Experimental investigation of nonlinear flow characteristics in cracked polypropylene fibre-reinforced concrete

Seepage has always been a major problem in concrete-faced rockfill dam projects. Splitting cracks were made in the laboratory and water permeability tests were carried out on specimens with different crack widths (100-400 mu m) to understand the influence of polypropylene fibre on the transporting characteristics of fluid through a single crack of concrete. The influence of polypropylene fibre content (0.6, 0.9, 1.2 and 1.5 kg/m(3)) on crack tortuosity and roughness was evaluated. We conducted six water permeability tests for each sample with different hydraulic gradients using our self-designed test instrument. The results show that the incorporated fibres can improve the tortuosity and roughness of concrete cracks. The nonlinear relationship between pressure gradient and volumetric flow rate in cracked concrete penetration was shown based on Forchheimer's law. An empirical formula is proposed to quantify the relationship between the coefficients of the linear contribution to the Forchheimer equation and the ones of the nonlinear part. Besides, the studied critical Reynolds number shows a decreasing tend with the increase in hydraulic crack width, and the range is between 1 and 32.