Journal of Materials in Civil Engineering

In this paper, the time-dependent properties of rheological parameters (${\tau }_0$, $\eta$, $A$) and electrochemical parameters ($R_b$) are investigated by preparing sulphoaluminate cement pastes with different water-to-cement ratios ($\mathrm{W}/\mathrm{C}$) of 0.3, 0.4, and 0.5, respectively. A new rheological microstructure model is proposed by combining hydration kinetics with a newly introduced hydration stage, with electrochemical parameter $R_b$. Meanwhile, the time-dependent nature of rheological parameters was evaluated by electrochemical parameters. The experimental results show that the time-dependent properties and microstructural evolution are closely related to the water content of cement paste. Based on hydration kinetics, the reconstruction curve of hydration rate conforms to the Krstulović–Dabić model and the hydration mechanism belongs to NG-I-D (where NG, I, and D stand for nucleation and crystal growth, interactions at phase boundaries, and diffusion, respectively). The time-dependent property of electrochemical parameter $R_b$ can be divided into four stages, which conform to the mathematical model of $R_b=kt$. However, the hydration mechanism that dominates those four stages is different. In addition, the rheological parameters (${\tau }_0$, $\eta$, and $A$) have a good linearly time-dependent relationship with electrochemical parameter $R_b$. As an in-situ nondestructive method, the electrochemical analyzer is feasible to monitor and evaluate the time-dependent properties of cement rheology.

Corrosion of reinforcement bar caused by chloride ions diffusion is a crucial durability problem for concrete structures. Deoxyribonucleic acid (DNA) is a new type of corrosion inhibitor. Previous research has concentrated primarily on the influence of DNA on the corrosion of reinforcement bar caused by chloride salts in simulated concrete pore solution and cement-based materials, with scant attention to the chloride diffusion behavior of cement-based materials with DNA. In this work, the chloride diffusion behavior of cement-based materials with DNA was studied using chloride binding isotherm, chloride rapid migration (RCM), and natural diffusion tests. The composition, content, and morphology of the hydration products and pore structure were monitored using X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) tests. The results show that DNA can improve the chloride-binding capacity and enhance the chloride diffusion resistance in cement-based materials. The lowest chloride migration coefficient and chloride diffusion coefficient were found in cement mortar with 4% by weight DNA, which were 45.58% and 42.36% lower than those of the reference group, respectively. DNA can stimulate the cement hydration reaction to produce more C-S-H gels and can increase the $\mathrm{Ca}/\mathrm{Si}$ ratio of C-S-H. This is conducive to physical chloride adsorption. DNA can be combined with calcium ions to form insoluble aggregates that can fill the pore structure of mortar. Mortar with 4% by weight DNA maintained the lowest porosity, which effectively enhanced the chloride diffusion resistance.

Recycled gypsum powder from waste drywalls is a new alternative that has been recently introduced for partial cement replacement in concrete for construction applications. It has been shown that the recycled gypsum, alongside fly ash, can partially replace cement in concrete to some extent without hurting the required properties of concrete. In this paper, the impact of recycled gypsum content on the durability of concrete (hereafter called gypsum concrete) exposed to different environmental exposures is evaluated. A total of 153 concrete cylinders ($100\times 200\mathrm{mm}$) with different recycled gypsum contents (0%, 10%, and 20% of cement replacement) were considered. Each mix was exposed to air-dry, freshwater, seawater, freshwater–air dry cyclic, and seawater–air dry cyclic conditions. The specimens were tested in compression loading after 1,000, 3,000, and 6,000 h of exposure. Recycled gypsum used in this research was in two types of a powder with fine particles only (hereafter called fine gypsum) and in the form of mixed fine, coarse, and paper particles (hereafter called whole gypsum). Other mechanical and physical properties of concrete such as absorption, volume change, and ultrasonic pulse velocity were analyzed. It was observed that the compressive strength of the specimens with 10% and 20% fine gypsum content at Day 28 was about 36% and 40% lower than that of the control specimens, respectively. However, the strength gap was reduced to about 16% and 7% at the end of 6,000 h in the air-dry condition. The specimens submerged in freshwater and seawater showed a rate of strength gain higher than that of the control specimens, bringing the compressive strength of the gypsum concrete specimens slightly higher than that of the control specimens after 6,000 h exposure. Overall, recycled gypsum in combination with fly ash not only does not hurt the long-term strength of concrete but also can enhance the strength under certain conditions, mostly those exposures involving water exposure.

The development of tests, standards, and specifications necessitates the establishment of technical validity while concurrently optimizing costs associated with the testing requirements. AASHTO TP 125-16 recommends the utilization of the bending beam rheometer (BBR) as a simple, rapid, relatively cost-effective, and reproducible method for assessing the low-temperature properties of asphalt concrete mixtures. However, the standard does not provide specific guidance regarding the representative sample size necessary for the BBR test. Therefore, this study used statistical techniques to calculate the sample size by scrutinizing data for two variables, i.e., creep moduli (stiffness) and stress relaxation capacity ($m$-value), which were obtained from testing a variety of asphalt concrete mixtures. In this regard, distinct asphalt mixtures were meticulously prepared and subjected to laboratory testing. A representative sample size of eight thin-beam specimens was determined. This recommendation was validated by sampling five different asphalt mixtures from pavement construction projects. It was found that testing and analyzing trimmed means of only eight specimens from a 2 in. thick asphalt concrete layer was adequate to represent the global low-temperature performance of those five pavement sections. So, an asphalt mixture’s low-temperature performance can be completed in 2 h by testing only eight specimens in the BBR without sacrificing accuracy and practicality. Therefore, this study contributes to a possible application of the BBR during pavement construction.

This research aimed to enhance the ultraviolet aging and long-term thermal oxidation aging resistances of styrene-butadiene-styrene (SBS)-modified asphalt simultaneously. For this purpose, antioxidant 1222–intercalated ultraviolet (UV) shielding material layered double hydroxides (LDHs) (LDHs-1222) were prepared and added into SBS-modified asphalt as an antiaging agent. The effect of LDHs-1222 on the physical properties, high and low temperature rheology, and chemical composition of SBS-modified asphalt was investigated. Meanwhile, the aging properties of the asphalts after short-term or long-term thermo-oxidative aging and 7-day ultraviolet aging were investigated. The results showed that LDHs-1222 significantly improved the resistance of SBS-modified asphalt to short-term thermo-oxidative, long-term thermo-oxidative, and UV aging while having less impact on the physical and rheological properties than LDHs. Compared with SBS-modified asphalt, the softening point increment, aging indices of viscosity, complex modulus and carbonyl index, and SBS index decrement of the asphalt with LDHs-1222 were significantly reduced, and their growth rates were significantly slowed, indicating that the aging rate and degree of SBS-modified asphalt were reduced by the addition of LDHs-1222. SBS-modified asphalt with 4% LDHs-1222 exhibited superior resistance to long-term thermal oxidation and UV aging compared to asphalt with an equivalent amount of LDHs.

