Investigation of Rheo-Mechanical Properties of ...

Proceedings of the 11th ECERS Conference, Krakow, 2009

Investigation of Rheo-Mechanical Properties of Asphalt Mixtures as Function of Temperatures and Pressures László A. Gömze1*, Róbert Géber2, Liudmila N. Gömze3 1,2

University of Miskolc, Department of Ceramics and Silicate Engineering, Miskolc-Hungary, 3 Igrex Ltd.,Igrici, Rakoczi út 2., H-3459, Hungary

Abstract

•

Asphalt mixtures are the one of the most popular building materials in Hungary, because of the highway programme of the government. In spite of this large popularity, some of the mechanical properties of asphalts have not been discovered enough till today. In particularly, there is no mechanical model usable to understand and explain the rheological behaviours of asphalt mixtures with different composition of bitumen and mineral raw materials. The present used in industry rheological model of Burgers is not reliable enough to understand mechanical properties of asphalt mixtures, because of the included Maxwell element. This means that under any kind of mechanical forces the asphalt surfaces of roads must be continuously deformed, in spite of these forces are as small as possible. The rheological model of Burgers suggests, the lifetime cycle of asphalt roads and highway must be very-very short, which is inconsistent with the real lifetime cycle of asphalt roads. On the basis of Rheo-tribometre the instrument developed and patented by Gömze A. L. and others [1], the authors have investigated and tested standard Marshall specimens of asphalt mixtures with a different composition of bitumens and mineral raw materials. In their experiments the authors used different temperatures, loading pressures, shear ratios and deformation speeds. As a result of these laboratory tests the authors could find out a new rheological model and mathematical terms to describe the real rheologichal properties of asphalt mixtures. The new rheological model developed by the authors and its mathematical equation for asphalt mixtures are shown in the article below. Finally, the authors could give not only the rheomechanical model, but the mathematical term of it as well.

% after laying and compaction; open: having a percentage of voids higher than 15 % after laying and compaction.

According to Skovrankó [9] asphalt can be divided to the following groups: • • •

Closed compacted; Open compacted; Post-compacted.

Asphalt pavements are suffering mainly shear strain and compression strain at high summer temperatures. Horizontal forces (shear forces) are generated under high traffic. Starting, braking and on the pavement, and in the case of speed changing the cars are also generating horizontal shear forces. The growth of deformations is more intensive at higher temperature, through the increase of the number of loads and the selfrighting of bitumen. There is also a slow deformation type of asphalt generated by the loads which take longer time. Because of these phenomena a critical state of deformations are formed. A special type of pavement deformations is constituted by unevennesses. These roughnesses are formed because of the rate of compacting in the case of different thicknesses of courses. The deformation types of asphalts are shown in Fig. 1.

Keywords: asphalt, microstructure, grain-sizes, composites, rheology, viscositiy, Young’s modulus, Voigt-Kelvin body, deformation, yield point, specific surface, shear stress, temperature

Fig. 1 Deformation types of asphalt

So these phenomena are triggering deformations in the materials of asphalt. Pavements have to satisfy the following requirements:

Introduction Asphalt is one of the most prevalented building material of modern pavements. It is a mixture of coarse aggregate, sand with or without filler, and hydrocarbon binder [2,3,4,5]. A distinction is made between the following types [6,7,8]: • closed or dense: having a percentage of voids of 5 % or less after laying and compaction (practically impervious); • semiclosed or semidense: having a percentage of voids higher than 5 % but not exceeding 15

• • • •

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Self-righting against deformations at high temperatures; Resistant to corrosion effects; Asphalt possesses elasticity at low temperature; Resistant to crack formation at low temperature;


• •

systematized by Gezencvej, L. B [2]. He was one of those, who also dealt with the research of rheological properties of asphalts and asphalt concretes. According to Gezencvej, asphalts and asphalt concretes are characterized as “elastic-viscous-plastic” material, but the rheological properties were modelled with an “elastic-viscous” model, also known as Burgers-body. This rheological model is shown on Fig. 3.

Resistant to wear; Resistant to aging.

