Journal of Materials in Civil Engineering

Owing to a severe shortage of natural aggregates in terms of quantity and quality, alternative aggregate resources must be utilized in civil engineering construction to meet significant increase in aggregate demand. This study focuses on manufacturing artificial aggregates for pavement applications using two waste materials- mine overburden waste from the coal mining industry and fly ash from thermal power plants. Liquid alkali activator, a mixture of sodium silicate and sodium hydroxide, is used as a binder. The centrifugal forces generated due to a rotating disc pelletizer enables mixing the said components resulting in formation of spherical-shaped pellets. The nucleated pellets are oven cured at 70°C for 7 days. Based on extensive laboratory test trials, the optimal features to produce competent aggregates in terms of angle and revolution speed of the disc pelletizer, dosage of the liquid alkali activator and the concentration of the NaOH are proposed. Finally, the manufactured aggregates are tested for properties relevant to flexible pavement applications. The aggregate impact and Los Angeles abrasion values are found to be 17% and 21.6%, indicating satisfactory resistance to impact and abrasion of aggregate particles under traffic loads. The basic material properties of these aggregates are found to conform to the Indian Roads Congress (IRC) and American Association of State Highway and Transportation Officials (AASHTO) standards for base and subbase layers. Moreover, base/subbase layers prepared with artificial aggregates and mine waste showed high California bearing ratio (CBR) of 54.3% and 80.5% for 2.5 mm and 5.0 mm penetration of the plunger, respectively, indicating high load-bearing capacity of pavement layers.

In this study, the performances of methylallyl ether (HPEG) type polycarboxylate ether-based water reducing admixtures (PCE) partially substituted with phosphate and sulfonate anionic groups were investigated. The effects of synthesized PCE’s on the fresh, rheological, and some hardened properties of mixtures prepared with cements having different ${\mathrm{C}}_3\mathrm{A}$ contents were examined. Increasing the phosphate and sulfonate substitution ratio of PCE up to a certain value improved the rheological properties of the mixtures. Best flow retention and rheological properties were obtained with 9% phosphate (P9) and 7% sulfonate (S7) PCEs. Due to the high PCE dosage used in the Marsh-funnel and mini slump experiments, the nonadsorbed PCE in the pore solution blocked the adsorbed polymers on the cement particles. Also, the hydrodynamic radius of the polymer had a significant effect on the adsorption and dispersion performance of PCE. Morover, with the increase of cement ${\mathrm{C}}_3\mathrm{A}$ content, the fresh properties of the mixtures were adversely affected. However, the increase in ${\mathrm{C}}_3\mathrm{A}$ content up to a certain value improved the hardened properties of the cementitious system.

This paper is aimed to study the corrosion resistance of Cr10Mo1 alloy corrosion-resistant steel (CR) in the seawater–sea sand concrete pore solution (SWSSCPS), compared with low-carbon steel (LC) and stainless steel (SS). X-ray photoelectron spectroscopy (XPS), SEM, atomic force microscope, and Mott–Schottky curve tests are applied to obtain information on the composition, structure, and morphology of the corrosion-resistant (CR) passive film. Finally, the difference between CR passive film and the other two kinds of steels under chloride attack is investigated, and the apparent morphology, microstructure, and chemical composition of the CR passive film during the attack are analyzed. With the exposure time increased, the passive film and interfacial integrity of CR are approximately equivalent to that of SS in terms of phase angle in the midband and low-frequency band modulus, indicating the anticorrosion performance of CR has a much better effect than that of LC and close to that of SS. The results reveal that the FeO in the passive film outer layer and a high amount of ${\mathrm{Cr}}_2{\mathrm{O}}_3/{\mathrm{Cr}(\mathrm{OH})}_3$ in the inner layer prevent CR from further corrosion by chloride ions.

Microbial induced carbonate precipitation (MICP) has the potential to have less hazardous impacts on the environment compared with traditional reinforcement technologies. In this paper, the mechanical property and cementing mechanism of MICP-treated mortar (MTM) are studied, and the double-layer rigid soaking mold is invented to prepare high-strength MTM samples. The effects of the cementation solution concentration (CSC), the concentration ratio of urea to calcium chloride (CRUC), aggregate particle size, and soaking time on the mechanical properties of MTM are researched. The results show that the strength of the MTM sample increases first and then decreases with the increase of CSC. The mean UCS of MTM samples reaches the peak of 8.19 MPa when the CSC is 1.5 M. The strength performance of MTM samples is relatively better when the CRUC is 1. For MTM samples with graded particle size, the sample with the particle size of 0.4–0.8 mm has the highest strength of 5.03 MPa. For MTM samples with full particle size, the mean UCS increases from 1.18 to 12.88 MPa with the increase of the maximum particle size from 0.2 to 2 mm. The MTM sample with full particle size has a higher strength when the maximum particle size is larger than 0.8 mm. The strength of MTM samples increases within 9 days over the soaking time and then tends to be stable at the later stage. The calcium carbonate mineral in the MTM sample is mainly calcite and a small amount of vaterite, and the strength of MTM is positively correlated with its ${\mathrm{CaCO}}_3$ content. The ${\mathrm{CaCO}}_3$ content of the sample shows a high surrounding and low middle distribution.

Recent disasters involving upstream raised tailings dams in Brazil have caused regulatory agencies to prohibit the construction of new upstream dams and demand the decommissioning of existing ones. As such, new alternatives are being sought to safely dispose of iron ore exploitation byproducts. The dry stacking of filtered tailings is an option to diminish the risks associated with tailings storage facilities and cope with new legislation. Accordingly, this paper studies new solutions for enhancing the performance of tailings for dry stacking purposes. The behavior of reinforced and nonreinforced iron ore tailings-alkaline-activated cement (AAC) blends was studied through unconfined compressive strength tests and conventional triaxial testing. The AAC is produced from the residues of iron ore exploitation (waste and tailings). The addition of fibers has enhanced the performance of cemented iron ore tailings with increased strength regardless of the fiber content and ductility. Also, reinforcement effectiveness values were greater than those reported for other cement agents, due to the lower stiffness of the cemented matrix from AAC compared with others. A comparative analysis between using only AAC and ACC plus 0.5% of fibers within the $\eta /B_{iv}$ framework was proposed. The dosage curves for the same $q_u$ value yielded an $\mathrm{AAC}=20.80\%$ for AAC only and $\mathrm{AAC}=3.80\%$ when using 0.5% of fibers. Therefore, using fibers can collaborate with the feasibility of using a new waste-based AAC to construct dry stacking facilities.

The influence of the curing methods on the flexural performances of the milling steel fiber reinforced ultra-high-performance concrete (UHPC) with a high fiber content was systematically evaluated in this study, alongside the flowability and compressive strength. The UHPC specimens were subjected to standard curing and steam curing, employing three steel fiber reinforcing schedules: single milling fiber, single straight fiber, and a combination of both. The flowability of the UHPC was found to be less affected by the milling fiber compared to the straight fiber. Steam curing significantly enhanced the compressive strength but had a slight negative effect on the flexural behavior. However, this adverse effect could be mitigated as the fiber content increased. The flexural strength and toughness of the UHPC with milling fiber were minimally influenced by steam curing, suggesting that standard curing was sufficient for the milling fiber-reinforced UHPC. Conversely, steam curing exhibited an improvement in the flexural behavior of the UHPC containing a hybrid combination of milling and straight fibers. In addition to developing an empirical model for compressive and flexural strengths, we proposed a data-driven model called Gaussian process regression (GPR) to predict the flexural behaviors of the UHPC with varying fiber content, types, and curing methods. The data-driven model demonstrated high accuracy, with an ${\mathrm{R}}^2$ value of 1.0 when compared to the experimental data.

Abstract

In the recent times, rejuvenators have been investigated as a potential solution to incorporate higher amounts of recycled asphalt (RA) in hot-mix asphalt (HMA). In this study, waste cooking oil (WCO) was used as rejuvenator to assess the performance of RA mixtures. A method was proposed to optimize WCO content in HMA with high RA content ($>45\%$), balancing the performance in the high and intermediate temperatures. The optimized mixtures with high RA content depicted rut depth and cracking properties similar to HMA. Simultaneously, the recycled mixtures utilizing WCO dosages derived from a blending equation exhibited pronounced rutting, implying that the blending equations yielded WCO dosages that exceeded the necessary dosages. A life cycle assessment (LCA) study considering a cradle-to-gate approach indicated that incorporating 45%, 60%, and 75% RA would decrease total embodied energy (TEE) by 25.08%, 33.30%, and 41.17% compared with HMA. Further, a sensitivity study with distance as the parameter indicated that the permissible distance of RA source for 45%, 60%, and 75% was 500, 300, and 300 km, beyond which RA mixtures showed higher TEE than HMA.

