Research On Construction Control Index And Overlays Of Cracked And Seated Old Cement Concrete Pavements

Crack and seat is one of the effective methods in old cement concrete pavements(CCP) rehabilitation. The construction control index of crack and seat in different subgrade strength and schemes of overlays for graded road after concrete slab fractured are presented. Popularization and application of old cement concrete pavement fractured technique have economic and social meaning because of resource conservation and environmental protection.The equivalent modulus of elasticity of pavement after rubblization and crack and seat which can be reference for finite element calculations is inspected on site using rigid bearing plate test.The crack state of concrete slab during crack is simulated basing on the crack and crush character of solid 65 element in ANSYS software. The influence of subgrade strength to it is also analysed.The construction control index of crack under different subgrade bearing strength has been put forward. It is shown that there is an obvious pertinency between subgrade strengh and hammer drop height, and different hammer drop height should accord with different subgrade strengh during crack and seat.The static response of pavement under different vehicle load is analysed using 2D model. It is considered that it is viable for grade one road to use semi-rigid base course plus 10cm asphalt concrete as overlays after rubblization. The fatigue failure of overlay is controlled by asphalt surface and will reduce when the thickness of base course decreases. Generally, the thickness of asphalt surface is not less than 10cm. The better the contact of cracked consrete slab and overlay is, the better the mechanics performance is.The modal and transient property are analysed for overlays after crack by using 3D pavement model. The results show as followed:(1)Half-wave displacement of nodes in the middle of the model is produced under the promptings of previous moving half-wave sine load. The displacement increases with the approach of the moving load and it gets its peak when the load acts exactly on the node.(2)Y peak stress appears at the bottom of the new base course underlayer. The shear stress of nodes changes sharply in short time,its effect is obvious and its value increases within certain thickness. So that,it commands highly for the interlayer contact of pavement,especially on the top of the cracked concrete slab.(3)It plays an important role for subgrade strength in the using property of overlays after crack and seat.(4)The dynamic responses of pavement increase significantly and the fatigue life decreases rapidly when the overload is 1.1 MPa. The overload influence is greater to asphalt surface than to base course.