Application of ductile fiber

8/12/2019 Application of ductile fiber

1/8

Application of ductile fiber reinforced cementitious composite in jointless

concrete pavements

Jun Zhang, Zhenbo Wang, Xiancun Ju

Department of Civil Engineering, Tsinghua University, Beijing 100084, China

Key Laboratory of Safety and Durability, Education Ministry of China, Tsinghua University, Beijing 100084, China

a r t i c l e i n f o

Article history:

Received 9 October 2012

Received in revised form 22 January 2013

Accepted 3 February 2013

Available online 27 February 2013

Keywords:

A. Ceramicmatrix composites

B. Mechanical properties

D. Mechanical testing

Fiber reinforced cementitious composites

a b s t r a c t

This paper presents an experimental study on the potential applications of the fiber reinforced engi-

neered cementitious composite with characteristic of low drying shrinkage (LSECC) in concrete pave-

ments for the purpose of eliminating joints that are normally used to accommodate temperature and

shrinkage deformation. It is found that a composite slab containing both plain concrete and LSECC, with

steel bars at the LSECC/concrete interface, and designed construction procedures, it is possible to localize

the tensile cracks into the LSECC strip instead of cracking in adjacent concrete slab. The crucial problem

that interfacial failure in composite slab was prevented by using reinforcing bars across the interfaces.

Due to the strain-hardening and high strain capacity of the LSECC, the overall strain capacity and the

integrity of the composite slab can be significantly improved. The temperature and shrinkage deforma-

tions can be accommodated by adequate selection on the length ratio of LSECC strip and concrete slab.

2013 Elsevier Ltd. All rights reserved.

1. Introduction

Concrete pavements are popular for roads subjected to heavy

traffic loads due to their high load carrying capacity and low main-

tenance requirement compared to flexible asphalt concrete pave-

ments. Several hundred thousand kilometers of Portland cement

concrete pavements had been built in China in the past decades

[1]. The average service life of a concrete pavement is determined

by many factors including initial design, material properties, traf-

fic, environment, salt application, presence and effectiveness of

protective systems and maintenance practices. All these factors

influence the development of cracks in concrete pavements during

service. It is well understood that concrete shrinkage and temper-

ature changes are the two major mechanisms leading to the initial

crack formation in concrete pavements. That is because pavement

has a much larger surface area compared with other structuralmembers, such as beams and columns. As a result, shrinkage and

temperature variation induced cracking in concrete pavements is

more obvious. In order to avoid cracking in concrete pavements,

the continuous pavement is normally pre-cut into separate slabs

with length of about 46 m in practice, and the cuts form the joints

of pavements. Due to the relatively short lengths of the jointed

slabs, shrinkage and temperature induced stresses should be lower

and cracking within the slab may be prevented. The joints open in

the winter and close in summer, and the difference of the joint

opening between winter and summer may achieve several milli-

meters. During service, the joint openings in pavements can lead

to concrete spalling and punchouts. Further, damage due to debris

accumulation within the joints can lead to leakage of water

through the joint or cracked pavement. Therefore, the areas close

to the joints are the places most frequently be damaged in practice,

which in turn, control the pavement life in general, as illustrated in

Fig. 1. In addition, due to the existence of joints, the running

uncomfortableness becomes another disadvantage for concrete

pavements compared with flexible asphalt concrete pavements.

Thus, the prevention of the formation of joints in concrete pave-

ment is crucial, and the sequence of deterioration stages described

above has to be interrupted before final pavement failure in order

to prolong the service life and improve the conformability of the

pavements.In the present study, ductile strips of fiber-reinforced cemen-

tious composites are investigated as replacements for conventional

joints in concrete pavements. The concept of using ductile strips in

concrete slabs was first introduced by Zhang et al. [2]. In these

strips between regular concrete slabs, a special kind of fiber rein-

forced cementitious composite (ECC), with strain-hardening and

high strain capacity compared to concrete is applied[3,4]. Through

proper material and structure designs, the temperature variation

and concrete shrinkage induced deformations may be compen-

sated by the formation of very fine cracks within the strips with

crack width less than 80lm. ECC exhibits macroscopic strain-

hardening after first crack. The strain energy produced by

1359-8368/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.compositesb.2013.02.007

Corresponding author at: Department of Civil Engineering, Tsinghua University,

Beijing 100084, China. Tel.: +86 10 62797422.

