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The expedient repair of damaged airfield pavements is important to eliminate long closure periods. Rapid-setting cement (RSC) is promising for achieving target strength in a much shorter duration (4–6 h) compared to conventional repair methods. However, when the objective is to reopen the pavement within 1–2 h, there is a lack of methods to quantify the development of mechanical properties during the first few hours. In this study, a simplified maturity method is proposed to monitor the very early-strength development of two commercially available RSC mixes with different strength development mechanisms. The results were validated using hydration chemistry data from scanning electron microscope (SEM) experiments and ultrasonic pulse velocity (UPV) tests. The experimental results show that such a maturity-based approach is effective and robust in characterizing the early-strength development of the two RSC mixes despite variations in ambient temperature conditions. [ABSTRACT FROM AUTHOR]

Developing low-carbon and green self-compacting concrete (SCC) is essential for advancing sustainable building materials. In this study, recycled steel fibers (RSFs) and industrial by-products were combined for the production of SCC made with recycled aggregates (RSCC), with the aim of introducing multiple waste materials to improve the sustainability of SCC. 14 RSF-reinforced RSCC mixtures (RSF-RSCC) were prepared by replacing natural coarse aggregates (NCAs) with recycled coarse aggregates (RCAs) and cement with supplementary cementitious materials (SCMs) and reinforced with RSFs. The parameters studied in this paper include replacement levels of RCAs (75%), SCMs (50% and 75%), and RSFs (0.5%, 1.0%, and 1.5%). The influence of different content of RSFs and SCMs combinations on workability and mechanical properties was studied, and the synergistic influence of RSFs and SCMs was investigated in detail. The microstructure characteristic was investigated using a scanning electron microscope. The test results show that the addition of SCMs can compensate for the adverse effects of RSFs on the fresh properties, and all RSF-RSCC exhibited superior workability. Furthermore, the incorporation of RSFs enhanced the mechanical properties of RSCC, resulting in remarkable improvement in the compressive and flexural strengths. The combined incorporation of RSFs and SCMs led to an excellent synergistic effect, which resulted in significant enhancements in the mechanical properties. [ABSTRACT FROM AUTHOR]

Phosphogypsum (PG) is an industrial solid waste generated during the preparation of phosphoric acid, which is produced in large quantities and stockpiled or discharged into the sea. This study aims to design sustainable pavement base materials constituting significant PG content. The physical and chemical properties of the raw materials were first tested. The optimum moisture content and maximum dry density of specimens were determined by compaction tests. The unconfined compressive strength (UCS), split tensile strength (STS), freeze-thaw cycles, and shrinkage tests were used to evaluate the mechanical performance of phosphogypsum pavement base material (PPBM). Furthermore, the interaction mechanism was investigated by applying scanning electron microscope (SEM) and Fourier-transformed infrared (FTIR) tests. The results showed that the 7-day UCS of PPBM with cement content 8%–12% was greater than 3 MPa. The specimens retained 91.3% unconfined compressive strength over five freeze-thaw cycles. Unlike traditional semirigid base materials, the PPBM exhibited no shrinkage strain, which is manifested by the growth of expansion strain with increasing amounts of PG. Through microscopic observation, the PPBM produced ettringite (AFt) and calcium-silicate-hydrate (CSH) with the extension of curing time, which is consistent with the analysis of FTIR spectrums. The crystallized water in the PG participates in the hydration reaction. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to investigate the impact splitting tensile property and microstructure characteristics of steel fiber recycled aggregate concrete (SFRAC) based on the split Hopkinson pressure bar (SHPB) and scanning electron microscope (SEM). The effects of fiber content, strain rate, and recycled aggregate replacement ratio on the mechanical parameters (static and dynamic splitting tensile strength, peak strain and ultimate strain, peak toughness and ultimate toughness) were analyzed. Then the microstructure characteristics of SFRAC at different interfaces were observed via SEM, and energy spectrum analysis of the interface transition zone (ITZ) was carried out. The results show that SFRAC is a strain-rate sensitive material whose mechanical properties are affected by the strain rate and improved with its increase. It is also found that steel fibers play a role in improving dynamic splitting tensile strength and toughness, and the optimal fiber content is about 1.0%. However, increasing the recycled aggregate replacement ratio will weaken the good effect of steel fibers on the mechanical properties. Furthermore, it can be seen by means of SEM that the fracture area of steel fiber is mostly pulled out. Also, there are more cracks and pores in the cement paste of recycled aggregate concrete (RAC) compared with normal concrete (NC), and the hydration products in the ITZ are significantly decreased. With the incorporation of steel fibers, the calcium content of the ITZ can be reduced. [ABSTRACT FROM AUTHOR]

This paper investigates the tensile behaviors and self-healing of engineered cementitious composite (ECC) under sulfate wet–dry cycles to reflect the durability. Four pretensile strain levels of 0%, 1%, 1.5%, and 2% were designed. The uniaxial tensile test, three-point bending test, and single-crack tensile test were performed, along with the microscopic characterizations of scanning electron microscope (SEM) and X-ray diffraction (XRD). The results indicated that the sulfate wet–dry cycle exposure had a positive effect on the tensile strength and initial cracking strength of the uncracked ECC, while that was negative on the tensile strain capacity. The insufficient margin of the σoc/σcr and Jb′/Jtip indices explained the lower tensile strain. The tensile strength and initial cracking strength of the cracked ECC with 1% pretensile strain surpassed those of the uncracked ECC after undergoing 80 sulfate wet–dry cycles (80 C), while that did not hold for the other cracked ECCs. All the cracked ECCs showed a similar tensile strain after undergoing 80 C. The crack with a width of less than 100 μm achieved complete self-healing. The self-healing products of ECC under sulfate wet–dry cycle exposure may comprise of calcium (alumino) silicate hydrate [C-(A)-S-H] gel, calcite, ettringite, and gypsum. The current findings could offer reference points for applying ECC use in coastal regions. [ABSTRACT FROM AUTHOR]

This study uses fly-ash-based superplasticized geopolymer by adding a naphthalene-centered superplasticizer to the geopolymerized soil. Alkali-binder ratios and alkali-activator ratios are varied simultaneously with a molarity of 10M. The optimum dosages of binder, geopolymer, and superplasticized geopolymer are found from unconfined compression tests. California Bearing Ratio (CBR), pH, consolidation, water-holding capacity, and microstructure tests were performed on optimum dosages. The clayey soil's undrained shear strength and CBR value increased as the geopolymer was superplasticized. The 28-day undrained shear strength of geopolymerized clay was around 300 kPa, attained within three days of the curing period with superplasticized geopolymer. This is because adding a superplasticizer increases the polymerization reaction rate and improves the geopolymer's performance. The maximum undrained shear strength was attained within seven days of the curing period for both cases. The undrained shear strength after a curing period of 7, 14, and 28 days for geopolymer and superplasticized geopolymer was found to be almost the same value, which shows that after seven days, curing has little role in strength improvement. The hydraulic conductivity and coefficient of consolidation of geopolymerized soil increased with the addition of superplasticizer due to the reduction in fine particles and plasticity of the residual soil. Microstructural studies using scanning electron microscope and x-ray diffraction techniques showed an interaction between soil, geopolymer, and superplasticizer, thus confirming the formation of geopolymer gel and increased polymerization rate with the superplasticizer. [ABSTRACT FROM AUTHOR]

