Journal of Materials in Civil Engineering

Cold-mix asphalt (CMA) can be produced more sustainably by using byproducts as fillers instead of conventional materials such as cement. This study used a new filler of calcined eggshell powder (cESP)-activated ground granulated blast furnace slag (GGBFS) in CMA mixtures to improve performance and reduce curing time. The outcomes were compared with those of CMA mixtures comprising limestone and cement fillers and two hot-mix asphalt (HMA) mixtures with AC10 and AC20 asphalt binders. This study used indirect tensile strength, cracking tolerance, and rutting performance as basic performance measurements and used moisture loss, volumetric properties, and microstructural analysis to visualize the mechanism behind the strength development. The results reveal that cESP-activated GGBFS can improve the performance of CMA mixtures at both early and late ages, and performs comparably to cement filler CMA and conventional HMA mixtures for application in pavement structural layers. The hydration products were visualized using microstructural analysis in the cement and cESP-activated GGBFS CMA mixtures, which can enhance the bond strength in the mixtures. Hydration reaction and moisture loss together contributed to strength development in cement and cESP-activated GGBFS CMA mixtures. Conversely, strength improvement in limestone and pure GGBFS mixtures was entirely attributable to the loss of water by evaporation. Because GGBFS and eggshells are byproducts, utilizing them in CMA construction will be economically and environmentally advantageous, and lead to improved mechanical performance and a shorter curing time.

The utilization of reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA) in road infrastructure construction projects contributes significantly to the sustainable reduction of solid wastes being landfilled. This research aims to evaluate the mechanistic performance of asphalt concrete with RAP and RCA modified with natural hemp fiber (HF) reinforcement (HF-RAP-RCA-AC). The effect of influence factors, such as RAP/RCA ratio, HF length, and HF content, on the static and dynamic-mechanistic performance was evaluated. The static performance of HF-RAP-RCA-AC was assessed through the Marshall stability (MS), strength index (SI), and indirect tensile strength (ITS), while the dynamic performance was evaluated through the indirect tensile resilient modulus (IT ${\mathrm{M}}_{\mathrm{r}}$), indirect tensile fatigue life (ITFL), and rutting resistance tests. The HF-RAP-RCA-AC sample was found to have comparable static properties (MS and SI) to conventional asphalt concrete. The dynamic-mechanistic performance of HF-RAP-RCA-AC was however found to be significantly lower and hence HF-RAP-RCA-AC was found to be suitable for low-traffic roads. The improved ITS due to the addition of RCA and HF was found to influence the IT ${\mathrm{M}}_{\mathrm{r}}$ improvement in the linear relationship. The improved resilient properties contribute to the ITFL and rutting resistance improvement. The optimum mix was found to be at 0.05%HF content, for all HF lengths and RAP/RCA ratios. The potential of HF reinforcement on the material properties was positively impacted by increasing the RCA content. The proposed distress model based on the critical analysis of the cyclic test data of HF-RAP-RCA-AC was developed and was found to have the same logarithm relationship. The outcome of this research will encourage the application of HF-RAP-RCA-AC as a sustainable pavement material for low-volume roads.

The occurrence of cracking, loosening, and other distresses in asphalt pavements is closely related to the failure of asphalt–aggregate adhesion. Studying the effect of asphalt film thickness on asphalt–aggregate adhesion can facilitate an understanding of the mechanism of disease in asphalt pavements. To study the impact of asphalt film thickness on asphalt–aggregate adhesion, this study tested and evaluated the adhesion between asphalt and aggregates at different asphalt film thicknesses from a macromechanical perspective via pullout tests. In addition, based on the surface energy theory, the effects of different film thicknesses on the adhesion of asphalt–aggregate were analyzed from a surface mechanics perspective. Further, the aggregates were subjected to surface property testing to further investigate the differences between the surface mechanics and the macromechanics results. The results showed that for an asphalt film thickness of 400 μm, the failure energy density (FED) and cohesive work ($W_A$) of the asphalt exhibited the same trend, and certain properties of asphalt influenced its adhesion to the aggregate. For an asphalt film thickness of 25 μm, the FED and the asphalt adhesion work ($W_{as}$) exhibited the same trend, and the combined effect of the asphalt and slag properties influenced the adhesion of asphalt to steel slag. Moreover, with decreasing asphalt film thickness, the adhesion between asphalt and aggregates was reduced owing to the influencing factors of the asphalt, which can effectively reduce the influence of the aging effect on adhesion.

