Journal of Materials in Civil Engineering

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 $\mathrm{C}─{\mathrm{CH}}_3$ 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 ${\mathrm{CH}}_2$ groups), and creating the aromatic and double bond structures due to the nature of rubber flexibility, the trend is reversed.

To evaluate the feasibility of mixing saline underground water (SUW) in the preparation of cemented fine tailings backfill (CFTB), the compressive strength, pore fluid pH, slag hydration degree, hydration phase composition/structure, and pore morphology of CFTB have been tested. The binder used was a one-part alkali-activated slag composed of ground-granulated blast furnace slag (67.8% by weight) as precursor and desulfurized gypsum (25.9% by weight) and hydrated lime (6.3% by weight) as composite activator. The results showed that using SUW instead of deionized water as mixing medium had both negative and positive effects on the strength development of CFTB, depending on the curing time. At the very early ages (1–3 days), mixing SUW resulted in a decrease of the pore solution pH, which is due to the reaction of positive ions in SUW with ${\mathrm{OH}}^{-}$ ions and the decrease of slag hydration rate, leading to a lower strength of CFTB. The positive effects were observed at the later ages (7–28 days). The higher later-age strength of SUW-mixed CFTB is attributed to two factors: (1) a smaller amount of ettringite (AFt) was generated at the very early ages, which reduced the encapsulation-hindering effect on the slag decomposition; and (2) SUW increased the slag hydration rate, promoting the condensation of calcium silicate hydrates, which results in increased formation of a calcium silicate aluminate hydrate [C-(A)-S-H] phase with rigid three-dimensional structure. These findings can provide important information for the use of SUW in CFTB in coastal and arid regions.

Abstract

This manuscript aims to utilize industrial wastes, i.e., ferrochrome slag (FS), ground granulated blast furnace slag, and fly ash to prepare alkali activated cementless controlled low strength material (CLSM). The physical properties, i.e., flowability, bleeding, unit weight, and mechanical properties such as strength, durability, and settlement were assessed for different CLSM mix designs and compared with cement-based FS-CLSM. The alkali activated FS-based CLSM achieved adequate flowability and unit weight with a strength value of 1.72 to 10.44 MPa for different CLSM mix propotions, with a California bearing ratio (CBR) value of 328% to make the CLSM mix a feasible pavement material. The study concludes that a high molar ratio of potassium hydroxide (KOH) accelerates the alkali activation process which helps in the formation of alkaline alumino/calcium silicate hydrates to bind the FS and produce CLSM with adequate strength. The high durability and low levels of toxic metals in the leachate cause the FS-based CLSM environment to be acceptable. Furthermore, life cycle analysis was carried out to investigate the effects of the FS-based CLSM on the ecosystem and human health.

Abstract

The present study aims to utilize a less explored industrial waste from the ferroalloys industry, ferrochrome slag (FS), in preparing controlled low strength material (CLSM) without the addition of cement. The CLSM is prepared by mixing FS with other industrial waste to achieve adequate properties and can be utilized as an unpaved road material or in structural filling. The study concludes that production of CLSM by using FS is economical and safe relative to the environment and human health. Since the developed construction material is prepared by using industrial wastes and without cement, it is an alternative solution to reutilize the industrial waste more efficiently particularly inside and in the vicinity of the industry. Based on the above results, a pilot study is in process to develop and repair the construction works of roads and trench filling in the plant premises and outside in the vicinity of the plant.

In recent times, the employment of recycled aggregate concrete (RAC) for sustainable infrastructure development has enticed special interest from the research community owing to a greater emphasis on resource conservation and environmental protection. To apply such concrete in the modern-day construction industry, in-depth knowledge and thorough understanding of its fire resistance is imperative and an urgent need at the present time. Hence, this experimental study investigates the effect of elevated temperatures (25°C–800°C) on residual mechanical, physical, and microstructure performances of RAC strengthened via the coupling effect of chopped basalt fiber (BF) and pozzolana slurry treated recycled concrete aggregate (TRCA). To mimic real building fire conditions, concrete test specimens were heated to a specific target temperature in a controlled heating manner, and then their performance was assessed in terms of residual properties including compressive strength, splitting tensile strength, flexural strength, mass loss, physical appearance, and microstructure. Overall, the test findings revealed significant enhancement in residual properties of modified recycled concrete prepared by combined utilization of BF and TRCA. Moreover, in comparison with a reference sample, the BF-based recycled concrete demonstrated lower mass loss and surface degradation, especially beyond 400°C, that is attributed to the excellent thermal stability and reinforcing effect of BF. The microstructure observation evidenced improved matrix quality that contained better interfacial transition zones alongside added nucleation sites by BF. Lastly, based on the experimental data, simplified numerical relationships are established that will help predict the postfire performance of BF-reinforced sustainable concrete.

The superior performance of styrene-butadiene-styrene (SBS) modified asphalt makes it widely used in asphalt pavement construction. However, SBS-modified asphalt pavement still faces an aging problem. Aging causes the performance of asphalt materials to decline and many pavement diseases. The dosage of SBS commonly used in industry is generally between 3% and 4.5%, and the performance of SBS with a high dosage needs to be explored. Therefore, in this paper, 12 modified binders were prepared with blending amounts of 3%, 5%, and 7% and the type of modifiers as linear and star. The softening point increment (SPI), viscosity aging index (VAI), rutting factor index (RFI), complex modulus aging index (CMAI), and phase angle aging index (PAAI) were used to study the antiaging performance of SBS-modified asphalt. Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) were used to study the microscopic and structural changes that occur during the aging process of modified asphalt. The result shows that when the amount of the same type of modifier is 3%–7%, the higher the amount of modifier, the better the performance of the modified asphalt. At the same content, a star modifier is not necessarily better than a linear modifier. For the same type of modifier, the larger the amount, the better the antiaging performance of the modified asphalt. Given an increase in aging time, the deterioration of the asphalt performance will deepen. Aging leads to the enhanced high-temperature performance of asphalt. The macroscopic performance of asphalt aging can be explained by the microscopic view. The aging process of modified asphalt is the cumulative process of oxidation products.

In recent decades, some of the main goals of pavement engineers have been to increase bearing capacity, enhance tensile strength, and improve the moisture susceptibility of asphalt mixtures. Because moisture and frost intensify the damage caused by traffic loads on pavements in cold climates, the life and safety of asphalt pavements in this climate are reduced. Finally, cracking at low temperatures and moisture damage leads to a decrease in the serviceability of asphalt pavement in cold climates relative to temperate climates. Hence, a comprehensive and accurate program is necessary to estimate the fracture toughness and moisture susceptibility of asphalt mixtures in cold climates. In recent years, nanotechnology has become very popular due to its unique features in enhancing the operation of bitumen and asphalt mixtures. For this purpose, in this study, the impact of $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ on pavement performance against cracking and moisture susceptibility is investigated. To achieve this objective, SCB specimens were fabricated with different ratios of $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ (0.0% and 0.9%) and studied at the three temperatures of $-5°\mathrm{C}$, $-15°\mathrm{C}$, and $-25°\mathrm{C}$ under pure mode I, pure mode II, and four distinct mixed-mode (I/II) loading (${\mathrm{M}}^{\mathrm{e}}=0.2$, ${\mathrm{M}}^{\mathrm{e}}=0.4$, ${\mathrm{M}}^{\mathrm{e}}=0.6$, ${\mathrm{M}}^{\mathrm{e}}=0.8$) for various crack geometry, including vertical and angular cracks for which the crack angle is 45° in samples with angular cracks. In addition, the indirect tensile strength (ITS) test was employed to estimate the moisture susceptibility. The results indicated that modifying the asphalt mixture properties with 0.9% $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ had a significant impact on the fracture behavior of the samples in both vertical and angular cracks under all temperatures. Additionally, with the application of $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ and decreasing temperature, the fracture toughness of the samples increased. Furthermore, the findings displayed that the employment of 0.9% $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ reduced the moisture susceptibility of asphalt mixtures by approximately 6%.

