Journal of Engineering Sciences, Assiut University, Vol. 39, No 5, pp.

1005-1019, September 2011

MECHANICAL PROPERTIES OF CONCRETE CONTAINING

RECYCLED CONCRETE AGGREGATES SUBJECTED TO
DIFFERENT FIRE DURATIONS
Associate Prof., Walid Safwat Fahmy,
Faculty of petroleum Engineering and Mining, Suez Canal University,
Suez, EGYPT. Email :Walid.Fahmy@gmail.com
Lecture, Erfan Abdel-Latif Heneidy,
Civil Engineering Dept., Faculty of Engineering, Suez Canal University,
Ismailia, EGYPT.
Lecture, Esraa Emam Ali,
Material Dept., Housing and Building National Research Center-Dokki-
Cairo, EGYPT.
Ibrahim Saad Mohammed Agwa,
Civil Structures Dept., Faculty of Industrial Education, Suez Canal Univ.,
Suez, EGYPT.
(Received July 4, 2011 Accepted August 7, 2011)
The amount of construction and demolition waste has increased
considerably over the last few years. Crushing concrete to produce
coarse aggregate for the production of new concrete is one common
means for achieving a more environment-friendly concrete. This
experimental study demonstrates the mechanical properties of concrete
containing recycled concrete aggregate (RCA) subjected to different fire
durations. In the experimental work, the fresh concrete properties (slump
test) and the hardened concrete properties, (compressive strength,
splitting tensile strength, flexural strength and modulus of elasticity)
were carried out. A total of thirty concrete mixes with different cement
contents (300, 350, and 400 Kg/m3) at w/c ratio (0.5) were made and the
percentage of substitution of natural concrete coarse aggregate by the
recycled concrete coarse aggregate subjected to fire durations (1,2 and 3
hours) at fire temperature (600ºC) was (0%, 25%, 50% and 100%). In
the process of mixing, equal consistence among all concrete mixes was
achieved. The obtained results indicate that the recycled coarse
aggregate subjected to fire can successfully be used for making
structural concrete.
KEYWORDS: Recycled concrete aggregate, fire duration,
Compressive strength. Tensile strength, Flexural strength and Modulus
of elasticity

1. INTRODUCTION
Shortage of natural aggregate in urban environments and increasing distance between
the sources of quality natural aggregate and construction sites compelled the
constructors to consider substituting the natural aggregate by recycled material
(construction ceramics, slag, concrete). On the other hand, large quantities of old
1005
1006 Walid Safwat Fahm et al.

concrete often occur in urban environments, whose removal and disposal presents an
environmental problem. Many authors from different countries study this point.
Solomon et al, [1] Marked an aggregate which is brought from demolished masonry
and concrete structures as potentially good for use in new concrete. Scope of usage of
recycled materials is determined by their quality. In general, the quality of recycled
aggregate depends on the quality of the original concrete it was obtained from, so prior
to the design of mixture; aggregates must be examined in detail. Tabsh and Abdelfatah,
[2] Conclude that the percentage loss in compressive or tensile strength due to the use
of recycled aggregate is more significant in a weak concrete than in stronger one. The
use of coarse aggregate made from recycled concrete with strength equal to 50 MPa
will result in concrete compressive and tensile strengths comparable with that achieved
when using natural coarse aggregate. Recycled concrete mixes require more water than
conventional concrete to maintain the same slump without the use of admixtures,
regarding that it is a relatively new material [3].
Concrete is a composite material consisting of aggregates and matrix as its
basic components. The effect of heating on both these components individually as well
as their interaction control the behavior of concrete at high temperatures. Purkiss, [4]
Concrete is a porous material with its pores filled with water and air. Surface heating of
the concrete at elevated temperatures during fire not only results in deterioration of its
properties like elastic modulus, tensile and compressive strength, but also in moisture
migration in the presence of liquid water, heat evolved from fire to the concrete, causes
the evaporation of liquid water. With the rise in temperature, the aggregate expands,
the expansion of the matrix, on the other hand, is substantially offset of sometimes
completely negated by shrinkage due to the evaporation of water. The resultant
expansion differential causes internal cracking in the concrete and reduction in its
stiffness. The extent of this phenomenon differs considerably with the type of
aggregate and is most pronounced in the case of concrete with siliceous aggregate
which at very high temperatures (575 ºC or above) also undergoes physical changes
accompanied by a sudden expansion in volume, thus sometimes causing aggregate
splitting and / or spalling. Concrete is a poor conductor of heat, but can suffer
considerable damage when exposed to fire. Unraveling the heating history of concrete
is important to forensic research or to determine whether a fire-exposed concrete
structure and its components are still structurally sound, [5]. At temperatures of 70–80
°C ettringite dissociates and at about 100 °C the water physically bound in both the
aggregates and the cement matrix starts to evaporate, increasing capillary porosity and
microcracking at these relatively low temperatures, concrete may only experience a
minor loss of strength. At temperatures ranging from 250 to 300 °C the loss of bound
water in the cement matrix becomes more prominent a significant loss of strength is
often observed. Up to 600 °C, most aggregates undergo thermal expansion and the
consequent internal stresses give rise to extensive cracking at 600 °C the mechanical
performance of concrete is already severely affected. From 600 to 800 °C, carbonates
suffer decarbonation for calcareous aggregates, a considerable contraction may occur
(due to the release of carbon dioxide) causing severe microcracking of the cement
matrix. Finally, from 800 to 1200 °C, calcareous constituents suffer complete
disintegration concrete becomes a calcinated material [6]. Producing concrete with
recycled aggregate subjected to fire has still been inadequately researched field. So the
effect of using aggregate obtained from demolished concrete has been studied
 MECHANICAL PROPERTIES OF CONCRETE CONTAINING … 1007
previously in several researchers, while in the current study the recycled aggregate
resulting from concrete subjected to fire will be used and its effect on the properties of
concrete will be studied.

