Journal of Materials in Civil Engineering

Ingress of chlorides (${\mathrm{Cl}}^{-}$) in concretes is influenced by external applied loads, and it is difficult to conduct a quantitative conclusion via experiments due to the geometry of concrete components and their different mechanical and chemical properties. To assist in-depth understanding on ${\mathrm{Cl}}^{-}$ ingress in loaded concretes, a numerical model considering different mechanical and transport properties of three concrete components (paste, aggregate, and interfacial transition zone), heterogeneously distributed stress generated by axial loads and the consequent change in ${\mathrm{Cl}}^{-}$ diffusion property at micro level, is established with COMSOL. Its accuracy and functionality have been verified with lab-based results from compressed and tensile samples at a macro level. The obtained results suggested that the model can effectively reveal stress distribution, generation, and propagation of cracks and ${\mathrm{Cl}}^{-}$ diffusion in loaded concretes. Based on this model, it can be deduced that without considering the heterogeneous mechanical and transport properties of concrete components, the extent of ${\mathrm{Cl}}^{-}$ ingress in concretes could be quite close when the induced stress is lower than 40% of the ultimate damaging stress; in comparison, it would be underestimated once the compressive or tensile loads exceed 60% of the ultimate damaging stress. Under 60% compressive loads, the ${\mathrm{Cl}}^{-}$ ingress depth is decreased by 66%, while that is increased by roughly 40% for a 60% tensile loads.

This study aims to develop a prefabricated flexible ultrathin overlay that can quickly and effectively repair cracks, particularly reticulation cracks, in old asphalt pavements while improving skid resistance. The overlay consists of a combination of an aggregate, a binder, and a geotextile; its unique structure results in a thickness of only about one-third of that of traditional ultrathin overlays. Its tensile strength, skid resistance, flexibility, waterproofing, interlayer bonding, and long-term service performance were evaluated through a series of tests. The results indicated that basalt, styrene butadiene styrene–modified emulsified asphalt, and warp-knitted polyester fiberglass fabric was the best combination. The proposed steady-state equation could reduce the test duration by more than 20%. The best interlayer binder was rubber asphalt with an optimum dosage of $0.9\mathrm{kg}/{\mathrm{m}}^2$. The effect of temperature on interlayer bonding properties was more significant than that of the loading rate. The overlay maintained good waterproofing, skid and crack resistance, and interlayer bonding properties after a medium-scale accelerated loading test.

Constructing a superhydrophobic coating on cement-based materials’ surface can effectively inhibit the invasion of external water and corrosive ions. However, current strategies of fabricating superhydrophobic coatings often require complex processes and some harmful solvents. Herein, an eco-friendly method is proposed for constructing superhydrophobic coatings on mortar surfaces to inhibit water penetration and chloride ion corrosion. The superhydrophobic coating was fabricated using superhydrophobic zeolite powders modified with nontoxic stearic acid. The mortar with superhydrophobic coating (SHC-mortar) possesses a water contact angle of 156° and water slide angle of less than 10°. In addition, the self-cleaning, waterproof and anticorrosion properties of SHC-mortar were explored. The results show that the fabricated superhydrophobic coating endows the mortar with a self-cleaning property, significantly reduces the capillary water absorption of the mortar, and improves the anticorrosion property of the mortar.

Seamless expansion joints for small- and medium-span bridges attract engineers due to their acknowledged integrity (durability), driving comfort and noise attenuation. Traditional asphalt plugin joints are easy and cheap to install, but they are hindered by premature failures frequently observed in situ. Comparatively, polyurethane (PU) possesses good durability and toughness and excellent chemical resistance, etc. The purpose of this study is to identify the proper PU material and devise a new seamless expansion joint. As such, the mechanical properties of three PU materials were tested, including initial setting time, tensile strength, rupture strain, hardness, wheel rutting, adhesion to pavement, water absorption, and aging. The appropriate mass ratio was identified to be polyol/isocyanate = 100/105. Subsequently, monotonic tensile/compressive, vertical loading and low-cycle fatigue tests were performed on the four full-scale expansion joints. It revealed that the rate-dependent behavior rendered the PU material suitable for seamless joints, as it was softer to accommodate the low-rate longitudinal deformation and was stiffer to sustain the high-rate vehicle loadings. Furthermore, the inclined angle between the PU and pavement would ameliorate the strain status and is recommended for practical use. Experimental and numerical results were synthesized into a proposed alternative polyurethane-based design that reduces the vertical displacement and circumvents the possible early failures under the effect of dynamic traffic loading.

With the use of intelligent aggregate (IA) and discrete element method (DEM), a method was proposed to predict the influence of aggregate motion on the rutting depth in asphalt mixtures. The IAs were embedded in the center and side position of the specimen in a wheel tracking test, and the characteristics of IA motion parameters were compared with those obtained from virtual tests. The suitable motion factors for prediction model of rutting depth were first selected based on the trend of curve changes from the comparing results. Evaluation of the correlation between motion factors (Z-axis displacement and X-axis rotation angle of different IAs) and rutting depth of asphalt mixture was used to build the correlation matrix. Based on the high correlation coefficients, the curves of Z-axis displacement for No. 1 and No. 2 IA and X-axis rotation angle for No. 1 IA were further selected as the predicted factors, the prediction models of rutting depth were established. The feasibility of prediction models was verified by returning the IA motion data in indoor test and virtual test separately to observe the fitting degree between the actual curve and the prediction curve. It showed that the deviation of the prediction curve with the displacement factors was less than 4%, which was suitable to use as the predicted factors. On the other hand, due to the large fluctuation range of the rotation angle, the prediction curve with the rotation angle factor was more appropriate as a confidence curve to validate the prediction curve.

Construction and demolition waste (CDW) produced in a construction work site generates problems in its management. Among the CDW, we can find polymers, which create an added problem because of their slow decomposition, nonreuse, and whose manufacture generates greenhouse gases, which are harmful to the environment. Therefore, to reduce and recycle CDW as an alternative raw material to manufacture construction materials and elements and minimize the waste sent to landfill is urgently needed. This article analyzes the incorporation of CDW polypropylene fibers from single-use slings into gypsum and plaster composites. Additionally, commercial polypropylene fibers were also incorporated to compare the results. For this, several specimens were prepared adding different weight percentages of CDW fibers from 1% to 4% and tested to determine their physical and mechanical properties: bulk density; superficial hardness; flexural and compression strength; and bonding strength. Results show that it is viable to use CDW polypropylene fibers to manufacture new gypsum-based composites, as all the results surpass the minimum values determined by the applicable standards. Better results were obtained when CDW polypropylene fibers were used instead of commercial ones. The increase of flexural strength is more representative than other mechanical properties. The inclusion of CDW fibers in composites allows the reduction of slings thrown into landfills, which reduces the generation of greenhouse gases to the environment in the manufacture of new fibers for mortar reinforcement.

To investigate the effects of mix proportion on the compressive mechanical properties of a flexible thin spray-on liner (TSL), a series of compression tests were performed on flexible TSL specimens with different styrene-acrylic emulsion contents ($m_s$), cement–sand ratios ($m_c/m_q$), and fiberglass contents ($m_F$). With an increase in $m_s$, the compressive strength of the flexible TSL first increased and then decreased, and the TSL gradually transformed from brittle to ductile. With an increase in $m_c/m_q$, the compressive strength increased. The increase of $m_F$ improved the compressive strength and elastic modulus of the TSL. Subsequently, three cyclic loading paths were selected to study the stress–strain behavior of a flexible TSL with a fixed mix proportion. The evolution characteristics of the irreversible axial strain, elastic modulus, dissipated energy, and damage variables under different cyclic loading paths were analyzed. The development of irreversible deformation accumulation reflects the characteristics of the damage evolution process under cyclic loading. Based on the experimental results, a stress–strain model is proposed to predict the stress–strain behavior of the TSL under different cyclic loading paths. The experimental results were used to calibrate and validate this model, demonstrating that the model can effectively predict the stress–strain behavior of a flexible TSL.

