics of hardened

concrete as a result of fiber addition. Consequently, FRSCC covers both FRSCC and SCC applications. An extensive

experimental program is carried out to monitor and record the damage energy dissipation of SCC and FRSCC cylinder

specimens under the uniaxial compression. For this purpose, four different SCC mixes including plain SCC, steel,

polypropylene, and hybrid FRSCC mixes are considered in the test program. The energy absorption per unit volume

under compression is determined as the area under the stress-strain curve. The compressive stress-strain curve is

plotted at 3, 7, 14, 28, 56, and 91 days. The experimental results indicate that the damage energy dissipation depends

uniquely upon the strain range that undergo by the specimen. Moreover, new relationships are proposed to predict the

energy dissipation of the specimens according to their age. The proposed models provide reasonable agreement with

the measured experimental values.

Keywords: Limestone powder, modeling, rheology, self-consolidating concrete

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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INTRODUCTION

Self-compacting concrete (SCC) can be placed and compacted under its own weight with little or no vibration and without segregation or bleeding. SCC is used to facilitate and ensure proper filling and good structural performance of restricted areas and heavily reinforced structural members. It has gained significant importance in recent years because of its advantages. Recently, this concrete has gained wider use in many countries for different applications and structural configurations. SCC can also provide a better working environment by eliminating the vibration noise and less labor efforts. Such concrete requires a high slump that can easily be achieved by addition of super-plasticizer to a concrete mix and special attention to the mix proportions. SCC often contains a large quantity of powder materials that are required to maintain sufficient yield value and viscosity of the fresh mix, thus reducing bleeding, segregation, and settlement. As use of a large quantity of cement increases costs and results in higher temperatures, use of additions such as fly ash, blast furnace slag, or limestone filler could increase the slump of the concrete mix without increasing its cost1. Incorporation of the fibers improves mechanical and engineering performance of structural and non-structural concrete. Use of fiber-reinforced concrete (FRC) is also of special interest for retrofit proposes and seismic design. Incorporation of metallic fibers can be problematic on some conditions, especially when the fiber volume is high and FRC is cast in the sections with moderate to high degree of reinforcement. The fiber content, length, aspect ratio, and shape play an important role in controlling workability of FRC. Such concrete presents greater difficulty in handling and requires more deliberate planning and workmanship than established concrete construction procedures. Additional compaction efforts require for such a concrete which adds to the construction cost. To provide sufficient compaction, improve fiber dispersion and consequently reduce the risk of entrapping voids, FRC is often proportioned such that the past to be fluid enough to facilitate placement by reducing vibration requirements. This approach can be extended to the use of SCC to eliminate, or greatly reduce, the need for vibration requirements and facilitate placement. A fiber-reinforced self-compacting concrete (FRSCC) should truly spread into mold under its own weight and achieve consolidation without internal or external vibration, ensure proper dispersion of fibers, and undergo minimum entrapment of air voids and loss of homogeneity until hardening. Lack of proper self-compaction or intentional vibration and compaction can result in macro- and micro-structural defects that can affect mechanical performance and durability2. FRSCC is a relatively recent composite construction material that combines the benefits of the SCC technology with advantages of the fiber addition to a brittle cementitious matrix. It is a ductile material that in its fresh state flows into the interior of the formwork, filling it in a natural manner, passing through the obstacles by flowing and consolidating under the action of its own weight. FRSCC can mitigate two opposing weaknesses: poor workability in fiber-reinforced concrete (FRC) and cracking resistance in plain concrete. In engineering terms, the greatest disadvantage of cementitious material is its vulnerability to cracking, which generally occurs at an early age in concrete structures. Cracking may potentially reduce the lifetime of concrete structures and cause serious durability and serviceability problems. A few studies have been carried out on optimization of the mix proportion for the addition of steel or polypropylene fibers in SCC. Addition of fibers into SCC mixtures has been studied by a number of researchers2-14.However, still there is insufficient research on the mechanical properties of FRSCC. The most beneficial properties of the fiber addition to the concrete in the hardened state are the impact strength, toughness, and energy absorption capacity. A detailed description of the fiber addition to concrete can be found elsewhere15-16. The fiber addition might also improve the fire resistance of cement-based materials, as well as their shear resistance. The possible applications of FRSCC include highways; industrial and airfield pavements; hydraulic structures; tunnel segments; bridge components and concrete structures with complex geometry that present high difficulties in being reinforced by conventional steel bars, especially those that have a high degree of support redundancy. This research aims to study the properties of SCC and FRSCC in the fresh and hardened stages. An extensive experimental program is carried out to monitor and record the damage energy dissipation of SCC and FRSCC cylinder specimens under the uniaxial compression. The investigated mechanical properties in this study are compressive strength and compressive stress-strain curve. These mechanical properties are tested at 3, 7, 14, 28, 56, and 91 days. Development of the above mentioned mechanical properties with time are monitored and investigated. Consequently, regression analyses are conducted on the measured experimental data to propose an energy dissipation model under compression based on the compressive strength and age of concrete.

