Journal of Materials in Civil Engineering

This paper investigates the incorporation of ordinary portland cement (OPC) to adjust/improve the workability, setting time, and compressive strength of Class F fly ash (FA)–based geopolymer binder. The geopolymer binder specimens were produced by mixing OPC with FA at a dosage of 0%, 5%, 10%, 15%, and 20% by weight of FA, respectively, and then mixing the mixture with a blended sodium silicate (SS) and sodium hydroxide (SH) solution at a SH concentration of 5 M and a SS/SH ratio of 1. A water-to-solid ($\mathrm{W}/\mathrm{S}$) ratio of 0.35, 0.40, 0.45, and 0.50, respectively, was used in preparing the specimens. The viscosity and setting time of the fresh geopolymer binder were measured by using a coaxial cylinder viscometer and a Vicat apparatus, respectively. The specimens were cured at 35°C in an oven for 7 days before tested to measure the unconfined compressive strength (UCS). The results show that the viscosity of the geopolymer binder increases with higher OPC content and lower $\mathrm{W}/\mathrm{S}$ ratio. The addition of OPC reduces the setting time. The shortest initial and final setting times of 16 and 46 min, respectively, were obtained at $\mathrm{W}/\mathrm{S}=0.35$ and 20% by weight OPC. The incorporation of OPC increases the UCS of the geopolymer binder. The highest UCS of 42.4 MPa was obtained at $\mathrm{W}/\mathrm{S}=0.35$ and 20% by weight OPC. Microstructural and chemical analyses including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were also carried out and the results indicate that the addition of OPC produces a denser microstructure by the formation of calcium silicate hydrate (CSH) gel along with geopolymer gel.

On a mesoscopic scale, concrete is considered to be a heterogeneous composite material which is composed mainly of cement mortar, aggregate, an interface transition zone (ITZ), and pores. The mesoscopic model of concrete was established by applying digital image processing (DIP). To study the impact of porosity on the compressive strength of concrete, the pore equivalent model was introduced to build concrete with different pore contents. The base force element method (BFEM) based on the complementary energy principle was used in the numerical simulation of concrete. This paper investigated the effect of porosity on the strength of concrete under uniaxial compression. The results showed that the mesoscopic model of concrete based on DIP technology can better simulate the strength test and failure mechanism of concrete by using BFEM. As the porosity in the ITZ increases, the peak strength of concrete under compression decreases. The compressive strength of concrete also decreases with the growth of porosity in the mortar matrix. The ITZ porosity has a greater effect on the compressive strength of concrete than the mortar porosity.

The crumb rubber (CR) derived from waste tires has been used widely to prepare rubberized asphalt for paving applications. However, rubberized asphalt severely suffers from poor compatibility and consequent storage instability. Therefore, a solution soaking pretreatment was used to activate the CR surface to improve the compatibility of rubberized asphalt in this study. Three different solutions—water, sodium hydroxide, and sulfuric acid—were employed. The Fourier-transform infrared spectroscopy (FTIR) spectra indicated the removal of zinc stearate from the CR surface after solution soaking. Consequent improvement of the surface hydrophilicity of CR was found from the promoted sedimentation in water and the reduced water contact angle. Dynamic dhear rheometer (DSR) test results showed that the effect of solution soaking on the rheology of rubberized asphalt was slight. However, according to the results of the segregation test and a novel drainage-based method, the solution soaking pretreatments significantly improved the compatibility of rubberized asphalt. This was reflected directly in the reduced segregation degree and promoted CR/asphalt interactions. The solution soaking pretreatment of CR had no adverse effect on the moisture susceptibility of rubberized asphalt according to the modified binder bonding strength (BBS) test results. Of the three pretreatments, sodium hydroxide performed best, followed by sulfuric acid and water.

In order to mitigate the serious rutting disease of the semirigid base asphalt pavement (SBAP), measuring the settings of a high modulus asphalt concrete (HMAC) layer in the SBAP structure was proposed in this study. In this paper, the mechanical structure model was established according to the typical structure in the perpetual pavement (PP) design, and the mechanical response of pavement structure was analyzed, and then, the reasonable calculation points, critical failure axle load, and minimum ${\mathrm{E}}^{*}$ value of HMAC applicable to the PP structure were demonstrated. On this basis, referring to the design concept and analysis process of the PP structure, the reasonable calculation points, critical failure axle load, and minimum ${\mathrm{E}}^{*}$ value of HMAC applicable to the SBAP structure were determined, and then, the antirutting behavior of HMAC was analyzed and discussed. The results show that under the vehicle load, the SBAP structure shows different mechanical responses with the PP structure. For the PP structure, the center of wheel gap should be used as the calculation control point; differently for the SBAP structure, the center of wheel gap, the center of the load action and the edge of the load action should be respectively taken as the analysis points of antifatigue, vertical compressive stress, and shear strain. Also, the critical failure axle load of the two pavement structures was both determined as 130 kN. In order to achieve the design goal of pavement durability, the minimum ${\mathrm{E}}^{*}$ value of HMAC applicable to the PP structure should not be less than $\mathrm{14,000}\mathrm{MPa}$ (20°C, 10 Hz); while for the SBAP structure, the minimum ${\mathrm{E}}^{*}$ value of HMAC should not be less than $\mathrm{13,000}\mathrm{MPa}$ (20°C, 10 Hz). In addition, setting the high modulus layer (HMAC) in the middle and lower surface layer of SBAP structure can effectively reduce the shear deformation and the vertical deformation of the structure layer, thus improving the rutting resistance of pavement structure.

This paper presents the experimental and numerical studies of flexural-fracture behaviors of steel fiber–reinforced rubber self-compacting concrete (SRSCC) materials. The scrap-tires rubber aggregate was used to partially (10%, 15%, and 25%) replace the fine aggregate based on its volume for SRSCC samples, and the microsteel fiber was introduced with an addition ratio of 0.2% based on the entire mixture volume. The plain self-compacting concrete (SCC) and the rubberized SCC specimens were produced for comparison. The three-point bending test on the single-edge notched beam showed the increased flexural strength and total fracture energy of SRSCC samples by adding steel fiber and rubber. The critical fracture parameters including initial fracture energy ($G_f$) and fracture toughness ($K_{\mathrm{І}c}$) were determined based on the Load-CMOD curves and two parameters fracture model. With these properties, the bilinear tension-softening model (aggregate interlock effect) and trilinear tension-softening model (aggregate interlock and fiber-bridging effects) were calibrated for normal SCC and SRSCC, respectively. The tension-softening functions were utilized in the FEM model to predict the flexural-fracture behaviors of corresponding specimens, and the numerical simulation results showed reasonable agreement with experiments. Overall, the experimental testing data and numerical simulation model can reveal the detailed fracture behavior of SRSCC for future improved material design.

