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Effects of rubber aggregates from grinded used tyres on the concrete resistance to cracking
Journal of Cleaner Production 23 (2012) 209e215
Contents lists available at SciVerse ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Effects of rubber aggregates from grinded used tyres on the concrete resistance to cracking Anh Cuong Ho a, Anaclet Turatsinze a, *, Rashid Hameed a, Duc Chinh Vu b a b
Laboratoire Matériaux et Durabilité des Constructions (LMDC), INSA-UPS, Génie Civil, 135 av. de Rangueil, 31077 Toulouse cedex 4, France Institut de Transport Science et Technologie (ITST), 1252 Duong Lang, Dong Da, Ha Noi, Viet Nam
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 March 2011 Received in revised form 12 September 2011 Accepted 16 September 2011 Available online 20 October 2011
In practice, pavements or slabs are subjected to wide range of length changes during their service life. In case of cement-based materials, their length changes due to shrinkage and/or temperature variations induce tensile stress which can result in cracking detrimental for durability. Generally, aggravating circumstances are observed due to the length change restraint. This contribution focuses on experimental results of tests performed on rubberized concrete produced by partly replacing natural sand (0 e4 mm) by rubber aggregates up to 40% by volume. The rubber aggregates are obtained by grinding of used tyres. Effect of rubber aggregate on brittleness index (BI) and on damage evolution was investigated by conducting three-point bending tests on notched beam. Results of these tests confirmed that the both BI and damage decrease with the increase of rubber aggregate content in the concrete. Acoustic emission (AE) technique was applied to detect damage mechanism in concrete by analyzing AE parameters. The Elastic Quality Index (EQI) was adopted to take into account two mutually exclusive properties which govern the sensitivity to cracking, namely strain capacity and tensile strength. Results obtained from the tests performed at 20 C, 40 C and 70 C showed that rubberized concrete exhibits EQI values within acceptable limits for the design of cement-based pavements. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Rubberized concrete Brittleness index Damage Strain capacity Elastic quality index
1. Introduction During the last 20 years, significant research work has been carried out to recycle the used tyres by grinding them into small particles (rubber aggregates) and also by obtaining steel fibers, and to use them in cement based materials like concrete (Garrick, 2005; Hernández-Olivares et al., 2007; Khatib and Bayomy, 1999; Sukontasukkul and Chaikaew, 2006; Topcu, 1995; Donaldson, 2010). Results of various research studies indicate that mechanical properties (such as compressive, splitting tensile and flexural strength) of concrete are degraded in the presence of rubber aggregates. In opposite to that strain capacity of cement based materials is significantly increased by the addition of rubber aggregates (Turatsinze et al., 2005). A recent study by Ho et al. (2008) confirmed that rubber aggregate incorporation improves the strain capacity of concrete before macro-crack localization. In the present state of knowledge, information about fundamental fracture properties of rubberized concrete is limited. Topçu (1997) observed that with the addition of rubber aggregates in the
concrete, brittleness index (BI) increases while compressive strength and toughness decrease. When resistance to the cracking due to imposed deformation is a priority, use of rubber aggregates should be considered as a suitable solution to improve durability in order to reduce maintenance expenses and an opportunity to recycle used rubber tyres. In this research study, three-point bending tests were performed to investigate the effect of rubber aggregates addition on fracture properties (BI and damage) of concrete. Classical acoustic emission (AE) technique was applied to detect damage mechanism. Elastic Quality Index (EQI) is usually adopted to decide between two mutually exclusive properties that govern the design of pavements on soil namely modulus of elasticity and tensile strength (Ruban, 2002). In this study, EQI of rubberized concrete is investigated. Moreover, effect of different ambient temperatures on the EQI is also highlighted. 2. Experimental program 2.1. Materials
* Corresponding author. Tel.: þ33 5 61 55 99 34; fax: þ33 5 61 55 99 49. E-mail address: [email protected] (A. Turatsinze). 0959-6526/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2011.09.016
The rubber aggregates used were obtained from the mechanical grinding of used tyres. They had sizes ranging from 0 to 4 mm and
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A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
Table 1 Concrete mix proportions (value in kg/m3). Composition
C0R
C20R
C30R
C40R
Cement Sand (0e4 mm) Rubber aggregates (0e4 mm) Gravel (4e10 mm) Water Super-Plasticizer Stabilizer
323 872 0
698 79
611 118
524 157
967 153 3.03 0.91
3.29
3.61
3.99
were characterized by a specific gravity of 1.2 and insignificant water absorption. CEMI 52.5R cement, rounded siliceous sand (0e4 mm, specific gravity of 2.62 and water absorption of 1.90%) and rounded siliceous gravel (4e10 mm, specific gravity of 2.66 and water absorption of 1.10%) were used. An acrylic copolymer based super-plasticizer (Sika Viscocretekrono 33, dry matter content 34.5%) and a viscosity agent (Sika Stabilizer 300 SCC) were used as admixtures to improve the fresh properties of rubberized concrete.
after removing from oven. RILEM CPC8 recommendations and European standard NF EN 12390-6 were followed to perform modulus of elasticity and splitting tensile strength tests, respectively. To evaluate the acoustic emission (AE), brittleness index (BI) and damage variable (D), three-point bending tests (3PBT) were performed on notched beams (notch depth ¼ 18 mm) with an effective span of 440 mm. For bending tests, procedure adopted by Zhang et al. (2002) was followed. The beams were notched one day before the testing date. The tests were controlled by the imposed deflection at the rate of 1.25 mm min1. The testing setup is shown in Fig. 1. During the bending test performed to study damage evolution, specimen was unloaded and reloaded at seven points of deflection; three points in pre-peak region (0,04; 0,05; 0.06 mm) and four in
2.2. Mix proportions Four different types of concrete mixes were prepared: one control and three rubberized concretes. Rubberized concretes were prepared by replacing a volume fraction of rounded siliceous sand by rubber aggregates in control concrete. Different concrete mixes were designated taking into account their rubber aggregate content, for example, C20R in which letter C is for concrete, letter R refers to rubber aggregates and 20 is volumetric ratio of rubber aggregates to natural sand. Mix proportions of all four concretes are given in Table 1, where it can be noticed that a stabilizer was added in the concrete mix to avoid the segregation problem. Moreover, a super plasticizer was also used to get slump value of 10 2 cm for each composition of concrete with or without rubber aggregates. 2.3. Specimen preparation and test setup All specimens were demolded after 24 h of casting and then placed in curing room with 20 C temperature and 100% relative humidity until testing day. To determine the EQI value of concrete composite used in flexible pavement construction, values of direct tensile strength and modulus of elasticity are required. In this study, the value of direct tensile strength is indirectly found from splitting tensile strength. For the splitting tensile and modulus of elasticity tests at different ambient temperatures, after 27 days of curing, twelve cylindrical specimens were capped with sulfur compound and then heated in oven up to temperature of 40 C and 70 C during 24 h. For each temperature, six specimens (three specimens for each test) were prepared and immediately tested
Fig. 1. Testing setup for 3PBT (all dimensions in mm).