Investigations into the dielectric properties of concrete form the basis for concrete quality testing and condition monitoring of internal structures when using ground penetrating radar (GPR). The formula used to describe the quantitative relationship between the dielectric properties of composite materials and the dielectric constant and volumetric ratio of each component is known as a dielectric model. In this study, a new dielectric model was deduced from circuit theory on the basis of structural abstraction to calculate the dielectric permittivities of concrete. To validate the applicability and accuracy of the proposed model, because concrete consists of matrix (cement mortar), aggregates (limestone), and air, the dielectric traits of concrete and its components were acquired using an open-ended coaxial probe. Compared with the Brown model, complex refractive index method (CRIM) model, Looyenga model, and Rayleigh model (i.e., the classical models), the results showed that among overall predictions of concrete dielectric constants, the proposed model has the greatest accuracy, because the theoretical results matched the test results more closely. This indicates that the proposed model can better interpret the dielectric properties of concrete, which lays the groundwork for future research into the application of GPR to the nondestructive testing and evaluation of concrete pavement.

Columnar jointed rock masses (CJRMs) have a complex network structure and, therefore, present a great challenge to geotechnical engineering design. A series of triaxial compression tests is performed on artificial CJRM specimens subjected to a confining pressure of 5 MPa, considering various pore pressures ($p_w=0\mathrm{MPa}$, 2 MPa, and 4 MPa). In this work, the influence of the joint dip angles and pore pressure on the anisotropic strength, deformation, and failure modes of the CJRM is investigated. The anisotropic characteristic stresses, strength parameters ($c$ and $\phi$) and elastic modulus of the CJRM specimens show a U-shaped pattern with increasing joint dip angles ($\beta$), while Poisson’s ratio changes inversely. The elastic modulus has a stronger anisotropy than Poisson’s ratio. Moreover, with increasing pore pressure, the characteristic stresses decrease, while the anisotropy of stresses and deformations increases. Finally, three failure modes of CJRM specimens with different joint dip angles are observed under triaxial compression conditions.

A reduction in ${\mathrm{CO}}_2$ emissions is necessary in the concrete industry. This study proposes a ${\mathrm{CO}}_2$ conversion technique by which ${\mathrm{CO}}_2$ gas is converted into solid nano ${\mathrm{CaCO}}_3$ and used to replace the partial binder of cement-slag blends in ratios of 2%, 4%, and 6%. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analyses confirmed the formation of hemicarboaluminate (Hc) and monocarboaluminate (Mc) due to the chemical reaction between nano ${\mathrm{CaCO}}_3$ and the ${\mathrm{Al}}_2{\mathrm{O}}_3$ phase in the binder. XRD analysis revealed that at 28 days, the addition of nano ${\mathrm{CaCO}}_3$ can inhibit the transformation of ettringite (AFt) to monosulfate (AFm). As the contents of nano ${\mathrm{CaCO}}_3$ increased, the hydration heat, strength, ultrasonic pulse velocity (UPV), electrical resistivity, and combined water content increased. The degree of increment of the electrical resistivity was more pronounced than that of the strength. For various specimens, the strength and combined water content presented a linear relationship, and the strength and UPV presented an exponential function. The reduction rate of normalized ${\mathrm{CO}}_2$ emissions (the ratio of ${\mathrm{CO}}_2$ emissions of the paste to its strength) was much higher than the replacement percentage of nano ${\mathrm{CaCO}}_3$. This was because nano ${\mathrm{CaCO}}_3$ increased the late strength and had a negative ${\mathrm{CO}}_2$ emission value.

To solve the problems of low flame retardant efficiency and weak low-temperature performance of asphalt modified by conventional flame retardants (CFR), in this study, halloysite nanotubes (HNTs) and CFR were used to prepare nanocomposite flame retardants (NCFR) to modify asphalt. A fluorescence microscope (FM), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) were used to characterize the microstructure of NCFR-modified asphalt. An oxygen index meter, Cleveland open cup, and cone calorimeter were used to test the flame retardant properties of the asphalt. A dynamic shear rheometer, bending beam rheometer, and force ductility tester were used to test the rheological properties of asphalt. At the same time, flame retardant–modified asphalt mixtures were prepared to verify the flame retardancy and road performance of the flame retardant–modified asphalt. The research results showed that the asphalt modified with 8% CFR and 1% HNTs (MA/CFR/1% HNTs) showed better dispersibility. The increase of limiting oxygen index and self-ignition temperature and the decrease of heat release rate and smoke production rate of MA/CFR/1% HNTs indicated that it has good flame retardancy. At 64°C, compared with modified asphalt (MA), the rutting factor of MA/CFR/1% HNTs increased by 88.17%, the creep recovery increased, and the irreversible creep decreased, indicating that its high-temperature performance improved significantly. At $-18°\mathrm{C}$, compared with that of MA/CFR, the low-temperature creep stiffness of MA/CFR/1% HNTs decreased by 36 MPa and the creep rate of MA/CFR/1% HNTs increased by 0.034, indicating that only 1% HNTs can improve the effect of degraded CFR on the low-temperature performance of MA. Simultaneously, MA/CFR and MA/CFR/1% HNTs can improve the high-temperature performance and water stability of asphalt mixtures. Adding 1% HNTs to a MA/CFR-modified asphalt mixture can improve the low-temperature performance of the asphalt mixture to the level of the low-temperature performance of the modified asphalt mixture. In summary, the modification of asphalt with 1% HNTs and 8% CFR can effectively improve the flame retardant efficiency and significantly improve the road performance of asphalt.

Ultrafine ettringite (UE) can accelerate the hydration of sulfoaluminate cement-based grouting materials (SCGMs). However, the mechanism of UE on the hydration of SCGM is not clear. Many researchers believe that ultrafine materials can serve as crystal nuclei for hydration products. How to prove that UE can supply crystal nuclei for hydrated products remains an open question. It is still unclear for which SCGM hydration products UE can supply a crystal nuclei. In this article, UE was synthesized in different solvent compositions by a separate nucleation and growth step method. Synthetic UE was enclosed in a dialysis bag with a molecular weight cutoff of 7 kDa, which allowed the diffusion of water and ions, and the mechanism of UE’s effect on the hydration of SCGM was investigated. The results indicated that with the increase of the amount of ethanol in the water–alcohol mixed solvent, the particle size of the prepared UE gradually became smaller. UE only provided a nucleation site for ettringite, which was one of hydration products, and thus promoted a cement hydration reaction. The smaller the size of the UE, the higher the cement hydration rate and the greater the amount of hydration products produced.

In this study, Buton rock asphalt (BRA), nano-aerogel (NA), and an antiaging agent (AA) were selected to modify base asphalt to improve its aging resistance. Based on the preliminary performance test results, the optimum dosage of the three modifiers was determined. The asphalt’s rheological properties and microscopic properties were tested under different aging methods. Its high- and low-temperature rheological properties were characterized by dynamic shear rheological tests and bending beam rheological tests. Fourier transform infrared spectroscopy (FTIR) analyzed changes in the asphalt’s functional groups before and after aging. The ultraviolet absorption capacity of the asphalt before and after aging was studied by an ultraviolet-visible spectrophotometer (UV-VIS). The results showed that the optimal dosing of the modifiers was 2% NA, 10% BRA, 0.3% antioxidant 1010, and 0.4% UV-327. Compared with the base asphalt, the composite modified asphalt with BRA, NA, and AA showed improvement in high- and low-temperature performance. The aging index of both the rheological test and the infrared spectroscopy test showed that the composite modified asphalt had the best resistance to aging. Its resistance to UV radiation was higher than that of the base asphalt, and the BRA/NA modified asphalt. Therefore, the addition of BRA and NA effectively improved the asphalt’s high- and low-temperature performance. Addition of the antioxidants 1010 and UV-327 effectively improved its aging resistance.