This paper proposes a new method of reusing uncalcined coal gangue (UCG) as a mineral admixture in magnesium ammonium phosphate cement (MAPC) blended with fly ash (FA). The effects of UCG on setting time, workability, hydration heat release, mechanical properties, hydration products, and microstructure of MAPC composites were systematically investigated. The results indicate that the addition of UCG decreased the maximum hydration temperature and extended the setting time of MAPC composites. The compressive strength of MAPC was improved by introducing an optimal amount of UCG. The XRD results showed no new crystal phase in UCG-0 (with 20% FA and 0% UCG) and some secondary hydration products, such as berlinite and lizardite, were observed in MAPC with UCG. The addition of UCG was found to inhibit the generation of dittmarite and promote the development of struvite. Results showed that differences in the crystal morphology of struvite and dittmarite influence the compressive strength of MAPC composites.

One of the most important factors influencing concrete durability is permeability. Permeability testing is conducted according to certain standards to measure the water permeation in concrete. After the test, the concrete specimens should be positioned under the concrete breaker jack and split into two sections to measure the permeability. In general, it is difficult to use the majority of permeability tests to determine concrete permeability in situ. As a result, the permeability and compressive strength of concrete with various strength classes were measured in this study by using the novel “cylindrical chamber” and “friction transfer” tests. Permeability-reducing admixtures, including Fibrous microsilica gel and waterproof, were used in several specimens that were subjected to 0, 50, 100, and 150 freezing and thawing cycles. A cylindrical chamber device can quantitatively display the permeation volume and rate of any liquid into concrete. By comparing the results of the nondestructive cylindrical chamber test with the standard destructive test, it was observed that there is a 97.6% correlation coefficient between the results. This correlation coefficient demonstrates the high accuracy of the cylindrical chamber test in measuring water permeability within concrete without the need for sample breakage. Furthermore, by comparing the results of the friction transfer test with the standard destructive test, a 94.2% correlation coefficient was observed. This correlation coefficient indicates the high accuracy of the friction transfer test in assessing the compressive strength of concrete without the need to break the concrete. In addition, the process of rising permeability rate has a greater value for low cycles. However, it progressively becomes smoother for higher cycles, in such a way that, on average, the permeation volume increased by 71% in the first 50 cycles, 21% in the second 50 cycles, and only 8% during the third 50 cycles. In concrete specimens without additives, the value of permeability rate increases under freezing and thawing cycles by approximately 36% and 19%–22% in specimens containing permeability-reducing admixture.

The environmental friendliness, good thermal performance and sustainable development of rammed earth structures have attracted the attention of numerous researchers and engineers in recent years. Nevertheless, the fire safety of rammed structures has not been extensively studied. The primary objective of this study is to investigate the mechanical properties of stabilized and unstabilized rammed earth exposed to direct fire under short elapsed time and high temperatures using a kiln. Rammed earth specimens with various mix designs were prepared and then exposed to high temperatures. Afterward, destructive and nondestructive tests were performed. Additionally, microstructural analysis was preceded to evaluate the change in chemical composition and microstructural of rammed earth specimens. The majority of the stabilized specimens exhibited thermal instability at 700°C. These specimens lost up to 85% of their compressive strength and 15% of their weight and change in their chemical composition. Under direct fire exposure, the rammed earth’s mechanical properties were not greatly impacted due to the short elapsed time. Compressive strength was increased in unstabilized (clay) RE specimens. A correlation between destructive and nondestructive properties was proposed. This study can be considered in the mix design of RE that experiences high temperatures.

Fly ash (FA) increases the performance of cement concrete through pozzolanic reaction and microstructure development at later ages. FA is usually associated with lower early age compressive strength especially at higher replacement levels. This study attempts at improving the early age strength of FA portland pozzolana cement with limestone calcined clay pozzolan (${\mathrm{LC}}^2$). Different proportions of limestone and calcined clay ($1:1$, $1:2$, and $2:1$) in tandem with FA at various replacements of cement clinker (30%, 40%, and 50%) were tested. The combined effect of using ${\mathrm{LC}}^2$ with FA has shown to enhance the early age hydration of cement along with improved compressive strength. Heat of hydration results showed increased heat release in FA mixes blended with ${\mathrm{LC}}^2$. Thermodynamic modeling analysis was used to study the change in phase assemblage of these mixtures. A higher solid volume observed in the thermodynamic simulations in the combined blends of FA and ${\mathrm{LC}}^2$ is hypothesized to be the cause of improved performance compared with only FA blended cement. Mercury intrusion porosimetry (MIP) results further confirmed an improvement in pore structure characteristics of FA cement blended with ${\mathrm{LC}}^2$. The possibility of reducing associated carbon emissions without compromising in strength are highlighted by using FA and ${\mathrm{LC}}^2$.

This study examined the self-cleaning and mechanical properties of basalt fiber–reinforced ground granulated blast furnace slag (GGBS)-based geopolymer mortar containing nano ${\mathrm{TiO}}_2$. The nano ${\mathrm{TiO}}_2$ and basalt fiber in mixtures were used at 0%, 0.25%, 0.5%, and 1% by weight of GGBS. The cubes ($50\times 50\times 50\mathrm{mm}$) and prisms ($40\times 40\times 160\mathrm{mm}$) samples containing nano ${\mathrm{TiO}}_2$ and basalt fiber were produced and cured in the oven for 24 h at 60°C. Then, these samples were kept at room temperature at $23°\mathrm{C}\pm 2°\mathrm{C}$ for 28 days. Lastly, the compressive strength, flexural strength, ultrasonic pulse velocity, capillary water absorption, and self-cleaning tests of GGBS-based geopolymer mortars were carried out. In this study, the Rhodamine-B test was used to determine self-cleaning. This study showed that the compressive strength, flexural strength, and ultrasonic pulse velocity values of the GGBS-based geopolymer mortars increased as the nano ${\mathrm{TiO}}_2$ and basalt fiber ratios increased, but their capillary water absorption coefficient decreased. Also, this study found that the self-cleaning rate of GGBS-based geopolymer mortars containing 1% nano ${\mathrm{TiO}}_2$ was obtained as 50.62% at 28 days.

Waste vegetable oil cold mix recycling technology can massively improve the resource utilization rate of solid waste in the road construction industry. This process can also reduce energy consumption and environmental pollutant emissions during road construction, making it an effective approach to achieve the carbon peak and carbon neutral strategy in this industry. This study employs a combination of macroexperiment and microscopic molecular simulation to analyze the component changes and mechanisms in the process of cold regeneration of aged asphalt with waste vegetable oil. The findings provide a scientific basis for the popularization and application of this technology. This study conducted a basic performance test, four-component test, atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR), and molecular simulation on waste vegetable oil cold regeneration asphalt (WVOCRA) with varying waste vegetable oil (WVO) content, which aims to determine the optimal amount of WVO for cold regeneration of asphalt and to understand the mechanism behind the change in components and properties of aged asphalt during the process. The study found that the addition of WVO improved the colloidal stability of cold regenerated asphalt. The asphaltene index in the four-component test and the ratio of honeycomb structure in the AFM test indicates that the optimal ratio of light and heavy components in WVOCRA was achieved with a 10% dosage of WVO. Furthermore, the macroscopic properties of WVOCRA were restored to the same level as that of the 70# asphalt. The rejuvenation of aged asphalt through WVO is primarily achieved through physical conditioning, without the generation of new chemical functional groups. WVO can be used to separate asphaltene dimers in aged asphalt, reducing the probability of asphaltene and resin aggregation, and degrading heavy component clusters in aged asphalt. The index of mutual diffusion rate $V_v$ indicates that increasing the temperature of simulated diffusion and the proportion of WVO can enhance the mutual diffusion rate and integration depth of WVO and aged asphalt. However, the increase of WVO will reduce the thermal stability of WVOCRA. Therefore, future research could explore process optimization for the cold regeneration of aged asphalt using WVO or investigate the combined use of WVO cold regeneration asphalt technology and composite modified asphalt technology.

