Desempeño del Concreto Auto-Compactante como refuerzo en vigas de concreto reforzado

8/10/2019 Desempeo del Concreto Auto-Compactante como refuerzo en vigas de concreto reforzado

1/101277ACI Structural Journal/November-December 2014

ACI STRUCTURAL JOURNAL TECHNICAL PAPER

Fiber-reinforced self-consolidating concrete (FR-SCC) was inves-

tigated to assess its potential value as a repair material of rein-

forced concrete beams. A total of 10 repair mixtures were optimized

to repair 10 full-scale beams. The mixtures included eight FR-SCC

mixtures, one ber-reinforced self-consolidating mortar, and a

reference self-consolidating concrete (SCC) made without bers.

Four types of ber reinforcement were employed: steel, two kinds

of polypropylene, and hybrid bers. Each ber type was used at

two volume contents of 0.3 and 0.5% for the FR-SCC mixtures and

at 1.4% for the steel bers in the mortar mixture. The beams were

3100 mm (122.05 in.) long, 250 mm (9.84 in.) wide, and 400 mm

(15.75 in.) deep. The beams were cast using conventional vibrated

concrete except for the lower 125 mm (4.92 in.) zone of the beam,representing a damaged area in the tension zone. After curing, the

bottom layer was repaired using the self-consolidating mixtures.

The beams were tested under four-point bending over a simply

supported clear span of 2600 mm (102.36 in.). Test results indicated

that the optimized self-consolidating repair mixtures can success-

fully restore the exural capacity of the test beams, showing a great

potential in repair and infrastructure rehabilitation. Key fresh and

hardened properties of the repair ber-reinforced self-consoli-

dating mixtures were evaluated and presented in this paper.

Keywords: bers; mixture; reinforced concrete beam; repair; self-

consolidating concrete.

INTRODUCTION

The development of self-consolidating concrete (SCC) has

recently been one of the most important developments in the

construction industry. According to ACI Committee 237,1

SCC can be dened as highly owable, non-segregating

concrete that can spread into place, ll the formwork, and

encapsulate the reinforcement without any mechanical

consolidation. The use of SCC in precast construction

and the cast-in-place industry is widely growing given the

numerous advantages of this advanced material, including

the possibility of reducing labor costs and construction

duration, elimination of consolidation noise on job sites,and production of high-quality surface nish and durable

concrete structures.2

It is well-established that the addition of discrete bers

with adequate mechanical properties can signicantly

improve many of the engineering properties of mortar and

concrete, notably impact strength and toughness. Flexural

strength, fatigue strength, and the ability to resist cracking

and spalling are also enhanced. The extent of improve-

ment in concrete properties varies with the type and quan-

tity of bers used and the quality of the concrete matrix. 3

Fibers are made of different materials and geometries, and

different ber types can lead to improvements of different

concrete properties. For example, steel bers are incorpo-

rated to enhance mechanical properties, whereas polypro-

pylene bers are mainly used to reduce cracking due to

plastic shrinkage.

Repair and rehabilitation of existing concrete elements is

one of the relatively new applications which can benet from

the combination of ber reinforcement and SCC, leading to

ber-reinforced self-consolidating concrete (FR-SCC). In

fact, most of the repair works are done in narrow spaces

where it is difcult to vibrate, making the use of SCC in

this application more effective and competitive. Gener-

ally, a good repair improves the function and performance

of a structure, restores and increases its strength and stiff-ness, enhances the appearance of the concrete surface, and

improves durability. This can be fullled by using FR-SCC

despite the negative effect of bers on the workability and

ow characteristics of concrete. Recent studies indicated that

using bers in SCC is feasible and that self-consolidating

properties can be maintained at signicant ber contents

(Vf).4-6Some adjustment, however, needs to be made to the

mixture properties to reduce the effect of bers on the ow

properties of SCC, such as reducing the length of bers and

the nominal size of coarse aggregates, and decreasing the

coarse aggregate volume.6-8

The aim of the present work was to develop and evaluatedifferent types of bers and ber-reinforced mixtures for use

in repair applications. The optimized mixtures were used

in the repair of full-scale reinforced concrete beams. This

paper investigates the effect of different types and contents

of bers on the structural performance of the repaired

beams. Key properties of the fresh material, including

deformability, passing ability, and segregation resistance,

as well as hardened concrete properties, are investigated.

The latter include pore-size distribution of capillary pores,

developments of compressive (fc) and splitting tensile (fsp)

strengths, elastic modulus (Ec), drying shrinkage, and rapid

chloride-ion permeability.

RESEARCH SIGNIFICANCE

The proper use of high volume of ber reinforcement

in self-consolidating materials is indeed challenging given

the hindering effect of bers on SCC characteristics. Mate-

rial properties and structural performance of the optimized

concrete materials should be of interest to engineers dealing

with the rehabilitation of concrete infrastructure. The objec-

Title No. 111-S108

Performance of Fiber-Reinforced Self-Consolidating

Concrete for Repair of Reinforced Concrete Beams

by Fodhil Kassimi, Ahmed K. El-Sayed, and Kamal H. Khayat

ACI Structural Journal, V. 111, No. 6, November-December 2014.MS No. 2012-090.R3 received September 1, 2013, and reviewed under Institute

publication policies. Copyright 2014, American Concrete Institute. All rightsreserved, including the making of copies unless permission is obtained from the

copyright proprietors. Pertinent discussion including authors closure, if any, will bepublished ten months from this journals date if the discussion is received within fourmonths of the papers print publication.


