some characteristics of ﬁbre-reinforced semi-lightweight · semi-lightweight concrete containing...

Magazine of Concrete Research, 2011, 63(1), 1–10

http://dx.doi.org/10.1680/macr.2011.63.1.1

Paper 1000145

Received 11/08/2010; last revised 08/01/2011; accepted 23/03/2011

Published online ahead of print xx/yy/zzzz

Thomas Telford Ltd & 2011

Magazine of Concrete ResearchVolume 63 Issue 1

Some characteristics of fibre-reinforcedsemi-lightweight concrete containingunexpanded perlite both as aggregate andas a supplementary cementing materialOkuyucu, Turanli, Uzal and Tankut

PROOFS

Some characteristics of fibre-reinforced semi-lightweightconcrete containingunexpanded perlite both asaggregate and as asupplementary cementingmaterialDilek OkuyucuPhD student, Middle East Technical University (METU), Ankara, Turkey

Lutfullah TuranliAssociate Professor, Middle East Technical University (METU), Ankara,Turkey

Burak UzalAssistant Professor, Middle East Technical University (METU), Ankara,Turkey

Tugrul TankutProfessor, Middle East Technical University (METU), Ankara, Turkey

Lightweight aggregate concrete is not a new invention of modern concrete technology, but dates back even to

before the Christian era. Natural aggregates like scoria or pumice were utilised in masterpieces such as Babylon of

the Sumerians, Hagia Sopia in Istanbul or the Pantheon of the Romans. The demand for lightweight aggregate

concrete increased over time because of its advantages, specifically properties such as its thermal insulating

properties and low density. It has also become an important structural material in off-shore construction during

recent years. A comprehensive study was carried out in METU Mechanics of Materials Laboratory in order to

investigate some characteristics of fibre-reinforced semi-lightweight concrete for seismic strengthening purposes of

reinforced concrete framed structures. Semi-lightweight concrete containing unexpanded perlite, both as lightweight

aggregate and as a supplementary cementing material, was reinforced by polypropylene and steel fibres, separately.

Compressive strength, split tensile strength and modulus of elasticity measurements were carried out on cylinder

specimens. Steel-mesh-reinforced semi-lightweight concrete plates were also tested as reference specimens for the

toughness test and the results were compared with those for fibre-reinforced semi-lightweight concrete plates.

Cylinder test results indicated a considerable increase in 28-day compressive strength in the case of unexpanded

perlite powder replacement; while providing lower tensile strength and modulus of elasticity. Toughness test results

indicated the superiority of polypropylene fibre-reinforced semi-lightweight concrete for seismic strengthening

purposes in the case of fibre utilisation.

IntroductionFibre-reinforced concrete (FRC) is defined as a concrete consist-

ing of hydraulic cements, water, aggregate and discrete fibres. It

may also contain mineral and/or chemical admixtures for specific

purposes. Steel fibres are commonly used in FRC applications,

although polypropylene, glass and natural fibres are also available

as alternative types. Introducing fibres into concrete mixtures not

only increases their tensile and flexural strength but also enhances

their toughness performance. The high toughness of FRC makes

it an attractive material for the retrofit of existing structures,

especially in applications of seismic strengthening (Mehta and

Monteiro, 2006).

Turkey is located in one of the most seismic zones of the earth.

Recent experiences, such as the 1992 Erzincan and 1999 Kocaeli

earthquakes, showed the vulnerability of existing building stock,

which basically consists of reinforced concrete framed structures.

These structures should be structurally assessed and their inade-

quate seismic performances should be upgraded in order to

survive an expected strong seismic excitation, if required. The

openings of existing vulnerable reinforced concrete frame struc-

tures are traditionally infilled by hollow clay brick infills accord-

ing to architectural needs or for aesthetic reasons. Although these

infill walls are taken into consideration as non-structural mem-

bers, their positive contribution to overall structural behaviour is

Article Number = 1000145

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2

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PROOFS

evident (Benjamin and Williams, 1958; Bertero and Brokken,

1983; Kahn and Hanson, 1979; Smith, 1962).

