Journal of Materials in Civil Engineering

In this study, the possibility of using rubber waste particles (RWP) as a substitute for fine aggregate type in mortar, which can provide valuable results in reducing both natural resource consumption and environmental pollution, was evaluated in terms of engineering properties. Due to the dimensional proximity of RWP and fine aggregate and the physical properties of RWP, substitution of these two materials was used in this study. In the mortar produced in this study, 4 different mixtures were produced in which RWP was substituted with fine aggregate and sand at 0%, 5%, 7.5%, and 10% by volume. The binder dosage was kept constant at $550\mathrm{kg}/{\mathrm{m}}^3$ and the water/cement ratio was 0.532. The changes in the mechanical properties (flexural tensile strength, compressive strength, and stress-strain) of the mixtures were evaluated after freeze-thaw cycles, a natural environmental effect. Prism specimens were subjected to compressive and tensile strength tests after 25, 50, 100, and 200 freeze-thaw (FT)-cycles, while the change in stress-strain behavior was studied on cube specimens after FT-cycles. The results showed that the losses in compressive and flexural tensile strength were in the range of 8%–27% and 5%–49%, respectively. Moreover, the load-displacement behavior varies with varying compressive strengths after different number of cycles.

Abstract

Soil improvement via cement-based stabilizers is often necessary to improve the workability and strength of problematic soils. However, understanding the underlying mechanisms of the stabilization process merits further study, particularly concerning changes in the microscale structure that affect macroscale behavior. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) are often paired to characterize the microstructure and pore networks and can be used to quantitatively describe pore structure and surface complexity. Fractal geometry (e.g., fractal dimension and lacunarity) has been shown to provide a quantitative description of structural complexity in nature. Therefore, these fractal geometry fundamentals (fractal dimension and lacunarity) were implemented in the analysis of SEM micrographs and MIP results of a single-mineral kaolinitic soil (SA-1 kaolinite) stabilized with a portland cement stabilizer (portland cement Type I/II) to better understand the evolution of the soil microstructure with curing time. Particle size distributions (PSD) were developed based on image analysis of SEM micrographs collected at curing times of 1, 7, 14, 28, and 90 days. The surface fractal dimension obtained via analysis of MIP results was used to describe changes occurring in the pore network with curing time. The formation of cementitious products was inferred from changes in the PSD as gels first formed and then fused with clay surfaces. Box-counting fractal dimensions and lacunarity showed evidence of particle restructuring with cementation. The transition pore size between intraaggregate and interaggregate pores, obtained via fractal analysis of MIP data, decreased with curing time, indicating the formation of hydration products with stabilization. Using fractal geometry to help analyze the microstructural properties of stabilized clays may lead to better insight into their engineering scale behavior.

Practical Applications

Problematic soils pose an expensive problem to engineers and are often treated with cement-based stabilizers to improve strength and decrease compressibility or the potential to deform or collapse. However, the underlying mechanism causing problematic behavior, such as low strength or shrinking and swelling, is not well understood and techniques to characterize these soils at the microscopic level are needed to better prevent the damage posed to infrastructure. The current standard of practice utilizes only qualitative measurements of the soil structure and cannot be used in models attempting to predict clay behavior. Therefore, concepts from fractal geometry were used in this study to provide a quantitative, measured value of the soil and pore surface which can be used in future models. Analysis of images at the microscale provided a quantitative measurement of the change in soil structure as stabilization reactions occurred. Moreover, the geometric parameters obtained showed strong correlations with strength values, indicating the utility of the technique for predicting engineering behavior. The results of this study show promise for adapting the box-counting procedure to other, more complex soils. Additionally, because there was a good correlation between the fractal parameters and strength, the results should be correlated with other soil parameters.

In this study, the influence of flame-retardant materials on the rheological properties of warm-mix asphalt was investigated. The rheological properties of base asphalt and styrene–butadiene–styrene-modified (SBS) asphalt modified with 2% Sasobit and flame-retardant materials, such as alumina trihydrate and organic montmorillonite (OMMT) in a proportion of 3:1 (AM), were systematically explored. The investigation was carried out under three dosages of AM; i.e., 4%, 8%, and 12%. Experiments including dynamic shear rheological tests, multiple stress creep recovery tests, bending beam rheometer tests, Fourier transform infrared (FTIR) spectroscopy tests, gel permeation chromatography (GPC) tests, and fluorescence microscopy (FM) tests were conducted to evaluate the rheological properties and micromechanism of warm-mix flame-retardant asphalt under different AM dosages. The results showed that the rheological properties of warm-mix flame-retardant SBS asphalt (SOA) at high and low temperatures were better than those of warm-mix flame-retardant asphalt (POA) at the same AM dosage. The increase in AM dosage improved the high-temperature rheological properties and decreased the low-temperature rheological properties. Based on the combined analysis of FTIR spectroscopy, GPC results, and FM results, the reason for this phenomenon was speculated to be the occurrence of wax-crystal structure and filler–asphalt interaction between asphalt and AM. Furthermore, organic cations in OMMT adsorbed the lightweight components present in asphalt, which reduced their proportion and improved the high-temperature and rheological properties. Moreover, the increase in AM led to the increase in physical volume filling, which increased the mechanical properties and brittleness of asphalt. The stress concentration led to the worsening of the stress-diffusion capacity of POA and SOA and eventually led to the decrease in the low-temperature rheological properties of POA and SOA.

The hydration reaction mechanism of geopolymers is intimately linked to their composition and structure. Additionally, pore structure characteristics play a vital role in the properties of hardened geopolymer pastes, significantly influencing the material’s strength, impermeability, and thermal conductivity. In this study, fly ash geopolymer (FAG) was synthesized by utilizing NaOH, ${\mathrm{Na}}_2{\mathrm{SiO}}_3$, and low-calcium fly ash. The pore structure characteristics of FAGs were analyzed using mercury intrusion porosimetry (MIP), and the fractal dimension of FAGs was calculated using the Menger sponge model ($D_f$) and a fractal model based on thermodynamic relationships ($D_s$). Fourier infrared spectroscopy (FTIR), thermogravimetric differential thermal (TG/DTA), and scanning electron microscopy secondary electron phase (SEM-SE) were used to test the composition of the hydration products of FAGs and their microscopic morphology. The results showed that after 90 days of maintaining ambient temperature, the porosity of FAG is between 20% and 30%, and the most available pore size is 10–50 nm. The fractal dimension calculated using the analytical model based on thermodynamic relations can more comprehensively determine the pore structure characteristics of FAG. The geopolymerization reaction process of fly ash particles can be categorized into four primary processes, forming an amorphous aluminosilicate gel as the hydration product.

In contrast with its strong compressive performance and durability, the low tensile strength of concrete often leads to a range of issues during long-term application, including deformation, cracking, and even fracturing of the structure. The addition of polyvinyl alcohol (PVA) fibers to concrete can effectively improve the toughness of materials. However, currently, the majority of studies on polyvinyl alcohol-engineered cementitious composites (PVA-ECC) have focused primarily on the influence of a single factor, such as the PVA fiber content, on the properties of materials, while research that elucidates the interplay between the mechanical properties of PVA-ECC and various mix parameters, to our best knowledge, is lacking. In this study, based on the principle of orthogonal testing, 25 groups of specimens with different mix ratios were designed for experiments, and the effects of the water–binder ratio, sand–binder ratio, fly ash content, and PVA fiber content on the properties of the materials were investigated. On the premise that the fluidity of the material can meet the basic working performance requirements, it was suggested that the content of fly ash should be 35%–52.5%, the water–binder ratio should be 0.375, the sand–binder ratio should be 0.375, and the PVA fiber content should be 1.5%. Under this mix ratio, the strength of the material could reach that of C40 concrete, the compressive toughness could reach more than 10 times that of ordinary concrete, and the ultimate tensile strain under uniaxial tension was close to 3%. These research results can provide a systematic and comprehensive reference for the mix design of PVA-ECC in engineering practice.

