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Journal of Cleaner Production 116 (2016) 217e222

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Journal of Cleaner Production

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Zones of weakness of rubberized concrete behavior using the UPV

Iqbal MarieCivil Engineering Department, Faculty of Engineering, The Hashemite University, Zarka, Jordan

a r t i c l e i n f o

Article history:Received 15 October 2015Received in revised form27 December 2015Accepted 28 December 2015Available online 6 January 2016

Keywords:UPVCrumb rubberOptimum percentageWeakness zonesRubberized concrete

E-mail addresses: Iqbal@hu.edu.jo, iamarie2002@y

http://dx.doi.org/10.1016/j.jclepro.2015.12.0960959-6526/© 2016 Elsevier Ltd. All rights reserved.

a b s t r a c t

Many studies have addressed the recycling of rubber tires as a replacement material for fine or coarseaggregates used in concrete mixes. This research has focused on detecting the optimal amount of crumbtires as a partial substitute for fine aggregates in concrete mixes without radically affecting its mainproperties. Moreover, the performance of rubberized concrete with crumb rubber partially substitutedfor fine aggregates in various percentages (from 0% up to 100%) by volume has been studied under axialcompression. The nondestructive, Ultrasonic Pulse Velocity (UPV) testing method has been implementedfor this purpose. This approach has not been used for this purpose in the literature so far. The test resultsindicated three zones of weaknesses in rubberized concrete. However, Zone A demonstrated that eventhough the compressive strength is reduced it remains within accepted limits. Therefore the optimalrubber percentage was found to be 25% which is the boundary of zone A.

© 2016 Elsevier Ltd. All rights reserved.

1. Introduction

Natural aggregates are definitely essential and valuable re-sources for the economic and social development of mankind, butthey must be produced and used according to the sustainabledevelopment principles (Blengini and Garbarino, 2010; Marie andQuiasrawi, 2012). Consequently, utilization of concrete that usesscrap tires as a partial replacement of the natural aggregates hasbeen emphasized and investigated within a large number ofresearch studies (Bravo and De Brito, 2012; Ho et al., 2012;Richardson et al., 2012; Khaloo et al., 2008; Batayneh et al., 2008;Eldin and Senouci, 1992). Some studies have been conducted toexamine the effect of recycled rubber on the properties of the freshand hardened concrete and therefore the possibility of applyingrubberized concrete in various civil engineering projects. The use ofrubber particles in lightweight aggregate concrete may providefurther opportunity to recycle waste tires (Lv et al., 2015).

The durability performance of rubberized concrete also studied.It was found that the rubberized concrete is highly resistant to theaggressive environment and can be implemented in the areaswhere there are chances of acid attack (Thomas et al., 2016).

Such applications may reduce the consumption of natural ag-gregates andminimize the accumulation of non-decaying scrap tirematerial. Other studies have concentrated on the ability ofenhancing some long term properties of concrete mixes such as

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resistance to water absorption and carbonation (Thomas andGupta, 2015).

In general, most of the studies found a reduction in the me-chanical properties when rubber content increases. Almost all in-vestigators reported significant reduction of 10e80% incompressive and tensile strength of rubberized concrete withincreasing rubber content (Batayneh et al., 2008). The strengthreduction is related to the rubber content and the low bondstrength between the cement base matrix and the tire rubberparticles (Ozbay et al., 2011). Other researches indicated advantagesto rubberized concrete as crumb rubber delays the crack initiationtime while reducing the crack length and width (Onuaguluchi andPanesar, 2014). When resistance to the cracking due to imposeddeformation is a priority, use of rubber aggregates is a goodconsideration as a solution to improve durability in order tominimize maintenance expenses and to recycle used rubber tiresand preserve the environment (Ho et al., 2012). The recycled tirerubber after chemical treatment proved to be an excellent aggre-gate to use in the concrete (Pelisser et al., 2011).