Due to several types of deterioration, such as rutting, fatigue cracking, and thermal cracking, that occur in the structure of pavements, researchers have developed solutions, including constructing pavements with enough resistance against permanent deformation, such as stone matrix asphalt (SMA) mixtures, and delaying the pavements’ deteriorations by modifying asphalt binder with various modifiers such as nanoparticles. To decrease the costs required for the construction of pavements and bring about some environmental advantages, researchers gave suggested the use of reclaimed asphalt pavement (RAP) materials in the construction or rehabilitation of pavements. In this study, SMA mixtures in conjunction with asphalt binders containing 0%, 20%, 30%, 40%, and 50% RAP materials modified with 0%, 2%, 4%, and 6% nanosilica were fabricated, and their performance was evaluated through several tests, including dynamic creep, resilient modulus, moisture susceptibility, semicircular bending (SCB) at the intermediate temperature, and bending beam rheometer (BBR) tests. The results showed that the use of nanosilica with RAP materials increased the rutting resistance of mixtures significantly. Moreover, a remarkable increase in resilient modulus values was observed, which was more evident at 25°C than at 5°C. The contemporaneous addition of RAP materials and nanosilica into SMA mixtures increased the moisture and fracture resistance of mixtures, but the effectiveness of nanosilica in increasing the tensile strength ratio (TSR) of mixtures was undermined when it was used in combination with RAP materials. However, the modification of asphalt binders with nanosilica decreased the low-temperature performance of binders, which was more evident in binders containing RAP binder.

This study investigated the use of portland cement (PC)–ground-granulated blast-furnace slag (GGBS) binary cement (BC), which was improved by chemical activation and nanomodification, as a potential alternative to PC for stabilization of dredged sediment (DS). The activators of ${\mathrm{Na}}_2{\mathrm{SiO}}_3$ (SM), ${\mathrm{Ca}(\mathrm{OH})}_2$ (CH), ${\mathrm{Na}}_2{\mathrm{SO}}_4$ (SS), and nanomodifiers of ${\mathrm{nano}\text{-}\mathrm{SiO}}_2$ (NS) and nano-MgO (NM) were used to improve the strength gaining of BC-stabilized DS (BCDS). A series of unconfined compressive strength (UCS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests were conducted to investigate the strength development and associated micromechanisms of nanomodified and activated BCDS. The results indicated that chemical activation can effectively improve the UCS of BCDS, and optimum single activator contents of SM, CH, and SS were respectively 6%, 4%, and 10%. Composite activators SM/SS with mass ratio of 1/9 exhibited more advantages than a single activator. Nanomodification can further improve the UCS of SM/SS-BCDS. The optimum single nanoparticle contents of NS and NM for SM/SS-BCDS were 6% and 8%, respectively. Compared with a single nanoparticle, composite nanoparticles NS/NM with mass ratio of 5/5 were more effective in improving UCS of SM/SS-BCDS. The 15% optimum NS/NM-SM/SS-BC can be used to replace 30% PC for DS stabilization. XRD and SEM results confirmed that the main hydration products of NS/NM-SM/SS-BCDS were calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH), and ettringite, which contributed to the strength enhancing.

Steel slag is increasingly applied during road construction and maintenance processes due to its superior surface and mechanical properties such as hardness, rough surface, and wear resistance. In this paper, the effects of steel slag on mechanical performances in varied skeleton structures of asphalt mixtures are evaluated. The Marshall mix design method is modified, and a concept of nominal asphalt-aggregate ratio is proposed to match the asphalt mix design that includes steel slag. The aforementioned methods are then applied to the asphalt concrete (AC) and stone matrix asphalt (SMA) gradations. The performance tests are carried out to further evaluate the influence of the modified method on the mechanical properties for both AC and SMA gradations. Results show that the performance indexes of the steel slag mixture can satisfy specification requirements by using the modified Marshall mix design method; then, its effectiveness is verified. In contrast to the mixtures without using steel slag, the asphalt mixtures with steel slag show better rutting resistance of SMA gradation due to the characteristics of strong internal friction resistance and higher strength; the low-temperature crack resistance can also be improved, especially for the SMA gradation. The steel slag mixture does not show strong volume expansion and has good water stability. The skid resistance performance of the steel slag mixture is improved at a small level for both skeleton structures. The overall results indicate that the performance improvement effects of steel slag for asphalt mixture are obvious, and the modified Marshall design method can be used to guide the mix design for the application of steel slag in the asphalt mixture, which can significantly reduce the engineering cost and environmental effect for producing the asphalt mixture, promoting the sustainability of asphalt pavement.

The open graded asphalt friction course (OGAFC) is a hot mix asphalt wearing course designed and constructed to mainly achieve the benefits of quick surface water drainage, high skid resistance, and low tire-pavement noise. OGAFC thus offers advantages of reduced hydroplaning, reduced splash and spray, reduced noise, and enhanced skid resistance and visibility (especially in wet weather). These mixes demand a uniform/open aggregate gradation for high permeability; establishment of proper stone-on-stone contact for good structural stability; and higher relatively stiff binder content for adequate resistance to moisture damage and binder draindown. Due to the lack of fines and higher binder content in OGAFC mixes, the asphalt binder tends to move down vertically under the influence of gravity when exposed to high temperatures during production (production-stage draindown) and over time at high pavement service temperatures (long-term draindown). This study evaluates long-term binder draindown of OGAFC mixes with both natural aggregates and basic oxygen furnace (BOF) steel slag, a waste/by-product of steel making, as a replacement for natural aggregates. OGAFC mixes with five replacement percentages (0%, 25%, 50%, 75%, and 100%) of BOF steel slag and two types of modified binders (polymer and modified crumb rubber) were subjected to different long-term binder draindown–conditioning protocols and then evaluated through determination of permeability characteristics, moisture susceptibility, raveling potential, and permanent deformation. The results revealed that aging in terms of temperature and duration has a significant effect on binder draindown. OGAFC mixes with higher BOF steel slag content showed better raveling, rutting, and moisture performance compared with a control mix after being subjected to long-term draindown. The inclusion of BOF steel slag up to 100% in OGAFC mixes produced encouraging results, with overall improvement in performance.

