SELF-CONSOLIDATING HIGH PERFORMANCE FIBER REINFORCED CONCRETE: SCHPFRC

Wen-Cheng Liao (1), Shih-Ho Chao (2), Sang-Yeol Park (3), and Antoine E. Naaman (4)

(1) Ph.D Student, University of Michigan, Ann Arbor, USA

(2) Post-Doctoral Research Fellow, University of Michigan, Ann Arbor, USA

(3) Associate Professor, Cheju National University, Jeju-si, Korea

(4) Professor, University of Michigan, Ann Arbor, USA

Abstract

Self-consolidating high performance fiber reinforced concrete (SCHPFRC) combines the self-consolidating property of self-consolidating concrete (SCC) with the strain-hardening and multiple cracking characteristics of high performance fiber reinforced cement composites (HPFRCC) (Naaman 1987, 1996, 2003). SCHPFRC is a highly flowable, non-segregating concrete that can spread into place, fill the formwork, and encapsulate the reinforcing steel in typical concrete structures. It is being addressed as part of a project for the U.S. Network for Earthquake Engineering Simulation (NEES) with the objective to develop a SCHPFRC that can be easily manufactured and delivered by ready-mix trucks for use on the job site, with particular application in seismic resistant structures. In this paper, the authors provide a brief summary of findings based on an extensive review of existing literature and numerous laboratory trials. Several SCHPFRC mixtures taken from previous studies were modified using the available local materials, leading to recommended mixtures with compressive strengths ranging from 35 to 65 MPa. These mixtures contain coarse aggregates having a 12 mm maximum size and 30 mm long steel fibers in volume fractions of 1.5% and 2%. The recommended SCHPFRC mixtures were achieved by adjusting the coarse to fine aggregate ratios, increasing paste volume, mixing in steps according to a pre-set procedure, and adding relevant admixtures. Spread diameter of the fresh SCHPFRC mixtures measured by using the standard slump flow test was approximately 600 mm. Results obtained from direct tensile tests showed that the strain-hardening response of the hardened composites were maintained up to large composite strains.

1. INTRODUCTION

Self-consolidating high performance fiber reinforced concrete (SCHPFRC) is the hybrid of self-consolidating concrete (SCC) and high performance fiber reinforced cement composites (HPFRCCs). It is a highly flowable, non-segregating concrete with a strain-hardening response under tension accompanied by multiple cracking. Six SCHPFRC mixtures with

Page 0

compressive strengths ranging from 35 to 65 MPa are recommended. These were first obtained from previous studies and modified using available local materials. Spread diameter of the fresh SCHPFRC mixtures measured by using the standard slump flow test was approximately 600 mm. Tensile response obtained from direct tensile tests showed that these composites exhibited significant strain-hardening behavior accompanied by multiple cracking. In addition, these mixtures were successfully used in large size applications; in some cases where heavier amount of reinforcing bars were present, minor vibration was needed.

2. PREVIOUS RESEARCH

Though adding fibers will extend the range of applications of SCC, a reduction in workability due to fiber addition may become a handicap in practice. Besides the fibers, there are also many parameters which affect the flowability of fresh SCC. Indeed, the type, diameter, aspect ratio, and volume fraction of fibers come in addition to the maximum aggregate size, coarse aggregate content, fine aggregate content to play an important role in flowability of SCC with fibers. An earlier study by Swamy and Mangat (1974) reported that the relative fiber-to-coarse aggregate volume and the fiber “balling up” phenomenon limit the maximum content of steel fibers. Edington et al (1978) observed a relationship between the size of coarse aggregate and the fiber volume fraction. Narayanan and Kareem-Palanjian (1982) found that the “optimum fiber content” (without balling) increased linearly with an increase in the percentage of sand to total aggregates. Johnston (1996) remarked that the distribution of fibers and coarse aggregates was mainly determined by their relative sizes. While considering the effectiveness in the hardened state, Vandewalle (1993) recommended choosing fibers longer than the maximum aggregate size. Gru¨newald (2006) also suggested that the fiber length be 2 to 4 times that of the maximum coarse aggregate size, a recommendation similar to that generally suggested by ACI committee 544. The addition of steel fibers into SCC mixtures has been studied by a number of researchers (Groth et al., 1999; Khayat et al., 1999; Massicotte et al., 2000; Gru¨newald et al., 2001, 2006; Bui et al., 2003, 2005; Corinaldesi et al., 2004; Busterud, 2005; Dehn, 2005; Sahmaran et al., 2005 2007; Suter et al., 2005). Moreover, numerous commercial laboratories have been involved in the development of SCC with fibers. Degussa Admixtures, Inc., (a division of Master Builders Technologies), which focuses on the development, manufacture and supply of chemicals and cementitious products for the construction industry, has been continuously improving the performance of SCC with fibers. Following are key findings based on their studies (Bui et al., 2005):