In this study, enzyme-induced carbonate precipitation (EICP) combined with xanthan gum curing technology was used to improve the engineering properties of standard sand, and the curing effect of EICP combined with different xanthan gum contents was studied by macroscopic tests such as unconfined compressive strength, direct shear, permeability, calcium carbonate content, and microscopic tests such as scanning electron microscope and nuclear magnetic resonance. The results show that the unconfined compressive strength, shear strength, cohesion and internal friction angle of EICP combined with xanthan gum solidified sand increases with the increase of xanthan gum content and reaches the maximum value at the content of 2%, in which the increase of unconfined compressive strength, shear strength, and cohesion is significant; further, the increase of internal friction angle is small. The permeability coefficient of EICP combined with xanthan gum solidified sand decreases with the increase of xanthan gum content, and the permeability coefficient of 2% xanthan gum is only 65.4% that of pure EICP treatment. The incorporation of xanthan gum promotes the deposition of calcium carbonate, increases the viscosity of the reaction solution, and produces colloidal encapsulation and bonding effect on the sand particles. In addition, the incorporation of xanthan gum effectively reduces the porosity of solidified sand and greatly reduces the proportion of large pores and medium pores by changing the pore size, which greatly improves the pore structure. [ABSTRACT FROM AUTHOR]

The large temperature differences between day and night in winter at plateau areas can lead to the reduction of skid resistance of roads. However, most of the traditional salt storage and deicing fillers are chlorides, and their long-term usage will cause damage to the ecological environment. In order to achieve green deicing of asphalt pavement, this paper developed efficient and environmentally friendly salt storage fibers for the anti-icing of asphalt pavement, and the optimal components of salt storage fibers were determined. On this basis, the morphology and rust resistance of salt storage fibers were characterized, and the ice suppression and deicing performances were also determined. The experimental results show that the optimal component ratio of anti-icing reagent for sodium acetate, potassium acetate and sodium formate follows 7∶2∶1 and the optimal component ratio of organic salt and fiber is 3∶1 , which can achieve a better ice-melting effect and sustainable economy. According to the scanning electron microscope (SEM) images, the salts in the salt storage fiber are fully absorbed, which has a certain slow-release performance due to the resin package. In addition, the effective anti-icing components of the salt storage fiber are less corrosive to the metal materials, and the asphalt mixtures doped with salt storage fibers can melt ice at the rate of (1,022 g/ h·m2) under relatively low temperatures. This can effectively weaken the freeze-bond strengths and ice–road interface adhesion. [ABSTRACT FROM AUTHOR]

Potholes are one of the common diseases of asphalt pavements. Cold patching asphalt mixtures (CPAM) are a common material for pothole repair. Reclaimed asphalt pavement (RAP) is a high-potential sustainable material that is commonly used in pavement construction. The aim of this study is to address the balance between performance improvement and cost reduction in CPAM. To achieve this objective, the CPAM was prepared with four different contents of cutback and 100% RAP (RAP-CPAM) and its performances were evaluated by laboratory tests. First, Fourier transform infrared spectroscopy (FTIR) test and scanning electron microscope (SEM) technique were used to analyze the diffusion mechanism between the cutback and the artificial aged binder. Then, the rationality of the cutback content was preliminary estimated by the mixing test and the draindown test. Finally, the adhesion performance, cohesion performance, strength, and resistance to water damage of RAP-CPAM were characterized through laboratory tests. From the FTIR test, the carbonyl index of aged asphalt layer decreased compared to that of the artificial aged binder as the storage time increased. Simultaneously, SEM imaging of the artificial aged binder showed less fractured surfaces after storage. The results of FTIR and SEM tests indicate that the cutback and the artificial aged binder were diffused. It was found that 1.6% content of cutback was slightly lower for RAP-CPAM, and 2.8% was not excessive. Boiling test results show that RAP-CPAM had good adhesion performance. Rolling screen test, Marshall stability test, and immersion Marshall test results reveal that RAP-CPAM had good cohesion performance, strength, and resistance to water damage. Based on the performance evaluation, the optimal content of cutback in RAP-CPAM was determined as about 2.4%–2.8%. In conclusion, the cutback and the RAP binder were successfully diffused, thereby ensuring good performances of RAP-CPAM. [ABSTRACT FROM AUTHOR]

The accumulation of alkali residue has led to significant contamination of soil, air, and water, posing a hazardous threat to the environment. To address this issue, a technology and method for producing alkali residue–based lightweight soil were proposed to facilitate the reuse of alkali residue, and the feasibility of this method was demonstrated. Compression tests, X-ray diffraction, X-ray fluorescence spectrometry, and scanning electron microscope (SEM) were conducted to investigate the strength characteristics and hardening mechanism of the material. The results indicate that the compressive strength of the alkali residue–based lightweight soil increases linearly with wet density, age, content of portland cement, and ground granulated blast slag. The optimal water–solid ratio was determined to be 0.6. Specimens with low and high strength exhibited plastic and brittle failures, respectively. The primary contributors to the material's compressive strength were identified as hydrated calcium silicate, ettringite, monosulfur calcium sulfoaluminate hydrate, hydrated calcium aluminate, and Friedel's salt. The 28-d compressive strength of the alkali residue–based lightweight soil, with a water–solid ratio of 0.6 and a wet density of 800.0 kg/m3 , was measured to be 1.17 MPa, meeting the requirements for most filling projects. [ABSTRACT FROM AUTHOR]

Foamed phosphogypsum (FPG) has recently attracted extensive interest owing to its potential consumption of phosphogypsum and its substitution for traditional gypsum building materials. However, as an important component in the preparation of FPG, the effect of foaming agent on the performance of FPG is still unclear. Herein, Legao 3210 (LG), sodium alpha-olefin sulfonate (AOS), animal protein compound (APC), cocoamidopropyl hydroxy sulfobetaine (CHSB), and tea saponin (TS) were chosen as the foaming agents for FPG. The foam stability and foam structure were studied, and the results showed that the foams produced by TS and APC were more stable. The effects of different foaming agents on FPG's fluidity, density, strength, water absorption, and thermal conductivity were also studied. The results showed that FPG prepared with TS exhibited the highest compressive strength, measuring up to 1.34 MPa, which represented a 97% increase compared with that of APC. Moreover, the dry density and thermal conductivity of FPG prepared with TS were 517 kg/m3 and 0.109 W/(m·K). The digital microscope analysis indicated that the keys to the simultaneous realization of high strength and light weight in the FPG were uniform pore size distribution, small pore size, and thicker pore gaps. Furthermore, through scanning electron microscope (SEM) analysis, it was suggested that the formation of strong interlocking structure by hydration products was the microstructural mechanism for improving the strength of FPG. This study suggested that FPG has the possibility to compete with traditional gypsum materials and it is also expected to solve the problem of phosphogypsum utilization. [ABSTRACT FROM AUTHOR]

