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Hardened properties of self-compacting concrete with different crumb rubber size and content
Accepted Manuscript Original Article/Research Hardened properties of self-compacting concrete with different crumb rubber size and content Nahla Naji Hilal PII: DOI: Reference:
S2212-6090(16)30161-3 http://dx.doi.org/10.1016/j.ijsbe.2017.03.001 IJSBE 161
To appear in:
International Journal of Sustainable Built Environment
Received Date: Revised Date: Accepted Date:
20 October 2016 13 March 2017 18 March 2017
Please cite this article as: N.N. Hilal, Hardened properties of self-compacting concrete with different crumb rubber size and content, International Journal of Sustainable Built Environment (2017), doi: http://dx.doi.org/10.1016/ j.ijsbe.2017.03.001
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Hardened properties of self-compacting concrete with different crumb rubber size and content Nahla Naji Hilal *Dams and Water Resources Engineering Department, College of Engineering, University of Anbar, Ramadi, Anbar , Iraq Abstract This paper aims at investigating the effect of crumb rubber size and content on hardened characteristics of self-compacting concrete.To this end, different self-compacting concrete mixtures were designed at constant water-to-binder ratio of 0.35 and 520 kg/m3 of binder content. The class F fly ash was replaced with cement as 30% by weight. Six designated crumb rubber contents of 5, 10, 15, 20, and 25% and three different sized crumb rubbers (No.18, No.5, and mixed crumb rubber) were considered as experimental parameters. According to the obtained results, the use of crumb rubber had a negative effect on the hardened properties of self-compacting concretes and the significant improvement was achieved with addition of all tire wastes types, for ductility.
Keywords: Crumb rubber content; Crumb rubber size; hardened property; Self-compacting concrete; Waste tire
1. Introduction Self-compacting concrete (SCC) is known as a revolution in concrete placement. Since SCCflows under its own weight, there is no need for any external vibration to compact concrete. SCC, as a highly workable concrete, was first introduced in the late 1980’s in Japan [1]. This was capable of flowing under its weight through restricted sections with no segregation and bleeding. This material needs to have a relatively low yield value in order to
guarantee a high flow capability and a moderate viscosity to resist segregation and bleeding. In addition, SCC should keep up its homogeneity during the processes of transportation, placing, and curing in order to guarantee long term durability and adequate structural performance. If SCC is developed successfully, an appropriate balance between stability and deformability can be ensured. In literature, there are some guidelines for mixture proportioning of SCC, including (i) to reduce volume ratio of aggregate to cementitious material [1-2]; (ii) to increase paste volume and water-cement ratio (w/c); (iii) to control carefully the maximum coarse aggregate particle size and total volume; and (iv) to make use of different viscosity enhancing admixtures (VEA) [1].
The changes of strength, usefulness and vibrant attributes of rubberized concretes with respect to magnitude and quantity of the rubber types and rubber scraps have been explored by many studies in last two decades [3]. The rubberized concrete is found to be a perfect material for the structural members exposed to rapid effects and for which preferred toughness or deformability holds greater significance than strength, like road foundations, jersey barriers and bridge barriers. Specifically, rubberized concrete has dynamic attributes to minimize the vibration and to absorb the impact energy more helpfully than the conventional concrete. It has been asserted by Gu¨neyisi et al. [4] that the rubber content decreases the strength of concretes that include silica fume, crumb rubber and tyre chips. It has been stated by these authors that a 40 MPa concrete can be produced by substituting a volume of 15% of aggregates with rubber waste.
Crumb rubber from scrap tyres (2-6mm) were employed by Najim and Hall [5] as a partial substitute for Fine Aggregate (FA), Coarse Aggregate (CA) and mixed Fine and Coarse Aggregate (FCA) in self compacting concrete at weighted proportions of 5%,10% and 15%. It has been asserted by these authors that the compressive strength decreases in the same manner as that shown for Plain Rubberised Concrete (PRC). To substitute both fine and rough aggregates with exact amounts of 10% and 20% according to weight, Piti Sukontasukkul , Chalermphol Chaikaew [6] use crumb rubber concrete in three different categories: (1) No. 6, (2) No. 20 and (3) Combined No. 6 + 20. The results obtained showed that the plain concrete block had greater flexural strength compared to crumb rubber concrete blocks. The tensile strength of concretes with silica fume, crumb rubber and tyre chips was examined by Güneyisi et al. [4]. In accordance with the rubber content, the tensile strength was reduced but the presence of silica fume gives it a higher filler effect to add to its benefits. The reduction in the tensile strength is not affected as much as compressive strength reduction is by the addition of rubber content. Even at similar compressive strengths, the NVC has greater tensile strength than the SCC and SCRC Najim and Hall [5]. The reason behind this is the dens microstructure in SCC mixes that causes greater brittleness and lesser splitting strength.
It was obviously seen that the increment in the elastic modulus was more diminutive as contrasted with that in the compressive and splitting tensile strengths Güneyisi et al. [4]. By and large, the plain and the rubberized concretes displayed an increment in the modulus of up to 15% relying upon the measure of silica fume utilized. Notwithstanding, for the same w/cm proportion and the content of rubber, all mixtures accomplished just about comparable results
Zheng et al. [7,8] specified that the crumb rubber (80 %< 2,62mm) has a lesser affect in the elasticity modulus compared to the crushed rubber (15-40mm). It is indicated by Gideon [9] that at 15% Crumb Rubber substitution, the concrete with Crumb Rubber has modulus of elasticity which is 11% higher than the control concrete. When contrasting the two concretes and silica smoulder, however, the Crumb Rubber adjusted concrete has a elasticity modulus which is 34% less contrasted with the control which additionally holds silica fume that has been indicated to build compressive strength and it likewise builds the modulus of elasticity By and large, the elasticity modulus rises as the strength rises.
Khalid Najim, Matthew Robert Hall [5] made study on plain rubberized concrete ( PRC) and they found that rubber total substitution diminished the Crack mouth open uprooting (mm) ( CMOD) at a given stacking level bringing about more excellent flexural durability values, no doubt, because of vitality retention by the rubber. Khalid Najim , Matthew Robert Hall [10] found that, after 0.1 mm avoidance, the specimens with (mortar precoated rubber total) (SCRC3) and bond glue (concrete glue precoated rubber total (SCRC2) P-T/C demonstrated unrivalled execution with relevance to further diminishing the Crack mouth open dislodging( CMOD) at a given burden. This likewise happened, yet to a lesser degree, with NaOH pretreatment and water washing. Such conduct could be ascribed to the capacity of the covered rubber to ingest more vitality by holding crack proliferation inside the concrete body, e.g. by lengthening crack ways and anxiety unwinding.
Seleem et al. [11] specified that the fracture durability for either self compaction or typical vibrated concrete diminished with expanding crack –depth proportion, and the Self compacting concrete recorded higher imperviousness to crack spread contrasted with ordinary vibrated concrete independent of the kind of coarse total. Hamid Eskandari et al. [12] report self compacting concrete (SCC) is more bendable than elite concrete (HPC). Consequently, it could be utilized in any event for vast size structures. Furthermore the qualities of trademark length of SCC (lch) are to be more when contrasted with the HPC, NC and high strength concrete. It may be presumed that the SCC is more flexible contrasted with HPC.
The strength of the bond of the self-compacting concrete as reported by P.Desnercketal[13] after studying large bar diameters; it is equally high as the bond strength of the traditional vibrated concrete. The bond strength of SCC with smaller bar diameters is somewhat greater and, with the smaller diameters, takes place the greatest variation. The bond strength is decreased owing to Portland cement substitution with dolomite powder as suggested by M. M. Kamal1 et al. [14]. The mechanical interaction was interfered with as the chemical adhesion characteristic was bettered. The bond strength was mainly due to the resistance by friction and silica fume or fly ash addition which effectively, with the increase of dolomite powder content, prevents extended degradation of the bond strength. The effect of rubber types and rubber content on mechanical properties of concrete. Studied by Farhad Aslani [15]. Report the following conclusions:
• The proposed compressive stress-strain relationship is simple and reliable for modeling the compressive behavior of RC.Moreover, using these relationships in the finite element method (FEM) is more simple and suitable.
• The proposed relationships for the compressive, tensile and flexural strengths, elasticity modulus, and peak strain of RC with different content of WTR are in good reasonable agreement with the experimental results. Also, the relationships for previously noted mechanical properties are proposed that can calculate these properties related to the CR, TC, and CR+CT contents.
• The proposed relationships for compressive strength of RC with CR, TC, and CR+CT contents at 7 and 28 days of age and with two different w/c ratio ranges (0.40–0.50, and 0.50– 0.60) are covered. Also, the proposed relationships for modulus of elasticity for three RC mixtures at 28 days of age and with two different w/c ratio ranges (i.e., 0.40–0.50 and 0.50– 0.70) are covered.
• These relationships are proposed for tensile strength, flexural strength, and peak strain of RC with CR, TC, and CR+CT contents at 28 days of age.
Farhad Aslani and Shami Nejadi [16]. Study bond strength model based on the experimental results from eight recent investigations of SCC and CC. In addition, the proposed model, code provisions, and empirical equations and experimental results from recent studies on the bond strength of SCC and CC are compared. The comparison is based on the measured bond between reinforcing steel and concrete utilizing the pullout test on the embedded bars at various heights in the mock-up structural elements to assess the top bar effect on single bars in small prismatic specimens by conducting beam tests. The investigated varying parameters on bond strength are the: steel bar diameter, concrete compressive strength, concrete type, curing age of the concrete, and height of the embedded bar along. The experimental results shown The ultimate and mean bond strengths are greater in SCC than in CC, For the top cast
bars, the local bond strength for SCC is greater than that for CC and the bond strength of SCC is as high as the bond strength for CC when large bar diameters are studied. For smaller bar diameters, the bond strength of SCC is slightly higher, with the largest difference occurring for the smallest bar diameters.
This study covers the effect of crumb rubber content and size on the hardened properties of SCC. Therefore, three different sized crumb rubbers (No.18, No.5, and mixed crumb rubbers) and their mixtures were replaced with the natural sand at five different contents of 5, 10, 15, 20, and 25% as a volume. The No.18 crumb rubber is a fine material passing from 1-mm sieve whereas the No.5 crumb rubber is a fine material retaining on 1-mm sieve and passing from 4-mm sieve. Moreover, No.18 and No.5 crumb rubbers are mixed to achieve a new fine material with a gradation close to the natural sand. The constant water-to-binder (w/b) ratio of 0.35 and binder content of 520 kg/m3 were designated to produce SCCs. To improve the workability of SCCs,the Class F fly ash (30% of total binder content by weight) was introduced in the mixture. The hardened properties of SCCs were investigated in terms of the compressive strength, splitting tensile strength, flexural, modulus of elasticity, fracture energy and bond strength .Totally 16 self-compacting rubberized concrete (SCRC) mixtures mixes were designed and tested at 90 day.