2/101278 ACI Structural Journal/November-December 2014

tives of this research are to evaluate the reparation processand study the deformation behavior and ultimate capacity of

such beams. In addition, this study compares the structural

behavior of full-scale repaired beams to values predicted

by various codes to validate the performance of different

brous self-consolidating materials.

EXPERIMENTAL INVESTIGATION

The experimental program described in this paper

included the development and evaluation of the perfor-

mance of eight FR-SCC mixtures, a ber-reinforced self-

consolidating mortar (FR-SCM) mixture, and a reference

SCC mixture made without any bers. The full-scale repairbeams measured 400 mm (15.75 in.) in depth, with the

bottom 125 mm (4.92 in.) used for casting the various repair

materials. This depth was chosen to represent the effective

tension zone (approximately, the area with steel bars along

the centroid) which can be repaired given advanced corro-

sion of bottom steel reinforcement.

The casting of the concrete beams representing existing

concrete elements was performed with the steel cage placed

inverted in the formwork with the tension reinforcement at

the top. The tension reinforcement and exposed stirrups were

temporarily covered with duct tape to prevent any contact

with substrate concrete and assure good bond between thereinforcement and repair material. After curing, the duct tape

was removed, and the beams were placed with the tension

reinforcement at the bottom. The repair layer was cast using

the optimized self-consolidating mixtures. The repair mate-

rial was placed through a funnel into a 140 mm (5.51 in.)

diameter hole located at the edge of the beam. The hole was

made by xing a plastic cylinder mold along the depth of the

beam during the casting of the conventional vibrated concrete

(CVC) beam. Three additional holes were made equidistant

along the length of the beam, as shown in Fig. 1, to expel air

and to monitor ow of the concrete. The plastic molds were

removed before the repair casting. The external sides of theformwork were fabricated using plexiglass to enable visual

observation of the ow of the self-consolidating repair mate-

rial during casting. To enhance bond between the existing

and new concrete, the surface of the existing concrete was

sprayed with a surface-retardant liquid soon after casting the

CVC. After 24 hours, the exposed concrete was cleaned by

removing the retarded surface mortar using water-spraying

to expose coarse aggregate and enhance bond to the repair

material, as illustrated in Fig. 2.

Materials and mixture proportioning

Four types of bers were used in this investigation,

including steel, polypropylene (two types), and hybrid

bers. Selection of these bers was based on variation in

ber characteristics and adaptation of ber length to dimen-

sions of the repair layer and clearance between steel rein-

forcement of the investigated beams. Each type of ber wasused at two volume replacement values of 0.3% and 0.5%,

hence yielding eight FR-SCC mixtures. Steel ber with a Vf

of 1.4% was also used to produce the FR-SCM.

The ber contents were chosen based on a previous inves-

tigation dealing with an optimization of the effect of Vfon

workability and exural toughness of brous self-consolidating

materials.7 The results of this preliminary investigation

showed that high owability can be obtained when the Vfis

limited to 0.5% for FR-SCC and 1.4% for FR-SCM. These

ndings are also supported by the ndings of Khayat and

Roussel.6 The FR-SCC mixtures were proportioned based

on the reference SCC matrix. The multi-aspect concept

suggested by Voigt et al.9 was considered in quantifying

the reduction in the coarse aggregate due to the inclusion

of bers. This concept is based on relating the thickness of

matrix layer (mortar) covering the ber and coarse aggregate

particles with the maximum crack width due to shrinkage. In

this study, however, the matrix thickness was related to the

ber factor (VfLf/df), whereLfand dfare the length and diam-

eter of bers in the mixture. This method is based on the

fact that with a given surface area of bers, the total surface

area of coarse aggregate should be reduced to maintain a

xed thickness of mortar as that of the reference mixture

without bers.

The repair mixtures were designed to develop 28-daycompressive strength (fc) of 45 to 50 MPa (6525 to 7250 psi).

The mixture proportions of the repair and CVC mixtures are

given in Table 1. For the mixture identication, CVC and

SCC refer to the conventional vibrated concrete and SCC

without bers, respectively. For FR-SCC mixtures, the rst

letter P, M, H, or S refers to the ber type in use: mono-

lament polypropylene, multilament polypropylene,

hybrid, or steel, respectively. The numbers 0.3 and 0.5 indi-

cate the Vf. The ber-reinforced self-consolidating mortar is

denoted as S-SCM-1.4.

A continuously graded crushed limestone aggregate with a

maximum size of 10 mm (0.39 in.) was used. The ne aggre-

Fig. 1Schematic of composite beam specimen. (Note:

Dimensions in mm; 1 mm = 0.039 in.)

Fig. 2Roughened surface of base concrete before casting

repair materials.



gate was well-graded natural sand with a neness modulus

of 2.6. The particle-size distributions of both aggregates

are in compliance with CSA Standard A23.110 recommen-

dations. The coarse and ne aggregates had specic gravi-

ties of 2.74 and 2.66, and water absorptions of 0.34% and

1.2%, respectively.A ternary cement containing approximately 70% Type

GU cement (ASTM portland cement Type I), 25% gran-

ulated blast-furnace slag, and 5% silica fume was used. A

polycarboxylate-based high-range water-reducing admix-

ture (HRWRA) with specic gravity of 1.1 and solid content

of 20% was used. A synthetic resin type air-entraining

agent (AEA) was used to secure the required air content.

