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The objective of this paper is to assess the impact of mineral grain size and grain size distribution of aggregates on the deterioration of pavement surface microtexture. For the study, aggregates were collected from nine different sources to cover a wide variation in mineralogical type. The grain size parameters were obtained by detecting mineral grain boundaries using scanning electron microscope electron back scattered diffraction (SEM EBSD) analysis on thin sections prepared from the aggregates. Scanning electron microscope (SEM) analysis was also carried out on thin sections of all aggregate types to determine their mineralogical composition. Microtexture deterioration was measured by collecting the British pendulum number (BPN) of the aggregate after every hour of polishing for six hours using an accelerated polishing machine. From the mineral composition analysis, it was observed that the aggregates in the study belonged to three rock types: granite, amphibolite, and basalt (three sources of each type). The BPN values of the polished stones indicated that aggregates with finer grains offer more resistance to polishing. Statistical analysis of the test results also suggests that a wide variation in grain sizes in aggregates positively contributes to resistance against polishing. The study confirmed that, for a given rock type, coarse aggregates with finer grains and greater variation in grain size can better withstand microtexture deterioration caused by mechanical polishing from vehicular loads when used in the surface course of pavements. [ABSTRACT FROM AUTHOR]

In this study, enzyme-induced carbonate precipitation (EICP) combined with xanthan gum curing technology was used to improve the engineering properties of standard sand, and the curing effect of EICP combined with different xanthan gum contents was studied by macroscopic tests such as unconfined compressive strength, direct shear, permeability, calcium carbonate content, and microscopic tests such as scanning electron microscope and nuclear magnetic resonance. The results show that the unconfined compressive strength, shear strength, cohesion and internal friction angle of EICP combined with xanthan gum solidified sand increases with the increase of xanthan gum content and reaches the maximum value at the content of 2%, in which the increase of unconfined compressive strength, shear strength, and cohesion is significant; further, the increase of internal friction angle is small. The permeability coefficient of EICP combined with xanthan gum solidified sand decreases with the increase of xanthan gum content, and the permeability coefficient of 2% xanthan gum is only 65.4% that of pure EICP treatment. The incorporation of xanthan gum promotes the deposition of calcium carbonate, increases the viscosity of the reaction solution, and produces colloidal encapsulation and bonding effect on the sand particles. In addition, the incorporation of xanthan gum effectively reduces the porosity of solidified sand and greatly reduces the proportion of large pores and medium pores by changing the pore size, which greatly improves the pore structure. [ABSTRACT FROM AUTHOR]

In this paper, fiber Bragg grating (FBG) sensors were applied to investigate the frost resistance of C60 concrete. First, the growth of both the static and dynamic elastic modulus of C60 concrete with curing age was investigated using an FBG, the standard method, and the resonance method, respectively. Second, to simulate the freezing and thawing conditions in cold regions, the concrete specimens were subjected to air freezing and water thawing using the slow freezing method. The authors explored the effect of freeze–thaw cycles on the mechanical properties of concrete and established a mathematical model relating its mechanical properties to freeze–thaw cycles based on an FBG sensor. Meanwhile, its compressive strength, dynamic elastic modulus, and mass loss rate were tested. Finally, the interface morphology and hydration products of concrete were observed using a scanning electron microscope (SEM) after freeze–thaw cycles. The results indicate that both the static and dynamic elastic modulus of C60 concrete increase with curing age. Its elastic modulus measured by FBG is approximately the same as that measured by the standard method, confirming the viability of using an FBG sensor to measure its elastic modulus. Furthermore, the authors highlighted the dependence of its compressive strength on the freeze–thaw cycles. The relationship of the static elastic modulus to freeze–thaw cycles is similar to that of the dynamic elastic modulus and mass loss rate. A static elastic modulus achieved from an FBG is proposed here to characterize the frost resistance of C60 concrete. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) is an environment-friendly cement often used for stabilizing soft soils because of its exceptional mechanical properties. In this study, the influence of curing temperature on the strength development of MOC-solidified clay is explored, considering different MgO/MgCl2 molar ratios. Different tests were carried out to study the corresponding effects. The results show that the effect of curing temperature on the strength of MOC-solidified clay differs greatly from that of cement-solidified soil. Increasing the curing temperature leads to strength reduction, whereas decreasing the curing temperature increases the corresponding strength. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses indicate that the variation in type and amount of hydration products of the solidified soil account for the strength development difference between MOC-solidified and cement-solidified soils. A model based on the experimental results is proposed to characterize the relationship between strength development and curing time. The strength influence factor (ηT) and the strength expedite factor (K) were introduced to demonstrate the relationship between strength development at a specific curing temperature as well as at room temperature. [ABSTRACT FROM AUTHOR]

