This paper presents the results of an experimental research on the normal and high- temperature
compressive strength of concretes with steel or textile fibres or rubber aggregates from recycled tires.
The studied compositions included a reference (RC), two textile fibers (TF), two steel fibres (SF) and
a rubber aggregates (RA) concrete. The specimens were tested in compression for different levels of
temperature (20, 300, 500 and 700ºC). During the heating the specimens were subjected to a constant
loading level of 0.5fcd. The results of this experimental program showed that steel and textile fibres
are a good solution in the compressive behaviour of the concrete regarding to cracking control. The
results for the rubber aggregate concrete revealed a loss on compressive strength with the increase of
the rate of these aggregates in concrete.info:eu-repo/semantics/publishedVersio

Rodrigues, J.P.C.

Santos, C.C.

Repositório Científico do Instituto Politécnico de Castelo Branco

IFireSS 2017 – 2nd International Fire Safety Symposium 
Naples, Italy, June 7-9, 2017 
 
COMPRESSIVE STRENGTH AT HIGH TEMPERATURE OF RECYCLED 
TIRE AGGREGATE CONCRETES 
 
  
Cristina Calmeiro dos Santos1 João Paulo C. Rodrigues2 
ABSTRACT 
This paper presents the results of an experimental research on the normal and high- temperature 
compressive strength of concretes with steel or textile fibres or rubber aggregates from recycled tires. 
The studied compositions included a reference (RC), two textile fibers (TF), two steel fibres (SF) and 
a rubber aggregates (RA) concrete. The specimens were tested in compression for different levels of 
temperature (20, 300, 500 and 700ºC). During the heating the specimens were subjected to a constant 
loading level of 0.5fcd. The results of this experimental program showed that steel and textile fibres 
are a good solution in the compressive behaviour of the concrete regarding to cracking control. The 
results for the rubber aggregate concrete revealed a loss on compressive strength with the increase of 
the rate of these aggregates in concrete. 
NOTATION 
d – diameter ; h – height  
ρ – specific weight  
fcd – design value of the compression strength of the concrete at normal temperature 
fc,T – compression strength of concrete at temperature T  
fcm,T – mean value of the compression strength of concrete at temperature T 
fcm,20 – mean value of the compression strength of concrete at normal temperature 
sx – standard deviation 
s – stress ; e – strain 
1 INTRODUCTION 
In civil construction industry the use of recycled materials, mainly in concrete manufacture is 
increasingly and seems a viable reality. In this sense, there are different studies of concrete with the 
insertion of recycled materials from tires. 
Schneider (1982) highlighted the type of aggregates, loading level and cooling process, as the main 
parameters responsible for concrete cracking and loss of strength [1].  
                                                
1
 Professor. Instituto Politécnico de Castelo Branco. ISISE. Portugal. e-mail: ccalmeiro@ipcb.pt.  
2 Professor. ISISE. Department of Civil Engineering. University of Coimbra. Portugal. e-mail: jpaulocr@dec.uc.pt. Corresponding 
Author.  
2    Compressive Strength at High Temperature of Recycled Tire Aggregate Concretes 
 
