PROPERTIES OF CONCRETE REINFORCED WITH RECYCLED TYRE ... · PROPERTIES OF CONCRETE REINFORCED WITH...

PROPERTIES OF CONCRETE REINFORCED WITH RECYCLED TYRE POLYMER FIBERS

Ana Baricevic1, Marija Jelcic Rukavina1, Martina Pezer1, Nina Stirmer1, Marijana Serdar1, Dubravka Bjegovic1, Matea Dzaja1, Marija Held1, Petra Ruzic1 1 University of Zagreb Faculty of Civil Engineering, Department of Materials, Fra Andrije Kacica Miosica 26, 10000 Zagreb, Croatia, email:[email protected], [email protected], [email protected], [email protected], [email protected], [email protected]

SUMMARY: The aim of the study presented in this paper is to research the possibility of replacing polypropylene fibres (PP) in concrete with recycled polymer fibres obtained from end-of-life tyres (RTPF). Therefore, reinforced concretes with RTPF mixed with rubber particles, as received from the factory, (in amounts of 5, 10 and 15 kg/m3) and mechanically cleaned RTPF (in amounts of 1, 2 and 5 kg/m3) were tested in compare with plain ordinary concrete and concrete with 1 kg/m3 of polypropylene (PP) fibres. Study comprised testing of fresh concrete properties (workability, air content and density), mechanical properties (compressive strength and modulus of elasticity) and early age deformations. Obtained results showed significant reduction in early age deformations within concrete mixes utilising RTPF compared to reference mixes with negligible difference in mechanical properties, in the same time.

SVOJSTVA BETONA ARMIRANOG POLIMERNIM VLAKNIMA IZ RECIKLIRANIH AUTOMOBILSKIH GUMA

SAŽETAK: Svrha studije prikazane u radu istraživanje je mogućnosti zamjene polipropilenskih vlakana u betonu recikliranim polimernim vlaknima dobivenim iz starih guma (engl. recycled polymer fibres obtained from end-of-life tyres, RTPF). Ispitani su betoni armirani takvim vlaknima koja su onečišćena česticama gume (u količini 5, 10 i 15 kg/m3) i mehaničkih očišćenih RTPF-a (u količinama od 1, 2 i 5 kg/m3) te uspoređeni s običnim nearmiranim betonom i betonom s 1 kg/m3 polipropilenskih vlakana. Obuhvaćeno je ispitivanje svojstava svježega betona (obradivost, sadržaj zraka i gustoća), mehanička svojstva (tlačna čvrstoća i modul elastičnosti) i određena veličina deformacije u ranoj starosti. Dobiveni rezultati pokazuju znatno smanjenje vrijednosti deformacija mladog betona za mješavine betona u kojima je upotrijebljen RTPF u usporedbi s referentnim mješavinama uz istodobno zanemarivu razliku u mehaničkim svojstvima.

1. INTRODUCTION

Tyre recycling belongs to the field of sustainable development as the recycling of used products results in valuable raw materials that can be used for manufacturing products with a new value [1]. Three raw materials can be obtained by waste tyre recycling: a) rubber granules, b) steel fibres, and c) polymer fibres. Only 5% of recycled waste tyres are currently used in construction industry. Apart from rubber granules and steel fibres, recycled tyre polymer fibres (RTPF) have not so far found their use in construction industry. The aim of Anagennisi project [2] is to develop innovative solutions to reuse all tyre components in high value innovative concrete applications with reduced environmental impact.

Since the dimensions and composition of RTPF obtained from waste tyre recycling are similar to dimensions of polypropylene (PP) fibres, a concept involving replacement of industrial fibres with fibres obtained by waste tire recycling has been developed. Previous research state that micro PP fibres are activated during early age cracking, meaning that low modulus of fibres are to be effective only during first 24 hours of hardening while stress are transferred through the cement matrix [3-5].

In study presented in this paper, as part of Anagennisi project, experimental study conducted on the influence of RTPF addition on properties of ordinary concrete in fresh and hardened state. Obtained properties were compared with those obtained on plain mix and mix with 1 kg/m3 of monofilament polypropylene fibres. The main goal was to define behaviour of this type of concretes in the exploitation.