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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EXPERIMENTIAL WORK

Materials Cement In this experimental study, Shrinkage Limited Cement (SLC) corresponding to the AS 397217 standard

was used. SLC is manufactured from specially prepared Portland cement clinker and gypsum. It may contain up to 5% of additions approved by AS 3972. The chemical, physical, and mechanical properties adhere to the limits specified in AS 2350.2, 3, 4, 5, 8, and 1118.

Fly Ash It is important to increase the amount of paste in SCC because it is an agent to carry the aggregates.

As a consequence, Eraring Fly Ash (EFA) has been used to increase the amount of paste. EFA is a natural pozzolan. It is a fine cream/grey powder that is low in lime content. However, since it is a very fine powder, in the presence of moisture it reacts chemically with calcium hydroxide at ordinary temperatures to form insoluble compounds possessing cementitious properties. The chemical, physical, and mechanical properties of the used EFA, adhere to the limits specified in AS 2350.218, AS 3583.1, 2, 3, 5, 6, 12, and 1319.

Ground Granulated Blast Furnace Slag Granulated blast furnace slag (GGBFS) is another supplementary

cementitious material that is used in combination with SLC. GGBFS initially used by Boral Company, Sydney-Australia, which compiles the AS 3582.220 specifications.

Aggregate In this study, crushed volcanic rock (i.e., latite) coarse aggregate was used with a maximum

aggregate size of 10 mm (0.393 in). Nepean river gravel with a maximum size of 5 mm (0.1968 in) and Kurnell natural river sand. Fine aggregates were also implemented. Methods for sampling and testing the aggregates were determined in accordance with AS 114121 and RTA22.

Admixtures A new generation of superplasticiser, Glenium 27; viscosity-modifying admixture (VMA); and

high-range water-reducing agent admixture were used in this study. Glenium 27 complies with AS 1478.123. In addition, High Range Water Reducer (HWR) and ASTM C49424 types A and F were used. The Rheomac VMA 362 viscosity modifying admixture that used in this study is a ready-to-use, liquid admixture that is specially developed for producing concrete with enhanced viscosity and controlled rheological properties. Pozzolith 80 was used as a high-range water-reducing agent admixture in the mixes. It reduces the quantity of water required to produce concrete of a given consistency and strength with greater economy. It meets the AS 147823 Type WRRe, requirements for admixtures.

Fibers In this study, two commercially available fibers, Dramix RC-80/60-BN type steel fibers and Synmix

65 type polypropylene (PP) fibers were used. The physical and mechanical properties of the steel and PP fibers are summarized in Table 1.

Table 1 The physical and mechanical properties of fibers

Fibre type Fibre name

Density (kg/m3*)

Length (l,

mm*)

Diameter (d, mm*)

Aspect ratio (l/d)

Tensile strength (MPa*)

Modulus of elasticity (GPa*)

Cross-section form

Surface structure

Steel Dramix RC-

80/60-BN

7850 60 0.75 80.0 1050 200 Circular Hooked end

Polipropylene (PP)

Synmix 65

905 65 0.85 76.5 250 3 Square Rough

*1 kg/m3 = 3.61E-5 lb/in3, 1 mm = 0.039 in, 1 MPa =0.145037 ksi, 1 GPa = 145.037 ksi Mixture proportions One SCC control mixture, (N-SCC) and three different types of fiber-reinforced SCC mixtures were used in this study.(i) Fiber-reinforced SCC mixtures contain steel fibers, (D-SCC). (ii) Fiber-reinforced SCC mixtures contain PP fibers, (S-SCC); and (iii) Fiber-reinforced SCC mixtures contain hybrid (steel + PP) fibers, (DS-SCC). The content proportions of these mixtures are given in Table 2.

