Journal of Materials in Civil Engineering

Polycarboxylate ether–based water-reducing admixtures (PCEs) have a significant impact on the workability of cementitious systems. The modifications of the chemical structures of the main and side chains can lead to the improvement of electrostatic repulsion and steric hindrance effect of PCEs, resulting in the superior performance of cementitious systems. In this study, the impact of main- and side-chain properties of PCEs on various characteristics, especially the rheology of cementitious systems, was examined in detail via prior studies in the literature. In addition, pH, adsorption conformation, and intercalation state, which affect the aforementioned properties of PCEs, also were studied. It was concluded that the geometric equilibrium between the main and side chains has a vital place in designing optimum molecular structures.

Freeze–thaw (F-T) cycle is a critical factor that deteriorates the mechanical properties of loess subgrade, leading to pavement structure distress. Phase change materials (PCMs) can be employed to stabilize loess subgrades. This study investigated the effect of PCMs on the mechanical properties of loess and explored the corresponding mechanism of stabilizing loess subjected to F-T cycles. First, macroscopic mechanical tests were conducted to examine the influence of PCMs on the mechanical properties of stabilized loess. Through a series of microscopic tests, the mechanism of PCM effects on loess before and after it was subjected to F-T cycles was analyzed from the chemical, thermal, and physical perspectives. The findings demonstrated that PCMs could considerably alleviate the adverse effects of F-T cycles on loess strength by 37%–182%. The strength of PCM-stabilized loess reached a maximum when liquid PCM (pPCM) and microencapsulated PCM (mPCM) doping were 8% and 5%, respectively. No new functional groups were generated after mixing the PCMs with loess. The strength of PCM-stabilized loess was mainly enhanced by physical gluing and filling. Additionally, the PCMs could counteract the external temperature by the latent heat of the phase change, thus increasing the thermal stability of the loess. Finally, through a scanning electron microscopy test, it was verified that the incorporation of PCMs improved the loess density and mechanical strength as well as enhanced sustainability against a few penetration cracks and large pores when the loess was subjected to F-T cycles. This study provides insights into the use of PCM-stabilized loess subgrade in seasonally frozen regions.

Pavements are exposed to different external factors such as traffic loading, levels of moisture, and ambient temperature fluctuations. External temperature change affects the pavement’s temperature profile and therefore its behavior. Previous research states that the pavement’s surface temperature cannot be addressed by adjusting its thermal properties because it primarily relies on the color of the surface. Furthermore, the temperature gradients in the pavement’s temperature profile can be associated with thermal cracking, which is an aspect that has not been fully investigated. The objective of this article is to analyze the temperature profile of a modified asphalt pavement and its effects on the thermal gradients in different seasons. Consequently, the thermal properties of a modified asphalt pavement with a novel silica-based composite, developed at Arizona State University (ASU), called “aMBx” were calculated. Three types of mixtures were considered in this study: Control (0% aMBx), 10% aMBx, and 30% aMBx contents by weight of asphalt binder in the mixture. Moreover, slabs of 7.5 cm and 15 cm in thickness were built to monitor the thermal behavior in the field using wireless thermocouples, where the temperature was monitored and recorded for one year. In addition, a pavement temperature model was implemented using validated software developed at ASU. The full pavement temperature profile was simulated for the three types of asphalt mixtures discussed in this study. The results showed that the pavement surface temperature can be managed by changing the thermal properties, which, in this case, was driven by the materials and thickness of the materials. The temperature gradient was lower for the aMBx-modified pavements. Therefore, it was concluded that aMBx-modified asphalt pavements may lead to lower thermal susceptibility.

Current masonry design standards allow for the use of lightweight concrete masonry unit (CMUs), but lightweight grout is not an approved building material. An experimental test program was conducted to compare the compressive strength and modulus of elasticity of masonry prisms constructed with lightweight and normal weight grout. Three strength categories were considered: 13,780, 20,670, and 27,560 kPa (2,000, 3,000, and 4,000 psi). The experimental results indicated that at prism compressive strengths near 13,780 kPa (2,000 psi), there was no statistical strength difference between prisms made with lightweight and normal weight grout. As a result, the authors suggest that for compressive strengths near 13,780 kPa (2,000 psi), lightweight grout should be a code-acceptable alternative to normal weight grout. At higher prism compressive strengths, the values obtained for lightweight and normal weight materials diverged, and the lightweight prisms could not sustain the same loads and stresses as those made with normal weight grout. The results suggest that the difference in strength between lightweight and normal weight prisms can be accounted for by applying a lightweight reduction factor to the data set.

The incorporation of steel fiber exhibits great benefits to reduce cracking risk and autogenous shrinkage (AS) of high-strength concrete (HSC). 5D hooked-end steel fiber (5DSF) is a kind of novel hooked-end steel fiber. Previous investigations mainly focused on the mechanical properties and shrinkage deformation of 5DSF reinforced HSC (5DSFRC). However, the early-age cracking risk of 5DSFRC under uniaxial restrained conditions considering temperature evolution, AS, and restrained stress simultaneously has not been thoroughly investigated. A temperature stress test machine, which is capable of measuring these factors simultaneously, was used to investigate the effect of 5DSF volume fraction (0%, 0.12%, 0.24%, and 0.36%) on the early-age cracking risk of HSC in the present study. Experimental results and analysis showed that the cracking age, cracking stress, ratio of cracking stress to axial tensile strength, and reserve strength of HSC increased with an increase in 5DSF volume fraction. The AS of HSC decreased with an increase in 5DSF volume fraction, and an AS formula was proposed to calculate the early-age AS of HSC reinforced with steel fiber considering the effect of the volume fraction and shape of the fiber. The cracking risk of HSC decreased with an increase in 5DSF volume fraction. The early-age cracking risk and AS of HSC reinforced with 5DSF were lower than that of HSC reinforced with 3D hooked-end steel fiber with a similar steel fiber volume fraction.

Abstract

Low-cost desert sand and coal fly ash were used to synthesize high-quality quartz-anorthite composite ceramics. The effects of the addition of fly ash on the densification of green bodies, phase transformation, microstructure, and mechanical and thermal properties were investigated. The results showed that the densification of green bodies occurred when they were sintered from $\mathrm{1,100}°\mathrm{C}–\mathrm{1,200}°\mathrm{C}$, and the phase transformation of anorthite mainly occurred in fly ash from 846.9°C to 982.7°C. Temperatures of densification and anorthite transformation increased with increased addition of fly ash. At 1,100°C, $\beta$-cristobalite formed in desert sand and remained at room temperature; the content increased with increased sintering temperature. The quartz-anorthite ceramics were composed of $\alpha$-quartz, $\beta$-cristobalite, anorthite, and amorphous phase. Anorthite was formed by the solid-state reaction of quartz, mullite, and other phases in the desert sand and fly ash and was promoted by liquid-phase sintering at higher temperatures. The highest bending strength of 115.6 MPa and highest hardness of 668.3 Vickers hardness (HV) were produced for samples with 40% by weight fly ash sintered at 1,100°C. Samples with 100% by weight added fly ash had the lowest mean thermal expansion coefficient (${5.1\times 10}^{-6}·{\mathrm{K}}^{-1}$), the highest linear shrinkage (24.2%), and the highest bulk density (${2.5\mathrm{g}/\mathrm{cm}}^3$) when sintered at 1,200°C. The samples with 0%–60%, 80%, and 100% by weight added fly ash exhibited a low water absorption of 0.8%–1.8% when sintered at 1,100°C, 1,150°C, and 1,200°C, respectively. This technique can be feasibly used to fabricate civil engineering materials such as decorative ceramics, roof tiles, wall bricks, and insulation and filling materials.

Practical Applications

Inexhaustible supplies of desert sand and huge reserves of industrial solid waste cause serious negative effects on the environment. In addition, the manufacturing of building materials consumes tremendous amounts of inorganic minerals. The use of idle desert sand and industrial solid waste to produce useful building materials is an effective route to reduce environmental problems and mineral consumption. Desert sand and fly ash contain quartz, feldspar, mullite, and amorphous phase—similar to the composition of silicate materials. Therefore, they can be used as sustainable raw materials for ceramic production through the use of new techniques. The present study introduces a new material—anorthite-based ceramic—and a method for synthesizing it using low-cost desert sand and fly ash as raw materials. The anorthite-based ceramic can be used in the construction and building fields—the largest consumer of silicate materials—in tiles, bricks, porcelain, lightweight filling materials, and insulation materials. This is of great significance to the economization of mineral resources, resource regeneration, and improvement to the environment.

