Search Results (44)

The inherent limitations of ordinary cement mortar—characterized by its high brittleness and low flexibility—result in a diminished load-bearing capacity, predisposing concrete pavements to cracking. A novel approach has been proposed to enhance material performance by incorporating emulsified asphalt and latex into ordinary cement mortar, aiming to improve the flexibility and durability of concrete pavements effectively. To further validate the feasibility of this proposed approach, a series of comprehensive experimental investigations were conducted, with corresponding conclusions detailed herein. As outlined below, the flexibility properties of the modified cement mortar were systematically evaluated at curing durations of 3, 7, and 28 days. The ratio of flexural to compressive strength can be increased by up to 38.9% at 8% emulsified asphalt content at the age of 28 days, and by up to 50% at 8% latex content. The mechanism of emulsified asphalt and latex-modified cement mortar was systematically investigated using a suite of analytical techniques: X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TG-DTG), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through comprehensive analyses of microscopic morphology, hydration products, and elemental distribution, the enhancement in cement mortar toughness can be attributed to two primary mechanisms. First, Ca²⁺ ions combine with the carbonyl groups of emulsified asphalt to form a flexible film structure during cement hydration, thereby reducing the formation of brittle hydrates. Second, active functional groups in latex form a three-dimensional network, regulating internal expansion-contraction tension in the modified mortar and extending its service life. Full article

To investigate the performance degradation of emulsified asphalt cold recycled mixtures (CRM) during service, this study selected a 10 km section of the cold recycled layer (CRL) from the Changjiu Expressway reconstruction project as the research subject. The deterioration patterns of key pavement performance indicators—including the Pavement Condition Index (PCI), Riding Quality Index (RQI), Rutting Depth Index (RDI), and Pavement Structure Strength Index (PSSI)—were analyzed in relation to cumulative equivalent axle loads over a 7-year service period. Concurrently, comparative evaluations were conducted on the mechanical properties, water stability, high-temperature performance, low-temperature crack resistance, and fatigue characteristics between in-service and laboratory-prepared emulsified asphalt CRM. The results demonstrate that after seven years of service, the emulsified asphalt cold recycled pavement maintained excellent performance levels, with PCI, RQI, RDI, and PSSI values of 92.6 (excellent), 90.1 (excellent), 88.5 (good), and 93.4 (excellent), respectively. Notably, while the indirect tensile strength and unconfined compressive strength of the CRL increased with prolonged service duration, other performance metrics—including the tensile strength ratio, shear strength, fracture work, and fracture energy—exhibited an initial improvement followed by gradual deterioration. Additionally, increased traffic loading during service led to a reduction in the residual fatigue life of the CRM. Interestingly, the study observed a temporary improvement in the fatigue performance of CRM during the service period. This phenomenon can be attributed to three key mechanisms: (1) continued cement hydration, (2) secondary hot compaction effects, and (3) diffusion and rejuvenation between fresh and aged asphalt binders. These processes collectively contributed to the partial recovery of aged asphalt strength, thereby improving both the mechanical properties and overall road performance of the CRM. The findings confirm that cold recycled pavements exhibit remarkable durability and maintain a high service level over extended periods. Full article

