Journal of Materials in Civil Engineering

Utilizing treated plant fibers in fiber-modified asphalt could reduce reliance on nonrenewable resources, contributing to environmental sustainability. To promote the utilization of plant fibers in asphalt mixtures, this review focuses on elucidating the reaction mechanism of surface-treated plant fibers and the resulting performance benefits in the composite. A comprehensive review of reinforcement mechanisms of fibers in composites, particularly asphalt mixtures, is provided to gain a mechanistic understanding of how fibers enhance performance. The review incorporates multiple perspectives to provide a thorough understanding of the performance-enhancing effects of fibers within asphalt. Plant fibers have significant potential to improve several aspects of asphalt mix performance, including high-temperature stability, low-temperature crack resistance, moisture stability, and fatigue durability. These properties also influence the optimal loading and fiber length for different fiber types, and this review provides a comprehensive overview along with recommended values. In addition, microscopic studies play a critical role in understanding the mechanism of plant fibers in asphalt mixes. The review discusses the microscopic changes induced by fiber surface treatment and sheds light on their effects at a fundamental level. The review provides a holistic reference for the application of plant fibers in asphalt mixtures for guiding asphalt pavement engineering applications, and prospect on the research direction of plant fibers in asphalt mixtures.

Ensuring good interface shear resistance is essential in structural applications. Hence, understanding the interface shear behavior of ultrahigh-performance fiber-reinforced concrete (UHPFRC) is essential. The interface behavior of UHPFRC will be different from conventional concrete due to the absence of coarse aggregates and the presence of steel fibers. Therefore, this study involves testing 10 monolithically cast UHPFRC Z-shaped interface specimens with different volume fractions and types of fibers. The parameters considered in the study are 1.0% and 2.0% fiber volume and straight and hybrid (a combination of hooked-ended and straight steel) fibers. The interface shear crack load and possible types of failure modes are identified using the digital image correlation (DIC) technique. A direct tensile stress–strain and interface shear stress–strain relationship is also identified to propose a simplified interface shear capacity model. The cracking tensile strain across the shear interface is identified beyond the direct tension localization strain range. Similarly, the crack slip and width at different loading stages are evaluated, and it is identified that the crack-slip response is the same along the interface plane. On the contrary, the crack opening varies along the shear interface plane. Shear cracking and ultimate shear stress increased at higher fiber volume fractions due to the increased tensile strength of UHPFRC. The reduction in interface shear capacity is significant with the addition of hybrid fibers compared to the specimens with only straight steel fibers. This reduction is due to the lesser number of fibers across the shear interface in hybrid fiber-reinforced specimens. A simplified interface shear design model was developed based on experimental and literature data, where concrete tensile strength is a critical parameter in determining interface shear resistance.

The orthogonal experimental method is currently the most commonly used tool for determining an appropriate composition of modified asphalt binders. However, it cannot automatically output a reasonable composition when dealing with multi objective optimization and must go through the process of repeated comparison manually. Obviously, the accuracy and efficiency of the orthogonal method are easily affected by subjective factors, which grow tremendously as the sizes of the experiments and data increase. In order to enrich the design method, the objective of this study is to develop a new framework to determine reasonable compositions of modified asphalt binder automatically, accurately, and efficiently. Hence, a data-driven multiobjective optimization method is established based on the experimental data, reduced order model (ROM), and simplicial homology global optimization (SHGO). The ROM is utilized to characterize the complex relationship between material composition and the corresponding performance. The average relative errors between experimental results and prediction values of the ROM are less than 1.5%, and the maximum relative errors are less than 8.7%. The SHGO is selected to determine the reasonable compositions in the global space. Finally, the properties and costs of the SBS-modified asphalt binders, orthogonal-based modified asphalt binder, and ROM-SHGO-based modified asphalt binder are tested to verify the feasibility of the developed method. The ROM-SHGO-based modified asphalt binder has the lowest cost under the premise of similar performance when taking the cost as the constraint. The developed ROM-SHGO method provides feasible, useful, and promising tools for composition design of modified asphalt binder based on laboratory test data.

The investigation of inhomogeneous materials under dynamic conditions presents several challenges, particularly with regard to testing the dynamic properties of concrete, which requires the use of a large-scale split-Hopkinson pressure bar (SHPB). The present study aims to address these challenges by designing and calibrating a 155 mm diameter SHPB. The design and construction of the apparatus are described, and its data processing, including wave pulse dispersion correction, is assessed to ensure accurate representation of stress and deformation conditions. The apparatus is validated through experiments on brittle (confined concrete) and ductile (copper) specimens. The results demonstrate the ability of SHPB to characterize the dynamic properties of large-scale specimens and to correct dispersed signals in the bar, allowing for the accurate determination of specimen surface pulses. Validity of the results is confirmed through one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) wave analyses. Therefore, the 155 mm diameter SHPB setup has shown excellent performance in deriving the dynamic properties of large-diameter specimens. This study provides evidence to support the conclusion that the utilization of a 155 mm SHPB setup enables the experimental assessment of dynamic properties in large-diameter specimens. This conclusion is directly supported by the analysis of test data obtained from confined concrete samples and copper materials.

The durability of bridges plays a vital role in their regular operation and transportation, particularly as service life increases. The ability of a bridge to reach its expected service life is closely linked to its durability. In cold regions, the deterioration of bridge concrete durability due to freeze-thaw damage is a common cause of failure, posing a threat to structural safety. In this study, a highway bridge over a sluice that was built 63 years ago was selected for coring and freeze-thaw testing. Two nondestructive testing methods were employed: three-dimensional optical scanning and X-ray computed tomography (X-CT). The former was used to observe and analyze the external surface of the concrete, while the latter was used to analyze its internal structure. The surface morphology was characterized using height, spatial, hybrid parameters, and fractal dimension, and the Abbott–Firestone curve reflected the profile characteristics of the material surface. Moreover, the internal components of concrete were identified and reconstructed in three dimensions based on threshold segmentation, and the changes in internal porosity, pore fractal dimension, and pore size distribution were calculated. Finally, the evolution of bandwidth in the color heat map was analyzed, combining the gray level cooccurrence matrix (GLCM) to reflect the growth of cracks and defects with freeze-thaw cycles.

The addition of dry ice as an admixture to cement pastes has many advantages such as improving the compressive strength and sequestration of ${\mathrm{CO}}_2$. However, its effect on the hydration mechanism of cement pastes is still unknown and will be investigated using electrochemical impedance spectroscopy in this paper. Based on the linear correlation of cumulative hydration heat from the isothermal calorimetry test and the logarithm of high-frequency resistivity, a modified Knudson equation is derived. Corresponding hydration kinetic parameters are calculated by applying the boundary nucleation and growth theory and kinetics model, including Avrami, geometrical contraction, and diffusion equations. The boundary area per unit volume ($O_v^B$) for the control specimen and specimens with 0.2% and 0.5% cement weight dry ice addition is 0.1171, 0.1250, and 0.1562, respectively, indicating that the dry ice addition increases the surface area of the nucleation process. In addition, the results show that the Avrami equation for monitoring the nucleation process is limited. Regarding the hydration curves, the transition from the nucleation and growth stage to the interaction of phase boundaries (I) stage is delayed by adding dry ice to the mixture.

Corrosion is important in the design, maintenance, and preservation of bridge steel pile foundation systems. It is an inevitable phenomenon when steel is exposed to the environment, as metals tend to return to their lower energy state. While the corrosion rate of steel is predictable for atmospheric exposures, it is highly variable and difficult to predict for steel buried underground because of the high variability of soils. Applying a protective sacrificial layer is a common protection method to prevent corrosion. This study aims to evaluate the efficiency of a galvanized and painted galvanized steel bridge pile for achieving a 100-year service life and to economically compare them for using piles without a coating. To meet this objective, 21 steel coupon samples and nine 30 cm pile samples with galvanized coating, painted-galvanized coating, and no coating were tested in a cyclic corrosion test chamber to investigate the efficiency of each coating. The test was conducted for 600 days simulating a 100-year service life. Results from the experimental test revealed that galvanized and painted-galvanized coating methods show remarkable performance in protecting the piles against corrosion, and both methods can protect the piles from corrosion for 100 years. Further evaluation showed that, while the cost to increase the pile size was determined to be less than the premium for galvanizing or galvanizing and painting the piles for the bridge in this study, a cost–benefit evaluation for each protection measure is suggested, knowing that costs can vary widely depending on specific project requirements, location, market prices, etc.

