Journal of Materials in Civil Engineering

The valorization of industrial wastes plays a significant aspect in decreasing the environmental pollution. The discussed study concerns the recovery of steelmaking slag (SS), produced by a local steel plant, to make this by-product a raw material for portland cement clinker production. A lab study looks at this slag’s influence on the raw meal reaction capacity and technological parameters (temperature and burning time). Two clinkers were tested, the first is representative of portland cement clinker made in a cement plant, while the second is a clinker made in our laboratory in which SS replaces the pyrites residue used in the first. The raw meals were determined for the second clinker using different lime saturation factors from 0.89 to 0.95, while in the first clinker, lime saturation was 0.89. Chemical and mineralogical analysis and microscopic examination revealed that the usage of SS did not affect the resulting portland cement clinker. This slag enables a gain of 100°C on the clinkering temperature, usually 1,450°C, and shortens the burning time by 10 min. The main clinker phases (${\mathrm{C}}_3\mathrm{S}$, ${\mathrm{C}}_2\mathrm{S}$, ${\mathrm{C}}_3\mathrm{A}$, and ${\mathrm{C}}_4\mathrm{AF}$) are present, with very few free-CaO, about 0.3%. The results of the physico-mechanical tests showed that adding SS had no impact on the cement’s quality. With a final compressive strength at 28-day of 43.5 MPa, the cement obtained satisfies the requirements for inclusion in Algeria’s CEM I 42.5 strength class.

To predict the properties of asphalt binder from a molecular point of view, energy index was introduced into asphalt binder performance analysis. The stability of asphalt binder was evaluated using energy as an indicator. The interaction between styrene-butadiene rubber (SBR) and asphalt binder components was analyzed by simulating the energy change of SBR added to the asphalt binder system. Firstly, molecular models of asphalt binder and SBR-modified asphalt binder (SBRA) were established. The structure of the asphalt binder and SBRA systems at room temperature during the pre-structural optimization were analyzed using molecular dynamics simulations and finally based on Materials Studio 8.0. Subsequently, the energies of the output trajectory file at high temperatures (393 K, 413 K, 433 K, 453 K) were analyzed. Finally, the simulation results were verified by macroscopic testing. The results showed that adding SBR did not significantly affect the structure of asphalt binder. However, the addition of SBR improved the energy of asphalt binder at high temperatures. The stability of the SBRA system was optimal at 433 K when the interaction energy between the asphalt binder and SBR was at a maximum. The largest contribution to the interaction energy was van der Waals energy. It is recommended to store SBRA at a temperature of around 433 K during engineering construction. The interaction of the four components of asphalt binder with SBR followed this order: resin-SBR > asphaltene-SBR > aromatic-SBR > saturate-SBR. The higher content of resin and lower content of saturate served to increase the stability between SBR modifier and asphalt binder. The macroscopic test results were consistent with the simulation results, verifying the accuracy of the simulation. Asphalt binder performance can be improved by changing the asphalt binder component content. Analyzing the stability of asphalt binder using energy index provides a new method to study the performance of asphalt binder.

Phosphogypsum is a solid waste generated when phosphate rock is wet treated with sulfuric acid during the production of phosphate fertilizers. It has been found that the improper handling and disposal of phosphogypsum can cause severe environmental harm. To promote sustainable development, anhydrous calcium sulfate whiskers (ACSWs) prepared from phosphogypsum have been proposed as an environmentally friendly asphalt modifier. This study investigated the effects of using ACSW and waste engine oil (WEO) as modifiers in hot mix asphalt (HMA). Various asphalts modified with ACSW and WEO were prepared, and their physical and rheological behaviors were systematically investigated. Results showed that incorporating ACSW into the asphalt binder considerably improved its high-temperature performance, but significantly weakened its low-temperature performance. However, the low-temperature performance degradation was compensated for by incorporating WEO, with a 5% ACSW to 2% WEO ratio being the optimal combination. Similarly, the pavement performance tests demonstrated that the HMA modified with 5% ACSW and 2% WEO considerably improved high-temperature antirutting deformation, low-temperature anticracking, and moisture stability. Moreover, the results from Fourier transform infrared spectroscopy showed that the ACSW-and-WEO-modified asphalt underwent only a physical reaction. Finally, a heavy metal leaching test was conducted to confirm that the ACSW-and-WEO-modified asphalt binder, as an environmentally friendly pavement material, was not hazardous to the environment. The findings of this study promote sustainable resource utilization and waste management in pavement engineering.

The present experimental study is focused on quantifying the initiation and propagation of desiccation cracking and strain localization in lime-treated compacted expansive soils subjected to controlled temperature and relative humidity conditions. Two bench-scale experimental setups were designed and developed in this study to capture the desiccation cracking and strain localization in soil specimens using digital image processing (DIA) and digital image correlation (DIC) techniques, respectively. A Python program was also developed for autodetection of optimum threshold intensity for crack segmentation, which considerably reduced the chances of noise in DIA and allowed accurate batch processing of multiple images. An open-source software Ncorr was used for two-dimensional DIC analysis to obtain strain localization plots during the desiccation process of soil. The effectiveness of the lime treatment technique for the stabilization of expansive soil was evaluated by considering the major issues of expansive soils such as swelling, shrinkage, unconfined compressive (UC) strength, and desiccation cracking. The results revealed that the lime treatment was ineffective in controlling the desiccation cracking of expansive soil. Only a small percentage of lime (2% or less) was found to slightly reduce the desiccation cracking. However, such small quantities of lime were not found enough to fully sway the swelling and shrinkage nature of the soil. A significant change in the crack pattern was observed in specimens treated with 3% or higher amount of lime. The total length of cracks increased up to 75% due to the addition of 6% lime compared with untreated soil. Similarly, more localized deformation zones were observed in strain localization plots of specimens treated with 3% or higher amounts of lime.

In this study, an attempt was made to use pond ash (PA), which is an industrial waste generated in power plants, as a replacement for fine aggregates (FA) in concrete. An experimental program was conducted on the mechanical properties (compressive strength, split-tensile strength, and flexural strength) of pond ash concrete. Five concrete mixes with varying proportions of pond ash replacing fine aggregates were designed to cast a total of 450 concrete samples. Thirty-two [two-parameter (2P), three-parameter (3P), and four-parameter (4P)] probability distributions were taken into consideration, and the statistical goodness-of-fit (GOF) tests Kolmogorov-Smirnov (KS), Kolmogorov-Smirnov-Lilliefors (KSL), Anderson Darling (AD), and chi-squared (CS) were carried out. The peak values for compressive strength, split-tensile strength, and flexural strength were observed at 20% replacement of FA by the PA. Based on the GOF test ranks, the most suitable probability distribution for modeling variations in compressive strength was the Cauchy distribution (2P). Similarly, Johnson-SB (4P), and Gumbel-Min (2P) were found to be the best distribution for the split-tensile strength and flexural strength, respectively. With an increase of pond ash substitution from 0% to 20%, there is a decrease in the probability of failure, and a further increase in FA substitution causes a decrease in concrete strength, which led to an increase in the probability of failure as shown by the fragility analysis.

To objectively characterize the time-temperature-stress equivalence of viscoelastic properties of asphalt mixture, the triaxial compressive creep test was carried out on an AC-13 asphalt mixture under the conditions of different temperatures and stress states in this paper and the nonlinear variation law of creep deformation was obtained. According to the characteristics of similar creep curves and the principle of time-temperature equivalence, two methods were used to shift the creep compliance under different confining pressure, temperature, and axial stress conditions, and the change of temperature and stress shift factors with confining pressure were obtained; in addition, the creep compliance principal curve was fitted by the Prony series and its principal surface was established. On this basis, the multiple stress creep recovery test under different confining pressures was conducted to measure the parameters of Schapery’s nonlinear viscoelastic model and their variation law with the triaxial stress ratio was obtained, which accurately characterized the synergistic effect of confining pressure and axial stress.

Water seepage in cement concrete structures is one of the main sources of degradation, especially for concrete bridge decks. Therefore, the protection of these strategic structures is a crucial task for civil engineers nowadays. In this context, this study focuses on the use of geocomposites as waterproofing systems for concrete bridge decks. Four geocomposites with different characteristics were compared based on a dedicated testing protocol. The influence of the concrete surface condition (dry or wet) as well as the type and dosage of the primer was also studied. Multilayered slabs, composed of cement concrete, primer, geocomposite, and asphalt concrete, were prepared in the laboratory. The proposed testing protocol includes four types of tests, i.e., shear bond tests (SBT) with the Leutner device, pull-off tests, binder bond strength (BBS) tests, and watertightness tests. Most configurations exhibited good shear resistance and adhesion properties. In general, the geocomposite type and the primer dosage had a significant influence on the behavior of the system, whereas the concrete condition and the primer type had no statistically significant effect. In most cases, the weak point of the system was the interface between cement concrete and primer or between primer and geocomposite. Finally, all geocomposites successfully passed the watertightness test. The proposed testing protocol can be useful for producers to design and optimize their products as well as for road agencies to prequalify the product in the laboratory on the basis of clear performance-based technical specifications.