Corrosion of steel rebar in reinforced concrete (RC) constructions is an issue of great concern toward ensuring the integrity of civil structures, and thus, detection of the on-set of corrosion process, if any, will tremendously help in taking timely and effective measures. To address this issue, the current work aims to evaluate the potential of using different nonlinear ultrasonic (NLU) methods to detect corrosion through analysis of the signal characteristics from both time and frequency domain. Three NLU parameters (from time and frequency domain response) are studied by using an indirect type of measurement obtained from RC specimens undergoing accelerated corrosion process. Signal subtraction method (SSM)-based time domain nonlinear parameter and sideband peak count (SPC)-based frequency domain nonlinear parameter are found to be effective in detecting the specific damage stages during the corrosion process. There exists a significant shift in the cumulative nonlinear parameter curve arrived based on SSM when the mass loss is around 14 g, corresponding to the time at which the first surface crack of about 0.2 mm width appeared. Cumulative nonlinear parameter curve arrived based on SPC, shows a drastic shift when the mass loss is only 2 g, i.e., at the time when microcrack initiates inside concrete. To provide a complete monitoring solution, the complementary abilities of both time and frequency domain NLUs are used for the first time to formulate a damage index that can effectively monitor the progression of damage caused by corrosion from the beginning of the process until the point of failure.

Comblike polycarboxylate superplasticizers (PCs) have been widely used as construction and building materials by means of high fluidity and fine dispersibility via electrostatic repulsion and steric hindrance. The conventional PCs are usually synthesized by free radical polymerization, which limit to understand and even distort the structure-property relationship due to the random molecular structure and the broad polydispersity. In this work, polycarboxylate ether superplasticizers of acrylic acid (AA) and ethylene glycol monovinyl PEG (EPEG) with controlled structure were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. The resultant copolymers (denoted as EPCs) were characterized by FT-IR, ¹H NMR and GPC spectroscopy. The effect of actual acid/ether (AA/EPEG) ratio on the adsorption capacity and dispersion ability of EPCs in cement paste were deeply investigated. These results demonstrate that the dispersibility of EPCs with controlled molecular weights and comparatively narrow polydispersity indexes ($\mathrm{PDI}=1.2–1.4$) strongly depends on the acid/ether ratio. With an increase of the feed molar ratio of AA/EPEG from $4:1$ to $8:1$, the molecular weight and their distribution of EPCs increases accordingly. In addition, the adsorption capacity and dispersion property of EPCs to cement are densely related to the molecular structure and composition and superior to that of conventional PC analogues. A possible mechanism was proposed that EPCs can act uniformly on the surface of cement particles due to the well-defined molecular structure and well-distributed molecular weight, which is different from the conventional PCs, which will offer the fundamentals of design and synthesis for polycarboxylate superplasticizers with controlled structures.

The development and application of asphalt plug joints have gained popularity due to their unique advantages, such as driving comfort, shock absorption, noise reduction, and convenient management and maintenance. However, these expansion joints are susceptible to damage at the interface due to long-term exposure to traffic loads and environmental factors. Specifically, the interface bond damage between the asphalt plug joint and the pavement directly impacts the service performance and durability of bridge expansion joints. To address these issues effectively, this paper proposes an interface binder with improved bonding performance based on pull-off and oblique shear tests, which is used to enhance the interface cracking resistance of the asphalt plug joint structure. The research focused on the interface layer between Marshall and concrete specimens. A finite-element model of the pull-off specimen, which includes a bilinear cohesive element, was established to simulate the cohesive damage process between the interface layers. The constitutive relationship of the bilinear cohesive element utilizes the bond-slip constitutive curve obtained from the tests. It combines the maximum nominal stress (Maxs criterion) and the linear softening method of energy to simulate the fracture process of the interface layer. The simulation results were compared with the experimental data. Additionally, a parameter design analysis was conducted to study the influence of individual parameter variables on the interface damage behavior. The analysis provided robust data support for simulating the interfacial crack resistance. The results indicate that the simulation analysis aligned well with the experimental data, and the bilinear cohesive model can effectively capture the nonlinear behavior of the interface layer bond-slip. The loading method and the type of binder were found to have a significant impact on the interface bond fracture energy. The results demonstrate the effectiveness of the proposed approach in capturing the nonlinear behavior of the interface layer and provide valuable insights into the influence of different parameters on interface damage behavior.

Fiber reinforcement has been widely used to improve the performance of concrete under different types of loading. Among various types of fibers, a combination of fiber types, namely hybrid fibers, has been shown to be more effective due to the combined features of different types of fibers. However, the dynamic performance of hybrid fiber-reinforced concrete (FRC) has been rarely studied. Recently, a new type of hybrid, consisting of 1% low Young’s modulus macro polypropylene (PP) fibers and 0.1% high Young’s modulus micro basalt fibers, has been proposed, showing improved static mechanical properties compared with traditional FRC. In this study, the dynamic compressive and splitting tensile properties of this new basalt-macro PP hybrid FRC with varying fiber volume dosages were investigated by using split the Hopkinson pressure bar (SHPB). Experimental results showed that the basalt–macro polypropylene hybrid FRC exhibits superior impact resistance compared with plain concrete under both dynamic compression and splitting tension. The hybrid FRC showed less crack initiation and propagation, a ductile failure pattern, and smaller crack opening displacement. The sensitivity of the concrete to strain rate was found to be more significant for 1% hybrid FRC under dynamic compression and 2% hybrid FRC under dynamic splitting tensile tests. Based on the test results, empirical formulas were derived to describe the dynamic increase factor (DIF) versus strain rate for both dynamic compressive and tensile strength of hybrid FRC.

Abstract

Large structures need to be monitored to ensure safety for users and increase their service life through predictive maintenance. Self-sensing cementitious composites have been studied for structural health monitoring applications. By adding carbon nanotubes (CNTs) to a cement matrix, the resulting composite exhibits piezoresistive properties, making it capable of monitoring strain and mechanical stresses. However, due to their porous microstructure, the electrical properties of these cementitious composites are affected by moisture. This work studies the influence of water in the pores of a cement paste on the electrical resistivity, self-sensing capability, and electrification effects of cement pastes with different amounts of CNT. It was found that for pastes with lower amounts of CNT, the presence of water decreased electrical resistivity and increased electrical polarization effects and self-sensing sensitivity to strain, but not to failure. On the other hand, pastes with higher CNT content were less affected by the presence of water in the pores of the cementitious matrix. It was concluded that a minimum amount of CNT, above the percolation region, can minimize the effects of moisture variations on electrical properties.

