Study On The Initial Durability Of Semi-Rigid Base Material

Semi-rigid pavement is the commonest pavement in China which has advantages like high carrying capacity, rare rutting and low expenditure. With the popularity of long-life pavement, new challenges are in front of Chinese civil engineers. To successfully build Semi-Rigid Long-Life Pavement, Qinling Sha invented a new method to design the base of pavement called "Cement Bound Granular (CBG-25)". The study object is initial durability of CBG-25.Fatigue performance is a key factor determines the initial durability of Semi-Rigid Base(S-RB). Shrinkage distortion caused by dropping in temperature and drying is another key point to the initial durability of S-RB. Initial cracks’quantity and propagation largely depends on shrinkage performance and stress/strain concentration caused by initial cracks will reduce the fatigue life of base. Accordingly, the initial durability of S-RB will be weakened. Above all, the main purposes of this paper are studying the fatigue performance and shrinkage performance of Semi-Rigid Material(S-RM) and improving the corresponding test methods.Fatigue tests include11groups of specimens with different cement contents, graduations and sizes. Two types of flexure fatigue test methods were used and they are conducted under two controlled-modes. Flexural stiffness, strength, fatigue life, fatigue limit etc. were obtained from tests. The results indicate:1) stiffness and fatigue life are influenced by strength.2) Failure disciplines significantly influence fatigue equations.3) Dissipated Energy Theory is applicable for fatigue analysis of S-RM and it can unify the results from fatigue tests under different controlled-modes.4) Size Effect has significant influence on stiffness, strength and fatigue performance.5) Compared with traditional S-RM, CBG-25has advanced fatigue performance; therefore, CBG-25is appropriate to be the long-life pavement’s base material.Uniform Design Method was used to make the shrinkage tests’plan which contains10kinds of S-RM. Through the test results with LVDTs,1) shrinkage performances and2) relationship between cement contents, graduations and temperature shrinkage were obtained. The results indicate that shrinkage performance can be improved by modifying the graduations of CBG-25rather than reducing the cement content which will lead to strength loss. By the "ratio of shrinkage and strength", fatigue and shrinkage performance are connected.In the next step, results in this paper can be used together with strucrture status, interlayer conditions, temperature and humidity conditions in real pavement so that the initial life model S-RB can be obtained.