The effect of powdery industrial solid wastes on the optimal proportion of pastes and self-compacting concrete (SCC) is investigated in this study. There were nine groups of powdery industrial solid wastes designed, including cement, fly ash (FA), limestone powder (LP), granulated blast furnace slag (GBFS), and modified phosphogypsum (MPG). The powder materials have different properties, such as zeta potential, density, and specific surface area. The paste rheological threshold theory was used to calculate the self-compacting paste (SCP) zone and the optimal proportion. To assess the effect of powder properties on the optimal mix proportion, a model was proposed. The linear regression method was used to obtain quantitative relationships between the optimal proportion and powder characteristics, which can benefit in the SCC optimization process. A new powder combination was designed, and the optimal water-to-powder ratio by volume (${\mathrm{V}}_{\mathrm{W}}/{\mathrm{V}}_{\mathrm{P}}$) and the dosage of superplasticizer by mass (SP%) can be calculated using the powder combination’s physical and chemical properties. The search area was narrowed, and the SCP zone was obtained, where a good SCC was achieved, validating the powder effect model’s effectiveness.

With advancements in artificial intelligence and computer vision, machine learning has become widely employed in location and detection of road pavement distresses. Recently, recognition methods based on convolutional neural networks (CNNs) have been implemented to segment pavement cracks at pixel level in order to evaluate the pavement condition. However, this method usually consists of some common processes, including manually predetermining the approximate location of cracks followed by selecting the image containing the cracks and then performing pixel-level segmentation, which is why it is worth automating the preprocessing to replace the manual selection step. Moreover, the issues of a low proportion of positive samples, complex crack topologies, different inset conditions, and complex pavement background make the task of automatic pavement location more challenging. Therefore, this paper proposes a novel method for preprocessing crack recognition, which automatically locates cracks and yields great savings in labor costs. Specifically, a real-world road pavement crack data set obtained from a common digital camera mounted on a vehicle is built to test the proposed crack location method, called Double-Head. It improves the accuracy of crack object localization by using an independent fully connected head (fc-head) and a convolution head (conv-head). The results show that our method improves average precision (AP) 6.5% over Faster R-CNN using only a fc-head, and outperforms many advanced object detection methods.

In the laboratory, there are significant differences in mechanical properties of asphalt mixtures with the same size gradation and asphalt binder, which is not conducive to evaluating and designing the pavement structure accurately. Meanwhile, the influence of aggregate segregation in height on the mechanical properties of asphalt mixtures is unclear. This study developed a new method to generate a three-dimensional (3D) model of the real composition and aggregate shape to characterize the aggregate segregation during Superpave gyratory compaction (SGC). The graphic segregation index (GPSI) is employed to assess the mixing degree of coarse aggregate and asphalt mortar within spatially variable specimens [i.e., Superpave-13, stone mastic asphalt (SMA-13), and open-graded asphalt friction course (OGFC-13) mixtures]. The results reveal that asphalt mixtures with different aggregate gradations have different compaction characteristics. For example, the increase of fine aggregates may reduce the strain energy and the average contact force during compaction. The compaction curves of the three gradation types were very different, which is attributed to different packing states and gyratory numbers. Aggregate segregation has a significant effect on micromechanical behavior. Specifically, the contact number and the proportion of strong contact force change considerably with height. In terms of segregation degree, the GPSI of OGFC-13 specimens was the highest, and the volume change of its fine particles created a leakage zone after the compaction. Additionally, this segregation had an increasing tendency with gyration numbers, and it was influenced by gradation types. Furthermore, the uniaxial compressive strength and cohesion of the Superpave-13 specimen decreased, whereas the friction angle increased with the increase of GPSI.

Freezing on asphalt roads affects driving safety. Spraying salt on roadways pollutes the environment. Mechanical deicing requires significant human and financial resources. This paper proposes a new approach to realize autonomous anti-icing of asphalt pavement, an acrylic/polytetrafluoroethylene coating (APC). The contact angle of a water droplet on the APC surface is 155.392°. Moreover, the freezing time of water droplets on the APC-coated asphalt mixture is 1.5 times longer than that of the uncoated asphalt mixture. Moreover, the skid resistance test results show that APC can increase the road friction coefficient, which is 1.2 times that of ordinary pavement. The water permeability test results confirm that APC can prevent water from penetrating into the road surface. In summary, APC improves the anti-icing performance of asphalt pavements and exhibits excellent anti-slip and waterproof properties.

The percentage of voids in mineral aggregates (VMA) is an important consideration in the design of asphalt mixtures. Accurate and precise prediction of VMA is critical in pavement engineering. This study reviewed and evaluated current VMA prediction methods. From the perspective of treating aggregate gradation, the methods were classified into four categories: the overall gradation prediction method (OGPM), gradual gradation prediction method (GGPM), indirect parameter prediction method (IPPM), and theoretical derivation method (TDM). Fifty-four groups of published test data from previous studies were used to evaluate the prediction results of the models, and the precision and accuracy of the prediction results were compared. From the perspective of the completeness of the modeling parameters and the theoretical foundation, the reasons for the differences in prediction results with different methods were analyzed. It was concluded that the TMD has a solid theoretical basis, especially the Yu method in TMD exhibited the best prediction precision and accuracy. Some modifications to the current methods were suggested, such as incorporating other factors affecting VMA and optimizing the particle shape indicators.

This paper aims to assess the durability of one-part geopolymer (OPG) pastes exposed to acidic environments. Two different acids (HCl and ${\mathrm{H}}_2{\mathrm{SO}}_4$) with different pH values (pH of 2, 4, and 6) were used to simulate the acidic environment in the current study. Acid resistance of the OPG paste activated by sodium hydroxide [NaOH (NH)] and sodium metasilicate [${\mathrm{Na}}_2{\mathrm{SiO}}_3$ (NS)], respectively, was assessed in terms of pH variation, mass change, visual appearance, deterioration depth, and compressive strength loss for varied immersion periods ($\sim 120\mathrm{days}$). The scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS) and mercury intrusion porosimetry (MIP) tests were employed to investigate the evolution of porosity, morphological change, and hydrate composition for the varied immersion times. The experimental results revealed that due to the formation of a dense structure, the NS-activated OPG paste had better resistance to the acid attack compared with the NH-activated paste. It was also found that the gypsum crystals formed in the sample immersed in ${\mathrm{H}}_2{\mathrm{SO}}_4$ solution could fill the open pores and adhere to the surface of the sample, which reduced the further acid attack to some extent. However, the expansion properties of gypsums would lead to a loss of mechanical performance at the later immersion period. Furthermore, higher porosity of the OPG paste developed as the pH value of the acid solution decreased, thereby inducing the loss of mass and compressive strength and the increase of deterioration depth. Finally, as the immersion age and acid concentration increased, decalcification in the sample tended to occur, which caused a greater loss of compressive strength and a higher porosity. The outcome of this study could provide guidance for the application of the novel material in acid soil layer improvements or acid-resistant geotechnical structures.

Styrene-butadiene-styrene-modified binders (SBS-MBs) are susceptible to property erosion even in the absence of air at elevated storage temperatures. The current study focused on monitoring the properties of SBS-MBs prepared using four different types of polymers: linear SBS (L-SBS), branched SBS (B-SBS), high vinyl SBS (HV-SBS), and diblock SBS (DB-SB). The four modified binders were stored at 180°C and 150°C for 14 days. The result shows significant property deterioration in L-SBS and B-SBS polymer-modified binders during storage at 180°C, while only marginal erosion in HV-SBS and DB-SB modified binders due to the higher vinyl content in the polymer structure. As the C═C bond in the butadiene segments is highly susceptible to thermal degradation, shifting the C═C bond to the side group protects the primary polymer chain from thermal scission during storage at 180°C. Asphalt mixes were prepared using unstored and stored modified binders, and their performance was scrutinized through Marshall stability, resilient modulus, water susceptibility, permanent deformation, and fatigue cracking behavior. The results showed that, similar to the deterioration in binder properties, asphalt mixes prepared with stored (7 days at 180°C) L-SBS and B-SBS modified binders exhibited a substantial drop in performance, while HV-SBS and DB-SB polymer-modified binders demonstrated only marginal property reduction ($\approx 5\%–10\%$). Moreover, irrespective of different SBS molecular structures, the performance properties of the binders were stable due to storage at 150°C. Therefore, in actual practice, if an SBS polymer with a vinyl content $\ge 30\%$ is used, no significant deterioration in binder properties due to thermal degradation should occur when stored for 7 days at 180°C.

