Mixture design and mechanical properties of synthetic fiber reinforced roller compacted concrete for pavements

Rigid and flexible pavements are different from each other in many ways. And, usage of both rigid and flexible pavements have a variety of advantages and disadvantages. Briefly, rigid pavements have higher strength and durability, and flexible pavements are more economic, as it allows fast construction. Therefore, selection of suitable pavement type is a critical issue for pavement applications. Roller Compacted Concrete (RCC) is a type of concrete which is used in pavement applications. RCC has similar ingredients with rigid pavements, but they are constructed by using the vehicles (dump truck, asphalt paver etc.) which are used in flexible pavement applications. Hence, RCC pavements yield advantages of both types of pavements. Thickness design process of RCC pavements is similar to conventional concrete pavements, due to the similar structural behaviour of pavements. Pavement thickness can be decreased with an increased flexural strength and fatigue resistance of concrete material for both RCCs and conventional concrete pavements. Some studies report that the addition of fibers may also result in decreased pavement thickness, since fatigue performance of material increases. Unfortunately, the number of studies that are concentrated on usage of fibers in RCC pavements are limited (especially for synthetic fibers) and further researches are needed to better understand the effects of using fibers for RCC pavements. Primary objective of this study is investigation of the effects of synthetic fibers on mechanical properties of RCC for pavements. First, to achieve desired concrete class (C30 / 37) plain RCC mixtures that have 11 – 12 – 13 wt% cement were designed, and cylindrical compressive strength specimens were prepared by using vibrating hammer method. Then, compressive strengths of the specimens made by using these plain mixtures were measured, and mixture that has 12 wt% cement was found suitable for required strength. After that specified cement ratio was used to design two RCC mixtures that have 0.5 vol% fiber (2 different synthetic fibers were used). Then, compressive strength, modulus of elasticity, flexural strength (by using three and four point bending tests) and impact resistance values of plain and synthetic fiber reinforced RCC mixtures (that have same amount of cement) were determined. Finally, by using test results, thickness design were made for a sample RCC pavement, and all results were compared. Results of the applied tests showed that maximum dry density (determined from modified proctor tests), compressive strength and flexural strength values decreases with usage of synthetic fibers, and this values are correlated with each other. On the other hand, residual flexural strength and flexural thoughness values were increased with usage of both types of fibers (54 mm and 36 mm synthetic fibers). Additionally, it was found that, thickness requirement of RCC pavements can be reduced by using synthetic fibers.