Journal of Road Engineering最新文献

Semi-flexible composite mixture (SFCM) is a kind of pavement material formed by pouring cement-based grout material into a porous asphalt mixture with air voids from 20% to 30%. SFCM is widely used for its outstanding anti-rutting performance. Its mechanical performance is complicated due to its heterogeneity and interlocking structure. According to the present study, asphalt deforms at different temperatures, whereas cement-based grout has no similar characteristics. Rare research focuses on the temperature-based performance of SFCM. Therefore, the study was on the thermal performance of SFCM by seven open-graded asphalt mixture skeletons with different porosities and two types of grouts with early strength (ES) and high strength (HS). The test temperatures ranged from −10 ​°C to 60 ​°C. The mechanical investigation was performed using the semi-circular-bending (SCB) and beam bending tests. The strain sensor was used for analyzing the thermal performance of SFCM. The results show that the temperature significantly affected the SFCM's performance. The porosity was selected for three sections based on the trend of fracture energy (G_f) curves at 25 ​°C. The turning points were the porosity values of 20% and 26%. The initiation slope during elastic deformation increases with the porosity increase. This trend was more evident at intermediate temperature. The shrink strain of SFCM was lower than that of the usual asphalt mixture (AC). The thermal stress of the SFCM filled with HS (HS-SFCM) was higher than that of the SFCM filled with ES (ES-SFCM) at −10 ​°C. Moreover, the thermal failure characteristics of SFCM were influenced by porosity.

Microbial-induced calcium carbonate precipitation is a promising technology for self-healing concrete due to its capability to seal microcracks. The main goal of this study was to evaluate the effects of adding hydrogel-encapsulated bacteria on the compressive strength and the self-healing efficiency of concrete. To achieve this objective, 12 sets of mortar samples were prepared, including three different mineral precursors (magnesium acetate, calcium lactate, and sodium lactate), at two concentrations (67.76 and 75.00 ​mM/L), and under two different biological conditions (with and without bacteria). In addition, a set of plain mortar samples was prepared to serve as a control. For each sample set, three mortar cubes and three beams were prepared and subjected to compression and flexural strength tests. From the compression tests, it was found that the sample containing calcium lactate along with yeast extract and bacteria displayed the best results. As for the flexural tests, once cracked, the beams were subjected to 28 ​d of wet/dry cycles (16 ​h of water immersion and 8 ​h of drying), where the bottom crack width was monitored (at 0, 3, 7, 14, 28 ​d of wet/dry cycles). Once the sample with the highest healing efficiency was identified (the one containing calcium lactate and hydrogel-encapsulated bacteria), the study was scaled up to concrete specimens. Two sets of concrete cylinders (consisting of three control samples and three samples with bacteria along with calcium lactate) were tested under compression in order to evaluate the effect of the bacteria-precursor combination on the concrete mechanical properties. The samples that yielded the greatest compressive strength were the ones containing calcium lactate and bacteria, displaying an improvement of 17% as compared to the control specimen. Furthermore, a flexural strength recovery analysis was performed on the concrete specimens revealing that the control showed better flexural strength recovery than the bacteria-containing variant (41.5% vs. 26.1%) after 28 ​d of wet/dry cycles. A healing efficiency analysis was also performed on the cracked samples, revealing that the control displayed the best results. These results are due to the fact that the control specimen showed a narrower crack width in comparison to the bacteria-containing samples.

Domestic waste incineration slag (WIS) includes fly ash and slag. Fly ash is classified as hazardous waste because it contains heavy metals. Most of slag are directly stacked or landfilled due to problems such as large output and low utilization rate. Harmless treatment is imminent. If WIS is used effectively in the road engineering, which can realize the high-quality and high-efficiency recycling of WIS, and it is of great significance to save resources and protect the environment. This study applies a geopolymer prepared from WIS fly ash as a stabilizing agent in WIS blending macadam for use as a pavement base mixture, and reports the mechanical properties (unconfined compressive strength, splitting strength, and resilience modulus) of the geopolymer-stabilized WIS blending macadam (GeoWIS). The leaching concentrations of harmful heavy metals of GeoWIS soaked in water were also investigated. Finally, the strength formation and heavy metal stability mechanisms were explored. The unconfined compressive strength, splitting strength, and compressive resilient modulus of GeoWIS all increased with increasing geopolymer content and decreasing WIS content. The strength of GeoWIS was derived from its geopolymerization and hydration products (C-S-H gel, N-A-S-H gel, and AFt). When the geopolymer content reached 12%–14%, the GeoWIS without natural macadam met the strength criterion of the asphalt pavement base. Through physical adsorption and chemical bonding, the geopolymer significantly reduced the leaching of harmful heavy metals. In GeoWIS with 50% WIS and stabilized with 10% geopolymer, the Cr, Ni, Cd, and Pb concentrations met the grade Ⅲ groundwater standard. Concentrations of heavy metals leached from GeoWIS are low and exert little impact on environment.