Semi-flexible pavement (SFP) mixture consists of porous matrix asphalt mixture and cement-based grouting material. This composite material gains advantages from both the rigid cementitious material and flexible asphalt mixture. It exhibits excellent anti-rutting capability while no joints are needed. However, SFP is prone to cracks in the field. This study employs water-based epoxy resin and emulsified asphalt as polymer additives to modify the grouting material. A response surface methodology (RSM) model was employed for multi-factor and multi-response optimization design. The ratio of water-based epoxy resin to emulsified asphalt (w/e ratio), polymer content, defoamer content, and mixing speed were considered in the model. Fluidity, compressive strength, and fracture energy were selected as response indicators. It was found that a low mixing speed was not able to produce grouting slurry with acceptable fluidity. The addition of higher polymer contents would lower the compressive strength of the grouting material due to the low stiffness of the polymer and entrained air produced during mixing. The addition of defoamer eliminated the bubbles and, therefore, increased the strength and fracture energy of the samples. By solving for the optimal model solution, the values of optimized parameters were determined to be a w/e ratio of 0.64, polymer content of 3.3%, defoamer content of 0.2%, and mixing speed of 2000 rpm. Microstructural analysis further confirmed that the synergistic effect of water-based epoxy resin and emulsified asphalt can effectively make the microstructure of the hardened samples denser. The anti-cracking ability of the SFP mixture can be increased by 22% using optimally designed grouting material. The findings in this study shed light on the design of toughness-reinforced SFP materials. Full article

Cement-emulsified asphalt mortar (CA mortar) is an organic–inorganic composite material composed of cement, emulsified asphalt, fine sand, water, and various admixtures. It is mainly used as the cushion layer for high-speed railway ballastless tracks. CA mortar cushion layers in North China often have to withstand the coupling effects of humidity and freeze–thaw, which has a very important impact on the fatigue performance of CA mortar. Based on the big data statistical results, the temperature conditions and cycle times of the CA mortar layer Freeze–Thaw cycle in North China were determined. Also, a fatigue performance test under humidity–freeze–thaw coupling conditions was designed and carried out. The fitting curve equations of fatigue stress and fatigue life under different humidity conditions and freeze–thaw coupling were established. The relationship between fatigue performance parameters K and n and humidity conditions was analyzed. This study shows that with the increase in humidity, the fatigue life of CA mortar under different humidity conditions shows an overall downward trend. The fatigue performance and fatigue life stress level sensitivity of CA mortar decrease with increasing humidity. The proportion of water damage and freeze–thaw damage to total damage increases with increasing humidity, which means that the humidity and freeze–thaw have a more significant impact on the fatigue properties of CA mortar. When the humidity is low, the fatigue cracks of CA mortar are mostly generated across the cement paste, and the macroscopic damage presents as longitudinal cracking. When the humidity is high, the fatigue cracks of CA mortar are mostly generated at the interface between aggregate and paste, and the macroscopic damage presents as oblique cracking. Based on the analysis of the damage mechanism, it is suggested that the humidity of CA mortar should be controlled below 25% in the actual project to ensure its durability. Full article

This study aims to explore the dynamic response of ballastless tracks under various temperatures of the cement-emulsified asphalt (CA) mortar layer and other environmental factors. CA mortar is the key material in the ballastless track structure, exhibiting notably temperature-dependent viscoelastic properties. It can be damaged or even fail due to the continuous loads from trains. However, the dynamic behaviors of ballastless tracks considering the temperature-dependent viscoelasticity of CA mortar have been insufficiently studied. This paper captures the temperature-dependent viscoelastic characteristics of CA mortar by employing the fractional Maxwell model and applying it to finite element simulations through a Prony series. A vehicle–track–subgrade (VTS) coupled CRTS I ballastless track model, encompassing Hertz nonlinear contact and track irregularity, is established. The model is constrained symmetrically on both of the longitudinal sides, and the bottom is fixed on the infinite element boundary, which can reduce the effects of reflected waves. After the simulation outcomes in this study are validated, variations in the dynamic responses under different environmental factors are analyzed, offering a theoretical foundation for maintaining the ballastless tracks. The results show that the responses in the track subsystem will undergo significant changes as the temperature rises; a notable effect is caused by the increase in speed and fastener stiffness on the entire system; the CA mortar layer experiences the maximum stress at its edge, which makes it highly susceptible to damage in this area. The original contribution of this work is the establishment of a temperature-dependent vehicle–track–subgrade coupled model that incorporates the viscoelasticity of the CA mortar, enabling the investigation of dynamic responses in ballastless tracks. Full article