Practical Applications

The incorporation of reclaimed asphalt pavements (RAP) using waste cooking oil as a rejuvenator presents significant practical implications for the asphalt industry and sustainability initiatives. By enabling the use of higher RAP content while maintaining the performance of traditional mixtures, this research offers a more environmentally friendly and cost-effective approach to road construction. Moreover, the life cycle assessment findings reveal substantial reductions in environmental impacts when including different RAP proportions, making a strong case for improved environmental sustainability. The sensitivity analysis regarding the distance between RAP sources and construction sites provides valuable insights for location-based decision-making, ensuring that the benefits of RAP utilization remain maximized. In summary, the potential application of the study emphasizes a greener and durable road infrastructure, with a focus on increasing RAP content using waste cooking oil as a rejuvenator in asphalt mixtures.

The current study investigated the efficacy of a protein-based biopolymer called casein for the modification of the primary and secondary compressibility characteristics and ability to resist sustained moisture attack in organic soils. The dry mixing method was adopted for the tests with dosages of 0.5%, 1%, 2%, and 4% added as a percentage of the dry weight of the soil. Incremental consolidation tests indicated that the compressibility reduced with the inclusion of casein, leading to lower void ratios with an increase in consolidation pressure and casein concentration. The primary compression index ($C_c$) and secondary compression index ($C_{\alpha }$) were reduced by 85% and 67%, respectively, for a 2% casein-soil mix at a consolidation pressure of 100 kPa. The compression ratio ($C_{\alpha }/C_c$) for the 2% treated soil fell outside the range of 0.01, similar to organic soils with fibrous materials. The permeability was reduced with an increase in casein concentration up to 2% (${10}^{-10}\mathrm{m}/\mathrm{s}$) but exhibited a rise at 4% due to the formation of effective flow paths by the formation of inter-aggregate voids. At extended curing periods, the fiber formations contributed to the strength gain in amended soils. However, the successive wetting and drying (w-d) cycles led to fiber detachment and reduced the resistance to moisture attack leading to collapse. The 2%-amended casein-soil mix proved to be most suitable in terms of reduced compressibility and sustained the highest number of w-d cycles. The findings from the current study support the inclusion of casein for short-term applications. The use of this novel material in the ground improvement industry will aid in waste management and recycling, and it can act as a replacement for unsustainable chemical stabilizers such as cement and lime.

The high-salt fog environment under a marine climate affects the capillary water absorption performance of porous building materials, causing changes in the thermal and wet properties of the materials and in their structural durability. Therefore, a capillary water absorption experiment of coral sand concrete (CSC) in different salt solution concentrations was designed in this study. The experimental results showed that salt had the effect of first promoting and then inhibiting capillary water absorption coefficient ($A_{\mathrm{cap}}$) with increased salt solution concentration. Salt had the effect of promoting liquid diffusivity ($D_l$). In addition, by analyzing the surface tension and viscosity of a sodium chloride solution, the mechanism of the influence of liquid properties on $A_{\mathrm{cap}}$ was briefly explored. The results provide a theoretical basis for the establishment of a coupled heat and moisture transfer model of porous building materials in marine climates.

This paper investigates the tensile behaviors and self-healing of engineered cementitious composite (ECC) under sulfate wet–dry cycles to reflect the durability. Four pretensile strain levels of 0%, 1%, 1.5%, and 2% were designed. The uniaxial tensile test, three-point bending test, and single-crack tensile test were performed, along with the microscopic characterizations of scanning electron microscope (SEM) and X-ray diffraction (XRD). The results indicated that the sulfate wet–dry cycle exposure had a positive effect on the tensile strength and initial cracking strength of the uncracked ECC, while that was negative on the tensile strain capacity. The insufficient margin of the ${\sigma }_{\mathrm{oc}}/{\sigma }_{\mathrm{cr}}$ and $J_{\mathrm{b}}^{\prime }/J_{\mathrm{tip}}$ indices explained the lower tensile strain. The tensile strength and initial cracking strength of the cracked ECC with 1% pretensile strain surpassed those of the uncracked ECC after undergoing 80 sulfate wet–dry cycles (80 C), while that did not hold for the other cracked ECCs. All the cracked ECCs showed a similar tensile strain after undergoing 80 C. The crack with a width of less than 100 μm achieved complete self-healing. The self-healing products of ECC under sulfate wet–dry cycle exposure may comprise of calcium (alumino) silicate hydrate [C-(A)-S-H] gel, calcite, ettringite, and gypsum. The current findings could offer reference points for applying ECC use in coastal regions.

This paper examines the merits of using fibers derived from cigarette butts to enhance the performance of stone matrix asphalt (SMA). To this end, mechanical and environmental performances of SMA mixtures contained cigarette butt fibers were determined and compared with conventional SMA mixtures contained cellulose fibers. Two methods were applied to use cigarette butt fibers in mixtures included encapsulation with asphalt binder and mixing with hot asphalt binder for periods of three, five, and eight minutes. Performance tests included Marshall stability, asphalt binder drainage, moisture susceptibility, semicircular bending (SCB) at low and intermediate temperatures, wheel tracking tests, and toxicity characteristic leaching procedure (TCLP) were carried out on SMA mixtures contained different fibers. Mechanical test results showed that using encapsulated cigarette butts has detrimental effects on durability, low and intermediate temperature fracture resistance, and rutting performance in comparison with cellulose fibers. Nevertheless, utilization of cigarette butt fibers mixed with hot asphalt binder for 8 min improve water resistance, fracture characteristics, and rutting performance of SMA mixtures. Furthermore, by reducing the mixing duration of fibers with hot asphalt binder, moisture susceptibility and mechanical properties of mixtures were adversely impacted. TCLP test results revealed that utilization of cigarette butt fibers in SMA mixtures does not exhibit any environmental consequences. Finally, it was concluded that cigarette butt fibers mixed with hot asphalt binder for 8 min are good replacement for conventional asphalt binder stabilizers.

Mesoscale contact networks for asphalt mixtures play a crucial role in load resistance. However, there is a lack of quantitative characterization methods for contact networks. Topology can describe the contact relationships between multiple objects through points and lines. In this study, aggregate information was extracted by industrial computed tomography (CT) and digital image processing technology (DIP). The classification of disruption aggregates was determined by a two-dimensional (2D) topological contact model. Then, the correlation mechanism between topological indices and topologies was established based on the topological matrix. The algebraic connectivity (La) of nine different asphalt mixture disruption aggregates was analyzed. The results revealed that each type of asphalt mixture disruption aggregate was dominated by a certain La with higher frequency. As the nominal maximum size (NMAS) increased, there was a shift in the dominant topologies of different asphalt mixture disruption aggregates from those associated with lower La to those linked to higher La. Based on the higher frequency of La, there were 8 topologies with frequencies exceeding 20%; 5 with frequencies surpassing 10%; and 14 and 17 with frequencies greater than 5% and 2%, respectively. Furthermore, it was observed that the topologies of disruption aggregates predominantly consisted of simple topologies. Additionally, the frequency of complex topologies decreased as the number of nodes and connectivity increased.

Foam concrete is a porous cement-based material that could accommodate a high-volume particle addition at the mid- to high-density range (0.8 to $1.6\mathrm{g}/{\mathrm{cm}}^3$). However, with low-density foam concrete (0.4 to $0.8\mathrm{g}/{\mathrm{cm}}^3$), conventional particle inclusion (e.g., sand) tends to degrade the cellular microstructure and mechanical performance. Therefore, to improve low-density foam concrete, the novel use of crumb rubber (the rubber particles recycled from waste tires) in foam concrete is studied, as its unique attributes can potentially allow for the retention of structure and improved performance in foam concrete. The influence of no inclusion, sand, and crumb rubber on the microstructure and mechanical performance in foam concrete with the density of cellularized cement paste as 0.40 and $0.60\mathrm{g}/{\mathrm{cm}}^3$ was studied. Computed tomography indicates that the inclusion of crumb rubber can mitigate the foam degradation concern associated with particle inclusion in low-density mixtures. A notable improvement was also observed in the mechanical properties of $0.40\mathrm{g}/{\mathrm{cm}}^3$ rubberized foam concrete mixtures—compressive strength, plateau strength, and impact resistance—when referenced to the sand inclusion counterpart.