Practical Applications

The construction industry is one of the most traditional in the world. Nevertheless, it has undergone a significant transformation and evolution through the adoption of new materials. Nanotechnology has played a pivotal role in the development of cementitious materials with novel properties, such as self-healing, energy absorption, self-cleaning characteristics, and the ability to monitor deformations, among others. It is within this context that smart cementitious composites emerge, maintaining their pre-existing properties and functionalities while incorporating new ones. Among these, self-sensing cementitious composites are specialized cement-based materials designed to monitor the safety performance of construction structures. When incorporated into structures, they can correlate their electrical properties with the deformations experienced, providing real-time monitoring of the conditions of these buildings. Self-monitoring cementitious composites serve as sensors for monitoring pavements and large structures such as dams, bridges, and viaducts. Their significant advantage lies in being manufactured from the same material as most structures, ensuring excellent compatibility and greater durability compared to other commercial sensors.

Water stability resistance and internal void evolution behavior of the cold mix emulsified asphalt mixture (CMA) specimens at multiple freeze–thaw cycles were evaluated based on the tensile strength ratio from the indirect tensile strength (ITS) test and x-ray computed tomography (CT) test, respectively. The ITS results show that the effect of multiple freeze–thaw cycles had a more negative impact on the CMA compared to that on the hot mix asphalt, and the water stability issue of the CMA could not be ignored. Moreover, the water stability was quantified by the porosity increase and void distribution of the CMA specimens from the x-ray CT; such test results indicate that early damage of the CMA specimens after freeze–thaw cycles shown as reduced tensile strength was mainly due to the rapid increase of the number of small voids, and late damage was induced by the formation of medium and large voids within the CMA specimens. As a result, the water stability of the CMA needs to be improved before it is used as pavement surface layers in cold areas with multiple freeze–thaw cycles.

This study investigated the effects of a diatomite/tetradecane composite shaped phase change material (CSPCM) on the mechanical properties and thermoregulation performance of styrene-butadiene-styrene (SBS)- and styrene-butadiene-styrene/crumb rubber (SBS/CR)-modified asphalt binders. The heat transfer and latent heat characteristics of phase change asphalt mortars (PCAMs) were analyzed using a thermal constant analyzer and differential scanning calorimeter. Furthermore, a thermoregulation test was devised to confirm the temperature-regulating characteristics of PCAMs. The rheological properties of PCAMs were analyzed using the dynamic mechanical analysis (DMA) method, and low-temperature fracture characteristics were evaluated using the single edge notched beam (SENB) test. The results indicated that the incorporation of CSPCM decreased the thermal conductivity and thermal diffusivity of SBS- and SBS/CR-modified asphalt binders but increased their specific heat capacity. CSPCM can be stably present in modified asphalt and still have good phase change properties in the phase change temperature range, as well as the temperature regulation effect of PCAMs is excellent. The melting enthalpy for the PCAMs was as high as $73.29\mathrm{J}/\mathrm{g}$. Compared to the modified asphalts, the heating time of the PCAMs increased by up to 34.1% as the dosage of CSPCM gradually increased. The incorporation of CSPCM enhanced the viscous components of modified asphalt binders, improved intermediate-temperature fatigue resistance and low-temperature fracture resistance, and reduced high-temperature permanent deformation resistance.

The chloride content is a critical factor influencing the corrosion of steel fibers in concrete. This study focused on the corrosion behaviors of steel fibers exposed to simulated concrete pore solutions with different chloride contents. The corrosion rates of the steel fibers were calculated based on the changes in the diameter and ultimate tensile load. The electrochemical parameters for the corrosion of the steel fibers were continuously monitored for 62 days. In addition, the surface micromorphologies of the corroded steel fibers were observed using scanning electron microscopy (SEM). The results showed that based on the change in the diameter, the corrosion rate of the steel fibers increased almost linearly when the NaCl content in the simulated solution increased from 2% to 5%. However, based on the variation of the ultimate tensile load, the corrosion ratio of the steel fibers increased linearly with the increase in the exposure time when the NaCl content was less than 3%, while it increased exponentially when the NaCl content exceeded 3%. According to the open circuit potential, Tafel polarization curves, and electrochemical impedance spectroscopy (EIS), the corrosion tendency and corrosion rates of the steel fibers exposed to the simulated solutions increased significantly when the NaCl content increased from 2% to 5%. Additionally, the corrosion damage on the surfaces of the steel fibers increased notably, and after 180 days of exposure to the simulated solution with 5% NaCl, the steel fiber was almost broken. These findings will help to understand the durability of SFRC in a chloride environment.

As a potential long-life pavement material, the high brittleness of epoxy asphalt prevents its application. Recycled from waste tires, crumb rubber (CR) can be used with styrene-butadiene-styrene (SBS) to prepare SBS/CR composite modified asphalt. The main objective of this paper is to conduct the material design of epoxy asphalt with SBS, CR, and core-shell rubber (CSR) to toughen the epoxy asphalt and enhance its performance. First, SBS modified epoxy asphalt and SBS/CR composite modified epoxy asphalt (CMEA) were prepared to optimize the toughening materials based on tensile tests. Subsequently, based on the optimized material, the optimal proportion was determined through the response surface method by the Design-Expert software. Third, the microscopic morphology of different epoxy asphalt was observed by laser scanning confocal microscopy (LSCM), and the changes in functional groups were tracked using Fourier transform infrared spectroscopy to reveal the toughening mechanism. Finally, the viscosity test was carried out on the optimal SBS/CR-CSR CMEA at different temperatures to determine its mixing temperature and allowable time. The results show that the SBS/CR-CSR CMEA is the best toughening method, and the optimal epoxy and CSR proportion is 37% and 12%, respectively. Its tensile strength increases by 467.11% and elongation at break increases by 68.73% compared with unmodified epoxy asphalt. The formation of interpenetrating polymer network structure between the SBS/CR network and epoxy resin network, as well as the change in the benzene ring that determines the softness and toughness, may be the main strengthening and toughening mechanisms. The suitable mixing temperature is 160°C for the optimal SBS/CR-CSR CMEA in this paper, which reduces about 20°C compared with conventional CR or SBS/CR composite modified asphalt, providing better environmental benefits. Overall, the SBS/CR-CSR CMEA presents a new solution for the promotion and application of epoxy asphalt.