To explore the application of heat-treated ribbed bar (HTRB) type HTRB630 high-strength steel bars in reinforced concrete bridges, the tensile test and high-cycle fatigue test are carried out. Then, the high-cycle fatigue properties of the specimens are analyzed and discussed from median stress-number of loading cycles ($S\text{-}N$) curve, $P\text{-}S\text{-}N$ curve, comparison with 500-MPa grade steel bars, and fatigue fracture mechanism. Finally, their high-cycle fatigue properties are investigated numerically, and the influence of stress ratio on their fatigue properties is discussed. The results indicated that the probability-stress-number of loading cycles ($P\text{-}S\text{-}N$) curve with a confidence level $\gamma =75\%$ and a reliability guarantee rate $P=97.7\%$ is more accurate than the median $S\text{-}N$ curves for the fatigue design of reinforced concrete bridges. In the $P\text{-}S\text{-}N$ curve, the stress ranges at 2 million and 10 million cycles are 237.03 and 203.38 MPa, respectively. In the median $S\text{-}N$ curve, the stress ranges at 2 million and 10 million cycles of fatigue life of steel bars are 262.77 and 236.08 MPa. The fatigue properties of the specimens are higher than those for the 500-MPa grade steel bars. The fatigue fracture of the specimens consists of a fatigue source zone, crack propagation zone, and transient fracture zone. Microscopically, it is a cleavage fracture in the crack propagation zone; it is micropore aggregation fractures in the instantaneous fracture zone. At a given fatigue life, the fatigue stress range decreases as the stress ratio increases. The fatigue properties of the specimens are better at a higher stress ratio with the same maximum stress.

The shear strength and stiffness characteristics of steel slag indicate that it can potentially be utilized as a competent base/subbase material of bound and unbound pavement layers. However, concerns with respect to the utilization of steel slag remain due to its long-term swelling, corrosivity, and leaching characteristics. In this study, long-term swelling and corrosivity tests were performed on basic-oxygen-furnace steel slag (BOFSS) and electric-arc-furnace ladle steel slag [EAF(L)SS] generated in Indiana, USA. In order to reduce the 1D swelling strains of these slags, 5%, 10%, and 20% Class C fly ash (CCFA) and 10% ground rubber replacement ratios were used to prepare steel slag mixtures for testing. The improvement due to CCFA replacement was evaluated by performing unconfined compression and long-term swelling tests on selected steel slag–CCFA mixtures. The seven-day unconfined compression strengths of 90% EAF(L)SS + 10% CCFA and 90% BOFSS + 10% CCFA mixtures were 2,387 and 3,768 kPa, respectively. After nine months of monitoring, the maximum 1D swelling strains of soaked samples of BOFSS and EAF(L)SS mixtures prepared with 10% CCFA replacement were 0.1% or less. The unconfined compression and swelling test results for the steel slag–CCFA mixtures indicated superior strength gain characteristics and negligible swelling strains with time than for steel slags.

This paper presents a high-tensile-strength engineered geopolymer composite (EGC) reinforced by polyethylene (PE) fibers. The influences of fiber dosage (1.5%, 1.75%, and 2.0%) and length (6, 12, and 18 mm) on the mechanical properties and strain-hardening performance of EGCs were examined. The results indicated that increasing either fiber dosage or length decreases the flowability of EGC due to the skeleton formed by fibers. The increase of fiber dosage from 1.5% to 2.0% enhanced the fiber bridging effect in the EGCs with 12-mm PE fibers and subsequently enhanced their compressive and tensile strengths by 9.0% and 12.7%, respectively. Differently, the increase of 18-mm fiber dosage from 1.5% to 2.0% introduced more voids inside the EGCs, which decreased their compressive and tensile strengths by 3.8% and 3.6%, respectively. Fiber clusters were more likely to occur in EGC with a higher dosage of longer fibers, which reduced its tensile strength. A higher fiber dosage improved both tensile strain capacity and crack control capacity of EGC. On the other hand, increasing the fiber length from 6 to 18 mm increased the tensile strength by 42.0%, strain capacity by 148.0%, and crack control ability of EGC by enhancing the fiber-bridging effect, although it was detrimental to the compressive strength of the EGCs with 18-mm fibers due to the magnified air-entrapping effect. In addition, a prediction model modified based on the test results can accurately predict the tensile strength of PE fiber–reinforced EGCs. The environmental assessment indicated that the developed EGCs exhibit dramatically lower environmental impacts than the conventional engineered cementitious composite.

Long-term vapor exposure generates persistent moisture gradients across asphalt pavement sections, driving moisture diffusion into asphalt concrete (AC). Moisture in AC weakens the materials and exacerbates the action of load, causing premature distress such as cracking in pavement. However, few investigations have focused on the effects of long-term vapor exposure on AC’s fracture performance. We approached this issue by simulating the fracture process of AC experiencing long-term vapor exposure under an indirect tensile load. The cohesive zone model (CZM) was introduced to depict the fracture process. We calibrated the CZM model by minimizing the difference between simulation and laboratory measurements. The results showed that long-term vapor exposure lowered the bonding strength in AC, accelerating the cracking initiation and propagation. The damage distribution showed that the interface between aggregates and mortar was more prone to damage since it bore more stress than the bulk of the asphalt mortar. This study reveals the fracture performance of AC under long-term vapor exposure, which helps develop measures to prevent premature cracking in the pavement and prolong the service life.

Spray-based three-dimensional (3D) concrete printing is an innovative method to automatically construct structures on vertical and overhead surfaces, which contributes to less labor investment and construction time. On the other hand, expanded graphite is widely known for its high thermal and electrical conductivity as a lightweight ingredient, and thus its potential in functional cementitious materials has been gradually realized in recent years. In this study, a lightweight cementitious material containing expanded graphite has been developed specifically for spray-based 3D concrete printing with added values. Through the characterization and overall evaluation of densities, mechanical and rheological properties, and Joule-heating performance, the appropriate expanded graphite content was determined as 1% by weight of cement. Afterward, silica fume was introduced into the matrix to tailor the rheological properties of the mixtures. The subsequent spray-based printing showed that the tailored mixture had significant improvements in the building capacity and spray quality. On the other hand, it also possessed superior Joule-heating performance than the control mixture without expanded graphite. The potential engineering applications of the developed material include deicing and structural health monitoring, and the compatibility with spray-based 3D concrete printing provides extra values of higher construction efficiency and adaptivity to the structures of complex contours.

This paper presents a study of the tensile behaviors of textile grid–reinforced engineered geopolymer composites (TR-EGCs) using both experimental and numerical methods. EGC is a novel ecofriendly fiber-reinforced geopolymer composite that exhibits ultrahigh ductility under tensile loading conditions. In this paper, the ambient cured EGC with local polyvinyl alcohol (PVA) fiber was designed and the mechanical behaviors of the EGC were investigated. Direct tensile tests of TR-EGC specimens were conducted and compared with those of conventional textile-reinforced mortar (TRM). It was found that the load-carrying capacity of TR-EGC with carbon fabric was 5.72 times greater than that of TRM. The influences of alkali concentrations and textile types on the tensile behaviors of TR-EGC are discussed. It was found that the increase of alkali concentration is beneficial to the tensile strength of EGC and TR-EGC. In contrast, the tensile ductility decreased gradually as the alkali concentration increased from 4 to $12\mathrm{mol}/\mathrm{L}$. A finite-element (FE) model is proposed to model the tensile behaviors of TR-EGC specimens, which was verified using the experimental results. Because the current calculation method significantly underestimated the composite behaviors of the EGC and the inner textile, a new calculation method is proposed. It was found that the proposed calculation method is more accurate in predicting the tensile load–carrying capacity of TR-EGC, although more experiments and numerical analyses with in-depth discussions still need to be conducted.

The individual effect of sodium hydroxide (NaOH) and magnesium chloride (${\mathrm{MgCl}}_2$) on the performance of magnesia-based cement is the main focus of this study. Different magnesium oxide–glass waste (MgO–GW) mixtures of $\mathrm{MgO}\text{-}\mathrm{to}\text{-}{\mathrm{SiO}}_2$ molar ratios ($\mathrm{MgO}/{\mathrm{SiO}}_2$) of 1, 2, and 3 were prepared and characterized. The results revealed that the mixture having $\mathrm{MgO}/{\mathrm{SiO}}_2=2$ showed the best performance at all curing ages. The addition of 3% by weight NaOH significantly enhanced the mechanical properties of the MgO–GW mixture at $\mathrm{MgO}/{\mathrm{SiO}}_2=2$. Further addition of NaOH (5% and 7% by weight) caused a notable reduction in the compressive strength values, suggesting the negative effect of high NaOH content on the binding capacity of the produced binder. Increasing the ${\mathrm{MgCl}}_2$ content up to 5% by weight improved the performance of the fabricated cement; meanwhile, the addition of 7% by weight ${\mathrm{MgCl}}_2$ showed the lowest effect. Furthermore, pH is regarded as the key point that affects the performance of magnesia-based cement materials. Two hydration mechanisms were identified, depending on the type of chemical admixture. NaOH increased the pH of the cementitious system, accompanied by speeding up the formation rate of magnesium silicate hydrate (M-S-H) through the improvement of the dissolution of the silicate network within the GW material. Another mechanism was detected in the ${\mathrm{MgCl}}_2–\mathrm{MgO}–\mathrm{GW}$ composite, in which an extra magnesium oxychloride phase (Phase 5: $5\mathrm{Mg}(\mathrm{OH}{)}_2·{\mathrm{MgCl}}_2·8{\mathrm{H}}_2\mathrm{O}$) was formed besides M–S–H, yielding hardened samples with the highest mechanical properties. Hence, the results herein show that desirable NaOH and ${\mathrm{MgCl}}_2$ contents enhance the feasibility of utilizing GW to produce a high-performance, eco-friendly binder.

