Journal of Materials in Civil Engineering

The objective of this study was to explore the engineering application potential of waste cigarette butts and to investigate the effect of waste cellulose acetate (WCA) as reinforcement material on the performance of asphalt mixtures. A performance prediction model was also constructed to explore the optimal mixture preparation scheme. In this study, a scanning electron microscope (SEM) was used to visually characterize the surface morphology of WCA. The elemental composition of the cellulose surface was determined semiquantitatively using an energy dispersive spectrometer (EDS). The experimental design was carried out following the face-centered central composite design (FCCD) of the response-surface methodology (RSM), taking WCA shearing time, WCA content, and asphalt-aggregate ratio as variable factors, and the splitting strength ($R_{\mathrm{dry}}$), freeze–thaw splitting strength ($R_{\mathrm{saturated}}$), and tensile strength ratio (TSR) of the mixtures as response variables. The software Design-Expert was adopted to construct and optimize the model under multiple responses. The road performance was verified by rutting test, low-temperature bending test, and water immersion Marshall test. The results showed that WCA is a kind of organic cellulose with a smooth surface and cloverlike cross section, which can significantly improve the mixture’s crack resistance and water stability. The performance prediction models all achieved a fit of 90% or higher. The best parameters recommended by Design-Expert were WCA content of 0.201%, WCA shearing time of 11.847 min, and asphalt-aggregate ratio of 5.683%, and the WCA-reinforced asphalt mixture $R_{\mathrm{dry}}$, $R_{\mathrm{saturated}}$, and TSR values were 1.38 MPa, 1.24 MPa, and 89.86%, respectively, all of which were within the 95% prediction interval of the model predicted values. In addition, the road performance tests showed that WCA significantly improved the mixture’s flexural strength and water stability, but harmed the high-temperature rutting resistance. WCA has a significant reinforcing effect on asphalt mixture, which has a certain reference value for recycling waste cigarette butts and developing green road materials. In addition, the FCCD model has high accuracy and can effectively guide the road material preparation process.

Abstract

Alkaline-activated cement, as an alternative to conventional portland cement, is being increasingly studied due to its environmental advantages and engineering properties. However, research on the feasibility of using both uncommon precursors and curing at ambient temperature is still limited. This study aims to investigate the potential of ceramic wastes, specifically from brick and tile production and ladle furnace slag, as precursors in alkaline activated cement reinforced with polyacrylonitrile fibers cured at 20°C. Sodium silicate, in solution form, was used to activate the precursors, and three different fiber contents were tested, namely 0%, 0.5%, and 1%, by volume. Physical properties, such as capillarity and porosity, were assessed. Moreover, the mechanical behavior was thoroughly characterized by uniaxial compressive, flexural, and elasticity modulus tests. In addition, a thorough microstructural characterization, including scanning electron microscopy, X-ray energy dispersive analyzer, X-ray diffraction, and Fourier transform infrared spectroscopy was conducted at 14, 28, and 90 days. The results revealed that environmentally friendly alkali-activated binders were produced from wastes with limited industrial recycling possibilities. The mixture with 0.5% fibers was the one that presented better results, i.e., a flexural strength of $8.84\mathrm{N}/{\mathrm{mm}}^2$ and compressive strength of $\sim 29\mathrm{MPa}$ at 90 days. The mechanical performance of this material is relevant, especially considering that a relatively low curing temperature was applied. The results also showed that calcium aluminum silicate hydrate (C-A-S-H) was detected as the main reaction product.

Practical Applications

Alkali-activated cement has been identified as a potential alternative to traditional portland cement due to advantages such as the reduction of ${\mathrm{CO}}_2$ emissions to the atmosphere, and the conservation of natural resources, because wastes can be transformed into useful products. All over the world, ceramic materials are widely used in different types of construction, and significant amount (between 30% and 45%), end up as waste. Therefore, this study aims to show the possibility of reusing ceramic waste for the development of a fiber-reinforced alkaline activated cement composite with acceptable physical and mechanical properties that allow it to be used in non-structural applications; for example, bricks, tiles, partition walls, and other building materials. It also is a low-energy consumption process, because curing can be done at ambient temperatures. Finally, the obtained results, e.g., flexural strength of $8.84\mathrm{N}/{\mathrm{mm}}^2$ and compressive strength of 29 MPa, open the door for several applications in the construction industry.

The natural aggregate crisis is an alarming concern for the construction industry worldwide. This study provides a detailed investigation of coal mine overburden (OB) from opencast mine dumps, to evaluate its potential as a sustainable alternative to natural aggregate. The microproperties, including mineralogy, morphology, and chemistry, were evaluated, and the macroproperties, including alkali–aggregate reaction, soundness, durability, flow value, ultrasonic pulse velocity, and other mechanical properties of crushed OB, OB-based mortar, and concrete, were determined. OB was found to be mineralogically more stable (55%–77% ${\mathrm{SiO}}_2$), mechanically comparable, and durable (volume change 3%–8%) than other alternatives of natural aggregate. The toxicity characteristic due to leaching was found to have no hazardous effects on local and regional soil and water quality. The cement mortar prepared using OB had similar performance in terms of fresh and hardened density, flowability ($>0.6w/c$), and durability [slake durability index (SDI) $>95\%$] as other industrial by-products. The compressive strength of the mortar with OB was found to be comparable to that of mortar with river sand. OB-based mortar and concrete were found to have good corrosion resistance. For bulk utilization of OB, a pilot-scale study is recommended to assess its performance under real-world exposure conditions.

Polyether polyurethane concrete (PPC) is a new type of cold-mixed and cold-paved material. In this study, the strength evaluation mechanism of PPC was systematically investigated through test methods at different scales. First, the strength evolution mechanism of the polyurethane binder itself was characterized by Fourier transform infrared spectrometer (FTIR). Subsequently, different significant influence factors including temperature, humidity, and catalyst dosage on the strength evolution of PPC were analyzed and quantified by indirect tensile test. Third, a systematic statistical analysis of these influencing factors was performed by statistical methods to quantify their contribution to the strength formation of PPC. The strength of PPC was closely related to the strength evolution of polyurethane binder, and the order of influence factors on strength evolution was temperature > humidity > catalyst dosage. Finally, considering these influence factors, a prediction model of PPC curing time was established. The predicted curing time was compared with the outdoor test results, and the results verified the validity and rationality of the model.

Phosphorites (PF) have small particle sizes and interesting chemical compositions to be used as filler in asphalt mixtures. The present study assessed the performance that a hot-mix asphalt (HMA) displays when the natural filler (NF) is completely replaced by PF. X-ray diffractometry (XRD), X-ray fluorescence (XRF), and scanning electron microscope (SEM) tests were carried out on NF and PF particles. Asphalt mastic was manufactured using a weight ratio of filler (NF and PF) to asphalt binder of $1:1.2$. Penetration, softening point, viscosity, and linear amplitude sweep test were performed on the asphalt mastic. The following tests were carried out on mixes manufactured with NF (control) and PF (HMA-PF): Marshall, indirect tensile strength, Cantabro, resilient modulus, permanent deformation, and fatigue under stress-controlled mode. Additionally, moisture damage resistance was assessed through the tensile strength ratio (TSR) parameter. The HMA-PF mix displayed a better performance in all the evaluated properties, without increasing the optimum asphalt binder content. PF as fillers could be an interesting alternative in the manufacture of HMA mixtures subjected to high temperature climates.

This study investigated the performance of two alkali-activated concretes (AACs) subjected to marine exposure for 2 years. The AACs were synthesized from a low-calcium Class F fly ash (FA) and a blast-furnace slag. Concrete specimens were exposed in a marine environment in a port facility in southern Australia for 2 years. The specimens were subject to a range of nondestructive testing (NDT) techniques, including resistivity, Schmidt hammer, and ultrasonic pulse velocity (UPV) tests. In addition, chloride diffusion coefficients were calculated from concrete cores taken from specimens exposed in the marine environment. Microscopy analysis was undertaken using Fourier-transform infrared (FT-IR), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA), and comparative data were taken on laboratory specimens at 28 days. Furthermore, the chloride diffusion coefficients were compared with the results of standard laboratory tests undertaken on the control samples at 28 days, including rapid chloride permeability testing (RCPT) using a 10-V driving voltage, an NT Build 492 test, and a bulk diffusion test, to determine the relationship between the 28-day laboratory tests results and the site performance. The data showed good correlation between the predicted performance based on the 28 day laboratory tests and the 2-year site data. The chloride diffusion of the ground granulated blast-furnace slag (GGBS) concrete agreed very accurately with the predicted value from the modified RCPT test, whereas the performance of FA concrete was superior to that predicted.

The incompatibility between the superplasticizer (SP) and cement can cause problems with the cementitious materials’ fresh and hardened qualities, such as unstable workability, uncontrollable setting times, excessive air entrainment, and so on. In this paper, five various types of SPs were prepared. Their interaction with pure tricalcium aluminate (${\mathrm{C}}_3\mathrm{A}$) and its hydration products were investigated and their effect on the generation of Ettringite (AFt) and single-sulfur calcium sulphoaluminate hydrate (AFm) in paste and their compatibility with cement were also studied. The results demonstrate that after 15 min of cement hydration, the AFt and AFm content of mixture with polycarboxylate SP and sulfonated acetone-formaldehyde superplasticizer (PCA-SAF) is 124.6% and 24.8% higher than that of SAF, respectively, which decreases the consumption of SPs molecules and improves the compatibility of SAF with cement. Compared with polynaphthalene sulfonate superplasticizer (PNS), PCA-PNS dramatically enhanced the SP’s compatibility with cement. Accelerating the production of AFt and AFm during the early stages of cement hydration may be one method to increase SP–cement compatibility.

