SYNTHETIC MACRO-FIBERS REINFORCED SELF COMPACTING CONCRETE FOR LIGHTWEIGHT PRECAST ELEMENTS. A CASE STUDY Jean Philippe Bigas (1) , Bruno Pellerin (1) , Fabien Deschryver (1) , Pietro Massinari (2) and Giovanni Plizzari (3) (1) CHRYSO, Sermaises, France (2) CHRYSO Italia S.P.A., Lallio, Italy (3) Università degli Studi di Brescia, Italy Abstract In the last decade Self Compacting Concrete has demonstrated an overwhelming development. More recently synthetic macrofibers have been introduced on the market. Those fibers constitute an optimal solution to reinforce concrete elements. Combination of both SCC and synthetic macrofibers allows to increase benefits of using SCC, especially in terms of labor work savings while at the same time achieving equal or even better mechanical performances. This study was performed in order to clearly established the benefits of such a combination in the fabrication of lightweight precast wall elements. Those lightweight wall elements are constituted of polystyrene insulation blocks embedded between two concrete layers. The paper describes the four steps process being used in order to replace existing reinforcement in the current panels by synthetic macrofibers: Step 1: Selection and characterization of the different macrofibers. Optimization of reference SCC mix design and characterization of mechanical performances. Step 2: At the lab scale, characterization of the mechanical performances (tensile strength, elastic modulus) of the different SCC macrofibers combinations in order to select the optimal macrofiber in terms of nature and dosage. Step 3: Dimensioning calculation of the lightweight precast elements. Step 4: Test of the best combination at real scale (11 m x 2.5 m x 0.2 m) lightweight panels and complete characterization of their mechanical performances. 1. INTRODUCTION Since their introduction in the precast industry, Self Compacting Concrete have been widely used. Such a success can be explained by increased productivity resulting from time savings at the pouring stage. Increased productivity is also coming from the improved facing aspects of concrete elements thus reducing the need for aesthetic repair. 1013 5th International RILEM Symposium on Self-Compacting Concrete 3-5 September 2007, Ghent, Belgium