Rheological and mechanical behavior of High Strength Steel Fiber-River Gravel Self Compacting Concrete

This study reports the results of a comprehensive experimental campaign aimed at demonstrating the feasibility of using river gravels in substitution of ordinary crushed aggregates for the production of high strength Steel Fiber-River Gravel-Self Compacting Concrete (SFRGSCC). Due to geomorphological reasons, the river gravels represent the most common type of aggregates used in Amazon region for ordinary structural concrete production but only few researches focused on the use of this kind of raw material for the production of high performance cement-based composites. In fact, the river gravels present different intrinsic characteristic in comparison with crushed rocks such as, higher density and elastic modulus, rounded shape with a smoother surface and a more brittle behavior. As a consequence, when embedded in a cement-based matrix they can significantly affect the rheology and mechanical performance of both self-compacting concrete matrices (RGSCC) and Fiber Reinforced Concrete (SFRGSCC). In this context, the present study firstly analyzes the physical and mechanical properties of the alternative aggregates and then, investigates how the complete replacement of crushed aggregate by river gravel can influence the flowability, segregation potential, yield stress and plastic viscosity of the RGSCC and SFRGSCC in the fresh state as well as the stress-strain behavior under compression, direct tension and bending in the hardened state. The results highlight as the river gravel aggregates shape and surface roughness have relevant effects on the concrete performance as they improve the concrete rheology increasing the concrete flowing and reducing the corresponding yield stress and entrapped air while, on the other hand, reduce the strain capacity of the matrix resulting in a more fragile mechanical response under compression, tension and bending. The addition of steel fiber to the RGSCC resulted being more beneficial than to the reference crushed aggregate SCC. The reinforcement significantly enhanced the RGSCC toughness being this improvement even more pronounced when the samples were submitted to direct tension and bending loads.