E-mail address: [email protected](J. Zhang).

Composites: Part B 50 (2013) 224231

Contents lists available at SciVerse ScienceDirect

Composites: Part B

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m p o s i t e s b
http://dx.doi.org/10.1016/j.compositesb.2013.02.007mailto:[email protected]://dx.doi.org/10.1016/j.compositesb.2013.02.007http://www.sciencedirect.com/science/journal/13598368http://www.elsevier.com/locate/compositesbhttp://www.elsevier.com/locate/compositesbhttp://www.sciencedirect.com/science/journal/13598368http://dx.doi.org/10.1016/j.compositesb.2013.02.007mailto:[email protected]://dx.doi.org/10.1016/j.compositesb.2013.02.007


2/8

shrinkage (under restrained condition) of hardened concrete and

temperature gradient can be released by the high deformation

within the ductile strips, and therefore, the damages occurred

around traditional joints in concrete pavement can be avoided.

Thus, the durability of concrete pavement can be improved, result-

ing in a longer service life. In addition, the running comfortable

problem normally occurred in jointed concrete pavements can be

overcome due to the replacement of joints with ductile strips.

Due to without coarse aggregate in ECC mixture, the drying shrink-

age of traditional ECC normally is much higher than concrete[5].

Such high shrinkage strain may lead longer strip requirement to

accommodate the deformations in the pavement and also may lead

un-expected shrinkage cracking inside of the strips. To implement

the concept of jointless concrete pavements and overcome the

problems that high drying shrinkage of traditional ductile material

may induced, an ECC with characteristics of low drying shrinkage

(LSECC) is used to form the ductile strips in the present paper

[5]. The cement used in LSECC has expansive property during hard-

ening and therefore the shrinkage of the composite can then be

compensated effectively, behavior as less shrinkage comparing

with traditional ECC. In addition, high early strength is another

mechanism for reducing drying shrinkage of the composite.

2. Design principles and experimental program

Thetarget of present work is concentrating the deformation pro-

duced by temperature change and concrete shrinkage in adjacent

concrete pavement slabs into the strips placed between the two

slabs, to form a jointless concrete pavement system, as illustrated

inFig. 2. To realize the above design concept, the tensile properties

of both concrete and LSECC material, as well as the interface be-

tween the two materials must be carefully tailored and designed.

First, the cracking strength of LSECC must be lower than the

strength of the adjacent concrete slabs. Second, the interfacial bond

strength between ECC and concrete slab must be high enough toconfirm the cracking should not occur at the interface. The strength

difference between LSECC and concrete can be satisfied relatively

easy by adjusting the mix proportions of the materials and/or cast-

ingthe stripsat later agethat theconcreteslab cast. Thedifficulty to

achieve above target may be the enhancement on the interface of

the ductile strip and adjacent concrete slab. Because if the failure

under tensile or bending loads occurs at the interface, the potential

higher strain capacity of ECC completely cannot be used and no

improvement on the performance of the pavement can be expectedcompared with conventional joint concrete pavements. Therefore,

present paper will focus on the interfacial design to prevent the

interfacial failure in the ECCconcrete composite pavements. Cer-

tainly, the tensile properties of concrete and LSECC are also be eval-

uated in order to satisfied the design requirements.

Three tests are involved in the experimental program. First, the

tensile properties of plain concrete and a kind of LSECC was exper-

imentally examined to guarantee the strength difference is satis-

fied the design requirement. Second, the drying shrinkage of the

selected LSECC used as ductile strips was examined in order to con-

firm the low shrinkage characteristic[5]. Third, the designed inter-

facial connection methods to enhance the interfacial bond between

the ECC strip and the concrete slab were evaluated by three points

bending tests on composite beams in order to learn the reliability

of the designs.