2. Experimental study
2.1. Materials
2.1.1. Cement and fly ash Ordinary Portland cement (CEM I 42.5R) with specific gravity of 3.15 g/cm3 and Blaine fineness of 326 m2/kg was utilized in this study. Class F fly ash (FA) according to ASTM C 618 [17] with a specific gravity of 2.25 g/cm3 and Blaine fineness of 379 m2/kg was utilized in the manufacturing of the SCCs. Physical properties and chemical compositions of the cement and fly ash are presented in Table 1.
2.1.2. Aggregates The coarse aggregate was river gravel with a nominal maximum size of 16 mm and the fine aggregate, a mixture of natural river sand and crushed limestone, was used with a maximum size of 4 mm. River sand, crushed sand, and river gravel had specific gravities of 2.65, 2.43, and 2.71, respectively. The particle size gradation obtained through the sieve analysis of the fine and coarse aggregates are given in Figure 4.
2.1.3. Crumb rubber The No.18 crumb rubber (No.18 CR) and No.5 crumb rubber (No.5 CR) are two different sizes of crumb rubbers. The No.18 CR is a fine material passing from 1-mm sieve whereas the No.5 CR is a material retaining on 1-mm sieve and passing from 4-mm sieve. Moreover, the No.18 CR and No.5 CR were mixed to obtain a new fine material with a gradation close to that of the sand. A crumb rubber (CR) of which gradation is very close to that of the sand was achieved by mixing 40% of No.18 CR and 60% of No.5 CR. The specific gravity of No.18
CR and No.5 CR are 0.50 and 0.67, respectively. The particle size distribution for the No.18 CR, No.5 CR, and Mixed CR is also presented in Figure 1. Additionally, the photographs of No.18 CR and No.5 CR are illustrated in Figure 2.
2.1.4. Superplasticizer A Polycarboxylic ether type of superplasticizer (SP), which acts by steric hindrance effect [18], with specific gravity of 1.07, was employed to achieve the desired workability in all concrete mixtures. 2.1.5. Steel bar Reinforcing ribbed steel bars having 16 mm diameter and minimum yield strength of 420 MPa were utilized for preparing the reinforced concrete specimens to be used for testing the bonding strength.
2.2. Mixture design SCRC mixtures were designed having a constant w/b ratio of 0.35 and total binder content of 520 kg/m3. The class F fly ash was used as a 30% of the total binder content as weight in all mixtures. The fine and coarse aggregates were replaced with t different graded crumb rubbers (No.18, No.5, and mixed crumb rubber)
respectively, at five designated contents of 5%,
10%, 15%, 20%, and 25% by volume. Totally 16 different SCRC mixtures were designed regarding to above variables. The detailed mix proportions for SCRCs are presented in Table 2.
3. Concrete casting To achieve the same homogeneity and uniformity in all SCRC mixtures, the batching and mixing procedure proposed by Khayat et al. [17] was followed since the mixing sequence and
duration are very vital in the self-compacting concrete production. According to this mixing procedure, the crumb rubber, fine and coarse aggregates in a power-driven revolving pan mixer were mixed homogeneously for 30 seconds, and then about half of the mixing water was added into the mixer and it was allowed to continue the mixing for one more minute. After that, the crumb rubber and aggregates were left to absorb the water in the mixer for 1 min. Thereafter, the cement and fly ash was added to the mixture for mixing another minute. Finally, the SP with remaining water was poured into mixer, and the concrete was mixed for 3 min and then left for a 2 min rest. At the end, to complete the production, the concrete was mixed for additional 2 min. Three 150-mm cubes were taken to measure the compressive strength, three100x200 mm cylinder were taken to measure the splitting tensile strength, Three 100x100x500-mm prisms were taken to measure the net flexural and fracture energy; and two150x300 mm cylinder were taken to measure the modulus of elasticity. Moreover three 150-mm cubes were taken to measure the bond strength of self-compacting rubberized concretes. Following the concrete casting, specimens were wrapped with plastic sheet and left in the casting room for 24 h at 20±2 °C and then they were demoulded and tested after 90-day water curing period.
2.4. Test procedure Compression test of self-compacting rubberized concrete sample was conducted using ASTM C39 [19] and the obtained results were presented as the average of three samples. Using ASTM C496, splitting test of self-compacting rubberized concrete sample was conducted [20] and the test results were given as the average of three samples. And splitting tensile strength of cylindrical concrete specimens was computed using the following equation.
st =
(1)
Where P, h, and Φ are the maximum load, length and diameter of the cylinder specimen, respectively. Static modulus of elasticity(E) was determined through testing the cylinders with a dimension of Φ150x300 mm using ASTM C469/C469M-10, 2010[21]. The results obtained for static modulus of the self-compacting rubberized concrete were presented as the average of two samples. The notched beams were applied to the calculation of the net flexural strength ( fflex ) using Equation (2) with the assumption that there is not any notch sensitivity, where P max signifies the ultimate load.
fflex=
(2)
To determine the fracture energy (Gf),a test was carried out with considering the recommendations given by the RILEM 50-FMC Technical Committee (RILEM 50-FMC, 1985) [22]. For the test of fracture energy, beams with 100x100 mm in cross-section and 500 mm in length were prepared. The notch to the specimens ’depth ratio (a/D) was 0.4 and the notch opening was obtained by decreasing the effective cross section to 60x100 mm through sawing to accommodate large aggregates in higher abundance, and distance between the supports was 400 mm. For each specimen, load versus deflection at the mid- span (δ) curve was found and the area under the load versus displacement at mid-span (Wo) was employed to determine the fracture energy that was computed using Equation (3) given by RILEM 50-FMC Technical Committee (RILEM 50-FMC, 1985). [22].
GF=
δs
(3)
where B, W, a, S, U, m, δs, and g are the width, depth, notch depth, span, length, mass, specified deflection of the beam .
The brittleness of materials in terms of characteristic length (lch) can be determined using the following equation (Hillerborg, 1985)[23].
lch
= !"
(4)
#$%
Where E, fst, and GF stand for the static modulus of elasticity, splitting tensile strength, and fracture energy, respectively. In the present study, the direct tensile strength was replaced with the splitting tensile strength.
The concrete’s bonding strength (ττ), was determined using the RILEM RC6 (RILEM RC6, 1996)[24].The bonding strength was computed using Equation (5):
τ=
&
'(
( 5)
Where F denotes the tensile load at failure (N), L and d signify the embedment length (mm) and the diameter (mm) of the reinforcing steel bar, respectively. In this study,150-mm cubic specimen and 16-mm steel bar were used; therefore, L and d were set to 150 and 16 mm, (see
Figure 3) respectively. For the purpose of loading, universal testing machine with the capacity of 600 KN was employed through installing specially-modified test apparatus to it (see Figure 4).
3. Results and discussion 3.1. Compressive strength The strength refers to a measure of the stress that is needed for fracturing a material and determined by the calculation of the maximum stress (fc′) that the specimen carries after being subjected to uni-axial compressive force. ((Kosmatka,Kerkhoff et al. 2002) [25 ]. Figure 5 presents the 90-day compressive strength of the mixtures. In this study, the compressive strength values obtained during 90days ranging from 39.28 MPa to 72.44 MPa were achieved. The control mixture showed the highest compressive strength result; and as the rubber content increased, the compressive strength systematically decreased. Compared to the natural aggregate, the crumb rubber is a soft material. If crumb rubber is used in concrete production, the compressive strength and the adhesion between rubber particles and surrounding cement paste are decreased .As a result, in literature, there are some recommendations for applying surface treatment of rubber particles in order to enhance its adhesion to the cement paste [27]. The lowest compressive strength was resulted from the self-compacting concretes produced with No.5 crumb rubber; whereas, the highest strength was resulted from those produced with No.18 crumb rubber. It has been shown that the coarse rubber particles have more negative effect on the properties compared to fine particles [27, 28]. The strength decrease with increasing rubber content is attributable to two reasons: (1) cracks are started rapidly near the rubber particles in the mix, which quickens the failure of the rubber–cement matrix as the rubber particles are much softer than the adjacent cement
paste on loading; and (2) rubber particles function as voids in the concrete matrix because of the absence of adhesion between the rubber particles and the paste [15]
3.2 Splitting tensile strength Splitting tensile strength values that are calculated from cylindrical specimens by means of Equation (1) are displayed in Table 3. The variation in splitting tensile strength noted during 90days for all SCRC associated with the content and size of crumb rubber is presented in Figure6. In this study, the splitting tensile strength values were obtained, ranging from 2.24 MPa to 4.36 MPa. The control mixture resulted in the highest splitting tensile strength, and the increase of rubber content led to a systematic reduction of splitting tensile strength. The splitting tensile strength decreased by 18.47%, 23.86%,and 21.44% for the concretes that were produced with No.18, No.5,and mixed crumb rubber, respectively, at proportions of 5%. Whereas the decreasein the splitting tensile strength at proportions of 25%was 80%, 94.64%and 92.92%. As shown by the obtained results, SCC produced by No.18crumb rubber resulted in the highest splitting tensile strength; while those produced by No. 5 crumb rubber resulted in the lowest splitting tensile strength. Additionally, it was found that the negative impacts of the coarse rubber particles on the properties were more than that of the fine particles [27, 29].Generally, the whole concretes have low tensile strength (~10% of compressive strength) and strain capacity [30].The tensile strength ,however, is of a great importance to airfield slabs, highway design, as well as in cases where crack resistance and shear strength are priority. These shortcomings are exacerbated by addition of the crumb rubber to SCC (see Fig.6) where a general tendency exists toward the reduction of the tensile strength, which may be attributed to the same reasons that affect the compressive strength. Many factors are effective on the relationship between splitting and compressive tensile strength, including aggregate type and particle size distribution, and curing age [31]and
powder and admixtures content and type. Farhad Aslani [15] show that the decrease in the tensile strength with the rubber content was lower than that in the compressive strength.