Abstract

This study analyzed the influence of asphalt binder nanostructures and inherent variability on their mechanical responses. This was achieved by reconstructing asphalt binder nanostructures using generative adversarial networks (GANs). GANs are able to detect hidden patterns in a given data set automatically, and they generate distribution-free data because they are not bound to specific probability functions. The mechanical responses of GANs-generated nanostructures were analyzed using finite-element (FE) analysis. The asphalt nanostructures were captured using atomic force microscopy (AFM). To overcome the limited number of AFM nanostructures, image augmentation techniques and stochastic random fields (RF) modeling were used to generate virtual images of asphalts’ nanostructures, which were utilized as the expanded training data set for the GANs. This approach helped to enhance the GANs’ generalization abilities and avoid training problems such as mode collapse. Modeling parameters were optimized to expedite the training process and reduce the computational time. The results demonstrated that GANs are capable of generating probable arrangements of nanostructures, thus expanding the body of knowledge regarding probabilistic analysis of asphalt mechanical behavior. The ability of GANs to reconstruct nanostructures indicates that the complex and variable nature of asphalt nanostructures can be identified and replicated by GANs, offering the opportunity to generate many replicates of nanostructures without the need to conduct many laboratory tests. The results successfully related the properties and distribution of the asphalt nanostructures to the variation in the mechanical response.

Practical Applications

This study proposes a methodology that combines aspects of AFM testing, GANs modeling, and FE modeling for the analysis of the mechanical response of asphalt binder nanostructures. The outcomes of this work link nanoscale properties to bulk properties. Consequently, practitioners and researchers can use the developed methodology to study uncertainty in mechanical response of asphalt binders and design blends with tailored properties and enhanced performance. Researchers also can benefit from this methodology to incorporate sustainable modifiers that enhance fundamental nanoscale properties of asphalt binders. Moreover, this work enables computational evaluation of various material designs that would be impractical to conduct in a laboratory environment, thus conserving resources. Finally, the methodology can be generalized to study nanostructures of other engineering materials to optimize their performance.

Dynamic mechanical analysis (DMA) applies an oscillating force to a specimen and analyzes the rheological and viscoelastic properties of a material. Since this method is used to characterize the frequency-dependent viscoelastic properties, it is mostly used for polymers, which have high sensitivity to the loading frequency. Cementitious composites are brittle and require more attention to specimen preparation and experimental settings to obtain reliable results. This work develops a DMA test protocol for cementitious composites which includes analyzing the effect of preload test, frequency pretest, and amplitude sweep on properties of cementitious composites. We propose a statistical method to analyze the variation between samples and determine the outliers among the specimens with the same mix to obtain valid test results from a sample group. The dynamic results obtained by using the proposed method are also discussed to serve as the baseline. The experimental setup parameters and statistical analysis presented in this work can be a robust foundation for the DMA analysis of cementitious composites.

In the precast concrete industry, steam curing is commonly used to accelerate early-stage strength development. Recently, ${\mathrm{CO}}_2$ curing also claims to offer advantages, including mitigating the ${\mathrm{CO}}_2$ burden and anticipating fast curing for cementitious materials. However, to the best of our knowledge, the environmental impacts of these fast-curing methods, compared with standard curing methods, have not been critically justified yet. In this study, a comparative evaluation for both dry-mix and wet-mix cement pastes adopting different curing methods was performed by life-cycle assessment (LCA), which is a commonly used evaluation method for the sustainability of concrete. The environmental impacts of each group, including global warming potential (GWP), ecosystem quality potential (EQP), and human health potential (HHP), were quantified. According to the results, adopting both ${\mathrm{CO}}_2$ or steam curing could reduce greenhouse gas (GHG) emissions by 20%–50% concerning the standard curing for both dry-mix and wet-mix cement pastes. Instead of purified ${\mathrm{CO}}_2$ gas, adopting flue gas for ${\mathrm{CO}}_2$ curing could further reduce GHG emissions by up to 80%. Comparing the GWP/strength ratio over the investigated times, the ${\mathrm{CO}}_2$ curing method exhibited the highest environmental benefits in the first 3 days of curing. Moreover, the use of renewable energy sources and flue gas carbonation will significantly reduce the environmental impact of ${\mathrm{CO}}_2$ and other GHG and add to the sustainability aspect by utilizing renewable resources and waste.

Calcium silicate aluminate hydrate (C-A-S-H) is the main hydration product of cement mixed with industrial wastes. The purpose of this study is to understand the dynamic mechanical behavior and structural transformations of molecular-scale C-A-S-H induced by shock waves. Three C-A-S-H models with Al/Si ratios of 0.0, 0.1, and 0.2 are constructed and reactive molecular dynamics simulations are used to perform shock compressions with different shock velocities from $0.1\mathrm{km}/\mathrm{s}$ to $3.6\mathrm{km}/\mathrm{s}$. The distributions of particle velocity, pressure, and density along the shock direction are calculated using the binning analysis method, allowing Hugoniot pressure-specific volume curves to be derived. The results reveal that shock waves may induce elastic, elastic-plastic, or shock Hugoniot responses in molecular-scale C-A-S-H, depending on the Al/Si ratio and the shock velocity. Below the Hugoniot elastic limit (HEL), higher Al/Si ratios cause the elastic wave to propagate farther due to the cross-linking effect of aluminate units. Above the HEL, higher Al/Si ratios give rise to a distinct two-wave structure characteristic comprising a plastic front and an elastic precursor. This characteristic becomes less pronounced as the shock velocity increases. Analysis of the molecular structural transformations of C-A-S-H revealed that the main atomic deformation behavior below the HEL involves a reduction of interatomic distances; above the HEL the main response is a densification of water molecules followed by a general collapse of the layered structure as the shock velocity increases.

The load-transfer mechanism in the fiber-reinforced polymer (FRP) bars is different from that of the conventional steel bars. The efficiency of stress transfer in FRP bars mainly depends on the mechanical properties of matrix resin, fibers, and fiber/matrix interface, which are easily degraded after long-term exposure to concrete environment. Herein, the interlaminar shear properties of a novel carbon/glass hybrid fiber-reinforced polymer (C/G-HFRP) bar were experimentally investigated by the accelerated aging tests at 60°C to study the effects of the ratio of carbon to glass fiber volume fractions, distribution configuration of carbon fiber, total fiber volume fraction, exposure environment, and exposure period. Water uptake tests, scanning electron microscopy, and Fourier transform infrared spectroscopy were employed to explore the degradation mechanisms of exposed samples. The results indicated that the interlaminar shear strength (ILSS) retention of exposed C/G-HFRP bars was higher than that of the single glass-FRP bar, which was decided by tooth force and friction. In addition, the degradation of C/G-HFRP bars was also related to water uptake rate, and then waterproof coating and fiber modification are recommended to improve the durability of C/G-HFRP bars. Finally, a model of ILSS retention was proposed for the C/G-HFRP bars after exposure to different concrete environments.

Expansive reactions such as delayed ettringite formation (DEF) can lead to mechanical and microstructural changes in concrete, resulting in considerable damage to the structures. DEF usually occurs in concrete that has reached a high temperature after being exposed to moisture. This paper presents the assessment of concretes with and without pozzolan in laboratory in order to monitor and evaluate expansions, as well as their main properties and characteristics over a period of 12 months, after undergoing DEF at a temperature of 85°C and with drying-wetting cycles. An increase in expansion caused by DEF was tracked through a series of microscopical observations, along with evaluations of concrete deterioration. Additional tools, such as the stiffness damage test (SDT) and deteriorated damage index (DRI), were also employed in the experiments. Furthermore, an overall approach to DEF was adopted, together with a performance appraisal based on data from the research program and a detailed analysis to quantify the extent of the damage to concretes and to estimate the different deterioration levels.

Abstract

In RC structures during construction, the bond behavior of deformed bars in concrete is governed by the age-related concrete strength, the local confining pressure, the bar diameter, and the concrete cover thickness. In this paper, an experimental investigation was performed to quantify the influences of the curing age and the bilateral pressure on the bond behavior of deformed bars in early-age concrete with 204 pull-out specimens for different concrete strengths, bar diameters, and relative concrete cover thicknesses. It was shown that the failure mode was associated greatly with the age-related concrete strength, the concrete cover thickness, and the pressure level, and that the bond strength increased with the pressure level and curing age, whereas the corresponding slip decreased with the curing age. Based on the regression analysis, calculation models were developed to predict the ultimate bond stress and the corresponding slip. A bond–slip model is proposed to describe the bond stress–slip relationship of deformed bars in early-age concrete under bilateral pressures, and the model was verified with the test results.

Practical Applications

For RC structures, there is experimental evidence that the lateral pressure around the bond region has a great effect on the bond behavior of deformed bars in concrete. From an engineering practice perspective, the early-age bond behavior of deformed bars in concrete under bilateral pressures plays an important role in the structural analysis of RC structures during construction, and is very meaningful for the entire life-cycle modeling of RC structures. In this study, an experimental investigation was conducted to predict the failure mode and bond parameters, and to propose a universal bond–slip constitutive model of deformed bars in concrete under bilateral pressures. The good agreement between the model predictions and the experimental results shows that the proposed bond–slip model can be used effectively for the design and reliability assessment of RC structures during construction, and therefore demonstrates the potential of the proposed bond–slip model in the entire life-cycle analysis for practical applications.