The porous structure in the porous asphalt concrete (PAC) mixture is achieved by incorporating a substantial amount of coarse aggregate and polymer-modified asphalt binder (PMA). Bottom ash (BA) was used to modify the properties of the conventional asphalt cement for PAC (BA-AC60/70-PAC) with various types of aggregates in Thailand such as basalt (B), granite (G), and limestone (L). With the lipophilic reaction between BA molecular and asphalt cement, the BA replacement results in the higher optimum asphalt cement, which contributes to the improvement of asphalt film thickness. Therefore, the BA replacement was found to have the potential to improve draindown, Marshall stability, resistance to particle loss, strength index, indirect tensile strength, indirect tensile resilient modulus, indirect tensile fatigue life, permanent deformation, rutting resistance, and skid resistance of PAC, which are comparable to those of PAC containing PMA (PMA-PAC) for all studied types of aggregates. Based on the analysis of cyclic test results, the distress model of both BA-AC60/70-PAC and PMA-PAC was developed and found to be unique and may also be applicable to other PMA-PAC with similar aggregates. The outcome of this research will promote the usage of BA by-products to develop a green and economical PAC.

The acoustic emission (AE) method is a nondestructive test method used when monitoring the damage propagation by detecting high-frequency elastic waves produced by the refraction process. Self-compacting concrete (SCC) is a special type of concrete that does not require vibration, has excellent fluidity, and is resistant to segregation. In this study, it is aimed to investigate the functioning of the AE technique, which is frequently used in normal concrete, in the behavior of SCC. For this purpose, simultaneous monitoring of SCCs under uniaxial compression load was performed with the AE method. In the concrete production, CEM I 42.5 R cement was used as binder, and fly ash (FA) and marble powder (MP) were used as mineral additives. The mineral additives used in the mixture were replaced with cement at a rate of 20%. In addition to the compressive strength of SCCs, crack analysis, AE amplitude, AE energy, ringing counts, and cumulative count results were investigated as a result of AE measurements. With the AE parameters obtained as a result of the simultaneous measurement, the behavior of SCCs under uniaxial load was successfully monitored. It has been observed that the behavior of SCC using different mineral additives changes according to the mineral additive type. Although the differences in compressive strengths are small, it has been demonstrated that the AE method can be followed successfully in different concrete types and different contents and the behavioral differences are revealed.

Although previous studies have broadly explored the aging process of styrene-butadiene-styrene (SBS)-modified asphalt, there still is a lack of understanding of the precise evolution patterns of its phase structure during aging, and whether aged SBS-modified asphalt retains its modified properties or reverts to conventional asphalt. To fill these gaps, this paper focused on key performance characteristics that differentiate SBS-modified asphalt from conventional asphalt, including viscosity, elasticity, and toughness properties; evaluated how aging influences mechanical properties; and examined morphological changes at different aging stages. The effective method for phase structure characterization was established. Based on the results, it was found that mechanical property variations, especially in the toughness curve, effectively indicate the phase structure. The fracture strength ${\sigma }_B$ and fracture elongation ${\epsilon }_B$ of SBS-modified asphalt after rolling thin-film oven (RTFO) aging for 8 h closely matched those of 70# base asphalt after RTFO aging for 8 h, with values of 1,364.32 and 0.005, compared with 1,421.07 and 0.007, respectively. This curve helps determine whether aged SBS-modified asphalt remains modified or reverts to conventional asphalt. Aging primarily affected instantaneous elastic deformation, and had a minimal impact on delayed elastic deformation. Morphological analysis supported these findings, and showed that SBS polymer degradation precedes significant network disruption, and increased toughness results mainly from SBS polymer presence.

Applying foamed warm-mix asphalt (FWA) containing recycled asphalt pavement (RAP) binder in pavement construction technology is an energy-saving and resource-recycling approach. However, the effectiveness of blended binders in improving road performance depends on the storage stability and compatibility in the binder’s composition to be effective and durable. To address the compatibility and storage stability issues of the foamed warm reclaimed asphalt (FWRA) in the actual practice, 15 FWRA samples were designed considering varying RAP binder contents and storage conditions. The conventional binder index properties, rheological property, storage stability, and compatible performances were fully characterized. Fourier transform infrared spectroscopy (FTIR) analysis was conducted to understand the internal chemical reactions and corresponding mechanisms, and bivariate correlation analysis was employed to evaluate the relationship between independent variables. The testing results showed that the proposed testing configurations were validated to simulate the storage condition in the actual practice. Increased RAP binder content can worsen the compatibility of unstored FWRA, but relatively satisfactory compatibility can be obtained when the RAP binder content is relatively low. Regardless of the content of RAP binder, the blended FWRA binder is less compatible after the final storage stability test, and thus appropriate modification methods should be proposed to improve the compatibility after storage in the future. FTIR results showed the macromolecular asphaltenes of RAP binder migrate downward during the storage stability test, leading to poor compatibility of FWRA. The $B$ of FTIR is suggested as the microscopic evaluation index, and $G^{*}/\sin \delta$ difference (35°C) is suggested as the macroscopic performance verification index of storage stability for FWRA.

As construction continues, a large number of concrete engineering facilities will be put into use in permafrost areas, which poses a challenge to the long-term service of concrete materials. To investigate the evolution of strength and pore structure of concrete under the cold permafrost environment, concrete compressive strength tests and mercury intrusion tests were performed at four molding temperatures (5°C, 10°C, 15°C, and 20°C) under continuous $-5°\mathrm{C}$ curing and standard curing conditions. Under negative-temperature curing, the strength of concrete at an early age reached about 80% that of standard curing; however, its strength at a later age was comparable to that at 28 days under standard curing. Under negative-temperature curing, the most probable pore size and porosity at 28 days of age were larger than those under standard curing. Increasing the molding temperature was beneficial for the promotion of the internal hydration reaction of concrete, refining its microscopic pore structure, and promoting its strength development. The strength of concrete with different porosities and average pore diameters could be predicted better using the Atzeni model or the bivariate Hasselmann model. Based on maturity theory, an equivalent age model of concrete under a permafrost temperature environment was established. The prediction deviation of the model was controlled within $\pm 5\%$, so the model can be used to predict the time-dependent strength of concrete in permafrost zones.

This study investigates the chloride transport and resulting corrosion-induced damage to reinforced recycled aggregate concrete (RAC) using finite-element simulations. A two-dimensional five-phase mesoscale-level time-dependent analysis was performed and chloride ingress, corrosion behavior, and corrosion product expansion induced RAC cracking were simulated. Material properties of aggregates, adhered mortar (AM) to the aggregates, old interfacial transition zone (ITZ), new ITZ, and the cement matrix were modeled. A series of RAC specimens with varying levels of AM contents were studied. The results indicated that chlorides moved faster in RAC specimens with more AM. Consequently, corrosion initiated quicker and more corrosion products were generated during the corrosion propagation process. The corrosion products’ expansion caused cracking that was more severe in RAC specimens, and increased with increasing levels of AM. In addition to the impact of AM content, aggregate shape and orientation effects on corrosion-induced cracking were explored through the meso-level modeling approach. A parametric study on the chloride diffusion coefficients of AM was also conducted. The results show that the impact of chloride transport properties of AM was insignificant when the AM level was low. This study provides important insights into the mechanisms of service life deterioration in reinforced RAC structures.