A commercial liquid viscosity-modifying admixture (VMA)

based on polysaccharide biogum was incorporated to

enhance the stability of the SCC. Hooked-end steel bers

with a tensile strength of 1300 MPa (188.5 ksi) were used.

The bers measured 30 mm (1.18 in.) in length and 0.55 mm(0.02 in.) in diameter, giving an aspect ratio of 55. Mono-

lament polypropylene bers with a tensile strength of

620 MPa (89.9 ksi) were also employed. They had a length

of 40 mm (1.57 in.) and a rectangular cross-section with

an equivalent diameter of 0.44 mm (0.017 in.), giving an

aspect ratio of 90. Multilament polypropylene bers with a

tensile strength of 575 MPa (83.4 ksi) were also used. They

had a length of 50 mm (1.97 in.) and an equivalent diam-

eter of 0.67 mm (0.026 in.), giving an aspect ratio of 74.

Hybrid bers comprised a blend of 92% crimped steel and

8% multilament polypropylene bers by mass were used.

The steel portion had a length of 42 mm (1.65 in.) and a rect-

angular cross-section with an equivalent diameter of 1.2 mm

(0.047 in.), giving an aspect ratio of 35. The polypropylene

portion had a length of 5 to 15 mm (0.20 to 0.59 in.) and

diameter less than 0.05 mm (0.002 in.), giving an aspect

ratio between 100 and 300. The tensile strength of the hybrid

bers ranged between 966 and 1242 MPa (140 and 180 ksi).

Deformed steel bars No. 20M (db= 19.5 mm [0.77 in.])and No. 10M (db= 11.3 mm [0.44 in.]) were used in rein-

forcing the test beams. The yield strength of the bars are

400 and 450 MPa (58.0 and 65.2 ksi), respectively, for 20M

and 10M bars, while the modulus of elasticity for the bars is

200 GPa (29,000 ksi).

Mixing, test methods, and curingThe concrete was mixed in the laboratory using an indus-

trial open-pan 400 L (14.1 ft3) capacity mixer with a speed

of 15 rpm. The mixing sequence consisted of mixing the

bers with all aggregates and 50% of the mixing water,

which had a temperature of 17C (62.6F), along with theAEA. After 1 minute of mixing, the cement was added

and followed by the HRWRA and remaining water. After

1 minute more of mixing, the VMA was introduced, and the

concrete was mixed for 3 minutes. The mixing was stopped

for 2 minutes, then the concrete was mixed for 2 additional

minutes. Concrete temperature during mixing and testing

was approximately 20C (68F).

The mixtures were sampled to evaluate slump ow diam-

eter, T50 spread time, and visual stability index (VSI) in

compliance with ASTM C1611.11The passing ability was

evaluated using the J-ring (ASTM C 162112), V-funnel, and

L-box test methods. For testing the FR-SCC and FR-SCM

mixtures, a modied J-ring setup with either eight bars (for

Table 1Mixture proportions and fresh concrete test results

Mixture VfLf/df

Composition Fresh state test results

Water,

kg/m3

Cement*,

kg/m3

Sand,

kg/m3

Coarseaggregate,kg/m3

HRWRA,

L/m3

VMA,mL/m3

AEA,mL/m3

Time,min

Slump-ow J-ring

d

d,mm

Density,

kg/m3

Air,

%

V-funnel,s

L-box

Fillingcapacity,%

Surfacesettlement,%

d,mm

T50,s

VSI

d,mm

h,mm

h2

/h1

T70,s

CVC 175 350 660 1070 200 10 108 2287 7

SCC

200 475

781 792 3.48

128 25

10 720 0.6 0 715 10 5 2225 5.9 2.7 0.99 0.7 100 0.23

40 690 1.1 0 680 15 10 2316 5.8 3.1 0.95 0.7 95

P-SCC-0.3 27.3 861 705 3.80 10 710 1.4 0 700 11 10 2110 8.9 3 1 0.8 97

P-SCC-0.5 45.5 883 673 4.5010 700 1.6 0.5 680 10 20 2201 9 4.1 0.91 1.4 93 0.37

40 630 3.1 1 600 12 30 2215 7.8 6 0.71 2 70

M-SCC-0.3 22.1 815 750 6.8 10 690 2.3 0 650 15 40 2226 8.4 3.4 0.8 1.1 95

M-SCC-0.5 36.8 845 715 7.5 10 680 3 0.5 630 10 40 2260 5 4 0.8 1.5 85

H-SCC-0.3 14.1 795 769 4.13 10 705 1.5 0 700 5 9 2118 6.3 3 0.96 0.7 97

H-SCC-0.5 23.8 802 756 4.65 10 700 1.7 0.5 675 8 25 2222 6.6 4.8 0.90 1.6 90 0.37

S-SCC-0.3 16.4 801 763 3.7410 715 1.2 0 708 10 7 2121 6.8 3 0.98 0.7 97

40 675 1.9 1 660 11 15 2134 6.3 3.3 0.88 0.8 90

S-SCC-0.5 27.3 813 745 4.19

10 705 1.3 0 687 9 18 2235 7 3.6 0.92 0.9 95 0.27

40 650 2.7 1 615 13 35 2267 6.4 4.6 0.75 1 88

S-SCM-1.4 77 280 666 1134 4.6810 720 0.6 0 716 10 4 2062 9 1.8 0.98 0.5 96 0.21

40 660 1 1 650 10 10 2140 8.5 2.4 0.96 0.6 90

*Type GU cement for base CVC and Ternary GUb-S/SF for remaining mixtures.20 mm MSA type.

Slump value.