The main objective of this study is to predict the performance ofrubberized concrete using nondestructive ultrasonic pulse velocity(UPV) test and to justify the optimal amount of crumb rubber thatcan be used in concrete as partial replacement for fine aggregateswithout significantly affecting its main engineering properties. Avery limited number of studies have been published on the evalu-ation of the performance of rubberized concrete using non-destructive tests (Mohammed et al., 2011).

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Eldin and Senouci (1992) reported that only the percentage byvolume of rubber in the mix has a significant effect on strengthwhile the size and shape was found insignificant. As a result, thisstudy is limited to the use of crumb rubber as replacement for fineaggregates.

The present investigation originates from an existing researchpaper by Batayneh et al. (2008) with objectives to widely explorethe effect of crumb rubber on concrete performance using UPV.

The methodology developed for this investigation aims to:

� Detect a practical optimum percentage of rubber replacementfor fine aggregates without affecting seriously the mechanicalproperties of concrete using UPV.

� Understand the performance of rubberized concrete withdiffering percentages of rubber under compression loading us-ing the UPV test.

Qasrawi and Marie (2003) studied the use of UPV to anticipatefailure in concrete under compressionwhich will be adopted in thisstudy to monitor in-depth the performance of rubberized concreteunder compression. The performance of concrete is assessed bymeasuring the time for an ultrasonic pulse to travel through aspecified length. The pulse velocity is calculated by dividing thelength by the time taken by the pulse to propagate through thatlength. The velocity is an indication about quality, uniformity andstrength of the concrete tested.

2. Experimental program

2.1. Materials

The waste tire particles used in this study were crumb rubber,which was obtained from a local industrial unit in Jordan. Thecrumb rubber has been reported to have a nominal size between4.75 mm (No. 4 sieve) and 0.075 mm (No. 200 sieve) as defined bySiddique and Naik (2004). The scrap tires originated from a scrapyard of tires from different types of vehicles. Fig. 1 shows the sieveanalysis results for both the crumb rubber particles and the fineaggregates (sand) used. The figure indicates that the gradation ofthe crumb rubber particles and the sand used fall between theminimum and maximum limits of the fine aggregates gradationlimits specified by BS882:1992 (Neville, 1995). The crumb rubberparticle size varied from 4.75 to 0.15 mm Fig. 1 (a and b) shows an

Fig. 1. Sieve analysis of crumb rubber and sand within BS882:1992 limits a. Crumbrubber particles b. sand particles.

image of the crumb rubber and the sand particles respectively. Thecrumb rubber was used in the concrete mixes to partially substitutefine aggregates in various percentages ranging from 0%, up to 100%by volume.

The raw materials used for preparing the concrete mixturesconsist of Ordinary Portland Cement (Type I) which is a generalpurpose cement with fairly high C3S content for good earlystrength development which conforms to ASTM C 150-92 specifi-cations, natural silica sand which is used as fine aggregates, andcrushed limestone coarse aggregates. All the materials used weresupplied from natural local resources in Jordan. The physical andmechanical properties of the coarse aggregate used in this study arelisted in Table 1. The absorption of the used crumb rubber is about2.3% of its dry weight. This absorption capacity is relatively lowwhen compared to local sand absorption of 3.55%. So this has beenaccounted for when proportioning the mixtures.

2.2. Specimen preparation and testing

In order to prepare the recycled crumb rubber concrete speci-mens, fine aggregates were replaced by waste materials of crumbrubber in several percentages. Mixes with 0% rubber were designedto target a compressive strength of 25 MPa at an age of 28 days. It isconsidered as a control mix for comparing the performance of thenatural aggregates concrete with the rubberized concrete speci-mens. Percentages range from 10% to 100% as volumetric ratio ofcrumb rubber to natural sand are prepared in separate concretemixes. For each mix, 6 cubes of 100 � 100 � 100 mm, were pre-pared. All the results taken are the average of the 6 cubes results. Allspecimens were fabricated and then cured in the laboratory in awater bath under a temperature of 23 �C ± 2 �C for 28 days inaccordance with ASTM/C192M-06 standard practice (ASTM, 2006).The casting and curing temperature has a significant effect on freshand hardened concrete properties (Burg, 1996). Therefore, it is keptconstant for all mixes and tests. The workability of all mixes weretested at the casting time of the specimens using the slump testaccording to ASTM C143. Mix proportions and fresh properties arepresented in Table 2. The compressive strength of the concrete wasdetermined by testing the prepared concrete cubes of size100 � 100 � 100 mm at the age of 28 days. As the rate of loadingused during compressive strength determination affects the results(Mali et al., 2015), all the compressive strength tests were per-formed at room temperature of 20 �C with a constant rate ofloading of 0.5 MPa/s.