Organic polymers have been extensively studied over the last decades, and most of the research focused on the mechanical performance of the soils treated with polymer at different dosages without addressing the effects of the unique polymer characteristics such as molecular weight and concentrations of polymer solutions. This paper investigates an anionic polyelectrolyte, sodium polystyrene sulfonate (PSS) as a soil stabilizer. The effects of the molecular weight of PSS, concentrations of PSS solutions, and the dosages on the strength of a siliceous sandy subgrade soil are examined. Fracture toughness of the PSS-treated soil is determined and discussed based on semicircular bending test. Three molecular weights (1,000,000, 200,000, and $\mathrm{70,000}\mathrm{g}/\mathrm{mol}$) along with solution concentrations of 10%, 17%, 23%, and 30% by weight are considered. The dosages of PSS solutions at 2%, 4%, 6%, and 8% by weight of dry soil are discussed. All the dosages studied showed strength improvement of the sandy soil that increased with concentrations of the PSS solutions as well as the increasing dosages. PSS with the highest molecular weight performed the best among all three molecular weights. The addition of the organic polymer also improved the fracture toughness of the soil, indicating better resistance to crack propagation. The stabilization mechanism in terms of particle linkage and aggregation morphology are examined using scanning electron microscope. Aggregation of the fine soil particles and binding between the fine and coarse soil grains are observed and discussed, which contribute to the improvement of mechanical strength of the soil.

The surface roughness of the particles in a granular material plays a significant role in its engineering behavior. Because the microsurface features that contribute to the roughness are highly complex and irregular in nature, precise topographical measurements and a mathematically rigorous computational approach are needed for the accurate quantification of surface roughness. In this study, surface roughness of particles from three different sands that represent different sizes and shapes was quantified using spectral methods. A 3D noncontact optical profilometer was used to obtain a high-resolution representative scan area of sand particles. Higher-order moments of the power spectral density (PSD) were used to compute surface roughness parameters such as asperity slope and curvature. The surface roughness values were found to increase with the slope and curvature of the asperities. The value of asperity density, which has a physical significance in contact mechanics, was estimated to be about eight for all type of sands studied. Fractal analysis was carried out on the data obtained from profilometer and microcomputed tomography ($\mathrm{\mu }\mathrm{CT}$) scans to compute the fractal dimensions of sand particles using these two different instruments and compare them. Further, the angle of repose of different sands was correlated to their surface roughness.

Freeze–thaw-cycle damage is one of the main aging problems of concrete engineering in cold regions, and the analysis of its damage mechanism has become a focus in the field of concrete aging. In this paper, on the basis of the rapid indoor freeze–thaw tests designed and carried out on concrete, computed tomography (CT) tests were carried out on concrete samples with different numbers of freeze–thaw cycles. Using CT image recognition and three-dimensional reconstruction technology, the pores, aggregates, cement matrix, and other components within the material were extracted during the freeze–thaw process. A detailed analysis for the size distribution of pores on a microscopic scale was conducted. The damage evolution law of the interfacial transition zone under the freeze–thaw action was analyzed, providing strong support for checking the validity of rapid freeze–thaw test results.

The long-term aging of bitumens and its effect on low-temperature performance is a detrimental phenomenon. In order to investigate the effects of the aging phenomenon on the low-temperature performance of bitumens, it is very important to accurately simulate the behavior of bitumens in repeated aging cycles and to investigate related viscoelastic, chemical, and microstructural changes. In this research, three types of bitumen with penetration grades of $40/50$, $60/70$, and $85/100$ were subjected to one to three cycles of pressure aging vessel (PAV) aging. Comprehensive data on the bitumen’s behavior were obtained by conducting bending beam rheometer, Fourier transform infrared spectroscopy, and atomic force microscopy tests. Using the results of the conducted tests, an attempt was made to find precise relationships between different indicators of bitumen aging in terms of chemistry and viscoelasticity. The results revealed a linear correlation between the aging index and the $\mathrm{\Delta }{T}_c$ and dissipated energy ratio (DER) values, as well as the aging index and the vertical shift factor of the stiffness-time curve. The fitting coefficients of these linear relationships were $R^2=0.8$ and above, indicating a strong linear relationship between these parameters. Furthermore, the viscoelastic indices DER and the derivation of creep compliance ($J^{\prime }$) exhibited a fairly good linear relationship.

In this investigation, four types of sands as alternatives to river sand, namely, crushed sand (CS), marine sand, fine recycled concrete aggregate (FRCA), and fine reclaimed asphalt pavement (FRAP), were studied for their potential for cement-concrete pavement applications. Initially, the physicochemical and morphological characteristics of these sands were understood and later linked to the hydration kinetics and the behavior of cement-mortar systems in both the fresh and hardened states. Due to their evenly graded particle size distribution, CS and FRCA exhibited higher packing densities despite having more gradient angularity, whereas the interlocking capacity of FRAP was found to be affected by the agglomerated particles. Morphology, fineness modulus, and chemical composition of the sands were observed to be the dominating parameters affecting the hydration kinetics and thus the performance of the mortar mixes. Improving these parameters, especially the grain size distribution, could help in enhancing the potential of these sands for pavement applications.

Abstract

This paper aims to study the influence of novel macro encapsulated phase change materials (PCMs) on the mechanical and thermal properties of concretes. Thermal energy storage aggregates (TESAs) were prepared using vacuum impregnation. The PCMs were a lauric-myristic acid (LA-MA) eutectic mixture and coconut oil, pure or mixed, and are impregnated in diatomite as a supporting material. Thermal energy storage concrete (TESC) was made by replacing gravel in ordinary concrete with TESAs. Thermal and mechanical properties of prepared TESC were studied using differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, compressive strength, and thermal performance analysis. The results showed that the melting temperature of coconut oil and the eutectic mixture of LA-MA were 25.2°C and 34.5°C, respectively. TESC with 80 wt.% of gravel replaced with TESA had a compressive strength of higher than 17 MPa, which indicates its usability as structural concrete. The results of thermal performance analysis also revealed that prepared TESC had the capability of storing thermal energy and can reduce energy consumption by damping temperature fluctuations caused by the outside environment.

Practical Applications

In this paper, a thermal energy storage concrete (TESC) was prepared by embedding phase change materials (PCMs) in diatomite used in TESC. Using this type of concrete in the building will reduce the energy consumption of the building and increase its thermal comfort. The produced concrete containing 80 wt.% of gravel replaced with diatomite saturated with PCM had a desirable 28-day cylindrical sample strength of 21 MPa. In the designed thermal test, the time required for this concrete to reach 40°C is almost twice that of concrete without PCM. The results show a reduction of the influence of outside temperature on the temperature inside the buildings made with this type of concrete.

Graded gravel is a typical filler for railroad subgrade and the procedures for designing and evaluating it are crucial. The current specifications only stipulate the physical indicators of graded gravel material groups and the mechanical indications following on-site compaction. The lack of indoor mechanical standards makes it impossible to predict the on-site construction. Furthermore, the specification specifies various varieties and vast ranges of gradation, making it difficult to construct a skeleton structure. The current specification uses the heavy compaction method (HCM) and static compaction method (SCM) for the test method of graded gravel, which are no longer compatible with the current vibration compaction molding process. In this work, the effects of grading types, compaction coefficients, and water content conditions on the mechanical properties of the subgrade surface grading gravel were studied. Then the correlation between the field and indoor mechanical indexes was investigated and the $K_{30}$ predictive index of graded gravel was proposed and verified by combining it with the test section. The results show that compared with HCM and SCM, the correlation between vertical vibration compaction method (VVCM) and the field was greater than 90%. Compared with standard graded gravel, the California bearing ratio (CBR), $R_{\mathrm{c}}$, and $E_0$ of the strongly embedded skeleton compact gradation (VGM) graded gravel can be increased by 55%, 162%, and 171%, respectively. When the compaction coefficient increases by 1%, the CBR, $R_{\mathrm{c}}$, and $E_0$ can be increased by 12%, 28%, 31%, respectively. Compared with graded gravel with the optimal water content, the CBR, $R_{\mathrm{c}}$, and $E_0$ of dry graded gravel can be increased by 7%, 94%, and 14%. The proposed $CB{R}_1$ design standard, $E_{vd}$ acceptance standard, and graded gravel design method can better predict the $K_{30}$ index on-site.