Fig. 2. Testing setup and measurements scheme of AE test (all dimensions in mm).
A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
211
post-peak region (0,1; 0,15; 0,2; 0.3 mm). The unloading was done up to 1.0 kN.
According to this approach, a damage variable (D) is defined as given by the Eq. (2).
2.4. AE monitoring equipment
D ¼ 1
Acoustic emission (AE) monitoring equipment was set on the same specimens tested in bending (refer to Fig. 2) to study the effect of rubber aggregates on the brittleness index (BI). Testing setup and procedure of measurements similar to that as adopted by Chen and Liu (2007), were used in this study. The AE measurement system was consisted of transducers, preamplifiers and AE signal monitor. Three-dimension source localization composed of six channels (PZT) was employed. Three R15a with resonance frequency of 150 kHz were fixed on the top face and three WD with frequency range of 100 kHz to 1.0 MHz were fixed on the bottom face of the test specimen as shown in Fig. 2.
Where E and E* are the modulus of elasticity of concrete at it initial state, supposed to be undamaged and damaged concrete, respectively. In this study, damage variable is defined by replacing E* and E with the value of slopes K* and K in Eq. (2) and new expression for damage variable (D) is given in Eq. (3) where i ranges from 1 to 7. Definitions of K* and K are given in Fig. 4.
3. Results and discussions 3.1. Brittleness index The definition of BI proposed by Zhang et al. (2002) was followed and is given by Eq. (1). In this study, specimen is considered to be fully fractured when load drops to a value of 0.2 kN.
BI ¼
Elastic energy Total energy
(1)
For an elasticeplastic material (or ductile material), BI approaches to zero since all energies become irreversible. For an elastic-brittle material, BI value approaches to one. In Fig. 3, it is observed that BI decreases with increasing rubber aggregate content. By replacing 20% and 40% sand with rubber aggregates, BI value of the concrete is decreased by 23% and 29%, respectively. Drop in BI values with the increase of rubber aggregate content in concrete shows that more is the rubber aggregate content, more ductile is the behavior of concrete. In other words, with lower values of BI, concrete is more ductile. However, it is important to note here that according to Topçu (1997), there exists an optimal rubber aggregate content at which brittle behavior of the material changes to ductile behavior. 3.2. Damage variable (D) In damage mechanics, among other approaches used to define damage, relative change in modulus of elasticity is also used.
Di ¼ 1
Ki* K
(2)
(3)
In Fig. 4, illustration to define the change of slope (K) of the curve at each unloading point in order to calculate the damage variable (D) is given. Loading and unloading loops of two concrete compositions C0R and C40R are given for two concretes as shown in Fig. 5. Evolution of damage variable (D) for C0R and C40R in three point bending tests is represented in Fig. 6. The damage variable (D) evolution can be assumed to have three parts with different slopes: First part in which damage is not clear to be observed. Load value at the end point of this part (point A) is about 60e70% of peak load while deflection value at this point is between 0.03 and 0.05 mm. In second part which is from point A to B, slope of the curve is steeper which shows significant increase in damage variable (D). During this stage, damage level in the specimen reaches up to 80%. In third part BC, although slope of the curve is decreased compared to second part but at point C, damage variable (D) is observed to be between 0.85 and 0.95. At this stage, specimen can be considered as completely fractured. Comparison of damage evolution curves of C0R and C40R in Fig. 6 shows that damage variable values of C40R are always lower than that of C0R. Lower values of D with C40R can be attributed to the energy absorption capacity of rubber aggregates when microcrack tips run into their interface with the cement paste. The resulting stress slows down the propagation of micro-cracks and delays macro-crack formation. 3.3. Acoustic emission (AE) In this study, AE technique was employed to verify the findings related to damage variable which has been presented in previous section. Through this technique, AE source location image, AE hits
0,13
Brittleness Index (BI)
E* E
0,12
0,11
0,10
0,09
0,08 0%
10%
20%
30%
40%
Rubber Aggregate Content (% ) Fig. 3. BI values of concrete with different rubber aggregate content.
Fig. 4. Loading and unloading curve to define change of slope (K).
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7
a
C0R
6
Load (kN)
5 4 3 2 1 0 0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
Deflection (mm) 7
b
6
C40R
Load (kN)
5 4 3 2 Fig. 7. AE source location for C0R: (a) AE source location before Fmax, (b) AE source location of complete test.
1 0 0,15
0,2
0,25
0,3
0,35
Deflection (mm) Fig. 5. The loops load-unload-deflection to determine D of C0R and C40R.
and load-deflection curve were obtained and analyzed. Fig. 7 shows a typical example of AE source location image. It is observed in Fig. 7a and b that AE events occur significantly at and around the tip of the notch and change with the propagation of crack Fig. 8a and b show AE events and load-deflection curve of C0R and C40R, respectively obtained in three-point bending test. Based on load-deflection behavior of concrete, cumulative AE event curve can be divided into two zones during the whole loading process.
Zone 2: Non-elastic stage with the occurrence of visible cracks. Non linear behavior starts from point A. From point B in cumulative AE hits-deflection response, there was a clear change in the slope of the curve. It shows that it is the moment when external load is about 80% of the ultimate load. At this
a
100 000
10 Load-deflection curve
8
Zone 1: The load-deflection curve is quasi linear and material is considered to be in elastic range. In this zone, no significant change in occurrence of AE events is observed.