Concrete is obviously affected by the loading strain rate, and concrete exists in the state of shear multiaxial stress in practical engineering. Studying the dynamic response of concrete under multiaxial shear states facilitates comprehensive analysis of its actual failure behavior under complex loading conditions, thereby establishing an experimental foundation for precisely formulating dynamic constitutive models of concrete. Therefore, in this study, five axial compression ratios (0, 0.138, 0.207, 0.276, and $0.414f_{\mathrm{c}}$) and four strain rates (${10}^{-5}/\mathrm{s}$, ${10}^{-4}/\mathrm{s}$, ${10}^{-3}/\mathrm{s}$, and ${10}^{-2}/\mathrm{s}$) were considered. A servohydraulic machine for compression and shear was applied to conduct experimental research on the shear multiaxial dynamic mechanical properties of concrete. Different failure patterns and shear mechanical characteristic values of concrete under different loading conditions were obtained from the experiments. The following conclusions were mainly drawn through comparative analysis: as the axial compression ratio increases, oblique cracks are gradually formed in the parallel shear direction of the concrete, accompanied by a small amount of concrete spalling. The strain rate parameter has no significant influence on the apparent failure pattern of concrete in the parallel shear direction; moreover, as the axial compression ratio increases, the ranges of increase in shear stress and residual stress for concrete under different strain rates are 357.02% to 291.65%. The increase of strain rate gradually leads to a decreasing trend of shear stress for concrete under the influence of the axial compression ratio; as the strain rate increases, the range of increase in shear stress for concrete under different axial compression ratios is 21.08% to 33.81%. Overall, the increase of axial compression ratio leads to a decreasing trend of shear stress for concrete under the influence of strain rate. Based on the compression-shear relation and the principal stress space, the combined dynamic failure criterion of plain concrete is proposed by considering the effect of strain rate, and the corresponding stress mechanism is analyzed. The research results are of great significance to the development and application of concrete engineering.

Porous asphalt concrete (PAC) is a low-impact medium with strong stormwater management capabilities. However, the air voids inside the PAC mixture will gradually be clogged due to sediment entering the interior of the PAC pavement in the service period. Meanwhile, the permeability of PAC pavements can be partially restored using cleaning equipment. This study investigates the changes in microscopic void characteristics of PAC under the effect of clogging and cleaning. Three kinds of PAC specimens with different void content were clogged by aeolian sand and cleaned by high-pressure water washing after complete clogging, in which the air void content, the shape parameters (roundness and aspect ratio), number, equivalent diameter, fractal dimension of air voids for the PAC mixes were quantified by X-ray computed tomography (CT) and image processing techniques before and after clogging and cleaning. Moreover, a relationship between air void microparameters and measured air void content (volume method) was established. It was found that air void shape, air void content, air void number, and equivalent diameter had a significant impact on the clogging and cleaning effect of PAC pavement, but the fractal dimension did not have a considerable impact. The migration depth of the clogging material increased gradually with the increase of air void content, and the most severe clogging was at about 10 mm from the top surface. The air void number within 1 mm increased significantly due to particle clogging. Before the construction of the road, some microscopic void parameters of PAC will be predicted from air void content measured by volume method, and combined with the results of local clogging particle size distribution, a reasonable PAC gradation will be selected to generate much larger voids than the clogging particles to improve the anticlogging performance of PAC pavement.

Concrete shrinkage and creep significantly affect the serviceability of bridges, especially long-span bridges. To investigate the long-term shrinkage and creep behaviors of low-shrinkage and low-creep C60 high-performance concrete (hereinafter referred to as LSLC HPC C60), 76 LSLC HPC C60 specimens are designed and subjected to shrinkage and creep tests for 270 days. The results indicate that the LSLC HPC C60 exhibits a similar trend in shrinkage and creep development as ordinary C60 concrete but with smaller creep and shrinkage values. New parameters for the two commonly used creep models are recommended based on experimental data. By comparing the measured data, it is determined that the parameter-recommended creep models are more suitable for predicting the creep performance of the LSLC HPC C60. A finite-element model of a long-span bridge is established, and the recommended models are imported into the bridge model. The multidecade deflections of the main span of the bridge are analyzed considering different creep models. The calculated results indicate that the parameter-recommended creep models can be used to predict the long-term deflections of long-span bridges with the LSLC HPC C60.

A compound warm-mix asphalt (WMA) technology, surfactant-foamed asphalt (SFA), was proposed to promote warm-mix reclaimed asphalt pavement technology and provide engineering and environmental benefits through nonrenewable materials recycling, cost saving, and energy and emissions reduction. The blending efficiency is critical for the design of SFA warm-mix reclaimed asphalt pavement (SFA-WMRAP) incorporating higher levels of RAP. This study investigated the blending efficiency of virgin and aged asphalt in SFA-WMRAP containing high RAP content. First, the effects of foaming temperature and foaming-surfactant additive dosage on the foaming characteristics and rheological properties of SFA were investigated, and the optimal foaming conditions were determined. Next, an atomic force microscope (AFM) test and fluorescence microscopy (FM) test were used to quantify its blending efficiency after using the stage extraction method. Results indicated that SFA under optimal foaming temperature and surfactant content achieved better workability, rutting resistance, and fatigue resistance. SFA-WMRAP with high RAP content showed a similar blending efficiency compared with the hot-mix process by using the gray mean value as an evaluating index, exhibiting great potential to promote WMRAP for incorporating high contents of RAP.

This study examined the chloride binding properties of slag-blended cement at different replacement ratios with two water-to-binder (w/b) ratios and two curing temperatures. Hydrated samples were immersed in NaCl solutions, and bound chloride at equilibrium was determined, respectively. It is found that at each w/b and temperature, chemically and physically bound chloride increased with increasing slag ratio up to 50%, whereas a further increase of slag ratio to 70% tended to reduce chloride binding. Physically bound chloride accounted for a major portion in total binding. Moreover, $\mathrm{Ca}(\mathrm{OH}{)}_2$ content and slag reaction degree were analyzed, indicating that slag reaction degree decreased with increasing slag ratio. According to the results, the influence of slag ratio on chloride binding is discussed. The relatively low chloride binding at 70% slag ratio is partially attributed to the low reaction degree of slag, resulting in a lower amount of C-S-H and AFm phase. It is also inferred that the decreased physical binding at 70% slag ratio is closely related to the changed surface electrical property of C-S-H.

In this study, magnesium ammonium phosphate cement (MAPC) was prepared with different dosages of silica fume. The physical properties of MAPC were tested and its high-temperature properties were investigated in detail. The results showed that the addition of silica fume decreased the fluidity and setting time of MAPC. The results also showed that the addition of silica fume was beneficial to improving the resistance of MAPC to high temperatures. After exposure to high temperatures (200°C, 600°C, 800°C, 1,000°C, and 1,200°C), the flexural strength of MAPC reached its maximum when the additional level of silica fume was 20%. At 20°C, struvite (${\mathrm{MgNH}}_4{\mathrm{PO}}_4·6{\mathrm{H}}_2\mathrm{O}$) was detected as the main hydration product in MAPC. Heating of MAPC to 800°C resulted in the transformation of ${\mathrm{MgNH}}_4{\mathrm{PO}}_4·6{\mathrm{H}}_2\mathrm{O}$ to anhydrous magnesium orthophosphate [${\mathrm{Mg}}_3({\mathrm{PO}}_4{)}_2$]. After exposure to $\ge \mathrm{1,000}°\mathrm{C}$, the sintering of ${\mathrm{Mg}}_3({\mathrm{PO}}_4{)}_2$ occurred, and meanwhile forsterite (${\mathrm{Mg}}_2{\mathrm{SiO}}_4$) was identified in the X-ray diffraction (XRD) pattern. After adding silica fume, more ${\mathrm{Mg}}_2{\mathrm{SiO}}_4$ with good thermal stability was formed, which made MAPC with better resistance to high temperatures.