2. EXPERIMENTAL PROGRAM

Experimental programme was based on the research of 8 different mixes divided into three groups according to type of added fibres, as follows:

Group I - 2 reference concrete mixes: plain concrete mix and mix with 1 kg of monofilament PP fibres,

Proceedings of the 1st International Conference on Construction Materials for Sustainable Future, Zadar, Croatia, 19 - 21 April 2017

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Group II – 3 mixes with 5, 10 and 15 kg/m3 of mixed RTPF,

Group III - 3 mixes with 1, 2 and 5 kg/m3 of mechanically sorted RTPF.

2.1. MIX DESIGN AND PREPARATION

All concrete mixes were prepared with CEM II/B-M (S, V) 42.5 N, crushed limestone as aggregate (0/4 mm, 4/8 mm and 8/16 mm) and superplasticiser (polycarboxylic ether hyperplasticiser). Following, maximum aggregate size was selected to be 16 mm and reference grading curve according Fuller`s equation was used [6, 7]. Properties of used types of PP fibres, as declared by the producer, used for reference mix is presented in table 1 and figure 1a.

Table 1: Properties of PP fibres

Type Length, mm Density, g/cm3 Tensile strength, MPa MMpaMPa

monofilament 6 mm 0.91 > 270

Properties of used RTPF are presented in Table 2, where mixed type is related to RTPF as received from the factory (Figure 1b), while sorted type of RTPF (Figure 1c) were obtained with cleaning procedure described in [8].

a) b) c)

Figure 1. a) Polypropylene fibres b) Mixed RTPF c) Sorted RTPF

Table 2. Properties of RTPF used in study

Concrete mix designs are presented in Table 3 where mixes are designed to satisfy consistency class S4 (160 – 210 mm) in fresh state.

All constituting materials were kept for at least 24 hours in the laboratory at a temperature of 20 ± 2°C before mixing. The mixing procedure was as followed: First, the aggregates and the recycled tyre polymer or polypropylene fibres were mixed together to ensure a good dispersion of fibres. Mixing was then proceeded for two minutes after adding half of the water. To allow the aggregates to absorb the needed amount of water, the mixing was stopped for about two minutes. The cement was then added and mixing started again with continuous addition of the residual water and superplasticiser. After the insertion of all materials, the mixing continued for another two minutes. The mixing procedure for the plain reference concrete excluded first stage and was the same from the second stage, as described previously.

Quality parameter Mixed RTPF Sorted RTPF

Length, mm 8.4 ± 3.8 9.5 ± 4.6

Fineness, μm (Diameter)

type 1 30.9 ± 2.5 30.1 ± 2.0

type 2 20.7 ± 1.8 20.2 ± 1.7

type 3 13.2 ± 1.8 12.4 ± 1.8


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Table 3. Concrete mix design

Group of mixes I II III

Components (kg/m3) OC 1PPm 5RTPFm 10RTPFm 15RTPFm 1RTPFs 2RTPFs 5RTPFs

Cement 370 370 370 370 370 370 370 370

Water 170 170 170 170 170 170 170 170

Superplasticizer 2.22 2.05 2.22 3.21 3.54 1.29 1.67 2.67

w/c 0.46 0.46 0.46 0.46 0.46 0.46 0.46 0.46

Fibres

Monofilament PP - 1 - - - - - -

Mixed RTPF - - 5 10 15 - - -

Sorted RTPF - - - - - 1 2 5

Aggregates

0-4 822 880 816 810 801 880 878 875

4-8 383 344 380 378 366 344 344 342

8-16 680 603 675 670 645 603 602 599

2.2. TESTING METHODS

Testing of concrete properties in fresh and hardened state was performed according to the standards listed in tables 4. As can be seen from the tables, all methods for testing concrete properties (for both fresh and hardened) are standardised except method for autogenous deformation. Detailed description of this testing method can be found in [9].