3.3 Static modulus of elasticity The test results of static modulus of elasticity are displayed in Fig. 7as a function of rubber and tire chip size and contents in the present study the Moduli of elasticity values, ranging from 30.98 GPa to 50.71 GPa, were obtained. The highest modulus of elasticity was obtained from the control mixture, and the increase of rubber content led to systematical reduction of modulus of elasticity. The decrease in the modulus of elasticity of rubberized concrete occurred for a number of reasons, including the inclusion of the waste tires rubber aggregate, acted similar to voids in the matrix, which was due to weak bond between the concrete matrix and waste tires rubber aggregate If the void content of concrete increases, the strength will decrease. The second reason is that waste tires rubber aggregate acts as weak inclusions in the hardened cement mass, hence producing high internal stress perpendicular to direction of the applied load. The third reason is that the strength of the Portland cement concrete depends mainly on the coarse aggregate, size, hardness, and density. The aggregates are replaced partially with rubber; for this reason, the decrease in strength is only natural. The last reason is that the failure of the sample is also due to the waste tire that is more elastically-deformable compared to the matrix. After loading the samples, the cracks form first at the softest areas. The rubber’s inclusion site is where these sites emerge[31].As shown by the graphs presented in Fig.7,the static elastic modulus was reduced when rubber size and content increased in a fashion comparable to that observed in both splitting and compressive tensile strengths. The results showed that SCCproduced with No.18 crumb rubber resulted in the highest static elastic modulus.
According to Turatsinze and Garros [32], the modulus of elasticity of SCC was expanded with rubber (4–10 mm) waste substance. In addition, they warned the risk of serious isolation with a high elastic waste concentration at the highest point of the samples, which could lead to a need for a fitting blend between a consistency executor and air-entraining operator in order to keep up a strategic distance from isolation. The modulus of elasticity was also affected by the particle size and amount of rubber as compressive strength according to [15].
3.4 Net flexural strength The net flexural strength values, which were evaluated using Equation (2) from the notched prismatic specimens (see Figure 8a) subjected to the three-point bending test (see Figure 8b), are displayed in Table 3. The variation in the net flexural strength of SCRC versus associated with crumb rubber content and size are displayed in Figure 9. The highest value was the net flexural strength of control mix 5.6 MPa. The SCC produced with No.5 crumb rubber resulted in the lowest net flexural strength, where as those produced with No.18 crumb rubber resulted in the highest net flexural strength.As shown by the obtained results, the control mix had greater net flexural strength in comparison with other mixture containing No.5, No.18, and mixed crumb rubber. Table 3clearly shows that the increase of the No.18 crumb rubber from 5-25% resulted in reducing the flexural strength up to 70% and, simultaneously, the mixture containing No.5 crumb rubber from 5-25% resulted in the reduction of the flexural strength up to 80%,whereas the decreasing the flexural strength with mixed crumb rubber (MCR) up to 78%.The decrease of fflex can be related to the same failure mechanism for splitting tensile strength, since this is a ‘theoretical’ measure for the highest tensile stress reached on the bottom fibre of a test beam. It is assumed that fflexis a ‘theoretical’ measurement since this is computed according to the elastic beam theory that assumes the stress–strain relationship is linear, thus the tensile stress in the beam is supposed to be proportional to the distance from the neutral axes [5]. In addition crack may initiate before the application of the maximum load. It is because micro cracks are formed once the
pre-peak zone is reached, and they are propagated after this stage [33]. In other words, the crumb rubber aggregate might work to delay the micro cracks formation because of a kind of stress relaxation. As a result, the incorporation of crumb rubber particles can lead to measurable improvements to pre-micro crack strain capacity [34].
The literature [34] shows that the tensile strength of concrete with chipped rubber replacement for aggregates is significantly lower than that of concrete that contains powdered rubber. First, a reduction from 30% to 60% occurs for a replacement level of 5-10%, as for the latter case, the reduction is 15-30%. This behavior might be related to the low adhesion between the cement and the chipped rubber. Previous study [15] shows that the flexural strength decreased with the increase of the rubber content in a fashion similar to that observed in the compressive strength. However, it was observed that the initial rate of strength reduction was steeper than that of the compressive strength. This is because of the weak bond between cement paste and rubber particles. 3.5 Fracture energy Fracture energy (GF) values evaluated with Equation (3) from notched beams (Figure 8a), which are subjected to three-point bending test (see Figure 8b), are shown in Table 3. The variations of fracture energy associated with crumb rubber size and content are presented in Figure 9. In the present study, GF values ranging from 110.21 N/mto155.8 N/m were obtained. The control mixture resulted in the highest GF, and it was observed that with an increase in the rubber content, the GF systematically decreased. Additionally, the highest was obtained by replacing fine aggregate with 5% no.18CR replacement, whereas the lowest was obtained by replacing fine aggregate with 25% No.5CR replacement. As shown in Figure 10,a reduction occurred in all GF values at 5%of No.18CR, No.5CR, and MCR; therefore,in both ultimate load and GF, the best improvement was obtained from No.18 crumb rubber.
As shown in Figures 11-13, the maximum displacement is corresponding to the maximum load for the control mix and this gradually decreases based on the size and amount of tire chip and crumb rubber, respectively. Figure 11 show that the concrete with 15%NO.18 CR has higher area under the load versus displacements curve; whereas the concrete with 25%NO.18 CR has lower area under the load. As can be seen in Figure 12, the concrete with 5%NO.5 CR has higher area under the load versus displacements curve, whereas the concrete with 15%NO.5 CR has lower area under the load. As shown in Figure 13, the concrete with 20%Mixed CR has higher area under the load versus displacement curve, on the other hand, the concrete with 25% Mixed CR has lower area under the load.
3.6 Characteristic length Using Equation (4), the concretes’ characteristic length, which is the measure of brittleness, was evaluated (the results are presented in Table3). Normally, in a typical concrete, (lch) is about200-500 mm [36, 37] and for SCC, (lch) it is 580-740 mm for notched beams and it ranges from 540 to 640 mm for un-notched beams. Additionally, it can be observed that (lch) decreases when the compressive strength and notch depth ratio increase.The variations occurred in the characteristic length of SCRCS associated with crumb rubber size and content are presented in Figure14. As shown in Table 3, the control mix has lower characteristic length compared to other mixtures; this is because of possessing higher compressive strength, which makes the concrete more brittle. The mixed crumb rubber (MCR) at 25% replacement enhances the characteristic length (lch) by 72%, as compared to the control mix.The use of crumb rubber enhanced the characteristic length of concrete. The characteristic length increased with an increase in the crumb volume fraction. With the increase of the No.18
crumb rubber volume fraction from 5%to25%, the characteristic length increased by 24%, 27%, 31%, 21%, and 61%, respectively.As shown by the obtained results, the improvement of characteristic length of the concrete with 25% mixed crumb rubber was more than that of the concrete with crumb rubber (No.18, No.5). This is due to better grading of the combined rubber.
3.7 Bond strength The axial force was transferred from reinforcing steel bar to the surrounding concrete by the development of tangential stress components along the contact surface. The stress that acts parallel to the bar along the interface is known as bond stress Pillai &Kirk, 1938, Hadi, 2008 [38]. Equation (5) was used to evaluate the bond strength values from cubic specimen, including the Φ16-reinforcement bar that was subjected to tensile load. The obtained results are displayed in Table 3. The control mixture resulted in the highest bond strength, and with the increase of the rubber content, the bond strength was systematically decreased. Whereas, the lowest bond strength values were measured on the 25% No.5CRmixture on the 90th day. This was because there was a low adhesion between rubber particles and surrounding cement paste. The 90-day bond strength of the mixtures presented in Figure 15indicates that the bond strength decreases with an increase in the crumb rubber size and content.The increase of No.18 crumb rubber from 5to25%led to the decrease of the bond strength by 7%,13%,37%,48%, and 70%, respectively. On the other hand, these rates for the No.5crumb rubber from 5to25%showed the decrease of the bond strength by 30%,42%,54%,74%, and 87%, respectively.
According to Emiroğlu et al. (2008) [39]. The decrease in the bond strength is due to poor bonding characteristic around cement paste and rubber tires. Many micro-cracks exist close to the ITZ in the rubberized concrete. Therefore, several studies have suggested the treatment for rubber in order to improve the bonding between the rubber and the cement paste. As shown by the obtained results, the bond strength of concrete with mixed crumb rubber MCR is developed more than the concrete with crumb rubber (No.18, No.5).
4. Conclusions •
Based on the results obtained from the experimental program presented above, the following conclusions can be drawn:
•
In total 16 SCRC mixtures were designed and produced by the replacing natural aggregate with rubber at six different replacement levels of 0%,5%, 10%, 15%, 20%, and 25%.
•
The compressive strength of self-compacting rubberized concrete having more than 30 MPa could be produced easily. The strength results indicated that the utilization of crumb rubber in self-compacting concrete manufacturing resulted in systematical decreasing of the compressive strength. Moreover, the coarse crumb rubber utilization decreased the compressive strength of self-compacting concrete more than the using of fine crumb rubber. It was found that the best replacement type was the MCR, which offered the best results as it was a compatible replacement for sand and gravel.
•
The highest splitting tensile strength result was obtained from control mixture, and the systematical decreasing of splitting tensile
strength was observed as rubber
content increased. The results indicated that the self-compacting concretes produced
with No.18crumb rubber gave the highest splitting tensile
strength, those produced
with No. 5 crumb rubber gave the lowest splitting tensile strength. •
The static elastic modulus decreased with increasing rubber size and content in a fashion similar to that observed in both compressive and splitting tensile strengths.
•
The net flexural strength of control mix is highest value. While the self-compacting concretes produced with No.5 crumb rubber gave the lowest net flexural strength, those produced with No.18 crumb rubber gave the highest net flexural
strength. .
The results obtained showed that the control mix had greater net flexural strength compared to other mixture containing (No.18, No.5, and MCR). •
The highest fracture energy (GF) result was obtained from control mixture, and the systematical decreasing of fracture energy (GF) was observed as rubber content increased. The highest fracture energy value was obtained when the natural fine aggregate was replaced with5%No.18 crumb rubber, while the lowest value was achieved when the natural fine aggregate was replaced with 25% No.5 crumb rubber. The most efficient results for utilization of crumb rubber were obtained in the fracture energy.
•
The characteristic length, which is a measure of ductility of the concrete, was increased significantly by the increasing the crumb rubber volume fraction. While the significant improvement was achieved with addition of all tire wastes types, the best value for ductility was obtained with 25% mixed crumb rubber.