Superabsorbent polymers (SAPs) can serve as effective internal curing agents in alkali-activated slag (AAS) systems, mitigating the risk of cracking. However, the influence of SAPs on the properties and microstructure of AAS systems is not yet fully understood. In this study, the effects of SAPs on the properties, reaction products, and internal moisture migration of AAS pastes were investigated. The water released by SAPs during curing supplemented the water consumption in the hydration process, maintained internal relative humidity, and reduced autogenous shrinkage by more than 80%. However, the addition of SAPs not only created voids in the hardened paste, as indicated by the mercury intrusion porosimetry (MIP) results, but also increased the microscopic pore volume of the paste. SAPs did not change the phase composition of AAS hydration products, but increased the differential thermogravimetry (DTG) peak corresponding to the main hydration product C(-A)-S-H gel at 28 days. The increase in chemically bound water in AAS pastes containing SAPs, along with the changes in the transverse relaxation time ($T_2$) peak area corresponding to SAPs in the ${}^1\mathrm{H}$ low-field NMR results, likely are due to the gradual release of water during internal curing by SAPs.

Waste concrete recycled powder (WCRP) occupies up to 30% of crushed old concrete and is hard to be reutilized due to its high porosity and low cementitious reactivity. Traditionally, the WCRP is reused as cement substitution in mortar/concrete production, but this substitution method has certain disadvantages. In this research, a novel substitution method, called the paste substitution method, was applied by replacing part of the cement paste with WCRP; a total of 28 trial mortar mixes containing WCRP added as either paste substitution or cement substitution were made for evaluation and analysis. By comparing the test results, it could be found that the incorporation of WCRP using the paste substitution method can remarkably enhance the compressive strength by at most 38.3%, densify the microstructure, and meanwhile greatly reduce the cement consumption by at most 26.7%. The cementing efficiency factor of WCRP in compressive strength was calculated for the first time, and its value is 0.289. Regression analysis showed that there exists good correlation between the compressive strength and effective water/cementitious materials (W/CM) ratio.

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

Organic corrosion inhibitors (OCI) have been widely accepted as a reliable method for enhancing the durability of marine reinforced concrete structures. However, the effect of OCI on steel corrosion is not clear in the case of cracks appearing in the concrete cover. In this paper, steel corrosion behaviors in cracked concrete with different crack widths, intact concrete containing OCI, and cracked concrete containing the OCI exposed to the marine tidal zone were investigated through open-circuit potential tests and EIS measurements. The obtained results illustrate that the corrosion rate of steel in cracked concrete is reduced with the decrease of crack width having an initial width of less than less than or equal to 200 μm in the marine tidal zone. Based on the $R_{\mathrm{f}}$ and $R_{\mathrm{ct}}$ values, it is found that the alcohol amine-based OCIs can improve the corrosion resistance of steel in intact concrete and concrete with microcracks (with a width of less than 100 μm) exposed to the marine tidal zone. The carboxylic acid-based OCIs aggravate the steel corrosion due to the hydrophobicity provided by carboxylic acids for seawater transport through cracks. The ester-based OCIs also increase the steel corrosion rate as it accelerates concrete carbonation.

The interfacial frictional resistance of anchor solids, bolt, and the surrounding soil of soil nails in the flexible support structures of frozen soil slopes is a key parameter for calculating and evaluating its stability. Based on a series of direct shear tests under the condition of a constant normal load boundary, the shear mechanical behavior of the interface between the soil and a cement slurry block under different soil temperatures, water contents, and normal pressures was studied, and the interfacial deformation mechanism was analyzed. The results show that in the thawing state, with the increase of water content, the shear surface moves from the side close to the soil to the side close to the cement slurry block. However, the shear plane is determined in the direct shear test, which makes the effect of the change of the soil’s own strength on the interfacial shear strength smaller. In the frozen state, the behavior of the interfacial shear stress–shear displacement behavior at the same water content varies from strain-hardening type to strain-softening type with the temperature decreasing. The normal displacement is affected by temperature, normal pressure, and water content. At the same temperature, the maximum normal displacement gradually decreases with the increase of water content and normal pressure. At the same normal pressure and water content, the maximum normal displacement tends to increase and then decrease as the temperature drops. Still, the maximum normal displacement in the frozen state is more significant than in the thawing state. At the same water content and normal pressure, the interfacial peak shear strength shows a nonlinear increase with the decrease in temperature. At the same normal pressure and temperature, the interfacial peak shear strength delivers a linear increasing law with increasing water content. The peak interfacial cohesion increases with the decreasing temperature and increasing water content, and this phenomenon is more evident at lower temperatures. The interfacial friction angle does not change significantly with the rise in water content at the same temperature, but as temperature decreases, its average value increases significantly. The research results can provide a reference for the design of slope support structures in cold regions.

This paper aims to propose an improved constitutive model based on the classical Chaboche mixed hardening model to describe the cyclic elastoplastic behavior of 6082-T6 aluminum alloy. First, 16 specimens from 6082-T6 aluminum alloy were tested under monotonic and cyclic loads. The variation law of the backstress, yield surface size, elastic modulus, and peak stress with equivalent plastic strain was obtained and analyzed. The results show that the kinematic hardening before and after the load reversal had a significant difference. Meanwhile, the elastic modulus and yield surface radius experienced a rapid decay at the early stage of equivalent plastic strain growth and then tended to flatten out. Based on these phenomena, a modified constitutive model based on the classical Chaboche mixed hardening model was proposed. The evolutions of isotropic hardening/softening, backstress, and elastic modulus were introduced. Then, the model was introduced to the ABAQUS software by the user subroutine to define a material’s mechanical behavior (UMAT) subroutine and corresponding parameters were provided. Finally, the proposed constitutive model was proven to capture the cyclic elastoplastic properties of 6082-T6 aluminum alloy well and had a significant improvement on the classical Chaboche mixed hardening model. Among them, the constitutive model can accurately describe the initial yield surface of 6082-T6, with an accuracy improvement of 26.6% compared to the Chaboche mixed hardening model, and an accuracy improvement of 7.44% in describing changes in elastic modulus.

The relationship between the characteristics of concrete pore structures and intrinsic permeability was investigated. The concrete pore structure incorporating fly ash was characterized by parameters including total porosity, pore size distribution (PSD), tortuosity, and characteristic pore sizes. The results indicate that: (1) there is a weak correlation between total porosity and critical pore size concerning oxygen permeability as interpreted by the Katz–Thompson model; (2) pores with diameters exceeding 100 nm serve as the primary tunnel for oxygen percolation in fly ash concrete; and (3) the porosity of pores larger than 100 nm and the average pore diameter exhibit the strongest correlation with oxygen permeability in fly ash concrete, as interpreted by the Katz–Thompson model.

To study the composition and migration of agglomerate in reclaimed asphalt pavement (RAP), two different RAPs were selected, and the aging performance of RAPs was evaluated. Then, the RAPs were sieved into a single particle size from 13.2 to 0.075 mm, and hot-mix and extraction tests were carried out on the RAPs with single particle sizes. Through the comparative analysis of gradations of the hot mixing and extraction of RAPs with single particle sizes, the composition and its migration rule of agglomerates of RAPs were analyzed. The thickness of gradation (TG), thickness of gradation ratio (TGR), degree of separation (DS), and degree of separation ratio (DSR) were proposed to evaluate the fragmentation characteristics of RAP agglomerates with single particle sizes. According to the DS index, the grading standard of RAP agglomerates was determined. The results show that the agglomerate of RAP at each particle size is mainly composed of the mineral aggregate of the initial particle size of RAP, the aggregate with one gradation lower than the initial particle size, and other aggregates with smaller and finer content. During the hot mixing, the RAP with the single particle size larger than 2.36 mm mainly undergoes old agglomerate fragmentation, whereas RAP with the single particle size $\le 2.36\mathrm{mm}$ will not only break into small particles, but also integrate new agglomerates. The RAP agglomerates can be divided into strongly bound agglomerates and weakly bound agglomerates according to whether they will be broken and separated during hot mixing. With the decrease of particle size of RAP, the proportion of strongly bound agglomerates gradually rises, whereas the proportion of weakly bound agglomerates declines.

