Research On Cold Recycling Technology With Foamed Bitumen Based On Cement Stabilization Mixing Plant

Due to historical reasons,the pavement design idea of stronger base layer and thinner surface layer has been emphasized for many years resulting in the most of the highways were constructed into asphalt pavement with cement stabilized semi-rigid base layer in China.Gradually,the early constructed highways are ready to be heavily maintained then it is extremely urgent to fulfil the need of the maintenance of asphalt pavement and the recycling of RAP materials.By the end of the year 2017,the total length of expressway had been 136,500 kilometers and 4,773,500 kilometers for highways in China,therefore there is a very good opportunity for the cold recycling technology with foamed bitumen to develop in China based on the background of huge traffic network increasingly day by day.The foamed bitumen is very suitable for cold mixing process as a new bitumen-based binder and the properties of the cold recycled mixture treated with the foamed bitumen are so unique in terms of road use,economy and environmental protection that there are many advantages and development prospects for the foamed bitumen technology.However,despite the cold recycling technology with foamed bitumen was introduced into China many years ago,there are still many shortcomings in terms of innovation,practicality and localization of equipment.Especially,the excessive price of imported equipment has become the biggest obstacle which is greatly limiting the promotion and application of cold recycling technology with foamed bitumen in China.This paper describes an innovative way of installing the foamed bitumen functional modules on the cement stabilization mixing plant to realize the bitumen foaming functionalization of the cement stabilization mixing plant in order to break through the platform constraints of imported equipment.The paper focuses deeply on the cold recycling technology with foamed bitumen based on the cement stabilization mixing plant by closely studying the key technologies in different stages of testing,design,construction and evaluation.The main content of the paper includes the development of indoor foamed bitumen testing instrument,foamed bitumen index evaluation,mix design,the modification of cement stabilization mixing plant,construction technology,construction uniformity evaluation and new composite pavement structure.The target of the paper is to propose a new kind of cold in-plant technology with foamed bitumen based on the cement stabilization mixing plant by achieving results of the intensive systematic research and analysis through a large number of indoor and outdoor tests to promote the research and application of cold recycling technology with foamed bitumen.In the stage of developing indoor foamed bitumen testing instrument,this paper analyzes the application limitations of Wirtgen WLB10 foamed bitumen testing instrument and uses a series of improvement measures to develop an improved foamed bitumen testing instrument named of iFoam which has been tested and verified successfully for its feasibility.In the stage of foamed bitumen index evaluation,this paper firstly analyzes the shortcomings of the existing evaluation indicators,then comprehensively considers the operability of the test method and the quantifiable test results from the practical point of satisfying the uniformity of foamed bitumen and aggregate mixing.To the extent,a new evaluation index of foaming performance of asphalt was proposed,which simplified the performance index and solved the mutual exclusion problem of the foaming performance evaluation index of traditional foamed bitumen based on the mimum expansion ratio and half-life.The test method is simple and reliable,and the test results can be quantitative,positive correlation.In the stage of mix design,the paper proposes a skeleton compact type of the gradation design curve based on a large number of foamed bitumen cold recycled mixture test which breaks through the cognition of the foamed bitumen mixture is born suspension type grading.At the same time the requirement of 0.075 mm sieving rate of filler is reduced to 3%,which breaks the requirement of not less than 6% specified by the specification,and significantly improves the utilization rate of RAP material.In the stage of the cement stabilization mixing plant modification,this paper developed a two-stage foaming technology through the series connection of foamed bitumen functional modules,which further optimized the foaming effect of asphalt and met the technical requirements of cold recycling for foamed bitumen.In this paper,the three-dimensional model of two-shaft pugmill of cement stabilization mixing plant was established by discrete element software.The uniformity of the foamed bitumen cold recycled mixture in the mixing process was simulated and analyzed.The feasibility of the cement stabilization mixing plant platform was demonstrated.The meta-software simulation obtained a reasonable blade mixing speed,which provided a solid theoretical basis for the actual equipment transformation and subsequent mixing production.Through the successful construction of the test section of foamed bitumen cold recycled pavement,this paper comprehensively expounds the cold recycling construction of foamed bitumen based on domestic cement stabilization mixing plant from the aspects of material requirements,mechanical requirements,construction preparation,construction technology,construction quality control and acceptance criteria.In order to evaluate the uniformity of the paved mixture,this paper uses industrial CT technology to scan the foamed bitumen cold-recycled core sample with high precision,and evaluates the mesostructure uniformity of the foamed bitumen cold recycled mixture designed by this paper.The cross-sectional images of industrial CT scanning were summarized by ABAQUS finite element three-dimensional reconstruction modeling to analyze the mechanical response of foamed bitumen cold recycled mixture at various depths,and the evaluation index of meso-mechanical uniformity was also proposed.The uniformity of the mesostructure and the meso-mechanical uniformity of the foamed bitumen cold recycled mixture.Further,in order to improve the application value of foamed bitumen cold recycled mixture used as the upper layer of asphalt pavement,this paper further proposes a new composite pavement structure of water borne epoxy seal plus foamed bitumen cold recycled layer based on the concept of functional design.Firstly,it is verified by experiments that the seal has good anti-sliding,waterproof and superficial reinforcement functions.Then a series of test evaluations on the road performance of the new pavement structure were carried out,which proved that the new cold reclaimed pavement structure has excellent road performance.Finally,the calculation and analysis of the mechanical structure of the pavement and the checking of the main indexes of the structural bearing capacity are carried out.The research results of this paper reflect the objective law of the spiral development of foreign technologies including introduction,digestion and promotion,and lay a good foundation for the popularization and promotion of cold in-plant recycling technology with foamed bitumen in China.There should be very good market value for the research results which can be used directly for the application of foamed bitumen cold in-plant recycling which is designed in the projects and played a role in attracting more researches and more applications.