Sisal fibers (SF) and polycarboxylate superplasticizers (PCE) contribute to the sustainable development of cementitious materials by improving and optimizing their hardening properties. In this study, the impact of SF and PCE on the workability of cement pastes was investigated. The workability was evaluated through spreading diameter, yield stress, and plastic viscosity measurements, and the adsorption behavior of PCE was analyzed. The results showed that the introduction of SF had a negative effect on the workability of PCE plasticized cement pastes, reducing flowability and increasing yield stress and plastic viscosity, regardless of aspect ratio or dosage. A contact angle tester and a scanning electron microscope (SEM) were employed to examine the surface properties of SF. The mechanism behind this interaction of cement-PCE-SF was explored and found to be due to the rough surface of SF, which increased the consumption of PCE, and the formation of hydrogen bonds between PCE and SF. Additionally, PCE modified the interfacial structure between SF and the cement matrix, strengthening the relationship between the different phases. These findings provide new insights into the modification of fiber-reinforced cementitious materials. This paper presents a comprehensive study on the workability and rheology behavior of cementitious material that coupled PCE superplasticizer and SF. The interaction between PCE and SF was experimentally studied by suitable tests, and the results and mechanism behind were well explained. The fresh properties were evaluated through a mini slump test, rheological properties, and the adsorption behavior of PCE on the surface of cement and SF was analyzed. The results showed that the introduction of SF decreases the spread diameter and increases the yield stress and plastic viscosity, regardless of aspect ratio and dosage, which indicate that a negative effect on the workability of PCE plasticized cement pastes. The mechanism behind the cement-PCE-SF interaction was explored in depth by the surface properties of SF, which revealed that the rough surface of SF increased the consumption of PCE. In addition, the formation of hydrogen bonds between PCE and SF provides an additional explanation. The significance of this study provides valuable guidance in using fibers and PCE together in cementitious materials. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

In an effort to tackle the issues of carbon dioxide (CO2) emissions from the cement industry and land pollution caused by the disposal of construction waste, this study aimed to investigate the potential of fly ash-ground granulated blast-furnace slag (GGBS)–based geopolymer concrete (FG-GPC) and demolition waste fine aggregate (DWF) as environmentally sustainable alternatives to conventional cement concrete and natural fine aggregate, respectively. The experimental procedure included optimizing the FG-GPC variables (Na2SiO3/NaOH and NaOH molarity) and investigating the properties of FG-GPC with the addition of DWF in various proportions (0%, 25%, 50%, 75%, and 100% by volume). To investigate the mechanical and physical parameters of FG-GPC with DWF, compressive strength, split tensile strength, flexural strength, elastic modulus, water absorption, density, effective porosity and ultrasonic pulse velocity were determined. The microstructural properties of FG-GPC were studied using scanning electron microscope (SEM) tests on selected samples. The experimental findings indicated that the strength and physical properties of FG-GPC were progressively diminished when adding DWF to the mix. Nonetheless, FG-GPC with 25%–50% DWF replacement showed a lower drop in concrete properties, indicating that employing construction and demolition (C&D) waste as a fine aggregate might have environmental and economic advantages. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the durability performance of marine concrete incorporated with nano–SiO2 and nano–Al2O3 under the joint effect of dry–wet cycles, Cl− erosion, and carbonation. Free Cl− content and carbonation depth were used as durability evaluation indexes of concrete with nanoparticles under the joint effect of the three factors. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), backscattered electrons (BSE), and X-ray diffraction (XRD) were used to analyze the morphology and phase composition of the concrete. The test results showed that the free Cl− content and carbonation depth of the concrete were significantly reduced after incorporating nanomaterials, indicating that nanomaterials improved the resistance of the concrete to Cl− erosion and carbonation under the joint effect of dry–wet cycles, Cl− erosion, and carbonation. Compared with plain concrete at 56 cycles, both nanomaterials showed the most significant improvement at a dosage of 1.8%, with a 20% and 37.5% reduction in free Cl− content and carbonation depth, respectively, for nano–SiO2 concrete, and 16.67% and 31.66% reduction, respectively, for nano–Al2O3 concrete. The improvement effect of nano–SiO2 was better than that of nano–Al2O3 , and the free Cl− content and carbonation depth of nano–SiO2 concrete were reduced by 3.33% and 5.84%, respectively, compared with those of nano–Al2O3 concrete at the optimal dosage. The microscopic test results showed that incorporating nanomaterials promoted the hydration process of cement and refined the pore structure of the concrete, improving the durability of the concrete under the joint effect of dry–wet cycles, Cl− erosion, and carbonation. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the physical, mechanical, sorptivity, and microstructural properties of high-strength alkali-activated slag (AAS) mixtures that were heat cured for 8 h. AAS mixtures were cured at room conditions, 50°C, and 75°C. Here, 0.25% and 0.50% polyvinyl alcohol (PVA) fiber (by volume) was used to prevent heat-cure cracks and increase flexural toughness. In addition, 200, 400, and 600 kg/m3 quartz aggregates were used instead of quartz powder in the mixtures. In this context, 36 different mixtures were produced for the experimental study. The physical, mechanical, and transport properties of AAS have been greatly improved by heat curing. As the quartz aggregate and PVA fiber content increased, the apparent porosity and water absorption of the mixtures increased also. Accordingly, the unit weights of the mixtures decreased relatively. The compressive strength of AAS varied between 43.5 and 102.5 MPa. In the case of heat-curing at 75°C, the compressive strength increased up to 1.8 times. The flexural strength of AAS was between 6.9 and 14.7 MPa. The PVA fibers prevented the brittle fracture observed in AAS. Whereas the PVA fiber ratio increases both compressive and flexural strength, the opposite situation was obtained for quartz aggregate. In addition, the PVA fibers reduced capillary water absorption. The embodied energy of AAS ranged from 4,998 to 5,768 MJ. The embodied energy of AAS was found to be relatively higher than that of conventional concrete. Withal, the scanning electron microscopes (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) analyses implied that the heat curing considerably improved the geopolymerization. As a result, more than 100 MPa compressive strength and approximately 15 MPa flexural strength can be obtained by using 0.25% PVA fiber in AAS mixtures cured at 75°C. [ABSTRACT FROM AUTHOR]