Abstract

This study aimed to address pavement cracking caused by the high swell-shrink behavior of expansive soils, resulting from fluctuations in moisture content and high clay content, by using an eco-friendly nontraditional additive: sugarcane bagasse ash (SCBA) based geopolymer. The study involved a dry mixture of soil and SCBA, mixed with a liquid alkaline activator consisting of a fixed $70:30$ weight ratio of 1 M sodium metasilicate and 10M sodium hydroxide. By varying the SCBA content from 5% to 30% by weight of dry soil and keeping the amount of liquid alkaline activator constant, the volume change behavior of the expansive soil was observed. The swelling and compressibility characteristics of treated samples were tested using an oedometer test, while the shrinkage and plasticity characteristics were observed through consistency limit tests after 1, 3, 7, and 14 days of curing. X-ray diffraction and field emission scanning electron microscope tests were utilized for chemical composition and microstructural analysis. The results showed a substantial decrease in the swelling pressure, shrinkage limit, compressibility index, and plasticity index of treated samples by 100%, 100%, 90%, and 100%, respectively. The study revealed that the aluminosilicates in SCBA react with the alkaline solution to form cementitious gels, which bind the soil particles and encapsulate them, thereby stabilizing the expansive soil for volume change. These findings have significant implications for the advancement of knowledge in soil stabilization based on geopolymers, presenting an alternative solution for stabilizing pavement subgrade.

Practical Applications

Roads are crucial infrastructure that require a stable foundation. Expansive soils can pose a significant challenge in road construction, leading to road damage and increased maintenance costs due to its swelling and shrinkage behavior when moisture is added or removed (i.e., in the rainy or dry season especially). Also, the foundation of structures is critical in ensuring the safety and stability of buildings. Expansive soils can lead to cracks or structural failures. This behavior can be controlled by adding some stabilizing material. One such material used in this study is SCBA-based geopolymer. It can provide a cost-effective solution to stabilize expansive soils and enhance the road’s durability by stabilizing its volume change behavior, enhancing its strength and the overall stability of the structure. The use of SCBA geopolymer has practical applications in a range of geotechnical applications such as road construction, airport runways, industrial parks, parking lots, and sports fields. By using this solution, we can improve the stability and durability of construction projects, reduce maintenance costs, and enhance safety.

As a pozzolan, waste glass powder (WGP) can improve the mechanical properties and durability of concrete, especially at a later age. However, the modification mechanisms should be fully understood and discussed. One of the effective approaches is to investigate the improvement in interfacial transition zones (ITZs) between aggregate and mortar matrix. In this paper, soda-lime WGP was used as a supplementary cementitious material and replaced 20% by weight cement in the sample with modeled aggregate. The phases and chemical composition within the ITZs and the adjacent mortar matrix were investigated by backscattered electron (BSE) imaging combined with image analysis. Advanced nanomechanical techniques were simultaneously applied, and the results obtained from nanoindentation and nanoscratch were compared. The results show that WGP can significantly reduce the width of ITZs and increase the content of calcium-silicate-hydrate (C-S-H) and Si/Ca ratio in both ITZs and matrix. The high heterogeneity of ITZ with WGP made it susceptible to errors caused by unreacted WGP during the measurement of C-S-H nano- and micromechanical properties. For the control group without WGP, the test results of nanoindentation and nanoscratch showed a high degree of consistency. However, for the samples with 20% by weight WGP, there are some differences in the test results between nanoindentation and nanoscratch. Nanoscratch was able to acquire abundant data in a short testing time and proved more suitable for the tests of homogeneous materials. On the other hand, for the sample with 20% by weight WGP, nanoindentation was found to more likely to reflect the real micromechanical properties of ITZs based on abundant indentation tests.

The use of sustainable materials in road construction has been gaining popularity to provide a better future for the next generations. This study investigates the possible use of two common sustainable road construction materials, recycled asphalt pavement (RAP) and recycled tire rubber (RTR), for pavement maintenance applications. Mixtures were produced either with combined RAP and RTRs or 100% RAP with petroleum-based (RAP-A) and bio-based (RAP-B) rejuvenating oils. Because pavement maintenance applications such as pothole patching have traditionally been performed with cold mixtures (CM), a typical cold patching mixture was also investigated along with six hot asphalt mixtures. RTR mixtures were produced using different rubber modification technologies. They were manufactured using crumb rubber wet (WET), crumb rubber dry (DRY), devulcanized rubber (DEV), and crumb rubber terminal blend (TB) technologies. Each RTR-modified mixture included 40% RAP and approximately 12% rubber content by weight of the binder. The performance of the mixtures was compared using dynamic modus (DM) testing for linear viscoelastic characterization, flow number (FN) testing for rutting potential, and tensile strength ratio (TSR) testing for moisture susceptibility. The cost-effectiveness of different mixtures was performed using the life cycle cost analyses (LCCA) approach for bituminous materials. The results showed that any recycled hot-mix asphalt outperformed the CM. The 100% hot RAP mixture with petroleum-based rejuvenator performed as well as any combined RTR-RAP mixtures, and it became the most cost-effective alternative for pavement maintenance applications.