Steel strips as soil reinforcements have two significant advantages over reinforcements with a circular cross section like solid and hollow steel bars. First, the contact area of steel strips is more than that of steel bars when they are compared in terms of their steel volume per unit length. Second, unlike steel bars, most of the contact surfaces of steel strips are perpendicular to the in situ vertical pressure. To further enhance steel strips’ efficiencies, denti-steel strips are presented in this study. This form of steel strips further integrates the aforementioned mechanical advantages by welding several dents along a smooth steel strip. The dents are small rectangular pieces of smooth steel placed at regular intervals. A total of 240 pullout tests consisting of 51 experimental tests and 189 numerical simulations were conducted to evaluate the performance of a denti-steel strip as an innovative bearing reinforcement in frictional soil. Three-dimensional numerical simulations were carried out using the finite-difference package FLAC3D and validated with the experimental results. It was found that the height, number, and relative spacing of dents are dominant factors in the pullout capacity, and, unlike ribbed steel strips with an unchangeable configuration, the optimum dent spacing of denti-steel strips can be designed based on the properties of granular soil. This research introduces a sawtooth failure surface for a denti-steel strip when there is no interference between dents. However, it proposes a block failure surface when there is severe interference between them. These failure surfaces are the bases of developing several rational equations for predicting the maximum pullout capacity of denti-steel strips. The results show that the intensity of interference between dents depends on the spacing-to-height ratio of dents. There are two critical ratios beyond which the interference between dents and failure mechanism significantly change. Numerical simulations indicate that the average normal stress on the reinforcement is more than the applied normal pressure. Furthermore, the average-to-applied ratio of normal stress increases with a decrease in the applied normal pressure.

This paper reports the influence of delay time on the index and engineering properties of geopolymer-, cement-, and lime-treated expansive soil. Locally available expansive soil was treated with different doses of slag-based geopolymer, cement, and lime. The index and engineering properties like Atterberg’s limits, free swell index, grain-size distribution, compaction properties, and unconfined compressive strength (UCS) were evaluated at delay periods of 0, 6, 12, 24, 48, 72, and 168 h. Further, the mineralogical characteristics and microstructure of the stabilized materials were examined using X-ray diffraction (XRD) and scanning electron microscopic (SEM) images. It was observed that with an increase in delay time, the plasticity and swelling characteristics of the treated soil reduced with improvement in the soil grain size along with the formation of hydration and geopolymeric compounds. The delay in compaction results in the decline of the compacted density and UCS. The formation of hydrated products and flocs during the delay period caused loose packing under dynamic loading and affects the mechanical properties. A significant improvement in plasticity and engineering properties of the expansive soil was observed with geopolymer stabilizers. Thus, it is noteworthy to consider geopolymers as a new generation eco-friendly stabilizer for treating expansive clays for geotechnical constructions.

In this work, we investigated the impact of moisture content on the dynamic mechanical properties of precast concrete members. The dynamic splitting impact test was applied to concrete specimens with different moisture contents using the split-Hopkinson pressure bar (SHPB) with a diameter of 75 mm. Further, variation laws of the waveform, stress–strain curve, damage pattern, dynamic splitting tensile strength (DSTS), strain rate, and damage evolution were analyzed. Experimental results indicate that specimen fragmentation degree increases with moisture content. The DSTS exhibited a “softening in the water” phenomenon when the moisture content was low, resulting in a decrease in strength. However, when the moisture content was high, the strength displayed a strengthening phenomenon, owing to the adhesion of internal pore water. The dynamic strength of the specimens is the macroscopic manifestation of the dynamic balance between the strain effect and moisture content. To model the effect of moisture content and strain rate, a viscoelastic damage constitutive model based on Weibull distribution was proposed and validated, considering the influence of water content and residual strength. The established model can reflect the damage stress–strain relationships of concrete with varying moisture contents under the impact load. The variation laws of associated parameters, such as Weibull distribution parameters, viscosity coefficient, and damage variables, were analyzed to explore the damage mechanism. From the experimental study, it can be concluded that moisture content is closely related to the specimens’ damage pattern, and the dynamic performance of concrete, both of which can be captured by the proposed viscoelastic damage model.

The twenty-first century is known as the “century of the ocean.” Artificial reefs have been extensively studied and used worldwide as the main infrastructure of marine pastures. At present, research has been primarily focused on developing new environmentally friendly artificial reef construction materials with low emissions, low alkalinity, low cost, and great durability. As a novel low-carbon and environmentally friendly construction material, geopolymer presents considerable potential for building artificial reefs. By changing the alkali-activator dosage, this investigation prepared fly ash geopolymer concrete (FGC) with different strength grades. FGC’s mechanics, durability, and marine environmental compatibility were systematically studied as a marine artificial reef construction material. The effect of curing temperature on the performance of FGC was also investigated. Results indicated that the design grade of FGC against sulfate erosion can reach above KS150, and the maximum electric flux of the experimental group is 300.76 C. Moreover, FGC has good compatibility with marine environments. High-temperature maintenance can significantly improve each performance of FGC. Microstructural analysis was performed through a scanning electron microscope secondary electron (SEM-SE), SEM backscattered electrons (SEM-BSE), energy-dispersive X-ray spectroscopy (EDS), and a mercury intrusion porosimeter (MIP). Results showed that the FGC matrix porosity decreases with the increase of alkali-activator dosage, which causes denser pore structures. In addition, the active calcium-containing components in the calcareous aggregate will participate in the geopolymer reaction and generate calcium-rich gel in the interfacial transition zone (ITZ), thus enhancing the mechanical and durability of the material. In conclusion, as a low-carbon construction material, FGC has a broad application prospect in marine artificial reef construction.

The direct action of salt on asphalt materials has received limited research despite the abundance of studies on salt erosion and its effects on the moisture stability of asphalt concrete. This study aimed to investigate the effects of chloride salt on the rheology of asphalt and erosion mechanisms. Microscopic properties of asphalt mortar were analyzed through scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), and the erosion degree of salt in asphalt mortar was evaluated based on three major indexes. Rheological properties of asphalt mortar were determined through temperature sweep and multiple stress creep and recovery (MSCR) tests, while the modified water-boiling test was conducted to evaluate the adhesion of asphalt mortar. Results showed that as salinity increases, the agglomerate phenomenon tends to occur in asphalt mortar, leading to physical aging effects on its basic properties. Meanwhile, chloride salt modified asphalt concrete is prone to cracking at low temperatures and has reduced durability at high temperatures, making it unsuitable for standard load or heavy traffic pavement requirements of PG64 modified asphalt. Furthermore, the presence of chloride in asphalt mortar was not conducive to its adhesion.

This work investigated whether and how a common agro-based additive, beetroot juice, alters the detrimental effects of chloride brines on the durability of cement concrete, by evaluating the frost resistance of ordinary portland cement concrete in various chloride brines. The presence of beetroot juice greatly slowed the ingress of ${\mathrm{Cl}}^{-}$ ions and mitigated the leaching of ${\mathrm{Ca}}^{2+}$, thus effectively mitigating the scaling-induced mass loss, strength reduction, and gas permeability change of the concrete. The microscopic investigation, including scanning electron microscopy, Fourier-transform infrared spectroscopy, and electron probe microanalysis, also proved that beetroot juice mitigated the degradation of C-S-H gel and C-A-S-H gel on the concrete surface and inhibited the formation of oxychloride and trichloroaluminate crystals, as confirmed by the lower $\mathrm{Na}(\mathrm{Mg})/\mathrm{Ca}$ and $\mathrm{Na}(\mathrm{Mg})/(\mathrm{Si}+\mathrm{Al})$ molar ratios in the deicer-weathered concrete. This study sheds light on the mechanistic roles of beetroot juice in improving the frost resistance of concrete in chloride-laden cold regions.

Mass timber construction has seen a growing interest in North America and worldwide. In the US, code provisions allow mass timber buildings to be up to 82 m tall, but with floor slabs requiring a noncombustible, usually cementitious, topping over mass timber panels (MTPs). Designing the MTP and concrete topping to act compositely can increase the strength and stiffness compared to noncomposite MTP floors. Several connections are available to create composite action between an MTP and a concrete topping, with self-tapping screws being the most widely considered practice. A new test fixture and testing method were developed to characterize connection properties and facilitate the selection of fasteners most suitable for developing composite action. Three conventional self-tapping screws were experimentally investigated at the single-fastener scale. The screws were subjected to withdrawal at 90° and 45° orientations to the interface plane between the MTP and concrete. Withdrawal from both the MTP substrate and concrete topping was investigated. Three MTP materials were tested: cross-laminated timber (CLT) consisting of two different wood species and a mass ply panel (MPP). Results demonstrated that the pullout failure of the screwhead from the concrete was the limiting failure mode. Comparisons were made between the experimental results and analytical models for screw withdrawal to assess the applicability of available models to the different MTPs. These models underestimated the capacity of the tested fasteners for all samples except for the fully threaded screws.