A large amount of soybean oil (20%–30% mass ratio of neat asphalt) was selected to partially replace petroleum asphalt. The high-temperature behavior of soybean oil bioasphalt was enhanced by polyphosphoric acid (PPA). Polyphosphoric acid/soybean oil composite modified asphalt (PSMA) was prepared. Temperature sweep, frequency sweep, multiple stress creep recovery, and bending beam rheometer tests were conducted to reveal the rheological behavior. Fourier infrared spectroscopy (FTIR), scanning electron microscope, and fluorescence microscope tests were carried out to reveal its microstructure characteristic. The results proved that polyphosphoric acid obviously increased the high-temperature properties of soybean oil bioasphalt. Compared with the neat asphalt at 0.1 kPa, the recovery rates of 20% bio/6% PPA, 25% bio/6% PPA, and 30% bio/6% PPA increased by 139.2%, 113.5%, and 86.4% respectively. PSMA was less sensitive to temperature and loading frequency, with remarkable elastic recovery and antirutting degeneration ability. PSMA could maintain excellent low-temperature crack resistance at −18°C. PSMA had better rheological properties when soybean oil and PPA were 20%–25% and 4%–6%, respectively. The FTIR tests verified that some new functional groups emerged in PSMA. There were evenly distributed fluorescent materials in the soybean oil bioasphalt under the fluorescence microscope. Under the modification effect of PPA, soybean oil and PPA could be evenly dispersed in PSMA. Laboratory tests verified the superior properties of bioasphalt with high content soybean oil. [ABSTRACT FROM AUTHOR]

Because a new magnesium phosphate cement (MPC) developed previously for the rapid repair of cement concrete structures has better mechanical properties and bonding properties, the high-temperature properties were further investigated and compared with ordinary MPC in this study. The mechanical properties of MPC, the hydration products, and the high-temperature mechanism were studied and revealed under the calcination conditions of normal [room temperature (20°C)], 70°C, 300°C, 600°C, and 900°C. As the temperature increased, the compressive strength first decreased and then increased with the lowest being at 300°C. Subsequently, analytical methods such as X-ray powder diffraction (XRD), mercury intrusion porosimeter (MIP), Fourier transform infrared spectrometer (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) were used to comprehensively characterize the changes in MPC hydration products under high-temperature conditions in order to reveal the mechanism of action. The MIP results showed that the detrimental pores gradually increased up to 300°C. When the temperature reached 600°C, the pores were formed and filled by more MgKPO4 crystals, which gradually reduced the harmful pores. XRD, FT-IR, and SEM/EDS results showed that at 300°C, the hydration products did not contain the crystalline struvite but transformed into an amorphous transition state. In particular, basalt fiber–reinforced polymer modified magnesium phosphate cement (BFPMPC) still showed polymer degradation and carbonization. The XRD results were verified by TGA. The hydration products of MPC and BFPMPC at 427°C in the process of amorphous to crystalline transformation were verified by DSC. The proposed MPC materials can be widely applied to the reinforcement and maintenance of key joints of buildings and concrete structures that are prone to fire accidents. [ABSTRACT FROM AUTHOR]

In this paper, quaternary hydrotalcite [layered double hydroxide (LDH)] (CoFeMgAl-LDH) was first fabricated based on the coprecipitation method, and then, CoFeMgAl-LDH/carbon nanotubes (CNTs) composite was synthesized by CNTs and CoFeMgAl-LDH through the solid phase mixing method. Subsequently, the physical-chemical properties of CoFeMgAl-LDH/CNT composite were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, energy dispersive spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) analysis. Meanwhile, the performance of CoFeMgAl-LDH/CNT composite for SO42− adsorption was evaluated under different conditions, including different initial concentration, contact time, adsorbent dosage, solution pH, temperature, and coexisting ions. Afterward, the SO42− adsorption capacity of CoFeMgAl-LDH/CNT in cement paste was further studied. The results showed that the CoFeMgAl-LDH/CNT composite exhibited a three-dimensional structure with high specific surface area. The maximum SO42− adsorption amount of the CoFeMgAl-LDH/CNT composite was 116.27 mg/g , which was significantly higher compared with other absorbents of the same type. Pseudosecond-order kinetic model could reasonably describe the adsorption kinetics, and Freundlich isotherm could fit the adsorption data accurately. The results also suggest that the synthesized CoFeMgAl-LDH/CNT composite can serve as a potential material for the sulfate binding in cementitious materials. [ABSTRACT FROM AUTHOR]

The application of waste tire rubber in the concrete industry is one of the most effective and environmentally friendly ways to solve the problem of so-called black pollution. However, the application of rubber particles (RP) in the concrete industry is hindered by their low stiffness and poor bonding performance with the cement matrix. In this paper, a novel modification method of polydopamine (PDA) modification was used to enhance the hydrophilicity of the RP surface. The surface morphology, element content, and hydrophilicity of RP treated with PDA and KMnO4 were analyzed through scanning electron microscope and energy dispersive spectrometer (SEM-EDS) and sedimentation methods. The unit weight, ultrasonic pulse velocity (UPV), compressive strength, compressive toughness, toughness index, and flexural strength were taken to determine the mechanical properties of ultrahigh-performance rubber concrete (RUHPC). The results showed that the adhesion between paste and RP and the sedimentation rate of RP with PDA or KMnO4 treatment methods exhibited a remarkable improvement. Compared with unmodified RUHPC, the basic mechanical properties of KMnO4 -modified RUHPC were improved slightly, and its toughness index was improved greatly. SEM and EDS results confirmed that PDA was deposited on the surface of RP, eliminating the gap of interface transition zone and significantly enhancing UPV, compressive strength, and flexural strength of RUHPC by 4.1%–5.8%, 17%–20%, and 6.1%–9.8%, respectively. In addition, the compressive toughness of unmodified and KMnO4 -modified RUHPC decreased, whereas that of PDA-modified RUHPC increased significantly. It can be concluded that the mechanical properties of RUHPC with treated RP have improved significantly and the application of RP in ultrahigh-performance composites (UHPC) offers more opportunities for recycling RP. [ABSTRACT FROM AUTHOR]

MgO-based cementitious materials have attracted increasing attentions due to their advantages of low energy consumption, fire resistance, and low CO2 emission. This study develops a new reactive MgO cement (RMC)-silica fume (SF) engineered cementitious composite (ECC). The effects of RMC∶SF mass ratio, fiber type, fiber content, and curing conditions on the mechanical properties and strain-hardening behavior of the RMC-SF ECC are investigated. The hydration characteristics of RMC-SF ECC under different curing conditions were studied through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analysis. It was found that the RMC-SF ECC obtained a tensile strain capacity of 5.7%. Polyethylene (PE) fibers achieved higher compressive strength, and polyvinyl alcohol (PVA) fibers yielded better tensile strain capacity. A RMC-SF mass ratio of 1∶1 obtained a higher ductility under high temperature curing at 50°C. Although carbon dioxide curing improves the mechanical properties of RMC-SF ECC due to the formation of MgCO3 , it greatly reduces its ductility. A large amount of brucite and M─ S─ H gels were generated under room temperature curing with plastic wrap. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (Rdry), freeze–thaw splitting strength (Rsaturated), 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 Rdry , Rsaturated , 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 FROM AUTHOR]