In this study, enzyme-induced carbonate precipitation (EICP) combined with chitosan curing technology was used to improve the mechanical properties of standard sand, and the curing effect of EICP combined with different chitosan contents was studied by macroscopic tests, such as the unconfined compressive strength test, direct shear test, and calcium carbonate content test, and microscopic tests, such as scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The results show that compared with the pure EICP treatment, the unconfined compressive strength, shear strength, and calcium carbonate content of the sand treated by EICP combined with chitosan were significantly improved, and increased first and then decreased with the increase of chitosan content, reaching the maximum value when the content is 1.5%. The calcium carbonate content is positively correlated with the strength, indicating that calcium carbonate crystals can effectively play a role in filling and cementation. After the incorporation of chitosan, the shape of calcium carbonate crystals is still mainly spherical, but the number and volume become larger. At the same time, the incorporation of chitosan can greatly reduce the proportion of large pores and medium pores, significantly increasing the proportion of small pores, which greatly improves the pore structure. [ABSTRACT FROM AUTHOR]

The large temperature differences between day and night in winter at plateau areas can lead to the reduction of skid resistance of roads. However, most of the traditional salt storage and deicing fillers are chlorides, and their long-term usage will cause damage to the ecological environment. In order to achieve green deicing of asphalt pavement, this paper developed efficient and environmentally friendly salt storage fibers for the anti-icing of asphalt pavement, and the optimal components of salt storage fibers were determined. On this basis, the morphology and rust resistance of salt storage fibers were characterized, and the ice suppression and deicing performances were also determined. The experimental results show that the optimal component ratio of anti-icing reagent for sodium acetate, potassium acetate and sodium formate follows 7∶2∶1 and the optimal component ratio of organic salt and fiber is 3∶1 , which can achieve a better ice-melting effect and sustainable economy. According to the scanning electron microscope (SEM) images, the salts in the salt storage fiber are fully absorbed, which has a certain slow-release performance due to the resin package. In addition, the effective anti-icing components of the salt storage fiber are less corrosive to the metal materials, and the asphalt mixtures doped with salt storage fibers can melt ice at the rate of (1,022 g/ h·m2) under relatively low temperatures. This can effectively weaken the freeze-bond strengths and ice–road interface adhesion. [ABSTRACT FROM AUTHOR]

The accumulation of alkali residue has led to significant contamination of soil, air, and water, posing a hazardous threat to the environment. To address this issue, a technology and method for producing alkali residue–based lightweight soil were proposed to facilitate the reuse of alkali residue, and the feasibility of this method was demonstrated. Compression tests, X-ray diffraction, X-ray fluorescence spectrometry, and scanning electron microscope (SEM) were conducted to investigate the strength characteristics and hardening mechanism of the material. The results indicate that the compressive strength of the alkali residue–based lightweight soil increases linearly with wet density, age, content of portland cement, and ground granulated blast slag. The optimal water–solid ratio was determined to be 0.6. Specimens with low and high strength exhibited plastic and brittle failures, respectively. The primary contributors to the material's compressive strength were identified as hydrated calcium silicate, ettringite, monosulfur calcium sulfoaluminate hydrate, hydrated calcium aluminate, and Friedel's salt. The 28-d compressive strength of the alkali residue–based lightweight soil, with a water–solid ratio of 0.6 and a wet density of 800.0 kg/m3 , was measured to be 1.17 MPa, meeting the requirements for most filling projects. [ABSTRACT FROM AUTHOR]