Physicochemical and microstructural evolution in lime-treated soil subjected to successive wetting and drying (W-D) cycles was investigated, and the relevance of the laboratory-implemented testing condition with in situ conditions was discussed. Lime-treated soils were exposed to 17 W-D cycles using different testing conditions. Two laboratory testing conditions were operated at laboratory temperature, consisting of W-D duration representing the saturation level close to the one experienced in the in situ soil during rainy and drought periods. The results obtained were interpreted in terms of those obtained using a reference procedure from current standards, which involved oven-drying specimens at 71°C. Drying of lime-treated soil at 71°C reduced the water content from about 20% to 0.85%. This has led to greater contact between soil particles, thus increasing the suction from about 143.5 to 270 MPa. Such a phenomenon increased the unconfined compressive strength (UCS) of the oven-dried soil up to about three times compared with the air-dried specimen, although the available cementitious bonding, reflected by the presence of pores smaller than 3,000 Å, was comparatively low in the former compared with the latter. Percentage leaching of calcium components with respect to the initial calcium content of the soil was significantly low during W-D cycles due to greater exposure of only the outer part of the compacted soil structure during wetting. However, the leaching was comparatively higher in the oven-dried soil. The implemented wetting duration and drying temperature influenced the wetting front velocity of water, which significantly affects the duration taken by infiltered water to invade the core of an earthen structure, and hence its durability.

The longitudinal joint is one of the most crucial parts of asphalt pavement construction becuase several types of distress of the pavement can occur if the target density does not meet at the joint. A low density of asphalt pavement causes the pavement at the joint to be more exposed to water penetration, accelerating the rate of deterioration. To address this issue, asphalt agencies use various construction techniques and innovative materials to improve the joint’s performance. Void-reducing asphalt membrane (VRAM) is an innovative adhesive liquid that consists of an asphalt binder, an elastomeric polymer, and a wax modifier. In this study, field cores were collected from an Indiana state road to evaluate the VRAM and tack coat performance at the joint. Semicircular bending Illinois flexibility index (SCB-IFIT) and modified pulloff strength tests were performed to investigate the fatigue resistance and bond strength of VRAM and tack coat at the joint. Digital image analysis confirms that VRAM can migrate up to 15.88 mm ($5/8\mathrm{in.}$) from the interface. In addition, the pulloff strength test reveals that the interface bonding of the pavement containing VRAM is less than the pavement containing tack coat at low and intermediate temperatures. One of the key findings from the SCB-IFIT test is that the flexibility index of VRAM-containing pavement is around eight times higher than tack coat–containing pavement. Moreover, the fatigue cracking resistance of the VRAM-containing pavement is higher than the laboratory-prepared asphalt mixtures with PG 64-22, PG 70-22, and PG 76-22.

Bond behavior is the mutual effect and the force transmission between concrete and reinforcing bar that directly influence the behavior of reinforced concrete structures. Considering the silica fume (SF) and marble waste powder (MWP) could enhance the concrete matrix and improve its adherence, the bond-slip behavior of corroded reinforcing bar in concrete containing SF and MWP as ordinary portland cement (OPC) is examined in this work. Three of 16 concrete mixes were selected for this investigation: one control mix, a second mix containing 10% SF and 5% MWP as OPC replacements, and the third containing 10% SF and 20% MWP as OPC replacements. The pullout test was applied to the specimens with 0%, 2%, 5%, and 10% corroded reinforcement. According to the results of specimens with uncorroded reinforcement, replacing 10% of cement by SF and 5% or 20% by MWP, the bond strength between concrete and reinforcing bar increased by 27% and 13%, respectively, compared to that of the control specimens. Also, the samples containing SF and MWP showed higher corrosion resistance and their bond strength’s loss due to the corrosion of reinforcing bars was less than the control samples. The results also indicate that bond stress at low corrosion (2%) levels is partially increased because of the friction resulting from the accumulation of corrosion products on reinforcement’s surface. However, for higher corrosion levels (5% and 10%), the bond strength decreases. By comparing the two diameters of reinforcing bars (12 and 16 mm), it was recognized that the reduction of bond strength due to the corrosion is more severe in the reinforcements with greater diameters.

The increased temperature at the early state of curing affects the fatigue properties of pavement base materials. The fatigue properties of stabilized pavement bases and subbases govern the performance and service life of pavement structures. This research study utilized natural rubber latex (NRL) to enhance the tensile fatigue properties of cement-stabilized base materials at various temperatures. The effects of influence factors such as cement content (3%, 5%, and 7%), NRL replacement ratio (0%, 10%, 15%, 20%, 25%, and 30%), and temperature (25°C, 40°C, and 60°C) on indirect tensile strength (ITS), indirect tensile resilient modulus (IT $M_r$), and indirect tensile fatigue life (ITFL) were studied in this research. NRL replacement was found to improve the UCS, ITS, IT $M_r$, and ITFL of cement (C)-stabilized soil up to the highest values at the optimum NRL replacement ratios, which were 20%, 15%, and 10% for cement contents of 3%, 5%, and 7%, respectively. The cement-NRL (C-NRL)-stabilized samples were found to have superior ITS, IT $M_r$, and ITFL values compared with C-stabilized samples for the same cement content but had the same rate of reduction in ITS due to the raised temperature. For the NRL replacement ratio on the dry side of optimum, the C-NRL-stabilized samples had lower rate of IT $M_r$ reduction than the C-stabilized samples, although they had the same ITS due to the higher toughness. Therefore, the rate of ITFL reduction of C-NRL-stabilized samples was lower than that of the C-stabilized samples. It was proven in this research that the NRL replacement could reduce the thickness (superior IT $M_r$) of a cement-NRL-stabilized base course for a given traffic volume and service life, and therefore the construction (material and operation) cost by 17.26% benchmarked to a C-stabilized base course. Finally, the cost-effective design method for C-NRL-stabilized bases course was proposed, which will promote the use of NRL as an alternative green additive instead of synthetic polymer.

This study aims to examine the chloride penetration resistance, chloride binding capacity, electrical resistivity, and compressive strength of multibinder systems, including ordinary portland cement (OPC), calcined kaolinite clay (C), fly ash (F), and limestone powder (L). At all tested ages, the results revealed that calcined kaolinite clay concrete had better chloride penetration resistance and chloride binding ability compared with the control OPC concrete. Moreover, at all tested ages, calcined kaolinite clay concrete had greater compressive strength compared with the control OPC concrete and fly ash concrete. At the curing age of 91 days, improved performance of fly ash concrete was observed. The overall performance of the ternary binder system of cement-fly ash-calcined kaolinite clay surpassed that of the binary binder systems. Among the tested combinations of binders, the ternary binder C30F15 (55% $\mathrm{OPC}+30\%\mathrm{C}+15\%$ F) demonstrated the best overall performance. The test results also indicate that fly ash can be beneficially integrated into the cement-calcined kaolinite clay binder system to obtain a ternary binder system, which is better than the ternary binder system of cement, calcined kaolinite clay, and limestone powder, at both tested early and later ages.

Due to the high resource requirements for specimen preparation and testing equipment, the direct tensile test method is seldom used to study the cracking behavior of asphalt mixture at low temperatures. In this study, three asphalt mixtures were prepared in which all of the basalt or part of the basalt and basalt aggregate was replaced by steel slag. Through the direct tensile creep test and direct tensile relaxation tests including the measurement of creep rate, cumulative strain change rate, and relaxation time, the variation law of rheological properties of low-temperature steel slag asphalt mixture was analyzed and the variation law of viscoelastic properties was explored. Meanwhile, based on the traditional viscoelastic constitutive model, the creep compliance and relaxation modulus were fitted. The mechanical response of the transformation from creep compliance to relaxation modulus of steel slag asphalt mixture was analyzed by a numerical method. The results show that, with the decrease of temperature, the creep rate ${\epsilon }_s$ and cumulative strain change rate of the three asphalt mixtures gradually decline, and the relaxation time gradually increases. In particular, when the temperature was reduced from $-20°\mathrm{C}$ to $-30°\mathrm{C}$, the cumulative strain change rate of all three asphalt mixtures reached the minimum, which was less than 10%. Moreover, none of them relax to 75% ${\sigma }_0$ within 3,600 s at $-30°\mathrm{C}$. The mixture specimens with steel slag replacing all basalt exhibited the best low-temperature deformation adaptation performance under different temperature conditions. Mixture specimens with basalt as aggregate have the worst low-temperature deformation adaptation performance. The relaxation modulus obtained by the measurement of creep compliance is similar to that obtained by testing, and the relaxation modulus calculated through the direct tensile test is more accurate.