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

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

The rapid increase in the generation of industrial ash alerted the authorities to seek efficient management of this harmful waste. This research seeks an entirely new use of industry ash to manufacture bricks. While brick is the most prominent construction product worldwide, the brick manufacturing industry cannot deliver the increased demand due to a new challenge: clay shortage. Two different industry waste ash types (IWA 1-CaO rich and IWA 2-SiO2 rich) were tested at different percentages of 10%, 20%, and 30% (by weight) for their suitability in manufacturing bricks. Compressive strength, water absorption, the initial rate of absorption, thermal conductivity test, 3D-CT scanning, scanning electron microscope analysis, x-ray diffraction analysis, x-ray fluorescence analysis, salt-resistance test, and heavy metals leaching test were performed to determine the physical, chemical, mechanical, durability and leachate characteristics of waste reformed bricks and to ascertain the product compliance of the lab prototype. The results indicated that the novel brick product manufactured from industrial waste can be superior to control brick (0% of waste ash) in thermal characteristics and compressive strength while achieving essential compliance requirements satisfying national standards. The thermal conductivity of ash reformed bricks was 40% lower compared to standard bricks when 30% ash is mixed into the composition. In addition, the maximum compressive strength of 72.53 MPa was achieved with the addition of 10% IWA 2 at a firing temperature of 1,050°C. The outcomes from this project could potentially provide a sustainable product for the brick industry, which has exponential demand in the current market, while resolving a growing solid waste catastrophe and clay shortage. [ABSTRACT FROM AUTHOR]

Sustained-release microcapsules provide a promising way to improve the curing efficiency and impermeability of cement-based composites. In this study, with potassium persulfate (KPS) as the core and polypyrrole (Ppy)/glycerol as the shell, KPS/Ppy microcapsules with excellent sustained-release performance were prepared using emulsion polymerization. The chemical structure, elemental composition, thermal stability, microstructure, and release properties of microcapsules were characterized by Fourier Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA), Laser Particle Sizing, and Conductivity Testing. Results indicate that the release characteristics of the microcapsules could be controlled by changing the content of polypyrrole/glycerol as well as the synthesis time, and a complete release time of 25 h could be realized with 1.43 wt% polypyrrole/glycerol synthesized for 6 h, which can meet the requirement that the polymerization is continually initiated to form a plugging structure after the initial hydration reaction of the cement mortar to realize the impermeability. Additionally, the sustained-release microcapsules, monomers, and coupling agents were mixed to prepare the cement mortar, which revealed significantly improved impermeability with no obvious loss of the compressive strength. Therefore, the prepared microcapsules have tunable sustained-release characteristics, which could be applied in cement-based composites for various requirements. [ABSTRACT FROM AUTHOR]

Unmodified epoxy adhesive is a brittle material, which limits its application in practical engineering. Adding nanomodified materials to epoxy adhesives is an effective method to improve the tensile property. In this study, the composites were artificially dispersed for 10 min, and then dispersed for 2 h in an ultrasonic cell crusher to ensure the nanoparticles were evenly dispersed in the epoxy adhesive. The influence of SiO2 and TiO2 nanoparticles (NS and NT) with different mass fractions on the tensile properties of epoxy adhesives was analyzed, and the tensile section morphology of 11 kinds of the composites was observed by scanning electron microscope (SEM). In addition, the nanomodified epoxy adhesive model was simulated using software, which was based the Python language; randomly distributed nanoparticles were generated in the two-dimensional representative volume element (RVE) model. The experimental results showed that the tensile properties of epoxy adhesive increased first and then decreased with the increase of the mass fraction of nanoparticles. When NS or NT with a mass fraction of 0.05% or 0.40% were added to epoxy adhesive, the tensile properties of the composites reached their highest value. Through the SEM observation of the colloid tensile section, it was observed that the nanoparticles could change the composites' fracture from brittle to ductile, which achieved the purposes of strengthening and toughening. The finite-element results showed that the difference between the simulated tensile properties and the experimental value of epoxy adhesive was within 5%, and thus the software model in this study has a certain reliability. [ABSTRACT FROM AUTHOR]

The high alkalinity and storage of red mud (RM) make it a major environmental problem. In this paper, the mineral composition, hydration process, and microstructure of red mud-cement based grouting materials (RCGM) are studied by means of the differential thermal analyzer, X-ray diffraction (XRD) diffractometer, isothermal calorimeter, and scanning electron microscope. The action mechanism of RM after thermal activation (TRM) and mechanical activation (SRM) on the mechanical properties of RCGM is summarized, respectively. The results show that a small amount of RM, SRM, and TRM can improve the early strength of RCGM, and the effect of TRM is the best. The RM will reduce the late strength of sample. The SRM and TRM still promote the strength of sample, and the compressive strength of SRM-80 and TRM-80 meet the requirements of grouting engineering. The RM, SRM, and TRM don't change the hydrate phase of RCGM, and hematite and nepheline mainly play a filling role in the material system. A small amount of RM, SRM, and TRM can promote the hydration process of ordinary portland cement (PC), whereas excessive RM, SRM, and TRM can delay the hydration process of PC. Before hydration heat release for 15 h, the RM, SRM, and TRM can accelerate the reaction rate in the early stage of hydration induction, which is independent of activation mode and dosage on RM. Among them, SRM-20 and TRM-20 have the best effect on promoting hydration. The microstructure analysis shows that RM, SRM, and TRM mainly improve the mechanical properties of RCGM through the microfilling. Mechanical activation and thermal activation can improve the activity of RM, and the effect of TRM is more obvious. [ABSTRACT FROM AUTHOR]

Attributes of filler play a significant role in the overall performance of asphalt mixtures through their direct influences on asphalt mastic. Alkali-activated slag (AAS), which is currently in the beta stage of development, is a promising and innovative cementitious replacement material. However, mass production AAS for experimental use generates significant quantities of waste discharge. The purpose of this study was to explore the potential of using AAS waste as a mineral filler in asphalt mastic. Properties of AAS waste were assessed and compared to limestone (LS) filler using scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, X-ray fluorescence (XRF) spectrometry, laser particle size analysis, hydrophilic coefficient, mesoscopic void characteristic, and Rigden void tests. The penetration, softening point, Brookfield viscosity, and rheological properties of the asphalt mastic samples made, respectively, using AAS and LS fillers, were examined using complex modulus (G*), phase angle (δ), and rutting factor (G*/sinδ) results and two interaction indices (ΔG* and K–B–G*). Furthermore, models used to test relative viscosity (ηr) were applied to predict the complex viscosity (η*) of the samples. Results indicated that comparing to LS filler, AAS filler was shown to deliver superior compatibility to asphalt matrix, and the properties of the asphalt mastic containing AAS filler were superior to those of the asphalt mastic containing LS filler. Of particular note, the models used to predict relative viscosity demonstrated validity in predicting the complex viscosity of asphalt mastics. The results support using AAS filler as a replacement for LS filler in asphalt mastic. Further research should be conducted to maximize the potential benefits of using AAS filler in asphalt mixtures. [ABSTRACT FROM AUTHOR]