•
The maximum displacement corresponds to the maximum load, the highest maximum load for the control mix and decreases gradually according to the amount and size of crumb rubber respectively.
•
Decreasing of bond strength with increasing the crumb rubber size and content. Moreover the development of bond strength of concrete with mixed crumb rubber (MCR) is more than development in concrete with crumb rubber (No.18, and No.5).
References [1] Nagamoto N., Ozawa K., Mixture properties of Self-Compacting, High-Performance Concrete, Proceedings, Third CANMET/ACI International Conferences on Design and Materials and Recent Advances in Concrete Technology, SP-172, V. M. Malhotra, American Concrete Institute, Farmington Hills, Mich. 1997, p. 623-637.
[2] Khayat K.H., Ghezal A., Utility of Statistical models in Proportioning Self-Compacting Concrete,Proceedings,RILEMInternational symposium on Self-Compacting Concrete, Stockholm, 1999, p. 345-359. [3]Petersson O., Billberg P., Van B.K., A model for Self-Compacting Concrete, Proceedings of Production Methods and Workability of Concrete,1996, E & FN Span, London, p. 483492. [4] Guneyisi E, Gesoglu M, Ozturan" T. Properties of rubberized concretes containing silica fume." J Cem Concr Res 2004;34:2309–17. [5] Khalid B. Najim , Matthew R. Hall “Mechanical and dynamic properties of selfcompacting crumb rubber modified concrete”. Construction and Building Materials 27 (2012) 522–524 [6] Piti Sukontasukkul *, Chalermphol Chaikaew"Properties of concrete pedestrian block mixed with crumb rubber"Construction and Building Materials 20 (2006) 450–457. [7] Zheng L, Huo S, Yuan Y. Experimental investigation on dynamic properties of rubberized concrete. Constr Build Mater 2008;22:939–47. [8] Zheng L, Huo X, Yuan Y. Strength, modulus of elasticity, and brittleness index of rubberized concrete. J Mater Civ Eng 2008;20:692–9. [9] Gideon Momanyi Siringi May 2012" Properties of concrete with tire derived aggregate and crumb rubber as a lightweight substitute for mineral aggregates in the concrete mix" The University Of Texas at Arlington. [10] Khalid B. Najim & Matthew Robert Hall "Crumb rubber aggregate coatings/pretreatments and their effects on interfacial bonding, air entrapment and fracture
toughness in self-compacting rubberized concrete (SCRC)" Materials and Structures ISSN 1359-5997 Volume 46. [11] M. H. Seleem, H. E. M. Sallam , A. T. Attwa , K. M. Heiza Y. B. Shaheen “Fracture toughness of self compacting concrete” MESOMECHANICS-2008 HBRC, Giza, Egypt, Jan 28 – Feb. 1, 2008 [12]Hamid Eskandari, S. Muralidhara, B.K. Raghu Prasad, B.V. Venkatarama “ Fracture properties of Self Compacting Concrete for Notched and Un-notched Beams” Global Journal of researches in engineering Civil And Structural engineering Volume 12 Issue 1 Version 1.0 January 2012. [13] Peter Helincks,Veerle Boel,Wouter De CorteGeert De SchutterPieter Desnerck Structural behaviour of powder-type self-compacting concrete: Bond performance and shear capacity,Engineering Structures Volume 48, March 2013, Pages 121–132.
[14] M. M. Kamal, M. A. Safan and M. A. Al ,Experimental Evaluation of Steel–Concrete bond Strength in Low-cost Self-compacting Concrete''concrete research letters Vol. 3 (2) – June 2012. [15] Farhad Aslani, Mechanical Properties of Waste Tire Rubber Concrete Mechanical Properties of Waste Tire Rubber Concrete(2016), J. Mater. Civ. Eng., 28(3): 04015152. [16] Farhad Aslani & Shami Nejadi,(2012) Bond Behavior of Reinforcement in Conventional and Self-Compacting Concrete, Advances in Structural Engineering Vol. 15 No. 12 [17] ASTM C 618-08. Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete, Annual Book of ASTM Standard, 2000. No. 04.02. [18] Collepardi M. Chemical admixtures today. In: Proceedings of second international symposium on concrete technology for sustainable February – development with Emphasis on Infrastructure, Hyderabad, India, 27 February–3 March, 2005. p. 527–41. [19] Khayat KH, Bickley J, Lessard M (2000) Performance of self-consolidating concrete for casting basement and foundation walls. ACI Mater J 97(3):374–380. [20]ASTM C39/C39M-12 (2012) Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens Annual Book of ASTM Standard, Philadelphia Vol. 04-02, 7 pages.
[21] ASTM C496. American Society for Testing and Materials. 2011 Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens. Annual Book of ASTM Standard. Philadelphia. Vol. 04-02, 5 pages.
[22] ASTM C469/C469M−10. American Society for Testing and Materials. 2010. Standard Test Method for Static Modulus of Elasticity and Poisson’s Ratio of Concrete in Compression. Annual Book of ASTM Standard. Vol. 04.02, 5 pages [23] RILEM 50-FMC. (1985). Committee of fracture mechanics of concrete. Determination of fracture energy of mortar and concrete by means of three-point bend tests on notched beams. Materials and Structures. 18(106),285–290. [24]Hillerborg, A. (1985). Theoretical basis of method to determine fracture energy GF of concrete. Materials and Structures. 18:291296. [25]RILEM RC6. (1996). Recommendations for the testing and use of constructions materials bond test for reinforcement steel. 2. Pull-out test, 3 pages. [26] Oikonomou N, Mavridou S. Improvement of chloride ion penetration resistance in cement mortars modified with rubber from worn automobile tires. CemConcr Compos 2009;31(6):403–7. [27]Eldin, N.N. and Senouci, A.B., (1993) “Rubber tyre particles as concrete aggregate” Journal of Materials in Civil Engineering, 5: 478-496. [28] Dong Q, Huang B, Shu Xiang (2013) Rubber modified concrete improved by chemically active coating and silane coupling agent. Construction and Building Materials 48:116-123. [29] Segre N, Joekes I (2000) Use of tire rubber particles as addition to cement paste. Cement and Concrete Research 30:1421-1425. [30] Neville AM. Properties of concrete. London: Longman Group; 1995 [31] K.P. Mehta, P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials, McGraw-Hill, New York, 2006
[32] Enrique Rocha-Rangel“Fracture Toughness Determinations byMeans of Indentation Fracture”Universidad Politécnica de VictoriaMéxico [33] B. Huang, G. Li, Su-Seng Pang, J. Eggers, Investigation into Waste Tire Rubber-Filled Concrete, J. Mater. Civ. Eng. 16 (2004) 187-194.
[34] H.A. Toutanji, Use of rubber tire particles in concrete to replace mineral aggregates", Cem. Concr. Compos. 18 (1996) 135-139
[35] Tasdemir, C. (2003). Combined effects of mineral admixtures and curing conditions on the sorptivity coefficient of concrete. Cement and Concrete Research, 33, 2637-1642.
[36] Karihaloo, B.: 1995, Fracture mechanics and structural concrete'. Longman Scientific and technical,UK. [37]Petersson, P.: 1980b, `Fracture energy of concrete: practical performance and experimental results'.Cem Con Res 10(1), 91-101. [38] Hadi, MNS 2008, Bond of high strength concrete with high strength reinforcing steel', The Open Civil Journal, vol. 2, pp. 143-147. [39]Emiroğlu., Halidun, M. and Yildiz, S., (2007) An investigation on ITZ microstructure of the concrete containing waste vehicle tire, in 8th International Fracture Conference, 7-9 November, Istanbul/Turkey.