Table 4. Tests on fresh and hardened concrete

Property Standard

Density HRN EN 12350-6:2009

Slump-test HRN EN 12350-2:2009

Air content -- Pressure method HRN EN 12350-7:2009

Autogenous deformation -

Compressive strength HRN EN 12390-3:2009

Modulus of elasticity HRN EN 12390-13:2013

Fresh concrete properties in terms of density, workability and air content were obtained immediately after mixing. Autogenous deformations were tested after the mixing, as well. For mechanical property testing, concrete was, after mixing, cast in cube moulds with dimensions 150x150x150 mm for compressive strength and cylinder of ᴓ/L = 100/200 mm for modulus of elasticity testing. After casting, the specimens were kept covered in the laboratory condition for 24 hours until demoulding, to prevent evaporation of water. After demoulding, the specimens were kept in the moist room at 20 ± 2°C and RH ≥ 95%, until testing at the age of 28 days.

3. RESULTS AND DISCUSSIONS

3.1. PROPERTIES OF CONCRETE IN FRESH STATE

Table 5 shows the results of fresh concrete properties, namely: consistency, density and air content. As seen from table, slump values of all tested mixes were in the range of 170 – 190 mm indicating that all mixes can be classified into target consistency class S4 (160-210 mm).

From mix design presented in table 3 and values presented in table 5, comparing concrete mixes with RTPF within the same group (both mixed and sorted types - group II and III), amount of superplasticizer was increased with increased amount of fibres. Higher demands for superplasticizer was especially highlighted in group comprising mixed RTPF where for mix 15RTPFm, addition of superplasticizer was about 40% higher compared to plain reference mix. The need for an increased amount of superplasticiser indicated that the consistency of fresh concrete mixes was decreased with the addition of mixed RTPF fibres, as previously demonstrated in the available literature [10, 11].


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Density of the studied mixes was between 2.32 kg/dm3 (for mix 5RTPFs) and 2.40 kg/dm3 (for reference plain mix, OC). The differences in density between mixes are up to 3.3 %, which leads to the conclusion that recycled tyre polymer fibres do not have significant influence on concrete density in its fresh state. Although fibres have a low specific gravity, if added in the studied amount, it represents replacement for a maximum of 1% aggregates by weight, which, in turn, cannot affect the density of concrete mix.

Obtained results of air content testing showed that all mixes with fibres (1PPm and all mixes with RTPF) had higher values (ranging 2.07 – 3.56 %) compared to plain concrete mix, OC, (1.83%). The air content is increased with increased amount of fibres in each group. Furthermore, groups of mixes containing mixed types of RTPF (group II) generally have higher values of air content indicating that residual rubber in fibres additionally entrap air during mixing of fresh concrete. Particularly, mix with 15 kg of mixed RTPF showed 1.9 times higher air content compared to plain concrete reference mix.

Table 5. Results of fresh concrete properties

Property Slump (mm) Density (kg/m3) Air content (%)

Mix Group

OC I

190 2.40 1.83

1PPm 180 2.36 2.87

5RTPFm

II

180 2.38 2.13

10RTPFm 180 2.36 3.40

15RTPFm 180 2.33 3.56

1RTPFs

III

180 2.37 2.07

2RTPFs 180 2.37 2.23

5RTPFs 170 2.32 3.13

3.2. COMPRESSIVE STRENGTH

Results of compressive strength testing at the age of 28 days are presented in Figure 2 with average and absolute deviation values based on testing of minimum 6 specimens per mix.

Figure 2. 28-days compressive strength and air content of tested concrete mixes

Compared to plain concrete mix, addition of 1 kg of fibres (PP and sorted RTPF) did not affect compressive strength significantly because the differences in the results are within 3%. Higher amounts of sorted RTPF (2 and 5 kg/m3), in group III, further decreased compressive strength up to 6.5%. Addition of mixed RTPF, resulted in decreased compressive strength up to 12% compared to plain reference mix. The latest obtained results could be explained with increased air content of mixes with mixed RTPF fibres (see Figure 2) which was, in turn, entrapped by the presence of high amount of residual rubber in this types of fibres.

