Workability and Hardened Characteristics of Self ...article.aascit.org/file/pdf/8120048.pdf80 Nahla...

International Journal of Information Engineering and Applications

2018; 1(2): 79-94 http://www.aascit.org/journal/information

Workability and Hardened Characteristics of Self-Compacting Rubberized Concrete

Nahla Naji Hilal

Department of Dams Engineering and Water Resources, Anbar University, Anbar, Iraq

Email address

Citation Nahla Naji Hilal. Workability and Hardened Characteristics of Self-Compacting Rubberized Concrete. International Journal of Information

Engineering and Applications. Vol. 1, No. 2, 2018, pp. 79-94.

Received: January 24, 2018; Accepted: February 18, 2018; Published: April 27, 2018

Abstract: The primary objective of this research study was to determine the influence of utilizing chip rubbers on characteristics of ‘self-compacting concrete’ (SCC). During study, a total of six concrete mixtures having new state properties towards different mixtures were testified with slump flow, T50 time, V-funnel time and L-box height ratio analytical tests. The inimitable results came forward that at water-cementitious (w/cm) having a ratio of 0.35, ‘self-compacting concretes’ (SCCs) were likely to be generated by swapping the summative with six selected contents of tire chips of 0%, 5%, 10%, 15%, 20% and 25% by the summative volume. Moreover, experimental results were analyzed statistically by using general linear model analysis of variance, namely GLM-ANOVA. Test results showed that utilization of tire chip negatively affects the fresh properties of self-compacting concretes as well as compressive strength. However, test results obtained from this study satisfy the criteria recommended by EFNARC. Besides, statistical analysis revealed that the tire chip content have significant effect on the fresh characteristics of concretes and the most remarkable parameter influencing the fresh properties and hardened properties is the tire chip content.

Keywords: Chip Rubber, Fresh Properties, Fly Ash, Hardened Properties, Self-compacting Rubberized Concrete

1. Introduction

Today the world is facing one of the major concerted issues of the disposal of material and substances and the disposal of d tires have been the most crucial matter since they cannot be easily biodegradable yet after having a longer-period of landfill management. Majority of people suggest using tires or rubber products as ‘fuel material’ or sometimes as ‘raw material’[7] but it is also proposed that material substances and energy can be utilized as alternatives [1-6] to disposal of the rubber products. On the other hand, the materials used for construction purposes are also centred with powder of rubber which is attained through tires’ cryogenic milling including mixture of asphalt or bituminous substances [15, 16], however, a huge range of d substances has been proposed as ‘additives’ for cement based substances [8-14] but still no significant concentration has been given to the utilization of d tire materials in concrete mixtures of ‘Portland cement’ which can also be used for the construction of highways. Few research works have been done by the researchers regarding utilization of d rubber tires in traditional methods of making concrete cement blends. According to the research study of Eldin and

Senouci [7], the tenacity and stiffness characteristics were probed that contained two types of rubber tires and found that concrete blends comprising rubber showed no fragile failure under ‘compression or tension’ conditions. In their study, the control mixes having 28 days compressive tenacity i.e. 35 MPa was swapped by various amounts of rubber tire particles having different sizes. The outcomes of their study ultimately show that approx. 85% reduction in the compressive tenacity was observed when the summative course was completely swapped by the rubber. On the contrary, approx. 65% of smaller reduction was detected when sand was completely swapped by rubber scraps. Therefore, it was finally determined that an optimum mix was required to be devised in order to provide maximum rubber tire substances in the concrete blend. In relation to the research study of Eldin and Senouci [7], the other investigators Khatip and Bayomy [17] also employed recycled rubber tires collectively in the concrete blends along with different rubber substances. In their study, 38 MPa of 28-day compressive strength was initially used for concrete blend of ordinary ‘Portland cement’ and the outcomes of their study subsequently exhibit that ‘compressive’ and ‘flexural’ strengths signified a huge reduction when greater rubber

