Journal of Materials in Civil Engineering

Recently, reactive nanoinorganic cement-based composite (RNICC) has attracted considerable attention as a high-strength and high-performance concrete. Understanding the mechanical properties and establishing a constitutive relationship of RNICC are of great significance for improving the numerical simulation of the mechanical behavior of RNICC structures under extreme impact and blast loading. In this study, quasi-static compression–tension and dynamic compression tests were performed on a RNICC to obtain the mechanical properties, strain rate effect, and damage modes. The results revealed that the compressive behavior of RNICC is sensitive to the strain rate effect. The main form of compressive damage of RNICC is cement matrix cracking at low strain rate. The cement matrix cracking and steel fiber fracture simultaneously occur at a high strain rate. The Holmquist–Johnson–Cook (HJC) constitutive model was used to describe the mechanical behavior of RNICC at high strain rates. Based on the experimental results, detailed test procedures and parameter characterization methods were established to determine the HJC model parameters for RNICC. The accuracy of the proposed HJC model parameters was validated by comparing the experimental data of the dynamic compression tests with finite-element simulation results based on LS-DYNA software.

The lack of bearing capacity of geotechnical materials is a recurrent problem that can be solved through chemical admixtures and densification methods. However, traditional materials/techniques are normally associated with energy-intensive processes and the extraction of natural resources and gaseous emissions. As a result, interest in more ecologically friendly solutions is rising. This paper evaluated the influence of several factors on the mechanical behavior of granular soil stabilized with an alternative alkali-activated cement produced from ceramic waste and carbide lime. Mixtures were tested for unconfined compressive strength, stiffness, durability, and strength parameters on simple shear equipment. The porosity/binder content index was applied to correlate all outcomes. Results showed that a lower silica modulus (${\mathrm{SiO}}_2/{\mathrm{Na}}_2\mathrm{O}$) resulted in lower strength and stiffness due to excessive alkalis presence; Lower silica modulus, however, also led to a smaller loss of mass under durability circumstances, indicating that the test conditions diluted any excessive alkalis. It has been demonstrated that the porosity/binder index is a useful tool for predicting mechanical behavior in terms of strength, stiffness, and durability. Finally, the monotonic shear response showed that the inclusion of the alkali-activated cement positively influenced the internal friction angle of the material and the cohesion intercept when compared to the natural granular soil.

Recently, there has been renewed interest in the incorporation of plant fibers in cementitious materials to substitute synthetic, steel, and polymer fibers. This interest has been mainly stimulated by the numerous inherent advantages in the use of natural fibers in composites, such as high supply and availability, cost-effectiveness, low density, and full recyclability. Despite the great interest in incorporating plant fibers in cement, the low compatibility between the fibers and cement generates several problems in the fresh and hardened states of the composite. This work aimed to enhance the mechanical behavior of a cement mortar by incorporating short flax fibers treated with a citric acid solution. This eco-friendly treatment was used to modify the flax fibers in order to improve their physicochemical compatibility with the cement matrix. The fibers were treated with a 5 wt.% citric acid solution, and the effects of the treatment were evaluated by analyzing the properties of the fibers’ surfaces and resulting composite. The mechanical behavior of the fiber-reinforced composite was evaluated on the samples prepared from treated and untreated fibers and compared with that of a control mortar through three-point bending and compression tests and the determination of the toughness index. The treatment was shown to be effective in modifying the surface roughness and wettability of the fibers and resulted in a 41% decrease in their water saturation rate. The cement mixture with treated fibers showed a considerable decrease in the initial setting time delay (24%), and the flexural strength was improved by 43.5% at 7 days and 18% at 28 days compared to that of the control mortar. Despite the expected decrease in the compressive strength of the composites compared to that of the control mortar, the composites containing the treated fibers showed a better performance (13% at 7 days and 6% at 28 days) than those prepared with the raw fibers. It can be concluded that treatment of flax fibers with 5 wt.% citric acid solution shows promise as a way of improving the mechanical properties of the cement mortar and could be beneficial for the production of higher quality composite materials.

Calcium sulfoaluminate cement (CSA) has excellent chloride (${\mathrm{Cl}}^{-}$) binding capacity, which is significantly influenced by the existence of calcium sulfate within mixes. However, impacts of dosage and type of the calcium sulfate on the binding performances and mechanisms are still unclear. In the paper, these impacts in CSA clinker-premixed ${\mathrm{Cl}}^{-}$ system were thoroughly explored with experimental studies, including parameters of fresh properties, hardened properties, and mineralogy aspects. Results showed that calcium sulfate accelerated CSA hydration, reduced the setting time, and sharply decreased ${\mathrm{Cl}}^{-}$ binding due to promoting formation of ettringite (AFt). The stability of Friedel’s or Kuzel’s salts formed by binding of monosulphoaluminate (AFm) and ${\mathrm{Cl}}^{-}$ was worse than that of AFt. Compressive strength reduced slightly with calcium sulfate increasing. Compared with anhydrite, dihydrate gypsum reduced shrinkage, improving volume stability.

The mechanical and durability properties of polyethylene terephthalate (PET) modified methyl methacrylate (MMA) polymer concrete (PC) composite based on industrial waste (palm oil fuel ash and red mud) were investigated for potential application at room temperature (RT) (27°C) and elevated temperature (ET) (100°C, 200°C, and 300°C). Taguchi’s design of experiments and particle packing density method for aggregates was used to optimize the PC mixture proportion and to increase the overall properties of the PC composite. The test specimens were subjected to mechanical testing, water absorption, TGA analysis, electric resistivity, ultrasonic pulse velocity, and SEM analysis. The results indicates that the palm oil fuel ash (POFA) PC specimens exposed to ET 200°C show 5.56% and 6.25% increases in compressive and flexure strength in comparison with POFA PC cured at RT 27°C. According to SEM analysis, the proposed mechanism behind the enhancement of mechanical properties is the increased polymerization reaction of modified PET resin at high temperature and the pozzolanic activity of POFA particles. PC containing red mud (RM) filler showed increased compressive strength by 7.8% in comparison with POFA PC at ET 300°C. The PET resin modified with MMA PC can be considered a promising alternative to ordinary portland cement concrete composite, especially in different types of buildings, precast walls/panels, and bridge deck pavements.

The effects of air-entraining admixture (AEA), curing process, and core direction were studied as parameters in terms of their effect on the physicomechanical properties of 3D printed concrete. Four different AEA dosages (0%, 0.1%, 0.15%, and 0.2% by dosage of binder) were used to prepare the mixtures used for 3D printing. The influence of anisotropy on the printed concrete was studied by testing the cores drilled from the horizontal and vertical directions of the 3D concretes. The study also examines the efficiency of a specific spray-deposited chemical curing technique for improving the strength characteristics of 3D concrete. The addition of AEA reduced the unit weight significantly, thereby making the concrete ideal for lightweight structural members. Ultrasonic pulse velocity (UPV) testing on 3D printed samples showed that voids and air entrainment during the deposition process reduced the wave velocities. The ultrasonic wave velocity of cores drilled parallel to the printing direction was found to be slightly higher than cores perpendicular to the printing direction. However, the observation from the nondestructive tests did not agree with the compressive strength studies. The compressive strength of the cores drilled perpendicular to the direction of printing was higher than those drilled parallel, which can be due to the layers formed in the concrete during the filament deposition process. The 3D printing process reduced the compressive strength and induced anisotropy. The compressive strengths were reduced with air entrainment in the sample that was not 3D-printed. However, in the 3D-printed samples, 0.1% of AEA increased the vertical and horizontal strength compared to the samples without AEA. AEA in small quantities was found to be capable of improving the rheology of the mix and reducing the possible defects during the printing process, which resulted in better interlayer bonding. The durability aspect of air entrainment was studied using capillary water absorption, and it was found that the capillary water absorption increased with the addition of AEA. Microstructural studies using the Brunauer–Emmett–Teller (BET), Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscopy (SEM) on the 3D concrete revealed that the volume and size of the pores in the hardened matrix increased with the addition of AEA. The mechanical and durability studies showed that the optimal percentage of AEA is 0.1%.

This study explores the possibility of partially replacing cement with crushed brick powder (CBP) and 6% hydrated lime (HL) in concrete. The results showed an increase in compressive strength compared with the control at the intermediate age of 56 days. Adding HL to the cement and CBP paste samples resulted in a 22% reduction in capillary pores and a 23% increase in gel pores. Although the control samples had less carbonation penetration, the corrosion rate was higher than that of blended cement concrete with HL. The half-cell potential measurement on carbonated samples indicated that, unlike chloride-induced corrosion, the depassivation of steel could not be identified by a stable demarcating half-cell potential value. Moreover, blended cement concrete with HL exhibited higher resistivity. Visual inspection of corroded bars revealed that the assumption of uniform corrosion by carbonation might not be entirely accurate. The use of HL with a cement-CBP binder improved the concrete’s characteristics and reduced the risk of carbonation-induced corrosion. The study provides supplementary information on the feasibility of using a blend of crushed brick powder and hydrated lime as sustainable alternatives in the field of concrete construction with environmental considerations.