 
Bazant and Kaplan (1996) referenced that due to the fact that the coefficients of thermal expansion 
of the aggregates and cement paste are not equal leads to thermo-differential stress with micro-
cracking and spalling in the concrete matrix [2]. 
Khoury (2000) developed important studies in this area studying the mechanical properties of the 
concrete at high temperatures. The author found that the mixing proportions of aggregates with 
cement and water has a major impact on the mechanical properties of the concrete at high 
temperatures because this influencing the chemical and physical reactions on concrete with losing of 
cohesion and degradation [3]. 
Lau and Anson (2006) studied the effect of the addition of 1% of steel fibers on the behaviour of the 
concrete at high temperatures. In this study the authors found that higher was the temperature, lower 
the permeability and higher the risk of spalling of the concrete were. The steel fibers improves the 
behaviour of the concrete at high temperatures and consequently the compressive strength [4]. 
Çavdar (2012) studied the effect of four different types of fibers on the concrete compressive strength 
at high temperatures. The fibers tested were polypropylene (PP), carbon (CF), glass (GF) and 
polyvinyl alcohol (PVA). The amounts used were 0.0%, 0.5%, 1.0%, 1.5% and 2.0% in volume, and 
the temperatures tested were 20, 100, 450 and 650ºC. Çavdar found that with the increasing of 
temperature the cement matrix change in a way that at 450ºC damages and some cracking and at 
650ºC extensive cracking and deterioration of concrete occur, respectively. He has also concluded 
that the compressive strength decreases with the temperature, being the value for the mixtures with 
PP and GF fibers about 40-50% at 450ºC and 55-70% at 650ºC of the resistance at ambient 
temperature. The mixtures with CF and with PVA fibres reduce about 3-8% at 450ºC and 50-60% at 
650ºC of the compressive strength at ambient temperature. The reduction in compressive strength is 
lower when the amount of CF fibres added to the mixture is between 0.5 and 1.5% in volume for any 
temperature in study [5]. 
Bangi and Horiguchi (2012) studied the influence of the length, diameter and fiber type in reducing 
the internal water vapor pressure of the high strength concretes subjected to high temperatures. In this 
study were tested polypropylene (PP), polyvinyl alcohol (PVA) and steel fibers (FA). All 
compositions were reinforced with the same amount of fibers (0.1% by volume) and subjected to a 
heating rate of 10ºC/min. 
The authors observed a significant reduction in the pressure of the concrete mixture regardless the 
type of fibre used and its geometry. They also found that the longer fibers with smaller diameters 
attenuate the increase of pressure at the mixture pores when compared with the shorter fibers with 
larger diameters and regardless of the type of fibre. On the other hand, found that concrete mixtures 
reinforced with PP fibers had a better behavior under fire conditions than the PVA fibers, because PP 
fibers have better bonding properties with the concrete matrix. 
The authors also found that the addition of steel and PP fibers reduce the cracking and spalling, 
respectively, since the last ones will sublimate for temperatures of around 170ºC, creating a net of 
micro-channels from which the water vapour can be released to outside reducing the internal pressure 
at concrete matrix pores. The experimental results showed that the addition of fibers with lower 
sublimation temperatures presented and improved the concrete performance when compared to fibers 
with higher melting temperatures [6]. 
In this context and in the light of increasing the need to manage natural resources rationally [7] 
appears this research which aimed to evaluate experimentally the compressive strength at normal and 
high temperatures of concretes made with recycled tire aggregates (rubber, textile and steel fibers). 
This research in this way contribute to the sustainability as an alternative solution to the tire deposit 
after its life time. 
High-Temperature Mechanical Properties 3 
 
 
2 EXPERIMENTAL RESEARCH 
2.1 Materials and methods 
Concrete compositions 
The materials used in this compositions were Portland cement (C) type II/AL 42.5R (chemistry 
composition: SO3 ≤ 4% e Cl ≤ 0.10%; compressive strength: 2 days - 20MPa and 28 days - 42.5MPa), 
natural sand (FA) and crushed aggregates (CA) (6.3 - 16mm). The choice of this cement was based 
on its enhanced workability, high strength and behaviour at high temperatures.  
In the concretes were also used different types of tyre recycled aggregates obtaining different concrete 
compositions: rubber aggregates (RA), nominal size between 6.3 - 12mm, steel (SF) and textile (TF) 
fibers. Different amounts of rubber aggregates or steel or textile fibers were added in the concretes. 
In total were studied seven concrete compositions: a reference one without fibers (RC), two textile 
fibers ones with 2 (TF1) or 4 (TF2) kg/m3of these fibers, two steel fibres ones with 30 (SF1) or 70 
(SF2) kg/m3 of these fibers and two rubber aggregate ones with 15% (RA1) and 30% (RA2) of these 
aggregates, respectively. The addition of recycled aggregates / fibers was carried out by replacing 
gravel limestone aggregates in the mixture.  
Table 1 shows the specific weight of the materials used in the concrete compositions while Table 2 
presents their compositions. 
Table 1. Specific weight of the aggregates, cement and water 
 ρ [kg/m3] 
Water (W) 1000 
Cement (C) 3100 
Natural sand (FA) 2600 
Crushed aggregate (CC) 2700 
Coarse recycled fraction (RA) 1100 
Table 2. Concrete compositions 
Concrete mixture RC TF1 TF2 SF1 SF2 RA1 RA2 
Water (dm3/m3)  122.5 122.5 122.5 122.5 122.5 122.5 122.5 
Cement (kg/m3)  400 400 400 400 400 400 400 
Natural sand (kg/m3)  567 567 567 567 567 567 567 
Crushed aggregate (kg/m3)  959 957 955 929 889 560 161 
Coarse recycled fraction (kg/m3)  - - - - - 165 330 
Textile fibers (kg/m3)  - 2 4 - - - - 
Steel fibers (kg/m3)  - - - 30 70 - - 
Water/Cement  0.31 0.31 0.31 0.31 0.31 0.31 0.31 
Compressive strength (MPa)  63.68 49.11 46.62 50.63 45.14 24.63 10.60 
at days:  28 28 28 28 28 28 28 
Strength class  C50/60 C35/45 C35/45 C35/45 C30/37 C16/20 C8/10 
 