2.1. Materials

In the present investigation, two types of cements, ordinary

Portaland cement used for concrete and the newly developed com-

posite cement with low drying shrinkage characteristic used for

ECC matrix. Natural sand and crushed limestone with a maximum

particle size of 5 mm and 20 mm, respectively, were used as fine

and coarse aggregates in concrete. The concrete mixture propor-

tions are listed inTable 1. A superplasticizing admixture was used

in the mixtures to guarantee the three fresh concrete having a

slump of 120140 mm. For ECC, silica sand with average particle

size 0.1 mm were used to form the matrix. Polyvinyl Alcohol

(PVA) fiber supplied by Kuraray Company in Japan was employedas reinforcement and the fiber properties are listed inTable 2. Mix-

ture proportions of the LSECC adopted in this study are given in

Table 3.

2.2. Specimens, curing and testing procedures

For drying shrinkage test of ECC, a prism shape specimen mea-

suring 40 40 160 mm with two embedded copper heads at the

Pavement

Existing joint or crackSubgrade

Damage susceptible zone

Fig. 1. Illustration of formation of joints and damages susceptible zone under traffic

load.

Pavement

Existing jointSubgrade

LSECC strip

Interfacial reinforcing bars

Fine cracks

Fig. 2. Ductile joints in concrete pavement.

Table 1

Mix proportions of concrete, kg/m3.

Cement Water Sand Stone Fly ash

345 185 685 1090 85

Table 2

Properties of the PVA fiber.

Density (g/

cm3)

Tensile strength

(MPa)

E

(GPa)

Diameter

(mm)

Length

(mm)

1.2 1620 42.8 0.039 12

Table 3

Mix proportions of LSECC.

Composite cement Water Sand Super plasticizer Fiber (volume, %)

1.0 0.35 0.3 0.012 1.7

J. Zhang et al. / Composites: Part B 50 (2013) 224231 225


3/8

two long ends for length measurement was used. After removing

from their molds (24 h after casting), the specimens were stored

in the room with constant temperature and relative humidity of

25 2C and 60 1.5% for drying shrinkage deformation measure-

ment. The length measurement starts immediately after specimen

demolding until 28 days after casting.

The uniaxial tensile tests give tensile stressstrain performance

and related mechanical parameters, such as tensile strength andstrain of materials. Rectangular coupon specimens with size of

40 150 15 mm were used for LSECC to conduct uniaxial tensile

test. The molds used to cast the tensile specimens were made of

steel. After removing from their molds, the tensile specimens were

stored in water at 20 2C for curing until tensile tests were car-

ried out. The tensile specimens were tested in uniaxial tension

with displacement control in a 250 kN capacity MTS 810 material

testing system with hydraulic wedge grips. Aluminum plates were

epoxy glued onto the ends of the specimens prior to loading at

least 6 h to enhance the ends for gripping. The actuator displace-

ment rate used for controlling the test was 0.0025 mm per second.

The strain was measured by two extensometers mounted on the

surface of the specimen. The measured gage length of extensome-

ter was 50 mm. The tensile test set-up and specimen with alumi-

num plates glued and extensometers mounted is shown in

Fig. 3a. For tensile tests of plain concrete, a loading holder devel-

oped by Li[4]was adopted (Fig. 3b). The holders were made of alu-

minum alloy. One was fixed to the load cell and the other to the

actuator with standard MTS grips. The tensile load was transmitted

to the specimen by the anchor action between holders and the en-

larged ends of the specimen. To further prevent failure due to

stress concentration at the loaded ends of the concrete specimens,

two steel bolts with 6 mm diameter and 12 mm length were used

to reinforce the specimen ends. One end of each bolt was con-

nected with a nut and the other end was fastened to a

118 45 7 mm steel plate through another nut. Thus the failure

of the specimen under tensile load can be ensured to be within the

central position with a uniform cross section. The minimum cross

section of the specimen was 76 45 mm. The overall uniaxial ten-

sile strain was measured with two LVDTs, one on each side of the

specimen. The details of experimental set-up and geometry of thetest specimen are shown inFig. 3b. The tensile tests were carried

out under displacement control with prescribed rate of 0.005 mm

per second in a 250 kN capacity MTS 810 material testing system.