2. EXPERIMENTAL PROGRAM
2.1 Materials
2.1.1Cement
The cement used in this investigation was CEM I 42.5 N. Testing of cement was
carried out as per the Egyptian Standard Specifications ESS 2421/2005 [7]. Mechanical
and physical properties and the chemical analysis of the used cement are given in
Tables (1) and (2) respectively.

Table (1): Mechanical and Physical Properties of Cement

Specifications
Property Results
Limits*
2 days 21.4 Not less than 10
Compressive Strength of Standard Not less than 42.50
Mortar (MPa) 28 days 47.7
Not more than 62.5
Soundness (La Chatelier) (mm) 1 Not more than 10
Initial 135 Not less than 60
Setting Time (min)
Final 180 ----------
*Limits of ESS 4756-1 / 2007 [7]
Table (2): Chemical Properties of Cement

Property Results
Silicon Oxide SiO2 21.0
Aluminum Oxide Al2O3 6.10
Ferric Oxide Fe2O3 3.00
Calcium Oxide CaO 61.5
Magnesium Oxide MgO 3.8
Sulfur Oxide SO3 2.5
Sodium Oxide Na 2O 0.4
Potassium Oxide K2O 0.3
Loss on Ignition (L.O.I) 1.6
Insoluble Residue 0.9

2.1.2 Fine Aggregates

Natural sand composed of siliceous materials was used as Fine Aggregate (FA) in this
study. Testing of sand was carried out according to the ESS 1109/2002 [8]. Table (3)
shows the physical properties of the sand.
1008 Walid Safwat Fahm et al.

Table (3): Physical Properties of Fine Aggregate

Property Results Limits*

Specific Weight 2.63 -----

Bulk Density (t/m3) 1.78 -----

Clay and Fine Dust Content (% By Volume) 1.4 Not more Than 3
*Limits of ESS 1109 /2002 [8]

2.1.3 Coarse aggregates

2.1.3.1 Natural coarse aggregates
Natural crushed stone (dolomite) was used in this study. Testing of natural coarse
aggregate (NCA) was carried out according to the ESS 1109/2002 [8]. Mechanical and
physical properties of the NCA comply with both ESS 1109/2002 [8] and the Egyptian
Code ECCS203-2007 [9]. Table (4) shows the physical and mechanical properties of
the Natural crushed stone (dolomite).

Table (4): Physical and Mechanical Properties of Natural Coarse

Aggregate
Property Results Limits
Specific Weight 2.61 -----
Bulk Density (t/m3) 1.56 -----
Water Absorption % 2.05 Not more than 2.5**
Clay and Fine Dust Content 2.4 Not more than 4*
%
Flakiness Index % 36.8 Not more than 40*
Elongation Index % 9.6 Not more than 25**
Abrasion Index % 17.8 Not more than 30*
Impact Value % 12.60 Not more than 45*
*Limits of ESS 1109/2002 [8]
**Limits of ECCS203-2007 [9]

2.1.3.2 Fired Recycled coarse aggregates

The recycled coarse aggregate used in this study were produced by crushing the
concrete elements subjected to fire. Jaw crusher type (BB300) was used to gash the
fined elements into wise recycled aggregate with fraction size 10 mm.
Testing of (RCA) was carried out according to the ESS 1109/2002 [8]. The
physical and mechanical properties of the RCA are shown in Table (5).
 MECHANICAL PROPERTIES OF CONCRETE CONTAINING … 1009
Table (5): Physical and Mechanical Properties of Recycled Coarse
Aggregates
Results
Property 600°C - 600°C - 600°C - Limits
1hr 2hrs 3hrs
Specific Weight 2.18 2.20 2.15 -----
Bulk Density (t/m3) 1.25 1.51 1.31 -----
Water Absorption % 4.95 6.65 7.65 Not more than 2.5**
Clay and Fine Dust
7 10 13 Not more than 4*
Content %
*Limits of ESS 1109/2002 [8]

2.1.4 Mixing water

Drinking water was used for mixing.

2.1.5 Superplasticizer
In this study, In order to obtain same workability without increased water, super
plasticizer admixture ADDICRETE BV was used. ADDICRETE BV is a
superplasticizer and flowing concrete admixture. (Complies with ASTM C 494 – 80
type A, DIN 10045, BS 5075PART1). Following properties, base material was lingo
sulphonates, density was 1.18± 0.01/1 at 25°C and it was combatable with types of
Portland cement.

2.2 Test setup of fire furnace and the Jaw crusher type BB300
The fire furnace was designed for the purposes of fire; the fire furnace system consists
of three main components the fire chamber the fire lighter, and temperature control
system as shown in Figure (1).The crusher used in this study was jaw crusher (type
BB300) was shown in Figure (2).

2.3 Concrete mixes

The concrete mixes were prepared in the laboratory of Housing and Building National
Research Center. A total of thirty concrete mixtures were made with different cement
contents (300,350, and 400 kg/m3) at w/c = (0.5), the superplasticizer dosage varied
from 0.6% to 2.9% of cement content to achieve the required level of workability
defined by a slump value of 10± 2cm. The percentage of substitution of natural
concrete coarse aggregate by the recycled concrete coarse aggregate subjected to fire
temperature 600°C for fire durations (1, 2, and 3hours) was (0%, 25%, 50% and
100%). Control mixes made with the natural aggregate, and the other concrete mixes
were made using a recycled concrete aggregates subjected to fire, the ratio of fine to
coarse aggregate was about 1:2 .Composition of designed mixtures has been shown in
Table (6).
1010 Walid Safwat Fahm et al.