Table 1 Physical properties and chemical compositions of Portland cement and fly ash Analysis Report (%) Cement
Fly ash
CaO
62.58
4.24
SiO2
20.25
56.2
Al2O3
5.31
20.17
Fe2O3
4.04
6.69
MgO
2.82
1.92
SO3
2.73
0.49
K2 O
0.92
1.89
Na2O
0.22
0.58
Loss on ignition
3.02
1.78
Specific gravity
3.15
2.25
Blaine fineness (m2/kg)
326
287
Table 2 Mix proportions for self-compacting rubberized concrete (kg/m3) Mix ID
Control 5CR18 10CR18 15CR18 20CR18 25CR18 5CR5 10CR5 15CR5 20CR5 25CR5 5MCR 10MCR 15MCR 20MCR 25MCR
Water-to- Cement Fly ash Water binder ratio (w/b) 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182
SP
3.4 3.6 3.9 4.2 4.4 4.7 3.6 3.9 4.2 4.4 4.7 3.6 3.9 4.2 4.4 4.7
N Cr ru
Coarse Fine aggregate aggregate Natural sand Crushed sand 819.4 819.1 818.7 818.4 818.1 817.8 819.1 818.7 818.4 818.1 817.8 819.1 818.7 818.4 818.1 817.8
573.6 544.9 516.2 487.5 458.9 430.2 544.9 516.2 487.5 458.9 430.2 544.9 516.2 487.5 458.9 430.2
GF N/m
lch N/m
245.8 233.5 221.2 208.9 196.7 184.4 233.5 221.2 208.9 196.7 184.4 233.5 221.2 208.9 196.7 184.4
Table 3 Results of hardened properties for SCRC Mix ID
Control No.18 CR5 No.18 R10 No.18CR15 No.18 R20 No.18 R25 No.5 CR5 No.5 CR10 No.5 CR15 No.5 CR20 No.5 CR25 MCR5
fc MPa
72.44 67.95 64.09 60.62 57.51 49.82 44.88 59.49 53.96 45.62 39.28 72.44
fst MPa
4.36 3.68 3.51 3.32 3.12 2.42 3.52 3.34 3.17 2.81 2.24 3.59
EGPa
50.71 48.68 46.34 44.51 40.27 34.14 45.76 41.43 37.61 35.83 30.98 46.52
fflex MPa
5.6 4.92 4.63 4.47 3.57 3.25 4.76 4.42 4.22 3.34 3.06 4.83
155.8 143.5 140.7 135.1 121.5 115.2 137.6 133.9 125.8 117.6 110.2 138.8
415.612 515.830 529.219 545.552 502.630 671.560 508.181 497.281 470.831 533.631 680.404 501.009
τ MPa
14.6 13.61 12.85 10.62 9.18 8.55 11.22 10.25 9.43 8.37 7.8 11.66
MCR10 MCR15 MCR20 MCR25
65.14 61.51 56.93 49.12
3.47 3.22 2.86 2.26
43.25 42.13 37.92 32.71
4.52 4.31 3.46 3.13
135.5 126.9 118.4 112.1
486.705 515.633 548.893 717.908
10.99 10.1 8.61 7.97
No.18 Crumb rubber
No.5 Crumb rubber
Mixed crumb rubber
100 90 80
Percent passing
70 60 50 40 30 20 10 0 0.1
1
10
Sieve size, mm
(a) Mixed crumb rubber
Fine aggregate
Coarse aggregate
100 90 80
Percent passing
70 60 50 40 30 20 10 0 0.1
1
10
Sieve size, mm
(b) Figure 1. Sieve analysis of a) No.18, No.5 and Mixed crumb rubbers, and b) Mixed crumb rubber, fine and coarse aggregates
100
Figure 2.The photographic views of No.18 and No.5 crumb rubbers
Figure 3: Details of the bond strength test specimen
Figure 4: Photographic view of the pullout test set up during testing the specimen
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
75
Compressive strength, fc (MPa)
70 65 60 55 50 45 40 35 0
5
10
15
20
25
Rubber content (%)
Figure 5: Variation of 90-day compressive strength with respect to crumb rubber size and content No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
5.0
Splitting tensile strength, fst (MPa)
4.5
4.0
3.5
3.0
2.5
2.0 0
5
10
15
20
Rubber content (%)
Figure 6: Variation of 90-day splitting tensile strength with respect to crumb rubber size and content
25
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
55
Modulus of elasticity, E (GPa)
50
45
40
35
30
25 0
5
10
15
20
Rubber content (%)
Figure 7: Variation of 90-day Modulus of elasticity with respect to crumb rubber size and content
a)
25
b)
Figure 8: Photographic view of: a) notched beam and b) subjected to three-point bending test
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
6.0
Net flexural strength, fflex (MPa)
5.5
5.0
4.5
4.0
3.5
3.0 0
5
10
15
20
25
Rubber content (%)
Figure 9: Net flexural tensile strength versus with respect to crumb rubber size and content No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
160
Fracture energy, GF (N/m)
150
140
130
120
110
100 0
5
10
15
20
Rubber content (%)
Figure10: Fracture energy versus with respect to crumb rubber size and content
25
4.0
Control 3.5
No.18 CR5 No.18 CR10 No.18 CR15
3.0
No.18 CR20 No.18 CR25
Load (kN)
2.5
2.0
1.5
1.0
0.5
0.0 0.0
0.3
0.6
0.9
1.2
1.5
Displacement (mm)
Figure 11: Typical loads versus displacement curves ofNo.18CRwith respect to control mix
4.0
Control 3.5
No.5 CR5 No.5 CR10 No.5 CR15
3.0
No.5 CR20 No.5 CR25
Load (kN)
2.5
2.0
1.5
1.0
0.5
0.0 0.0
0.3
0.6
0.9
1.2
1.5
Displacement (mm)
Figure 12: Typical load versus displacement curves ofNo.5CRwith respect to control mix
4.0
Control 3.5
Mixed CR5 Mixed CR10 Mixed CR15
3.0
Mixed CR20 Mixed CR25
Load (kN)
2.5
2.0
1.5
1.0
0.5
0.0 0.0
0.3
0.6
0.9
1.2
1.5
Displacement (mm)
Figure 13: Typical load versus displacement curves of MCR with respect to control mix
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
800
Characteristic length, lch (N/m)
750
700 650 600 550 500 450 400
0
5
10
15
20
25
Rubber content (%)
Figure 14: Characteristic length versus with respect to crumb rubber size and content
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
15
Bond strength, τ (MPa)
14
13 12 11 10 9 8 7
0
5
10
15
20
Rubber content (%)
Figure 15: Bond strength versus with respect to crumb rubber size and content
25
S2212-6090(16)30161-3 http://dx.doi.org/10.1016/j.ijsbe.2017.03.001 IJSBE 161
To appear in:
International Journal of Sustainable Built Environment
Received Date: Revised Date: Accepted Date:
20 October 2016 13 March 2017 18 March 2017
Please cite this article as: N.N. Hilal, Hardened properties of self-compacting concrete with different crumb rubber size and content, International Journal of Sustainable Built Environment (2017), doi: http://dx.doi.org/10.1016/ j.ijsbe.2017.03.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Hardened properties of self-compacting concrete with different crumb rubber size and content Nahla Naji Hilal *Dams and Water Resources Engineering Department, College of Engineering, University of Anbar, Ramadi, Anbar , Iraq Abstract This paper aims at investigating the effect of crumb rubber size and content on hardened characteristics of self-compacting concrete.To this end, different self-compacting concrete mixtures were designed at constant water-to-binder ratio of 0.35 and 520 kg/m3 of binder content. The class F fly ash was replaced with cement as 30% by weight. Six designated crumb rubber contents of 5, 10, 15, 20, and 25% and three different sized crumb rubbers (No.18, No.5, and mixed crumb rubber) were considered as experimental parameters. According to the obtained results, the use of crumb rubber had a negative effect on the hardened properties of self-compacting concretes and the significant improvement was achieved with addition of all tire wastes types, for ductility.
Keywords: Crumb rubber content; Crumb rubber size; hardened property; Self-compacting concrete; Waste tire
1. Introduction Self-compacting concrete (SCC) is known as a revolution in concrete placement. Since SCCflows under its own weight, there is no need for any external vibration to compact concrete. SCC, as a highly workable concrete, was first introduced in the late 1980’s in Japan [1]. This was capable of flowing under its weight through restricted sections with no segregation and bleeding. This material needs to have a relatively low yield value in order to
guarantee a high flow capability and a moderate viscosity to resist segregation and bleeding. In addition, SCC should keep up its homogeneity during the processes of transportation, placing, and curing in order to guarantee long term durability and adequate structural performance. If SCC is developed successfully, an appropriate balance between stability and deformability can be ensured. In literature, there are some guidelines for mixture proportioning of SCC, including (i) to reduce volume ratio of aggregate to cementitious material [1-2]; (ii) to increase paste volume and water-cement ratio (w/c); (iii) to control carefully the maximum coarse aggregate particle size and total volume; and (iv) to make use of different viscosity enhancing admixtures (VEA) [1].
The changes of strength, usefulness and vibrant attributes of rubberized concretes with respect to magnitude and quantity of the rubber types and rubber scraps have been explored by many studies in last two decades [3]. The rubberized concrete is found to be a perfect material for the structural members exposed to rapid effects and for which preferred toughness or deformability holds greater significance than strength, like road foundations, jersey barriers and bridge barriers. Specifically, rubberized concrete has dynamic attributes to minimize the vibration and to absorb the impact energy more helpfully than the conventional concrete. It has been asserted by Gu¨neyisi et al. [4] that the rubber content decreases the strength of concretes that include silica fume, crumb rubber and tyre chips. It has been stated by these authors that a 40 MPa concrete can be produced by substituting a volume of 15% of aggregates with rubber waste.
Crumb rubber from scrap tyres (2-6mm) were employed by Najim and Hall [5] as a partial substitute for Fine Aggregate (FA), Coarse Aggregate (CA) and mixed Fine and Coarse Aggregate (FCA) in self compacting concrete at weighted proportions of 5%,10% and 15%. It has been asserted by these authors that the compressive strength decreases in the same manner as that shown for Plain Rubberised Concrete (PRC). To substitute both fine and rough aggregates with exact amounts of 10% and 20% according to weight, Piti Sukontasukkul , Chalermphol Chaikaew [6] use crumb rubber concrete in three different categories: (1) No. 6, (2) No. 20 and (3) Combined No. 6 + 20. The results obtained showed that the plain concrete block had greater flexural strength compared to crumb rubber concrete blocks. The tensile strength of concretes with silica fume, crumb rubber and tyre chips was examined by Güneyisi et al. [4]. In accordance with the rubber content, the tensile strength was reduced but the presence of silica fume gives it a higher filler effect to add to its benefits. The reduction in the tensile strength is not affected as much as compressive strength reduction is by the addition of rubber content. Even at similar compressive strengths, the NVC has greater tensile strength than the SCC and SCRC Najim and Hall [5]. The reason behind this is the dens microstructure in SCC mixes that causes greater brittleness and lesser splitting strength.
It was obviously seen that the increment in the elastic modulus was more diminutive as contrasted with that in the compressive and splitting tensile strengths Güneyisi et al. [4]. By and large, the plain and the rubberized concretes displayed an increment in the modulus of up to 15% relying upon the measure of silica fume utilized. Notwithstanding, for the same w/cm proportion and the content of rubber, all mixtures accomplished just about comparable results
Zheng et al. [7,8] specified that the crumb rubber (80 %< 2,62mm) has a lesser affect in the elasticity modulus compared to the crushed rubber (15-40mm). It is indicated by Gideon [9] that at 15% Crumb Rubber substitution, the concrete with Crumb Rubber has modulus of elasticity which is 11% higher than the control concrete. When contrasting the two concretes and silica smoulder, however, the Crumb Rubber adjusted concrete has a elasticity modulus which is 34% less contrasted with the control which additionally holds silica fume that has been indicated to build compressive strength and it likewise builds the modulus of elasticity By and large, the elasticity modulus rises as the strength rises.
Khalid Najim, Matthew Robert Hall [5] made study on plain rubberized concrete ( PRC) and they found that rubber total substitution diminished the Crack mouth open uprooting (mm) ( CMOD) at a given stacking level bringing about more excellent flexural durability values, no doubt, because of vitality retention by the rubber. Khalid Najim , Matthew Robert Hall [10] found that, after 0.1 mm avoidance, the specimens with (mortar precoated rubber total) (SCRC3) and bond glue (concrete glue precoated rubber total (SCRC2) P-T/C demonstrated unrivalled execution with relevance to further diminishing the Crack mouth open dislodging( CMOD) at a given burden. This likewise happened, yet to a lesser degree, with NaOH pretreatment and water washing. Such conduct could be ascribed to the capacity of the covered rubber to ingest more vitality by holding crack proliferation inside the concrete body, e.g. by lengthening crack ways and anxiety unwinding.
Seleem et al. [11] specified that the fracture durability for either self compaction or typical vibrated concrete diminished with expanding crack –depth proportion, and the Self compacting concrete recorded higher imperviousness to crack spread contrasted with ordinary vibrated concrete independent of the kind of coarse total. Hamid Eskandari et al. [12] report self compacting concrete (SCC) is more bendable than elite concrete (HPC). Consequently, it could be utilized in any event for vast size structures. Furthermore the qualities of trademark length of SCC (lch) are to be more when contrasted with the HPC, NC and high strength concrete. It may be presumed that the SCC is more flexible contrasted with HPC.