To understand the mechanical behavior of CRTS (China Railway Track System) II cement emulsified asphalt mortar (CA mortar), this study tested the compressive strength and flexural strength of CA mortar at different ages under varying water-to-cement ratios and dosages of water-reducing agent. Based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) results, the hydration products and microstructure of CA mortar at different ages were analyzed. The main conclusions are as follows. As the water-to-cement ratio increases, the compressive strength and flexural strength of CA mortar generally exhibit a decreasing trend. The strength increases rapidly in the early stages, with the 7-day compressive strength reaching over 80% of the 28-day compressive strength, and the 7-day flexural strength reaching over 93% of the 28-day flexural strength. As the dosage of water-reducing agent increases, both the compressive strength and flexural strength of CA mortar first increase and then decrease, with a reasonable range of water-reducing agent dosage being between 0.2% and 1.0%, and 0.5% is most appropriate. The hydration reaction of CA mortar is nearly complete at 3 days, with the increase in ages, the cement hydration slows down due to the coating action of asphalt, and the strength no longer changes greatly. Hydration products are mainly Ettringite, which is the main source of strength of CA mortar. After the emulsified asphalt breaks, it adsorbs onto the hydration products and sand surfaces, gradually forming a continuous phase, which enhances the structural toughness of the CA mortar. Full article

Existing research shows that using waterborne epoxy resin (WER) instead of emulsified asphalt as the binder for cold mix asphalt (CMA) can enhance the rutting resistance, high-temperature performance, fracture performance, and early performance of CMA. In order to eliminate the potential drawbacks such as insufficient strength and low-temperature performance of CMA during application, a novel method was proposed in this study for the preparation of waterborne epoxy-acrylate resin (WER), specifically tailored to modify emulsified asphalt, resulting in waterborne epoxy-acrylate resin emulsified asphalt (WEREA). The modification effect of WER on emulsified asphalt was evaluated through rheological tests and direct tensile tests. A modified design method based on the conventional Marshall design method was proposed to determine the optimal mix proportions, including the key parameters of specimen compaction and curing. The results revealed that the incorporation of WER led to a substantial improvement in the complex shear modulus and a concurrent decrease in the phase angle. When the temperature exceeded 60 °C, the phase angle exhibited a diminishing trend, indicative of a reduced viscosity as temperatures escalated. As the WER content increased, a decrease in the direct tensile strain rate was observed, accompanied by a substantial elevation in direct tensile strength. At various stress levels, the shear strain of WEREA decreases with increased content of WER, indicating that the incorporation of WER can enhance the hardness of emulsified asphalt and improve its deformation resistance. The results from MSCR tests indicate that WER could significantly improve the elasticity and hardness of emulsified asphalt, transitioning it from a viscoelastic material to an elastic material, thereby improving its deformation resistance, resistance to rutting, and high-temperature performance. The results of fatigue life are consistent with those of the amplitude sweep, both reflecting the improvement of resistance to deformation of emulsified asphalt by WER. This indicates that WER has a significant improving effect on the fatigue resistance of emulsified asphalt. Furthermore, the Marshall design tests further confirmed the advantages of WEREA in asphalt mixtures. The optimal preparation for the WEREA mixture was proposed as follows: double-sided compaction for 50 times each, aging at 60 °C for 48 h, optimal moisture content of 5.14%, cement content of 2.5%, and emulsion content of 8.4%. The optimal mix proportions identified through these tests yielded asphalt mixtures with significantly improved stability, reduced flow value, and enhanced rutting resistance compared to the hot-mix asphalt mixture (HMA) of AC-16. These findings suggest that WEREA has the potential to significantly enhance the durability and longevity of asphalt pavements. For future applications, it can be explored for use in producing cold recycled asphalt mixtures. In addition to designing the WEREA mixture according to AC-16 gradation, consideration can also be given to using a gradation with a smaller nominal maximum aggregate size for the application in the surface layer or ultra-thin wearing course. Full article