The original red clay can be used as a construction material after being stabilized. The use of the Consolid system for reinforcement has the advantages of being green, convenient, and fast. The improvement of the Consolid system on the mechanical properties and durability performance of red clay was investigated and the enhancement mechanism was revealed in terms of micromorphology, pore structure, soil-water characteristics, and water repellency. The effects were also compared with those of traditional lime and cement stabilization. The results show that the Consolid system can significantly enhance the mechanical properties and durability of red clay, far exceeding lime stabilization and approaching or slightly exceeding cement stabilization. The Consolid system improves the mechanical properties of the soil by increasing the attraction and bonding between the clay particles, leading to agglomeration of soil particles and the formation of flocculent structures. In addition, the components of the Consolid system can further fill the pores, increasing the overall compactness and reducing the pore volume, so that the suction of the soil matrix is reduced and the water absorption capacity is weakened. This is demonstrated by the fact that the original structure can remain undamaged after being washed with water.

This study aimed to assess the suitability of lime treatment for use in dikes in the Netherlands. The effect of this technique on the behavior of a Dutch clay was addressed by comparing the detailed response of lime-treated and natural samples at different lime contents (1.25% and 2.25%) and curing periods. A series of laboratory tests consisting of index classification, constant rate of strain, and triaxial and hole erosion tests were performed. The results demonstrated that lime treatment altered the soil response. Differences were observed in the physical, compressibility, strength, and erodibility properties. It was found that lime improved considerably the resistance to compression and erosion, but the effect on hydraulic conductivity was limited. The triaxial test results showed that lime treatment was particularly effective at low stress ($<25\mathrm{kPa}$) and low strain levels ($<10\%$). During shearing, lime-treated samples exhibited dilative tendencies and enhanced effective strength properties until a stress-strain state was reached that was believed to be related to the breakage of the bonding structure of the sample. The findings of this study demonstrate that the merits of lime treatment can be of particular benefit in dike applications, particularly when the focus is on improving soil erosion resistance.

Curing temperature and curing mode could affect the mechanical properties of cement-stabilized soil, which is of both scientific and practical importance for cement mixing performance. This paper aims to present the strength development of cemented soil cured in a water and 95% relative humidity (RH) environment with a series of curing temperatures ($T$) based on laboratory tests and model characterization. The base soil was low-liquid-limit organic clay (OL) classified by the Unified Soil Classification System (USCS). Unconfined compression (UC) testing was conducted in this study, and a combination of Fourier transform infrared spectroscopy (FTIR), scanning electronic microscopy (SEM), and energy-dispersive spectroscopy (EDS) was used to further investigate the microcharacteristics of the stabilized specimens. Results showed that the unconfined compressive strength (UCS or $q_u$) of cemented soil increased with the increment of temperatures $T$ both at early (7 days) and long-term (90 days) curing periods. Nevertheless, the cemented soil cured in 95% RH mode constantly achieved higher strength compared with that cured in water. The $q_u$ of 28 and 90 days gained in 95% RH mode can be taken as 1.2–1.5 times and 1.4–2.0 times of that in the water bath. In addition, the crossover effect was observed in samples cured in water when $T$ reached 80°C, which was verified by the decalcification of calcium silicate hydrates (C-S-H) formed inside cemented soil through microtests. Based on the observations, a modified hyperbolic model characterizing the strength development of samples was proposed, in which the effects of curing temperature and curing time could both be considered regardless of the crossover effect. Moreover, the failure pattern of samples under different curing conditions was also analyzed. The findings presented in the current study are expected to provide insights and references for cement mixing engineering design.

For long-term hot and rainy climate areas, the moisture susceptibility of asphalt pavement is the most serious issue during the service of pavement, which primarily depends on the adhesion between asphalt binder and aggregate. To explore the adhesion between different asphalt binders and aggregates, two types of asphalt binders and three kinds of aggregates were selected in this study. The water boiling test was modified by increasing the boiling time, quantifying the stripping rate and increasing the sample weight. The contact angle test and the energy dispersive spectrometer test were also conducted. The results showed that longer boiling time, longer aging time for asphalt binder, and higher $Si$ content in aggregates will increase the stripping rate between the asphalt binder and the aggregate. For base asphalt, the stripping rate of sandstone is about 35.76% at long-term aging. The stripping rate calculated by boiling loose mixture for 30 min has the good correlation with the silicon content in the aggregates, with R-square about 98.77%, which indicates a good indicator to evaluate the asphalt-aggregate adhesion.

Shear failure is a major distress in steel bridge deck pavement (SBDP). To investigate the shear behavior of steel-asphalt interface (SAI), experimental study and numerical analysis were proposed and performed. First, the direct shear tests at two temperatures of 30°C and 60°C were carried out to provide verification for numerical analysis. Second, the virtual tests were conducted under the same condition as laboratory test using discrete element (DE) method to evaluate the shear behavior of SAI and analyze the influence of temperature on the development of interlaminar mesocracks. Third, factors affecting the interlaminar mesomechanical properties, including interface roughness and interfacial bubbles, were proposed and analyzed at 30°C. Results show that with the increase of shear displacement lots of interlaminar mesocracks occur rapidly with the decreasing of shear stress. The mesocracks occur more easily under high temperature. The shear strength of SAI increases at first and then decreases with the increase of interface roughness and decreases with the increase of interfacial bubbles.

This study investigated the different geotechnical characteristics of soil stabilization with the addition of lime and rice husk ash (RHA) in varying amounts (3%, 5%, 7%, and 9% lime, and 4%, 8%, 12%, and 16% RHA). A series of compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), pH, and X-ray diffraction (XRD) tests were performed in the laboratory to assess the impact of the considered admixtures on the stabilized soil parameters. This study also proposes the successful integration of an artificial neural network (ANN) and a Gaussian process regression (GPR) with the experimental UCS observations. The lime concentration, RHA concentration, and curing period were considered as the input parameters, and UCS was considered as the response. The proposed framework was extended to analyze the compressive behavior of treated soil on the minuscule level. Such coupled machine learning-based experimental investigation can provide deep insight into the soil behavior which otherwise would have remained unexplored due to the prohibitive nature of performing laboratory experiments on a large scale. The findings demonstrated the effectiveness of RHA in addition to lime in stabilizing the considered expansive soil. With the addition of lime and RHA mix, the UCS and CBR values of the treated soil increased significantly.

To explore the effect of waterborne polyurethane (WPU) on the performance of styrene-butadiene rubber (SBR) emulsified asphalt and broaden the application range of polymer-modified emulsified asphalt, WPU-SBR-modified emulsified asphalt with 0%, 3%, 6%, 9%, and 12% WPU was prepared. The penetration, softening point, ductility, and storage stability tests were used to explore the effect of different contents of WPU on composite-modified emulsified asphalt. Meanwhile, the rheological properties of five modified emulsified asphalts were analyzed by temperature scanning test, multiple stress creep recovery test, and low-temperature bending creep test. The results show that the addition of WPU improved the performance of SBR emulsified asphalt, and the improvement effect varied with the addition amount. With the increase of WPU content, the penetration and unrecoverable creep compliance $J_{nr}$ of WPU-SBR-modified emulsified asphalt gradually decreased, and the softening point, rutting factor $G^{*}/\sin \delta$, and creep recovery rate $R$ gradually increased, indicating that the high-temperature stability of modified emulsified asphalt was enhanced, and when the WPU content was 9%, the best improvement effect was obtained. However, excessive content of WPU will deteriorate the low-temperature performance of WPU-SBR-modified emulsified asphalt, and thus the content of WPU should be appropriately selected in practical engineering applications.