Potholes are one of the common diseases of asphalt pavements. Cold patching asphalt mixtures (CPAM) are a common material for pothole repair. Reclaimed asphalt pavement (RAP) is a high-potential sustainable material that is commonly used in pavement construction. The aim of this study is to address the balance between performance improvement and cost reduction in CPAM. To achieve this objective, the CPAM was prepared with four different contents of cutback and 100% RAP (RAP-CPAM) and its performances were evaluated by laboratory tests. First, Fourier transform infrared spectroscopy (FTIR) test and scanning electron microscope (SEM) technique were used to analyze the diffusion mechanism between the cutback and the artificial aged binder. Then, the rationality of the cutback content was preliminary estimated by the mixing test and the draindown test. Finally, the adhesion performance, cohesion performance, strength, and resistance to water damage of RAP-CPAM were characterized through laboratory tests. From the FTIR test, the carbonyl index of aged asphalt layer decreased compared to that of the artificial aged binder as the storage time increased. Simultaneously, SEM imaging of the artificial aged binder showed less fractured surfaces after storage. The results of FTIR and SEM tests indicate that the cutback and the artificial aged binder were diffused. It was found that 1.6% content of cutback was slightly lower for RAP-CPAM, and 2.8% was not excessive. Boiling test results show that RAP-CPAM had good adhesion performance. Rolling screen test, Marshall stability test, and immersion Marshall test results reveal that RAP-CPAM had good cohesion performance, strength, and resistance to water damage. Based on the performance evaluation, the optimal content of cutback in RAP-CPAM was determined as about 2.4%–2.8%. In conclusion, the cutback and the RAP binder were successfully diffused, thereby ensuring good performances of RAP-CPAM. [ABSTRACT FROM AUTHOR]

Foamed phosphogypsum (FPG) has recently attracted extensive interest owing to its potential consumption of phosphogypsum and its substitution for traditional gypsum building materials. However, as an important component in the preparation of FPG, the effect of foaming agent on the performance of FPG is still unclear. Herein, Legao 3210 (LG), sodium alpha-olefin sulfonate (AOS), animal protein compound (APC), cocoamidopropyl hydroxy sulfobetaine (CHSB), and tea saponin (TS) were chosen as the foaming agents for FPG. The foam stability and foam structure were studied, and the results showed that the foams produced by TS and APC were more stable. The effects of different foaming agents on FPG's fluidity, density, strength, water absorption, and thermal conductivity were also studied. The results showed that FPG prepared with TS exhibited the highest compressive strength, measuring up to 1.34 MPa, which represented a 97% increase compared with that of APC. Moreover, the dry density and thermal conductivity of FPG prepared with TS were 517 kg/m3 and 0.109 W/(m·K). The digital microscope analysis indicated that the keys to the simultaneous realization of high strength and light weight in the FPG were uniform pore size distribution, small pore size, and thicker pore gaps. Furthermore, through scanning electron microscope (SEM) analysis, it was suggested that the formation of strong interlocking structure by hydration products was the microstructural mechanism for improving the strength of FPG. This study suggested that FPG has the possibility to compete with traditional gypsum materials and it is also expected to solve the problem of phosphogypsum utilization. [ABSTRACT FROM AUTHOR]

Sisal fibers (SF) and polycarboxylate superplasticizers (PCE) contribute to the sustainable development of cementitious materials by improving and optimizing their hardening properties. In this study, the impact of SF and PCE on the workability of cement pastes was investigated. The workability was evaluated through spreading diameter, yield stress, and plastic viscosity measurements, and the adsorption behavior of PCE was analyzed. The results showed that the introduction of SF had a negative effect on the workability of PCE plasticized cement pastes, reducing flowability and increasing yield stress and plastic viscosity, regardless of aspect ratio or dosage. A contact angle tester and a scanning electron microscope (SEM) were employed to examine the surface properties of SF. The mechanism behind this interaction of cement-PCE-SF was explored and found to be due to the rough surface of SF, which increased the consumption of PCE, and the formation of hydrogen bonds between PCE and SF. Additionally, PCE modified the interfacial structure between SF and the cement matrix, strengthening the relationship between the different phases. These findings provide new insights into the modification of fiber-reinforced cementitious materials. This paper presents a comprehensive study on the workability and rheology behavior of cementitious material that coupled PCE superplasticizer and SF. The interaction between PCE and SF was experimentally studied by suitable tests, and the results and mechanism behind were well explained. The fresh properties were evaluated through a mini slump test, rheological properties, and the adsorption behavior of PCE on the surface of cement and SF was analyzed. The results showed that the introduction of SF decreases the spread diameter and increases the yield stress and plastic viscosity, regardless of aspect ratio and dosage, which indicate that a negative effect on the workability of PCE plasticized cement pastes. The mechanism behind the cement-PCE-SF interaction was explored in depth by the surface properties of SF, which revealed that the rough surface of SF increased the consumption of PCE. In addition, the formation of hydrogen bonds between PCE and SF provides an additional explanation. The significance of this study provides valuable guidance in using fibers and PCE together in cementitious materials. [ABSTRACT FROM AUTHOR]