In recent years, studies in the Middle East Technical University

(METU) structural mechanics laboratory on strengthening of

existing reinforced concrete framed structures have focused on

developing new practical and occupant-friendly methods. With

this perspective, a convenient approach was used to convert non-

structural infill walls into load-bearing structural elements. For

this purpose, the application of carbon-fibre-reinforced polymer

(CFRP) sheets on wall diagonals and the placement of high-

strength (,40–45 MPa) precast concrete panels in the existing

infill walls using a thin layer of epoxy mortar have been identified

as two alternative pre-quake strengthening methods (Baran, 2005;

Duvarci, 2003; Erdem, 2003; Susoy, 2004). Precast concrete

panel application provides a considerable amount (,3 times that

referenced) of seismic performance improvement for reinforced

concrete framed structures by means of seismic performance

indicators such as lateral strength, initial stiffness, total energy

dissipation, etc. (Okuyucu and Tankut, 2009).

Manageable sized, high-strength precast concrete panels rein-

forced by one layer of welded wire steel mesh was used for

precast concrete panel application. Since welded wire steel mesh

causes a number of preparation difficulties, resulting in a time-

consuming production process, the usability of fibres as reinfor-

cing materials was to be investigated by means of assessing

toughness improvement. In the case of seismic strengthening with

precast concrete panels, the concrete mixture must have high

ultimate strength, low unit weight and considerable toughness for

an optimal design and performance of a strengthening scheme.

Therefore, fibre-reinforced lightweight concrete (FRLC) mixtures

should be investigated in terms of strength, unit weight and

toughness to achieve the optimum performance of the precast

concrete panels to be used for strengthening purposes.

In structural lightweight concrete mixtures, use of normal-weight

sand as fine aggregate with lightweight coarse aggregate is a

common practice in order to obtain a proper mixture in terms of

workability and other properties. Although expanded clay and shale

aggregates are commonly used for the production of structural

lightweight concrete, natural lightweight aggregates have been

favoured in recent years because of the high energy consumption

required for the production of expanded type lightweight aggregates

(Mehta and Monteiro, 2006). The published literature contains

many papers on the properties of normal or high-strength fibre-

reinforced lightweight concretes produced with expanded types of

aggregates (Balaguru and Dipsia, 1993; Balendran et al., 2010;

Johnson and Malhotra, 1987; Kayall et al., 2003; Zhang and

Paramasivam, 2004). However, knowledge regarding the perform-

ance of fibre-reinforced lightweight/semi-lightweight concrete mix-

tures consisting entirely of natural lightweight aggregate is limited.

In this study, fibre-reinforced semi-lightweight concrete (FRSLC)

mixtures prepared by using unexpanded perlite (UP) both as

natural aggregate and as a supplementary cementing material

were experimentally evaluated in terms of production of precast

concrete panels for seismic strengthening of existing reinforced

concrete framed structures. Steel fibres (SF) or polypropylene

fibres (PF) were used in the UP aggregate concrete mixtures,

prepared with or without unexpanded perlite powder (UPP)

replacement in order to obtain semi-lightweight mixtures with

unit weights of 1900–2100 kg/m3 in the fresh state. Compressive

strength, splitting tensile strength and modulus of elasticity of the

hardened FRSLC mixtures were determined on cylindrical speci-

mens. Test panels of dimensions 6003 600 3 100 mm were

prepared with the mixtures and the out-of-plane load–deforma-

tion behaviour and flexural toughness performance of FRSLC

panels was also determined. In addition to fibre-reinforced mix-

tures, a reference concrete mixture was also made without fibre

inclusion and it was used to prepare steel-mesh-reinforced con-

crete panels for the purpose of comparison.

Experimental work

Materials

Cement

An ordinary Portland cement (OPC) (CEM I 42.5N according to

EN 197-1) was used in semi-lightweight concrete mixtures and

its chemical composition and physical properties are shown in

Table 1.

Unexpanded perlite aggregate

Unexpanded perlite aggregate (UPA) as a mixture of fine and coarse

particles with maximum aggregate size of 19 mm was used. The

gradation curve and physical properties of the combined (fine and

coarse) aggregate are given in Figure 1 and Table 2, respectively.