Compacted cement-stabilized soils are important geomaterials for construction projects involving backfilling, embankment construction, and ground improvement. In general, unconfined compressive strength (UCS) serves as an important design parameter for such types of materials, but it remains difficult to characterize the UCS owing to complex interactions of various influencing factors. This study aims to obtain practical insights into the effects of water and fines content on the UCS of cement-stabilized clayey sand, which is commonly encountered in reclamation projects. The experimental results show that the water content and fines content affect the strength in a combined manner. The strength decreases monotonically with increasing water content for clean sand, while it first increases and then decreases with the increase in water content for cemented clayey sands. In addition, the effects of fines content on the UCS are also affected by water content. The threshold water content and threshold fines content were identified and characterized. The maximum strength corresponding to these threshold parameters was also characterized. Finally, a new sequential framework to predict the UCS of cement-stabilized clayey sands is proposed.

The main objective of this work is to characterize the stress–strain relationship of cross-laminated timber (CLT) wall panels when loaded in compression and how different confinement mechanisms provide compression reinforcement for the CLT panels. CLT crushing tests were performed to define the behavior of CLT under compression up to the failure point, defined here as the strain at which the gross stress falls by 20% from the peak value. Testing included monotonic uniform compression experiments of five-ply CLT with specimens that were 0.457 m wide by 1.52 m long. The motion of the specimens perpendicular to loading direction was restrained at midlength to prevent buckling. Twelve specimens were tested, including six bare CLT specimens and six reinforced specimens of CLT—three with self-tapping screws while the other three with self-tapping screws and an additional U-shape steel plate at the bottom of the specimens. Various damage points were observed during the tests, including (1) point at the onset of damage (through visual observation and instrumental observation) (2) point of initiation of strength degradation, (3) point at which buckling occurs, (4) point at which 25.4 mm delamination was observed, and (5) failure point. Three axial compression stress–strain models were adopted, calibrated, and compared. Results indicate that a stress–strain model combining linear and cubic functions for the elastic and softening responses, respectively, captures well the CLT inelastic behavior under compression.

The high-quality reutilization of waste styrene-butadiene-styrene (SBS) modified asphalt (SBSMA) mixtures has been a focus area for researchers in recent times. Commonly used rejuvenators are generally unsatisfactory to fully restore their overall properties because it has no effect on the SBS modifier in aged binders. A significant research gap still exists regarding the restoration of the molecular structure and properties of aged SBS to instigate the performance recovery of aged SBSMA binders that will concurrently lead to enhancement of mixture performance. On this basis, this study considered the adoption of reactive organic materials, namely, polyurethane (PU) precursor and 1, 4-butanediol diglycide ether (BUDGE) for the investigation of the reaction-rejuvenation of aged SBSMA binders and mixtures. For the binder study, conventional rheological tests such as softening point, penetration, ductility, and infrared spectra spectroscopy were employed to evaluate the rejuvenation of the collective use of PU precursor and BUDGE on aged SBSMA binder. For the mixture study, two rejuvenator addition approaches, namely, carrier-free method and carrier-support method, were applied for aged SBSMA mixtures, and the high-temperature property, moisture-induced damage resistance, and low-temperature crack resistance were comparatively analyzed. The results indicated that PU precursor contributes to improving the softening temperature of aged SBSMA binder, and in combination with BUDGE, increased low-temperature ductility and flexibility can be attained. From the mixture performance results, the carrier-supported rejuvenation method can recover the permanent deformation resistance of the rejuvenated SBSMA mixture to similar levels as that of the fresh SBSMA mixture. Additionally, it can also effectively improve the moisture-induced damage resistance of the aged SBSMA mixture as well as providing a superior resistance to low-temperature cracking compared to the carrier-free rejuvenation method.

Understanding the cracking behaviors and failure mechanisms of soft rocks with existing cracks is crucial in designing rock engineering structures. Hence, we studied the influence of crack parameters, including crack inclination angle, crack number, and crack form, on the strength characteristics and cracking behaviors of silty mudstone using uniaxial compression tests and numerical simulation. The mechanisms of crack initiation, propagation, and coalescence in silty mudstone with preexisting cracks are discussed in this paper. The results showed that the stress-strain curves of silty mudstone with preexisting cracks can be divided into three stages: the load compaction, crack extension, and postpeak damage stages. Preexisting cracks had a weakening effect on the mechanical properties of silty mudstone, and the main order of influence of the various factors was crack inclination angle, crack number, and crack form. The failure mode of silty mudstone with preexisting vertical cracks was mainly composite tensile-shear failure; the failure modes of rocks with single and double cracks were tensile failure, shear failure, and composite tensile-shear failure. The damage process of silty mudstone with preexisting cracks under stress was as follows. The propagation and coalescence of cracks caused cracking of weak surfaces within the rock mass. The cracks propagated along the axial stress direction or preexisting crack direction under different stress states to form macroscopic crack surfaces, which ultimately led to rock mass failure. In addition, the strength characteristics and cracking behaviors of silty mudstone simulated using FLAC3D version 6.0 were consistent with the experimental results.

High-strength concrete (HSC) has been widely used in various engineering structures due to its excellent mechanical properties. However, the low water/cement ratio in HSC causes greater shrinkage and increases the cracking potential under restrained condition. Shrinkage reducing admixture (SRA) is extensively applied due to its excellent performance in reducing shrinkage. Although the influence of SRA on the mechanical properties and drying shrinkage has been investigated, investigations on tensile creep and cracking resistance are still lacking. Investigations on the tensile creep, autogenous shrinkage, restrained stress, and cracking resistance of HSC with SRA were conducted under uniaxial restrained condition in the current research. Four groups of mixtures with different dosages of SRA were tested under adiabatic conditions by utilizing temperature stress test machine. The experimental and analytical findings indicated that (1) the addition of SRA reduced the temperature rise and cracking temperature of HSC under adiabatic conditions; (2) the autogenous shrinkage and basic tensile creep of HSC decreased when the dosages of SRA increased; (3) the cracking time, cracking temperature drop, and cracking stress of HSC increased when the dosages of SRA increased; and (4) the cracking resistance of HSC increased with the increase of SRA dosages.