A digital camera of 3� optical zoom and 2048�1536 pixel res-olution have been used to visualize the crumb rubber particledistribution within each different hardened rubberized concretemix as shown in Fig. 2. The visual inspection indicates that thedistribution of aggregates, cement and crumb rubber particlesseems to be homogeneous.

2.3. UPV measurement

The UPV measurements were conducted according to ASTMC597 using the direct method with the transducers firmly coupled

Table 1Physical and mechanical properties of coarse aggregates.

Property Crushed limestone coarse aggregates

Specific gravity (SSD) 2.57Water absorption 1.67Prodded bulk density (kg/m3) 1502LA abrasion (%) 25

SSD: surface saturated dry.LA: los Angeles.

Table 2Mix proportions and fresh rubber concrete properties.

% Rubber Mix proportions (kg/m3 of finished concrete) Nominal w/c ratio Slump (mm) Unit weight kg/m3

Water Cement C.A* F.* Rubber

0 252 446 961 585.0 0.0 0.56 75 2399.05 252 446 961 556.0 13.7 0.56 74.3 2331.110 252 446 961 526.5 32.3 0.56 73.5 2298.715 252 446 961 497.0 50.8 0.56 72.0 2266.220 252 446 961 468.0 67.5 0.56 60.5 2217.030 252 446 961 409.5 106.3 0.56 56.0 2169.040 252 446 961 351.0 135.0 0.56 35.5 2068.350 252 446 961 292.5 180.4 0.56 24.0 2039.360 252 446 961 234.0 202.5 0.56 17.5 1987.070 252 446 961 175.6 248.0 0.56 14.0 1909.880 252 446 961 117.2 270.0 0.56 10.5 1830.690 252 446 961 58.6 321.0 0.56 6.0 1779.8100 252 446 961 0.0 376.0 0.56 4.5 1740.6

*C.A: Coarse Aggregates.*F.A: Fine Aggregates.

Fig. 2. Scrap rubber particles distribution in different rubberized concrete mixes.

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to the opposite ends of the specimens using petroleum jelly as thecouplant between the transducer and the specimen. The UPV isobtained by measuring the time, in microseconds (ms), that an ul-trasonic pulse takes to pass through a known distance of concretebetween a transmitter and a receiver. The velocity (km/s) is thepath length divided by the transit time (Qasrawi and Marie, 2003).Transducers having 54 kHz frequency are employed. Cubes fromeach of the different mixes were tested. To maintain stability ofcubes during testing, the compression-testing machine was used toapply a very small load which allows the cube to remain in position.Each pair of opposing surfaces were cleaned and prepared fortesting. A schematic diagram of the experimental set up for thedirect UPV test is shown in Fig. 3. The time for the pulse to prop-agate through the length of the cube was recorded. Then the ve-locity of transmission of the UPV was calculated. A plot relating theUPV versus the corresponding rubber content is shown in Fig. 4.The load was then applied at a constant rate of 0.5 MPa/s untilfailure. At each load increment, the time was recorded and thevelocity was calculated. The Ultimate compressive stress versus

rubber percentage was also plotted as shown in Fig. 5. However,plots for each rubber content relating stress versus UPV were alsoobtained as shown in Fig. 7.