The modification of asphalt binder with natural rubber latex (NR) significantly improves the rutting and fatigue resistance of asphalt mixtures. However, NR-modified binder is prone to low workability and wettability due to its high viscosity. Therefore, this research focuses on examining the influences of silane and wax-based additives on the wettability of natural rubber-modified binders and the binder-aggregates adhesion performances. In this study, experimental and analytical approaches were used. The contact angles of asphalt binder were measured using a goniometer through the sessile drop method with three solvents: deionised water, formamide, and glycerol. The C++ algorithm was adopted to compute the surface free energy (SFE) elements of the asphalt binder. Analytical methods were employed to analyse the results based on the Young-Dupre equation, followed by linear regression to establish a correlation between the compatibility ratio (CR) and the SFE components. The results inferred that modified asphalt binders with additives possessed improved moisture resistance, wherein dry work adhesion values were less than 210 ​mJ/m² under granite interfaces, whereas the limestone interface exhibited higher dry adhesion values of 340 ​mJ/m² and below. Similar performance results were observed under wet adhesion conditions; with granite wet adhesive values observed below 120 ​mJ/m², while limestone wet adhesion values were ascertained below 180 ​mJ/m² for all tested samples and conditions. According to the spread–ability coefficient results, the limestone interface has greater spread-ability than granite interfaces. Meanwhile, compatibility ratio values indicated better compatibility of 1.9 or higher for tested samples under granite interfaces, whereas compatibility values of 1.7 and below were observed under limestone interfaces. Among the SFE components studied for correlation with CR, the acidic SFE component demonstrated excellent correlations (with R² values greater than 0.91) under all ageing conditions. An inclusion of micro-level additive enhanced binder adhesion properties, resulting in a more resilient asphalt pavement.

Traditional cement concrete has the disadvantages of low tensile strength, poor toughness, and rapid development of cracks while cracking, which causes a significantly negative influence on the safety and durability of concrete road pavement. This paper presents a state-of-the-art review of toughness improvement mechanisms and evaluation methods of cement concrete for road pavement. The review indicates that (i) The performance of concrete material depends on its material composition and internal structure. Aggregate size, cement properties and admixtures are the main factors of concrete toughness. (ii) The incorporation of rubber or fiber in pavement concrete improves the toughness of concrete materials. However, these additions must be maintained within a reasonable range. The amount of rubber and fiber are encouraged not more than 30% of the volume of fine aggregate and 2% of the volume of concrete, respectively. (iii) The toughness of pavement concrete material includes the toughness regarding bending, impact and fracture. The toughness of cement concrete for highway and municipal pavement is generally evaluated by bending and fracture toughness, while the toughness of airfield pavement concrete is more focused on impact toughness. (iv) The toughening measures of cement concrete for road pavement are mainly mixed with rubber or fiber, while these two materials have their defects, and the application of high-toughness cement concrete in the actual road still faces many challenges. For example, the synergistic effect of rubber and fiber, the development and application of new flexible admixtures, and the formulation of the toughness index of pavement cement concrete materials need further research.

In recent years, with the improvement of the requirements of road performance, modified emulsified asphalts with better performance has gradually replaced the emulsified asphalt and become the primary material for road maintenance. This paper introduces the modified emulsified asphalt materials commonly used in pavement maintenance projects, definitions and modified mechanisms of polymerized styrene butadiene rubber (SBR) modified emulsified asphalt, styrene butadiene styrene block polymer (SBS) modified emulsified asphalt and waterborne epoxy resin (WER) modified emulsified asphalt are summarized. The analysis focused on comparing the effects of modifiers, preparation process, auxiliary additives, and other factors on the performance of modified emulsified asphalt. In this paper, it is considered that the greatest impact on the performance of emulsified asphalt is the modifier, emulsifier mainly affects the speed of breaking the emulsion, stabilizers on the basic performance of emulsified asphalt evaporative residue is small; and when the modifier is distributed in the asphalt in a network, the dosage at this time is the recommended optimum dosage. Finally, this study recommends that in the future, the polymer-asphalt compatibility can be improved through composite modification, chemical grafting and other methods to continue to develop broader applicability and better performance of modified emulsified asphalt.

