Journal of Materials in Civil Engineering

US waste-to-energy (WTE) plants generate about 7 million tons of fly ash and bottom ash annually, mixed to combined ash (CA), which, after metal recycling, is disposed of in landfills. Fine-combined ash (FCA), the sandy fraction ($<2\mathrm{mm}$) of CA after water washing, crushing, and size separation, amounts to about 25% of total CA. This study examines two uses of FCA in cement mortar based on tests of mechanical properties, workability, mineral transformation, and leachability of heavy metals: (1) directly using FCA as a sand substitute by up to 50% by volume (37% by weight); and (2) milling the FCA to powder (MFCA) and using it as a cement substitute by up to 25% by volume (24% by weight) substitution of portland cement. When FCA was used as a sand substitute, water was added during mixing to improve workability and increase the FCA replacement. When MFCA was used as a cement substitute, it chemically reacted with the hydration system and contributed to the formation of more amorphous phases. The calcite in MFCA reacted with hydrated cement and transformed into hemicarboaluminate and monocarboaluminate. Metallic aluminum in the ash can cause hydrogen gas expansion during cement hydration, which limited the substitution level of FCA or MFCA in cement mortars to 50% and 25% by volume, respectively. The study showed that all FCA or MFCA cement mortars were effectively stabilized/solidified and transformed into nonhazardous materials.

This study investigates the change in the acoustic emission (AE) parameters emitted in rubberized concrete under abrasion action at a sub-freezing temperature ($-20°\mathrm{C}$). Seven concrete mixtures were developed with two coarse-to-fine aggregate ratios (C/F) (2.0 and 0.7), various crumb rubber (CR) content (0%, 10%, 20%, and 30%), and different rubber particle sizes [4.5 mm CR and 0.4 mm powder rubber (PR)]. Rotating cutter tests were conducted on three 100 mm cubic samples from each mixture at $-20°\mathrm{C}$ and 25°C while monitored via an AE system. AE parameters such as amplitude, number of hits, and signal strength were collected and underwent two parameter-based analyses: $b$-value and intensity analysis approaches, resulting in three additional parameters: $b$-value, severity ($S_r$), and the historic index [$H(t)$]. Results showed that testing concrete samples under abrasion at cold temperature,$-20°\mathrm{C}$, resulted in a decrease in the emitted number of hits, cumulative signal strength (CSS), $S_r$, $H(t)$, and an increase in $b$-values compared to testing at 25°C. Furthermore, incorporating rubber particles was found to decrease the AE signals’ amplitudes significantly at 25°C and slightly at $-20°\mathrm{C}$, which manifested the higher wave attenuation occurrence at ambient temperature compared to cold temperature. AE analysis also showed a decrease in the abrasion resistance for mixtures with higher C/F, higher CR content, and larger rubber particle size. These decreases were more noticeable at 25°C compared to $-20°\mathrm{C}$. Finally, the study developed two damage classification charts to estimate the ranges of abrasion mass loss percentage and wear depth in terms of the intensity analysis parameters: $S_r$ and $H(t)$.

This work used electrical resistivity over the first 72 h of hydration to measure the impact of air, sealed, and wet curing on mortar samples at different depths. The resistivity measurements provide new insights that are not easily obtained with other techniques and provide direct insights into the moisture change. The resistivity correlates with the porosity, degree of saturation (DOS), and a novel splitting test. This work also provides important insights into how curing impacts the porosity, DOS, and strength of mortar samples at different depths. This work is the basis for future real-time sensing techniques with resistivity.

Abstract

Elastic creep theory is used herein to investigate the characteristics of the loading and unloading creep of hydraulic concrete in water. First, tensile and compressive loading and unloading creep tests were designed for hydraulic concrete of different loading ages (14, 28, and 60 days), and the tests were executed in water under unified test conditions. The complete experimental data acquired for creep were then used for comparison and analysis. Next, the whale optimization algorithm was applied to optimize and identify an eight-parameter specific creep model for concrete under tensile and compressive stress. Additionally, the superposition principle was used to predict the specific tensile and compressive creep recovery of concrete in water after unloading. The results reveal that the specific tensile creep of hydraulic concrete in water exceeds the specific compressive creep of hydraulic concrete in water, and that the ratio of specific tensile creep to specific compressive creep is 1.92–3.82 when loading is held for 30 days. Furthermore, the eight-parameter specific creep-prediction model well reflects the temporal evolution of the tensile creep and of the compressive creep of hydraulic concrete in water. When the superposition principle is used to analyze the elastic aftereffect following unloading, the research results reveal that the specific tensile creep is superposed during unloading for the specific tensile creep, whereas the specific compressive creep is superposed during unloading for the specific compressive creep. Under these circumstances, the predicted specific creep recovery is consistent with the measured results and the mean absolute percentage error was 2.99%–17.75%.

Practical Applications

Thousands of concrete dams have been built around the world to control and divert natural surface water and groundwater. The upstream faces of these dams are long-term affected by water and are subjected to loads such as self-weight and hydrostatic pressure, which produce two important phenomena: wet expansion and creep. When water seeps into the concrete through microscopic pores, the concrete undergoes wet expansion, which modifies the strain state of the concrete. Under a sustained load, the concrete structure deforms and gradually creeps over time. To describe the creep of concrete, numerous creep tests under nonsubmerged conditions have been conducted. However, few reports discussed the wet expansion of concrete under submerged conditions, especially as concerns loaded and unloaded creep tests in water, which provides information on both wet expansion and creep. Therefore, this investigation uses creep tests to determine the physics of concrete under loading and unloading in water. The results reveal that the specific tensile creep of concrete in water exceeds the specific compressive creep of concrete in water. The use of the superposition principle to analyze the elastic aftereffect following unloading reveals some new physical mechanisms. These mechanisms are useful to investigate the real strain state of concrete dams.

The salt erosion environment will lead to the deterioration of asphalt pavement performance and seriously restrict the service life and sustainability of asphalt pavement. In this research, the evolution mechanism of asphalt performance induced by chloride salt erosion was explored by atomic force microscopy (AFM) and molecular dynamics (MD) simulation from the nanoscale. The AFM test results demonstrated that with increasing chloride salt concentration and erosion time, the adhesion force, adhesion energy, surface free energy, and dissipated energy of asphalt binder decreased significantly. The fitted modulus of the four contact mechanics models all decrease with increasing chloride erosion time. It is recommended to use the Cone Sphere or Johnson-Kendall-Roberts (JKR) model to fit the Young’s modulus of asphalt binder. The MD simulation results show that the tensile strength and shear strength of asphalt binder in the three directions decreased after chloride salt erosion, and there are differences in the magnitude of reduction in different directions. Chloride salt erosion not only inhibits the translational migration behavior of SARA fractions [saturates (S), aromatics (A), resin (R), and asphaltenes (A)] but also limits the rotational migration behavior. Although chloride salt erosion has little effect on the aggregation behavior of asphaltene, it still affects the degree of molecular entanglement of SARA fractions. The distribution of asphalt molecules becomes heterogeneous after chloride salt erosion. This research not only presents the erosion damage mechanisms of the asphalt binder but also helps to promote the sustainability of the asphalt pavements exposed to a chloride salt environment.

The effects of the exposure to elevated temperatures on the mechanical performances of a PBO FRCM (fabric reinforced cementitious matrix) composite system, consisting of polypara-phenylene-benzo-bisthiazole (PBO) fiber meshes embedded into an inorganic mortar, widely used in the strengthening of existing degraded reinforced concrete structures, are analyzed and discussed in the paper. The residual tensile properties of PBO FRCM composites and the residual bond properties of PBO FRCM-to-concrete are analyzed through the results of an experimental investigation conducted on specimens subjected to heating-cooling regimes at temperatures ranging from 20°C to 300°C, and then tested at ambient temperature (20°C). Direct tensile (DT) tests on PBO FRCM coupons and direct single lap shear (DS) tests on PBO FRCM-concrete elements were performed. The parameter varied was the target temperature value, namely 20°C, 100°C, 200°C, and 300°C. Test results are reported in terms of cracking stress, tensile strength, ultimate tensile strain, uncracked and cracked elasticity moduli, failure mode, bond strength, and corresponding slip values. The obtained results are evidence that the effects of exposure at the target temperatures were different for each mechanical parameter. Significant reductions of the values measured at ambient temperature were observed only at 300°C. Temperature-dependent relationships for both tensile and bond mechanical parameters, useful for thermo-mechanical simulations and fire design of reinforced concrete structures strengthened with PBO FRCM composites, are also defined. Finally, the results of a comparative analysis between the experimental results described in the present paper and those available in the literature are reported and discussed.

