THE STUDY OF PERMANENT DEFORMATION USING THE STATIC CREEP TEST J.V.Merighi1, R.M.Fortes1 1Professor of the Department of Civil Engineering, Presbyterian University Mackenzie

ABSTRACT The study of the asphalt mixtures when well made can reduce the appearance of the permanent deformation substantially, mainly in tropical regions where the temperatures in the pavement can exceed 60 C during 8 months of the year. The literature has presented studies using procedures that involve equipment whose price is very beyond the available financial resources to the road managers of the countries with emergent economy. This paper presents the study of the permanent deformation with the purpose to implement the static creep that is very simple and has low cost, it can be used by communities that do not make use of more sophisticated equipment. They are presented resulted of study of behavior to the permanent deformation using the Pavement Rutting Tester from Laboratorie Central des Ponts et Chausses (LCPC) and creep static as well as a study of repeatability of the two types of procedures. Keywords: Creep, Design of pavement, Direct Tension Test, Permanent Deformation, Testing 1. INTRODUCTION Permanent deformation or rutting is one of the major distresses that affects the asphalt concrete pavement structures performance [1]. The development of rutting is based on the increase of load applications and it is caused by a combination of not only densification but also shear-related deformation. It may occur in any layer of pavement structure. Its origin can be associated with the results from vertical permanent deformation on one intermediate layer of the structure, the sum of partial vertical deformation of all layers or permanent deformation caused by the asphalt pavement layer. After the asphalt mix layer construction , the deformation firstly occurs, and consequently there is a densification caused by the traffic load. The mixture can lose the balance and because of this, it can cause the shear and consequently lateral deformation. Historically, Hubbard-Field Test (USA) was the first test method developed in the 20s. Its goal was to evaluate the strength of asphalt concrete. In the 50s, in the USA, two new methods for mix design were developed: Hveem and Marshall. In Brazil, the Marshall Test was adopted by the majority of the Department of Transportation (DOT), Municipal Government, and also by the National Department of Highway (DNER). In the 70s , new procedures to evaluate the rutting performance had been used and in the last 20 years, several loaded wheel tester had been developed . It had been used in Europe and the USA. There are French Wheel-Tracking Rutting Tester (France); Nottingham Rutting Tester (UK); Hamburg Wheel Tracking Device (Germany); Georgia Loaded Wheel Tester and Asphalt Pavement Analyzer both from the USA. The roads in Brazil have about one hundred and sixty five thousand km and approximately the same number of urban pavement . The roads administration dont have enough money to manage it , thus we have to figure it out, focusing on simple and easy solutions for public management. Full-scale wheel tracking tests are expensive moreover impractical for most construction project. The main goal of this paper is to make a comparative study of the results from French Wheel-Tracking Rutting Tester (France), dynamic and static creep test besides, explain about the static creeps potential as a simple test to evaluate the rutting of the asphalt mixture . 2. PERMANENT DEFORMATION BACKGROUND By the Interamerican Bank of Development Program of the Pavement Rehabilitation in So Paulo (Brazil), that was created in 2000, was possible to analyze the main distresses among more than 2000 km of roads in 52 projects. The major distress observed had cracked and other distress had a permanent deformation. When the value was until 7 mm it was slow and it was moderate when the rutting was between 7 and 20 mm. In the first case, it corresponds about 10% of the test sections and considering the second case; the average was about 15%.