This research paper presents the results and analysis obtained via the evaluation of calcium nitrate as an effective stabilizer to alter the thermal properties as well as improve the compressive strength of frost-susceptible soil. Two silty sand soils with 15% and 25% fines content that are categorized as high to very high frost-susceptible soil were considered and treated with varying dosages of calcium nitrate contents (1.5%, 3.0%, 4.5%, 10%, 15%, and 20% of soil weight). The thermal properties, including thermal hysteresis, thermal conductivity, specific heat capacity, freezing point depression, and phase changes (freezing and thawing point) were determined for the untreated and treated soil samples. It was observed that the treated samples’ thermal properties were significantly altered with respect to untreated soils. The effects of fines content on the thermal properties were evaluated using a stabilizer–silt content ratio. The threshold calcium nitrate dosage content was established, and a new correlation was established to evaluate the freezing point and thawing point. The unconfined compressive strength (UCS) tests performed on the treated soils depicted a significant increase in compressive strength compared to the untreated soil. Further analysis showed that fines content has a significant role to play on the compressive strength of treated silty sand. A qualitative analysis performed on images from a scanning electron microscope (SEM) showed that increasing the calcium nitrate dosage reduced the pore size and improved the cementation between the sand and silt grains.

Ultrahigh-performance concrete (UHPC) has great potential for applications in civil and military structures due to its outstanding performance and ability to withstand impact and blast load. This performance can be attributed mainly to the materials and their proportions, especially metallic fibers. Hence, understanding the behavior of UHPC under static and dynamic conditions through the effect of hybridization of steel fibers is essential. Compressive strength and flexural strength were studied in quasi-static mode. In flexural mode, strain characterization was done using a digital image correlation (DIC) technique. Fracture studies were also conducted with notches using a crack mouth opening displacement (CMOD) technique. In high-strain mode, dynamic tensile strength was evaluated using a split Hopkinson pressure bar (SHPB) with a Brazilian disk. Owing to optimized hybridization, enhancement in (1) toughness, (2) energy absorption, (3) crack-resistance capacity, (4) reserve strength, (5) limit of proportionality, (6) fracture energy, (7) stress intensity factor, (8) tensile strain carrying capacity, and (9) dynamic tensile strength were observed. In the process, other findings in relation to fracture, strain rate, and dynamic increase factor were also exemplified. The SHPB dynamic tensile test results, as well as the technical information provided regarding UHPC’s hybrid steel fibers’ strength, failure, and fracture behavior, can be used to improve the design of UHPC building structures to protect against impact and blast attacks.

Scabbing on the rear face of concrete under impact produces fragments that act as additional projectiles causing fatality or severe damage to the occupants or systems. Ultrahigh-performance concrete (UHPC) has outstanding properties and has proven efficacy in the impact-resistant design of structures. However, the potential damage due to the impact of fragments of scabbed pieces still prevails. This study developed a new approach for preventing ejection of scabbed materials of UHPC under single and repeated bullet impact (using a single-stage gas gun facility). The ejection of scabbed materials was controlled using woven carbon–epoxy and glass–epoxy laminated composite sheets attached to the rear face of UHPC samples. The ejection of scabbed pieces was controlled in UHPC targets with composite backing in the case of both single and repeated impact under similar conditions. Furthermore, a numerical simulation based on nonlinear finite-element code was performed for repeated impact on a UHPC target with a carbon–epoxy laminated composite. The results of the numerical simulation had a good agreement with the experimental data. Thus, the synergistic effects of steel fiber–reinforced UHPC with composite backing can be used to enhance the impact performance of UHPC.

High-viscosity asphalt binder is a key material for porous asphalt pavement, but its susceptibility to aging limits its applications. Three recycled-based high-viscosity binders (RHBs), including RH-1, RH-2, and RH-3, were prepared by recycled rubber powder (RRP), recycled polyethylene (RPE), and waste vegetable oil (WVO), and compared with SINO TAFPACK-SUPER (SINO-TPS) high-viscosity asphalt (THA). The feasibility of recycling waste to prepare high-viscosity asphalt was verified by viscosity test, storage stability test, and thermogravimetric (TG) test. The rheological properties and aging resistance of binders were investigated by dynamic shear rheometer (DSR), bending beam rheometer (BBR), Fourier transform infrared (FTIR) spectrometer, and gel permeation chromatography (GPC). The results showed that the storage stability of RHBs is close to that of THA, and the viscosity is higher than that of THA but meets the specification requirements of high-viscosity asphalt binder. In addition, RRP/RPE can improve the high-temperature performance of the binder, and the addition of RRP/WVO can reduce the negative effect of low-temperature cracking of RPE. According to the changes of functional group index and binder molecular size in different aging states, ternary recycling waste can significantly improve the aging resistance of binders. The findings in this work contribute to reducing waste pollution and provides a method for high-viscosity asphalt binder production.

To evaluate influence of blast vibrations on the long-term mechanical deterioration and damage anisotropy of fresh concrete, blast vibration tests were conducted by preparing concrete test blocks at different curing ages. On this basis, the internal relationships of factors including the curing age during vibrations, vibration blast velocity, and number of blast vibrations with the damage evolution were investigated. The results show that fresh concrete is more susceptible to blasting vibration in the initial setting stage, which changes the bonding performance between cementing materials and aggregates. Then irreversible damage is generated along the main direction of vibration, and cumulative damage occurs with the increasing number of blast vibrations. Fresh concrete was affected most by blasting vibration at an age of 1 day, and the compressive strength at 28 days was reduced by 44.17% under a single vibration event. The damage increased slowly in the concrete at curing ages from 1 to 7 day. Blast vibrations with a velocity of less than $96.2\mathrm{mm}/\mathrm{s}$ had a slight influence on changes in the compressive strength of concrete cured for 28 days. As the blast vibration velocity increased from 96.2 to $180.6\mathrm{mm}/\mathrm{s}$, the decrease rate of compressive strength in various directions accelerated and the strength decreased by as much as 40.59%. Therefore, it is suggested that the influence of the blast vibration velocity and the number of blast vibrations should be considered in alternating and parallel construction of blasting and concrete pouring work. Furthermore, blast vibration velocity, number of blast vibrations, and maximum attenuation coefficients of longitudinal wave velocities of vibrated concrete test blocks with the same curing age during vibrations differed along three directions, showing anisotropic characteristics. As the velocity and number of blast vibrations increased, the damage anisotropy became more significant. Therefore, the influence of anisotropy of cumulative damage evolution should be considered when establishing the safety criteria for fresh concrete subjected to blast vibrations.

The rheological property of epoxy grout is related to whether the grouting material can completely fill the early cracks of the cast-in-situ concrete on the bridge deck. To reveal the rheological properties of epoxy grouting materials, epoxy grouting materials epoxy grouting material mixed with active diluent BGE (EP-I) and epoxy grouting material mixed with active diluent 1,4-BDE (EP-II) were prepared. The viscosity change of epoxy slurry with time under different diluent content was revealed. And the operational viscosity index was put forward to comprehensively evaluate the working characteristics of epoxy slurry with different diluents. Then, the gel time and groutability of two kinds of epoxy grout were compared and analyzed. Finally, the isothermal viscosity time-varying model of EP-I epoxy slurry was established. The results show that the viscosity of epoxy slurry decreases with the increase of diluent content, and the viscosity of epoxy slurry changes with time in the form of an exponential function. And the operational viscosity of EP-I epoxy slurry is significantly lower than that of EP-II, but its gel time was longer than that of EP-II. Both types of epoxy grout with 15% diluent can effectively fill the concrete early cracks (width 0.8 mm) within 10 min. Based on diffusion theory, single epoxy diluent butyl glycidyl ether (BGE) was more conducive to the penetration and diffusion of epoxy slurry. The isothermal viscosity time model of epoxy slurry can better reflect the relationship between viscosity and temperature, time. The goodness of fit between the model curve and the measured value is higher than 0.90, which has good reliability.

The reclaimed asphalt pavement materials have been used for sustainable cold-recycling, significantly benefiting air quality and resource conservation, while its microscale interface properties greatly affected road performance during the cold-recycling processes. In this investigation, the cold recycled asphalt mixtures were prepared with different mixing proportions, considering the effects of cement content and mixing water amount. The adhesion characteristics of the asphalt-aggregate interface in different cold recycled asphalt mixtures have been comprehensively investigated based on the atomic force microscopic (AFM). The microscale morphology and the adhesion properties, including roughness, inclination angle, adhesion force, Derjaguin–Muller–Toporov (DMT) modulus, and dissipated energy were evaluated at the interface and noninterface regions. The micromorphology results showed that the addition of cement could enhance the roughness and inclination in interface regions. In addition, the content of mixed water showed the most significant effect when the water amount was 80%. The results showed that the adhesion force, DMT modulus, and dissipated energy increased with the addition of cement, indicating that the cement could improve the microscale mechanical properties of cold recycled asphalt mixtures. With the increase of mixing water content, the adhesion characteristics showed varied results, and the optimum water content of 80% contributed to the adhesive properties. In addition, the adhesion force, DMT modulus, and dissipated energy were all higher in the interface region by comparing with the noninterface region. The correlations between the macroscale splitting tensile strength and microscale adhesion characteristics of cold recycled asphalt mixtures were established.