High-modulus asphalt mixtures (HMAMs) are potential materials for achieving long-life pavement performance, and understanding their long-term performance degradation mechanism is crucial for analyzing pavement performance degradation under long-term exposure to traffic and environmental coupling conditions. This paper aims to examine the long-term evolution of high- and low-temperature performance and water stability in HMAMs derived from modified nature asphalt, prepared using microparticle suspension technology, under heavy load and humid heat conditions. Four asphalt mixtures (AC-13, BBME-13, SMA-13, SBSAC-13) were prepared, and then their dynamic moduli were tested. A test plan for the long-term performance of the mixtures was designed, and the performances of HMAMs with different gradations and time were analyzed. Furthermore, corresponding long-term performance degradation models of HMAMs were established. The results show that the HMAMs of modified natural asphalt have better high-temperature performance than HMAMs of high-modulus agent/SBS-modified asphalt. However, following prolonged thermal aging and freeze-thaw cycles, the low-temperature performance shows the opposite trend. In addition, thermal aging had the same effect on the long-term low-temperature performance of both types of HMAM, with the HMAMs of modified natural asphalt being less affected by long-term freeze-thaw cycling. The long-term bending tensile strain attenuation of HMAMs can be simulated using an exponential function. Both types of HMAMs display similar water stability under dry-wet cycles and dynamic water erosion condition. The variations in residual stability during dry-wet cycles can be accurately represented using a power function.

This study evaluated the individual and cumulative impact of different design factors on moisture damage of hot-mix asphalt (HMA) using the modified Lottman test. This study considered five different types of design aggregate gradations (DAG), three binder types, and three levels of compactive effort. To evaluate the significance of the influential factors that affected the moisture sensitivity of the mix, statistical analysis was performed. This study also investigated the influence of volumetric parameters of the bituminous mixes on moisture damage. The correlation of different design factors and various volumetric parameters with the tensile strength ratio (TSR) was further investigated through analysis using the Pearson correlation coefficient. The need for this investigation arises from the scarcity of comprehensive studies examining the individual and combined effects of various factors and the impact of volumetric parameters on moisture susceptibility. Additionally, linear regression models were developed to predict TSR based on the design factors and volumetric parameters considered in the study. The final model showed a close fit, with low mean absolute percentage error ($\mathrm{MAPE}=0.931$) and a good coefficient of determination ($R^2=0.752$). Moreover, based on the tested mixtures, the study establishes a threshold value of dry indirect tensile strength (${\mathrm{ITS}}_{\mathrm{dry}}=750\mathrm{kPa}$) and wet indirect tensile strength (${\mathrm{ITS}}_{\mathrm{wet}}=650\mathrm{kPa}$), along with TSR (= 0.85).

Abstract

The portland cement (PC) industry is responsible for approximately 7% of all carbon dioxide (${\mathrm{CO}}_2$) emissions in the world. Blast furnace slag (BFS) has been increasingly used as a substitute for PC, due to the efficient disposal of steel industry waste and reductions in ${\mathrm{CO}}_2$ emissions. The present work investigated the environmental benefits of cementitious materials with large volumes of BFS (up to 90% PC replacement for the S90 mixture) and the influence on porosity and compressive strength. By X-ray computed microtomography and mercury intrusion porosimetry, pore size distribution was assessed. Porosity was also evaluated by water absorption. The environmental impacts were investigated by analyzing the embodied ${\mathrm{CO}}_2$ emissions (${\mathrm{ECO}}_2$) and embodied energy (EE) by using life cycle assessment methodology. Reductions of around 40% in the compressive strength of S90 were found, while reductions in EE and ${\mathrm{ECO}}_2$ were above 80%. The S90 showed higher porosity at the age of 28 days, but then promoted a more active pore closing effect over time, being nevertheless feasible for use in terms of porosity. The use of S90 is expected to increase durability due to its thinner porous matrix, and contribute to reducing environmental impact and advancing cleaner production.

Practical Applications

Today, there is a global call to action to end poverty, protect the environment and climate, and ensure that people everywhere can enjoy peace and prosperity. Objectives set for the United Nations aim to help developing countries, like Brazil, achieve the 2030 Agenda for Sustainable Development. A highlight is given to “Sustainable Development Goal 9: Industry, Innovation and Infrastructure” (SDG 9), which aims to build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation. The portland cement (PC) industry is responsible for approximately 7% of all carbon dioxide (${\mathrm{CO}}_2$) emissions in the world. The study carried out here points to the feasibility of using blast furnace slag (BFS) to replace up to 90% of PC clinker, and demonstrates the environmental advantages in terms of reducing ${\mathrm{CO}}_2$ emissions and energy consumption. In this context, the use of clinkers with higher concentrations of BFS, up to 90%, has emerged as a way to contribute to the sustainable development proposed by SDG 9.

Lately, dry stacking of filtered tailings has emerged as a safer alternative to traditional slurry disposal in ponds as it comprehends the compaction of the unsaturated cake to form piles. A cementing agent can be added to the mixture to improve the mechanical properties of the compacted tailings; however, it is essential to understand its response under different conditions. The present study examines the mechanical behavior of compacted iron ore tailings (IOT)-binder blends for dry stacking purposes, highlighting the effect of the cement type on the behavior of the tailings: two commercially available types of binders, portland pozzolan cement (PPC) and high early-strength portland cement type III (PC III); and one green alkali-activated cement (AAC). A full factorial design approach was used to study the influence of the following parameters on the strength and stiffness of the studied mixtures: dry unit weight (${\gamma }_d$), cement content ($C$), type of cement ($TC$), and curing period ($CP$). To do so, a set of unconfined compression, ultrasonic pulse velocity, and consolidated drained triaxial tests were carried out. To compare the microstructural and compositional characteristics of the three different cement types, secondary scanning electron microscopy (SSEM) and backscattered scanning electron microscopy (BSEM)/energy dispersive spectrometry (EDS) analyses were performed. The stiffness and strength results have been successfully correlated to the porosity/cement index ($\eta /C_{iv}$) and the statistical analysis has unveiled the great effects attributed to the cement content, type, and CP. Additionally, microstructural and macrostructural observations revealed that after seven days of curing, the IOT mixtures stabilized with PC III exhibited more robust microstructures and superior mechanical performance: around five times greater strength and stiffness than AAC-containing samples and two times higher considering the PPC-containing specimens. With extended CPs (90 days), the performances of PC III and PPC samples are equivalent, whereas the strength is around three times greater than that of the AAC samples. That is, there was a notable enhancement in the cementitious matrix for IOTs stabilized with PPC and AAC for a more extended CP.

Cement grout is widely used in underground excavations and constructions. Recent research reveals that coal char, a sustainable coal-derived material, can enhance the engineering properties of traditional cement grouts, such as higher compressive strength and lower bleeding at room temperature. However, the effect of coal char addition on the heat of hydration and rheological behaviors of char-cement grouts at lower or higher temperatures remains unclear. In this study, considering different w/c ratios (0.8–1.2) and char contents (10%–30%), the heat of hydration of char-cement is investigated to understand the hydration mechanism of cement with adding char. The rheological behaviors of new char-cement grouts at two different temperatures of 5 and 35°C are studied. It is found that the addition of char at the same w/c ratio leads to a higher first heat flow peak in the initial reaction period and facilitates hydration reaction in cement grouts based on cumulative heat evolution over a longer period (typically $>14\mathrm{h}$). The effect of 5 and 35°C on rheological behaviors of char-cement grouts is consistent with the respective pure cement grouts. A simple model based on cumulative flow resistance is proposed for describing the rheological behavior and can well fit all pure cement and char-cement grouts with a relatively high average ${\mathrm{R}}^2$ value of 99.7%.