Welded joints and surrounded material discontinuity zones in metallic infrastructures are highly vulnerable to severe corrosion-induced damage, which significantly shortens the service life and leads to enormous economic loss. Despite great efforts in protective coatings used for corrosion control, lack of sufficient damage tolerance and corrosion resistance of these existing coatings makes weldments the most common contribution to premature malfunction and even structural failure. Nanomodified composites showed great potentials toward high-performance protective coatings for metallic substrates. Therefore, this study investigated the performance of welded joints that are protected by nanocomposite coatings. Carbon-based nanoparticles, carbon nanotubes, graphene, and fullerene-C60 were selected as one-, two-, and zero-dimensional materials. Results revealed that the nanocomposite coatings had provided excellent protection properties for weld joints. The electrochemical impedance spectroscopy (EIS) results suggested that the addition of graphene and fullerene-C60 led to enhance anticorrosion performance, while significant improvement in abrasion resistance and mechanical properties were observed in the nanocomposite reinforced by carbon nanotube and fullerene-C60. Viscosity and particle size distribution tests were utilized to study the interaction between nanoparticles and epoxy resin.

To investigate the characteristics of high-altitude concrete, the influences of atmospheric pressure on the air content, bubble stability, and pore structure of air-entrained concrete were tested by simulating a low-pressure condition using an environmental chamber. The pumping process was simulated using a resistance tester to investigate the effects of atmospheric pressure on the concrete slump, slump flow, V-funnel time, and pumping resistance. The results showed that the air content of air-entrained concrete decreases significantly with decreasing atmospheric pressure and that the pore structure of hardened concrete deteriorates. Among the admixture components, the effect of the air-entraining agent (AEA) on reducing concrete pumping resistance was the most evident. The pumping resistance of concrete increases at low atmospheric pressure, but that of concrete with AEA increases minimally. Combined with the ideal gas state equation, the air-entraining mechanism of high-altitude concrete was explained.

A review of the published literature shows that although intensive research has been conducted on corrosion of steel in soils, accurate prediction of corrosion pit growth remains a serious challenge. This study aimed to develop a new model for predicting the maximum pit depth in buried steel pipes and verify it with data obtained from actual corrosion measurements in the field. A method was developed that integrates advanced data mining techniques, shape descriptive modeling, and evolutionary polynomial regression in deriving the underlying relationships between corrosion-influencing factors and model parameters. It was found that the area effect $\psi$ is closely related to the ion content of the soil (${\mathrm{Na}}^{+}{,\mathrm{K}}^{+}$, ${\mathrm{Mg}}^{2+}$, ${\mathrm{Cl}}^{-}$, and ${\mathrm{SO}}_4^{2-}$) and that the correlation between model parameter $K_u$ and soil properties varies among soils with different aeration. It was also found that the developed predictive model exhibits superiority over existing models in quantifying multiple-phase corrosion growth. The proposed method can effectively correlate model parameters with the main contributing factors, which enables researchers and practitioners to accurately predict the maximum corrosion pit depth in buried steel pipes.

Using the Moon’s natural resources to build infrastructure is the first step toward lunar colonization. Lunar regolith, rich in aluminosilicate, has the potential to prepare geopolymer for construction. In this paper, carbon nanofibers (CNFs) were added to geopolymers based on lunar regolith simulant, aiming at reinforcing mechanical and microstructural properties. A ball-milling method of CNF dispersion into the lunar regolith simulant was evaluated. The mechanical properties of the resulting geopolymer nanocomposites was investigated. X-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectrometry, and mercury intrusion porosimetry were used to characterize the microstructural properties. The results indicated that the mechanical properties were improved by CNFs and that the optimal content was 0.3% by weight. Also, flexural strength, Young’s modulus, flexural toughness, peak displacement, and compressive strength were reinforced by 34.8%, 7.5%, 83.9%, 21.4%, and 13.1%, respectively. Microstructural results suggested that the CNFs acted as nucleation, fillers, and bridges in the nanocomposites, leading to lower porosity, higher energy requirement for failure, and higher mechanical properties, which are considerable for lunar-based construction.

Textile-reinforced concrete (TRC), a new composite material commonly used for repair and reinforcement of engineered structural surfaces, is easily affected by high temperatures in the event of fire. Therefore, when investigating the fire resistance of this material, it is important to evaluate and improve its high-temperature mechanical properties. In this study, ordinary portland cement and high-alumina cement TRC were prepared, with various proportions of metakaolin used to replace the cement, to investigate the changes in the mechanical properties of TRC and its deterioration mechanism. The experimental results showed that metakaolin improved the mechanical properties of ordinary portland cement sheets at low temperatures, with optimum substitutions of 15% and 20% in ordinary portland cement and high-alumina cement, respectively. Moreover, basalt fiber woven mesh was shown to significantly improve the ductility and flexural properties of TRC sheets, and high-alumina cement-based TRC exhibited superior bending properties at 800°C with 216.4% ultimate improvement over ordinary portland cement. The results of microscopic analysis and X-ray diffraction (XRD) experiments revealed that the decrease in the high-temperature mechanical performance of the TRC sheets was caused by a combination of high-temperature damage to the matrix concrete, deterioration or oxidative deterioration of the fibers themselves, and damage to the bonding surface of both the concrete and the fibers. At high temperatures, the microstructure of the high-alumina cement TRC was tighter and bonded more effectively to the basalt fiber grid.

With advances in materials science, the performance of concrete materials has continued to improve, especially its compression strength. However, increases in compression strength often result in ductility decreases and sudden failures. The addition of steel fibers can improve the tensile strength of concrete materials and its ductility. This investigation developed an analytical material model for steel fiber–reinforced concrete (SFRC) based on a variable engagement model. This model was extended to an analytical method that predicts the precracked and postcrack flexural behavior of SFRC beams, with various fiber orientations. To validate the proposed model, direct tension and pullout fiber tests and flexural beam tests on a variety of fiber configurations were used to evaluate the effect of fibers added in mortar beams. The proposed analytical models were used to predict the tensile behavior of proposed steel fiber–reinforced composites, including precrack and postcrack flexural behaviors. Comparisons show that although more work is needed in precrack behavior, reasonable agreement was found between predicted and measured behavior.