Three-dimensional (3D) printing technology is replacing most of the conventional manufacturing processes of civil engineering materials because of the control that can be offered on the properties of the materials produced. 3D printing is particularly beneficial for printing polymeric geosynthetics, which are used in soils to perform various functions. Various controlling parameters that affect the strength and surface features of the printed geosynthetics are not understood so far. This study highlights the importance of various printing controls on the mechanical response of 3D-printed polypropylene (PP) sheets, which are close to geomembranes used for landfill liners and barrier systems. The number of layers used to achieve the thickness, speed of printing, and orientation of printing were varied, and the mechanical response of printed sheets were compared. The printed PP sheets were tested for tensile strength using strip tension tests and interface shear response with sand using direct shear tests. Results showed that speed of printing did not have a significant effect on the mechanical response of printed PP sheets. An increase in the number of layers for the same thickness caused an increase in tensile strength but decreased the interface shear strength. Orientation of printing is the major factor that influenced the mechanical response of the printed sheets among the parameters considered. Among the three printing orientations used, diagonal printing produced PP sheets of highest tensile strength and interface shear strength compared to horizontal and vertical printing. Sheets printed in the horizontal direction showed least tensile strength and interface shear strength. Reasons for these variations were investigated through image analysis to bring out important recommendations for 3D printing of PP sheets for geotechnical applications.

Abstract

Compatibility holds great importance because it can predict the overall performance of asphalt mixtures. Incompatible aggregate-binder duos can result in a weak and friable mix as well as increase mixtures’ stripping potential. Being unaware, local agencies and contractors often struggle with premature pavement failure, which consequently places unexpected strain on the budget. Thus, this study assessed the compatibility among 18 asphalt binders with a performance grade (PG) of PG 64-22, PG 70-22, and PG 76-22, each collected from six different refineries; and eight different types of aggregates (sandstone, novaculite, limestone, and dolomite, each collected from two different quarries). Viscosity, penetration, pH, and work of cohesion values of binders were used to develop a binder ranking system. Similarly, the aggregates were ranked based on physical (specific gravity and absorption), durability (abrasion resistance and soundness), and chemical (pH and surface free energy) properties. Overall relative rankings of aggregates and binders were also provided by assigning weight factors to different tested parameters. A total of 144 aggregate-binder mixture systems were ranked based on their dry and wet work of adhesion values as well as Texas boiling test results. The compatibility ratio (CR) was also computed, and each of the systems was designated A, B, C, or D based on their relative CR values. Upon analysis, three binders (S2B2, S3B1, and S4B1) and three aggregates (DM2, LS2, and DM1) were designated as the most preferable construction materials. CR values predicted LS2, DM1, and DM2 mixtures as the most compatible mixtures. SS2, LS1, and DM2 mixtures showed the highest stripping resistance in the Texas boiling test. These databases are expected to help the agency and asphalt producers to select compatible binders and aggregates for producing durable asphalt concrete.

Practical Applications

This study covered a wide variety of aggregates and asphalt binders prevalent in but not limited to Arkansas. A database developed under this project was based on observed individual aggregates’ and binders’ performances as well as their combined performances. The information provided in this study will help contractors and agencies to choose the most appropriate aggregate-binder system within their reach for producing quality asphalt mixtures. By knowing the rankings, state agencies can adjust project budgets and assign timely rehabilitation due to the usage of less compatible aggregate-binder systems. Contractors can tweak the existing mix design if they must use local but inferior materials. This ranking will also help them to select project-specific materials depending on the project’s significance. The refineries as well will have the opportunity to improve their products to be more compatible with local materials.

The goal of this study is the quantitative characterization of the degree of natural alteration of marble samples by using image analysis for the automatic characterization and comparison of the pore structure of rock samples before and after weathering. The proposed methodology is based on a pore exploration path-finding algorithm for the identification of paths developing within the porous domain of marble samples in both natural conditions and after weathering. Along each identified path, the pore radius is measured, providing a thorough description of the pore space statistical distribution. The ${\mathrm{A}}^{*}$ path-finding approach was developed and applied to binarized images obtained from two-dimensional (2D) thin sections of marble samples in both natural conditions and after 10 years of natural decay. The results are expressed in terms of 2D porosity and statistical distributions of the pore radius of the samples preweathering and postweathering. A comparison with the information obtained from standardized laboratory tests used for the physical and mechanical characterization of stone material is also provided. From a computational point of view, the presented approach is highly parallelizable. The presented approach works wells in complex porous structures characterized by high path tortuosity, pore-size heterogeneity, and pore surface roughness. Moreover, the methodology is less affected by small-scale pore features and noise produced during image binarization, compared with other algorithms for pore structure morphological analysis such as skeleton-based and maximal ball approaches.

Steel is prone to rusting in a corrosive environment, which results in a reduction of the effective bearing section of the steel structure. The stress concentration at the location of rusting causes brittle fracture of the steel structure during service. Although there is valuable research on the mechanism of corrosion and corrosion failure, research on the high-temperature mechanical properties of corroded steel is still limited. In this study, one-sided artificial accelerated corrosion of Q500 steel was performed, and a high-temperature steady-state tensile test was conducted on it. The degradation law and influencing factors of the high-temperature mechanical properties of corroded steel were discussed and analyzed using scanning electron microscopy (SEM) to quantify the corrosion surface morphology, and the volume corrosion ratio was used to characterize the degree of corrosion. The results showed that when the temperature was below 500°C, the attenuation of the ultimate load of corroded steel was influenced by the combined effect of temperature and corrosion. When the temperature exceeded 500°C, the influence of corrosion on the attenuation of the ultimate load tended to decrease due to the reduction in the material properties of steel. Furthermore, after the temperature exceeded 500°C, the elongation of the corroded section of the specimen increased gradually with the increase in temperature, and the elongation tended to be consistent even at different degrees of corrosion.

The main aim of this research was to investigate the effectiveness of liquid antistrips (LASs) as compared with mineral admixtures such as lime and cement in treating moisture sensitivity of asphalt concrete (AC) mixtures produced with aggregates that are severely susceptible to moisture damage. The study involved evaluating the moisture susceptibility of four mix designs that featured two aggregate sources, two asphalt binder types, and both cement and lime as mineral admixtures. Five different liquid antistripping additives were evaluated. Liquid antistrips were directly added to the binder, and the mineral admixtures in the mix were replaced with mineral filler. The experimental plan involved a volumetric assessment of the mixtures after the filler adjustment and baseline characterization of aggregates and mixtures used in the study. A multipoint moisture sensitivity assessment protocol with a moisture conditioning procedure that includes multiple freeze-thaw cycles was used. Moisture susceptibility was evaluated using a fracture experiment and its parameters in addition to the standard indirect tensile strength. The replacement of both mineral admixtures led to a considerable increase in the air voids and the voids in mineral aggregates for all four mixes. Cement and lime were shown to be effective in retaining strength and fracture energy after several conditioning cycles. The performance of the mixtures containing liquid antistrips showed sensitivity to the additive used. While one of the additives showed overall significant deterioration in strength and fracture energy after the first freeze-thaw cycle, a different additive retained 70% of its initial properties after up to three freeze-thaw cycles. Overall, it was shown that a compatible LAS can aid asphalt mixtures’ moisture resistance but not to the same efficiency of lime or cement for the mixtures included in the study.

Pore structures are critical for most properties of cementitious materials. To describe the initial pore structure of fresh cement paste, which is the foundation of the evolution of a pore network induced by hydration of cement particles in hardened concrete, statistical modelling of pore structure is carried out based on a concentric-shell sphere model, by taking cement paste as a random two-phase media. Calculations by the dispersion models agree well with the pore size distributions tested by the low-field ${}^1\mathrm{H}$ nuclear magnetic resonance (NMR) technique. For cement paste that disperses completely with the help of a dispersant, a hard sphere model is practical. However, in most real conditions, an agglomeration of cement particles will occur both before and after mixing with water, which can be characterized by the redistribution of pore size determined by the critical grain size and the hardness parameter in the concentric-shell model, respectively. Calculation results suggest that agglomeration of particles leads to coarser pores. This work will promote the understanding of the formation mechanisms of pore networks and further offers a foundation for modelling the evolution of pore structures in cementitious materials.