However in the same place, where the last intervention had been made in the last 3 years, it was observed that there were concentrations of wheel path with rut depths that were greater than 12 mm with traffic levels ranging from 2 x106 ESALs (Equivalent single axle load) per year. On the order hand, not only in the bus line but also in the urban area, the main distress is the rutting. Generally , the width in this specific road is 3.00 m because of the limited area in the towns. There is a load concentration on wheel path. For YODER & WITCZAK [2], the rutting deformation can be defined as a distortion in the pavement surface caused by the consolidation of one or more layers of it. American norm ASTM D 5340 [3] defines i t as a superficial depression in the rutting. It can appear in the survey of the edges along the track, and can increase the permanent deformation. It can also damage the pavement structure. The Brazilian norm of the DNER, and the TER 001/78 terminology document about defects in the flexible and semi-rigid pavements [4], define it as permanent deformation characterized by the depression of the pavement surface. It can be followed by the waves or not. According to HUBER & DECKER [5], the mixtures asphalt projects were based on empirical properties . When it was well controlled , its execution had great probability of presenting good performance. The concept of air voids and also the relation of mineral associated with the asphalt mixtures were already used at the beginning of the last century. During the First Great War, the Hubbard Fields method was introduced for the project of asphalt mixtures. It had concepts about voids mineral aggregate (V.M.A) and Field Stability Test. In the 30s , the Marshalls method was introduced and in the 40s, the Hveems method. Both methods were based on volumetric properties besides the mechanical empiricists type fluency and balance. According to HUDSON [6], during the 60s, there had been introduced the conception of the laboratory tests. Tests had been developed to measure the modulus of elasticity of the asphalt mixtures by different methods. The rigidity was observed from the tests used by specimens molded undergone the beam form or cylindrical one . In this case they could test in a diametrical or vertical position, with or without repeated load. Each procedure was studied yet it did not have a common result, therefore each parameter depended on the geometry shape and the load shape application. Throught the consulted bibliography, can be concluded that three trends of models for forecast of performance of asphalt mixtures exist how much to the formation of permanent deformation: models from rheological tests of behavior type creep dynamic and static; developed models to give birth of results gotten with simulator equipment type loaded wheel tester, and correlations between the traffic and the rutting. The field correlations are limited to the conditions of comparison similarity, having prepondered the use of the two firstly cited in relation to the others two types, not having a trend defined for the community technique. 3. EXPERIMENTAL RESEARCH The laboratory test specimens used in this research can be classified according to two sets: cylindrical specimens that were prepared using the same type of procedure and the Marshall method . It is compacted into 100 mm diameter, about 4 inch, and 75 blows per face, moreover there are plaques for LPC Wheel-Tracking Rutting Tester (WTRT), and the LCPC recommendations [7]. The specimens production used in this case will be reported in chapter 5. 3.1 Types of Mixture Tested: There are two types of mixture that were studied in this research. The most common surface course mix used in So Paulo (Brazil) is a hot mix asphalt. It is known as GRADATION III and the open graduated asphalt, GRADATION II. The aggregate gradation of these mixtures are showed in Figures 1 and 2 and the asphalt binder of each mix are shown in Table 1. There is also a comparative study about the aggregate gradation effects in the result test . The cement asphalt that was used presented penetration and grade 60/70. The main technical characteristics of asphalt mixtures are shown in Table 2. 3.2 Specimen Preparing The specimens used in the static creep test had been capped by the use of resinous materials. The capping plate was lightly coated. The capping material was made by the use of about 70 g of resinous material and 15g of catalyst. Firstly, this material was mixed and placed into the plate , its diameter is 100 mm. Secondly, the asphalt specimens were put over the resinous materials and we had to wait for 40 minutes, controlling the leveling using a level (See Figure 3). Then the same procedure was adopted on the other face of the specimen and each one was capped about 24 hours before the tests.