In this study, the effects of zero-valent iron (ZVI) nanoparticles (NPs) on the mechanical performance of cementitious composites were investigated. For this purpose, the use of a novel nanomaterial containing ZVI NPs blended with carboxymethyl cellulose (CMC) and ${\mathrm{SiO}}_2$ was introduced. ${\mathrm{CMC}/\mathrm{SiO}}_2\text{-}\mathrm{ZVI}$ NPs were prepared by a green and low-cost sonochemical method at room temperature and characterized using scanning electron microscopy/energy dispersive X-ray spectroscopy, thermal gravimetry analysis, Brunauer–Emmett–Teller, and X-ray diffraction techniques. The values of intrinsic viscosities of ${\mathrm{CMC}/\mathrm{SiO}}_2\text{-}\mathrm{ZVI}$ NPs were examined to determine the optimal miscible condition as affected by the different mass ratios of ${\mathrm{CMC}/\mathrm{SiO}}_2$ and sonication time. Then, eight different cement mortar specimens containing ${\mathrm{CMC}/\mathrm{SiO}}_2$ and ${\mathrm{CMC}/\mathrm{SiO}}_2\text{-}\mathrm{ZVI}$ NPs were prepared in ratios of 0.2%, 0.5%, 1%, and 2% by weight, and flexural and compressive strengths of the specimens were determined at the ages of 7 and 28 days. The microstructure of the specimens was also evaluated. Comprehensive results proving the improvement in the mechanical properties have been obtained in the specimens containing 1% and 2% ${\mathrm{CMC}/\mathrm{SiO}}_2\text{-}\mathrm{ZVI}$ NPs.

The vibratory probe compaction method may sometimes fail to proceed smoothly due to the hard layer encountered during treatment of collapsible loess foundation. To this end, high-pressure water jetting around the traveling drill bit was used to soften the soil layer to assist the vibratory probe in sinking. However, due to the shortage of water resources in northwest China, a measure to reduce water consumption and add hydrochloric acid solution was adopted. To clarify the effect of the hydrochloric acid solution on the engineering characteristics of loess, this study conducted a series of geotechnical tests on remolded loess samples mixed with different concentrations of hydrochloric acid solution at the same dry density. The test results showed the pH values of all the sample leachates ranged from 7.83 to 7.64, and they had little effect on the surrounding environment. The coagula generated from the reaction between the acid solution with the original cementing material inside the loess enhanced the cementation between the soil particles and filled the gaps between the particles. The formation of this new structure gave the sample a strong ability to resist collapsing deformation, which was reflected in the acid-added sample having a smaller collapse coefficient than the water-added sample after the last stage of the collapsibility test. However, because the maximum dry density of the mixture increased with the increase of the acid concentration, the degree of compaction of the acid-added sample at the same dry density was insufficient, resulting in considerably bigger and more macro pores than that of water-added sample. It further caused the strength and disintegration characteristics of the sample to deteriorate with the increase of the acid concentration. The application of acid-added loess as a compacted filler is feasible for the construction of the vibratory probe compaction method in the loess area, which provides a new method for the treatment of collapsible loess foundation.

The replacement rates of portland cement by ceramic waste powder (CWP) are generally limited to few percentages (i.e., less than 10%), as increased additions lead to inferior concrete strength and durability. This paper assesses the importance of blending CWP with blast furnace slag (BFS) to foster synergistic pozzolanic reactions and reinstate strength development despite increased cement replacement rates. Tested binders contained different cement-CWP-BFS proportions, while the evaluated properties included the compressive, splitting tensile, and flexural strengths in addition to the modulus of elasticity, freeze/thaw resistance, and thermal transmittance. Test results showed that concrete strength and durability gradually degraded when the cement was partially replaced by 10%–20% CWP, given the dilution effect that alters hydration reactions and overall porosity. Yet, the concrete properties significantly improved when the CWP and BFS materials were both incorporated in the same binder, indicating the occurrence of synergistic pozzolanic reactions that refined the matrix microstructure. Hence, concrete prepared with ternary binder containing 50% cement, 15% CWP, and 35% BFS exhibited durability and strength properties at 56 days comparable to the control mix made with 100% cement.

Mechanical vibrations have a significant impact on the performance of cement-based materials in engineering. In this study, the particle distribution characteristics and hydration mechanism of cement-based paste during mechanical vibrations were clarified, including examination of hardened properties and thermodynamic modeling. X-ray fluorescence was used to determine the distribution of raw material particles. Differential thermal analysis was employed to characterize the in situ hydration process of paste. Thermodynamic modeling determines the dependency between raw material distribution and the corresponding hydration process. The results indicated that low-frequency vibrations extend the setting time and induce lower flexural strength of cement paste during early ages. Mechanical vibrations result in significant inhomogeneous distribution of element content, which was attributed to the difference in raw material composition. The hydration degree after mechanical vibrations decreased the pore-size distribution of hardened paste. The calculated particle distributions were inconsistent with the obtained hydration process and porosity development.

Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and contact angle measurements were conducted in the present research to analyze the characteristics of warm-mix rubber-modified asphalt during water damage under different immersion times. The evolution of characteristics of asphalt binders was investigated based on their chemical compositions, functional group indexes, nanomechanical characteristics, and surface free energies. It was found that water molecules changed the proportion of each component of asphalt binders. With the increase of immersion time, the functional group index representing the damage degree increased and more water molecules interacted with polar components of asphalt binders, resulting in more molecular fracturing and recombination. Water molecules penetrated asphalt binders, and the interfacial tension and the hydrostatic pressure in the presence of water caused the redistribution and aggregation of molecules in asphalt binders, forming a new morphology and structure. The increase of the immersion time aggravated the reduction of the adhesion force and the increase of the Derjaguin-Muller–Toropov (DMT) modulus of asphalt binders. In addition, with the increase of the immersion time, the surface free energy (and its dispersion component) of asphalt binders decreased gradually and, in turn, the van der Waals force between asphalt molecules also decreased. The addition of warm-mix additives (EM and SDYK) changed the morphology of the rubber-modified asphalt (60MCR) and increased the adhesion force, DMT modulus, and surface free energy of asphalt binders. Simultaneously, the antiwater damage ability of asphalt binders was also improved. After different immersion periods, it was found that for the rubber-modified asphalt with SDYK additive (0.6S-60MCR), the increment degrees of the DMT modulus and the functional group index as well as the reduction degrees of the adhesion force and the surface free energy of asphalt binders were lower than those of the rubber-modified asphalt (60MCR) and the rubber-modified asphalt with EM additive (1E-60MCR), indicating its superior resistance to water damage.