Chemical composition OPC

SiO2: % 20.16

Al2O3: % 5.08

Fe2O3: % 3.80

CaO: % 63.32

MgO: % 2.45

SO3: % 3.02

Loss on ignition: % 1.34

Physical properties

Specific gravity 3.11

Blaine fineness: m2/kg 341

Initial setting time: min 150

Final setting time: min 210

Compressive strength: MPa

3 days 26.8

7 days 33.5

28 days 51.1

Table 1. Chemical composition and physical properties of the

Portland cement (PC)

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Some characteristics of fibre-reinforcedsemi-lightweight concrete containingunexpanded perlite both as aggregateand as a supplementary cementingmaterialOkuyucu, Turanli, Uzal and Tankut

PROOFS

Unexpanded perlite powder

Unexpanded perlite material used as aggregate in concrete mix-

tures was also used as a supplementary cementing material after

being crushed and finely ground in a ball-mill so as to have

45 �m passing value of 80%. Chemical composition and physical

properties of UPP are shown in Table 3.

Superplasticiser

A sulfonated naphthalene polymer-based superplasticiser in a

liquid form (BASF Rheobuild 1000) was used in the concrete

mixtures to obtain the desired workability, by adding it into the

mixing water.

Fibres

Properties of steel fibres (SF) and polypropylene fibres (PF) are

given in Table 4. The SF had hooks at both ends, whereas the PF

had a type of regular deformed shape for better bonding, as seen

in Figure 2. SF has the aspect ratio of 54.5 while PF has 55.5;

these values can be reasonably accepted to be equal.

Concrete mixtures

The acronyms and definitions for the six different semi-light-

weight concrete mixtures studied are given in Table 5. Two

mixtures were prepared with and without 35% by mass of UPP

for each type of fibre, namely SF and PF, in addition to two

unreinforced (without fibre) reference mixtures with and without

UPP replacement. The mixtures without fibre were prepared so

that they could be used in the preparation of welded wire steel-

mesh-reinforced concrete panels. The volume content of the

fibres was 1.5% for the fibre-reinforced mixtures. The mix

proportions are given in Table 6.

Specimens and experimental methods

Cylindrical specimens, 100 3 200 mm, were cast to determine

the compressive strength, splitting tensile strength and modulus

of elasticity of the mixtures in accordance with ASTM C 39,

ASTM C 496 and ASTM C 469, respectively. The cylindrical

specimens were removed from the moulds after 24 h and cured in

lime-saturated water until the test ages. Compressive strengths

were determined at age 7 days and 28 days, whereas splitting

tensile strength and modulus of elasticity were tested only at

28 days after casting. These properties were determined as an

average of the results of tests performed on at least three identical

specimens.

In order to investigate the toughness behaviour and energy

absorption of the FRSLC mixtures to be used in production of

precast concrete panels for strengthening of existing vulnerable

reinforced concrete framed structures, test panels of

600 3 600 3 100 mm were cast and tested under centre point

load in a manner similar to that used in the European specifica-

tion for sprayed concrete (EFNARC, 1996). Three panels for each

FRSLC mixture in the experimental programme were cast, as

well as three panels prepared with steel mesh reinforcement

(welded wire steel mesh: diameter, 6.5 mm; mesh spacing,

150 mm, yield strength, 572 MPa, which corresponds to the

requirement of common precast concrete panel application) for

each no-fibre mixture specified in Table 5. Steel-mesh-reinforced

0102030405060708090

100

No.100

No.50

No.30

No16

No.8

No.4

3/8 1/2 3/4

Standard sieves

Pass

ing:

%

Figure 1. Gradation curve of combined UPA

Physical properties*

Bulk specific gravity (SSD) 2.16

Bulk specific gravity (dry) 2.03

24 h water absorption: % by weight 5.9

Los Angeles abrasion: % 67

*Properties were determined in accordance with ASTM standard testmethods.

Table 2. Physical properties of combined UPA

Chemical composition: RPP

SiO2: % 70.96

Al2O3: % 13.40

Fe2O3: % 1.16

CaO: % 1.72

MgO: % 0.28

Na2O: % 3.20

K2O: % 4.65

Loss on ignition: % 3.27

Physical properties:

Specific gravity 2.38

Fineness

Passing 45 �m: % 80

Blaine fineness: m2/kg 413

Median particle size: �m 19.1

Strength activity index (ASTM C 311):

7 days: % 78

28 days: % 80

Table 3. Chemical analysis and physical properties of UPP

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PROOFS

semi-lightweight concrete panels prepared with SLC and SLC-P

mixtures specified in Table 5 were denoted SMRSLC and

SMRSLC-P, respectively. Figure 3 shows a photograph of the

experimental set-up, with plan and section views. The panels

were demoulded after 24 h and cured under wet burlap until the

test age of 28 days. The test panels were simply supported on

four edges by a rigid metallic frame and a centre point load was

applied using a 400 kN universal testing machine through a

contact surface of 100 3 100 mm. The rate of deformation at the

mid-point was approximately 1.5 mm/min.