When exposed to fire, load-bearing mass timber structures, such as cross-laminated timber (CLT), soften and decompose, which causes significant deformation and weakening, ultimately leading to failure. A combined experimental and modeling analysis is presented to predict the postfire residual compression properties of CLT. Multiple experimental fire exposure and postfire mechanical tests were performed under identical conditions to respectively characterize the internal and external thermal response of the CLT and assess the residual postfire compression properties. An analytical modeling strategy based on the measured through-the-thickness temperature profile during fire exposure is presented to predict the residual postfire compression properties of the CLT. X-ray computed tomography analysis revealed the charring rate to be nonconstant, which is in line with current research findings but not in line with Eurocode design suggestions. The analytical analysis revealed the transverse (cross) lamina to provide minor contribution to the axial compression properties but critically to the thermal protection and structural integrity of longitudinal (load-aligned) laminae during fire exposure.

The composition and properties of the interface are the key points which determine the properties of fiber-reinforced cement–based composites. The bonding performance between fibers and different hydration products at the interface is the basis for the understanding of the interface transition zone. In this paper, the influence of different hydration products on interfacial bonding performance was investigated using the molecular dynamics method. The three models were established to study the difference in the static structure of the interface between different hydration products and polyvinyl alcohol (PVA) fibers, and then the influence of different hydration products on the interfacial adhesion properties was analyzed using fiber pull-out simulation. The results showed that the interfacial adhesion properties between PVA fiber and calcium silicate hydrate (PVA–CSH) was the best. The PVA–CSH interface is connected mainly by Ca-O bonds and H bonds, and the stability of the chemical bonds is very high. The strong interface interaction gives the CSH–PVA interface good adhesion performance, so it is necessary to overcome a large interfacial adhesion force when the fiber is pulled out. The PVA–AFt (ettringite) interface also is connected by Ca-O bonds and H-bonds. However, the stability and coordination number of the chemical bond are lower than those of the CSH–PVA interface. There are only a few weak H-bonds at the PVA–calcium hydroxide (CH) interface, which resulted in the worst interfacial adhesion performance; the force required to pull fibers out of the matrix was very small.

The strength development of pavement polyurethane mixture is primarily dependent on the degree of curing reaction of polyurethane adhesive. In this work, the effects of temperature, humidity, and curing time on the curing rate of a dense polyurethane mixture, stone mastic polyurethane mix (SMPU), were investigated. Two strength-age prediction models were established to forecast the compressive strength and the splitting strength development of SMPU under different curing conditions, respectively. The results indicate that the optimal curing conditions for SMPU are at a temperature of 30°C and a humidity of 55%. Furthermore, the two types of strength of cured SMPU can exceed 90% of their corresponding maximum strength values, respectively, when cured at temperatures between 20°C and 40°C, and at a humidity range of 30% to 70%. Finally, the validity of the strength-age prediction models was confirmed through experiments, thereby providing a theoretical basis and reference for on-site construction technology of SMPU.

Foam lightweight soil (FLS) has been widely used in geotechnical engineering because of their high strength, low density, and thermal insulation. However, few scholars have researched its application to subgrade engineering, especially roadbed widening. In this case, this special artificial soil can significantly reduce the differential settlement of subgrades due to its lightweight and high strength. In the research background, a series of laboratory experiments were conducted to investigate the effects of mixing ratio and fibers on the physical, mechanical, and microporous structural properties of clay-based foamed lightweight soils (CFLS), with clay and cement as the main raw materials. The experimental results indicate that preparing CFLS for road widening using clay soils from around highways as raw materials is an alternative treatment method. During the application process, one should select the optimal mixing ratio and fiber content considering the fluidity, stability, and mechanical strength of CFLS. In addition, the dynamic modulus of elasticity and cumulative plastic strain of CFLS samples also indicate that CFLS has superior dynamic properties compared with cohesive soils and can meet the criteria for road construction.

Stone mastic polyurethane concrete (SMPC) is a new pavement material that is mixed at room temperature and has excellent pavement performance. To accurately evaluate the moisture susceptibility of SMPC with varying polyurethane content, the trend of residual splitting strength was analyzed and quantified through laboratory freeze-thaw splitting tests. Then scanning electron microscopy (SEM) was used to characterize the microscopic morphology of the fracture surface of SMPC samples after freeze-thaw cycles. Next, the porosity distribution was quantified using MATLAB version 2015b, and the strength attenuation mechanism was analyzed. Finally, the relationship between residual splitting strength, freeze-thaw cycles, and varying polyurethane content was established by the grey Verhulst model. The results showed that the splitting strength increased with increasing polyurethane content. It also increased with increasing polyurethane content at the same number of freeze-thaw cycles. In addition, at the same polyurethane content residual splitting strength decreased with the increase in the number of freeze-thaw cycles and reached stability after three cycles. The SEM scanning images were analyzed by MATLAB, and it was found that the increase in porosity caused by interface failure between the aggregate and the polyurethane binder was the main reason for the decrease in SMPC residual splitting strength. Finally, the established relationship model was used to fit the residual splitting strength at different freeze-thaw cycles, elucidating the connection between residual splitting strength and various freeze-thaw cycles.

Two-dimensional nano graphene oxide (GO) has attracted the attention of researchers due to its excellent high aspect ratio and intrinsic strength. However, its effectiveness in improving cement composite’s performance is significantly dependent on the uniform dispersion of GO in the host matrix. In recent years, the use of pozzolans, such as fly ash, silica fume, and metakaolin, to enhance the dispersion of GO in cement medium has become a focus of research. This study considered the effect of rice husk ash (RHA) on the GO dispersion quality in simulated cement pore solution (SCPS). The findings obtained were validated by the compressive and flexural strengths of cement paste samples. According to ultraviolet–visible (UV-vis) spectroscopy, zeta potential analysis, and other measurements, this research demonstrated that the addition of RHA to SCPS minimizes the size of GO agglomerations and considerably enhances dispersion. The compressive and flexural strength results of cement paste samples incorporating RHA-GO after 56 days of curing improved by 46.7% and 38.7%, respectively, compared with those of the reference samples. The results of this study could pave the way for application of binary GO-pozzolans containing cementitious nanocomposites.

The use of microbially induced calcium carbonate precipitation (MICP) to self-repair concrete cracks has received extensive attention. The production of mineralization precipitates reflects the repair capability of the self-healing agents. However, using a single type of microorganism in the self-healing agent, such as Bacillus pasteurii, usually produces a low amount of mineralization products in the direction of crack depth; therefore, the cracks cannot be well repaired. In this work, a binary microorganism self-healing agent was developed, and its crack repair capability was investigated. In the binary microorganism system, Bacillus pasteurii and Saccharomyces cerevisiae were mixed at six mixing ratios, 10:0, 8:2, 6:4, 4:6, 2:8, and 0:10. The results show that the highest concentration of the microorganism cells, the highest weight of the mineralization precipitates, and the purest calcite crystals were produced when the mixing ratio was 6:4. Besides, after 28 days of repair, cracks in mortar specimens were repaired with the binary microorganism self-healing agent, with the mixing ratio of 6:4 showing the highest area percentage of repair (97.1%) and the strongest capability to repair deep cracks (9–12 mm from the specimen surface). The synergic mineralization mechanism is that Bacillus pasteurii plays a major role in the closure of the fractured surface, while Saccharomyces cerevisiae promotes the production of carbonate ions by decomposing glucose under oxygen-poor conditions, resulting in the formation of calcium carbonate precipitates and facilitating the repair of deep cracks where there is a lack of oxygen. This work provides a promising binary microorganism self-healing agent and an understanding of the mechanism involved in the mineralization process, and experimentally confirms its superior self-healing capability over the single-type microorganism system considering the repair depth.

Soft clay is characterized by high compressibility, low permeability, low strength, and high water content, making it a poor substrate for construction. Hence, soil treatment is often required for soft clay. However, the traditional treatment methods, such as stacking and on-site mixing, involve large space, long time, and high cost. In contrast, lime is stable and cheap, but slow to set and harden. In this paper, the microbially induced carbonate precipitation (MICP) and lime composite curing of soft clay was investigated. Tests were carried out on soft clay samples with different lime ratios. By comparing the changes of strength, composition, and microstructure before and after curing, the mechanism of MICP/lime composite solidification of soft clay was systematically studied. The results showed that (1) a reasonable proportion of lime can react with water and ${\mathrm{CO}}_2$ in clay to generate ${\mathrm{CaCO}}_3$, and also promote the induction of more ${\mathrm{CaCO}}_3$ precipitation by microorganisms, contributing to the improved strength of solidified clay; (2) MICP/lime composite curing can effectively reduce water in soft clay and help to improve the strength of solidified soil; (3) MICP and lime were complementary in terms of curing time, leading to continuous improvement of curing effect; and (4) the MICP/lime composite has a good effect on the solidification of soft clay. Under the experimental conditions in this study, the best solidification effect was observed for soft clay with a water content of 30% and a lime ratio of 30%.

