Journal of Materials in Civil Engineering

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.

To study the effects of aging and freeze–thaw cycles on the low-temperature performance of styrene–butadiene–styrene (SBS)/crumb rubber (CR) composite modified asphalt mixtures. Digital image correlation (DIC) technology was combined with the three-point bending test to compare the strain field changes of SBS/crumb rubber composite modified asphalt mixture (SBS/CRMA) and SBS-modified asphalt mixture (SBSMA) during loading. A new index, linear strain density ($G_E$), is proposed to evaluate the crack resistance of asphalt mixtures; $G_E$ is the cumulative value of linear strain from loading to failure. In addition, using the bending beam rheometer (BBR) test and asphalt–aggregate contact angle test, the cracking characteristics of two kinds of asphalt mixtures under different conditions were analyzed from two aspects: low-temperature rheological properties, and adhesion and bond failure. The results indicated that the new index ($G_E$) and the macroscopic index ($F_E$) for evaluating the cracking characteristics of asphalt mixtures have a good correlation with BBR and contact angle test results. After aging and freeze–thaw cycles, the crack resistance and adhesion of the two modified asphalts decreased, decreasing the crack resistance of SBS/CRMA and SBSMA. Under the same conditions, the cracking resistance, aging resistance, and freeze–thaw resistance of SBS/CRMA were better than those of SBSMA. SBS/CRMA could better meet the demands of pavement materials in cold regions.

Investigation of the adhesion mechanism during the aging process of the asphalt-aggregate interface from a microscopic point of view contributes to the solution of water damage of asphalt pavements. So far, some work has been done to reveal the influence of aging on the adhesion strength of the asphalt from the nanoscale factors. However, due to the lack of direct chemical analysis means to test the chemical composition of asphalt at the nanoscale, the inferences made among different scholars are somewhat controversial. The objective of this study is to reveal the evolution of adhesion characteristics of the asphalt binders during the aging process based on their chemical components. Five asphalt binders at different aging degrees were prepared via laboratory simulated aging procedure. State-of-art technologies, atomic force microscopy–based infrared spectroscopy (AFM-IR) and AFM PF-QNM (peak force quantitative nanomechanical mapping) mode, were adopted to analyze the nanoscale adhesion and chemical components of the prepared asphalt. And binder bond strength (BBS) testing was performed to interpret and verify the nanoscale mechanism of asphalt adhesion behavior from macroscale. The results of the AFM test indicated that both sulfoxide and carbonyl functional group content contribute to the adhesion force of the asphalt binders. Compared with the carbonyl group, the sulfoxide content affects the nanoscale adhesion force more significantly. Meanwhile, the results of the BBS test are found in accordance with the AFM trends. Finally, an estimation model was established to roughly estimate the nanoscale adhesion force of asphalt at varying aging conditions based on these two functional groups.

To investigate the dynamic response of silt-based foamed concrete as filler in subgrade, this paper conducted staged cyclic loading experiments to examine its dynamic properties. Influence factors such as wet density and silt content were also addressed in experiments. The results of tests indicated that the hysteretic curves of silt-based foamed concrete presented obvious elastoplastic characteristics, and the dynamic stress–cumulative strain curves have a strain-hardening phenomenon. Dynamic strength increased a mean level of 65% when density increased by an average of $100\mathrm{kg}/{\mathrm{m}}^3$ at the range of density $600–800\mathrm{kg}/{\mathrm{m}}^3$. Meanwhile, the dynamic strength decreased by an average of 14.2% if silt content increased by a mean of 10%. Furthermore, the addition of silt transformed the pore structures from uniformly distributed sphericity into irregular combined bubbles with larger diameters. Besides, during the staged cyclic loading process, it was deduced that dynamic elastic modulus of material has a variation with cycles, but can be basically assumed constant in tests. Thus, the dynamic stress–cumulative strain curves of silt-based foamed concrete subjected to staged cyclic loads were derived based on the Ramberg-Osgood equation. The parameters of the Ramberg-Osgood equation were also analyzed according to the test data. Finally, the damage variable expressions versus plastic strain and cyclic numbers were established respectively. It was found that density and silt content can significantly affect damage evolution.

In this paper, the influence of lime-anhydrite ($\mathrm{L}/\mathrm{A}$) ratio on the strength development, cement hydration, and setting time of calcium sulfoaluminate cement (CSA) is systemically investigated. Based on Raman spectroscopy and Thermogravimetric and differential thermal analysis (TG-DTA), the results showed that the hydration rate and the amounts and proportion of hydration products [monosulfate ettringe (AFm), ettringite (AFt), and ${\mathrm{AH}}_3$] were strongly influenced by $\mathrm{L}/\mathrm{A}$. When $\mathrm{L}/\mathrm{A}$ was 1:3, the AFt formation was present by the fastest rate and accounted for the largest proportion of the whole hydration products, further resulting in the highest strength. When $\mathrm{L}/\mathrm{A}\le 1:3$, the process of cement hydration can be divided into induction, the formation of AFt and AFm, interconversion between AFm and AFt, and stabilization stage, respectively. However, when $\mathrm{L}/\mathrm{A}>1:3$, there was no induction stage, and hydration process directly went into the accelerated period.