80 Nahla Naji Hilal: Workability and Hardened Characteristics of Self-Compacting Rubberized Concrete

contents were used. They also suggested a distinguished ‘characteristic function’ for ‘compressive and flexural’ strengths in order to gauge the loss of strength while using rubber substances. It is also stated that for proper function utilization of different designs of rubber concrete mixtures, a vast range of research is needed to be developed which exhibit an association between testified properties of concrete and the volume of the rubber utilized in the blend because it was examined that parameters of function are largely dependent on the testified properties of concrete and the potential strength of the control mixture. Topcu [18] has also probed the characteristic properties of rubber substances. In his study, both physical as well as mechanical characteristics of rubber concretes having initial compressive strength of 20 MPa were studied. The study outcomes exposed a general reduction in the compressive strength when the total aggregate volume of 15%, 30% and 45% rubber was used. Further to this, energy capacity of plastic for ordinal concrete was also enhanced with the addition of rubber because such concretes exhibit greater tension due to greater energy capacities of plastic more specifically under the ‘impact effects’. The studies pertaining to the utilization of the particles of rubber tires in cement based substances concentrate on the aggregate utilization of rubber tires into the concrete mixtures. The exclusive utilization of particles of rubber is probable to impact the properties even more pessimistically as compared to the utilization of fine particles [7, 17, 18, and 23] and that is why majority of the aforementioned research studies have exhibited a significant reduction in the mechanical characteristics when rubber tire particles were added in the concrete mixture. On the other hand, few researches have been established to study and investigate the combined use of fine and particles of rubber into the concrete blend [17], therefore, Khatip and Bayomy [17] described such loss of strength as the lack of linkage between the particles of rubber and the paste. This has also been observed that particles of rubber are usually enhanced through concentrated aqueous solution of NaOH to maximize its adhesiveness with the surrounded paste of cement. As a result, most of the researchers proposed that the strength loss can be optimally reduced by initial surface treatment of the particles of the rubber tires [7, 13, 26, and 27]. Nevertheless, it is also stated that a greater material strength might be attained when ‘silica fumes’ are used as extremely fine mineral admixture which is ultimately capable to enhance the ‘homogeneity’ as well as reduce the larger number of pores in cement blend [29–31]. In this study, tire chip obtained from used automobile tires has been ground, granulated and used as aggregate in SCC mixture ranged from 0-25%. 30% by mass of Fly ash (FA) was used as a substituent of Portland cement (PC). First of all, control SCC mixture providing self-compatibility criteria has been obtained in accordance with the Europe SCC Specifications [32]. The fresh and hardened properties for SCRC mixtures have been compared to control SCC mixtures without TC content. Wang HerYung et. al. [33]. They replaced part of the fine aggregate by waste tire rubber powder filtered through #30 and #50 sieves to produce (SCRC). at volume ratios of 5%, 10%, 15% and 20%,

respectively The results showed that when 5% waste tire rubber powder that had been passed through a #50 sieve was added, the 91 day compressive strength was higher than the control group by 10%. Alper Bideci et. al [34]. were used Different rubber lengths and volumetric fractions to produce SCRCs it was determined that RA replacement decreases unit weight of fresh concrete; when RA length ratio increases, it becomes difficult for the concrete to pass through reinforcement openings; in hardened concrete samples dry unit weight decreases; 10% fibre addition increases compressive strength values. Matthew R. Hall and Khalid Battal Najim [35] were used crumb rubber as partial aggregate replacement to produce (PRC) and (SCRC) They reported that the increase in fractal energy dimension was similar for PRC and SCRC suggesting that changes in energy dissipation at the concrete–steel interface in rubberized concretes may be related to the modulus of elasticity of the rubber aggregates.

E. Güneyisi et. al [36] study rheological behavior of fresh self-compacting rubberized concrete. The results indicated that replacing the natural aggregate with waste rubber decreased the compressive strength.

The significance of this study includes the main aim to estimate the percentages of rubber in the mixture in order to develop possible improvements of the self-compacting concrete abilities. Waste rubber will be the cost effective component of concrete as compared to other components and cheaper than sand and natural aggregates.

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 fly ash type F according to ASTM C- 618 [37] with a specific gravity of 2.25 g/cm3 Physical properties and chemical compositions of the cement and fly ash are presented in Table 1.

Table 1. Chemical compositions and physical properties of Portland cement

and fly ash.