Quartzite aggregates have poor adhesion with asphalt binder due to the higher silica content present in the mineral composition. Apart from conventional asphalt mixture testing methods, the surface free energy (SFE)-based adhesion evaluation method is most widely used in recent times to predict compatibility between aggregate and asphalt binder and moisture susceptibility in asphalt mixtures. This study tried to improve quartzite aggregates’ adhesion properties by modifying the aggregates’ surface with a nano-organosilicon (NOS), and two silane coupling agents (SCA) were used in modifying the aggregates’ surface. Results showed that surface modifications by chemical treatments reduced the aggregate’s SFE by increasing the aggregate nonpolar components to make a better bond with asphalt binder, which is also a non-polar material. From tensile strength ratio (TSR) results, it is found that the asphalt mixtures prepared with surface-modified aggregates showed better resistance to moisture damage with a 12%–15% increase in TSR. SFE indices like adhesion energy and energy ratio (ER) also showed significant improvement in adhesion between aggregates and asphalt binder, even in the presence of moisture. The ER values were above acceptable limits after surface treatments and showed a 100% increase compared with control mixes. SCA-1 and SCA-2 treatments effectively improved moisture damage in hot-mix asphalt with quartzite aggregates. One-way ANOVA was used to predict the effect of treatment methods and aggregate types on conventional TSR values and advanced SFE indices. The statistical results proved significant improvements in TSR and ER after the treatment of aggregates, but aggregate types do not make significant changes.

The cinnamic acid intercalated layered double hydroxides (CA-LDHs) were prepared by anion exchange method and analyzed by X-ray diffractometer (XRD) Fourier transform infrared (FTIR) spectrometer, scanning electron microscopy (SEM), contact angle goniometer, ultraviolet and visible (UV-vis) spectroscopy, and thermogravimetric (TG) analysis system. Then, the CA-LDHs were added to styrene-butadiene-styrene (SBS) modified bitumen together with an antioxidant composed of octadecyl-3-(3,5di-tert-butyl-4-hydroxyphenyl)-propionate (1076) and tris(2,4-di-tert-butylphenyl) phosphite (168) at a mass ratio of $1:1$. The effects of antioxidant/CA-LDHs on the physical and rheological properties and chemical composition and characteristics of SBS-modified bitumen before and after pressurized aging vessel (PAV) and ultraviolet (UV) aging were investigated. The results revealed that CA was successfully intercalated into the interlayer space of LDHs. Meanwhile, the CA-LDHs performed improved hydrophobicity and UV absorption capacity compared with LDHs, resulting in enhanced compatibility of LDHs with SBS-modified bitumen, and then the antiaging properties of SBS-modified bitumen could be further strengthened, especially the anti-UV aging properties. Moreover, the mixture of antioxidants and CA-LDHs could synergistically improve the SBS-modified bitumen’s thermal- and photo-oxidative aging resistance.

The combination use of stainless steel (SS) bars and seawater sea-sand concrete (SSC) is attractive for coastal and marine infrastructures due to the excellent corrosion resistance of SS and the eco-friendly property of SSC. Against this background, a total of 88 central pullout specimens were tested to investigate the bond behavior of SS reinforcement and SSC under different confinement levels provided by stainless steel stirrups and fiber-reinforced polymer (FRP) sheets. Several variables were designed in the present test, including the concrete type and strength, the thickness of concrete cover, rebar type, embedment length, and confinement type and level. The failure modes, bond-slip relationships, and ultimate bond strength were analyzed systematically. Test results reveal that splitting failure can be effectively prevented under sufficient confinement. The ultimate bond strength of SS bars in SSC can improve by at least 13.19% compared to counterparts in normal concrete (NC), and the enhancement of bond strength ranges from 0.49% to 37.49% with varying embedment length ratio. The confinement effects of concrete cover, stirrup, and FRP are also interpreted quantitatively by using a developed coefficient. Finally, a new bond-slip model considering dual confinement of FRP sheets and steel stirrups for SSC is developed and the proposed model performs well by comparing the theoretical predictions with the test results from this study and other relevant literature.

Expanded polystyrene (EPS) beads mixed with soil and cement are a new type of artificial lightweight fill material used in geotechnical practices. Hence, it is necessary to adopt an exhaustive procedure for evaluating the EPS composite attributes. In this study, Firoozkuh No. 161 sand was treated with portland cement and EPS beads, and the results of the two types of tests were combined to recommend the best mix ratio for geotechnical applications. Unconfined compression tests were carried out to investigate the mechanical characteristics of EPS composite and specify the optimum scope for EPS, cement, and water contents that were used in the strain-controlled cyclic experiments. Moreover, cyclic triaxial tests were conducted to evaluate the influence of mixing ratios, confining pressure, strain level, and the development of modulus reduction curves. The results indicate that increasing the cement content by 4%–6%, along with EPS beads up to 10% in volume, significantly enhances the composite’s uniaxial compressive strength and shear modulus at higher strain levels. According to the results, there is a small variation in the damping ratio caused by cementation, which indicates that cement percentage has a greater impact on the damping ratio of the mixture than EPS beads.

Patching is a common pavement treatment, and it is implemented using hot and cold process patching. Hot process patching is not an efficient implementation method because keeping asphalt temperature in long hauls is difficult, on-site mixing equipment is required, and transport costs are generally high. Moreover, hot process patching requires a significant amount of energy, so it is not an eco-friendly process. Although cold process patching significantly reduces the energy consumption of patching, its implementation reduces the patching quality. To this end, this study aimed to propose a new cold process patching using induction heating. Furthermore, this study attempted to apply waste materials in the proposed mixtures to preserve the environment. Accordingly, high percentages of reclaimed asphalt pavement (RAP) were used in the proposed mixture. Since induction heating was applied in the introduced patching method, two waste materials, including steel slag and electronic waste, were utilized in the mixtures to enhance the sensitivity to electromagnetic radiation. Moreover, different experimental tests were conducted to evaluate the mixtures’ mechanical properties. Ultimately, gray relational analysis was performed to assess the proposed mixtures’ sustainability. The results indicated that using steel slag and electronic waste as conductive materials could considerably reduce the heating time to raise the fabricated mixtures’ temperature. Moreover, replacing the Neat mixture with the proposed asphalt mixtures containing the waste materials significantly reduced the unit price, greenhouse gas emission, energy consumption, and raw material utilization.

Abstract

Sisal fibers (SF) and polycarboxylate superplasticizers (PCE) contribute to the sustainable development of cementitious materials by improving and optimizing their hardening properties. In this study, the impact of SF and PCE on the workability of cement pastes was investigated. The workability was evaluated through spreading diameter, yield stress, and plastic viscosity measurements, and the adsorption behavior of PCE was analyzed. The results showed that the introduction of SF had a negative effect on the workability of PCE plasticized cement pastes, reducing flowability and increasing yield stress and plastic viscosity, regardless of aspect ratio or dosage. A contact angle tester and a scanning electron microscope (SEM) were employed to examine the surface properties of SF. The mechanism behind this interaction of cement-PCE-SF was explored and found to be due to the rough surface of SF, which increased the consumption of PCE, and the formation of hydrogen bonds between PCE and SF. Additionally, PCE modified the interfacial structure between SF and the cement matrix, strengthening the relationship between the different phases. These findings provide new insights into the modification of fiber-reinforced cementitious materials.

Practical Applications

This paper presents a comprehensive study on the workability and rheology behavior of cementitious material that coupled PCE superplasticizer and SF. The interaction between PCE and SF was experimentally studied by suitable tests, and the results and mechanism behind were well explained. The fresh properties were evaluated through a mini slump test, rheological properties, and the adsorption behavior of PCE on the surface of cement and SF was analyzed. The results showed that the introduction of SF decreases the spread diameter and increases the yield stress and plastic viscosity, regardless of aspect ratio and dosage, which indicate that a negative effect on the workability of PCE plasticized cement pastes. The mechanism behind the cement-PCE-SF interaction was explored in depth by the surface properties of SF, which revealed that the rough surface of SF increased the consumption of PCE. In addition, the formation of hydrogen bonds between PCE and SF provides an additional explanation. The significance of this study provides valuable guidance in using fibers and PCE together in cementitious materials.