The raw data of tensile tests consisted of time, load, position of the

piston and displacement from each extensometer. The tensile

behavior can then be determined from these test data.

The interfacial connection tests were used to evaluate the reli-

ability of the bond between the concrete slab and the ductile strips,

meanwhile to check the effectiveness of the replacement of con-

ventional joints with ductile strips. A composite beam with overall

dimension of 100 100 515 mm is employed with three bend-

ing load applied to the beam as a general loading condition. The

specimen is composed of two concrete blocks to simulate the

two adjacent concrete slabs and a ECC block with size of

100 50 300 mm placed in the top center of the beam to simu-

late the ductile strip. A steel bar with 10 mm diameter was used to

enhance the connection of concrete block and ECC strip. Two con-

necting steel bars having enlarged nut with outer diameter of 17

mm at ends, with different embedment length in concrete and/or

ECC, were placed at each interface. The detailed dimension of each

part of the composed beam is shown inFig. 4. The concrete blocks

used for the composite beams were cast first and designed steel

bars was embedded inside of concrete at prescribed locations.

75

120

165

180

165

45

Loading Hold

LVDT

Specimen

Unit: mm

Strengthen Element

(b)

(a)

Fig. 3. Test set-up and geometry of specimen of LSECC (a) plain concrete and (b) in tension.

226 J. Zhang et al. / Composites: Part B 50 (2013) 224231


4/8

The space left for ECC strip was formed by pre-placed wood blockwith required dimensions in the mold. These concrete blocks were

cast and demolded 24 h after casting. After demolding, the blocks

were cured in moisture room at 20 3C and relative humidity lar-

ger than 95% for 2 weeks. Then the blocks were placed back into

the mold again and the empty space left for ECC strip was cast.

The composite beams were demolded 24 h after the ECC strip

was cast and were cured in the moisture room for another 2 weeks

before testing. As control, specimens without steel bars were cast

also at the same time. Conventional concrete and mortar mixers

were used to prepare the fresh materials. For plain concrete, the

mixing time was 5 min. For LSECC about 10 min mixing time was

used to ensure good fiber distribution in the matrix.

Deflection is carefully monitored during bending testing using a

reference beam attached to the top of the beam by three steelblocks glued to the beam surface. A standard Toni linear variable

differential transducer (LVDT) is used for measuring the movement

of the actuator displacement. A extensometer mounted on the cen-

ter of the beam is used for measuring the deflection. The loading

configurations for three point bending test is shown inFig. 5. The

bending test is conducted at a prescribed deformation rate of

0.05 mm per minute using the signal from the LVDT as feedback.All tests are carried out on a Toni testing machine equipped for

close-loop testing. The raw data consisted of time, load and dis-

placement reading from load cell, LVDT and extensometer respec-

tively. Data are recorded by the test machine and transferred to a

computer for further processing. All types of the composite beams

used in the experiments are summarized inTable 4.

3. Results and discussions

3.1. Drying shrinkage behavior of LSECC

The measured drying shrinkage up to 28 days of conventional

ECC using normal Portland cement in matrix [5] and LSECC made

by low shrinkage cementitious material is shown in Fig. 6. Wecan clearly see that the drying shrinkage deformation of the com-

posites using the new cementitious material in matrix is greatly re-

duced. The shrinkage strain at 28 days is only 242 106 of the

new developed ECC. For traditional ECC, the shrinkage strain at

28 days is nearly 1200 106 that is almost five times larger than

the shrinkage of LSECC. Further, the result indicates that the drying

shrinkage of the LSECC is even lower than that of normal concrete,

which normally has the magnitude of shrinkage strain of 400

600 106 at 28 days under the similar testing conditions. This

means that under the same or similar curing periods and environ-

mental conditions, as cracking does not occur in normal concrete

structure, the same or even higher no-cracking guarantee can be

provided as using LSECC to replace normal concrete in the struc-

ture. Therefore, after applying the LSECC as the ductile strip in con-crete pavement, un-expected shrinkage cracking can be reduced

and the requirement on the overall deformation capacity to com-

pensate temperature strain produced by the adjacent concrete

slabs may become small and the required strip length may be

shorter than that when conventional ECC was used [2]. Further,

due to its low drying shrinkage strain, the shrinkage cracking along

the traffic direction should be able to be avoided that may happen

as using normal ECC as the ductile strips.