In fiber-reinforced cementitious composites, the fiber/matrix interfacial bonding is a governing factor for bridging cracks, load transfer, and toughening mechanisms. Basalt fiber pellets (BFP) are a novel form of macrofibers consisting of basalt fiber strands encapsulated by a polymeric resin, with textured microgrooves, which can be used to produce high-performance fiber-reinforced cementitious composites (HPFRCC). Hence, the current study focused on the synergetic evaluation of the flexural performance and single pellet pull-out of BFP in homogenized nano-modified [nano-silica (NS); nano-crystalline cellulose (NCC)] cementitious matrices, without/with micro [polyvinyl alcohol fibers (PVA)], or nano-fibers [nano-fibrillated cellulose (NFC)]. Integrated experimental and modeling studies were conducted to evaluate the effect of BFP interfacial bonding with various nano-modified cementitious matrices. Key results showed that NS-modified matrices led to improvement by 17% and 5%, respectively, in terms of bonding strength with BFP and debonding energy, compared with matrices comprising NCC. Reduction of BFP interfacial bond strength and debonding energy by 11% and 10% was observed for cementitious matrices comprising NCC and reinforced with NFC, relative to mixture G-NCC. Conversely, using PVA fibers in matrices comprising NS led to noticeable enhancement of bonding with BFP (highest bonding strength and debonding energy), which suggests their promising potential for field applications requiring HPFRCC.

To study the influence of temperature and reclaimed asphalt pavement (RAP) content (0%, 30%, 50%, and 70%) on the high-temperature performance and anti-reflection cracking performance of warm-mix recycled asphalt mixture, triaxial repeated creep tests and overlay tests (OT) based on digital image correlation technology (DIC) were used to analyze the high temperature and anti-reflection cracking performance of recycled asphalt mixtures. Based on the improved Burgers model, a permanent deformation (PD) model was established to evaluate the high-temperature performance of recycled asphalt mixtures. The anti-reflection cracking performance of recycled asphalt was quantitatively analyzed from macro and meso perspectives by using a macro index (load loss rate) and a meso index (vertical strain density ${\mathrm{D}}_{\mathrm{E}}$). In addition, a reflection cracking damage model was developed by cumulative load loss rate relative change rate, and the fractal characteristics of reflection cracks were studied according to the fractal theory. The results show that with an increase in RAP content, the anti-deformation ability of a recycled asphalt mixture is enhanced, and the anti-reflection cracking performance becomes worse. However, with an increase in temperature, the anti-deformation ability of recycled asphalt mixture is weakened, and the anti-reflection cracking performance is enhanced. A PD mechanical model can well describe the high-temperature deformation resistance of recycled asphalt mixtures. The established reflection cracking damage model has high fitting accuracy and accurately describes the reflection cracking damage evolution process of recycled asphalt mixture. In addition, the analysis of the fractal characteristics of reflection cracks shows that the reflection cracks of a recycled asphalt mixture have fractal characteristics of statistical significance. DIC technology can be used to evaluate the anti-reflection cracking performance of recycled asphalt mixtures qualitatively and quantitatively from the mesoscopic perspective, which makes up for the current deficiency in macroscopic evaluation.

This study investigated the effects of using silver nanoparticles (Ag NPs) on the microstructure and mechanical properties of cementitious composites. Ag NPs were synthesized with an ultrasonic irradiation method using konjac gum–polyethylene glycol (KG/PEG) and locust gum–polyethylene glycol (LG/PEG) and characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), high-resolution transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) analyses. To identify the effect of the Ag NPs on the mechanical properties of mortar, four different cement mortar mixtures were prepared with varying percentages of Ag NPs (0%, 0.5%, 1%, 2%, 3%, 4%, and 5% by weight). Clear improvements were observed in the 7- and 28-day compressive and flexural strengths of nanocomposites with Ag NPs. A thorough microstructure investigation using SEM, EDS, XRD, and thermogravimetric analysis (TGA) was presented, and the relationship between microstructure and the mechanical properties of cementitious composites including Ag NPs was discussed.

With the increasing requirements of shield tunnel construction, the demand for the development and application of high-performance lining segments continues to rise. During the manufacture and forming process of high-performance composite segments, large-scale shear key welding is an important factor affecting the mechanical performance of segments. This paper aims to study the effect of shear key welding on the mechanical properties of composite segments. In this study, the algorithm transformation of the welding heat source model was first conducted. Then, a comprehensive analysis of the shear key was presented using the finite-element method, and a welding experiment was conducted to verify the reliability of the adopted numerical model. It was found that the temperature of the welding point changes with the movement of the heat source in the shear key welding, in which the maximum temperature peak can reach 2,236 K. The welding residual stress was mainly concentrated in the range of about 30 mm from the welding point, and then the value decreased gradually. In the welding of multiple shear keys, the residual stress at the central axis of adjacent shear keys will be superimposed, and the mutual influence of adjacent shear keys during welding should be avoided. Through a key-panel welding experiment, the numerical simulation results of the shear key-panel model were verified. The panel deformation at the edge position was also affected by the boundary conditions.

To study the effects of sulfate drying and wetting cycles on the bond performance between fiber-reinforced polymer (FRP) and clay brick, a test was performed in this study by simulating the sulfate environment through the cyclic accelerated sulfate drying and wetting cycles. Results showed that the failure mode of the carbon fibre-reinforced polymer (CFRP) and clay brick interface was greatly affected by the sulfate wetting and drying cycles. Furthermore, the interfacial bonding properties (including ultimate bearing capacity and peak shear stress) increased slightly at the beginning and then showed a rapid decline. Based on the experiment and the existing interface theory, a bond–slip model that considers the cycle times is proposed. After comparing the predicted data with the experimental data, the results showed that the model can well reflect the degradation law of the interface bonding performance under the actions of sulfate drying and wetting cycles.

The backfill mining method is an effective method to control ground pressure and prevent surface subsidence in the process of underground resources exploitation. Tailings backfill not only relieves the pressure of tailings reservoir but also protects the environment. However, traditional Portland cement as the cementing material results in groundwater pollution. In addition, the production process of Portland cement consumes a significant amount of mineral resources and causes air pollution. Therefore, a cementation method for tailings based on microbially induced calcite precipitation (MICP) is proposed in this paper. Tailings cementation by the MICP technology with facultative anaerobic bacteria (Castellaniella denitrificans) can overcome the problems of MICP technology based on urea hydrolysis of aerobic bacteria (Sporosarcina pasteurii), which cannot be applied in anoxic or anaerobic environment. In addition, in view of the small amount and poor uniformity of calcium carbonate precipitation in the specimens cemented by facultative anaerobic bacteria alone, a mixture of facultative anaerobic bacteria and aerobic bacteria was adopted for tailings cementation in this study. The results showed that, with increasing Castellaniella denitrificans concentration, the cementation effect improved. The tailings sand was cemented into a compact specimen when the ${\mathrm{OD}}_{600}$ of the bacterial solution was one and the uniaxial compressive strength could reach 987.93 kPa. Compared to cementation induced by a single strain, the amount of calcite precipitation induced by the mixed bacteria increased from 2.54% to 3.59%, the uniaxial compressive strength was enhanced by 29.9%, and the shear strength increased by 24.4%. This study indicates that MICP technology with facultative anaerobic bacteria has great potential in tailings cementation, and it can provide a solution to replace cement as the cementing material for tailings.