The compressive strength and resistance class of the concretes were evaluated according to EN 206-
1 (2007) [8]. The results achieved are reported in Table 2. As expected the rubber aggregate (RA) 
concretes had significantly lower compressive strength than the reference concretes (RC). The 
decreasing in the strength and stiffness of the concrete is strictly connected to the rubber compressive 
strength and rubber particles in the concrete matrix that causes voids making the concrete vulnerable. 
Specimens and Test procedure 
The compressive strength tests were carried out on cylindrical specimens of 75mm diameter and 
225mm height, that corresponded to a height/diameter ratio of 3:1. The specimens were provided 
with five type K thermocouples in order to register the temperatures inside the concrete. The location 
4    Compressive Strength at High Temperature of Recycled Tire Aggregate Concretes 
 
 
of thermocouples in the specimens was based on the recommendations of RILEM TC 200 HTC [9] 
(Fig. 2). 
 
 
 
 
 
 
 
 
 
 
 
Fig. 1. Specimens and location of thermocouples 
The specimens were cured, during 28 days, in a vapour saturated ambient (relative humidity > 98%) 
and temperature of 20ºC. After this they were removed and left in the lab ambient temperature 
(between 18 and 20ºC) and humidity (between 40 and 50%) waiting for testing. The specimens were 
tested at least with three months of age. 
The characteristics of the specimens and the test plan are summarized in Table 3. Three tests as a 
minimum were developed for each combination of parameters. 
The experimental set-up for the compression strength tests were composed by a universal 
tensile/compression machine of 600kN where was accomplished an electric tubular oven for heating 
the specimens and a data acquisition system for data recording (Fig. 2).  
Table3. Test plan 
Test Specimen dimensions (mm) Loading level Temperature (ºC) 
compressive 
strength cylinders, d=75:h=225 0.5fcd 20, 300, 500, 700 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 2. Test-setup 
 
The specimens during the heating process were subjected to a constant compressive load level equal 
to 0.5 of the design value of the compression strength of the concrete at normal temperature (0.5fcd). 
This load tried to simulate the conditions of the concrete when in a real compressed structural element.  
High-Temperature Mechanical Properties 5 
 
 
The specimens were heated up at a rate of 3ºC/min up to the desired level of temperature. The 
temperature was considered achieved when the average temperatures on the three superficial 
thermocouples match the temperature of the oven. The maximum axial temperature differences 
between the three superficial thermocouples could not exceed 1ºC at 20ºC, 5ºC at 100ºC and 20ºC at 
700ºC. The specimens were then kept at that temperature for an hour to stabilize. This test procedure 
was adopted according to RILEM TC 200 HTC recommendations [9].  
After this the compressive tests were carried out. The compressive load was increased at a rate of 
0.25kN/s up to the rupture of the specimen. 
3 RESEARCH RESULTS 
3.1 Compressive strength 
The results of the compressive strength of tested concretes are summarized in Figures 3, 4 and 5.  
 
 
 
 
 
 
 
 
 
 
Fig. 3. Compressive strength of the reference (RC) and 
textile fibers (TF1 and TF2) concretes with temperature 
 
Fig. 4. Compressive strength of the reference (RC) and 
steel fibers (SF1 and SF2) concretes with temperature 
 
 
 
 
 
 
 
 
 
 
 
 
Fig 5. Compressive strength of the reference (RC) and rubber 
aggregate (RA1 and RA2) concretes with temperature 
 
Figure 3 shows the results for the concretes with 2kg/m3 (TF1) and 4kg/m3 (TF2) of textile fibers 
compared with the ones of the plain concrete (RC) all related to their values at normal temperature. 
The results show at 300ºC an increasing on the compressive strength of around 47% for the RC, 56% 
for the TF1 and 43% for the TF2 concrete. At 500ºC the RC presented a strength similar to and the 
others 20% higher than the one at normal temperature. For 700ºC all specimens have suffered rupture 
before reaching this temperature making impossible the test for this temperature level. 
 
Figure 4 shows the results for the concretes with 30kg/m3 (SF1) and 70kg/m3 (SF2) of steel fibers 
related to its value at normal temperature. The values are also compared with the ones of the plain 
concrete (RC). The addition of steel fibers to the concrete also resulted in an increasing of the 
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
20 100 200 300 500 600 700
f c
m
, T
/ f
cm
, 2
0
(M
P
a)
Temperature (ºC)
RC
TF1
TF2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
20 100 200 300 500 600 700
f c
m
, T
/ f
cm
, 2
0
(M
P
a)
Temperature (ºC)
RC
SF1
SF2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
20 94 100 200 300 500 700
f c
m
, T
/ f
cm
, 2
0
(M
P
a)
Temperature (ºC)
RC
RA1
RA2
6    Compressive Strength at High Temperature of Recycled Tire Aggregate Concretes 
 