The direct action of salt on asphalt materials has received limited research despite the abundance of studies on salt erosion and its effects on the moisture stability of asphalt concrete. This study aimed to investigate the effects of chloride salt on the rheology of asphalt and erosion mechanisms. Microscopic properties of asphalt mortar were analyzed through scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), and the erosion degree of salt in asphalt mortar was evaluated based on three major indexes. Rheological properties of asphalt mortar were determined through temperature sweep and multiple stress creep and recovery (MSCR) tests, while the modified water-boiling test was conducted to evaluate the adhesion of asphalt mortar. Results showed that as salinity increases, the agglomerate phenomenon tends to occur in asphalt mortar, leading to physical aging effects on its basic properties. Meanwhile, chloride salt modified asphalt concrete is prone to cracking at low temperatures and has reduced durability at high temperatures, making it unsuitable for standard load or heavy traffic pavement requirements of PG64 modified asphalt. Furthermore, the presence of chloride in asphalt mortar was not conducive to its adhesion. [ABSTRACT FROM AUTHOR]

The search for alternatives to filler used in asphalt pavement has been focused on recently due to the lack of traditional materials sources and the aim of sustainable development goals. Novel environmental protection material—alkali-activated slag (AAS) with a prospective substitution for cementitious binder—has been developed widely; however, the possibility of application of AAS in practice is still under investigation, and hence, mass production of AAS for the testing phase generates significant quantities of solid laboratory waste materials. This study paved the way for safe disposal and evaluating the potential of utilizing AAS as filler in asphalt concrete mixes. To understand the influence of filler types on the performance of asphalt concrete, the physical and chemical properties of AAS filler were analyzed and compared to the conventional limestone (LS) filler by applying laser particle size analysis, scanning electron microscope (SEM), x-ray diffraction (XRD) analysis, and x-ray fluorescence (XRF) spectrometry. The monotonic indirect tensile test (IDT) was adopted to characterize the behavior of asphalt mixes over a range of performances at low, intermediate, and high temperatures; additionally, to practice the balanced mix design (BMD) into quality assurance (QA) of asphalt mixes. Testing methods involving monotonic IDT used in this study are indirect tensile strength (ITS), indirect tensile asphalt cracking test (IDEAL-CT), toughness index (TI) and fatigue index (fi), low-temperature IDT, high-temperature indirect tension (HT-IDT), and moisture susceptibility test. The results indicated that asphalt concrete using AAS filler delivers superior engineering performance, such as resistance to cracking, rutting, and moisture damage, compared to the one made with LS filler. This supports the use of AAS filler as a potential substitution for LS filler in the production of asphalt concrete. Besides, the practice of BMD by implementing monotonic IDT for QA of asphalt mixes showed high feasibility. [ABSTRACT FROM AUTHOR]

The twenty-first century is known as the "century of the ocean." Artificial reefs have been extensively studied and used worldwide as the main infrastructure of marine pastures. At present, research has been primarily focused on developing new environmentally friendly artificial reef construction materials with low emissions, low alkalinity, low cost, and great durability. As a novel low-carbon and environmentally friendly construction material, geopolymer presents considerable potential for building artificial reefs. By changing the alkali-activator dosage, this investigation prepared fly ash geopolymer concrete (FGC) with different strength grades. FGC's mechanics, durability, and marine environmental compatibility were systematically studied as a marine artificial reef construction material. The effect of curing temperature on the performance of FGC was also investigated. Results indicated that the design grade of FGC against sulfate erosion can reach above KS150, and the maximum electric flux of the experimental group is 300.76 C. Moreover, FGC has good compatibility with marine environments. High-temperature maintenance can significantly improve each performance of FGC. Microstructural analysis was performed through a scanning electron microscope secondary electron (SEM-SE), SEM backscattered electrons (SEM-BSE), energy-dispersive X-ray spectroscopy (EDS), and a mercury intrusion porosimeter (MIP). Results showed that the FGC matrix porosity decreases with the increase of alkali-activator dosage, which causes denser pore structures. In addition, the active calcium-containing components in the calcareous aggregate will participate in the geopolymer reaction and generate calcium-rich gel in the interfacial transition zone (ITZ), thus enhancing the mechanical and durability of the material. In conclusion, as a low-carbon construction material, FGC has a broad application prospect in marine artificial reef construction. [ABSTRACT FROM AUTHOR]