A
6
Zone 1
0
C
C40R
0
0,6 0,4
0,1
0,15
0,2
0,25
12000 Load-deflection curve Cumulative AE Hits
4
Zone 2
3
6000 4000
Zone 1
2000
1 B
0
0
0,05
0,1
0,15
0,2
0,25
0,3
10000 8000
A
A 0,0
0,3
Deflection (mm)
2
0,2
0,05
6 5
B
0,8
20 000
B
Load (kN)
Damage Variable (D)
C0R
60 000 40 000
4 2
b
1,0
Cumulative AE Hits Zone 2
0
1,2
80 000
Cumulative AE Hits
0,1
Cumulative AE Hits
0,05
Load (kN)
0
0
0,05
0
0,1
0,15
0,2
0,25
0,3
0,35
0,4
Deflection (mm)
Deflection (mm) Fig. 6. Evolution of damage variable of C0R and C40R.
Fig. 8. a. Load-deflection curve and cumulative AE hits of C0R. b. Load-deflection curve and cumulative AE hits of C40R.
A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
The variation of AE events during the loading of C0R and C40R are shown in Fig. 9, where it is observed that before the peak load, AE activity increases rapidly. During this stage, AE hits mainly result from the micro-crack propagation in the matrix. Slope of AE hits diagram of C40R is less steep than that of C0R. Moreover, for C40R, deflection value at peak of the AE hits is greater than that of C0R. It can also be observed that amplitude of AE hits for C40R at each point of deflection is smaller than that in case of C0R. In the descending branch of the load-deflection curve of C40R, AE hits decrease quickly and approaches to zero. This observation is further clarified by the results shown in Fig. 10, where it can be observed that cumulative AE hits of C0R are six times more than that C40R. After the peak load, cumulative AE hits of C0R keep on increasing while they increase a little up to deflection of 1 mm and then become almost constant in case of C40R. There are three hypotheses to explain the less AE hits in rubberized concrete.
8
Load (kN)
6
4
2
0
Fig. 9. Relationship between Load- Deflection curve and AE characteristics of C0R and C40R.
stage micro-cracking starts inside the specimen. The AE event occurrence keeps on increasing while load-deflection curve starts descending after attaining load bearing capacity of the beam. At this stage, first micro-cracks coalesce and macrocracks develop and propagate. According to damage or fracture mechanics of solids, fracture is a continuous process and is divided in to three stages: (1) microcracking stage; (2) micro-cracks propagate to form macro-crack; and (3) a rapid propagation of macro-cracks (Chen and Liu, 2008). In Fig. 8, it can be noticed that damage starting point (point A) can be determined by AE technique.
120 000
C0R
100 000 80 000 60 000 40 000
C40R 20 000 0 0
0,5
1
1,5
Deflection (mm) Fig. 10. Effect of rubber aggregate content on cumulative AE.
First hypothesis: the presence of rubber aggregates is assumed to act like a hole at the crack tip which decreases the tip sharpness of first micro-crack resulting in stress relaxation and ultimately slowing down the kinetics of micro-cracks propagation. This phenomena further delays micro-crack coalescence to form macro-cracks. As a result, AE hits are decreased significantly. Second hypothesis: when micro-cracks reach the interface of rubber aggregate and cement paste, they propagate along this interface and develop a new micro-crack at another point along the interface. Cracking along the interface causes reduction in strength and this could make events smaller than those obtained in cement paste or natural aggregates that have greater strength. In this way, occurrence of AE hits decreases during this stage. Third hypothesis: rubber aggregate is expected to have great capacity to absorb sound and vibration and therefore, they can absorb much of the elastic waves resulting from cracks. As a consequence, AE hits are decreased. Relationship between cumulative AE hits and damage variable (D) is depicted in Fig. 11 and it can be approximately presented by the following Eqs. 4 and 5:
C0R : AE ¼ 0:98D2 þ 2:45D þ 3:29
(4)
C40R : AE ¼ 2:06D2 þ 5:13D þ 0:96
(5)
Using these two equations, damage of microstructure can be predicted through the measurement of cumulative AE hits. Chen
Cumulative AE Hits, log10(hit)
Cumulative AE Hits
213
2
6 5 4 3 C0R
2
C40R
1 0 0,0
0,2
0,4
0,6
0,8
Damage Parameter Fig. 11. Relationship between damage variable and cumulative AE hits.
1,0
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A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
and Liu (2008) confirmed that the comparison of analysis between electrical resistance measurement and AE technique indicated that these two techniques are complementary for monitoring damage in carbon fiber-reinforced concrete.
3.4. Elastic quality index (EQI) The ideal material for pavements and similar applications must have low modulus of elasticity and high tensile strength, but unfortunately, these properties are mutually exclusive. In this study, performance of the rubberized concrete has been evaluated through a single parameter known as Elastic Quality Index (EQI). Modulus of elasticity and tensile strength are taken into consideration simultaneously in EQI. This parameter enables to define the thickness «h» of the layer of pavements for given loading conditions and life period. Pavements or slabs are subjected to wide range of temperature variations during their service life. Sometimes temperature change is too high to decrease their resistance to external loads. In order to evaluate the effect of temperature variation to resistance, splitting tensile strength and compressive modulus of elasticity tests were performed at three different temperatures 20 C, 40 C and 70 C after 28 days of specimens casting. These three temperatures correspond to normal condition inside of the laboratory, natural weather condition of the pavement in summer in temperate and tropical countries, respectively. For C30R, only results for tests performed at 20 C are now available. For the determination of EQI, direct tensile strength ‘ft’ was obtained from splitting tensile strength according to EN 1992-1-1 standard using the relation given in Eq. (6).
ft ¼ 0:9fct
(6)
The low tensile strength of rubberized concrete is usually explained by weak bond between rubber aggregate and cement matrix. However, Pelisser et al. (2011) demonstrated that it was possible to reduce this detrimental effect on the strength using rubber modified with alkaline activation and silica fume addition allowing a large amount of recycled rubber aggregate to be used for concretes that do not require higher level of strength. EQI results are given in Table 2 and graphically illustrated in Fig. 12. In Figs. 12 and 13, the numbers 20, 40, 70 after the composite name indicate different ambient temperatures. Fig. 12 shows that EQI of C20R and C30R at 20 C are greater than that of C0R. The greatest value of EQI at 20 C is obtained with C40R. It is also observed that EQI increases with increasing of temperature for all of studied composites. In Fig. 12, it can be noticed that EQI for all the rubberized concretes tested in this study remains within the limits used for the design of pavement on soil. With regard to classification of concrete composite for the pavement design, although replacement of find aggregate with rubber aggregate causes decrease in the direct tensile strength and modulus of elasticity of cement based composite used for the pavement design, but the resulting EQI values suggest that concrete composite incorporating rubber
Fig. 12. EQI values of different concretes tested in this study.