Due to viscoelastic characteristics, the strength values of the high-modulus asphalt mixtures (HMAM) obtained under different conditions (temperatures, loading rates, and stress states) are quite different, and the serving conditions of asphalt pavements are also varied. Thus, the strength under fixed conditions cannot reflect the mechanical performances of materials under real serving conditions, which leads to inaccuracies in the asphalt pavement structural design. To develop a precise strength evaluating method for high-modulus asphalt mixtures, the strength tests of high-modulus asphalt mixtures were implemented under different conditions (temperatures, loading rates, and stress states) in this study. The test results indicated that for each stress state, the variation of strength with loading rates under different temperatures can be characterized by power functions, and the variation of strength with temperatures under different loading rates can be characterized by exponential functions. The uniform characterizing model of strength under different conditions was established through the dimensionless method and the sigmoidal function. With the effects of temperature, loading rates, and stress states included, the strength obtained can better reflect the mechanical performances in actual pavement serving conditions. The research results contribute to the improvement of the structural resistance design of the asphalt pavement with high-modulus asphalt mixtures.

Individual and synergistic effects of microsilica (MS) and nanosilica (NS) on the bond properties between moderate–high strength concrete and plain–ribbed steel rebar were investigated. Two different concrete series with water–cementitious material ratio ($\mathrm{W}/\mathrm{Cm}$) of 0.55 and 0.36 were studied. Pull-out tests were performed to analyze the bond strength and bond-slip behavior. Compressive strength, splitting tensile strength, and elastic modulus of the samples were also reported. Results have revealed that although the compressive strength showed a considerable increase after adding MS and/or NS, the modulus of elasticity and splitting tensile strength were not affected considerably. With the addition of MS and/or NS, while an increment was seen in the bond strength for the plain rebar, no significant effect was observed for the ribbed one. In addition, despite residual bond strengths showing an increase in the plain rebar, a reduction was seen for the ribbed one. In terms of slip energy, the use of MS and/or NS for plain rebar made a positive contribution, i.e., the slip energies for both concrete strength groups increased. On the other hand, for the ribbed rebar case, slip energy was negatively affected for the concrete with $\mathrm{W}/\mathrm{Cm}$ of 0.55, while no significant trend was observed for the $0.36\mathrm{W}/\mathrm{Cm}$ group. Based on the bond-slip data obtained, new prediction models were proposed to estimate bond strength and bond-slip behavior for both rebar types. These are compared with other models available in the literature. For the ribbed rebar, the slip amount, where the plateau region on the bond stress versus slip curves begins, was significantly lower than the assumptions considered in the other models. Considering the descending parts of bond stress versus slip relations, the residual bond stress can be maintained more efficiently in plain compared to ribbed rebar.

In order to improve the thermo-oxidative and ultraviolet (UV) aging resistance of bitumen, ultraviolet absorber (UVA) was intercalated into organo-montmorillonite (OMMT) and ultraviolet absorber-intercalated organo-montmorillonite (UVA/OMMT) was used to modify bitumen. Four kinds of UVA/OMMT, including UV326/OMMT, UV328/OMMT, UV531/OMMT, and UV770/OMMT, were prepared by organic intercalation of OMMT with different UVAs (UV326, UV328, UV531, and UV770). X-ray diffraction testing was used to evaluate the intercalation effect of UVA/OMMT. UVA/OMMT-modified bitumen was prepared by melt blending of the base bitumen with different UVA/OMMTs. Then, thin film oven testing and ultraviolet aging testing were carried out on the UVA/OMMT-modified bitumen. The effects of UVA/OMMT on rheological properties, generic fractions, and functional groups of bitumen before and after thermo-oxidative and ultraviolet aging were studied by dynamic shear rheometer testing, thin-layer chromatography with flame ionization detection, and Fourier transform infrared spectroscopy, respectively. Based on these, the thermo-oxidative and UV aging resistance of different UVA/OMMT-modified bitumens were evaluated based on the rheological and chemical indexes. Results show that UV326/OMMT and UV328/OMMT have better effects on the thermo-oxidative aging and UV aging resistance of bitumen than OMMT, while the UV531/OMMT and UV770/OMMT exhibit worse effects on the thermo-oxidative aging and UV aging resistance of bitumen than OMMT, which is related to the better intercalation effects of UV326/OMMT and UV328/OMMT, and the poor intercalation effects of UV531/OMMT and UV770/OMMT.

Abstract

Plastic waste is harmful to the environment and takes thousands of years to decompose naturally. Pyrolysis is an effective method of plastic waste management, and the oil obtained from the process can be used as a modifier for bituminous binders. The polymer modification of bitumen is an effective and commonly used method for improving the rheological performance of the binders. The mixing temperatures are considerably elevated after the addition of polymers to the binders. Various pyrolytic oils are used to reduce the mixing and compaction temperatures of the polymer-modified binders (PMBs). This study analyzed the effect of the addition of high-density polyethelene (HDPE) pyro-oil in viscosity graded (VG30), styrene-butadiene-styrene (SBS), and ethylene vinyl acetate (EVA)-modified binders on the mixing temperatures and rheological properties. The concept of rheograms and Carreau–Yasuda (CY) model fitting were used to determine the mixing temperatures. The rheological investigation involved frequency sweep, temperature sweep, steady shear test, and multiple stress creep and recovery tests using a dynamic shear rheometer. The variation of black diagrams was studied for the binders along with the variation in phase angle and complex modulus of the binders. Fourier-transform infrared spectroscopy was used to assess the chemical changes after the modification and aging of the binders. Damping energy characteristics were investigated for the unmodified, polymer-modified, and HDPE pyro-oil–modified bituminous binders. With increasing shear rates from 100 to $\mathrm{10,000}{\mathrm{s}}^{-1}$, the mixing temperatures of the modified binders decreased by about 8°C–16°C. The addition of pyro-oil to the base and polymer-modified binders decreased the percentage rate of increase in carbonyl and sulfoxide indexes, in turn increasing the resistance to aging of the binders. The addition of pyro-oil reduced the mixing temperatures of base and SBS-modified binders, and the rutting performance of SBS-modified binders. This reduction in mixing temperatures and aging will lead to less energy consumption at the mixing plants, and longer service life of pavements.

Practical Applications

The use of HDPE plastic waste in the form of pyro-oil in flexible pavements will help reduce the amount of plastic waste. The modification of bitumen with pyro-oil will decrease the amount of bitumen used in pavement construction, ultimately reducing the use of nonrenewable crude reserves that are depleting rapidly. The concept of rheograms for evaluating the flow behavior of the modified binders suggested in this study and its application in mixing plants will be beneficial in reducing mixing temperatures at higher shear rates. The use of pyro-oil for the modification of polymer-modified binders will lead to a reduction of mixing temperatures. This will help save energy at the plants. The application of pyro-oil along with polymers will produce aging-resistant, rutting-resistant, and damping-resistant binders, which will lead to stronger and durable pavements for longer service periods. Hence, the analysis in this research will be beneficial for researchers, highway engineers, hot-mix plant owners, pavement designers, and consultants.

Ulexite is one of the most commonly used minerals in boron elements. Especially with the increase in infrastructure investments, new raw materials and new asphalt mixtures with higher performances than traditional asphalt mixtures are needed against the deterioration caused by increasing traffic loads. Stone mastic asphalt (SMA), one of the asphalt mixture types, is preferred due to some superior performances. It is important for mixture performance because the filler material ratio in SMA mixtures is higher than in other hot-mix asphalt (HMA) types. In this study, the influence of ulexite in SMA mixtures was examined by Marshall, indirect tensile strength (ITS), resilient modulus, and moisture sensitivity (modified Lottman) tests using ulexite and basalt in various combinations as filler, providing that the optimum bitumen ratio remained constant. It resulted in increased stability, ITS, and resilient modulus values by a maximum of 8%, 25%, and approximately 79% compared with the control mixture, respectively. In addition, using ulexite provided significant improvements in SMA performance by increasing the resistance to water damage by 13%. Based on the results of the tests, the combination of 4.5% ulexite and 5.5% basalt is recommended for the best SMA performance.

The search for alternatives to filler used in asphalt pavement has been focused on recently due to the lack of traditional materials sources and the aim of sustainable development goals. Novel environmental protection material—alkali-activated slag (AAS) with a prospective substitution for cementitious binder—has been developed widely; however, the possibility of application of AAS in practice is still under investigation, and hence, mass production of AAS for the testing phase generates significant quantities of solid laboratory waste materials. This study paved the way for safe disposal and evaluating the potential of utilizing AAS as filler in asphalt concrete mixes. To understand the influence of filler types on the performance of asphalt concrete, the physical and chemical properties of AAS filler were analyzed and compared to the conventional limestone (LS) filler by applying laser particle size analysis, scanning electron microscope (SEM), x-ray diffraction (XRD) analysis, and x-ray fluorescence (XRF) spectrometry. The monotonic indirect tensile test (IDT) was adopted to characterize the behavior of asphalt mixes over a range of performances at low, intermediate, and high temperatures; additionally, to practice the balanced mix design (BMD) into quality assurance (QA) of asphalt mixes. Testing methods involving monotonic IDT used in this study are indirect tensile strength (ITS), indirect tensile asphalt cracking test (IDEAL-CT), toughness index (TI) and fatigue index (fi), low-temperature IDT, high-temperature indirect tension (HT-IDT), and moisture susceptibility test. The results indicated that asphalt concrete using AAS filler delivers superior engineering performance, such as resistance to cracking, rutting, and moisture damage, compared to the one made with LS filler. This supports the use of AAS filler as a potential substitution for LS filler in the production of asphalt concrete. Besides, the practice of BMD by implementing monotonic IDT for QA of asphalt mixes showed high feasibility.

