Emission Reduction Performance of Modified Hot Mix Asphalt Mixtures

Three novel asphalt modifiers with pollutant emission reduction effects and new emissions measurement equipment compatible with several preexisting asphalt production systems are developed in this paper. The effects of various modifier, asphalt binder type, and gradation of hot mix asphalt (HMA) on pollutant emissions are evaluated in the lab through a comprehensive experimental design. Furthermore, road performances are monitored to evaluate the emissions reduction of modified HMA mixture for production. With increasing modifier content, the emissions reduction performance is improved markedly, with maximum reduction of 70.5%. However, the impact of modifier content on pollutant emissions reduction tends to be insignificant for dosages greater than 20% of the initial asphalt weight. Changes in asphalt type and asphalt mix gradation are found to moderately impact the emissions reduction effect. Finally, the mechanisms of emissions reduction are investigated, primarily attribute to their physical and chemical adsorption and pollutant reductive degradation characteristics

Fatigue Damage Analysis of Cement-Stabilized Base under Construction Loading

Cement-stabilized macadam is commonly used in pavement base courses. The disadvantage of this material is that it easily cracks because construction vehicles cause irreversible fatigue damage to the pavement. Fatigue damage is caused by an insufficient number of maintenance days and overloading by construction vehicles. In order to analyze the influence of the number of maintenance days and overloading by construction vehicles, Miner theory and ABAQUS software were used, and an unconfined compressive strength test, an indirect tensile strength test, a bending tensile strength test, and a fatigue test were carried out simultaneously. The relationship between compressive strength and the splitting strength of water-stabilized macadam as well as compactness, water content, and temperature at different ages were determined. Fitting shows that the bottom tensile stress of the most disadvantageous layer increased with increasing subbase modulus, and its reduction rate increased slowly with the increasing of cement-stabilized macadam subbase thickness. The fatigue prediction equation for cement-stabilized macadam was obtained using bending tensile strength and fatigue tests. Subbase fatigue damage caused by different construction loads under different working conditions was calculated using Miner theory according to actual engineering data. Therefore, the number of pavement maintenance days should be increased. For harsh natural environments and strict time constraints, the design should increase the strength and thickness of the subbase material. When laying the base, overloaded vehicles should be limited, and the construction period of the loaded vehicles should be reduced to minimize road damage

Emission Reduction Performance of Modified Hot Mix Asphalt Mixtures

Three novel asphalt modifiers with pollutant emission reduction effects and new emissions measurement equipment compatible with several preexisting asphalt production systems are developed in this paper. The effects of various modifier, asphalt binder type, and gradation of hot mix asphalt (HMA) on pollutant emissions are evaluated in the lab through a comprehensive experimental design. Furthermore, road performances are monitored to evaluate the emissions reduction of modified HMA mixture for production. With increasing modifier content, the emissions reduction performance is improved markedly, with maximum reduction of 70.5%. However, the impact of modifier content on pollutant emissions reduction tends to be insignificant for dosages greater than 20% of the initial asphalt weight. Changes in asphalt type and asphalt mix gradation are found to moderately impact the emissions reduction effect. Finally, the mechanisms of emissions reduction are investigated, primarily attribute to their physical and chemical adsorption and pollutant reductive degradation characteristics

Low-Temperature Performance and Evaluation Index of Gussasphalt for Steel Bridge Decks

Gussasphalt is widely used in steel deck pavement in cold regions; thus, it should have good low-temperature performance. A method for evaluating the low-temperature performance of gussasphalt is presented in this paper. Low-temperature bending, bending creep, and splitting tests were used to study the performance of different types of gussasphalt. The sensitivity and correlation between low-temperature indices obtained from three methods were compared and analyzed with sensitivity factors and the grey relational coefficient, respectively, and the low-temperature evaluation index and standard of gussasphalt in cold regions were determined. Flow, penetration at 50°C, low-temperature bending, and bending fatigue tests of the trabeculae were carried out after secondary mixing of gussasphalt asphalt concrete. Degradation of the material performance after different storage times was studied. Finally, taking the strain energy density as the main control index and considering the fluidity, the high-temperature performance, fatigue characteristics, technical requirements for storage, and mixing time of gussasphalt in cold weather after two mixing procedures are discussed

Effects of Cement–Mineral Filler on Asphalt Mixture Performance under Different Aging Procedures

Cement-containing mineral powder can effectively improve the moisture stability of an asphalt mixture; therefore, this study systematically summarizes the research status of cement–mineral fillers on the performance of an asphalt mixture and determines the limitations of related studies. In this study, long-term performance tests of styrene-butadiene-styrene- (SBS)-modified asphalt mixtures are designed and evaluated with different blending ratios of the cement–mineral powder under three aging conditions. Moreover, the effect of the cement–mineral composite filler on long-term performance of the asphalt mixture using different blending ratios is determined. Cement improves the high-temperature performance and water stability of asphalt mixtures, but only for certain aging conditions. Considering the regulations for the road performance of asphalt mixtures for three aging conditions, as well as long-term performance considerations, the results indicated that the mass ratio of Portland cement to mineral powder must not exceed 2:2. Low-temperature bending and splitting tensile tests confirmed that an excessive amount of cement filler will embrittle the modified asphalt mixture during long-term aging, thereby deteriorating the tensile properties. The mechanism by which the filler influences the performance of the asphalt mixture should be further studied from the perspective of microscopic and molecular dynamics