Abstract

Rubber-coated ballast (RCB) is a new innovative ballast aggregate obtained by coating natural aggregates with recycled crumb rubber by using polyurethane binder. The objective of RCB is to reduce the ballast degradation, thereby reducing the deterioration of rail track geometry and also maintenance costs. Natural ballast; crumb rubber of sizes 0.4, 0.8, and 2 mm; Elastan polyurethane; and geogrid (triangular, 69 mm aperture size) were used in this study. The results of abrasion, impact value, and soundness tests show that RCB has a higher resistance to abrasion, impact, and weathering compared to natural ballast. Subsequently, the shear behavior and particle breakage of natural ballast, RCB, unreinforced, and geogrid-reinforced RCB–natural ballast mix was explored using the large-scale direct shear apparatus at different normal stresses and shearing rates ($S_r$). The test results indicate that due to rubber coating the peak friction angle ($\phi$) of RCB samples reduces as compared to natural ballast. The reduction in $\phi$ of RCB samples is attributed to a change in surface texture. Moreover, 0.4-RCB (RCB made with rubber crumbs of size 0.4 mm) shows the least reduction in $\phi$ compared to 0.8-RCB and 2-RCB (RCB made with rubber crumbs of size 0.8 and 2 mm). It was further observed that with the increase in proportion of 0.4-RCB in geogrid-reinforced natural ballast both the peak friction angle and particle breakage ($B_g$) of ballast decreased significantly. The current study established the optimum content of 0.4-RCB to be mixed with geogrid-reinforced natural ballast to be in the range of 44%–53%.

Practical Applications

The problem of excessive degradation of ballast particles and the associated changes in the track geometry owing to the repeated application of heavy axle loads is addressed by coating the natural ballast with crumb rubber generated from waste tires. The rubber-coated ballast (RCB) is found to offer better abrasion, impact, and weathering resistance when compared to natural ballast. Moreover, it undergoes negligible particle breakage under direct shear conditions. The decrease in the extent of particle breakage helps in reducing the frequency of ballast replacement operations and hence tracks maintenance costs. Furthermore, RCB, when reinforced with geogrid, offers better shear strength than that of natural ballast alone. These observations imply that the tracks with geogrid-reinforced RCB can effectively reduce the risk of track instability.

Steel structures under fire often remain in corrosive environments for a long period of time. However, research on the high-temperature mechanical properties of corroded steels remains limited. In this study, an artificially simulated corrosion method is adopted to investigate the high-temperature mechanical properties of corroded Q500MC steel that usually used in bridge engineering in China. The effect of corrosion on the degradation of the high-temperature mechanical properties of steel is investigated by using steady tensile tests and numerical simulations. The results show that below 500°C, the fracture characteristics of steel containing artificial pits are affected by the minimum cross-sectional area. At 500°C, the corrosion rate increasingly influences the reduction of the high-temperature ultimate load of steel. Above 600°C, only the temperature determines the reduction degree of the ultimate load of corroded steel. Finally, the influence of the corrosion rate is greater than that of the minimum cross-sectional area proportion.

Graphene can significantly improve the mechanical performance and durability of a bitumen composite. However, the underlying reinforcement mechanism of this enhancement is not yet clear. Here, we use molecular dynamics (MD) simulation to study the mechanisms of tensile fracture and shear fracture in a graphene-reinforced bitumen composite. Two representative volume elements were developed from a single-crystal graphene-reinforced bitumen composite: graphene in the parallel plane and orthogonal plane. The MD results show that graphene in the orthogonal plane is better able to support and transmit shear loads, as evidenced by a 33% higher shear strength than graphene in the parallel plane. Under tensile loading, the failure type of the base bitumen and the graphene in the parallel plane is cohesive; for the graphene in the orthogonal plane, the failure type is adhesive. The shear failure for graphene in the parallel plane is an adhesive failure, which typically occurs at the graphene–bitumen interface. The shear failure for graphene in the orthogonal plane and for base bitumen is likely to be a cohesive failure. The results of the pull-off test validated the results of the simulation, which indicated that the interlayer sliding of graphene and the fracture of the bitumen matrix are the failure modes of a graphene-reinforced bitumen composite under tensile loading. This study provides atomic-level insight into the mechanical reinforcement mechanism of graphene-reinforced bitumen, and can contribute to the future application of advanced carbon nanomaterials in transportation infrastructure.

Aggregate and air void distribution determined by compaction commonly affects damage appearance and development inside asphalt mixture and is related to asphalt pavement durability and quality. The main objective of this study is to investigate the recycled aggregate (RA) effect on asphalt mixture compaction behavior under different engineering conditions. First, the aggregate fragmentation caused by compaction effort was simulated using the superpave gyratory compactor. In this regard, the influences of aggregate type and RA content were investigated. Second, the indoor experiment scheme was determined using the Taguchi method to obtain compaction data of recycled aggregate asphalt mixture (RAAM). Finally, a genetic algorithm-based backpropagation (GA-BP) artificial neural network (ANN) model using the 216 data sets of the indoor experiment was developed to predict and explore the relative contribution of engineering-conditions-related parameters to RAAM compaction difficulty. The results showed that the aggregate particles suffer fragmentation mainly in the early compaction of recycled aggregate asphalt mixture. The effect of RA on aggregate fragmentation during the compaction process is not statistically significant. The 10-14-1 GA-based BP ANN model developed in this study is an effective method in predicting the compaction energy consumption of RAAM with a correlation coefficient $({\mathrm{R}}^2)$ of 98.59% and a mean-squared error value of 0.6266. The gradation shape, NMAS, $F{I}_{3\mathrm{d}}$, $A{I}_{3\mathrm{d}}$, and $T_{3\mathrm{d}}$ and incorporated content of recycled aggregate have a considerable positive correlation with the compaction difficulty. The limitation of this study is that the compaction difficulty prediction model is developed according to indoor test data. Therefore, the model’s applicability to field pavement projects required further practical verification.

In this paper, the performance of basalt fiber-reinforced concrete (BFRC) during the thermal treatment and the subsequent recovery in water are investigated by adopting the ultrasonic second harmonic generation (SHG) technique. The nonlinear parameter is calculated by the noncontact SHG technique as the evaluation indicator to characterize the microstructural variation of concrete. Meanwhile, the longitudinal wave velocity and the resonance frequency are also measured as a comparison. Results show that the participation of chopped basalt fiber has a significant improvement on the concrete performance of resistance to thermal damage and recoverability after the water curing, but an appropriate mixing ratio is required to ensure the best performance. Furthermore, for a better understanding of the performance difference of concretes with different mixing ratios, the X-ray computed tomography (CT) technique and scanning electron microscopy (SEM) are employed to reconstruct the microstructural images, and the underlying reason of the change in the nonlinear parameter is analyzed from the perspective of microstructure.

Evaluation of the pavement condition is expensive, time-consuming, and labor-intensive and becomes even more challenging in remote areas. Nondestructive remote-sensing techniques can enable pavement condition assessment over a large areal extent. Remote-sensing sensors, capable of acquiring the emitted and reflected energies of the target with respect to the wavelength, can help in the identification and characterization of various asphalt mixtures prepared at a laboratory or field scale. This study aims at studying the spectral signature of asphalt mixtures with respect to aggregate gradation, binder type, binder concentration, aging, moisture conditions, and distress. In addition, an attempt has been made to identify the correlation between spectral features and asphalt mixture properties utilizing spectral metrics such as the Visible (VIS2) index and Shortwave Infrared (SWIR) index in visible and shortwave infrared regions of the electromagnetic spectrum, respectively. Indian and US specifications were followed for the fabrication and simulation of various states/conditions of asphalt mixtures. It was found from the analysis of spectral signatures that characteristic absorption features present between 1,700 and 2,300 nm can be used to identify different asphalt mixtures with distinct binder types and aggregate gradations. Also, variations in the intensity of these features were detected following various conditioning and distress simulations. Moreover, the statistical analysis indicated that the distressed samples exhibit a higher magnitude of spectral metrics (VIS2/SWIR) compared with the undamaged samples. The spectral characteristics of asphalt mixtures under different material compositions identified in the study offer great potential for pavement surface condition assessment through hyperspectral remote sensing.

With the increasing consumption of polyurethane (PU) products, more and more waste polyurethane (WPU) needs to be handled, resulting in the inefficient utilization of post-consumer PU becoming a key problem in the recycling of waste polymers. Therefore, this paper aims to explore the properties of WPU modified asphalt and assess the feasibility of using WPU materials for asphalt pavement applications. At the same time, the conventional properties, rheological properties, stability, and microscopic properties of the modified asphalt were analyzed. The results show that the rheological properties and permanent deformation resistance of the modified asphalt are improved when the WPU content is increased from 5% to 25%, while the storage stability of the WPU modified asphalt decreases with the WPU content. The optimal amount of WPU modified asphalt is accordingly recommended to be 20%.