The maximum permissible content of reclaimed asphalt pavement (RAP) is restricted due to its negative effect on the stability of hot mix asphalt with RAP (HMA-RAP) performance. To address this problem, characteristics of materials, including aggregate gradation, aged asphalt content, and aged asphalt properties, were quantified by testing RAP obtained from different sources. Additionally, the changing law and variability of the indexes are also analyzed. In accordance with the quality requirements of hot mixture asphalt stipulated by the Chinese standard, a control model of the maximum RAP content embraced in recycled asphalt mixture for hot central plant recycling is established. Furthermore, the distribution characteristic of asphalt content with respect to particle size is analyzed. Eventually, a fluctuation range model of blended asphalt penetration is established. The results indicate that (1) the variabilities of aggregate gradation, asphalt content, and aged asphalt properties of RAP are nonnegligible; (2) a control model regarding maximum permissible RAP content in HMA-RAP is proposed based on aggregate gradation and asphalt content; (3) the asphalt content and particle size of RAP are exponentially distributed, and the particle size elevates with the decrease of asphalt content; and (4) the fluctuation range of blended asphalt penetration is related to the asphalt content and penetration of aged asphalt, and the fluctuation range extends with the increasing of RAP content. This paper suggests that, to characterize the variability of RAP with its aggregate gradation and asphalt content, for RAP without pretreatment, the maximum permissible RAP content in HMA-RAP is recommended to be controlled under 30%.

Shear stress is one of the main design parameters for structures subjected to seismic demands. Steel fibers are a viable option for the shear reinforcement of concrete elements because they tend to increase the tensile strength and post-cracking performance of concrete. This study evaluated the direct shear strength of steel fiber-reinforced concrete (SFRC) using standardized specimens. The experimental program included direct shear tests of 14 column- and beam-type specimens using three test methods: FIP, JSCE-SF6, and Z-type. The steel fibers had double hooks at the ends and an aspect ratio of 65. The nominal fiber dosages (FD) were 30 and $60\mathrm{kg}/{\mathrm{m}}^3$, which correspond to fiber contents of 0.38% and 0.76%, respectively. The analysis of 887 data points measured during direct shear tests of the 14 specimens from this study and 69 specimens reported in the literature was performed by analyzing the trends of the shear strength parameters at the first cracking, maximum strength, and residual shear as a function of the reinforcement index. The measured results showed that the shear strength of SFRC at the limit states of cracking, maximum, and residual with FD of $60\mathrm{kg}/{\mathrm{m}}^3$ was between 3% and 52%, 5% and 50%, and 29% and 63%, respectively, greater than the values associated with FD of $30\mathrm{kg}/{\mathrm{m}}^3$. The study also proposed models to estimate the toughness, and the maximum and the residual shear strengths associated with specific displacements.

The interfacial bonding between precast conventional concrete (CC) segments and cast-in place high-performance fiber-reinforced cementitious composites (HPFRCC) has received significant attention for jointing applications such as shear key fillers in bridge connections. Poor bonding of materials in these connections may lead to cracking, premature deterioration, and loss of monolithic behavior among segments. Among the emerging composites, cementitious composites comprising a multiscale reactive powder (nanosilica, slag, and cement) and strengthened with single and hybrid fiber systems of basalt fiber pellets (macro-BFP) and polyvinyl alcohol (micro-PVA) were prepared for potential use in shear transfer joints. BFP is a novel class of basalt fibers, where a polymeric resin of textured surface microgrooves was utilized to encapsulate the basalt strands. The study focused on the synergetic evaluation of the mechanical (compressive strength and tensile strength) performance of HPFRCC, and its bonding capacity (slant shear, bishear, and rebar pull-out) with CC and steel rebars. The mechanical trends were corroborated using thermal, microscopy, and mercury intrusion porosimetry studies. The results indicated that nanosilica enhanced the mechanical performance and interfacial bonding with CC and steel rebars. Reduction in mechanical strength and interfacial bonding were observed for specimens comprising a higher dosage (4.5%) of BFP (single fiber system) up to 21%; however, the tensile strain-hardening behavior and rebar interfacial bonding capacity were significantly improved up to 394%, and 174%, respectively. Comparatively, 1% micro-PVA fibers with 2.5% or 4.5% macro-BFP (hybrid systems) in the nanomodified composites resulted in marked improvement in terms of their mechanical properties (up to 47%) and interfacial bonding capacity with CC (up to 82%) and steel rebar (up to 29%), which suggests their promising use as fillers for shear key bridge joints.

In this paper, the thermal oxygen aging test was conducted on the styrene-butadiene-styrene block copolymer (SBS) type high viscosity modifier (HVM), and the appearance, solubility, functional groups, and molecular weight changes were analyzed. The penetration, ductility, softening point, viscosity, high and low temperature performances, fatigue resistance, functional groups, molecular weight, and microscopic morphology changes of base asphalt and high viscosity asphalt (HVA) after thermal oxygen aging were tested. For the original and aged HVA, the diffusion of water or oxygen into HVA and the interface interaction between aggregate and HVA were studied by molecular dynamics simulation. Results show that the influence of temperature on the HVM aging is much greater than that of time. As the HVA aging degree deepens, the penetration and ductility decrease, the softening point and complex modulus increase, and the low-temperature performance and fatigue resistance deteriorates. The degradation of SBS component and the aging of asphalt component in HVA dominate in short-term and long-term aging, respectively. Therefore, the 60°C dynamic viscosity and 170°C Brookfield viscosity of HVA decrease first and then increase, while the phase angle increases first and then decreases. The SBS component and asphalt component in HVA mutually delays the aging. The van der Waals force plays a dominant role in the original or aged HVA-aggregate interface adhesion compared with the Coulomb force. With the HVA aging deepening or water addition, the absolute value of the interface interaction energy decreases, which reflects the adhesion weakening. Aging increases the free volume in HVA, exacerbating the diffusion of oxygen and water molecules into HVA. In the HVA–water–aggregate system, the asphalt-aggregate hydrogen bonds only account for less than 2% in different hydrogen bonds. As the HVA aging deepens, the water–asphalt hydrogen bond proportion increases, which weakens the water stripping resistance of the interface.

The bonding performance between a thin overlay and the pavement is an important basis for good performance of asphalt pavement. To research the effect of interlayer bonding on the fatigue life of thin overlays, three-point bending fatigue test was carried out on the double-layer beams with interlayer (DLBI). The equivalent fatigue life obtained by the Weibull distribution function was used to analyze the influence of stress ratio, loading frequency, immersion times, and freeze–thaw cycles on the fatigue life. The results suggest that the fatigue performance of DLBI was affected significantly by stress ratio, loading frequency, immersion times, and freeze–thaw cycles. The higher the loading frequency, the greater the effect of the stress ratio on the fatigue performance of the DLBI. The lower the stress ratio, the greater the effect of the loading frequency on fatigue performance of the DLBI. The fatigue life of the DLBI declined by 31.4% and 24.7% after 6 immersion days and five freeze–thaw cycles, respectively. The damage to DLBI caused by one freeze–thaw cycle was equivalent to that caused by 4 days of immersion. Models that take into account four kinds of environment factors to equivalent fatigue life prediction based on 50% failure probability and 5% failure probability, respectively, are proposed, with the equivalent fatigue life method. Taking the equivalent fatigue life as the indicator, the DLBI crack length expansion model is obtained, and the axle load conversion coefficients considering the influence of dynamic loads and adverse seasons factors are calculated. A method is proposed to judge the fracture of double-layer beams.

Heat-treated ribbed bar 630 (HTRB630) is a new type of reinforcing steel produced in China. The tensile properties and low-cycle fatigue properties of HTRB630 high-strength steel bars after exposure to high temperature are crucial for the seismic performance of reinforced concrete structures potentially subjected to fire. With this aim, HTRB630 high-strength steel bar specimens were heated to high temperatures (200°C, 400°C, 600°C, and 800°C), and cooled to the room temperature by water. The appearance and microstructures of the specimens with different exposure temperatures were observed. The tensile tests and different constant strain amplitude low-cycle fatigue tests were carried out. Test results indicated that the specimens exposed to high temperature below 600°C had good tensile properties and low-cycle fatigue properties. Variations of the metallographic structures of the specimens resulted in different tensile properties and different low-cycle fatigue properties. After exposure to the same temperature, as the strain amplitude increased, the shape of the hysteresis curve of the specimen was fuller, its plastic strain amplitude and plastic strain range and elastic strain range ratio increased, its maximum stress per cycle increased slightly, its softening characteristic was more obvious, and its residual dissipated energy density decreased. All specimens performed ductile fracture failures. Therefore, HTRB630 high-strength steel bars have broad application prospects in antifire reinforced concrete structures.