 
compressive strength for the different levels of temperature up to the 500ºC. At 300ºC there was an 
increase on the compressive strength of about 47% for the RC, 54% for the SF1 and 41% for the SF2 
concretes. At 500ºC the compressive strength of the RC and SF2 concretes are similar and the SF1 is 
15% higher than the one at normal temperature. Once more the strength was null at 700ºC. The results 
showed that an addition of 30kg/m3 of steel fibers to the concrete presented a better result than the 
70kg/m3. 
Figure 5 shows the results for the rubber aggregate concretes with 15% (RA1) and 30% (RA2) of 
these aggregates. The analysis of the Figure shows that for temperatures 300ºC it was only possible 
to carry out tests on the reference and 15% rubber aggregate concretes since the specimens for the 
30% rubber aggregate concrete suffered rupture before reaching this level of temperature. At this 
temperature it was verified that the compressive strength of the reference concrete increased about 
50% regarding to the one at normal temperature. This was not verified for the 15% rubber aggregate 
concrete that presented a reducing of about 24% on the compressive strength when comparing to the 
one at normal temperature. 
Figures 6 and 7 present a comparison of the stress-strain curves in the compressive tests, for the three 
specimens tested on the 500ºC series, between the SF1, SF2 and the RC and between the TF1, TF2 
and the RC concretes, respectively. Figure 8 presents the same type of curves but for the RA1 and 
RA2 concretes and again comparing with the RC, but in this case for the 300ºC series. 
 
 
 
 
 
 
 
 
 
Fig. 6. Stress-strain curves – 500ºC - RC, SF1 and SF2 
 
 
 
 
 
 
 
 
 
 
Fig. 7. Stress-strain curves – 500ºC - RC, TF1 and TF2 
 
 
 
 
 
 
 
 
 
Fig. 8. Stress-strain curves – 300ºC - RC, RA1 and RA2 
 
0
4
8
12
16
20
24
0 0.05 0.1 0.15 0.2
σ
(M
Pa
)
Ɛ (%)
RC(S1)
RC(S2)
RC(S3)
SF1(S1)
SF1(S2)
SF1(S3)
SF2(S1)
SF2(S2)
SF2(S3)
0
4
8
12
16
20
24
0 0.05 0.1 0.15 0.2
σ
(M
Pa
)
Ɛ (%)
RC(S1)
RC(S2)
RC(S3)
TF1(S1)
TF1(S2)
TF1(S3)
TF2(S1)
TF2(S2)
TF2(S3)
0
4
8
12
16
20
24
0 0.05 0.1 0.15 0.2
σ
(M
Pa
)
Ɛ (%)
RC(S1)
RC(S2)
RC(S3)
RA1(S1)
RA1(S2)
RA1(S3)
RA2(S1)
RA2(S2)
RA2(S3)
High-Temperature Mechanical Properties 7 
 
 
The observation of Figures 6-8 show faster increasing on the tensile in fiber (SF and TF) than in 
rubber aggregate concretes (RA), being the tensile higher, for the same level of strain, in the steel 
fiber concretes.  
4 CONCLUSIONS 
The following conclusions may be drawn from the present study: 
• The concrete compositions with textile or steel fibers presented, for temperatures lower than 
500 ºC, compressive strengths higher than the ones at normal temperature. 
• For temperatures, between 300 and 500 °C, the smaller addition of steel fibres in concrete 
gave better results. The steel fibres, when not excessive, have a beneficial effect on the 
concrete preventing its degradation with the temperature. A quite similar result was observed 
for the concrete compositions with textile fibres. 
• The concretes with steel fibers presented a gentle rupture when comparing to the plain 
concrete attesting the effectiveness of these fibers in concrete ductility and cracking control. 
• The textile and steel fibres recycled from tires showed to be a good solution in concrete 
composition to control cracking and spalling and can be a good solution for replacing the 
commercial polypropylene and steel fibers, respectively. 
• The concretes with 30% of rubber aggregates presented a higher degradation in the 
compression strength with the temperature than the ones with 30% of rubber aggregates. 
• The results showed that the insertion of rubber aggregates in concrete did not give good results 
at high temperatures but the use of rubber fibres is maybe a good solution. 
ACKNOWLEDGEMENTS 
The authors grateful acknowledge Recipneu Lda (www.recipneu.com) by the kind offer of the 
recycled tire aggregates used in this investigation. 
REFERENCES 
[1] Schneider U. (1982). Behavior of concrete at high temperatures. Beuth Verlag, Berlin, 122pp. 
[2] Bazant P.Z., Kaplan M.F. (1996). Concrete at high temperatures, Material, properties and mathematical 
models. Longman, Harlow, England, 412pp. 
[3] Khoury G.A. (2000). Effect of fire on concrete and concrete structures. Progress in Structural Engineering 
and Materials, 2(4), 429-447 pp. 
[4] Lau A., Anson M. (2006). Effect of high temperatures on high performance steel fibre reinforced 
concrete. Cement and Concrete Research, 36(9), 1698-1707 pp. 
[5] Çavdar A. (2012). A study on the effects of high temperature on mechanical properties of fiber reinforced 
cementitious composites. Composites Part B, 43(5), 2452-2463 pp. 
[6] Bangi M.R., Horiguchi T. (2012). Effect of fibre type and geometry on maximum pore pressures in fibre-
reinforced high strength concrete at elevated temperatures. Cement Concrete Res., 42(2), 459-466 pp. 
[7] Olivares F.H., Barluenga G. (2004). Fire performance of recycled rubber-filled high-strength concrete. 
Cement and Concrete Research, 34, 109-117 pp. 
[8] NP EN 206-1. (2007). Concrete Part 1: Specification, performance. Production and conformity, 84 pp. 
[9] RILEM TC - 200 HTC. (2005). Mechanical Concrete Properties at High Temperature – Modelling and 
Applications. Materials and Structures, 38(284), 913-919 pp. 