aggregates up to 40% fulfill the requirement of class G4 for concrete pavers (refer to Fig. 13). Results of ring-tests performed according to ASTM standard C 1581-04 on rubberized concrete by Ho et al. (2008) showed that incorporation of rubber aggregates improves resistance to cracking
Table 2 Effect of rubber aggregates and temperature on EQI. Mix
20 C Ec
C0R C20R C30R C40R
40 C fct
Ec
70 C fct
Ec
IQE (cm) fct
GPa
MPa
GPa
MPa
GPa
MPa
34.07 23.53 17.78 16.65
4.01 2.96 2.55 1.87
31.78 22.08
3.36 2.69
30.42 19.19
3.10 2.32
13.07
1.74
4.99
1.05
20 C
40 C
70 C
11.7 12.5 13.5 16.5
12.4 14
12.7 14.5
17
19.5 Fig. 13. Classification of concrete composites based on EQI values.
A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
due to length changes such as shrinkage cracking which is important for pavements. With regard to real world applications of rubberized concrete, findings of the present research study confirm that this material is suitable for the construction of slabs-on-grade especially side walks for which high strength is not required but joints are needed, but such joints are starting points of future distresses particularly because of the penetration of aggressive agents, curling and spalling which can be limited using rubberized concrete due its high strain capacity before localization of macro-crack. Another application, for which this composite is relevant, is the Controlled Modulus Columns (Pearlman and Porbaha, 2006). They are well adapted to high surface loading conditions and strict settlement requirements and are used to support slabs-on-grade, isolated footings and embankments on compressible clays, fills and organic soils. They require a cementitious material whose modulus of elasticity lower than ordinary concrete and the low strength induced by the presence of rubber aggregates is not prohibitive. Last but not least, rubberized concrete provides an opportunity to recycle used rubber tyres resulting in following threefold benefit: an industrial byproduct recovery to minimize the consumption of natural wealth, to meet the demand for a clean environment and to make applications more sustainable. 4. Conclusions and future work In this paper, different approaches were used to evaluate the performance of rubberized concrete. In addition to mechanical tests, classical AE technique was applied to monitor the damage of composite. Based on obtained results, the following conclusions can be drawn: Brittleness of the concrete composite is decreased by the addition of rubber aggregates. Brittle index decreases with the increase of rubber content in the concrete and it is almost zero for a concrete composite containing 40% rubber aggregate content. Kinetics of fracture process of rubberized concrete is slow in comparison to concrete without rubber aggregates. Acoustic emission technique with three-dimensional orientation feature can be applied to study the fracture properties of concretes and to verify the reliability of the damage evolution study. Results obtained by applying AE technique showed that before the peak load, there is a micro-cracking zone at the tip of the notch while from the peak load, the micro-cracks coalesce to form a localize macro-crack. AE hits are significantly small for rubberized concrete in comparison with concrete. The Elastic Quality Index of rubberized composite decreases with the increase of temperature.
215
The values of EQI for concrete composite containing rubber aggregates up to 40% remain within the limits for the design of pavement on soil. Use of rubber aggregates in concrete may address the demand for the conservation of a clean environment by recycling used tyres. The ongoing work is focusing on a field experience of pavements design and construction with the aim to validate the findings of this research study under actual conditions of operation. Acknowledgments The authors wish to acknowledge Agence Universitaire de la Francophonie (AUF) and Laboratoire Matériaux et Durabilité des Constructions (LMDC) for their financial and technical supports for this research study. References Chen, B., Liu, J., 2007. Investigation of effects of aggregate size on the fracture behavior of high performance concrete by acoustic emission. Construction and Building Materials 21, 1696e1701. Chen, B., Liu, J., 2008. Damage in carbon fiber-reinforced concrete, monitored by both electrical resistance measurement and acoustic emission analysis. Construction and Building Materials 22, 2196e2201. Donaldson, L., 2010. Research news; concrete revolutionises road construction. Materials Today 13, 10. Garrick, G.M., 2005. Analysis and testing of waste tire fiber modified concrete. Thesis (PhD), B.S., Louisiana State University. Hernández-Olivares, F., Barluenga, G., Parga-Landa, B., Bollati, M., Witoszek, B., 2007. Fatigue behaviour of recycled tyre rubber-filled concrete and its implications in the design of rigid pavements. Construction and Building Materials 21, 1918e1927. Ho, A.C., Turatsinze, A., Vu, D.C., 2008. In: Alexander, M.G., Beushausen, H.D., Dehn, F., Moyo, P. (Eds.), On the Potential of Rubber Aggregates obtained by Grinding End-of-life Tyres to Improve the Strain Capacity of Concrete. Taylor & Francis Group, London, pp. 123e129. Khatib, Z.K., Bayomy, F.M., 1999. Rubberized Portland cement concrete. Journal of Materials in Civil Engineering 11, 206e213. Pearlman, S.L., Porbaha, A., 2006. Design and monitoring of an embankment on controlled modulus columns. Transportation Research Record: Journal of the Transportation Research Board 1975, 96e103. Pelisser, F., Zavarise, N., Longo, T.A., Bernardin, A.M., 2011. Concrete made with recycled tire rubber: effect of alkaline activation and silica fume addition. Journal of Cleaner Production 19, 757e763. Ruban, M., 2002. Quality Control in Road Construction. Taylor & Francis, London. Sukontasukkul, P., Chaikaew, C., 2006. Properties of concrete pedestrian block mixed with crumb rubber. Construction and Building Materials 20, 450e457. Topçu, I.B., 1997. Assessment of the brittleness index of rubberized concretes. Cement and Concrete Research 27, 177e183. Topcu, I.B., 1995. The properties of rubberized concretes. Cement and Concrete Research 25, 304e310. Turatsinze, A., Bonnet, S., Granju, J.L., 2005. Potential of rubber aggregates to modify properties of cement based-mortars: improvement in cracking shrinkage resistance. Construction and Building Materials 21, 176e181. Zhang, B., Bicanic, N., Pearce, C.J., Phillips, D.V., 2002. Relation ship between brittleness and moisture loss of concrete exposed to high temperatures. Cement and Concrete Research 32, 363e371.