Abstract

Insufficient compaction of the subgrade can result in nonuniform deformation, leading to severe subgrade distress. To address this issue and find a new method for rapid detection and evaluation of subgrade compaction, we used the lightweight deflectometer (LWD) to analyze the dynamic deformation modulus ($E_{vd}$) of subgrades filled with four types of soils—silt (ML), well-graded gravel (GW), lean clay (CL), and poorly graded sand (SP)—in different regions of Gansu province, China. Concurrently, we measured the degree of compaction ($D_{oc}$) using the sand replacement method (SRM) to establish its correlation with dynamic deformation modulus ($E_{vd}$). A strong correlation between the degree of compaction and dynamic deformation modulus was established for soils ML, GW, CL, and SP, and suitable formulas were selected based on curve variations. The developed formulas enabled back-calculation of the dynamic deformation modulus requirements corresponding to different degrees of compaction ranging from 90 to 100, facilitating direct queries and quick field checks. Results demonstrated that the LWD, as a reliable rapid detection method, effectively controlled subgrade compaction quality in field construction. Moreover, it extended the testing area and increased measurement frequency, thus providing a practical means for quickly evaluating the qualification rate and uniformity of subgrade compaction.

Practical Applications

When we build roads, most subgrade underneath the roads needs to be filled with soil. If we don’t pack the soil properly in the filling process, the subgrade can crack and become uneven over time. It’s hard to fix this problem once the road is open, so it’s important to make sure the soil is packed tightly enough before the road is finished. There are two ways to check if the soil is packed properly: one is a traditional method called the sand replacement method, and the other is a machine called the lightweight deflectometer. These methods help identify insufficient compaction of the subgrade and prevent uneven deformation problems during the filling process. What’s more, the lightweight deflectometer is a fast, convenient, and reliable tool that can assist or serve as an alternative to the traditional sand replacement method for controlling subgrade construction quality. This study is important because it helps us understand how to evaluate compaction of the filled subgrade in a different way.

Xinjiang has a temperature difference of 20°C between day and night, interannual temperature difference of 50°C, the control of the temperature cracks in mass concrete becomes difficult. Although low-heat portland ($\mathrm{P}·\mathrm{LH}$) cement concrete containing fly ash (FA) can reduce hydration heat, the mismatch between its mechanical and thermal properties is still not fully resolved. An attempt to explore the effect of FA on the competitive hydration reaction of ${\mathrm{C}}_3\mathrm{A}$ and ${\mathrm{C}}_3\mathrm{S}$ at super-early ages, and how this effect changes the physical and chemical properties of hardened cement pastes by electrical resistivity and zeta potential and common microstructure test methods, and to provide a theoretical basis for optimization of mechanical and thermal properties of $\mathrm{P}·\mathrm{LH}$ cement concrete with FA. Results showed that in the fast dissolution stage, a numerous ${\{\mathrm{Ca}}_6{[\mathrm{Al}(\mathrm{OH})}_6{]}_{2}24{\mathrm{H}}_2{\mathrm{O}\}}^{6+}$ ions and a very small amount of ${\mathrm{H}}_3{\mathrm{SiO}}_4^{-}/{\mathrm{H}}_2{\mathrm{SiO}}_4^{2-}$ ions were formed, and incorporating 20%, 30%, 40% FA primarily inhibited the ${\mathrm{Al}(\mathrm{OH})}_6^{3-}$ hydration and the ${\{\mathrm{Ca}}_6{[\mathrm{Al}(\mathrm{OH})}_6{]}_{2}24{\mathrm{H}}_2{\mathrm{O}\}}^{6+}$ generation, resulting in the generation time of AFt in comparison with pure cement, respectively, delayed by 44%, 140%, and 524%. This phenomenon decreased the nucleation and crystallization growth rate of AFt and ${\mathrm{Ca}(\mathrm{OH})}_2$ in the induction stage, and reduced the consumption of gypsum in the acceleration stage. Hence, monosulfoaluminate did not exist for pastes with more than 30% FA, and the number of particles involved in the reaction for the $\mathrm{P}·\mathrm{LH}$ cement stone with 20%, 30%, and 40% FA decreased by 4.0%, 46.5%, and 52.0% in the deceleration stage compared with the pure cement. The research results can provide a theoretical reference for modifying chemical properties of FA to meet the matching of mechanical strength and thermal of $\mathrm{P}·\mathrm{LH}$ cement.

In this study, nano-${\mathrm{SiO}}_2$ was synthesized using the sol-gel method to modify the properties of fly ash-slag geopolymers (FASGs). FASGs with six contents of sol-type nano-${\mathrm{SiO}}_2$ (0, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%) and two alkali dosages (5% and 7% of ${\mathrm{Na}}_2\mathrm{O}$) were prepared. The influences of sol-type nano-${\mathrm{SiO}}_2$ and alkali content on the compressive strength, flexural strength, drying shrinkage, and microstructure of FASG were studied. The results demonstrated that the early-age compressive and flexure strength of FASG can be enhanced by sol-type nano-${\mathrm{SiO}}_2$ due to the improved microstructure and the reaction products. The improvement effect of sol-type nano-${\mathrm{SiO}}_2$ on mechanical properties was more significant for FASGs with lower alkali dosages. The optimized content of sol-type nano-${\mathrm{SiO}}_2$ in FASG was 0.2% for the mechanical properties. The addition of the sol-type nano-${\mathrm{SiO}}_2$ can mitigate the drying shrinkage of the FASG when the content is lower than 0.4%. The sol-type nano-${\mathrm{SiO}}_2$ can promote the formation of reaction products in FASG and result in a denser microstructure of FASG.

This research investigated the synergistic adoption of sodium silicate (SS) and the synthetic calcium silicate hydrates (C-S-Hs)/polycarboxylate (PCE) nanocomposites on the hydration behavior of portland cement containing 20% by weight of lithium slag (LS). Effects of SS and C-S-Hs-PCE on rheological performance, mechanical strength development, and hydration process were evaluated. Results showed that C-S-Hs-PCE was advantageous for modifying the rheological performance of fresh LS-cement binder, while SS increased the rheology and yield stress and shortened setting time of the LS-cement binder. C-S-Hs-PCE promoted the hydration of silicates to form abundant CH, and SS generated the dissolution of metallic ions from LS. The hastened dissolution of LS accelerated the formation of ettringite (AFt) as well as C-S-H gel. Because the hydration of cement and pozzolanic reaction of LS were both promoted, the hydration products of hardened matrix were increased, and the interlaced combination structure of hydrates in the matrix was greatly improved, which was favorable for the development of mechanical strength. The findings provide theoretical guidelines for modifying the properties of blended cements by uniting nanoparticles and chemicals.

Abstract

Peach shell, a distinctive agricultural residue in China, exhibits the potential to substitute concrete aggregates, facilitating the creation of eco-lightweight concrete. This study determines the optimal volume substitution rate based on strength and density for peach-shell concrete. It delves into microscopic features, hydration outcomes, mechanical traits, sound absorption, impermeability, and techniques to enhance the impermeability. The outcomes reveal that peach-shell concrete’s compressive, flexural, and splitting tensile properties are comparatively lower than ordinary concrete due to reduced peach-shell aggregate, cement paste, and interfacial bonding strength. However, it excels in sound absorption owing to larger biological pores. While its impermeability trails ordinary concrete, polyvinyl alcohol coating proves effective for improvement. In essence, this research comprehensively examines peach-shell concrete’s attributes, offering insights for practical applications of lightweight peach-shell concrete.