In wet process–modified asphalt, the modifier is easily separated from the asphalt, resulting in poor storage stability. For traditional dry-mixed modified-asphalt mixtures, adding a single modifier to the mixture, it is difficult to improve the comprehensive performance of asphalt mixtures. In this study, rubber–polyethylene composite modified particles were added to a dry-mixed asphalt mixture. The rubber powder was first desulfurized using a twin-screw extruder and then blended and extruded with low-density polyethylene particles to form rubber–plastic composite particles. Then, the high- and low-temperature performance and water stability of the dry-mixed rubber–plastic composite modified asphalt mixture were evaluated. Finally, the asphalt in the rubber–plastic composite modified mixture was extracted. The microscale properties were tested to investigate the mechanism of the composite particles. The results indicated that the rubber–plastic composite modified particles improved the high-temperature deformation resistance of the mixture. Additionally, the low-temperature crack resistance and water stability were slightly improved. Compared with adding desulfurized rubber powder alone, the comprehensive performance of the asphalt mixture can be significantly improved by using a rubber–plastic composite.

Crystalline wax in asphalt binder greatly affects the low-temperature performance of the asphalt pavement, and the composition of the phase separation at the microscopic scale has not been completely determined. In this paper, it is demonstrated that of the different observing systems of a microscope, the reflected polarization system is the best method to observe the morphology of the crystalline wax clearly. The components of the phase separation (excluding asphaltene) is also validated. On this basis, base asphalts doped with pure wax and eight asphalts at three aging states were observed. The results showed that the shape of the pure wax changed first from round to polymorphic, and then to an aggregate with an increase in the carbon number of the pure waxes. In addition, aging increased the intermolecular force and solubility of the wax in the asphalt binder. Finally, low temperature reduced the solubility of the wax in the asphalt binder to form a crystalline wax, which can provide an explanation for the physical (thermoreversible) aging of the asphalt binder at low temperature.

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 ($T_g$) 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, $T_g$ 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.

This study evaluated tire pyrolytic oil (TPO) derived from waste tire pyrolysis as a rejuvenating agent for three types of aged asphalt binders (unmodified, polymer-modified, and crumb rubber–modified). Gas chromatography–mass spectrometry (GC–MS) was performed to identify chemical compounds present in TPO. The rheological characteristics of all binders were examined through the complex viscosity–frequency profile, zero-shear viscosity, failure temperature, Black space diagrams, Cole–Cole plots, Superpave fatigue parameter, Glover–Rowe parameter, and linear amplitude sweep (LAS) tests. Mass loss was also determined for the rejuvenated binders. All binders were subjected to Fourier transform infrared (FTIR) analysis, and sulfoxide and carbonyl indices were computed. Atomic force microscopy (AFM) was conducted to study the effect of TPO on the micromorphology of the binders. The normalized Euclidean distance approach was used to rank the rejuvenated binders with respect to the proximity of their rheological and FTIR characteristics to that of the unaged binder. The use of TPO as a rejuvenating agent enabled the aged binders to achieve properties comparable to those of the unaged asphalt binder. The AFM-based rejuvenation index (RI) indicated a good potential of TPO as a rejuvenator. The results of the binder rheological parameters and the FTIR indicators investigated in the study indicated that a 9% dosage of TPO as a rejuvenating agent was the most effective.

Concerns exist over the potential moisture damage and adhesion of asphalt mixtures. This research aims to evaluate the adhesion and moisture susceptibility of asphalt mixtures containing two nanomaterials [nano zycotherm (NZT) and nano hydrated lime (NHL)]. Various tests [tensile strength ratio (TSR), coating ratio (CR), and surface free energy (SFE)] were conducted and compared. The findings of this research indicate that the nanomaterial-modified asphalt mixtures demonstrated a higher TSR. The image processing results for the CR of the boiling water test and modified bitumen coating on the aggregate’s surface also improved. Moreover, the amounts of SFE indicated that the free energy of cohesion in modified bitumen increased substantially compared to the base bitumen. Additionally, the free energy of adhesion in the modified bitumen with limestone and granite demonstrated higher values. Consequently, the debonding energy for the bitumen-aggregate composition and the probability of stripping in modified mixtures decreased. Considering all the adhesion indices of the bitumen-aggregate composition, including SFE, CR, and TSR, the NZT-containing mixtures had higher moisture resistance than NHL.

Rejuvenator seal material (RSM) is designed to revitalize an aged asphalt binder by spraying it on the surface of roads. It restores the mechanical properties of the existing pavement. This paper studied the effectiveness of RSMs containing cooking oil residue, motor oil residue, coal oil, solvent, and virgin or styrene-butadiene-styrene (SBS) modified $60/70$ bitumen to improve the behavior of an in-service pavement. Three stages were followed to formulate RSMs. To achieve the effective oil, the penetration grade and softening point changes of rolling thin-film oven (RTFO) + pressure aging vessel (PAV) aged $60/70$ bitumen mixing with different percentages of oils were studied. Then, the penetration depth of benzene, toluene, and xylene in hot mix asphalt (HMA) samples were measured to choose the most efficient solvent. Finally, the penetration depth of RSMs with various mixing ratios in HMA mixes was measured to determine the mix design and application values ($\mathrm{g}/{\mathrm{m}}^2$). RSM-A ($5\%\mathrm{COR}+5\%\mathrm{MOR}$ and $60/70$ bitumen), RSM-B ($5\%\mathrm{COR}+5\%\mathrm{CO}$ and $60/70$ bitumen), and RSM-C ($5\%\mathrm{COR}+5\%\mathrm{CO}$ and SBS modified $60/70$ bitumen) were selected for further assessments. Other than the aforesaid RSMs, RejuvaSeal was used as a generic commercial substance. A British Pendulum Test was used to ensure sufficient skid resistance to reopen the traffic soon after distributing the RSMs. Dynamic shear rheometer and bending beam rheometer tests were used to investigate the rheological properties of extracted bitumen from the upper 1.5 cm layer of the pavement with and without RSMs. Moreover, the fatigue behavior of rejuvenated asphalt mixtures was studied by the 4-point bending test. Based on the results, all RSMs had a positive effect on the softening of the aged bitumen. All RSMs regained the fatigue performance of the aged binder. However, they showed the reverse effect on the rutting resistance. RSM-C containing $5\%\mathrm{COR}+5\%\mathrm{CO}$ and SBS modified $60/70$ bitumen considerably modified the rheological properties of the aged binder even better than those mixtures rejuvenated by RejuvaSeal.