The theory of viscoelastic collision mechanics is used to explore the rebound and adhesion mechanisms of single aggregates in shotcrete at the meso-level in this study. Abrasive balls with different radiuses were used, fully considering the characteristics of the aggregates and the sprayed wall, to build multifactor physical models for the shotcrete rebound of the aggregate. The movement trajectories, velocities, and energy dissipations of abrasive balls are analyzed, and the shotcrete-rebound mechanical model of a single aggregate based on wet-mix shotcrete is proposed. The results of the study show that there are obvious differences in the rebound velocity of the aggregate in different collision forms, and the viscoelastic properties of aggregates affect the jet stability of wet-mix shotcrete. According to the quantitative and qualitative analyses, the energy loss during the collision-rebound of the aggregate is inversely proportional to the rebound velocity and proportional to the rebound resistance. The functional relationship between the resistance $F$ and the particle radius $R$ during the rebound and adhesion of aggregate can be expressed as $F=C{R}^{1/5}$, where $C$ is a constant.

Abstract

Quantifying recycled asphalt binder availability in recycled asphalt pavement (RAP) mix design is very essential, as the widely adopted 100% RAP binder availability assumption in RAP mix design never holds correct. Depending on the mix production condition, recycled binder stiffness, and virgin binder properties, the degree of binder availability in the mix is always partial. The present study proposes a simple procedure to estimate the degree of recycled binder availability in RAP mix design. In the proposed methodology, the designer needs to compare optimum binder content of bituminous mixes prepared using white rock aggregate gradation and virgin aggregates, along with mixes designed by blending black rock gradation and virgin aggregates blended in proportion to achieve the target white rock gradation. The binder content in the RAP fraction used in the blending exercise was determined using ignition oven method. RAP mix designs were performed for RAP material collected from two different sources, and design was performed for three mixing durations in a laboratory pug mill—60, 120, and 180s. The mixes were prepared with 50% RAP incorporation level. RAP material was conditioned at 110°C for 2 h, whereas virgin aggregates were superheated to 175°C. Using the methodology proposed, RAP binder availability was found to vary between 92.5% and 96.6% for softer RAP material, 75.9% to 91.5% for mixes incorporating stiffer RAP. With increasing mixing time, even though the total active binder content did not change significantly, a mixture performance test quantified the implication of increased RAP binder availability in mixes. A higher degree of binder activation resulted in mixes being rut resistant, while the same mixes exhibited relatively higher cracking susceptibility.

Practical Applications

Recycling of bituminous mixes has been considered as one of the sustainable practices in the highway construction industry. In a recycled bituminous mix, the milled material contributes good quality aggregates, and aged bituminous binder. The amount of aged bituminous binder that can be mobilized in the recycling process largely depends on mix production condition, milled, and virgin material property. The paper presents a simple methodology to quantify the degree of bituminous binder which becomes available in recycled mix design. The methodology can be used by mix designers to account for appropriate adjustment in virgin binder grade selection. The knowledge of degree of binder availability would also enable, if one targets to synthesize recycled mixes of a definite binder content. The paper also investigated the implication of different degree of binder availability on mix performance, arising due to different mixing time (production condition) and milled material property.

This study investigated chloride binding and corrosion of carbon steel in calcium sulfoaluminate (CSA) cement concrete exposed to external chloride solutions. CSA pastes and concrete specimens were prepared using three water-to-cement ratios ($w/c$) (0.4, 0.5, and 0.6) followed by wet and air curing for 55 days. Ordinary portland cement (OPC) paste and concrete specimens also were prepared and analyzed for comparison. The primary hydration product of CSA was ettringite, and its quantity increased with the increase in $w/c$. Compared with OPC, the CSA pastes had a significantly lower chloride binding capacity and higher porosity, exhibiting poor performance in protecting the steel embedded in the concrete. In general, considering the compressive strength, chloride binding, and corrosion, air-cured CSA concrete performed worse than wet-cured CSA concrete.

Reclaimed asphalt pavement (RAP) mixtures consist of clusters of aggregates bonded together by the aged asphalt. Declustering of RAP particles during new asphalt mixing changes the gradation of the mixture, which affects the performance of the new asphalt mixtures containing the RAP. In this study, RAP materials with different degrees of clustering were used to make new Superpave mixtures. The degree of clustering in each RAP material was associated to its gradation change before and after the asphalt extraction. The Hamburg wheel tracking device (HWTD) was used to evaluate the rutting and stripping performance of the asphalt mixtures at regular and elevated temperatures. Finally, statistical analyses were performed to evaluate the relationship between the HWTD test performance and the degree of clustering of the original RAP material. The research results showed that clusters of the original RAP material has a negative impact on rutting and stripping performance of asphalt mixtures with a nominal maximum size of 9.5 to 25 mm. The impact is most evident under the HWTD test at elevated test temperatures.

An examination was undertaken on the alkali-silica reaction (ASR) in alkali-activated slag (AAS) mixtures in comparison with ordinary portland cement (OPC) mortars and concretes. The ASR expansion in AAS mortars and concretes with different alkali contents (5%, 6%, 7%, and 8%) was examined. Changes in mechanical properties (compressive strength, tensile strength, and flexural strength) resulting from ASR expansion were evaluated. A correlation was sought between the changes in the mechanical properties of mixtures caused by ASR and ASR expansion. The test results revealed that the ASR expansion of all AAS mixtures was less than that of OPC mixtures. The expansion of AAS mixtures was below the threshold value established by the standard specifications. Additionally, it was possible to use mechanical properties to assess the occurrence of ASR due to the significant drop in these parameters caused by ASR.

Concrete tends to develop cracks once damaged, and wide cracks specifically would affect the whole structure negatively. When used for repairing wide cracks, traditional cement-based grouting materials could no longer meet the demand for tensile strength. The paper aims to develop a high-performance grouting material for crack repair and further investigate its fluidity, and compressive strength, flexural strength, and splitting tensile strength after hardening. Based on the design of ultrahigh-performance concrete (UHPC), this grouting material consists of cement, sand, water, superplasticizer, expansion agent, silica fume, fly ash, and flat copper-plated steel fiber. The initial fluidity and 30-min fluidity of the grouting material decreased with the addition of fly ash, silica fume, and flat copper-plated steel fiber, among which the silica fume had the greatest influence on the fluidity, followed by fly ash and steel fiber. The optimal content of flat copper-plated steel fiber, fly ash, and silica fume was 2%, 10%, and 15%, respectively. Furthermore, the prediction model of compressive strength of grouting material was established. It indicated that cement grade, water-cement ratio, curing age, silica fume, fly ash, and flat copper-plated steel fiber and can be used for the mix proportion design of grouting materials.

Styrene-acrylic emulsion (SAE)-modified mortar is typically used as an impermeable cement-based material. Although high-volume SAE-modified mortar shows excellent penetration resistance performance, this property can also cause compressive strength loss. In this work, sodium oleate (SO) is used as a hydrophobic agent to enhance the antipermeability of mortar with low SAE content. The influence of the incorporation of hydrophobic agent on the mechanical properties, hydration characteristics, water absorption, and impermeable and hydrophobic properties of low content polymer emulsion-modified cement mortars was investigated. The results show that the mortar with 5% SAE and 1% SO has better impermeability, hydrophobicity, and compressive strength than a mortar with 15% SAE only, which is attributed to the physical barrier of SAE and the hydrophobicity of SO. SO works well with 5% SAE-modified mortar, and the improvements in all aspects of the performance are greater than that of the high content SAE-SO–modified mortars. However, increasing the amount of SO will not bring continuous improvement in antipermeability, as the air-entraining effects of SO increase the porosity of the matrix.

Postfire mechanical properties and fracture resistance of G20MnQT cast steels were investigated experimentally and effects of different cooling procedures were studied. G20Mn5QT cast steels were heated to 600°C, 700°C, 800°C, and 900°C and cooled to ambient temperature in air or in water. Metallographic examination found significant phase transformations only in G20Mn5QT cast steels cooled quickly in water from elevated temperatures of 800°C (800W) and 900°C (900W). Original ferrite and pearlite transformed to harder phases, such as martensite and bainite, in these two postfire materials. Vickers hardness tests, Charpy impact tests, and tension coupon tests were conducted on original and postfire G20Mn5QT cast steels. All test results confirmed the findings about phase transformation in metallographic examination. The martensite and bainite generated in phase transformation caused significant hardening of 800W and 900W. With no significant phase transformation, most mechanical properties of 600A, 600W, 700A, 700W, 800A, and 900A varied within $\pm 15\%$ compared with those of the original material, and the postfire Charpy impact energies increased moderately due to improvement of material homogeneity. Smooth notched tensile specimens were tested and material parameters in the void growth model were calibrated to evaluate the postfire fracture resistance of G20Mn5QT cast steels at high stress triaxialities. It was found that the fracture of 600A, 600W, 700A, 700W, 800A, and 900A was almost as ductile as that of the original G20Mn5QT cast steels, whereas 800W and 900W fractured brittlely, and had fracture resistance 87.6% and 78.4% lower than that of the original material.