Bituminous mixtures with low nominal maximum aggregate size, NMAS, have appreciable acoustic performance. Their surface texture is crucial to balance acoustic- and safety-related requirements. Unfortunately, there is a lack of models to predict surface texture and consequently, the main objective of this study is to analyze the impact of the composition and production of low-NMAS mixtures on their macrotexture. Based on the hexagonal packing model, a model for mean texture depth (MTD) was set up, calibrated and validated. To this end, low-NMAS mixtures were produced and tested. Results show that MTD variance can be explained through air void content, AV, and NMAS but their explanatory effectiveness depends on NMAS and AV range. Analyses involved different ranges of AV and NMAS. Results demonstrate that AV explains more than 70% of MTD variance, while AV and NMAS can explain up to about 90% of MTD variance. Nonlinearities and subdomains of AV and NMAS were addressed.

In order to study the relationship between the compressive strength and pore structure of carbonized concrete, normal concrete (NC), basalt-polypropylene hybrid fiber-reinforced concrete (BPC), and steel-polypropylene hybrid fiber-reinforced concrete (SPC) were prepared. The compressive strength and pore structure of concrete with carbonation ages of 0, 7, 14, 28, and 56 days were tested, and the empirical formulas of total air content–compressive strength were obtained. The results show that the compressive strength can be well predicted from the total air content of concrete through all the empirical formulas of linear, logarithmic, exponential, and power functions. The formulas of air content in specific pore size range and compressive strength of concrete were obtained. The air content of both small and medium pores has a strong negative linear correlation with compressive strength. The applicability of the two formulas is good. Most of the theoretical and measured values deviate within $\pm 15\%$. The air content–compressive strength model based on specific pore size range is more accurate than the total air content–compressive strength model. By summarizing a large number of literature data and analyzing the measured data, this study obtained widely applicable compressive strength–air content relationship formulas, which is of great significance to the compressive strength prediction of normal concrete and hybrid fiber-reinforced concrete.

Experimental investigations are presented on the effect of fiber dosage in a high strength cementitious composite (HSCC) with superelastic fibers with an L-shape at both ends. Superelasticity is one of the smart properties of shape memory alloys, and another property is shape memory effect. Out of the superelasticity and shape memory effect, only superelasticity is exploited in this present application. The rheological properties of the fresh composite system are investigated first using the slump flow table test. The slump test shows that although the fibers with L-shaped ends adversely affect the rheological properties of fresh concrete, the consistency of the mix is hardly compromised. The three-point bending test is conducted thereafter to assess the flexural performance of several beam specimens in the hardened state. The results from the three-point bending test are employed to quantify the influence (of fiber dosage) on the post-peak behavior using alternative protocols for the quantifying measures. The increase in fiber content generally increases flexural toughness. However, a fiber content beyond 0.75% in volume is required to achieve post-peak hardening. Alternative standards for evaluating flexural toughness are assessed in reference to the post-peak behavior of the composite system under flexure. The recentering capability using the cyclic three-point bending test is also calculated. Finally, the failure modes of the fiber are assessed to show the combined effect of the anchorage offered by the L-shape of the fibers and the interfacial bond strength. It is observed that the anchorage of HSCC is sufficient to hold the fibers until rupture. The failure modes of the fibers are noted to be irrespective of the fiber content yet sensitive to the orientation and length of embedment.

To mitigate issues pertaining to reinforced concrete damage under the action of various strong corrosive ions in saline soil areas, the corrosion characteristics of reinforced concrete are investigated via electrochemical tests [performed based on electrochemical impedance spectroscopy (EIS) and polarization curves] and chloride ion concentration tests, as well as based on the degree of concrete damage. The morphology and microstructure of the reinforced concrete are characterized via field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Two deterioration indices, i.e., the reinforcement corrosion current and concrete damage degree, are selected to establish a deterioration model of reinforced concrete based on the Weibull distribution function and to conduct a competitive failure analysis. The results show that the degree of deterioration of reinforced concrete increases nonlinearly with time. A surface crack was first observed in a specimen with 3.0% mass loss rate (MLR). The surface crack of the specimen and the corrosion depth of the internal steel bars expanded from 0.02 to 0.27 mm and from 55 to $130\mathrm{\mu m}$, respectively, when the MLR increased from 3.0% to 4.5%. Based on the results, the corrosion current density and concrete damage degree can be used as effective indices for evaluating deterioration in reinforced concrete, and the changes with time in saline soil environment are in accordance with the Weibull distribution function.

With the variety of supplementary cementitious materials (SCMs) available, there have been fundamental questions regarding how they influence the hydration development of ultrahigh-performance concrete (UHPC), especially at early age. To provide a holistic perspective and side-by-side comparisons, the current study explored the partial replacement of cement with silica fume, natural zeolite, and limestone, which represented artificial pozzolans, natural pozzolans, and non-pozzolanic SCMs, respectively. To evaluate the most critical micro- and macro-scale properties of UHPC, the experimental investigations included temperature and free water measurements, further to thermogravimetric analyses (TGA) performed to determine the amount of physically and chemically bound water in the developed mixtures. Moreover, the X-ray diffractometry (XRD) method was employed to obtain the XRD patterns, which were then paired with the TGA results to quantify the crystalline phases of the UHPC mixtures using the Rietveld refinement method. With a detailed assessment of the UHPC’s degree of hydration over time, the outcome of this study shed light on how various SCMs are capable of reducing the heat of hydration, while enhancing the degree of hydration of cement particles.

Abstract

This paper explored the relationship between microstructure characteristics and macroscopic properties of asphalt under different concentrations of snowmelt agent. Using penetration tests, ductility tests, softening point tests, dynamic shear rheological tests, infrared spectrum tests, and multistress creep recovery tests, the variation law of the microstructure characteristics and macroscopic properties of asphalt under the action of different concentrations of snowmelt agent was determined. Using grey correlation theory, the correlation between different concentrations of snowmelt agent and the macroscopic performance of asphalt was determined, and the correlation between the microstructure index and the macroscopic performance index of asphalt after different concentrations of snowmelt agent was determined. The results show that the penetration and softening point of asphalt increased under the action of different concentrations and snowmelt agent types. The ductility and the 135°C and 180°C Brinell viscosity decreased; the sulfoxide index, butadiene index, and loss modulus increased; and the phase angle decreased to varying degrees compared with the control asphalt. The relationship model of microstructure and macroscopic performance indicates that the concentration of snowmelt agent has a good correlation with the macroscopic mechanical indexes of asphalt, among which the correlation with penetration was the best, and the correlation with 180°C Brinell viscosity was poor. The $\mathrm{S}=\mathrm{O}$ index and $\mathrm{C}=\mathrm{C}$ index of asphalt had a good correlation with the macroscopic mechanical properties of asphalt, among which the correlation with penetration, softening point and ductility was good, and the correlation with $\tan \delta$ and $G^{*}/\sin \delta$ was poor. The experimental analysis showed that different concentrations of chloride snowmelt agents and mixed snowmelt agents had a great influence on the macroperformance of asphalt, whereas nonchloride snowmelt agents had little influence on the macroperformance of asphalt. When the concentration of nonchloride snowmelt agent was 10%, the decline of macroperformance of asphalt was relatively small. The grey correlation analysis indicated that under the action of different concentrations and different types of snowmelt agents, there is a correlation between the microstructure and macroscopic performance of asphalt. When the concentration of nonchloride snowmelt agent was 10%, the macroscopic performance of asphalt decreased the least. The $\mathrm{S}=\mathrm{O}$ index had the best correlation with the penetration of asphalt, and the $\mathrm{C}=\mathrm{C}$ index had the best correlation with the softening point of asphalt.

Practical Applications

This paper mainly explores the correlation between the microstructure and macroscopic properties of asphalt under the action of different concentrations and different types of snow melting agents. The research in this paper further clarified the influence of different types of snow melting agents on asphalt materials. According to the research conclusions of this paper, it is recommended to use nonchlorine salt snow melting agents when spreading snow melting agents on snowy pavement.

Waste tire pyrolysis has the advantages of economy, environmental protection, and high energy conversion rate; however, there is little research on the application of pyrolysis carbon black (PCB), which accounts for a high percentage of pyrolysis products, in asphalt and asphalt mixtures. The objectives of this study were to investigate the effect of PCB ash on the physical properties of asphalt binders, the effect of coupling treatment on the dispersibility of PCB-modified asphalt, and the effect of mixing process on the road properties of PCB asphalt mixtures. The physical properties of co-pyrolytic carbon black (CPCB) and low-temperature vacuum pyrolytic carbon black (VPCB) blended with 70# base asphalt and styrene-butadiene-styrene (SBS)–modified asphalt (SBSMA) were evaluated. Mechanisms behind the differences in the dispersion of CPCB in asphalt were revealed. In addition, the road performance of different PCB asphalt mixtures was compared. The results indicate that the optimum admixtures of VPCB and CPCB in 70# base asphalt are recommended to be 20% and 10%–15%, respectively, and the optimum admixtures of VPCB and CPCB in SBSMA are 10%–25% and 10%–20%, respectively. Acid washing reduces the ash content of the CPCB surface, and coupling agent can promote the dispersion of CPCB in asphalt. The wet-prepared CPCB-modified asphalt mixtures showed overall better road performance than the dry-prepared ones. Dry CPCB asphalt mixtures with 50% cement instead of equal mass of mineral powder have the potential to replace the wet process.