Ground penetrating radar (GPR) technology is used for nondestructive testing of roads. It relies on the processing and analysis of electromagnetic waves reflected due to the differences in dielectric properties encountered by electromagnetic pulses during propagation for road quality assessment and detects distresses. The moisture content of the asphalt mixture in asphalt pavement undergoes dynamic changes, affecting the pavement’s relative humidity (RH). This alteration in RH has a direct impact on the dielectric properties of the asphalt mixture, thus influencing the accuracy of GPR road detection. Therefore, it is essential to quantify the relationship between RH and the dielectric properties of asphalt mixtures. This study utilized electromagnetic field theory to establish the correlation between air dielectric constant and RH. Dielectric constant tests were performed on commonly used single-phase component materials (limestone, 70# asphalt, SBS-modified asphalt) of asphalt mixtures and different types (asphalt type, asphalt-aggregate ratio, nominal maximum aggregate size) of asphalt mixtures under varying RH. The study quantified the impact of RH on the dielectric properties of asphalt mixtures and developed a CRIM optimization dielectric model that incorporates the RH effect. The research results showed that the dielectric constants of air, limestone, asphalt, and asphalt mixtures increase with the increase in RH. Specifically, the dielectric constants of air and asphalt mixtures exhibit a linear relationship with RH. Moreover, the increase in the dielectric constant of 70# asphalt with RH is greater than that of SBS-modified asphalt. Under identical conditions, reducing the impact of RH on the dielectric properties of asphalt mixtures can be achieved by increasing the asphalt-aggregate ratio, decreasing the nominal maximum particle size of the aggregates, or utilizing SBS-modified asphalt. The CRIM optimization model yielded an overall average relative error of 3.33% for calculating the dielectric constants of different types of asphalt mixtures under the influence of RH, representing at least a 1.67% improvement compared to classical models and the improved model proposed from existing literature. The research outcomes provide significant guidance for enriching and developing the fundamental theory as well as detection evaluation technology of GPR.

The study of the reaction mechanism of sea salt solution (SSS) on asphalt binder was important for the development of perpetual asphalt pavements in coastal areas. For this, a novel modifier (MPGJ-I) was developed in this study using phosphogypsum whiskers (PSW) synthesized from phosphogypsum (PSP) wastes, then the prepared composite-modified asphalt binders and base asphalt binders were immersed in the SSS with six concentrations. Then, the surface free energy (SFE) test, rheological tests, and Fourier transform infrared spectroscopy (FTIR) test were used to investigate the function mechanism of SSS on the surface properties, rheological properties, and chemical structure. The results showed that the salt in SSS would gradually transfer to the inside of asphalt binder, and with the increase in SSS concentration, the mass accumulation rate of base asphalt binders increased by 0.84% and 0.72%, whereas the modified asphalt binders only increased by 0.64% and 0.61%, respectively. The MPGJ-I effectively alleviated the decline trend of surface properties, with the incorporation of MPGJ-I, the SFE and cohesive work of base asphalt binders increased by 29.14%–32.83% and 5.23%–48.63%, respectively. In addition, with the increase in SSS concentration, the rutting factor (${\mathrm{G}}^{*}/\sin \delta$), and creep recovery rate (R) of base asphalt binders increased by 15.44%–57.69% and 7.58%–22.34%, respectively, and the fatigue life (${\mathrm{N}}_{\mathrm{f}}$) decreased by 6.08%–47.24%. Whereas ${\mathrm{G}}^{*}/\sin \delta$ and R of modified asphalt binders increased by 10.07%–50.77% and 2.15%–19.35%, respectively, and ${\mathrm{N}}_{\mathrm{f}}$ decreased by 1.79%–8.89%, which meant that the incorporation of MPGJ-I effectively restrained the attack action of SSS on base asphalt binders. There was a chemical reaction between SSS and asphalt binder, and the peak intensity of the new characteristic peaks in asphalt binder was positively correlated with SSS concentration, the incorporation of MPGJ-I could reduce the increasing rate of peak intensity to a certain degree. In addition, the principal component analysis (PCA) model showed that the surface properties and fatigue performance were closely related to the SSS concentration, and this correlation was not affected by the modification effect of MPGJ-I.

Concrete-filled steel tubes (CFSTs) have attracted increasing interest in research during the last decade as a construction system that increases its performance due to the use of self-stressing concrete. The efficiency and confining pressure of this construction solution mainly depends on the expansion of the concrete mixture introduced into the steel tube. This study shows the importance of the correct design of the expansive mixes and the correct selection of components. The effect of three types of chemical admixtures (air-entrained, setting retarder, and hardening accelerator) commonly used in the ready-mixed concrete industry when added to a self-stressing concrete made with a K-type calcium sulfoaluminate–based expansion agent has been analyzed. This study showed that certain chemical admixtures, added in a fixed proportion, conditioned both the compressive strength and the magnitude and kinetics of the expansion in a restricted regime of the reference self-stressing concrete mix. The efficiency of the CFST and self-stressing concrete construction solution represented by the bond failure strength and the sliding load of the concrete core against the steel tube was influenced not by the compressive strength of the expansive concrete but by the degree of restrained expansion (confinement effect) achieved. In this research, an alternative test method for measuring expansion was proposed, which allows continuous recording of positive strains (expansions), eliminating the dependence on setting time for demolding; this method even allows the exact identification of the expansion beginning. Finally, it was proposed that the ettringite detectable by the X-ray diffraction (XRD) technique was not representative of the magnitude of expansion generated from K-type calcium sulfoaluminate expansive agents because the proportion of ettringite was not related to the expansion determined by the different test methods proposed.

This research studied an innovative method for improving the properties of fly ash–based geopolymer mortar by using ultrafine two-dimensional (2D) graphitic carbon nanoplatelets (GCNPs) derived from sustainable biomass sources. These low-cost and eco-friendly GCNPs were synthesized through a thermochemical process involving biomass-derived sucrose solution. Both fly ash and GCNPs were processed and activated to optimize their performance in the geopolymerization process. The graphitic carbon reinforced geopolymer mortar (GCGPM) composite was optimized by employing different dosages of GCNPs (0, 0.1, 0.2, 0.3% [by weight of binder]), and the resulting GCGPM was examined through various instrumental analyses. It was observed that the addition of GCNPs results in reduced workability of the geopolymer mortar. Importantly, the maximum compressive strength of the GCGPM was significantly enhanced, up to 34.21%, with a 0.2% GCNPs addition over a 28-day curing period. Furthermore, incorporating 0.1% GCNPs into the composite led to an increased composite density, resulting in a substantial reduction of water absorption, up to 76.49%. These outcomes hold promise for achieving a more compact microstructure through the integration of GCNPs into geopolymer composites. The study suggests that novel synthesized GCNPs can effectively and sustainably enhance the properties of geopolymer composites in a cost-effective manner.