Fig (1) Test setup of fire furnace Fig (2) Jaw crusher BB300

Table (6): Concrete Mixes Proportions at Fire Temperature 600°C for Fire
Durations (1, 2, and 3 Hours)
SP
Mix NO. Designation W C FA NCA FRCA
1hr 2hrs 3hrs
Control M1 (M-0% -300 ) 150 1 1 1 300 659 1317 -
M2 (M-25%-300 ) 150 1.15 1.2 1.3 300 638 957 319
G1 (1,2
and 3 hrs) M3 (M-50%-300 ) 150 1.7 1.9 1.95 300 618 618 618
9 mixes
M4 (M-100%-300 ) 150 2.6 2.8 2.9 300 582 - 1164
Control M5 (M-0%-350 ) 175 0.8 0.8 0.8 350 623 1246 -
M6 (M-25%-350 ) 175 1 1.1 1.2 350 604 906 302
G2 (1,2
and 3 hrs) M7 (M-50%-350 ) 175 1.35 1.45 1.6 350 585 585 585
9 mixes
M8 (M-100%-350 ) 175 2.3 2.45 2.55 350 550 - 1100
Control M9 (M-0% - 400 ) 200 0.6 0.6 0.6 400 588 1176 -
M10 (M-25%-400 ) 200 0.9 1 1.1 400 569 854 285
G3 (1,2
and 3 hrs) M11 (M-50%-400 ) 200 1.25 1.3 1.45 400 551 551 551
9 mixes
M12 (M-100%-400) 200 1.7 1.9 2 400 519 - 1038
3
W= Water (Litre/m )
SP%; Superplasticizer percentage of cement content
C (kg/m3) = Cement content
FA (kg/m3) = Fine aggregates (sand)
NCA (kg/m3) = Natural coarse aggregates
FRCA (kg/m3) = Fired Recycled coarse aggregates
 MECHANICAL PROPERTIES OF CONCRETE CONTAINING … 1011
2.4 Concrete Tests
All the concrete mixes were mixed in the laboratory of Housing and Building National
Research Center (HBRC). The slump test was conducted on fresh concrete to
determine the slump value. For each concrete mix, six 150*150*150 mm cubes were
cast for the determination of compressive strength at 7 and 28 days. Three 150 mm *
300 mm cylinders were cast for the determination of indirect tensile strength at 28
days. Three beams of dimensions 100 * 100 * 500 mm were cast for the determination
of flexural strength at 28days. Two 150 mm * 300 mm cylinders were cast for the
determination of static modulus of elasticity at 28 days. After casting, all the cast
specimens were covered by plastic sheets and water saturated burlap and left in the
laboratory at 20 ± 3 °c for 24 h. the specimens were then demoulded and transferred to
a saturated water curing tank at 25°c until the age of testing.

3. RESULTS AND DISCUSSION

3.1 Properties of Fired Recycled Coarse Aggregate
Water absorption
The water absorption of fired recycled coarse aggregates is much higher than that of
the natural coarse aggregates due to the large amounts of old mortar and cement paste
attached to fired recycled coarse aggregates and dehydration. The water absorption of
fired recycled coarse aggregates is ranged from 4.95% to 7.65%.
Specific gravity
The large amount of old mortar and cement paste adhering to fired recycled coarse
aggregates, their specific gravity will be 15% to 17% lower than that of the natural
coarse aggregates. The specific gravity of fired recycled coarse aggregates is ranged
from 2.15 to 2.20.
Bulk Density
The bulk density of fired recycled coarse aggregates obtained from fired concrete at
600°C temperature for fire durations (1, 2, and 3 hours) are 19%, 3% and 16%
respectively lower than that of natural coarse aggregate.
3.2 Fresh concrete properties
The dosage of superplasticizer added to different concrete mixes to maintain a constant
slump of 10 ± 2 cm was shown in figure (3).
Figure (3) shows the comparison between concrete groups (600°C - 1hr, 600°C
-2hrs, and 600°C -3hrs), it can be noticed that the dosage of superplasticizer was
increased significantly by increasing the percentage of replacement of FRCA and fire
duration.
In general, recycled concrete needed more superplasticizer dose than the
control concrete (without recycled materials) regardless of fire duration, and this agree
with D. M. Sadek [10] who found that the recycled concrete needed more
superplasticizer dosage than the control concrete (without recycled materials)
regardless of w/c ratio or type of recycled materials.
1012 Walid Safwat Fahm et al.