Water absorbency of foamed alkali-activated binders (FAABs) with various pore distributions were investigated in this study, where the pore structures were characterized and analyzed quantitatively to expound the mechanism of water absorption. Initially, workability consisting of fluidity and the aerating procedure of fresh FAABs pastes were studied, which revealed the fluidity evolution of the pastes and volume development with respect to time. On this basis, the effect of hydrogen peroxide (${\mathrm{H}}_2{\mathrm{O}}_2$) dosages on pore distributions was elaborated and a numerical model was proposed to assess the porosity in the kernel part of a sample. Two bubble stabilizers, sodium dodecyl sulfate (SDS) and calcium stearate (CS), were employed to improve the pore structures of FAABs. It was found that the fractions of small pores increased in the bubble stabilizer-modified FAABs and the fractions of independent pores increased markedly. Tests on water absorption indicated that CS was able to decrease the moisture content attributed to its hydrophobicity as well as the redistribution of pores in the FAABs. However, SDS failed to control the water absorption of the FAABs due to the difference in chemical properties.

Because of its low water-to-binder ratio and high cementitious material content, ultrahigh performance concrete (UHPC) exhibits significant autogenous shrinkage at an early age, which makes shrinkage cracking a common occurrence. This study addresses this issue by combining a multiscale MgO expansion agent and a super absorbent polymer (SAP) internal curing material to significantly enhance or completely compensate for the early age autogenous shrinkage of UHPC. The effect of multiscale MgO expansion agent and SAP on the mechanical, working, and shrinkage properties of UHPC was investigated, and the synergistic mechanism of mixing multiscale expansion agent and SAP was elucidated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), mercury intrusion porosimetry (MIP), and thermal gravimetric (TG) analyses. The results indicate that the multiscale MgO expansion agent is more conducive to the development of the mechanical properties of UHPC than the single-scale expansion agent, and provides a constant expansion source throughout the entire hydration process of the UHPC system. Because of the additional water introduced by SAP, which supports the hydration of the cementitious material and the multiscale MgO expansion agent, the introduction of SAP can enhance the workability of UHPC while further reducing the autogenous shrinkage of UHPC at an early age. This study can provide statistical support and theoretical guidance for resolving the issue of significant autogenous shrinkage in the early stages of UHPC.

Foamed phosphogypsum (FPG) has recently attracted extensive interest owing to its potential consumption of phosphogypsum and its substitution for traditional gypsum building materials. However, as an important component in the preparation of FPG, the effect of foaming agent on the performance of FPG is still unclear. Herein, Legao 3210 (LG), sodium alpha-olefin sulfonate (AOS), animal protein compound (APC), cocoamidopropyl hydroxy sulfobetaine (CHSB), and tea saponin (TS) were chosen as the foaming agents for FPG. The foam stability and foam structure were studied, and the results showed that the foams produced by TS and APC were more stable. The effects of different foaming agents on FPG’s fluidity, density, strength, water absorption, and thermal conductivity were also studied. The results showed that FPG prepared with TS exhibited the highest compressive strength, measuring up to 1.34 MPa, which represented a 97% increase compared with that of APC. Moreover, the dry density and thermal conductivity of FPG prepared with TS were $517\mathrm{kg}/{\mathrm{m}}^3$ and $0.109\mathrm{W}/(\mathrm{m}·\mathrm{K})$. The digital microscope analysis indicated that the keys to the simultaneous realization of high strength and light weight in the FPG were uniform pore size distribution, small pore size, and thicker pore gaps. Furthermore, through scanning electron microscope (SEM) analysis, it was suggested that the formation of strong interlocking structure by hydration products was the microstructural mechanism for improving the strength of FPG. This study suggested that FPG has the possibility to compete with traditional gypsum materials and it is also expected to solve the problem of phosphogypsum utilization.

To study the crack resistance of steel slag crumb rubber modified asphalt mixture (CR-steel slag) under salt freeze–thaw cycles, we selected styrene-butadiene-styrene (SBS)-steel slag and CR-basalt as the reference group. The relationship between CR-steel slag interfacial adhesion properties and crack resistance under salt freeze–thaw (FT) cycles was investigated through semicircular bending (SCB), pull-out, and contact angle tests. The results show that the salt FT will accelerate the process of micro-cracks in the mixture to macro-cracks. With the increase of FT cycles, the crack resistance will gradually deteriorate, and significant damage will occur in the mixture at 15 freeze–thaw cycles. The mutation point of freeze–thaw times will move forward in different degrees under the action of salt solution. At the same time, with the increase of salt solution concentration, its anticracking performance first decreases and then increases, reaching an extreme value of 8%. The magnitude of the crack resistance of the three asphalt mixtures is CR-steel slag > SBS-steel slag > CR-basalt. The macroscopic cracking index of asphalt mixtures has an excellent positive correlation with the matching index, and the matching index model has sufficient accuracy in evaluating the cracking resistance of three asphalt mixtures under the action of salt freeze–thaw cycles. Based on the surface energy theory to evaluate the crack resistance of the mixture from a microscopic perspective, combined with macroscopic evaluation indexes, the evaluation results are accurate and more reliable.

Environmental issues, such as global warming and pollution, could be solved by reducing the carbon dioxide (${\mathrm{CO}}_2$) footprint on the surrounding atmosphere. Utilizing by-products as a cement substitute in cement production, such as cement kiln dust (CKD), could reduce ${\mathrm{CO}}_2$ emissions from burning raw materials in cement plants. This study investigated the effect of cement kiln dust on cement mortar’s physical, flow, and mechanical properties. Cement was replaced with CKD up to 100% (by weight of dry cement). The optimum content of CKD was determined based on compressive strength; loss on ignition (LOI); and chloride (Cl), sulfate (${\mathrm{SO}}_3$), and magnesium oxide (MgO) contents. Standard sand with a maximum diameter of 2 mm was used in this study, with a sand-to-binder ratio ($s/b$) of $3:1$. Three different models—multiexpression programming (MEP), nonlinear regression (NLR), and an artificial neural network (ANN)—were employed for estimating the compressive strength of CKD-modified cement mortar using the present study data (110 data sets) and 152 data collected from other research studies. The compressive strength of cement mortar was predicted as a function of water-to-binder ratio ($w/b$), sand-to-binder ratio, cement kiln dust content, silicon dioxide content in the binder, calcium oxide content in the binder, the maximum aggregate diameter (MDA), and curing ages ($t$). Based on the statistical assessments, the ANN models outperformed the MEP and NLR models in the testing phase. According to the sensitivity analysis, curing time is the most critical parameter affecting the compressive strength of CKD-modified cement mortar, and the ${\mathrm{SiO}}_2$ content percentage affected the compressive strength more than did the CaO content percentage.

Cast steels are inherently suitable for fabricating complex joints in steel constructions. These joints may suffer from ductile fracture under ultralow cycle fatigue (ULCF) loadings during earthquakes. This problem could be even worse for cast steel joints working at subzero temperatures. In this investigation, ULCF tests on 48 smooth notched tensile specimens were carried out at 20°C, $-20°\mathrm{C}$,$-40°\mathrm{C}$, and $-60°\mathrm{C}$ for G20Mn5QT cast steel. Notches with three different radii were designed for different stress triaxialities. Two load patterns, cycle to fracture and cycle and pull to fracture, were applied for the tests. Ductile fracture caused by the ULCF loadings was observed and fatigue lives were obtained for all test specimens. The characteristic lengths were determined for G20Mn5QT cast steel at the four temperatures through scanning electron micrograph analysis of the fracture surfaces. The cyclic damage degradation parameters in the cyclic void growth model were then calibrated for G20Mn5QT cast steel at 20°C, $-20°\mathrm{C}$, $-40°\mathrm{C}$, and $-60°\mathrm{C}$ based on test results and complementary finite element (FE) analysis. The cyclic damage degradation parameter decreases with the drop of temperature, which indicates that the material’s resistance to ductile fracture degrades faster at lower temperatures under ULCF loadings, especially when the temperature drops below $-40°\mathrm{C}$.

Due to the differences of physical and mechanical properties of asphalt pavement materials, asphalt pavement (asphalt mixture) presents complex characteristics. To explore the acoustic emission (AE) wave characteristics of asphalt pavement materials, the automatic sensor test (AST) method was used on coarse aggregate, asphalt, and asphalt mixture at different temperatures. The results show that the peak amplitude and frequency of AE waves in coarse aggregate is the largest, followed by asphalt, and asphalt mixture is the smallest. For asphalt mixture, the larger the nominal maximum size of aggregate, the more serious the waveform distortion, the more complex the frequency distribution, and the smaller the amplitude range of AE waves. AE waves in coarse aggregate is not sensitive to temperature, while the peak amplitude of AE waves in asphalt is linearly related to temperature. The peak amplitude and temperature of AE waves in three gradations of asphalt mixtures can be fitted to obtain the corresponding second-order polynomial. AE wave attenuation is mainly reflected in asphalt mixture, while low-temperature sensitivity is mainly reflected in asphalt and asphalt mixture.