Note: 1 kg/m3= 1.686 lb/yd3; 1 mm = 0.039 in.



bers S, P, and H) or six bars (for bers M) was used.8This

resulted in a clearance between adjacent bars of 140 and

105 mm (5.51 and 4.13 in.), respectively, instead of the

typical value of 42.9 mm (1.69 in.) with the 16-bar standard

setup. This clearance represented at least 2.5 times the ber

length to prevent blockage. The difference in height (h) of

the J-ring test was determined as follows

h= 2(b c) (a d) (1)

where a, b, and care the concrete heights at the center, just

inside, and just outside the bars, respectively, in the J-ring

setup, and dis the median height between aand b.

All self-consolidating mixtures were characterized using

the V-funnel with a bottom outlet measuring 65 x 75 mm

(2.56 x 2.95 in.). The L-box setup was used with three

blocking bars for the SCC and with a single bar for FR-SCC

and FR-SCM mixtures,7 giving a clear spacing of 35 and

80 mm (1.38 and 3.15 in.), respectively. The blocking ratio

(h2/h1) of the L-box was determined using the h1 and h2

values corresponding to the heights of the concrete at both

ends of the horizontal leg of the device. The T70time spentto cross the horizontal leg of 700 mm (27.56 in.) was also

determined. The lling capacity was evaluated using a 300 x

500 x 300 mm (11.81 x 19.68 x 11.81 in.) caisson box.2A

column measuring 800 mm (31.50 in.) in height and 150 mm

(5.91 in.) in diameter, instrumented with an linear variable

displacement transducer (LVDT) and a methylmethacrylate

plate, was used to evaluate static stability by surface settle-

ment measurements during plastic stage.2

Concrete cylinders measuring 100 x 200 mm (3.94 x

7.87 in.) were prepared to evaluatefc,fsp, andEcat different

ages, and cores from these cylinders were prepared for rapid

chloride-ion permeability (RCP) testing (ASTM C120213

)and mercury-intrusion porosity tests at 56 days of age. Two

cores for porosity and two cores for RCP were taken from

the top and the bottom of each cylinder prepared for each

concrete. Concrete prisms measuring 75 x 75 x 285 mm

(2.95 x 2.95 x 11.22 in.) were prepared for drying shrinkage

measurements (ASTM C15714). For the SCC, FR-SCC, and

FR-SCM mixtures, cylinder and prism specimens were cast

in one layer without any mechanical consolidation. Immedi-

ately after casting, the repaired beams, cylinders, and prisms

were covered with plastic sheets and wet burlap to prevent

moisture loss. The prisms were demolded after 1 day and

transferred to a 100% humidity chamber for 6 days beforestorage at 23 2C (73.4 3.5F) and 50 4% relative

humidity to evaluate drying shrinkage.

Standard cylinders were cast along with the full-scale

beams and demolded after 24 hours and covered with wet

burlap and plastic sheets. The burlap was kept moist for

14 days, then the beams and accompanying cylinders were

air-dried until the time of testing.

Test beams and setup

The designation of the 11 full-scale beams given in Table 2

is the same as the mixtures listed in Table 1. All beams were

reinforced with two 20M bars as the main tensile reinforce-

ment and two 10M bars as the top reinforcement. The shear

reinforcement was double-legged stirrups of 8 mm (0.31 in.)

in diameter spaced at 150 mm (5.91 in.). The beam prepared

with the CVC was cast monolithically to serve as a refer-

ence beam, while the other beams were composite beams

consisting of CVC and a repair section along the bottom of

the beams (Fig. 1). The beams were tested approximately at

180 days under four-point bending over a simply supported

span of 2600 mm (102.36 in.), as shown in Fig. 3.

The load was monotonically applied at a stroke-controlled rate

of 1.2 mm/min (0.047 in./min) using a 500 kN (112.4 kip)

closed-loop MTS actuator. All beams were instrumented

with electrical resistance strain gauges bonded on rein-forcing bars and the top concrete surface at midspan. The

midspan deections were measured using two LVDTs

fastened at each side of the beam. Two high-accuracy LVDTs

(0.001 mm [3.93 105in.]) were installed at positions of

rst cracks to measure crack width. The test setup is illus-

trated in Fig. 4. The two lateral strain gauges for concrete

and two LVDTs for quarter-span deection were used only

for control quality; their results are not presented herein.

To monitor the bonding of the repair layer, an LVDT was

xed in the interface between the base and repair concretes.

During loading, the formation of the cracks on the sides of

the beams was marked and recorded (Fig. 5). The applied

load, displacements, and strain readings were electronically

recorded during the test using data acquisition system moni-

tored by a computer.

TEST RESULTS AND DISCUSSION

Fresh concrete properties

The fresh properties of all mixtures are summarized

in Table 1. The self-consolidating repair mixtures were

designed to secure initial slump ow d of 700 20 mm

(27.56 0.79 in.). This value was chosen based on the

work of Hwang et al.,15 having proposed a slump ow

range of 620 to 720 mm (24.41 to 28.35 in.) for SCC that

Fig. 3Beam dimensions (in mm). (Note: 1 mm = 0.039 in.)

Fig. 4Loading and strain-control systems (dimensions in

mm). (Note: 1 mm = 0.039 in.)



can be used in structural applications and repair of concrete

infrastructure.