The strength of the bond of the self-compacting concrete as reported by P.Desnercketal[13] after studying large bar diameters; it is equally high as the bond strength of the traditional vibrated concrete. The bond strength of SCC with smaller bar diameters is somewhat greater and, with the smaller diameters, takes place the greatest variation. The bond strength is decreased owing to Portland cement substitution with dolomite powder as suggested by M. M. Kamal1 et al. [14]. The mechanical interaction was interfered with as the chemical adhesion characteristic was bettered. The bond strength was mainly due to the resistance by friction and silica fume or fly ash addition which effectively, with the increase of dolomite powder content, prevents extended degradation of the bond strength. The effect of rubber types and rubber content on mechanical properties of concrete. Studied by Farhad Aslani [15]. Report the following conclusions:
• The proposed compressive stress-strain relationship is simple and reliable for modeling the compressive behavior of RC.Moreover, using these relationships in the finite element method (FEM) is more simple and suitable.
• The proposed relationships for the compressive, tensile and flexural strengths, elasticity modulus, and peak strain of RC with different content of WTR are in good reasonable agreement with the experimental results. Also, the relationships for previously noted mechanical properties are proposed that can calculate these properties related to the CR, TC, and CR+CT contents.
• The proposed relationships for compressive strength of RC with CR, TC, and CR+CT contents at 7 and 28 days of age and with two different w/c ratio ranges (0.40–0.50, and 0.50– 0.60) are covered. Also, the proposed relationships for modulus of elasticity for three RC mixtures at 28 days of age and with two different w/c ratio ranges (i.e., 0.40–0.50 and 0.50– 0.70) are covered.
• These relationships are proposed for tensile strength, flexural strength, and peak strain of RC with CR, TC, and CR+CT contents at 28 days of age.
Farhad Aslani and Shami Nejadi [16]. Study bond strength model based on the experimental results from eight recent investigations of SCC and CC. In addition, the proposed model, code provisions, and empirical equations and experimental results from recent studies on the bond strength of SCC and CC are compared. The comparison is based on the measured bond between reinforcing steel and concrete utilizing the pullout test on the embedded bars at various heights in the mock-up structural elements to assess the top bar effect on single bars in small prismatic specimens by conducting beam tests. The investigated varying parameters on bond strength are the: steel bar diameter, concrete compressive strength, concrete type, curing age of the concrete, and height of the embedded bar along. The experimental results shown The ultimate and mean bond strengths are greater in SCC than in CC, For the top cast
bars, the local bond strength for SCC is greater than that for CC and the bond strength of SCC is as high as the bond strength for CC when large bar diameters are studied. For smaller bar diameters, the bond strength of SCC is slightly higher, with the largest difference occurring for the smallest bar diameters.
This study covers the effect of crumb rubber content and size on the hardened properties of SCC. Therefore, three different sized crumb rubbers (No.18, No.5, and mixed crumb rubbers) and their mixtures were replaced with the natural sand at five different contents of 5, 10, 15, 20, and 25% as a volume. The No.18 crumb rubber is a fine material passing from 1-mm sieve whereas the No.5 crumb rubber is a fine material retaining on 1-mm sieve and passing from 4-mm sieve. Moreover, No.18 and No.5 crumb rubbers are mixed to achieve a new fine material with a gradation close to the natural sand. The constant water-to-binder (w/b) ratio of 0.35 and binder content of 520 kg/m3 were designated to produce SCCs. To improve the workability of SCCs,the Class F fly ash (30% of total binder content by weight) was introduced in the mixture. The hardened properties of SCCs were investigated in terms of the compressive strength, splitting tensile strength, flexural, modulus of elasticity, fracture energy and bond strength .Totally 16 self-compacting rubberized concrete (SCRC) mixtures mixes were designed and tested at 90 day.
2. Experimental study
2.1. Materials
2.1.1. Cement and fly ash Ordinary Portland cement (CEM I 42.5R) with specific gravity of 3.15 g/cm3 and Blaine fineness of 326 m2/kg was utilized in this study. Class F fly ash (FA) according to ASTM C 618 [17] with a specific gravity of 2.25 g/cm3 and Blaine fineness of 379 m2/kg was utilized in the manufacturing of the SCCs. Physical properties and chemical compositions of the cement and fly ash are presented in Table 1.
2.1.2. Aggregates The coarse aggregate was river gravel with a nominal maximum size of 16 mm and the fine aggregate, a mixture of natural river sand and crushed limestone, was used with a maximum size of 4 mm. River sand, crushed sand, and river gravel had specific gravities of 2.65, 2.43, and 2.71, respectively. The particle size gradation obtained through the sieve analysis of the fine and coarse aggregates are given in Figure 4.
2.1.3. Crumb rubber The No.18 crumb rubber (No.18 CR) and No.5 crumb rubber (No.5 CR) are two different sizes of crumb rubbers. The No.18 CR is a fine material passing from 1-mm sieve whereas the No.5 CR is a material retaining on 1-mm sieve and passing from 4-mm sieve. Moreover, the No.18 CR and No.5 CR were mixed to obtain a new fine material with a gradation close to that of the sand. A crumb rubber (CR) of which gradation is very close to that of the sand was achieved by mixing 40% of No.18 CR and 60% of No.5 CR. The specific gravity of No.18
CR and No.5 CR are 0.50 and 0.67, respectively. The particle size distribution for the No.18 CR, No.5 CR, and Mixed CR is also presented in Figure 1. Additionally, the photographs of No.18 CR and No.5 CR are illustrated in Figure 2.
2.1.4. Superplasticizer A Polycarboxylic ether type of superplasticizer (SP), which acts by steric hindrance effect [18], with specific gravity of 1.07, was employed to achieve the desired workability in all concrete mixtures. 2.1.5. Steel bar Reinforcing ribbed steel bars having 16 mm diameter and minimum yield strength of 420 MPa were utilized for preparing the reinforced concrete specimens to be used for testing the bonding strength.
2.2. Mixture design SCRC mixtures were designed having a constant w/b ratio of 0.35 and total binder content of 520 kg/m3. The class F fly ash was used as a 30% of the total binder content as weight in all mixtures. The fine and coarse aggregates were replaced with t different graded crumb rubbers (No.18, No.5, and mixed crumb rubber)
respectively, at five designated contents of 5%,
10%, 15%, 20%, and 25% by volume. Totally 16 different SCRC mixtures were designed regarding to above variables. The detailed mix proportions for SCRCs are presented in Table 2.
3. Concrete casting To achieve the same homogeneity and uniformity in all SCRC mixtures, the batching and mixing procedure proposed by Khayat et al. [17] was followed since the mixing sequence and
duration are very vital in the self-compacting concrete production. According to this mixing procedure, the crumb rubber, fine and coarse aggregates in a power-driven revolving pan mixer were mixed homogeneously for 30 seconds, and then about half of the mixing water was added into the mixer and it was allowed to continue the mixing for one more minute. After that, the crumb rubber and aggregates were left to absorb the water in the mixer for 1 min. Thereafter, the cement and fly ash was added to the mixture for mixing another minute. Finally, the SP with remaining water was poured into mixer, and the concrete was mixed for 3 min and then left for a 2 min rest. At the end, to complete the production, the concrete was mixed for additional 2 min. Three 150-mm cubes were taken to measure the compressive strength, three100x200 mm cylinder were taken to measure the splitting tensile strength, Three 100x100x500-mm prisms were taken to measure the net flexural and fracture energy; and two150x300 mm cylinder were taken to measure the modulus of elasticity. Moreover three 150-mm cubes were taken to measure the bond strength of self-compacting rubberized concretes. Following the concrete casting, specimens were wrapped with plastic sheet and left in the casting room for 24 h at 20±2 °C and then they were demoulded and tested after 90-day water curing period.
2.4. Test procedure Compression test of self-compacting rubberized concrete sample was conducted using ASTM C39 [19] and the obtained results were presented as the average of three samples. Using ASTM C496, splitting test of self-compacting rubberized concrete sample was conducted [20] and the test results were given as the average of three samples. And splitting tensile strength of cylindrical concrete specimens was computed using the following equation.
st =
(1)
Where P, h, and Φ are the maximum load, length and diameter of the cylinder specimen, respectively. Static modulus of elasticity(E) was determined through testing the cylinders with a dimension of Φ150x300 mm using ASTM C469/C469M-10, 2010[21]. The results obtained for static modulus of the self-compacting rubberized concrete were presented as the average of two samples. The notched beams were applied to the calculation of the net flexural strength ( fflex ) using Equation (2) with the assumption that there is not any notch sensitivity, where P max signifies the ultimate load.
fflex=
(2)
To determine the fracture energy (Gf),a test was carried out with considering the recommendations given by the RILEM 50-FMC Technical Committee (RILEM 50-FMC, 1985) [22]. For the test of fracture energy, beams with 100x100 mm in cross-section and 500 mm in length were prepared. The notch to the specimens ’depth ratio (a/D) was 0.4 and the notch opening was obtained by decreasing the effective cross section to 60x100 mm through sawing to accommodate large aggregates in higher abundance, and distance between the supports was 400 mm. For each specimen, load versus deflection at the mid- span (δ) curve was found and the area under the load versus displacement at mid-span (Wo) was employed to determine the fracture energy that was computed using Equation (3) given by RILEM 50-FMC Technical Committee (RILEM 50-FMC, 1985). [22].
GF=
δs
(3)
where B, W, a, S, U, m, δs, and g are the width, depth, notch depth, span, length, mass, specified deflection of the beam .
The brittleness of materials in terms of characteristic length (lch) can be determined using the following equation (Hillerborg, 1985)[23].
lch
= !"
(4)
#$%
Where E, fst, and GF stand for the static modulus of elasticity, splitting tensile strength, and fracture energy, respectively. In the present study, the direct tensile strength was replaced with the splitting tensile strength.
The concrete’s bonding strength (ττ), was determined using the RILEM RC6 (RILEM RC6, 1996)[24].The bonding strength was computed using Equation (5):
τ=
&
'(
( 5)
Where F denotes the tensile load at failure (N), L and d signify the embedment length (mm) and the diameter (mm) of the reinforcing steel bar, respectively. In this study,150-mm cubic specimen and 16-mm steel bar were used; therefore, L and d were set to 150 and 16 mm, (see
Figure 3) respectively. For the purpose of loading, universal testing machine with the capacity of 600 KN was employed through installing specially-modified test apparatus to it (see Figure 4).