English

Compressive strength at high temperature of recycled tire aggregate concretes

Repositório do Instituto Politécnico de Castelo Branco

IFireSS 2017 – 2nd International Fire Safety Symposium Naples, Italy, June 7-9, 2017  COMPRESSIVE STRENGTH AT HIGH TEMPERATURE OF RECYCLED TIRE AGGREGATE CONCRETES    Cristina Calmeiro dos Santos1 João Paulo C. Rodrigues2 ABSTRACT This paper presents the results of an experimental research on the normal and high- temperature compressive strength of concretes with steel or textile fibres or rubber aggregates from recycled tires. The studied compositions included a reference (RC), two textile fibers (TF), two steel fibres (SF) and a rubber aggregates (RA) concrete. The specimens were tested in compression for different levels of temperature (20, 300, 500 and 700ºC). During the heating the specimens were subjected to a constant loading level of 0.5fcd. The results of this experimental program showed that steel and textile fibres are a good solution in the compressive behaviour of the concrete regarding to cracking control. The results for the rubber aggregate concrete revealed a loss on compressive strength with the increase of the rate of these aggregates in concrete. NOTATION d – diameter ; h – height  ρ – specific weight  fcd – design value of the compression strength of the concrete at normal temperature fc,T – compression strength of concrete at temperature T  fcm,T – mean value of the compression strength of concrete at temperature T fcm,20 – mean value of the compression strength of concrete at normal temperature sx – standard deviation s – stress ; e – strain 1 INTRODUCTION In civil construction industry the use of recycled materials, mainly in concrete manufacture is increasingly and seems a viable reality. In this sense, there are different studies of concrete with the insertion of recycled materials from tires. Schneider (1982) highlighted the type of aggregates, loading level and cooling process, as the main parameters responsible for concrete cracking and loss of strength [1].                                                  1 Professor. Instituto Politécnico de Castelo Branco. ISISE. Portugal. e-mail: ccalmeiro@ipcb.pt.  2 Professor. ISISE. Department of Civil Engineering. University of Coimbra. Portugal. e-mail: jpaulocr@dec.uc.pt. Corresponding Author.  2    Compressive Strength at High Temperature of Recycled Tire Aggregate Concretes   Bazant and Kaplan (1996) referenced that due to the fact that the coefficients of thermal expansion of the aggregates and cement paste are not equal leads to thermo-differential stress with micro-cracking and spalling in the concrete matrix [2]. Khoury (2000) developed important studies in this area studying the mechanical properties of the concrete at high temperatures. The author found that the mixing proportions of aggregates with cement and water has a major impact on the mechanical properties of the concrete at high temperatures because this influencing the chemical and physical reactions on concrete with losing of cohesion and degradation [3]. Lau and Anson (2006) studied the effect of the addition of 1% of steel fibers on the behaviour of the concrete at high temperatures. In this study the authors found that higher was the temperature, lower the permeability and higher the risk of spalling of the concrete were. The steel fibers improves the behaviour of the concrete at high temperatures and consequently the compressive strength [4]. Çavdar (2012) studied the effect of four different types of fibers on the concrete compressive strength at high temperatures. The fibers tested were polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA). The amounts used were 0.0%, 0.5%, 1.0%, 1.5% and 2.0% in volume, and the temperatures tested were 20, 100, 450 and 650ºC. Çavdar found that with the increasing of temperature the cement matrix change in a way that at 450ºC damages and some cracking and at 650ºC extensive cracking and deterioration of concrete occur, respectively. He has also concluded that the compressive strength decreases with the temperature, being the value for the mixtures with PP and GF fibers about 40-50% at 450ºC and 55-70% at 650ºC of the resistance at ambient temperature. The mixtures with CF and with PVA fibres reduce about 3-8% at 450ºC and 50-60% at 650ºC of the compressive strength at ambient temperature. The reduction in compressive strength is lower when the amount of CF fibres added to the mixture is between 0.5 and 1.5% in volume for any temperature in study [5]. Bangi and Horiguchi (2012) studied the influence of the length, diameter and fiber type in reducing the internal water vapor pressure of the high strength concretes