The limited early strength of low-heat cement (LHC) restricts its extensive application. This work compared the hydration degree, hydration products, and pore structure of the early strength of low-heat cement (ESHLC) in standard (P) and low-pressure (0.5P) curing by XRD, TG, SEM, and MIP. Also, the mechanical strength under different curing conditions was tested and compared. The results showed that compared with standard curing, the hydration degree of the early strength low-heat cement (ESLHC) lessens at 0.5P. Besides, by 90 days, the quantity of AFt had significantly declined, and the C─ S─ H gel displayed a loose cluster-like structure at 0.5P, showing that low atmospheric pressure has the potential to hasten the development of defects in hydration products. The ESLHC paste cured at 0.5 P displayed a coarser pore structure than that cured at P. At last, the low atmospheric pressure adversely affected the ESLHC mortar’s strength. This work delves into the hydration characteristics of ESLHC under low-atmospheric-pressure conditions, providing theoretical support for applying ESLHC in plateau areas.

In recent years, the construction industry has shifted toward sustainability, replacing traditional binders with eco-friendly alternatives. One such alternative is vinyl acetate-ethylene (VAE) polymer, known for its hydrophobic properties and used in various construction materials. This study explores the potential of VAE polymer to stabilize expansive clay as road subgrade material. VAE polymer was introduced into low-plasticity clay in varying percentages (1%, 1.5%, and 2% by dry weight of clay), and the mixtures underwent a series of geotechnical tests (compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), resilient modulus, shrinkage-swelling, and soil-water retention curve) and microstructural and chemical analyses [x-ray diffraction (XRD), x-ray fluorescence (XRF), microcomputed tomography (MicroCT), and thermogravimetric analysis (TGA)]. The results show that 1 adding 1% polymer resulted in the highest increase in mechanical strength (UCS, CBR, resilient modulus) by 34%, 40%, and 51%, respectively. Moreover, the incorporation of 2% polymer reduced the swelling-shrinkage potential by 67%. Microstructural analyses support these findings.

Nanopore-rich high porosity aerated cement (NHPAC) was prepared by introducing nanomontmorillonite slurry (NMS) into aerated cement paste, and the rheology of slurry, pore structure (air voids and microscopic pores), performance of NHPAC, and related mechanisms were investigated. The results indicated that NMS can generate rich microscopic pores in NHPAC and successfully achieve the part replacement of air void, increasing 0% to 30% of NMS rose microscopic pore porosity from 40.4% to 57.2% and from 40.5% to 54.9% for density grade of 250 and $400\mathrm{kg}/{\mathrm{m}}^3$, respectively. In addition, the content of air voids below 0.5 mm increased with increasing NMS. Due to the creation of small air voids, the replacement of air voids by microscopic pores, the pozzolanic reaction of nanomontmorillonite, and the performance of NHPACs were enhanced. 20% of NMS improved 56-day compressive strength by 34.8% and 10.9%, and reduced thermal conductivity by 15.3% and 9.3% for density grades of $250\mathrm{kg}/{\mathrm{m}}^3$ and $400\mathrm{kg}/{\mathrm{m}}^3$, respectively. This development might allow for the use of high porosity aerated cement.

Interface bonding between different asphalt pavement layers is crucial in maintaining the integrity of the pavement structure. To improve the interface bonding, bitumen emulsion is commonly used as the tack coat material. However, the bonding performance of conventional bitumen emulsion is limited. This study investigated the possibility of using waterborne epoxy resin modified bitumen emulsion as a novel tack coat material. The resistance to moisture damage of waterborne epoxy resin modified bitumen emulsion was evaluated using the boiling water test, followed by the characterization of the interface adhesion between waterborne epoxy resin modified bitumen emulsion and aggregate using the binder bond strength test. To further determine the interface bonding between different asphalt layers bonded by waterborne epoxy resin modified bitumen emulsion, a two-layer asphalt mixture structure was fabricated, and the shear strength was measured. The results indicated that the incorporation of waterborne epoxy resin can increase the interface bonding between the two asphalt mixture layers.

In this paper, research was conducted to evaluate and analyze the macromechanical properties and micromechanism of stone mastic asphalt (SMA) containing an eco-friendly fibrous substance, calcium sulfate whisker (CSW). The investigation included the preparation of SMA specimens containing the lignin fiber (0.3% by wt. of mixture) and CSW (0%, 6%, 8%, and 10%, by wt. of asphalt binder). Then, wheel tracking, low-temperature flexural bending, Marshall immersion, freeze-thaw indirect tensile strength, and flexural bending fatigue tests were carried out to evaluate the pavement performance of these mixtures. Scanning electron microscopy (SEM) analysis were selected to observe the microstructure and micromorphology of the mixture. The results of laboratory tests revealed that the rutting resistance, moisture susceptibility, and fatigue performance of SMA were improved by the addition of CSW, while the crack resistance at low temperatures decreased slightly. The flexural bending tensile strain, tensile strength ratio, and fatigue life of the mixtures (under different stress levels) showed a trend of initial increase followed by a decrease with increasing CSW content, while optimal results were present at 8% CSW. SEM images revealed that CSW and lignin fiber were uniformly distributed and formed a three-dimensional network structure. Besides physical infiltration and adsorption effects, an anchoring force similar to the mechanical bonding force also existed between CSW and asphalt binder. The economic benefit analysis indicated that SMA with 8% CSW showed the most cost-effective performance. Consequently, about 8 percent should be the ideal CSW content. The outcomes provide critical insights into improving the performance of SMA pavement and serve as an important reference for the development of sustainable pavement.

Abstract

The present study illustrates the susceptibility of optimized-quality recycled concrete aggregate (RCA) to supplementary cementitious materials (SCMs), such as silica fume (SF), ground granulated blast slag (GGBS), and mechanically produced recycled fine (M-Fine or MF), in concrete. According to the present research, old interfacial transition zone (OITZ) characteristics may be controlled if RCA is developed in such a way as to reduce mortar adhesion optimally. It may facilitate the penetration of binder particles, strengthening the OITZ even further. A high-quality surface may improve RCA’s self-cementing properties, which strengthen the new ITZ (NITZ). The combined effect may yield RCA characteristics equivalent to parent aggregate when interacting with a cement matrix based on SCMs. Substituting the cement with SF (11%), GGBS (14%), and MF (15%) contributes to the compressive strength of recycled aggregate concrete (RAC) up to 11.61% via strengthening the OITZ. SF and GGBS further enhance RAC tensile strength in a similar way to how they enhance natural aggregate concrete (NAC) tensile strength. The elastic modulus (MOE), fracture energy, and durability characteristics of RAC with SF and GGBS are significantly improved. RAC with MF (15%) shows compressive and tensile strength comparable to RAC with GGBS (14%) with marginal reductions in flexural strength. In comparison to RAC, RAC with MF has a 2.9% lower MOE. RAC-MF has 1.82% higher fracture energy than RAC. RAC-SF, RAC-GGBS, and RAC-MF have significantly reduced water absorption and water absorption rate (sorptivity) than RAC. There is a strong correlation between the compressive strength of RAC, RAC-SF, RAC-GGBS, and RAC-MF, and their UPV with ${\mathrm{R}}^2=0.92$. The sorptivity and electrical resistivity are also correlated with ${\mathrm{R}}^2=0.86$. SEM images show uniform and dense microstructure and EDS analyses shows Si-rich C-S-H gel formation, resulting in superior mechanical and durability properties in RAC with SCM compared to RAC.

Practical Applications

About 20% to 30% of recycled fines (M-Fines) below 150 μm are generated during RCA processing from construction and demolition waste. In addition, M-Fines are also generated during the removal of the mortar attached to the RCA. Thus, M-Fines as by-products of mechanical processing of RCA could be used as cementitious materials. Despite M-Fine’s low reactivity compared to SF, it may produce strength and durability characteristics comparable to other conventional supplementary cementitious materials like GGBS. In structural concrete, optimized-quality recycled concrete aggregates with supplementary cementitious materials, including M-Fines, can be used. In this way, it may be possible to promote construction and demolition waste recycling operations. Moreover, the effectiveness of SF and GGBS with RCA, as well as the performance of RAC-MF, may encourage the use of RAC as structural concretes and M-Fines as supplementary cementitious materials.