Densified wood (DW) dowel is worth considering as an alternative to steel rod for timber joints with glued-in rods, because it is more naturally harmonized with timber members, and has better resistance against corrosion and lower thermal conductivity. This paper compares the pull-out performance of timber joints with glued-in DW dowels to that of threaded steel rods, loaded parallel to the grain in two ambient environments with a temperature of 20°C and relative humidity (RH) of 65%, and with a temperature of 20°C and relative humidity of 85%. After being conditioned at a temperature of 20°C and relative humidity of 65%, the pull-out capacity of the glued-in DW dowels having an anchorage length of 10 times the dowel diameter was close to 75% of that of the glued-in threaded steel rods. The impact of service environment was found to be greater for the timber joints with glued-in threaded steel rods than the timber joints with glued-in DW dowels.

Polymer-modified fast-hardening cement mortar is widely used as road repair material due to its excellent performance attributes of shorter setting time and good workability as well as high adhesive strength. However, in the complex actual service environment, whether it can still maintain stable performance has become a concern. Therefore, this study performed an indoor freeze–thaw cycle test to investigate the frost resistance of polymer-modified fast-hardening cement mortar under winter climate conditions in Lanzhou. The macro properties of the fabricated mortar were characterized by compressive strength and flexural strength, and the microstructures were investigated by MIP, FTIR, and SEM. It was found that with increasing polymer doses, the frost resistance of the fast-hardening cement mortar was improved, and the flexural strength increased gradually, but the compressive strength showed an opposite evolutionary trend. The overall performance of mortars was best when the content of polymer admixture was 4%, by mass, of the cementitious material. In addition, the polymer significantly refined the pore structure in the range of 3–10 nm, which made the total porosity of the system increase. Meanwhile, the polymer could be involved in the chemical reaction to generate polymer film and interlap with the needlelike ettringite (AFt) to form a spatial network structure, as shown by FTIR and SEM analysis. This means that incorporating polymer 5010N improved the microstructure of the fast-hardening cement mortar, leading to improved frost resistance.

The rapid increase in the generation of industrial ash alerted the authorities to seek efficient management of this harmful waste. This research seeks an entirely new use of industry ash to manufacture bricks. While brick is the most prominent construction product worldwide, the brick manufacturing industry cannot deliver the increased demand due to a new challenge: clay shortage. Two different industry waste ash types (IWA 1-CaO rich and IWA $2\text{-}{\mathrm{SiO}}_2$ rich) were tested at different percentages of 10%, 20%, and 30% (by weight) for their suitability in manufacturing bricks. Compressive strength, water absorption, the initial rate of absorption, thermal conductivity test, 3D-CT scanning, scanning electron microscope analysis, x-ray diffraction analysis, x-ray fluorescence analysis, salt-resistance test, and heavy metals leaching test were performed to determine the physical, chemical, mechanical, durability and leachate characteristics of waste reformed bricks and to ascertain the product compliance of the lab prototype. The results indicated that the novel brick product manufactured from industrial waste can be superior to control brick (0% of waste ash) in thermal characteristics and compressive strength while achieving essential compliance requirements satisfying national standards. The thermal conductivity of ash reformed bricks was 40% lower compared to standard bricks when 30% ash is mixed into the composition. In addition, the maximum compressive strength of 72.53 MPa was achieved with the addition of 10% IWA 2 at a firing temperature of 1,050°C. The outcomes from this project could potentially provide a sustainable product for the brick industry, which has exponential demand in the current market, while resolving a growing solid waste catastrophe and clay shortage.

The surface performance of basalt aggregate shows a great influence on the interfacial adhesion between basalt aggregate and asphalt binder and further affects the moisture stability of the asphalt mixture. To improve the interfacial adhesion between basalt aggregate and asphalt binder, as well as to increase the moisture stability of asphalt mixture in hot and humid environments, the basalt aggregate surface was hydrophobically modified by silane coupling agents (SCAs). Microscopically, the surface properties of basalt aggregate before and after surface modification by SCAs were characterized by environmental scanning electron microscope and Fourier transform infrared spectrometer, as well as the adhesion work between basalt aggregate and asphalt was calculated. Macroscopically, the moisture stability of the asphalt mixture was verified by boiling test and asphalt mixture tests. Test results indicate that the surface free energy values of basalt aggregates modified by SCAs and the stripping work values are decreased. Additionally, silanols, hydrogen bonds, and fibrous protrusions are introduced to the aggregate surface for improving the compactness of the asphalt-aggregate system. Finally, the loss rates of asphalt film and immersion scattering are decreased, as well as the freeze-thaw splitting tensile strength ratio is increased. The hydrophobic surface modification of basalt aggregate can enhance the moisture stability of the asphalt mixture.

There has been an ever-climbing trend toward environmental concerns in addition to road technical issues, resulting in the testing of new high-quality pavements. First, due to the presence of acidic contaminants in surface runoffs in developed areas rooted in acid rainfall, researchers have discovered that these polluted runoffs can pollute groundwater reserves and are harmful to humans. Second, the porous asphalt (PA) mixtures as a hot mix pavement with an empty space structure have significant performance limitations such as low strength and durability because of their large amount of air voids. Therefore, a novel high-quality and photocatalyst PA pavement with the ability to absorb contaminants from acidic water was introduced at the lab scale in this study. For this aim, PA mixes modified with photocatalytic nanoparticles such as nano zinc oxide (ZnO) and nanosilica (${\mathrm{SiO}}_2$) were fabricated. The sol-gel method was used to manufacture photocatalytic based on $\mathrm{ZnO}/{\mathrm{SiO}}_2$ (ZS) in this research. The aforementioned compound reacts with UV light and oxidizes pollutant particles, including nitrogen oxides (${\mathrm{NO}}_{\mathrm{x}}$) and sulfur oxides (${\mathrm{SO}}_{\mathrm{x}}$). This novel PA mix was tested by environmental tests (pollutants absorption) and mechanical performance tests (dynamic creep, resilient modulus, moisture susceptibility, and fatigue life). The results demonstrated that adding the photocatalytic nano-ZS to the bitumen effectively removed acidic contaminants such as ${\mathrm{NO}}_3$ and ${\mathrm{SO}}_4$ from the water by an average of 48% in 24 hours. Besides, results showed that the addition of nano-ZS increased the moisture susceptibility and stiffness of PA mixtures by an average of 45% and caused a dramatic improvement in the rutting resistance of mixes. Moreover, nano-ZS-modified PA mixes had longer fatigue lives than conventional ones. It should be noted that the optimum amount of nano-ZS in PA mixes in this study was 7%.

As an important stage in the three-stage dispersion system of asphalt mixtures, the structure and properties of asphalt mastics have a significant impact on the road performance and dielectric properties of asphalt mixtures. With changes in atmospheric temperature, the polarization process of the asphalt mixture is affected, and the dielectric constant changes. In this study, the dielectric properties of asphalt mastics and their single-phase media at different temperatures were studied, and the changes in the dielectric properties were analyzed using infrared spectroscopy, scanning electron microscopy, and a synchronous thermal analyzer. Finally, a dielectric model of the asphalt mastics considering the temperature effect was established. The results show that the dielectric constant of asphalt mastics increases with an increase in the filler-bitumen ratio, and the dielectric constant of bitumen, block, limestone filler, and asphalt mastics increases linearly with an increase in temperature. The combination of bitumen and filler does not produce new functional groups and chemicals, and the dielectric constant gradually increases during the transition from the glassy state to the viscous flow state. A dielectric model of asphalt mastics that considers the temperature effect was established by introducing the temperature influence factor. Compared with the classical dielectric model, the proposed model shows higher accuracy. Compared to the test results, the relative error was less than 5%. This study provides a basis for the study of dielectric models of asphalt mixtures in complex climates and further improves the accuracy of ground penetrating radar in the nondestructive testing of asphalt pavement.

Carbon fiber–reinforced polymers (CFRPs) deliver positive outcomes compared with traditional steel retrofitting techniques. This study aims to determine the effect of underwater exposure condition and different temperatures along with the exposure duration on the performance of the CFRP/steel bond. A series of experimental investigations were conducted for CFRP strengthened steel test coupons subjected various exposure conditions for a period 300 days. Specimens were subjected to various environmental conditions, including (1) distilled water at room temperature, 20°C, and 35°C, and (2) natural seawater at room temperature, 20°C, and 35°C. Tensile tests were conducted out to determine the bond strength and failure patterns of the composite at 75-day regular intervals for a duration of 300 days. Noticeable reductions in bond strength were recorded for all specimens after environmental aging when compared with that of the initial. Prolonged exposure to higher temperatures exhibited the greatest decline of 48%, whereas that under lower temperatures were affected to a lower degree. Overall, the failure modes showed the impact of the adhesive strength on the composite joint capacity.