1) The coarse-to-fine aggregate ratio in the mix needs to be reduced so that individual coarse aggregate particles are fully surrounded by a layer of mortar. Paste amount must be sufficient to fill the void between aggregates and fibers, and also cover around the aggregate particles and the fibers. Reduced coarse aggregate volume and higher paste volume are required for higher volume of fibers. Furthermore, it is recommended by Johnston (2001) to reduce the volume of coarse aggregates at least 10 % compared with plain concrete to facilitate pumping.

2) Before addition of fibers, slump flow of SCC must be relatively high (as influenced by a lower coarse aggregate content, increased paste content, low water-to-powder ratio, increased superplasticizer rather than excess water, sometimes a viscosity modifying

Page 1

admixture). Johnston (2001) indicated that initial slump of plain concrete should be 50 to 75 mm more than the desired final slump.

3) Everything else being equal, addition of fibers reduces slump flow of SCC; higher fiber volume and higher aspect ratio of fibers reduce slump flow of SCC as well, thereby leading to higher possibility of blocking.

3. EXPERIMENTAL PROGRAM

3.1 Materials The cementitious materials used in this study are ASTM Type III Portland cement and a

class C fly ash. The fine aggregate is #16 flint silica sand (ASTM 50-70). The coarse aggregate of 12 mm maximum size consists of solid crushed limestone or pea gravel from a local source with a density of 2.70 g/cm3. Two polycarboxylate-based superplasticizers (SP1 and SP2) were used in all concrete mixtures. In addition to the superplasticizer, a viscosity modifying admixture (VMA) was used in some mixtures to enhance the viscosity and reduce fiber segregation in the presence of higher water to cementitious ratios. The physical and chemical properties of chemical admixtures are shown in Table 1. Two types of steel hooked fibers with circular cross section, one having high tensile strength (SF1) and the other one having regular tensile strength (SF2), were used. Table 2 gives the properties of fibers used.

Table 1: Physical and chemical properties of chemical admixtures used in this study

ID Physical State pH Boiling

Point (ºC)Freeze

Point (ºC)Water

Solubility Specific Gravity

VOC* Concentration as applied (g/l)

SP 1 Liquid 5-7 100 N/A Miscible 1.1 0

SP 2 Liquid 8.0 100 0 Completely soluble 1.002 0

VMA Liquid 6.5 100 -6 Completely soluble 1.08 0

*VOC: Volatile Organic Compounds

Table 2: Properties of fibers used in this study

Fiber ID Type Diameter,

(mm) Length,(mm)

Density, (g/cc)

Tensile Strength, (MPa)

Elastic Modulus, (GPa)

SF 1 Hooked 0.38 30 7.85 2300 200 SF 2 Hooked 0.55 30 7.85 1100 200

3.2 Mix Proportions Six different SCHPFRC mixtures were developed to cover a broad range of strength

requirements. The mix proportions are summarized in Table 3. Their mechanical properties are described in Tables 4, 5, and 6. In this study, the amount of superplasticizer (SP) and the

Page 2

ratio of water-to-cementitious materials were selected as primary means to modify the compressive strengths. In addition, the fiber volume fraction for all mixtures was larger than or equal to 1.5%. Mixture 1 (Table 3) was the basis for numerous trial mixtures in extensive preliminary tests to estimate the feasibility of SCC with high volume fractions of fiber; the mixture was essentially taken from Bui et al. (2005).