To address the challenges of slow curing speed and suboptimal microwave absorption during the paving of cold-mixed and cold-laid asphalt mixtures, this study introduces SiC-Fe₃O₄ composite material (SF) into emulsified asphalt mixtures to enhance microwave absorption and accelerate curing via microwave heating. Initially, based on the maximum density curve theory, an appropriate mineral aggregate gradation was designed, and the optimal ratio of emulsified asphalt mixture was determined through mixing tests, cohesion tests, wet wheel wear tests, and load wheel sand adhesion tests. Subsequently, the influence of SF content on the mixing performance of emulsified asphalt mixtures was analyzed through mixing and consistency tests. Finally, the microwave absorption performance of the mixture was evaluated by designing microwave heating tests under different conditions, using temperature indicators and quality indicators. The experimental results indicate that when SF content ranges from 0% to 4%, the mixing performance of the emulsified asphalt mixture meets specification requirements. The dosage of SF, SF composite ratio, and microwave power significantly impact microwave absorption performance, whereas environmental temperature has a relatively minor effect. The optimal mix ratio for the emulsified asphalt mixture is mineral aggregate:modified emulsified asphalt:water:cement = 100:12.8:6:1. The ideal SF dosage is 4%, with an optimal SiC to Fe₃O₄ composite ratio of 1:1, and a suitable microwave power range of 600–1000 W. Full article

To develop a cement emulsified asphalt composite (CEAC) that can be sprayed under a plateau negative temperature environment, the effects of the water–solid ratio, calcium aluminate cement substitution rate, emulsified asphalt content, sand–binder ratio, and polyvinyl alcohol (PVA) fiber content on the spraying performance and rheological parameters of CEAC were explored through the controlled variable method. Additionally, the correlation between the spraying performance and rheological parameters of CEAC was established, and the optimal proportion of CEAC was determined. Then, the difference in frost resistance and pore structure between the cement slurry (CS) without emulsified asphalt and CEAC at the optimum proportion was analyzed. The results showed that the optimum proportions for sprayed CEAC were 0.14 water–solid ratio, 0.5 sand–binder ratio, 25% substitution of calcium aluminate cement, 5% emulsified asphalt content, and 1.5% PVA fiber volume mixing. The yield stress and plastic viscosity of CEAC were positively correlated with the build-up thickness, whereas the rebound rate and the latter showed a negative correlation. The spraying performance may be described by the rheological parameters; the ranges of yield stress and plastic viscosity of 2.37–3.95 Pa·s and 77.42–108.58 Pa, respectively, produced the best spray ability. After undergoing an equivalent number of freeze–thaw cycles, CEAC exhibited lower mass and strength loss rates compared to CS, thereby demonstrating superior frost resistance. In addition, the pore structure analysis showed that the difference in capillary and macropore contents was the main reason for the variability in frost resistance between CS and CEAC. Full article

The decks of steel–concrete composite bridges are constantly exposed to severe environmental conditions, which frequently give rise to significant issues, including cracks and holes. These problems occur due to the formation of blisters under the paving layer with waterproofing membranes. This paper aims to delve into the characteristics of blisters during their expansion and propagation stages. Additionally, it proposes a rating index and a simplified calculation formula to assess the interface propagation performance of bridge deck pavement. To achieve this, the research group developed a simulated blister test device and employed the digital image correlation (DIC) technique. The study investigated the impact of pavement structure, waterproofing layer, and air voids on blister propagation behavior. It was discovered that the pavement blister test encompassed two distinct stages: expansion and propagation. Furthermore, the SMA-13 asphalt mixture exhibited slightly superior resistance to blistering compared to AC-13. It was also observed that when the mixture void ratio is less than 3.5%, it becomes more susceptible to blistering deformation, ultimately leading to debonding damage. Among the waterproofing materials tested, SBS-modified emulsified asphalt demonstrated the weakest adhesion to cement concrete substrates, while SBS-modified asphalt performed slightly better than rubberized asphalt. Full article