3. Results and discussions

The results from Fig. 4 reveal that the UPV values decrease withan increase in crumb rubber content from 0% to 100%. This reduc-tion in the UPV is due to air content and crumb rubber, whichentraps air on its surface. Therefore, as the air content in therubberized concrete mixture increases due to an increase in thepercentage of the crumb rubber replacement, the UPV value de-creases (Mohammed et al., 2011). The relation between the UPVand the percentage of rubber shows three different trend lines ofstrong correlation between these two variables as the R2 valueswere above 0.99. This tolerates dividing the performance ofrubberized concrete mixes into three zones according to UPVvalues. These zones will be referred to as the zones of weakness.The boundaries separating the three zones are determined by the

Fig. 3. Schematic diagram of the experimental setup for the direct UPV test.

Fig. 4. Crumb rubber percentage versus UPV zones.

Fig. 5. Ultimate compressive stress versus rubber percentage.

Fig. 6. Relative ultimate compressive strength versus rubber percentage showing thelower boundary relative strength per each zone.

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intersection of each two linear trend lines as shown in Fig. 4. Theboundaries in terms of UPV and rubber percentage are tabulated inTable 3.

Zone A shows that increasing the crumb rubber content to alimit of 25% keeps the changes in the mechanical properties of therubberized concrete mix within the acceptable range. As far as theUPV values fall in the range of 3.66 km/se 4.58 km/s, the specimenscan be categorized as being in good condition which implies thatthe concrete is free from any large voids or cracks that may affect itsstructural reliability (Malhotra, 1976). Therefore, the rubberizedconcrete with 25% rubber is still considered suitable as long as itachieves the target strength which depends mainly on the appli-cation of the concretemix. Using higher strength concrete with 25%rubber that targets 60% compressive strength of a non-rubberizedconcrete may be the acceptable strength for structural applications.

Using crumb rubber of less density to replace harder densenatural aggregates in concrete mixes will cause micro cracks togenerate in the concrete matrix. The presence of these cracks willcause a reduction in strength, which consequently reduces the UPV(Khatib and Bayomy, 1999). The reduction trend in the compressivestrength with increasing the percentage of crumb rubber isclearly presented in Fig. 5. A plot relating the relative strength

(compressive strength of the rubberized concrete with respect tothat of the reference concrete mix) to the percentage of crumbrubber is shown in Fig. 6. It clarifies the reduction in compressivestrength of the rubberized concrete in each weakness zone.

Zone B of (25e53%) rubber replacement has a reduction in theUPVmore than 50%. It shows a higher rate of reduction than zone A.The UPV values continue to demonstrate a concrete in good con-dition which is free from large voids or cracks since it falls in therange of 3.66 km/s e 4.58 km/s according to Malhotra (1976). Thehigh rate reduction in the UPV may be related to the rubber char-acteristics and the adhesion between cement paste and rubber.While increasing the rubber content the cement paste is becominginsufficient to cover all rubber particles, resulting in cavities be-tween cement and rubber. Aggregate properties such as porosity,permeability and absorption influence properties such as adhesion

Fig. 7. Relation between stress level and UPV for each different Rubber percentage.

Table 3Zone of weakness boundaries.

Zone UPV boundaries (km/s) Rubber %

A >5.1 0e25B 3.2e5.1 25e53C 2.0e3.1 53e100

Fig. 8. Stress strain diagrams for mixes with different rubber content (Batayneh et al.,2008).

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between aggregates and cement paste and also play an importantrole in concrete strength (Neville, 1995).

Zone C shows an enormous reduction in the UPV which isclearly contributed to the entrapped air, which increases as therubber content increases. The rubber-cement matrix interface wasstudied by Segre and Joekes (2000), using scanning electron mi-croscope (SEM). Their study revealed that discontinuance isobserved in the rubberematrix interface indicating that rubberadhesion to cement paste is poor (Segre and Joekes, 2000).