Chemical analysis (%) Portland cement Fly ash

CaO 63.84 2.24 SiO2 19.79 57.2 Al2O3 3.85 24.4 Fe2O3 4.15 7.1 MgO 3.22 2.4 SO3 2.75 0.29 K2O - 3.37 Na2O - 0.38 Loss on ignition 0.87 1.52 Specific gravity 3.15 2.04 Fineness (m2/kg) 326 379

2.1.2. Aggregates

The 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

International Journal of Information Engineering and Applications 2018; 1(2): 79-94 81

specific gravities of 2.65, 2.43, and 2.71, respectively. The particle size gradation obtained through the sieve analysis of

the fine and aggregates are given in Figure 1.

Figure 1. Sieve analysis of fine and coarse aggregates.

2.1.3. Tire Chip

The specific gravity of tire chips was 1.02. The photograph of TC is illustrated in Figure 2.

Figure 2. The photographic views of tire chips.

2.1.4. Superplasticizer

A Polycarboxylic ether type of superplasticizer (SP), which acts by steric hindrance effect [38] 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

Self-compacting rubberized concrete (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 total binder content in all mixtures. The aggregates were replaced with tire chips at six designated contents of 0%, 5%, 10%, 15%, 20%, and 25% by volume. Totally 6 different SCRC mixtures were designed regarding to above variables. The detailed mix proportions for SCRCs are presented in Table 2. The concrete mixtures were designed according to slump flow diameter of 700 ± 50 mm which was achieved by using the superplasticizer at varying amounts.


Table 2. Mix proportions for concrete (kg/m3).

Mix ID Water-to-binder

ratio (w/b) Cement Fly ash Water SP* aggregate

Control 0.35 364 156 182 3.4 819.4 5TC 0.35 364 156 182 3.6 778.4 6TC 0.35 364 156 182 3.9 737.4 15TC 0.35 364 156 182 4.2 696.5 20TC 0.35 364 156 182 4.4 655.5 25TC 0.35 364 156 182 4.7 614.5

Table 2. Continued.

Mix ID Fine aggregate

No. 18 Crumb rubber No. 5 Crumb rubber Tire chips Unit weight Natural sand Crushed sand

Control 573.6 245.8 0.0 0.0 0.0 2344.1 5TC 573.6 245.8 0.0 0.0 15.4 2318.9 6TC 573.6 245.8 0.0 0.0 30.8 2293.6 15TC 573.6 245.8 0.0 0.0 46.3 2268.3 20TC 573.6 245.8 0.0 0.0 61.7 2243.0 25TC 573.6 245.8 0.0 0.0 77.1 2217.7

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. [39] was followed since the mixing sequence and duration are very vital in the self-compacting concrete production. According to this mixing procedure, the tire chip, and aggregates in a strength-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 tire chip and aggregates were left to absorb the water in the mixer for 1 min. Thereafter, the fine aggregate, cement and fly ash were 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. The workability and passing ability of the SCRC were tested by means of different tests. Moreover, three 150-mm cubes were taken to measure the compressive strength of self-compacting rubberized concret, two 60*200mm cylinders were taken to measure the splitting tensile strength, two 150*300 mm cylinders were taken to measure the modulus of elasticity, three 60*60*500 prisms were taken to measure the net flexural and fracture properties and finally three 150-mm cubes were taken to measure the bond strength of self-compacting rubberized concret. 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 28-dayand 90-day water curing period.

2.4. Test Procedure for Fresh Properties

The recommendations in EFNARC [32] committee (European Federation for Specialist Construction Chemicals and Concrete Systems) were followed to carry out the slump

flow diameter, T50 slump flow time, V-funnel flow time, L-box height ratio, and L-box T20 and T40 flow time tests of which test apparatus sketching was given in Figure 3. Slump flow value, which is used for the description of the flowability of a fresh concrete in unconfined conditions, is a sensitive test. It is the primary check for the fresh concrete consistence to meet the specification. Thus, it can normally be specified for all self-compacting concretes. Moreover, additional information about segregation resistance and uniformity of concrete can be achieved from the visual observations during the test and/or measurement of the T50 time that is the measured time for flowing of concrete to a diameter of 500 mm [32]. EFNARC classify the typical slump flow for the range of applications in three classes. The upper and lower limits for these classes as well as typical application areas are given in Table 3.