Table 3: Proportions by weight of cement for SCHPFRC mixtures used

Mix Proportion by weight of cement Series ID Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6

Cement C3* 1 1 1 1 1 1 Mineral

Admixture FA** 0.48 0.5 0.5 0.875 0.67 0.875

Fine Aggregates

Silica Sand (Flint)*** 1.7 1.7 1.7 2.5 2.1 2.2

Crushed Limestone + 1.1 1 1 1.25 1.2 Coarse

Aggregates Pea gravel ++ 1.1 Water Water 0.45 0.6 0.6 0.84 0.67 0.8

SP 1 0.027 0.015 0.01 0.013 SP 2 ×× 0.0055 0.005 Chemical

Admixture VMA××× 0.012 0.0095 0.065 0.013 0.038 SF 1 0.325 0.244 0.31 0.289 0.315 Steel Fiber SF 2 0.325

Total Weight 5.082 5.152 5.0635 6.8455 5.871 6.433 fV (%) 1.96 1.92 1.47 1.38 1.50 1.50

* ASTM Type III Portland cement; ** fly ash class C; *** ASTM 50-70; + max size about 12mm; ++ max size about 8mm; × these three chemical admixtures are typically added with the initial mix water and their concentration could be seen as 1.0; that is, it is not necessary to consider the amount of water in these chemical admixtures while calculating the total amount of water needed.

3.3 Mixing Procedure Mixing procedure and mixing time are more critical in SCC as compared to conventional

concrete mixtures. In addition, previous experimental studies suggest that each mixture proportion has its own optimum mix procedure, including the sequence by which different materials are placed in the mixer, the percentage of water demand added with time, the total time of mixing, and the total time of casting, etc. (Sedran, 1996; Brodowski, 2005; Sahmaran et al., 2005, 2007; Gru¨newald, 2006; Denarie, 2006). Not only a minor change in proportioning, but a minor change in the mix procedure itself may change significantly the properties of freshly mixed concrete, such as its rheological behavior. The sequence of mixing is very important as well. According to the previous research of various mixing procedures for SCC, the sequence of placing the various materials in the mixer plays an important role, especially when higher

Page 3

volume fraction of fibers are added. The advantages of two procedures found in prior studies have been incorporated in this study.

1) Pre-mixing water, SP, and VMA (if needed), then pouring the resulting fluid in several steps in order to develop a homogenous matrix without paste lumps before adding the coarse aggregates and fibers.

2) Reducing the coarse-to-fine aggregate ratio to provide a well-developed paste layer which can fully surround individual coarse aggregate. Paste amount must be sufficient not only to fill the void between aggregates and fibers, but also fully cover the aggregate particles and the fibers.

In this study the premixed liquid ((Water + SP + VMA (if needed)) was added in several steps as described below. This allowed supervision of the status of the mixtures in order to limit paste lumps. The following steps were used:

1) Dry-mix the cement, fly ash, and sand for 30 seconds. 2) Pour 1/2 of liquid (Water+SP+VMA) in the mixer. After mixing for about 1 minute,

pour 1/4 of the remaining liquid (Water+SP+VMA). 3) After mixing for about 1 minute, pour 1/8 of liquid (Water+SP+VMA). 4) After mixing for about 1 minute, pour 1/16 of liquid (Water+SP+VMA). 5) After mixing for about 1 minute, pour all of the remaining liquid (Water+SP+VMA). 6) After mixing for about 1 minute, add all coarse aggregates in the mixer. 7) After mixing for about 2 minutes, slowly add all steel fibers in the mixer. 8) Continue mixing for about 3 minutes after all the fibers have been added. The mixture

is then ready for pouring. Note that if other types of SP and VMA are used, it is important to ascertain from the manufacturer’s guidelines that they could be mixed together with the water in the same container, in order for the above procedure to succeed. It is also important to note that the quality of fresh SCHPFRC, such as flowability and segregation resistance, will be achieved only if the mix procedure is strictly followed.