3.3 Testing Conditions The procedure temperature that had been used in the static test was 25, 40 and 50C. It had been expected to show the same stabilization .We could control the temperature using a thermometer. 4. STATIC CREEP TEST In the static creep test, the specimen was placed in a load device. This apparatus was suitable to apply vertical loads for the specimen. The device should be able to maintain specific loads for long periods . Approximately 0.5% of the applied load. The same apparatus was used in these tests . There is a method test for one-dimensional consolidation, that was adapted by the use of a box , its temperature was lower than the other one. It is showed in Figure 4. Firstly it was applied 0.2 MPa of preliminary normal stress. Thus the test was developed in four steps. Each step showed a normal stress and it was applied 0.55 MPa (approximately 80 psi). The deformation was registered during 0, 10, 20, 30, , 90, 100, 200, 500 and 1000s, using a dial gage graduated in units of 0,001 mm and it was able to register a maximum deflection of 5 mm. Secondly, the load was removed and its deformation had been registered during 1010, 1020, 1030, , 1090, 1100, 1200, 1500 and 2000 s. In addition to this, it was applied a new loading (step). This operation was repeated three times , the total was four times. The results are shown in Table 3 and the Figure 5 shows the graphics about the permanent deformation versus time. The average of deformation is 70, 80% and it occurred in the first loading. The permanent deformation, in the last time represented the average of 5% of the total test. The repeatability static creep test was made to compare with LPC wheel-tracking rutting testes and to know the accuracy of this test. This test was carried through in the temperatures of 25C, using 10 specimens. To assess the evolution of this test, a statistical indicator, the coefficient of variation (COV) was established. This coefficient is the quotient of the standard deviation and the average, and is often expressed as a percentage. In Table 4 is presented the permanent deformation express in mm for all steps. The average of permanent deformations was 0.52 mm while the COV was 10.1 %.

5. USE OF LPC WHEEL-TRACKING RUTTING TESTER The lornireur type LPC, developed in 1968-70 , is a tool used in rutting performance studies of asphalt mixes. The test material is previously compacted into a specimen slab, its dimensions are 180 mm x 500 mm and presents 50 mm and 100 mm high; a specific section of the slab is submitted to a large number of wheel tracking cycles, as reported by GRIMAUX [7]. The simulator works at 1Hz, the temperature can be kept in 20oC to 70oC and the pressure may vary up to 0.7 MPa. In this research, the temperature test was 25, 40 and 50 C (see Figure 6). The Figure 7 shows both lab compactor (a) and the simulator (b). The samples were compacted in 50 mm plate and at the same Marshall method compacting degree. Brosseaud et al. [8] recommend that the test should be finished after 30,000 cycles unless rut depth exceeds 15 percent, but the test can be carried out for a greater number of cycles. The results are shown in Table 5, the specific permanent deformation () when temperature was 25, 40 and 50C, expressed in percentage for gradation II and III. It was observed that the specific permanent deformation increased when the temperature increased and it is bigger in gradation III than II. The permanent deformation versus cycles in different gradation temperatures II and III, respectively, is shown in Figures 7 and 8. A repeatability study was done to show the test efficiency using 10 specimens. When it was on the left side of the simulator it was called L and R on the right one [9]. Permanent deformation at 25C is shown in Table 6. It was done until 100,000 cycles. It was carefully observed that in 30,000 cycles the COV was 6.9% and in 100,000 cycles it was 8.5%.

SUMMARY AND CONCLUSIONS The major goal of this research was to study the potential of the static creep test, which is simple and has low cost, used to preview the performance of asphalt mixtures applied to study the permanent deformation for the mixture. After the repeatability statistical analysis done with two kinds test realized, it is possible to conclude the following: The repeatability is compatible with the usual dispersion found in another asphalt mixtures tests, such as indirect

tensile strength test ; The Static Creep Test time is very small; The equipment and specimens preparation cost are very cheap; The Static Creep Test procedure is very simple. Fro the analysis of table 3 and 6 results, it is possible to conclude that:

a) the Static Creep Test results are compatible with the Wheel Tracking Test, because both dont enable any conclusion or correlation about the roads axle. It is only possible to find relative information, for instance, in terms of permanent deformation minor or major tendency between different mixtures;

b) The Static Creep Test enables the temperature effects verification. The table 3 showed the increase of the permanent deformation when occurred the increase of temperature;

c) Both gradations II and III are presented in Table 6. The gradation II showed better performance

Finally, the authors agree that the Static Creep Test is potentially recommended for preliminary analysis about the asphalt mixtures performance. Nevertheless, they understand that in high costs constructions, the engineers must try other studies like the simulation in real scale.

The authors intend to do more test with another samples to improve the information of the performance of this test.