3.5 0% RCA

Superplasticizer Dose (% of cement Content)

25% RCA
3
50% RCA
2.5 100% RCA

1.5

0.5

0
300 C.C 350 C.C 400 C.C 300 C.C 350 C.C 400 C.C 300 C.C 350 C.C 400 C.C

600Co at 1hr 600Co at 2hrs 600Co at 3hrs

Concrete mixes

Fig (3): Superplasticizer Dosage for Concrete Mixes

3.2 Hardened concrete properties Compressive strength

The compressive strength results at 7 and 28 days of concrete mixtures subjected to fire
temperature 600°C for fire durations (1, 2, and 3 hours) were presented in Table (7).
It was observed that the compressive strength of concrete mixtures with
percentage of replacement ratios of FRCA (0% , 25% ,50 % and 100%)were increased
by (26%,35%,25% and 30 %) , (28%,31%,22%and 20%) and (34%, 36%, 29 and 25%)
at cement contents 300,350 and 400 kg/m3 from 7 to 28 days, respectively, at fire
duration 1hour.
Figure (4-a) shows the concrete mixtures subjected to fire temperature 600°C
for 1hour, it can be noticed that at replacement ratio 25% FRCA, there is a slight
increase in the compressive strength by (2% and 1%) at cement contents of (300 and
350kg/m3) respectively, the compressive strength at cement content 400kg/m3
decreased by 1% comparing to control mixtures at 28 days. This agree with Etxeberria
et al, [11].Who found that the results up to 25% RCA has no major effect on
compressive strength, and also with F.A. El-Latif, [12].Who reported that there is an
increase in the compressive strength at replacement ratio 25% by (4% and 2%) for
cement contents (350 and 400kg/m3) respectively, comparing to control mixtures at 28
days. (Notice that the RCA used in the previous studies was not exposed to fire). While
at replacement ratios (50% and 100%) FRCA, there is a reduction in the compressive
strength by (10% and 17%), (13% and 21%) and (13% and 20%) at cement contents
300,350 and 400kg/m3 respectively, comparing to control mixtures at 28 days. This
may be attributed to the weak bond between the fresh mortar and the old mortar
adhering to the fired recycled coarse aggregates in addition to the low resistance of the
fired recycled coarse aggregates to the mechanical action compared with the natural
aggregates.
Figure (4-b) shows the concrete mixtures subjected to fire temperature 600°C
for 2hours, it can be demonstrated that at replacement ratio 25%FRCA, there is a slight
decrease in the compressive strength of concrete by 3% at cement contents (300 and
350 kg/m3), while the compressive strength decreased by 4% at cement content 400
 MECHANICAL PROPERTIES OF CONCRETE CONTAINING … 1013
kg/m3. At replacement ratios (50% and 100%) FRCA, there is a reduction in the
compressive strength by (18% and 24%), (19% and 30%) and (18% and 28%) at
cement contents 300,350 and 400 kg/m3 respectively, comparing with control mixes.
Also, figure (4-c) shows the concrete mixtures subjected to fire temperature
600°C for 3hours, it can be noticed that as fire temperature and fire duration increased
there is a significant disintegration of the calcium silicate hydrate as well as partial
disintegration occurs in the aggregate. Where at replacement ratio 25%FRCA, there is
a reduction in the compressive strength of concrete by 7% at cement contents (300 and
350 kg/m3) and decreased by 10% at cement content 400 kg/m3, while at replacement
ratios (50% and 100%) FRCA, there is a reduction in the compressive strength by
(20% and 34%), (23% and 34%) and (23% and 36%) at cement contents 300,350 and
400kg/m3, respectively, comparing with control concrete. So as the fire duration
increase the cohesion between the cement matrix and aggregate is starting to release,
leads to the predominance of microcracks where the space between the cement matrix
and aggregate increased intermingled with voids due to increase in porosity, the
dehydration of calcium hydroxide is take place Ca(OH)2, and C-S-H gel. So we can
concluded that as the duration of recycled concrete aggregate exposed to fire increased
the loss in compressive strength increased at different cement contents and different
percentage of replacements.

Table (7) Compressive Strength of Concrete Mixtures at Fire Temperature

600°C for Fire Durations (1, 2, and 3 Hours) at 7 and 28 days
Compressive strength at 7 Compressive strength at
days (N/mm2) 28 days (N/mm2)
Group Designation
1-hr 2-hrs 3-hrs 1-hr 2-hrs 3-hrs

M1(M-0%-300) 22.9 22.9 22.9 28.95 28.95 28.95

M2(M-25%-300) 21.8 20.05 19.5 29.45 28 27

G1
M3(M-50%-300) 20.90 19.05 17.15 26.15 23.95 23

M4(M-100%-300) 18.4 16.5 14.65 24 22.05 19.5

M5(M-0%-350) 25.55 25.55 25.55 32.8 32.8 32.8

M6(M-25%-350) 24.5 22.05 22 32.15 31.7 30.6

G2
M7(M-50%-350) 23.3 20.90 19.2 28.5 26.5 25.5

M8(M-100%-350) 21.6 19.15 17.45 26 23 21.5

M9(M-0%-400) 28 28 28 37.75 37.75 37.75

M10(M-25%-400) 27.7 23.1 23.5 37.9 36.4 33.9

G3
M11(M-50%-400) 25.4 22.65 20.45 33 31 29

M12(M-100%-400) 24.1 21.35 19.2 30.2 27.2 24.1

 1014 Walid Safwat Fahm et al.

(M-%–C-G)
Where
M, refers to mix
% refers to fire recycled coarse aggregates
C, refers to cement content (kg/m3)
G, refers to group number
40 40 40

35 35 35

Compressive Strength (N/mm )

Compressive Strength (N/mm )

2
Compressive Strength (N/mm )

2
2

30 30 30

25 25 25

20 20 20
CC=300Kg/m3 CC=300Kg/m3
15 15 CC=350Kg/m3 15 CC=300Kg/m3
CC=350Kg/m3
CC=350Kg/m3
CC=400Kg/m3 CC=400Kg/m3 10
10 10
CC=400Kg/m3