Asphalt pavement faces the threats of load-induced cracks. The cracks result in several diseases and shorten the service life of the pavement. In the pavement, the asphalt binder can heal cracks via its self-healing capacity. The self-healing capacity can mitigate the negative impact of the cracks. Thus, the capability has the value of being strengthened. As a maintenance measurement, microwave heating has been used to improve the healing capacity. The existing research on microwave heating and healing can be extended in two ways. First, the correlation between temperature and asphalt flow state needs further clarification. Second, the healing state judgement method with average temperature is not comprehensive because temperature distribution is not considered. This research studied these two aspects in three steps. First, the temperature data of asphalt mixture were obtained with an infrared camera. The second step was to investigate the correlation among temperature, flow state, and healing state of asphalt binder. The crucial temperature values were determined using a dynamic shearing rheometer (DSR) and capillary flow test. The third step was to include temperature distribution in the judgement of heating and healing states. The correlation determined in the second step and the temperature data from the first step were integrated with an analysis of area proportion. The area proportion corresponds to certain temperature ranges. Corresponding to the two researched issues, the main results can be summarized in two aspects. First, the initial temperature of capillary flow is over 40°C higher than that of Newtonian flow. Second, the area proportion is influenced by heating time and admixture content. The increase in heating time and admixture content changes the asphalt flow states between Newtonian flow and capillary flow, and is accompanied by variation of healing promotion modes.

Fly ash (FA) and granulated blast furnace slag (GBFS) were used as a precursor for geopolymerization to develop a low-carbon pavement base construction material. Based on the orthogonal test method, three levels were set separately for the L9 ($3^4$) test considering the proportion of FA (raw fly ash to grained fly ash), ratio of sodium hydroxide to liquid alkaline activator (LAA), and proportion of GBFS mixed with FA and solid–liquid ratio [(FA + GBFS): LAA] as factors influencing the geopolymer. The influence of these factors on the unconfined compressive strength (UCS) of soil stabilized by geopolymer was studied. The optimal combinations of levels and factors were determined. The UCS with these ratios combined was 5.1 MPa. According to the above compositions, the mechanical (UCS, splitting tensile strength, and flexural tensile strength) and durability (drying shrinkage, water stability, freezing and thawing resistance, and wet–dry cycle) properties of soil samples stabilized using the aforementioned geopolymer were investigated. Moreover, scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis were performed to determine the effect of the change in hydration silicate gel in the UCS development. According to the SEM and XRD test results, hydrated silicate gels exist in the sample, filling the pores of the soil, making the soil more compact, bonding the soil particles, and enhancing the engineering performance of the soil. This study enables waste material utilization as a replacement and partially reactive material in pavement applications.

${\mathrm{CO}}_2$-cured fiber-reinforced boards (CFBs) were fabricated from low-calcium clinkers (CaO content from 48.0% to 53.5%) by ${\mathrm{CO}}_2$ curing. Key synthesizing factors, including clinker composition, compaction pressure, water content, carbonation duration, carbonation temperature, and partial pressure of ${\mathrm{CO}}_2$, were investigated. Further, a performance comparison between CFB and autoclaved calcium silicate board (ACSB) was made. The results showed that the CFB with water-saturated flexural strength of 17.8 MPa, ${\mathrm{CO}}_2$ sequestration content of 18%, water adsorption of 9.2%, and bulk density of 2,059 $\mathrm{kg}/{\mathrm{m}}^3$ was successfully prepared. CFBs, prepared at the compaction strength of 10 MPa, water content of 16%–18%, carbonation temperature of 50°C, and ${\mathrm{CO}}_2$ partial pressure of 0.3 MPa, were preferred to reach superior performance. CFB showed slightly higher water-saturation flexural strength, 59.3% lower water adsorption, and 22.5% lower calcium carbonates induced ${\mathrm{CO}}_2$ emission in comparison with ACSB. Owing to the higher increase in solid weight and volume during carbonation, CFB is much denser than autoclaved ACSB. Rhombohedral crystals of calcite could be observed in CFB, rather than the crystals of vaterite (cauliflower-like) and aragonite (needle-like), although diffraction signals of the latter two were detected.

Traditional tests for low-temperature cracking mainly focus on bitumen or overall mixture properties, overlooking the contribution of asphalt mixture elements. This study investigated the fundamental material properties influencing low-temperature cracking by considering mix design and surface free energy (SFE) parameters. The SFE elements of four aggregate types and eight bitumen types were measured using the universal sorption device and Wilhelmy plate methods, respectively. Based on these measurements, important SFE parameters such as cohesion free energy (CFE), adhesion free energy (AFE), and the ratio between base and acid elements (RBA) in the aggregate SFE were calculated utilizing bitumen and aggregate SFE data. Additionally, material parameters, including the bitumen’s creep stiffness (CS) and CS diagram slope (m-value), were determined through bending beam rheometer tests. Further, factors related to the mix design, such as the aggregates’ specific surface area (SSA), bitumen film thickness (BFT) on aggregate surfaces, and aggregate index (${\mathrm{I}}_{\mathrm{a}}$), were examined. A semicircular bending (SCB) test was conducted on 32 fabricated asphalt mixtures to assess the correlation between these parameters and their impact on low-temperature cracking potential in the asphalt mixtures. Multiple linear regressions were employed to predict the objective functions. The statistical analysis demonstrated that SFE concepts can effectively determine the potential for low-temperature cracking in asphalt mixtures. According to SCB test results concerning fracture toughness and fracture energy, our proposed models indicated the significantly positive influence of factors such as BFT, ${\mathrm{I}}_{\mathrm{a}}$, AFE, CFE, SSA, and RBA.

Solid waste recycling and reuse have attracted great interest as environmentally friendly modifiers for asphalt pavements in recent years, and phosphogypsum whiskers (PSWs) synthesized by phosphogypsum (PSP) wastes were used as the main modifying material to develop an environmentally friendly asphalt binder in this study. PSWs could significantly enhance the deformation resistance and fatigue performance of asphalt binder but were prone to cracking at low temperature. To alleviate this problem, the novel idea of developing a PSW composite modified asphalt binder was proposed in this study. The organic coating method was used to surface modify PSWs by using surfactants and ultrasonic vibrator to enhance the compatibility of PSWs with asphalt binder. Then a composite modifier containing modified PSW (MPSW) was developed by the uniform design method (UDM), and the preparation process of the modifier was investigated by response surface method (RSM) on this basis. The physical performance of modified asphalt binder was investigated by conventional performance tests; the high-temperature performance, rutting resistance, and fatigue performance were investigated by several rheological tests; and the low-temperature performance was evaluated by the force ductility test (FDT). The microstructure and modification mechanism were characterized by the Fourier transform infrared spectroscopy (FTIR) test and differential scanning calorimetry (DSC) test. The results showed that the self-developed modifier (MPGJ-I) could effectively reduce the negative effects of MPSW on conventional physical properties, and it exhibited a significant aging resistance compared with other commonly used modifiers. In addition, the modified asphalt binder showed a significant enhancement in high-temperature performance, rutting resistance, and fatigue performance. The MPGJ-I not only solved the adverse effect of MPSW on low-temperature performance, but also enhanced the low-temperature performance to a certain degree. The MPGJ-I was only physically mixed with asphalt binder and did not change its chemical structure. The MPGJ-I reduced the influence of MPSW on glass transition temperature ($T_g$) and improved the thermodynamic properties of asphalt binder at low temperatures. The comparison study revealed that the MPGJ-I could comprehensively enhance the service performance of virgin asphalt binder, and the recommended dosage of MPGJ-I was 6%.

In this study, the hydration kinetics of ultrahigh-performance concrete (UHPC) with carbon nanofibers (CNFs) are investigated. According to classic nucleation theory, nanomaterials, such as CNFs applied in cementitious materials, can act as nucleating sites for hydration products, accelerating the hydration process. While the increased surface area governs the hydration reaction rate in classic nucleation theory, test results for CNFs in UHPC have provided the opposite trend. Namely, the addition of CNFs caused retardation of the hydration reaction. This observation could be due to the pretreatment of CNFs: the application of chemical surfactant and the ultrasonic dispersion process (UDP). Due to van der Waal’s forces and the hydrophobic property of the fibers, CNFs tend to bundle together during the mixing stage with cementitious material. The chemical surfactants and UDP are applied to CNFs to avoid this agglomeration and enable dispersion. The selected chemical surfactant, a polycarboxylate-ether-based high-range water reducer (HRWR), has been proven to retard the hydration process. In this study, we find that the UDP further enhances the functionality of the effects of the HRWR, such that the retardation action of the HRWR dominates the hydration kinetics. Different amounts of HRWR and CNFs were used in this study, and their effect on hydration kinetics was studied using an isothermal conduction calorimeter (ICC). The behavior of the modified samples was compared with UHPC controls without any modifications. A new hydration model was developed based on the data collected from the ICC results. This model enables the prediction of the heat production rate as a function of the fineness modulus and the HRWR:CNF ratio (R).