To explore the influence of water on the multiscale adhesive behavior between asphalt binder and aggregate, the nanosurface morphology and microsurface energy of asphalt binder and the macrobonding force between the asphalt binder and aggregate over different soaking times were examined using atomic force microscopy (AFM) and the pull-off test. Relationships between the macrobonding and the nanosurface roughness as well as the microsurface energy were analyzed. The results demonstrated that the effect of water on the surface morphology of asphalt binder was important. After immersion in water, water-induced bulges occurred on the asphalt binder surface, which further changed the nanosurface roughness and the surface energy of asphalt. As per the sensitivity results, it can be concluded that the surface energy of asphalt and the effective contact area between asphalt and aggregate were reduced because of moisture, thus resulting in the failure of adhesion.

Top-down (TD) cracking is the main concrete pavement cracking type in seasonal frozen areas. A two-lift concrete (2LC) pavement, including a polypropylene fiber reinforced concrete (PFRC) top lift and a portland cement concrete (PCC) bottom lift, is proposed to mitigate TD cracking. This study conducted prenotched three-point bending beam tests (3PBBTs) in the laboratory and numerical models have been developed to evaluate the fracture characteristics of concrete materials, including PCC, PFRC, and 2LC, in a freeze–thaw (FT) environment. Based on the double-$K$ fracture model, the fracture characteristics of concrete materials have been obtained. In the mesoscale, progressive damage constitutive models have been developed based on the Mori-Tanaka homogenization theory and three-dimensional (3D) Hashin failure criterion. Three-dimensional finite-element models have been developed to simulate the prenotched 3PBBTs with the progressive damage constitutive models coupled. It has been found in experiments that 2LC has better fracture resistance than PCC with and without FT treatments. Validated by experimental data, the developed FE models are capable of describing the fracture characteristics of concrete materials in the FT environment. Sensitivity analyses on factors that may influence the fracture resistance of 2LC have been conducted. This study validates that the proposed 2LCP has better TD cracking resistance than conventional PCC pavements and also suggests useful measurements enhancing the TD cracking resistance of 2LCP.

In this study, to ameliorate the abrasion resistance of limestone aggregates and extend the service life of bituminous pavement, limestone aggregates were impregnated by lithium silicate-styrene acrylic and lithium silicate-silicone acrylic to prepare bitumen mixtures. From this research, through a combination of macroscopic property tests and microstructural analysis approaches, the effect and corresponding reinforcement mechanism of lithium silicate mixed solution (LSMS) on the microstructural morphology and characteristics of limestone aggregates were investigated, and the road performance of the bitumen mixture using limestone aggregates impregnated with the lithium silicate mixture solution (LALS) was validated. The experimental results indicated that the impregnation treatment utilizing the LSMS with ratios of $6:4$ and $8:2$ could remarkably strengthen the abrasion resistance and anti-crushing ability, as well as enhance the ability to maintain angularity and surface texture in limestone aggregates. Furthermore, the utilization of LALS might hinder the further attenuation process and retard the loss rate with respect to the skid resistance properties of bituminous pavement, while exerting an insignificant effect on the high-temperature performance and fatigue resistance and a slight decrease in low-temperature performance and moisture damage resistance.

The asphalt binder is exposed to aging conditions during production, placement, and service. This results in physical hardening, oxidation, and volatilization of the asphalt binder. The aging phenomenon affects the performance and, in turn, affects the pavement’s service life. Understanding the aging behavior of asphalt binders in terms of physical and chemical properties will help to extend the pavement’s service life. In the present study, the aging effect of the asphalt binder was investigated using chemomechanical evaluation. Five asphalt binders, namely viscosity grade 30 (VG30), viscosity grade 40 (VG40), polymer-modified binder (PMB), crumb rubber–modified binder (CRMB), and Sasobit-modified binder (SMB) at three aging levels (unaged, short, and long term) were selected for the investigation. The rolling thin-film oven (RTFO) and pressure aging vessel (PAV) were used to simulate short- and long-term aging conditions. Dynamic shear rheometer (DSR), Fourier-transform infrared (FTIR) spectroscopy, surface free energy (SFE), and thin-layer chromatography–flame ionization detector (TLC-FID) tests were performed to analyze the aging behavior of asphalt binders. Further, multiple stress creep and recovery (MSCR) and linear amplitude sweep (LAS) tests were performed to understand the effect of aging on rutting and fatigue damage of binders. From the FTIR test, the aging of binders showed a substantial increase in the formation of ketones and sulfoxide functional groups. The asphaltenes and resins contents increased, whereas aromatics and saturate contents reduced after aging. The higher asphaltenes content increases the stiffness of aged binders and improves rutting resistance. At the same time, aging is detrimental to the fatigue resistance of asphalt binders. Again, it is observed from the results that aging decreases the dispersive component of SFE and increases in the polar component. The effect of aging is less pronounced in PMB and CRMB than in unmodified binders (VG30 and VG40). This study will help in understanding the interrelation among chemomechanical behavior of a binder at different aging levels and will be useful for the selection of a better performing binder for field applications.

