Semi-rigid Layer Research Articles

Field evaluation and statistical analysis of the dynamic response of semi-rigid pavement under full-scale moving truck load

Mechanistic-based pavement distress prediction models or transfer functions are often used to assess damage or predict the service life of the pavement structure. The reliability of pavement structure design and performance predictions is highly dependent on the accuracy of the critical responses. The present study provides an experimental and statistical evaluation of the relationship between influencing factors such as traffic speed, vehicle axle load, and seasonal temperature, and the pavement mechanical response. In addition, the level of impact of each influencing factor and their two-way interaction or coupling effect on the pavement critical response was investigated. The results of the experimental investigation and the statistical analysis of the pavement mechanical response were presented, analyzed, and discussed. Besides, by combining the application of the orthogonal array test and multivariate regression analysis, the current study proposes a prediction model to predict the critical stress response at the bottom of the semi-rigid layer.

Experimental Study on Interlayer Mechanical Properties of Semi-Rigid Base Asphalt Pavement Using Interlayer Treatment Method

In order to improve the interlaminar mechanical properties of semi-rigid layer and asphalt layer in asphalt pavement, the method of the base surface treated pits was studied and their properties at different temperatures were explored. The experimental results show that at 20 °C, compared with the base surface untreated, the interlayer shear strength of the base surface treated 9 pits of q>20 mm was increased by 27.95%, and the tensile strength was increased by 57.51%. Within a certain range, increasing the diameters of the pits can improve the bonding effect between the layers. In the temperature range of 0 °C-40 °C, the interlayer bonding effect of the base surface treated 9 pits of q>20 mm and spread oil is been better than the other three interlayer treatment methods in the experiment. These results show that the base surface treated the pits can form mortise structure, which can improve the mechanical properties between layers and weaken the negative effect of high temperature on the adhesion between layers.

Investigation of structural resistance for semi-rigid layers in an actual stress state

As the primary high-grade pavement structure, asphalt pavement with semi-rigid layers has been extensively applied in China. Among the semi-rigid layers materials, cement-treated aggregates (CTA) are an essential pavement element, and its fatigue life significantly affects the durability of the asphalt pavement structure. Various fatigue tests have been adopted to evaluate the fatigue properties of CTA. However, the fatigue resistance of the CTA measured under various methods is different, which seriously affects the accuracy of the structural design of the semi-rigid layers. Hence, this work aims to establish a design criterion for CTA to characterize the structural resistance of semi-rigid layers. The uniaxial compression (UC), four-point bending (4 PB), and indirect tensile (IDT) strength and fatigue tests for CTA were carried out. According to the traditional S-N fatigue model, the curves of fatigue performance and stress ratio of CTA under various stress states are quite different. To intuitively compare the structural resistance of CTA under various test types, the mean stress and effective stress of CTA under different loading rates were obtained. The yield surface was then established based on the Ayyagari model, considering the multiaxial yield criterion of CTA. The effective stress ratio was defined, and its relationship with the fatigue life of CTA was established. Based on the Ayyagari model and the normalized equation, the fatigue resistance criterion of semi-rigid layers under the three-dimensional stress state was proposed.

CuO-containing oil-based nanofluids for concentrating solar power: An experimental and computational integrated insight

The thermal properties of the heat transfer fluid (HTF) used in concentrated solar power (CSP) technology are still considered one of the main limitations to the expansion of this energy source as a solid alternative to fossils fuels. The addition of nanoparticles has been shown to have a positive contribution in this sense. In this study, CuO nanoparticles were dispersed into the typical HTF used in CSP plants, their stability assured by using a surfactant which reduces the tension at the solid-liquid interface. Three nanofluids were prepared using different sonication energy values in the dispersion process. All of them were characterised for stability and thermal properties over two months. The one prepared with the lowest energy value was the most stable and exhibited an improvement in the heat transfer coefficient of about 10%, also showing improvements in isobaric specific heat and thermal conductivity. In addition, a theoretical approach was applied to the system to provide more information about the heat transfer mechanisms, presented as one of the main challenges in this regard. Molecular dynamics simulations were performed under the same conditions as the experimental scenario, and once the model was validated it was used for a more in-depth molecular level understanding. The enhanced thermal conductivity was analysed by means of the heat flux autocorrelation function, which showed a larger phonon mean free path for the nanofluid system. Radial distribution functions showed the formation of a semi-rigid layer that could explain the increase in isobaric specific heat.