Polycarboxylate superplasticizers (PCEs) have been extensively used in the areas of construction and building; however, the application limitation of PCEs has emerged owing to their sensitivity to clay. In this work, three anticlay PCEs were synthesized by introducing acrylamide (AM), methacryloxyethyltrimethyl ammonium chloride (DMC), or 3-[2-(methacryloyloxy) ethyl] dimethylammonio-propane-1-sulfonate (DMAPS) into the polycarboxylate copolymer of ethylene glycol monovinyl polyethylene glycol ether (EPEG) and acrylic acid (AA), denoted as A-PCE, D-PCE, and S-PCE, respectively. The structures of these superplasticizers were characterized by gel permeation chromatography (GPC) and Fourier-transform infrared spectroscopy (FTIR). Compared with the common polycarboxylate superplasticizers (O-PCEs), the resultant anticlay PCEs showed better dispersion as far as the fluidity of cement paste and mortar were concerned. With the content of 0.5% per weight sodium bentonite in place of cement, these anticlay PCEs exhibited better clay resistance than O-PCE. In addition, the compressive strengths of mortar and concrete by the addition of A-PCE, D-PCE, or S-PCE were slightly higher than those of O-PCE. Total organic carbon (TOC) revealed that the sensitivity of A-PCE, D-PCE, and S-PCE to clay was lower than that of O-PCE. X-ray diffraction (XRD) proved that the layer spacing of clay increased after treatment with superplasticizer. In combination of adsorption determination with XRD analysis, a possible mechanism was proposed. Unlike the PEG side chains inserting into the clay layers for O-PCE, the cations in functional groups entered the clay layers through cation exchange for anticlay PCEs preferentially.

Subway plays an important role in building a three-dimensional urban transportation system and alleviating urban traffic congestion due to its advantages of land conservation, green environmental protection, safety and reliability, large transportation volume, and high efficiency. With the large-scale development of urban subway engineering and subway network, the vibration and noise problems generated during subway operation have become increasingly serious, especially low frequency vibration problems. First, this paper proposes a phononic-like crystal model based on local resonance theory, and based on this, a new type of vibration reduction material for phononic-like crystal polymer concrete has been developed. Second, the indoor test of phononic-like crystal polymer concrete is introduced, and trial mix tests are conducted on prefabricated and cast-in-place phononic-like crystal polymer concrete track bed. Finally, based on the indoor test and trial mix tests, prefabricated and cast-in-place phononic-like crystal polymer concrete track bed are designed for different subway engineering application environments, and applied to Nanjing metro line S6 and the north extension line of Nanjing metro line 1 in Nanjing of China for subway vibration control. The vertical vibration attenuation range of the prefabricated phononic-like crystal polymer concrete track bed is 1.25–125 Hz, and the lateral vibration attenuation range is 1.25–100 Hz, with maximum insertion losses of 12.2 dB for vertical vibration and 9.6 dB for lateral vibration, respectively. The vertical vibration attenuation range of the cast-in-place phononic-like crystal polymer concrete track bed is 2.5–250 Hz, and the lateral vibration attenuation range is 1.25–200 Hz, with maximum insertion losses of 11.82 dB and 6.98 dB for vertical and lateral vibrations, respectively. In the frequency range of 1–80 Hz, the maximum vertical Z-vibration level difference between the prefabricated and cast-in-place phononic-like crystal polymer concrete track bed and the ordinary concrete track bed of the tunnel wall is 5.662 dB and 5.057 dB, respectively. The results indicate that both prefabricated and cast-in-place phononic-like crystal polymer concrete track bed have good vibration reduction performance in subway operation, opening up low frequency vibration reduction band gap and achieving good low frequency vibration reduction effect. The phononic-like crystal polymer concrete track bed not only has good low frequency vibration reduction effect, but also has the advantages of low construction cost and good economy, so it has broad application prospects in subway engineering.

Based on investigated mechanical properties of alkali residue-based foamed concrete (A-FC), this paper presents a comprehensive examination of the microstructural features of A-FC and their impact on compressive properties. A detailed investigation of the compressive performance and pore structure characteristics was conducted through compression tests and low-field nuclear magnetic resonance (NMR) tests. The results demonstrate that the primary pore size in A-FC falls within the microscale, and the pores can be categorized into three types—gel pores, capillary pores, and air voids. In addition, the $T_2$ spectrum of A-FC exhibits three distinct relaxation peaks, each of which is attributed to different water components, i.e., adsorbed water, pore water, and free water. As the pore size, air void ratio, and porosity increase, the compressive strength of A-FC decreases. The main reasons for the increased in strain in low-strength A-FC include compression at the bottom, internal stress dissipation through the pore structure, and changes in the failure mode.

This research aims to propose a framework for selecting the optimum filler–binder (F-B) ratio in an asphalt mixture, with the objective to achieve desired fatigue performance at the lowest possible binder content. The asphalt mixtures were prepared with two types (VG-30 and PMB-40) of binders and three waste fillers (red mud, marble dust, and limestone dust), at varying filler contents (3%, 5%, and 7% by weight of aggregates). The fatigue resistance of the mixtures was quantified by the critical strain energy release rate ($J_c$), obtained from semicircular bending test. The results indicate that the fineness modulus, specific surface area, and Rigden voids were the primary filler characteristics influencing the behavior of unmodified mixtures, whereas the role of binder was determinant in the modified mixtures. Based on the findings of the study, it is proposed that the parameter $\mathrm{F}\mathrm{S}\mathrm{R}/|G^{*}|·\sin \delta$ (where FSR is the ratio of fineness modulus and the product of specific surface area and Rigden voids, and $|G^{*}|·\sin \delta$ is a rheological parameter of the asphalt binder) can be used to estimate the optimum F-B ratio during the mix design of asphalt mixtures.

This study aims to analyze the degradation behavior and mechanisms of amine-cured epoxy asphalt (EA) under the combined effects of ultraviolet (UV) radiation, oxygen, and temperature. To achieve this, amine-cured epoxy resin (ER) and EAs containing 35%, 45%, and 55% asphalt content were prepared and subjected to simulated UV-based aging. Various analytical techniques were employed to investigate the mechanical properties, microstructure, morphology, and oxidation layer of ER and EAs. The results indicate that after UV-based aging, ER and EAs with 35%–45% asphalt content experienced an increase in mass, a decrease in strength and glass transition temperature. In comparison, EAs with 55% asphalt content exhibited the opposite trends. The elongation and $(\mathrm{Tan}\delta {)}_{\max }$ of ER and EAs reduced, whereas the storage modulus and hardness at mid to high temperatures rose. At the microstructural level, the degradation of the resin phase was confirmed by changes in ether, ester, and amide groups, whereas the generation of sulfoxide groups was associated with the oxidation of the asphalt phase. Compared with ER, the surface of EA has obvious defects after aging, which is the main reason for the decrease in contact angle. As the asphalt content increases, EAs exhibit higher carbonyl concentration, more profound oxidation, and more obvious performance degradation. This trend suggests that the resin phase mitigates the aging of the asphalt phase by absorbing harmful UV radiation and oxygen.

Stainless steel wires (SSWs)-modified asphalt concrete with stable long-term properties and high electrical conductivity as well as without puncturing vehicle tires is expected to become a promising multifunctional pavement material especially for solving road icing problems in cold climates. Hence, the electrical/thermal, self-heating, and self-deicing properties of SSWs-modified asphalt concrete were investigated in this study. Meanwhile, the measures for increasing the electro-thermal conversion efficiency of composites were explored. 0.75 vol% SSWs reduced the resistivity of asphalt concrete by at least eight orders of magnitude and increased the thermal conductivity by 30.38%. Preapplying a 60 V voltage instantaneously before applying voltage to utilize the breakdown effect on interface capacitors between SSWs, and employing the three-piece electrode arrangement for improving the overlapping probability of SSWs, significantly enhanced the self-heating power, peak/average temperature increase, and self-heating rate of SSWs-modified asphalt concrete by at least three times. The temperature on the top surface of SSWs-modified asphalt concrete slab (with size of $30\mathrm{cm}\times 30\mathrm{cm}\times 5\mathrm{cm}$) under 60 V voltage increased by 24.1°C with a power density of $827.37\mathrm{W}/{\mathrm{m}}^2$ for 90 min in a windless condition at $-10°\mathrm{C}$. Meanwhile, the composites exhibited stable resistivity and good self-heating repeatability as well as temperature homogeneity during the self-heating process. The SSWs-modified asphalt concrete slab could melt a 4 mm ice layer within 2 h with an energy efficiency as high as 88.59% at the voltage of 60 V, and the cooling residual heat could theoretically melt a 2.4 mm ice layer to improve the self-deicing energy efficiency by 15.21%. Therefore, the low content SSWs-modified asphalt concrete exhibits promising application prospects in self-deicing pavement.