Utilization of waste concrete has been become an urgent requirement for sustainable development due to the huge amounts of construction waste. The most promising strategy is to treat construction wastes by ${\mathrm{CO}}_2$ curing. This study investigates the properties and microstructure of cement mortar with ${\mathrm{CO}}_2$-cured waste cement powder (CWCP). The results showed the CWCP showed a rapid pH value decline from 12.9 to 10.2 within 12 h, the value was maintained at 8.4, and showed no obvious change after carbonation after 72 h. The ${\mathrm{CO}}_2$ uptake of CWCP increased rapidly in the first 2 h and reached 26.4% at 168 h. The C-S-H, $\mathrm{Ca}{(\mathrm{OH})}_2$, and traces of ettringite in waste cement powder (WCP) were transformed to calcium carbonate and silica gel after carbonation treatment. The flowability of cement mortar decreased with addition of WCP and CWCP content. The compressive strength of cement mortar with WCP decreased with replacement of cement beyond 10%, and incorporation of below 20% CWCP increased the compressive strength of mortar. In addition, the replacement of cement with 10%–20% CWCP or 10% WCP showed a lower water absorption compared with control cement mortar. The presence of calcium carbonate in the CWCP resulted in the formation of monocarbonate, which stabilized the ettringite and led to a denser microstructure compared with control cement paste.

Microcracks inevitably occur over time in cement composites, and they pose a threat to the safety and durability of concrete structures, especially when environmental conditions are considered. Microstructural analysis can be an effective alternative for the estimation of compressive strength, which is often difficult to monitor and follow and requires destructive analysis techniques. For this study, macrostructure and microstructure analyses were conducted of cementitious composites prepared with the nanofillers with the highest performance in the literature. In cementitious composites, 2.41 times more calcite content was obtained with the use of 0.05% graphene nanopellets, and 2.59 times more portlandite content was obtained with the use of 0.1% carboxylated-multiwall carbon nanotubes. It was concluded that the linear regression model was effective for the estimation of the compressive strength of nanofiller-blended cementitious composites, demonstrated by an $R^2$ value of 0.984. Based on the macrostructure and microstructure analyses results, the optimum nanofiller was determined by the technique for order preference by similarity to ideal solution (TOPSIS) method to be carboxylated–multiwall carbon nanotubes with a usage rate of 0.1%.

The purpose of this paper is to investigate the effect of magnetic water (MW) on the chloride diffusivity of mortar exposed to 5% NaCl solution in the presence of various sulfate concentrations (2%–7%). Cement was replaced with 0%–1.5% nanometakaolin (NMK). MW of 1.2 T was used in magnetic specimens. The degradation in mortars was evaluated in terms of compressive strength, mass change, chloride profile and penetration depth, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction analysis after exposure times up to 52 weeks. Using MW rather than tap water resulted in a significant decrease in the degradation level of all tested specimens. When compared to nonmagnetic mortars, the loss of compressive strength and the formation of ettringite in magnetic specimens were retarded by approximately 4 weeks. The chloride content and penetration depth decreased with increasing sulfate concentration. The 1.5% NMK magnetic mortar showed the minimum degradation in the hardened paste matrix.

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.

The bond properties of deformed rebar in frost-damaged recycled coarse aggregate concrete (RAC) under repeated loading (R-L) was studied. It is found that the bond failure modes of specimens for R-L is similar to that for monotonic loading (M-L), whereas the crack width for R-L is larger than that for M-L. The bond strength has a tendency to decrease after frost damage, whereas the peak slip has a tendency to increase, whether under R-L or M-L. The bond strength under R-L is lower than that under M-L, whereas the peak slip under R-L is higher than that under M-L. The experimental results of the pullout specimens in water are contrasted with that in salt solution. Through contrasting research, the frost-damage resistance coefficient and the R-L resistance coefficient in salt solution are lower than that in water, whereas the rebar slip in salt solution is higher than that in water. An ultimate bond strength calculation expression of deformed rebar in frost-damaged RAC under R-L is presented.

This paper investigates the viability of recycling construction and demolition waste as aggregate in porous asphalt pavement for stormwater runoff management. The influence of granulometric composition, recycled aggregate content (0%, 12.5%, 25%, and 37.5%), and binder content (4% to 6%) was investigated. A comprehensive characterization to identify the minimum binder content that might ensure a suitable hydraulic conductivity with minimum influence in the mechanical properties and moisture-induced damage was performed. The tested mixtures presented suitable particle loss, tensile strength, moisture-induced damage, and hydraulic conductivity for application as porous asphalt mixture for urban stormwater runoff management. The use of recycled aggregate resulted in acceptable air voids content only in mixtures produced with a binder content of 4.5%. The porous asphalt mixture produced with granulometric composition GC3, 25% recycled aggregate, and 4.5% asphalt binder could be potentially used for the intended application in stormwater runoff management.