Sieve size Percent passing (%) sieve size, mm (in or #) Gradation 38.0

(1 ) 25.0 (1)

19.0 (3/4)

12.5 (1/2)

9.5 (3/8)

4.75 (#4)

2.36 (#8)

2.00 0.42 0.175 0.075 (#200)

II 100.0 100.0 100.0 - 60.8 40.4 - 27.3 16.0 10.1 5.4 III - - 100.0 98.8 81.4 61.1 44.2 - 20.5 12.8 8.8

Table 1: Gradation of aggregates used in the tests.

Gradation Theoretical maximum

density (kg/cm3)

Unit weight

(kg/cm3)

Opt AC

(%)

VMA

(%)

Stability

(150C) (kg)

Flow (150C)

(x 10-2 mm)

II 2.529 2.424 4.3 4.6 1270 12.8

III 2.491 2.407 5.2 3.6 1140 13.5

Table 2: Summary of mixture properties.

Total permanent deformation (mm) Temperature

Gradation 25C 40C 50C II 0.34 0.42 0.51 III 0.51 0.77 0.92

Table 3: Permanent deformation of the average of two gradations in static creep test.

Permanent deformation - 25 C - Gradation III (mm)

Step Sample 1 2 3 4 Total

1 0.338 0.078 0.032 0.019 0.467 2 0.384 0.064 0.028 0.022 0.497 3 0.399 0.070 0.056 0.037 0.561 4 0.339 0.083 0.057 0.033 0.512 5 0.370 0.093 0.047 0.033 0.543 6 0.454 0.109 0.025 0.019 0.606 7 0.368 0.073 0.044 0.037 0.522 8 0.334 0.082 0.038 0.024 0.478 9 0.350 0.074 0.042 0.032 0.498

10 0.338 0.070 0.047 0.028 0.483 Average (mm) 0.369 0.082 0.039 0.028 0.52

Standard Deviation 0.049 0.016 0.009 0.007 0.05 Variance 0.002 0.000 0.000 0.000 0.003 COV (%) 13.3 19.5 21.9 25.5 10.1

Table 4 Study of repeatability using tem specimens in static creep test.

Specific permanent deformation - (%) Temperature (C )

25 40 50 Gradation

Cycles

II III II III II III 0 0.0 0.0 - - 0.000 0.000

100 0.040 0.289 0.128 0.548 0.145 0.740 300 0.077 0.360 0.260 0.953 0.260 1.153

1000 0.116 0.475 0.457 1.434 0.541 1.600 3000 0.186 0.563 0.872 2.204 0.960 2.521

10000 0.273 0.733 1.502 3.336 1.563 3.412 30000 0.418 0.983 2.120 4.939 2.496 4.907

Table 5 The specific of permanent deformation in temperatures of 25, 40 and 50C.

Permanent deformation (mm) Cycles

Specimens 30 100 300 1,000 3,000 10,000 30,000 70,000 100,000 24 L and R 0.40 0.63 0.95 0.32 2.04 3.10 4.19 5.00 5.33 25 L and R 0.28 0.47 0.69 1.01 1.56 2.61 3.54 4.13 4.24 26 L and R 0.36 0.56 0.81 1.19 1.80 3.01 4.11 4.59 4.77

100 L and R 0.12 0.18 0.24 0.78 1.55 2.96 3.75 4.36 4.67 101 L and R 0.06 0.14 0.28 0.99 1.81 3.12 4.06 4.68 5.01

Average (mm) 0.24 0.40 0.59 0.86 1.75 2.96 3.93 4.55 4.80 Stardard Desviation 0.15 0.22 0.32 0.33 0.20 0.20 0.27 0.33 0.41

Coefficient of Variation (%) 60.7 55.7 53.2 38.6 11.6 6.9 6.9 7.3 8.5 Table 6 Study of repeatability in wheel tracking test [9].

010

20

30

40

50

60

70

80

90

100

0,0 0,1 1,0 10,0 100,0

0

10

20

30

40

50

60

70

80

90

PENEIRAS (mm) 0,075 0,175 0,42 2,00 4,8 9,52 19,1 25,4 38,1

Dimetro em(mm)

Figure 1: Aggregate of asphalt mixture Gradation II used in Tests.