The fabric-reinforced cementitious matrix (FRCM) has begun to show great application prospects in structural strengthening, especially for seismic strengthening. However, a poor monolithic response of fabric and mortar limits the utility ratio of the fabric and the mechanical properties of FRCM. A simple, fast, and efficient method for improving the bonding properties of the fabric–mortar interface to enhance the performance of the FRCM plate remains to be investigated. In this study, uniaxial tensile tests on 42 carbon fabric-reinforced cementitious matrix (C-FRCM) plates with anchored carbon fiber bundles were performed to analyze the influence of anchorages on their mechanical properties, and to compare them to the prior results of pull-out tests of anchored carbon fiber bundles. The results show that the ultimate tensile stress, the energy dissipation, and the fiber utility ratio can be increased significantly after anchoring, but the anchorage cannot fully restrict the slippage of fiber fabrics. The effect of other variables, such as the bond length of steel plates, the number of fabric layers, and mortar strength, were also tested and discussed.

An efficient method to produce ecoefficient cementitious mixtures is using particle packing models (PPMs) combined with limestone fillers (LF). Yet, key outcomes obtained in the fresh and hardened states, including slump and compressive strength, are variable and remain mostly not fully understood. Therefore, in this work, the concept of interparticle separation distance (IPS) is employed to describe the overall performance of ecoefficient cement paste mixtures with high LF dosages [up to 81% of ordinary Portland cement (OPC) replacement]. In this scenario, twenty-one cement paste mixtures displaying three water-to-powder ratios (0.32, 0.40, and 0.50), two distribution factors ($\mathrm{q}=0.21$ and 0.37), and three cement contents (100, 150, and ${250\mathrm{kg}/\mathrm{m}}^3$) were studied. Next, fresh-state properties (i.e., rheological profile and slump flow over time) along with compressive strength were appraised. Densely packed systems containing moderate to high LF dosages have shown to yield better compressive strength results than pure OPC mixtures, yet the inclusion of LF negatively influenced the cement paste mixtures’ slump loss. Thus, the $\mathrm{w}/\mathrm{p}$ (i.e., in mass) combined with the $\mathrm{w}/\mathrm{c}$ ratio from Abram’s law was successfully observed as an important parameter to better predict the compressive strength performance of the ecoefficient cement pastes. Results suggest that the fresh state behavior of packed mixtures containing high LF content can be predicted through the IPS/dp; therefore, this parameter might be adjusted to reach targeted viscosity values when proportioning cementitious materials. Finally, the concept of ${\mathrm{IPS}}_{\mathrm{cement}}$ is proposed to precisely describe fresh and hardened properties of cementitious mixtures with significant dosages of LF and reduced OPC contents.

This study sheds light on the analysis of the thermodynamic properties of the asphalt-aggregate interface under the modification of low-dimensional carbon nanotubes (CNTs) with styrene-butadiene-styrene (SBS) copolymers through molecular modeling techniques, and mainly addresses the following queries: How do asphalt, modifiers, moisture, and mineral molecules interact with each other? What are the regulations of the thermodynamic properties and energy conversions in asphalt-aggregate systems, especially in the presence of oxidation and moisture? How does the failure pattern and bond strength of the asphalt-aggregate system modified by CNTs develop under tensile forces? Supported by molecular dynamics (MD) simulation approaches, molecular models such as 12-component asphalt, three mineral components (CaO, ${\mathrm{SiO}}_2$, and ${\mathrm{Al}}_2{\mathrm{O}}_3$), long-chain SBS copolymer, and CNT tubular were developed for subsequent calculations. The surface energy of each component of the asphalt-aggregate model was determined at the molecular scale to quantify the intermolecular forces between the components and the integral tensile strength of the molecular structure. The effectiveness of aging behavior and moisture on thermodynamic properties and failure patterns of asphalt-aggregate systems containing polymer/CNT composites was evaluated. The results suggested that CNT molecules can promote the intermolecular interaction forces and interfacial energies at the asphalt-aggregate interfaces. The oxidative aging caused a degradation of the surface energy, cohesion energy of the asphalt modified by SBS/CNT additives, and leaded to complicated response on adhesive energies at asphalt-aggregate interface. The combination of alkaline mineral (CaO) and CNT was beneficial in decreasing the moisture susceptibility of the asphalt mix. The failure pattern was in cohesive cracking form within the asphalt and the bond strength was enhanced by CNTs. The increase in temperature weakens the intermolecular energies of the asphalt-aggregate system and its bond strength. This paper provided an explanation for the molecular energy conversion and the mechanical enhancement mechanism of low-dimensional CNTs in petroleum asphalt-based composites.

Train vibrations can travel through the track, tunnel structure, and surrounding strata as well as into the structure of buildings near tunnels, where they can be radiated as low-frequency vibration waves and noises inside the building. Low-frequency vibration reduction is a major challenge for vibration control technology. Herein, the new phononic-like crystal metaconcrete material was invented to make the track bed for decreasing vibration induced by trains because it can open low-frequency bandgaps to reduce the low-frequency vibration in actual subway engineering. First, the original phononic-like crystal model was optimized to improve the vibration reduction effect for low-frequency bandgaps. Second, the metaconcrete track beds were conducted according to the new phononic-like crystal model based on the vibration reduction need. Finally, the metaconcrete track beds were installed in the Ning-Ju line of Nanjing Metro in Nanjing, China, and the vibration reduction effect was monitored. The monitoring results in the Ning-Ju line demonstrate that the new phononic-like crystal structure metaconcrete track bed has excellent vibration reduction performance for rail transportation.

Snow and ice accumulation on asphalt pavement can increase the risk of traffic issues. The traditional method of removing snow and ice manually or mechanically from the road surface is time-consuming and labor-intensive. Another common method of spraying salt pollutes the surrounding environment. To overcome these issues, the objective of this study is to study a polyurethane superhydrophobic coating on asphalt pavement and characterize its anti-icing and road properties. A polyurethane superhydrophobic coating (PSC) using polyurethane and carbon nanotube particles (CNTPs) was developed in the lab. The contact angle and roll angle tests, surface roughness test, water droplet icing test, differential scanning calorimetry (DSC) test, ice adhesion test, pavement skid resistance test, water permeability test, and load wheel rolling test were conducted. The results show that the static contact angle and the rolling angle of the water droplet on the PSC surface are 161.176° and 6.6°, which satisfy the requirements to be superhydrophobic. The icing time of the water droplet on the asphalt mixture coated with PSC (AMC) is twice that of the surface of the ordinary asphalt mixture (OAM). In the differential scanning calorimetry test, the PSC released heat slower than polyurethane and asphalt binder during the cooling process. The ice adhesion strength of AMC is 82.78% smaller than that of the OAM. This means the PSC has great anti-icing and deicing properties. In addition, the pendulum value on the AMC surface is 45.7, satisfying the pavement skid resistance requirement. The results of the water seepage test show that the AMC is impermeable to water, thus reducing the risk of water damage to the pavement. Finally, the contact angle of the AMC after the indoor load wheel rolling is still greater than 150°, which proves that the PSC has good wear resistance. In summary, the PSC has good anti-icing properties and road performance.

This study aims to connect asphalt binder mechanical properties to their dynamic microscopic morphology and chemical indices to provide a more thorough and fundamental picture of aging and cracking phenomena. Unmodified and modified asphalt binders were aged to five levels for a comprehensive representation of the asphalt binder service life. Rheological indices used covered linear viscoelastic cracking indicators and nonlinear parameters including fatigue life obtained by the linear amplitude sweep test. A recently validated asphalt binder cracking test, the poker chip test, was used to provide new insight into the mechanical performance of asphalt binders as they stretch into the nonlinear regime and experience cavitation damage. Rheological and mechanical properties were compared to static surface topography from atomic force microscopy (AFM) and time-sensitive asphalt binder microstructure based on electron beam loading using an environmental scanning electron microscope (ESEM). Results indicated that the parameters based on linear viscoelastic analysis and fatigue life derived from the linear amplitude sweep (LAS) test are not adequate to delineate the evolution of asphalt binder behavior with aging among different asphalt binders, due to poor ranking based on known phenomena. However, it was confirmed that the poker chip test was sensitive to longer aging cycles and could capture the total degradation of the asphalt binder’s ductility for both modified and unmodified asphalt binders. The consistency between ESEM and AFM was ensured by observing static surface structures; however, quantification of the fibril formation in ESEM images was the most critical morphological observation when it came poker chip results, because both sharing similar deformation mechanisms. Chemical characterization using Fourier transform infrared spectroscopy was also able to capture asphalt binder aging well, and could be best related to the strength of the asphalt binder. Overall, it was established that the surface microstructure has some relationship to mechanical properties, but not a definitive one, and that using ESEM as an energy absorption indicator was most similar to the comprehensive results from mechanical and chemical testing.

This study investigated the modification mechanism of polyurethane (PU) on the high- and low-temperature properties of asphalt based on experimental and molecular dynamics (MD) simulations. PU-modified asphalt was prepared using an in situ polymerization method. The high- and low-temperature properties of asphalt containing various PU contents were investigated via a series of laboratory tests. The asphalt molecular model, the PU molecular model, and the PU–asphalt mixes system were modeled using software. Based on reasonable models, the influence of PU content on the physical modulus and molecular motion of asphalt at high temperatures was researched using MD simulations. The glass transition temperature of PU-modified asphalt with different contents was obtained using software, and the free volume theory and molecular diffusion movement were used to interpret the improvement mechanism of PU content on the low-temperature performance of asphalt. The results indicate that PU effectively can improve the high- and low-temperature properties of asphalt. PU has a significant positive effect on the physical modulus of asphalt, and the effect becomes more significant with the increase of PU content. In addition, PU can form a tight structure with asphalt and increase the stability of the asphalt system. The free volume ensures the free movement of PU molecules in the asphalt, allowing PU to be dispersed homogeneously in the asphalt. However, the free volume decreases when the PU content exceeds 15% by weight, which limits the improvement of the low-temperature performance of asphalt. The results of molecular simulation can explain the enhancement mechanism of PU, providing a reference for the performance enhancement of PU-modified asphalt.