3. Results and discussion 3.1. Compressive strength The strength refers to a measure of the stress that is needed for fracturing a material and determined by the calculation of the maximum stress (fc′) that the specimen carries after being subjected to uni-axial compressive force. ((Kosmatka,Kerkhoff et al. 2002) [25 ]. Figure 5 presents the 90-day compressive strength of the mixtures. In this study, the compressive strength values obtained during 90days ranging from 39.28 MPa to 72.44 MPa were achieved. The control mixture showed the highest compressive strength result; and as the rubber content increased, the compressive strength systematically decreased. Compared to the natural aggregate, the crumb rubber is a soft material. If crumb rubber is used in concrete production, the compressive strength and the adhesion between rubber particles and surrounding cement paste are decreased .As a result, in literature, there are some recommendations for applying surface treatment of rubber particles in order to enhance its adhesion to the cement paste [27]. The lowest compressive strength was resulted from the self-compacting concretes produced with No.5 crumb rubber; whereas, the highest strength was resulted from those produced with No.18 crumb rubber. It has been shown that the coarse rubber particles have more negative effect on the properties compared to fine particles [27, 28]. The strength decrease with increasing rubber content is attributable to two reasons: (1) cracks are started rapidly near the rubber particles in the mix, which quickens the failure of the rubber–cement matrix as the rubber particles are much softer than the adjacent cement
paste on loading; and (2) rubber particles function as voids in the concrete matrix because of the absence of adhesion between the rubber particles and the paste [15]
3.2 Splitting tensile strength Splitting tensile strength values that are calculated from cylindrical specimens by means of Equation (1) are displayed in Table 3. The variation in splitting tensile strength noted during 90days for all SCRC associated with the content and size of crumb rubber is presented in Figure6. In this study, the splitting tensile strength values were obtained, ranging from 2.24 MPa to 4.36 MPa. The control mixture resulted in the highest splitting tensile strength, and the increase of rubber content led to a systematic reduction of splitting tensile strength. The splitting tensile strength decreased by 18.47%, 23.86%,and 21.44% for the concretes that were produced with No.18, No.5,and mixed crumb rubber, respectively, at proportions of 5%. Whereas the decreasein the splitting tensile strength at proportions of 25%was 80%, 94.64%and 92.92%. As shown by the obtained results, SCC produced by No.18crumb rubber resulted in the highest splitting tensile strength; while those produced by No. 5 crumb rubber resulted in the lowest splitting tensile strength. Additionally, it was found that the negative impacts of the coarse rubber particles on the properties were more than that of the fine particles [27, 29].Generally, the whole concretes have low tensile strength (~10% of compressive strength) and strain capacity [30].The tensile strength ,however, is of a great importance to airfield slabs, highway design, as well as in cases where crack resistance and shear strength are priority. These shortcomings are exacerbated by addition of the crumb rubber to SCC (see Fig.6) where a general tendency exists toward the reduction of the tensile strength, which may be attributed to the same reasons that affect the compressive strength. Many factors are effective on the relationship between splitting and compressive tensile strength, including aggregate type and particle size distribution, and curing age [31]and
powder and admixtures content and type. Farhad Aslani [15] show that the decrease in the tensile strength with the rubber content was lower than that in the compressive strength.
3.3 Static modulus of elasticity The test results of static modulus of elasticity are displayed in Fig. 7as a function of rubber and tire chip size and contents in the present study the Moduli of elasticity values, ranging from 30.98 GPa to 50.71 GPa, were obtained. The highest modulus of elasticity was obtained from the control mixture, and the increase of rubber content led to systematical reduction of modulus of elasticity. The decrease in the modulus of elasticity of rubberized concrete occurred for a number of reasons, including the inclusion of the waste tires rubber aggregate, acted similar to voids in the matrix, which was due to weak bond between the concrete matrix and waste tires rubber aggregate If the void content of concrete increases, the strength will decrease. The second reason is that waste tires rubber aggregate acts as weak inclusions in the hardened cement mass, hence producing high internal stress perpendicular to direction of the applied load. The third reason is that the strength of the Portland cement concrete depends mainly on the coarse aggregate, size, hardness, and density. The aggregates are replaced partially with rubber; for this reason, the decrease in strength is only natural. The last reason is that the failure of the sample is also due to the waste tire that is more elastically-deformable compared to the matrix. After loading the samples, the cracks form first at the softest areas. The rubber’s inclusion site is where these sites emerge[31].As shown by the graphs presented in Fig.7,the static elastic modulus was reduced when rubber size and content increased in a fashion comparable to that observed in both splitting and compressive tensile strengths. The results showed that SCCproduced with No.18 crumb rubber resulted in the highest static elastic modulus.
According to Turatsinze and Garros [32], the modulus of elasticity of SCC was expanded with rubber (4–10 mm) waste substance. In addition, they warned the risk of serious isolation with a high elastic waste concentration at the highest point of the samples, which could lead to a need for a fitting blend between a consistency executor and air-entraining operator in order to keep up a strategic distance from isolation. The modulus of elasticity was also affected by the particle size and amount of rubber as compressive strength according to [15].
3.4 Net flexural strength The net flexural strength values, which were evaluated using Equation (2) from the notched prismatic specimens (see Figure 8a) subjected to the three-point bending test (see Figure 8b), are displayed in Table 3. The variation in the net flexural strength of SCRC versus associated with crumb rubber content and size are displayed in Figure 9. The highest value was the net flexural strength of control mix 5.6 MPa. The SCC produced with No.5 crumb rubber resulted in the lowest net flexural strength, where as those produced with No.18 crumb rubber resulted in the highest net flexural strength.As shown by the obtained results, the control mix had greater net flexural strength in comparison with other mixture containing No.5, No.18, and mixed crumb rubber. Table 3clearly shows that the increase of the No.18 crumb rubber from 5-25% resulted in reducing the flexural strength up to 70% and, simultaneously, the mixture containing No.5 crumb rubber from 5-25% resulted in the reduction of the flexural strength up to 80%,whereas the decreasing the flexural strength with mixed crumb rubber (MCR) up to 78%.The decrease of fflex can be related to the same failure mechanism for splitting tensile strength, since this is a ‘theoretical’ measure for the highest tensile stress reached on the bottom fibre of a test beam. It is assumed that fflexis a ‘theoretical’ measurement since this is computed according to the elastic beam theory that assumes the stress–strain relationship is linear, thus the tensile stress in the beam is supposed to be proportional to the distance from the neutral axes [5]. In addition crack may initiate before the application of the maximum load. It is because micro cracks are formed once the
pre-peak zone is reached, and they are propagated after this stage [33]. In other words, the crumb rubber aggregate might work to delay the micro cracks formation because of a kind of stress relaxation. As a result, the incorporation of crumb rubber particles can lead to measurable improvements to pre-micro crack strain capacity [34].
The literature [34] shows that the tensile strength of concrete with chipped rubber replacement for aggregates is significantly lower than that of concrete that contains powdered rubber. First, a reduction from 30% to 60% occurs for a replacement level of 5-10%, as for the latter case, the reduction is 15-30%. This behavior might be related to the low adhesion between the cement and the chipped rubber. Previous study [15] shows that the flexural strength decreased with the increase of the rubber content in a fashion similar to that observed in the compressive strength. However, it was observed that the initial rate of strength reduction was steeper than that of the compressive strength. This is because of the weak bond between cement paste and rubber particles. 3.5 Fracture energy Fracture energy (GF) values evaluated with Equation (3) from notched beams (Figure 8a), which are subjected to three-point bending test (see Figure 8b), are shown in Table 3. The variations of fracture energy associated with crumb rubber size and content are presented in Figure 9. In the present study, GF values ranging from 110.21 N/mto155.8 N/m were obtained. The control mixture resulted in the highest GF, and it was observed that with an increase in the rubber content, the GF systematically decreased. Additionally, the highest was obtained by replacing fine aggregate with 5% no.18CR replacement, whereas the lowest was obtained by replacing fine aggregate with 25% No.5CR replacement. As shown in Figure 10,a reduction occurred in all GF values at 5%of No.18CR, No.5CR, and MCR; therefore,in both ultimate load and GF, the best improvement was obtained from No.18 crumb rubber.
As shown in Figures 11-13, the maximum displacement is corresponding to the maximum load for the control mix and this gradually decreases based on the size and amount of tire chip and crumb rubber, respectively. Figure 11 show that the concrete with 15%NO.18 CR has higher area under the load versus displacements curve; whereas the concrete with 25%NO.18 CR has lower area under the load. As can be seen in Figure 12, the concrete with 5%NO.5 CR has higher area under the load versus displacements curve, whereas the concrete with 15%NO.5 CR has lower area under the load. As shown in Figure 13, the concrete with 20%Mixed CR has higher area under the load versus displacement curve, on the other hand, the concrete with 25% Mixed CR has lower area under the load.
3.6 Characteristic length Using Equation (4), the concretes’ characteristic length, which is the measure of brittleness, was evaluated (the results are presented in Table3). Normally, in a typical concrete, (lch) is about200-500 mm [36, 37] and for SCC, (lch) it is 580-740 mm for notched beams and it ranges from 540 to 640 mm for un-notched beams. Additionally, it can be observed that (lch) decreases when the compressive strength and notch depth ratio increase.The variations occurred in the characteristic length of SCRCS associated with crumb rubber size and content are presented in Figure14. As shown in Table 3, the control mix has lower characteristic length compared to other mixtures; this is because of possessing higher compressive strength, which makes the concrete more brittle. The mixed crumb rubber (MCR) at 25% replacement enhances the characteristic length (lch) by 72%, as compared to the control mix.The use of crumb rubber enhanced the characteristic length of concrete. The characteristic length increased with an increase in the crumb volume fraction. With the increase of the No.18
crumb rubber volume fraction from 5%to25%, the characteristic length increased by 24%, 27%, 31%, 21%, and 61%, respectively.As shown by the obtained results, the improvement of characteristic length of the concrete with 25% mixed crumb rubber was more than that of the concrete with crumb rubber (No.18, No.5). This is due to better grading of the combined rubber.