Dry modified Styrene-Butadiene-Styrene block copolymer (SBS) is an innovative method of modifying asphalt mixture that has gained attention due to its convenience, low carbon footprint, and high efficiency. To understand the diffusion behavior and micromechanism of dry modified SBS at the asphalt-aggregate interface, molecular dynamic simulation technology was employed to investigate its behavior at various temperatures. The mean square displacement, diffusion coefficient, statistical relative concentration distribution, and interfacial energy were used to calculate the diffusion and migration mechanism of dry modified SBS at the asphalt-aggregate interface. Additionally, the water-boiling test and Fourier transform infrared spectroscopy (FTIR) test were conducted to analyze the interfacial stripping form and SBS dispersion in the asphalt film. The results indicated that at high temperatures, dry modified SBS exhibited the highest mean square displacement and diffusion coefficient, suggesting that higher temperatures promoted its diffusion toward the asphalt layer. Dry modified SBS clusters and asphalt displayed opposite migration diffusion tendencies, with the migration of dry modified SBS toward the asphalt film becoming more pronounced over time. The introduction of SBS altered the distribution of asphalt components on the aggregate surface, increasing the interfacial energy and adhesion strength between asphalt and aggregate. Laboratory experiments supported these findings, confirming that dry modified SBS enhanced diffusion distribution and interfacial strength. The diffusion distribution of dry modification was found to be similar to that of wet-process SBS modified asphalt under sufficient temperature and time. Therefore, in engineering applications, raising the mixing temperature can improve the diffusion distribution of dry modified SBS, further enhancing its modification efficiency and effectiveness.

Highway traffic loads and environmental conditions, including temperature and moisture at the layer interface, could cause debonding or delamination between adjacent asphalt pavement layers in tensile, shear, or mixed-mode failures. Thus, studying the tensile and shear strengths of interface bonding is crucial to maintaining durable and functional pavement structures. The main objective of this research is to evaluate and estimate the interface bonding strength (IBS) between asphalt pavement layers under the mixed shear-tension loading mode. To this end, an experimental, statistical, and machine-learning (ML) approach was adopted. A total of 164 double-layered hot-mix asphalt specimens consisting of hot-mix asphalt AC-13 in the upper layer and AC-20 in the lower layer were tested via a direct tensile device with a supplementary shear fixture. The effects of test temperature, shear stress, and tack coat application rate on the IBS were considered. The results revealed that with increasing tack coat dosage, the IBS peaked at $0.8\mathrm{kg}/{\mathrm{m}}^2$ and was subsequently decreased. It was also found that the IBS was very sensitive to temperature changes and heavily dependent on shear stress at elevated temperatures. On the other hand, with increasing shear stress from 0 to 0.20 MPa, the IBS at temperatures of 5°C, 20°C, and 35°C declined by 10.96%, 61.85%, and 83.16%, respectively. Two prediction models for the IBS based on the conventional statistical models of multiple linear regression (MLR) and nonlinear regression were successfully developed. However, the nonlinear model outperformed with a better prediction accuracy of 24.2% compared with linear regression ($R^2=71.8\%$). Finally, a highly accurate feed-forward back-propagation (FFBP) artificial neural network (ANN) model was developed to predict and form a relationship between the IBS and independent variables with an extremely low margin of error. It was revealed that the developed FFBP-ANN model could capture 99% of the measured data. Finally, a comparative analysis demonstrated that the developed FFBP-ANN model was superior to regression modeling in terms of predicting the IBS.

In this study, the effects of the incorporation of various supplementary materials such as fly ash, limestone powder, silica fume, and portland cement as the secondary precursor on the early age reaction, structural buildup, rheology, and microstructure of alkali-activated slag cements (AAC) in the presence of two different activators (sodium hydroxide and sodium silicate) have been investigated. Test results showed that the activator type influenced the reaction process and the setting time of AAC pastes could be estimated by the specific cumulative heat release or ultrasonic pulse velocity range. AAC pastes containing the investigated secondary precursors showed Bingham fluid behavior. Early structural buildup tests suggested that the silica fume or portland cement addition seems beneficial for 3D printing applications, while the fly ash or limestone addition could be preferred for multilayer casting. The main reaction products for the AAC pastes incorporating various secondary precursors were characterized as a chain-like C-(N)-A-S-H/C-(A)-S-H or C-S-H using SEM/EDX analyses.

Microbially induced calcium carbonate precipitation (MICCP) is widely employed in various engineering applications, including repairing cracks in cementitious materials. Many of these studies were performed using heterotrophic bacteria that utilize urea and releases harmful foul-smelling environmental pollutant. Cyanobacteria have emerged as potential substitutes for heterotrophic bacteria to overcome this concern. This study used photosynthetic cyanobacteria Synechocystis pevalekii to develop an ecofriendly and sustainable grout for crack remediation in concrete. To improve the fluidity characteristics of the grout, fly ash was incorporated as a partial cement replacement in the cementitious grout. The cementitious grouts were tested for fresh properties at different dosages of fly ash (0%–50%) by keeping water (or bacterial culture) to binder ratios of 0.45, 0.47, and 0.50. Based on flowability results, a $0.47\mathrm{culture}/\mathrm{binder}$ ratio was selected to examine different FA dosages for hardened properties. A 40% FA substituted cementitious biogrout was selected for repairing cracks at the lab scale. Different cracked concrete specimens were repaired and cured using ponding and spray treatment for 28 days. At the end of the experiment, a significant improvement in strength and permeability was recorded in biogrout-remediated cracked specimens. The sample was collected from healed cracked region to confirm the healing mineral using field emission surface electron microscope (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The developed fly ash incorporated biogrout will help as an economical and ecofriendly MICCP technology for the remediation of existing cracks in the concrete structures.

Responsive polymers can be combined with clay particles to form adaptable, or “tunable,” clay–polymer composites. The purpose of this study is to investigate the potential for “tunability” of a nanocomposite at the mesoscale through changes in material properties—swelling behavior, Atterberg limits, hydraulic conductivity, and shear strength—with varying pH and ionic concentration of the surrounding fluid. The composite was synthesized from a nonionic form of the polymer polyacrylamide and an expansive clay, montmorillonite. An attempt was made to induce changes in behavior of the composite by exposing the material to a selected range of pH and ionic concentration conditions, thereby influencing the conformation (shape and size) of the responsive polymer molecules under different stress levels and solid contents. Behavior was compared for the cases of predicted coiled, partially extended, and extended conformation. The test results demonstrate that conformation of responsive polymer and tunability of composite depends primarily on solution type, stress levels, and solid content. The “tuning” response of a nanocomposite is maximized with a significant change in ionic concentration of the surrounding fluid. Nanocomposite swelling was 30% less than pure clay and had a friction angle 12° greater than pure clay at high ionic concentration. At low or high pH conditions, nanocomposite tunability was limited.

Municipal solid waste incineration (MSWI) fly ash containing heavy metals is hazardous solid waste that requires safe disposal. Alkali-activated treatment can effectively improve the environmental safety of MSWI fly ash. Due to the low alumina content of MSWI fly ash, the addition of nanoalumina (NA) solves the defect to enhance the ability of solidification/stabilization (S/S) and maximize the utilization of MSWI fly ash. NA/MSWI fly ash solidified body was prepared by alkali-activated technology in this work. In this study, NA was added (0–3 wt.%) to explore its effects on mechanical properties and heavy metal immobilization efficiency of NA/MSWI fly ash solidified body. Research results revealed that when the addition of NA was 2 wt.%, the compressive strength of solidified bodies can significantly increase by 38.0% and 42.8% at 7 and 28 days, respectively. Meanwhile, the leaching concentration of heavy metals in NA/MSWI fly ash solidified body can noticeably reduce with the immobilization efficiency of above 99.5%. Adding NA promoted the ratio of stable state on Pb and Zn in solidified bodies. A series of microscopic characterization analyses indicated that NA stimulated gels and Friedel’s salt formation, and N–A–S–H was also found in the NA/MSWI fly ash solidified body, enhancing S/S heavy metals by physical adsorption, physical encapsulation, and chemical bonding. Therefore, this study paves a potential new way for the application of nanomaterials in S/S MSWI fly ash through alkali-activated technology, and nanoalumina is a more promising candidate.

This study investigates the behavior of bamboo geocells (BGs) and jute geocells (JGs) under a repeated wheel load test. A series of wheel load tests (WLTs) was conducted to measure the performance of the geocells by varying three types of infill materials, i.e., sand, crushed aggregate (CA), and recycled asphalt pavement (RAP). Further, the effect of basal geosynthetics with a geocell is also investigated under the wheel load. The wheel load was applied stepwise based on the ultimate bearing capacity of the system, and the test was continued until failure due to rutting. The test results showed that the unreinforced system with infill material CA could sustain more repetition than RAP and sand under the wheel load. With the inclusion of JG in the granular base layer, the traffic benefit ratio increases marginally, i.e., 1–2 at a rut depth of 50 mm. However, the BG increases the traffic benefit ratio (TBR) significantly, i.e., 3–5 at the same rut depth. With the addition of basal geosynthetics, with both geocells, the TBR value increases extensively. The reinforcement effect of the jute geocell is higher in the RAP base layer. However, the impact of the bamboo geocell is greater in the sand base layer. Due to the elastoplastic nature of the RAP particles, it exhibits more resilient deformation than sand and CA. The performance of the BG in terms of load repetitions and TBR value with the infill material RAP and CA is substantial and can be used for low-volume unpaved roads.

