Study on Mechanical Properties of Recycled Mixture with High Content of Iron Tailings Sand

This paper focuses on the disposal of iron tailings sand (ITS) and reclaimed inorganic binder stabilized aggregate (RAI), and a new “ITS plus RAI” solid waste treatment method is innovatively proposed, which uses ITS and RAI as a new base course material to replace of new aggregates by 100%. It is found that the new ITS and RAI mixture has excellent compressive performance by designing the material composition of the mixture, which can meet the design strength of different levels of pavement under various load conditions. A series of laboratory tests are used to study the effect of the content of special cementitious material and iron tailings on the uniaxial compressive strength, flexural-tensile strength, compressive resilience modulus, and flexural-tensile resilience modulus of recycled mixture. And, the scanning electron microscope test (SEM) and X-ray diffraction test (XRD) are used to compare the surface morphology characteristics and hydration products of the recycled mixture under different ratios and to discuss the formation mechanism of the strength of the mixture. The test results show that the macroscopic change pattern in laboratory tests is basically consistent with the results in microanalysis. The relationship between compressive strength and compressive resilience modulus and flexural resilience modulus is also established by linear regression. This solid waste treatment method is applied to the pavement renovation project of national and provincial roads in Shanxi Province (within Linfen), to replace the existing base material by using recycled mixture, and the results show that it can save not only the carbon emission from stone mining and processing but also the construction cost, while producing good social and economic benefits and promoting the process of carbon neutralization in the world.

Effect of variations in layer thickness and resilience modulus on flexible pavement performance

A pavement mechanistic-empirical analysis is based on a pre-designed structure checked for required performance criteria. In case the latter are not met, this structure is modified and reprocessed. In this context, analyzing the effect of variations in project parameters on pavement performance prediction subsidizes a better understanding of results provided by computer programs. The objective of this study is to assess the effect of layer thickness and resilience modulus variations on flexible pavement performance. To do so, performance was estimated for the 20th project year through Elastic Layered System Model 5 (ELSYM5) software and American Association of State Highway and Transportation Officials (AASHTO) Mechanistic-Empirical method (ME). Using multiple regression models for result adjustment and through statistical assessments on regression coefficients calculated, it can be concluded that pavement lifespan consumption, predicted by simulations on ELSYM5, is sensitive to variations in coating and subbase thickness and in subgrade resilience modulus. For AASHTO ME method, predicted values for distresses were significantly sensitive to variations in coating, base and subbase thickness, and in base and subgrade resilience modulus. Comparing both approaches, it is concluded that ELSYM5 can be a viable alternative to the application of a ME pavement design method.

Posttraumatic Orbital Emphysema: A Numerical Model

Orbital emphysema is a common symptom accompanying orbital fracture. The pathomechanism is still not recognized and the usually assumed cause, elevated pressure in the upper airways connected with sneezing or coughing, does not always contribute to the occurrence of this type of fracture. Observations based on the finite model (simulating blowout type fracture) of the deformations of the inferior orbital wall after a strike in its lower rim. Authors created a computer numeric model of the orbit with specified features—thickness and resilience modulus. During simulation an evenly spread 14400 N force was applied to the nodular points in the inferior rim (the maximal value not causing cracking of the outer rim, but only ruptures in the inferior wall). The observation was made from1·10-3to1·10-2second after a strike. Right after a strike dislocations of the inferior orbital wall toward the maxillary sinus were observed. Afterwards a retrograde wave of the dislocation of the inferior wall toward the orbit was noticed. Overall dislocation amplitude reached about 6 mm. Based on a numeric model of the orbit submitted to a strike in the inferior wall an existence of a retrograde shock wave causing orbital emphysema has been found.

Influence of Strength Attenuation for Silt Soil on the Fatigue Life of Semi-Rigid Base

Influence of water content on the resilience modulus for silt soil in Yellow River alluvial plane is studied by laboratory tests. And its found that resilience modulus decrease dramatically when the water content exceeds the optimum. So the subgrade cant support the pavement structure enough, which could make the fatigue life of semi-rigid base little than the design value. Basing on the distribution of the water content in real, the silt subgrade is divided into three parts in accordance with the difference of resilience modulus. Then, the tensile stress and fatigue life of semi-rigid base is gotten, and results show the strength decay of subgrade reduced the fatigue life of semi-rigid base up to 50%, which exposes the causes of early damage of semi-rigid base asphalt pavement on silt subgrade.