3.2. Uniaxial tensile behavior of LSECC and plain concrete

ECC is a cement based composite reinforced with short ran-

domly oriented fibers. The composite has been micro-structurally

engineered to strain-harden via multiple cracking in uniaxial ten-sion [3,4]. ECC exhibits macroscopic strain-hardening after first

Fig. 4. Design of composite beam.

Fig. 5. Experimental set-up for composite beam under bending load.

Table 4

Interfacial details used in the composite beams.

Number of interfacial steel reinforcements Embedment length (mm)

No 0

Two 25

Two 50

Two 100



5/8

crack. During strain-hardening, multiple cracks develop with con-

tinuously reducing crack spacing until localization occurs at one of

these cracks. The fracture site is not necessary the first crack site.

The evolution of multiple cracking appears to be a stochastic pro-

cess associated with distributed initial flaw sizes[6].

As an important material property, the tensile behavior of

LSECC and plain concrete used in the composite beams is deter-

mined first.Fig. 7displays the tensile stressstrain curves of plainconcrete and LSECC at 28 days of moisture curing. From the tensile

results, first we may clearly see that the tensile strength of plain

concrete is about two times higher than that of LSECC. Such behav-

ior can guarantee the cracking should occur inside of the ductile

strip in the composite structure under tensile or bending loads as

long as the bond between concrete slab and ECC strips is sufficient

high that the interfacial failure can be prevented. Second, the

LSECC can well maintain the strain-hardening and multiple crack-

ing performance along with tight crack width less than 0.05 mm

[5], that normal ECC displayed. This performance confirms that if

cracking can be leaded into the inserted strips, the deformation

of the structure due to temperature variation, live load, and shrink-

age can be accommodated effectively by the formation of micr-

cracks inside of the strip. Clearly, the success on the jointless

concrete pavement now depends on the interface of concrete slab

and ECC strip. This is crucial to realize the concept apart from the

material properties tailoring.

3.3. Bending performance of LSECCconcrete composite beams

The objective performing bending test on concreteECC com-

posite beams is to examine if the present interfacial design can

prevent the interfacial failure in current jointless concrete pave-

ment system. Such interfacial failure had been observed in the

experiments of ECC linked steel reinforced slab and the interfacial

transition zone was designed to overcome the interfacial failure inECC linked steel reinforced slab [7,8]. In present study, the ECC

concrete interface is simply enhanced by steel reinforced bars with

enlarged end nuts only. The simplicity in construction is important

for its application in jointless concrete pavements.

The bending performance of the composite beams with differ-

ent concreteLSECC interfacial enhancing bars is displayed in

Figs. 8 and 9in terms of load and middle point deflection diagrams.