Cold-mixed epoxy-asphalt mixture (CMEAM) has gradually received increased attention in steel bridge pavement construction due to its excellent road performance and low harmful gas emissions. According to previous studies, EA-05 and EA-10 (epoxy asphalt mixture with nominal maximum particle sizes of 4.75 and 9.5 mm, respectively), are advised to be applied in CMEAM and hot mixed epoxy asphalt mixture (HMEAM), respectively. This only considers the temperature factor and ignores the gradation influence. To make a clear gradation design illustration for CMEAM, fractal theory was introduced to quantitatively distinguish the differences among various gradations from EA-05 and EA-10 using fractal dimension as an index. In addition, to offer more design parameters for CMEMA, the passing percentage on key sieves whose passing percentages have high correlation coefficients with road performance, mixture structure parameters including stone-on-stone contact (SSC) and stability of coarse aggregates (S) are also considered as indexes. According to the requirements in the foregoing specifications, the Marshall stability test, low-temperature indirect tensile strength test (ITS), and freeze-thaw splitting test were carried out on CMEAM. Test results showed that Marshall modulus (MM), tensile strain (${\epsilon }_T$), and tensile strength ratio (TSR) have a good quadratic relation function with fractal dimensions. When the fractal dimension ranges from 2.4522 to 2.4782, the low-temperature performance and moisture stability of EA-05 are better than those of EA-10, and Marshall stability also meets technical requirements. Meanwhile, the key sieves of EA-05 are confirmed as 0.075 mm, 0.15 mm, and 2.36 mm, and those of EA-10 are 0.075 mm, 1.18 mm, 2.36 mm, and 4.75 mm. Finally, the optimum ranges of SSC for EA-05 and EA-10 are 110.4%–110.6% and 67.5%–72.7%, respectively; and of S are 118.5%–118.7% and 70.2%–73.4%, respectively.

The increasing use of recycled materials has led to balanced mix design (BMD), which combines volumetrics design with performance tests. Achieving air void and voids in mineral aggregate (VMA) to meet the volumetric stage of specifications is currently done through a trial-and-error process that is labor-extensive and time- and resource-consuming. Previous researchers have studied different methods to facilitate achieving optimal volumetrics, with limited success. In addition, past studies did not consider the effect of recycled asphalt pavement (RAP) or recycled asphalt shingles (RAS), especially high RAP/RAS designs. This study evaluated 70 different mix designs that vary in terms of material sources, nominal maximum aggregate sizes (NMAS), design numbers of gyrations, binder properties, and RAP/RAS materials. The significant parameters affecting the mix VMA were identified using stepwise statistical analysis. It was found that the inclusion of RAP/RAS increases VMA, whereas the asphalt film thickness had a parabolic correlation with the VMA. Regression models of VMA and air void were developed based on these parameters and verified with the $K$-fold cross-validation technique, showing a fitting coefficient of 82% or higher. The verified models show the potential to assist mix designers to effectively design asphalt mixtures, especially those with RAP and RAS.

Internal curing with sand-like zeolite particles is effective in reducing shrinkage of cement-based materials, but it decreases the compressive strength. In order to obtain cement-based materials with lower shrinkage and higher strength, zeolite can be used as both internal curing agent and supplementary binder, due to its pozzolanic activity. In this study, the effects of particle size and calcination treatment on internal curing performance and supplementary binding performance of zeolite in cement mortar were experimentally investigated. The pore structure, chemical bond characteristics, water absorption/release behaviors, and pozzolanic activity of zeolite particles were investigated. Cement hydration products, interior relative humidity, and drying moisture loss of mortar specimens containing zeolite were also investigated. The results show that (1) fine zeolite particles can improve the compressive strength, relative humidity, water retention property, and pore structure of cement mortar more obviously than coarse zeolite particles, because they have larger pore size and higher pozzolanic activity; (2) calcination treatment can improve the internal curing performance of coarse zeolite particles, because coarse particles can lose more combined water after calcined; and (3) calcination decreases the pozzolanic activity of zeolite, especially for fine particles.

The long-term durability of asphalt pavements is closely related to the oxidative aging of asphalt binders. Oxidative aging depends on the oxygen diffusion in asphalt mixtures. To further investigate oxidation reactions and guide the design of age-resistant asphalt mixtures, we conducted a combined experimental and molecular dynamics (MD) study to investigate the oxygen diffusion in the asphalt mixture and to analyze the effects of volumetric characteristics of the asphalt mixture and environmental factors on the oxygen diffusion. A diffusion apparatus was used to measure oxygen diffusion in compacted asphalt mixtures. MD simulations were performed on the asphalt mixture-oxygen diffusion model to simulate the oxygen transport process. The results showed that oxygen diffusion was influenced by the temperature, oxygen concentration, air void, and height of the asphalt mixture. The intrinsic mechanism was that the temperature accelerated the oxygen transport by increasing the self-diffusion coefficient of the oxygen molecules. Although the oxygen concentration did not affect the oxygen self-diffusion coefficient, it increased the oxygen base, which in turn increased the number of oxygen molecules passing through the asphalt mixture. Moreover, the increased air voids of the asphalt mixture decreased the obstruction in the oxygen diffusion process and increased its transmission speed, whereas the increase in the height of the asphalt mixture increased the oxygen transmission path, thereby reducing the oxygen transmission efficiency. The results of MD simulation were consistent with the experimental results. Therefore, it is feasible to use MD simulations to investigate diffusion behavior of oxygen in asphalt mixtures.

The microstructures of seawater cement-based materials normally are influenced by the salinity in seawater, which could result in different properties. The thermal conductivity ($\lambda$-value) of seawater cement-based materials is a key input parameter for the heat transfer analysis. However, few studies have been conducted on this issue. This study investigated the $\lambda$-value of seawater cement-based materials using experimental and numerical methods. The influences of water-to-cement (w/c) ratio, curing age, and sand content on the $\lambda$-value of seawater cement-based materials were examined experimentally. Then a three-dimensional mesoscale finite-element model was established to assess the influences of pore size and porosity on the $\lambda$-value of cement-based materials. It was found that the $\lambda$-value of seawater cement-based materials increases with increasing curing age or sand content, and a low w/c ratio contributes to a high $\lambda$-value, similar to that of the tap-water cementitious material. The $\lambda$-value of seawater cement paste with curing ages of 1 and 7 days was slightly greater than that of the tap-water cement paste. However, no significant difference was found between the $\lambda$-values of the 28-day seawater and tap-water cement pastes. Pore size had a negligible influence on the $\lambda$-value. The $\lambda$-value of cement-based materials decreased with increasing porosity, and the decrease in $\lambda$-value of cement-based materials with pores filled with air was more significant than that with pores filled with water, indicating that the pore-water saturation has a great effect on the thermal conductivity.

The pH plays a key role in the hydration process of cement clinker and thus determines the morphology and mechanical performance of cement-based materials. Herein the effect of pH on the nucleation rate, morphology, and mechanical performance of calcium-silicate-hydrate (C-S-H) gel was explored by performing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation. The results show that the packing fraction of C-S-H gel increases correspondingly as the pH increases. Concerning the morphology of C-S-H gel, the results of specific surface area, coordination structure, cluster size distribution, and pore size distribution indicate that with the increase of pH, the spatial distribution is more heterogeneous and the shape of cluster changes from fibril-like to spherical. In addition, as the decrease of pH, the particles are distributed uniformly thus leading to the increase of mechanical properties. These results acquired from this mesoscale simulation provide insights into the role of pH during cement hydration which is a vital step connecting the nanoscale characterization to its engineering application and designing high-performance cement-based materials.

To clarify the effective load transfer capacity of asphalt mixture skeletons, granular material mechanics and the discrete-element method (DEM) were introduced to analyze the morphological characteristics of skeleton main force chains (MFCs). Results indicate that the greater number of MFCs is not relevant to higher effective transfer load capacity for the skeleton. An increase in the relative ratio of the III type of force chain in MFC is not conducive to transferring external loading effectively. The MFC number gradually decreases with an increase in nominal maximum aggregate size (NMAS), and the proportion of MFC increases for dense-graded asphalt concrete (AC). For stone matrix asphalt (SMA), the increase of NMAS will reduce the quasilinearity of MFC and be conducive to forming longer MFC, especially for the I type of force chain. An increase of content with aggregate size less than 2.36 mm can improve the number ratio of the III type of force chain. Therefore, an increase in the passing rate of 2.36 mm ($P_{2.36}$) is not conducive to transferring external loading for AC.

The use of reclaimed asphalt pavements (RAP) is an increasing trend nowadays due to environmental and economical appeal. The use of higher percentages of RAP might result on cracking issues associated with the performance of the aged binder. In order to enable the use of RAP, recycling agents of distinct natures have been used to enhance the performance of recycled asphalt mixtures. Diffusion of the recycling agent into the RAP binder is a complex phenomenon influenced by many variables such as temperature and time of exposure to heat. This paper aims to investigate the influence of the diffusion time and mixing temperature on the fatigue performance of fine-aggregate matrices (FAMs) because more studies at this scale are needed to broaden the knowledge on the diffusion process and to improve the techniques for mixture recycling. In this study, the diffusion process is evaluated by comparing the fatigue performance of FAM samples comprised of 40% RAP and bio-oil with a target air void of $5.0\%\pm 0.5\%$. The analyzed samples were produced under 10 different scenarios, varying the diffusion time (0, 40, 80, 120, and 160 min) and temperature (135°C and 160°C). Linear-viscoelastic properties and fatigue parameters of the FAMs were monitored by means of tests carried out in a DSR, and by applying the simplified viscoelastic continuum damage (S-VECD) theory. The best fatigue performance of the FAM mixtures was achieved for a diffusion time of 80 min at 135°C. The temperature of 160°C also presented the best performance for the diffusion of 80 min. Longer diffusion times did not improve the fatigue performance due to prolonged aging, and the impact of extended aging on the linear-viscoelastic properties showed that the higher the mixing temperature the greater the impact of aging on the material stiffness and damage evolution rate.