The use of byproducts as supplementary cementitious materials (SCMs) and recycled coarse aggregates (RCAs) can contribute to the production of more sustainable self-compacting concrete (SCC) while modifying the durability properties of these mixtures. Thus, this study addresses the combined use of concrete waste (CW) as RCA and residue of masonry (RM) as SCM, the CW and RM obtained from construction and demolition waste, to generate SCC mixtures and to evaluate the performance of these mixtures under sulfate attack (5% ${\mathrm{Na}}_2{\mathrm{SO}}_4$ and 5% ${\mathrm{MgSO}}_4$ solutions). In detail, a reference SCC (M1) and three SCCs with 25% of RM and different level RCAs (0%, 50%, and 100% replacement by volume) were cast. The hardened properties of the SCC mixtures were assessed in terms of compressive strength and sulfate attack. The results showed that the SCC mixtures with RM and RCA, cured in water, exhibited lower compressive strength results in all the evaluated ages compared with M1 (reference mixture, without RM and RCA). However, the SCC mixture with RM presented the maximum compression strength result among the different mixtures at 180 and 360 days. When mixtures were exposed to sulfate solutions, the SCC mixture with RM showed the best performance, and even the SCC mixtures with RM and RCA exhibited lower linear expansion and loss of compressive strength when compared with M1. The presence and severity of the sulfate attack were assessed via X-ray diffraction and scanning electron micrograph, which confirmed the presence of ettringite and gypsum in all the exposed SCC mixtures in the ${\mathrm{Na}}_2{\mathrm{SO}}_4$ and ${\mathrm{MgSO}}_4$ solutions.

Microscopic characterization and macroscopic specific experiments are combined to explore the influence of functional graphene oxide (GO) on cementitious composites performance. The simulation through molecular dynamics (MD) characterizes the adsorption at the GO/C–S–H interface by analyzing the adsorption energy, radial distribution function (RDF), mean square displacement (MSD) and time correlation function (TCF), and the adsorption morphology of GO by radius of gyration (Rg) and concentration profile, reflecting the interface contact area used to further characterize interfacial bonding. The mechanical properties of mortar were tested, scanning electron microscopy (SEM) observed the mortar interface, and energy dispersive spectroscopy (EDS) calculated the ratio of Ca/Si. The durability of mortar was characterized, showing that the adsorption capacity of GO/C–S–H interface is: GO-C > GO-O > GO-N > GO-S. The GO-C has the strongest adsorption effect, and the interface adsorption effect of GO-S is the weakest. When the functionalized GO incorporation is 0.1%, GO-C can significantly improve the mechanical properties and durability of mortar. The enhancements of GO-O and GO-N are secondary, while GO-S showed the least improvement.

Abstract

Chloride profiles can be used to assess the durability of concrete structures against corrosion in the marine environment. However, the models proposed to adjust these chloride profiles are diverse and have varied complexities. Therefore, the objective of this article was to compare the performance of five chloride penetration models using a database with different profiles found in the literature. For this, 63 chloride profiles were selected. The response of the models was evaluated through a strong statistical analysis to compare the accuracy of these equations. The results demonstrated that standardized models based on Fick’s second law should adjust only the data in the diffusion zone of the profiles by minimizing the sum of the squared residuals and applying a simple iteration, showing a coefficient of determination ($R^2$) above 0.90, mean absolute error (MAE) below 0.20, and root mean square error (RMSE) close to 0.20. However, traditional models were less effective to fit the entire profiles (convection and diffusion zones), especially when a triple iteration was applied. For this case, Holliday’s model showed better results ($R^2=0.84$, $\mathrm{MAE}=0.25$, and $\mathrm{RMSE}=0.30$). Therefore, a new analysis method is suggested in this article to better adjust the chloride profiles by the diffusion models.

Practical Applications

The analysis of chloride profiles is an important tool to evaluate the service life of reinforced concrete structures. In this case, considering the reinforcement corrosion as the main degradation mechanism observed in these structures, the knowledge regarding the service life of field structures highlights the importance of research on this area, mainly if the structure is present in the marine environment, since the port infrastructure is vital to several international trade relations. Furthermore, artificial islands have been built to expand the marine infrastructure for tourists up to aeronautical purposes, thus increasing the number of structures exposed to this severe aggressive environment. Different models have been proposed to represent the chloride penetration in concrete structures, although many of them have difficulty representing the chloride penetration, adjusting only the diffusion zone by the solution of Fick’s second law of diffusion for a semi-infinite medium. The full representation of the chloride profiles, with clear physical variables, has been the subject of research in the last years. In this sense, a general model based on the modified Holliday equation was successfully applied to chloride profile modeling in different coastal structures around the world, attesting its worldwide applicability.

The need for conversion between viscoelastic functions arises in that strain-controlled relaxation test is quite difficult to run than a stress-controlled creep test, especially on rigid sample and at low temperatures. A new theoretical method aimed at converting shear creep compliance to relaxation modulus within linear viscoelastic region based on the Cauchy residue theorem was proposed and investigated experimentally in this research. A numerical example was presented and then its effectiveness and accuracy were verified by the experimental results. Prior to the conversion, the oscillatory amplitude sweep test, shear creep test, and shear stress relaxation test were conducted on three asphalt binders to obtain their linear viscoelastic region, creep compliance as well as relaxation modulus data. It was found that polynomial was equally competent as the power law and Prony series in terms of emulating short-term creep behavior of the asphalt, which laid a firm foundation for reasonable conversion. Furthermore, statistics show the converted modulus could give a good description on the measured shear relaxation modulus, suggesting the proposed method was effective in the discussed material and temperature range. Finally, in terms of signal and system theory, the relaxation modulus had three poles and one double zero on the complex plane: one negative real pole and a pair of conjugate complex poles. All the poles lie to the left of the imaginary axis of the complex plane (excepting a simple pole at the origin), which agreed well with the requirement for a linear viscoelastic behavior.

The influence of aggregate properties and natural rubber latex (NRL) additive on the performance of natural rubber modified asphalt (NRMA) concrete mixtures was investigated. The NRMA mixtures were prepared using three types of aggregate (granite, limestone, and basalt), asphalt cement AC60/70 and NRL with different rubber to binder (R/B) ratios of 3%, 5%, and 7%. A series of laboratory tests including Marshall stability and flow, indirect tensile strength, indirect tensile fatigue, resilient modulus, wheel tracking test, dynamic creep, and skid resistance tests were conducted to investigate the mechanical properties and mechanistic performance of the NRMA mixtures. Statistical analysis was performed using the NLOGIT software program to evaluate the influence factors including strength, shape, and chemical properties of aggregate and R/B ratio. The R/B ratio of 3% was found to be the optimum value which provided the best mechanical properties and performance. The strength parameters and mineral compound were found to control the Marshall stability. As such, the NRMA mixtures with basalt and granite of high Marshall stability led to the high resilient modulus, rutting resistance, and permanent deformation. Because of the good strength and shape parameters of granite, the NRMA mixture with granite indicated a significant rate of improvement of fatigue life compared with the NRMA mixtures with other aggregates. Limestone’s predominant mineral compounds (CaO, MgO, and ${\mathrm{SiO}}_2$) were found to influence the indirect tensile strength and skid resistance of NRMA mixtures.

Compared with portland cement, sulphoaluminate cement (SAC) is considered a low carbon emission and low energy consumption cement. To further reduce the cost of SAC and promote extensive engineering application, the hydration and hardened properties of SAC blended with different dosages (0%, 5%, 10%, and 20% by weight) of limestone were investigated over 360 days. Isothermal calorimeter, X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were used to determine the hydration rate, hydration products, micromorphology, and pore structure of the hardened cement paste. In addition, the mechanical strength and deformation of the mortars were monitored over 360 days. The results show that the addition of limestone has a negative effect on the hydration of SAC due to its large particle size. The compressive strength of the mortars with 0%–20% limestone exhibited a continuous increase within 360 days of curing, even though it decreased gradually as the limestone content increased from 0% to 20% due to the dilution effect. Moreover, all mortars exhibited excellent dimensional stability, and linear deformation over 360 days was less than 30 microstrain.

Abstract

The main purpose of this study was to understand the failure mechanism of fly ash fiber–reinforced asphalt specimens under uniaxial compression loading and splitting loading, respectively. The variation of acoustic emission (AE) parameters in the acoustic emission tests during this fracture process was analyzed. The results showed that under uniaxial compression, the failure process of the fiber asphalt specimens could be divided into four stages: the formation of internal microcracks, microcrack propagation, rapid crack propagation, and finally, failure. Shear failure is the main failure form of asphalt specimens, and with the gradual increase of fiber content, the failure mode of specimens gradually changes from shear failure to shear-tensile failure. The correlation analysis between peak value and frequency of acoustic emission parameters shows that there are three frequency bands of fly ash fiber asphalt specimen, namely, 0–30, 30–60, and 150–200 kHz, which correspond to the initial dislocation failure of the interface between aggregate and asphalt mortar, the fracture failure of the interface between fly ash fiber and asphalt mortar, and the complete dislocation failure of the interface between aggregate and asphalt mortar.