Low exothermic polyurethane grouting material, as a new type of material, is used for road reinforcement and repair engineering in frozen earth areas. This study investigates the mechanical properties of this grouting material under different ambient temperatures. The effects of temperature and density on the expansion pressure, compressive strength, and tensile strength of the materials were determined in this study. The characteristics of the material’s stress–strain curves were analyzed microscopically. The results demonstrate that temperature significantly influenced the material properties. The expansion properties of the material decreased with decreasing temperature. In contrast, the tensile and compression properties of the material increased with decreasing temperature, which is shown in the tensile and compressive strengths. From the view of failure mode, lower temperature makes the material more brittle. Moreover, the constitutive model based on the temperature variation was established according to the experimental results. This provides a basis for a simple evaluation of the compressive strength and elastic modulus of materials. Finally, the mechanical response of road cavitation in cold areas before and after repair was analyzed through finite-element numerical simulation and full-scale model test. The low exothermic polyurethane grouting material effectively reduced the vertical deformation of the wheel load in the distressed area. This study provides a reference for road reinforcement and repair projects in cold regions.

When a material is subjected to cyclic loading, there are changes in the material’s geomechanical behavior that need to be known and characterized for a safe design. To this end, a series of unconfined compressive strength (UCS) tests was performed, with and without the application of cyclic loading, to study the effect of the number of loading cycles on the behavior of a soft soil stabilized with different binder contents, unreinforced and reinforced with polypropylene fibers. The results were analyzed in terms of the evolution of elastic and plastic deformation energy, and it was observed that plastic energy prevailed in the first cycles, but decreased with the increase in the number of loading cycles. The accumulated plastic deformation occurring during the cyclic loading induced a strain-hardening effect that was responsible for the increase in the undrained resilient modulus and in the postcyclic unconfined compressive strength, regardless of the binder content and fiber reinforcement. The addition of polypropylene fibers led to a reduction in the elastic deformation energy, which was more noticeable in the first cycles, leading to an increase in the accumulated plastic axial strains and to a reduction in the undrained resilient modulus during the cyclic loading. These facts are explained by the high compressibility of the fibers and by the weakening of the stabilized matrix as a result of the physical presence of the fibers which may prevent the development of some cementitious bonds. However, the addition of fibers led to an increase in the energy absorption capacity, explained by the fact that the deformations occurring during the cyclic loading allow an earlier mobilization of the fibers as the UCS test proceeds.

In this research, nano-${\mathrm{TiO}}_2$ and graphene composite were added to asphalt to enhance the performance of asphalt by synergistically improving the dispersion of each other. The physical properties of the modified asphalt were assessed using penetration, softening point, and ductility tests, and the rheological performance of the asphalt was studied using dynamic shear rheometric (DSR) and bending beam rheometric (BBR) tests. In addition, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and nanoparticle size analyzer (DLS) were used for microscopic analysis of asphalt. The results demonstrated that the incorporation of nano-${\mathrm{TiO}}_2$ and graphene in asphalt could improve the high-temperature properties and the aging resistance of base asphalt. In terms of low temperature performance, the composite of nano-${\mathrm{TiO}}_2$ with graphene improves the negative effects of the single addition of nano-${\mathrm{TiO}}_2$ or graphene. Microscopic analysis indicated that the dispersion of the nano-${\mathrm{TiO}}_2$ and graphene in the asphalt synergistically was improved significantly. The optimum amount of 1% nano-${\mathrm{TiO}}_2$ and 0.04% graphene is recommended for the composite. This study provides a basis for the diversified application and development of nanomaterial modified asphalt in the future.

Marl soils with different carbonate contents usually show more unpredictable behavior than other problematic soils. In some marl soil groups, freezing–thawing (F-T) cycles can result in slaking and detrimental effects on the soil mechanical properties. However, up to now, studies on the performance of stabilized marl with alkali-activated materials under F-T cycles have been noticed to be quite limited. Moreover, the filled pores in the marl layered matrix and cementing materials bonded particles during the formation mechanism have not been clearly explored yet. This study investigated the improvement of slaking marl soil with a geopolymer based on recycled glass powder (RGP) activated with sodium hydroxide (NaOH) for complete replacement of industrial cement. The study evaluated the effects of the changes of the curing times (7, 28, and 90 days), RGP content (5%, 10%, and 15%), alkali concentration (2, 4, and 6M), curing temperatures as close to research conditions as possible (20°C and 50°C), volumetric strain, and 12 cycles of F-T for the unconfined compression strength (UCS) and consolidation test results. The control sets, comprising natural and cement-stabilized samples, were prepared and examined to provide a reference baseline. The mineralogical and microstructural characteristics were determined through X-ray diffractometer (XRD) and scanning electron microscopy (SEM) techniques. The results revealed that the cyclic F-T actions damaged the bonding between marl layers and made an irreversible structure with a lower UCS value. The results indicated that after conducting F-T cycles, the UCS of stabilized samples (15% RGP content, 2 M NaOH, 90 days curing) diminished from 3,667 to 2,668 kPa (27% reduction) after 12 F-T cycles. The one-dimensional consolidation test results confirmed a considerable reduction (92% for 90-day cured samples) in the settlement.

Massive infrastructure constructions have resulted in scarcity of river sand resources. Previous studies and applications proved dune sand can partially replace river sand used in engineering to alleviate the supply and demand contradiction of river sand. However, due to the dune sand is finer, rounder and smoother than river sand, determining the appropriate proportion of dune sand for designing engineered dune sand concrete (DSC) remains challenging. To tackle this challenge, a mix design method for DSC was proposed via close packing model and mortar film thickness theory. Specifically, the close packing model was used to confirm dune sand content and sand ratio, then the dune sand and river sand were mixed to obtain engineering-standard mixed sand. The mortar film thickness theory was utilized to determine the mortar volume and to tailor the concrete slump. By proper design, the DSC achieved the 28-d compressive strengths of 50 MPa along with good workability. Increasing the thickness of the mortar film from 0.3 to 0.9 mm leads to significant changes in DSC performance. For per 0.1 mm increase in thickness, there is an average change of 14.25 mm in slump, $11.35\mathrm{kg}/{\mathrm{m}}^3$ in dry density, 0.90 MPa in compressive strength at 28 d, $15.06\mathrm{kg}/{\mathrm{m}}^3$ in ${\mathrm{CO}}_2$ emission, $85.3\mathrm{MJ}/{\mathrm{m}}^3$ in energy consumption, and $1.2\mathrm{USD}/{\mathrm{m}}^3$ in cost. The designed DSC achieved a relatively low cement intensity (CI) value of $6.23\mathrm{kg}/{\mathrm{m}}^3/\mathrm{MPa}$, implying that DSC exhibits good eco-efficiency. Therefore, the proposed hybrid design approach can guide the design of engineered DSCs with excellent mechanical properties as well as environmental and economic performance.

In order to effectively evaluate the regeneration effects of different rejuvenators on aged asphalt binder, this study carried out a series of tests and evaluations on the macroperformance of virgin asphalt binder at various aging-regeneration stages. A commercial rejuvenator, aromatic oil, and warm mix agent were selected as rejuvenators. Fifteen asphalt binder samples involved various aging methods, including water-ultraviolet aging, water-free ultraviolet aging, rolling thin film oven test (RTFOT), and accelerated aging by pressurized aging vessel (PAV). High-temperature properties of asphalt binders were evaluated by softening point, and low-temperature properties of asphalt binders were evaluated by stiffness modulus and m-value. The viscoelastic properties were evaluated by complex modulus $G^{*}$. Test results show that the regeneration effects of different rejuvenators were reflected in the reduction of softening point, stiffness modulus, and complex modulus. Based on performance changes of asphalt binder before and after aging, the reversibility indexes $R_{sp}$, $R_{G*}$, $R_S$, and $R_m$ for quantitative evaluation of macroperformance of rejuvenated asphalt binders were proposed. Through linear fitting, it was found that $R^2$ between the reversibility index $R_{sp}$ and the reversibility index $R_{G*}$ reached 0.7574, and $R^2$ between $R_S$ and $R_m$ reached 0.8683. This provided the possibility of mutual transformation between those reversibility indexes. Last, the macroreversibility index of virgin asphalt binder (ARIV) was proposed. The softening point and stiffness modulus were taken as representative indexes to comprehensively evaluate the recovery of high-temperature, low-temperature, and viscoelastic properties of aged asphalt binder by different rejuvenators. This study provided a unified indicator to quantitatively evaluate the regeneration effect of rejuvenator on virgin asphalt binder. It is helpful for better understanding the aging-regeneration process of virgin asphalt binder and determining the optimum regeneration time and rejuvenator.