The use of high contents of recycled materials in asphalt mixtures has an adverse effect on the low-temperature cracking performance of these mixtures if not accounted for properly due to the high stiffness and poor relaxation properties of the reclaimed asphalt pavement (RAP) binder. This concern has driven some to suggest using recycling agents (RAs) in the asphalt mixture to restore the rheological properties of the RAP binder without compromising the short- and long-term performance of the mixture. However, the relationships between RA type and dosage, virgin and RAP binder characteristics, and low-temperature properties, i.e., creep stiffness and $m$-value, need to be investigated further to assess the acceptance of RAs. In this study, 26 recycled binder blends from a combination of three virgin binders, four RAP sources, and eight RAs were used to study these relationships. First, the use of a method based on the dynamic shear rheometer to predict low-temperature properties of recycled binder blends successfully is demonstrated. Second, a linear relationship is found to exist between the low-temperature properties and RA dosage of these blends. Third, a parameter based on low-temperature properties is proposed to select an RA that yields a balance in the stiffness and relaxation properties of the recycled binder blends. Fourth, a conceptual framework is proposed to assess the acceptance of RAs based on low-temperature performance-related parameters.

Phosphogypsum (PG) is a solid waste generated by phosphate fertilizer industries that is currently used in concrete materials. However, adding PG to concrete usually results in reducing its water resistance and corrosion resistance. This paper presents a new method of applying PG to concrete to improve its water resistance. In this paper, a green superhydrophobic PG (SPG) coating was prepared using modified PG as a hydrophobic medium and cement as the bonding material. The contact angle between the superhydrophobic phosphogypsum coating (SPG coating) and water was 156°, and the coating reached a superhydrophobic state with good self-cleaning ability. Even when sandpaper was used to polish the coating, the water contact angle of the coating was still greater than 150°, indicating that the coating had good wear resistance. In addition, the results of water absorption and electrochemical experiments indicated that mortar coated with SPG had better water resistance and corrosion resistance than ordinary mortar. The SPG coatings with water resistance, wear resistance, and self-cleaning properties have potential applications in building exterior walls.

The expedient repair of damaged airfield pavements is important to eliminate long closure periods. Rapid-setting cement (RSC) is promising for achieving target strength in a much shorter duration (4–6 h) compared to conventional repair methods. However, when the objective is to reopen the pavement within 1–2 h, there is a lack of methods to quantify the development of mechanical properties during the first few hours. In this study, a simplified maturity method is proposed to monitor the very early-strength development of two commercially available RSC mixes with different strength development mechanisms. The results were validated using hydration chemistry data from scanning electron microscope (SEM) experiments and ultrasonic pulse velocity (UPV) tests. The experimental results show that such a maturity-based approach is effective and robust in characterizing the early-strength development of the two RSC mixes despite variations in ambient temperature conditions.

This study explores the effect of nanosilica (NS) and ground granulated blast furnace slag (GGBFS) in varied quantities (0%–5% NS and 0%–25% GGBFS) on the postfire mechanical and endurance characteristics of concrete at temperatures ranging from 200°C to 1,000°C. To examine bonding performance and structural endurance, a full range of experimental evaluations was methodically carried out, including bond strength evaluations, rapid chloride permeability, chloride attack tests, and water penetration testing. Advanced methods like scanning electron microscopy and X-ray diffraction were used to examine the postfire internal structure. The combination of NS and GGBFS in concrete compositions resulted in noticeable improvements in mechanical resilience and endurance. This was evident by increased bond strength (a notable 12% rise with 4% NS and 20% GGBFS), decreased chloride permeation (a significant 26% drop), and decreased water penetration (about 20% reduction). Interestingly, this optimum concrete mix performed well even at high temperatures, with modest performance improvements at 200°C–400°C but apparent structural deterioration at greater temperature levels. Nonetheless, the composite concrete was demonstrated to perform well at higher temperatures in contrast with control samples. Further, this research develops a reliable correlation for forecasting concrete performance under high heat circumstances as well as providing essential insights critical for the precise design of concrete buildings in extreme situations.

The higher production temperature and greenhouse gas emissions restrain the use of crumb rubber (CR) obtained from recycled tires in pavement construction. Warm mix asphalt (WMA) technology is a sustainable solution for crumb rubber–modified bitumen (CRMB) as it allows the production of asphalt mixtures at lower temperatures. In addition, WMA lowers fuel consumption and greenhouse gas (GHG) emissions, leading to the cleaner production of asphalt mixtures. The primary objective of the study is to minimize the production temperature of crumb rubber–modified (CRM) binders with the use of WMA technology. This study explores the mixing and compaction temperatures using a workability approach. The study found that the conventional viscous-based methods do not yield appropriate production temperatures for CRM asphalt binders. The workability approach used in this study was able to quantify the mixing and compaction temperatures for different CRM mixture incorporated with WMA technologies. About 4%–13% and 5%–22% reduction in mixing and compaction temperatures, respectively, were obtained for different WMA technologies. Finally, the reduction in GHG and energy consumption were studied for WMA technology at their reduced mixing and compaction temperature. The use of WMA technology reduced the energy consumption by around 4%–12% and GHG emissions by 4%–13% relative to base CRM mixture. The amount of reduction in emission and energy consumption was found to be the function of fuel type, WMA additives, and their respective dosages.

The study of the adhesion properties between asphalt and aggregate plays a critical role in deciphering the fracture behavior and damage characteristics in asphalt mixtures. This research is dedicated to exploring the impact of various aging behaviors on adhesion properties and the reinforcing effects of modifiers. In this context, a novel composite modifier (MPM), was synthesized from phosphogypsum whisker, derived from phosphogypsum waste. Asphalt specimens, encompassing both virgin and modified asphalt with the different dosages of MPM, were prepared under a spectrum of eight aging conditions. The mechanical properties of these specimens were meticulously analyzed using multiscale tests to assess the adhesion properties under diverse aging conditions and modifier dosages. Furthermore, the study delved into the microscopic effects of aging and modification on adhesion properties. The results highlighted that aging detrimentally impacts the adhesion properties of asphalt, with this negative effect progressively intensifying over time. In contrast, the enhancement of adhesion properties by MPM exhibited variation in accordance with its dosage. Limestone, characterized by a rougher external interface and a higher prevalence of high-valent cations, demonstrated more pronounced adhesion properties to asphalt compared to granite. The aging process introduced new diffraction patterns and characteristic peaks in the asphalt, with their intensities showing a direct correlation with the duration of aging. The MPM modification was found to effectively mitigate the deterioration in the structural stability of the virgin asphalt. Overall, this study offers comprehensive insights into the aging and modification mechanisms affecting adhesion properties between asphalt and aggregate, contributing significantly to the resource utilization of solid waste.

In recent years, lignin has received increasing attention due to its wide availability, low cost, renewability, and potential for improving the performance of asphalt pavement. The purpose of this study is to investigate the rheological properties and microscopic mechanism of modified asphalt by using different types of lignin. The effects of different aging durations on the rheological properties, as well as the chemical and morphological changes of different lignin-modified asphalts, were analyzed using dynamic shear rheometer (DSR), Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). The results of the rheological tests demonstrated that the addition of lignin had a positive effect on the permanent deformation of the asphalt matrix and significantly improved the rutting resistance of the asphalt at high temperatures, with the most significant change observed in enzymatic lignin. The addition of lignin improves certain fatigue resistance and good fatigue life. The chemical test results indicate that lignin, as a blending agent, can compensate for the molecular weight changes caused by the aging of the matrix asphalt when degrading, maintaining a balanced distribution of molecular weight, which is the main mechanism of resistance to thermal oxidation aging of lignin-modified asphalt.