The corresponded failure model of the beams are displayed in

Fig. 10, in which the smaller photographer present in the figure

displays the finer cracks formed inside of the ductile strip at side

Fig. 10b and topFig. 10c faces respectively. From the results dis-

played in the figures, first we can see that as without reinforcing

bars connecting the concrete slab and ECC strip (Fig. 8), the com-

posite beam behaviors immediate failure along the interface be-

tween concrete and LSECC. The load carry capacity of the beam is

simply controlled by the physical bond of LSECC and concrete

block, which is the weakest part in the composite system in the

current situation. The maximum flexural stress achieved under

bending load is only about 4 MPa, which reflects the magnitude

of flexural strength of cold jointed concreteLSECC interface. The

loaddeflection curves display apparent brittle nature behaving

as load carrying capacity suddenly drops after the peak load. No

fine cracks can be find in the ECC strip. As using two reinforcing

bars at the interfacial zone to bridge the each interface, with

embedment length of 25 mm, 50 mm and 100 mm respectively,

the bending performance of the composite beams were completely

changed from interfacial failure to cracking inside of ECC strips, see

Fig. 10ac respectively for different embedment length of the steel

bars.Flexural strain hardening behavior was occurred, along with

larger deformation and ductile failure characteristic. Meanwhile,

the bending strength of the beam is also significantly increased

compared with the case of interfacial failure, for example, the

bending strength of the composite beams with interfacial failure

and ductile strip cracking are 4 MPa and 8 MPa respectively. The0 7 14 21 28

Time (days)

0

400

800

1200

Dryingshrinkage(x10-6)

Traditional ECC

LSECC

Fig. 6. Drying shrinkage of LSECC and traditional ECC.

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Tensile strain (%)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

Tensilestress(MPa)

Plain Concrete

LSECC

Fig. 7. Tensile stressstrain curves of plain concrete and LSECC.

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Deflection (mm)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

Flexuralstress(MP

a)

L=450mm

No steel bars

No steel bars

Fig. 8. Bending performance of composite beam without interfacial reinforcingbars.



6/8

load transferring ability of the interfaces is greatly improved,

which is an importance aspect needed to be considered in the de-

sign of conventional jointed concrete pavement. As expected, with

increase of embedment length of the steel bars, from 25 mm to

100 mm, the bending performance is improved, but it looks that

little difference can be found between embedment length of

50 mm and 100 mm. This means that the 50 mm embedment

length is sufficient to achieve the target of leading the cracking intothe LSECC strips. For the specimens with embedment length of

25 mm of the steel bars, the interface of LSECC and concrete failure

is still observed, but the bending behavior is improved compared

to the case without any reinforcement at interface, as shown in

Fig. 8. From the photographers attached inFig. 10, we can clearly

see that the without steel reinforcing bars at interface, the interfa-

cial failure cannot be prevented and the cracking inside of the duc-

tile strip cannot occurs. By contrast, as using steel reinforcing bars

and with embedment length of 50 or 100 mm length, the interfa-

cial failure can be prevented and the fine cracks had been displayed

within the ductile strip.

3.4. Further discussions

3.4.1. Construction procedures for jointless concrete pavements

As state above, if the interfacial bond strength between ECC and

concrete slab is high enough and the interfacial failure can be pre-

vented, in order to realize the cracking occurs only inside of the

ductile strips, the cracking strength of LSECC must be lower than

the strength of the adjacent slabs. Such difference in cracking

strength can be realized by mix proportion design and/or casting

the strip later than the concrete cast. In practice, the pavements

may be constructed with traditional manners just at the location

where a joint notch should be cut, to put a prefabricated filler with

required steel bars in it and the thickness may be less than the

thickness of pavement, generally half of the pavement thickness

is sufficient to maintain a tight crack opening at pavement top after

the joint crack reflecting into the ECC layer[9]. After concrete con-struction, the filler is picked out and the space is left for ECC strips

cast that should be cast afterwards. In such construction proce-

dure, the weakest location in the continuously constructed pave-

ment is still at the place where the prefabricated filler is put in.

Several days after concrete cast, the joint crack should be formed

around the center of the prefabricated filler due to reflection of

existing joint in the concrete slab. This predestined location of

existing joint crack is important also for completely avoid cracking

in adjacent concrete slab because the unsymmetrical joint cracking

in the base concrete may lead interfacial shear failure. After the

ECC strips were cast, the existing joint crack should reflect into

the ECC layer in the manner of formation of many fine cracks, with-

out loss of load transferring capacity[9].

