Publication: Effects of silane- and wax-based surfactants on behavior of latex modified asphalt binders and mixtures
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Date
2020-08-01
Authors
Sani, Ashiru
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Abstract
Modification of hot mix asphalt (HMA) with natural rubber latex (NRL) is a technology that provides significant improvements in the rutting and fatigue resistance of the conventional asphalt mixtures. It is a cost effective and environmental friendly technology that can mitigate the vulnerability of an asphalt mixture to early deterioration, as well as increasing its stiffness. However, an NRL modified HMA is prone to low workability and wettability due to its high viscosity property. Low wettability may induce reduction in the adhesion rate between an asphalt binder and the aggregate interface. Therefore, 0.1% Zycotherm (silane-based) and 0.3% Gripper (wax-based) additives were used as surfactants to enhance the 3%, 6% and 9% NRL modified asphalt binder adhesion with aggregate. In this research, the overall laboratory results demonstrated that the incorporation of surfactant posed significant influence on the rheology of the NRL modified asphalt binders. A novel approach was adopted using a micro-scale mechanism to quantify the surface morphology, chemical changes, wettability, and work of adhesion of the test specimens at different aging conditions. The influence of short-term aging conditioning and the addition of surfactants had enhanced the homogeneity and interconnectivity of the asphalt binders owing to the enhanced absorption and assimilation processes. The chemical changes evaluation showed that an increase in the bond indices (C-H and O-H) of latex-modified asphalt binders causes a simultaneous increase in its viscosity, which makes it stiffer to withstand the effect of degradation at high temperature. However, excessive stiffness and viscosity should be avoided to maintain its workability. The presence of both Zycotherm and Gripper surfactants help to adequately lower the C-H and O-H bonds within the binder to balance the adhesion force that may affect the energy required during mixing, with the Gripper providing the best results at both aging conditions. Analytical measurements based on the surface free energy (SFE) results showed that the surfactants had improved the spreadability of asphalt binder over the limestone aggregate surface. Likewise, the adhesion characteristics was improved with the addition of a surfactant. Compatibility ratio has also been used as an indicator of moisture resistance. The result indicated that limestone aggregate is less resistant to moisture damage compared to granite. The adhesive bonding results revealed that the specimens subjected to combined long-term aging and accelerated moisture conditioning are more susceptible to degradation. Specimens with granite aggregates showed a higher affinity towards binder as demonstrated by a higher tensile strength than the limestone specimen. The mixture performance tests showed that the performance of NRL modified HMA in terms of resilient modulus, dynamic creep, accumulated micro-strains, indirect tensile strength and Leutner shear is highly dependent on the presence of surfactant and NRL content. Overall, finding explained the interaction between the asphaltic materials, rubber modifier, and surfactant at micro and macro levels to enhance the durability of asphalt pavement. The presence of Gripper as surfactant in NRL modified HMA has better improved the mechanical properties of asphalt mixtures than that without surfactant.