The Performance Improvement of Hot Mix Asphalt and Enhanced Applicability to Pavement Structure Thickness Design Using DAMA (Drain Asphalt Modified Additive) Jung-hoon, Jin* * University of Incheon ITS. R.C. Researcher 3. Laboratory Test Methods and Results 3.5 Resilient modulus test Pavements are subject to repetitive loading by the vehicles passing on them. As shown in figure 20, the pavement materials are stabilized by strain-hardening due to repetitive loading. And as the number of repetitive loading increases sufficiently, it even displays recoverable strain characteristics. Resilient modulus is defined as the slope of this strain vs. rate of change curve. The elements effecting the resilient modulus are varied according to the pavement material, but temperature is known to be the most influential element for the asphalt mixture as shown in figure 20. The resilient modulus, which determines the resiliency of the asphalt mixture, is very sensitive to temperature, and as shown in figure 21, it shows a inversed-linear relationship with temperature. Because of this extreme sensitivity of resilient modulus to temperature, the resilient modulus should be set at the locally appropriate seasonal temperature in the analysis and design of the asphalt mixture. SHELL suggested temperature vs. weighting factor relationship as shown in figure 22 by selecting typical pavement structural model and using BISAR, which is a computational program used for the analysis of resiliency of multi-layered pavement, in order to analyze the temperature effect on the pavements. The idea is to determine a typical annual temperature used for the design of the pavement structure by calculating weighted average of annual temperature (weighted average monthly temperature divided by 12 months). Using figure 22, the typical temperature calculated from the data obtained at Seoul and two other areas, which were selected as the representative domestic annual temperature distribution, is shown in table 11. From table 11, it is seen that the design temperature for domestic asphalt pavement should be appropriately set at 17¡É. And also, 23¡É is chosen as the evaluation temperature of the properties of the asphalt mixture during the design stage. Figure 20 Stress vs. strain Figure 21 MR vs. Temperature Figure 22 Average month temperature vs. Weight Factor ¢Æ Table 11 SHELL suggested temperature vs. weighting factor relationship ¢Æ Table 12 Resilient modulus ¡Ø 1 MPa = 10.197 kg/§² (a) DAMA 0% (b) DAMA 0.5% (c) DAMA 1.0% Figure 23 The results of resilient modulus The resilient modulus test was carried out at 5¡É, 25¡É and 40¡É according to the KS F 2376. The resilient modulus is used as the sensitivity test of hot mix asphalt on temperature. And the mixture, which shows decreased change in MR at various temperatures, is evaluated to be a superior mixture due to its lower sensitivity to temperature. In addition, mixtures with lower MR at low temperature has lower stiffness compared to that with higher MR. And it is preferred because of its lower cracking incidence at low temperature. The result of the resilient modulus test per five kinds of HMA is shown in the following table 12 and figure 23.