Industrial production of chemical cement leads to extreme emissions of greenhouse gases. Biological or bio-inspired sustainable materials for soil treatment projects can be employed instead of chemical cement to heal the carbon cycle in the ecosystem. The enzyme-induced calcite precipitation (EICP) method is one of the novel bio-inspired technologies that can be employed in soil treatment projects to increase desired properties of soils. While the monotonic and cyclic behavior of the enzymatically treated sands has been investigated comprehensively, the strain accumulation pattern in these improved soils under cyclic traffic loads has not been evaluated yet. In this paper, confined and unconfined cyclic compression tests are applied to the enzymatically lightly cemented sands, and the effects of the different parameters on their strain accumulation pattern are investigated for the first time in the literature. This study uses two types of specimens with unconfined compression strengths (UCS) equal to 42 ​kPa and 266 ​kPa. It is shown that the treated specimens have a rate-dependent behavior where cyclic loads with low frequencies lead to more resilient and plastic strains in the specimens. The results show that by approaching the maximum applied stresses to the UCS of the specimens (by breaking more calcite bonds between sand particles), the rate dependency behavior of specimens will reduce. Investigation of the effects of the cementation level demonstrated that by increasing the amount of the precipitated calcite from 0.38% to 0.83%, accumulated plastic strains are reduced almost 95% under the same loading condition. Effects of the initial static loads, confining pressures, the number of cycles, and amplitudes of the cyclic loads are also evaluated.

As an important part of steel bridge deck, the engineering quality and service condition of steel bridge deck pavement (SBDP) directly affects the capacity and operational efficiency of the bridge. This paper reviews the history of the development of SBDP in China over the past 20 years from the exploration stage, rapid development stage and prosperity stage. The development and application of SBDP at different stages are discussed in terms of materials, structure, design, performance evaluation, maintenance and rehabilitation, respectively. The advantages and disadvantages of different pavement materials and structures, and the application of different research methods are summarized. The review shows that the improvement of pavement materials and structures and the development of new materials should be further studied on the multi-scale to enhance the durability of pavement materials, so as to extend the service life of pavements. The design method of SBDP related to the synergistic effect of vehicle, pavement and bridge should be established, and the design concept and method standard of rigid base pavement structure should be improved and formulate a complete design standard. In addition, multi-disease intelligent identification system and equipment should be studied to track the entire course of disease development in real time. And it is necessary to develop appropriate algorithms to select and classify the complex data of disease and maintenance history.

The base layer constructed by cement-stabilized macadam (CSM) has been widely used in highway construction due to its low elasticity deformation and high carrying capacity. As a bearing layer, the CSM base is not exempt from fatigue cracking under cyclic loading in the service process. Cracks in the base will create irreversible structural and functional deficiencies, such as the potential for reflective cracking of subsequently placed asphalt concrete overlays. The fracture of the base will shorten the service life of the pavement. The quality of the CSM base is directly related to the bearing capacity and integrity of the whole pavement structure. It is of practical significance to further study the fatigue failure behavior of CSM material for the long-term performance of the pavement. The CSM material is a typical heterogeneous multiphase composite. On the mesoscale, CSM consists of aggregate, cement mortar, pores, and the interface transitional zone (ITZ). On the microscale, the hardened mortar contains a large number of capillary pores, unhydrated particles, hydrated crystals, etc., which makes the spatial distribution of its material properties stochastic. In addition, cement hydration, dry shrinkage, and temperature shrinkage can also produce micro-crack defects in cement mortar. These microcracks will have cross-scale evolution under load, resulting in structural fracture. Macroscopic complex deformation and mechanical response are the reflections of its microscopic and even mesoscale composition and structure. This study summarized the existing studies on the mesoscopic properties of CSM materials, respectively from the three aspects of mesostructure, structural characterization, and mesoscale fatigue damage analysis, to help the development of long-life pavement. The future research direction is to explore the mesoscale characteristics of CSM using multi-scale representation and analysis methods, to establish the connection between mesoscale characteristics and macroscopic mechanical properties.

Asphalt mixtures and cement concrete are an important material in the construction of roads, highways and buildings, and there has been a lot of research about the improvement of their performance. Among them, fibers are commonly used in the construction industry because of their superior properties as reinforcing materials that can provide a proper interfacial action between the fibers and the substrate. This review classifies fibers into natural fibers, inorganic fibers and polymer fibers according to their sources and properties. It summarizes and compares the characteristics, modification methods, usage requirements and research status of each type of fiber in asphalt and cement construction materials, and analyzes the problems and challenges faced by fibers in their applications. The evaluation results show that various types of fibers can enhance the fracture resistance, tensile strength and rutting resistance of asphalt to a certain extent, improve the high temperature performance and viscoelasticity of asphalt, and have a certain effect on the fatigue resistance and road water resistance of asphalt mixes. The fibers also provide better tensile, compressive and abrasion resistance to cement concrete and improve the brittleness and crack resistance of ordinary cement. Besides, for some defects of various types of fibers in construction materials, such as biodegradability, dispersibility and surface inertness of fibers, the targeted modification of fibers is introduced based on physical and chemical modification methods to improve the performance impact of modified fibers in various conditions of application.