Study On Comprehensive Technology Of Ultra-Thin Asphalt Overlay On Old Cement Concrete Pavement

Asphalt overlay is an approved way to rehabilitate old cement concrete pavements. To provide enough crack resistance, the thickness of overlay is usually about 16-18 cm. However, many engineering cases proved that even with an enough thickness, the crack resistance is still not satisfying. Besides this, a too large thickness brings a series of abuses, such as heightening the elevation of appurtenant works along the road, then causing the difficulties in joining permanence constructs; reducing overlay rutting resistance performance; increasing construction cost remarkably, and so on. So, this dissertation developed the comprehensive technology of ultra-thin asphalt overlay to rehabilitation treatment existing cement concrete pavement, design and application of high performance interlayer material and combinatorial design of overlay structure to prevent and curing the occurring and spreading of crack, thinning overlay thickness. The main researches were included as following:Three-dimensional finite element analysis all factors of asphalt overlay's stabilization, the result showed thickness of overlay is little when its thickness exceed certain value; high-powered interlayer can improve stress of slab and asphalt overlay; old slab still support main loading ,the life of asphalt overlay base on the old slab's stabilization. Synthetically make use of thickness design, old slab stabilization technology and crack resistance technology maybe make ultra-thin asphalt overlay into fact.As one of the bottle-neck questions in existing cement concrete pavement, void identification and treatment technology is deeply studied in this dissertation. Impact vibration frequency domain analysis uses formant frequency as characteristic parameter, imposes"Fisher"function identification method, and establishes identification function for void cement slab. The void identification detection apparatus and program were also developed in the dissertation. This technology was applied in several freeways in cement concrete pavement void detection; and testified with comparison to other void identification technologies, its identification rate is much more veracious than Falling Weight Defectormeter (FWD). Moreover, the study gave a standardized and formalized grouting construction technology; put forward a physical index, slurry flowing degree, as quality controlling parameter during construction. Interlayer physical properties and performance is mainly determined by material. A special material with high mechanical capability and performance, termed as Stress Absorbing Waterproof Interlayer (SAWI) was developed and its influence factors were study. Since bitumen was found is the primary factor for SAWI crack resistance, high elastic modified asphalt and its technological indices (elastic recovery @3Min was invented as an important index for performance evaluation) with standards was given by study. SAWI has different performance with different bitumen contents and/or gradations, adding proper content of sand will not only greatly improve SAWI asphalt mixture in its construction workability, but also increase crack resistance remarkably. After influence factors analysis, a series of SAWI proposal technological indices was given.This dissertation reconstructed patterns of Automatic Asphalt Pavement Analyzer (AAPA), evaluated the integrative crack resistance capability of overlay, and achieved real time auto-video in whole testing process, which provides an technological for identify and observe fatigue damage by rule and line. The test results showed that SAWI interlayer can notable lengthen overlay's service life. By observing the section of fatigue damaged sample, it can be found that cracks occurred only in surface, SAWI interlayer undamaged, inferred that SAWI effectively interdict cracks developing from top to down and prevent water infiltration, consequently protect the pavement structure out of water aggrieving.In conclusion, this dissertation fulfill ultra-thin asphalt overlay technology on existing cement concrete pavement by analysis ultra-thin overlay structure design theory and feasibility, fix on application conditions, study void identification and treatment for existing cement concrete, interlayer material and overlay integrative performance test methods and facilities. The 7cm thickness ultra-thin asphalt overlay has been applied in Humen freeway, Guangzhou the first loop freeway, and accepted prospective effects.