Practical Applications

In recent years, acoustic emission technology has been widely used in the field of nondestructive testing of cement concrete and bridge structures. Nevertheless, the damage identification methods commonly used in asphalt pavement, such as the computational simulation method and image processing method, have low working efficiency, large error, and lack of dynamic perception of the whole damage process, which limits their applicability in practical engineering applications. In this paper, acoustic emission technology has been employed to characterize the damage and crack propagation law of fiber asphalt specimens under various stress states. Through the analysis of the evolution characteristics of acoustic emission signal parameters, the fracture damage characteristics of fiber asphalt samples under different stresses are invested. The research results are of great significance for the popularization and application of acoustic emission technology in the field of nondestructive testing of asphalt pavement.

The research on the strength characteristics of rubberized asphalt pavement materials could provide calculation parameters for structural resistance design. However, the strength results of different methods varied significantly, potentially significantly affecting the structural resistance design. Therefore, for the purpose of overcoming the design deviation caused by the randomness of the laboratory strength, three different tests of unconfined compressive strength, splitting strength, and direct tensile strength were carried out at various loading speeds and test temperatures. The time-temperature properties of the strength under diverse stress loading paths were compared, and the characterization model of rubber asphalt mixture strength was proposed by a dimensionless method. The results showed that loading speed and temperature significantly affect the strength of the rubber asphalt mixture. In the three different tests, the unconfined compressive strength was much larger than the other strength, and the splitting strength was the smallest. The speed sensitivity of direct tensile strength was the highest, while that of unconfined compressive strength was the lowest. With the temperature rising, the speed sensitivity of strength decreased. The power function could express the speed correlation of strength, and the quadratic polynomial function could express the temperature dependence of strength. In addition, the linear model could describe the strength master curve well. The unified strength characterization model of rubber asphalt mixture considered the impact of stress loading path and material viscoelasticity. The research could improve the efficiency of obtaining pavement materials’ damage resistance and the structural resistance’s design accuracy, so as to improve the durability of asphalt pavement, and play a role in promoting the application of rubber asphalt materials.

In this work, we investigated the effects of clay mineral content on the mechanical damage behavior and cracking mechanism of rock-like specimens with different bentonite (montmorillonite) contents by performing uniaxial compression tests. Based on the obtained stress–strain curves, the damage evolution stages and stress thresholds of the specimens were determined. The evolution of internal microcracks and microstructural characteristics of fracture surfaces was analyzed using acoustic emission (AE) technology and scanning electron microscopy. The results showed that the bentonite content remarkably affects the damage behavior and AE patterns of the specimens. With increasing bentonite content from 10% to 40%, the stress thresholds and elastic modulus decreased, the peak strain increased, and the cumulative AE ring count and energy decreased (following a negative power function), indicating that the AE activities were significantly weakened. Moreover, the transformation of AF-RA distribution pattern, the decrease in b-value and increase in proportion of the high peak frequency indicated that the dominant cracking mechanism has been changed from small-scale microtensile modes to large-scale microshear modes. The AE source location results reproduced the formation process of macrofractures. These differences in damage behaviors and AE characteristics caused by bentonite content are closely related to the microstructure features of the specimens. The critical slowing down phenomenon of aforementioned AE parameters can serve for predicting rock instability.

The use of bacteria-based self-healing concrete for substructures in ground conditions is an area of increasing interest for enhancing the durability and longevity of infrastructure. In line with this objective, the present study investigates the bio-self-healing performance of a cementitious material embedded in clay soil with varying chemical exposures and water saturation regimes. Laboratory experiments were conducted on pre-cracked mortar specimens with Bacillus subtilis encapsulated in perlite. The specimens were incubated in the soil with different pH and sulphate levels, representing three exposure classes (based on Eurocodes). The crack healing ratio was evaluated through visual inspection and capillary-water absorption—before and after soil incubation. Findings showed that all inoculated specimens exhibited healing ratios noticeably larger than those of the control specimens, which mainly experienced small autogenous healing. Of note, the best healing performance was observed when the soil was fully saturated and pH-neutral. From the design perspective of bio-concrete, this study emphasizes the consideration of groundwater regime as well as acidity and sulphate of the soil.

Waste powder materials (WPM) is a by-product of mosaic tile polishing facilities in Iraq. The use of WPM has a positive impact on both economic and environmental issues. The current study investigates the potential of using WPM as a filler in asphalt mixtures. For the investigation, hot mix asphalt (HMA) combinations, which were made of waste powder materials and 40–50 penetration grade asphalt binder, were built and tested, then compared with the ${\mathrm{CaCO}}_3$–HMA virgin mix. While the WPM mass in the HMA mixes between 4.0% and 6.0% (by aggregate mass), the ${\mathrm{CaCO}}_3$ dosage in the HMA mixtures was selected as 5.0%. The mechanical properties of ${\mathrm{CaCO}}_3$ and WPM/HMA mixes were tested using the Marshall stability and Marshall rigidity, besides the unconditional and conditional tensile strength and the tensile strength ratio (TSR). The HMA combinations consisting of 5% and 6% WPM have slightly higher tensile strength, stability, TSR, flexibility index, cracking resistance index, Jc-integral, and deformation resistance values than the ${\mathrm{CaCO}}_3$-HMA mixture. All WPM-HMA mixes agree with the minimal limits of ASTM of 8 kN stability, 2–4 mm flow, and 3–5 percent air voids when the optimal binder concentration is used. This study found that 5–6 percent of the aggregate by weight can be replaced with the WPM as a green mineral filler for paving construction. WPM is available and cheaper than ${\mathrm{CaCO}}_3$ filler materials.

The use of seawater as the mix water has been thought to be inevitable for the near future as a result of increasing water scarcity. Hundreds of papers related to seawater mixed cement-based materials were published in recent years. Even though sulfate-resistant cement can be beneficial for internal sulfate attack and binding chloride ions, there is no related study on the sulfate-resistant cement together with seawater. In this study, the microstructure of seawater mixed sulfate-resistant pozzolanic cement was studied for the first time to understand possible reactions. Tap water and seawater mixes were designed by using Portland cement and sulfate-resistant cement with and without fibers. To examine the effect of seawater as the mix water on the microstructure quantitatively and to construct bridge between mechanical properties and microstructure, Rietveld refinements were performed on the obtained X-ray diffraction patterns. Thermogravimetric analyses were also carried out to correctly interpret and verify X-ray diffraction data. The possibility of internal sulfate attack, possible reactions and resulting hydration products were discussed. The results showed that internal sulfate attack is not a threat for seawater mixed concrete and sulfate-resistant cement can be a better alternative than portland cement owing to more chloride binding ability for seawater-mixed concretes.

An investigation was carried out to analyze the flexural fatigue performance of pavement quality concrete (PQC) of M40 and M50 grades, made with conventional materials out of which river sand (RS) was replaced by copper slag (CS) by varying concentrations to the extent of 100% by volume. Experiments were conducted in the laboratory to determine the 90-day flexural strength of PQC samples ($100\times 100\times 500\mathrm{mm}$) under four-point loading. Based on respective flexural strength, repeated loads were applied for the conduct of flexural fatigue tests of PQC specimens at stress levels of 0.7, 0.8, and 0.9, each at 1 Hz frequency. In terms of fatigue life distributions, the flexural fatigue performance of several PQC mixtures has been evaluated. Three methods were used to estimate various parameters for the Weibull distribution. It is observed that the fatigue life distribution of both M40 and M50 grade PQC mixes made with CS can be modeled by a two-parameter Weibull distribution with a correlation coefficient of more than 0.95. The estimation of fatigue life of PQC mixes has also been done at different failure probabilities. The 90-day flexural strength of PQC mixes (both grades) with CS replacing RS, increased compared with conventional PQC. Further, X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) images of PQC mixes confirmed the homogeneity of the concrete. The fatigue performance was also enhanced with CS replacing RS. The goodness-of-fit test also indicated that the present model is valid at the 5% significance level for PQC (both grades) made with CS.