Magnesium oxychloride cement (MOC) is a new type of cement with high early strength and good brine corrosion resistance. However, the water resistance of MOC is poor, which limits its current application. Highland barley straw ash (HBSA) contains a large amount of silica and, when calcined and ground under certain conditions, has a higher pozzolanic effect. This study investigated the effect of adding HBSA on the water resistance and pore structure of MOC mortar (MOCM), and the correlation between them. HBSA was mixed with MOCM in different proportions to test the water adsorption and water resistance. Nuclear magnetic resonance technology and the Brunauer–Emmett–Teller method were then used to test the distribution of full pores and micropores, respectively, in MOCM. Finally, the gray entropy theory was used to analyze the correlation between all the pore parameters of MOCM and the water resistance, and the numerical relationship between the softening coefficient reflecting the water resistance of MOCM and the characteristic pore parameters was determined. Results showed that the water adsorption of MOCM with added 10% HBSA decreased by 2.11%, the water resistance increased by 6.80%, and the proportion of harmful pores and more harmful pores decreased by 25.11% compared with that without HBSA. Three pore characteristic parameters—the proportion of less harmful pores, most probable diameter within the range of 20 nm, and accumulated micropore volume—had a good linear correlation with the water resistance of MOCM.

Polycarboxylate ether (PCE) superplasticizers are widely used in concrete, but in some cases, PCE aggravates the occurrence of cracks. This study evaluates the shrinkage reduction and plasticizing properties of a newly synthesized shrink-reducing polycarboxylate polymer (KH-SRPC) modified with ester and silane groups. When the KH-SRPC was implemented at a dosage of 0.3% by weight of cement, the adsorption capacity on the surface of the cement particles and the spreading diameter of the cement improved with respect to traditional PCE. Furthermore, the autogenous shrinkage and drying shrinkage of the mortar containing KH-SRPC were also investigated. When the KH-SRPC content was 0.2% of the weight of the cementitious material, the autogenous shrinkage of the KH-SRPC mortars at 3 and 7 days was reduced by 72.6% and 43.5%, respectively. The drying shrinkage of KH-SRPC mortars decreased by 38.3% at 3 days, 39.0% at 7 days, 39.1% at 14 days, and 35.7% at 28 days. It was found that KH-SRPC changed the pore structure of the solidified mortar, reduced the surface tension of the pore solution, and slowed down the rate of hydration, thereby reducing the total shrinkage of the mortar system.

To predict the long-term behavior of high-density polyethylene (HDPE) drainage pipes, HDPE coupon specimens with 0%, 49%, and 98% postconsumer recycled (PCR) material content were loaded incrementally in tension following the stepped isostress method (SSM) to establish their master creep curves. A reference stress of 15% ultimate tensile strength and a dwell time of 24 h were used. The 0% and 49% PCR content specimens elongated by more than 600%, whereas the 98% PCR content specimen elongated much less and broke a few minutes after adding the final load. The trend of the SSM shift factors in terms of creep stress agreed with the Eyring equation for all the HDPE coupon specimens. From the rupture time results, it was shown that as the percentage of recycled material increased, the coupon ruptured faster. The maximum percentage of recycled material allowed in HDPE is interpolated at 57% (39%) for 50-year (75-year) service life and the corresponding linear notched constant ligament stress (NCLS) failure time is interpolated at 15.2 h (21 h).

One of the most important factors affecting the durability of concrete structures is reinforcement corrosion, which is caused by oxygen concentration. Therefore, it is important to investigate oxygen diffusion in cement pastes. However, current research on oxygen diffusion models of unsaturated cement pastes has led to unclear conclusions. In this study, we propose a single-pipe oxygen diffusion model that considers five diffusion mechanisms: surface, Knudsen, transition, bulk, and water curtain. Further, a three-stage method is used to set up the model, and the division mode of this method is based on the mean free path (MFP) and the Mohycan model. The accuracy of the model is verified by comparing the calculated results with the experimental data. The proposed single-pipe model can be used to further analyze the durability degradation of reinforced concrete structures caused by steam, carbon dioxide, and other gases in the atmospheric environment.

The interfacial zone of new–old concrete in precast concrete structure is the natural weak part in durability, and fatigue stress and an aggressive medium will accelerate the durability degradation of the interfacial zone. To study the chloride transport behavior in the interfacial zone of new–old concrete joints of precast prestressed bridges under the combined action of fatigue load and chloride penetration, a set of long-term (90–360 days) and low-frequency (0.3 Hz) experiments was carried out in this paper, where three fatigue stress ranges and four exposure durations were set as the main variables. The results indicated that the chloride content in the interfacial zone is higher than that present elsewhere, which shows the interfacial zone effect (IZE). By introducing the index of IZE, the influence laws of fatigue stress range and exposure duration on the IZE are revealed, namely as the fatigue stress range increases, the IZE first increases and then decreases, and as the exposure duration increases, the IZE decreases invariably. Moreover, the influence mechanism of fatigue stress range and exposure duration on the distribution and evolution of chloride concentration in the interfacial zone is analyzed. Considering the heterogeneous distribution of mesocomposition and internal defects (pores) in the interfacial zone of new–old concrete, the model of the chloride diffusion coefficient is established. Based on the relationship between volume strain and porosity, and the relationship between strain and specific crack area, a revised model of the effective chloride diffusion coefficient in the interfacial zone under fatigue stress is proposed. The accuracy of the revised model was verified by physical experiments.