Implementing the zones of weakness detected earlier in thisstudy, a maximum reduction in the compressive strength of up to37% of the control mix strength is noticed within zone A, while areduction of 70% occurs within zone B. Zone C shows a reduction ofmore than 90%. Concrete of such reduced strength is unreliable forconstruction application. Rubberized concrete that fails to bewithin acceptable strength zone can have non structural applica-tions because it's acoustical and insulation properties are improvedat high rubber volume fractions (Aliabdo et al., 2015).

As long as the UPV values lie within zone A, it implies that aparticular concrete does not contain any large voids or cracks whichwould affect the structural integrity. The main factor whichcontributed to the strength loss is the reduced adhesion of crumbrubber to cement paste which could create soft spots in the matrix.On load application, these weak spots initiate micro-crack forma-tion in specimens (Onuaguluchi and Panesar, 2014).

The performance of rubberized concrete under axial compres-sion has been studied and the results are plotted in Fig. 7.

The reduction in the UPV through rubberized concrete withrespect to the crumb rubber percentage under axial compressionillustrates different trends according to the percentage of crumbrubber. Fundamentally this is due to the formation of cracks in theconcrete and the dislocation of rubber particles from the cementpaste due to the lack of adhesion as approved by Segre and Joekes

(2000). Comparing the behavior of rubberized concrete under axialloading with the behavior of the reference concrete of 0% rubberdemonstrates that the UPV through the reference concrete underloading drops with a higher slope than rubberized concrete up to astress level of about 85% of its ultimate stress and then dropssharply. As justified by Qasrawi and Marie (2003) due to crackspropagation and increases in crack widths. The crumb rubber de-lays the crack initiation time of restrained shrinkage mortar spec-imens while reducing the crack length andwidth (Onuaguluchi andPanesar, 2014).

Regression linear trends lines for each data within stress levelsof less than 37% (that kept the control mix within zone A) areplotted in Fig. 7. It is clear that the slope reduces when increasingrubber percentage content. The reduction in slopes may be relatedto the ductile behavior of rubberized concrete that increases whenincreasing the rubber content as shown in Fig. 8 which can beconsidered as an improvement of the brittleness of concrete. Con-crete containing up to 37.5% tire-rubber particles fails gently and

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uniformly under compressive force without any separation in thespecimen (Khaloo et al., 2008).

Moreover the results showed that rubber percentages of about20% under axial compressive loading remains within zone A witha lower rate of strength reduction as compared to 0% rubber mix.High rubber content of concrete UPV lies within zone C that havestrength below the accepted level for structural purpose. Asincreasing the rubber content specimens stayed intact with lowrate of crackswidth increment. Such behavior is clearly indicated bythe reduction in the slope of the trend lines (Kaloush et al., 2005).

4. Conclusion

Based on the experimental investigation, the following can beconcluded:

1. The optimal content of rubber in concrete mixes, where the mixdesign incorporates the most scrap tire material for the inten-ded applications was found to be up to 25% which is acceptableand does not significantly reduce the compressive strength

2. Three zones of weakness are specified for categorizing rubber-ized concrete quality according to the UPV.

3. Good rubberized concrete performancewill have UPVwhich liesabove 5 km/s

4. Mixes with rubber content more than 25% and up to 50% liewithin zone B. In this zone rate of reduction in UPV is low due tothe ductility behavior of rubberized concrete, therefore it can beapplied in nonstructural elements where high ductility isrequired.

5. Rubberized concrete within zone C of UPV is less than 3.1 km/sshow a significant reduction in strength.

5. Further research

This research can be considered as part of a wide-ranging bodyof research designed to evaluate the properties of rubberizedconcrete using non-destructive techniques and detect the effect ofthe added crumb rubber on the end properties of concrete. Theresearch will include the effect of various factors, such as curingtemperature, air content, the ultimate design strength of concreteon the mechanical properties of rubberized concrete andmainly onthe zones of weakness detected in this study.

Acknowledgment

The author acknowledges Mrs. Maha Nayfeh, a Bachelor of Artsand Education/University of Queensland, Australia for her efforts incross checking this article.

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