Developing new and efficient methods to simulate the aging of asphalt binders and mixtures continues to be an important area of research for the asphalt community around the world. Temperatures exceeding pavement service temperatures are typically used to accelerate and simulate long-term aging in laboratory settings. However, it is unclear whether the use of such higher temperatures would have an adverse influence when simulating the aging of typical polymer modified binders. Specifically, the influence of thermal degradation of polymers at elevated temperatures and the resulting deterioration of the aging-related properties of the asphalt binder could be unrealistic when considering polymer degradation in the field. This study explores the use of an oxidative and nonoxidative environment to deconvolute the different aging characteristics of unmodified and styrene butadiene styrene (SBS) modified asphalt binders. Six binders, including two unmodified binders and four SBS-modified binders with two polymer contents (3% and 4.5% binder weight), were aged in two different aging conditions, i.e., under an air blanket and nitrogen blanket, at a temperature of 100°C. The resulting changes in material behavior were investigated using thin film poker-chip testing, dynamic shear rheometer testing, and Fourier transform infrared spectroscopy. Overall, the results from this investigation suggest that long-term aging of asphalt binders or mixtures conducted using temperatures not exceeding 100°C does not result in any significant degradation of polymers in modified asphalt binders.

A new method of ballast stabilization wherein a layer of geogrid is placed toward the bottom of the ballast layer, and the top zone of ballast beyond the geogrid influence zone is treated with polyurethane, was investigated in this study. The deformation and degradation behavior of geogrid–polyurethane composite-stabilized ballast (CSB) was assessed based on large-scale cyclic tests conducted at a frequency ($f$) of 32 Hz. The test results indicated that the CSB had significantly reduced vertical and lateral deformations, by about 63% and 65.9%, respectively, compared with those of unstabilized ballast (USB), and by 38.8% and 26% compared with those of geogrid-stabilized ballast (GSB). Furthermore, the composite stabilization helped to improve the resilient modulus from 216.75 to 280.83 MPa, the damping ratio from 0.230 to 0.340, and the track stiffness from 41.33 to $68.13\mathrm{MN}/\mathrm{m}$ compared with the values for USB. The breakage of ballast also was reduced significantly owing to ballast–polyurethane bonds that remained intact even after 250,000 load cycles. It was found that the geogrid placement location and its corresponding influence zone play a significant role in the overall performance of CSB. The test results further indicated that the geogrid when placed 76 mm from the ballast–subballast interface and a polyurethane treatment depth of 152 mm measured from the sleeper soffit exhibited significantly improved performance under cyclic loading.

The creation of lightweight aggregate self-compacting concrete (LWA-SCC) is a challenging endeavor with substantial consequences for the construction sector. However, the absence of firmly established design suggestions and recommendations as well as the limited availability of design approaches pose a noteworthy obstacle. To accomplish the anticipated mechanical properties while minimizing production costs as well as preserving natural resources, a thorough comprehension and understanding of the optimal combination of binders and coarse aggregate content is required. This study examines the impact of several supplementary cementitious materials (SCMs) such as silica fume (SF) and metakaolin (MK) on the fundamental mechanical characteristics of ecofriendly LWA-SCC mixes prepared with 100% sintered fly ash aggregate (SFAA) as a replacement of natural coarse aggregates (NCAs). A total of nine LWA-SCC mixes were prepared including one base SCC mix. The base SCC mix (C-SFAA100) encompasses 100% ordinary portland cement (OPC) as the sole binder, and 100% natural fine aggregates (NFAs) along with 100% SFAA. The remaining eight mixes were further parted into two Series. Series I and Series II comprise SF and MK as a replacement for OPC by 7.5%, 10%, 12.5%, and 15%, respectively. The fundamental mechanical characteristics such as compressive strength, split tensile strength, direct shear, and elastic modulus were measured after several intervals. In addition, microstructural analyses were also executed to appraise the overall efficacy of LWA-SCC combinations. The results such as the compressive strength of the SCC mixes CSF15-SFAA100 and CMK15-SFAA100 increased by 11.3% and 18.5%, respectively, after a curing time of 90 days compared to the base SCC mix C-SFAA100 confirmed that the incorporation of SCMs into LWA-SCC mixtures improves their mechanical characteristics.

This study prepared modified alkali-activated slag repair materials by incorporating an ethylene-vinyl acetate copolymer emulsion (EVA). Sulfate attack tests, shrinkage tests, scanning electron microscopy, and mercury intrusion porosimetry tests were conducted to examine the durability and microstructural features of the alkali-activated slag repair materials. The experimental results demonstrated that adding EVA can enhance the shrinkage and strength of alkali-activated slag mortar, but that the materials exhibit poor resistance to sulfate attack. Optimizing the ratio design can yield alkali-activated cementitious materials with high strength, good durability, high bonding strength, and low shrinkage. This can reduce brittleness and increase the shrinkage rate of the material’s defects, which has significant implications for subsequent fracture repair. The image of the microstructure showed that the section of alkali-activated slag paste is smooth and exhibits polymer emulsion filling gaps in the amorphous cementitious material. A connection between fibrous filaments on the cross section of the matrix crack enhances the strength of the material. The proportion of microcracks is increased and material strength is decreased after sulfate attack.

The utilization of calcium sulfoaluminate (CSA) cement, known for its rapid strength gain and low carbon footprint, has been increasingly prevalent in the field of construction. This research aims to enhance the mechanical properties of CSA cement-based materials by incorporating ethylene-vinyl acetate (EVA) and styrene acrylate ester (SAE) copolymers. Various dosages (expressed as mass fractions) of EVA and SAE were utilized in the production of CSA cement pastes. The fluidity, setting time, electrical resistivity, and mechanical properties, including flexural strength, compressive strength, and drying shrinkage behavior, were thoroughly assessed for the CSA cement pastes, and the products of hydration in the cement pastes were analyzed. The findings suggest that the inclusion of polymer emulsions in CSA cement pastes resulted in prolonging setting time and hindering hydration. While the addition of SAE did not enhance flexural and compressive strength, the incorporation of 10% SAE effectively reduced drying shrinkage and significantly improved the flexural-to-compressive strength ratio of the CSA cement pastes after 6 h. When the SAE content reached 5%, the fluidity of cement paste could be effectively increased. On the other hand, the inclusion of EVA improved the early-age flexural strength at 6 h but did not effectively reduce drying shrinkage in the CSA cement pastes. When 5% EVA was used, the 28-day compressive strength exceeded that of the control sample (with no polymer).

In this paper, alkali-activated materials (AAMs) were prepared combining waste coral powder (CP) and blast furnace slag (BFS) as precursors, artificial seawater and deionized water as mixing water, and blends of NaOH and sodium silicate solution as alkaline activators. The effect of CP and seawater on the fluidity, mechanical properties, and hydration was discussed. The experimental results showed that a 15% CP content effectively improved the fluidity of fresh paste while having little effect on compressive strength of the samples. Compared with deionized water, the use of seawater for sample preparation resulted in a reduction of the fluidity and mechanical properties of the samples. The pore structure could be refined by CP and seawater, but gel micropores increased significantly when the CP content reached 25%. The use of CP and seawater did not cause significant changes in the type of hydration products. Although the amount of hydration products in the early stages of the samples prepared with seawater was relatively low compared with those prepared with deionized water, it gradually surpassed that in samples prepared with deionized water with increasing curing time. Increasing the CP content led to a higher reaction degree, and a CP content of 25% resulted in a reaction degree of approximately 30%–50%, which was roughly twice that of a sample containing 5% CP. These findings have important implications for the development of sustainable construction materials for utilization in marine engineering.