Capturing ${\mathrm{CO}}_2$ and using solid waste effectively has become a focus of attention. During this study, carbide slag (CS), a calcium-rich waste, was treated through carbonation. The characteristics of CS and carbonated carbide slag (CCS) were examined, and their influence on blended cement paste performance was investigated. The results showed that ${\mathrm{Ca}(\mathrm{OH})}_2$ and ${\mathrm{CaCO}}_3$ were the main mineral composition in CS and CCS, respectively. The pH value of CS decreased with carbonation time, and the CS could absorb $618\mathrm{g}/\mathrm{kg}{\mathrm{CO}}_2$ using a carbonation treatment. The presence of CCS in blended cement pastes accelerated cement hydration. It was found that cement pastes with CS had a reduced compressive strength, whereas the incorporation of less than 10% CCS improved the compressive strength. Calcium monocarbonate was detected in the hydration product of blended cement paste with CCS because of the reaction of ${\mathrm{CaCO}}_3$ in CCS with aluminate. In summary, carbonated carbide slag, as a novel ${\mathrm{CO}}_2$-storage material, can enhance the performance of blended cement paste. This research promotes the application of CS as supplementary cementitious materials in cement-based materials.

This paper evaluated the effect of a biobased polyurethane modifier on the moisture resistance of asphalt binder. Biomodifiers with high acid values have been implicated in moisture damage to asphalt. Here, castor oil with a relatively high acid value of $190\mathrm{mg}\mathrm{KOH}·{\mathrm{g}}^{-1}$ was used to produce biobased polyurethane. Biobased polyurethane was produced by combining castor oil, toluene diisocyanate (TDI), and diethylene glycol (DEG) at a molar ratio of $1:2:1$. Asphalt binder was modified with 3%, 6%, or 9% of the biobased polyurethane (by weight of asphalt binder), and the moisture susceptibility of the modified asphalt was evaluated with a comprehensive laboratory experiment plan using the boiling water test, the indirect tensile strength test, the bitumen bond strength test, the water contact-angle moisture-susceptibility test, and the moisture-induced shear-thinning index test. Study results showed that the introduction of biobased polyurethane enhanced the bond between the aggregate and asphalt, thereby increasing the asphalt mixture’s resistance to moisture damage. Consequently, the resistance of asphalt binders to cohesive failure and adhesive failure was enhanced in biobased polyurethane, as evidenced by respective increases of 19%, 40%, and 49% in tensile strength ratio for dosages of 3%, 6%, and 9% biobased polyurethane. Compared with neat asphalt, the asphalt blend containing 9% polyurethane had the highest bond-strength increases, 55.73% and 37.93%, for dry and wet conditions, respectively. This improvement is attributable to the phenol and amide components in biobased polyurethane, which increase the polarity of asphalt binder and increase the affinity of asphalt binder to siliceous aggregate. In addition, the moisture-induced shear-thinning index and the contact-angle moisture-susceptibility index showed that increased doses of biobased polyurethane resulted in increased resistance of asphalt to moisture damage. The study outcomes promote the sustainability of asphalt construction by introducing biobased polyurethane as a sustainable modifier for asphalt.

Proper disposal of waste medical masks has become increasingly urgent in order to protect the ecosystem. Our exploratory study has proven the feasibility of producing waste mask microfibers (WMMF) and pretreating them with graphene oxide (GO) to enhance the strengths of cement composites. This study further explored the resistance of designed WMMF/GO-WMMF mortar ($w/c$ of 0.40) to chloride migration and frost damage, to address the knowledge gap related to durability. The GO-pretreated WMMF improved the chloride migration resistance (by $\sim 50\%$) and the freeze–thaw resistance (by $\sim 20\%$), likely due to the tortuosity-increasing, hydration-accelerating, and hydrates-regulating roles of GO in the cementitious material. The microscopic investigation, including backscatter electron imaging, scanning electron microscopy, and thermogravimetric analysis, shed light on the mechanistic roles of GO and WMMF in cement composites. In addition, the two-parameter Weibull distribution was employed to model the frost damage and compare the remaining capacity of freeze–thaw resistance of the three designed mortar samples at the same reliability level; the Bayesian method was also utilized to model the uncertainty during the cyclic freeze–thaw process.

This study utilized a heat-moisture coupling model to characterize the internal microenvironment of concrete and establish the relationship between environmental temperature, humidity, external chloride ions, corrosion potential, corrosion current density, and rust layer thickness distribution on steel surface. The model enables dynamic characterization of steel depassivation, corrosion propagation, and rust layer expansion under natural climate environments. The development of temperature, humidity, chloride ions concentration, and corrosion current density in concrete under a time-varying environment was verified by experiment and the data obtained from literature. The research results show that taking heat-moisture coupling into account is necessary in steel corrosion modeling. Temperature and humidity are nonuniformly distributed in concrete leading to nonuniform distribution of chloride ions diffusivity. The growth rate of chloride ions concentration responds to environment temperature change more rapidly than humidity change. Under a time-varying environment, corrosion current density may increase briefly due to the increase of environment temperature and humidity.

The dynamic behavior of ultrahigh-performance cementitious composite (UHPCC) structures under impact loads is a topic of great importance because such loads usually cause severe structural damage, which may impose potential hazards to the personnel and facilities protected by the UHPCC structure. In the present work, a new UHPCC was developed, and five kinds of UHPCC specimens with different fiber types and fiber content were prepared. A series of impact compression tests were conducted by using a split Hopkinson pressure bar system to study the dynamic properties of different types of UHPCC in the strain rate range of $50–180{\mathrm{s}}^{-1}$. The dynamic compressive strength, peak strain, failure pattern, and dissipated energy were obtained and analyzed to reveal the effects of steel fiber type and content on the impact resistance of UHPCC, and the waved steel fiber reinforcement mechanism was also discussed. In addition, two indexes, i.e., the critical strain rate and the energy absorption efficiency, were introduced to evaluate the impact resistance of UHPCC materials. It is interesting to find that the maximum energy absorption efficiency is the same for all types of UHPCCs (equal to 0.47) and the strain rate when the maximum energy absorption efficiency is reached is almost identical with the critical strain rate.

Abstract

The development of microcracks in recycled aggregate concrete (RAC) directly impacts its durability; hence, these cracks need to be treated. The authors propose bacterial self-healing by introducing Bacillus megaterium strains into 50% and 100% RAC mixes to heal cracks in RAC on their own. A protective bacterial carrier is needed to protect the bacteria in the high-pH environment of concrete and in a dense microstructure so that the ${\mathrm{CaCO}}_3$ production capacity of the bacteria is not affected. For this purpose, diatomaceous earth (DE) and reused concrete aggregate (RCA) were investigated in this study as potential carriers for the immobilization of bacterial spores that heal cracks in RAC on their own. Filling of surface cracks, the self-healing ratio within concrete, recovery of compressive strength, and water impermeability were examined to test self-healing, and were compared with those of samples containing directly inserted bacteria. Cracks with a maximum width of 0.47, 0.50, and 0.55 mm were completely filled in the specimens containing directly inserted bacteria, immobilized bacteria in RCA, and immobilized bacteria in DE, respectively. Specimens containing bacteria immobilized in DE and RCA had better self-healing performance in terms of recovery of concrete properties and self-healing ratio within concrete than did specimens containing bacteria directly added. Additionally, specimens containing bacteria immobilized in DE exhibited better self-healing results in precracked specimens up to 56 days of age, whereas self-healing by bacteria immobilized in RCA was found to be more effective in precracked specimens at 120 days of age. Overall, it was concluded that DE and RCA can be used as carriers for bacterial immobilization in self-healing RAC, which would not only maintain the durability of RAC but also increase its service life.

Practical Applications

Biobased self-healing in recycled aggregate concrete offers practical applications in the construction industry. This innovative technology incorporates biobased materials such as bacteria and encapsulated healing agents into the concrete mix, allowing for autonomous healing of cracks and damage. The use of recycled aggregates further enhances the sustainability of the concrete, reducing the environmental impact. The self-healing mechanism operates by activating the bacteria and releasing the healing agents upon crack formation, which then react with the surrounding environment to seal the cracks. This self-healing capability extends the lifespan of concrete structures, reducing the need for costly repairs and maintenance. Additionally, the biobased nature of this approach aligns with sustainable development goals, promoting the use of renewable resources and reducing reliance on traditional repair methods that involve energy-intensive processes and nonrenewable materials. The practical application of biobased self-healing in recycled aggregate concrete demonstrates the potential for more-durable and eco-friendly construction practices.

The use of coral aggregate (CA) in marine concrete can greatly reduce project costs and periods. An environmentally friendly alkali-activated material (AAM) was used to grout CA to produce preplaced alkali-activated coral concrete (PAACC), reducing the binder amount and achieving environmental benefits. The alkali-activated grout (AAG) determined the performance of PAACC and acted as the main load-bearing structure, and the size of the CA slightly affected the PAACC. The compressive strength of PAACC reached about 55% that of AAG, ranging between 35 and 46 MPa at 28 days, with low chloride content (0.006%–0.016%), meeting the requirements for most marine structures. Additionally, PAACC had accelerated early strength development (approximately 5% higher than grout) due to the moisture released from the CA. PAACC had an excellent interfacial transition zone, with strengthened CA in the concrete composite, potentially increasing the practical use of PAACC.