This study investigated the sensitivity of the Illinois flexibility index test (I-FIT) and the disc-shaped compact tension [DC(T)] test with respect to oxidative aging and testing temperature. For this purpose, five plant-produced surface course asphalt mixtures covering a wide range of performance-graded asphalt cement (PGAC) were utilized. As for oxidative aging sensitivity, two methods of forced-draft oven aging, at 85°C for 120 h and at 95°C for 72 h, were utilized. Furthermore, to measure the temperature sensitivity, the I-FIT test was conducted at 23°C, 24°C, 25°C and PGAC intermediate temperatures, while the DC(T) test was conducted at $-18°\mathrm{C}$, $-24°\mathrm{C}$, and $-30°\mathrm{C}$. In this study, the analysis of the I-FIT test results from oxidative aging showed that both methods of aging caused a reduction in flexibility index values of asphalt mixtures, and the flexibility index values after two methods of aging were statistically comparable. Moreover, even though oxidative aging caused a reduction in DC(T) fracture energies of asphalt mixtures containing hard PGAC, the fracture energies before and after the two methods of aging were statistically similar for asphalt mixtures. The analysis of the I-FIT test results from testing temperature sensitivity showed that the flexibility index values of asphalt mixtures containing hard PGAC at 23°C were statistically dissimilar to those at 25°C when the testing temperature dropped from 25°C to 23°C. Consequently, regarding the I-FIT test, the comparable flexibility index values from the two methods of oxidative aging suggested utilization of forced-draft oven aging at 95°C for 72 h as a less time-consuming method compared to forced-draft oven aging at 85°C for 120 h to evaluate the effect of oxidative aging. In addition, the variability in flexibility index values due to the drop in testing temperature suggested exercising caution when conducting the test on asphalt mixtures containing hard PGAC.

Wax-based Sasobit synthetic hard wax can be designed for producing asphalt with less energy consumption and lower carbon emissions in the pavement industry. This study investigated the effectiveness of Sasobit synthetic hard wax on microscopic properties, fatigue-fracture behavior, and healing potential of polymer-modified asphalt (PMA) from two perspectives: asphalt binder and fine aggregate matrix (FAM). First, microscopic morphology, dispersion mechanism, and thermal stability of styrene-butadiene-styrene (SBS)– and crumb rubber (CR)–modified asphalt binders under the influence of Sasobit synthetic hard wax were characterized. Second, linear viscoelastic properties and evolution law of fatigue life of Sasobit synthetic hard wax/polymer-modified asphalt binders and FAM with and without healing interval were assessed under the framework of the simplified viscoelastic continuum damage (S-VECD) model. Third, the correlation between properties of the modified asphalt binder and FAM was statistically analyzed by radar chart. Thermodynamic analysis indicated that Sasobit synthetic hard wax enhanced the thermal stability of PMA but slightly reduced the low-temperature performance. Morphological observations showed that Sasobit synthetic hard wax had limited effectiveness on the dispersion of the polymer particles in PMA. Dynamic modulus master curves and fatigue and healing tests demonstrated that Sasobit synthetic hard wax contributes to the stiffness, fatigue resistance, and self-healing capability of the asphalt binder and mixture. Finally, statistical analysis revealed that the asphalt binder performance lacked a close correlation with the FAM owing to the complex composition system.

The necessity of low-cost building and mortar-free wall construction (dry stack masonry) led to the development of a newly proposed block called a fly ash-lime-slag dry stack block (FaL-S DSB) with ingredients from industrial waste materials (fly ash, lime, and ground-granulated blast-furnace slag). The perforations in the proposed DSB accommodate the connecting element between the courses of masonry and headed to mortar-free construction. The scaled FaL-S DSB was produced with five different mix proportions (L10S20, L15S20, L15S25, L20S20, L20S25) by pressing method. The experimental studies were carried out to examine the physical, mechanical, and durability properties and also analyzed the embodied energy and carbon emissions of FaL-S DSB. The compressive strengths of a prism and wall panel made of FaL-S DSB were also studied. Out of five mixes, L20S25 resulted in higher dry and wet compressive strength values of 11.50 and 7.89 MPa, respectively. The values were compared with commercially available red brick (RB). The FaL-S DSB was also observed for loss in weight and loss in strength by immersing in acid (${\mathrm{H}}_2{\mathrm{SO}}_4$) for 1, 3, 7, 28, 56, and 90 days. The L20S25 mix FaL-S DSB exhibited minimum loss in weight (5.69%) and loss in strength (11.50%) compared to other proportions.

To generate sustainable mortars, this study investigated the impacts of adding two wastes into portland cement mortar: polyurethane powder waste (PU), and foundry exhaust sand (FES). The tests were carried out utilizing a response surface methodology (RSM) configuration with four different manufacturing variables: sand to cement ratio, coarse sand content (CS), FES, and PU replacing natural sand (NS). Compressive strength, modulus of elasticity, void index, and water absorption (Wa) all had substantial fitting values in the data. Furthermore, the experimental findings show that the adopted model is capable of accurately predicting the outcomes, and an optimized mortar combination was discovered and is presented.

Pumice concrete is a lightweight porous building material. Under the continuous low temperature in permafrost regions, the interstitial water of concrete is frozen, which can improve its mechanical properties. In this research, the interstitial water freezing law of pumice concrete is obtained by nuclear magnetic resonance, the frozen-heave stress and compressive strength of pumice concrete under a low-temperature environment are tested, and the relationship among the three is studied. A compressive strength model for pumice concrete considering frost-heave stress is also established using parallel bar theory. Finally, the hydrothermal coupling frost-heave model of concrete is established. Results showed that in the rapid change stage of 0°C to $-10°\mathrm{C}$, the interstitial water with the largest proportion of medium pores (0.1–1 μm) in this temperature range is rapidly frozen and expanded, which makes the frost-heave stress and compressive strength increase rapidly. The frost-heave stress caused by pore-water freezing can be regarded as prestressing force against external load, which is the main reason for the increase in low-temperature compressive strength of pumice concrete. The maximum error between the calculated value of the parallel bar compressive strength model and the experimental value was 7.42%, indicating that the model has good accuracy and certain rationality. The hydrothermal coupling model can reflect the frost-heave process of concrete, and the error between the simulated and experimental values of frost heaving strain was small, which proves that the model has high accuracy.

The amount of high-performance concrete (HPC) in construction engineering is growing at a predictable high rate following rapid urban development. However, the utilization of HPC waste as secondary building materials has received little attention until now because previous investigations have focused on the reclamation of ordinary concrete waste. Therefore, this work studied the characterization of mortar containing high-quality recycled aggregate (HRA) and high-quality recycled powder (HRP), both sourced from HPC waste. HRP contains some active components, and the pore structure of paste incorporated with HRP is finer than that of paste containing ordinary recycled powder. Incorporating HRP in paste shortens the setting time and improves the fluidity, and mixing HRA with coarse surface benefits the performance of interfacial transition zone. Incorporating HRA and HRP can both reduce the drying shrinkage, and the maximum shrinkage value of HRA mixed mortar is obviously lower than that of ordinary recycled-aggregate mixed mortar. The mechanical strength first increases and then drops with the HRA incorporation. The incorporated HRP reduces the mechanical strength, but decreasing HRP particle size enhances the mechanical strength of mortar. The water absorption of mortar increases as HRA or HRP is incorporated, but decreasing HRP particle size reduces the water absorption of HRP-incorporated mortar. The mortar with both HRA and HRP has a distinct lower water absorption than the mortar with both ordinary recycled aggregate and powder. High-quality recycled mortar owning good performance can be made by intermixing a suitable amount of HRA and HRP.

The use of nanomaterials has brought about a huge revolution in the development of various industries. Moreover, in the pavement industry, researchers have been applying nanomaterials for many years due to their unique properties to enhance the features of asphalt mixtures and increase their resistance to various failures. In this study, nanographene oxide (GO) has been used in the amount of 0.2, 0.5, and 0.8 percent of consumed bitumen to improve the low-temperature cracking resistance and the high-temperature rutting resistance of hot-mix asphalt (HMA). For this purpose, to examine the impact of this material on the HMA, the semicircular bending (SCB) fracture test and Hamburg wheel tracking (HWT) test were applied. In addition, conventional bitumen tests were performed to investigate the impact of nanoGO on virgin bitumen in this study. The outcomes of conventional bitumen experiments displayed that the addition of nanoGO to pure bitumen augments viscosity, specific gravity, and softening point and reduces the penetration and ductility of pure bitumen. Furthermore, outcomes of the SCB fracture test indicated that nanoGO enhances the stress intensity factor (SIF) of the asphalt mixture and improves the low-temperature cracking resistance of asphalt specimens. Moreover, the addition of nanoGO to the asphalt mixture increased rutting resistance and decreased rutting depth. In addition, the results of the ANCOVA statistical analysis demonstrated the significant effect of this nanomaterial on the improvement of the low-temperature cracking resistance and the rutting resistance of HMA.

