# Interface Shear Performance between Porous Polyurethane Mixture and Asphalt Sublayer
## 3 Experimental Materials  
Laboratory composite specimens were prepared for shear test with the upper layer and the bottom layer. Three types of upper layer materials were used, including one porous polyurethane mixture with the nominal maximum aggregate size of 9.5 mm (PPM-10) and two asphalt mixtures with the nominal maximum aggregate size of 13 mm (AC-13 and OGFC-13). The sublayer material is asphalt mixture with the nominal maximum aggregate size of 19 mm (AC-20).  
Polyurethane was prepared by mixing two components with certain proportion followed by adding catalyst. The mass ratio of catalyst with respect to the two components is determined by the curing time of polyurethane. Based on recommendations from the manufacturer of polyurethane, 2% catalyst is usually used if the curing time is required within 15 min after mixing. The two components were isocyanate prepolymer (component A) and the mixture of polyether polyol and pentaerythnitol (component B). The polyurethane before solidification was transparent yellow liquid under room temperature. Table 1 gives the basic properties of polyurethane. On the other hand, the SBS modified asphalt was obtained by mixing 70\(\#\) base asphalt with 4% SBS polymer at high temperature. The epoxy resin was obtained by manually mixing the resin with curing agent at mass ratio of 1:1 at the temperature of 20-30 \({}^{\circ}\)C. It is noted that the mixing should be done unidirectional at constant speed for about one minute in order to prevent the generation of bubbles during mixing or non-uniform mass distribution after mixing.  
To prepare porous polyurethane mixture (PPM), basalt aggregates with single grain size of 4.75-9.5 mm were mixed with polyurethane at the mass ratio of 94:6 under room temperature. It should be noted that the mass ratio of polyurethane to aggregate particles was determined by the inverse relationship between the dosage of polyurethane and the Cantabro mass loss of specimen measured following AASHTO T108. It was found that the scattering loss rate achieved its minimum value of 6.4% when the dosage of polyurethane was 6%. The aggregate gradation and polyurethane binder content of PPM-10 can be found in authors' previous work [23].  
Three types of asphalt mixture, AC-20, AC-13 and OGFC-13, were prepared by mixing limestone aggregates with 70\(\#\) base bitumen. The aggregate gradations, asphalt contents (AC), and air void (AV) contents of different asphalt mixtures are showed in Table 2. The air void contents of PPM and OGFC were determined from the measured bulk specific gravity using paraffin-coated method (AASHTO T275) and the measured theoretical maximum specific gravity (AASHTO T209); while the saturated surface dry method (AASHTO T166) was used for the bulk specific gravity of dense-graded AC specimens.  
Three types of adhesive materials were used at the interface of composite specimen, including polyurethane, epoxy resin, and SBS modified asphalt. It should be noted that the desired thickness of adhesive material applied at the interface was achieved by controlling the mass of adhesive material after knowing the density and coating area. The density of polyurethane, epoxy resin, and SBS modified asphalt is 1.003 g/cm\({}^{3}\), 0.971 g/cm\({}^{3}\) and 1.030 g/cm\({}^{3}\), respectively.