Deformation measurements were taken by linear variable displa-

cement transducers (LVDTs) with a measurement capacity of

100 mm and precision of 0.01 mm. In total, five LVDTs were

placed on a panel; four of them were positioned at corners to

observe corner movements during loading and the last one was

placed to measure mid-point deflection, as shown in Figure 3.

A load cell of 200 kN compression and 100 kN tension force

measurement capacity with 0.20 kN precision was used to obtain

the digital test data. A data acquisition system with eight

channels was used for data recording of load and mid-point

deflection. Three identical panels were tested for each mixture

and the load–deformation curves were later plotted as an

average of the results of three panels for evaluation of the

results.

Length:

mm

Diameter:

mm

Aspect

ratio

Min. tensile

strength:

MPa

Numerical

density:

number/kg

Steel fibre* 30 0.55 54.5 1100 16 750

Polypropylene

fibrey50 0.90 55.5 — 42 500

* Steel fibre corresponds to the requirements of ASTM A 820 and TS 10513.y Polypropylene fibre corresponds to the requirements of DIN EN ISO 9001, DIN EN ISO14001 and OHSAS 18001

Table 4. Properties of fibres

(a) (b)

Figure 2. Fibres in semi-lightweight concrete: (a) polypropylene

fibre; (b) steel fibre

4



PROOFS

Results and discussions

Mechanical properties of the concrete mixtures

Mechanical properties of the concrete mixtures at various ages

are shown in Table 7. Compressive strength of semi-lightweight

concrete mixtures was not significantly affected by the presence

of fibres, whereas UPP replacement resulted in considerable

increase in 28-day compressive strength of all the mixtures. UPP

replacement decreased 7-day compressive strength owing to a

lower degree of pozzolanic activity at early ages.

Fibre-reinforced semi-lightweight concrete mixtures exhibited

significantly higher splitting-tensile strength when compared to

the plain (no fibre) mixture, since the presence of fibres hinders

the propagation of microcracks, and postpones the inception of

tension cracks. The SFRSLC and PFRSLC mixtures showed 85%

and 40% higher 28-day splitting tensile strength than the SLC

mixture without fibre. It was also observed that UPP replacement

slightly decreased the 28-day splitting-tensile strength of the

mixtures with or without fibre inclusion, unlike its significant

positive effect on 28-day compressive strength. This is a common

occurrence for concrete mixtures containing supplementary

cementing materials and it could be explained by the pore-filling

characteristic of pozzolanic reaction products, which increase

strength in compression when the additional binding products are

formed as a result of pozzolanic reaction, but this phenomenon is

less effective in the tensile stress condition.

Modulus of elasticity of the FRSLC mixtures without UPP

replacement at 28 days was determined as 13.5 GPa and 14.9 GPa

for SF and PF reinforcement, respectively, and similar to that of

the plain mixture (SLC) without fibre, which was 14.0 GPa.