3.3. MODULUS OF ELASTICITY

The results of modulus of elasticity at the age of 28 days are presented in Figure 3 with average and absolute deviation values based on testing of 3 specimens per mix.

The obtained values ranged from 34.7 GPa for a concrete mix 15RTPFm to 37.6 GPa for mix 1PPm. Results of modulus elasticity followed almost the same trend as per compressive strength results. Addition of PPm and sorted RTPF in


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amounts up to 5 kg/m3 resulted in negligible differences up to 4% compared to reference plain concrete. Modulus of elasticity was decreased with higher amounts of mixed RTPF fibres (up to 7.7 % for mix 15RTPFm compared to plain reference mix OC). The obtained results were in a good agreement with available literature data [12].

Figure 3. Modulus of elasticity of tested concrete mixes

3.4. AUTOGENOUS DEFORMATIONS

Figure 4 presents results of early age deformations and temperature profiles of studied concrete mixes as average values based on testing of three specimens per mix. These results are concerned only mixes with sorted fibres (group III) in compare to mix with PPm fibres. Results of early age deformations for other mixes concerned in this study can be found in [13] where positive effect of added mixed RTPF on autogenous deformations are observed.

Deformations concerned here are sum of the autogenous and thermal deformations, where later are caused by the temperature increase of fresh concrete mix. Thermal deformations are not separated from autogenous shrinkage, because the thermal coefficients of studied mixes were not determined and their influence on total deformations is negligible after 24 hours. Therefore, early age deformation is considered here as an autogenous deformation.

Figure 4. Results of the autogenous deformations measurements for the second stage of testing

All specimens could not be prepared at the same time. This is the reason why the initial temperatures presented in Figure 4 at the beginning of the measurement are not the same for all mixes. The greatest difference amounted up to 3°C. In accordance to Saje et al. [14] the initial temperature has the negligible influence on the size of the autogenous deformations. In accordance to Tazawa et al. [15] start of the autogenous deformations can be taken as the time of cement setting which approximately coincides with the start of temperature rise in the specimens put in the environment with constant temperature. Therefore, ˝time zero˝ or start of autogenous deformation was determined from the moment when cooling of the concrete becomes influenced by the liberated heat of hydration.

In figure 4, autogenous deformations are presented from the ˝time zero˝ as defined before. These results also show positive influence of added sorted RTPF on autogenous deformations compared to addition of monofilament PP

Age, h0 4 8 12 16 20 24

Early

age d

efo

rma

tion,

‰

-0,08

-0,06

-0,04

-0,02

0,00

0,02

0,04

0,06

0,08T

em

pera

ture

, oC

0

5

10

15

20

25

30

1PPm

1RTPFs

2RTPFs

5RTPFs


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fibres. At the end of measuring period, autogenous shrinkage of mix with PP fibres were 0.035 ‰, while for mixes with 2 and 5 kg/m3 of sorted fibres, autogenous shrinkage were 0.009 and 0.013 ‰, respectively. In the same time, mix with 1 kg/m3 of sorted RTPF had swelling in the range of 0.004 ‰. Although, there were not consistent link regarding amount of added fibres and magnitude of autogenous deformation, this testing showed that, compared to mix with monofilament PP, there were decrease in total deformation in the range from 62.8 to 77.9 %.

4. CONCLUSIONS

In the framework of this study, 6 mixes of fibre reinforced concrete made with RTPF (mixed and sorted types) were prepared and tested for fresh (density, workability and air content), hardened properties (compressive strength and static modulus of elasticity) and early age deformation. For comparison purposes, plain concrete mix and mix with 1 kg/m3 of monofilament polypropylene fibers were prepared and tested as well. The obtained results of fresh concrete indicate that there is no significant difference in concrete densities between tested mixes. Increased amount of superplasticizer with increased amount of RTPF fibres, for the same workability class (S4 in this case), indicate that amount of added fibres decrease workability of fresh concrete. Furthermore, air content in fresh concrete was increased with increased amount of fibres, especially in mixes with mixed RTPF indicating that rubber, resided in fibres, entraps additional air in the fresh mix. Results of mechanical properties showed that studied amount of RTPF fibres (especially sorted) do not have significant influence those properties. In compare to plain mix, within mixes comprising sorted fibres the obtained differences are up to 6.4% and 3.5% for compressive strength and modulus of elasticity, while within group comprising mixed RTPF the differences are up to 11.7% and 7.4%, respectively. The main expected influence of the addition of mixed RTPF is on deformation properties. There was not consistent link regarding amount of added fibres and magnitude of autogenous deformation. Nevertheless, this testing showed that, compared to mix with monofilament PP, there were decrease in total deformation in the range from 62.8 to 77.9% with mixes using sorted RTPF.