Both the T50 slump flow time and V-funnel flow time can be used to measure the viscosity of the self-compacting concrete. The direct viscosity cannot be achieved by these tests but the results of these tests describe the rate of flow which is related to the viscosity. V-shaped funnel is used to measure the V-funnel flow time, it is filled with fresh concrete and then it is allowed to flow out from the funnel, the elapsed time of fully flowing is recorded as the V-funnel flow time. Viscosity classifications with respect to EFNARC [32] are also presented in Table 3 according to the measured V-funnel and T50 slump flow times. The passing ability of the fresh concrete mix to flow through confined spaces and narrow opening such as areas of congested reinforcement without segregation, loss of uniformity or causing blocking can be measured in terms of L-box test. A measured volume of fresh concrete is allowed to flow horizontally through the gaps between vertical, smooth reinforcing bars and the height of the concrete beyond the reinforcement is measured. Passing ability classes with respect to L-box height ratio values is also given in Table 3.


Figure 3. Sketch of test apparatus used for measuring the fresh state of SCC.

Table 3. Slump flow, viscosity, and passing ability classes with respect to EFNARC [32].

Class Slump flow diameter (mm)

Slump flow classes SF1 550-650 SF2 660-750 SF3 760-850 Class T50 (s) V-funnel time (s) Viscosity classes VS1/VF1 ≤2

≤8 VS2/VF2 >2 Passing ability classes PA1 ≥ 0.8 with two rebar

9-25 PA2 ≥ 0.8 with three rebar

2.5. Test Procedure for Hardened Properties

Compression test of self-compacting rubberized concrete sample was carried out with respect to ASTM C39 [40]. The results for compressive strength of self-compacting rubberized concrete were given as the average of three samples. The splitting test of self-compacting rubberized concrete sample was conducted [41] by using ASTM C496, and the test results were given as the average of three samples and 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-6, 206 [42]. 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 Pmax 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) [43]. For the test of fracture energy, beams with 60x60 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 60x60 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). [43].

GF��

�

�

�� δs (3)

lch = !"

#$%� (4)

The concrete’s bonding strength (τ), was determined using the RILEM RC6 (RILEM RC6, 1996) [44]. The bonding

strength was computed using Equation (5):

τ=&

�'( (5)

3. Results and Discussion

3.1. Slump Flow Test and Slump Flow Time

Filling ability, or flowability, is the ability of the concrete to completely flow (horizontally and vertically upwards if necessary) and fill all spaces in the formwork without the addition of any external compaction. The flowability of SCC is characterized by the concrete’s fluidity and cohesion, and is often assessed using the slump flow test. Visual observations during the test and/or measurement of the T50 time can give additional information on the segregation resistance and uniformity of each delivery. T50 is a measured time that shows the concrete has flowed to a diameter of 500 mm [32]. According to EFNARC, there are three typical slump flow classes for the range of applications. Amongst the fifth group of sample containing TC25 demonstrated the smallest flow diameter i.e. 56cm, whereas TC5 demonstrated the largest flow diameter i.e. 71cm. Values for the time taken by mixtures to acquire the flow diameter of 50cm were in the range of 4.14-8.14 seconds. As shown in Figures 4 and 5, an increment in quantity of the TC caused lesser workability and higher values for T50. It implies that the SCRC has a tendency to lose workability in lesser time as compared to conventional SCC.

Figure 4. Variation of slump flow diameter and slump classes of SCC with tire chip content.

550

650

750

850

0 5 10 15 20 25 30

Slu

mp

flo

w d

iam

eter

(m

m)

Rubber content (%)

SF

2S

F3

Slu

mp

flow

cla

sses

SF

1


3.2. Determination of V-funnel Flow Time

The flowability and viscosity of SCCs was evaluated by means of V-funnel flow time. The concrete having a V-funnel flow time within 6 to 12 sec may be highly resistant to possible segregation. Values of V-funnel flow time for the mixtures containing TC were in the range of 13.64-27.73 seconds. Moreover, it was noticed that increment in the quantity of the TC from 5-25% caused a stable increase in V-funnel flow times recorded for SCRC samples in addition,

according to the European Self-Compacting Concrete Specifications, specimens demonstrating a funnel time the range of 9-25 seconds in a TV- funnel test are considered to be not suitable [32]. As per a general observation, an increase in the TC content of the SCC is accompanied with segregation. Good flowable and stable concrete would take a short time to flow out. From Figure 5. showen the time measured through the V-funnel flow was depending mainly on the concrete composition.

Figure 5. Variation of fresh properties of SCCs with respect to tire chip content.