The loss in slump ow at 40 minutes was lower than 70 mm

(2.76 in.) without the use of any set retardant. The HRWRA

demand needed to obtain the target slump ow is given in

Table 1. The HRWRA demand increased with the increase

of Vf. Increasing the Vf from 0.3% to 0.5% resulted in an

increase in HRWRA demand by approximately 18%, 10%,

12%, and 13% for mixtures made with mono- and multi-

lament polypropylene, hybrid, and steel bers, respec-

tively. The T50values, which provide an indication of the

relative viscosity of SCC,16increased with the increase in Vf.

The measured T50times, however, were less than 3 seconds

for all mixtures. All optimized repair mixtures had a VSI of

0 and 0.5 and a maximum surface settlement value of 0.37%

(lower than 0.5%), which indicate adequate static stability.2

All tested mixtures had the same dosage of AEA and had

fresh air volumes of approximately 6 to 9%; the air volume

increased slightly with the increase in Vf, given the increase

in HRWRA demand.

The optimized SCC mixtures also had excellent passing

abilities with L-box blocking ratios of 0.8 to 1.0 and excel-

lent deformability without blockage with V-funnel ow

times ranging between approximately 2 and 5 seconds

(Table 1). The J-ring spread (d) decreased with the increase

in Vf; yet the J-ring spread was systematically greater than

630 mm (24.80 in.), and the blocking assessment (d d)

was lower than 40 mm (1.57 in.), which is considered not

visible as per ASTM C1621.12The lling capacity decreased

as the Vf increased; however, all repair mixtures developed

excellent lling capacities ranging between 85 and 100%.

During casting of the composite beams, each of the

10 optimized self-consolidating mixtures was able to ow

horizontally along the total length of the beam without any

blockage. After stripping the formwork, the beams did not

exhibit any surface voids or areas of poor consolidation.

Hardened concrete properties

The fc results are summarized in Table 2. The 28-day

fc of the repair mixtures varied between 41 and 56.4 MPa

(5950 and 8180 psi), which achieved the target range of

45 to 50 MPa (6525 to 7250 psi). With regard to the FR-SCC

mixtures, all mixtures developed similar strength regardless

of the ber type and volume. The 56-day Ecvalues of the

repair concrete ranged between 26 and 36 GPa (3770 and

5221 ksi). Signicant inuence of coarse aggregate content

Table 2Summary of hardened results of concrete used in beams

Beam Use*

100 x 200 mm cylinder specimens 100 x 200 mm coresDrying

shrinkage,

microstrain

RCP,

Coulomb

MIP, mm3/g

fc cylinder, MPa fsp, MPa Ec, GPa

fc core A/

fc cylinder

fc core B/

fc cylinder 50 nm >50 nm

7 d 28 d 56 d 91 d 180 d 56 d 180 d 56 d 180 d 180 d 120 d 56 d 56 d

CVC M 26 33 35.9 36.4 37.8 3.4 3.5 27 27.5 545

SCC S 25 33.2 34.8 35.1 36.4 3.8 3.9 29 29.5

R 38 49.6 55.1 55.5 57 4.5 4.6 30.5 31.1 1 0.94 780 640 36 41P-SCC-

0.3

S 36.1 3.4 28.5

R 36 50 54.2 55.1 56.9 5.2 5.6 28 28.6 0.97 0.91 525 610 26 24

P-SCC-

0.5

S 25 33.2 34.8 35.1 36.4 3.8 3.9 29 29.5

R 40 56.4 60.8 60.8 61.1 5.3 5.7 26 28 1.01 0.89 605 800 35 30

M-SCC-

0.3

S 25 39.1 4.2 32.7 1.2 1.18

R 32 41 41.2 42.1 42.9 5 5.5 30.8 36 1.01 1.1 741 600 22 34

M-SCC-

0.5

S 37.5 45.4 3.8 4.9 32.6 33.5 0.98 0.95

R 38 48.5 58.3 58.7 60.6 5.6 6.8 29.8 32 0.97 0.96 750 635 25 33

H-SCC-

0.3

S 36.1 3.4 28.5

R 38 53.8 55.1 57.4 58.1 5.3 5.7 28 30 0.91 0.84 575 1310 25 33

H-SCC-

0.5

S 31 40.6 3.5 32

R 33 47.9 51.5 52.4 55.1 5.5 6.1 26.5 28 1.04 0.91 680 1800 31 26

S-SCC-

0.3

S 36.1 3.4 28.5

R 37 48.8 53.8 54.5 55.4 5.5 6 28 28 0.95 0.93 625 2320 29 40

S-SCC-

0.5

S 31 40.6 3.5 32 6250 27 38

R 34 47.6 51.2 52.2 53.3 5.9 6.2 26.5 27.5 1.06 1.05 645 3180 30 36

S-SCM-

1.4

S 31 40.6 3.5 32

R 34 48.7 51.5 52.8 53.5 6.7 6.8 20.5 21 1.03 0.88 1260 38 53

*M is monolithic beam; S is substrate of conventional concrete; R is repair layer (SCC, FR-SCC, or FR-SCM).

Test interrupted (high charge due to connectivity of high volume of steel bers conducting the electrical current).

Notes: 1 MPa = 0.145 ksi; 1 GPa = 145 ksi; 1 mm = 0.039 in.; 1 nm = 3.94 108in.; 1 mm3/g = 0.028 in.3/lb.



is noted for theEcin comparing the results obtained for the

S-SCM-1.4 mixture made without any coarse aggregate

which was 27% lower than the average value reported for

the FR-SCC mixtures.

As in the case ofEc, thefsp was evaluated at 56 days and

on the day of beam testing. As shown in Table 2, the addition

of 0.3% to 0.5% bers increased the 56-dayfsp by 11 to 31%.