As the core admixture of shotcrete, the accelerator promotes the rapid setting of shotcrete. In order to promote the rapid development of strength, the synergistic effect and the synergistic mechanism of early-strength agents [$\mathrm{Al}({\mathrm{NO}}_3{)}_3$ (AN), and $\mathrm{Mg}({\mathrm{NO}}_3{)}_2$ (MN)], and aluminum sulfate liquid accelerator on the strength of mortar were investigated. The aluminum sulfate liquid accelerator used in this paper was named AF. The results show that the 1-day strength of the mortar reached 8.8 and 10.73 MPa when AF was added with 2.4% AN and 1.8% MN, respectively. When AF and 2.4% AN were used, the initial and final setting times of the cement paste were 1 min 32 s and 3 min 50 s, respectively, whereas the AF and a very small amount of MN would prolong the setting time of the paste. The synergistic mechanism of AN/MN and AF is as follows: AF provides a large amount of ${\mathrm{SO}}_4^{2-}$ and ${\mathrm{Al}}^{3+}$, which promotes the rapid formation of ettringite (AFt). In addition, ${\mathrm{NO}}_3^{-}$ in AN and MN promotes the formation of the AFt phase $3\mathrm{CaO}·{\mathrm{Al}}_2{\mathrm{O}}_3·\mathrm{Ca}({\mathrm{NO}}_3{)}_2·{\mathrm{XH}}_2\mathrm{O}$ (${\mathrm{NO}}_3\text{-}\mathrm{AFt}$). Compared with AN, ${\mathrm{Mg}}^{2+}$ dissolved by MN will first precipitate $\mathrm{Mg}(\mathrm{OH}{)}_2$ with ${\mathrm{OH}}^{-}$, providing crystal nuclei for the hydration system and accelerating the hydration of ${\mathrm{C}}_3\mathrm{S}$. It is concluded that AF and MN have a better synergistic effect on improving early strength.

Asphalt concrete is a typical heterogeneous composite material at the mesoscale. Under the action of external load, its internal dispersion cracks interact with each other, thereby changing the crack propagation behavior, especially in low-temperature environments. In this context, this study developed a meso-structure model of asphalt concrete with randomly distributed dispersion cracks based on the Taylor medium model and the discrete element method. A virtual semicircular bending test was performed to obtain macro and micro parameter data, including stress–strain curves, data regarding the crack propagation process, and the crack-area stress field, to analyze the propagation characteristics of dispersion cracks with various crack density parameter values, $f$, in asphalt concrete. The results indicated that (1) the predictions based on the Taylor medium model exhibit a good correlation with the numerical simulation results, demonstrating the reliability of the simulation. Moreover, the interference between dispersion cracks hinders crack propagation, significantly enhancing the low-temperature crack resistance of asphalt concrete. This interference effect is most pronounced when $f$ is set to 0.6. (2) Crack interference between dispersion cracks primarily occurs during the crack incubation stage, extending the incubation time of internal cracks in asphalt concrete and improving early crack resistance. (3) When $f$ is less than or equal to 0.6, the predominant failure mode of asphalt concrete is tensile stress failure. However, when $f$ exceeds 0.6, the fracture mode of asphalt concrete shifts from tensile fracture to shear fracture.

This study uses fly-ash-based superplasticized geopolymer by adding a naphthalene-centered superplasticizer to the geopolymerized soil. Alkali-binder ratios and alkali-activator ratios are varied simultaneously with a molarity of 10M. The optimum dosages of binder, geopolymer, and superplasticized geopolymer are found from unconfined compression tests. California Bearing Ratio (CBR), pH, consolidation, water-holding capacity, and microstructure tests were performed on optimum dosages. The clayey soil’s undrained shear strength and CBR value increased as the geopolymer was superplasticized. The 28-day undrained shear strength of geopolymerized clay was around 300 kPa, attained within three days of the curing period with superplasticized geopolymer. This is because adding a superplasticizer increases the polymerization reaction rate and improves the geopolymer’s performance. The maximum undrained shear strength was attained within seven days of the curing period for both cases. The undrained shear strength after a curing period of 7, 14, and 28 days for geopolymer and superplasticized geopolymer was found to be almost the same value, which shows that after seven days, curing has little role in strength improvement. The hydraulic conductivity and coefficient of consolidation of geopolymerized soil increased with the addition of superplasticizer due to the reduction in fine particles and plasticity of the residual soil. Microstructural studies using scanning electron microscope and x-ray diffraction techniques showed an interaction between soil, geopolymer, and superplasticizer, thus confirming the formation of geopolymer gel and increased polymerization rate with the superplasticizer.

Both the corrosion resistance and bond strength of silica particle-modified enamel (SPME)-coated steel bars are experimentally investigated, and uncoated and pure enamel (PE)-coated bars are also prepared for comparison. The microstructure of SPME coating is analyzed by using scanning electron microscopy (SEM), and the corrosion performance in simulated concrete pore solutions is assessed by using a series of electrochemical techniques. Pull-out tests were conducted to obtain the bond behavior with concrete. SEM images show that silica particles are completely embedded in the enamel matrix. The corrosion resistance of SPME-coated smooth and deformed steel bars is 68 and 28 times lower, respectively, than that of the uncoated bars. The bond strength, bond stiffness, bond ductility, and bond toughness of SPME-coated smooth steel bars are 4.33, 4.61, 35.86, and 20.66 times greater than those of the uncoated bars, while they are 1.29, 4.72, 2.21, and 1.24 times greater than those of the uncoated ones for the deformed steel bars. SPME-coated steel bars can be used to enhance the seismic performance of reinforced concrete structures in earthquake-prone zones, while also improving corrosion resistance.

Due to the behavior of low-density and high-energy absorption efficiency, rubber materials are now being extensively applied to solve geotechnical problems. In order to ensure the rational and economical use of rubber sand mixtures in geotechnical engineering, it is necessary to systematically study the compression behavior of rubber sand mixtures, especially under repeated loading–unloading mode. In this study, three series tests, including one-dimensional compression tests and repeated loading–unloading tests, were conducted on rubber sand mixtures with various rubber contents. The development of the void ratio, compression coefficient, elastic strain, and plastic strain of the mixtures under different load modes was investigated. Results showed that compared to pure sand, rubber sand mixtures exhibited different compression deformation behavior. The rubber content had a significant impact on the compression behavior of rubber sand mixtures. The compression behavior of the rubber sand mixture changed from low to high compressibility when the rubber content was greater than 10%. Also, with the increase of rubber content from 0% to 20%, the ratio between elastic and plastic strain of the mixtures increased from $1:5$ to $2:3$. When subjected to loading and unloading cycles within a large stress range (0–1,600 kPa), the rubber sand mixture underwent significant elastic strain, and plastic strain gradually accumulated with the number of cycles. When the repeated loading and unloading test started at a certain initial pressure (800–1,600 kPa), the elastic deformation of the rubber sand mixture decreased to a smaller level and did not change significantly with the number of cycles. At this point, plastic strain mainly occurred in the first cycle, and almost no plastic strain occurred in subsequent cycles. Rubber content below 10% has lower compressibility and is a recommended rubber content (RC) value for use in engineering. In addition, setting a certain initial pressure is an effective method to reduce the elastic strain of mixtures and improve the accumulation of plastic strain in engineering applications.

Cemented gangue backfill bodies (CGBBs) are characterized by high brittleness and poor toughness in backfill mining technology. According to different types of waste tires corresponding to different processing and crushing means, waste tire steel fiber (WTSF) was divided into S-WTSF, P-WTSF, and H-WTSF. The influence of CGBBs with different types and amounts of WTSF on the early mechanical properties of the modified samples was studied. Uniaxial compressive strength (UCS) and scanning electron microscopy (SEM) tests on the modified CGBB samples were carried out. The results show that as the WTSF content increased from 0% to 1.5%, the UCS of CGBB samples modified with S-WTSF, P-WTSF, and H-WTSF at a curing time of 3 d first increased and then decreased; the turning point for S-WTSF and P-WTSF was 1%, and the turning point for H-WTSF was 0.5%, whereas the UCS of these modified CGBB samples at a curing time of 7 d decreased continuously with the increasing addition of WTSF content. The addition of WTSF made CGBB samples change from brittleness to ductility. With the increasing content of S-WTSF and P-WTSF, the toughness of the modified CGBB samples at a curing time of 3 d first increased and then decreased (the turning point was 1%), and that at the curing time of 7 d continued to increase. The toughness of CGBB modified with H-WTSF first increased and then decreased (the turning point was 0.5%) with the increase of the H-WTSF content. The toughness enhancement mechanism of CGBB modified by WTSF can be illustrated from a microscopic perspective as follows: WTSF is wrapped by hydration products, and the inlaying and bridging effects of WTSF are formed in the CGBB matrix. This research provides a basis for the improvement of mechanical properties of CGBB modified by WTSF and a new method for the reuse of discarded tires.