A milled recycled asphalt pavement (RAP) particle can be a cluster of one or more aggregates coated with an aged RAP binder. While RAP material is added to virgin aggregates and binder in a pugmill, the RAP cluster undergoes dissociation or agglomeration, depending on the cluster size and thermo-physical conditions inside the pugmill. The degree of dissociation or agglomeration of RAP material has an important relation with the degree of RAP binder availability. The RAP binder availability in mix design depends on the exposed surface area of dissociated coarse RAP particles and also on the agglomeration tendency of fine RAP particles. In the present study, the degree of RAP binder availability (DoAv), cluster dissociation of course RAP, and agglomeration tendency of fine RAP particles were examined at different mixing durations inside an asphalt pugmill—60 s, 120 s, and 180 s. The study examined whether the RAP cluster dissociation and postmixing agglomeration has any effect on the RAP binder availability. The degree of RAP binder availability of RAP mix was found by determining the virgin binder requirement of RAP mixes in excess of optimum binder content determined for the control mix prepared using virgin aggregates. Cluster dissociation and agglomeration was studied by hot mixing of RAP fractions in a pugmill with abrasive charges, followed by sieving. The statistical analysis of data found that RAP mixes incorporating fractionated fine RAP material exhibited higher DoAv at every mixing duration. For mixes incorporating fractionated coarse RAP, cluster dissociation index was positively correlated with DoAv, which implied that RAP cluster dissociation is a possible reason for RAP binder availability. In mixes incorporating fractionated fine RAP fractions, the RAP particles got agglomerated. The agglomeration index was found to correlate well with RAP binder availability, thereby establishing that agglomeration tendency in fine RAP fractions can be considered as an indicator of RAP binder availability.

In recent years, the recycling and reutilization of shield tunneling residues (STR) have received extensive attention in underground engineering. To optimize the method of resource utilization of STR, this paper introduces a replacement method of STR slurry. The STR are incorporated into concrete and prepared as STR concrete (STRC) using a coarse and fine aggregate shell production process. By optimizing the mixing method of STR slurry, we obtained the best mixing process, and studied the influence of STR dosage and water–binder ratio ($\mathrm{w}/\mathrm{b}$) on the compressive strength of STRC. The results revealed that the air-dried STR preliminarily crushed to about 15 mm can be used to prepare STRC by extending the mixing time of STR slurry. The compressive strength of the concrete significantly depends on the dosage of STR slurry. The strength decreases significantly with the increase of STR dosage, and the recommended dosage is about 10%. The influence of the $\mathrm{w}/\mathrm{b}$ on compressive strength is similar to that of ordinary concrete. A predictive model for the compressive strength of STRC was established by analyzing the relationship between the dosage of STR, $\mathrm{w}/\mathrm{b}$, age, and the strength of STRC.

Digital fabrication of concrete structures has gained substantial research traction over the last decade, enabling efficient material use and adding more architectural freedom. Current research focuses on chemical and mineral admixtures, as well as manipulating the cement hydration reaction to control the yield stress evolution with time in the cement paste. Instead of providing yield stress through the concrete fluid properties, a high yield stress can be provided by interparticle friction from the use of high aggregate volumes and large nominal maximum aggregate size, with flow enhanced for material extrusion by vibration. Granular physics was applied to concrete mixture design to develop concrete mixtures with excellent edge retention abilities that flow easily under vibration. A linear regression analysis of concrete yield stress after vibration revealed that water content is most important, followed by fineness modulus of the aggregate combination and density after vibration. A decrease in water content, increase in fineness modulus and increase in density after vibration were found to increase the static yield stress after vibration.

Wind turbine blades are primarily composed of fiberglass composite, posing a significant recycling challenge for the wind energy industry. This paper introduces a novel recycling approach by comprehensively analyzing the pozzolanic reactivity of recycled powder as a new supplementary cementitious material (SCM). A systematic characterization using laboratory techniques is first described, establishing both the chemical and morphological properties of the powder and suggesting that the material was likely to be capable of acting as a pozzolan. The effects of thermal and mechanical processing on the reactivity characteristics of the material were elucidated using a suite of analytical and standardized characterization approaches. It was found that through heat treatment to remove impinging resin and subsequent mechanical processing to synthesize a fine powder, the reactivity of the material could be improved to an extent at which the performance characteristics of a conventional class F fly ash were closely matched. For instance, mortar containing 10% of thermally-mechanically processed powder achieves 95% of the 28-day strength of cement mortar. This paper opens the door for both the use of these materials to bolster dwindling supplies of supplementary cementitious materials, and to provide a much-needed reprocessing route for waste fiberglass which are otherwise highly challenging to dispose of cost-effectively.

Although crumb rubber (CR) modified bitumen has been widely used in bitumen pavement, the issue of storage stability has not been resolved. Waste low-density polyethylene (LDPE), a new modifier, has been introduced to improve the performance of CR-modified bitumen. However, the interaction behavior among LDPE with different ultraviolet (UV) aging degrees, crumb rubber, and bitumen is not clear, depending on the environment and source. In this study, virgin LDPE (LDPE-0)/CR blends, LDPE with 8 days UV aging (LDPE-8)/CR blends and LDPE with 64 days UV aging (LDPE-64)/CR blends were prepared by melt compounding using a twin-screw extruder and mixed with bitumen. The samples were evaluated by various tests such as dynamic shear rheometer (DSR) tests, storage stability, fluorescence microscopy, and scanning electron microscope (SEM). Then, molecular dynamics (MD) simulation was used to explore the interaction behavior between LDPE/CR blends with different UV aging degrees and bitumen. The virgin bitumen model was validated by density, radial distribution function (RDF), and glass transition temperature (${\mathrm{T}}_{\mathrm{g}}$). The interaction behaviors were characterized based on diffusion coefficient and concentration distribution. The results showed that LDPE/CR blends were able to improve the rheological properties and storage stability, especially in LDPE-8/CR-modified bitumen. From the microscopic analysis, it was also observed that a network of LDPE/CR blends in the modified bitumen was well dispersed. Furthermore, the addition of LDPE/CR blends inhibited the aggregation behavior of the light component and slowed down the diffusion rate of bitumen molecules. The research findings provide insights for improving the storage stability of bitumen.

This study investigates the use of an interlocking gap gradation and rubber powder to improve the crack resistance of a cement-stabilized macadam (CSM) mixture. First, a crack-resistant interlocking gap gradation was designed by controlling the percentage of passing of the critical sieve size and the maximum nominal particle diameter. Second, the effect of different addition orders of rubber powder on the crack resistance of the CSM mixture was explored. Finally, the properties and crack resistance of the CSM mixture were analyzed based on the types of gradation and types of rubber powder. The test results show that the crack-resistant interlocking gap gradation not only strengthens the mechanical properties of the CSM mixture but also improves its crack resistance. CSM mixtures with modified rubber powder and cement added simultaneously exhibit the best crack resistance property and mechanical properties.

In order to study the effect of water erosion on the adhesion characteristics of warm-mix crumb rubber-modified asphalt (WCR)-steel slag interface, hot-mix crumb rubber-modified asphalt (HCR) was used as the control group. The WCR-aggregate interface adhesion model was established based on the surface energy test. According to the surface energy theory, the adhesion work of WCR-aggregate can be used to calculate their contact angle. Then, the permeability work and spreading coefficient of asphalt-aggregate were obtained. Three processes of asphalt wetting aggregate (adhesion wetting, immersion wetting, and extended wetting) and the compatibility of asphalt-aggregate were analyzed. The interfacial pull-out test and freeze-thaw splitting test were also used to further analyze the adhesion characteristics and water stability of asphalt-aggregate under the action of hydrothermal coupling. Finally, the low-temperature beam bending test of warm/hot-mix crumb rubber-modified asphalt mixture was carried out to verify the experimental results of adhesion characteristics of the asphalt-aggregate interface. The results show that with the erosion of water, the adhesion and water stability of the WCR-steel slag interface and the low-temperature crack resistance of warm/hot-mix crumb rubber-modified asphalt mixture gradually weaken. At the same time, the higher the water bath temperature, the faster the asphalt film destruction, the positive effect of the warm agents on asphalt-aggregate adhesion was weakened, and the WCR-steel slag interface adhesion characteristics were better. The experimental results of low-temperature performance also verify the accuracy of the adhesion characteristics of the asphalt mixture. Finally, the correlation analysis revealed that there was a strong correlation between mechanical indexes (the pull-out strength P, the residual strength ratio, the pull-out strength loss rate $\eta$) and water stability index (the freeze-thaw splitting strength ratio). All of them could characterize the water stability of the asphalt-aggregate well. Furthermore, the correlation between $\eta$ and TSR was the highest, so it is more reliable for evaluating the water stability and adhesion of asphalt and aggregate.