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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Table 2 Proportions of the concrete mixtures (based on SSD condition)

Constituents N-SCC D-SCC S-SCC DS-SCC Cement (kg/m3*) 160 160 160 160 Fly Ash (kg/m3) 130 130 130 130 GGBFS (kg/m3) 110 110 110 110 Cementitious content (kg/m3) 400 400 400 400 Water (lit/m3) 208 208 208 208 Water cementitious Ratio 0.52 0.52 0.52 0.52 Coarse Sand (kg/m3) 660 660 660 660 Fine Sand (kg/m3) 221 221 221 221 Coarse aggregate (kg/m3) 820 820 820 820 Superplasticiser (lit/m3*) 4 4.86 4.73 4.5 VMA (lit/m3) 1.3 1.3 1.3 1.3 High range water reducing agent 1.6 1.6 1.6 1.6 Steel Fibre content (kg/m3) - 30 - 15 PP Fibre content (kg/m3) - - 5 3

*1 kg/m3 = 3.61E-5 lb/in3, 1 lit/m3 = 3.61E-8 lb/in3 Samples preparation and curing conditions We used standard cylinders 150 mm 300 mm (5.90 in 11.81 in) for the determination of compressive strength. These cylinders were prepared by direct pouring of concrete into molds without compaction and kept covered in a controlled chamber at 20 2oC (68 36 oF) for 24 hours until de-molding. Thereafter, the specimens are placed in presaturated water with lime at 20 oC (68oF). Finally, they were tested at 3, 7, 14, 28, 56, and 91 days. Samples test method The compressive strength test performed on 150 mm 300 mm cylinders, following the AS 1012.1425 and ASTAM C3924 requirements for compressive strength of cylindrical concrete specimens. The cylinders were loaded in a testing machine under load control at the rate of 0.3 MPa/s up to failure. Since some investigators have shown that the ASTM C49624 test is applicable to fiber-reinforced concrete specimens, the ratio of fiber length to cylinder diameter took a low value of 0.23 in the test. It should be noted that the axial strains of the concrete in compression were obtained from the full height shortening of the cylinders using LVDTs. Properties of fresh concrete Generally, most of the SCC experiments are carried out worldwide under laboratory conditions. These experiments include flow-ability, segregation, placement, and compaction of fresh concrete. Conventional workability tests are not sufficient for the evaluation of SCC. Some test methods to measure the flow-ability, segregation, placement, and compaction of SCC are developed and defined in the European guidelines26 and ACI 237R-0727. These test methods include V-funnel, U-box, L-box and fill-box tests for specification, production and use as slumpflow.

In this study slump flow, T50cm time, J-ring flow, V-funnel flow time, and L-box blocking ratio tests were performed. In order to reduce the effect of loss of workability on the variability of test results, the fresh properties of the mixes were determined within 30 min after mixing. The order of testing was as follows: 1. Slump flow test and measurement of T50cm time; 2. J-ring flow test, measurement of difference in height of concrete inside and outside the J-ring and measurement of T50cm time; 3. V-funnel flow tests at 10 s T10s; and 4. L-box test.

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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EXPERIMENTIAL RESULTS

Properties of fresh concrete

The results of various fresh properties tested by the slump flow test (slump flow diameter and T50cm); J-ring test (flow diameter); L-box test (time taken to reach 400 mm distance, T400mm, time taken to reach 600 mm distance, T600mm; time taken to reach 800 mm distance, TL); ratio of heights at two edges of L-box [H2/H1]); V-funnel test (time taken by concrete to flow through V-funnel after 10 s, T10s); the percentage of entrapped air; and the specific gravity of mixes are given in Table 3. The slump flow test benches the capability of concrete to deform under its own weight against the friction of the surface with no restraint present. A slump flow value ranging from 500 to 700 mm for self-compacting concrete was suggested26. At a slump flow > 700 mm, the concrete might segregate, and at

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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Figure 1 Compressive strength of SCC mixtures at different ages

Figure 2 Compressive stress-strain curve of N-SCC mix at different ages

Figure 3 Compressive stress-strain curve of D-SCC mix at different ages

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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Figure 4 Compressive stress-strain curve of S-SCC mix at different ages

Figure 5 Compressive stress-strain curve of DS-SCC mix at different ages Energy dissipation under compression The energy absorption per unit volume under compression was determined as the under curve area of the stress ()/strain () curve; the value can be calculated using Eq. (1): u dGc

0

(1)

The Gc value is determined up to ultimate deformation, u, of 0.05, where it is expected that the residual strength would be small.Table 4 and Fig 6 include the average values of Gc.In general, the concrete energy absorption increases with age. The major part of the energy is released in the softening phase which depends on the fiber reinforcement mechanisms provided by fibers crossing the cracks. The efficiency of those mechanisms depend considerably on the fiber bond length and fiber orientation toward the cracks that they bridge, whose homogeneity cannot be assumed between two, apparently, equal batches12.The variation of the energy dissipated under compression with the strain is represented in Figs. 7 to 10. Overall, Gc increases with strain more quickly for the older specimens, (56 and 91 days) than the younger specimens (3, 7, 14 and 28 days).