To reduce air pollution during asphalt pavement construction in road tunnels, and to increase fire safety of asphalt pavement when exposed to a tunnel fire, a porous warm-mix agent (WMA) was used to load composite fire retardant (CFR) for developing fire-retarding-type WMA (FWA). Then, the inhibition behaviors of CFR and FWA on asphalt pyrolysis and volatile emission were investigated by thermogravimetric mass spectrometry and nonisothermal pyrolysis kinetics, among other methods. Results indicate that many pore structures of WMA contain crystal water and provide necessary carrier space for loading CFR to prepare FWA. WMA improves the dispersion of CFR in asphalt. The asphalt pyrolysis is a single-stage thrmal decomposition reaction. The higher heating rate causes asphalt to release more heat and gaseous products. Additionally, the developed CFR effectively inhibits the pyrolysis behaviors of asphalt. As the temperature rises, the four fire retardant constituents in CFR are successively decomposed to synergistically inhibit the pyrolysis behaviors of asphalt in the condensed and gas phases. The mass loss of asphalt and the emission of pyrolysis volatiles are reduced. Also, WMA effectively promotes CFR to form a thicker and more pyknotic carbonization layer on asphalt, obviously improving the fire resistance of asphalt in the condensed phase. FWA modified asphalt has a higher thermal stability than CFR-modified asphalt. FWA hinders the nucleation and aggregation of gaseous products, effectively inhibiting the escape of toxic volatiles from asphalt. Finally, the emission of toxic volatiles at the construction temperature range of asphalt is effectively inhibited by FWA, reducing air pollution during asphalt pavement construction and lowering the harm to the health of construction workers.

Despite the use of fuel-resistant asphalt binder in airport pavement, oil or fuel contaminants still lead to pavement deterioration or softening, which may pose a risk to aircrafts during their landing and taking-off. The identification and evaluation of the contaminants is a prerequisite for developing preventative or maintenance measures. In this study, Fourier-transform infrared spectroscopy (FTIR) and mechanical tests were used to characterize asphalt pavements contaminated by four typical contaminants, including jet fuel, diesel, lubricant, and vegetable oil. The FTIR spectra of the contaminants, their blends with asphalt binder, and extracted binders from contaminated mixtures were comprehensively analyzed. Compacted asphalt mixture samples were treated by immersion into the four types of contaminants for different time durations and subsequently evaluated by visual observation, mass loss, and resistance to permanent deformation. The results indicate that FTIR is a rapid and reliable method to identify certain contaminants, and different types of contaminants lead to significantly different impacts on asphalt mixtures. Construction and maintenance strategies are recommended based on the research findings.

E-glass fiber-reinforced polymer (FRP) composite wind turbine blades are nonbiodegradable, and their end-of-life recycling solutions are limited. Research on reusing and repurposing applications, where minimal amounts of refabrication are needed, is being conducted to address this issue. To design new structures from decommissioned blades, their as-received mechanical and physical properties are needed. Even though some long-term property data for FRP composites exist in the literature, very little actual data for the as-received residual properties of decommissioned blades have been reported. The current work is aimed at developing a methodology to obtain as-received material property data for decommissioned wind turbine blades that are being proposed for use as second-life structural components. In this paper, details of the methods used and the test results for the key physical and mechanical properties of glass FRP material specimens extracted from the spar cap of a decommissioned 1.5-MW GE37 wind turbine blade are reported (the blade is from a General Electric 1.5 MW turbine which is known as a GE37 blade), including burnout testing for constituents’ weight and volume fractions as well as fiber architecture and tension, compression, and shear testing in the longitudinal and transverse material directions. Comparisons between test results of other investigators and the experimental data obtained show promising strength and stiffness retention levels of the material for different properties. The results show that structural integrity still exists for the tested composite materials and no deterioration, crack propagation, or delamination was observed in the materials due to the cyclic loading levels experienced in their first life.

Water repellent (WR) has been widely used to improve the durability of cementitious materials (CMs) by reducing the absorption of water and aggressive ions. In this study, cement pastes were prepared with three types of WR, namely, waterborne pure nanosilicone emulsion (NS), isobutyltriethoxysilane (IS), and octyltriethoxysilane (OCT). The effects of WR on setting time, compressive strength, and water absorption were investigated. The influence of WR on the transverse relaxation time spectrum from 0 min to 28 days during the hydration process was monitored with a low-field nuclear magnetic resonance (LF-NMR). In addition, X-ray diffraction (XRD) and heat flow were employed to study the effect of WR on hydration characteristics. The results showed that the WR specimens exhibited a limited reduction of compressive strength compared with the control sample at 28 days. The use of WR reduced the water absorption of cement paste when compared to that of the control specimens. The results showed that the WR exhibited a retarding effect on hydration reactions, and the capillary and gel pores of the cement paste increased compared with that of the reference sample. XRD analysis showed that the formation of hydration products had been restricted with the addition of WR. The heat flow results showed that the retardation effect was enhanced as the WR dosages increased.