This study aims to design a double-gradation functional asphalt mixture considering continuous paving action and to investigate the effect of different gradation volume ratios on the mechanical behavior and functional performance of double-gradation asphalt mixture. The open graded friction course (OGFC) and asphalt concrete (AC) gradations were selected as the upper and lower layers of the double-gradation asphalt mixture. Three double-gradation volume ratios ($2:1$, $1:1$, and $1:2$) were considered to compare the high- and low-temperature performance, water stability, permeability, and noise reduction coefficient of asphalt mixture with different gradation combinations. In addition, a discrete element numerical model based on a digital image processing technique was developed to analyze the mesoscale mechanical response and damage behavior of the double-gradation functional asphalt mixture. The research results show that the crack width and initiations of the double-gradation asphalt mixtures reduced significantly with the increasing volume percentage of AC-graded mixtures, while the larger OGFC- graded volume ratios are more conducive to functionality of the double-gradation asphalt mixtures. In addition, the volume ratio of OGFC-AC double-gradation asphalt mixture can be selected in the range between $1:1$ and $1:2$, which can simultaneously satisfy the mechanical properties and functionality of large pore asphalt pavement.

To comprehensively investigate the impact of chloride salt erosion on the multiscale bonding behavior between asphalt and aggregate, atomic force microscopy (AFM) and pull-off tests were employed. A thorough study was conducted on the microsurface morphology, nanoscale surface roughness, microsurface energy, and macro pull-off strength between asphalt and aggregate under different chloride salt concentrations. Furthermore, the relationship between the microscopic structural characteristics of asphalt and macroscopic bonding performance was analyzed. The results revealed that, except for the crumb rubber (CR) modified asphalt, the surface of asphalt exhibited an alternation of peaks and valleys forming a beelike structure both before and after chloride salt erosion. The erosion caused the reaggregation of asphalt surface particles, resulting in prominent nano-protrusions and white spots, thereby increasing the surface height and roughness of asphalt. In chloride salt solutions, the infiltration of ions and water molecules into the asphalt may lead to irregular depressions and pits on the surface, consequently reducing the surface energy of the asphalt. This further diminished the effective contact area between the asphalt and aggregates, forming microscopic voids and subsequently weakening the bonding strength at the asphalt-aggregate interface.

Improving asphalt mixtures has become increasingly important due to the rise in traffic volume, high maintenance costs, and the challenges associated with their implementation. Previous studies have examined various additives and modifiers. This study investigated the effect of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ on two significant potential damages in asphalt pavements: low-temperature cracking and moisture sensitivity. The results of this study can be used to propose a suitable solution to minimize the probability of these failures occurring in asphalt pavements. Moreover, this study examined the impact of loading modes, temperature, and crack type on the fracture toughness of asphalt mixtures. In addition to exploring pure mode I and pure mode II, four distinct mixed modes (I/II) were also studied because, usually, this mode is the critical mode of the asphalt mixture. Temperature was another variable observed to validate the elasticity of asphalt mixtures at low temperatures. Lastly, the study investigated the effect of incorporating nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ on the fracture toughness of the asphalt mixture under different temperatures and crack geometries. To achieve the objectives of this study, the semicircular bending and indirect tensile tests were conducted. The results showed that adding 0.6% nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ can increase the crack resistance of asphalt mixtures by up to 12%. Additionally, the study demonstrated that incorporating 0.6% nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ can decrease the vulnerability of asphalt mixtures to moisture by 5.1%. The response surface method technique was employed to analyze the laboratory data statistically. A reduced cubic model was utilized to assess the relationship between independent factors (loading mode, temperature, crack type, and nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ content) and fracture toughness due to its superior fit with the laboratory results Next, sensitivity analysis was used to find the effect value of each parameter on the fracture toughness of the asphalt mixture. The sensitivity analysis results showed that the loading mode, temperature, crack type, and use of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$, respectively, will significantly impact the fracture toughness of the asphalt mixture.

Freeze-thaw resistance ability of concrete is an important issue when evaluating its durability. In this research, the objective was to predict concrete resistance to such cycles by analyzing water absorption based on the critical water saturation theory. In order to achieve this goal, detailed experiments were conducted, including water absorption, pore structure scanning, and mercury intrusion porosimetry of concrete with air-entraining admixture and different fiber content to obtain critical indicators, such as water absorption, porosity, and air void spacing factor, which formed the basis for predicting the service life of concrete. To predict the service life of concrete under freeze-thaw cycles, the critical saturation theory was utilized, taking into account environmental parameters and experimental indexes. The service life of concrete against freeze-thaw using air-entraining admixture and fibers had been calculated quantitatively in this paper. The results show that the predicted service life of concrete with air-entraining admixture was increased by more than 50 times, and using both air-entraining admixture and fiber could increase the service life by more than 80 times, even reaching 249 years.

The application of warm-mix flame retardant rubber asphalt (WFRA) in tunnel pavement offers a promising solution that enhances both energy conservation and tunnel safety. First, a commercial halogen-free flame retardant (ZK), alumina trihydrate (ATH), and organic montmorillonite compound ATH flame retardant (OMMT/ATH) were melt-blended with warm-mix rubber asphalt (WRA) to prepare different types of WFRAs. Then, the effects of various flame retardants (FRs) on flame retardancy and rheological properties of the WRA were evaluated. Moreover, the functional groups of FR, WRA, and WFRA were investigated. Finally, the synergistic mechanism of FR on the WRA was explored based on the analysis of flame retardancy, rheological properties, and functional groups. Results show that the flame-retardant effect of OMMT/ATH on the WRA is much better than that of single FRs (ZK and ATH), indicating that the OMMT and ATH exhibit synergistic flame-retardant effect. The addition of OMMT/ATH enhances the high-temperature performance but shows little effect on the fatigue performance of the WRA. The synergistic flame-retardant mechanism of OMMT/ATH on the WRA is mainly attributed to the physical barrier effect of OMMT, the cooling and dilution effect of ATH, and the synergistic covering layer effect of OMMT and ATH.

Compound modified asphalt with waste plastic and crumb rubber can enhance the application of crumb rubber–modified asphalt (CRMA) in engineering, and enable the recycling of waste resources. In this study, waste cooking oil (WCO) was used to activate crumb rubber and acrylonitrile-butadiene-styrene (ABS) to obtain crumb rubber–modified asphalt with excellent storage stability and low viscosity. The viscosity and storage stability of crumb rubber–modified asphalt were tested by rotational viscosity test and cigar tube test. The force ductility test and bending beam rheological (BBR) test were used to evaluate the low-temperature performance of different crumb rubber–modified asphalt samples. The effect of the addition of waste cooking oil and acrylonitrile-butadiene-styrene on the low-temperature performance of crumb rubber–modified asphalt was explored by using the Burgers model fitting parameters and the $\mathrm{\Delta }{T}_c$ value between the limit temperature of the critical low-temperature performance grade. The test results showed that cooking oil reduces the rotational viscosity of crumb rubber–modified asphalt, and acrylonitrile-butadiene-styrene enhances its storage stability. When the acrylonitrile-butadiene-styrene and waste cooking oil contents reached 4% and 3%, respectively, the rotational viscosity and separation index values of crumb rubber–modified asphalt decreased by 11.2% and 49.8%, respectively. Waste cooking oil notably enhanced the crumb rubber–modified asphalt’s ductility, particularly in the case of crumb rubber–modified asphalt compounded with 4% acrylonitrile-butadiene-styrene and 3% waste cooking oil, exhibiting the longest ductility and the highest toughness value, which were 85% and 75.6% higher than the original crumb rubber–modified asphalt, respectively. Insights from Burgers model parameters and $\mathrm{\Delta }{T}_c$ values revealed that waste cooking oil improves CRMA’s stress relaxation ability and reduces its critical low temperature, and acrylonitrile-butadiene-styrene has no adverse impact on CRMA’s resistance to low-temperature thermal cracking. Fourier transform infrared spectroscopy (FTIR) test results demonstrated that the addition of acrylonitrile-butadiene-styrene does not lead to a chemical reaction with crumb rubber–modified asphalt.

