Advanced Materials Research Vols. 446-449

Abstract: In order to make the performance evaluation of highway asphalt pavement more scientific and reasonable, carrying out pavement maintenance management is more necessary. Taking advantage of excellent adaptability of neural network technology to deal with nonlinear mapping problem, a breakage condition evaluation model based on radial basis function (RBF) neural network is presented. This model considers four main affecting factors including pavement rut condition, crack condition, pit slot condition and repair condition. Certain number of sample data is chosen to train and simulate the RBF neural network model. The tests results, accordant with expectation, indicate that the model is qualified for practical engineering applications.

Abstract: In order to effectively assess the concrete strength and deformation property under sea water erosion environment, concrete stress and strain curve was researched with the number of wet and dry cycle of 0 times, 10 times , 20 times, 30 times, 40 times, 50 times and 60 times based on the large-scale static and dynamic stiffness servo test set. The stress - strain curves of concrete was tested for the lateral pressure 10.8MPa, 14.4MPa, and 18.8MPa at different dry-wet cycles, The failure modes and superficial cracking characteristics of specimens are reported at different dry-wet cycles. Concrete elastic modulus and compressive strength were researched. Based on concrete mechanical theory , the classic Kufer-Gerstle strength criteria of concrete was used, a large number of test samples of multivariate data were nonlinear regressed, a biaxial concrete strength criterion was established taking into account the stress ratio and the number of dry-wet cycles.

Abstract: Based on the definition of fractional derivative, the paper proposed a unique new idea to describe the viscoelastic property of asphalt mixture with fractional calculus. According to the SPT (Simple Performance Tests) test results, the dynamic modulus and phase angle of asphalt mixture were determined. The result of the test was fitted with the classical Kelvin model, the Maxwell model, the solid model with three elements, respectively. It showed that the classical viscoelastic model did not simulate the dynamic mechanical properties of asphalt mixture properly. Since the existing constitutive relation cannot describe well the dynamic viscoelastic properties of asphalt mixture, the fractional derivative viscoelastic model with three elements was adopted and its fitting effect analyzed. The result shown a good fitting for the fractional derivative viscoelastic model with three elements, and a few test parameters were required to build the mode. In addition, these simulating parameters were significant in physics. The order  of the fractional derivative has good correlation with the phase angle, incarnating the viscoelastic proportion of asphalt mixture. So the fractional derivative viscoelastic model with three elements can accurately describe the dynamic mechanical properties of asphalt mixture.

Abstract: Moisture can be defined as the early loss of strength and durability caused by moisture penetrating through the asphalt-aggregate mixture. This failure can be adhesive occurring at the asphalt-aggregate interface or cohesive occurring within the matrix (asphalt binder plus mineral filler). Therefore, the knowledge of chemical thermodynamics theory will help a great deal in understanding the adhesive properties of the asphalt mixture within the water. Water damage model of asphalt mixture are presented based on surface and interface theory. Two types of aggreates, a limestone and sandstone, two asphalt binder of base asphalt and SBS modified asphalt are used to produce four different mixutres of HMA in the paper. The four mixtures are subsequently tested using the method and ranked. According analysis of results, the methods based on chemical thermodynamics theory offers viable alternative to the assessment of water susceptibility of HMA. This method is simple, quicker and equipment utilized can easily and cheaply be assembled.

Abstract: Based on Beijing-Shanghai high speed railway, the numerical simulation mainly researched on the seismic behavior for the saturated silty soil ground, which was treated by compacted gravel pile composite foundation. It has been analyzed that the region of liquefaction distribution and the transferring rule of excess pore water pressure under a series of input acceleration seismic loads in the treated and untreated foundation. The research results indicate that the untreated saturated silty soil ground is almost whole liquefaction when the amplitude of input acceleration is more than 0.15 g. While for compacted gravel pile composite foundation, out of treated region is less liquefaction when the amplitude of input acceleration is 0.15 g, with the increasing of input acceleration, liquefaction region is further more and gradually expands to the inner soil between piles, and compacted gravel pile composite foundation is only partial liquefaction when the amplitude of input acceleration is 0.25g. Excess pore water pressure is increased with the increasing of input acceleration seismic load, and the increasing of excess pore water pressure can be restrained effectively by compacted gravel pile composite foundation, and the quality of liquefaction resistance is improved. The design of compacted gravel pile composite foundation can satisfy the seismic requirements of Beijing-Shanghai high speed railway under the condition of 7 degree seismic fortification.

Abstract: On the basis of settlement analysis of small non-sand concrete pile composite foundation under the action of anaphase load, optimal design method of the post-processing technology for soft-foundation is researched on the basis of settlement control in this paper. Which provides theoretical basis for the design of small pile composite foundation.

Abstract: Depending on a project of constructing a tunnel of high-speed railway which crosses underneath the foundation of tall buildings in weathered rock area, the paper analyzes the failure process and its law of anti-seismic mortar anchors under the foundation of tall buildings by simulating the whole process of construction with finite element model. Then the coverage scope, influence rules and extent of tunnel excavation on the anti-pulling effect and stability of mortar anchors are analyzed according to the changes of lateral pressure and axial force of anti-seismic mortar anchors before and after construction. The results show that the influence area can be divided into three parts， of which the main area where the anti-seismic mortar anchors are badly affected is on the top of the tunnel and extends horizontally to a certain range. Finally, the paper gives an applicable method to estimate the area where the anti-seismic mortar anchors should be strengthened by grouting, which also applies to the similar projects in weathered rock area.

Abstract: In order to efficiently evaluate the shear properties of asphalt mixture, the circle shear test method is proposed. However, the thickness of upper layer surface and the middle-surface of the asphalt pavement in China are usually less than the height of standard specimen in circle shear test, as well as some laboratory specimens. In order to determine the shear strength for samples at different height, the circle shear test is conducted to the specimens at different height, and the height calibration coefficient for non-standard specimens are proposed. With which the shear strength for samples at different height can be unified and easily determined.

Abstract: In this paper, the authors study the anti-freeze-thaw performance of a new type of semi-rigid base material named polypropylene fiber reinforced cement-stabilized aggregate, and freeze-thaw mass loss rate, freeze-thaw compressive strength, freeze-thaw splitting strength are used to evaluate the effect of polypropylene fiber on the anti-freeze-thaw performance, and the relationship of polypropylene fiber content, polypropylene fiber length with the anti-freeze-thaw performance are analyzed. The test after 10 freeze-thaw cycle shows that the mix of polypropylene fiber increase the freeze-thaw compressive strength and freeze-thaw splitting strength, and decrease the mass loss rate greatly. At the same time, the paper also determine the reasonable fiber content and fiber length, under this mix proportion, the mass loss rate reduce by 80%, the freeze-thaw compressive strength increase more than 12.1% and freeze-thaw splitting strength increase more than 13.4%. This research has laid an important foundation for the follow-up research and practice.

Abstract: Semi-flexible pavement was a type of pavements in good service performance and its material composition belonged to dense-skeleton structure. However, the material composition of its parent asphalt mixture was a form of skeleton-void structure. In order to achieve better volume characteristics and technical performance of parent asphalt mixture, the parent asphalt mixture design method of semi-flexible pavement based on main mineral aggregate void filling was developed. The parent asphalt mixture was studied using Marshall test and the results indicated that all volume parameters and technical performance indicators of parent asphalt mixture completely satisfied the corresponding technical requirements. The effectiveness of method of main mineral aggregate void filling to design parent asphalt mixture was verified.