3.4.2. Strip length requirements to accommodate the deformation of

pavement

The strip length required to accommodate the deformation of

pavement depends on the strain capacity of the ductile material

and the space length between the strips, as well as local tempera-

ture variation and shrinkage of concrete. Assume a composite slab

is composed of two kinds of materials, LSECC and plain concrete

with lengthlIand lIIrespectively. The slab has the same cross sec-

tion along the length. Further assume that the two materials are

perfectly joined together without failure at the interface under ten-

sile load, above experimental study already demonstrates it is pos-

sible by simply introducing steel reinforcing bars at interfacial

zone. The general dimension of the slab and the corresponding

stressstrain relationship under tensile load of individual materialsare shown inFig. 11, where the concrete tensile strength is higher

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Deflection (mm)

0.00

2.00

4.00

6.00

8.00

10.00

Flexuralstress(MPa)

L=450mm

R_L=25mm

R_L=25mm

(a)

0.00 0.50 1.00 1.50 2.00 2.50

Deflection (mm)

0.00

2.00

4.00

6.00

8.00

10.00

Flexuralstress(MPa)

L=450mm

R_L=50mm

R_L=50mm

(b)

(c)

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Deflection (mm)

0.00

2.00

4.00

6.00

8.00

10.00

Flexural

stress(MPa)

L=450mm

R_L=100mm

R_L=100mm

Fig. 9. Bending performance of composite beam with interfacial reinforcing bars

and embedment length (a) 25 mm, (b) 50 mm and (c) 100 mm.



7/8

Bottom face

(a)

(b) (d)

(c)

Fig. 10. Photographers of composite beams at ultimate failure, (a) without interfacial reinforcing bars, (b) embedment length 25 mm, (c) embedment length 50 mm and (d)

embedment length 100 mm.

(a)

(b)

ECC PC

l

lI lII

I II

Stre

ss

Strain

I II

t,ECC

t,PC

fc,ECC

I-II

F F

Fig. 11. (a) A ECC/PC tensile bar and (b) schematic stressstrain behavior of ECC and concrete under uniaxial tensile load.



8/8

than that of ECC. Under uniaxial tension, the overall strain capacity

of the slab in length direction, ec, can be given by

ec e I lIl

eII lII

l

1

where eI is the strain capacity of ECC and eII is the strain value of

plain concrete corresponding to the tensile load. l is the total length

of the slab. Therefore, the composite strain capacity, ec, is a function

of eI, eII and l Ior l II. For given material properties, ec is influenced

only by the individual element length lIor lII. For safety, we assume

eI is equal to 12%, which can easily achieved for ECC materials.

Fig. 12displays the overall strain capacity, ecas a function oflIwith

given strain capacity of ECC, eIof 1% and 2%. It shows that for a given

ECC element length the higher the strain capacity of ECC used, the

higher the overall strain capacity of the composite bar. Second, a

high composite strain capacity can also be obtained through adjust-

ing the length of the ECC strip.

On the demand side, the required strain capacity for the com-posite slab is determined from the imposed strain mainly due to

the combined effect of thermal deformation and shrinkage of con-

crete, as shown in the following equation:

eR aTDT esh 2

where eR is the required total tensile strain. aT is the coefficient of

thermal expansion of concrete, generally equal to 0.001%/C. DTis

annual temperature variation, approximately 5060 C for Beijing

for example[10]. eshis shrinkage strain of concrete, normally equal

to 0.06%. Using DT= 60 C and esh= 0.06% in Eq. (2), we may obtain

eR= 0.12%. FromFig. 12,we may get the ratio of the length of ECC

strip to the total length of the composite pavement is about 0.05

and 0.10 for 2% and 1% tensile strain of ECC used respectively,

means for 6 m length slab, which is the general joint space in tradi-tional concrete pavement[1], the required ductile strip is 0.60 and

0.30 meter for strain capacity of ECC of 1% and 2% respectively. It

should be noted that Eq. (2) does not take the effect of live load into

account. As live load is considered, the strip length may increase a

little.