This study evaluated the mechanical properties and self-healing performance of freshly casted and 19-month-aged bioconcrete samples with integrated sulfate-reducing bacteria (SRB) and nitrate-reducing bacteria (NRB) granules that were cultivated in an upflow anaerobic sludge blanket (UASB) reactor with synthetic wastewater. The 28-day compressive strength fulfilled the design requirement of 50 MPa. The apparent volume of permeable voids (AVPV) of fresh and aged bioconcrete met the limit of 13%. The self-healing ability was determined by exposing cracked bioconcrete to water media such as glucose, calcium acetate, tap water, and wastewater, which have shown calcite deposition in fresh and aged samples. The highest amount of calcite deposition was seen on fresh samples after glucose exposure ($420\mu \mathrm{m}$) and on aged bioconcrete after calcium acetate exposure ($320\mu \mathrm{m}$). Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS/XRD) results demonstrated that SRB/NRB granules survived mortar integration and deposition of calcite in both fresh and aged samples. The water permeability and acid resistance of bioconcrete samples were correlated to the amount of deposited calcite.

More robust methods for predicting the performance of asphalt mixtures in the field have been established in recent years. However, the tests carried out to obtain the data generally make use of samples compacted in the laboratory with diameters that make it impossible to extract samples from field layers. This problem can be solved with the use of small samples with a diameter smaller than the compaction thicknesses used in the field. Although characterization tests of asphalt mixtures with small samples have already been performed in the literature, few studies have been carried out, thus denoting the need for more tests for a larger number of mixtures. This research aims to verify the behavior of smaller samples ($38\times 110\mathrm{mm}$) and to evaluate if they can provide the same linear viscoelastic (LVE) analyzed from the master curves and the rheological Model 2S2P1D (two springs, two parabolic elements, and one dashpot), the same fatigue characterization, and the same performance over time results for fatigue damage by pavement simulation in FlexPAVE software. The observation of LVE domain suggests a great consistency between the results obtained for the two test geometries. The same was observed for fatigue analysis based in the simplified viscoelastic continuum damage (S-VECD) model. The accumulated fatigue damage curves along the traffic and the cracked area (CA%) prediction obtained by FlexPAVE showed that the characterization by standard and small samples lead to concordant results. The small-scale specimen geometry tested in this research is an accurate and alternative method to full-size samples, with the ability to characterize the LVE behavior, the fatigue phenomenon, and performance simulations in the context of forensic analysis or other investigations that require the use of samples extracted from pavements in field.

Abstract

The commercial use of aggregate is ubiquitous in the construction of buildings and roads because aggregates provide strength, resistance, and support. This paper analyzes the constraints of aggregate rock use in Kurram district, Northwest Pakistan, and to demarcate aggregate resource locations using GIS techniques, weighted overlay analysis, and the analytic hierarchy process (AHP). The undertaken study has considered several appropriate socioeconomic and environmental factors such as land use, distance from highways, rock type, elevation, and slope to diminish conflicts between land users. These variables were mapped using the weighted overlay analysis and the AHP analysis and then ranked in order of importance. The geographical relationships between all thematic data were used to generate the final suitability map of weighted overlay analysis and AHP analysis. The enumerated results have depicted that a number of aggregate prospective areas are prevalent in the study area. The research areas have been classified as low, moderate, or highly suitable based on environmental constraints, transportation network availability, current land use, and mineral-deposit availability. Furthermore, an accuracy comparison between AHP and weighted overlay analysis revealed that AHP analysis has a very high level of precision. As a consequence, the AHP-GIS approach is highly recommended for investigating land resources and resource categorization, which assists policymakers and regional authorities in making decisions and approving quarry authorizations.

Practical Applications

The purpose of this research is to analyze aggregate resources using GIS techniques. The authors defined the aggregate resources using two different approaches: weighted overlay analysis and the analytic hierarchy process (AHP). The criteria for selecting the quarry site were developed and implemented in a GIS environment. These criteria consider a variety of factors, including the slope, the distance to the road, land use and land cover, accessibility, slope, elevation, and geology. The final suitability maps were generated, and the locations were classified into three parts: low, medium, and high. Operators and decision-makers can use the undertaken analysis as a reference to create an appropriate aggregate plan for spatial development and management. This will make it easier to ensure that aggregate resources are accessible to both present and future generations while balancing extraction activities with an environmentally friendly perspective.

Organic rectorite (OREC) can significantly improve the resistance of asphalt to deformation and aging, but it tends to cause low-temperature cracking. To solve this defect, a novel idea that develops an OREC and polyurethane (PU) composite-modified asphalt binder has been put forward in this work. Various modified asphalt binder systems containing different combinations of OREC and PU contents were prepared by the melt blending method. The storage stability of the OREC/PU-modified asphalt binders was studied. The high- and low-temperature properties of binders were investigated by dynamic shear rheometer and bending beam rheometer tests. The microstructure and modification mechanism of the binders were characterized by gel permeation chromatography, differential scanning calorimetry, and Fourier transforms infrared spectroscopy. The results showed that the OREC/PU-modified asphalt binder displayed good high-temperature storage stability. However, excessively high content of OREC will adversely affect the storage stability of asphalt. In the 2% by weight OREC/9% by weight PU modified asphalt system, OREC and PU exhibited excellent synergistic effects. And the high- and low-temperature properties of the asphalt were significantly improved. The introduction of OREC/PU reduces the $T_g$ of the asphalt binder and the enthalpy during temperature change. The modified asphalt has good low-temperature flexibility through the physical and chemical interaction between polyurethane and asphalt during the modification process. PU can intercalate OREC and react with active hydrogens in asphalt to generate cross-linked structures to enhance the high- and low-temperature properties of the asphalt binder.

To investigate the water damage effects and aging mechanism of warm-mix asphalt (WMA) after oxygen isolation and light–oxygen coupling ultraviolet (UV) aging, contact angle and adhesion performance tests were performed. The UV aging mechanism of WMA was analyzed using Fourier transform infrared spectroscopy and atomic force microscopy. The relationship between adhesion and surface roughness of WMA after UV aging was established. The test results indicated that as aging time increased, the water damage resistance of WMA gradually weakened. After the UV aging time exceeded 150 h, the adhesion performance of WMA gradually stabilized, and the addition of oxygen increased the UV aging effect. Additionally, the formation of strong polar substances and oxygen-containing functional groups precipitated by asphaltene gelation is the main reason for the attenuation of WMA adhesion performance.

Certain salts of calcium and magnesium can mitigate alkali-silica reaction (ASR) by reducing the pH of concrete pore solution. In a previous study, eight such promising salts were identified out of more than 700 possible salts using a systematic approach. This study presents the performance of these admixtures in paste, mortar, and concrete mixtures. Paste mixtures were used to evaluate the long-term pore solution pH (up to 6 months) and pore size distribution. The flow, flow retention, setting time, and drying shrinkage were evaluated using mortar mixtures. ASR mitigation potential of these admixtures was evaluated with a highly reactive aggregate using a concrete prism test. Finally, concrete mixtures were designed with specific performance targets and evaluated for slump, plastic air content, compressive strength, and bulk resistivity. It was observed that the salts maintained a reduced pore solution pH over the long term. The pore size characteristics were found to be similar to or better than the control mixture. The salts mitigated ASR successfully and had minimal impact on workability, air content, and compressive strength. Most salts behaved as set accelerators. Drying shrinkage was found to be slightly higher when compared with the control, but within the limits specified by the standards. Overall, it is concluded that these pH-reducing admixtures can be used with minimal adjustments to concrete mixture proportioning in order to reliably mitigate ASR.

Smart concrete is capable of self-assessing its state of stress and strain. It is produced by tailoring the electrical conductivity of concrete with the addition of conductive materials such as carbon fiber. This paper aims at determining the electrical conductivity of smart concrete materials with randomly dispersed carbon fibers. It unravels the conduction mechanism and establishes a theoretical basis of the percolation threshold for conduction. A numerical model for concrete with carbon fiber is developed. The electrical conduction through the concrete is calculated by solving the governing equations based on Kirchhoff’s reformulation of Ohm’s Law. More than ten thousand cases with varying fiber topologies, fiber fraction ratios and aspect ratios have been generated to account for the randomness of distribution and their electrical properties are evaluated. By analyzing those results, the mechanism behind the percolation threshold is explained. Finally, an algebraic relationship is posited to determine the percolation threshold has been evaluated. The relationship has been validated with experimental results. The results are extremely valuable for the design of self-sensing smart concrete.

The physical and mechanical characteristics of a novel mortar that uses recycled PET powder as a replacement for natural sand are examined in this paper. This study specifically looks at the impacts of replacing recycled polyethylene terephthalate (PET) powder in place of fine aggregates in mortars. To create five distinct mortar mixes, recycled PET powder was substituted in varying proportions (0%–30% by volume of the sand). The investigation focuses on the physical and mechanical characteristics of the material, including density, slump, water absorption, ultrasonic pulse velocity, flexural and compressive strength, and microstructural and interface characterization. Results reveal that the substitution of recycled PET powder reduces slump, compressive strength, ultrasonic pulse velocity, dry and wet density, and slump, whereas flexural strength and fracture energy exhibit the reverse tendency. The slump variation indicates the controllable workability of the mortar in the fresh state. The latter feature is quite important for the application of such a material where flowability is a dominating parameter, e.g., 3D printing. Two data-driven models for the compressive and flexural strength reduction factors as a function of the substitution ratio based on symbolic regression techniques are proposed using the findings of this study in conjunction with data from the literature.