Fiber-reinforced emulsified asphalt (FEA) is widely used in asphalt pavement structures as a stress-absorption layer. This study aimed at developing a multifunctional fiber-reinforced emulsified asphalt (MFEA) by empowering the FEA with the self-sensing ability. To achieve this purpose, carbon nanotubes (CNTs) were grafted onto the basalt fibers in the FEA. An optical microscope and scanning electron microscope (SEM) were respectively used to investigate the distribution of CNTs onto the fibers and the microstructure of CNT/fiber composite (CFC). The fabrication process of CFC was optimized based on the distribution homogeneity of the CNTs. The self-sensing ability of the MFEA was then evaluated in the laboratory using an electrochemical workstation. Based on the experimental and analytical results, 1.5 mg/mL was recommended as the optimal dosage of the suspension of CNTs for grafting CNTs onto the fiber. The electrical resistance of the developed MFEA was found to be isotropic and sensitive to the demulsification state, EA/CFC mass ratio, temperature, loading speed, and deformation magnitude, which confirms the potential of using developed MFEA as a self-sensing layer to monitor its response to environmental and traffic variation. Besides, the direct tension and pull-out tests indicate the positive influence of grafting CNTs onto basalt fibers on the mechanical performance of FEA. [ABSTRACT FROM AUTHOR]

As a high-performance composite material, polyvinyl alcohol (PVA) fiber-reinforced engineered cementitious composites (PVA-ECCs) are often used in sub-elevated temperature environments (< 200°C) for long-term service. However, the effect of exposure time in sub-elevated temperature on the performance of PVA-ECCs is not still clear. In this study, the properties of PVA-ECCs in sub-elevated temperature environments were examined, with emphasis on the effect of exposure time (1, 3, 6, and 9 h). Furthermore, the microstructure and tensile behavior of single PVA fibers exposed to a sub-elevated temperature environment was investigated. Results showed that PVA-ECCs have enhanced tensile ductility at different sub-elevated temperature exposure times below 100°C. However, the tensile properties of PVA-ECCs at 150°C showed a strain retraction phenomenon at 6 and 9 h. The strain-hardening characteristics of PVA-ECCs gradually disappeared with the increase of the sub-elevated temperature exposure time at 200°C. The results of thermogravimetric-differential scanning calorimetry (TG-DSC), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscope (SEM) revealed that the degradation of PVA fibers was accelerated by exposure time in sub-elevated temperature, which caused the reduction of mechanical properties of PVA-ECCs. [ABSTRACT FROM AUTHOR]

In an effort to tackle the issues of carbon dioxide (CO2) emissions from the cement industry and land pollution caused by the disposal of construction waste, this study aimed to investigate the potential of fly ash-ground granulated blast-furnace slag (GGBS)–based geopolymer concrete (FG-GPC) and demolition waste fine aggregate (DWF) as environmentally sustainable alternatives to conventional cement concrete and natural fine aggregate, respectively. The experimental procedure included optimizing the FG-GPC variables (Na2SiO3/NaOH and NaOH molarity) and investigating the properties of FG-GPC with the addition of DWF in various proportions (0%, 25%, 50%, 75%, and 100% by volume). To investigate the mechanical and physical parameters of FG-GPC with DWF, compressive strength, split tensile strength, flexural strength, elastic modulus, water absorption, density, effective porosity and ultrasonic pulse velocity were determined. The microstructural properties of FG-GPC were studied using scanning electron microscope (SEM) tests on selected samples. The experimental findings indicated that the strength and physical properties of FG-GPC were progressively diminished when adding DWF to the mix. Nonetheless, FG-GPC with 25%–50% DWF replacement showed a lower drop in concrete properties, indicating that employing construction and demolition (C&D) waste as a fine aggregate might have environmental and economic advantages. [ABSTRACT FROM AUTHOR]