This range was increased to 20 to 48% at 180 days. SCC

with monolament polypropylene bers gave the lowestfsp

of the FR-SCC mixtures. On the other hand, the S-SCM-1.4

mixture yielded the highestfsp given the high Vfof 1.4%.

The drying shrinkage strain (esh) results at 120 days are

reported in Table 2. It can be observed that the highest esh

belongs to the mortar mixture given the absence of coarse

aggregate. Concrete mixtures reinforced with monolament

polypropylene bers exhibited the lowest eshcompared with

those made with the rest of bers of similar Vf. Regardless

of the ber type, eshincreased with Vf. This can be attributed

to the decrease of coarse aggregate content associated with

the increase in Vf. The coarse aggregate contributes in

decreasing esh.

As noted in Table 2, compared to the SCC mixture,

FR-SCC had lower capillary pores with apparent diameterslower and greater than 50 nm. The FR-SCM had the greatest

porosity among the FR-SCC mixtures. Higher volume of

large-size pores can lead to higher permeability and lower

fc (Table 2).17The RCP values of the SCC at 56 days was

640 Coulomb, indicating very low electrical resistivity of the

concrete made with ternary cement containing 25% slag and

5% silica fume. The incorporation of polypropylene bers at

0.3% or 0.5% did not change considerably the RCP values.

On the other hand, the incorporation of hybrid and steel

bers in the SCC and SCM mixtures increased considerably

the RCP values. The increase in electrical conductivity was

proportionate to the steel Vf. Given the low capillary porosityof these mixtures, the inclusion of steel bers does not seem

to change the impermeability of the material; however, the

RCP test is obviously not suitable to evaluate the chloride-ion

permeability of concrete containing metallic bers.

Load-deflection response

A summary of the structural performance results of the

test beams is given in Table 3. The load-deection relation-

ships of the control monolithic beam and beams repaired

with steel FR-SCC are shown in Fig. 6(a). Figure 6(b)

shows the load-deection relationships of remaining beams.

The load-deection relationship is trilinear for all beams.The initial part up to exural cracking was similar for all

beams, which represents the behavior of the uncracked

beam that depends on the gross moment of inertia of the

concrete cross-section. The second part, corresponding to

post-cracking up to steel yielding, represents the cracked

beam with reduced moment of inertia. The third part,

corresponding to steel yielding up to failure, shows degra-

dation in the stiffness of the beams due to yielding of the

reinforcing steel.

Table 3 gives the post-cracking exural stiffness of the

beams which is determined as the slope of the second part

of the deection curve. It can be noticed from Fig. 6(a) and

Table 3 that the S-SCC-0.3 and S-SCC-0.5 beams repairedwith steel FR-SCC and the S-SCM-1.4 beam repaired with

concrete equivalent mortar incorporating steel bers had

relative stiffness values of 93%, 98%, and 96%, respectively,

of the value obtained for the monolithic control beam. This

result indicates that the relatively higher content of steel

bers in the FR-SCM compensated for the absence of coarse

aggregate. On the other hand, the other repaired beams

showed lower stiffness ranging between 75 and 90% of the

exural stiffness to the control beam (Fig. 6(b)). Therefore,

the use of steel bers with a high modulus of elasticity and

deformed shape is shown to be more efcient in restoring the

exural stiffness of the repaired beams in comparison to theother bers used in this study.

Fig. 5Cracking of repaired beam with P-SCC-0.5.

Fig. 6Load-deection response of control beam with: (a)

beams repaired with SCC and mono- and multilament poly-

propylene FR-SCC; and (b) beams repaired with hybrid and

steel FR-SCC, and steel FR-SCM. (Note: 1 kN = 0.2248 kip;

1 mm = 0.039 in.)



Cracking behavior and strains

Similar characteristics of the cracking patterns were

observed for all 11 beams. Crack formation was initiated inthe exural span between the two concentrated loads where

the exural stress is highest and shear stress is zero. The

cracks were vertical and perpendicular to the direction of the

maximum principal tensile stress induced by pure bending.

As load increased, additional exural cracks opened within

the shear span. However, because of the dominance of

the shear stresses, the cracks became progressively more

inclined and propagated towards the load point. As the

load reached the yielding capacity of the beams, the crack

opening rate increased, and the beams failed due to crushing

of the concrete in the constant moment zone. This failure

mode was observed for all beams.Figure 7 shows, schematically, the cracking patterns

at failure of the tested beams. The shaded part represents

the crushed concrete. With some repaired beams, very thin

and stable horizontal cracks were observed in the interface

between the substrate and repair concretes; the LVDT read-

ings were constantly near zero, indicating negligible interfa-

cial bond failure.

The cracking load values are reported in Table 3. All

repaired beams gave higher cracking load in comparison to

the control beam. The beam repaired with nonbrous SCC

had a cracking load of 111% that of the control beam. On the

other hand, the beams repaired with FR-SCC or FR-SCMshowed cracking loads of 122 to 162% over that of the

control beam. It can be noted that the beams repaired with

multilament (M) and steel (S) bers experienced higher

cracking loads compared with those repaired with other

bers due to their lengths and mechanical properties, respec-

tively. The increase of Vf from 0.3% to 0.5%, increased

slightly the cracking load (4 to 12%) for the four ber types.