To reduce carbon emissions in the construction industry, more and more researchers have paid attention to engineered bamboo, a natural and green material. This research focused on laminated flattened-bamboo (LFB), a new bamboo composite produced by the advanced non-notched flattened-bamboo technology which can improve the utilization rate of bamboo and reduce production costs by reducing the use of adhesive compared with the gluing process of conventional bamboo laminates. The basic mechanical properties under compression, tension, three-point bending, and shearing of LFB in three orthogonal directions were mainly studied. Experimental results showed that compressive and tensile strength (modulus) along the grain direction were 56.2 MPa (9,542.7 MPa) and 106.9 MPa (10,151.1 MPa), respectively; in the radial direction were 43.1 MPa (580.9 MPa) and 1.8 MPa (1,459.6 MPa), respectively; in the tangential direction were 19.0 MPa (1,124.5 MPa) and 4.3 MPa (5,112.5 MPa), respectively; the mean bending strength (modulus) was 80.8 MPa (8,076.8 MPa), and the shear strength (modulus) was 17.3 MPa (1,878.8 MPa). The measured properties were comparable to that of other structural bio-based materials, showing LFB has the potential to be an alternative to timber in future construction applications. The modulus and Poisson’s ratio was analyzed, and the result showed that LFB could be regarded as orthotropic material approximately. The failure types under various loading conditions were summarized. Based on the Ramberg Osgood relation, the stress-strain models of LFB composite under compression, tension, and shearing were proposed, and the characteristic value of ultimate strength and elastic modulus was determined by parametric analysis.

New ways to apply sustainable materials, such as biomass components, are essential for reducing dependence on fossil fuels. This work investigated the engineering properties of unsaturated expansive subgrade soils stabilized by bio-based energy coproducts containing lignin. Lignin is a waste by-product of the paper and pulp industry that is frequently burned. Highway subgrade could consume lignin as an environmentally benign, low-cost, and energy-efficient chemical substance for soil stabilization. Swell and shrink behavior of expansive subgrade soils complicates highway construction and causes damage to existing highways. However, research on the hydromechanical properties and volume change behavior of lignin-stabilized expansive soil is limited, and better insight is required into its unsaturated behavior for safe and economical pavement design practices. In this research, a series of geotechnical laboratory tests were conducted to characterize expansive subgrade soils treated with lignin by determining the Atterberg limits, compaction and consolidation behaviors, swelling characteristics, and water retention properties. The mechanisms influencing the changes in engineering properties of lignin-treated expansive soils were further investigated using soil pH, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis. The study shows that the optimal lignin content contributed to an acceptable degree of soil stabilization. The lignin-based cementing material effectively bonds soil particles together and fills pores, thereby preventing water infiltration into the soil and reducing the swell–shrink potential of stabilized soils.

The goal of this study was to investigate the effect of styrene-butadiene-styrene (SBS) polymer on the aging properties of high-content terminal blend rubber modified asphalt (HCTBMA). All asphalt was tested for chemo-rheological properties using an attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR) test, temperature sweep test, frequency sweep tests, and multiple stress creep recovery (MSCR) test. According to ATR-FTIR observations, SBS can retard the oxidation effect of HCTBMA during short-term aging, but its inhibitory effect is reduced during long-term aging. Furthermore, aging aggravates the degree of desulfurization of crumb rubber in HCTBMA as the SBS content increases. Compared with HCTBMA, neat asphalt has a lower elasticity at high temperatures and a higher elasticity at low temperatures. The addition of SBS to HCTBMA improves the elasticity of the material. The elasticity of HCTBMA decreases and then increases after aging, and SBS can reduce the aging degree of HCTBMA after aging. Moreover, based on Pearson correlation analysis, the correlation between the desulfurization of rubber and the degradation of polybutadiene in HCTBMA during aging is high.

The utilization of acidic aggregates in hot-mix asphalt (HMA) is often inevitable due to the limited supply of locally available aggregates, posing a potential threat of moisture damage to asphalt pavements. In this regard, the use of urban waste plastic to coat the low-quality aggregates is a promising way to improve the moisture resistance. This study fundamentally evaluated the compatibility between asphalt and plastic-coated aggregate by measuring surface energy, and for the first time compared the effects of different types of waste plastic including high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polypropylene (PP). The plastic-coating significantly altered the chemistry of aggregate surface by increasing the nonpolar components and reducing the polar components. Such changes remarkably increased the dry adhesion energy between asphalt and aggregate and enhanced the wettability of aggregate. For the acidic aggregates, the polymeric treatment could decrease the value of wet adhesive, which indicated the debonding tendency in the presence of water was reduced. Finally, the energy ratios of the asphalt-aggregate combinations significantly increased by the surface pretreatment, which proved the effect of waste plastic coating on improving the moisture damage resistance of asphalt mixtures. By comparison, the HDPE coating was the most effective way to enhance the compatibility with asphalt, followed by PP and LDPE coatings. The PVC and PET coatings were investigated as the least effective way. This study cannot only contribute to the potential large-scale utilization of waste plastic but also remove the obstacles of using large quantities of acidic natural aggregate in asphalt pavements.

Calcium carbide residue (CCR) can be reutilized to solidify the loess for road construction as a base or subbase due to its rich ${\mathrm{Ca}(\mathrm{OH})}_2$ facilitating pozzolanic reaction with water and soil particles. This study examines the effect of curing time, CCR contents, and dry unit weights on the tensile strength ($R_t$) of CCR-stabilized loess through the splitting tensile test. Aiming to predict the $R_t$ values, the ratio of porosity ($n$) controlled by compacted effort and initial volumetric CCR content ($L_{iv}$), namely $n/L_{iv}$, was chosen as a prediction parameter and then modified to $n/L_{iv}^{0.064}$ for compatible variation rate with $R_t$ values. A prediction model for the splitting tensile strength of CCR-treated soil was proposed considering the modified ratio $n/L_{iv}^{0.064}$ and curing days. The results indicate that $R_t$ values showed a nearly linear positive correlation with CCR contents and dry unit weights, logarithmic increase with the extension of curing time, but no apparent relationship with the ratio $n/L_{iv}$. The modified ratio $n/L_{iv}^{0.064}$ can reflect the trend of $R_t$ values at different curing days since the coefficients of determination were almost greater than 0.90 except for the specimens cured for seven days. The proposed prediction model had a good fit for laboratory data with 97% acceptability and close to 3% error. It can be applied for estimating the $R_t$ values of CCR-stabilized loess using curing time and an optimized ratio of porosity and initial volumetric CCR content. From the aspect of practical engineering, the reutilization of CCR can reduce construction costs, waste disposal costs, and environmental pollution.

This study aims to use two types of brick aggregates as partial replacements for natural stone and checks their feasibility as road aggregates in dry lean concrete (DLC) mixes. Laboratory studies were performed by partially replacing natural stones with both types of brick aggregates, and the optimum contents were evaluated. The paper describes a detailed analysis of DLC mixes with several percentages of bricks including a number of laboratory tests such as the moisture density, strength parameters, ultrasonic pulse velocity, and resistance to acid attack. For the replacement of stone with brick aggregate, the prime focus was paid to the usage of cement content and the aggregate to cement (A/C) ratio. An A/C ratio of 10:1 is found to be suitable for 100% replacement of natural stone aggregate (NSA) with first-class brick aggregate (FCBA), whereas an A/C ratio of 11:1 may be suitable for the use of 100% overburnt brick aggregate (OBBA). However, high contents of the A/C ratio can also be used if NSA is partially replaced by OBBA or FCBA. The strength parameters of DLC mixes such as flexural strength or split tensile strength showed a reduction of about 20%–22% when replaced by 50% OBBA and FCBA, while the compressive strength was within the limit (i.e., 7 MPa after 7 days of curing). Finally, the cost analysis showed that the production cost of DLC mixes can be reduced by about 15.6%–16.2% and 29%–32%, if the stone aggregates are partially (50% by volume) or fully replaced by FCBA and OBBA, respectively. Thus, the paper indicates that not only the scarcity of stone aggregates can be minimized but the cost can also be reduced by partially or fully replacing NSA with FCBA and OBBA.

Using recycled materials can help solve the pollution caused by industrial development, which has severe and irreparable consequences on the environment, in addition to reducing the production costs of fiber reinforced concrete. Therefore, in the present study, the effects of using tire-recycled steel fibers on the mechanical properties of ultrahigh performance concrete and ordinary concrete, including compressive strength, tensile strength, flexural strength, residual flexural strength, toughness, and elastic modulus, have been investigated. In addition, the coefficient of environmental impact and cost in order to achieve sustainable and eco-friendly concrete has been calculated and compared with concretes without recycled fibers. The results show that using tire-recycled steel fibers in both types of concrete improves mechanical properties. In addition, environmental assessment and cost analysis showed that using recycled fibers has positive effects in reducing environmental impact and the cost of concrete.