Cold-mix asphalt is a greener alternative to pavement construction, processed at 10–40 °C, which is typically lower than other techniques like warm-mix asphalt and hot-mix asphalt. Huge amounts of construction and demolition waste, such as broken bricks, recycled concrete aggregates, reclaimed asphalt pavement, ceramic waste, etc., are generated every year due to the acceleration in infrastructure development. The production of such massive amounts causes landfilling issues, and their disposal is a serious issue nowadays. This study examines the effect of binary blended fillers on the performance of cold asphalt mixes using emulsified binders and 50% reclaimed asphalt pavement materials. Moreover, three types of binary blended fillers (BBFs), cement, fly ash, and Stabil Road, were used at different dosages. Overall, 500 samples were prepared for the mix design, and the optimum emulsion content was determined as 11% and 9% for the CM and 50R mixes, respectively, based on the Marshall stability peak value and volumetric properties such as voids in the mineral aggregates, total voids, and dry density. The moisture susceptibility of the recycled cold-mix asphalt (RCMA) mixture was evaluated using the tensile strength ratio. Cantabro abrasion loss was used to assess the cohesion resistance of the mixtures. The dynamic response of the mixes to the applied load was evaluated using the resilient modulus. The results of the present study reveal that using BBFs in the RCMA improved the inter-particle bonding and strength. Furthermore, BBF incorporation enhanced the performance of the recycled cold-mix asphalt. Full article

To improve the performance of shotcrete in high-altitude and low-temperature environments, emulsified asphalt shotcrete (EASC), which can be used in negative-temperature environments, was prepared by using low-freezing-point emulsified asphalt, calcium aluminate cement, and sodium pyrophosphate as modified materials. The effect of emulsified asphalt on the performance of shotcrete was investigated through concrete spraying and indoor tests. Then, the modification mechanism of emulsified asphalt with respect to EASC was analyzed by combining scanning electron microscopy images and the pore structure characteristics of EASC. The results showed that in a negative-temperature environment, the incorporation of emulsified asphalt delayed the formation of the peak of the cement hydration exotherm, slowed the rate of the cement hydration exotherm, reduced the thermal perturbation of permafrost by EASC, increased the cohesion of the concrete, improved the bond strength between EASC and permafrost, and reduced the rate of rebound. The mechanical strength of the studied EASC decreased upon increasing the amount of emulsified asphalt in the admixture, and its resistance to cracking gradually improved. A content of less than 5% emulsified asphalt could improve the internal pore structure of EASC, thus improving its durability. Increasing the content of emulsified asphalt affected the hydration process of the cement, and the volume content of the capillary pores and macropores increased, which reduced the durability of the EASC. Full article

The interfacial bonding capacity between cement emulsified asphalt composite binder (CEACB) and reclaimed asphalt pavement (RAP) plays a critical role in improving the pavement performance of cold recycled asphalt emulsion mixtures (CRAEMs). This study aims to investigate the formation and development of the interfacial bonding capacity between CEACB and RAP. First, the dynamic wettability and the spreading behaviors of CEACB on RAP surfaces were explored according to the surface free energy theory. Second, digital image processing (DIP) technology was employed to recognize interfacial failure patterns. Lastly, the influence of internal and external factors on the interfacial bonding capacity between CEACB and RAP during the curing process was analyzed via grey relational analysis (GRA). The results indicate that a moderate cement content with a mass ratio of asphalt to cement equivalent to 1.0 can significantly enhance the wettability of CEACB on RAP surfaces. By appropriately prolonging the curing time and controlling the curing temperature, it is possible to increase the bonding strength between CEACB and RAP. Additionally, a strong correlation exists between initial wettability and ultimate bonding capacity during the bonding strength curing process. The good wettability that developed in the initial stage of interfacial strength formation relates to the decreased spalling rate of CEACB on the RAP surface. This study is not only devoted to understanding the mechanisms that can enhance CRAEM performance but also provides important guidance for practical engineering applications of cold recycled asphalt pavements. Full article