ACKNOWLEDGMENTS

The research presented in this paper are conducted within the project "Anagennisi - Innovative Reuse of all Tyre Components in Concrete" funded by the European Commission under the 7th Framework Programme Environment topic. Authors would also like to thank Prof. Edita Vujasinovic, PhD and Marijana Pavunc Samarzija, mag. ing. techn.text, Faculty of textile technology, Department of Materials, Fibres and Textile Testing, Centre for Development and Transfer of Textile and Clothing Technologies and Fashion Design, for their contribution for geometrical characterization of RTPF fibres. Authors would like to thank GUMIIMPEX for their support and students Kristina Vujnović, Ivana Vladić and Anita Mihaljević for their contribution during experimental work.

REFERENCES [1] Serdar, M. et al: Possibilities of use of products from waste tyre recycling in concrete industry, Journal of

Applied Engineering Science, 12 (2014) 1, 89–93, ISSN 2284-7197 [2] Anagennisi Project. 2015. Retrieved from http://www.anagennisi.org/ [3]Swamy, R.N., Stavrides, H. 1979, Influence of Fiber Reinforcement on Restrained Shrinkage and Cracking. ACI

Journal Proceedings, 76, 3, 443-460. [4]Saje, D., Bandelj, B., Sustersic, J., Lopatic, J., Saje, F., 2012, Autogenous and Drying Shrinkage of Fibre

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by ACI Committee 544. 5R-10. [6]Fuller, W. B., Thompson, S. E., 1907, The laws of proportioning concrete.Trans. ASCE, 59(2), 67–143. [7]Collepardi, M., 2010, The new concrete. Grafiche Tintoretto, Second edition, Italy. [8]Pezer, M., Pavunc Samaržija, M., Baričević, A., Vujasinović, E., Jelčić Rukavina, M., Štirmer, N., 2016, Textile

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[9]Gabrijel I., Jelcic Rukavina M. and Bjegovic, D., 2014, Autogenous deformations of dolomite based self-compacting concretes with different mineral, Bjegovic, D.; Beushausen, H. and Serdar, M., editors, Proceedings of the RILEM International workshop on Performance-based specification and control of concrete durability, Zagreb, Croatia, RILEM Publications S.A.R.L., 507-514.

[10]Mavridou S., 2011, Utilization of Textile Fibres from Worn Automobile Tires in Cement based mortars, Global Nest Journal, 13(2), 176–181.

[11]Serdar M, Baricevic A, Bjegovic D, Lakusic S., 2014, Possibilities of use of products from waste tyre recycling in concrete industry, Journal of Applied Engineering Science, 12(1), 89-93.

[12]Baricevic, A., Pezer, M., Stirmer, N, 2015, Utilization of polypropylene fibre reinforced cement composites as a repair material: a review. Concrete Repair, Rehabilitation and Retrofitting IV - Proceedings of the 4th


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[13]Serdar, M., Baricevic, A., Jelcic Rukavina, M., Pezer, M., Bjegović, D., Stirmer, N., 2015, “Shrinkage Behaviour of Fibre Reinforced Concrete with Recycled Tyre Polymer Fibres,” International Journal of Polymer Science, International Journal of Polymer Science. http://dx.doi.org/10.1155/2015/145918.

[14]Tazawa, E., 1999, Autogenous shrinkage of concrete. E&FN Spon, London. [15]Saje, D., Bandelj, B., Šušteršič, J., Lopatić F., 2011, Shrinkage of polypropylene fibre reinforced high

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