Figure 8(a) shows the variation of measured crack width

with the applied load for the control beam and beams repaired

with SCC without bers and SCC with the two polypropylene

ber types, while Fig. 8(b) shows the load-crack width rela-

tionships of the control beam and other repaired beams. All

repair beams are shown to experience lower crack widths

at the same load levels in comparison to the control beam.

This is attributed to the inclusion of bers which restrict the

opening of the cracks under loading. However, the effectof Vf on crack width was not clearly observed because of

the relatively small difference in Vf. Beams repaired with

multilament polypropylene and steel ber experienced the

smallest crack widths compared with other ber types given

the lengths and hooked ends, respectively, that enhance bond

strength. Beams with monolament polypropylene ber

exhibited smaller crack width compared to beams made

with the hybrid ber. This is due to the difference in ber

length (40 mm [1.57 in.] versus 19.5 mm [0.77 in.]) which

can increase the resistance of ber slipping and bond that

decreases crack width. The beam repaired with SCC experi-

enced smaller crack widths compared to the reference CVC.This may be due to the dense microstructure of the SCC

offering better tensile and crack-opening resistances.

The strains of steel reinforcement and concrete of the

reference beam and beams repaired with SCC containing

different ber types and volumes, as well as FR-SCM of

steel bers are shown in Fig. 9. The strains were propor-

tional to the midspan deections and consistent with crack

widths shown in Fig. 6 and Fig. 8, respectively.

Ultimate capacityThe ultimate load capacity results are given in Table 3. The

ultimate load capacity of the control monolithic beam was216 kN (48.6 kip) and those of the repaired beams ranged

between 204 and 230 kN (45.9 and 51.7 kip) showing a

spread of 6% of the strength of the monolithic beam. There-

fore, 94% of the initial load capacity can be restored using

the novel repair materials. The maximum load-carrying

capacity was attained with the SCC and S-SCC-0.3 beams,

while the H-SCC-0.5 beam had the lowest load-carrying

capacity. All beams repaired with steel FR-SCC exhibited

higher ultimate strength compared to the control beam. The

improved strength behavior shown by the beams repaired

with multilament polypropylene and steel FR-SCC over

those repaired with monolament polypropylene or hybrid

FR-SCC (exhibiting equal or lower strength than that of

Table 3Test beams and summary of test results

Beam Cracking load, kN Stiffness, kN/m

Experimental ultimate

loadPu exp, kN Pu exp/Pu cont

Calculated ultimate load

(Eq. (2))Pu calc, kN Pu exp/Pu calc

CVC 45 18.1 216 1.0 153 1.41

SCC 50 14.1 230 1.06 153 1.50

P-SCC-0.3 56 13.6 206 0.95 157 1.31

P-SCC-0.5 58 14.5 213 0.99 160 1.33

M-SCC-0.3 65 14.9 224 1.04 157 1.49M-SCC-0.5 73 16.2 226 1.05 159 1.42

H-SCC-0.3 55 13.5 216 1.0 156 1.39

H-SCC-0.5 57 13.8 204 0.94 157 1.29

S-SCC-0.3 60 16.9 230 1.06 156 1.47

S-SCC-0.5 65 17.8 227 1.05 159 1.43

S-SCM-1.4 62 17.3 224 1.04 168 1.33

Notes:Pu contmeans ultimate load of control monolithic beam of CVC; 1 kN = 0.2248 kip.



the control beam) can be attributed to the ber length andhigher mechanical properties, respectively. The steel bers

used in this study had hooked ends, providing better bond

behavior, and higher tensile strength compared to the mono-

lament polypropylene and hybrid bers. This made steel

bers effective in contributing to the tensile strength of the

concrete beam. This tensile strength is added to that contrib-

uted by the reinforcing bars to obtain the ultimate capacity

of the beam. However, given the relatively low Vfand small

thickness of the repair layer relative to beam depth made

that contribution not quite signicant. Table 3 indicates that

increasing the Vf from 0.3 to 0.5% had no clear effect on

the ultimate load capacity of repair beams, due to the small

difference between the two Vf.

In-place compressive strength of repaired beams

In addition to the compressive strength tests performed

on concrete cylinders, in-placefc of the repair mixtures was

evaluated. From each repaired beam, two 100 mm (3.94 in.)

core samples (ASTM C4218) were taken after beam testing.

The cores were taken from both the end holes lled with

the repair concrete at the conclusion of the repair; the fc

results are summarized in Table 2. The A end corresponds to

the casting position, whereas the B end represents the other

end, as shown in Fig. 1. The results indicate that a differ-

ence of approximately 1 to 15% can be observed between

thefc of core samples from both ends of the repair beams.

The strength is generally higher at the casting end given thehigher consolidation energy.

The mean ratio of core-to-cylinder fc for all repair

mixtures was 0.94 for cores tested at the leading B end.

Such mean value was 1.0 at the casting location of the beam.

These comparable results indicate good self-consolidation

characteristics of the concrete and are comparable to varia-

tions that are typically obtained for CVC.19

PREDICTION OF FLEXURAL STRENGTH CAPACITY

The theoretical exural strength of the repaired beams can

be calculated assuming composite behavior and linear strain

distribution in the beam between two cracks, as shown in

Fig. 7Cracking patterns of tested beams at failure.

Fig. 8Load-crack width relationship of control beam and:

(a) beam repaired with SCC and with mono- and multi-

lament polypropylene FR-SCC; and (b) beams repaired

with hybrid and steel FR-SCC. (Note: 1 mm = 0.039 in.)