One of the main problems that reduces the prevalence of alkali-activated binders is the heat-curing process that is required to produce them. In addition, the chemical alkaline solutions used can be corrosive, caustic, and expensive. With this innovative study, the production of alkali-activated mortar made entirely from waste materials without the use of thermal curing or a chemical solution was carried out. In this study, the physical and mechanical effects of alkali-activated mortars produced by using ground granulated blast-furnace slag (GGBFS) and hazelnut shell bottom ash (HA) were investigated. Instead of GGBFS, 10%, 20%, 30%, 40%, 50%, and 60% HA was substituted in the samples produced. In addition, the samples produced at ambient temperature were subjected to four different curing conditions. Unit weight, porosity, water absorption, ultrasonic pulse velocity, and compressive strength tests were applied to the mortar samples on Days 3, 7, and 28. Moreover, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray fluorescence analysis (XRF), and X-ray diffraction analysis (XRD) were used to examine the changes in the microstructures of the mortars. As a result of the study, it was determined that the use of HA up to 50% improved the compressive strength and other physical properties. The mortars containing 50% HA obtained 14.45 MPa when kept under ambient conditions and 19.54 MPa when kept under ambient conditions for 3 days and in water for 25 days. Also, water-cured samples showed better performance in other tests.

Use of scrap tire derivatives for civil engineering applications is an emerging field. In spite of extensive characterization of these materials, most of the studies focused on smaller-sized tire derivatives, i.e., tire crumbs. Furthermore, only a few studies are available on the cyclic response of these tire derivatives. The present study details the dynamic properties and liquefaction behavior of tire chips and sand–tire chip mixes. A series of strain-controlled cyclic triaxial tests were carried out considering confining pressure, strain amplitude, and tire chip content as variables. The tests were performed on seven different mixes with varied proportions of sand and tire chips by weight. The addition of tire chips to the sand increased the liquefaction resistance and threshold shear strain of the mixes significantly. The addition of the tire chips decreased the shear modulus and increased the damping ratio of the mixes. Furthermore, based on the behavior of the mixes with different tire chip contents, an optimum mix was suggested.

Water absorbing polymers (WAP) have shown their potential as vegetation growth promoters in various soil infrastructures by minimizing the downward migration of water and conserving adequate moisture in the vadose zone under semiarid climates. However, the moisture movement mechanism in a soil–WAP system has not been well recognized in previous studies. There is a need to evaluate the moisture diffusivity value of soil in contact with swollen WAP to understand the performance of WAP as soil amendment under water stress conditions. Therefore, the present study demonstrates a laboratory procedure to characterize the moisture sorption and diffusion mechanism from swollen WAP to soil particles. A horizontal diffusion cell was developed to study the moisture transfer and transport mechanism corresponding to three different textured surface soils. The measured moisture profiles with time were used to determine the Boltzmann transformation constant to verify the validity of Fick’s law of diffusion for moisture movement in a WAP–soil system. A tangential relationship between the Boltzmann constant and soil moisture content was proposed to calculate the moisture diffusivity value. The results indicated that the moisture content of the WAP–soil interface was significantly influenced by both soil and WAP characteristics. Moreover, the moisture movement through the soil column (in contact with swollen WAP) follows the Fickian diffusion mechanism, and the proposed laboratory setup is suitable for determination of moisture diffusivity values. The wetting soil–water retention curves (SWRC) of the used soils were measured using suction sensors (T5, TEROS21) and a moisture sensor (${\mathrm{ECH}}_2\mathrm{O}$ 5TM) in a PVC column connected to a water reservoir to estimate the moisture diffusivity values. The observed moisture diffusivity curves showed that the addition of WAP serves as an additional water reservoir in soil and can be used for vegetation maintenance on landfill covers, green infrastructures, and bioengineered slopes under semiarid climates.

The performance of the recycled asphalt pavement is directly influenced by the content of the used regenerant (i.e., rejuvenator and/or unaged asphalt binder). The goal of this study is to optimize regenerant content of aged styrene-butadiene-styrene (SBS) modified asphalt binder based on high-temperature creep and low-temperature relaxation performance tests. Initially, penetration, ductility, softening point, multiple stress creep recovery (MSCR), and bending beam rheometer (BBR) tests were carried out to investigate the rheological behavior of the aged SBS modified binder (AMB) regenerated with different contents of the rejuvenator and unaged SBS modified binder (UMB). A method is proposed, based on the rheological behavior of the regenerated AMB, to determine the optimum contents of the regenerants (i.e., rejuvenator and UMB). To reach a successful trade-off between low- and high-temperature properties of the regenerated AMB, the relaxation rate $V_R$ and nonrecoverable creep compliance $J_{3.2}$ (at 3.2 kPa) were selected as the evaluation indices to settle the optimum contents of the rejuvenator and UMB. The results showed that the ductility of regenerated AMB is on par with the UMB when the contents of rejuvenator and UMB are 4% and 70%, respectively. The nonrecoverable creep compliance and relaxation rate of the regenerated AMB tended to increase with the increase in the content of the rejuvenator and UMB, whereas the recovery rate and relaxation modulus decreased. It indicated that the low-temperature performance increased while the high-temperature performance was adversely affected by the increase in the content of the regenerants. The $V_R$ and $J_{3.2}$ of the regenerated AMB were comparable to those of unaged state, when the contents of the rejuvenator and UMB in the aged binder were 5% and 70%, respectively. It indicated that the high-temperature creep and low-temperature relaxation performance of the AMB reach a balance.

