Issue 45

C. Huang et alii, Frattura ed Integrità Strutturale, 45 (2018) 108-120; DOI: 10.3221/IGF-ESIS.45.09 115 Figure 7(c) : Five units and eight parameters model. L OAD P HASE he model parameters of FRAC in Eqn. (9) with different V f and R a were obtained from fitting the experimental data and listed in Tab. 2. It can be noticed that the E 1 and  1 firstly increase and then decrease with the increase of V f . When V f is 0.35%, E 1 and  1 are at peak values and FRAC has stronger resistance to both elastic deformation and permanent deformation. When V f is 0.69%, E 1 and  1 of FRAC are smaller than those of AC matrix. It indicates that fiber can enhance the elasticity and viscosity of the FRAC only with proper fiber volume fraction; excessive fiber may decrease the resistance of AC to the instantaneous elastic and viscous flow deformation. Both the relaxation time  1 / E 1 and the delay time  2 / E 2 firstly increase and then decrease with the increase of V f . It means that a certain V f can increase the anti-rutting deformation capacity of FRAC. When V f is 0.35%, both the relaxation time and delay time are at maximum, and FRAC has the highest temperature stability at this time [12]. The a firstly decrease and then increase with the increase of V f , while  0 , b, and b/2a firstly increase and then decrease with increase of V f . It indicates that rheological time of FRAC first increases and then decreases with increasing V f . It is worth mentioning that when V f is 0.35%, rheological time reaches the maximum value and FRAC show the best resistance to permanent deformation. When fiber aspect ratio increase, E1,  1 ,  1 / E 1 ,  2 / E 2 ,  0 , a, b and b/2a have the similar trend with V f varying. When R a is 324, FRAC has better resistance to elastic deformation, viscous flow deformation, viscoelastic deformation and rutting deformation capacity. The viscoelastic properties of FRAC described by the present model coincide with that performed by the creep strain–time curve shown in Fig. 6. U NLOADING P HASE y using Eqn. (10) to simulate the test data, the model parameters of FRAC with different fiber volume fraction and aspect ratio are shown in Tab. 3. Obviously, it can be observed that E2,  1 ,  2 ,  0 , a, b, and c have the same pattern as that of the creep loading stage. When fiber volume fraction and aspect ratio increase. When fiber volume fraction is 0.35% and fiber aspect ratio is 324, E2,  1 ,  2 ,  0 , b, and c reach the maximum while a is the minimum. At the same time, FRAC has better deformation recovery performance. By comparing with the stage of the creep loading, the model parameters E2,  2 , and delay time  2 / E 2 in the unloading phase are greatly reduced,  1 and  0 decrease a little, while a, b, and c increase a lot. The reason is that the stage of accelerating creep is the stage of creep damage of FRAC, and after deceleration and constant velocity creep processes, its internal slippage occurs between the aggregates which result in the damage of the creep beam structure and attenuation of material properties. The actual permanent deformation characterized by the model parameters in the stage of unloading stage is bigger than the theoretical permanent deformation characterized by the same parameters in the stage of the uploading and actual deformation recovery rate is smaller than the theoretical deformation recovery rate of loading phase by the same parameter characterization, but it is not suitable to use the model parameters in the stage of creep loading to study the characteristics of the actual deformation of FRAC after unloading. From Tab. 3, it should be noticed that the correlation between the test data of unloading phase and the Eqn. (10) model decreases and T B