45 International Journal of Concrete Structures and Materials Vol.4, No.1, pp. 45~49, June 2010 DOI 10.4334/IJCSM.2010.4.1.045 Study of the Anisotropy of the Roller Compacted Concrete (RCC) for Pavement Mustapha Zdiri, 1,2) Nor-edine Abriak, 2) Mongi Ben Ouezdou, 1) and Jamel Neji 3) (Received September 17, 2009, Revised April 30, 2010, Accepted April 30, 2010) Abstract : The roller compacted concrete (RCC) is supposed to be isotropic, whereas the compaction of this material, which is achieved using the same machines used for the soil, appears only unidirectional, making the RCC an anisotropic material. In this experimental work, the influence of the phenomenon of compaction on the isotropy of the RCC is studied. This study was carried out through an evaluation of the compressive strengths and ultrasonic tests which were used for measurements of the elastic modulus and the dynamic Poisson's ratio of the RCC as well as a qualitative judgement of the RCC aspect at the hardened state. The results of this work proved the anisotropy of the RCC and they showed the sensitivity of the mechanical strengths and the elastic modulus to the compaction direction. Keywords : roller compacted concrete (RCC), vibro-compaction, anisotropy, strength, elastic modulus. 1. Introduction The isotropy is defined when the material presents the same physical and mechanical properties in all the directions taken around an unspecified point of its mass. Based on this fundamental definition, the Roller Compacted Concrete (RCC) seems to be an isotropic material. But the method of implementation by compac- tion of this material, which differs from that of the Conventional Concrete (CC), leads to wonder about the isotropy of this material and to seek and identify this intrinsic property of the RCC mixture. The RCC employed as a construction material in the base or course roadways, must show the best characteristics. In a fresh state, it behaves like a soil not compacted. The compaction of the RCC is identical to the compaction of a soil or a gravel layer in pavement. The main objective is to reduce the volume of the inter- stices in this material and to prevent the resulting slow compaction and settlement under the loads. The second objective is to carry out a preventive action by anticipating these deformations before the putting into operation of the roadways. 1 The vibrator rollers are generally used for the compaction of the RCC implemented in pavement. And to model this type of com- paction in the laboratory, we used the mode of Vibro-compaction which includes the combination of the vibrations using a vibrating table and the pressure of a load placed directly on the surface of the RCC. By this manner, the concrete is confined in all the direc- tions and its segregation is thus limited. 2 The operation of RCC compaction is achieved in practice by the technique of Vibro-com- paction. This compaction is carried out along only one direction and the edges can be or not confined. The material obtained is in a sufficiently compacted state and it must present suitable mechani- cal characteristics in all the directions since the strength tests are generally made along only one direction. The objective of this paper is to study the RCC isotropy on an experimental basis. It includes consequently an evaluation of the RCC strength along several directions of loading. It includes also the measurements of the elastic modulus and the dynamic Pois- son's ratio using the ultrasonic tests as well as a qualitative judge- ment of the RCC aspect in a hardened state. 2. Preparation of the mixtures and the specimens 2.1 The used materials Based on the various aggregates beforehand identified, the authors considered four mixtures obtained by combination of the two types of sand: siliceous and limestone, and of the two different gravel structures and gradation (d/D in mm) 4/16 and 0/20. The binder that is used is hydraulic cement Portland type CEM 2 II/C-L 32.5 and had a relative density equal to 3,029 kg/m 3 . Characteristics and data relative to these aggregates are presented in Table 1 and Fig. 1. For the formulation of these mixtures, the authors employed the Compressible Packing Model, developed at “Laboratoire Central des Ponts et Chaussées en France (LCPC).” 3 Through the soft- ware “Rene LCPC,” 4 the percentages of the various components were determined. The components of the four mixtures are pre- sented in the Table 2. 2.2 Densification of the RCC At the exit of the mixer, the RCC behaves like a slightly wet Civil Engineering Laboratory, National Engineering School of Tunis, Tunis-Belvédère 1002, Tunisia. E-mail: zdiri_ms@yahoo.fr. Laboratoire de Génie Civil et Environnemental Ecole des Mines de Douai, rue Charles Boursel BP 838-59508 France. Applied Mechanics and Systems Research Laboratory - Polytechnic School of Tunis, Tunisia. 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