3.4 Testing The slump flow test (shown in Figure 2(a); EFNARC 2002; Nowak et al. 2005; Sahmaran

et al., 2005), compression test (ASTM C39), and direct tension test were carried out to estimate flowability, compressive strength, and tensile response, respectively. The slump flow test was the easiest and most familiar way to evaluate the horizontal free flow (deformability) of SCC in the absence of obstructions. The test method is very similar to the conventional ASTM standard slump test of fresh concrete. However, instead of the loss in height, the diameter of the spread concrete is measured in two perpendicular directions and recorded as slump flow (Figure 2(b)). In general, the average of diameters in two perpendicular directions should be larger than 600 mm for qualified SCC. According to ASTM C39, the compressive strength of hardened concrete is determined from compression tests on standard cylindrical specimens. The cylinder specimens cast for this study had dimensions of 100 mm (diameter) × 200 mm (height). The cylinder specimens were submerged in water for curing after de-molding. During testing, 3 linear variable differential transformers (LVDTs) were used to measure the strains during compression tests. The direct tension tests were needed to ascertain that the developed SCHPFRC composites give a strain-hardening response in tension after first cracking. Dog-bone shaped tensile

Page 4

specimens were prepared and tested for each SCHPFRC mixture. A typical specimen and the test setup are shown in Figure 3. These specimens have a cross-sectional dimension of

mm. The applied load was monitored by the load cell of the testing machine and elongation was recorded by a pair of LVDTs attached to the specimen, with a gauge length of about 175 mm.

25 50×

Base Plate

Slump Cone

600 mm

(a) (b) Figure 2: Slump flow test: (a) test setup; (b) Spreading diameter

(a) (b)

Figure 3: Photos illustrating the direct tensile test: (a) geometry of specimen; (b) test setup

4. EXPERIMENTAL RESULTS

4.1 Slump Flow Test As described earlier, the final diameters of the concrete in two perpendicular directions

were measured for each mix proportion, and are shown in Table 4. Minor segregation was observed in Mix 1 which did not contain VMA. Because the mechanical performance of the hardened composite depends very much on fiber dispersion, it

Page 5

is better to trade off some loss in flowability for a reduced risk of segregation. Although the flowability of each SCHPFRC mixture was slightly lower than SCC without fibers, it can be considerably increased with a minimal external vibration.

4.2 Compressive Strength

Table 4 Slump flow test results and average compressive strength ( cf ) of SCHPFRCs

Series ID Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6

Fiber Type

(SF1: high strength, L/d=79;

SF2: regular strength, L/d=50)

SF 2 SF 1 SF 1 SF 1 SF 1 SF 1

fV (%) 1.96 1.92 1.47 1.38 1.50 1.50

Slump flow (mm) 565

578

518

525

603

601

582

568

613

602

579

552

( cf ) 14-day (MPa) N/A 53.6 50.7 25 40.7 36.4

( cf ) 28-day (MPa) 65 67.9 65 36.4 43.6 39.3

( cf ) 90-day (MPa) N/A N/A N/A 47.1 50 48.6

The average compressive strengths of the mixtures with fibers tested in this study are

shown in Table 4. Figure 4(a) gives a comparison of the average compressive stress-strain curves for Mix 3, Mix 4, Mix 5 and Mix 6. As can be seen, SCHPFRCs behave as well-confined reinforced concrete in compression.

4.3 Tensile Response As described earlier, the stress-strain curves were recorded from the dog-bone specimens

tested. Typical curves are shown in Figure 4(b). It can be observed that the tensile stress increases with an increase in strain after the first crack. Multiple cracks developed up to peak stress (post-cracking strength) at which crack localization occurred (Figure 5). Thus these five mixtures all satisfy the requirement of strain-hardening behavior of HPFRCC. Beyond the peak stress, the tensile stress dropped gradually due to fiber pull out from the matrix. Some key results are summarized in Table 5. Tests for Mix 1 were not carried out.

Table 5: Average results of tensile tests for SCHPFRCs

Series ID Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6Average Post-Cracking Strength

(MPa) N/A 6.57 5.41 3.59 4.64 3.61

Average Strain at Peak Stress (%) N/A 0.25 0.34 0.25 0.39 0.45 Stress at apparent strain = 0.5% N/A 5.80 4.85 2.99 3.86 3.54

Page 6

(% of peak stress) ( ( ( (83%) (88%) 90%) 83%) 98%)Average Number of Cracks in the

middle portion N/A 5 9 6 9 6

Average Crack Spacing (mm) N/A 29.7 18.0 25.7 18.0 25.6

(b)

; (b) typical tensile stress-strain curves

(a)

Figure 4: (a) compressive stress-strain curves

s observed in SCHPFRCs

, the following conclusions can be drawn:

Figure 5: Multiple crack

5. CONCLUSIONS

Based on the experimental studies and analyses1. Flowability: on bserve workability.