3.3. L-box Height Ratio, T20 and T40 Times

Passing ability is the ability of the concrete to flow though restricted spaces without blocking. This property is related to the maximum aggregate size and aggregate volume, and the L-Box test is the most common method used to assess this property. A visualization experiment conducted by Dr. Hashimoto (Okamura 1997) showed that blockage occurred from the contact among aggregates. As the distance between particles decreases, the potential for blocking increases due to particle collisions and the build-up in internal stresses. Inter-particle interaction can be reduced by decreasing the aggregate volume and it has been shown that the energy required to initiate flow is often consumed by the increased internal stresses and aggregates. Therefore, Okamura recommends that the aggregate content should be reduced in order to avoid blockage (Okamura and Ouchi 1999) [45]. The Value of H2/H1 ratio for the TC mixtures was in range of 0.852-0.55. Considering the abovementioned results, it can be stated that specimens containing TC ranging from 5-15 met the EFNARC standard for flow ability. While the mixture containing on the highest proportions of TC unacceptable. T20 and T40 times to be taken for the mixture to reach a distance of 200 and 400 mm along the horizontal section from the sliding door of the L-box were also given in Table 2. These results gave some indication about the easy flow of the concrete mixtures with the TC compared to the

control mixture. The values of T20 for the mixtures containing TC were between 2.89 and 4.67 seconds. These values were affected by the quantity of tire chip as well as the superplasticizer. Figure 5 present the values for the T20 and T40 for different specimens and show that replacement of aggregates with the TC results in greater T20 and T40 values. As compared with the control mix this is due to the roughness particles of tire chip.

3.4. Compressive Strength

The compressive strength values at 28-day ranging from 31MPa to 62.8 MPa were achieved in this study is given in Figure 7. The tire chip is a soft material when compared with natural aggregate. The utilization of tire chip in concrete production results in decreasing of compressive strength. Besides, the adhesion between rubber particles and surrounding cement paste is low. Therefore, some authors recommend surface treatment of rubber particles to increase its adhesion to cement paste [46]. While the 90-day compressive strength of mixtures is given in Figure 7. The compressive strength values ranging from 35.45-72.44MPa. The highest compressive strength result was obtained from control mixture, and the systematical decreasing of compressive strength was observed as tire chip content bigger. This indicates that the self-compacting concrete of which compressive strength is higher than 30 MPa can be produced simply.


Figure 6. Variation of L-box height ratio and passing ability classes of SCC with tire chip content.

3.5. Splitting Tensile Strength

The variation in splitting tensile strength of 90-day for all SCRC with respect to tire chip content is given in Figure 6. The splitting tensile strength values ranging from 2.38 MPa to 4.36 MPa were achieved in this study. The maximum splitting tensile strength result was obtained from control mixture, and the systematical lessening of splitting tensile strength was observed as rubber content increased. All concrete typically has low tensile strength (~10% of compressive strength) and a low strain capacity [47].

However, tensile strength is important in highway design, airfield slabs, and when shear strength and crack resistance are a priority. The addition of chip rubber to SCC exacerbates these shortcomings as shown in Figure 7. Where there is a general tendency towards tensile strength reduction which may be attributed to the same reasons affecting compressive strength. The relationship between compressive and splitting tensile strength is controlled by several factors including aggregate type and particle size distribution, and curing age [48] as well as powder and admixtures content and type.

Figure 7. Variation of compressive strength and splitting tensile strength with respect to tire chip content.

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

0 5 10 15 20 25 30

L-b

ox

hei

gh

t ra

tio

Rubber content (%)

PA

2

Pa

ssin

ga

bil

ity

cla

ss


3.6. Modulus of Elasticity E

Static modulus of elasticity test results as a function of rubber and tire chip contents are depicted in Figure 8. The Moduli of elasticity values ranging from 29.26 GPa to 50.71 GPa were achieved in this study. The highest modulus of elasticity result was obtained from control mixture, and the systematical decreasing of modulus of elasticity was observed as rubber content increased. The decreasing in modulus of elasticity of rubberized concrete for several reasons including the inclusion of the tires rubber aggregate acted like voids in the matrix. This is because of the weak bond between the tires rubber aggregate and concrete matrix. With the increase in void content of the concrete, there will be a corresponding decrease in strength. Second reason is tires rubber aggregate act as weak inclusions in the hardened

cement mass and as a result produced high internal stress that are perpendicular to the direction of applied load. Third reason is Portland cement concrete strength is dependent greatly on the aggregate, density, size, and hardness. Since the aggregates are partially replaced by rubber, the reduction in strength is only natural. Last reason is the failure of the sample is also because of the tire being more elastically deformable than the matrix. When the samples were loaded the cracks form first at the softest areas. The site of the inclusion of rubber is where these sites appear [29]. Their results indicated that the self-compacting concretes produced with tire chip (TC) gave the lowest static elastic modulus. The rubber particles affect the properties more negatively than do fine particles [7, 46].