subjected to high temperatures. In this study were tested polypropylene (PP), polyvinyl alcohol (PVA) and steel fibers (FA). All compositions were reinforced with the same amount of fibers (0.1% by volume) and subjected to a heating rate of 10ºC/min. The authors observed a significant reduction in the pressure of the concrete mixture regardless the type of fibre used and its geometry. They also found that the longer fibers with smaller diameters attenuate the increase of pressure at the mixture pores when compared with the shorter fibers with larger diameters and regardless of the type of fibre. On the other hand, found that concrete mixtures reinforced with PP fibers had a better behavior under fire conditions than the PVA fibers, because PP fibers have better bonding properties with the concrete matrix. The authors also found that the addition of steel and PP fibers reduce the cracking and spalling, respectively, since the last ones will sublimate for temperatures of around 170ºC, creating a net of micro-channels from which the water vapour can be released to outside reducing the internal pressure at concrete matrix pores. The experimental results showed that the addition of fibers with lower sublimation temperatures presented and improved the concrete performance when compared to fibers with higher melting temperatures [6]. In this context and in the light of increasing the need to manage natural resources rationally [7] appears this research which aimed to evaluate experimentally the compressive strength at normal and high temperatures of concretes made with recycled tire aggregates (rubber, textile and steel fibers). This research in this way contribute to the sustainability as an alternative solution to the tire deposit after its life time. High-Temperature Mechanical Properties 3   2 EXPERIMENTAL RESEARCH 2.1 Materials and methods Concrete compositions The materials used in this compositions were Portland cement (C) type II/AL 42.5R (chemistry composition: SO3 ≤ 4% e Cl ≤ 0.10%; compressive strength: 2 days - 20MPa and 28 days - 42.5MPa), natural sand (FA) and crushed aggregates (CA) (6.3 - 16mm). The choice of this cement was based on its enhanced workability, high strength and behaviour at high temperatures.  In the concretes were also used different types of tyre recycled aggregates obtaining different concrete compositions: rubber aggregates (RA), nominal size between 6.3 - 12mm, steel (SF) and textile (TF) fibers. Different amounts of rubber aggregates or steel or textile fibers were added in the concretes. In total were studied seven concrete compositions: a reference one without fibers (RC), two textile fibers ones with 2 (TF1) or 4 (TF2) kg/m3of these fibers, two steel fibres ones with 30 (SF1) or 70 (SF2) kg/m3 of these fibers and two rubber aggregate ones with 15% (RA1) and 30% (RA2) of these aggregates, respectively. The addition of recycled aggregates / fibers was carried out by replacing gravel limestone aggregates in the mixture.  Table 1 shows the specific weight of the materials used in the concrete compositions while Table 2 presents their compositions. Table 1. Specific weight of the aggregates, cement and water  ρ [kg/m3] Water (W) 1000 Cement (C) 3100 Natural sand (FA) 2600 Crushed aggregate (CC) 2700 Coarse recycled fraction (RA) 1100 Table 2. Concrete compositions Concrete mixture RC TF1 TF2 SF1 SF2 RA1 RA2 Water (dm3/m3)  122.5 122.5 122.5 122.5 122.5 122.5 122.5 Cement (kg/m3)  400 400 400 400 400 400 400 Natural sand (kg/m3)  567 567 567 567 567 567 567 Crushed aggregate (kg/m3)  959 957 955 929 889 560 161 Coarse recycled fraction (kg/m3)  - - - - - 165 330 Textile fibers (kg/m3)  - 2 4 - - - - Steel fibers (kg/m3)  - - - 30 70 - - Water/Cement  0.31 0.31 0.31 0.31 0.31 0.31 0.31 Compressive strength (MPa)  63.68 49.11 46.62 50.63 45.14 24.63 10.60 at days:  28 28 28 28 28 28 28 Strength class  C50/60 C35/45 C35/45 C35/45 C30/37 C16/20 C8/10  The compressive strength and resistance class of the concretes were evaluated according to EN 206-1 (2007) [8]. The results achieved are reported in Table 2. As expected the rubber aggregate (RA) concretes had significantly lower compressive strength than the reference concretes (RC). The decreasing in the strength and stiffness of the concrete is strictly connected to the rubber compressive strength and rubber particles in the concrete matrix that causes voids making the concrete vulnerable. Specimens and Test procedure The compressive strength tests were carried out on cylindrical specimens of 75mm diameter and 225mm height, that corresponded to a height/diameter ratio of 3:1. The specimens were provided with five type K thermocouples in order to register the temperatures inside the concrete. The location 4    Compressive Strength at High Temperature of Recycled Tire Aggregate Concretes   of thermocouples in the specimens was based on the recommendations of RILEM TC 200 HTC [9] (Fig. 2).            