0

10

20

30

40

50

60

70

80

90

100

0,0 0,1 1,0 10,0 100,0

PENEIRAS (mm) 0,075 0,175 0,42 2,00 4,8 9,52 12,7 19,1 25,4 38,1

00

10

20

30

40

50

60

70

80

90

100

Figure 2: Aggregate of asphalt mixture Gradation III used in Tests.

Sieve size, mm

Sieve (mm)

Perc

ent P

assin

g (%

)

Sieve size, mm

Sieve (mm)

Perc

ent P

assin

g (%

)

Figure 3: Capping the specimens.

Figure 4: The apparatus used in the test method.

Figure 5: Typical graphic of deformation versus time in Static Creep Test.

Figure 6: View of the compactor (a) and the LCPC traffic simulator (b) [10]

STATIC CREEPGradation III

25C

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000 2500

Time (s)

Def

orm

atio

m (m

m)

step 1

step 2

step 3

step 4

SPECIFIC PERMANENT DEFORMATION x CYCLES Gradation II P = 0,55 MPa (5,6 kg/cm2) (%) = 10-6,02999 C0,447344 T2,67073 R2 = 0,964

0,01

0,1

1

10

1 10 100 1000 10000 100000

Cycles

(%

)

25 C40 C50 C

Figure 7: Specific permanent deformation from Wheel Tracking Test gradation II [9].

SPECIFIC PERMANENT DEFORMATION x CYCLES Gradation III P =0,55 MPa (5,6 kg/cm2)

(% ) = 10 -4,19221 C 0,340585 T 2,025723 R2 = 0,956

0,1

1

10

1 10 100 1000 10000 100000CYCLES

(%

)

25 C40 C50 C

Figure 8: Specific permanent deformation from Wheel Tracking Test gradation III [9].

REFERENCES

[1] KALOUSK, K. E. and WITCZAK, M. W. Simple Performance Test for Permanent Deformation of Asphalt Mixtures, TRB, 2002.

[2] YODER, E.J. & WITCZAK, M. W. "Principles of Pavement Design." John Wiley & Sons, Inc. New York , Second Edition,1975.

[3] ASTM - "AMERICAN SOCIETY FOR TESTING AND MATERIALS D5340/1993" Standard Test Method for Airport Pavement Condition Index Surveys . ASTM, EUA, 1992.

[4] DNER - "DEPARTAMENTO NACIONAL DE ESTRADAS DE RODAGEM TER 001/78 -Defeitos nos Pavimentos Flexveis e Semi-Rgidos" -

[5] HUBER, A. H. & DECKER, D.S., "Engineering Properties of Asphalt Mixtures and the Relationship to Their Performance", in AMERICAN SOCIETY FOR TESTING AND MATERIALS STP 1265, USA, p. 1, 1995.

[6] HUDSON, W.R, "Future Directions of Pavement Management" in 2nd Asphalt Technology Conference of The Americas, University of Texas at Austin, USA, p 1 a 7, 1998.

[7] GRIMAUX, J-P. & HIERNAUX, R., Utilisation de L'Ornireur Type LPC, in Liaison Laboratire Ponts et Chausses, spcial p. 165 Bull, 1977.

[8] BROSSEAUD, Y.; DELORME, J.; HIERNAUX, R. Use of LPC Wheel-Tracking Rutting Tester To Select Asphalt Pavements Resistant to Rutting Transportation Research Record 1384, Transportation Research Board, National Research Council, 1994.

[9] MERIGHI, Joo Virgilio "Estudo da Deformao Permanente de Misturas Asflticas em Ensaios de Laboratrio" Tese apresentada Escola Politcnica da Universidade de So Paulo para obteno do ttulo de Doutor em Engenharia, Engenharia de Infra-Estrutura de Transportes, Escola Politcnica da Universidade de So Paulo, p. 255, 1999.

[10]MERIGHI, J.V. et al. A study of HMA rutting performance using accelerated pavement testing SECOND INTERNATIONAL SYMPOSIUM ON MAINTENANCE AND REHABILITATION OF PAVEMENTS AND TECHNOLOGICAL CONTROL, Alabama, USA, julho de 2001.