This study explores the development of performance-based blending charts for recycled binder blends, considering the rutting and fatigue resistance of recycled binder blends. For developing the blending chart, the nonrecoverable creep compliance $J_{nr}$ evaluated in the multiple stress creep recovery (MSCR) test and the bitumen fatigue performance parameter $N_f$ estimated from the linear amplitude sweep (LAS) test were utilized. These parameters are recognized for their superior representation of rutting and fatigue performance. Blending charts were initially developed separately for $J_{nr}$ and $N_f$, then combined to create a performance-based blending chart that illustrates how $J_{nr}$ and $N_f$ change with reclaimed asphalt binder in total binder ($R/T$). The study demonstrates the aforementioned concept for a laboratory-synthesized reclaimed asphalt pavement (RAP) binder when blended separately with two virgin binders (viscosity grades VG10 and VG20). Because viscosity grade VG40 binder is recommended for wearing-course and binder-course mixes for high-volume roads in India, the RAP blends were synthesized targeting the $J_{nr}$ and $N_f$ values estimated for VG40 binder at 60°C and 25°C, respectively. The performance-based blending charts identify an $R/T$ range where the blend outperforms the target binder in both rutting and fatigue performance. The study revealed that when the softer virgin binder (VG10) was used to rejuvenate RAP properties, the desired $R/T$ range was broader compared with VG20. As the strain level increased from 2.5% to 5%, the desired $R/T$ range narrowed, indicating that the $R/T$ range was influenced by both the type of soft binder and the strain level in the LAS test. This also implied that higher RAP incorporation is advisable in the case of thick pavements when compared with thin layers.

Current production of fiber-reinforced asphalt concrete (FRAC) is associated with challenges related to performance inconsistencies, workability, and economic feasibility. Understanding fundamentals of fiber-matrix interaction in FRAC is key to identifying root causes of the observed inconsistencies and enhancing the performance of FRAC mixtures. There is no model or experimental method to predict fiber behaviors in viscoelastic AC. A novel fiber pullout test procedure was designed and developed to characterize interfacial properties of fibers in a viscoelastic AC medium. The test method was used to develop a fundamental understanding of fiber pullout behavior where fiber diameter, embedment length, and mixture characteristics are considered as key test parameters. The test method allowed characterization of the effects of temperature and loading rate as well considering fiber reinforcement in viscoelastic AC application. The pullout tests were successfully completed for the key variables. The experiments were extended to mixture scale to apply some of these key fundamental principles learned from the pullout tests. Embedment length and fiber diameter emerged as the key variables of pullout behavior of fibers in the AC. The fiber-matrix interface was not found to be sensitive to temperature and loading rate as much as bulk viscoelastic AC is. The proposed testing method designed and developed in this paper will help in building fundamental constitutive relationships of fiber-matrix behavior in viscoelastic AC and design FRAC mixes using a mechanistic approach.

Asphalt aging and fatigue cause the pavement performance to decline, affecting the service life of the pavement. However, limited research on impact laws and the mechanism of asphalt oxidation kinetic aging on fatigue performance, and no consistent conclusions about this issue as well. In this study, the asphalt aged for different periods, then time sweep tests were performed. The fatigue performance of asphalt at different aging periods was studied through various fatigue life indicators that were determined according to different fatigue failure criteria. It is found that the longer the aging time, the greater the asphalt fatigue life when the strains are 5% and 10%, and the increase rate is faster at the shorter aging time and slower at the longer aging time, while the change rate is relatively small when the strain is 15%. There are strong linear correlations among the various indicators. The quadratic equation model is established to predict bitumen fatigue life by response surface method, and the significance of the model is studied by analysis of variance. The results show that the model is accurate and reasonable. The impact of aging time and strain level as well as their interaction on the model were analyzed. It is found that the effect of aging time on the fatigue life of asphalt is more significant when the strain is small, and the effect of aging time on the fatigue life of asphalt decrease with the increase of strain. The influence of strain level on the fatigue life of asphalt is relatively small when the aging time is shorter, and the effect of strain on fatigue life gradually increases with the increase of aging time.

Concrete made using recycled aggregates may become less durable due to sulfate attack. In this study, the degradation of recycled aggregate concrete (RAC) under external sulfate assault was investigated using a mesoscale numerical analysis method. A random convex polygon aggregate model with five phases—(1) aggregate, (2) aggregate–old bonded mortar interface transition zone (ITZ), (3) old bonded mortar, (4) old bonded mortar–new bonded mortar ITZ, and (5) new bonded mortar—was established using a self-compiled program in order to take into account the heterogeneity of RAC. The aggregate was considered an impervious phase, but the four other phases were considered pervious. In the model, the only chemical byproduct was the ettringite that causes expansion. The proposed method for modeling sulfate attack on RAC was validated by experiments. Sulfate diffusion, the impact of ITZ thickness, water:cement ratio, and surface sulfate content were investigated. The simulation results showed that (1) there was limited influence of surface sulfate ion concentration on the rate of sulfate erosion in RAC, (2) water:cement ratio has a significant impact on sulfate resistance in RAC, and (3) the sulfate attack procedure is largely unaffected by ITZ thickness.

Cu-Al-Mn (CAM) shape memory alloys (SMAs) are cost effective, have a high low-cycle fatigue life and superelastic limit, and a wide temperature application range compared with other types of SMAs. These characteristics of CAM SMAs have resulted in increased interest in their use in civil engineering applications, particularly as reinforcement in concrete structures and as dampers in steel structures. However, these applications require machining of the CAM SMA bars for connection with other structural elements. This study presents the methods and results of the first systematic research on the machinability of CAM SMAs. The key machinability characteristics of CAM SMAs: chip formation, cutting temperature, tool wear, workpiece surface roughness, and diameter deviation, were studied and compared with those of conventional NiTi SMAs and commonly used steels: mild steel (MS) and 304 stainless steel (SS). The effects of a wide range of cutting parameters: cutting speed ranging from 15 to $120\mathrm{m}/\min$, feed rate ranging from 0.1 to $0.2\mathrm{mm}/\text{revolution}$, and depth of cut ranging from 0.5 to 1.5 mm, were investigated. The results from this study showed that the tool wear from machining CAM SMAs was close to that from machining SS and slightly higher than that from machining MS, but much lower than that from machining NiTi SMAs. In all the cases considered here, the tool wear from machining CAM SMAs was found to be 0.6–1.8 times that from machining SS, 0.8–2.4 times that from machining MS, and 1/7–1/21 that from machining NiTi SMAs. After a continuous machining test with a total cutting length of 4.5 m, the nose wear from machining CAM SMAs was found to be 1.6 times that from machining MS, the average flank wear from machining CAM SMAs was found to be three times that from machining MS, and the diameter deviation (relative diameter difference from that of the first sample) of CAM SMAs was only 10 μm larger than that of MS.

The hoisting safety and the difficulty of the main reinforcement connection are directly affected by stiffness of reinforcement parts. Quantifying the stiffness of reinforcement parts has become a key technology problem. Firstly, an independent mechanical solution model of three-dimensional rotational stiffness ($R_x$, $R_y$, and $R_z$) for the welded joints is proposed from the perspective of mechanical mechanism. Considering the influence of the rebar diameter, 105 sets of T-type welded reinforcement specimens and 2 types of loading devices were designed, and graded loading tests were performed. On this basis, considering the randomness of the rotational stiffness of the welded joints, a deformation calculation method for the welded reinforcement parts based on Monte Carlo random sampling is proposed, and six groups of two-dimensional (2D) reinforcement mats and six groups of three-dimensional (3D) reinforcement cages tests were performed. The results show that the rotational stiffness of the welded joints is random and has the Gaussian distribution characteristics. The rotational stiffness of the welded joints has a significant effect on the deformation of the welded reinforcement parts. Under the same welding conditions, the rotational stiffness of the welded joints increases with the increase of reinforcement diameter. Under the same reinforcement diameter, the three-dimensional rotational stiffness of the welded joints is in the order $R_x>R_z>R_y$. The cross-sectional area of the welded joint can better characterize the rotational stiffness. The verification test of welded reinforcement shows that the error of the calculation method proposed in this paper is within 10%, while the error of rigid connections and hinge connections are less than 30% and 130%, respectively.

The incorporation of supplementary cementitious materials (SCMs) into cementitious materials can be used to offset the overall carbon footprint of cement in addition to improving performance and promoting circular economy. Synthesized silicomanganese fume (SiMnF), silica fume (SF), and ordinary portland cement (OPC) based binary and ternary cementitious mortar specimens were designed and optimized using the Taguchi method. Four factors with three levels each were investigated—SiMnF content of 0%–40% and SF content of 0%–10% (by mass) of the total cementitious, sand-to-binder of 1.5–2.5, and water-to-binder ratio of 0.35–0.45. Based on the orthogonal array proposed by the Taguchi method, nine mortar mixes were batched and their flow after mixing and compressive strength at 3, 7, and 28 days of casting were measured. The strength data were statistically analyzed using ANOVA to investigate the effects of the chosen experimental variables. It was observed that the strength is considerably reduced from the addition of SiMnF, but the reduction is marginal from increasing the sand-to-binder ratio. The addition of 5% SF increased the strength. A restricted analysis indicated that specimens prepared with 20% SiMnF, or 20% SiMnF and 5% SF can yield mortar strengths of up to 30.5 MPa and 48.8 MPa, respectively. Microstructural investigations revealed that the mixes with SiMnF have detectable pores at $\mathrm{1,000}\times$ magnification, however, the addition of 5% SF densifies the matrix with no visible pore at the same magnification. This corroborates the strength data. The life-cycle assessment (LCA) indicates that the utilization of SiMnF in the mortar mixtures can reduce ${\mathrm{CO}}_2$ emissions by up to 25% at a reasonably acceptable compressive strength.