5 5 5

0 0
0
0 25 50 75 100 125 0 25 50 75 100 125 0 25 50 75 100 125
Percentage of Replac ement of Recycled Concrete Percentage of Replacement of Recycled Concrete Percentage of Replacement of Recycled Concrete
Aggregate Aggregate Aggregate

a- Duration – 1hr b- Duration – 2hrs c- Duration – 3 hrs

Fig. (4) Relationship between Compressive Strength and Percentage of Replacement of
(RCA) for Different Cement Contents at Fire Temperature 600°C at 28 Days

Tensile Strength
It can be noticed from Fig (5-a) that at replacement ratio 25%FRCA, there is decrease
in the tensile strength by ( 5%, 4%and 2%) at cement contents (300,350 and 400kg/m3)
when subjecting to fire temperature 600°C for fire duration 1 hour respectively,
comparing to control mixtures . While at replacement ratios (50% and 100%) FRCA,
there is a reduction in the tensile strength by (14% and 22%), (12% and 23%) and
(12% and 21%) at cement contents 300,350 and 400 kg/m3respectively, comparing to
control mixtures.
It can be noticed from Fig (5-b) that at replacement ratio 25% FRCA, there is
decrease in the tensile strength by ( 7%,5% and 5%) at cement contents (300,350 and
400kg/m3) when subjecting to fire temperature 600°C for 2 hours respectively,
comparing to control mixtures. While at replacement ratios (50% and 100%) FRCA,
there is a reduction in the tensile strength by (17% and 27%), (15% and 25%) and
(15% and 26%) at cement contents 300,350 and 400 kg/m3 respectively, comparing to
control mixtures.
Also, it can be noticed from Fig (5-c) that at replacement ratio 25% FRCA,
there is high decrease in the tensile strength by ( 10%,10% and 7%) at cement contents
(300,350 and 400kg/m3)when subjecting to fire temperature 600°C for 3 hours
respectively, comparing to control mixtures. While at replacement ratios (50% and
100%) FRCA, there is a reduction in the tensile strength by (19% and 30%), (17% and
29%) and (19% and 31%) at cement contents 300,350 and 400 kg/m3 respectively,
 MECHANICAL PROPERTIES OF CONCRETE CONTAINING … 1015
comparing to control mixtures. This agree with Hansen [13] Who stated that the full
replacement of RCA, the tensile strength of recycled aggregate concretes produced
with both fine and coarse aggregate to be reduced by 35%. (Notice that that the RCA
used in the previous studies was not exposed to fire).
4 4
4

3.5 3.5
3.5

3 3
3
Tensile Strength (N/mm 2)

Tensile Strength (N/mm )

2
Tensile Strength (N/mm )
2
2.5 2.5
2.5

2 2
2

C C = 300Kg /m3
1.5 1.5 1.5
C C = 300Kg /m3 CC=300Kg/m3
C C = 350Kg /m3
1 C C = 350Kg /m3 1
1 CC=350Kg/m3
C C = 400Kg /m3
C C = 400Kg /m3
0.5 0.5 0.5 CC=400Kg/m3

0 0 0
0 25 50 75 100 125 0 25 50 75 100 125 0 25 50 75 100 125
Percentag e of R eplacement of R ecycled C oncrete P erc entage of Repl ac em ent of Rec yc l ed Conc rete Perc entage of Replacem ent of Recycled Conc rete
Ag g reg ate A ggregate Aggregate

a- Duration – 1hr b- Duration – 2hrs c- Duration – 3 hrs

Fig. (5) Relationship between Tensile Strength and Percentage of Replacement of
(RCA) for Different Cement Contents at Fire Temperature 600°C at 28 Days

Flexural strength
Figure (6-a) shows the concrete mixtures subjected to fire temperature 600°C for
1hour, it can be noticed that at replacement ratio 25%FRCA, there is a slight increase
in the flexural strength by 1% at cement content 300 kg/m3 and decreased by (1% and
6%) at cement contents (350 and 400kg/m3) respectively, comparing to control
mixtures, while at replacement ratios (50% and 100%) FRCA, there is a reduction in
the flexural strength by (13% and 27%), (18% and 27%) and (14% and 25%) at cement
contents 300,350 and 400kg/m3respectively, comparing with control concrete. This
agree with A. Rao et al, [14] Who stated in his literature that the full replacement of
RCA, the flexural strength produced with both fine and coarse aggregate reduced by 26
%.( Notice that the RCA used in the previous studies was not exposed to fire).
Figure (6-b) shows the concrete mixtures subjected to fire temperature 600°C
for 2hours, It can be noticed that at replacement ratio 25%FRCA, there is a decrease in
the flexural strength by (5%, 4% and 9%) at cement contents (300,350 and 400 kg/m3)
respectively, comparing to control mixtures, while at replacement ratios (50% and
100%) FRCA, there is a reduction in the flexural strength by (18% and 30%), (20%
and 31%) and (18% and 30%) at cement contents 300,350 and 400kg/m3 respectively,
comparing with control concrete.
Also, figure (6-c) shows the concrete mixtures subjected to fire temperature
600°C for 3hours, It can be noticed that replacement ratio 25%FRCA, there is decrease
in the flexural strength by (6%, 8% and 5%) at cement contents (300,350 and
400kg/m3) respectively, comparing to control mixtures, while at replacement ratios
(50% and 100%) FRCA there is a reduction in the flexural strength by (24% and 36%),
(22% and 34%) and (24% and 37%) at cement contents 300,350 and 400 kg/m3
respectively, comparing with control concrete.
1016 Walid Safwat Fahm et al.