Fiber-reinforced emulsified asphalt (FEA) is widely used in asphalt pavement structures as a stress-absorption layer. This study aimed at developing a multifunctional fiber-reinforced emulsified asphalt (MFEA) by empowering the FEA with the self-sensing ability. To achieve this purpose, carbon nanotubes (CNTs) were grafted onto the basalt fibers in the FEA. An optical microscope and scanning electron microscope (SEM) were respectively used to investigate the distribution of CNTs onto the fibers and the microstructure of CNT/fiber composite (CFC). The fabrication process of CFC was optimized based on the distribution homogeneity of the CNTs. The self-sensing ability of the MFEA was then evaluated in the laboratory using an electrochemical workstation. Based on the experimental and analytical results, $1.5\mathrm{mg}/\mathrm{mL}$ was recommended as the optimal dosage of the suspension of CNTs for grafting CNTs onto the fiber. The electrical resistance of the developed MFEA was found to be isotropic and sensitive to the demulsification state, EA/CFC mass ratio, temperature, loading speed, and deformation magnitude, which confirms the potential of using developed MFEA as a self-sensing layer to monitor its response to environmental and traffic variation. Besides, the direct tension and pull-out tests indicate the positive influence of grafting CNTs onto basalt fibers on the mechanical performance of FEA.

Utilization of ultrafine supplementary cementitious materials (SCMs) instead of ordinary ones has shown great potential to enhance the strength development of concrete mixtures. Replacing large amounts of portland cement with ultrafine SCMs, however, may not be feasible due to their negative effect on the water demand of concrete, and extra cost and energy consumption associated with the ultrafine grinding of SCMs. It is therefore important to explore practical methods for efficient use of ultrafine SCMs in producing low portland cement content concretes. To achieve this goal, the current study focused on the use of ultrafine granulated blast furnace slag (GBFS) in combination with a commercial one to replace 30%, 40%, and 50% by weight of portland cement in preparing mortar samples. The compressive strength of the mortars was measured at different ages ranging from 1 to 91 days. Cement paste samples with modified (combination of ultrafine and commercial) and commercial GBFS were also prepared and tested by the isothermal calorimetry, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDS) techniques. The results showed that the samples with 30% and 40% by weight modified GBFS as portland cement replacement had higher compressive strength compared with those made with the same amount of commercial GBFS or 100% by weight portland cement at all the testing ages. The microstructural analyses indicated increased calcium hydroxide consumption and higher reaction degree of clinker phases after 1 day of hydration for the sample incorporating 40% by weight modified GBFS compared with that with the same amount of commercial one, resulting in the superior compressive strength of this sample at such an early age of hydration.

The present study aims to characterize the microvoid sizes and their statistical distribution at the instance of fracture from the fracture surface of steel specimens. To this end, uniaxial tensile tests are conducted on circumferentially notched specimens made of 17-4 PH stainless steel and ASTM A992 high-strength structural steel. The fracture surfaces of the steel test specimens are studied using a digital microscope to quantify the statistical microvoid size distribution. Furthermore, the evaluated microvoid sizes of different fracture locations are mapped with the stress and strain fields. Finally, based on the experimentally evaluated microvoid sizes, an uncoupled fracture model was adopted to predict the fracture displacement and location of ductile fracture initiation in the fractured specimens. The fracture displacements predicted using the calibrated uncoupled fracture model are within the acceptable limit. The fracture initiation locations coincided with the peak strain-averaged stress triaxiality in the fracture specimens.

The purpose of this paper is to compare the dynamic viscosity and steady viscosity characteristics of high-viscosity modified asphalt binder (HVA) and to analyze the applicability of the Cox–Merz rule as well as of the different zero shear viscosity (ZSV) test methods for HVA. To this end, seven kinds of asphalt binders including base asphalt binder, traditional modified asphalt binder with 4.5% styrene-butadiene-styrene (SBS), commercial HVA, and four self-shearing HVAs were prepared. The frequency sweep test and shear rate sweep test were conducted to obtain dynamic viscosity and steady viscosity, and the Cross model, Carreau model, and Carreau–Yasuda model were used to calculate ZSV based on these two types of viscosity. The results show that both the dynamic and steady viscosity tests prove that asphalt binder exhibits shear-thinning and yield stress behavior. Besides, there is a critical shear rate in the shear rate sweep test and the critical shear rate decreases with the increase of modifier content. The empirical Cox–Merz rule has good applicability in the Newtonian plateau region of base asphalt binder, but it is only applicable to a partial shear-thinning range of modified asphalt binder. Noteworthily, it fails when applied to HVA-C. The frequency sweep test is only suitable for determining the ZSV of base asphalt binder but not applicable at all to the modified asphalt binder because there is no Newtonian plateau in the dynamic viscosity, and the fitting results based on model extrapolation have huge errors as well as vary with the number of iterations. However, the shear rate sweep test is suitable for testing ZSV for both base and modified asphalt binders. Furthermore, it should be pointed out that ZSV obtained by model fitting is not a steady viscosity at zero shear rate but a Newtonian viscosity at a low shear rate, so low shear viscosity (LSV) is a more accurate concept.

Warm mix asphalt (WMA) has recently gained popularity as a pavement engineering alternative because it has the potential to significantly reduce energy utilization and the carbon footprint of the pavement industry. However, due to lower mixing and compaction temperatures, concerns have been raised about the material’s durability and the possibility of water damage. The current research evaluates the effect of the simultaneous usage of two additives [styrene–butadiene rubber (SBR), and polyphosphoric acid (PPA)] on the moisture damage resistance of warm-stone matrix asphalt (SMA) mixtures containing anti-tripping agents (ASAs). Different mixture tests were performed to investigate the moisture susceptibility of the samples. A two-way analysis of variance was performed to investigate whether additives have a significant effect or not. The outcomes show that the combination of two polymers improves the indirect tensile strength, fracture energy, and resilient modulus of samples. Also, the combination of Sasobit and Zycotherm and ASAs enhances the performance of samples, and among mixtures containing ASAs, specimens containing ASA (B) have the best moisture strength performance. In addition, a numerical method through a regression tree ensemble (RTE) model was designed to estimate the resilient modulus ratio (RMR), fracture energy ratio (FER), and tensile strength ratio (TSR) values. The outcomes indicated the high accuracy of this model in predicting the mentioned values.

Internal vibration is a commonly used method for consolidating fresh concrete. Proper vibration causes entrapped air voids to float to the surface of the concrete or collapse at the water–air interface. However, if vibration is excessive, it may introduce air into the concrete under certain circumstances. The consequence of this is an uneven distribution of air voids, resulting in heterogeneous concrete and subsequently undesirable strength and freeze–thaw durability. This study investigated the mechanism by which air voids are induced in concrete due to vibration. Concrete mixtures were prepared and vibrated at several frequencies for a range of durations. Air-void distribution within different zones from each sample was obtained using the linear traverse method. It was found that rotary movement of a high-frequency, vertical vibrator created a vortex inside the liquefied fresh concrete that sucked air into the concrete from the surface. In general, increasing the frequency of vibration will cause more air addition, and the amount of air added with increasing duration of vibration is dependent on the amount of unreacted air-entraining agent (AEA) remaining in the system.

The waterproof performance of shield-tunnel gaskets determines the long-term operation of shield tunnels. To study the long-term waterproofing performance of shield-tunnel gaskets, first, high-temperature aging tests of ethylene–propylene–diene monomer (EPDM) rubber specimens were performed, and an EPDM rubber aging model was constructed based on the Arrhenius equation using the time–temperature equivalence principle. Uniaxial compression tests were then conducted on the EPDM rubber with different degrees of aging to analyze the changes in material parameters $C_1$ and $C_2$ of the rubber intrinsic model with time. Subsequently, a rubber gasket used in a shield tunnel in Nanjing was used as the sample material, and aging tests were conducted on the inner and outer channel gaskets considering different joint displacements. The test results were combined with the $p\text{-}T\text{-}t$ ternary model based on the Arrhenius equation to predict the 100-year waterproof performance of the shield-tunnel gasket. The results show that the final stress relaxation coefficients of EPDM rubber for 100 years are 0.65 and 0.44 for initial compressive stresses of 1.1 and 1.6 MPa, respectively, as predicted by the aging coefficient model. Furthermore, a clear relationship was observed between the $C_1$ and $C_2$ parameters in the Mooney–Rivlin rubber constitutive model, and the hardness and modulus of elasticity of the rubber material gradually increased over time. The short-term stress relaxation in the early stage of the inner and outer channel gaskets under different openings amounted to approximately 20%–30% of the total relaxation, and the chemical stress relaxation in the later stage accounted for approximately 70%–80%.

