| Insufficient durability of pavement mixture is the main problem faced by concrete bridge deck pavement in my country,which is manifested as premature rutting,pushing,cracking and other diseases in the pavement layer,which may even affect the safety of the main girder structure in serious cases.Previous engineering practice has shown that the use of high modulus of the pavement is an ideal method to prevent early disease and increase the service life of the pavement structure.The high-modulus solution for bridge deck paving means that the upper and lower layers are made of high-modulus concrete with excellent performance.According to the functions of each layer,the paving layer is divided into an upper high-performance wear layer and a lower permanent support layer.The layer provides excellent road performance,reduces the stress on the underlying layer,and protects the underlying layer,while the permanent support layer has excellent anti-fatigue and anti-rutting ability,and can provide stable lower support for the pavement structure.The wear layer is maintained and structural reconstruction is avoided,thereby increasing the durability of the pavement structure over the design life and improving the engineering economy.Relying on the bridge deck pavement project of Jingde Expressway in Hebei Province,this paper uses the method of combining finite element simulation and laboratory test to make a detailed study on the effect of high modulus scheme in improving the durability of Jingde Expressway bridge deck pavement.First of all,based on the typical cross section of Jingde Expressway bridge,this paper establishes the finite element model of the local beam section of box girder and T girder.Combined with the investigation of common diseases of the pavement layer and the load position analysis,the longitudinal and lateral unfavorable load positions and characteristic mechanical response indexes of the box girder and the I beam are determined.The mechanical characteristics of the pavement under the two main beam structures under the most unfavorable load position are compared and analyzed.The effects of different modulus combinations and load levels on the mechanical response index of bridge deck pavement characteristics are studied.The results show that increasing the overall modulus of the pavement layer can not only increase the resistance of the pavement layer to accumulated permanent deformation,but also reduce the interlayer Shear stress,increasing the integrity of the pavement and the bridge deck.Based on the engineering environment and simulation analysis results,considering that the extreme maximum temperature in Hebei Province is41 °C,and the pavement layer diseases mostly occur in low-speed driving sections,it is recommended that the modulus(40 °C,10Hz)of the upper pavement layer is greater than1200 MPa,and the lower layer of the pavement should be installed.The modulus of the mixture(40℃,10Hz)is greater than 1440 Mpa.Secondly,based on market research,a high-modulus asphalt scheme(modified with rubber powder,SBS,HPT)was designed,and compared with the high-modulus asphalt(modified with rubber powder,SBS)and the commonly used rubber asphalt in Hebei Province.The results showed that after adding HPT modifier,the penetration of asphalt decreased by 12.8%,the ductility decreased by 25.5%,the softening point increased from 71 to 85,and the segregation(softening point difference)decreased from 1.4 to 0.2,indicating that HPT modified The additive can improve the high-temperature performance of asphalt and improve the segregation of polymer-modified asphalt,but it also loses part of the low-temperature performance.Comparing the phase angles,it is found that the addition of HPT reduces the phase angle of the asphalt by 20%,indicating that HPT promotes the absorption of light components in the asphalt by rubber and SBS,improves the elasticity of the asphalt,and thus improves the high temperature deformation resistance of the asphalt.;Further analysis of the low temperature performance of high modulus asphalt shows that although HPT will reduce the low temperature performance of asphalt,it does not reduce the PG classification of asphalt;Therefore,it is considered that high modulus asphalt can meet the climatic requirements of Hebei.Then,for the three kinds of asphalt,the mixture ratio design of the upper and lower layers of the pavement was carried out,and in order to verify the applicability of ARHM-20 grade to highmodulus asphalt,the high-modulus mixture gradation HMAC-20 recommended by the specification was introduced..By studying the high temperature performance,low temperature performance,fatigue performance and water stability of the mixture,it is found that: the high modulus asphalt has better performance under the ARHM-20 gradation;in addition to the low temperature performance,the high modulus asphalt mixture High temperature performance,fatigue performance and water stability are all excellent.Compared with the construction drawing scheme,the 60 ℃ dynamic stability of the upper and lower layers of the high-modulus scheme is increased by 30.7% and30.4% respectively,the fatigue life(stress ratio of 0.4)is increased by 25.2% and 43.5%respectively,and the freeze-thaw splitting strength ratios are respectively improved.Improved by5.3% and 5.6%,low temperature performance decreased by 7.5% and 8.3%,respectively,but still within specification tolerance.On the whole,it is believed that the application of high-modulus asphalt mixture to the deck pavement of Jingde Expressway can improve its durability.Finally,based on the dynamic modulus master curve test,the effect of temperature and frequency on the dynamic modulus of the mixture was studied,and it was found that the HPT modifier increased the modulus of the asphalt mixture by 15% to 25%;when the temperature was lower than At 25℃,the dynamic modulus of the mixture showed higher temperature sensitivity;the dynamic modulus of the mixture was more sensitive in the low frequency range,and the higher the frequency,the lower the modulus change rate.According to the Sigmoidal model and the timetemperature equivalence principle,the main curve of dynamic modulus at different reference temperatures was drawn,and the improvement effect of HPT modifier on the dynamic modulus of asphalt mixture was evaluated.Finally,the modulus results obtained in the test meet the values recommended in Chapter 2,and it is believed that this scheme can improve the durability of the pavement and the performance of the road. |