Nowadays, mass production of tires and construction operations adjacent to saturated soils have become a concern for engineers. The present study aimed to explore the potential of the combined effect of a waterproof polymer and rubber powder, confining pressure, and cyclic stress ratio on the static and dynamic properties of sand-rubber-polymer mixtures using a scanning electron microscope (SEM), attenuated total reflectance (ATR) analysis, unconfined compressive strength (UCS), and cyclic triaxial tests. The findings indicated that with the inclusion of 4% rubber, rough polymer chains are extended due to creating C─ CH3 bonds, uniform distribution of rubber particles between rigid materials, and interlocking rubbers in hydrocarbon chains. These chains increase adhesion with sand particles and prevent rubber flexibility, increasing UCS and shear modulus. In contrast, with the inclusion of 8% rubber, due to several mechanisms, including poor adhesion between particles because of the high surface area of the mixture and low polymer content (i.e., 2%), the dominance of weak rubber–polymer and rubber–rubber bonds over polymer–polymer and sand–polymer bonds, emerging free rubber particles (free CH2 groups), and creating the aromatic and double bond structures due to the nature of rubber flexibility, the trend is reversed. [ABSTRACT FROM AUTHOR]

Steel slag needs aging treatment before being used for the coarse aggregate of asphalt mixtures because it has volumetric instability due to the hydration of calcium oxide. This paper investigates the effect of hydration products on the bonding properties between asphalt binder and steel slag coarse aggregates subjected to natural aging treatment. A scanning electron microscope, a fluorescence microscope, and X-ray diffraction testing were used to study the surface morphology, microstructure, and mineral phase of the hydration product layer generated on the aggregate surface of steel slag. A modified water boiling test was conducted to evaluate the water stripping resistance of asphalt film with different boiling times. Pull-off testing on real steel slag aggregates was performed to investigate the effect of the hydration product layer and surface treatment on the bonding strength and interface failure mode. Test results indicated that the hydration products exhibited a loose and porous structure and formed an interlayer to prevent the asphalt film from directly adhering to the aggregate surface of steel slag. The hydration product layer could improve the initial stripping resistance but impair the long-term stripping resistance with increased boiling time. The interlayer of hydration products tended to be the weakest link between asphalt film and steel slag aggregate when subjected to pull-off strength damage. The bonding strength showed a negative linear relation with the stripping rate of asphalt film. After steel slag surface treatment with water-based capillary inorganic waterproofer, the pull-off failure of hydration product layer was avoided and thus improved the bonding strength between asphalt film and steel slag aggregate. The bonding strength and failure mode between asphalt-slag adhesion could be well examined by using pull-off tests. Better insights into asphalt–slag adhesion are useful to design durable asphalt mixtures containing steel slag aggregate. [ABSTRACT FROM AUTHOR]

The corrosion of steel fibers is a direct cause of the deterioration of steel fiber-reinforced concrete in chloride environments. This study mainly investigated the corrosion behavior of steel fibers exposed to NaCl solutions with pH=7 , 10, 11, 12, and 13. The corrosion rate of the steel fibers was calculated according to the change of the diameter and ultimate tensile load. The electrochemical parameters of the steel fibers corrosion were continuously monitored. The morphology of the steel fibers affected by chloride attack was observed by scanning electron microscope (SEM). The results reveal that the corrosion rate of the steel fibers decreased as the pH of the NaCl solution increased from 7 to 13, and it was very small at pH≥12. According to the open circuit potential, corrosion potential, corrosion current density, and electrochemical impedance spectroscopy, the steel fibers exhibited a high corrosion tendency and corrosion rate when exposed to NaCl solutions with pH≤12. However, they exhibited low corrosion tendency in the chloride solution with pH=13. The surface roughness of the steel fibers exhibited only a slight increase after exposure to the NaCl solution with pH=13 for 180 days. [ABSTRACT FROM AUTHOR]

This study aims to compare the microstructural and mechanical properties of lightweight polymer concrete (LPC) and lightweight ordinary cement concrete (OCC) before and after exposure to a corrosive acidic environment. In this regard, LPC mixes were prepared with five different unsaturated polyester resin contents (15%–27%) and combinations of lightweight expanded clay aggregate (LECA) and natural river sand. Thereafter, specimens were exposed to sulfuric acid solution for up to 90 days. In addition to visual inspections, physical and mechanical properties [mass and volume changes, compression strength, and modulus of elasticity (MOE)], petrographic inspections, and scanning electron microscope investigations were carried out. Mechanical results showed that LPCs had by far better mechanical features compared with OCC, where at the optimum mix comprised of 24% polymer, reduction of 6% for compression, and 7% for MOE was observed, whereas these values were respectively 70% and 55% for OCC at the same conditions. Outcomes of microscopic observations indicated that increasing the polymer content resulted in strengthening the bond between binder and aggregates where pores were filled by resin. In addition, the impact of the acidic solution on the LPC mixes was less pronounced than for OCC mixes, and lamination of the matrix and affected polymer areas were reduced in LPC mixes with a resin content of 24% and 27%. After 90 days, a slight reduction in properties of LPC specimens and degradation was observed due to the reaction of the acid with the surface of LPC specimens. [ABSTRACT FROM AUTHOR]

In order to solve the current problem of insufficient toughness of epoxy asphalt and immiscibility between resin and asphalt binder (not aged) in epoxy asphalt, nanomodifiers (GOs-CS-Ca2+) were prepared by a biomimetic mechanism from chitosan (CS), calcium ions (Ca2+), and graphene oxide nanoplatelets (GOs). In GOs-CS-Ca2+ , CS connects GOs through calcium ion coordination bonds and amide bonds. GOs-CS-Ca2+-modified epoxy asphalt was prepared by directly adding different percentages of GOs-CS-Ca2+ to epoxy asphalt. Then, the properties of GOs-CS-Ca2+-modified epoxy asphalt were analyzed through macro and micro tests. The macroscopic tests included tensile, cyclic, and stress relaxation tests. The microscopic tests included fluorescence microscopy (FM) and scanning electron microscopy (SEM) tests. Tensile tests showed that after adding 0.05% GOs-CS-Ca2+ to the total mass of epoxy asphalt, the tensile strength and fracture toughness of epoxy asphalt increased by 29.6% and 20%. Cyclic tensile tests showed that GOs-CS-Ca2+-modified epoxy asphalt had greater consuming work recovery capacity, and stress relaxation tests showed that the addition of GOs-CS-Ca2+ delayed the relaxation modulus decline of epoxy asphalt. The infrared spectrum, scanning electron microscope, X-ray diffraction, and Raman spectra of GOs-CS-Ca2+ in the micro test can show the successful synthesis of GOs-CS-Ca2+. FM and SEM of GOs-CS-Ca2+-modified epoxy asphalt showed that the addition of GOs-CS-Ca2+ could reduce the particle-size distribution of the asphalt phase in epoxy resin and establish a miscible bridge between epoxy resin and asphalt, which led to the improvement of macroscopic mechanical properties of GOs-CS-Ca2+-modified epoxy asphalt. Finally, the modification mechanism of GOs-CS-Ca2+-modified epoxy asphalt was proposed by combining macroscopic and microscopic test results. [ABSTRACT FROM AUTHOR]