8 8 8

7 7 7

Flexural Strength (N/mm 2 )

Flexural Strength (N/mm 2 )

Flexural Strength (N/mm 2)

6 6
6
5 5 5
4
4 4
3
CC= 300Kg /m3 3 CC=300Kg/m3 3
CC=300Kg/m3
2 CC= 350Kg /m3 CC=350Kg/m3
2 2 CC=350Kg/m3
CC= 400Kg /m3 CC=400Kg/m3 CC=400Kg/m3
1 1
1
0
0
0 25 50 75 100 125 0
Percentag e of Replacement of Recycled C oncrete 0 25 50 75 100 125
0 25 50 75 100 125
Ag g reg ate Percentage of Replacement of Recycled Concrete
Percentage of Replacement of Recycled Concrete
Aggregate
Aggregate

a- Duration – 1hr b- Duration – 2hrs c- Duration – 3 hrs

Fig. (6) Relationship between Flexural Strength and Percentage of Replacement of
(RCA) for Different Cement Contents at Fire Temperature 600°C at 28 Days

Modulus of Elasticity
Figure (7-a) shows the concrete mixtures subjected to fire temperature 600°C for
1hour, It can be noticed that at replacement ratio 25%FRCA, there is a reduction in the
modulus of elasticity by (14%, 12% and 14%) at cement contents (300,350and
400kg/m3) respectively, comparing to control mixtures, while at replacement ratios
(50% and 100%) FRCA, there is a reduction in modulus of elasticity by (21% and
39%), (22% and 41%) and (20% and 40%) at cement contents 300,350 and
400kg/m3respectively, comparing to control mixtures. This may be attributed the
presence of more micro cracks and weaker interfaces in recycled aggregate concretes.
In addition to large amount of old mortar which is attached to original aggregate
particles in recycled aggregates. This agree with Juan and Gutiérrez, [15] Who found
out that the elasticity modulus is one of the most affected properties of recycled
concretes, for percentages of RCA 20%, 50% and 100% the values of modulus of
elasticity were 10%, 20% and 40% lower than the corresponding natural aggregate
concretes. (Notice that RCA used in the previous studies was not exposed to fire).
Figure (7-b) shows the concrete mixtures subjected to fire temperature 600°C
for 2hours, It can be noticed that at replacement ratio 25%FRCA, there is a reduction
in the modulus of elasticity by (16%,15% and 17%) at cement contents (300,350and
400kg/m3) respectively comparing to control mixtures, while at replacement ratios
(50% and 100%) FRCA, there is a reduction in modulus of elasticity by (24% and
45%), (25% and 46%) and (22% and 46%) at cement contents 300,350 and 400kg/m3
respectively, comparing with control concrete .
Also, figure (7-c) shows the concrete mixtures subjected to fire temperature 600°C
for 3hours, It can be noticed that replacement ratio 25%FRCA, there is a reduction in
the modulus of elasticity by (18%,19% and 20%) at cement contents (300,350and
400kg/m3) respectively, comparing to control mixtures, while at replacement ratios
(50% and 100%) FRCA, there is a reduction in modulus of elasticity by (25% and
51%), (27% and 52%) and (24% and 51%) at cement contents 300,350 and 400 kg/m3
respectively, for different cement content when compared with the control concrete.
 MECHANICAL PROPERTIES OF CONCRETE CONTAINING … 1017

30000 30000 30000

25000 25000 25000

Modulus of Elasticity (N/mm 2)

Modulus of Elasticity (N/mm )

Modulus of Elasticity (N/mm )

2

2
20000 20000 20000

15000 15000 15000

CC=300Kg/m3
CC=300Kg/m3 CC=300Kg/m3
CC=350Kg/m3
10000 10000 CC=350Kg/m3 10000 CC=350Kg/m3
CC=400Kg/m3
CC=400Kg/m3 CC=400Kg/m3

5000 5000 5000

0 25 50 75 100 125 0 25 50 75 100 125 0 25 50 75 100 125
Percentage of Replacement of Recycled Concrete
Percentage of Replacement of Recycled Concrete Percentage of Replacement of Recycled Concrete
Aggregate
Aggregate Aggregate

a- Duration – 1hr b- Duration – 2hrs c- Duration – 3 hrs

Fig. (7) Relationship between Modulus of Elasticity and Percentage of Replacement of
(RCA) for Different Cement Contents at Fire Temperature 600°C at 28 Days

4. CONCLUSIONS
1- The variation in density and water absorption ratio of fired recycled concrete aggregates
are much higher than those of natural aggregates. The variations are mainly due to the
adhered mortar as reported by many other researchers. This may cause a quality control
problem.
2- The dosage of superplasticizer was increased significantly by increasing
percentage of replacement ratio of recycled concrete aggregates in the concrete
mixtures to achieve acceptable workability of concrete.
3- The high strength relative observed in mixtures with 300 kg/m3 cement content , so
it can be concluded that it could be more useful to use recycled concrete aggregates
in lower strength concrete.
4- Replacement of natural aggregate by 25% recycled concrete aggregates subjected
to fire temperature 600°C for fire durations (1, 2 and 3hours) has a very minor
effect on both of compressive, tensile strength and flexural strength.
5- The compressive strength of concretes containing full replacement of natural
aggregate by recycled aggregates subjected to fire temperature 600°C for fire
durations (1, 2 and 3hours) decreased with range (18% to 36%), comparing to
control mixtures.
6- The tensile strength of concretes made with 100% recycled concrete aggregate
subjected to fire temperature 600°C for fire durations (1, 2 and 3hours) decreased
with range (23% to 30%), comparing to control mixtures.
7- The modulus of elasticity of concretes made with 100% recycled concrete
aggregate subjected to fire temperature 600°C for fire durations (1, 2 and 3hours)
decreased with range (40% to 50%), comparing to control mixtures.
1018 Walid Safwat Fahm et al.