Although UPP replacement considerably increased 28-day com-

pressive strength of the mixtures, modulus of elasticity of the

semi-lightweight concrete mixtures decreased as a result of UPP

replacement, not only for fibre-reinforced mixtures but also for the

mixture without fibre. The reduction in modulus of elasticity in the

case of UPP replacement was more pronounced for the fibre-

reinforced mixtures. The nature of the cement paste matrix and the

nature of the transition zone are two important factors affecting

modulus of elasticity of hardened concrete. It is well known that

partial replacement of Portland cement by supplementary cement-

ing materials results in a decrease in average pore diameter but

causes an increase in total porosity of the hardened pastes when

compared to neat Portland cement systems (Mehta, 1981; Papada-

kis, 1998, 1999). Therefore, reduced modulus of elasticity of the

concrete mixtures in the case of UPP replacement could be

explained by the increased total porosity of the cement paste

matrix. More pronounced reduction in modulus of elasticity of the

concrete mixtures containing fibres in the case of UPP replacement

could be attributed to the factors affecting the transition zone

between the cement paste matrix and the fibres, such as capillary

voids, microcracks and oriented calcium hydroxide crystals, which

Acronym Definition

SLC Semi-lightweight concrete

SLC-P Semi-lightweight concrete with 35% UPP

replacement

SFRSLC Steel-fibre-reinforced semi-lightweight concrete

SFRSLC-P Steel-fibre-reinforced semi-lightweight concrete

with 35% UPP replacement

PFRSLC Polypropylene-fibre-reinforced semi-lightweight

concrete

PFRSLC-P Polypropylene-fibre-reinforced semi-lightweight

concrete with 35% UPP replacement

SMRSLC Steel-mesh-reinforced semi-lightweight concrete

SMRSLC-P Steel-mesh-reinforced semi-lightweight concrete

with 35% UPP replacement

Table 5. Notation and definition of concrete mixtures

Material Mixtures

No fibre Steel fibre Polypropylene fibres

SLC SLC-P SFRSLC SFRSLC-P PFRSLC PFRSLC-P

OPC: kg/m3 500 325 500 325 500 325

UPP: kg/m3 — 175 — 175 — 175

Water: kg/m3 175 175 175 175 175 175

w/cem 0.35 0.35 0.35 0.35 0.35 0.35

UP aggregate: kg/m3 1380 1340 1348 1309 1348 1309

Superplasticiser: kg/m3 5.0 5.0 5.0 5.0 5.0 5.0

Steel fibres: kg/m3 — — 120 120 — —

Polypropylene fibres — — — — 14 14

Table 6. Mixture proportions

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PROOFS

are relatively more common in the transition zone. Introducing the

fibres into the concrete mixtures provides additional transition

zones, which negatively affect the modulus of elasticity of

hardened concrete mixtures.

Flexural toughness of the concrete panels

The load–deflection curves of the panels prepared with FRSLC

mixtures as well as the steel-mesh-reinforced panels were

obtained as an average of the results of three identical panels for

each mixture by using the test set-up shown in Figure 3. Load–

deflection curves together with corresponding energy–deflection

curves obtained by integrating the area under these curves are

shown in Figure 4 and Figure 5 for the concrete mixtures without

and with UPP replacement, respectively. In addition, some data

revealed from the load–deflection and energy–deflection curves,

such as first-peak load and corresponding deflection, ultimate

d3: mm d2: mm

d4: mm d1: mm

d: mm

P: kN

100

100

a

b

b

700

600

500

700

600

500

Load

100 100 100� �

(a–a) or (b–b) view

a

(a)

(b)

Figure 3. Experimental set-up for testing of load–deflection

behaviour of the panels: (a) plan and section views of loading

set-up (dimensions: mm); (b) schematic view and photograph of

loading set-up

6



PROOFS

load as well as energy absorption corresponding to deflection of

25 mm, are summarised in Table 8.

As shown in Figure 4 and Table 8, the SFRSLC panel exhibited

significantly higher first-peak load when compared to PFRSLC

and SMRSLC panels, which showed a similar trend up to first-

peak point. Each panel type behaved completely differently after

the first-peak load, depending on the type of reinforcement. The

SMRSLC panel exhibited a traditionally reinforced concrete

behaviour with considerable increase in load-carrying capacity

after the first-peak load, followed by a fast drop in load–

deflection curve up to a certain level of deflection, and reached

Property Mixtures

No fibre Steel fibre Polypropylene fibres

SLC SLC-P SFRSLC SFRSLC-P PFRSLC PFRSLC-P

Compressive strength: MPa

7-day 35.0 31.5 36.0 26.8 31.9 28.7

28-day 36.4 52.2 37.9 44.7 35.2 52.8

Splitting-tensile strength: MPa

28-day 3.06 2.53 5.67 4.23 4.28 3.85

Modulus of elasticity: GPa

28-day 14.0 10.4 13.5 9.1 14.9 9.2

Table 7. Mechanical properties of the hardened concrete

mixtures

0

10

20

30

40

50

60

0 5 10 15 20 25Deformation: mm

(a)