Flow diameters about 600 mm were achieved in most cases. While the flowability of as not as high as for conventional SCC without fibers, it was deemed

le

ly the slump flow test was used in this study to o

SCHPFRCs wsufficient for practical implementation with slight vibration. In addition, larger scaspecimens have been cast by using these mixtures and the flowability was quite satisfactory with no segregation observed (Figure 6).

Page 7

2. Segregation: segregation of fibers was greatly reduced by using viscosity modifying agent, VMA. The mixtures became viscous enough to bring fibers to the edge of the

3. slump base plate during slump flow test. Mixing Procedure: In order to achieve a good quality in fresh SCHPFRC mixtures, it is essential to strictly follow the recommended mixing procedure, in terms of time of

4. mixing, addition of components, and sequence of material addition. Mechanical Properties: Specimens made from the hardened composites were tested for compressive strength and tensile stress-strain response. The SCHPFRCs developed

have compressive strengths ranging from about 35 to 65 MPa and a tensile strengths ranging from 3.5 to 6.5 MPa. They also showed strain-hardening response in tension, accompanied by multiple cracking. The peak strain capacity after first cracking in tension ranged from 0.25 % to 0.45 %.

(b) (a)

Figure 6: Application o de el ed SC er scale specimeSCHPFRC in the fresh state; (b) Pouring th minor vibration

The research described herein onal Science Foundation under Grant No. CMS 0530383 . The o per are those of the authors and do

ES [1] Liao, W.-C., Chao, S.-H., Park, S.-Y ., 'Self-Consolidating High Performance

Fiber Reinforced Concrete (SCHPFR vestigation', Report No. UMCEE 06-02,

[2]

[4] ogy of Fiber-Reinforced Cementitious Materials,” pp. 221-232.

005, Session C-3: Fiber-Reinforced SCC, 2005.

f the v op H FRC mixtures in largof coupling beam wi

P ns (a)

ACKOWLEDGEMENTS

was sponsored by the Natipinions expressed in this pa

not necessarily reflect the views of the sponsor.

REFERENC., and Naaman, A. EC)—Preliminary In

University of Michigan, Ann Arbor, MI, 2006. ASTM C39-96, “Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens”, West Conshohocken, PA., 1998.

[3] Brodowski, D., private communication with A.E. Naaman, 2005. Bui, V. K.; Geiker, M. R.; Shah, S. P., “RheolRILEM PRO30 High Performance Fibre Reinforced Composites HPFRCC4, 2003,

[5] Bui, Van K. and Attiogbe, Emmmanuel., Degussa Admixtures, Inc., Seminar at UM on Oct. 27, 2005.

[6] Busterud, Lars; Johansen, Kåre and Døssland,Åse Lyslo, “Production of Fiber Reinforced SCC,” SCC 2

Page 8

[7] Corinaldesi, V. and Moriconi, G., “Durable fiber reinforced self-compacting concrete,” Cement and Concrete Research 34, 2004, pp. 249-254.

[8] Dehn, Frank, Leipzig Germany, Private communication with Naaman, A.E., 2005. Denarie, E., private communication with A.E. N[9] aaman, 2006.

n ret ” Fiber d, 1978, pp. 112-128.

[12] Skarendahl self-

[13]ay 2001.

and Workability of Concrete, Edited by Bartos, Marrs and

[16]

etersson O, editors. Proceedings of the first international RILEM

[18]ruction,” RILEM PRO15 Fibre-Reinforced Concretes BEFIB, 2000, pp. 119-128.

[20] s of the pp.

[21]omposites—HPFRCC,” High Performance Fiber Reinforced Cement Composites 2

[22]

5-48, Part 2: Vol. 17, No. 2,

[24]Piotr J., “US-Specific Self-Consolidating Concrete for Bridges,” Final Report,

[25]elf-compacting concrete,” Building and Environment 40, 2005, pp. 1672-1677.