This study investigated the feasibility of applying a polyurethane-bonded mixture (PUM) on the pavement overlay for construction or maintenance. Styrene butadiene styrene (SBS) asphalt and epoxy asphalt, the two most common and widely adopted mix designs for highway steel bridge pavement, were selected for a comparative study. First, the performance evaluations and failure analysis of the asphalt mixture and PUM were investigated comprehensively, in terms of low-temperature property, rutting, fatigue, and freeze-thaw resistance. The results showed that the dynamic stability of PUM was over $\mathrm{30,000}\mathrm{cycles}/\mathrm{mm}$ and fatigue life was over one million cycles under 800 με. The tensile strength ratio (TSR) value was higher than 90%, which also indicated an excellent freeze-thaw resistance. Then, bond and shear strengths between the steel plate and the mixture were evaluated for the interlayer of the steel bridge pavement structure. X-ray CT scan analysis was adopted to visualize the internal structure of various mixtures, and the average void diameter of PUM was 0.569 mm. Finally, a statistical analysis was conducted for Kendall consistency and Grey correlation. This research established that PUM is a cost-effective and long-lasting solution for pavement overlay on highway steel-bridge.

Geopolymers are widely considered be low-carbon and cost-effective binders and are used for the stabilization of soft soils in recent years. The current study investigated the stabilization efficacy of low-calcium fly ash (FA) geopolymer for soft clay. The influence of FA content, initial water content, and curing time on stabilization efficacy was investigated. A range of laboratory tests were conducted to investigate the strength and permeability performance of the geopolymer-stabilized clay, including unconfined compressive strength (UCS), falling head permeability, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicated that the mechanical performance of the soft clay at high water content was greatly improved by low-calcium FA geopolymer, exhibiting obvious characteristics of continuous long-term strength development and more ductility compared with cemented clay. A linear empirical relationship was proposed to overcome the shortcomings of the traditional logarithmic function for predicting the long-term strength evolution of low-calcium FA geopolymer–stabilized clay. The UCS of the mixtures increased rapidly with increasing FA content from 16% to 30% and from 25% to 30% for clay water content at liquid limit (LL) and 1.4 LL, respectively. Thirty percent FA content is needed for stabilizing soft clay at 1.0 LL by the deep soil mixing (DSM) method but is obviously not enough at higher initial water content. The major reduction in permeability of the geopolymer-stabilized clay occurred within 28 days of curing while the FA content reached 12%. Despite the increase in curing time up to 90 days and the increase in FA content to 30%, permeability decreased quite slowly. Comparing with the cemented clay, the stabilized clay showed better hydraulic performance but slightly lower permeability.

Thermal-photo-oxidative coupled aging, anaerobic and thermal-oxidative aging testing were conducted on styrene-butadiene-styrene (SBS) type copolymer -modified asphalt at different aging temperatures. The changes in functional group index before and after aging of modified asphalt were deeply analyzed by the attenuated total reflection (ATR) method of Fourier transform infrared (FTIR) spectroscopy. The results show that the carbonyl index $I_{C=O}$, the sulfoxide index $I_{S=O}$, the polybutadiene index $I_{\mathrm{PB}}$, and the polystyrene index $I_{\mathrm{PS}}$ can properly characterize the changes in the microscopic chemical structure of SBS-modified asphalt during aging, and can accurately quantify the degree of aging of SBS-modified asphalt at the microscopic level.

In this paper, quaternary hydrotalcite [layered double hydroxide (LDH)] (CoFeMgAl-LDH) was first fabricated based on the coprecipitation method, and then, CoFeMgAl-LDH/carbon nanotubes (CNTs) composite was synthesized by CNTs and CoFeMgAl-LDH through the solid phase mixing method. Subsequently, the physical-chemical properties of CoFeMgAl-LDH/CNT composite were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, energy dispersive spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) analysis. Meanwhile, the performance of CoFeMgAl-LDH/CNT composite for ${\mathrm{SO}}_4^{2-}$ adsorption was evaluated under different conditions, including different initial concentration, contact time, adsorbent dosage, solution pH, temperature, and coexisting ions. Afterward, the ${\mathrm{SO}}_4^{2-}$ adsorption capacity of CoFeMgAl-LDH/CNT in cement paste was further studied. The results showed that the CoFeMgAl-LDH/CNT composite exhibited a three-dimensional structure with high specific surface area. The maximum ${\mathrm{SO}}_4^{2-}$ adsorption amount of the CoFeMgAl-LDH/CNT composite was $116.27\mathrm{mg}/\mathrm{g}$, which was significantly higher compared with other absorbents of the same type. Pseudosecond-order kinetic model could reasonably describe the adsorption kinetics, and Freundlich isotherm could fit the adsorption data accurately. The results also suggest that the synthesized CoFeMgAl-LDH/CNT composite can serve as a potential material for the sulfate binding in cementitious materials.

This study aimed to investigate the feasibility of using waste ferrochrome electric arc furnace fume–based geopolymer and styrene-butadiene-styrene (SBS)/geopolymer composite as sustainable and eco-friendly materials in asphalt applications. Three percentages of geopolymer (5%, 10%, 15%) and varying amounts of SBS (2.5%, 3%, and 3.5%) were added to the bitumen. The results revealed that both geopolymer and SBS/geopolymer composite improved the mechanical properties of the neat binder and provided bitumen with improved stiffness and elasticity at high temperatures (58°C to 82°C). Analysis of variance (ANOVA) indicated statistically significant results with a 95% confidence interval. Life-cycle cost analysis showed that the use of SBS/geopolymer in bitumen modification reduces production costs and energy consumption. Further research is recommended to compare the effects of geopolymer materials from various waste sources on binder properties.

In hot in-place recycled (HIR) technology, the in-place mixing paving construction method suffers from the problems of low mixing temperature and short mixing time, which lead to incomplete rejuvenator diffusion in waste asphalt binder. Quantitative evaluation of rejuvenator diffusion degree and the corresponding microscopic characteristics are beneficial in guiding HIR construction technology. In this study, the interface model of virgin asphalt, rejuvenator, and aged asphalt was established through molecular dynamics (MD) simulations. Rejuvenator diffusion rates at the virgin–aged asphalt interface (VAAI) at different temperatures were investigated. The results showed that temperature increased rejuvenator diffusion rate. Relative concentrations at different diffusion times were used to quantitatively evaluate rejuvenator diffusion degrees at the interface. The results showed that diffusion degree and uniformity of rejuvenators could be improved by the passage of time. At the same time, the modulus and stress–strain curves of various VAAI models with different diffusion degrees were drawn. The results showed that increase of diffusion degree increased modulus and maximum tensile stress and strain of VAAI; that is, stability at high temperature and crack resistance at low temperature were improved. At low rejuvenator diffusion degrees, rejuvenators accumulated at VAAI, which had a negative effect on reclaimed asphalt performance. According to MD simulation results and site conditions, it was suggested that the HIR technology construction temperature had to remain above 428 K. At the same time, it was suggested that rejuvenator diffusion degree had to be increased to improve road performance.

In recent decades, C-S-H (calcium-silicate-hydrate) nanoparticles have been regarded as promising accelerators for early-age compressive strength enhancement of cementitious materials. In previous research, C-A-S-H (calcium-alumina-silicate-hydrate) nanoparticles were synthesized and exhibited superior acceleration performance than C-S-H nanoparticles. However, how the synthesis conditions affect the performance of C-A-S-H nanoparticles has not been comprehensively investigated, limiting the optimization of the performance of C-A-S-H nanoparticles. This study explores the effect of synthesis conditions (i.e., pH value, reactant droplet rates, and reaction time) of C-A-S-H nanoparticles to accelerate the hydration of portland cement. The results show that the obvious differences in acceleration performance among C-A-S-H nanoparticles are derived from varing pH values, reactant droplet rates, and reaction times, and the optimal synthesis condition is identified to provide guidance on the production of high-performance C-A-S-H nanoparticles.