The present study envisaged the development of a novel admixture based on the composites of amino trimethylene phosphonic acid and boric acid (AB) that exhibited an intense inhibition of the hydration effects for Portland cement. The study was aimed to lay a solid foundation for the utilization of AB in large volume concrete by reducing the temperature control measures. The setting time at different temperatures, and the compressive strength of the cement pastes containing AB were examined. The hydration characteristics of the Portland cement containing AB were investigated using isothermal calorimetry measurements, X-ray diffraction, thermogravimetric analysis, Zeta potential, and scanning electron microscope. The results showed that the fitting curves for the setting time of amino trimethylene phosphonic-based material (ATMP) exhibited a linear relation in the concentration range of 0.02% to 0.40%. However, the fitting curves for the setting time of AB presented an exponential relation in the concentration range of 0.02% to 0.20%, and exhibited a linear relation at the addition dosages from 0.20% to 0.40%. It was observed that, at 0.40% concentration, the initial and final setting times of the AB sample was longer by 1,954 min and 3,767 min, respectively, than those of the ATMP sample. ATMP and AB exhibited intensive retarding effects at higher temperatures, and the temperature adaptability of both ATMP and AB was excellent. The reduction in the cumulative hydration heat and heat evolution rate effect in the Portland cement was significantly higher in AB than ATMP. AB substantially inhibited the formation of Ca(OH)2 (CH) and ettringite (AFt) than ATMP. Thus, the inhibition of cement hydration by AB was clearly superior to that of ATMP, which could be attributed to the inhibition of C3S and C3A hydration by AB. [ABSTRACT FROM AUTHOR]

In this paper, secondary recycled concrete was modified using basalt fiber (BF) and nanosilica (NS) to form modified secondary recycled concrete (MSRC), to promote the recycling of concrete. The flexural toughness and influence of pore size distribution of the MSRC were analyzed through the four-point flexural mechanics test and nuclear magnetic resonance test, respectively. The results showed that with an increase in the content of BF and NS, the fracture of the coarse aggregate increased and the flexural strength of MSRC increases. According to different evaluation standards, the flexural toughness of the MSRC exhibited a similar trend in different evaluation standards. As the NS content increased, the equivalent flexural strength increased, and as the BF content increased from 2 to 4 kg·m−3 , the equivalent flexural strength decreased. Additionally, scanning electron microscope and nuclear magnetic resonance spectroscopy showed that NS and BF had significant influence on the pore structure of the MSRC. When the BF content was 2 kg·m−3 , the content of micropores was minimal; and with further increase in BF content, the content of micropores increased, the internal defects increased, and the flexural toughness decreased. Moreover, with the increase in NS content, the content of internal pores decreased and the flexural toughness increased. Therefore, the results showed that BF and NS had a significant toughening effect on the MSRC. [ABSTRACT FROM AUTHOR]

The current study aims to construct a synthetic polymer (or family of polymers) with superior plasticizing properties in a highly alkaline medium. An invented laboratory-prepared superplasticizer (SP), namely phenol-formaldehyde sulfonilate (PFS), was synthesized, and its performance was measured against two types of commercial superplasticizers [naphthalene-based (Nb) and polycarboxylate-based (PCb)]. Fourier transform infrared (FTIR) and gel permeation chromatography (GPC) tests were performed to verify the admixture's stability in a highly alkaline medium. The interaction between different SPs and alkali-activated slag (AAS) surface was investigated via zeta potential and adsorption measurements. The flowability, setting time, and compressive strength developments were evaluated for AAS mixes. The hydration products' morphologies and phase compositions were studied using scanning electron microscope (SEM) and X-ray diffraction (XRD). The results reveal that the prepared PFS SP has a high stability against the highly alkaline medium. The dispersing efficiency of PFS SP resulted from the highly negative zeta potential value (−49.8 mV) compared with Nb (−41.5 mV) and PCb (−15.8 mV), as well as its high adsorption percentage as PFS, Nb, and PCb adsorbed by 18.5%, 9.2%, and 3.7%, respectively. The PFS SP enhanced the physicomechanical properties for AAS because it combined several advantages at the same time compared to commercial superplasticizers; for instance, AAS pastes admixed with PFS SP have superior workability, acceptable setting time, and high early strength. [ABSTRACT FROM AUTHOR]

This paper is based on the basic mechanical properties and volume deformation test, as well as the characterization of hydration products and microstructure properties such as x-ray diffraction (XRD), scanning electron microscope (SEM), and mercury injection method (MIP). The effects of CO2 curing on the mechanical properties, hydration product composition, and microstructure of magnesium oxysulfate (MOS) cement were studied. The results show that the carbonation properties of MOS cement are closely related to the standard air curing age after demolding. The CO2 curing immediately after demolding is not conducive to the development of compressive strength of MOS cement, while the compressive strength of MOS cement in standard air curing for 14 or 28 days after demolding is increased during CO2 curing. The CO2 can prevent the continuous hydration of residual MgO to form Mg(OH)2 or 5·1·7 phase, which affects the development of the compressive strength of MOS cement. The appropriate addition of low-calcium fly ash (L-FA) can compensate the effect of CO2 on the mechanical properties of MOS cement. During CO2 curing, some Mg(OH)2 is transformed into an amorphous phase to increase the compactness of its microstructure and a small amount of Mg(OH)2 reacts with CO2 to form MgCO3·3H2O. The results provide an important theoretical and experimental foundation for the further study of the effects of CO2 on the properties of MOS cement and the use of CO2 curing modification. [ABSTRACT FROM AUTHOR]

In this study, the effects of a recycled mineral admixture based on glass wool residue (GWR) in microstructural and mechanical properties of ordinary portland cement (OPC)-based composites are examined. The GWR was dried and milled into a fine powder, whereby it was physicochemically characterized. Physicomechanical tests, quantitative X-ray diffraction, and scanning electron microscope observation were performed in pastes and mortars at 28, 56, and 90 days of age. Moreover, the potential application of the GWR was evaluated by determining the pozzolanic activity and the fiber reinforcement effect. The results showed that the partial replacement of cement by 25% by weight of GWR presented no reductions in flexural strength at 28 and 56 days of curing, whereas the long-term flexural strength increased by 17%. This replacement also increased the long-term compressive strength of the composites—reaching a strength activity index of 1.06. The results also showed that GWR presented some fiber reinforcement effect—depending on the particle size. Promising properties were observed for samples blended with GWR, yielding technical, environmental, and economic benefits. [ABSTRACT FROM AUTHOR]

G20Mn5QT cast steels have been widely used in cast steel connections, which may suffer from ductile fracture at ambient temperature. Northern climates make the problem even worse because the ductility of the cast steels deteriorates with the drop of temperature. For ductile fracture analysis of cast steel connections working at low temperatures, Gurson-Tvergaard-Needleman (GTN) models were calibrated and validated for G20Mn5QT cast steels at 20°C, −20°C , −40°C , and −60°C based on previous test results. The effects of the drop of temperature on material parameters in GTN models of G20Mn5QT cast steels were determined. A simplified strategy was proposed to address the effects of the drop of temperature by two GTN parameters, the void nucleation strain εN and the critical void volume fraction fc. It was found that εN decreased almost linearly with the drop of temperature, and fc had a similar relationship with the drop of temperature as the Charpy impact energy. The relationships between these two parameters and the drop of temperature were presented for the establishment of GTN models for G20Mn5QT cast steels at any possible low temperatures. Scanning electron microscope (SEM) micrographs indicated that the dimple-based ductile fracture mechanism was dominant in the fracture of G20Mn5QT cast steels, which was accompanied by possible quasi-cleavage fracture at low temperatures. [ABSTRACT FROM AUTHOR]