Contents lists available at SciVerse ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Effects of rubber aggregates from grinded used tyres on the concrete resistance to cracking Anh Cuong Ho a, Anaclet Turatsinze a, *, Rashid Hameed a, Duc Chinh Vu b a b
Laboratoire Matériaux et Durabilité des Constructions (LMDC), INSA-UPS, Génie Civil, 135 av. de Rangueil, 31077 Toulouse cedex 4, France Institut de Transport Science et Technologie (ITST), 1252 Duong Lang, Dong Da, Ha Noi, Viet Nam
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 March 2011 Received in revised form 12 September 2011 Accepted 16 September 2011 Available online 20 October 2011
In practice, pavements or slabs are subjected to wide range of length changes during their service life. In case of cement-based materials, their length changes due to shrinkage and/or temperature variations induce tensile stress which can result in cracking detrimental for durability. Generally, aggravating circumstances are observed due to the length change restraint. This contribution focuses on experimental results of tests performed on rubberized concrete produced by partly replacing natural sand (0 e4 mm) by rubber aggregates up to 40% by volume. The rubber aggregates are obtained by grinding of used tyres. Effect of rubber aggregate on brittleness index (BI) and on damage evolution was investigated by conducting three-point bending tests on notched beam. Results of these tests confirmed that the both BI and damage decrease with the increase of rubber aggregate content in the concrete. Acoustic emission (AE) technique was applied to detect damage mechanism in concrete by analyzing AE parameters. The Elastic Quality Index (EQI) was adopted to take into account two mutually exclusive properties which govern the sensitivity to cracking, namely strain capacity and tensile strength. Results obtained from the tests performed at 20 C, 40 C and 70 C showed that rubberized concrete exhibits EQI values within acceptable limits for the design of cement-based pavements. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Rubberized concrete Brittleness index Damage Strain capacity Elastic quality index
1. Introduction During the last 20 years, significant research work has been carried out to recycle the used tyres by grinding them into small particles (rubber aggregates) and also by obtaining steel fibers, and to use them in cement based materials like concrete (Garrick, 2005; Hernández-Olivares et al., 2007; Khatib and Bayomy, 1999; Sukontasukkul and Chaikaew, 2006; Topcu, 1995; Donaldson, 2010). Results of various research studies indicate that mechanical properties (such as compressive, splitting tensile and flexural strength) of concrete are degraded in the presence of rubber aggregates. In opposite to that strain capacity of cement based materials is significantly increased by the addition of rubber aggregates (Turatsinze et al., 2005). A recent study by Ho et al. (2008) confirmed that rubber aggregate incorporation improves the strain capacity of concrete before macro-crack localization. In the present state of knowledge, information about fundamental fracture properties of rubberized concrete is limited. Topçu (1997) observed that with the addition of rubber aggregates in the
concrete, brittleness index (BI) increases while compressive strength and toughness decrease. When resistance to the cracking due to imposed deformation is a priority, use of rubber aggregates should be considered as a suitable solution to improve durability in order to reduce maintenance expenses and an opportunity to recycle used rubber tyres. In this research study, three-point bending tests were performed to investigate the effect of rubber aggregates addition on fracture properties (BI and damage) of concrete. Classical acoustic emission (AE) technique was applied to detect damage mechanism. Elastic Quality Index (EQI) is usually adopted to decide between two mutually exclusive properties that govern the design of pavements on soil namely modulus of elasticity and tensile strength (Ruban, 2002). In this study, EQI of rubberized concrete is investigated. Moreover, effect of different ambient temperatures on the EQI is also highlighted. 2. Experimental program 2.1. Materials
* Corresponding author. Tel.: þ33 5 61 55 99 34; fax: þ33 5 61 55 99 49. E-mail address: [email protected] (A. Turatsinze). 0959-6526/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2011.09.016
The rubber aggregates used were obtained from the mechanical grinding of used tyres. They had sizes ranging from 0 to 4 mm and
210
A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
Table 1 Concrete mix proportions (value in kg/m3). Composition
C0R
C20R
C30R
C40R
Cement Sand (0e4 mm) Rubber aggregates (0e4 mm) Gravel (4e10 mm) Water Super-Plasticizer Stabilizer
323 872 0
698 79
611 118
524 157
967 153 3.03 0.91
3.29
3.61
3.99
were characterized by a specific gravity of 1.2 and insignificant water absorption. CEMI 52.5R cement, rounded siliceous sand (0e4 mm, specific gravity of 2.62 and water absorption of 1.90%) and rounded siliceous gravel (4e10 mm, specific gravity of 2.66 and water absorption of 1.10%) were used. An acrylic copolymer based super-plasticizer (Sika Viscocretekrono 33, dry matter content 34.5%) and a viscosity agent (Sika Stabilizer 300 SCC) were used as admixtures to improve the fresh properties of rubberized concrete.
after removing from oven. RILEM CPC8 recommendations and European standard NF EN 12390-6 were followed to perform modulus of elasticity and splitting tensile strength tests, respectively. To evaluate the acoustic emission (AE), brittleness index (BI) and damage variable (D), three-point bending tests (3PBT) were performed on notched beams (notch depth ¼ 18 mm) with an effective span of 440 mm. For bending tests, procedure adopted by Zhang et al. (2002) was followed. The beams were notched one day before the testing date. The tests were controlled by the imposed deflection at the rate of 1.25 mm min1. The testing setup is shown in Fig. 1. During the bending test performed to study damage evolution, specimen was unloaded and reloaded at seven points of deflection; three points in pre-peak region (0,04; 0,05; 0.06 mm) and four in
2.2. Mix proportions Four different types of concrete mixes were prepared: one control and three rubberized concretes. Rubberized concretes were prepared by replacing a volume fraction of rounded siliceous sand by rubber aggregates in control concrete. Different concrete mixes were designated taking into account their rubber aggregate content, for example, C20R in which letter C is for concrete, letter R refers to rubber aggregates and 20 is volumetric ratio of rubber aggregates to natural sand. Mix proportions of all four concretes are given in Table 1, where it can be noticed that a stabilizer was added in the concrete mix to avoid the segregation problem. Moreover, a super plasticizer was also used to get slump value of 10 2 cm for each composition of concrete with or without rubber aggregates. 2.3. Specimen preparation and test setup All specimens were demolded after 24 h of casting and then placed in curing room with 20 C temperature and 100% relative humidity until testing day. To determine the EQI value of concrete composite used in flexible pavement construction, values of direct tensile strength and modulus of elasticity are required. In this study, the value of direct tensile strength is indirectly found from splitting tensile strength. For the splitting tensile and modulus of elasticity tests at different ambient temperatures, after 27 days of curing, twelve cylindrical specimens were capped with sulfur compound and then heated in oven up to temperature of 40 C and 70 C during 24 h. For each temperature, six specimens (three specimens for each test) were prepared and immediately tested
Fig. 1. Testing setup for 3PBT (all dimensions in mm).