External sulfate attack is a remarkable and complex phenomenon of degradation of cement matrixes. This paper proposes a method to calculate sulfate diffusion coefficients based on ion migration testing, in order to establish parameters for concrete service life prediction models based on a fast test. The influence of the type (sodium and magnesium) and concentration (5% and 10% ${\mathrm{SO}}_4^{2-}$) of the sulfate solution for a concrete matrix was evaluated in the tests. Sulfate concentrations were monitored by measuring the electrical conductivity of the anode compartment. The results were validated by comparing them with those obtained in natural diffusion tests. Similar sulfate profiles were obtained for concrete samples after 1 month of migration and after 3 and 6 months of diffusion, mainly for magnesium sulfate. The greatest correlations between the calculated diffusion coefficients were achieved at higher concentrations of ${\mathrm{SO}}_4^{2-}$ in the cathode compartment. The results indicated that the proposed migration method enables the calculation of the sulfate diffusion coefficients in concrete.

In this study, both free and restrained shrinkage tests were performed to derive the total tensile strain behavior (i.e., creep effect) of wet-mix and dry-mix shotcretes. A simple analysis procedure is presented to quantify the tensile creep properties of shotcrete using results obtained from standard ring tests and mechanical property tests. The results showed that the rings dried along the axial direction had higher total tensile strain properties compared with those dried along the radial direction. The results further showed that coarse aggregate content of shotcrete affects the total tensile strain properties. Similarly, adding silica fume, fly ash, polymer, shrinkage-reducing admixture (SRA), and crack-reducing admixture (CRA) reduces the total tensile strain properties of shotcrete. However, the decrease observed when using SRA and CRA does not increase the risk of early-age cracking because shrinkage is also reduced proportionally. Thus, a higher total tensile strain capacity is only beneficial in reducing cracking if it does not cause a proportional increase in shrinkage. Overall, the analysis indicates that the effect of creep is a crucial factor in the evaluating of the risk and sensitivity to cracking of shotcrete.

Fatigue damage has become one of the key issues affecting the service safety of steel bridges with the continuous increase of vehicle load and traffic volume. In this paper, fatigue crack growth (FCG) tests were performed on the base metal and butt-welded specimens of Q550E high-strength steel with various stress conditions. The fatigue crack propagation model parameters and fatigue life of Q550E steel compact tensile specimens under four stress ratios were discussed, and the fractographic analysis of the fatigue fracture of the specimens was also executed. The fatigue fracture mechanisms of Q550E steel under different stress ratios were revealed. Based on the experimental results, a particle filter-based FCG behavior prediction method of Q550E high-strength steel was developed considering the uncertainty of the FCG process. The results showed that the FCG behavior of the butt-welded specimen is more sensitive to stress ratio than that of the base metal specimen. The particle filter-based algorithm reduced the uncertainty of physical model parameters. The theoretical results were in good agreement with the experimental observations. This study can provide a basis for the antifatigue design of high-strength steel.

To increase the surface roughness of basalt fiber (BF) and heighten its adhesion to the concrete matrix, three types of modified solutions were prepared [nanosilica (NS) solution, $\gamma$-aminopropyl triethoxy silane (KH550) solution, and NS and KH550 hybrid solution] to modify the surface of BF. After treatment with the modified solutions, scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy were used to analyze the changes in the surface microstructure of the BF. The effects of BF modified by different solutions on the mechanical properties of basalt fiber concrete (BFC) were studied by compressive strength and splitting tensile tests. The results showed that the three types of modified solutions improved the roughness of the BF surface. However, the improvements in roughness differed, with the pure NS solution being less effective. The NS and KH550 hybrid solutions exhibited the most significant modification effects, and the roughness of the BF surface increased as the NS and KH550 contents increased. BF treated with the modified solution improved the compressive and tensile strengths of the BFC. In terms of mechanical improvements, the modification effect of the pure NS solution was the worst. The NS and KH550 hybrid solutions demonstrated the best performance. The pure KH550 solution was in between the other two solutions. In general, the mechanical properties of the BFC improved with increasing NS and KH550 contents. When microstructure and macroscopic mechanical properties were comprehensively considered, the modification effect was better when NS was 5% and KH550 was 2.91%.

Water hyacinth (WH) is abundant in tropical regions. As a result of high sources of fiber, the WH is possibly used for producing biodegradable geotextile, but WH-based geotextiles have low tensile strength and durability against the thermal environment, especially in tropical climates. Therefore, this research aims to develop a more durable geotextile by coating its surface with natural rubber (NR). The test results indicated that NR-coated WH geotextile specimens had significantly higher durability against wet/dry cycles when compared to the uncoated WH geotextile specimens because the NR could prevent the change in water content of the WH fiber in the thermal environment, and hence insignificant change in the fiber structure during wet/dry cycles. Moreover, the coating layer can also effectively minimize the damage from the sharp coarse aggregates to the geotextile during the installation. The field coated specimens had significantly higher tension force compared to the field uncoated specimens. The results of microstructure analysis confirmed that the NR acted as an impervious layer, preventing the water evaporation of woven WH geotextiles. The woven WH-NR geotextile had an ultimate tensile strength of $14.8\mathrm{kN}/\mathrm{m}$ with corresponding strain at break of 20% and very low water absorption, which is suitable for erosion control. The outcome of this research promotes the usage of WH and NR in sustainable geotechnical applications.

In order to study the influence of split grouting times on the anchorage performance of prestressed anchor cable, a field test of multisplit grouting was carried out using fiber Bragg grating monitoring technology. The ultimate bearing capacity, displacement, axial force, and shear stress distribution of the anchor cable under different split grouting times were studied. The test results show that (1) compared with conventional grouting methods, multiple split grouting can increase the bearing capacity of the anchor cable by two to three times, and the improvement effect is most obvious in secondary grouting; (2) the number of split grouts has no effect on the axial force of the anchorage section and does not change the shear stress distribution of the anchorage section. The axial and shear stresses of the anchor cable are mainly concentrated at the first 8 m of the anchorage section. With the increasing tension load, debonding and sliding will occur at the front of the anchorage section, and the peak shear stress will move to the depth of the anchorage section. (3) When the anchor cable fails, the total displacement increases with the increase in splitting and grouting times. The conventional grouting anchor cable begins to produce plastic displacement early, while the plastic displacement of the split grouting anchor cable occurs when the external load is close to the failure load. (4) The multiple high-pressure split grouting technology is applicable to the reinforcement of foundation pits or slope engineering and is a valuable support and reinforcement technology.

This paper presents a cross-scale prediction of the dielectric properties of long-term-cured tricalcium silicate (${\mathrm{C}}_3\mathrm{S}$) paste specimens and investigated the effect of different phase geometry models on the prediction results. Firstly, the dielectric properties of ${\mathrm{C}}_3\mathrm{S}$ paste specimens cured for 180 days were tested. Based on tests such as X-ray diffraction (XRD) and mercury intrusion porosity (MIP), the types of phases and the volume fractions of individual phases in the ${\mathrm{C}}_3\mathrm{S}$ paste specimens were determined. Subsequently, the dielectric performance of the phases was measured. The dielectric performance linkage between each phase and the ${\mathrm{C}}_3\mathrm{S}$ paste specimen was established based on the effective medium theory. The effects of three morphological models of the phase on the predicted results were dissected. The results showed that the volume fraction and dielectric constant of calcium silicate hydrates (C-S-H) gel were significantly higher than those of other phases in the ${\mathrm{C}}_3\mathrm{S}$ paste specimens. Among the three computational models of phase geometry, the standard spherical phase model produced the best prediction. The prediction results of the standard spherical model improved the accuracy by more than 45.8% compared with that of the oblate phase model and the prolate phase model. Among the phases, the trend of the dielectric constant of C-S-H gels with frequency was the most similar to the results obtained by the three prediction models.

Significant efforts have been made to improve concrete mix design for shrinkage reduction and crack control, including reduction of cement content and selection of cement type with less heat of hydration, maximizing aggregate contents, and introduction of discrete fibers in concrete to increase internal restraint. Although high-performance concrete (HPC) mixes including fibers [e.g., steel fibers, polypropylene fibers, or polyvinyl alcohol (PVA) fibers] have reduced the level of shrinkage cracking, they have not eliminated it. Thus, understanding the level of tensile strain the fibers take in the concrete could provide valuable information to aid engineers to make an informed decision on the need for fibers in tension demand in the concrete and determine the appropriate fiber detailing and concrete mix additives. As such, this study aimed to explore a multiscale, hierarchical fiber gradation through a combination of nanoscale nanofabrillated cellulose (NFC) with microscale sisal fibers and macroscale steel fibers in concrete to mitigate the causes of concrete shrinkage cracking at an early age. A total of 22 mixtures were designed and tested. The results show that nanofabrillated cellulose, sisal fiber, and steel fiber can play an excellent synergistic effect to inhibit the early-age shrinkage of concrete. The test data reveal that, when steel fiber is partially replaced by sisal fiber, the early shrinkage of steel fiber concrete is significantly reduced by 26.91% at maximum. Meanwhile, when the NFC content reached 0.15%, the 7-day shrinkage value of concrete reinforced by steel fiber, sisal fiber, and NFC was the lowest, and the shrinkage strain value decreased by 25.03% compared with N0. Compared with the experimental group in which sisal fiber partially replaced steel fiber, the 7-day shrinkage value of the experimental group in which sisal fiber mixed with NFC, sisal fiber mixed with NFC and steel fiber decreased to a certain extent, among which SF1.1FF0.4NFC0.15 showed the best shrinkage inhibition performance, and the shrinkage strain value decreased by 82.56% and 45.39% compared with N0 and SF1.1FF0.4, respectively.

