# Bonding Evaluation of Asphalt Emulsions used as Tack Coats through Shear Testing
## 4 Results and Discussion  
To determine the necessary shear stress to separate two layers of the asphalt mixtures with slow and fast emulsions, specimens were created with asphalt residue contents of 50%, 55%, and 60%. In addition, the specimens had different setting times and emulsion dosages according to the LCB test. The fracture energy was also determined from the area delimited above by the load-displacement curve obtained from the test. Figure 4 shows a load-displacement curve obtained from LCB shear testing; this was representative of 72 tests. From Figure 4 it is evident that asphalt samples manufactured with slow setting emulsion had the highest resistance to applied loads but deformed more than those made with rapid setting emulsion. Therefore, more energy was required to fracture the samples, as can be seen in Figure 5.  
Figure 3: Schematic of forces and tensile stresses on the asphalt test samples: (**A**) specimen part into the casing and (**B**) upper specimen layer under pure shear stress. The above shows that samples with slow setting emulsion were more tenacious, more ductile, and less fragile than mixtures made with rapid emulsion; therefore, again, more energy was required to fracture these samples. The resistances of emulsion adherence for the two asphaltic layers are presented in a boxplot diagram which represents schematically the resistance distribution of the mixture adherence, with the slow and rapid setting emulsions, for the different asphalt test samples (Figure 6). The results show that the rapid setting emulsion with different dosages of asphalt and setting times presented less resistance to applied loads in comparison to the slow setting emulsion, with the exception of the 0.3 L/m\({}^{2}\) dosage with 5 days of curing. Figure 4: Representative load–displacement curves for all Laboratorio de Caminos de Barcelona shear tests. Figure 5: Box and whisker chart of the specimen fracture energy. Then, the parameters of the fracture energy were analyzed, which allowed us to evaluate the energy necessary to separate the two asphaltic layers. Figure 5 shows that the slow emulsion presented greater fracture energy over all the curing times and percentages of asphaltic residues. As a result, it was decided that the energy parameters for all the doses should be considered, including asphaltic contents, and curing times since the results from the fracture energy presented increased reliability with regard to the maximum resistance results of the specimens. The statistical summary results for all specimens are presented in Tables 3 and 4. In Figure 7, the rapid setting emulsion is seen to have its highest fracture energy under a 0.3 L/m\({}^{2}\) dosage, a 3 day curing time, and an asphaltic content between 55% and 60%. The highest values reached were between 8 J/m\({}^{2}\) and 10 J/m\({}^{2}\). According to the mechanical properties, the use of a rapid setting emulsion combined with 60% of asphalt residue content and at a dosage of 0.3 L/m\({}^{2}\) with 3 days of curing proved to be the best option using this kind of emulsion. This was due to it having the best resisting loads and less deformation, thus requiring the highest possible fracture energy. Figure 6: Box and whisker chart of the specimen adhesive bond. Figure 7: Fracture energy diagram of the rapid setting asphalt emulsions for different dosages and cure times. In Figure 8, the slow emulsion is observed to have the highest fracture energy with a 0.5 L/m\({}^{2}\) dose, a 5 day curing time, and an asphalt content of 60%. The highest values reached were between 16 J/m\({}^{2}\) and 17 J/m\({}^{2}\). However, most of the fracture energies were between 7 J/m\({}^{2}\) and 10 J/m\({}^{2}\). The foregoing evidence showed that the use of a slow setting emulsion combined with 60% asphalt residue content and at a dosage of 0.5 L/m\({}^{2}\) with 5 days of curing proved to be the best option using this kind of emulsion. This was due to it having the best resisting loads and less deformation, thus requiring the highest possible fracture energy.