Abstract

The current study presents an investigation into the optimal content determination of the mix parameters in their acceptable ranges through fresh, mechanical, and durability characteristics in ground granulated blast furnace slag (GGBFS) based self-compacting geopolymer concrete (SCGC) cured under ambient temperature. Ordinary portland cement (OPC) based self-compacting concrete (SCC) was prepared as a control concrete. Both the M25 SCGC and SCC were characterized through fresh property tests satisfying the flowability, passing ability, and segregation resistance; mechanical tests by both nondestructive and destructive tests; and durability tests through water absorption, sorptivity, acid attack, sulfate attack; and rapid chloride permeability test (RCPT). The prime mix parameters considered in SCGC with their variation ranges were molar concentration of sodium hydroxide (10M, 12M, 14M, 16M), sodium silicate to hydroxide ratio (1.5, 2.0, 2.5, 3.0), superplasticizer (SP) dosage (5%, 6%, 7%, 8%), and percentage of extra water (EW) (15%, 18%, 21%, 24%). The results of SCGC were compared with the control SCC and discussed. The mix parameter optimal values derived from all the fresh and hardened concrete properties were a 12M concentration of sodium hydroxide, sodium silicate to hydroxide ratio of 2.5, SP dose of 7%, and EW percentage of 21%. SCGC thus prepared is stable, workable, and exhibits superior properties to OPC-based concrete to promote sustainable development.

Practical Applications

The current study estimates the optimal quantity of mix parameters, i.e., 12M NaOH, AAS ratio of 2.5, 7% SP, and 21% EW to produce ground granulated blast furnace slag (GGBFS)-based self-compacting geopolymer concrete (SCGC) cured under ambient temperature. The SCGC-optimized mix-parametric values are evaluated based on the mix materials whose physical and chemical properties are declared in the manuscript. The cementless concrete thus prepared is GGBFS based, which is an industrial byproduct, yielding sustainable concrete. Under ambient temperature, the SCGC can be cured, which is practically beneficial for the in situ construction work. The self-compacting capability of SCGC involves minimal energy in producing a dense, smooth concrete surface, reducing both the construction period and cost involvement. Being a stable workable concrete, its nonsegregation nature makes it homogeneous with minimal entrapped air. The reduced permeability nature renders it a larger insulating potential. Concerning OPC-based concrete, SCGC has larger mechanical and durability characteristics, making it a better choice. Thus, the SCGC has a huge potential in the global construction sector and is practically applicable.

Using recycled asphalt pavement (RAP) materials in the pavement industry is a hot issue now, which can reduce carbon emissions significantly. The agglomeration and variability of the RAP materials treated by a conventional crushing and screening process present a challenge for the gradation design and variability control of the reclaimed asphalt mixture, resulting in a lower RAP content and thus a limited environmental and economic benefit. To address it, a refined crushing and screening process was employed for the RAP material to separate the asphalt mortar and the coarse aggregates in this study. To evaluate its applicability on the RAP material, the basic composition, agglomeration degree, variability, and gradation refinement of the RAP material were discussed. The aggregate dispersion uniformity and road performance of the reclaimed asphalt mixtures made with the obtained RAP materials were further investigated; the correlation between the RAP properties and the road performance of the reclaimed asphalt mixture was explored. The results show that the agglomeration degree and variability of the coarse RAP material are reduced significantly by the refined crushing and screening process. The use of the RAP material treated by the refined crushing and screening process can largely improve the uniformity of aggregate dispersion and conventional road performance compared with the use of the RAP material treated by conventional methods. Pearson correlation analysis demonstrates that the RAP agglomerates increase the variability of 4.75 mm sieve passage rates and the asphalt-aggregate ratio, resulting in an uneven distribution of aggregates in the structural composition, thus reducing the moisture sensitivity and fatigue performance. By utilizing the refined crushing and screening process, the variability of the RAP materials can be considerably reduced, thereby enhancing the RAP content and the key performance of reclaimed asphalt mixture. The popularization of the refined crushing and screening process is an effective approach to promote the high-quality use of the RAP materials.

Abstract

Cracks are inevitable in concrete structures, and the deterioration of concrete crack interfaces in intertidal zones is often accelerated due to seawater dry–wet cycles. This paper aims to analyze the morphology and deterioration of crack interfaces under seawater dry–wet cycles. First, concrete crack surface specimens were obtained through splitting tests. Then, the specimens were placed in seawater solutions of different concentrations to undergo seawater dry–wet cycles. Furthermore, three-dimensional (3D) laser surface profile scanning was performed on the specimens after 0, 10, 30, and 60 seawater dry–wet cycles. Finally, the changes in morphological parameters were analyzed and calculated to derive the effect patterns of seawater dry–wet cycles on the 3D morphology of concrete crack interfaces. The results showed that the crack surface deterioration of the specimens in clear water was only affected by the dry–wet cycles, while that in seawater was jointly affected by seawater erosion and dry–wet cycles. The crack surface deterioration of the specimens in seawater can be divided into two stages. In the first 10 seawater dry–wet cycles, the chemical products generated by seawater erosion played a dominant role. The 3D morphological parameters and 3D fractal dimension changes of the specimens in seawater showed opposite trends to those in clear water. From the 10th seawater dry–wet cycle, erosion and flaking by the dry–wet cycles were dominant. The changes in the 3D morphological parameters and 3D fractal dimension of the specimens in seawater were consistent with those in clear water. Moreover, higher seawater concentrations led to more significant trends in the crack surface 3D morphological parameter and 3D fractal dimension changes.

Practical Applications

Concrete structures are common in marine engineering, such as port wharves, sea crossing bridges, drilling platforms, and island reef revetments. Concrete structures exposed to tides/splashes for long periods are susceptible to seawater dry–wet cycles, which may lead to structural cracking during their service life. To ensure the safety and service life of concrete structures, cracks must be addressed with repairs or reinforcements. Numerous studies have shown that the concrete crack surface morphology determines the repair and reinforcement effects and affects the interfacial bonding performance, mechanical properties, and durability. Therefore, studying the surface morphology variation patterns of concrete cracks under seawater dry–wet cycles is important for concrete repair and reinforcement. In this paper, we produce concrete cracks through splitting and conduct seawater dry–wet cycle tests on concrete crack interfaces under different seawater concentrations to study the 3D morphological characteristics of cracks under seawater dry–wet cycles and provide experimental data to reveal the concrete crack surface changes for future repair. This study could serve as a guideline for repairing cracks in concrete structures in tidal/splash zones.

Concrete structures partially immersed in seawater will be subjected to severe chloride and sulfate erosion under the capillary and diffusion actions. Nevertheless, the present studies only discuss the capillary action in a static water level environment, without considering the capillary action in a water level fluctuating environment. In this paper, the mechanical properties and ions transmission law of concrete under the capillary and diffusion actions in water level fluctuating environment were investigated through a series of indoor exposure tests. Three erosion solutions were set to study the interaction effects of chloride, sulfate, and magnesium within concrete. Based on the compressive strength tests, the mechanical properties of concrete in a water level fluctuating environment were explored. The natural diffusion tests were carried out to research the sulfate and chloride transmission law within concrete above and in the water level fluctuating zone (WLFZ). Scanning electronic microscopy (SEM), X-ray diffractometer (XRD), and mercury injection porosimeter (MIP) measurements were conducted to analyze the microstructures at various zones of concrete under different erosion solutions. The results show that the concrete partially immersed in WLFZ suffers from severe sulfate attack on mechanical properties due to the dual influences of sulfate chemical and physical crystallization attack. The chloride concentration within concrete above WLFZ is significantly higher under the capillary action. The sulfate concentration within concrete above WLFZ is lower because of the chemical binding of sulfate within concrete. The higher porosity and more capillary pores exist in concrete above WLFZ due to the carbonization and water evaporation. By decreasing the porosity of concrete, sulfate will inhibit the chloride transmission and magnesium will restrain the sulfate and chloride transmission. The transmission mechanisms of erosion ions within concrete above WLFZ consist of vertical transmission under the capillary action and lateral transmission under the diffusion action and water evaporation.

Mixing material such as fibers into concrete is an effective method to change the brittle behavior of concrete. To reduce the internal defects of concrete and improve the mechanical performance and crack resistance of concrete, this study proposed the design concept of multiscale modified concrete. To further investigate the feasibility of the design concept, the two-stage test method is adopted to study the performance of multiscale modified concrete. First, carbon nanotubes (CNT) and ${\mathrm{CaCO}}_3$ whiskers were mixed into concrete, and the optimum contents of CNT and ${\mathrm{CaCO}}_3$ whiskers were determined by uniaxial compression test. Subsequently, based on the optimum contents of CNT and ${\mathrm{CaCO}}_3$ whiskers, polyvinyl alcohol fibers (PVAF), steel fibers (SF), and rubber particles (RP) were further mixed into concrete, and the uniaxial compression test and scanning electron microscopy (SEM) test were completed. From the test results, the influence of materials contents on the mechanical performance of concrete was analyzed, an accurate and reasonable compressive stress–strain model was established, and the comprehensive toughness evaluation index of concrete considering the multiple factors influence was presented. The comprehensive toughness evaluation results show that the multiscale modified concrete has outstanding compressive strength and toughness when the contents of CNT, ${\mathrm{CaCO}}_3$ whiskers, PVAF, SF, and RP are 0.6%, 6.0%, 0.075%, 1.0%, and 0%, respectively. The SEM results revealed that adding materials of various sizes into concrete can hinder the growth of cracks and improve the cracking pattern of concrete.