Design and Research on the Warm-Mix Rubber-Modified Asphalt Mixture Based on the GTM Method

By using GTM method, with equal volume parameters as the criterion, determined the suitable temperature of Evotherm warm-mix rubber-modified asphalt mixture, and applied Marshall method for repeated experiments, holding that GTM method could increase the cooling rate. Then, it firstly proposed a two-stage design method to conduct design of warm-mix rubber-modified asphalt mixture based on the two-parameter system; on the basis of hot-mix asphalt mixture test, it carried out staged design of asphalt content and temperature to ensure the pavement performance in terms of material composition and volume parameters. Finally, the paper conducted performance test of the designed warm-mix mixture and made comparative analysis of the corresponding hot-mix mixture. The results showed that the low and high temperature performances as well as the water damage resistant performance of Evotherm warm-mix rubber-modified asphalt mixture were superior than that of hot-mix mixture, and its compression resilience modulus was roughly equal to that of the hot-mix mixture, which would not affect the pavement structure design.

Experimental Study on Mechanical Behaviors of Lime-Stabilized Soils with Small Lime Content

In order to investigate the mechanical behaviors of lime-stabilized soils with small lime content, the specimens with 4%~8% lime content and 90%~95% degree of compaction are prepared, and then in use for the unconfined compression strength test, the diametral compression test and the compression resilience modulus test after they have cured in a standard curing room for 7 to 180 days respectively. These test results show that all of the unconfined compression strength, the splitting strength and the compression modulus of resilience increase with the degree of compaction and the curing time. Thereinto, the compression modulus of resilience does rapidly between 28 and 90 curing days, and the unconfined compression strength of the soil with 4% lime content does little after 28 curing days while the compression strengths and the splitting strengths of the other soils do quickly until 90 curing days. In addition, for a given degree of compaction, these strengths of the soils with the less lime content are potentially greater at the early curing time.

Experimental Study on Compression and Rebound Characteristics of High Liquid Limit Clay of the Yellow River Alluvial Plain

Based on indoor compression test material of high liquid limit clay about Ji-He expressway,analyzed the relationship among compression modulus,compression coefficient,cuts modulus and resilience modulus of high liquid limit clay of the Yellow River alluvial plain with its moisture content and dry unit weight,and their changing rules.The results show that in a certain dry unit weight condition,free expansion ratio of high liquid limit clay is decreasing with the increasing of natural moisture content, however, in a certain moisture content condition,the free expansion ratio is increasing with increase of the dry unit weight.Compression modulus decreases along with the rising of moisture content,while increases to gether with the increasing of the dry unit weight.The compression coefficient increases with moisture content,while decreases together with the increasing of the dry unit weight.Cuts modulus reduces when moisture content goes up,certain as moisture content is, it is going to magnify along with the increasing of dry unit weight,when both dry unit weight and moisture content are constant,cuts modulus will increase with the pressure.In certain dry unit weight conditions, the resilience modulus decreases as the moisture content increases,by contrast in certain moisture content conditions,the resilience modulus increases with the increasing of the dry unit weight.

Study on the Correlation between Strength Parameters and Shear Wave Velocity of Pavement Subgrade Soil

By using three kinds of subgrade soil and controlling dry density and moisture content，the correlation between strength parameters of pavement subgrade soil, California Bearing Ratio(CBR) and Resilience modulus E, and their shear wave velocity are studied through CBR Penetration test, lever pressure meter test and shear wave velocity test. Then the analytical models of CBR and Resilience modulus E by shear wave velocity are proposed. These models are valuable to acquire airport pavement subgrade soil parameters by nondestructive technique.

Impact of Subgrade Resilience Modulus on Heavy Load Asphalt Pavement Mechanical Properties

Subgrade resilience modulus is an important mechanical parameter in pavement design. It will directly influence the design result of pavement structure. Using BISAR3 of SHELL design method, the impacts of subgrade resilience modulus on pavement surface deflection, base and subbase bottom tensile stress, surface layer bottom tensile stress of the heavy load asphalt pavement structure were analyzed. And the influencing laws were analyzed, too. The results show that the mechanical and deforming characteristics of heavy load asphalt pavement were influnced significantly by subgrade resilience modulus. With the increasing of subgrade resilience modulus, the pavement surface deflection, base bottom tensile stress would significantly decrease, and fatigue life would be improved.

Dynamic Characterization of Cement-Treated High-Speed Railway Subgrade

In order to ensure the high-speed railway train running safety and stabilization, the subgrade should keep adequate strength, rigidity and long-term stabilization under the repeated train load. When the subgrade soil is poor, we can treat it with cement. Whether the performance of cement-treated soil can meet the demand of high-speed railway, so the dynamic triaxial test of cement-treated soil is studied in this paper. The dynamic performance of cement-treated soil under repeated train load is analyzed. The variation and influence factors of critical dynamic stress, accumulated plastic strain, elastic strain and resilient module of cement-treated soil are studied.When the dynamical stress more than the critical dynamical stress, the cumulate plastic strain and the elastic strain will rapidly increase with the increase of the loading time of the dynamical stress. The resilience modulus will decrease along with the increase of the dynamical stress. When the dynamical stress less than the he critical dynamical stress, the elastic strain and the resilience modulus remain constant with the increase of the loading time of the dynamical stress. And the elastic strain and the resilience modulus linearly increase with the increase of the dynamical stress.