Magnesium oxychloride cement recycled concrete (MOCRC) has the advantages of low carbon emissions and energy savings. To better understand the rebar corrosion problem in MOCRC under a salt lake environment, this paper presents the investigation of rebar corrosion behavior in MOCRC, as well as the difference of protective influence between single and double protective methods. During the investigation, the concrete surface strengthening materials and rebar type selection were selected as protective methods, and an electrochemical test based on linear polarization method and Tafel method was introduced. According to the time-varying characteristics of corrosion current density and mass loss of rebar in different specimens, a time-varying model of corrosion current density of rebar was established. The results show that the $B$ values of corroded hot-rolled plain steel (HS), corroded HS with self-developed coating (CS), uncorroded CS, and uncorroded stainless steel (SS) were 28, 34, 41, and 45 mV, respectively. Also, the rebar type selection has far better protective influence than the concrete surface strengthening materials, and the double protective method was better than the single protective method. Besides, it was noticed that the time-varying characteristic of rebar corrosion in MOCRC conformed to the logarithmic-type time-varying model, which has an upward trend in the earlier stage and exponential-type time-varying model with a downward trend in the later stage. Finally, this study presents a profound investigation for the reinforcement corrosion in low-carbon and energy-saving building MOCRC structures.

The performance of a structure is primarily determined by its material characteristics under different loading conditions, strain rates, and temperatures. In the present work, the plastic flow response of a homogenized AT61 magnesium alloy was constitutively analyzed under a wide variety of quasi-static and dynamic strain rates. The quasi-compression test was conducted at 25°C–250°C with strain rates from ${10}^{-4}$ to ${10}^{-1}{\mathrm{s}}^{-1}$. The dynamic loading of AT61 alloy was performed on a split Hopkinson pressure bar (SHPB) apparatus under a strain rate of $\mathrm{1,000}–\mathrm{4,000}{\mathrm{s}}^{-1}$. The material shows hardening behavior throughout the strain rate regime, whereas the plastic flow stress significantly reduces with an increase in deformation temperature. At a very high strain rate, the accumulated energy around the cracks is attributed to the dynamic recrystallisation with the onset of adiabatic temperature rises in the materials. A phenomenological Johnson-Cook (JC) model was also calibrated and used for numerical simulation in ABAQUS/Explicit to predict the material flow response. It was observed that a strong correlation exists between experimental and numerical results.

Abstract

This study outlines a method for identifying high-quality recycled concrete aggregate (RCA) obtained after mechanical treatment. In the present approach, the physical and mechanical properties of RCA are considered as quality parameters. As a first step, mechanically treated (Los Angeles) RCA is produced with 28 combinations of charges and drum revolutions. Twenty-eight sets of mechanically treated RCA are produced, each with different physical and mechanical properties. Furthermore, the 28 sets of RCAs are compared using the performance-based quality optimization approach. The performance index for each set of RCAs is calculated applying a multicriteria decision-making approach named “technique for order of preference by similarity to ideal solution.” This approach considers physical and mechanical properties as a response and the combination of charges and drum revolutions as alternatives to obtain the performance index of alternatives. Based on its performance, the leading rankings RCAs are selected for an experimental study to validate the methodology. As a result of RCA’s optimized quality, recycled aggregate concrete (RAC) has excellent physical, mechanical, and durability characteristics that agree with natural aggregate concrete (NAC) composed of parent aggregate. The 28- and 91-day compressive strengths of RAC exceed those of NAC by 8.5% and 30.65%, respectively. Flexural strength, split tensile strength, fracture energy, ultrasonic pulse velocity (UPV) values, rapid chloride-ion penetration test values, water absorption, and abrasion resistance are comparable with NAC. The quality optimization approach identifies RCA with superior shape, texture, and elastic properties. An RCA with optimized qualities also strengthens the new interfacial transition zone and old interfacial transition zone as well as RAC’s associated properties. The RAC’s dynamic modulus of elasticity is superior to the reported values and is 0.95 fractions of NAC. Optimized quality of RCA reduces the sorptivity of RAC compared with the reported values. The RAC may not have equivalent sorptivity to NAC without lowering RCA parts, whether mortar-attached, mortar-covered, or mortar-only type aggregate or applying other treatments that may increase the production cost.

Practical Applications

This research presents a standard procedure for identifying mechanically treated recycled concrete aggregate with properties (physical properties and mechanical properties) similar to those of the parent aggregate (natural aggregate). The method demonstrated in this study may be adapted to real-life worksite conditions—but not exactly. In Los Angeles abrasion machines, recycled concrete aggregates obtained from a source can be processed by varying drum revolutions and charges. Based on the charges and drum revolutions selected for treatment, treated recycled concrete aggregate can be prepared with different sets of physical and mechanical properties. Based on the present research, the physical and mechanical properties of treated recycled concrete aggregate can be compared between these sets. In this way, recycled concrete aggregates can be produced that resemble their parent aggregates. Using this process, recycled concrete aggregates may be used to replace natural aggregates without compromising the concrete’s physical, mechanical, or durability properties.

Recently, nano materials that have high active surface area and small particle size are used to improve the properties of the asphalt binder and mixture. However, the most important factor that limits the use of nano materials is cost. Therefore, in this study, nano waste tea, which is economical, environmentally friendly, sustainable, and less energy consuming was obtained via incineration of waste tea. To study its use in pavement for the first time, the effects of nano waste tea on asphalt binder and mixture were evaluated with three different usages. Initially, the properties of asphalt mixtures prepared with 1%, 3%, and 5% nano waste tea instead of filler were examined. Then, asphalt binder was modified with 2%, 4%, and 6% nano waste tea and asphalt mixtures produced with these binders tested out. Finally, the mixture properties of asphalt binders modified with 1%, 3%, and 5% bio-oil obtained from the pyrolysis of waste tea were investigated. In the present study, it was determined that asphalt binder and asphalt mixtures prepared with nano waste tea used in three different ways all provided specification limit values. According to the obtained results, although the indirect tensile strength of asphalt mixtures containing nano waste tea decreased for both the dry and wet methods, it was observed that nano waste tea had a positive effect on moisture susceptibility. Thus, the present study has determined a nano material that is economical, environmentally friendly, and sustainable and can be used in pavement.

This study provides a systematic evaluation of the pullout behavior of steel fibers embedded in ultrahigh-performance concrete (UHPC) with calcium carbonate whiskers and carbon nanotubes at the micrometer and nanoscale levels. This study investigated mechanical and the bonding properties of the matrix at two different scales using the compressive test, flexural test, and single-fiber pullout test, which are important for the further improvement of concrete. The results show that at a specific dosage, both calcium carbonate whiskers and carbon nanotubes effectively improve the compressive and flexural properties of concrete. The pullout behavior at both scales is significantly optimized compared with the reference system. Comparing the bonding strength and pullout energy at the two scales, the calcium carbonate whiskers are better at improving the fiber-matrix bonding properties. Scanning electron microscopy (SEM) was used to observe the pulled-out fibers. The fracture mechanism of the matrix and the influence of the added material on the bonding properties of the matrix were validated microscopically.

Abstract

This study evaluates the degradation of glass fiber reinforced polymer (GFRP) rebars in alkaline environment under accelerating aging in terms of tensile strength retention (TSR). In addition to environmental conditions such as the pH of the surrounding solution, temperature, and aging duration, the manufacturing parameters of GFRP rebars (i.e., diameter of rebar, $d_b$) and volume fraction ($V_f$) are vital in the degradation of GFRP rebars in alkaline environments as well as scarcely reported. To assess the effect of these variables on the degradation (i.e., TSR), shapely additive explanations (SHAP analysis) based on light gradient-boosting machine (Light GBM), and statistical analysis using response surface methodology (RSM) were used. The Light GBM and RSM models were developed using 715 experimental results of TSR obtained from the existing literature. The performance of both models was reliable in terms of correlation and error analysis. The interaction among the variables was further analyzed using detailed explanations of how each variable affected the prediction of TSR. The results revealed that the TSR generally increases at higher $V_f$ and $d_b$ of GFRP rebars; however, it decreases with increasing pH, temperature, and duration of exposure. Furthermore, maximum TSR was recorded for pH of 12.6 ($V_f=0.62-0.70$ and $d_b=14–16\mathrm{mm}$). Finally, severe degradation was observed for rebars having $0.55>V_f>0.70$. The findings of this study suggest that the current practice of various structural codes using GFRP rebars having minimum mass fraction of 70% ($\approx 0.48V_f$) could be improved by using the range of $V_f$ determined in this study to minimize the degradation in alkaline environments.

