Influence of tack coat rate on the properties of paving geosynthetics

The use of geosynthetic reinforced asphalt overlay technique is becoming increasingly used to enhance the performance of cracked asphalt pavements. However, the compilation of design specifications for paving geosynthetics used as anti-reflective cracking systems has been a difficult task, leading to largely empirical procedures. Stiffness has been identified as the governing property to quantify the potential contribution of the interlayer to the asphalt overlay strength. Additionally, the asphalt binder forms a low hydraulic conductivity barrier that enhances bonding of the geosynthetic to the existing overlay. The type and rate of tack coat impregnation can significantly influence the reinforcement and waterproofing mechanism, potentially leading to early overlay failure. This paper presents the results of an experimental testing program conducted to quantify the influence of tack coating contents on the tensile strength and stiffness as well as the hydraulic conductivity of paving geosynthetics after emulsion asphalt impregnation. Both nonwoven geotextiles and composites involving geotextile and geogrid are considered in the study. Evaluation of the geosynthetics changes in tensile properties provides insight on the identification of an optimum bitumen dosage to enhance tensile strength and stiffness of impregnated geosynthetics. A tack coat rate equal to the asphalt retention capacity was specifically evaluated as baseline dosage, which was ultimately found to be an optimum dosage to enhance the mechanical properties for the effect of the tack coat rate on the tensile behavior of the geosynthetics. The use of asphalt emulsions were found to lead to a significant reduction in the hydraulic conductivity of paving geosynthetics.