Construction Quality Control Study of Double-Layer Continuous Paving for Large-Thickness Cement-Stabilized Base

In order to verify the interlayer bonding effect of double-layer continuous paving technology of the thick cement-stabilized base and solve the construction quality control problem of the double-layer continuous paving, based on the interlayer bonding mechanism and the evenness passing mechanism, the laboratory interlayer adhesion test, field test of evenness disturbance, and compaction test were conducted to verify the continuous paving interlayer bonding state. The effect of interval time on interlayer bonding state, evenness, and compactness was analyzed, and construction quality control measures were proposed. The test results show that the double-layer continuous paving process could significantly improve the interlayer bonding state, but there is still a gap from the ideal state (completely continuous). The pull-off strength of continuous paving specimens was 2.1 times that of the discontinuous paving specimens; the shear strength was 2.4 times that of discontinuous paving specimens. At different paving intervals, the longitudinal evenness of the upper and lower layers has little difference. The 140 kN axle load controls the transverse evenness disturbance within 3 mm, which met the requirements of the specification. Based on the evenness passing mechanism, the evenness control standard of double-layer continuous paving base was proposed. The compaction process of double-layer continuous paving base was proposed, and the feasibility was verified through the field test of compaction. The best interval time for double-layer continuous paving was also proposed; it is recommended that the best time for paving the upper layer is after the lower layer is laid for 6 hours (the final setting time of the cement). The construction quality control measures proposed in this study provide a theoretical basis for the construction of double-layer continuous paving technology with thick cement-stabilized base

Mechanical Response of Typical Cement Concrete Pavements under Impact Loading

In order to study the mechanical response of cement concrete pavements under impact loading, four types of typical cement concrete pavement structures are investigated experimentally and numerically under an impact load. Full-scale three-dimensional pavement slots are tested under an impact load and are monitored for the mechanical characteristics including the deflection of the pavement surface layer, the strain distribution at the bottom of the slab, and the plastic damage and cracking under the dynamic impact load. Numerical analysis is performed by developing a three-dimensional finite element model and by utilizing a cement concrete damage model. The results show that the calculation results based on the cement concrete damage model are in reasonable agreement with the experimental results based on the three-dimensional test slot experiment. The peak values of stress and strain as monitored by the sensors are analyzed and compared with the numerical results, indicating that the errors of numerical results from the proposed model are mostly within 10%. The rationality of the finite element model is verified, and the model is expected to be a suitable reference for the analysis and design of cement concrete pavements

Microwave Deicing Efficiency: Study on the Difference between Microwave Frequencies and Road Structure Materials

A method of deicing using microwave heating is proposed to make scientific and economical road deicing in a cold area, and to make up for deficiencies in the existing methods for melting snow and ice. This paper proposes to define microwave deicing efficiency as the heating rate of a concrete surface when heated to 0 °C (the efficiency of deicing is equal to the difference divided by heating time, which is between 0 °C and the initial temperature at the junction of ice and concrete). Based on the mechanism of microwave heating and deicing, a method combining the finite element simulation model with indoor experiments was proposed to study the deicing efficiency of microwaves, and the effects of different microwave frequencies and different road structure materials on microwave deicing efficiency were analyzed. The results show that the microwave frequency and road structure materials have a great influence on microwave deicing. For asphalt concrete, the ice melting efficiency of 5.8 GHz is 4.31 times that of 2.45 GHz, but the heating depth is less than that of 2.45 GHz. At 2.45 GHz, the melting efficiency of cement concrete is 3.89 times that of asphalt concrete. At 5.8 GHz, the melting efficiency of cement concrete is 5.23 times that of asphalt concrete. Through the consistency of the simulation and experimental results, the validity of the simulation model based on the finite element theory is verified. The results provide theoretical guidance and a practical basis for future applications of microwave deicing

Research on Subgrade Differential Settlement Control Standard and Treatment Technology Based on Driving Comfort

At present, the geogrid is commonly used to treat the differential settlement of the subgrade at the joint of the filling and excavation effectively. In order to further improve the utilization rate of geogrid in the treatment of subgrade, the driving comfort index was proposed innovatively to control the subgrade differential settlement. Based on the human-vehicle-road coupling system model, the influence of subgrade differential settlement area, subsidence value, and vehicle speed on the maximum vertical acceleration of the human body was analyzed. The correlation between the vertical acceleration of the human body under different vehicle speeds and the differential settlement value was obtained through multiple regression calculations, and the subgrade differential settlement control standard based on driving comfort was proposed. By establishing the finite element model of the cut to fill subgrade, the characteristics of differential settlement at the top surface of the subgrade under different geogrid laying positions, densities, and lengths were calculated and analyzed. In addition, the differential settlement layout scheme of the geogrid disposal subgrade based on driving comfort was proposed, and the effectiveness of the scheme was verified by experiments. The results show that the position and length of the grid are the main factors affecting the treatment effect of the vertical and horizontal cut to fill subgrade. The proposed layout scheme can effectively control the differential settlement of the subgrade and raise the utilization rate of the geogrid. The research results can provide theoretical value and reference for the laying of geogrid in mountainous roads