Analysis of the variation in the stiffness modulus through four-point bending tests

Universidade do Minho, Portugal

J.C. Pais; P.A.A. Pereira; M.J.C. MinhotoL.P.T.L. Fontes; D.S.N.V.A. Kumar; B.T.A. Silva

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Background

The number of test samples used to evaluate the stiffness modulusdepends on the variability presented during the test

European standard EN 12697-26, 2004defines that from each slab six specimens should be preparedfour specimens shall be tested (two shall be held in reserve)

Although the time needed to perform four tests is very shortit is important to investigate whether it is sufficient to obtain a suitable precision for pavement design

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Objective

This paper presents a study to evaluate the number of tests to assess the stiffness modulus

A separate study is conducted to define the variation of the stiffness modulus allowed to ensure a certain precision in the pavement design

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Mixtures

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Stiffness modulus

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Pavement used in the study

Fatigue models

( )

5

36.008.1856.0

−

− ⎟⎟⎠

⎞⎜⎜⎝

⎛

+=

mixb

t

SVN ε

4

018.0

−

⎟⎠⎞

⎜⎝⎛= cN ε

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Combinatory analysis – pavement life – mixture 1

1 specimen

2 specimens

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Combinatory analysis – pavement life – mixture 1

3 specimens

4 specimens

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Combinatory analysis – pavement life – mixture 1

5 specimens

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Combinatory analysis – error of pavement life – mixture 1

1 specimen

2 specimens

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Combinatory analysis – error of pavement life – mixture 1

3 specimens

4 specimens

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Combinatory analysis – error of pavement life – mixture 1

5 specimens

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Combinatory analysis – 2 specimens – mixture 2, 3, 4 and 5

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Combinatory analysis – 3 specimens – mixture 2, 3, 4 and 5

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Conclusion

The use of 2 or 3 specimens in stiffness tests is suitable for pavement design

This conclusion is valid for tests with small dispersion in the stiffness results

For tests with a large dispersion in the stiffness results, a higher number of specimens are needed.

5 specimens can produce an error in the predicted pavement life higher than 8%.

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Variation of the stiffness modulus

objective

determination of the stiffness modulus variation whatproduces a certain error in pavement life

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Tensile strain at the bottom of the asphalt layer

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Pavement life

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Variation in the stiffness modulus (PAV-20-YY-60)

Universidade do Minho, Portugal

Analysis of the variation in the stiffness modulus through 4PB tests

Conclusion

The variation in percentage of the stiffness should be

about the same one allowed for the pavement life

example:if the allowed variation in the pavement life is 5%

the variation in the stiffness of the asphalt layer should be also about 5%