This study was designed to analyze the characteristics of two recycled fillers, hollow concrete block (HCB) powder and brick powder (BP), and to assess their respective impacts on the mechanical properties of hot-mix asphalt (HMA) when used as complete replacements for limestone (LS) filler. The recycled and LS fillers are obtained from construction and demolition wastes and naturally mined for commercial uses, respectively. Filler characteristics were examined using Brunauer–Emmett–Teller, X-ray diffraction, scanning electron microscope, and energy dispersive X-ray spectroscopy. The respective effects of the fillers and the mechanical properties of the HMA mixtures were assessed using Marshall stability, indirect tensile strength, moisture damage by tensile strength ratio, indirect tensile cracking index, and permanent deformation tests. The results demonstrated that HCB powder significantly improved moisture, rutting, and crack resistance in HMA, which are factors critical to extending the life of asphalt concrete. In contrast, using BP resulted in mixed values and negative effects, particularly in terms of moisture resistance and rutting.

The deep surrounding rock under true triaxial stress is easy to break at the new excavation face, which will induce engineering disasters to threaten personnel and equipment. Many studies have shown that the intermediate principal stress (IPS) has a great influence on rock failure. To accurately understand the influence of IPS on the gradual failure mechanism of the new excavation face under true triaxial stress and extract the key precursor information of rock failure, this study is based on true triaxial tests of acoustic emission (AE) monitoring, which provides a creative explanation to the phenomenon that sometimes the sudden increase of the AE counts rate (ACR) and the energy release rate (ERR) changes asynchronously. This paper analyzes the influence of IPS on the crack type in the failure process, studies the transitional behavior and gradual evolution of AE dominant frequency, and presents the precursor information index for rock failure. The results show that the sudden increase times of ACR and ERR under different IPS values are different. The rock under lower IPS is prone to produce intergranular fracture with low energy consumption, while the rock under higher IPS is prone to produce transgranular fracture with high energy consumption. Near the peak stress, the dominant frequency at lower IPS shows obvious downward transitional behavior, and the dominant frequency under higher IPS presents downward and upward transitional behavior. This study verified that $t_{\mathrm{III}-\max }$ can be used as the key precursor information for predicting rock failure.

AASHTO has provisionally endorsed the use of a three-wheel polishing device (TWPD) for polishing and the dynamic friction tester (DFT) for measuring the friction of the coarse aggregates used in hot mix asphalt (HMA). Despite ample studies showing the feasibility of such a system for HMA specimens, research efforts related to quantifying the coarse aggregates that are used in those mixes have been less common. The results of a study to accelerate the test and to decrease the tedium of specimen preparation for aggregates are reported here. Three identical TWPD devices that complied with the AASHTO provisional specification were fabricated. A new specimen preparation method was introduced to reduce the associated time and cost. Several operational parameters that can impact the repeatability and reproducibility of the process, such as tire type and tread condition, specimen preparation, and DFT rubber pad thickness, were investigated. This study verified that the TWPD/DFT test method can delineate the polishing/friction performance of different aggregates with acceptable repeatability and reproducibility. The TWPD/DFT test time and cost can potentially be decreased considerably by using the proposed practical and analysis modifications.

This study builds a large database from an extensive survey of existing bond strengths between ultrahigh-performance concrete (UHPC) and normal-strength concrete (NC), with total 563 specimens being collected. To make up for some factors not included in the existing tests, an additional 38 specimens were tested with the improved slant shear method to enrich the database. The four governing factors for the interface strength were identified from the test results of the total $563+38$ specimens: compressive strengths of UHPC and NC materials, interface roughness, normal stress level, and casting sequence. It is highlighted that this work discusses the effect of casting sequence. To obtain an accurate prediction formula, an artificial neural network (ANN) model is constructed, where the effect of casting sequence was firstly introduced. Based on the trained ANN model, an explicit formula is presented that significantly minimizes the prediction error. A modified shear-friction formula is also proposed for the UHPC–NC interface shear strength. Compared with other calculation models for concrete interface strength, this proposed formula with multiple parameters has a better accuracy.

No-fines concrete (NFC) has a large volume of voids and a porous nature which reduces the rainwater runoff, recharges the groundwater table, and reduces noise from vehicle tire movement. The elimination of sand and the high amount of voids in NFC leads to a decrease in the strength. Therefore it can be used only in limited practical applications. An attempt was made in this study to improve its strength without compromising its porosity and permeability properties by utilizing optimum levels of supplementary cementitious materials (SCM)—rice husk ash (RHA) and silica fume (SF)—as partial replacement of cement. Results indicated significant improvement in compressive strength by 16.40% with 10% replacement of cement by SF at 90 days, and 25.04% increase with 5% RHA at 90 days. The results were well supported by microstructural analysis of NFC mixes with SCM replacement, which showed a dense and compact micrograph. Permeability and porosity decreased very marginally with SF and RHA replacement at optimum levels without much affecting the drainage properties. The improved compressive and flexural strength and abrasion resistance of NFC with RHA and SF as SCMs indicated applicability in medium-traffic applications.