Numerical investigation of the mechanical response of semi-rigid base asphalt pavement under traffic load and nonlinear temperature gradient effect

The effectiveness of any pavement design based on the mechanistic procedure depends on the accuracy of the mechanical parameters used such as stresses and strains. Hence, an effective and realistic prediction of these parameters when traffic and environmental data are provided is a step towards the future design of more sustainable pavement structures. This study investigated the distribution of the mechanical parameters in three new semi-rigid pavement structures with typical functional and structural requirements, specially designed to withstand various distresses of semi-rigid pavements. The response of these pavements to the combined effect of the nonlinear thermal gradient and moving axle load was examined by means of an advanced 3D pavement FE modeling. The model integrated mechanical and thermophysical properties of each pavement material, studied the transient dynamic effect of wheels load, and employed transient heat transfer and implicit dynamic analysis. Field measurements of these experimental pavement structures at the RIOH-Track test site in Beijing, China, as well as relative climatic data were used to verify and validate the accuracy of the developed model. Comparison of the numerical and experimental results indicated that the developed model predicted accurately the characteristic non-linear distribution of temperature along with the pavement depth and the pavement response to the combined effect of the nonlinear temperature gradient and traffic load. The influence of three main factors affecting the distribution of the mechanical parameters, namely; the bonding conditions between the pavement’s layers, the vehicle speed and the axle load amplitude were evaluated. In addition, fatigue analysis of the asphalt layers and the semi-rigid layers was performed to evaluate the theoretical service life of each pavement structure. The findings of this study underscored that the non-linear temperature gradient, despite being often neglected in mechanistic modeling, is a key parameter for accurate prediction of the distribution of stresses and strains in pavement system. Moreover, the results indicate that the lowest traffic speed and the extra weight extension of the truck axle have an adverse effect on mechanical parameters. Furthermore, the improvement of contact conditions at the interface results in good performance. Overall, the conclusions obtained in this study provides a reference for the design of semi-rigid pavement structures.

Comparison of Real Response and Theoretical Modeling of Pavement with Thick Asphalt Layers under Heavy Traffic Load

Two kinds of asphalt pavement with thick asphalt layers were used to construct two samples. In structure I, a semirigid base and graded crushed stone subbase were used. In structure II, a granular base and semirigid subbase layer were used. Responses of the two structures under traffic loads were measured using optical fiber sensors, and the differences between theoretical model results and field measurements were analyzed. Field measurements show that vertical compressive stress in structure I is larger than that in structure II. The maximum tensile strain of the asphalt layer is located at the bottom of the AC‐25C layer in structure I and at the bottom of the AC‐25F layer in structure II. The latter is significantly larger than the former, indicating the possibility of fatigue cracking induced by traffic load is higher in structure II. The measured tensile horizontal strain at the bottom of the semirigid layer is relatively low (<30εμ) in both structure I and structure II. In theoretical model, static modulus, dynamic modulus, and interface bonding ability are considered and theoretical responses are calculated. There are significant differences between the theoretical results and field test data. In the theoretic model, the material properties of layers and bonding status of adjacent layers all influence the results. In order to reduce the difference between the calculated and measured results, numerous material tests and field tests should be carried out.

Mechanism Analysis of the Use of LSPM for Reflection Crack Prevention of Semi-Rigid Base Asphalt Mixture

The damage mechanism of reflective cracking, particularly on semi-rigid asphalt pavement with large stone porous asphalt mixture (LSPM) is investigated in this study.An asphalt pavement model with multilayered base (i.e., LSPM and semi-rigid layer) using discrete element methodis developed.This study analyzes the influence of the inner structure of asphalt mixture on the stress field around the crack tip, which is under the vehicle load after the cracking of a semi-rigid layer. The focus is on the mechanism of cracking and the influence of the inner structure of the mixture, such as gradation, the geometric feature of coarse aggregate, and space.The crack expansion rate is also analyzed.Results show that, under vehicle load, the crack in the semi-rigid layer causes stress concentration, which decreases around the bottom of the LSPM.The load on the top of the crack tip produces stress level concentration, the unbalanced load produces shear stress concentration, and the stress decreases progressively from the crack tip to the surrounding area. In the LSPM, a large grain size of the coarse aggregate is better than a small grain size. Its overall stress level is low and the crack development rate is slow on the stress field of the crack tip. The LSPM can reduce stress concentration and prevent the development of reflective cracking effect.

Investigating and Comparing Traffic Induced and Restrained Temperature Stresses in a Conventional Rigid Pavement and Semi-Rigid Layers

The paper investigates and compares the magnitude of restrained temperature stresses that can be achieved in both a rigid pavement and a flexible pavement with a grouted macadam surfacing. The analysis is based on well known Westergrad equation that commonly applicable for concrete and BISAR from Shell that used for flexible pavement A hypothetical pavement is designed to assess the properties of the materials under traffic induced stresses and temperature restrained stresses. The results indicate that grouted macadams could be as vulnerable to combinations of thermal and traffic stress as concrete and with respect to traffic induced stresses at the underside of the surfacing layer. westergaard's analysis is more applicable to the a concrete slab and BISAR is more suitable for grouted macadam surfacing

The Study on the Asphalt Pavement with Composite Base

Semi-rigid layer is widely used as the base in China. However, the structure has resulted in many premature distresses in asphalt concrete layer. In order to overcome the problem, the composite base is introduced which is composed by both flexible and chemically stabilized material. The internal stresses are calculated by linear multilayer elastic theory and then, a comparison of the stresses of asphalt pavement with semi-rigid base and composite base is provided. The result shows that the composite base composed by all, consisting of the asphalt treated layer, graded crushed stone and cement treated layer is more suitable structure to resist cracking and the structure also has good adaptability to heavy load.