In recent years, there has been great interest in cold weather concreting methods that utilize cold materials, which require less energy and emit less ${\mathrm{CO}}_2$ during cold weather. The aim of this research is to evaluate the combined effects of ethylene glycol (EG) and a polycarboxylate superplasticizer (PCE) on calcium sulphoaluminate (CSA) cement pastes, which are mixed using a cold weather concreting method with cold materials, at a temperature of $-10°\mathrm{C}$. The temperature curves were recorded using a temperature logging device for CSA cement mixed with water or EG solution at $-10°\mathrm{C}$. The compressive strength was measured after 3, 7, and 28 days. X-ray diffraction (XRD), thermogravimetry analysis (TGA), and backscattered electron image analysis (BSE-IA) were used to analyze the evolution of hydration. The results showed that CSA cement paste mixed with EG solution did not freeze at $-10°\mathrm{C}$, whereas CSA cement paste mixed with water froze at the same temperature. Reducing the water-to-cement (W/C) ratio improved the compressive strength but had no significant impact on the amount of hydration product or the degree of hydration. Lowering the ethylene glycol-to-cement (E/C) ratio increased the amount of hydration products and the degree of hydration. The addition of PCE significantly accelerated the hydration evolution of CSA cement, which effectively improved the compressive strength. The 28-day compressive strength (36.5 MPa) of cement paste ${\mathrm{CP}}_{\mathrm{WE}}$, with a W/C ratio of 0.23, E/C ratio of 0.1, and 1.8% PCE, significantly increased, reached 570% of that measured in cement paste ${\mathrm{C}}_{\mathrm{O}}$ (6.4 MPa), which had a high degree of hydration and a dense microstructure.

In a fire, the high-temperature creep effect of steel cables can cause structural failure. Due to differences in fabrication and composition, the high-temperature creep behaviors of full-locked/Galfan-coated steel cables significantly differ from those of general structural steel wires. To accurately predict the creep effects of full-locked and Galfan-coated steel cables, it is necessary to obtain their creep strain at high temperatures. This study conducted high-temperature creep tests on full-locked and Galfan-coated steel cables in the range of 350°C to 500°C under different stress ratios and performed tensile strength tests after the creep test. The results showed that under high-temperature and high-stress conditions, the creep strain rate increases rapidly, and different temperatures and stress levels have an impact on the tensile strength of full-locked and Galfan-coated steel cables after exposure to high temperatures. An improved high-temperature creep time strengthening model is proposed to describe the creep behavior of full-locked and Galfan-coated steel cables at high temperatures. The creep behavior obtained in this experiment and the updated model parameters can provide essential data for accurately predicting the creep effects of full-locked and Galfan-coated steel cables. Tensile strength testing can also serve as a reference for the safety assessment and repair of prestressed structures after a fire.

Conventional rejuvenation techniques, such as adding oil-based substances, are proved very effective to improve some properties of aged styrene-butadiene-styrene modified asphalt (SBSMA), including low-temperature cracking resistance and fatigue characteristic. However, its significant reduction of high-temperature properties needs to be closely focused on because it is related to the deformation resistance to rut. The major reason is that these rejuvenators play as viscosity-reducing agents to physically soften the aged SBSMA binder, whereas it does not work to repair the molecular structure and properties of aged SBS. Therefore, this study adopted polyurethane (PU) prepolymer as reactive chemical together with tall oil (TO) as common asphalt rejuvenator for the physicochemical rejuvenation of aged SBSMA. A series of tests including Fourier transform infrared (FTIR) spectra, softening point, viscosity, dynamic shear rheology (DSR), and multiple stress creep recovery (MSCR) were carried out to identify the above-mentioned issues. The results obtained showed that the chemical rejuvenation of PU contributes to fix the molecular structure of SBS degradation products in the aged binder, which is able to improve the high-temperature deformation resistance and elastic recovery of aged SBSMA binder. TO can help supplement partial loss of light components for a better workability of PU rejuvenated binder. Surprisingly, limited use of TO will not significantly decrease the elastic recovery of PU rejuvenated SBSMA at high temperature based on the physicochemical rejuvenation effects. The research achievements can address the worrying issues, especially the early-stage rutting deformation resistance, in terms of fresh rejuvenated SBSMA mixtures.

Feedback-controlled statistical-based nanoindentation creep and stress relaxation tests are performed on cementitious material to characterize the viscoelastic properties. Closed-form linear viscoelastic analytical solutions are derived based on the elastic–viscoelastic correspondence principle to study the creep and stress relaxation response. The solution developed to model the relaxation behavior is inverted in the transform domain to obtain the creep response, thus cross-validating the stress relaxation solution. The viscoelastic properties obtained from testing hardened cement paste and standard polycarbonate indicate strong agreement between the measured and fit data. The creep compliance curve developed as the inverse of stress relaxation function shows good correlation with creep compliance curves obtained by the analytical viscoelastic solution. Additionally, the nanoindentation-based stress relaxation test appears to provide more converged data compared with creep tests; hence, the study proposes nanoindentation as an additional and efficient tool to characterize the stress relaxation of cementitious materials.

This study investigated bacteria-based crack healing of nanosilica and carbon nanotube modified engineered cementitious composites (ECC). Nanosilica (NS) and carbon nanotubes (CNT) were used in ratios of 0%, 0.25%, 0.50%, and 0.75% of the cementitious materials by mass. NS and CNT modified ECC samples were produced and cured in plastic bags at $23°\mathrm{C}\pm 2°\mathrm{C}$ for 28 days. After 28 days, the microcracks were formed in the ECC specimens. Then, the healing procedure by a bacterial solution containing Sporosarcina pasteurii was applied to these samples. After this procedure, the splitting tensile strength, ultrasonic pulse velocity water permeability, and rapid chloride permeability were performed on the samples. Also, energy-dispersive X-ray (EDX), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) analyses were used to examine the morphology of healing products. This study found that 0.75 NS-ECC had a higher healing ability than all samples, and the splitting tensile strength recovery rate of this sample was 131.46%.

Due to increasing awareness of the indoor environmental quality, efforts to maintain human indoor thermal comfort have been intensely carried out worldwide in recent decades. Particularly, thermal insulating materials with good mechanical performance are of great interest to suit this functionality. In this respect, construction materials should be able to impede heat transfer while achieving the required mechanical strength. Silica aerogel (SA) is attractive to fit these criteria due to its favorable characteristics such as low thermal conductivity, lightweight, and sustainability. Therefore, the present work studies the mechanical properties of both mortar with sand replaced by silica aerogel and sandwiched mortar with silica aerogel mat core. First, the optimal mix design was determined for the mortars with 0%, 15%, 20%, and 25% sand replaced by volume with silica aerogel through compressive strength on Days 7 and 28. Flexural strength and modulus of elasticity were also assessed. In terms of sandwiched mortar with silica aerogel mat core, both edgewise and flatwise compressive characteristics were examined for 9-, 12-, and $15\text{-}\mathrm{mm}$ core thicknesses. Additionally, the optimal parameters of both specimen types were linked to their microstructures and failure modes. According to the result, 15% by volume of silica aerogel (by replacing sand) was determined as the optimum ratio for the SA powder mortar. Meanwhile, for silica aerogel sandwiched mortar, samples with 15- and $12\text{-}\mathrm{mm}$ core thicknesses achieved the highest flatwise and edgewise compressive strengths, respectively.

A novel chlorine- and fluorine-free liquid accelerator was developed in this study. The proportion of each component of the accelerator was determined using an orthogonal test method. Various additives’ impact on the cement setting time and concrete compressive strength was analyzed. The mechanism of the accelerator on cement hydration was examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) experiments. The results showed that the optimal ratios for the raw materials were 45% aluminum sulfate, 15% sodium metaaluminate, 5% magnesium sulfate, 3% citric acid, 7% triethanolamine (TEA), and 1% polyacrylamide to make the liquid accelerator. At a concentration of 5% accelerator, the initial setting time of cement was 210 s and the final setting time was 380 s. The compressive strength of the concrete test block was 11.4 MPa after 1 day and it increased to 28.32 MPa after 28 days. This represents a 141.6% increase in compressive strength after 28 days. The addition of the accelerator consumes ${\mathrm{Ca}}^{2+}$ and promotes the formation of ettringite (AFt) and gypsum (Gyp), thus promoting cement hydration, reducing initial setting time, and densifying cement’s internal structure. The accelerator not only has low production cost and excellent quick-setting effect, but also can improve the strength of concrete, making it suitable for a wide range of applications.