3.7 Bond strength The axial force was transferred from reinforcing steel bar to the surrounding concrete by the development of tangential stress components along the contact surface. The stress that acts parallel to the bar along the interface is known as bond stress Pillai &Kirk, 1938, Hadi, 2008 [38]. Equation (5) was used to evaluate the bond strength values from cubic specimen, including the Φ16-reinforcement bar that was subjected to tensile load. The obtained results are displayed in Table 3. The control mixture resulted in the highest bond strength, and with the increase of the rubber content, the bond strength was systematically decreased. Whereas, the lowest bond strength values were measured on the 25% No.5CRmixture on the 90th day. This was because there was a low adhesion between rubber particles and surrounding cement paste. The 90-day bond strength of the mixtures presented in Figure 15indicates that the bond strength decreases with an increase in the crumb rubber size and content.The increase of No.18 crumb rubber from 5to25%led to the decrease of the bond strength by 7%,13%,37%,48%, and 70%, respectively. On the other hand, these rates for the No.5crumb rubber from 5to25%showed the decrease of the bond strength by 30%,42%,54%,74%, and 87%, respectively.
According to Emiroğlu et al. (2008) [39]. The decrease in the bond strength is due to poor bonding characteristic around cement paste and rubber tires. Many micro-cracks exist close to the ITZ in the rubberized concrete. Therefore, several studies have suggested the treatment for rubber in order to improve the bonding between the rubber and the cement paste. As shown by the obtained results, the bond strength of concrete with mixed crumb rubber MCR is developed more than the concrete with crumb rubber (No.18, No.5).
4. Conclusions •
Based on the results obtained from the experimental program presented above, the following conclusions can be drawn:
•
In total 16 SCRC mixtures were designed and produced by the replacing natural aggregate with rubber at six different replacement levels of 0%,5%, 10%, 15%, 20%, and 25%.
•
The compressive strength of self-compacting rubberized concrete having more than 30 MPa could be produced easily. The strength results indicated that the utilization of crumb rubber in self-compacting concrete manufacturing resulted in systematical decreasing of the compressive strength. Moreover, the coarse crumb rubber utilization decreased the compressive strength of self-compacting concrete more than the using of fine crumb rubber. It was found that the best replacement type was the MCR, which offered the best results as it was a compatible replacement for sand and gravel.
•
The highest splitting tensile strength result was obtained from control mixture, and the systematical decreasing of splitting tensile
strength was observed as rubber
content increased. The results indicated that the self-compacting concretes produced
with No.18crumb rubber gave the highest splitting tensile
strength, those produced
with No. 5 crumb rubber gave the lowest splitting tensile strength. •
The static elastic modulus decreased with increasing rubber size and content in a fashion similar to that observed in both compressive and splitting tensile strengths.
•
The net flexural strength of control mix is highest value. While the self-compacting concretes produced with No.5 crumb rubber gave the lowest net flexural strength, those produced with No.18 crumb rubber gave the highest net flexural
strength. .
The results obtained showed that the control mix had greater net flexural strength compared to other mixture containing (No.18, No.5, and MCR). •
The highest fracture energy (GF) result was obtained from control mixture, and the systematical decreasing of fracture energy (GF) was observed as rubber content increased. The highest fracture energy value was obtained when the natural fine aggregate was replaced with5%No.18 crumb rubber, while the lowest value was achieved when the natural fine aggregate was replaced with 25% No.5 crumb rubber. The most efficient results for utilization of crumb rubber were obtained in the fracture energy.
•
The characteristic length, which is a measure of ductility of the concrete, was increased significantly by the increasing the crumb rubber volume fraction. While the significant improvement was achieved with addition of all tire wastes types, the best value for ductility was obtained with 25% mixed crumb rubber.
•
The maximum displacement corresponds to the maximum load, the highest maximum load for the control mix and decreases gradually according to the amount and size of crumb rubber respectively.
•
Decreasing of bond strength with increasing the crumb rubber size and content. Moreover the development of bond strength of concrete with mixed crumb rubber (MCR) is more than development in concrete with crumb rubber (No.18, and No.5).
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Table 1 Physical properties and chemical compositions of Portland cement and fly ash Analysis Report (%) Cement
Fly ash
CaO
62.58
4.24
SiO2
20.25
56.2
Al2O3
5.31
20.17
Fe2O3
4.04
6.69
MgO
2.82
1.92
SO3
2.73
0.49
K2 O
0.92
1.89
Na2O
0.22
0.58
Loss on ignition
3.02
1.78
Specific gravity
3.15
2.25
Blaine fineness (m2/kg)
326
287
Table 2 Mix proportions for self-compacting rubberized concrete (kg/m3) Mix ID
Control 5CR18 10CR18 15CR18 20CR18 25CR18 5CR5 10CR5 15CR5 20CR5 25CR5 5MCR 10MCR 15MCR 20MCR 25MCR
Water-to- Cement Fly ash Water binder ratio (w/b) 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182 0.35 364 156 182
SP
3.4 3.6 3.9 4.2 4.4 4.7 3.6 3.9 4.2 4.4 4.7 3.6 3.9 4.2 4.4 4.7
N Cr ru
Coarse Fine aggregate aggregate Natural sand Crushed sand 819.4 819.1 818.7 818.4 818.1 817.8 819.1 818.7 818.4 818.1 817.8 819.1 818.7 818.4 818.1 817.8
573.6 544.9 516.2 487.5 458.9 430.2 544.9 516.2 487.5 458.9 430.2 544.9 516.2 487.5 458.9 430.2
GF N/m
lch N/m
245.8 233.5 221.2 208.9 196.7 184.4 233.5 221.2 208.9 196.7 184.4 233.5 221.2 208.9 196.7 184.4
Table 3 Results of hardened properties for SCRC Mix ID
Control No.18 CR5 No.18 R10 No.18CR15 No.18 R20 No.18 R25 No.5 CR5 No.5 CR10 No.5 CR15 No.5 CR20 No.5 CR25 MCR5
fc MPa
72.44 67.95 64.09 60.62 57.51 49.82 44.88 59.49 53.96 45.62 39.28 72.44
fst MPa
4.36 3.68 3.51 3.32 3.12 2.42 3.52 3.34 3.17 2.81 2.24 3.59
EGPa
50.71 48.68 46.34 44.51 40.27 34.14 45.76 41.43 37.61 35.83 30.98 46.52
fflex MPa
5.6 4.92 4.63 4.47 3.57 3.25 4.76 4.42 4.22 3.34 3.06 4.83
155.8 143.5 140.7 135.1 121.5 115.2 137.6 133.9 125.8 117.6 110.2 138.8
415.612 515.830 529.219 545.552 502.630 671.560 508.181 497.281 470.831 533.631 680.404 501.009
τ MPa
14.6 13.61 12.85 10.62 9.18 8.55 11.22 10.25 9.43 8.37 7.8 11.66
MCR10 MCR15 MCR20 MCR25
65.14 61.51 56.93 49.12
3.47 3.22 2.86 2.26
43.25 42.13 37.92 32.71
4.52 4.31 3.46 3.13
135.5 126.9 118.4 112.1
486.705 515.633 548.893 717.908
10.99 10.1 8.61 7.97
No.18 Crumb rubber
No.5 Crumb rubber
Mixed crumb rubber
100 90 80
Percent passing
70 60 50 40 30 20 10 0 0.1
1
10
Sieve size, mm
(a) Mixed crumb rubber
Fine aggregate
Coarse aggregate
100 90 80
Percent passing
70 60 50 40 30 20 10 0 0.1
1
10
Sieve size, mm
(b) Figure 1. Sieve analysis of a) No.18, No.5 and Mixed crumb rubbers, and b) Mixed crumb rubber, fine and coarse aggregates
100
Figure 2.The photographic views of No.18 and No.5 crumb rubbers
Figure 3: Details of the bond strength test specimen
Figure 4: Photographic view of the pullout test set up during testing the specimen
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
75
Compressive strength, fc (MPa)
70 65 60 55 50 45 40 35 0
5
10
15
20
25
Rubber content (%)
Figure 5: Variation of 90-day compressive strength with respect to crumb rubber size and content No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
5.0
Splitting tensile strength, fst (MPa)
4.5
4.0
3.5
3.0
2.5
2.0 0
5
10
15
20
Rubber content (%)
Figure 6: Variation of 90-day splitting tensile strength with respect to crumb rubber size and content
25
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
55
Modulus of elasticity, E (GPa)
50
45
40
35
30
25 0
5
10
15
20
Rubber content (%)
Figure 7: Variation of 90-day Modulus of elasticity with respect to crumb rubber size and content
a)
25
b)
Figure 8: Photographic view of: a) notched beam and b) subjected to three-point bending test
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
6.0
Net flexural strength, fflex (MPa)
5.5
5.0
4.5
4.0
3.5
3.0 0
5
10
15
20
25
Rubber content (%)
Figure 9: Net flexural tensile strength versus with respect to crumb rubber size and content No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
160
Fracture energy, GF (N/m)
150
140
130
120
110
100 0
5
10
15
20
Rubber content (%)
Figure10: Fracture energy versus with respect to crumb rubber size and content
25
4.0
Control 3.5
No.18 CR5 No.18 CR10 No.18 CR15
3.0
No.18 CR20 No.18 CR25
Load (kN)
2.5
2.0
1.5
1.0
0.5
0.0 0.0
0.3
0.6
0.9
1.2
1.5
Displacement (mm)
Figure 11: Typical loads versus displacement curves ofNo.18CRwith respect to control mix
4.0
Control 3.5
No.5 CR5 No.5 CR10 No.5 CR15
3.0
No.5 CR20 No.5 CR25
Load (kN)
2.5
2.0
1.5
1.0
0.5
0.0 0.0
0.3
0.6
0.9
1.2
1.5
Displacement (mm)
Figure 12: Typical load versus displacement curves ofNo.5CRwith respect to control mix
4.0
Control 3.5
Mixed CR5 Mixed CR10 Mixed CR15
3.0
Mixed CR20 Mixed CR25
Load (kN)
2.5
2.0
1.5
1.0
0.5
0.0 0.0
0.3
0.6
0.9
1.2
1.5
Displacement (mm)
Figure 13: Typical load versus displacement curves of MCR with respect to control mix
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
800
Characteristic length, lch (N/m)
750
700 650 600 550 500 450 400
0
5
10
15
20
25
Rubber content (%)
Figure 14: Characteristic length versus with respect to crumb rubber size and content
No. 18 crumb rubber
No.5 crumb rubber
Mixed crumb rubber
15
Bond strength, τ (MPa)
14
13 12 11 10 9 8 7
0
5
10
15
20
Rubber content (%)
Figure 15: Bond strength versus with respect to crumb rubber size and content
25