Practical Applications

The current research identifies the key production parameter effects of GFRP rebars on durability in harsh alkaline environments. The effect of high pH, surrounding temperature, and aging duration, among others, is well understood. However, a study on the effects of GFRP rebar size (diameter of rebar, $d_b$) and volume fraction ($V_f$) of fibers would help manufacturers to improve the quality of the GFRP rebars impregnated in vinyl ester resin. Also, the practitioners may use the recommended $d_b$ and $V_f$ in designing durable GFRP-reinforced structures. This study also identifies the research gaps, where a scarce amount of literature is available on GFRP rebars exceeding 16 mm. The formulated models can further be used for long-term extrapolation of service life of the GFRP rebars based on surrounding harsh alkaline environmental conditions. The basic assumptions considered in evaluating the durability of the GFRP rebars can be overcome.

This paper presents the details of experimental testing of soil, adobe masonry units, and assemblages for the first time in Pakistan. Adobe units were tested both in compression and bending. The compressive strength of adobe masonry was determined by experimentally testing masonry prisms and wallettes, whereas diagonal compression wallettes were tested for determining shear strength. Five and three specimens were used, respectively, for compression and shear strength testing, and an average of these was used as a representative of a particular mechanical property. A soil sample was tested for classification and particle size distribution, which showed that it contained 96% silt and clay contents, which were higher as compared to the soil used for adobe structures in other parts of the world. Both adobe units and soil mortar presented shrinkage cracks upon drying. The compressive strength of adobe units complied with the requirements of international codes despite very high silt and clay contents in the employed soil. The compressive strength of the prism was higher compared to the wallette. The elastic moduli of the adobe masonry prism and wallette were found to be 113 and 114 MPa, respectively. Although the adobe masonry shear strength was comparable to the shear strength reported in the existing literature, its modulus of rigidity was considerably small. The presented data in this paper are essential for improving the built environment in Pakistan.

Clay brick masonry is a construction system used worldwide due to its economy and technical viability. While its behavior when subjected to high temperatures is relatively well known, civilian construction has evolved and introduced lighter and more slender elements with no assessment of the potential decrease in performance. This study sought to develop a clay brick masonry system of reduced thickness and high fire resistance. In order to accomplish this objective, heat transfer in bricks of different geometries was analyzed with a finite element numerical model calibrated with experimental data. A wall sample was constructed in real scale with the optimum geometry obtained from the numerical analysis and evaluated experimentally. Results showed a satisfactory agreement between the model and experimental wall sample and produced a possible nonload-bearing compartmentalization system of reduced thickness with a 180 min fire resistance rating.

The drying shrinkage of concrete is predicted in this study from shrinkage tests conducted on cement paste specimens, combined with mesoscale analysis of mortar and concrete images that were obtained from X-ray micro computed tomography (CT) scanning. A series of shrinkage tests were carried out on cement paste, mortar, and concrete prisms for a period of 6 months to generate input data and validate the model. The effect of aggregate size on drying shrinkage of concrete was also experimentally and numerically investigated. The proposed model uses a quadtree decomposition algorithm to convert digital images of mesostructures into meshes, which are then solved using the scaled boundary finite-element method. In the analysis, mortar was considered as a composite of viscoelastic cement paste and fine aggregates, whereas concrete was considered as a composite of viscoelastic mortar and elastic aggregates. A parametric study was carried out on mesostructures with various aggregate volume ratios to examine the ratio’s influence on shrinkage of concrete and to compare the proposed model with other simplified composite shrinkage models in the literature.

Glued laminated bamboo (glubam) is an engineered bamboo for the potential usage in structures as an alternative to timber-based glulam. This paper focuses on the impact toughness and static bending strength of glubam, with the goal to provide basic understanding and experimental data for impact design of engineered bamboo structures. Two types of glubam, i.e., thin-strip and thick-strip glubams were investigated through impact pendulum and quasi-static bending tests. For the thick-strip glubam, testing parameters also included three types of manufacturing conditions with different degrees of carbonization of composing bamboo strips. Both comparisons among different types of glubam, and between dynamic and static bending results can effectively identify the impact resistance and mechanical properties of glubam. The dynamic impact loading resulted in higher instability and had failure modes different from quasi-static tests for glubam specimens. Experimental values of toughness, modulus of elasticity (MOE) and modulus of rupture (MOR) at different loading speed conditions are obtained.

X-ray computed tomography (XCT) was used to monitor microstructure changes of hardened cement paste, with different water/cement ratios during a one-dimensional carbonation process. After removing equipment-induced measurement errors by a volume-constant method, the pores, dense hydration products, loose hydration products, and unhydrated cement in the sample were classified. Consequently, variation of each component with depth and carbonation duration were obtained, based on which mechanism of carbonation on hardened cement paste was conducted. Results showed that microstructure changes in hardened cement paste under ${\mathrm{CO}}_2$ effects is a coexisting simultaneous densification and cracking process. Within the entire carbonation process, the changes exhibited a general alternate pattern of densification–cracking–redensification, leading to connection of micropores into macro ones in hardened cement paste (i.e., the so-called carbonation-induced cracking); entire volume of the pores bigger than 4.4 μm did not present obvious changes during carbonation; a ${\mathrm{CO}}_2$ influence depth can be obtained by this method, which has an approximate linear relationship with the square root of carbonation duration and has limited influence with the water/cement ratio used in this study.

The disposal of waste face masks (FM) caused by COVID-19 has become an increasingly severe problem. In order to alleviate this issue, this paper proposes an approach of adding face mask waste as modifiers to asphalt. Extensive performance tests evaluated the feasibility of FM in asphalt binders, including rotational viscosity and rheological behaviors at different temperatures, aging performance, separation tendency, and modification mechanism. Based on this, the road performance of FM-modified asphalt mixtures were also investigated. The results showed that FM increased the rotational viscosity, high-temperature performance, and anticreep performance, whereas it had a negative effect on the stress change sensitivity, low-temperature performance, aging performance, and storage stability of asphalt binder. Based on the linear amplitude sweep test results, the incorporation of FM contributed to the material integrity and load resistance capacity of asphalt binder, whereas it was not conducive to its antideformation performance. According to Fourier transform infrared spectroscopy and fluorescence images, the modification process of FM with a chemical composition of polypropylene was mainly a physical blend, and 5% FM had the best compatibility with asphalt. The addition of FM could improve Marshall stability, rutting resistance, low-temperature cracking resistance, and moisture susceptibility of an AC-13 mixture. The 5% FM-modified asphalt and asphalt mixture met the specific road requirements. The experiment results could provide a new way to deal with waste FM by recycling.

Abstract

This experimental investigation studied the development and use of a new self-compacting sand concrete (SCSC) to perform repairs on ordinary concrete (OC) substrates. This type of concrete should have the following characteristics: excellent fluidity, optimum stability, and acceptable bond strength. In addition, a new pouring method was used for the application of the repair layers. For this, nine SCSC compositions were tested for slump flow using an Abrams cone, passing ability by the L-box test, segregation resistance by the screen stability test, and compressive strength. The results obtained from these tests were then employed for selecting the best composition to use as a repair material. In addition, the volume of permeable pore and water absorption was determined by immersion tests. The compressive strength tests were carried out at three different ages, i.e., 7, 28, and 90 days, for the purpose of determining the physical and mechanical characteristics of ordinary concrete (OC) and those of SCSC, separately. The bond strength between the substrate (OC) and the repair concrete (SCSC) was evaluated by performing two tests: a tensile splitting test (indirect tension test) and a concrete pull-off test (direct tensile test), which was also used for the evaluation of the tensile strength of the concrete substrate (OC) and that of the repair concrete (SCSC). The resulting bond strength values showed that it is indeed possible to use SCSC as a repair material in thin and narrow places, and even those having complex geometries.

Practical Applications

This research aims to develop a novel, highly fluid, self-compacting sand concrete (SCSC) that is intended to be used as a cementitious repair material for the rehabilitation or reinforcement of civil engineering structures. The high fluidity of this type of concrete makes it an exceptionally workable material that has the capacity to flow through tightly reinforced elements or circulate into sections having geometrically complex shapes. SCSC is exceptionally effective for repairing narrow areas, such as the intersection of reinforced concrete members where reinforcement is overlapped, and for fixing sections below horizontal surfaces, such as bridge decks and other similar structures. The results obtained are very encouraging, with more than 70 MPa for the compressive strength and more than 3 MPa for the tensile strength. In addition, the ingredients making up this concrete are readily available almost everywhere. They can be utilized without specific manufacturing efforts. Some of the constituents of self-compacting sand concrete are fine natural sand, recycled sand and aggregates, and sand recovered from limestone waste.

Due to the corrosion of fasteners by water-based preservatives, the preserved timber in outdoor environments can decrease the service life of the metal fasteners. In addition, the segregation of timber members and metal fasteners is also difficult during the demolition of timber structures. Wooden fasteners can be a promising alternative to metal fasteners because they have favorable resistance against corrosion and are more naturally harmonized with timber members. This paper studied the pull-out performance of dried densified wood (DW) dowels embedded into glued laminated timber (glulam) parallel to the grain with three different embedded lengths in two ambient environments with a temperature of 20°C and relative humidity (RH) of 65% and with a temperature of 20°C and relative humidity of 85%. The hygroscopic swelling of the dried DW dowels with a long embedded length can provide the favorable friction locking to transfer the axial load.