To predict the long-term skid resistance of steel slag asphalt mixtures, accelerated wear tests were conducted using an indoor accelerated loading device on the steel slag asphalt mixtures with different aggregate types, different steel slag blends, and different temperatures. The skid resistance decay law applied to the steel slag asphalt mixture under different influencing factors was investigated. Based on the skid resistance evaluation index measured during testing, a grey residual grey model (GM)(1,1)-Markov model was established to predict skid resistance. The results showed that the incorporation of steel slag significantly improves skid resistance while helping to reduce skid attenuation loss. Skid resistance increased with the increase in steel slag incorporation. With 100% steel slag incorporation, it was optimal. In addition, the test temperature did not change the decay law of the skid resistance index. With changes in temperature, skid resistance showed a decreasing trend. The prediction accuracy of the grey residual GM(1,1)-Markov model was significantly better than that of the grey GM(1,1) model and so can be used for skid resistance prediction. The results of the study can help to determine the attenuation characteristics of skid resistance of steel slag asphalt mixtures, and provide a simple and reliable method for predicting the skid resistance of these mixtures and other pavement aggregates. At the same time, it is certain guidelines for the establishment of the prediction model of asphalt mixture skid resistance under small sample conditions.

Ultrahigh-performance concrete (UHPC) is a new cementitious composite material that exhibits a high bond strength with steel reinforcement. To investigate the splice performance levels of steel bars in UHPC, mutual pullout tests on lap-spliced specimens and direct central pullout tests on bond-anchorage specimens were conducted in this work. The main variables included loading mode, concrete cover, and steel bar position. The results showed that the splice strength of lap-spliced steel bars was approximately 0.76 times the bond strength of the anchored steel bar with the same bond length. The splice strengths of specimens under one-way repeated loading were lower than those under monotonic loading; increasing the splice length or concrete cover thickness reduced the weakening effect of one-way repeated loading on lap-spliced specimen performance. The concrete cover thickness showed a strong positive linear correlation with the splice strength in the range of $0.75d_b$ to $2.25d_b$ and played an important role in stopping crack development in the specimens. The splice strengths decreased when the loading steel bar was moved from the middle of the structure to the side. Based on the experimental results, formulas for the splice strength and critical splice length of lap-spliced steel bars in UHPC under monotonic loading and one-way repeated loading are suggested. Finally, an analytical model for the bond slip of lap-spliced steel bars is proposed, providing a good fit with the test results.

Concrete cracking provides a path for water and other detrimental agents into structures leading to accelerated deterioration. To address this issue, several bacterial self-healing technologies have been implemented. Even though bacterial concrete has been thoroughly studied, a consensus regarding which protection method and mineral precursor would optimize the self-healing abilities of the material have not been determined. In this investigation, Bacillus pseudofirmus bacteria was encapsulated along with yeast extract and three mineral precursors (i.e., magnesium acetate, calcium lactate, and sodium lactate) using three protection methods (i.e., hydrogel beads, vacuum impregnation into porous aggregates, and electrostatic attachment with cellulose nanocrystals). Compressive and flexural strength tests were performed to characterize the mechanical properties of the materials. Moreover, cracked beam specimens were subjected to wet/dry cycles for 28 days to allow for self-healing. During healing, the crack closure was monitored, and by day 28, the flexural strength recovery was determined. Finally, scanning electron microscopy (SEM) along with x-ray energy dispersive spectroscopy (EDS) was performed to characterize the healing products. Experimental results showed that the addition of calcium lactate enhanced the compressive strength regardless of the encapsulation method. Furthermore, the flexural strength and the flexural strength recovery were not affected by the protection mechanism. In terms of self-healing efficiency, the hydrogel beads were the best-performing protection technology among the three analyzed. Furthermore, the SEM-EDS analysis revealed a high presence of calcium-rich particles (i.e., calcite) as the main healing product of this investigation

Asphalt mastic is a binary composite in which the bitumen matrix is embedded with filler particles. By taking interparticle interactions and the effects of bitumen origins and filler types into account, this research seeks to achieve a higher predictive precision of the modulus of asphalt mastics using micromechanical models. To achieve this goal, five classical micromechanical models and the Ju-Chen model (JCM) that effectively considers interparticle interactions were adopted to predict the moduli of 25 kinds of asphalt mastics composed of five bitumen origins and five filler types. The results show that the prediction accuracy of the general self-consistent model (GSCM) is the highest among the classical models, which is close to the accuracy of JCM (uniform) with the uniform distribution assumption for the radial distribution function. The JCM (P-Y) with the Percus-Yevick (P-Y) distribution assumption has the highest accuracy of all models, with average goodness of fit of 0.984 for all asphalt mastics. The dilute model (DM) exhibits higher accuracy in two bitumen with smaller low-temperature moduli, whereas the other five models in this study demonstrate higher accuracy in the other three bitumen with bigger low-temperature moduli. For the two models with the highest accuracy, the GSCM and JCM, the filler types have basically no effect on the prediction accuracy of these models. For other models except for GSCM and JCM, the smaller volume fractions of fillers lead to higher prediction accuracy, which can be attributed to the lower filler concentrations in asphalt mastics exhibiting weaker interparticle interactions. This study provides a certain reference for the performance prediction of asphalt mastic composites.

In an effort to tackle the issues of carbon dioxide (${\mathrm{CO}}_2$) emissions from the cement industry and land pollution caused by the disposal of construction waste, this study aimed to investigate the potential of fly ash-ground granulated blast-furnace slag (GGBS)–based geopolymer concrete (FG-GPC) and demolition waste fine aggregate (DWF) as environmentally sustainable alternatives to conventional cement concrete and natural fine aggregate, respectively. The experimental procedure included optimizing the FG-GPC variables (${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}$ and NaOH molarity) and investigating the properties of FG-GPC with the addition of DWF in various proportions (0%, 25%, 50%, 75%, and 100% by volume). To investigate the mechanical and physical parameters of FG-GPC with DWF, compressive strength, split tensile strength, flexural strength, elastic modulus, water absorption, density, effective porosity and ultrasonic pulse velocity were determined. The microstructural properties of FG-GPC were studied using scanning electron microscope (SEM) tests on selected samples. The experimental findings indicated that the strength and physical properties of FG-GPC were progressively diminished when adding DWF to the mix. Nonetheless, FG-GPC with 25%–50% DWF replacement showed a lower drop in concrete properties, indicating that employing construction and demolition (C&D) waste as a fine aggregate might have environmental and economic advantages.

Based on the general Marshall design method for asphalt mixtures, the difference of asphalt mixture density was determined according to the mechanical design method and volume design method. To improve the control accuracy of asphalt concrete pavement density, two design methods were established to determine the correlation of asphalt mixture density. In this study, samples were divided into original, core, and road core samples and selected as the research objects. First, the core samples of original asphalt concrete were formed and drilled by gyratory shear compacting press (PCG) compaction and core-drilling equipment in laboratory tests. Second, the density and volume indicators calculated by the quality of the original and core samples were measured according to the water gravimetric method. A correlation between the testing and the core samples could be established for the original samples. Finally, the corresponding data of the core samples obtained by Marshall test were compared with the data of mechanical design method. Test results show that the density and saturation of original samples increased by 1.4% and 9.8% compared with core samples, and inversely, the porosity and mineral gap ratio reduced by 24.8% and 7.6%. Data of the original and the core samples have a linear relationship and the correlation coefficients of density, porosity, saturation, and mineral gap ratio are 0.979, 0.975, 0.968, and 0.982, respectively. The optimum asphalt content of the Marshall test core samples is consistent with that of the gyratory testing machine (GTM) test; the density and volume index of the core samples are between the GTM and the Superpave test data. In conclusion, the degree of road compaction could be evaluated by the Marshall core samples more accurately than that of the original samples. For the units or areas without sufficient equipment for mechanical design of asphalt mixture, the density of Marshall core sample could be suggested to use for the detection and evaluation of asphalt pavement.

The main purpose of this work was to combine the advantages of increased material greenness, waste upcycling, reduced raw material demand, and the superior characteristics of traditional engineered cementitious composites (ECCs). To this end, engineered geopolymer composites (EGCs) with matrices based entirely on components from construction and demolition waste (CDW) as precursors and aggregates were developed. The CDW-based precursors included roof tiles, red clay bricks, hollow bricks, glass, and concrete. Different combinations of sodium hydroxide, sodium silicate, and calcium hydroxide were used as alkaline activators. Hybridized polyethylene and nylon fibers were used as fibers. To investigate the influences of the additional calcium source, slag-substituted versions of the same mixtures were produced. At the fresh state, Marsh cone and mini-slump tests were performed. At the hardened state, mechanical property tests (compressive strength and four-point bending) and microstructural characterization tests (X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy) were conducted. The findings revealed that, regardless of the mixture composition, all EGCs exhibited a deflection-hardening response coupled with multiple microcracking behavior. The 28-day average ranges for compressive strength, flexural strength, and midspan deflection results were 25.2–42.1 MPa, 6.2–9.5 MPa, and 14.1–28.3 mm, respectively. Slag substitution mostly improved the mechanical performance of EGCs. The main geopolymerization products were sodium aluminosilicate hydrate (NASH), calcium aluminosilicate hydrate (CASH), and C-(N)-ASH gels, the formation of which varied depending on the type of precursor and activator.