Recycled polyethylene (PE) has been used in asphalt modification for sustainability benefits but shows complex interaction with asphalt matrix. This study investigated compatibility and self-healing properties of asphalt/PE blends using coarse-grained molecular simulation. The mesoscale model based on three-component asphalt binder was first built and validated by physical and thermodynamic properties in terms of density, glass transition temperature, diffusion coefficient of asphaltene, and viscosity. The compatibility of asphalt and PE with various molecular structures was then studied using interaction energy at different temperatures. The two-layer model was further used to explore self-healing characteristics of asphalt binder. The results show that medium-density PE (MDPE) presents the strongest compatibility with asphalt binder, followed by high-density PE (HDPE) and low-density PE (LDPE), respectively. This finding was consistent with the compatibility index (tube testing) results from the literature. The interaction energy between PE and asphalt decreases with the increasing temperature, while the relative trend among three PE-modified asphalts remains unchanged. The morphology and confirmation of PE molecules further indicate that MDPE has better interaction with asphalt binder, while LDPE shows an aggregation pattern. On the other hand, HDPE-, MDPE-, and LDPE-modified asphalt experience smaller diffusion and greater activation energy than neat asphalt binder, which indicates a higher barrier for self-healing. The study findings provide a fundamental understanding on the interaction mechanism of asphalt and PE from the molecular scale.

Microbially induced carbonate precipitation (MICP) is a new foundation treatment technology, which can improve the mechanical properties of soil. In this study, sand specimens containing different magnesium/calcium ion concentration ratios (${\mathrm{Mg}}^{2+}/{\mathrm{Ca}}^{2+}=0/0.5$, $0.1/0.4$, $0.2/0.3$, $0.25/0.25$, $0.4/0.1$, and $0.5/0$) were selected. Moreover, the effects of magnesium ions on the mechanical properties and mechanism of the biocemented sand were explored by oedometer tests, unconfined compressive strength tests, cyclic triaxial tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that when the ${\mathrm{Mg}}^{2+}$ concentration is low, with increasing ${\mathrm{Mg}}^{2+}/{\mathrm{Ca}}^{2+}$, the compressibility of the biocemented sand decreases, the unconfined compressive strength increases, and the antiliquefaction performance improves. When ${\mathrm{Mg}}^{2+}/{\mathrm{Ca}}^{2+}=0.2/0.3$, the sand specimen showed the worst compressibility and the best unconfined compressive strength and antiliquefaction performance. When the ${\mathrm{Mg}}^{2+}$ concentration was high, all the mechanical properties of the specimen were weakened. Low ${\mathrm{Mg}}^{2+}$ concentrations promote the formation of aragonite, whereas high ${\mathrm{Mg}}^{2+}$ concentrations promote the formation of dolomite. In addition, the SEM and XRD results verified the effect of ${\mathrm{Mg}}^{2+}$ on the crystal morphology and composition. This study showed that low ${\mathrm{Mg}}^{2+}$ concentrations can be added to improve the mechanical properties of the sand specimen and achieve a better reinforcement effect when using MICP to consolidate the soil.

The bonding property plays a crucial role in the durability of the asphalt mixture. Warm-mix asphalt (WMA) commonly is used for energy-efficient pavements. The addition of warm-mix additives makes the behavior of the bonding property more complex, especially its atomic-level mechanism. To better clarify the multiscale behavior of WMA bonding property, three typical WMA binders, namely Sasobit-modified asphalt binder, Evotherm-modified asphalt binder, and waste cooking oil (WCO)-modified asphalt binder were selected. The binder bond strength (BBS) test was carried out to evaluate the bonding fracture type and bonding strength. Based on molecular dynamics (MD) simulation, cohesion and adhesion work, radial distribution function (RDF), mean square displacement (MSD), and molecule polarity were calculated to reveal the mechanism. The tensile strength ratio (TSR) of corresponding mixtures was calculated to perform mixture-level characterization. Strong correlations ($R$-squared $>0.9$) were found between BBS testing results and interaction work derived from the MD simulation (for both cohesion and adhesion behavior). In addition, the fracture type in the BBS testing can be predicted accurately by the MD simulation. BBS tests found higher cohesion strength and lower adhesion strength with the addition of Sasobit, whereas adding Evotherm and WCO resulted in lower cohesion strength and higher adhesion. The change in cohesion is explained by RDF calculations. Sasobit wax encourages the stacking of asphaltene molecules, whereas Evotherm and WCO aid in its dispersion. MD simulation also confirmed that molecule polarity plays an important role in the adhesion work ($R$-squared $>0.9$). Polar functional groups in Evotherm and WCO facilitate better asphalt–mineral adhesion. Nonpolar Sasobit weakens asphalt–mineral adhesion. MSD calculation indicated that diffusion behavior is governed by the combination of molecular mass and adhesion behavior. Molecules with larger molecular mass and stronger adhesion exhibit slower diffusion. Mixture-level evaluation (tensile strength ratio) correlated well with adhesion work ($R$-squared = 0.822) but poorly with cohesion work ($R$-squared = 0.667), indicating that adhesion is more important than cohesion in water-damage resistance.

This study tried to show the quantitative impact of explosive parameters (explosive ratio, standoff distance and orientation, and thickness of the flyer) on the explosive welding quality. Based on the ANSYS AUTODYN software version 2019 R3 package, 27 tests were performed by iterating those three explosive parameters. It was observed that jetting, which is essential for the bonding mechanism in explosive welding, occurs when the explosive ratio becomes high. Unlike the explosive ratio, the standoff distance is inverse to the impact pressure. Relatively, although the flyer plate thickness varies, this investigation cannot discern any discernible variation. Therefore, the effect of flyer plate thickness is found to be insufficient. It can be deduced that explosive welding with an explosive ratio of 2 set at a 3-mm standoff distance and a 2-mm flyer plate thickness with an inclined orientation can produce better results.

Herein, a vertical vibration compaction method (VVTM) is proposed to stimulate the practical compaction loading condition for a large stone asphalt mixture with nominal maximum size of 53 mm (LSAM-50) and its reliability is verified. The physical and mechanical properties of LSAM-50 specimens formed using VVTM and the static pressure method (PCT) were compared. The results show that the compression strength and splitting strength of VVTM specimens are 1.29 times and 1.31 times that of the PCT specimens, respectively. Compared with the field test, the compressive strengths of the VVTM and PCT specimens are 94.4% and 72.9% of the field core, respectively. The splitting strengths of the VVTM and PCT specimens are 89.5% and 68.0%, respectively. Additionally, the extraction test revealed that the degree of damage to the internal aggregates of VVTM specimens was considerably less than that of the PCT specimens. Therefore, the performance of VVTM specimens surpasses that of the PCT specimens, and the compaction effect of VVTM is more relevant to field compaction, making it a better choice for evaluating the mechanical and volumetric properties of LSAM-50.

This study investigated the compatibility of waste plastic, a serious environmental and recycling concern, with styrene-butadiene-styrene (SBS) in asphalt binders. An extensive storage stability analysis of binders modified with varying dosages of low-density polyethylene (LDPE) from postcommercial usage with SBS as a compatibilizer and the understanding of behaviors of each component was conducted in this study. Although SBS-LDPE blends were stable with separation index in terms of $G^{*}/\sin \delta$, percent recovery from multiple stress creep recovery (MSCR) detected nonhomogeneity of polymer dispersion in the asphalt blend. To address this nonhomogeneity, waste cooking oil was used to pretreat LDPE to enhance the dispersion and reaction with the binder. Ultimately, 4.5% SBS + 1.5% oil-treated LDPE (TLDPE) was observed to yield a stable SBS-TLDPE blend with a top-bottom separation index ratio of 1.0 in terms of $G^{*}/\sin \delta$ and percent recovery difference of 3.5% and 1.4% at 0.1 and 3.2 kPa, respectively. The study identified that the presence of LDPE negatively influences the recovery and cracking performance of asphalt binders at low temperatures. From critical temperature differential ($\mathrm{\Delta }{T}_c$), Glover-Rowe (G-R) parameter and Black space diagrams at different aging levels, it was concluded that unlike SBS, SBS + LDPE combination had resistance against extended long-term aging.