Fig. 2. Testing setup and measurements scheme of AE test (all dimensions in mm).
A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
211
post-peak region (0,1; 0,15; 0,2; 0.3 mm). The unloading was done up to 1.0 kN.
According to this approach, a damage variable (D) is defined as given by the Eq. (2).
2.4. AE monitoring equipment
D ¼ 1
Acoustic emission (AE) monitoring equipment was set on the same specimens tested in bending (refer to Fig. 2) to study the effect of rubber aggregates on the brittleness index (BI). Testing setup and procedure of measurements similar to that as adopted by Chen and Liu (2007), were used in this study. The AE measurement system was consisted of transducers, preamplifiers and AE signal monitor. Three-dimension source localization composed of six channels (PZT) was employed. Three R15a with resonance frequency of 150 kHz were fixed on the top face and three WD with frequency range of 100 kHz to 1.0 MHz were fixed on the bottom face of the test specimen as shown in Fig. 2.
Where E and E* are the modulus of elasticity of concrete at it initial state, supposed to be undamaged and damaged concrete, respectively. In this study, damage variable is defined by replacing E* and E with the value of slopes K* and K in Eq. (2) and new expression for damage variable (D) is given in Eq. (3) where i ranges from 1 to 7. Definitions of K* and K are given in Fig. 4.
3. Results and discussions 3.1. Brittleness index The definition of BI proposed by Zhang et al. (2002) was followed and is given by Eq. (1). In this study, specimen is considered to be fully fractured when load drops to a value of 0.2 kN.
BI ¼
Elastic energy Total energy
(1)
For an elasticeplastic material (or ductile material), BI approaches to zero since all energies become irreversible. For an elastic-brittle material, BI value approaches to one. In Fig. 3, it is observed that BI decreases with increasing rubber aggregate content. By replacing 20% and 40% sand with rubber aggregates, BI value of the concrete is decreased by 23% and 29%, respectively. Drop in BI values with the increase of rubber aggregate content in concrete shows that more is the rubber aggregate content, more ductile is the behavior of concrete. In other words, with lower values of BI, concrete is more ductile. However, it is important to note here that according to Topçu (1997), there exists an optimal rubber aggregate content at which brittle behavior of the material changes to ductile behavior. 3.2. Damage variable (D) In damage mechanics, among other approaches used to define damage, relative change in modulus of elasticity is also used.
Di ¼ 1
Ki* K
(2)
(3)
In Fig. 4, illustration to define the change of slope (K) of the curve at each unloading point in order to calculate the damage variable (D) is given. Loading and unloading loops of two concrete compositions C0R and C40R are given for two concretes as shown in Fig. 5. Evolution of damage variable (D) for C0R and C40R in three point bending tests is represented in Fig. 6. The damage variable (D) evolution can be assumed to have three parts with different slopes: First part in which damage is not clear to be observed. Load value at the end point of this part (point A) is about 60e70% of peak load while deflection value at this point is between 0.03 and 0.05 mm. In second part which is from point A to B, slope of the curve is steeper which shows significant increase in damage variable (D). During this stage, damage level in the specimen reaches up to 80%. In third part BC, although slope of the curve is decreased compared to second part but at point C, damage variable (D) is observed to be between 0.85 and 0.95. At this stage, specimen can be considered as completely fractured. Comparison of damage evolution curves of C0R and C40R in Fig. 6 shows that damage variable values of C40R are always lower than that of C0R. Lower values of D with C40R can be attributed to the energy absorption capacity of rubber aggregates when microcrack tips run into their interface with the cement paste. The resulting stress slows down the propagation of micro-cracks and delays macro-crack formation. 3.3. Acoustic emission (AE) In this study, AE technique was employed to verify the findings related to damage variable which has been presented in previous section. Through this technique, AE source location image, AE hits
0,13
Brittleness Index (BI)
E* E
0,12
0,11
0,10
0,09
0,08 0%
10%
20%
30%
40%
Rubber Aggregate Content (% ) Fig. 3. BI values of concrete with different rubber aggregate content.
Fig. 4. Loading and unloading curve to define change of slope (K).
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7
a
C0R
6
Load (kN)
5 4 3 2 1 0 0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
Deflection (mm) 7
b
6
C40R
Load (kN)
5 4 3 2 Fig. 7. AE source location for C0R: (a) AE source location before Fmax, (b) AE source location of complete test.
1 0 0,15
0,2
0,25
0,3
0,35
Deflection (mm) Fig. 5. The loops load-unload-deflection to determine D of C0R and C40R.
and load-deflection curve were obtained and analyzed. Fig. 7 shows a typical example of AE source location image. It is observed in Fig. 7a and b that AE events occur significantly at and around the tip of the notch and change with the propagation of crack Fig. 8a and b show AE events and load-deflection curve of C0R and C40R, respectively obtained in three-point bending test. Based on load-deflection behavior of concrete, cumulative AE event curve can be divided into two zones during the whole loading process.
Zone 2: Non-elastic stage with the occurrence of visible cracks. Non linear behavior starts from point A. From point B in cumulative AE hits-deflection response, there was a clear change in the slope of the curve. It shows that it is the moment when external load is about 80% of the ultimate load. At this
a
100 000
10 Load-deflection curve
8
Zone 1: The load-deflection curve is quasi linear and material is considered to be in elastic range. In this zone, no significant change in occurrence of AE events is observed.