Figure 8. Variation of 90-day Modulus of elasticity with respect to tire chip content.

3.7. Net Flexural Strength

As shown in Figure 9. Net flexural strength of control mix 5.6 MPa this is maximum value. While for SCRC mixes produced with tire chip (TC) was 3.2 MPa has resulted in decreasing the flexural strength by 75%. The reduction in net flexural strength could be attributed to the same mechanism of failure for splitting tensile strength, as it is a ‘theoretical’ measure for the maximum tensile stress reached on the bottom fiber of a test beam. The net flexural strength is assumed to be a ‘theoretical’ measurement because it is calculated based on elastic beam theory that assumes the

stress–strain relationship is linear so the tensile stress in the beam is assumed to be proportional to the distance from the neutral axes [47]. Previous studies [51] Reporting that the tensile strength of concrete with chipped rubber replacement for aggregates is considerably lower than for concrete containing powdered rubber. In the first case a reduction between 30% and 60% takes place for a replacement level of 5–10%, as for the latter case the reduction is between 15% and 30%. This behavior may be related to the very low adhesion between the chipped rubber and the cement.

25

30

35

40

45

50

55

0 5 10 15 20 25

Mo

du

lus

of

ela

stic

ity,

E (

GP

a)

Rubber content (%)


Figure 9. Net flexural tensile strength versus with respect to tire chip content.

4. Fracture Parameters

4.1. Fracture Energy (GF)

The term toughness is a measure of this energy. Fracture energy (GF) values, evaluated with Equation 3 from notched beams (Figure 10 a) subjected to three-point bending test (Figure 10b), The variations in fracture energy with respect to tire chip content are shown in Figure 11. Fracture energy (GF) values ranging from 155.8 N/m to 16.21 N/m were achieved in this study. The uppermost fracture energy (GF) result was obtained from control mixture, and the systematical decreasing of fracture energy (GF) was observed as rubber content increased. While replacing aggregate with 5% t replacement offered the highest fracture energy and replacing aggregate with 25% TC replacement offered the lowest fracture energy. Figure 11 show the reduction in fracture energy values at 5% TC was 10%. Huang et al. [52] and Toutanji [53] also found that rubberized concrete had very high toughness when they replaced aggregate with rubber chips. As seems in Figure 12, the concrete with 10%TC has higher the area under the load versus displacement curve while, the concrete with 25% TC has

lower the area under the load. Such an increase could be a result of the considerable enhancements in strain capacity and energy absorption that may result from stress relaxation at the rubber–cement interface [25].

4.2. Characteristic Length (lch)

Generally for normal concrete (lch) is about 200 to 500 mm [54, 55] and for SCC, (lch) it varies from 580 to 740 mm for notched beams and varies between 540 to 640 mm for un-notched beams. It is also seen the (lch) decrease with an increase in compressive strength and notch depth ratio. The variations in characteristic length of SCRCS with admiration to tire chip content are indicated in Figure 13. The control mix has the lower characteristic length than other mixture it is due to the having higher compressive strength, and this makes the concrete more brittle. Utilization of tire chip increases the characteristic length of the concrete. The Increasing of the TC volume fraction from 5-25 resulted in increasing the characteristic length by up 7%, 9%, 8%, 12% and 50% respectively. As the result show, the enhancement of characteristic length of concrete with TC25 more considerably as compared with control mix.

3.0

3.5

4.0

4.5

5.0

5.5

6.0

0 5 10 15 20 25

Net

flex

ura

l st

ren

gth

, f f

lex

(MP

a)

Rubber content (%)


a)

b)

Figure 10. Photographic view of: a) notched beam and b) subjected to three-point bending test.


Figure 11. Fracture energy versus with respect to tire chip content.