Desiccation cracking is a common phenomenon for red clay due to alternating wet and dry weathers. The presence of cracks definitely affects the strength of the soil; however, characterizing the development of desiccation cracks inside the soil has been a challenge. The purpose of this study was to propose a method to quantify the volumetric crack rate (VCR) of red clay and investigate the influence of VCR on the unconfined compressive strength (UCS) of red clay. First, the relationship between wave speed and VCR was quantified by a prefabricated crack method to obtain the equivalent VCR (EVCR). Then, the EVCR was compared with the surface crack rate (SCR) to determine the reliability of the method. Finally, unconfined compression tests were carried out to explore the relationship between EVCR and UCS. The results show that the relationship between the prefabricated VCR and wave velocity can be described by a logarithmic equation. The calculated VCR by this equation is linearly correlated to the SCR of red clay, indicating that the logarithmic equation is effective to quantify the VCR of red clay caused by wet and dry cycles. The UCS and residual strength of red clay containing cracks reduce following an exponential function with increasing EVCR. Gray relational analysis showed that the correlation between UCS and EVCR is better than that between UCS and SCR, suggesting that it is more reliable to express the crack rate by EVCR when studying the UCS of red clay.

Because a new magnesium phosphate cement (MPC) developed previously for the rapid repair of cement concrete structures has better mechanical properties and bonding properties, the high-temperature properties were further investigated and compared with ordinary MPC in this study. The mechanical properties of MPC, the hydration products, and the high-temperature mechanism were studied and revealed under the calcination conditions of normal [room temperature (20°C)], 70°C, 300°C, 600°C, and 900°C. As the temperature increased, the compressive strength first decreased and then increased with the lowest being at 300°C. Subsequently, analytical methods such as X-ray powder diffraction (XRD), mercury intrusion porosimeter (MIP), Fourier transform infrared spectrometer (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) were used to comprehensively characterize the changes in MPC hydration products under high-temperature conditions in order to reveal the mechanism of action. The MIP results showed that the detrimental pores gradually increased up to 300°C. When the temperature reached 600°C, the pores were formed and filled by more ${\mathrm{MgKPO}}_4$ crystals, which gradually reduced the harmful pores. XRD, FT-IR, and SEM/EDS results showed that at 300°C, the hydration products did not contain the crystalline struvite but transformed into an amorphous transition state. In particular, basalt fiber–reinforced polymer modified magnesium phosphate cement (BFPMPC) still showed polymer degradation and carbonization. The XRD results were verified by TGA. The hydration products of MPC and BFPMPC at 427°C in the process of amorphous to crystalline transformation were verified by DSC. The proposed MPC materials can be widely applied to the reinforcement and maintenance of key joints of buildings and concrete structures that are prone to fire accidents.

The rutting and cracking distresses of asphalt pavement severely affect its service life. Enhancing the visco-toughness and mechanical properties of asphalt by using graphene may improve the durability of asphalt pavement. To enhance the visco-toughness and mechanical properties of asphalt, dimethyl sulfoxide pretreated graphene (DG) was utilized to modify asphalt, and its effects on the microstructure and mechanical properties of asphalt were investigated using X-ray diffraction, Charpy impact, bending fracture, and other tests, thus revealing DG’s enhancement mechanism Results indicate that the layer spacing of DG is increased, indicating that intercalation structures between asphalt and DG are formed. When the crack tip meets the intercalated DG, the partial fracture energy is absorbed, enhancing the asphalt’s tenacity and hindering crack propagation. The energy absorption capacity and impact visco-toughness are also enhanced. Finally, the DG intercalation structure disperses the primary crack propagation by producing many microcracks, so that the brittle fracture is reduced at low temperatures. DG shows much promise as an application for improving the mechanical properties of asphalt.

The development of new functional pavement materials and the application of sustainable concepts in road construction have led to a dramatic change in functional roads. Pouring semiflexible pavement (SFP) has superior advantages over traditional concrete and asphalt pavements in terms of road performance and convenient construction. The purpose of this research is to investigate the feasibility of SFP in terms of healing capacity, noise reduction, and electrical conductivity. First, the self-healing properties of the cement-asphalt-aggregate (C-AS-A) interface are analyzed by pull-out test, and the cracking characteristics and crack-healing capacity of SFP are investigated by semicircular bending (SCB) test and X-ray computed tomography (CT), respectively. Subsequently, the noise reduction performance of SFP, asphalt mixture, and cement concrete are compared by tire vertical drop test. Finally, different conductive SFP materials including graphite powder, carbon fiber, and steel fiber are prepared and their resistivity and road performance are analyzed. The results show that the C-AS-A interface has a significant self-healing ability; the cracks in SFP mainly occur at the C-AS-A interface (accounting for 53.12%) at $-10°\mathrm{C}$. Moreover, when heated with microwave radiation, the heating-healing ratio of the SFP specimen increases by 63.33% with the addition of steel fiber. Besides, the noise reduction capability of SFP material is between that of asphalt mixture and cement concrete. By combining graphite powder and carbon fiber, the electrical conductivity and road performances of SFP are significantly improved. The results provide references for further design and development of SFP with heating healing capacity, noise reduction ability, and electrical conductivity.

A new cement based on belitic calcium sulfoaluminate (BCSA) was investigated, which featured a unique combination of advantages such as fast setting time, increased tensile strength, and net positive expansion over conventional, commercial BCSA and portland cements. These advantages are achieved by combining commercially available BCSA and mixing the cement with pure, finely ground anhydrite. Mortar bars prepared using this new cement (referred to as supersulfated BCSA or SBCSA) achieve nearly seven times the expansion of conventional BCSA at 28 days. SBCSA concrete exhibits restrained and unrestrained expansions greater by nearly eight times compared with standard BCSA concrete at 28 days. The compressive and flexural strengths of SBCSA concretes are nearly 50% and up to 25% higher compared with BCSA, according to standard test methods. The use of cut-sheet continuously deformed steel fibers in the SBCSA concrete mixes at a dosage of 0.75% shows only minor improvements in terms of restrained expansions and flexural strengths. X-ray diffraction (XRD) analysis showed that the amount of ettringite increased by nearly 30%, and the hydration of belite is enhanced in SBCSA at 28 days compared with BCSA. Due to the unique combination of expansive and fast-setting characteristics, SBCSA offers a potential opportunity to improve the structural design of portland cement concrete. For example, the combination of high early strength and expansion allows the concrete to sustain expansions typically destructive in portland-based expansive cements.

This experimental research investigates the influence of geopolymerization factors such as ${\mathrm{Na}}_2\mathrm{O}$ dosages, water and mineral admixture [bentonite (BT), burnt lime (BL), and ground granulated blast furnace slag (GGBS)] on physiomechanical properties of the pelletized fly ash (FA)–based aggregates. Taguchi’s ${\mathrm{L}}_9$ orthogonal array was adopted to design the mixing ratios for three kinds of fly ash–based aggregates (in the combinations of FA-BT, FA-BL, and FA-GGBS). The degree of geopolymerization of the produced aggregates was characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and a scanning electron microscope (SEM). Most influential response indices in the production of pelletized aggregates were identified using gray relational analysis. The physiomechanical characteristics of the fly-ash aggregates were significantly improved by admixing BL than that of GGBS and BT. However, pelletization efficiency was seen to be superior for GGBS-substituted fly-ash aggregates. The quantified amount of hydration products, i.e., sodium alumino-silicate hydrate (N-A-S-H)/calcium alumino-silicate hydrate (C-A-S-H) for fly ash–based aggregates intensified on increasing ${\mathrm{Na}}_2\mathrm{O}$ and mineral admixture dosages. The results strongly suggest the existence of a linear relationship between the quantified amount of N-A-S-H/C-A-S-H and individual pellet strength of produced aggregate. The FTIR spectrum showed strong and broadened bands of Si-O terminal for all types of aggregates, representing the conversion of unreacted minerals to chains of aluminosilicate gel (geopolymerized hydration product). Further, it can also be inferred from gray relational analysis that among all other factors, ${\mathrm{Na}}_2\mathrm{O}$ content significantly impacted the engineering properties of produced fly ash–based aggregates.