Practical Applications

As the planet warms up and its impact on our future becomes more apparent, many researchers have been working on finding ways to use building materials that help cut down on carbon emissions. One effective strategy is adding biochar to concrete, which is exactly what this article looks into. It is all about how replacing a significant portion of the concrete aggregate with peach shells—a type of agricultural waste in China—affects the concrete’s physical, mechanical, and acoustic properties, and how well it resists water seepage. What the article discovered is that this peach-shell concrete is not as strong when it comes to bearing weight, pulling forces, or bending. Additionally, it is not as watertight. But here is the upside: it is lighter in weight and can soak up sound better. This means it could be a good option for making lightweight walls inside buildings that do not have to hold heavy loads. The whole point of this paper is to explore whether we can create useful lightweight concrete using peach shells.

The compressive strength retention rates of ordinary, 10wt% fly ash (FA) modified, and 15wt% silica fume (SF) modified potassium magnesium phosphate cement (MKPC) mortar blocks at different ages were measured, under the curing of water, 5%NaCl solution, and $5{\%\mathrm{Na}}_2{\mathrm{SO}}_4$ solution. This was used to investigate their water resistance and salt resistance abilities. The freeze-thaw cycle deterioration was further compared and analyzed. Finally, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the hydration products. The results indicated that the compressive strength retention rate of the SF-modified MKPC mortar was 82.7% when it was cured in water for 150 days and above 85% when in the two mentioned salt solutions for 150 days. Compared to FA, the water resistance, salt erosion resistance, and freeze-thaw resistance of MKPC mortar were all improved by the SF because of its good physical filling and chemical effect.

This study examined the effect of hydrogels containing urease and proteins on the self-healing of cracked cementitious materials. The encapsulation of proteins and urease decreased the absorption of hydrogels. It was shown that proteins were able to release from hydrogels into the surrounding cementitious matrix. TGA, FTIR, and SEM showed increased calcium carbonate formation, and optical imaging indicated enhanced crack filling in the samples with hydrogels containing urease and proteins, compared to the control sample. This is attributed to the enhanced autogenous healing provided by water absorption/desorption of hydrogels as well as enzymatic reaction. Calcite was shown to be the dominant polymorph of calcium carbonate in the healing products. Interestingly, the mechanical strength regain was markedly higher in the samples with hydrogels containing urease and proteins compared to the control sample. Improved interfacial strength at the microstructure level enhances cohesion within healing products and adhesion between the healing products and crack surface, leading to overall increased mechanical strength regain. The electrical resistivity results were shown to be in agreement with the mechanical strength regain.

Repair materials for concrete infrastructure applications are designed to minimize closure time and subsequent effect on traffic. Available material choices are typically limited to expensive prepackaged materials or high-early-strength (HES) concrete mixtures. HES concrete mixtures are often designed with high paste content and limited inclusion of supplementary cementitious materials so to promote higher early-age strengths. The traditional approval for HES concrete mixtures has relied on testing the strength of concrete cylinders cured at room temperature. This practice has often resulted in the overdesign of these HES mixtures, primarily because it fails to consider the higher temperatures that typically develop during the in situ curing. Moreover, as highlighted in several reports by state agencies, the high cement content and the near absence of proper curing practices have likely contributed to the premature failure of some of these mixtures. In this study, isothermal calorimetry was explored as a potential tool to quickly evaluate HES concrete formulations in terms of early-age mechanical performance. It was found that this test method, when combined with maturity, can provide reasonable estimations of the concrete strength development for isothermal and nonisothermal curing conditions up to 8 h after the initial mix. The proposed test method can be used as a first step in the optimization of HES concrete mixtures and can help predicting the time to reopening for in situ conditions.

The asphalt binder is exposed to unfavorable coupling aging of UV radiation, high temperature, and moisture, which accelerates the deterioration of the binder’s rheological properties. To investigate the effect of this coupled aging on the rheological properties of asphalt binder, an accelerated environmental aging oven considering ultraviolet (UV) radiation, temperature, and moisture was used in this paper to carry out multifactor coupling aging tests for the binder. The coupling aging test parameters are determined by the central composite design-response surface methodology (CCD-RSM). The rheological properties of asphalt binder before and after aging were examined by dynamic shear rheometer, and the effects of the coupling aging on the viscoelastic, high-temperature, fatigue, and low-temperature properties of the binders were evaluated by employing the complex shear modulus ($G^{*}$); the aging index (GI), which was established with $G^{*}$; the rutting factor ($G^{*}/\sin \delta$); the Glover–Rowe (G-R) parameter; and the ratio of asphalt binder creep rate to stiffness modulus ($m/S$), respectively. Further, the effect of the coupling aging on the chemical properties of the asphalt binder was evaluated with carbonyl index obtained from the Fourier transform infrared spectrometer. The results showed that the optimal values (temperature: 68.3°C; irradiation intensity: $\mathrm{2,221}\mathrm{W}/{\mathrm{m}}^2$; spraying interval: 250 min) of the coupled aging parameters were determined by the CCD-RSM, and the relationship between the coupled aging time and the carbonyl index was established by the Verhulst model with an $R^2$ value larger than 0.98. As the coupling aging degree increases, the $G^{*}$, $GI$, and $G^{*}/\sin \delta$ show an increasing trend, whereas the G-R parameter, $m/S$, shows a decreasing trend, indicating that the aging increases the stiffness and high-temperature resistance of the binder and decreases its fatigue properties and low-temperature properties. Based on the correlation analysis, the G-R parameter showed good correlation with the $GI$, $G^{*}/\sin \delta$ (45°C, 55°C, and 65°C), $m/S$ ($-6°\mathrm{C}$, $-12°\mathrm{C}$, and $-18°\mathrm{C}$), respectively, and the average $R^2$ value is larger than 0.98. Therefore, the G-R parameter can be used as a comprehensive index for evaluating the rheological properties of binders.

The bonding performance of carbon fiber–reinforced polymer (CFRP)–concrete interface is an important research area, with adhesives serving as mediators for the transfer of interface stresses. However, there is significant variation in the mechanical properties of adhesives available in the market, and currently there is limited research on the patterns of how adhesive mechanical properties affect interfaces. First, dynamic thermomechanical analysis was used to investigate the glass transition temperature of the adhesive, $T_g$. Following this, tensile tests were conducted to assess the mechanical properties of the adhesive at various temperatures. Finally, the effects of the adhesive on the interface bonding properties of CFRP-concrete were studied by single shear tests at different ambient temperatures. The test results indicated that when the ambient temperature is lower than the glass transition temperature ($T_g$), as the temperature increases, although the mechanical properties of the adhesive decreased, the effective bonded length of interface increased significantly, leading to a gradual increase in interface load-bearing capacity. Furthermore, the interface constitutive model was modified by finite-element model inversion. The modified parameters $K$ and ${\tau }_{\max }$ exhibited a linear increase relationship with the elastic modulus of the adhesive, and the modified parameter $G_f$ showed a negative exponential power function relationship with the elastic modulus of the adhesive.

Sticky rice–lime mortar, a representative ancient binding material widely employed in construction applications across Asian countries, has been a subject of substantial academic research and development efforts for its restoration. However, conventional sticky rice–lime mortar is characterized by suboptimal strength and limited toughness, necessitating further enhancements to expand its practical utility. This study presents the formulation of a high-performance sticky rice–lime mortar by incorporating metakaolin and hemp fibers. A comprehensive investigation of various parameters influencing the compressive and flexural properties of the resulting composite was undertaken, encompassing the volume content of hemp fibers, the mass content of sticky rice paste, and the mass content of metakaolin. The experimental outcomes demonstrate the efficacy of metakaolin and sticky rice paste in significantly elevating the compressive strength of the sticky rice–lime composite. Notably, the presented sticky rice–lime mortar attains a remarkable compressive strength of up to 3.5 MPa, exceeding that of conventional sticky rice–lime mortar by more than threefold. Moreover, the introduction of hemp fibers effectively enhances the flexural strength of the sticky rice–lime composite through fiber bridging mechanisms. The research culminates by proposing a relationship equation, derived from the empirical data, to characterize the compressive and flexural strength of the high-performance sticky rice–lime composite. Overall, these findings emphasize the importance of optimizing sticky rice–lime mortar through the integration of advanced constituents, thus highlighting its potential as a durable and versatile binding material for historical preservation and sustainable construction practices within Asian contexts and beyond.