Developing low-carbon and green self-compacting concrete (SCC) is essential for advancing sustainable building materials. In this study, recycled steel fibers (RSFs) and industrial by-products were combined for the production of SCC made with recycled aggregates (RSCC), with the aim of introducing multiple waste materials to improve the sustainability of SCC. 14 RSF-reinforced RSCC mixtures (RSF-RSCC) were prepared by replacing natural coarse aggregates (NCAs) with recycled coarse aggregates (RCAs) and cement with supplementary cementitious materials (SCMs) and reinforced with RSFs. The parameters studied in this paper include replacement levels of RCAs (75%), SCMs (50% and 75%), and RSFs (0.5%, 1.0%, and 1.5%). The influence of different content of RSFs and SCMs combinations on workability and mechanical properties was studied, and the synergistic influence of RSFs and SCMs was investigated in detail. The microstructure characteristic was investigated using a scanning electron microscope. The test results show that the addition of SCMs can compensate for the adverse effects of RSFs on the fresh properties, and all RSF-RSCC exhibited superior workability. Furthermore, the incorporation of RSFs enhanced the mechanical properties of RSCC, resulting in remarkable improvement in the compressive and flexural strengths. The combined incorporation of RSFs and SCMs led to an excellent synergistic effect, which resulted in significant enhancements in the mechanical properties.

The global increase in water consumption has led to significant domestic wastewater (DW), with only 55.5% being treated properly. Discharging untreated DW has serious environmental consequences and wastes a valuable resource. Therefore, this study proposed replacing 25%–100% potable water with DW in preparing alkali-activated slag (AAS) mortars. The results indicated that the use of DW promoted the hydration of AAS. Pore structure analysis revealed that DW enhanced the formation of gel pores while reducing mesopores, resulting in a higher elastic modulus and a denser microstructure of AAS mortars. Consequently, the compressive strength of AAS mortars increased by 9.0%–20.3%, and the autogenous shrinkage decreased by 7.5%–34.5%. Moreover, replacing 100% of potable water with DW maximizes its utilization and improves the cost–benefit and eco-efficiency of AAS mortars by 9.4% and 10.0%. These findings demonstrate the feasibility of using DW as mixing water for AAS mortars, offering a sustainable approach to the utilization of DW.

Carbon nanotube (CNT) is a material with high modulus, high tensile strength, good flexibility and large specific surface area. This material has become very popular and has been also applied as an asphalt modifier. In the current research, multi-walled carbon nanotubes (MWCNTs) and styrene-butadiene-styrene (SBS) were employed as modifiers to fabricate MWCNTs/SBS composite-modified asphalt binder (hereinafter referred to as MCSA). The technical performance of MCSA was evaluated by performance tests and the optimal content of MWCNTs was determined. MCSA dispersion characteristics and interactions of components were investigated by microscopic test methods. Interactions of molecules and tensile behavior of MWCNTs in MCSA were explored by molecular dynamics (MD) simulation. The modification mechanism of MWCNTs was studied at the macro, micro and molecular levels. The following conclusions were drawn: According to macroscopic test results, the optimal content range of MWCNTs was 0.4% to 0.6%. MWCNTs modification process on asphalt binder was a physical modification. MWCNTs enhanced interactions among components and this effect was most obvious when MWCNTs content was 0.6%. The results of the macroscopic test were verified by the microscopic test. MWCNTs molecules could couple with SBS modifier as well as asphalt component molecules, thereby enhancing the interaction of each component in the system. MWCNTs mainly enhanced molecular interactions by increasing van der Waals energy in MCSA system, to make it more stable. MWCNTs do not break during the pull-out process. The molecules of asphalt component, SBS modifier and MWCNTs penetrated each other, which enhanced system stability to resist external loads and improved the mechanical properties of MCSA.

Silicon carbide powder, as a high-performance microwave-absorbing material, can be used for self-healing of microcracks in asphalt pavements, which is promising to lift the limitation of the application of microwave heating technology in road maintenance. The primary adhesive skeleton in asphalt mixtures, known as asphalt mastic, plays a crucial role in determining the overall properties of the mixtures. In this study, conventional limestone asphalt mastic and silicon carbide powder asphalt mastic with high microwave absorption capacity were designed and prepared using varying filler-bitumen ratio (FBR). The performance and properties of the filler were tested by XRD and SEM. The microwave heating test and DSR test were carried out on the fillers and asphalt mastics to study the microwave heating properties and rheological properties. Based on rheological properties, initial and optimal temperatures for self-healing are determined. The results show that the addition of silicon carbide powder had a significant increase in the initial self-healing temperature of asphalt mastic, but had little effect on the optimal self-healing temperature. Moreover, the difference in temperature to achieve the same rutting factor (1 or 10 kPa) is not significant. These indicate that it is feasible to consider silicon carbide powder as a filler in asphalt mixtures from the point of view of self-healing temperature. The exceptional microwave absorption capabilities of silicon carbide powder boost the microwave absorption of silicon carbide asphalt mastic, significantly reducing the time required to reach the necessary self-healing temperature. Overall, silicon carbide powder can be used in road engineering to enhance the microwave absorption properties of asphalt mixtures, which advances the application of microwave maintenance technology in road engineering.

Phosphorus tailings are solid wastes generated from mineral processing. It limits the green development of phosphorus chemical industries. Phosphorus tailings mainly consist of dolomite, fluorapatite, and quartzite, so they are used as mineral admixtures to prepare concrete, which not only reduces carbon emissions but also eliminates phosphorus tailings and solves the issues caused by the large accumulation of phosphorus tailings. In this paper, C40 concrete was prepared with different content and fineness of phosphorus tailings, and the effects of phosphorus tailings on its workability, mechanical properties, and durability were investigated. The harm of heavy metals leaching of concrete mixing with phosphorus to the environment was evaluated. The mechanism of the effect of phosphorus tailings on concrete was also analyzed by using characterization methods such as heat of hydration, XRD, and SEM. The results showed that the workability of concrete increased with the phosphorus tailings amount increased, but the mechanical property of concrete decreased. The fineness of phosphorus tailings has little effect on the workability and mechanical properties of concrete. The durability properties of concrete were impaired with the increase in the admixture of phosphorus tailings, but the fineness of phosphorus tailings has no significant effect on the durability properties of concrete. With the increase of the curing time, the structure of the concrete mixed with phosphorus tailings became denser than the concrete without phosphorus tailings incorporated. The concrete mixing with phosphorus tailings had little detriment to the environment. Finally, using the particle size of 20 μm and the content of 20% of phosphorus tailing to replace the cement was suggested.

To achieve efficient utilization of reclaimed asphalt pavement (RAP) materials, a bioregenerant (BR) was developed in this research, and waste vegetable oil (WVO), alkylphenol polyoxyethylene ether (APEO), plasticizer [tributyl acetylcitrate (ATBC)] and tackifying resin (FTR) were chosen as components of the regenerant. The composition ratio of BR was designed based on the response surface method (RSM), and the optimal BR dosage and the regeneration effect of BR on the bioregenerated mixture (BRM) with different RAP contents were determined and investigated. Results showed that the optimal composition ratio of BR was found to be $\mathrm{WVO}\text{-}\mathrm{APEO}\text{-}\mathrm{ATBC}\text{-}\mathrm{FTR}=100:2:23:10$. The addition of BR significantly reduced the high-temperature stability and aging resistance of the mixture, but improved its low-temperature cracking resistance and fatigue resistance. Additionally, BR prominently contributed to the improvement for the water stability of the regenerated mixture, and its regeneration effect was found to be similar to that of two commercial regenerants, although excessive BR led to the decline of water stability. Moreover, the high-temperature stability and aging resistance of BRM when mixed with 20%, 30%, and 40% RAP were similar to those of the new asphalt mixture (NAM). At 20%, 30%, and 40% RAP content, both the low-temperature cracking resistance and fatigue resistance of BRM met the requirements. However, when the RAP content exceeded 40%, the water stability of BRM went beyond the specification limit. Taking into account the overall road performance, it is suggested that the optimal BR dosage is 5%–9%, and the maximum RAP content ensuring the road performance of BRM meets the requirements is 40%. These research findings will contribute to addressing the stacking problem of reclaimed asphalt pavement materials and environmental pollution, aligning with green and environmentally friendly sustainable development principles.