A
6
Zone 1
0
C
C40R
0
0,6 0,4
0,1
0,15
0,2
0,25
12000 Load-deflection curve Cumulative AE Hits
4
Zone 2
3
6000 4000
Zone 1
2000
1 B
0
0
0,05
0,1
0,15
0,2
0,25
0,3
10000 8000
A
A 0,0
0,3
Deflection (mm)
2
0,2
0,05
6 5
B
0,8
20 000
B
Load (kN)
Damage Variable (D)
C0R
60 000 40 000
4 2
b
1,0
Cumulative AE Hits Zone 2
0
1,2
80 000
Cumulative AE Hits
0,1
Cumulative AE Hits
0,05
Load (kN)
0
0
0,05
0
0,1
0,15
0,2
0,25
0,3
0,35
0,4
Deflection (mm)
Deflection (mm) Fig. 6. Evolution of damage variable of C0R and C40R.
Fig. 8. a. Load-deflection curve and cumulative AE hits of C0R. b. Load-deflection curve and cumulative AE hits of C40R.
A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
The variation of AE events during the loading of C0R and C40R are shown in Fig. 9, where it is observed that before the peak load, AE activity increases rapidly. During this stage, AE hits mainly result from the micro-crack propagation in the matrix. Slope of AE hits diagram of C40R is less steep than that of C0R. Moreover, for C40R, deflection value at peak of the AE hits is greater than that of C0R. It can also be observed that amplitude of AE hits for C40R at each point of deflection is smaller than that in case of C0R. In the descending branch of the load-deflection curve of C40R, AE hits decrease quickly and approaches to zero. This observation is further clarified by the results shown in Fig. 10, where it can be observed that cumulative AE hits of C0R are six times more than that C40R. After the peak load, cumulative AE hits of C0R keep on increasing while they increase a little up to deflection of 1 mm and then become almost constant in case of C40R. There are three hypotheses to explain the less AE hits in rubberized concrete.
8
Load (kN)
6
4
2
0
Fig. 9. Relationship between Load- Deflection curve and AE characteristics of C0R and C40R.
stage micro-cracking starts inside the specimen. The AE event occurrence keeps on increasing while load-deflection curve starts descending after attaining load bearing capacity of the beam. At this stage, first micro-cracks coalesce and macrocracks develop and propagate. According to damage or fracture mechanics of solids, fracture is a continuous process and is divided in to three stages: (1) microcracking stage; (2) micro-cracks propagate to form macro-crack; and (3) a rapid propagation of macro-cracks (Chen and Liu, 2008). In Fig. 8, it can be noticed that damage starting point (point A) can be determined by AE technique.
120 000
C0R
100 000 80 000 60 000 40 000
C40R 20 000 0 0
0,5
1
1,5
Deflection (mm) Fig. 10. Effect of rubber aggregate content on cumulative AE.
First hypothesis: the presence of rubber aggregates is assumed to act like a hole at the crack tip which decreases the tip sharpness of first micro-crack resulting in stress relaxation and ultimately slowing down the kinetics of micro-cracks propagation. This phenomena further delays micro-crack coalescence to form macro-cracks. As a result, AE hits are decreased significantly. Second hypothesis: when micro-cracks reach the interface of rubber aggregate and cement paste, they propagate along this interface and develop a new micro-crack at another point along the interface. Cracking along the interface causes reduction in strength and this could make events smaller than those obtained in cement paste or natural aggregates that have greater strength. In this way, occurrence of AE hits decreases during this stage. Third hypothesis: rubber aggregate is expected to have great capacity to absorb sound and vibration and therefore, they can absorb much of the elastic waves resulting from cracks. As a consequence, AE hits are decreased. Relationship between cumulative AE hits and damage variable (D) is depicted in Fig. 11 and it can be approximately presented by the following Eqs. 4 and 5:
C0R : AE ¼ 0:98D2 þ 2:45D þ 3:29
(4)
C40R : AE ¼ 2:06D2 þ 5:13D þ 0:96
(5)
Using these two equations, damage of microstructure can be predicted through the measurement of cumulative AE hits. Chen
Cumulative AE Hits, log10(hit)
Cumulative AE Hits
213
2
6 5 4 3 C0R
2
C40R
1 0 0,0
0,2
0,4
0,6
0,8
Damage Parameter Fig. 11. Relationship between damage variable and cumulative AE hits.
1,0
214
A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
and Liu (2008) confirmed that the comparison of analysis between electrical resistance measurement and AE technique indicated that these two techniques are complementary for monitoring damage in carbon fiber-reinforced concrete.
3.4. Elastic quality index (EQI) The ideal material for pavements and similar applications must have low modulus of elasticity and high tensile strength, but unfortunately, these properties are mutually exclusive. In this study, performance of the rubberized concrete has been evaluated through a single parameter known as Elastic Quality Index (EQI). Modulus of elasticity and tensile strength are taken into consideration simultaneously in EQI. This parameter enables to define the thickness «h» of the layer of pavements for given loading conditions and life period. Pavements or slabs are subjected to wide range of temperature variations during their service life. Sometimes temperature change is too high to decrease their resistance to external loads. In order to evaluate the effect of temperature variation to resistance, splitting tensile strength and compressive modulus of elasticity tests were performed at three different temperatures 20 C, 40 C and 70 C after 28 days of specimens casting. These three temperatures correspond to normal condition inside of the laboratory, natural weather condition of the pavement in summer in temperate and tropical countries, respectively. For C30R, only results for tests performed at 20 C are now available. For the determination of EQI, direct tensile strength ‘ft’ was obtained from splitting tensile strength according to EN 1992-1-1 standard using the relation given in Eq. (6).
ft ¼ 0:9fct
(6)
The low tensile strength of rubberized concrete is usually explained by weak bond between rubber aggregate and cement matrix. However, Pelisser et al. (2011) demonstrated that it was possible to reduce this detrimental effect on the strength using rubber modified with alkaline activation and silica fume addition allowing a large amount of recycled rubber aggregate to be used for concretes that do not require higher level of strength. EQI results are given in Table 2 and graphically illustrated in Fig. 12. In Figs. 12 and 13, the numbers 20, 40, 70 after the composite name indicate different ambient temperatures. Fig. 12 shows that EQI of C20R and C30R at 20 C are greater than that of C0R. The greatest value of EQI at 20 C is obtained with C40R. It is also observed that EQI increases with increasing of temperature for all of studied composites. In Fig. 12, it can be noticed that EQI for all the rubberized concretes tested in this study remains within the limits used for the design of pavement on soil. With regard to classification of concrete composite for the pavement design, although replacement of find aggregate with rubber aggregate causes decrease in the direct tensile strength and modulus of elasticity of cement based composite used for the pavement design, but the resulting EQI values suggest that concrete composite incorporating rubber
Fig. 12. EQI values of different concretes tested in this study.