Two-dimensional (2D) random mesostructure models have been broadly utilized to study mechanical behavior and damage mechanisms of asphalt concrete due to their high availability and efficiency. The 2D aggregate gradation that characterizes the area fractions of the simulated aggregates of different sizes significantly affects the simulated mesomechanical properties of asphalt concrete. However, there are very few methods for determining the 2D aggregate gradation from the actual three-dimensional (3D) one. This study proposed a 2D aggregate gradation conversion framework integrating a 3D random aggregate method and machine learning models. First, 3D asphalt concrete mesostructures were generated using polyhedral coarse aggregates with random gradations and shapes. Virtual cutting and sieving procedures were then developed to obtain the 2D aggregates at sections with 1 mm intervals in each mesostructure and acquire the area fractions of aggregates of different sizes, respectively. By averaging the results for the sections in each cutting direction, so-called 2D representative area fractions of aggregates within different grading segments in different directions were obtained. The gradation conversion data sets were established by collecting the volume fractions of coarse aggregates in the 3D mesostructures as input variables and the corresponding 2D representative aggregate area fractions as output variables. Based on the data sets, machine learning models, including linear regression, support vector regression, bagging of regression tree, and neural network (NN), were trained using a 5-fold cross-validation approach and then tested. The results showed that the NN model generally provided the most accurate predictions of the 2D representative aggregate area fractions. The effectiveness of the proposed framework was validated by using both the test sets regarding different sizes of random mesostructures and a mesostructure rebuilt from computed tomography (CT) images of actual asphalt concrete.

The permeability performance made of recycled aggregate pervious concrete with macropores (M-RAPC) relates greatly to the macropore structure and seepage behaviors. However, the mechanism of the influence of pore structure on the permeability of M-RAPC is still unclear. Based on the high-resolution X-ray computer tomography (CT) and image processing technology, a three-dimensional (3D) pore structure model with macropore ($>0.15\mathrm{mm}$) was constructed, and the dimension of the representative elementary volume (REV) was determined to be $450\times 450\times 450{\mathrm{voxel}}^3$. Then, the quantitative characterization of the topological structure of macropore space and the simulation of pore flow were conducted. Finally, the relationship between macropore structure parameters and seepage behavior was discussed. The results showed that about 80% of macropores are in the range of 0.15–1 mm, and the pore coordination number is mostly concentrated within 20. The macropore distribution shows a great spatial heterogeneity, showing that the permeability anisotropy index is mainly larger than 1, and even up to 8. Besides, the permeability performance of M-RAPC is significantly correlated with macropore parameters (effective porosity, tortuosity, and fractal dimension). In summary, this study can better reveal the relationship between pore structure and seepage behaviors in M-RAPC and provide a reference for the skeleton structure and permeability performance optimization design of M-RAPC.

Moisture damage resistance assessment in asphalt mixtures traditionally relies on the tensile strength ratio (TSR) method, which may not capture the complex behavior of asphalt under moisture ingress. This study proposes an innovative multifaceted approach for assessing moisture susceptibility, challenging the overreliance on TSR, and integrating multiple intricate aspects of asphalt behavior. Employing two dense-graded and one gap-graded polymer-modified binder mixtures with nominal maximum aggregate size (NMAS) of 13 and 19 mm, the study defines threshold values for total air voids, effective air voids, indirect tensile strength, and percentage density change. Evaluations were conducted using a device selected for its dynamic capabilities in inducing stresses and creating pore pressure under elevated temperatures. This research proposes a new zone-based approach to classify mixtures as moisture-resistant, partially moisture-resistant, or moisture-susceptible. This innovative method, grounded on maximum effective air voids and percentage density change, offers nuanced insights for more accurate moisture resistance assessments. Furthermore, the study explores the effect of effective air void size on moisture damage resistance by image processing for dense and gap-graded gradation of 13.2 NMAS, unveiling clogging behavior especially in dense-graded mixture due to smallest pore size. In conclusion, the study provides an in-depth understanding of asphalt mixture behavior under moisture ingress. By offering a novel approach that integrates multiple parameters and extends beyond the conventional TSR approach, it contributes a practical solution for mitigating moisture damage in asphalt mixtures. This research sets the stage for a potential paradigm shift in the approach to moisture susceptibility assessment, enriching the asphalt field with critical insights.

The main objective of this article is to study the role of the widely adopted crushing techniques, viz., impact and compression, on the physical, chemical, and morphological properties of recycled concrete aggregates (RCA). Five fundamental parameters of RCA, viz., hydrated cement-mortar paste (HCMP) concentration, specific density and absorption, aggregate comminution, chemical composition, and surface characteristics, were studied to achieve this objective. These parameters were studied for various coarse and fine RCA size ranges, including concrete fines. The results indicated that the shattering of concrete chunks in an impact crusher could lead to the production of well-graded RCA with less HCMP; this detached HCMP from coarser fractions was found to increase the reactivity of concrete fines by around 29%. In addition, the produced RCA was found to possess a high concentration of cubical and spherical particles. Both these benefits, i.e., lower HCMP and regular shape characteristics, were found to significantly affect the strength properties of recycled aggregate concrete. However, due to cleavage failure in compression crushing, coarser RCA with higher concentrations of blade and disc-shaped particles and higher HCMP content were produced. The fracture failure associated with compression crushing led to the production of less amorphous concrete fines with $\sim 45\%$ higher quartz content. However, the fineness of these concrete fines was 44% higher, indicating its potential as a filler material. Interestingly, the HCMP was found to reduce the surface roughness of natural aggregates, and this might be one of the additional reasons for the poor interfacial transition zone between RCA and the new mortar matrix.

To reduce energy consumption and save economic costs, waste-derived secondary resources can be considered as cement substitutes for emulsified asphalt. Considering emulsion type and red mud–based alkali-activated materials dosage and curing time, this study determined the feasibility of using red mud–based geopolymer to replace the commonly used cement in emulsified asphalt. Experimental tests, including pH tests, optical microscopy tests, dynamic shear rheological (DSR) tests, and Fourier-transform infrared (FTIR) spectroscopy tests were performed to characterize the rheological properties, interaction, and microstructure characteristic of red mud–based geopolymer emulsified asphalt composite binder (REACB). Cement emulsified asphalt composite binder (CEACB) was selected for comparison. The pH test and optical microscope tests demonstrated that the influence of red mud–based geopolymer on demulsification speed of stearyl trimethyl ammonium chloride (STAC) emulsion was greater than that of sodium dodecylbenzene sulfonate (SDBS) emulsion. The dynamic shear rheological test results showed that with the increase of curing time and red mud–based alkali-activated materials dosage, both the deformation resistance and the elastic recovery ability of REACB were improved, and the interaction ability between red mud–based geopolymer and SDBS emulsified asphalt gradually became stronger than that of STAC emulsified asphalt. Moreover, geopolymerization reactions in two kinds of REACB were proved using stretching vibration peaks of the asymmetric functional group T-O-Si. This study will promote the utilization of red mud–based aluminosilicate waste in emulsified asphalt.