The properties of asphalt mastic are crucial in determining the moisture sensitivity of asphalt mixtures, but the adhesion performance of the mastic has not been quantitatively described. To address this gap, this study calculated the asphalt mastic surface energy using the equation-of-state method, and established a moisture sensitivity ($MS$) index based on it. The effectiveness of this index was verified through Marshall testing. First, the surface energy of asphalt and filler was measured, and the critical volume fraction of the mastic was determined using the two-point method. Second, the interaction parameters of asphalt and filler were calculated using the equation-of-state method, and the surface energy of the mastic was obtained. Then the $MS$ index was established to evaluate the moisture sensitivity of asphalt mixtures. This new index utilizes the surface energy and aggregate to quantitatively evaluate adhesion, considering the specific surface area of the aggregate and the thickness of asphalt film. Finally, the $MS$ was validated through Marshall tests of asphalt mixtures. The results demonstrated that the $MS$ obtained by the calculated surface energy exhibits a strong linear correlation with the moisture sensitivity of asphalt mixtures. The goodness of fit reached above 0.90 and the highest was 0.965. This study provided a novel approach to characterize the moisture sensitivity of asphalt mixtures.

Colored asphalt mixtures have recently found extensive applications in roads and public spaces due to their contribution to traffic management as well as aesthetics and landscaping. The development of durable colored asphalts using various materials has been a hot research topic in recent years. Colored asphalt can be developed through the durable colored slurry seal mixture (CSSM) technology. The desired quality of CSSM requires particular attention to the mechanical performance and resistance against crack propagation due to temperature variations and traffic loads. This research aimed at investigating the effect of steel slag (SS) aggregate compared with natural aggregate (NA) on the fracture behavior and performance of CSSM in five different mixtures: NA100% (control sample), $\mathrm{SS}10\%+\mathrm{NA}90\%$, $\mathrm{SS}20\%+\mathrm{NA}80\%$, $\mathrm{SS}30\%+\mathrm{NA}70\%$, and $\mathrm{SS}40\%+\mathrm{NA}60\%$. The performance of CSSM was evaluated using an edge-notched disk bend (ENDB) specimen fracture test at three different temperatures (0°C, $-10°\mathrm{C}$, and $-20°\mathrm{C}$). Additionally, cohesion test, wet track abrasion test, loaded wheel test (LWT)-displacement and LWT-sand adhesion were carried out to further examine the samples. Comparison of the fracture behavior of colored mixtures revealed that the $\mathrm{SS}40\%+\mathrm{NA}60\%$ mixture outperformed other mixtures. The results of other performance tests showed that the unique characteristics of $\mathrm{SS}40\%+\mathrm{NA}60\%$ mixture improved CSSM performance against vertical displacements, bleeding, cohesion, and moisture sensitivity by approximately 40.2%, 4 7.3%, 28.6%, and 52.7%, respectively. This comprehensive assessment offers valuable insights into the effectiveness of SS as a proper alternative to NA in CSSMs.

This study explored the influence mechanism on the water resistance of magnesium phosphate repair mortars. The fluidity, setting time, mechanical properties, water resistance, and interfacial bonding strength of red mud–modified magnesium phosphate repair mortars (RMPMs) were systematically investigated. Through capillary absorption tests, the effect of the water-binder ratio (W/B) on the water transfer characteristics was explored, and then the actuating mechanism of capillary porosity and capillary absorption coefficients on water resistance was clarified. The results show that the fluidity and setting time of RMPM increase with the increase of W/B. When W/B increased from 0.18 to 0.20, the compressive strength, flexural strength, strength retention, and interfacial bonding strength of RMPM changed little and decreased linearly. And the interfacial bonding strength of RMPM was significantly reduced after 7 days of water curing. The capillary water absorption of RMPM was linear with the square root of time. The capillary absorption coefficient and capillary porosity of the RMPM increased greatly with increasing W/B when the W/B is between 0.20 and 0.28, while the water resistance, mechanical properties, and interfacial bonding property decreased linearly. Variations in W/B changed the capillary pore characteristics of the RMPM, which in turn affected the mechanical properties, capillary water absorption characteristics, and water resistance.

The geotechnical tube technology has been widely used in the dewatering treatment of high-water-content slurries, such as engineering waste muds, mine water sludges, and dredging slurries. However, the existing engineering practice adopting the traditional geotextile tubes is characterized by low efficiency and difficult quality control. To address these issues, a new approach was developed by combining the geotextile tubes and vacuum preloading technology. In this method, several plastic drain boards were embedded in a geotextile tube as prefabricated horizontal drains (PHDs), and a vacuum was applied to promote drainage. The effectiveness of the proposed method was verified by a comparison test. A two-dimensional plane-strain analytical consolidation problem with a distributed drainage boundary was then formulated and solved to predict the consolidation process of soil in a vacuum preloaded geotextile tube. The analytical solution was validated against the results of a pilot field test, and then the influence of PHD spacing on the consolidation process was also discussed. Compared to the traditional geotextile tubes, the approach proposed in this paper promises good applicability and can effectively shorten the treatment time by 73.3% and reduce the water content of treated soils by 51.9%.

Calcium sulfoaluminate belite (CSAB) cement has gained prominence as a viable environmentally friendly substitute for conventional portland cement (PC). The current study investigates the relative performance of expansive and nonexpansive CSAB cement-based concretes, and PC-based concretes when subjected to chloride-rich conditions. Multiple testing methodologies, including surface resistivity measurements, chloride migration, rapid chloride penetration, long-term bulk diffusion, and water sorptivity, were employed to assess the durability of these concrete systems. Surface resistivity measurements indicated that CSAB systems exhibited significantly higher resistivity when compared with PC-based counterparts. Increased resistivity in CSAB systems was influenced by the conductivity of the pore solution, emphasizing that the formation factor provides a more accurate representation of the pore structure within the system. The expansive and nonexpansive CSAB cement–based concrete outperformed PC-based concrete in migration-based tests and rapid chloride penetration test (RCPT). In contrast, the CSAB and PC systems demonstrated similar performance in the long-term bulk diffusion-based test. Although CSAB systems exhibit finer pore structures than PC-based counterparts, their performance in chloride-rich environments is affected by their reduced binding capacity. The study emphasizes that the conclusions drawn from accelerated tests and resistivity measurements of CSAB cement–based concrete must be cautiously interpreted because these results may not indicate real-world performance.

To study the internal stress transfer law and the evolution of the fine structure of asphalt mixtures after being subjected to traffic load during the service phase, finite element (FE) models of porous asphalt mixtures (PAMs) and dense asphalt mixtures (DAMs) were developed for virtual uniaxial compression tests. By controlling the two asphalt mixtures to produce different longitudinal deformation, their damage patterns in the service phase are analyzed from a fine perspective. The results show that PAMs are capable of forming internal force chains when resisting external loads, and the displacement generated within the PAM is not uniformly distributed. Moreover, when resisting external loads, the internal stress distribution of DAMs is more uniform, as is the internal displacement distribution. The stress transfer law of the PAM is more conducive to transferring the load from the upper surface to the lower surface of the mixture than that of the DAM.

Welding residual stress will increase the risk of stress corrosion cracking of welded joints in service. It is crucial to study the distribution of welding residual stress in welded joints. In order to study the mechanical property and microstructure of the joint, a two-dimensional model is established based on the actual morphology. The results show that the maximum residual stress occurs in the welded metal. The Mises stress is 355 MPa, and the circumferential stress is 362 MPa. After welding, the outer surface maximum circumferential residual stress is 388 MPa, and the maximum axial residual stress is 357 MPa, which is in good agreement with the simulation results. The microhardness distribution appears as base metal $>$ heat-affected zone $>$ welded metal. The distribution of maximum shear strength is similar to the microhardness. The main phase composition consists of proeutectoid ferrite, acicular ferrite, massive ferrite, and a small amount of granular carbide precipitates.