Fig. 2. represents the typical deformations of asphalt pavements.

viscous-plastic

Fig. 3. The rheological model of Burgers-type materials

Where: • • • • • • •

E1: Hookean dynamic modulus E2: Elasticity modulus of the Voigt-Kelvin body εE: Actual elastic deformation εP: Permanent viscous deformation εD: Delayed elastic deformation η1: Viscosity of the Newton body η2: Viscosity of the Voigt-Kelvin body

It is easy foreseeable by Burgers-model, when the amount of generated mechanical stresses in asphalt by the external force is: σ > 0;

(1)

then the response function of the total deformation of the system is: ε0(t) = εE(t)εP(t)εD(t);

(2)

where: • εE(t)=σ/E1: The response function of the deformation of Hookean body; • εP(t)=σt/η1: The response function of the deformation of Newtonian body; • εP(t)=σ/E2(1-expE2t/η1): The response function of the deformation of VoigtKelvinean body;

Fig. 2. Viscous-plastic deformations of asphalt pavements

The testing methods of the structural, morphological and mechanical properties of asphalts are developed and

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According to the above Burgers model, the asphalt surface is under permanent deformation in all cases, when σ ≠ 0, and εP(t) = σ(t)/η1.

τ = f(p, Q, T. v), [Mpa]

(4)

(3)

This deformation is irreversible and increasing with the time. Experiments At the University of Miskolc there have been about 2530 years experiments in examination of rheomechanical properties of materials with complex material structure compositions [10,11,12,13,14,15,16,17]. As it is shown in Fig. 4. the asphalt pavements and asphalt concretes have complicated material structures.

Fig. 5 The rheotribometer instruments

The data, which come via the data recorder (16), are captured and processed by the computer (17). Our goals with experiments and rheo-mechanical tests were the following: • Understand the phenomena of rheomechanical properties of complex material systems like asphalt mixtures; • Understand and disclose the influences of temperatures and loaded mechanical pressures on the rheo-mechanical properties of asphalt pavements • Set up a better rheo-mechanical model to support engineers in the development of more durable asphalt concretes and asphalt pavements

Results and discussion Fig. 4 The materials structures of asphalt pavements and asphalt concretes

It is obvious that rheo-mechanical properties of asphalt pavements very strongly depend on used raw materials and many other parameters. This dependence can be described by the following:

To realize shear strength tests and complex rheomechanical tests of such a complicated material system a new rheo-tribometer instruments (Fig. 5) was developed with the participation of the authors [1]

Rmp = f(Cch, Ccm, Dgs, Fib, Pos, Rls, Rms, T) ˙´(5) where. Cch - chemical composition and structure; Ccm – Mineralogical composition and structure; Dgs – Grain sizes and structures of components; Fib – Interatomic bonding forces; Pos – Porosity, pore size and structures; Rls – Loading shear stress; Rms – Mechanical strength of components T - Temperature

This new developed rheo-tribometer instrument has a temperature controlled speciment holder (9) and a control unit with a frequency changer (15). With these instruments it is possible to measure the mechanical stresses of asphalt mixtures during shearing. These mechanical stresses (τ) can be characterized by the loading pressures (p), material compositions (Q), temperature (T) and shear ratio (v) using the following equation:

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In our investigations the actual (E1) and delayed (E2) elastic modulus, the plastic viscosity (η1) of destructs and viscosity (η2) of non-destructed material structures, as well as static yield point (τo) of asphalt pavements were examined as a function of temperatures and loading compressive pressures. The achieved values are shown in Fig. 6. and in Fig. 7.

Using the developed new rheo-tribometre instrument the deformation–time curves were also built. On the basis of these deformation-time curves described in the works [5] and [6] we were able to build up the new rheo-mechanical model of asphalt concretes and asphalt mixtures as it is shown in Fig. 8.

Fig. 8 The developed new rheo-mechanical model of asphalt alt concretes and asphalt nd asphalt concretes and asphalt pavements

The materials, characterised with this kind of rheomechanical model can be matematicaly described with the following equation: •

••

•







••

η τ (t ) = τ 0 + η1 ε + η1t r ε − τ t fr − t r 1 −  − t r t fr τ ;[ MPa] η



Fig. 6 Values of actual (E1) and delayod (E2) elastic modulus of asphalt pavements



1

2



(6)

•

ε.