REFERENCES
[1] C.Poon, S .Kon, L .Lemi. (2007) “Influence of Recycled Aggregate on Slump
and Bleeding of Fresh Concrete” Material Structural, Vol. 40, pp 981-988.
[2] S .Tabsh, A .Abdelfalah. (2009)"Influence of Recycled Concrete Aggregate on
Strength Properties", Construction Building Materials, Vol. 23, pp 1163-1170.
[3] Esraa Emam Ali, Sherif H. Al-Tersawy, "Self Compacting Concrete Using
Recycled Concrete Aggregates", (2010), HBRC Journal, Egypt.
[4] J.A .Purkiss. " An Engineering Model for Coupled Heat and Heat and Mass
Transfer Analsyis in Heated Concrete" School of Scinece and Applied Science,
Aston University, Birmingham,UK,july (2001).
[5] Esraa Emam Ali, (2008), “The Behaviour of Rienforced Concerto Frames
Subjected to Fire“ Phd. Thesis, Faculty of Engineering, Helwan University,
Egypt.
[6] Vieira, J.P.B., Correia, J.R., Brito, J. de .(2011)" Post-fire residual mechanical
properties of concrete made with recycled concrete coarse aggregates coarse
aggregates" Journal of Cement and Concrete Research, Vol. 41 ,pp 533–541.
[7] ESS 2421/2005, Egyptian Standard Specification “Cement-Physical and
Mechanical Tests”.
[8] ESS 1109/2002, Egyptian Standard Specification, “Aggregate for Concrete”.
[9] Egyptian Code of Practice for Design and Construction of Concrete Structures
ECCS (203-2007).
[10] Dina Mahmoud Sadek. (2008) "Durability of Concrete Containing Some Local
Industrial Wastes" Phd. Thesis, Faculty of Engineering, Cairo University, Egypt.
[11] M. Etxeberria, E. Vázquez, A. Marí, M. Barra.(2007) “Influence of amount of
recycled coarse aggregates and production process on properties of recycled
aggregate concrete ” Journal of cement and concrete research , Vol. 37, pp 753–
742.
[12] Fatma Al Zahraa Ibrahim Abd El-Latif. (2009) “Structural Behavior of
Reinforced Concrete Beams With Recycled Concrete Aggregates”. Msc. Thesis,
Faculty of Engineering, Cairo University, Egypt.
[13] T. C. Hansen “Concretes of Demolished Concrete and Masonry” Report of
Technical Committee 37 –DRC –Demolition and Reuse of Concrete , Hartnolls
Ltd ,Bodmin, Great Britain, 1992.
[14] A .Rao, K. Jha, S.Misra. (2007) “Use of aggregates from recycled construction
and demolition waste in concrete” Journal of Resources Conservation and
Recycling, Vol. 50, pp 71–81.
[15] M.S. Juan , P.A. Gutiérrez “Influence of Attached Mortar Content on the
Properties of Recycled Concrete Aggregate”, International RILEM Conferences
on the Use of Recycled Materials in Building and Structures , Barcelona,
Spain,9-11 November 2004.
 ‫… ‪MECHANICAL PROPERTIES OF CONCRETE CONTAINING‬‬ ‫‪1019‬‬