Load

: kN

PFRSLCSFRSLCSMRSLC

0

200

400

600

800

1000


(b)

Ener

gy a

bsor

ptio

n: J

PFRSLCSFRSLCSMRSLC

Figure 4. (a) Load–deflection and (b) energy–deflection curves for

semi-lightweight concrete mixtures without UPP replacement

0

10

20

30

40

50

60


(a)

Load

: kN

PFRSLC-PSFRSLC-PSMRSLC-P


(b)

0

200

400

600

800

1000

Ener

gy a

bsor

ptio

n: J

PFRSLC-PSFRSLC-PSMRSLC-P

Figure 5. (a) Load–deflection and (b) energy–deflection curves for

semi-lightweight concrete mixtures with UPP replacement

7



PROOFS

its ultimate load capacity. The behaviour of the PFRSLC panel

after the first-peak load was similar to the SMRSLC panel in a

manner of slight increase after a fast drop, whereas the SFRSLC

panel exhibited a relatively slow and continuous decrease in load-

carrying capacity, providing more ductility. This behavioural

difference between the load–deflection curves of steel fibre and

polypropylene FRC panels could be the result of a combination

of differences in their shape and their texture. Total energy

absorption of the SMRSLC panel up to 25 mm of deflection, that

is the area under the load–deflection curve, was approximately

1.5 times higher than the results for fibre-reinforced panels,

because considerable hardening occurred in the case of steel

mesh reinforcement. On the other hand, the SFRSLC panel, when

compared to the PFRSLC panel, absorbed somewhat higher

energy for small deflections; however, the energy absorbed by the

PFRSLC panel reached the value absorbed by SFRSLC panel at

25 mm of deflection owing to the stable load-carrying capacity of

the PFRSLC panel after the first peak. SFRSLC and PFRSLC test

panel examples are provided in Figure 6.

Partial replacement (35% by mass) of Portland cement by UPP

did not change the general load–deflection behaviour of the

semi-lightweight concrete panels (Figure 5). However, the first-

peak load decreased for all types of panels in the case UPP

replacement, whereas the total energy absorbed corresponding to

25 mm deflection reduced for the fibre-reinforced panels, but

slightly increased for the steel-mesh-reinforced panel (Figure 5

and Table 8). The decreases in the first-peak load of the panels,

when 35% of Portland cement was replaced by UPP, could be

associated with reduced tensile strength of the concrete mixtures

(Table 7). UPP replacement resulted in 24% and 17% decreases

in energy absorption for 25 mm deflection for SFRSLC and

PFRSLC panels, respectively. This negative effect of UPP re-

placement on toughness of the fibre-reinforced panels is probably

related to the reduced tensile strength capacity of the cement

paste matrix, which is also unfavourable in terms of bond

strength of fibres. SFRSLC-P and PFRSLC-P test panel examples

are provided in Figure 7.

Consequently, PFRSLC panels were found to be favourable when

compared to SFRSLC panels, since the PFRSLC panels showed a

more pronounced toughening behaviour after first cracking and

thus absorbed somewhat higher energy up to 25 mm of deflection.

In addition, polypropylene fibres are preferable in comparison

Type of

reinforcement

Mixture First-peak load:

kN

Deflection at the first-

peak load:

mm

Ultimate load:

kN

Energy absorption for

a 25 mm central

deflection: J

Steel fibre SFRSLC 43.1 0.9 43.1 539

SFRSLC-P 29.5 0.5 29.5 411

Polypropylene PFRSLC 33.5 0.5 33.5 571

fibre PFRSLC-P 28.0 0.4 28.0 473

Steel mesh SMRSLC 30.6 0.4 49.9 835

SMRSLC-P 24.6 0.5 47.3 860

Table 8. Summary data revealed from load–deflection and

energy–deflection curves

(a)

(b)

Figure 6. Panel specimen views after test: (a) SFRSLC panel

specimen; (b) PFRSLC panel specimen

8



PROOFS

with steel fibres, which are susceptible to corrosion phenomena.