The structural behavior of an innovative wood-based composite system, manufactured out of $2\times 6$ southern yellow pine lumber, was studied through destructive experiments. The composite panel system consisted of profiled 34.9-mm-thick surface laminations with precut rectangular grooves and 25.4-mm-thick cross-laminations fitted (embedded/dadoed) into the grooves. The cross-laminations were oriented across the surface layers at a specified repetitive spacing. Given that the 34.9-mm-thick surface laminations were in direct contact with each other in those places where the cross-laminations were absent, the total depth of the panels was 69.9 mm. The flexural and shear performance of this composite system, which is called embedded cross-laminated timber (ECLT), were compared against that of the conventional three-ply cross-laminated timber (CLT) panel with the same thickness. The ECLT panel specimens were expected to perform better than the CLT panel specimens in bending because they have more wood fibers aligned parallel to their neutral axes. The effective bending stiffness ($E{I}_{\mathrm{eff}}$) and moment carrying capacity of the two composite systems were obtained by conducting four-point bending tests at a span-to-depth ratio of $26.4:1$. The ECLT specimens exhibited an average moment carrying capacity of $10.9\times {10}^6\mathrm{N}·\mathrm{mm}$ and $E{I}_{eff}$ of $89.4\times {10}^9\mathrm{N}·{\mathrm{mm}}^2$, while the conventional CLT specimens achieved corresponding properties of ${10.2\times 10}^6\mathrm{N}·\mathrm{mm}$ and $84.2\times {10}^9\mathrm{N}·{\mathrm{mm}}^2$, respectively. Also, the effective shear stiffness ($G{A}_{eff}$) and shear force capacity of the composite systems were estimated and measured, respectively, by conducting four-point bending tests at a span-to-depth ratio of $11.6:1$. On average, the ECLT specimens resisted the shear force of $38.2\times {10}^3\mathrm{N}$, while the conventional CLT specimens resisted $36.7\times {10}^3\mathrm{N}$. The average estimated $G{A}_{eff}$ values of ECLT and CLT were $2.57\times {10}^6\mathrm{N}$ and $1.93\times {10}^6\mathrm{N}$, respectively. Thus, these study results indicate that the proposed cross-laminated wood composite product might outperform conventional CLT in the major direction under bending.

The constitutive compressive stress–strain response of hybrid high-performance, fiber-reinforced concrete (HyHP-FRC) containing steel and polyvinyl alcohol (PVA) fibers is scarcely reported. In this study, the compressive stress–strain behavior of plain high-performance concrete and 18 HyHP-FRC mixtures containing steel-PVA fiber systems were experimentally measured and analyzed. The incorporation of steel-PVA fibers significantly enhanced the postcracking stress–strain response of HyHP-FRC, including its compressive strength. Additionally, physical measurements revealed that the dosage and geometry of the steel fibers significantly affected the postcracking toughness of the concrete. Using the least-squares fitting approach and additional independent data, the volumetric reinforcing index of the fibers ($R{I}_v$) and the predictive equations for the properties of the HyHP-FRC under uniaxial compression were established in terms of $R{I}_v$. These equations indicated that the compressive strength of HyHP-FRC was linearly proportional to $R{I}_v$; however, nonlinear correlations were observed for the elastic modulus and strain at the peak stress of HyHP-FRC. Finally, straightforward and more refined models for the full-scale constitutive compressive stress–strain curve of HyHP-FRC were developed and validated against the test and other data. The proposed models can be used to accurately predict the entire stress–strain response of cement-based composites containing hybrid combinations of metallic and synthetic fibers.

Polycarboxylate ether (PCE) of different charge densities has been synthesized via free radical polymerization. The molecular structure is characterized by gel permeation chromatography (GPC) and proton nuclear magnetic resonance (${}^1\mathrm{H}\mathrm{NMR}$). The interaction between PCE and three different-${\mathrm{C}}_3\mathrm{A}$-content cements has been systematically studied. The results of rheological properties, specifically apparent viscosity and yield stress, demonstrate that there are two cement paste loss stages in cement hydration process. This theory could provide guidance for the design of PCE with slump retention ability. By matching PCE release rate with the cement hydration process, we could ensure a cement paste with smooth and steady slump retention. PCE with moderate charge density shows the best compatibility with cement owing to the smallest differences in adsorption amount in different cements. Moreover, the influence of PCE on the early-age properties of cement paste confirms that the interaction of PCE with ${\mathrm{C}}_3\mathrm{A}$ or its hydration products determines the compatibility between PCE and cement, especially in the first cement paste loss stage.

An asphalt pavement with gravel base (AP-GB) is used to alleviate the occurrence of reflective cracks. However, its interlaminar stability is affected by the gravel base’s looseness and interlaminar complex contact form. In this situation, a viscoelastic model-cohesive zone model-random aggregate model (VM-CZM-RAM) composite structure model of AP-GB is proposed to describe the interlaminar complex contact form through the finite-element method. Meanwhile, the influences of gravel embedded in AP-GB interlamination stability are considered. Then based on this model, the effects of vertical load, horizontal shear speed, and interlaminar asphalt spraying dosage on interlaminar stability are investigated systematically. Results show that the interlaminar shear strength is positively correlated with the vertical load and shear speed under the model with the optimal interlaminar gravel embedded rate (5%). The best shear strength is obtained when the interlaminar asphalt spraying dosage is $0.8\mathrm{L}/{\mathrm{m}}^2$. Finally, a no-demolding specimen and its shear test method were designed to verify the feasibility of the model. The conclusions of this paper can highly help the structural design and application of the AP-GB.

Aggregate segregation is an important factor affecting the early distress and durability of asphalt pavement. To analyze the segregation tendency of aggregates on the mesoscopic scale, first, the segregation tendency of the particle system was measured using an aggregate segregation machine and compared with that of an aggregate-asphalt system. Then composite geometric indexes were calculated and a contact-slip test conducted. The effect of composite geometric characteristics of coarse aggregates on the contact and friction properties of particles was analyzed. Finally, the relations of the segregation index and mesoscopic parameters, including composite geometric indexes and contact-friction indexes, were respectively discussed. The results show that the composite angularity index exhibits a good linear correlation with the segregation index. A larger composite angularity index and composite texture index imply a stronger contact-friction strength of the particle system, which leads to the segregation of coarse aggregates. Fine aggregates move through voids among the coarse aggregates during the falling process. A larger composite shape index indicates more air voids among coarse aggregates, and fine aggregates easily move through voids at higher speed. The bonding/lubrication properties of asphalt can effectively reduce the segregation degree of aggregates.