The preservation of natural resources has been gaining considerable space in recent decades, encouraging the use of industrial and civil construction waste. In this work, the recycled asphalt pavement (RAP) from the milling of the pavements was used to replace virgin aggregates for the construction of road base layers. Due to the large amounts of materials involved in road construction, it is necessary to develop alternative binders. Particularly when it comes to alkali-activated materials, the use of residues in the production of sodium silicate has not yet been investigated for RAP stabilization. Therefore, in this study, rice husk ash (RHA) was activated in an alkaline environment, playing the role of an alternative source of silica, for the formation of an alkali-activated binder (AAB). The exposure of these mixtures to seasonal variations in humidity and temperature was evaluated through durability tests from wet–dry cycles and the unconfined compressive strength (UCS) retained in the samples after the cycles. AAB permanence was also verified through long-term mechanical performance and its environmental impact through leaching tests. The results indicated that mixtures with a RAP to AAB ratio = 40:40, 50:30, and 50:40 reached the minimum design strength (2.1 MPa) even after wet–dry cycles; however the mixture with RAP:AAB = 40:40 is potentially superior for better performance in field conditions, possibly without premature failure. In addition, this mixture has no environmental impact because the results of environmental tests did not show any significant risk or hazardous characteristics.

Alternative building materials, such as adobe and rammed earth, can help reduce construction costs and carbon-dioxide emissions, making them an important part of sustainable building practices. Rammed earth building walls are substantial, long-lasting, heat-resistant, and recyclable because they are constructed by compressing naturally damp soil between temporary forms. Using mud in contemporary buildings presents several challenges, including durability and strength. This study investigated the impact of incorporating regular portland cement, quicklime (calcium oxide), and a self-polymerizable acrylic-based resin (a transparent bonding agent) into a soil mixture to address these problems. The optimal moisture content that maximizes compressive strength was also investigated. The results demonstrated that the optimum moisture content for maximum compressive strength and dry density was identical as the soil content in a mixture increased. The increase in the compressive strength and reduction in cracking can be attributed to the optimal proportions of regular portland cement, self-polymerizable acrylic-based resin, and quicklime. This study can serve as a guide for mixing appropriate proportions of materials that would yield the optimum mechanical properties for rammed earth construction in hot arid regions.

The initial weight and volume relationships play a crucial role in determining the strength of cement-stabilized soils. Since 2007, the porosity/binder ratio has been widely utilized as a control index for stabilized soil mixtures. However, this approach does not take into account the water content used during the stabilization process, which can affect the strength of the final product. To address this issue, this paper introduces the porosity-water and binder relationship as a new index to predict the strength of artificially cemented soils. The strengths of different stabilized soils were compared based on the new index and the comprehensive results were analyzed to demonstrate the efficacy of the new index. The findings indicate that the new index is an appropriate design parameter for soil–lime, soil–cement, and geopolymerized soil mixtures; moreover, the water content was identified to have no effect on the splitting tensile strength to compressive strength ratio. The results of this study provide valuable insights on the optimization of stabilized soils and development of improved soil stabilization processes.

As a high-performance composite material, polyvinyl alcohol (PVA) fiber-reinforced engineered cementitious composites (PVA-ECCs) are often used in sub-elevated temperature environments (<$200°\mathrm{C}$) for long-term service. However, the effect of exposure time in sub-elevated temperature on the performance of PVA-ECCs is not still clear. In this study, the properties of PVA-ECCs in sub-elevated temperature environments were examined, with emphasis on the effect of exposure time (1, 3, 6, and 9 h). Furthermore, the microstructure and tensile behavior of single PVA fibers exposed to a sub-elevated temperature environment was investigated. Results showed that PVA-ECCs have enhanced tensile ductility at different sub-elevated temperature exposure times below 100°C. However, the tensile properties of PVA-ECCs at 150°C showed a strain retraction phenomenon at 6 and 9 h. The strain-hardening characteristics of PVA-ECCs gradually disappeared with the increase of the sub-elevated temperature exposure time at 200°C. The results of thermogravimetric-differential scanning calorimetry (TG-DSC), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscope (SEM) revealed that the degradation of PVA fibers was accelerated by exposure time in sub-elevated temperature, which caused the reduction of mechanical properties of PVA-ECCs.

This paper presents research about a mixture design method of pavement concrete coblending rubber and fiber into ordinary concrete. Mechanical-based tests regarding the compressive strength, elastic modulus, splitting tensile strength, flexural strength, and four-point bending stiffness were conducted to evaluate the flexural toughness of concrete, and a slab-based three-point bending test was designed to evaluate the bending toughness improvement of the road pavement concrete slab. The results indicated that with the increase in single rubber content, the compressive strength and elastic modulus of concrete decreased continuously. The rubber concrete specimen remained relatively complete in appearance during destruction, showing the satisfied ductile failure characteristics to pavement usage with the optimal rubber content of 10%. After adding basalt fiber (BF) or polypropylene fiber (PPF), with the increase of fiber content, the bending stiffness of concrete decreased, the corresponding deflection of peak load increased continuously, and the bending deformation capacity of concrete could be significantly enhanced. Compared with the reference group, when the rubber content is 10%, and basalt fiber content is 0.5%–2%, the equivalent initial bending strength of fiber-reinforced rubber concrete is increased by 105.4%–164.4%. In general, BF is better than PPF in improving the toughness of rubber concrete, and the optimal dosage of BF is 1% of concrete volume in this test. When loaded to the limit load, the deflection of the basalt fiber–reinforced rubber concrete slab in the middle of the bottom span was about four times higher than that of the benchmark concrete slab, the bending deformation capacity and toughness of the basalt fiber–reinforced rubber cement concrete slab have been greatly improved. From the test results, the mixture design method of flexible pavement cement concrete based on rubber and fiber coblending was proposed, which contributes to the development of flexible materials for concrete pavement.

The design and development of environmentally oriented cements with predominant content of widespread noncalcined precursors contribute to a more promising future for constantly evolving alkali-activated materials (AAMs). In this study, natural and designed blends of calcined clays and abundant raw calcium carbonate minerals were investigated as binary precursors for one-part AAMs using standard techniques, thermal, X-ray diffraction, and scanning electron microscopy/energy dispersive spectroscopy (EDS) analyses. The influencing factors to set optimal parameters were the mineralogical assemblage, precursors fineness, formulation details, means of alkali reactant incorporation, and curing regimes. It was stated that hydraulic one-part AAMs can be derived from calcined marl incorporated with limestone powder containing 5.8%–7.0% of calcined clay minerals and 54.6%–60.5% of calcite or nonhydraulic one-part AAMs from a mixture consisting of 20%–30% metakaolin and 70%–80% limestone powder. It was found that, compared with a metakaolin-limestone-based binary precursor, alkali activation of calcined marl–limestone results in the formation of a higher amount of binder gel with a greater extent of Ca incorporation into the structure of Na aluminosilicate gel and the formation of Ca aluminosilicate and Ca silicate hydrogels. This provides an alkali-activated calcined marl–limestone binder system with better mechanical properties and continuous strength development, including under wet conditions.

Geopolymer is a promising candidate for green cement. However, the supply of Class-F fly ash is declining rapidly. This research developed the sectioned compaction self-assembly (S-CSA) technique to produce strong brick-sized geopolymer samples. The fly ash content is only $\sim 15\%$, nearly half the level of conventional geopolymer mortars. The compressive and flexural strengths are comparable to those of typical steel-reinforced concrete. The key S-CSA step is compaction of the premixed materials. The sectioned operation helps to minimize the required force. The material properties are quite uniform and repeatable. These findings are important not only for minimizing the fly ash consumption, but also for reducing the use of alkali activators.

Glued-in rods in timber joints are efficient to transfer axial forces, and their pullout performances are not only related to the anchorage length, rod diameter, and glue-line thickness, but also to the angle of the rod to the grain—or the rod-to-grain angle. The limited available results on the effect of the rod-to-grain angle from literature are mostly based on the pullout tests with short anchorage lengths under the pull-compression loading, which do not correspond with the practical applications of glued-in rods. This paper explored the pullout performances of the glued-in rods with an anchorage length 10 times the rod diameter at 0° (parallel) to the grain under pull-pull loading pattern, and at 30°, 45°, 60°, and 90° (perpendicular) to the grain under pull-beam loading patterns, which are closer to practice than pull-compression loading pattern. The pullout capacity and slip modulus of timber joints with the glued-in rods parallel to the grain were greater than those at an angle to the grain. The empirical formulas were derived from the experimental results to predict the pullout capacities and slip moduli of the glued-in rods at an angle to the grain using the pullout capacity and slip modulus of the glued-in rods parallel to the grain.