Solid waste generation and its sustainable disposal are big concerns in the present decade. Mine tailings and incinerated bottom ash are among the greatest solid waste contributors to the environment. To promote sustainable development, material reuse and recycling are important. In the present study, a feasibility study was conducted by utilizing such tailings and bottom ash for the production of controlled low-strength material (CLSM). The amount of cement was utilized less, and by controlling the design mix with a targeted flow, low-strength material was produced. Three different cement contents (60, 80, and ${100\mathrm{kg}/\mathrm{m}}^3$) and 100% mine tailings or incinerated bottom ash were used as fine aggregate material. Fresh properties of different CLSM mixes, mechanical performance, and leaching behavior were conducted to confirm the final product. It was observed that both the mine tailings and bottom ashes are suitable as an aggregate material for CLSM mixes. The compressive strength values of different CLSM mixes at 28 days were observed between 0.13 and 1.88 MPa for various aggregate materials (mine tailings and bottom ash) and cement content. Moreover, there is an influence in the reactivity of cement hydration by the aggregate (tailings and ash), which was confirmed by the calorimetry study. The selected mine tailings and bottom ashes are not inert (like natural aggregate) within the CLSM mixes, and the chemical composition of the raw materials affects their fresh and hardened properties. The leaching test further shows that the final product could leach different heavy metals beyond the limit for inert materials, but within the nonhazardous limits by international standards. The present work deals with CLSM mixes with locally available industrial side streams; some important properties such as hardening time, penetration resistance, shrinkage, excavatability, and other durability properties (i.e., acid attack, freezing and thawing resistance) were not considered in the study and can be studied further.

Multiwalled carbon nanotubes (MWCNTs) improve ultraviolet (UV) aging resistance and storage stability of asphalt modified with styrene-butadiene-styrene (SBS). However, MWCNTs have the disadvantages of poor dispersivity, easy agglomeration, and insolubility in various solvents, which greatly affect the modification effect. The application of silane coupling agent KH550 has the potential to improve the dispersion of original MWCNTs in asphalt. In this research, the high-speed shearing method was used to prepare KH550–modified MWCNTs/SBS composite–modified asphalt, and then Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to observe and evaluate the MWCNTs before and after surface modification. Sensitivity analysis was conducted on the impact of MWCNTs on the performance of SBS-modified asphalt. The softening point test, ductility test, dynamic shear rheology test, and UV aging resistance test were carried out, and the optimal content of MWCNTs after surface modification was determined after comparing with the composite-modified asphalt without coupling agent modification. The results showed that oxidized MWCNTs could be grafted with silane molecules to have a molecular bridging effect on the surface after chemical modification by the silane coupling agent KH550. When the content of SBS was 5% unchanged, the asphalt with 1% surface-modified MWCNTs had excellent performance in softening point, ductility, complex modulus, rutting factor, and UV aging resistance.

There are four critical factors that affect air voids (VA) of asphalt concrete over time: traffic loads and repetitions, environmental regimes, compaction, and asphalt mix composition. Because of the high as-construct VA content of the material, it is expected that voids will reduce over time, causing rutting during initial traffic periods. Eventually, the material will undergo shear flow when it reaches its most dense state with optimum aggregate interlock or refusal VA content. Furthermore, to accurately model the performance of an asphalt mixture, the VA must be predicted over time. This study aims to implement two ensemble learning methods namely Cubist and gradient boosting regression tree (GBRT) hybridized with equilibrium optimizer algorithm (EOA) to predict the VA percentage of asphalt concrete during the service life of flexible pavements. For this purpose, 324 data records of VA were collected from the literature. The variables selected as inputs were original as-constructed air voids, $V{A}_{\mathrm{orig}}$ (%); mean annual air temperature, MAAT (°F); original viscosity at 77°F (25°C) , ${\eta }_{\mathrm{orig},77}$ (Mega-Poises); and time (months). GBRT-EOA and Cubist-EOA were found to be superior to other classical single ML approaches [for instance, artificial neural network (ANN), support vector machine (SVM), and Gaussian process regression (GPR) and M5Tree] and existing nonlinear regression models. In the training phase, the GBRT-EOA had ${\mathrm{R}}^2$, root mean square error (RMSE), mean absolute error (MAE), and mean of absolute percent error (MAPE) values of 99.8%, 0.136%, 0.093%, and 1.324%, respectively, while these values changed to 95.1%, 0.701%, 0.53%, and 7.825% in the testing phase. Also, only less than 5% of the records were predicted using this model with more than 20% deviation from the observed values. As determined by the sensitivity analysis, time (months) is the most significant of the four input variables, while MAAT (°F) is the least one. A parametric study showed that regardless of the MAAT, the ${\eta }_{\mathrm{orig},77}$ of 1.0 Mega-Poises, and the $V{A}_{\mathrm{orig}}$ above 6% can be ideal for improving the pavement service life in terms of the VA of the asphalt concrete layer during service life.

In order to investigate the influence of carbonation treatment on the rebound strength measurement curve of machine-made sand concrete, this study conducted research on the carbonation mechanism sand concrete rebound strength measurement curve through rebound and compressive strength tests using carbonation degree and concrete strength grade as control variables. The results showed that in the short aging period, carbonation treatment had little effect on the compressive strength of manufactured sand concrete but could cause an increase in the rebound value measured by the high-strength and heavy rebound hammers. As the strength grade of the manufactured sand concrete increased, the rebound value measured by both the high-strength and heavy rebound hammers increased accordingly. Compared with the high-strength rebound hammer, the heavy rebound hammer had higher accuracy in detecting the rebound of the carbonated manufactured sand concrete. This study established measurement curves for uncorrected and corrected carbonation depths, among which the accuracy of the corrected carbonation depth measurement curve was higher. At the same time, this measurement curve has been applied to the rebound test of the Pinglu Canal Extra-Large Bridge Project in Guangxi, China, and its practicality and reliability have been verified.

An indoor aging simulation was carried out to investigate the effect of ultraviolet (UV) aging on the performance of polymer and crumb rubber modified asphalt (PRMA) and its mixtures. At the macro level, the apparent morphology change in the asphalt after UV aging and the changing rates of penetration, ductility, and softening point were analyzed to evaluate the effect of UV aging on the asphalt binder. Fatigue life, dynamic stability, freeze-thaw splitting strength, and failure strain were used to determine the effect of UV aging on the asphalt mixtures. At the micro level, using the large molecular weight and functional group index of asphalt after aging as the evaluation index, the effect of UV aging on the performance of asphalt and asphalt mixtures was quantitatively analyzed. The results for the asphalt binders and mixtures under the same UV aging condition showed that PRMA surface cracking appeared later and crack development was slower; the changing rates of the three indexes of PRMA and the performance reductions, including low- and high-temperature properties and moisture resistance, were smaller. The results also showed that the large molecular weight of the two asphalt binders increased gradually, but the increase in large molecular weight of PRMA appeared later and the range was smaller. Also, the changing rules of the three characteristic functional groups of the two binders were basically the same, and the incorporation of rubber powder delayed UV aging of PRMA to a certain extent.

This research developed and evaluated the corrosion-inhibiting efficiency of a natural inhibitor prepared from a bamboo tree [referred to as bamboo leaf extract (BLE)]. The corrosion behavior of steel in BLE-admixed cementitious systems was examined using dynamic-polarization tests and salt-fog tests. The effect of the addition of BLE on the workability and compressive strength of cementitious systems was studied using flow-table and compression tests on mortars. Increased concentration of BLE and the preimmersion period of steel in BLE-admixed pore solution resulted in the increase of corrosion potentials and the reduction of corrosion currents. Furthermore, the addition of BLE improved the workability and compressive strength of mortars, and the mass loss of steel in BLE-admixed mortar was observed to be less than that in the control (BLE-free) specimens. The inhibitor’s adsorption on the steel followed the Langmuir isotherm model, suggesting the formation of a protective layer at the steel–electrolyte interface, and accordingly, a 99% reduction of the corrosion current was achieved by preimmersing the steel in simulated concrete pore solution containing 700 ppm BLE for 7 days.