Fig. 10. This is similar to the ACI 31820 ultimate strength

design method considering the extra tensile strength of the

brous concrete and adding the strength provided by the

reinforcing steel to obtain exural strength. The ultimate

exural capacity of the beam can be calculated as follows

M A f d a

A f a

d b h e h e a

u s y s y t =

+

+ ( ) +

2 2 2 2 2

(2)

whereAsandAs are the areas of tensile and compressive steelreinforcement, respectively;fyandfy are the yield stresses of

tensile and compressive steel reinforcement, respectively; d

and d are the distances from the extreme compression ber

to the centroids of tensile and compressive steel reinforce-

ment, respectively; ais the depth of rectangular stress block;

bis the width of the beam; his the overall thickness of the

beam; eis the distance from extreme compression ber to

the top of brous concrete; and st is the tensile stress of

brous concrete, which can be calculated according to the

following equation for concrete with steel bers21

t

f

f

f be

L

dV F= 0 00772. (MPa) (3)

where Lf is the ber length; df is the ber diameter; Vf is

the percent by volume of bers; and Fbe is the bond ef-

ciency of the ber, which varies from 1.0 to 1.2 depending

on ber characteristics.

Equation (2) was used to calculate the exural capacity of

the test beams considering the effect of brous concrete of

the repair layer, which was 125 mm (4.92 in.) for all repairedbeams. The predicted ultimate capacities of the beams as

well as the comparison with the experimental capacities are

given in Table 3. It can be seen that Eq. (2) provides reason-

able conservative and consistent prediction of the ultimate

exural capacity of the test beams. The mean Pu exp/Pu calc

ratio was 1.40 with a coefcient of variation of 5%.

CONCLUSIONS

The main ndings of this investigation can be summarized

as follows:

1. Highly workable FR-SCC can be made using steel,

synthetic, and hybrid bers, similar to those used in thisinvestigation, incorporated at Vfof up to 0.5%. The inves-

tigated mixtures fullled all the passing ability, lling

capacity, and stability requirements and resulted in proper

air volume.

2. The investigated ber-reinforced self-consolidating

mixtures were found to be suitable for repair applications.

They were able to ow horizontally under their own weight

along the length of 3100 mm (122.05 in.) beams and achieve

good compaction in the absence of vibration without exhib-

iting defects due to segregation and blockage.

3. The beams repaired with the various self-consolidating

mixtures made with or without bers showed comparableload-carrying capacities and higher cracking loads than the

reference monolithic beam.

4. The beams repaired with steel and long multilament

polypropylene ber-reinforced self-consolidating mixtures

exhibited better structural performance in terms of load-

carrying capacity and stiffness than those repaired with

either monolament polypropylene or hybrid bers rein-

forced SCC. For the four types of bers used in this inves-

tigation, the effect of increasing Vffrom 0.3 to 0.5% did not

lead to signicant improvement in structural performance

given the small difference between ber contents and small

thickness of repair zone relative to the beam depth.

Fig. 9Load strains of steel reinforcement and concrete

response of control beam compared with: (a) beam repaired

with SCC and mono- and multilament polypropylene

FR-SCC; and (b) beams repaired with hybrid and steelFR-SCC, and steel FR-SCM. (Note: 1 kN = 0.2248 kip.)

Fig. 10Stress and strain variation in FR-SCC repairedbeams.


10/10ACI S l J l/N b D b

5. Repair with FR-SCC can restore at least 95% of the

initial load-carrying capacity of structural elements made

of CVC. This is due to the high workability properties

that can be offered by FR-SCC (lling and passing ability,

lling capacity, and stability), adequate durability, and high

mechanical and structural performances. The performance

mainly depends on characteristics of bers used in SCC.

6. Based on the structural repair performance obtained

in this study, FR-SCC is strongly recommended for repair

applications of concrete infrastructures such as bridges,parking beams, walls, and other similar applications. This

investigation would promote use of FR-SCC in the concrete

industry, particularly as an alternative and innovative repair

material for rehabilitation of concrete infrastructures.

ACKNOWLEDGMENTSThe authors would like to acknowledge the support of the Natural

Sciences and Engineering Research Council of Canada (NSERC) and the17 partners of the Industrial Research Chair on High-Performance FlowableConcrete with Adapted Rheology.

AUTHOR BIOS

Fodhil Kassimi is a Postdoctoral Fellow at CANMET Mining, NaturalResources Canada, Ottawa, ON, Canada. He received his MSc and PhDfrom the University of Sherbrooke, Sherbrooke, QC, Canada. His researchinterests include the engineering applications of ber-reinforced self- consolidating concrete and the stabilization of radioactive and nuclearwastes using cement-based materials.

ACI member Ahmed K. El-Sayedis an Associate Professor in the Centerof Excellence for Concrete Research and Testing at King Saud University,

Riyadh, Saudi Arabia. He received his PhD from the University of Sher-brooke. His research interests include the structural analysis and designof reinforced concrete members and the use of innovative materials inconcrete structures.

Kamal H. Khayat,FACI, is a Professor of civil engineering at the Universityof Sherbrooke and Missouri S&T, Rolla, MO. He is Chair of ACI Committee237, Self-Consolidating Concrete, and a member of ACI Committees234, Silica Fume in Concrete; 236, Material Science of Concrete; 238,Workability of Fresh Concrete; 347, Formwork for Concrete; and 552,Cementitious Grouting. His research interests include rheology, concreterepair, and the design and behavior of advanced cement-based materials,including self-consolidating concrete, high-performance concrete, ber-reinforced concrete, and lightweight aggregate concrete.

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