The comprehensive properties evaluation index of asphalt mixture has the characteristics of multilevel and multifactor. The weight of each road performance index is the key factor to assess the comprehensive properties of the asphalt mixture. However, how to determine the weight objectively is a very key problem in the performance evaluation model. In this study, the comparison matrix method was used to determine the performance weight objectively of rock asphalt modified bio-asphalt mixture (RABAM). First, the neat asphalt mixture (NAM), bio-asphalt mixture (BAM), rock asphalt modified asphalt mixture (RAM), and RABAM were prepared. Second, the high-temperature and low-temperature properties, water damage resistance, and fatigue characteristics of the different asphalt mixtures was analyzed. Finally, the comprehensive properties were evaluated under different climate zones in China. The results indicated that the rock asphalt improves the comprehensive performance of BAM. Applying the comparison matrix method to the field of road materials can effectively evaluate the applicability of road materials in different regions.

Temperature variation during the welding will cause different solid-state phase transformations in the welding area and result in a heat-affected zone (HAZ) between the weld metal (WM) and the base metal (BM). Depth-sensing indentation (DSI) is a doable technique to characterize mechanical properties of materials in the HAZ, which is usually not big enough for the fabrication of coupons for traditional tension tests. The basic idea of DSI technique is to push a hard tip into the surface of the material and then reveal its mechanical properties based on the response of the material. In this study, mechanical properties of butt welds of Q355D steel were investigated with DSI tests and reverse analytical approach. Different welding zones, including BM, subcritical HAZ, fine-grain HAZ, coarse-grain HAZ, top pass of WM and middle pass of WM, were distinguished by microstructures observed by scanning electron microscope (SEM). DSI tests were conducted on these welding zones. Mechanical properties were characterized based on load-penetration depth ($P\text{-}h$) curves obtained by DSI tests. These mechanical properties were adopted in finite-element (FE) simulation of DSI tests. $P\text{-}h$ curves obtained by FE simulation agree well with results of DSI tests for all welding zones, especially for the loading curves. The agreement validates the applicability of DSI technique in characterizing mechanical properties of materials. Tension coupon tests were conducted on the BM and the middle pass of WM to verify the accuracy of the DSI technique. Variation of mechanical properties across the welding area were discussed in accordance with microstructures of materials in different welding zones.

The properties of slag-rich cement paste are fundamentally associated with slag chemistry. In the present research, 10 slags covering the common chemistry range, including eight synthetic slags of $\mathrm{CaO}─{\mathrm{SiO}}_2─{\mathrm{Al}}_2{\mathrm{O}}_3─\mathrm{MgO}$ system and two commercial slags, were adopted to evaluate the influence of slag composition on the early (7 days) and later (3 months) age properties of blended paste. Mixture containing ${\mathrm{Al}}_2{\mathrm{O}}_3\text{-}\text{rich}$ slag performed better at 7 days as it favored the formation of ettringite and/or monosulfate. The MgO-rich slag cement paste exhibited good properties at both early and later ages, and it effectively promoted the precipitation of Mg-Al hydrotalcite-like phase. It was also noted that the $\mathrm{Mg}/\mathrm{Al}$ atomic ratio of hydrotalcite-like phase was positively related to the $\mathrm{Mg}/\mathrm{Al}$ atomic ratio of slag itself. Conversely, with the increasing MgO content in slag, the Al/Si atomic ratio of C─ S(A)─ H gel phase decreased. High ${\mathrm{Al}}_2{\mathrm{O}}_3$ and/or MgO contents can compensate the negative effect of reduced $\mathrm{CaO}/{\mathrm{SiO}}_2$ ratio at early age while not at later age. Overall, attention should be paid to aluminum- and sulfur-rich slags. These two elements in slag promoted the formation of ettringite and/or monosulfate at an early age; however, this positive effect disappeared at later ages.

The microstructural characterization of Basalt Fiber Reinforced Polymer (BFRP) bars under seawater deterioration (dry–wet cycles modes and immersion modes) was performed by scanning electron microscopy (SEM) and X-ray energy spectrum analyzer (EDS). Then, uniaxial compressive tests were carried out on the corroded BFRP bars to explore the effects of different corrosion periods, diameters, and slenderness ratios on the degradation of compressive performance and durability in seawater corrosion and constraint condition. The results showed that dry–wet cycles of seawater caused patchy pitting on the surfaces of BFRP bar, and white granular foams adhered to the bar surface after seawater immersion. The internal microstructure of BFRP bar was deteriorated, and the bonding force between the fiber and resin was reduced with the increase of dry–wet cycles. Five failure modes of BFRP bars occurred in uniaxial compressive tests, namely crushing failure, transverse cracking failure, shearing failure, splitting failure, and buckling failure. The increase of corrosion cycles significantly decreased the bearing capacity and compressive strength, but had little effect on the compressive elastic modulus of BFRP bars. The dry–wet cycles of seawater was more harmful to the mechanical properties of BFRP bars than immersion corrosion. Meanwhile, the mechanical properties of BFRP bars were affected by their diameters and slenderness ratios to some extent.

In this paper, the plastic mold compaction device (PM Device) was used successfully during full-scale construction of lime- and cement-stabilized pavement layers for which strict quality control measures were taken, such as multiple spread rate calibration, frequent moisture contents, and close attention to compaction timing and density measurements. Even with these precautions to minimize variability, there was quantifiable variation in density, unconfined compressive strength (UCS), and elastic modulus ($E$) for soil–cement and soil–lime mixtures. Over the 61-m test section, density varied by 5.2% for soil–cement and by 5.0% for soil–lime, UCS varied by 861 kPa for soil–cement and by 246 kPa for soil–lime, and $E$ varied by 2,628 MPa for soil–cement and by 1,036 MPa for soil–lime. There also were noticeable differences in PM Device density and $E$ measurements compared with nuclear gauge and falling weight deflectometer–calculated modulus. This paper also serves as the first known and documented use of the PM Device with lime-stabilized material, and is the first known and documented comparison of PM Device specimens and beams compacted with a Proctor hammer. Compared with other field projects in which the PM Device was implemented, the variability of density and UCS in this project was lower than in other typical Mississippi Department of Transportation (MDOT) projects. When using the data collected at the National Center for Asphalt Technology (NCAT) test track as a baseline for soil–cement materials, variability likely will be no less than 5% for density as a percentage of the target density and 75% for UCS as a percentage of the average UCS value when using current MDOT construction protocols.

The application of aeolian sand as the full aggregate to produce high-performance concrete is significant for engineering construction in desert areas. However, high-performance concrete with full aeolian sand (FA-HPC) is characterized by a low water-binder ratio, high content of cementitious materials, and no restriction of coarse aggregates, resulting in a high risk of shrinkage cracking. The main purpose of this work is to investigate the reinforcement effect of different types of fibers and their combinations on FA-HPC. Three types of fibers, i.e., steel fiber (SF), basalt fiber (BF), and polyvinyl alcohol fiber were employed in the FA-HPC matrix to explore the most promising reinforcement method. The workability, strength, shrinkage, cracking resistance, and chloride resistance of FA-HPC were investigated by laboratory tests. Moreover, the fiber-reinforcement mechanism was analyzed in terms of the micromorphology of FA-HPC. The results indicated that the incorporation of fibers could improve the previously mentioned properties except for the decrease of fluidity with content dependence, especially for 12 mm fibers. The single SF has a considerable advantage in strength enhancement and shrinkage reduction presenting a variation of 56.7% and 19.5% at 1% by volume, respectively. Moreover, the hybrid fibers exhibited better behavior in durability showing 95.88% crack reduction and 48.5% improvement in chloride resistance. Eventually, two selected schemes were recommended presenting for 1% by volume single SF and hybrid fibers (0.75% by volume SF with 0.25% by volume BF) from an integrated perspective. Furthermore, microscopic characterization revealed that the mechanism of fiber reinforcement mainly played a bonding and bridging effect, refining the pores at different scales and making the structure of FA-HPC dense. This research can optimize the material composition of FA-HPC and promote the utilization of aeolian sand resources.