Figure 12. Typical load versus displacement curves of tire chip with respect to control mix.

100

110

120

130

140

150

160

0 5 10 15 20 25

Fra

ctu

re e

ner

gy,

GF

(N/m

)

Rubber content (%)


Figure 13. Characteristic length versus with respect to tire chip content.

4.3. Bond Strength (τ)

The 90-day bond strength of mixtures is given in Figure 14. The maximum bond strength result was obtained from control mixture, and the lowest bond strength values have been measured at the 25% TC mixture at the end of 90- day. Emiroğlu et al. 2008 [56]. Reported that the decreasing in

bond strength, because of poor bonding characteristic around rubber tires and cement paste. There are a lot of micro- cracks near the ITZ in the rubberized concrete. For this reason a large number of researches suggested treatment for rubber to improve the bonding between it and the cement paste.

Figure 14. Bond strength versus with respect to tire chip content.

400

450

500

550

600

650

700

750

800

0 5 10 15 20 25

Ch

ara

cter

isti

c le

ng

th, l c

h(N

/m)

Rubber content (%)

7

8

9

10

11

12

13

14

15

0 5 10 15 20 25

Bo

nd

str

eng

th,

τ(M

Pa

)

Rubber content (%)


5. Statistical Evaluation of Test

Results

The analysis of variance (ANOVA) was used to find out that whether an independent variable has an effect on dependent variable or not. The effectiveness of the test parameters was determined by the general linear model analysis of variance (GLM-ANOVA) which is an important statistical analysis and diagnostic tool which helps to quantify the dominance of a control factor by reducing the control variance. The fresh properties such as slump flow diameter, T50 slump flow time, V-funnel flow time, and L-box height ratio and the 28-day compressive strength of self-compacting concretes were analyzed separately and assigned as dependent variable while the tire chip content was selected as independent factors. The software called Minitab used to analyze the test results obtained from this study and the analysis was carried out at a 0.05 level of significance to specify the statistically significant experimental parameters on the fresh properties and the 28-day compressive strength of self-compacting rubberized concrete. The statistical analysis results achieved from GLM-ANOVA are presented

in Table 4. The P-values in the fifth columns show the significance of the test parameters on the fresh properties. P-value less than 0.05 means that the parameter is acceptable as a significant factor on the test result. Besides, percent contribution was also determined to have an idea about the degree of effectiveness of each independent variable on the dependent variable. When the percent contribution of one parameter is higher, the effectiveness of that parameter on the analyzed property is higher. Likewise, if the percent contribution is low, the contribution of the factors to that particular response is less.

The statistical analysis results indicated that all fresh properties and the 28-day compressive strength of self-compacting rubberized concrete were affected by the tire chip content regarding the P-values obtained from the two-way ANOVA. Moreover, the statistical analysis also revealed that the dependent parameters, slump flow diameter, T50 slump flow time, V-funnel flow time, L-box height ratio and the compressive strength, were more affected by the tire chip content than the tire chip content when the percent contribution values of independent variables were considered.

Table 4. Statistical evaluation of slump flow diameter, slump flow time, V-funnel flow time and L-box height ratio of self-compaction rubberized concretes.

Dependent variable Independent variable Sequential sum of

squares Computed F P value Significance Contribution (%)

Slump flow diameter

Rubber content 12079.2 193.27 0.000 Yes 96.15 Rubber size 358.3 14.33 0.001 Yes 2.85 Error 125.0 - - - 1.00 Total 12562.5 - - - -

T50 slump flow time


V-funnel flow time


L-box height ratio


Compressive Strength


6. Conclusions

The using of tire waste having in consideration some advantages such as: the good behavior in tension, ductile type of failure, lightweight concrete. In this study, the usability of TC as a partial substitute of normal gravel in the application of self-compacting concretes was investigated experimentally. Using of TC increased the need of superplasticizer of the mixtures to obtained the slump required additional Using TC increased both T50 and V-funnel flow times of the produced concretes. Moreover, increasing the TC content increased T50 and V-funnel flow

times gradually and The utilization of tire chip in self-compacting concrete manufacturing resulted in systematical decreasing of all hardened properties, 5% tire chip increased the fracture energy and characteristic length Significantly. With performing the GLM-ANOVA test, the statistical result indicated that tire chip content have strong effect on the fresh characteristics of mixtures.

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