Waste tires, used in combination with polymers, have been extensively employed in the construction of asphalt pavements. The performance of these hybrid asphalts varies depending on the manufacturing process, the characteristics of the neat binder, and other factors. The present study aims to investigate the effect of crumb rubber, polymer, and neat asphalt on physicochemical and rheological properties of terminal blend rubberized asphalt (TBRA). Thermal gravimetric (TG) testing was performed to analyze the component distribution of different crumb rubber modifiers (CRMs). Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and solubility and storage stability tests were used to characterize the physicochemical properties of TBRA binders. The rotational viscosity (RV) test, high-temperature performance grade (PG), and rheological master curve were used to compare the rheological properties of various TBRA binders, respectively. Results indicated that crumb rubber and neat binder characteristics, as well as the addition of polymer, impact TBRA performance. However, the influence of neat binder and polymer is more significant than that of crumb rubber. The primary differences in the physicochemical properties of TBRA prepared with different crumb rubber types are related to solubility and degradation degree. The interaction between Zhonghai neat asphalt and crumb rubber is weaker than that of ESSO and Jinshan asphalt, as evidenced by a comparison of molecular weight distribution. Moreover, 3.0% styrene-butadiene-styrene (SBS) polymer can significantly improves the elastic property of TBRA produced with ESSO neat asphalt, which is evidenced by similar phase angle plateau region with 4.5% SBS modified asphalt.

The multiple regeneration of aging asphalt pavements has emerged as a pavement maintenance approach. However, the micromechanisms and performance deterioration patterns associated with multiple regenerations remain unclear. The present work aims to investigate the rheological and physicochemical properties of styrenic block copolymers (SBS)-modified asphalt during multiple recycling processes. The rheological properties, nanostructure, and functional group evolution of SBS-modified asphalt during multiple recyclings were evaluated using rotational viscosity, frequency scanning, multistress creep recovery (MSCR), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) tests. The key findings demonstrated that the viscoelasticity of asphalt is affected by both SBS degradation and asphalt aging. During the initial aging phase, SBS degradation mainly affects the asphalt properties, whereas the subsequent aging process becomes the dominant factor. Moreover, the viscoelasticity of the asphalt binder is primarily influenced by aging rather than the SBS degradation. Importantly, the SBS-modified asphalt continues to meet specification requirements even after multiple recycling rounds, demonstrating the feasibility of aging SBS-modified asphalt binder through multiple regeneration techniques.

The accumulation of phosphogypsum (PG) has become a significant environmental and economic challenge, making PG reuse an urgent concern. This study aims to explore the potential of combining PG with steel slag (SS), ground granulated blast-furnace slag (GGBS), and cement clinker (CC) to create excessive-sulfate phosphogypsum slag cement (EPSC) for use in self-compacting concrete (SCC). However, residual acid and other impurities in PG can significantly slow down the setting time of EPSC. To optimize the setting time, different methods including wet grinding, washing, and the addition of pure gypsum, limestone powder (LP), and aluminum cement (AC) are used. Results show that the wet grinding method and washing method remove soluble phosphorus impurities and reduce fluorine ion levels by 64%. However, nonsoluble impurities that cannot be removed by wet grinding and washing continue to affect EPSC’s setting time. Furthermore, the addition of LP shortens the setting time, but not enough. Using a 3% dosage of AC successfully reduces the setting time to a satisfactory level and EPSC SCC with a 28-day strength greater than 40 MPa is produced using the paste rheological threshold method.

High-strength carbon steel bolts were fractured by the tension, shear, or combined failure mode in semirigid and flexible beam-to-column connections as observed from natural fire incidents and full-scale fire tests. This phenomenon is attributed to the temperature-sensitivity of quenching and tempering procedures on these bolts. However, provided that these bolts are replaced by stainless steel bolts in these connections, the connection performance of the latter can be better improved compared to that of the former. Accordingly, this paper documents an experimental investigation of low-carbon austenitic high-strength A4L-80 bolts after fire exposure to determine the temperature-based stress-strain curves. The residual properties of Young’s modulus, yield and ultimate strengths, and ultimate strain obtained from the experimentally measured stress-strain curves were compared with those of base materials regarding A4L-80 and carbon steel bolts including Grade 8.8, 10.9, and 12.9. Considering the limitations of prediction accuracy of reduction models of base materials in the existing standards and design manuals, reduction models after fire exposure were proposed for five mechanical parameters (Young’s modulus, yield and ultimate strengths, ultimate strain, and strain-hardening exponent in the Ramberg-Osgood model). In combination with the currently proposed reduction models, the temperature-dependent constituent model of A4L-80 was formulated using five mechanical parameters at ambient temperature. It is concluded that austenitic high-strength bolts after fire exposure are capable of providing a more pronounced enhancement to the fire resistance of semirigid connections than carbon steel bolts, and the formulated material model showed good consistency with stress-strain curves acquired from experimental tests. Finally, a finite element model (FEM) with this material model was established based on the previous experimental study of web angle cleat connections with A4L-80 after fire, according to which the moment-rotation curves obtained from FEM can correspond well to those done from tests in previous study. This confirms the further validation and prediction accuracy of the formulated material model.

Microbially induced carbonate precipitation (MICP) utilizing a urease active bioslurry is an ecofriendly method that can improve soil strength. However, the micromechanisms, such as ion diffusion, production rate of ${\mathrm{CaCO}}_3$, porosity, and permeability of pile reinforced by bioslurry, require further investigation. In this study, both biopile model tests and a coupled fluid-flow, solute transport and biochemical reactive model were conducted to analyze the mechanical property and biocementation mechanism of pile formed by urease active bioslurry. Results showed that the simulated ${\mathrm{CaCO}}_3$ content along the biopile length after 120 h grouting was close to test results. The UCS of the biopile decreased from 3.44 MPa to 0.88 MPa and the ${\mathrm{CaCO}}_3$ content decreased from 13.5% to 9.1% with increasing depth. The largest reduction in ${\mathrm{CaCO}}_3$ content was observed in the middle part of the biopile as the ${\mathrm{CaCO}}_3$ crystals in the upper part hindered the downward transport of the cementation solution. The morphology of ${\mathrm{CaCO}}_3$ crystals was influenced by cementation solution concentration, as evidenced by the predominance of spherical vaterite crystals in the upper part of the biopile and rhomboidal calcite crystals in the middle and lower parts. During the grouting process, the concentration of calcium ions and urea decreased, while the ammonium ion levels increased with depth due to the utilization of calcium ions and urea for ${\mathrm{CaCO}}_3$ precipitation and ammonium ion production. The production rate of ${\mathrm{CaCO}}_3$ first increased rapidly to reach a peak value and then decreased. The porosity and permeability demonstrated both linear and nonlinear decreasing trends as the ${\mathrm{CaCO}}_3$ concentration increased. The largest reduction in porosity and permeability, reaching 20% and 58% in the biopile top.

In this study, we investigate the water and chloride ion (${\mathrm{Cl}}^{-}$) transport properties of aeolian sand mortar (ASM) in an unsaturated state. Capillary absorption tests were conducted on ASM with varying water-to-binder ratios and different concentrations of chloride salts in clear water solutions. The ${\mathrm{Cl}}^{-}$ content at different depths in ASM was determined using layered drilling, powder extraction, and chemical titration. The relationship between water and ${\mathrm{Cl}}^{-}$ transport properties under capillary absorption was examined. The results indicate that moisture serves as a transport medium for ${\mathrm{Cl}}^{-}$ in mortar, but its transport depth is significantly smaller than that of water, revealing a non-synchronization between the two transports. The transmission depth and capillary absorption ratio of water in the mortar decrease with increasing initial saturation. A linear relationship between water and ${\mathrm{Cl}}^{-}$ transport depths is observed within the first 7 days of capillary absorption. Beyond 7 days, the water transport rate gradually slows down, while ${\mathrm{Cl}}^{-}$ continues to be transported due to the presence of an ion concentration gradient. As the initial saturation increases, the percentage of gel pores decreases, and the percentage of transition pores and capillary pores in the matrix increases. Finally, incorporating the theory of unsaturated capillary water absorption, we introduce Boltzmann variables and develop a predictive model for the relative water content distribution under capillary water absorption in ASM. This study provides a theoretical foundation for the widespread application of ASM, and the proposed research model offers new insights into the underground environment and the durability of concrete structures affected by moisture transport.