This paper aims to study the fabrication of geopolymers from precursors synthesized by the sol-gel process. Two precursors were produced: the first one from a physical mixture of silica and alumina synthesized separately by the sol-gel technique, and the second one from a one-step co-condensation sol-gel process. The sol-gel products and a commercial metakaolin were activated with sodium hydroxide and sodium silicate to produce the geopolymers. The physically-mixed precursor did not lead to enough hard geopolymers, thus presenting a rubbery behavior. However, the geopolymers derived from the one-step sol-gel aluminosilicate reached adequate strength at 28 days with a lower density than from the commercial metakaolin. This confirms the good alkaline activity of this sol-gel precursor, which could be an alternative source to produce geopolymers or to be used as a reinforcement additive. Such results also underline that a uniform composition of the precursor is a key factor to produce geopolymers with adequate properties.

This study focused on evaluating the rutting performance of three different highly polymer-modified asphalt (HiMA) binders (i.e., O, T and B) using binder-based [i.e., multiple stress creep recovery (MSCR) and force ductility (FD)] and mix-based [flow number (FN) and Hamburg wheel tracking test (HWTT)] rutting performance tests. The binder-based rutting indicators were compared with mix rutting performance to determine a parameter that can help in the correct prediction of HiMA rutting resistance. In addition, the study looked into application of a simple performance test, the indirect rutting tolerance index (IDEAL-RT), for HiMA mix rutting prediction. The MSCR test revealed different rankings of recovery at 0.1- and 3.2-kPa stress levels. Moreover, the T and B binders did not satisfy the stress sensitivity criteria (${\mathrm{J}}_{nr\_\mathrm{difference}}$) of Max 75%. The force ductility tests revealed that the peak force observed for polymer network phase in HiMA was significantly higher than base binder stiffness, which is in contrast with force distribution in polymer-modified binders (PMBs). The mix rutting resistance ranking ($\mathrm{O}>\mathrm{T}>\mathrm{B}$) was similar in all the tests (i.e., FN, HWTT, and IDEAL-RT). Although IDEAL-RT can be used to compare the rutting resistances of HiMA mixes, detailed future work is required to establish its acceptability in comparing various types of mixes and the minimum requirements of ${\mathrm{RT}}_{\mathrm{Index}}$. The comparison between binder and mix rutting indicators demonstrated that MSCR testing on binder at stress levels of 6.4 kPa and higher can be used to predict the rutting resistance of HiMA binders. Parameters like slope and cohesion energy and a newly introduced parameter—work done for polymer activation (${\mathrm{W}}_{\mathrm{PA}}$)—from FD tests can be used to determine the polymeric phase dominance in HiMA binders. Overall, this study provides pavement stakeholders with a framework for rightly predicting the rutting resistance and polymeric phase dominance of HiMA binders and mixes using MSCR, FD, and IDEAL-RT tests.

Asphalt binder aging is a complex phenomenon that plays an essential role in reducing flexible pavement serviceability. The aging resistance of asphalt binder can be enhanced through the binder modification. This research investigates the impact of aging on unmodified and organo-montmorillonite (OMMT) nanoclay modified asphalt binders. In this study, laboratory aging is carried out for asphalt binders modified with two types of OMMT nanoclays at different dosages (2% and 4% by weight of the binder). The asphalt binders are subjected to short-term and long-term aging using a rolling thin-film oven and pressure aging vessel equipment. Rheological properties of the aged and unaged binders are determined using a dynamic shear rheometer. In addition, storage stability, full performance grading, and rutting resistance of the binders are evaluated and compared. Aging indices were calculated to investigate the aging behavior of the unmodified and modified binders. The results showed that the montmorillonite nanoclay-modified asphalts had improved resistance to aging compared with the unmodified binder.

An ultrahigh-performance engineered cementitious composite (UHP-ECC) is a cementitious composite with both high compressive strength and tensile ductility, which has been regarded as a promising strengthening material for the retrofitting of existing concrete structures. Thus, the bond behavior between UHP-ECC and old concrete has become a concern because the interface is inevitably subjected to shear and tensile loads. To this end, this paper intends to investigate the shear and splitting tensile properties of the interface between UHP-ECC and old concrete. The effect of roughness on the bond behaviors and the failure mechanisms were intensively analyzed. The roughness of old concrete was first quantitatively characterized with a three-dimensional (3D) laser scanner, and the surface roughness index (SRI) was defined. Then, the old concrete specimens with different surface roughness indexes in the range of 1.0 to 1.5 were prepared and postcast with UHP-ECC. After that, the single-side shear test and splitting tensile test were conducted using the digital image correlation (DIC) technique. The results showed that the surface roughness of the old concrete significantly influenced the interfacial bonding properties. When the SRI was set as 1.3, the shear strength of the interface increased by 128.4% compared with the reference group, i.e., a plain concrete surface with SRI of 1.0. When the SRI was set as 1.4, the splitting strength of the interface increased by 221.24% compared with the reference group. However, the excessive roughness, e.g., when the SRI was set as 1.5, also led to the deterioration of interfacial properties due to the internal damage of the old concrete. Thus, it is concluded that the surface roughness index for the interfacial properties of UHP-ECC and concrete substrate is recommended in the range of $1.3-1.4$.

The bond performance of corroded reinforced concrete (RC) subjected to fire has a significant influence on evaluating the structural load-bearing capacity and early warning for structure collapse. However, the bond deterioration mechanism of corroded RC subjected to fire has not been sufficiently studied. Therefore, in this study, the bond behavior between corroded reinforcement and concrete at elevated temperatures was systematically investigated by testing 76 corroded specimens obtained by the accelerated corrosion method. Eccentric pull-out tests were performed immediately when the temperature at the interface of the reinforcement and concrete reached the target values. The main parameters include the degree of corrosion (i.e., 0%, 2%, 5%, 10%, and 20%), concrete cover thickness (20, 30, and $40\mathrm{mm}$), and temperature (20°C, 100°C, 200°C, 400°C, 500°C, 600°C, and 800°C). The test results indicated that when exposed to temperatures below 400°C, the bond strength at elevated temperatures is less than that after natural cooling. The bond strength changed minimally at elevated temperatures between 200°C and 400°C, while a significant reduction was observed after natural cooling. Moreover, the bond strength increased by 8.7% at less than 3.4% corrosion degree. However, severe corrosion (with a corrosion degree exceeding 13.2%) and high temperature (exceeding 500°C) decreased the bond strength by 16.3% and 29.6%, respectively. In addition, methods for calculating the bond strength and residual bond strength based on the deterioration of concrete compressive strength at elevated temperatures are proposed.

Hot in-place recycling (HIR) technology, 100% recycling reclaimed asphalt pavement (RAP), has been widely used as a sustainable maintenance treatment. However, the inhomogeneity of RAP makes it impossible to securely assume that the produced mixture properties will match the laboratory design. For HIR projects, a virgin asphalt mixture (VAM) is added to modify the gradation of the existing rutted pavement. However, once the quantities of VAM added to areas of rutting are varied along the driving direction, the desired construction quality cannot be maintained. In this paper, a method to estimate the quantities of VAM needed for areas with rutting along the driving direction is proposed. To verify the feasibility of the proposed method and explore the effects of varying VAM content caused by rutting depth (RD) distribution variation on construction quality, performance tests of all samples, including two gradation types of virgin aggregates and five VAM contents, were conducted in the laboratory. Test results indicate that the pavement performance of the recycled mixture with continuously graded virgin aggregates is more stable due to the similar gradation of RAP, while the performance of the recycled mixture with gap-graded virgin aggregates possesses substantial fluctuation. Specifically, when the required VAM content is lower than 15%, namely, all monitored RDs less than 10 mm, gap-graded virgin aggregates are more highly recommended from a high-temperature stability perspective. When the required VAM content ranges from 10% to 15%, namely, all monitored RDs ranging from 5.9 to 10 mm, the continuously graded virgin aggregates should be considered first with respect to low-temperature performance. To improve moisture susceptibility, the continuously graded virgin aggregates are more appropriate.

This study assesses the performance of coal-fouled ballast upon treatment with a hydrophobic elastomeric polyurethane, Elastan [Elastan-stabilized fouled ballast (ESFB)] and compares it with ballast that was initially clean but became fouled after its treatment during the track service life [fouled Elastan-stabilized ballast (FESB)]. The cyclic test results revealed that the performance of ESFB was significantly poorer compared with FESB for similar levels of fouling. The ESFB had undergone higher extent of deformations and had exhibited lower damping and resilient modulus values when compared with FESB. However, the extent of breakage of ballast particles was almost similar in both ESFB and FESB samples. Further, the extent of shear strains developed in ESFB samples, especially at higher void contamination index (VCI) values and loading frequencies, exceeded the shear strain at which breakage of bonds occurred under direct shear loading conditions. Accordingly, the critical loading frequency and fouling content up to which the polyurethane-based treatment is effective is proposed in the current study. In addition, the deformations of both stabilized and unstabilized ballast are seen to be directly influenced by the interface shear strength of ballast.