Fig. 1. Specimens and location of thermocouples The specimens were cured, during 28 days, in a vapour saturated ambient (relative humidity > 98%) and temperature of 20ºC. After this they were removed and left in the lab ambient temperature (between 18 and 20ºC) and humidity (between 40 and 50%) waiting for testing. The specimens were tested at least with three months of age. The characteristics of the specimens and the test plan are summarized in Table 3. Three tests as a minimum were developed for each combination of parameters. The experimental set-up for the compression strength tests were composed by a universal tensile/compression machine of 600kN where was accomplished an electric tubular oven for heating the specimens and a data acquisition system for data recording (Fig. 2).  Table3. Test plan Test Specimen dimensions (mm) Loading level Temperature (ºC) compressive strength cylinders, d=75:h=225 0.5fcd 20, 300, 500, 700              Fig. 2. Test-setup  The specimens during the heating process were subjected to a constant compressive load level equal to 0.5 of the design value of the compression strength of the concrete at normal temperature (0.5fcd). This load tried to simulate the conditions of the concrete when in a real compressed structural element.  High-Temperature Mechanical Properties 5   The specimens were heated up at a rate of 3ºC/min up to the desired level of temperature. The temperature was considered achieved when the average temperatures on the three superficial thermocouples match the temperature of the oven. The maximum axial temperature differences between the three superficial thermocouples could not exceed 1ºC at 20ºC, 5ºC at 100ºC and 20ºC at 700ºC. The specimens were then kept at that temperature for an hour to stabilize. This test procedure was adopted according to RILEM TC 200 HTC recommendations [9].  After this the compressive tests were carried out. The compressive load was increased at a rate of 0.25kN/s up to the rupture of the specimen. 3 RESEARCH RESULTS 3.1 Compressive strength The results of the compressive strength of tested concretes are summarized in Figures 3, 4 and 5.            Fig. 3. Compressive strength of the reference (RC) and textile fibers (TF1 and TF2) concretes with temperature  Fig. 4. Compressive strength of the reference (RC) and steel fibers (SF1 and SF2) concretes with temperature             Fig 5. Compressive strength of the reference (RC) and rubber aggregate (RA1 and RA2) concretes with temperature  Figure 3 shows the results for the concretes with 2kg/m3 (TF1) and 4kg/m3 (TF2) of textile fibers compared with the ones of the plain concrete (RC) all related to their values at normal temperature. The results show at 300ºC an increasing on the compressive strength of around 47% for the RC, 56% for the TF1 and 43% for the TF2 concrete. At 500ºC the RC presented a strength similar to and the others 20% higher than the one at normal temperature. For 700ºC all specimens have suffered rupture before reaching this temperature making impossible the test for this temperature level.  Figure 4 shows the results for the concretes with 30kg/m3 (SF1) and 70kg/m3 (SF2) of steel fibers related to its value at normal temperature. The values are also compared with the ones of the plain concrete (RC). The addition of steel fibers to the concrete also resulted in an increasing of the 0.00.20.40.60.81.01.21.41.61.820 100 200 300 500 600 700f cm, T/ fcm, 20(MPa)Temperature (ºC)RCTF1TF20.00.20.40.60.81.01.21.41.61.820 100 200 300 500 600 700f cm, T/ fcm, 20(MPa)Temperature (ºC)RCSF1SF20.00.20.40.60.81.01.21.41.61.820 94 100 200 300 500 700f cm, T/ fcm, 20(MPa)Temperature (ºC)RCRA1RA26    Compressive Strength at High Temperature of Recycled Tire Aggregate Concretes   compressive strength for the different levels of temperature up to the 500ºC. At 300ºC there was an increase on the compressive strength of about 47% for the RC, 54% for the SF1 and 41% for the SF2 concretes. At 500ºC the compressive strength of the RC and SF2 concretes are similar and the SF1 is 15% higher than the one at normal temperature. Once more the strength was null at 700ºC. The results showed that an addition of 30kg/m3 of steel fibers to the concrete presented a better result than the 70kg/m3. Figure 5 shows the results for the rubber aggregate concretes with 15% (RA1) and 30% (RA2) of these aggregates. The analysis of the Figure shows that for temperatures 300ºC it was only