56.

y

[28]

[10] Edgington, J.; Hannant, D. J.; Williams, R. I. T., “Steel fiber reinforced co c e,reinforced materials, The Construction Press, Lancaster, Englan

[11] EFNARC, “Specification and Guidelines for Self-Consolidating Concrete,” February 2002. Groth, P. and Nemegeer, D., “The use of steel fibres in self-compacting concrete.” In:A, Petersson O, editors. Proceedings of the first international RILEM symposium oncompacting concrete. Stockholm, Sweden: 13-14 September 1999. pp. 497-507. Gru¨newald, Steffen and Walraven, Joost C., “Parameter-study on the influence of steel fibers and coarse aggregate content on the fresh properties of self-consolidating concrete,” M

[14] Gru¨newald, Steffen, “Performance-based design of self-compacting fibre reinforced concrete,” Ph.D. thesis, June 2006, p20-24.

[15] Johnston, C.D., “Proportioning, mixing and placement of fibre-reinforced cements and concretes,” Production MethodsCleland, E&FN Spon, London, 1996, pp. 155-179. Johnston, C.D., “Fiber-Reinforced Cements and Concretes,” Gordon and Breach Science Publishers, Amsterdam, 2001.

[17] Khayat, K. H. and Roussel, Y., “Testing and performance of fiber-reinforced, self-consolidating concrete.” In: Skarendahl A, Psymposium on self-compacting concrete. Stockholm, Sweden: September 13-14, 1999. pp. 509-521. Massicotte, Bruno; Degrange, Gerard; Dzeletovic, Nikola, “Mix Design for SFRC Bridge Deck Const

[19] Reinforced Concrete and other Advanced Composites, Toronto, Canada, March 26-29, 1995. Naaman, A.E., "High Performance Fiber Reinforced Cement Composites," ProceedingIABSE Symposium on Concrete Structures for the Future, Paris, France, September 1987,371-376. Naaman, A. E., and Reinhardt, H. W., “Characterization of High Performance Fiber Reinforced Cement C(HPFRCC 2), Proceedings of the Second International RILEM Workshop, Naaman, A. E., and Reinhardt, H. W., eds., RILEM Publications, s.a.r.l., Cachan Cedex, France, 1996, pp. 1-24. Naaman, A. E., “Strain Hardening and Deflection Hardening Fiber Reinforced Cement Composites,” HPFRCC 4 RILEM PRO 30, June 2003, pp. 95-113.

[23] Narayanan, R., Kareem-Palanjian, A.S., “Factors influencing the workability of steel-fibre reinforced concrete,” Concrete, Part 1: Vol.16, No. 10, 1982, pp.41982, pp. 43-44. Nowak, Andrzej S.; Laumet, Pascal; Czarnecki, Artur A.; Kaszynska, Maria; Szerszen, Maria M. and Podhorecki, July 2005. Sahmaran, Mustafa; Yurtseven, Alperen and Yaman, I. Ozgur, “Workability of hybrid fiber reinforced s

[26] Sahmaran, Mustafa and Yaman, I. Ozgur, “Hybrid fiber reinforced self-compacting concrete with a high-volume coarse fly ash,” Construction and Building Materials 21.1, Jan 2007, pp.150-1

[27] Sedran, T., De Larrard, F., Hourst, F. y Contamines, C., “Mix design of self-compacting concrete,” International RILEM Production Methods and Workability of Concrete, Edited bP.J.M. Bartos, D.L. Marrs y D.J. Cleand, Editorial: E & FN Spon, Londres, 1996, pp. 439-450. Suter, R., and Butschi, P.Y., "Tunnel du Oenzberg / Voussoirs en Beton, avec ou sans fibres," in French, Mandat de Recherche No. P.0209, EIA-Fribourg, Switzerland, 2001.

Page 9

[29] Swamy, R.N. and Mangat, P.S., “Influence of fiber-aggregate interaction on some properties of steel fiber reinforced concrete,” Materials and Structures, Volume 7, Number 5 / September 1974,

[30]euven, Departement Burgerlijke Bouwkunde, 1993, pp. 77-98.

pp. 307-314. Vandewalle, L., “Vezelversterkt Beton, Studiedag Speciale Betonsoorten en Toepassingen,” Universiteit L

Page 10