This study aimed to study the effects of different carbonation–hydration processes and carbonation degrees on the mechanical properties and leaching behavior of heavy metals in stainless steel (SS) slag paste. SS slag powders were carbonated at different water/solid ratios, and cement paste containing 50% by weight carbonated SS slag were prepared and employed in different carbonation–hydration approaches. ${\mathrm{CO}}_2$ uptake of SS slag powders seriously depended on water/solid ratio, and the optimum water/solid ratio for carbon sequestration was 8% in the experimental range. The long-term cumulative leaching fractions of Cr and Ni in carbonated SS slag powder decreased with carbonation progress, whereas excessive carbonation showed negative effects on the immobilization of heavy metal ions. The 30-day cumulative leaching fraction of Cr and Ni of SS slag powder with carbonation degrees of 36.2% were 65.8% and 43.2% lower than raw SS slag. Carbonation–hydration curing approaches showed obvious effects on mechanical property development and leaching characteristics of heavy metals of SS slag paste. The ${\mathrm{CO}}_2$ uptake of SS paste were positively correlated to the hydration period before carbonation curing, and ${\mathrm{CO}}_2$ uptakes of 14.5% and 17.2% were obtained for H3C6 and H28C6 (H3C6 and H28C6 refer to SS paste specimens first cured in a concrete-curing room for 3 and 28 days, respectively, and then subjected to carbonation curing for 6 h). Carbonation curing for 2 h after hydration first for 3 days can increase the 28-day compressive strength by 27.7%, and the cumulative leaching fractions of Cr and Ni of H3C6 decreased by 58.2% and 44.4%, respectively.

The cold recycled mixtures using foamed asphalt (CRMF) has been widely used in pavement construction with many ecofriendly advantages. However, the material with a large void fraction is more vulnerable to freeze-thaw cycles in seasonal frozen regions usually. Although some efforts on the properties and applications of CRMF are expended, the regular of decay of the material in seasonally frozen region remains insufficient with urgently further studies. This paper intends to investigate the deterioration of CRMF under seasonal freeze-thaw cycles. First, the cylindrical CRMF specimens experienced various freeze-thaw cycles to simulate the seasonal frozen environment. Second, the indirect tensile asphalt cracking test (IDEAL-CT) and the indirect tensile fatigue (ITF) test were conducted. The strain field was recorded by the digital image correlation (DIC) technology in the IDEAL-CT and the ITF test. The influences of freeze-thaw cycles on the properties of CRMF were evaluated with the void fraction, failure energy, cracking tolerance index, fatigue life, and crack tortuosity. The IDEAL-CT and ITF results showed the specimen has a primary cracking area. A good correlation between void content and failure energy was verified. As the void content rose, the crack tortuosity and fracture energy fell with the increase of freeze-thaw cycles. Moreover, the failure energy is a more accurate index to describe the cracking resistance of the CRMF from the aspects of crack initiation and propagation. The decay of fracture resistance and fatigue life of the CRMF with freeze-thaw cycles can be accurately described by the exponential model. In the ITF test, the average strain in the primary cracking area represented the nature of fatigue damage of CRMF better than that collected according to BS EN12697-24.

This study comprehensively describes the viscoelastic behavior of high-elasticity modified asphalt mixtures under varying strain conditions. The commonly used sigmoidal model, which relies on a single parameter (dynamic modulus) to depict viscoelastic behavior, has limitations. In this research, by utilizing the dynamic modulus master curve and the Kramers–Kronig relationship, master curve models developed for the phase angle, storage modulus, and loss modulus enable a more comprehensive understanding of the materials’ viscoelastic response functions. Dynamic modulus tests were conducted on the high-elasticity modified asphalt mixtures using the simple performance tester (SPT) at various temperatures (5°C, 15°C, 25°C, 40°C, and 55°C) and frequencies (0.1, 0.5, 1, 5, 10, 20, and 25 Hz). The results indicate that the master curves of the phase angle, storage modulus, and loss modulus, established using the dynamic modulus master curve and Kramers–Kronig relationship, are well-fitted, demonstrating that the method feasibly can be used to draw the master curves for each viscoelastic parameter. Additionally, mathematical models based on the Kramers–Kronig relationship were developed to explain the correlations among parameters under dynamic loading conditions, and the accuracy of the master curve models for various parameters was validated. This deeper insight into material responses under varying loading conditions and temperatures can help researchers better model and predict the mechanical performance of pavements.

This paper studies the chemo-mechanics of cement beams containing polypropylene (PP) functionalized using ultraviolet (UV) irradiation. It is hypothesized that UV irradiation enhances the load transfer at the interface of cement and PP while facilitating the valorization of waste PP. In this study, we use UV-irradiated polypropylene (UVPP) plastic particles as an ingredient in cement paste, using the enhanced cement-UVPP interaction to improve the capacity for load transfer. Using atomic force microscopy based infrared spectroscopy (AFM-IR) on a UVPP-cement composite, we first show that the UV bombardment of PP promoted the formation of oxygen functional groups at the interface between UVPP and cement, indicating a possible increase in the affinity of the UVPP particles toward water and thus their hydrophilicity. This in turn is expected to enable the formation of bonds between the UVPP and cement, enabling stress transfer at the interface. We further show that this stress transfer increases the work-of-fracture, ductility, and mechanical energy absorption of the notched three-point bending cement-UVPP composite beam. This is accomplished when the two fracture surfaces that form during crack propagation are bridged by the UVPP-cement interaction. Since the ductility of these beams is size dependent, we performed fracture tests on two-dimensional (2D) geometrically scaled beams of four sizes. In addition to the mechanical improvements, this work forms the foundation for future work focused on reducing the carbon footprint of structures, since the UVPP replaces some of the cement and eliminates some of the plastic waste from landfills.

Steel fiber (SF) has been widely used in asphalt mixtures to provide efficient induction heating and improve performance. However, the application of SF in asphalt mixtures still faces the issues of mixing difficulty, further performance improvement, and increased cost. To try to alleviate these issues, brucite fiber (BF) and fiber granulation technology have been adopted. First, SF and BF were mixed into the mixture according to different volume ratios. Based on the research results of engineering performance, the optimal total content and optimal volume ratio of SF and BF were determined. respectively. Then, SF and BF were prepared into a composite granular fiber (CGF). Finally, the performance of the mixture including CGF was verified, its economy was evaluated, and its mechanism was analyzed. The results show that the optimal total content of SF and BF is 0.6% and the optimal volume ratio of SF to BF is 3:2. The high-temperature rutting resistance, low-temperature cracking resistance, and moisture sensitivity of CGF are superior to that of the control sample and SF asphalt mixture, with percentages of 15.1%, 4.2%; 49.4%, 23.4%; 14.5%, 6.7% respectively. A mechanistic analysis described why CGF performed better than SF. The cost performance of the asphalt mixture with CGF surpasses that of SF, with CGF being 32.2% higher.

Asphalt pavement will crack under the action of traffic load and harsh environment, and the cracks can be repaired by the self-healing properties of asphalt itself, but the healing efficiency is lower. This study developed a novel self-healing asphalt based on disulfide-crosslinked polyurethane elastomer. A low-cost crosslinking agent (CY-OA) was synthesized from cystamine dihydrochloride as raw material, and then a disulfide-crosslinked polyurethane prepolymer (PU-SS) was synthesized using a stepwise copolymerization method for modification of asphalt to obtain a self-healing polyurethane-modified asphalt. The chemical properties, microscopic morphology, and self-healing capability of disulfide-crosslinked polyurethane elastomer and polyurethane-modified asphalt were evaluated in this study. Infrared spectroscopy confirms the introduction of CY-OA into the polyurethane main chain. Thermal gravimetric analysis shows excellent thermal stability of PU-SS. Healing tests demonstrate that disulfide bonds enhance the self-healing ability between polyurethane elastomer and asphalt binder. PU-SS exhibits a healing efficiency as high as 96.33% within 12 h at 60°C. With an increase in PU-SS content and repair time in the modified asphalt, the repair efficiency increases, with a maximum fatigue recovery index of 80%. The objective of this study is to introduce dynamic covalent bonds to enhance the self-healing performance of asphalt and improve the long-term crack resistance of asphalt pavement.

Waste cooking oil (WCO) was investigated as an asphalt rejuvenator and found to have good potential. The properties of the WCO itself will change with usage and the WCO under different stages may affect the bond between the asphalt and minerals. In this study, the effect of WCO under different stages on adhesion behaviors of aged asphalt-mineral interfaces was explored through molecular dynamics (MD) simulations. The results show that triglycerides and treated fatty acids with low acid value can better improve the adhesion work between aged asphalt and acidic mineral (e.g., quartz), while fatty acids with high acid value may increase the adhesion work of aged asphalt to alkaline minerals (e.g., calcite and albite). Treated free acids are less effective in improving the moisture resistance of interfaces than free acids. Considering the coupling effect, WCO under different stages mostly can have restorative effects on the adhesion sensitivity of interfaces. The results can provide a reference for the selection of aggregates for WCO application in asphalt mixtures.