Cement-emulsified asphalt (CEA) has been widely used in slab ballastless track and asphalt pavement cold recycling projects because of its high stiffness and toughness. In CEA material, emulsifiers and asphalt affect the cement’s hydration process and microstructure. Thus, to further investigate the effects of anionic emulsifiers (AEs) and anionic emulsified asphalt (AEA) with different demulsification rates on the hydration process and microstructure of cement, two types of AE (rapid-setting and slow-setting) and their corresponding AEA were used to prepare modified cement pastes. First, it was confirmed that the AEs and AEA delayed cement hydration by measuring the setting time, X-ray diffraction (XRD) patterns, and electrical resistivity of the cement paste. Then, the microstructure of the cement paste was determined with mercury intrusion porosimetry (MIP) and a scanning electron microscope (SEM), and it was found that AEs and AEA have varying degrees of inhibitory effects on the formation of the cement paste microstructure. Finally, based on the energy dispersive spectrometer (EDS) element content of the cement paste and Fourier transform infrared spectroscopy (FTIR) on the two AEs, the inhibition mechanism of AE and AEA with different demulsifier rates on the cement hydration process was analyzed. The experimental results showed that both AEs and AEA delayed the hydration process of cement to varying degrees and altered the microstructure of cement, and slow setting anionic emulsified asphalt (SAEA) had the greatest impact on the hydration process and microstructure of cement. Compared to pure cement paste, the initial setting time of cement paste mixed with SAEA was delayed by 73.9%, and the final setting time was delayed by 66.7%. After adding SAEA, the most probable aperture of the cement paste increased from 62.50 nm to 71.19 nm after one day of hydration. Due to the fact that there were more carboxyl groups with negative charges, more -COO⁻ was adsorbed onto the surface of cement particles in the slow-cracking anionic emulsifier (SAE); compared with the rapid-setting anionic emulsifier (RAE) and the rapid-setting anionic emulsified asphalt (RAEA), the SAE and the SAEA had a stronger delaying effect on the hydration reaction of cement. Full article

Semi-flexible pavement material (SFPM) combines the advantages and avoids the disadvantages of asphalt concrete flexible pavement and cement concrete rigid pavement. However, due to the problem of interfacial strength of composite materials, SFPM is prone to cracking diseases, which limits the further application of SFPM. Hence, it is necessary to optimize the composition design of SFPM and improve its road performance. In this study, the effects of cationic emulsified asphalt, silane coupling agent and styrene–butadiene latex on the improvement of SFPM performance were compared and analyzed. The influence of modifier dosage and preparation parameters on the road performance of SFPM was investigated by an orthogonal experimental design combined with principal component analysis (PCA). The best modifier and the corresponding preparation process were selected. On this basis, the mechanism of SFPM road performance improvement was further analyzed by scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) spectral analysis. The results show that adding modifiers can significantly enhance the road performance of SFPM. Compared to silane coupling agents and styrene–butadiene latex, cationic emulsified asphalt changes the internal structure of cement-based grouting material and increases the interfacial modulus of SFPM by 242%, allowing cationic emulsified asphalt-SFPM (C-SFPM) to exhibit better road performance. According to the results of the principal component analysis, C-SFPM has the best overall performance compared to other SFPMs. Therefore, cationic emulsified asphalt is the most effective modifier for SFPM. The optimal amount of cationic emulsified asphalt is 5%, and the best preparation process involves vibration at a frequency of 60 Hz for 10 min and 28 days of maintenance. The study provides a method and basis for improving the road performance of SFPM and a reference for designing the material composition of SFPM mixes. Full article