In Brazil, large quantities of iron ore tailings (IOT) are produced as a result of iron mining, which may affect the environment negatively. This work evaluated the use of IOT in hot mix asphalt type C (HMA-C). For this purpose, IOT was incorporated as a filler (at 1% in relation to the total mass of HMA-C). The hot asphalt mix with IOT (called HMA-IOT) was designed and compared with a control HMA-C. The behavior of the mixtures under monotonic (indirect tensile strength, ITS, and the Marshall stability test), under dynamic (fatigue and resilient modulus tests), and static (static creep test) loading conditions was evaluated. Also, the resistance to induced moisture damage (tensile strength ratio, TSR) was calculated. As a general conclusion, it was shown that the use of IOT in HMA improves its mechanical response without increasing mixing and compaction temperatures and using less effective asphalt binder content. This could provide a new form of environmentally safe disposal of IOTs.

In this study, the fresh properties, fracture energy, compressive strength, and flexural strength of self-compacting concrete including glass or basalt fibers were examined, and the effect of fibers on these properties were studied comparatively. For this purpose, fibers having three different lengths (6, 12, and 24 mm) were used in two different contents (2 and $4\mathrm{kg}/{\mathrm{m}}^3$). The workability of concrete mixtures decreased with fiber addition. The negative effect of basalt fibers on workability was greater than that of the glass fibers. The reduction in flow diameter was up to 40% and 44% as well as the reduction in L-box ratio was up to 41% and 48% in glass and basalt fiber mixtures, respectively. While the fiber addition generally reduced the compressive strength, it increased the flexural strength and fracture energy significantly. Increase in flexural strength was up to 58.6% in glass fiber and 43.5% in basalt fiber mixtures. The fracture energies of glass and basalt fiber mixtures were up to 55.1% and 30.4% higher than that of the control mixture, respectively.

Macrocell corrosion is a frequent and detrimental problem plaguing reinforced concrete structures exposed to chloride environments. This paper investigates the rate-limiting step(s) of macrocell corrosion of reinforcing steel bars in concrete by quantifying the respective contributions of anodic polarization, cathodic polarization, and ohmic subprocesses to the overall macrocell corrosion. Experiments were carried out to study the impact of the distance between active and passive steels, the active-to-passive steel area ratio (A/P), and the microcell corrosion rate of active steel. Numerical simulations were further performed to extrapolate experimental results to large-scale concrete structures. Results demonstrated that with a decreasing A/P, the contribution of the anodic polarization subprocess was increased, while that of the cathodic polarization subprocess was decreased. The macrocell effect that aggravated the total corrosion rate of active steel was weakened as the microcell corrosion activity increased or with increasing the relative humidity.

Cement-stabilized pond ash is often used as an alternative to conventional materials in compacted subgrade and subbases in pavements. The addition of cement to pond ash increases cohesion and improves strength. The effects of cement content, compaction energy, and moisture content on parameters such as deviator stress at failure, resilient modulus, and permanent deformations are studied by using cement dosages of 2% and 3%, two compaction conditions (standard and modified Proctor compaction), and three water contents [optimum moisture content (OMC), $\mathrm{OMC}-2\%$, and $\mathrm{OMC}+2\%$]. The stress-strain response of cement-stabilized pond ash is similar to cement-treated soils, which show peak stress followed by softening. The cement content is the dominating factor influencing these parameters. The influence of confining pressure and compaction energy is less significant in cemented pond ash. The peak deviator stresses and resilient modulus are the highest at OMC compared to dry and wet of optimum. The resilient modulus of cemented pond ash varies from 70 to 210 MPa, making it a suitable material for pavement applications. The Uzan and National Cooperative Highway Research Program models are used to predict the resilient modulus values of untreated and cemented pond ash. There are no distinct shakedown criteria available for multistage testing of materials. A criterion is proposed for establishing shakedown ranges for untreated and cemented pond ash based on permanent strain variation with the number of cycles. A grading criterion is also defined based on these parameters in which untreated pond ash belongs to the lowest grade and cannot be used in pavements. However, the addition of cement, as low as 2%, improves the properties of pond ash considerably and makes it a suitable material for compacted subgrades in pavements.

An experimental and statistical study on the impact resistance of ultrahigh-performance concrete (UHPC) is presented. The impact resistance was evaluated by conducting the drop-weight impact test with a hammer of 10 kg following ACI Committee 544 (ACI 544.9R-17). Three mixture types, namely ordinary concrete, nonfibrous UHPC matrix, and UHPC were designed, and each type was prepared with 40 cylindrical specimens with dimensions of $\mathrm{\Phi }150\times 63.5\mathrm{mm}$ for impact test. The commonly used distribution functions for material properties (normal distribution and Weibull distribution) were selected to examine the test data, and the goodness of fit of these two distributions was evaluated using a Anderson-Darling test. Results indicate that the designed UHPC endured an average of 623 drops of impact weight before the first crack, while the ordinary concrete and nonfibrous UHPC matrix showed the first crack only after 26 drops and 17 drops, respectively. The higher-strength nonfibrous UHPC matrix broke with a fewer number of drops under impact load than the ordinary concrete (with coarse aggregate) due to the greater brittleness of the UHPC matrix. Both the normal and Weibull distribution can describe the impact resistance of ordinary concrete, while the nonfibrous UHPC matrix and UHPC showed poor fitness to either the normal or Weibull distribution. Statistical analysis results indicate large scatters in the impact resistance of UHPC, and tests with small sample size may result in unreliable judgment. In this paper a baseline of UHPC drop-impact resistance to inspire proper qualification of UHPC members designed to withstand impact loading is provided.

This study investigates the suitability of low-calcium fly ash (FA) for stabilizing expansive soil (ES) using the in-situ deep soil mixing (DSM) technique. The primary objective of the study was to control the swell-shrink behavior of ES and achieve higher strength characteristics. Owing to the presence of a low amount of calcium oxide (CaO) in Class-F fly ash (FA), an alkali environment is required to produce pozzolanic reactions involving silica and alumina. In this study, the alkali environment in the FA was created by adding a 50:50 ratio of sodium hydroxide (NaOH) and liquid sodium silicate (${\mathrm{Na}}_2{\mathrm{SiO}}_3$) solution, referred to as liquid alkali activator (LAA). The properties of stabilized ES were investigated through Atterberg limits, one-dimensional swell tests, linear shrinkage tests, consolidation tests, and unconfined compressive strength tests. Further, scanning electron microscopy images and X-ray diffraction tests were performed on stabilized samples to understand the microstructural and physicochemical reaction mechanisms. The tests were conducted by varying the binder ratio (LAA/FA) from 0 to 1.5 for curing periods of 7, 14, and 28 days. The results showed that the binder ratio $\mathrm{LAA}/\mathrm{FA}=1.5$ effectively controlled the swell-shrink behavior of ES. A 10-fold improvement in UCS was observed for $\mathrm{LAA}/\mathrm{FA}=1.50$ at a 28-day curing period. Linear shrinkage strains and swell potential of the ES were reduced by 97% and 83%, respectively, with $\mathrm{LAA}/\mathrm{FA}=1.5$ at 28 days of curing. Overall, $\mathrm{LAA}/\mathrm{FA}=1.5$ is considered an optimum binder ratio to prepare DSM columns.