In the fatigue design and analysis of concrete structures, an understanding of the dissipated energy characteristics of the material under cyclic loading is important. However, due to the heterogeneity of concrete, the quantitative analysis of dissipated energy is extremely challenging. To investigate the evolution characteristics and influencing factors of dissipated energy, a series of fatigue tests were conducted. Four variable-amplitude cyclic loading schemes were designed to study the relationship between dissipated energy and stress levels, loading frequency, and loading history. The results show a three-phase characteristic of falling-stable-rising in the evolution of single-cycle dissipated energy. The steady value in the second phase is related to the fatigue damage accumulation rate and presents an exponential function with the maximum and minimum stress level. A stress level of 0.75 is considered as the threshold for evaluating the effect of loading history on fatigue damage. The total energy dissipated in the fatigue test has a lower limit close to the energy absorbed in the static test. The relationship between the total dissipated energy and the fatigue life can be described by a linear function in logarithmic coordinates. Based on the evolution characteristics of dissipated energy, a nonlinear fatigue life prediction formula was proposed from the linear damage accumulation model. This study is of great significance for the development and application of the energy-based concrete fatigue damage models.

Due to a shortage of river sand for concrete production, manufactured sand (MS) made from crushed rock has gradually become a substitute. It inherently contains some fines content, which has significant effects on the performance of concrete. To study the effects of the MS type and fines content on the workability, cohesiveness, and strength, concrete mixes made with granite MS or limestone MS and different fines contents at various water/binder ratios were tested. Moreover, the packing density, water film thickness (WFT), paste film thickness (PFT), and microstructures of the concrete mixes produced were examined to investigate if their changes were the root causes of the effects of the MS used. It was found that the use of granite MS attained higher workability and strength but lower cohesiveness, which apparently were caused by the higher packing density and larger WFT and PFT. Also, regardless of the MS type, a fines content of about 10% was the optimum for highest packing density and best concurrent workability-cohesiveness-strength performance. Correlation analysis revealed that the MS and fines content exerted their influences on the workability and cohesiveness through the WFT and PFT, and on the strength through the packing density and microstructure.

${\mathrm{H}}_2{\mathrm{O}}_{(\mathrm{g})}$ adsorption-desorption of cementitious materials and their permeability is a vital indicator for their durability designs, which significantly affects the occurrences of corrosion, carbonization and freeze–thawing, but its quantitative characterization has yet to be investigated in depth. In this study, ${\mathrm{H}}_2{\mathrm{O}}_{(\mathrm{g})}$ adsorption-desorption of cementitious materials with various $w/c$ ratios (0.35–0.55) and its induced permeability were investigated using a self-created cup apparatus under isothermal steady-state flow and compared with ${\mathrm{N}}_2$ gas permeability by the modified Cembureau method. The results showed that the cementitious materials with a low $w/c$ ratio have stronger water-holding characteristics, and there is an obvious inflection point in the adsorption curve [i.e., relative humidity $(\mathrm{RH})=70\%]·{\mathrm{H}}_2{\mathrm{O}}_{(\mathrm{g})}$ permeability measurement of cementitious materials was successfully carried out using a self-created cup apparatus, which is fundamentally an exponential function relationship to its ${\mathrm{N}}_2$ gas permeability. The conversion relation is helpful to enhance the multimedium evaluations of durability for cementitious materials.

Water reduces the stability and safety of paving material, and this has been extensively studied in traditional asphalt pavement. However, the influence of water on emerging cold-mixed epoxy asphalt (CEA) has not yet been acknowledged. In addition, the microstructure composed of epoxy resin (ER) and asphalt determines the performance of the CEA binder, and the influence of water entering this structure should be focused on. Here, CEA interfacial water models were established based on experimental and molecular dynamics (MD) simulations. The distribution and motion of the interfacial water and their influence on the energy, compatibility, and mechanical properties of CEA were explored. The results showed that CEA had desirable water stability when the water content was less than 5%. Water moved and was rearranged at the interface of the CEA and tended to move toward the ER. The water diffusion coefficient increased proportionally to the quadratic of the water content, and the structure of the CEA changed from an ordered short-range arrangement to a disordered one. Water reduced the interaction between the ER and asphalt by a maximum of 41.7% but had little effect on the compatibility of the CEA. Water plasticized CEA because the glass transition temperature of the CEA decreased, and less than 3% of water decreased the modulus of the CEA by a maximum of 27.0%. Simultaneously, water also destroyed the isotropy of the properties of the CEA. The gyration radius of the CEA dropped to approximately half of the value without water. This study is positive for promoting the performance improvement of CEA and provides a framework for studying CEA modeling and evaluation with MD simulations.

Soy methyl ester-polystyrene (SME-PS) is a biodegradable and nontoxic blend of soybean oil and waste polystyrene that can be used as a surface treatment to improve concrete deterioration and rebar corrosion caused by freeze–thaw cycles and chloride salt exposures. Although SME-PS has shown promising results for concrete protection, the mechanism by which it protects concrete is relatively unknown. The current study utilizes thermal analysis techniques to explore the physical and chemical protecting mechanism of SME-PS. The potential chemical reaction, reaction rate, and reaction products among SME-PS, hydrated cement paste, and cement hydration products are investigated using isothermal calorimetry and thermogravimetric analysis. Dynamic vapor sorption analysis is conducted to physically evaluate the effect of SME-PS on the pore structure of concrete. The results indicated that the SME-PS can occupy the pores with sizes smaller than 50 nm, physically preventing the ingress of detrimental ions and water into the concrete porous structure. It was also found that SME-PS can chemically interact with cement paste products rapidly occurring at the first 12 min of blending of cement paste powder with SME-PS. The thermogravimetric results indicated the SME-PS reaction mainly occurs among calcium hydroxide, pore solution, and gypsum. Additionally, the hydrophobic nature of SME-PS is beneficial in terms of protecting the cementitious material surface from aggressive chemicals.

The low cycle fatigue properties of Q355B structural steel subjected to different levels of corrosion were investigated in the present study. The corroded Q355B steel coupons were obtained by means of cyclic wet–dry immersion corrosion, and the low cycle fatigue tests of coupons with different corrosion degrees, featuring both constant and variable strain amplitudes, were carried out. The cyclic stress response, cyclic skeleton curve, and hysteretic curve of the corroded steel were analyzed. The low cycle fatigue life of the corroded steel was predicted, and a constitutive model of the corroded steel was proposed. The results show that corrosion reduced the low cycle fatigue life of Q355B structural steel. Finite-element (FE) models were developed, and the FE results were in good agreement with the experimental curves, indicating the accuracy of the constitutive model proposed in this paper. The findings from the present research provide a valuable reference for the accurate assessment of the low cycle fatigue properties of steel structures with varying degrees of corrosion.

This paper investigates the viability and advantages of incorporating off-specification fly ash (OSFA) into the production of strain-hardening cementitious composites (SHCC). Influences of variables in mix design on key properties of SHCC were experimentally investigated. The underlying mechanisms were explored by means of analysis on hydration kinetics and hydration products. The results show SHCC mixture incorporating OSFA achieved high mechanical properties such as crack resistance, ductility, and controlled crack width, as well as economic benefits, lower carbon footprint and embodied energy, and low leachability of heavy metals. This research demonstrates a synergistic way to utilize OSFA and produce SHCC.

Slag, a by-product of the iron and steelmaking industry, has been identified as an alternative construction material; however, there are currently limited engineering reuse applications for some slags. Steel slag coarse aggregates ($>6\mathrm{mm}$) has been successfully used in the asphalt mix for the surface course in pavement constructions; nonetheless, the construction applications of finer slag particles ($<6\mathrm{mm}$) are limited due to their expansive properties when hydrated. Therefore, this research aims to investigate the potential of using granulated blast furnace slag (GBFS) in controlling the swelling of fine particles of fresh basic oxygen furnace slag (BOFS). A series of laboratory tests were conducted to evaluate the engineering properties, swelling, and shear behavior of BOFS-GBFS mixtures to identify controlling factors and governing mechanisms of swelling, followed by acceptable mix proportions for potential use in pavement applications. Both accelerated swell tests and long-term swell consolidation tests demonstrated an exponential reduction in the hydration-induced expansion of BOFS with the addition of GBFS. For example, up to 77% of the swelling reduction was observed by replacing 30% of BOFS particles with GBFS. In contrast, the peak deviatoric stress of BOFS was reduced linearly with an increase in GBFS content, causing a 15% reduction of friction angle with a 30% addition of GBFS content. Optical microscopy and micro-computed tomography (CT) analysis revealed the bond formed between BOFS-GBFS particles due to the chemical reaction between the free lime in BOFS with silica and alumina in GBFS in the presence of water. The overall laboratory results were summarized by developing a design chart in which the optimal mix of GBFS to BOFS lies between 25% and 30%, volumetric swelling is less than 1%, and the peak friction angle is about 43°.