‫اﻝﺨواص اﻝﻤﻴﻜﺎﻨﻴﻜﻴﺔ ﻝﻠﺨرﺴﺎﻨﺔ اﻝﺘﻲ ﺘﺤﺘوي ﻋﻠﻰ رﻜﺎم اﻝﺨرﺴﺎﻨﺔ اﻝﻤﻌﺎد ﺘدوﻴرﻩ واﻝﻤﻌرض‬
‫ﻝﻠﺤرﻴق ﻝﻔﺘرات زﻤﻨﻴﺔ ﻤﺨﺘﻠﻔﺔ‬
‫ﺘﻼﺤظ ﻓﻲ اﻵوﻨﺔ اﻷﺨﻴرة اﻝزﻴﺎدة اﻝﻤطردة ﻓﻲ اﻝﻤﺨﻠﻔﺎت اﻝﻨﺎﺘﺠﺔ ﻋن ﻫدم اﻝﺨرﺴﺎﻨﺔ ﺤﻴث ﻴﺘم اﻝﺘﺨﻠص ﻤﻨﻬﺎ ﻋن‬
‫طرﻴق ﺘﺠﻤﻴﻌﻬﺎ ﻓﻲ ﻤداﻓن ﺼﺤﻴﺔ ﺨﺎﺼﺔ ﻤﻤﺎ ﻴﻤﺜل ﻀر ار ﺒﻴﺌﻴﺎً ﻤن ﺤﻴث إﻫدار اﻝﻤوارد اﻝطﺒﻴﻌﻴﺔ و اﻝﻤﺘﻤﺜﻠﺔ ﻓﻲ‬
‫اﻝرﻜﺎم اﻝطﺒﻴﻌﻲ وﻤن ﺜم ﺒدأ اﻝﺘﻔﻜﻴر ﻓﻲ أﻨﺤﺎء ﻤﺘﻔرﻗﺔ ﻤن اﻝﻌﺎﻝم ﻓﻲ اﺴﺘﻐﻼل ﻫذﻩ اﻝﻤﺨﻠﻔﺎت ﻋن طرﻴق إﻋﺎدة‬
‫اﺴﺘﺨداﻤﻬﺎ ﻓﻲ إﻨﺘﺎج اﻝﺨرﺴﺎﻨﺔ ﺒﺤﻴث ﺘﺤل ﻤﺤل اﻝرﻜﺎم ﺒﻨﺴب ﻤﺨﺘﻠﻔﺔ و ذﻝك ﺒﻌد ﺘﻜﺴﻴر ﻤﺨﻠﻔﺎت اﻝﺨرﺴﺎﻨﺔ‬
‫ﺒﺎﺴﺘﺨدام اﻝﻜﺴﺎرات ﻝﻠوﺼول اﻝﻰ اﻝﻤﻘﺎﺴﺎت اﻝﻤطﻠوﺒﺔ‪ .‬و رﻏم وﺠود اﻝﻌدﻴد ﻤن اﻷﺒﺤﺎث اﻝﺘﻲ ﺘم ﻤن ﺨﻼﻝﻬﺎ دراﺴﺔ‬
‫اﻝﺨواص اﻝﻤﻴﻜﺎﻨﻴﻜﻴﺔ ﻝﻠﺨرﺴﺎﻨﺔ اﻝﻤﺤﺘوﻴﺔ ﻋﻠﻰ ﻜﺴر اﻝﺨرﺴﺎﻨﺔ ﻜﻨﺴﺒﺔ ﻤن اﻝرﻜﺎم أﻻ أﻨﻪ ﺤﺘﻰ اﻵن ﻝم ﻴﺘم دراﺴﺔ ﺘﺄﺜﻴر‬
‫اﺴﺘﺨدام ﻤﺨﻠﻔﺎت ﻫدم اﻝﺨرﺴﺎﻨﺔ اﻝﻨﺎﺘﺠﺔ ﻤن اﻨﻬﻴﺎر اﻝﻤﻨﺸﺂت ﺒﺴب اﻝﺤرﻴق ﻋﻨد اﺴﺘﺨدﻤﻬﺎ ﻜﻨﺴب ﻤن اﻝرﻜﺎم ﻓﻲ‬
‫اﻝﺨرﺴﺎﻨﺔ ‪.‬‬
‫وﻝذﻝك ﻓﺎن ﻫذﻩ اﻝدراﺴﺔ ﺘﻌﺘﻨﻲ ﺒدراﺴﺔ ﺘﺄﺜﻴر زﻤن ﺘﻌرض رﻜﺎم اﻝﺨرﺴﺎﻨﺔ اﻝﻤﻌﺎد ﺘدوﻴرﻩ واﻝﻤﻌرض ﻝﻠﺤرﻴق ﻋﻠﻲ‬
‫ﺨواص اﻝﺨرﺴﺎﻨﺔ اﻝﺘﻲ ﻴﺸﻜل ﻓﻴﻬﺎ ﻜﺴر اﻝﺨرﺴﺎﻨﺔ ﻨﺴﺒﺔ ﻤن اﻝرﻜﺎم ﺤﻴث ﺘم دراﺴﺔ ﺘﺄﺜﻴر ﺘﻌرض رﻜﺎم اﻝﺨرﺴﺎﻨﺔ‬
‫اﻝﻤﻌﺎد ﺘدوﻴرﻩ واﻝﻤﻌرض ﻝﻠﺤرﻴق ﻋﻨد درﺠﺔ ﺤ اررة ‪ 600‬درﺠﺔ ﻤﺌوﻴﺔ ﻝﻔﺘرات زﻤﻨﻴﺔ ﻤﺘﻐﻴرة ﻝﻤدة ﺴﺎﻋﺔ و ﺴﺎﻋﺘﻴن‬
‫وﺜﻼث ﺴﺎﻋﺎت و ذﻝك ﻝﻌدد ﻤن اﻝﺨﻠطﺎت اﻝﺨرﺴﺎﻨﻴﺔ اﻝﻤﺨﺘﻠﻔﺔ )‪ 30‬ﺨﻠطﺔ ﺨراﺴﺎﻨﻴﺔ( ﻤن ﺤﻴث ﻤﺤﺘوي اﻷﺴﻤﻨت‬
‫)‪ 300‬و ‪ 350‬و ‪ 400‬ﻜﺠم‪/‬م‪ (3‬وﻜذﻝك ﺘم اﻷﺨذ ﻓﻲ اﻻﻋﺘﺒﺎر ﻨﺴﺒﺔ اﺴﺘﺒدال اﻝرﻜﺎم اﻝطﺒﻴﻌﻲ اﻝﻜﺒﻴر ﺒﻨﺎﺘﺞ ﻜﺴر‬
‫اﻝﺨرﺴﺎﻨﺔ )‪ %0‬و ‪ %25‬و ‪ %50‬و ‪ (%100‬وﺘﺴﺘﻌرض ﻨﺘﺎﺌﺞ اﻝدراﺴﺔ اﻝﺨواص اﻝﻤﺨﺘﻠﻔﺔ ﻝﻠﺨرﺴﺎﻨﺔ ﻤﺜل اﻝﺨواص‬
‫اﻝطﺎزﺠﺔ )اﺨﺘﺒﺎر اﻝﻬﺒوط( واﻝﺨواص اﻝﻤﺘﺼﻠدﻩ ﻤﺜل )ﻤﻘﺎوﻤﺔ اﻝﻀﻐط ‪ -‬ﻤﻘﺎوﻤﺔ اﻝﺸد – ﻤﻘﺎوﻤﺔ اﻻﻨﺤﻨﺎء‪ -‬ﻤﻌﺎﻤل‬
‫اﻝﻤروﻨﺔ(‪.‬‬