Clearly, with a reasonable combination of plain concrete and

ECC strips, it is possible to achieve a prescribed strain capacity

requirement without a loss of load carrying capacity. In such situ-

ation, cracking can be avoided within the plain concrete section as

the structure is subject to tensile stress, such as shrinkage and tem-

perature stresses. Instead, the ECC strip plastically yields to

accommodate the imposed strain. In addition, the formation of

tight cracks within the ductile strips should form the base of crack

healing under moisture environments that should also be of great

interests for improvement of durability of concrete pavements and

prolong its service life. Further, such combination can still follow

the traditional construction procedures just leaving the required

space for the ductile strips which should be cast afterwards. Mean-

while remaining the total cost of the jointless concrete pavements

comparable with traditional jointed concrete pavements due to thelimited strip length required, but with super service ability and

long service life.

4. Conclusions and future work

This paper presents an experimental study on the potential

applications of the fiber reinforced engineered cementitious com-

posite in concrete pavements for the purpose of eliminating joints

that normally used to accommodate temperature and shrinkage

deformation. It is found that a composite slab containing both plain

concrete and LSECC strips, with a simply enhancement at the

LSECC/concrete interfaces by using steel bars, and designed con-

struction procedures, it is possible to localize the tensile cracks into

the ductile strip instead of cracking in adjacent concrete slab. The

crucial problem that interfacial failure in composite slab of LSECC

and concrete was prevented by using reinforcing bars at the inter-

faces. Due to the strain-hardening performance of the ECC material

with high strain capacity, the overall strain capacity and the integ-

rity of the composite slab can be significantly improved. The tem-

perature and shrinkage deformations can be accommodated by

adequate selection on the length ratio of ductile strip and concrete

slab. Further experiments with larger scale specimens are needed

in order to apply the concept explored in the present work in more

realistic field situations.

Acknowledgments

Support from the National Science Foundation of China (Nos.

50878119, 51278278) and Twelfth Five-Year plan projects from

the National Science and Technology (No. 2011BAJ09B01) to Tsing-

hua University are gratefully acknowledged.

References

[1] Chinese specification for construction of concrete pavements. JTG F30-2003 [inChinese].

[2] Zhang J, Li VC, Nowak NS, Wang S. Introducing ductile strip for durabilityenhancement of concrete slabs. ASCE J Mater Civil Eng 2002;14(3):25361.

[3] Li VC. From Micromechanics to structural engineering the design ofcementitous composites for civil engineering applications. JSCE J Struct MechEarthq Eng 1993;10(2):3748.

[4] Li VC. Engineered cementitious composites tailored composites throughmicromechanical modelling. In: Banthia N, Bentur A, Mufti A, editors. Fiberreinforced concrete: present and the future. Montreal: Canadian Society forCivil Engineering; 1998. p. 6497.

[5] Zhang J, Gong CX, Zhang MH, Guo ZL. Engineered cementitious composite withcharacteristic of low drying shrinkage. Cem Concr Res 2009;39(4):30312.

[6] Wu HC, Li VC. Trade-off between strength and ductility of randomdiscontinuous fiber reinforced cementitious composites. J Cem ConcrCompos 1994;16(1):239.

[7] Gilani A, Jansson P. Link slabs for simply supported bridges. Report no. MDOTSPR-54181, Michigan Department of Transportation; June 2004. 129p.

[8] Qian S, Lepech MD, Kim Y, Li VC. Introduction of transition zone design forbridge deck link slabs using ductile concrete. ACI Struct J 2009;106(1):96105.

[9] Zhang J, Li VC. Monotonic and fatigue performance of engineered fiberreinforced cementitious composite in overlay system. Cem Concr Res2002;32(3):41523.

[10] Zhang J, Huang Z, Li Z, Yan P, Zhang P. Calculation and analyses of temperaturefield in external walls with different thermal insulation models. J Harbin EngUniv 2009;30(12):135665 [in Chinese].

I

0.00 0.04 0.08 0.12 0.16 0.20

l /l

0.00

0.10

0.20

0.30

0.40

0.50

Overallst

raincapacity(%)

=0.01%, = 2%, 1%II I

Fig. 12. Overall strain capacity of ECCconcrete composite bar as a function of ECC

strip length, lI.


Application of ductile fiber

Documents

Transcript of Application of ductile fiber