Finding stone aggregates with desirable properties in terms of durability for use in railway ballast is one of the most important concerns of railway projects. This study investigated the suitability of some types of igneous rocks (acidic to basic groups) for use as railway ballasts in Yazd Province, Iran. Los Angeles abrasion (LAA) and ${\mathrm{MgSO}}_4$ test results for the samples were compared. The results revealed that the acidic rock group, especially dacite samples, showed lower LAA and ${\mathrm{MgSO}}_4$ weight loss compared with the basic rock group. The LAA and ${\mathrm{MgSO}}_4$ weight loss values decreased with increasing ${\mathrm{SiO}}_2$ content in both acidic and basic rocks. With an increase in ${\mathrm{Al}}_2{\mathrm{O}}_3$, the ${\mathrm{MgSO}}_4$ weight loss increased for acidic rocks and decreased for basic rocks. Normative mineralogy content was meaningfully correlated ($R^2>0.93$ in multivariate regression) with the LAA and ${\mathrm{MgSO}}_4$ weight loss values. The chlorite carbonate pyrite (CCP) weathering index, which is defined based on changes in mineralogical content, showed a strong positive relationship with the LAA. Also, the Ruxton ratio index R (${\mathrm{SiO}}_2/{\mathrm{Al}}_2{\mathrm{O}}_3$) showed good to very strong correlations with ${\mathrm{MgSO}}_4$ weight loss. The porphyry ratio index (PR) did not individually succeed in predicting the durability properties. Therefore, the PR was used along with porosity and geochemical properties to estimate the LAA and ${\mathrm{MgSO}}_4$ weight loss. The use of variables of porosity, the PR and ${\mathrm{SiO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$ oxides developed very strong and reliable relationships ($R^2>0.98$) to estimate the LAA and ${\mathrm{MgSO}}_4$ weight loss.

A polyurethane (PU) mixture was used to replace the wearing course of asphalt pavement because of its excellent mechanical properties, which necessitated the selection of suitable interlayer bonding materials between the polyurethane mixture wearing course and the asphalt mixture bottom course. Five types of tack coat materials were designed, including styrene-butadiene-rubber modified emulsified asphalt (SBREA), waterborne epoxy resin modified emulsified asphalt (WEREA), waterborne polyurethane modified emulsified asphalt (WPUEA), polyurethane, and polyurethane-stabilized fine sand (PUFS). Their cohesion performance under elevated temperature, high-temperature immersion, and freeze–thaw conditions was evaluated with tensile tests and shear tests. The results show that PUFS has the best adhesive properties, followed by PU, WPUEA, WEREA, and SBREA. WPUEA offers remarkable high-temperature stability, but is greatly affected by moisture. PU and PUFS exhibit outstanding freeze–thaw resistance, with the residual tensile strength and shear strength remaining above 75%. By incorporating fine sand into the composition, PUFS enhances interfacial friction compared with PU. However, this modification results in a slight reduction in its water stability.

Fiber-modified asphalt mixture has been the focus in functional pavement materials because of its excellent mechanical and self-healing performance. In this paper, an indirect tensile fatigue test was conducted to study the fatigue-healing performance of fiber-modified asphalt mixtures under different fatigue damage degrees and influencing factors, and the optimal timing of healing was determined based on the degree of fatigue damage. According to the results, due to the rough surface and microwave-absorbing ability of fibers, fiber-modified asphalt mixtures exhibit significantly higher fatigue-healing performance than plain asphalt mixtures. Under the given experimental conditions, the fatigue life of fiber-modified asphalt mixtures can up to three times higher than ordinary asphalt mixtures. Although the enhancement effect of fibers on the fatigue-healing performance of the mixture decreases with the increasing fatigue test repetitions, when the healing timing is 10% of fatigue damage, the fatigue life of the fiber-modified asphalt mixtures after five repetitions is almost equivalent to its initial fatigue life. According to a comprehensive evaluation of the fatigue-healing performance of two fiber-modified asphalt mixtures, asphalt mixture with steel wool additive is considered to be a more suitable material for self-healing pavement applications.

To study the durability of magnesium oxychloride cement (MOC) in practical applications, samples from 6 to 80 years in different regions of China, including both north and south China, were collected. Phase composition and microstructure of MOC were analyzed, and phase transition patterns and microstructure characteristics of MOC were explored. The results show that, for MOC material, the main hydration product is $5{\mathrm{Mg}(\mathrm{OH})}_2·{\mathrm{MgCl}}_2·{8\mathrm{H}}_2\mathrm{O}$ (phase $5·1·8$), and the carbonation products are ${\mathrm{Mg}(\mathrm{OH})}_2·{\mathrm{MgCl}}_2·2{\mathrm{MgCO}}_3·6{\mathrm{H}}_2\mathrm{O}$ (phase $1·1·2·6$) and $4{\mathrm{MgCO}}_3·{\mathrm{Mg}(\mathrm{OH})}_2·4{\mathrm{H}}_2\mathrm{O}$ (phase $4·1·4$). For MOC samples with ages less than 20 years, the content of phase $5·1·8$ and the total content of carbonized phases (phase $1·1·2·6$ and phase $4·1·4$) increases and decreases in turn. The change of the total content of the carbonized phase is opposite to that of the phase $5·1·8$ and is affected by phase $5·1·8$. A calculation formula for the carbonation degree of MOC material system is proposed. The calculation results show that when the age is less than 14 years, the carbonation rate of MOC samples in the dry environment from north China is slow, but obviously increases when the age exceeds 14 years. Carbonation degree of the MOC samples at 6 years in the high humid environment of south China is close to that of the samples at about 20 years in north China. The crystal morphologies of different phases in MOC are varied. There are needle rod-like and flocculent crystals of phase $5·1·8$, short rod-like crystals of phase $1·1·2·6$, flaky crystals of phase $4·1·4$, and nubbly crystals of ${\mathrm{MgCO}}_3$ in MOC. Phase $5·1·8$ ensures the integrity of the glass fiber, while sawdust shows disadvantages on the long-term service of MOC.

The welded hollow sphere is formed by hot stamping of the steel plate, and the mechanical properties of the steel after hot stamping are the key to accurately evaluate the stress performance of the welded hollow sphere. In this paper, the Q235 steel used to manufacture the welded hollow sphere and the formed welded hollow spheres were made into tensile coupons. The mechanical properties of hot-stamped spherical shell Q235 steel without flattening treatment after water cooling from elevated temperature were studied by experiments. The stress–strain curves, elastic modulus, percentage elongation of fracture, yield strength, and ultimate strength of steel were analyzed. The results showed that hot stamping can improve the mechanical properties of Q235 steel to some extent. The exposure temperature and the method of water cooling have little effect on the elastic modulus of the hot-stamped spherical shell Q235 steel, but they have significant effects on the percentage elongation of fracture, yield strength, and ultimate strength. With the increase of exposure temperature, the percentage elongation of fracture presented a decreasing trend, and the higher the exposure temperature, the more obvious the decreasing trend. Before 500°C, the yield strength and ultimate strength of steel showed a decreasing trend, and it increases with the increase of exposure temperature after 500°C. Based on the experimental results, the stress–strain model and the mechanical properties calculation formula of the hot-stamped spherical shell Q235 steel after water cooling were proposed, and the mechanical properties relationship between the hot-stamped spherical shell Q235 steel and the original Q235 steel was obtained.

To provide a new cold patch for asphalt pavement rehabilitation. In this study, emulsified asphalt (EA) was combined with Magnesium phosphate cement (MPC) to create an organic–inorganic composite repair material with rapid repair performance. The impact of material components on the performance of the MPC-EA was investigated, the ratio range to satisfy field construction performance requirements was optimized, and field tests were conducted on a section of Liaoyang East Road in Qingdao. The results showed that the borax retarder primarily functioned to regulate the setting time of the MPC-EA and enhanced its compressive strength under test conditions. Increasing borax from 6% to 12% increased the setting time of the MPC-EA by about 80% to 97% and had an increase of about 10% on the fluidity. However, increasing the content of EA considerably delayed the setting time of the MPC-EA, while reducing its fluidity and compressive strength. Increasing A/C from 0 to 0.2 increased the setting time of MPC-EA by about 80% to 135%, reduced the fluidity by about 14% to 25%, and reduced the compressive strength of the MPC-EA by about 60% to 65%. As ambient temperature significantly affects the setting time of the material, the ratio and performance should be adjusted based on climatic conditions, disease type, and restoration needs. This study introduces a novel organic–inorganic composite material with exceptional performance for the fast repair of asphalt pavement diseases. Additionally, it provides a valuable practical example of applying MPC materials in the realm of road rehabilitation.