Oxidation degrees of recycled polyethylene (RPE) particles affect the compatibility between RPE and bitumen, resulting in the low properties of RPE-modified bitumen and uncontrolled production technology. In this study, polyethylene (PE) samples were subjected to photo-oxidative aging for 0, 8, 32, 64, and 128 days using a fluorescent ultraviolet (UV) lamp test chamber, labeled as PE-D0, PE-D1, PE-D2, PE-D3, and PE-D4. The changes in molecular functional groups at each aging condition were obtained by Fourier transform infrared spectroscopy (FTIR). Based on the FTIR result, the interaction mechanism between virgin bitumen and PE with different photo-oxidative aging degrees was studied using molecular dynamics (MD). The compatibility of the two-phase structures was characterized by the fluorescence microscope (FM). The rheological properties were evaluated by dynamic shear rheometer (DSR). The MD result showed that the binding energy of PE-D1 saturates, and PE-D1 aromatics were the largest, increasing by 26.31 and $64.07\mathrm{kcal}/\mathrm{mol}$, respectively. The diffusion coefficients decreased with the interaction strength. The DSR result showed that PE with slight photo-oxidative aging improved the rutting resistance of the modified bitumen. The FM indicated that PE-D1 was dispersed more uniformly in the bitumen phase and also had a better compatibility performance. The results showed that PE with slight oxidation benefits the compatibility between PE and bitumen components. The mechanisms in this study provide new insights for a better comprehension of the compatibility of bitumen and PE and the creation of high-performance modified bitumen from recycled waste plastics.

This paper evaluated the cement-based materials incorporated with novel solid–gel phase change materials (PCMs) for improving the energy efficiency of building envelopes. This novel PCM is form-stable, which will not leak as solid–liquid PCMs do and not need encapsulation, and it features high energy-storage capacity. Experimental results showed that the thermal properties of cement-based materials were improved as the increase of PCM content. A 30% replacement of sand by volume with PCM can increase the latent heat of the mixture from around 0 to $7\mathrm{J}/\mathrm{g}$ and decrease the thermal conductivity of PCM mortar based on the generalized self-consistent (GSC) model by about 20%. However, the workability and mechanical properties were compromised. The simulation results indicated that 30% PCM-incorporated walls can contribute to 5% energy saving for cooling in a whole year and 12% reduction in peak cooling load compared with the reference without PCM. The proposed PCM composite offers a promising avenue to achieve energy-efficient building envelopes.

This paper presents the influence of temperature on the shear response of the carbonate sand–concrete interface to better understand the behavior of energy piles drilled in sandy soils. Direct shear tests were performed on a carbonate sand–concrete interface under monotonic (8°C, 13°C, and 18°C) and cyclic (8°C–18°C) thermal loadings. The monotonic temperature has no impact on the shear stress mobilization. The 10 cyclic thermal cycles result in an overall slight compaction on the sand samples. Sand particle breakage is evaluated by analyzing particle size distribution curves before and after the shear tests. Very few sand particles are crushed during the tests. Shearing under higher normal stress results in more particle breakage; however, the breakage is expected but not significant. The variation of interface friction angles is small after monotonic and cyclic temperature loadings, indicating that the effect of temperature on the friction angles of carbonate sand–concrete interface is nearly negligible.

The present study assessed the effect of cement type and water-to-binder ratio (W/B) on the cementing efficiency factor ($k$-value) of low-calcium fly ash (FA) for the compressive strength of concrete in a chemical approach. The results indicated that the $k$-values increased with an increase in the FA reaction degree for each cement type. Despite the higher FA reaction degree in high-early-strength Portland cement (HSPC) paste, the $k$-value in the HSPC concrete was lower than that in OPC (ordinary Portland cement) concrete. For OPC concrete, a lower W/B has a higher $k$-value at the early ages mainly because of cement hydration that is enhanced by FA, and all the $k$-values increased significantly after 28 days due to the pozzolanic reaction of FA. A modified equation of portlandite consumption for the FA reaction assessment that considers the cement-hydration-enhancement effect was proposed to assess the FA reaction degree more appropriately than the conventional one.

This study evaluated the aging resistance of asphalt mixtures containing various percentages of reclaimed asphalt pavement (RAP) and rejuvenators after short-term (ST) and long-term (LT) aging. To this end, rubberized waste oils (i.e., waste engine and cooking oils) and pure waste oils were used as rejuvenators in asphalt mixtures including different percentages of RAP materials (i.e., 25%, 50%, and 75% by the weight of mixtures). The rejuvenated RAP mixtures underwent ST and LT aging processes separately. Afterward, the dynamic modulus (DM) test, semicircular bending (SCB) test, and moisture sensitivity (MS) test were conducted to evaluate the mechanical properties of different samples. The outcome results showed that before exposing samples to LT aging, the efficiency of all rejuvenated mixtures’ stiffness and also their cracking resistance were close together. After applying LT aging, the mechanical properties of RAP mixtures including rubberized rejuvenators were much better than pure rejuvenators. This issue indicated that rubberized rejuvenators and, consequently, RAP mixtures containing these rejuvenators, are more aging resistant and have a superior LT performance. Additionally, there was no concern observed regarding the moisture susceptibility of rejuvenated RAP mixtures before and after applying the aging process.

A composite rapid soil stabilizer (CRSS) is used to rapidly solidify sludge, endowing it with characteristics of fast setting, fast hardening, and high strength. The effects of freeze–thaw (FT) cycles, CRSS content, and moisture condition of the sample on physical and mechanical properties of the solidified sludge were studied through FT cycle tests, and the microscopic evolution mechanism during FT cycles was analyzed. The research results showed that with the increase of FT cycles, the mass of solidified sludge gradually increased, and the unconfined compressive strength (UCS) first increased and then decreased. With the increase in CRSS content, the appearance of the sample was more complete, and final losses in the mass and strength were smaller. After 25 FT cycles, the DR20 sample lost only 0.33% in mass and only 6% in strength. The moisture condition of the samples before FT cycles had a significant effect on the durability against FT cycles, and increasing the content of CRSS could offset the FT erosion caused by high moisture content. After 25 FT cycles, the number of pores in the sample, the most probable pore size, and the cumulative pore volume increased. Macroscopic and microscopic analyses revealed the microscopic evolution mechanism, especially the strength evolution mechanism, of the solidified sludge resistance to FT cycles. Thus, CRSS-solidified sludge exhibits good durability against FT cycles, which lays a theoretical foundation for its application.

Environmental and financial concerns have motivated road authorities to limit the utilization of natural resources in road construction, particularly the resources that cannot be renewed. To fulfill such requirements, pavement researchers have successfully utilized reclaimed asphalt pavement (RAP) materials as an attractive alternative to their natural counterparts. In practice, rejuvenators are often used to amend the properties of the RAP binder. The addition of the rejuvenator in the mixtures containing RAP materials could completely change the behavior of the mixtures. Such changes in the mechanical responses of the asphalt mixtures are essential aspects of pavements’ lifetime performance and should be considered during the asphalt mix design. Although the self-healing performance of asphalt mixtures prepared by virgin materials is well researched, a few research studies have been carried out to investigate the healing properties of asphalt mixtures prepared by RAP materials. This paper examines the influence of the addition of rice bran oil (RBO) capsules on the self-healing performance and mechanical properties of the asphalt mixtures containing various amounts of RAP: 20% and 40% and control mix containing no RAP material. In general, it was found that the addition of the capsules into the mixtures with RAP materials decreased the resilient modulus and flow number (FN) values. As a consequence of the fact that some part of the rejuvenator inside capsules is released into the mixture during mixing and compaction; moreover, the skeleton structure of capsules is weaker than aggregates, which allows the reduction in the maximum density. Further, the addition of capsules into the asphalt mixture without RAP has increased the fracture energy since the inclusion of capsules would increase the bond between asphalt binder and aggregates. In contrast, encapsulated mixtures containing RAP materials had lower fracture energy values compared with their corresponding mixtures without capsule addition. Furthermore, the results revealed that the addition of RBO capsules to the mixtures with RAP materials increased the healing performance of mixtures due to the fact that the reduced viscosity of aged asphalt binder had increased following the gradual release of the rejuvenator; therefore, the microcracks were closed and prevented further damages.

The construction industry is in search of massive energy-saving structures that are light, durable, thermally insulating, economical, and environmentally sustainable. An alternative that can fulfill these requirements is foamed concrete which possesses low density, high workability, thermal and acoustical insulation, lightweight, etc. As the density of foam concrete plays a significant role in its thermal properties, incorporating lightweight aggregates can enhance the thermal insulating property, reduce the deadweight of concrete, and promote sustainability. In the current study, exfoliated vermiculite powder, a mica-type mineral generated through hydrothermal expansions, is used as a sand replacement material. When heated over 300°C, vermiculite expands up to 30 times its original volume and is added in foam concrete by 5 and 8 replacement percentages along with coir fiber as a reinforcement. The utilization of fibers in foam concrete improved the load transfer, enhanced durability and reduced shrinkage cracks. From the test results, 8% addition of vermiculite as a replacement to fine aggregate along with 0.3% by weight of cement of coir addition enhanced the thermal and acoustic properties along with strength.