possible to carry out tests on the reference and 15% rubber aggregate concretes since the specimens for the 30% rubber aggregate concrete suffered rupture before reaching this level of temperature. At this temperature it was verified that the compressive strength of the reference concrete increased about 50% regarding to the one at normal temperature. This was not verified for the 15% rubber aggregate concrete that presented a reducing of about 24% on the compressive strength when comparing to the one at normal temperature. Figures 6 and 7 present a comparison of the stress-strain curves in the compressive tests, for the three specimens tested on the 500ºC series, between the SF1, SF2 and the RC and between the TF1, TF2 and the RC concretes, respectively. Figure 8 presents the same type of curves but for the RA1 and RA2 concretes and again comparing with the RC, but in this case for the 300ºC series.          Fig. 6. Stress-strain curves – 500ºC - RC, SF1 and SF2           Fig. 7. Stress-strain curves – 500ºC - RC, TF1 and TF2          Fig. 8. Stress-strain curves – 300ºC - RC, RA1 and RA2  048121620240 0.05 0.1 0.15 0.2σ(MPa)Ɛ (%)RC(S1)RC(S2)RC(S3)SF1(S1)SF1(S2)SF1(S3)SF2(S1)SF2(S2)SF2(S3)048121620240 0.05 0.1 0.15 0.2σ(MPa)Ɛ (%)RC(S1)RC(S2)RC(S3)TF1(S1)TF1(S2)TF1(S3)TF2(S1)TF2(S2)TF2(S3)048121620240 0.05 0.1 0.15 0.2σ(MPa)Ɛ (%)RC(S1)RC(S2)RC(S3)RA1(S1)RA1(S2)RA1(S3)RA2(S1)RA2(S2)RA2(S3)High-Temperature Mechanical Properties 7   The observation of Figures 6-8 show faster increasing on the tensile in fiber (SF and TF) than in rubber aggregate concretes (RA), being the tensile higher, for the same level of strain, in the steel fiber concretes.  4 CONCLUSIONS The following conclusions may be drawn from the present study: • The concrete compositions with textile or steel fibers presented, for temperatures lower than 500 ºC, compressive strengths higher than the ones at normal temperature. • For temperatures, between 300 and 500 °C, the smaller addition of steel fibres in concrete gave better results. The steel fibres, when not excessive, have a beneficial effect on the concrete preventing its degradation with the temperature. A quite similar result was observed for the concrete compositions with textile fibres. • The concretes with steel fibers presented a gentle rupture when comparing to the plain concrete attesting the effectiveness of these fibers in concrete ductility and cracking control. • The textile and steel fibres recycled from tires showed to be a good solution in concrete composition to control cracking and spalling and can be a good solution for replacing the commercial polypropylene and steel fibers, respectively. • The concretes with 30% of rubber aggregates presented a higher degradation in the compression strength with the temperature than the ones with 30% of rubber aggregates. • The results showed that the insertion of rubber aggregates in concrete did not give good results at high temperatures but the use of rubber fibres is maybe a good solution. ACKNOWLEDGEMENTS The authors grateful acknowledge Recipneu Lda (www.recipneu.com) by the kind offer of the recycled tire aggregates used in this investigation. REFERENCES [1] Schneider U. (1982). Behavior of concrete at high temperatures. Beuth Verlag, Berlin, 122pp. [2] Bazant P.Z., Kaplan M.F. (1996). Concrete at high temperatures, Material, properties and mathematical models. Longman, Harlow, England, 412pp. [3] Khoury G.A. (2000). Effect of fire on concrete and concrete structures. Progress in Structural Engineering and Materials, 2(4), 429-447 pp. [4] Lau A., Anson M. (2006). Effect of high temperatures on high performance steel fibre reinforced concrete. Cement and Concrete Research, 36(9), 1698-1707 pp. [5] Çavdar A. (2012). A study on the effects of high temperature on mechanical properties of fiber reinforced cementitious composites. Composites Part B, 43(5), 2452-2463 pp. [6] Bangi M.R., Horiguchi T. (2012). Effect of fibre type and geometry on maximum pore pressures in fibre-reinforced high strength concrete at elevated temperatures. Cement Concrete Res., 42(2), 459-466 pp. [7] Olivares F.H., Barluenga G. (2004). Fire performance of recycled rubber-filled high-strength concrete. Cement and Concrete Research, 34, 109-117 pp. [8] NP EN 206-1. (2007). Concrete Part 1: Specification, performance. Production and conformity, 84 pp. [9] RILEM TC - 200 HTC. (2005). Mechanical Concrete Properties at High Temperature – Modelling and Applications. Materials and Structures, 38(284), 913-919 pp. 

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Compressive strength at high temperature of recycled tire aggregate concretes

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