In a bacteria-based self-healing concrete system, it is generally necessary to protect the bacteria from the harsh conditions of high alkalinity inside the concrete and limited physical space due to the on-going hydration of cement. The artificial functional aggregates (AFA) were developed as the protective carrier of bacteria in this paper. Self-healing capability of mortars containing AFA encapsulated bacteria was investigated. Moreover, crack-healing products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS). The results showed that AFA encapsulated bacteria effectively promoted self-healing of cracks. Compared with control mortars, the effects of surface crack healing, internal crack healing, water tightness regain, and mechanical performance recovery of mortars with AFA encapsulated bacteria were significantly improved. Healing products in specimens with AFA encapsulated bacteria were observed, including CaCO3 , C-S-H gel, hydromagnesite, and ettringite. Among them, the main healing product was CaCO3 , which was not only formed on the walls of shallow cracks, but also largely deposited on the walls of deep cracks. Self-healing of mortars with AFA encapsulated bacteria can be attributed to the combined effects of chemically derived calcium carbonate, microbially induced calcium carbonate, on-going hydration of unhydrated cement particles, and pozzolanic activity reaction of the slag from AFA. [ABSTRACT FROM AUTHOR]

Bacteria-based self-healing concrete with simultaneous application of calcium lactate as bacteria precursor, and metakaolin as cement replacement, was investigated to observe its behavior under inappropriate environmental conditions and microstructural change. Samples of weight loss, compressive strength, stereoscope photography, and scanning electron microscope (SEM) imaging were studied after water curing and acid immersion. Increase in the compressive strength due to the addition and increase in the amount of calcium lactate and decrease of compressive strength by presence of metakaolin were observed. Application of calcium lactate and bacteria in the concrete with metakaolin decreased strength reduction and even resulted in a higher strength than the ordinary concrete. Metakaolin was effective to improve concrete resistance against acid attack. However, the concomitant role of calcium lactate as a precursor for bacteria in concrete that led to surface crack healing, even after 1 year, with metakaolin as a cement replacement component, can be supportive to produce a durable biofriendly concrete. [ABSTRACT FROM AUTHOR]

The oxygen diffusion coefficient of coastal concrete structures under cyclic drying–wetting and carbonation is one of the most crucial factors in its durability performance. In this work, the oxygen diffusion coefficients of cement mortar and concrete after 28-day cyclic drying–wetting cycles and carbonation were tested. The microstructure development of mortar and concrete after drying–wetting cycles and carbonation was characterized by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) methods. It was found that porosity and critical pore diameter have strong correlation with oxygen diffusion coefficient on plain mortar and concrete. After drying–wetting cycles, the refined porosity and critical pore diameter did not show obvious correlation with the oxygen diffusion coefficient. Nevertheless, the reduction of the oxygen diffusion coefficient after drying–wetting cycles was proportional to the change of porosity and critical pore diameter. A theoretical model based on Fick's law was derived to calculate the oxygen diffusion coefficient of the carbonated area. It was found that with the development of carbonation duration, the oxygen diffusion coefficient in carbonated area decreased. The influence of porosity on oxygen diffusion coefficient after carbonation is similar with plain cementitious materials, while the oxygen diffusion coefficient in the carbonated area is less influenced by the critical pore diameter change. It can be concluded that the retarding effect on oxygen diffusion coefficient by drying–wetting cycles and carbonation can delay the corrosion rate for reinforced concrete structures. [ABSTRACT FROM AUTHOR]

Anhydride-cured epoxy asphalt (AC-EA) is an asphalt/resin two-phase system, the properties of which are affected by the asphalt and resin contents. This study aims to investigate the effect of asphalt content on the tensile properties, hardness, dynamic mechanical parameters, chemical components, and microscopic structure of AC-EA through experimental methods. Thermal aging resistance and mechanism of AC-EA with the asphalt content of 25%, 35%, 45%, 55%, and 65% were also investigated. The results show that as the asphalt content increased from 25% to 65%, the tensile strength and hardness of AC-EA binder increased first and then decreased, the elongation decreased, the glass transition temperature (Tg) rose, and the carbonyl absorption band changed from a single peak to double peak. The absorption bands of aromatic ether and sulfoxide in AC-EA binder overlapped with each other. The carbonyl ester index (CEI) and sulfoxide index (SI) showed a good linear correlation with the asphalt content. Besides, phase inversion occurred in the AC-EA system when the asphalt content was between 45% and 55%. AC-EA binder with an asphalt content less than 45% is a resin-based composite, and that with the asphalt content higher than 45% is an asphalt-based composite. At the thermal aging process, AC-EA binders with asphalt content higher than 45% were more likely to cause significant changes in the tensile parameters, hardness, and modulus than those with asphalt content less than 45%, indicating that the existence of the resin network can reduce the sensitivity of AC-EA to oxidation. After aging, Tg of resin-based composites increased, whereas that of asphalt-based composites decreased. The Fourier transform infrared (FTIR) and scanning electron microscope (SEM) analyses indicated that the AC-EA binder had both postcuring and oxidative degradation during thermal aging. The postcuring was dominant in the resin-based AC-EA composite, whereas the oxidative degradation was dominant in the asphalt-based composite. [ABSTRACT FROM AUTHOR]

With the recent upsurge in the construction of new ballasted railway tracks and their maintenance, the high requirement of ballast and subballast materials has become an important challenge. The use of industrial by-products in the construction of railroads can be an approach for the sustainable development of railway. With an increase in steel production, the generation of steel slag is also expected to increase at an alarming rate in India. At present, the utilization of this by-product of the steel industry is marginal; however, it has an enormous potential to be used in railroad construction. Therefore an attempt has been made to use steel slag as the subballast material in the present work. The objective of this study is to assess the strength and stiffness, leaching behavior, and mineralogical characteristics of the cement-stabilized steel slag (CSS) as a subballast layer and its implications in the design methodology. A series of laboratory tests such as compressive strength, splitting tensile, flexural strength, and flexural modulus tests were carried out on the CSS with four different (1%, 3%, 5%, and 7%) cement contents. In addition, X-ray diffraction (XRD) and scanning electron microscope (SEM) were also employed to examine the mineralogical characteristics. The results suggest that cement stabilizations lead to strength and stiffness gain along with resistance to the leaching of the trace metals such as arsenic, barium, cadmium, chromium, lead, and zinc. The results show the steel slag has the potential to be used as subballast material. A step-by-step design methodology suitable for cement-stabilized steel slag as a subballast layer has been proposed by modifying the existing Association of American Railroads (AAR) method along with a practical design example. [ABSTRACT FROM AUTHOR]