This study investigated the effect of alkalis on ${\mathrm{C}}_3\mathrm{S}$ hydration with and without incorporating aluminate phases. Pastes of 100% ${\mathrm{C}}_3\mathrm{S}$ and 90% ${\mathrm{C}}_3\mathrm{S}+10\%$ metakaolin (MK) were prepared at 1%, 2%, and 3% ${\mathrm{Na}}_2\mathrm{O}$ content. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterize the solid phase assemblages, and then the hydration degree of ${\mathrm{C}}_3\mathrm{S}$. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to analyze the aqueous composition of pore solution. Mercury intrusion porosimetry (MIP) was used to measure the porosity of the hydrated pastes. The results highlighted the promoting effect of Na and the inhibiting effect of Al in pore solution on ${\mathrm{C}}_3\mathrm{S}$ hydration after a period of curing (90 days). Without incorporating metakaolin, the hydration degree of ${\mathrm{C}}_3\mathrm{S}$ continuously increased with the increase of Na concentration. Incorporating metakaolin into ${\mathrm{C}}_3\mathrm{S}$ can generate aluminate hydrates (carboaluminates, in this study), and the increased Na concentration can increase the dissolution or instability of carboaluminates and elevate the equilibrium Al concentration. Under this condition, the hydration degree of ${\mathrm{C}}_3\mathrm{S}$ fluctuated depending on the combined effect of Na and Al concentrations in pore solution on ${\mathrm{C}}_3\mathrm{S}$ hydration.

In this study, nanocomposite-modified bitumens were prepared and mechanically tested as an alternative to polymer-modified binder. Halloysite nanotube and sepiolite nanoclay were employed along with some polymers to form nanocomposites through the melt intercalation method. The storage stability of the nanocomposite-modified bitumens was tested to evaluate the compatibility. Conventional tests were conducted to compare the physical changes after nanocomposite modification. The viscosity of the nanocomposite-modified binders was determined using a rotational viscometer. Finally, the high- and low-temperature performance grades were evaluated using a rheological testing program. The results showed that the compatibility of the nanocomposites was within acceptable limits, while certain nanocomposite types significantly increased the stiffness of bitumen compared to polymer modifiers alone, resulting in an improvement in the physical performance of bitumen.

A rejuvenating composite seal (RCS) consists of a chip seal and a micro-surfacing (MS). There are two reasons for RCS’s poor application effect in China and less frequent application than that of MS: first, the material amount of a composite seal is determined largely based upon experience and lacks a theoretical basis; and second, the composite seal cannot achieve the expected service life. The objective of this study is to determine an appropriate technique to prepare RCS in the laboratory and verify its long-term water stability. Based on an improved sweep test, a method to determine the rate at which to apply the rejuvenating emulsified asphalt used in a chip seal was established. Through the wet track abrasion test and the loaded wheel test, the proper proportion of materials in the MS mix was determined. The material dosage and technique to prepare the RCS was determined by the matrix analysis method based on a multitarget orthogonal test, and its long-term water stability was determined by immersion and freeze-thawing. The results showed that the material dosage of the chip seal was quantitatively determined by an improved sweeping test, the preparation process and material dosage of the composite seal were quantitatively determined by matrix analysis, and the resulting composite seal had reasonable structure and good comprehensive performance. The findings of this paper can provide theoretical guidance for the promotion and application of composite seals in China.

Concrete structures are at risk of fire and explosion effects during service. This paper mainly conducted static and dynamic mechanical test research of concrete after high temperature. Five different target temperatures and two cooling methods (air cooled with furnace and water cooled by immersion in water) were set to investigate its effects. Hydraulic servo machine and split Hopkinson pressure bar (SHPB) were used to obtain static and dynamic mechanical behavior, failure patterns, and mechanical characteristic parameters of concrete. The research results indicated that the compressive strength of concrete at 800°C was reduced by 77% and 67% under air-cooled and water-cooled methods, respectively. When the temperature was below 600°C, the compressive strength of water-cooled concrete was lower than that of the air-cooled specimen. The failure patterns of the concrete vary from a small amount of aggregate crushing at low strain rates to a large amount of coarse aggregate crushing at high strain rates. The increase in temperature weakens the dynamic increase factor (DIF) of concrete and causes a significant strain-softening phenomenon in the concrete stress–strain curve. By utilizing scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and X-ray computed tomography (X-CT) techniques, the microstructural features of concrete were obtained. The deterioration and enhancement mechanisms of the mechanical properties of concrete under high temperature and strain rates were studied by combining the results with static and dynamic mechanical properties analyses. Meanwhile, a dynamic constitutive model for concrete considering high-temperature influencing factors is established.

This paper aims to propose a short-distance water impact method to test the hydraulic erosion resistance of ultrahigh performance concrete materials (UHPC). The method used high-velocity water flow to simulate a complex hydraulic erosion environment, and an erosion zone was applied to evaluate the erosion resistance of materials. The erosion depth and mass loss of the specimens were tested. The results showed that a water pressure of about 2 MPa can be applied by short-distance water impact. At an impact time of 3 h and an impact distance of 1 cm, the erosion depth and mass loss of specimens were maximized. Thereinto, the erosion depth of mortar was 37.6% higher than that of UHPC. The mass loss of UHPC was 40.7% lower than that of mortar. Three indices for evaluating erosion resistance, including erosion rate expressed in %, erosion rate expressed in $\mathrm{g}/\mathrm{h}$, and erosion resistance strength, were compared. In addition, the erosion rate expressed in % could take into account the instantaneous state of the erosion process and reflect the deterioration trend with respect to impact time. According to the surface fitting, a predictive model between the erosion rate and impact condition was established. The variation trend of UHPC will be flat after a long period of erosion. The underwater method is compared, and the field test result is discussed.

This study presents a method for identifying sustainable concrete that incorporates toughened waste glass aggregate (TWG). The study takes into account the physical and chemical properties of TWG as quality parameters. Initially, TWG was mechanically treated to produce cubical-shaped aggregates ranging from 6 to 10 mm. Based on their performance, TWG aggregates were selected for an experimental study to validate the methodology. Several tests were conducted to establish the workability, mechanical strength, durability, and microstructural properties of TWG concrete, aiming to examine its feasibility. The results indicated that TWG concrete exhibits favorable fresh and hardened properties, and durability characteristics that are comparable to those of conventional concrete. The compressive strength of TWG concrete at 28 days was 17.95% lower than that of conventional concrete. In parallel, the split tensile strength and flexural strength values of TWG concrete are lower than those of conventional concrete. Additionally, TWG concrete demonstrates lower water absorption and better resistance to rapid chloride ion penetration (RCPT) than conventional concrete. The obtained experimental results were supported by morphological studies, reinforcing the findings of the study. These findings indicated that TWG aggregates possess the necessary quality to be utilized as a construction material, thus presenting the potential for future use in the construction field.

In order to clarify the flame retardant mechanism and microscopic performance of modified asphalt, a new inorganic flame retardant was prepared using three flame retardants, and antimony trioxide and decabromodiphenyl oxide were selected for comparative testing. Twelve groups of asphalt samples were prepared as research materials, including eight groups of short-term and long-term aging samples. The effects of different types of flame retardants on the performance of modified asphalt were compared by macroscopic performance test, infrared spectroscopy and thermogravimetric analysis. The changes in functional groups of asphalt samples before and after aging were studied. The mass loss before and after aging was analyzed, and the flame retardant modes of various types of flame retardants were explored. The results showed that the functional groups of asphalt were not altered by the inorganic flame retardant and antimony trioxide. Both flame retardants were physically mixed with the modified asphalt. The hydrogen ions in the unsaturated bond C═C were partially replaced by bromine ions of decabromodiphenyl oxide, indicating that a chemical reaction occurred. The basic properties of modified asphalt were well maintained by the inorganic flame retardant; the formation of carbonyl groups was reduced, and the oxidation reaction during aging was also alleviated. In the combustion of inorganic flame retardants and decabromodiphenyl oxide, gas molecules were decomposed, oxygen concentration was reduced, and oxide-coated asphalt was formed. In contrast, only oxide-coated asphalt was formed in the combustion of antimony trioxide. Therefore, the study provides an approach to improve the aging resistance and pavement performance of flame retardant–modified asphalt, and also demonstrates its potential for practical applications.