To investigate the effects of aging on the microstructure, mechanical behavior, and thermal performance of bitumen surfaces, this study utilizes atomic force microscopy (AFM) for a qualitative and quantitative assessment of the surface morphology, roughness, and surface energy evolution at the microscopic scale during the fusion process of both virgin and aged bitumen. The formation mechanism of beelike structures is also analyzed. Additionally, the thermal stability of bitumen is evaluated through thermogravimetric (TG) and derivative thermogravimetry (DTG) curves. Results revealed substantial differences in polarity and structure between asphaltene and surrounding bitumen molecules, leading to ineffective dissolution and dispersion of asphaltene in surrounding bitumen molecules, ultimately forming distinct striped beelike structures. With an increase in the content of virgin bitumen, the quantity and total area of beelike structures significantly increase, whereas their size and average area decrease. Aging induces the migration and alteration of bitumen internal components, resulting in the aggregation, dispersion, and fusion of biomass on the microsurface, thereby increasing surface roughness and decreasing surface energy. With the introduction of virgin bitumen and rejuvenators, bitumen surface roughness markedly decreases, whereas surface energy exhibits an increasing trend. This suggests that the microstructural properties of rejuvenated bitumen are effectively restored, with high fusion homogeneity between virgin and aged bitumen. Thermal analysis results indicate that the characteristic temperature and residual weight of rejuvenated bitumen are lower than aged bitumen, approaching the virgin bitumen. Specifically, the residual weight for virgin bitumen, aged bitumen, and rejuvenated bitumen are 17.23%, 22.03%, and 17.65%, respectively. This suggests that the introduction of rejuvenators increases the content of light components in bitumen, leading to a lower thermal decomposition temperature due to the volatilization of light components during heat treatment.

Spent waterglass foundry sand (SWFS) is a major waste in foundry industries and should be disposed of preferentially. Two SWFS subjected to working temperatures of 100°C (${\mathrm{SWFS}}_1$) and 800°C (${\mathrm{SWFS}}_8$) were prepared to investigate their effects on the flow, compressive strength, micromechanical properties, and pore structure of alkali-activated slag (AAS). Experimental results confirmed that the overall performance of AAS was determined by the dissolved properties of the dried waterglass coating and the content of SWFS. The flow values of AAS in the first 1 h were increased by adding two SWFS. ${\mathrm{SWFS}}_1$ can release abundant silica tetrahedra into the activation system, contributing to micromechanical and macromechanical properties. The compressive strength of ${\mathrm{SWFS}}_1$-added AAS mortars was increased by 28.8% to 49.0% at 28 days. In contrast, ${\mathrm{SWFS}}_8$ exerted weaker dissolved properties. The compressive strength of AAS mortars was slightly enhanced and the maximum increment at 28 days was only 8.5%. In summary, this paper confirmed the feasibility of using SWFS as reactive fine aggregates for AAS owing to the dried waterglass coating.

Phosphogypsum (PG) is an industrial solid waste generated during the preparation of phosphoric acid, which is produced in large quantities and stockpiled or discharged into the sea. This study aims to design sustainable pavement base materials constituting significant PG content. The physical and chemical properties of the raw materials were first tested. The optimum moisture content and maximum dry density of specimens were determined by compaction tests. The unconfined compressive strength (UCS), split tensile strength (STS), freeze-thaw cycles, and shrinkage tests were used to evaluate the mechanical performance of phosphogypsum pavement base material (PPBM). Furthermore, the interaction mechanism was investigated by applying scanning electron microscope (SEM) and Fourier-transformed infrared (FTIR) tests. The results showed that the 7-day UCS of PPBM with cement content 8%–12% was greater than 3 MPa. The specimens retained 91.3% unconfined compressive strength over five freeze-thaw cycles. Unlike traditional semirigid base materials, the PPBM exhibited no shrinkage strain, which is manifested by the growth of expansion strain with increasing amounts of PG. Through microscopic observation, the PPBM produced ettringite (AFt) and calcium-silicate-hydrate (CSH) with the extension of curing time, which is consistent with the analysis of FTIR spectrums. The crystallized water in the PG participates in the hydration reaction.

The production of pulp and paper from recycled paper generates significant quantities of deinking paper sludge (DPS). This sludge contains a significant amount of organic matter (36%) as well as heavy metals such as Pb, Zn, and Cr. In this work, the incorporation of DPS (0%, 8%, 10%, and 12%) in the manufacture of clay bricks leads to valorization of this waste by showing that two of its contents considered problematic (organic matter and heavy metals) have several positive effects. It was found that the organic parts were transformed into pores after brick firing (850°C), which improved thermal insulation while keeping mechanical resistance in conformity with usual standards. For the heavy metals, which make DPS a hazardous waste, a leaching test was employed. The results show that these metals were trapped in the ceramic matrix after the firing of bricks at a high temperature, resulting in a final product that was not dangerous. Other tests were carried out on bricks with DPS to evaluate density, water absorption, shrinkage, loss on ignition, porosity, and microstructure in order to characterize this new product. It was concluded that DPS can be used in clay bricks as an asset for the formation of pores to enhance thermal insulation. The addition of DPS can be optimized at 10% to comply with the standard and not exceed the required values for shrinkage, water absorption, and loss on ignition.

Major global consumption of coffee has led to the generation of a substantial amount of spent coffee grounds (SCG), which contribute to environmental burdens. Research on using SCG for asphalt modification is limited. This study aimed to investigate the effectiveness of using biochar from spent coffee grounds (SBC) produced through low-oxygen pyrolysis as a modifier for asphalt, to enhance high-temperature performance and aging resistance. The results demonstrated excellent compatibility between SBC and asphalt binder without causing agglomeration. The introduction of SBC significantly enhanced asphalt’s high-temperature stability and resistance to deformation, while some adverse effects on low-temperature performance were found. The inclusion of SBC improved the anti-aging properties of asphalt, as indicated by various aging performance indices. A decreasing trend was observed for sulfoxide ($\mathrm{S}═\mathrm{O}$) $\mathrm{1,030}{\mathrm{cm}}^{-1}$. Atomic force microscopy (AFM) images revealed the changes in the size and shape of beelike structures, with smaller bee structures observed in SBC-modified asphalt (SBCMA). Overall, these microscopic structures were consistent with the rheological properties. Due to the improvement of high-temperature stability and anti-aging properties, SBC could prove to be an environmentally friendly and sustainable modifier for asphalt.

Incineration bottom ash (IBA) is a by-product generated from incineration of municipal solid wastes, and it is mostly landfilled, especially for fine IBA. Reusing IBA with waste soils as filling materials in civil engineering can be a potential solution. However, the existing studies only focused on the air-cured IBA-soil mixtures in the laboratory, whereas in the field, the mixtures may contact water or immerse in water. Because IBA is rich in sulfates, the stability of IBA-soil mixtures in water may be compromised. Therefore, this study investigated the stability of IBA-marine clay (MC) mixtures in water. Ordinary portland cement (OPC) and granulated blast-furnace slag (GGBS) served as binders to stabilize/solidify IBA-MC. The appearance, strength, mineralogy, and microstructure of IBA-MC, OPC-IBA-MC, and GGBS-IBA-MC were studied. The results showed that all mixtures performed well when cured in air, but some deteriorated after soaking in water. IBA-MC and OPC-IBA-MC subjected to a short precuring period developed significant cracks and strength loss. Long precuring can reduce or eliminate the cracks on specimens during soaking, leading to higher strength. However, GGBS-IBA-MC had no surficial defects and only a slight strength decrease under both precuring periods. The mineralogy and microstructure of IBA-MC and stabilized IBA-MC revealed that the formation and growth of ettringite were responsible for the deterioration of IBA-MC and OPC-IBA-MC soaking in water.

Bonding of soil grains can be achieved by melting added polymer particles initially mixed with dry soil. Salient challenges associated with conventional external heating via boundary conduction include long treatment durations and inhomogeneous bonding. The current study aims to overcome these challenges via the use of microwaves to induce quick internal heating. Results of experiments on sand-silt specimens that contain a 10% fraction of natural microwave susceptor grains confirmed that internal heating produces homogeneous bonding much quicker than external heating (by a factor of 20), particularly when the target soil mass is relatively large. The tensile strength ($q_t$) of specimens bonded via microwave heating was found to be inversely proportional to their fines content (FC), although the temperatures sustained by soils increased with increasing FC. Bonded specimens subject to a wetting–drying cycle exhibited lower tensile strengths than the unwetted counterparts. Yet, specimens subject to reexposure to microwaves after a wetting–drying cycle exhibited tensile strengths of at least 85% that of analogous unwetted specimens. The power penetration depth for 2.45 GHz microwaves was calculated to be $0.5\mathrm{m}<{\mathrm{S}}_{\mathrm{p}}<0.8\mathrm{m}$ for dry soils. Therefore, applications deemed worthy of future consideration include large brick manufacturing, rapid repair of temporary runways, and treatment of polymer particle-laden rammed-earth walls.