On the other hand, 35% replacement of Portland cement by UPP

was found to be efficient in terms of 28-day compressive strength,

but a small reduction in toughness was observed for FRC

mixtures in the case of UPP replacement. It is well known that

the use of supplementary cementing materials as a partial re-

placement for Portland cement provides many benefits to the

properties of fresh and hardened concrete, such as improvement

in workability, reduction in the heat of hydration, low permeabil-

ity, high ultimate strength and control of alkali–silica expansion,

as well as cost saving and environmental benefits. Considering

these benefits, FRSLC panels produced with a concrete mixture

containing UPP replacement seem to be favourable, despite the

small reduction in toughness.

Concluding remarksAn experimental research programme was carried out in METU

materials of construction laboratory in order to evaluate some

characteristics of FRSLC containing unexpanded perlite both as

aggregate and as a supplementary cementing material. The

environmentally friendly material mixes are basically targeted for

use in structural seismic performance improvement of reinforced

concrete framed structures by way of high-strength precast

concrete panel application. Mechanical characteristics of the

semi-lightweight concrete mixes were evaluated as a feasibility

study for providing an alternative reinforcement and relatively

lighter material to use precast in concrete panel production. The

following concluding remarks can be made from the research.

(a) UPP replacement resulted in a considerable increase in 28-

day compressive strength of semi-lightweight concrete

mixtures when compared with that of the reference concrete

mix, which had no replacement of ordinary Portland cement.

(b) UPP replacement provided lower tensile strength and

modulus of elasticity when compared with that of the

reference concrete mix without UPP replacement.

(c) UPP replacement also affected flexural toughness behaviour

of the panels by decreasing load and energy dissipation

capacities. This effect is more pronounced in the case of steel

fibre reinforcement. Therefore, for precast concrete panel

application, polypropylene FRSLC mixtures may be

preferred.

(d ) In cases where steel mesh is preferred as reinforcing material

for precast panels, semi-lightweight concrete mixtures with

and without UPP replacement can be taken into

consideration, since their splitting tensile strength did not

vary a lot. However, the considerable difference of

compressive strength values should be taken into

consideration.

(e) A considerable increase in compressive strength values from

7 days to 28 days was observed in the study. The study

included the 7-day compressive strength value so as to

provide early compressive strength information and the

compressive strength, modulus of elasticity and splitting

tensile strength values for 28 days, which are widely used as

design strength values for concrete structures. The common

tendency in concrete mixes with mineral admixtures is to

observe continuity of strength increase in the later ages.

Therefore, it is recommended to perform studies that cover

90-day and 360-day strength value evaluations for these kinds

of concrete mixes.

( f ) It should be finally concluded that this research is a view

from the perspective of the materials characteristics of the

envisaged panel concrete mixes, which has provided some

reasonable suggestions from the comprehensive

experimentation. Reinforced concrete frame tests are required

in order to discover the exact contribution of the precast

concrete panels produced by semi-lightweight concrete with

the suggested polypropylene fibres on overall seismic

performance improvement of the evaluated structural system.

Such tests would enable a reasonable comparison to be made

between the contributions of steel mesh and the suggested

polypropylene-fibre-reinforced panels to the seismic structural

(a)

(b)

Figure 7. Panel specimen views after test: (a) SFRSLC-P panel

specimen; (b) PFRSLC-P panel specimen

9



PROOFS

upgrading of reinforced concrete framed structures by precast

concrete panel application.

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1: Very long title – does not fit allocated space in running heads.Please shorten if possible.2: Please check that all author names/order/job title and affiliationaddresses are correct and complete3: Balendran et al - please check date, cited here as 2010, listed in refsas 2002. Also Johnson and Malhotra cited in text, Johnston andMalhotra listed in refs, please check spelling4: Zhang and Paramasivam, 2004 not in the reference list or spelling/year doesn’t match, please check.5: Would it be helpful to add full references to these ASTM standards?6: Papadakis - cited as 1998 here, but 1999 in refs list. Please checkyear7: Balendran et al. - please give names of all authors (if up to 5 authorslisted) or names of first three authors plus ’et al.’ if 6 or more authorslisted8: Please give page numbers/range9: Please give issue no.10: Papadakis - Please give issue no. if possible. Also should this be1998, as cited in text? If both Papadakis refs are 1999, then pleasedistinguish between them using ’1999a’ and ’1999b’11: Please give issue no. if possible

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