aggregates up to 40% fulfill the requirement of class G4 for concrete pavers (refer to Fig. 13). Results of ring-tests performed according to ASTM standard C 1581-04 on rubberized concrete by Ho et al. (2008) showed that incorporation of rubber aggregates improves resistance to cracking
Table 2 Effect of rubber aggregates and temperature on EQI. Mix
20 C Ec
C0R C20R C30R C40R
40 C fct
Ec
70 C fct
Ec
IQE (cm) fct
GPa
MPa
GPa
MPa
GPa
MPa
34.07 23.53 17.78 16.65
4.01 2.96 2.55 1.87
31.78 22.08
3.36 2.69
30.42 19.19
3.10 2.32
13.07
1.74
4.99
1.05
20 C
40 C
70 C
11.7 12.5 13.5 16.5
12.4 14
12.7 14.5
17
19.5 Fig. 13. Classification of concrete composites based on EQI values.
A.C. Ho et al. / Journal of Cleaner Production 23 (2012) 209e215
due to length changes such as shrinkage cracking which is important for pavements. With regard to real world applications of rubberized concrete, findings of the present research study confirm that this material is suitable for the construction of slabs-on-grade especially side walks for which high strength is not required but joints are needed, but such joints are starting points of future distresses particularly because of the penetration of aggressive agents, curling and spalling which can be limited using rubberized concrete due its high strain capacity before localization of macro-crack. Another application, for which this composite is relevant, is the Controlled Modulus Columns (Pearlman and Porbaha, 2006). They are well adapted to high surface loading conditions and strict settlement requirements and are used to support slabs-on-grade, isolated footings and embankments on compressible clays, fills and organic soils. They require a cementitious material whose modulus of elasticity lower than ordinary concrete and the low strength induced by the presence of rubber aggregates is not prohibitive. Last but not least, rubberized concrete provides an opportunity to recycle used rubber tyres resulting in following threefold benefit: an industrial byproduct recovery to minimize the consumption of natural wealth, to meet the demand for a clean environment and to make applications more sustainable. 4. Conclusions and future work In this paper, different approaches were used to evaluate the performance of rubberized concrete. In addition to mechanical tests, classical AE technique was applied to monitor the damage of composite. Based on obtained results, the following conclusions can be drawn: Brittleness of the concrete composite is decreased by the addition of rubber aggregates. Brittle index decreases with the increase of rubber content in the concrete and it is almost zero for a concrete composite containing 40% rubber aggregate content. Kinetics of fracture process of rubberized concrete is slow in comparison to concrete without rubber aggregates. Acoustic emission technique with three-dimensional orientation feature can be applied to study the fracture properties of concretes and to verify the reliability of the damage evolution study. Results obtained by applying AE technique showed that before the peak load, there is a micro-cracking zone at the tip of the notch while from the peak load, the micro-cracks coalesce to form a localize macro-crack. AE hits are significantly small for rubberized concrete in comparison with concrete. The Elastic Quality Index of rubberized composite decreases with the increase of temperature.
215
The values of EQI for concrete composite containing rubber aggregates up to 40% remain within the limits for the design of pavement on soil. Use of rubber aggregates in concrete may address the demand for the conservation of a clean environment by recycling used tyres. The ongoing work is focusing on a field experience of pavements design and construction with the aim to validate the findings of this research study under actual conditions of operation. Acknowledgments The authors wish to acknowledge Agence Universitaire de la Francophonie (AUF) and Laboratoire Matériaux et Durabilité des Constructions (LMDC) for their financial and technical supports for this research study. References Chen, B., Liu, J., 2007. Investigation of effects of aggregate size on the fracture behavior of high performance concrete by acoustic emission. Construction and Building Materials 21, 1696e1701. Chen, B., Liu, J., 2008. Damage in carbon fiber-reinforced concrete, monitored by both electrical resistance measurement and acoustic emission analysis. Construction and Building Materials 22, 2196e2201. Donaldson, L., 2010. Research news; concrete revolutionises road construction. Materials Today 13, 10. Garrick, G.M., 2005. Analysis and testing of waste tire fiber modified concrete. Thesis (PhD), B.S., Louisiana State University. Hernández-Olivares, F., Barluenga, G., Parga-Landa, B., Bollati, M., Witoszek, B., 2007. Fatigue behaviour of recycled tyre rubber-filled concrete and its implications in the design of rigid pavements. Construction and Building Materials 21, 1918e1927. Ho, A.C., Turatsinze, A., Vu, D.C., 2008. In: Alexander, M.G., Beushausen, H.D., Dehn, F., Moyo, P. (Eds.), On the Potential of Rubber Aggregates obtained by Grinding End-of-life Tyres to Improve the Strain Capacity of Concrete. Taylor & Francis Group, London, pp. 123e129. Khatib, Z.K., Bayomy, F.M., 1999. Rubberized Portland cement concrete. Journal of Materials in Civil Engineering 11, 206e213. Pearlman, S.L., Porbaha, A., 2006. Design and monitoring of an embankment on controlled modulus columns. Transportation Research Record: Journal of the Transportation Research Board 1975, 96e103. Pelisser, F., Zavarise, N., Longo, T.A., Bernardin, A.M., 2011. Concrete made with recycled tire rubber: effect of alkaline activation and silica fume addition. Journal of Cleaner Production 19, 757e763. Ruban, M., 2002. Quality Control in Road Construction. Taylor & Francis, London. Sukontasukkul, P., Chaikaew, C., 2006. Properties of concrete pedestrian block mixed with crumb rubber. Construction and Building Materials 20, 450e457. Topçu, I.B., 1997. Assessment of the brittleness index of rubberized concretes. Cement and Concrete Research 27, 177e183. Topcu, I.B., 1995. The properties of rubberized concretes. Cement and Concrete Research 25, 304e310. Turatsinze, A., Bonnet, S., Granju, J.L., 2005. Potential of rubber aggregates to modify properties of cement based-mortars: improvement in cracking shrinkage resistance. Construction and Building Materials 21, 176e181. Zhang, B., Bicanic, N., Pearce, C.J., Phillips, D.V., 2002. Relation ship between brittleness and moisture loss of concrete exposed to high temperatures. Cement and Concrete Research 32, 363e371.