Acid rain has detrimental effects on the pavement performance of asphalt mixtures. This research investigated the effects of acid-rain immersion on the physical properties and pavement performance of rubber asphalt mixtures containing steel slag; the mechanism behind these effects was also determined. A simulated acid-rain-immersion experiment was designed based on changes in the air voids and Marshall stabilities of the mixtures. Penetration, softening-point, ductility, and viscosity tests evaluated the physical properties of rubber asphalt after acid rain erosion. Rutting, low-temperature bend, and freeze–thaw splitting tests also were conducted. The mechanisms by which acid rain immersion impact the rubber asphalt mixtures containing steel slag were studied via Fourier-transform infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. The results revealed that the rubber asphalt becomes brittle and hard after acid rain immersion due to its lightweight components being converted into heavier components due to rubber degradation and asphalt oxidization. Acid rain also reduced the adhesion between the asphalt binder and aggregates by eroding the asphalt film and reacting with components in the steel slag. The results of this research provide reference information for the application of steel slag asphalt mixture in areas affected by acid rain.

An experimental investigation was conducted in order to evaluate the effectiveness of six new microfine cement grouts obtained by pulverizing three ordinary cements with different chemical composition. Both consolidated-undrained with pore pressure measurement (CU-PP) triaxial compression and hydraulic conductivity tests were conducted on each grouted sand specimen. Grouting increased the stiffness and reduces the hydraulic conductivity of the sands. The shear-strength behavior of the grouted sands was described satisfactorily by the Mohr-Coulomb failure criterion. The bleed capacity of the injected suspensions was a good indicator of the grouting-induced mechanical and hydraulic behavior improvement. Grouting with stable [water to cement ratio $(W/C)=1$] microfine cement suspensions was superior to grouting with coarser cements at $W/C=1$, yielded hydraulic conductivity values as low as $5.5\times {10}^{-8}\mathrm{cm}/\mathrm{s}$, added cohesion reaching 2 MPa and, on the average, increased the initial modulus of elasticity by 10 times, reduced failure deformation by 5 times, and increased the peak strength by 8.5 times. Grouting with unstable microfine cement suspensions provided measurable, but not as pronounced, improvement. A change in stress–strain–strength behavior of grouted sands, associated with the beginning of cementitious bonds breakage, was systematically observed at low axial deformation (0.2%–0.7%).

Waste polyethylene (WPE) is a common waste that easily pollutes the environment. WPE has been used as a modifier to improve the high-temperature stability of asphalt. However, the performance change of WPE modified asphalt during oxidative aging is still unknown. The purpose of this article is to study the effect of WPE on the performance of asphalt before and after oxidative aging by using the molecular dynamics method. First, the density, viscosity, glass transition temperature, and cohesive energy density (CED) of WPE modified asphalt before and after oxidative aging were calculated. WPE reduces the viscosity change of asphalt during oxidative aging. WPE reduces the CED value of asphalt, thereby weakening the force between asphalt molecules. In addition, the glass transition temperature indicates that WPE can alleviate the effect of oxidative aging on the reduction of the viscoelastic properties of asphalt. The viscoelasticity of 4wt% WPE modified asphalt remains almost unchanged before and after oxidative aging. In addition, WPE molecules can improve the self-healing ability of asphalt during oxidative aging.

Fiber-matrix interface bonding is an important area of concern in fiber-reinforced composites because it is directly related to the mechanical behavior of composites. In this study, interfacial bond properties of four types of fiber at different curing ages were investigated by analyzing fiber pull-out responses. Special attention was given to the fiber–matrix bonding behavior, including fiber tensile strength, average bond strength, equivalent bond strength, and average pull-out energy. Pull-out tests were conducted at 7, 14, 28, and 56 days of curing. Different failure modes in steel fiber, synthetic macrofiber, polyacrylonitrile (PAN)-based carbon fiber, and pitch-based carbon fiber were investigated. According to the pull-out force versus slip curves, different failure patterns were recorded based on the fiber type. Carbon fibers experienced a sudden drop after reaching the peak load, whereas the load decrease in steel and synthetic fiber was not as abrupt. Results also confirmed that steel fibers exhibited the highest pull-out load and energy absorption capacity followed by lower values for synthetic and carbon fibers. While monofilament of steel fiber was able to absorb 1,050 N·mm, monofilament of synthetic fiber and twisted bundles of carbon fibers could absorb 277 and 55 N·mm, respectively. However, the bond strength of straight carbon fibers was comparable to that of synthetic fiber and still lower than steel fiber. It was also derived from the experimental data that an increase in cement matrix age correlates to an improvement in fiber maximum pull-out load, bond strength, and tensile strength. These parameters were identified and compared in all fiber types.

In order to mitigate the effects of thermal-oxidative and ultraviolet (UV) aging on asphalt pavements during service, we explored the influence law of rare earth compounds on the aging properties of asphalt and the antiaging mechanism. The asphalt was subjected to thermal-oxidative and UV aging tests by using a thin-film aging oven as well as a UV aging oven. The changes of macroscopic and microscopic properties of three rare earth–modified asphalts before and after aging with base asphalt were studied by using basic physical property tests, dynamic shear rheology tests, and Fourier infrared spectroscopy comparisons. The results showed that the rare earth–modified asphalt had significantly improved in deformation resistance and high-temperature stability compared with the base asphalt. After aging, the change of carbonyl and sulfoxide functional group indexes of rare earth–modified asphalt was significantly slowed down compared with the base asphalt. It showed that the incorporation of rare earth compounds has a direct effect on the improvement of the aging resistance of asphalt. Regarding the three types of rare earth–modified asphalt, cerium oxide–modified asphalt showed better improvement in thermal-oxidative and UV aging resistance.