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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Figure 6 Energy dissipated under compression (Gc) at different ages

Figure 7 Energy dissipated under compression (Gc) versus strain of N-SCC mix at different ages

Figure 8 Energy dissipated under compression (Gc) versus strain of D-SCC mix at different ages

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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Figure 9 Energy dissipated under compression (Gc) versus strain of S-SCC mix at different ages

Figure 10 Energy dissipation under compression (Gc) versus strain of DS-SCC mix at different ages Table 4 The energy dissipation under compression

Mix

Age (days)

3 7 14 28 56 91

N-SCC 0.658 0.833 1.228 1.255 1.544 1.612

Gc (MPa)

D-SCC 0.747 1.117 1.327 1.494 1.683 1.825

S-SCC 0.701 0.988 1.304 1.421 1.617 1.745

DS-SCC 0.762 1.239 1.359 1.535 1.700 1.865

ANALYTICAL RELATIONSHIPS FOR THE f'cm AND Gcm

To estimate the compressive strength (f'cm) and energy dissipation of the SCC mixes under compression (Gcm) at various ages, mathematical relationships (Eqs. 2 to 9) are proposed based on regression analyses of the experimental data. Fig. 11 shows that the proposed time-related relationships of compressive strength and energy dissipation under compression are in good agreement with the experimental results.

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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54.2ln47.3

tftf cNcm (2) 66.6ln75.3

tftf cfDcm (3) 87.3ln84.3

tftf cfScm (4) 54.4ln96.3

tftf cfDScm (5) where f'cN is the N-SCC mix; f'cfD is the D-SCC mix; f'cfS is the S-SCC mix and f'cfDS is the DS-SCC mix compressive strengths. 340.0ln

33.4 tGtG cNcm (6) 476.0ln

91.4 tGtG cfDcm (7) 411.0ln

69.4 tGtG cfScm (8) 541.0ln

16.5 tGtG cfDScm (9)

where GcN is the N-SCC mix; GcfD is the D-SCC mix; GcfS is the S-SCC mix and GcfDS is the DS-SCC mix energy dissipations under compression.

Figure 11 Predicted time-related compressive strength and energy dissipation under compression values versus

measured experimented results

CONCLUSIONS

The following conclusions can be drawn from the presented study:

(1) An experimental program was performed by testing and monitoring four different types of SCC mixes. These mixes include N-SCC (normal), D-SCC (steel fiber-reinforced), S-SCC (PP fiber-reinforced), and DS-SCC (hybrid fiber-reinforced).

(2) The compressive strength and strain are monitored and measured at ages of 3, 7, 14, 28, 56 and 91 days. Subsequently, compressive stress-strain curves for each SCC mixes are plotted. The results indicate that the discrepancy between the different SCC mixes decreases with time.

Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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(3) The average compressive strength of the DS-SCC mix is higher than that of the N-SCC, D-SCC, and S-SCC mixes. The results show that compressive strength of the DS-SCC mix at 91 days is 10.71%, 1.62% and 8.32% higher than that of the N-SCC, D-SCC, and S-SCC mixes respectively.

(4) The energy absorption per unit volume under compression is determined as the under-curve area of the stress-strain curve. The average energy absorption per unit volume of the DS-SCC mix is higher than that of the N-SCC, D-SCC, and S-SCC mixes under compression. The results indicate that the energy dissipated under compression of the DS-SCC mix at 91 days is 15.72%, 3.17% and 8.09% higher than that of the N-SCC, D-SCC, and S-SCC mixes respectively.

(5) Analytical expressions to predict the compressive strength and energy absorption per unit volume for SCC

mixes under compression at any age up to 90 days were proposed. The proposed models provide reasonable

agreement with the measured experimental values.

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Proceedings of the Fifth North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, Illinois, USA, May 1215, 2013 Aslani, Nejadi, and Samali

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