The cumulative damage to rock and soil mass caused by blasting in tunnel, highway, hydropower, and other projects is very complex, but the process of damage evolution is still unclear. This study took Zhujiapo mining area limestone as the research object and analyzed the change in its strength and mechanical parameters with periodic blasting loads. Combined with damage mechanics theory and microcrack propagation zone theory, a micromechanics constitutive model considering cumulative damage evolution was developed. The results show that (1) periodic blasting loads have a continuous cumulative effect on microcrystalline limestone, the peak strength and elastic modulus of which decrease exponentially with increasing blasting cycles; (2) periodic blasting loads cause crystal fractures, microcrack initiation, and propagation; and (3) the micromechanics damage constitutive model considering confining pressure and periodic blasting loads well describes the micromechanics behavior of microcrystalline limestone in the Zhujiapo mining area. The research results provide a theoretical reference to the study of rock damage mechanical properties under periodic blasting loads.

Polyurethane mixtures (PUMs) have excellent deformation resistance and fatigue resistance. However, their inferior water stability and stripping resistance have been hindering their wider application. To better understand the critical factors to PUMs’ stripping resistance and water stability, we investigated the statistical relationships among the stripping resistance, splitting strength, water stability, binder-to-aggregate ratio (BAR), gradation type, and fine aggregate content (FAC). A series of tests, including direct tensile test, binder bond strength test, and water boiling test, were used to study the flexibility and adhesion strength of polyurethane (PU) binder. Three gradation types with different FACs were designed. Three types of tests, namely the Cantabro test, the splitting test, and the water stability test, were employed to study the effects of gradation type, FAC, and BAR on the performances of PUM. The significant factors to water stability and stripping resistance of PUM were identified using a mixed-effects regression model (MERM). The results showed that the unsolidified PU binder has high fluidity and low adhesion strength, and the solidified PU binder has excellent adhesion strength and low flexibility. Increasing the BAR and FAC improved the risk of the PUM specimen’s volume bulge. Dewatering of raw materials of PU binder and aggregates was beneficial to solve the bulging problem. The fine aggregate can prevent the PU binder from flowing away under the gravity action, resulting in the film thickness of the PU binder increasing and the enhancement of stripping resistance and water stability of PUM. The gradation type and FAC affected the failure mechanisms of the PUM specimen in the splitting test. The MERM results indicated that the BAR and FAC significantly affect the stripping resistance, splitting strength, and water stability.

The primary purpose of this study was to reveal the effect of aging and moisture on the failure behavior of asphalt binder–aggregate interfaces from thermodynamic properties and the molecular scale and to provide ideas for improving the service life and weather resistance of materials. A 12-component asphalt binder model, an oxidation-aged asphalt binder model, three types of aggregates (i.e., ${\mathrm{SiO}}_2$-, CaO-, and ${\mathrm{Al}}_2{\mathrm{O}}_3\text{-}\mathrm{based}$) models, and corresponding confined asphalt-aggregate models in dry or wet conditions were developed using Materials Studio version 2019 software. Thermodynamic parameters that characterize interfacial failure behavior, including surface free energy, cohesive work, and adhesion work between asphalt binder (unaged and aged samples) and aggregates were obtained by molecular dynamics simulations. A pull-off test was simulated using molecular dynamics to analyze asphalt-aggregate failure patterns and mechanisms. Five tensile rates were applied in tensile simulations of $\mathrm{asphalt}\text{-}{\mathrm{SiO}}_2$ aggregate, and bond strength at various temperatures was investigated. The findings suggested that oxidative aging reduces thermodynamic properties such as the surface free energy and cohesive energy of asphalt binders but enhances the potential and nonbond energy of asphalt binders. The ranking of the adhesion between unaged asphalt binder and various aggregates is as follows: ${\mathrm{SiO}}_2{>\mathrm{CaO}>\mathrm{Al}}_2{\mathrm{O}}_3$. Oxidative aging has a distinct influence on the adhesion properties of the aforementioned asphalt binder–aggregate interfaces. Furthermore, outcomes for debonding energy and energy ratio (ER) value in the asphalt-CaO aggregate system exhibited the best water stability. Increasing tensile rate caused the failure patterns of the asphalt-aggregate mixes to change from adhesive failure damage between asphalt and aggregate to cohesive failure within the asphalt binder. Temperature had a nonnegligible impact on bond strength at the asphalt-aggregate interface.

Abstract

The effects of cement dosage (percentage by dry soil weight) and initial moisture content ($w_{\mathrm{o}}$) on cement stabilized soft estuarine clay were investigated by effective integration of multi-quantitative analyses, including quantitative X-ray diffraction (XRD), thermalgravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) test and scanning electron microscopy (SEM) with image processing. These quantitative analyses are highly complementary, which greatly improved the scientificalness of this research. The results revealed that the strength development of cement stabilized soft estuarine clay with varying cement dosages, and initial moisture content was ascribed to the combined influence of both soil fabric improvement and cementation bonding enhancement. The increase of $w_{\mathrm{o}}$ resulted in larger clay particle spaces, which can counteract the enhancement of soil structure due to the rising hydration products. The hydration degrees of samples with fixed cement dosage but different $w_{\mathrm{o}}$ are quite similar, while clay particle spaces were enlarged with an increase of initial moisture content. Thus, the same quantity of hydration products may bind more soil particles when pores are small at lower $w_{\mathrm{o}}$, thus increasing unconfined compressive strength (UCS). Furthermore, BET and quantitative SEM results illustrate that hydration degree plays a dominant role in the development of intra-aggregate pores ($<0.2\mathrm{\mu m}$), while $w_{\mathrm{o}}$ affects inter-aggregate pores (0.2 μm–2 μm) more.

Practical Applications

Construction of buildings and infrastructure on marginal ground is becoming more common due to rapid urbanization and population growth. These phenomena has led to the utilization and development of coastal and estuarine plains surrounded by relatively softer and weaker soils that require improvement or strengthening before being constructed upon. One such ground improvement method is termed deep soil mixing (DSM), which involves mixing cement with the in situ weak soils to increase the soil strength so that the ground can sustain the weight of the buildings or infrastructure. This manuscript presents a novel interpretation based on the results from advanced laboratory tests to succinctly explain the complex chemical reactions that occur when cement is mixed with soft soils having varying characteristics. It is envisaged that this evidence-based explanation will help engineers and scientists bring to life land that was previously deemed unsuitable for construction.

This work investigated the feasibility of replacing quartz aggregates with discarded high-density polyethylene (HDPE) particles in a cementitious matrix for secondary structural applications in civil construction. A mixture design technique was used to assess the effect of the constituents on the physical-mechanical properties of composites, such as density, water absorption, flexural strength, compressive strength, and dynamic modulus. The aggregate/cement ratio ranged from 3.76 to 5.25, and the water/cement ratio was kept constant at 0.5, whereas a minimum of 30 vol% HDPE particles was considered in the system. The optimized responses and fractions were determined by considering five different scenarios through the statistical method desirability. The gradual replacement of quartz aggregates by HDPE led to a more porous material, increasing water absorption and reducing mechanical properties. However, these composites exhibited a less rigid characteristic, revealing a less brittle failure mode. Whereas the optimized density was obtained for the minimum matrix and maximum HDPE fractions, the optimal response for the mechanical properties and water absorption presented an opposite behavior, that is, maximum cement matrix fraction and minimum HDPE fraction. Multiobjective optimization proved to be a promising technique for identifying the optimal mix of recycled microconcrete for a given application.