Experimental Study On The Engineering Characteristics Of Renewable Building Aggregate Used In Pavement Structure Layer

The disposal of numerous construction waste used to being piled or buried during our country's modernization,which caused land occupancy and environment pollution.Meanwhile a lot of natural aggregate,which is difficult to regeneration in a short term,has been consumed for the large-scale construction of transportation infrastructure.Macadam has been widely used in the pavement structure layers,while the recycled old concrete and recycled brick concrete can partially and totally substitute it because of the greater strength after being broken,sorted and screened,which significantly benefits social environment protection.So this study carried out the engineering characteristic tests involved in the pavement structure layers used by the reworked constructional aggregate,which compared with the related norms and the graded broken stone(the new),then presented the sphere of application of the pavement layers utilized by recycled aggregates to providing the reference for engineering.Firstly,the tests involved with the physics and mechanical properties of the new material,recycled old concrete and recycled brick concrete were carried out and indicated that the reworked ones have smaller density,greater water absorption,faster bibulous rate and larger crushing value than the new one.After the composition design of recycled aggregates,the maximum dry density and optimum moisture content of each ingredient were observed by compaction tests to supply control parameters to follow-up engineering characteristic tests.Besides,the CBR and dynamic triaxial tests were carried out to obtain the strength and dynamic elasticity modulus of each aggregate,which indicated that with the same grading and experimental conditions,the recycled old concrete got the maximum values of CBR and dynamic elasticity modulus,the new one got the minimum values,the values of the reworked brick concrete were between the values of the old and the new,and the values of the mixed aggregate blended by the new and the old increased with the proportion of the old increasing.Additionally,the permanent deformation characteristic tests of the all three materials were carried out by the previous dynamic triaxial apparatus,the simulation and extension of test data were established by some empirical models,and each aggregate's principal stress ratio of ultimate stability were determined by the shakedown theory.There have been three observed phenomena as follows:The permanent deformation was mainly occurred at the beginning of loading,followed by a relate equilibrium.The deformation and deformation rate increased with the principal stress ratio increasing during the stage of equilibrium.The non-deformability of the recycled old one was greater than the new one,moreover the non-deformability of the new one was greater than the reworked brick concrete.Afterwards,the formulas to evaluate the permanent deformation of each aggregate were obtained by fitting the relationship of the stress ratio and the loading times needed for the ultimate deformation under the shakedown condition.Finally,this study presented the sphere of application of each recycled aggregate for pavement structure layers,through a comprehensive correlation of the characteristics of the strength and the permanent deformation among the two recycled aggregates and the new material,and considering requirements of relevant technical specifications.