To study the impact of the strain rate effect and size effect on the compressive dynamic behavior of lightweight concrete (LC), 3 cube sizes and 10 strain rates were set up, and uniaxial compression tests were conducted utilizing a servohydraulic compression-testing machine. The failure modes and compressive strength of LC under varying load cases were obtained via testing. Following an examination of the change law of strain rate effect and size effect on failure modes and compressive strength and a discussion of the relevant literature on normal-weight concrete for comparison and assessment, the primary conclusions obtained are as follows: under a strain rate effect, failure modes of LC develop from vertical cracks with an even distribution at a low strain rate to oblique cracks dominant at a high strain rate, which resembles that of normal-weight concrete. It is found that as the strain rate rises, the compressive strength of LC gradually increases while the percentage increase in the compressive strength gradually decreases withthe rise of cube sizes affected by the strain rate. The compressive strength of LC at three varying cube sizes (70, 100, and 150 mm) is increased by 53.70%, 44.71%, and 33.76%, respectively. The compressive strength of LC gradually decreases as the cube size increases. The higher the strain rate, the greater the percentage decrease of the compressive strength of LC due to size effects. The percentage decrease in the compressive strength of LC at different strain rates is between 18.24% and 28.85% under the size effect. The influence of the strain rate effect and size effect on the compressive strength of LC is more obvious than on the compressive strength of normal-weight concrete. In this study, the coupling effects of strain rate and size on the compressive strength of LC were examined from a quantitative perspective. The findings of the study have important implications for project applications and model tests of LC.

Material parameters in the Gurson, Tvergaard and Needleman (GTN) model were calibrated for G20Mn5QT cast steels based on tests of tension coupons and smooth notched tensile specimens, and complementary FEA. The mesh sensitivity of the calibrated GTN model was discussed regarding the efficiency of the FEA. As the mesh size decreases to 0.15 mm or finer, the prediction of the ductile fracture by the calibrated GTN model tends to converge. Four single-edge notched plate specimens of G20Mn5QT cast steels were tested under uniaxial tension, and the entire ductile fracture processes of the specimens were obtained. The ductile fracture of a double-hole plate specimen and the single-edge notched plate specimens were then simulated using the calibrated GTN model. The accuracy of the calibrated GTN model was verified by comparing the numerical simulation with the test results. Also validated was that the GTN model is applicable to not only the ductile fracture prediction but also the simulation of the stable fracture propagation.

Fiber-reinforced cementitious matrix (FRCM) materials are well-recognized as suitable for the strengthening of reinforced concrete (RC) and masonry existing structures. However, one of the main issues regarding these materials is the lack of knowledge about their behavior when subjected to elevated temperatures or fires. In this study, the effects of thermal actions on both the mechanical properties of the PBO (short of polypara-phenylene-benzo-bisthiazole)–FRCM materials (textile, mortar, and FRCM) and the structural response of unconfined and PBO-FRCM-confined concrete cylinders were analyzed. An experimental investigation was conducted on PBO fabrics, PBO-FRCM coupons, and unconfined and PBO-FRCM confined concrete cylinders. All specimens were thermally conditioned at temperatures ranging from 20°C to 200°C and then tested at room temperature (20°C). The thermal treatment consisted of five heating/cooling down cycles (one per day); in each cycle, the specimens were kept in an electric oven, heated at a predefined temperature over a period of 6 h, and then left to cool down at ambient temperature before the beginning of the next cycle. The test results evidenced that the thermal conditioning affected both the mechanical properties of the FRCM materials and the effectiveness of the concrete confinement. To predict the strength of the PBO-FRCM confined concrete cylinders after thermal conditioning, a semiempirical model defined through the analysis of a database of experimental results (those described in this paper and others available in the literature) was also proposed.

Lateral track stability is a critical parameter in ballasted railway tracks considering track buckling. The sleeper type has a direct impact on lateral track stability. Due to the Y-shape sleeper tracks’ truss structure, the lateral resistance increased in comparison with the monoblock sleepers, which is an efficient alternative, particularly in sharp curves. In this study, the lateral resistance of Y-shaped steel sleepers is examined using the single tie push test (STPT) as an alternative for the improvement of lateral ballast resistance. Furthermore, the discrete element method (DEM) was used to estimate the contribution of ballast components to the lateral resistance of the single sleeper. In addition, the effect of shoulder ballast width on the lateral resistance was considered in DEM models. DEM simulations confirmed that the higher sufficient lateral resistance (about 14 kN) could be achieved with a shoulder width of 200 mm.

When any material is subjected to dynamic loads, the evaluation of the repercussions of the cyclic loading on the mechanical properties is essential to understand its behavior better. Thus, based on the results of unconfined compression strength tests carried out with and without the application of cyclic loading, this work analyzes the effect of the frequency of the cyclic stage on the behavior of a stabilized sandy soil, unreinforced and reinforced with polypropylene and sisal fibers. The inclusion of fibers induces a decrease in the accumulated permanent axial strain obtained at the cyclic stage; this reduction is more significant for a frequency of 1.0–2.0 Hz and for the use of sisal fibers, due to the greater roughness and higher mechanical properties of this type of fiber. The cyclic stage induces an increase in stiffness for all frequencies studied. In terms of the unconfined compressive strength, the frequency has a low impact on unreinforced material, contrary to the effect on reinforced material, which induces a decrease in strength for a frequency of 1.0 Hz and an increase in strength for frequencies of 2.0 and 4.0 Hz for both types of fibers. Reinforcement with sisal fibers is more effective than the use of polypropylene fibers in terms of the improved unconfined compressive strength and stiffness of the specimens submitted or not to cyclic loading.