Polyoxymethylene (POM) fiber is a new type of reinforcement material developed in recent years, which provides a new way and choice for the modification and reinforcement of cement-based materials. In order to improve the application of POM in the construction field, fiber-reinforced cementitious materials were prepared using 6- and 12-mm POM fibers. The effects of at two lengths of POM fibers on fluidity, compressive strength, flexural strength, flexural toughness, and tensile strength of cement mortar were investigated, and the bonding interface between fibers and the cement mortar matrix was observed using scanning electron microscopy (SEM). The results show that the addition of POM fibers reduced the fluidity and 7-day compressive strength of cementitious composites, but had little effect on 28-day compressive strength. With the increase of POM fiber volume fraction and length, better flexural toughness and ultimate tensile strength can be obtained. When the POM fiber length was 12 mm and the volume fraction was 0.90%, the equivalent flexural strength and ultimate tensile strength of the POM fiber–reinforced cement-based composite (POM-FRCC) increased by 46.3% and 13.5%, respectively, compared with the control group. Microscopic analysis revealed that the POM fibers were tightly bonded to the cement mortar matrix, and the fibers had a severe surface scraping in the resistance to damage.

In this study, the changes in the phase and microstructure of alkali-activated slag (AAS) in ultralow-temperature environments ($-170°\mathrm{C}$) was experimentally studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric (TG), scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS), ${}^{29}\mathrm{Si}$ magic-angle spinning nuclear magnetic resonance (MAS NMR), and pore structure. The results show that as the modulus of water glass increased, the mass loss of AAS after the ultralow-temperature freeze–thaw cycles (ULT-FTC) decreased, the freeze–thaw resistance increased. The ULT-FTC caused the internal structure of the AAS samples using different activators to slip and rearrange. Partial calcium-(alumina)-silicate-hydrate gel [C─ (A)─ S─ H] gel was decalcified. The gel structure formed using 2.0 M water glass as the activator was the most stable. The dense structure with a lower Ca/Si ratio enables the AAS to maintain a relatively stable microstructure after undergoing ULT-FTC.

Abstract

The conventional design approaches for reclaimed asphalt pavement (RAP) mix follow blending rules to select the grade of the virgin binder for hot recycled bituminous mixtures. The interactions of RAP binder with the virgin binder are highly complex in the presence of the rejuvenator. Identifying the optimal proportion of RAP binder, virgin binder, and rejuvenator is often a trial-and-error procedure, involving considerable experimental data collection. The current research study proposes the statistical-based design of experiments (DoE) framework to design ternary RAP binder blend, develop response surface prediction models, and optimize the proportions to meet targeted binder properties of viscosity grade (VG30) binder. A desirability-based multiple response optimization is carried out, and the optimal blend proportions with target binder properties are arrived at with different desirability levels. A total of 13 RAP binder blends are formulated using the I-Optimal algorithm in the current study. Experimental data such as softening point, high-temperature performance grade (PG), and linear viscoelastic parameters in the temperature range of 46°C to 70°C and frequency range of 0.1 to 50 Hz are collected. The binder blends are evaluated using master curve parameters and relaxation spectrum. The response surface models are developed for two measured parameters (high-temperature PG and softening point), three computed master curve parameters, and four relaxation spectrum parameters. These models capture the possible individual component effects and combined component effects on the final RAP binder blend through linear and nonlinear terms. A desirability-based simplex optimization is adopted to identify combinations of constituents at various levels of desirability that comprises only direct measurements, direct measurements and master curve parameters, and direct measurements, master curve parameters, and relaxation spectrum. Using this proposed approach, a wide range of solution zones are identified with various levels of desirability.

Practical Applications

Reclaimed asphalt pavement (RAP) consisting of aged bitumen coated on mineral aggregates is used for recycling in pavement construction. Many challenges exist related to the optimal use of such material. The aged binder may need to have the required properties suitable for recycling. Generally, rejuvenators are added to the RAP to enhance the properties of aged binder. However, how much rejuvenator should be added is unclear. Aged bitumen from different sources of RAP can have different degrees of aging. In addition, it may not be easy to estimate the extent of blending of the RAP with the virgin materials (aggregates and bitumen), as it is linked to the characteristics of aged binder and the choice of fresh bitumen and rejuvenator. Also, the aged bitumen, when mixed with a rejuvenator and virgin bitumen, may not necessarily result in a final mix with bitumen that meets the requirements. As can be seen, the choices are entirely diverse and varied. This research attempts to solve such issues using a statistics-based tool called design of experiments (DoE). Using such a tool, this study demonstrates how to optimally choose the proportions of virgin bitumen, RAP bitumen, and rejuvenator. This work presents a methodology that can be implemented efficiently using commercial software by any asphalt mix designer.

The mechanical properties of organic/inorganic composites at a macroscopic level are largely determined by the interaction mechanisms at the interface. However, there have been limited microscopic studies on these interactions. To address this knowledge gap, this study used molecular dynamics (MD) simulation to examine the interfacial structures, kinetics, and energetics between calcium silicate hydrate (CSH) and polymers. The purpose of this investigation is to shed light on the factors contributing to the variations in mechanical properties of the materials and to provide atomic-level guidance for nanocomposite toughening studies. Three polymers, polyacrylamide (PAM), sodium polyacrylate (PAAS), and polymethacrylic acid sodium sulfonate (PAMAS), were incorporated into the nanochannels of CSH sheets to create polymer/calcium silicate hydrated composites. Our simulations revealed that calcium atoms at the CSH surface act as intermediaries bridging polymers and the CSH through ${\mathrm{O}}_{\mathrm{b}}─{\mathrm{Ca}}_{\mathrm{sur}}─{\mathrm{O}}_{\mathrm{p}}$ and metal atoms in polymer functional groups through ${\mathrm{O}}_{\mathrm{b}}─{\mathrm{M}─\mathrm{O}}_{\mathrm{p}}$. Furthermore, hydrogen bonds between the interface water molecules and the polymer and CSH matrix were observed through ${\mathrm{O}}_{\mathrm{p}}─{\mathrm{Ca}}_{\mathrm{sur}}─{\mathrm{H}}_2{\mathrm{O}─\mathrm{O}}_{\mathrm{b}}$ and ${\mathrm{O}}_{\mathrm{p}}─{\mathrm{M}─\mathrm{H}}_2{\mathrm{O}─\mathrm{O}}_{\mathrm{b}}$ bonds. Uniaxial tensile simulations were carried out to assess the mechanical behavior of composites, with results indicating that all three materials failed at their interfaces. Analysis of chemical bonding at the point of failure revealed that PAM/CSH exhibits the highest number and stability of chemical bonds and thus the best mechanical properties, followed by PAAS/CSH, with the worst being PAMAS/CSH. Our study provides fundamental atomic-level insights into the differences in interaction mechanisms and macroscopic mechanical properties of composites through molecular dynamics simulation, offering a theoretical basis for polymer modification of CSH and the genetic improvement of cementitious materials.

In the present study, the effect of high-volume fly ash blending in the concentration of 15%, 25%, 35%, 45%, and 55% with different effective water-to-cement (W/C) ratios has been investigated for rheology, compressive strength (CS), and durability of self-compacting mortar (SC-mortar). The rheology of SC-mortar was evaluated in terms of slump flow diameter, v-funnel flow time, and developed yield stress and plastic viscosity. The CS of SC-mortar was evaluated at 7 and 28 days of curing, whereas the water permeability and rapid chloride penetration tests were performed to evaluate the durability of SC-mortar at 28, 90, and 180 days. The consumption of ordinary portland cement was reduced using the k-factor or cementing efficiency factor in mix design, where the value of the k-factor decreases with increasing fly ash content. The experimental study revealed that the addition of a high volume of fly ash has a significant impact on rheology and durability, whereas CS of SC-mortar was affected marginally. Scanning electron microscopic (SEM) examination revealed that the fly ash blending has improved the packing and reduced the pore density to compensate for the loss of CS on account of lower cement content. An increase in W/C has increased the porosity, causing a negative impact on CS and durability. The durability of SC-mortar has increased with increasing fly ash content, and there was an exceptional increment in water ingression time (T25) with an increase in fly ash content from 25% to 35%, but with higher content of fly ash (above 35%) and low value of W/C, SC-mortar become very sticky, thus reduced the workability significantly. Compared with the control mix, there is a significant reduction in the cost of SC-mortar with fly ash blending of 15%, thereafter, the cost reduction is marginal with a further increase in fly ash dosage which is due to the rise in admixture dosage. Based on the rheology (within EFNARC limits), CS, and durability of SC-mortar, the optimized dosage of fly ash has been recommended in the range of 25%–40% with different W/C.