First derivative by time of the deformation of the material system ••

ε : second derivative by time of the deformation of the material system τ0: static yield point of the material system; [Mpa] •

τ

: first derivative by time of the shear stress

••

τ : second derivative by time of the shear stress tr: delay time of elastic deformation; [s] tfr. Tension-relaxion time of the material system; [s] Conclusions • • •

Fig. 7 Values of plastic of destructed (η1) and non-destructed (η) material parts of asphalt pavements

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A new instrument was developed for rheomechanical tests of such complicated material compositions and structures as asphalt pavements. A new rheo-mechanical model and its mathematical terms were developed for such complicated material as asphalt mixtures and pavements. The very strong influences of temperatures and loding normal pressures on rheo-mechanical properties of asphalt pavements were also proved by the authors.


[10] Gömze A.László – Chirskoi, A. S. – Silenok, S. G.: Rheology and flow conditions of clay during smoth roller comminution; Épíıanyag vol: 33., No. N-12, pp. 441-6 (19819 [11] Gömze A. L.: Rheology and flow conditions of clay during smooth roll comminution; Építıanyag, Vol. 33. no. 12., pp.: 441. (1981) [12] Gömze A. L.- Eller E. A. – Silenok S. G.: Rheological principles of asbestos cement body extrusion; Építıanyag Vol.: 34., no.N-1, pp.: 17-22. (1982) [13] Gömze A. L. – Eller E. A.: Rheological examination of extrudable asbestos cement bodies; Építıanyag, Vol: 35. no. N-1, pp.: 28-34. (1983.) [14] Papp I. – Gömze A. L. – Olasz-Kovács K. – Nagy A.: Alteration of the rheological properties of kaolin A1; Keramiche Zeitschrift Vol: 52, no. 9. pp.: 788, 791795. (2000.) [15]Mannheim V.: Empirical modeling and determination of the grindability in stirred ball mills; Építıanyag, no. 2., pp.: 36-40, (2007.) [16] Gömze A. L.: Problems of dimensioning smooth rollers for crusching clay; Építıanyag, Vol: 32, no. N11, pp.: 428-32. (1980.) [17] Eller E. A. – Gömze A. L.: Patent No. 1038879 CCCP, ustrojostvo dlya otsenki formovochnih svojtstv plastichnih materialov; Moscow (1983.)

References [1] Gömze A. L. – Kocserha I.- Czél Gy.: Patent No.U0200079 számú mintaoltalmú találmány. Hungarian Patent Organization, Budapest (2002.) [2] Gezencvej L. B.: Aszfaltbeton útburkolatok. KPM – kiadvány, Budapest (1964.) [3] J. P. Planche – P. M. Claudy – J. M. Létoffé – D. Martin: Using thermal analysis methods to better understand asphalt rheology; Thermochimica Acta 324, pp. 223-227 (1998.) [4] J. Murali Krishnan – K. R. Rajagopal: On the mechanical behaviour of asphalt; Mechanics of Materials 37, pp. 1085-1100 (2005) [5] Gömze A. L. – Kovács A.: Examination of rheological properties of asphalt mixtures; Éptıanyag v. 57., N.2, pp. 34-38 (2005.) [6] Laszlo A. Gömze – Robert Géber – Judit Csányi Tamásné: The effect of temperature and composition to the rheological properties of asphalt pavements; Materials Science Forum Vol. 589, pp 85-91 (2008.) [7] Y. Edwards – Y. Tasdemir – U. Isaccson: Rheological effects of commercial waxes and polyphosphoric acid in bitumen 160/220 – high and medium temperature performance; Construciton and Building Materials 21. pp. 1899 – 1908 (2007.) [8] H.S. Do - P.H. Mun – R.S. keun: A study on engineering characteristics of asphalt concrete using filler with recycled waste lime; Waste Management, A vailable online 3 April 2007. [9] Skovranko E.: Fundaments of asphalt technology, Manuscript, Bautest Ltd., Miskolc pp. 1-78. (2002)

*Corresponding author: László A. Gömze; Address: University of Miskolc, Department of Ceramics and Silicate Engineering, Miskolc, Hungary E-mail address: [email protected]

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