This paper presents the details of experimental testing of masonry prisms, which were tested in compression. The experimental program consisted of prisms made with hollow and solid blocks of thickness 100 and 150 mm. Five different proportions of mortars were employed in the casting of these prisms, which included 1:2, 1:3, 1:4, 1:5, and 1:6 by weight. Three prisms were cast and tested using each of these mortar types for each block type. It was found that the failure modes and compressive behaviors of the prisms were not significantly influenced by the mortar types, although these were different for the prisms made of solid and hollow blocks. The deformation behaviors of the prisms in the postpeak region were also different for these block types. The compressive strength of the prisms ($f_p$) varied with the block strength and was not dependent on the block type. All the prisms exhibited typical behaviors of uniaxially compressed prismatic members. An average elastic modulus of 1,720 $f_p$ was found for the tested prisms, while Poisson’s ratio varied from 0.10 to 0.15. Analytical models for estimating $f_p$ and strain corresponding to $f_p$ have been proposed for design practice. A new constitutive equation for capturing the falling branch of the stress–strain curve of block masonry prisms has also been proposed.

The mechanical properties of loess are strongly dependent on the environment where it is deposited. To investigate the effects of acidic, alkaline, and saline environments on the strength and deformation properties of compacted loess, the consolidation test and direct shear test were carried out on loess samples contaminated with different concentrations of acetic acid, sodium hydroxide, and sodium sulfate. In addition, changes in zeta potential, mineralogy, chemical composition, and microstructure of the loess samples at different chemical environments were also measured. The results show that the reduction in the thickness of the diffuse double layer for the loess contaminated with acetic acid leads to the aggregation of clay particles, laying the foundation for the expansion of loess pores, while the dissolution of carbonate cement and chemical cement makes the soil structure looser. Hence, the compacted loess has significantly lower shear strength and higher compressibility in an acidic environment. The mechanical properties in the saline environment show similar variation characteristics to the acidic environment, but this is mainly due to carbonate solubilization. In the alkaline environment, the degree of interparticle cementation of the loess is enhanced by the generation of calcite due to dedolomitization and the generation of colloidal flocs of $\mathrm{Al}(\mathrm{OH}{)}_3$, $\mathrm{Fe}(\mathrm{OH}{)}_3$, and ${\mathrm{H}}_2{\mathrm{SiO}}_3$. In addition, the pore connectivity is greatly reduced by the extensive distribution of clay particles caused by the development of a diffuse double layer. As a result, its compressibility and shear strength are improved compared to uncontaminated loess. These findings can be used as a reference for geoengineering practice in loess areas.

Pavement engineers are paying attention to the stabilization of granular layers in the modern era of sustainable construction. A well-drained pavement can extend the service life to its design life if properly designed and maintained. The water infiltrating into the pavement causes detrimental effects and reduces the service life of the pavement. The open-graded cement-stabilized macadam (OGCSM) can act as a drainage layer in sustainable pavements. Cement cannot be considered as a long-term sustainable material due to its high carbon footprint. This paper investigated the suitability of a supplementary cementitious material, ground granulated blast furnace slag (GGBFS), as a partial replacement of cement in OGCSM, a drainage layer in pavements. The strength and permeability characteristics of the mix were studied using an unconfined compressive strength (UCS) test and specially fabricated permeameters, respectively. OGCSM was optimized at 7% cement content, and cement in the OGCSM was partially substituted with GGBFS at various replacement levels. The mix was optimized at 80% replacement of cement with GGBFS, which satisfied the specified requirements for strength, permeability, and durability. The UCS, coefficient of effective permeability, and water resistance index of the optimized mix were 2.88 MPa, $60.58\mathrm{m}/\mathrm{day}$ and 96.33%, respectively. The morphology and mineralogy characteristics of the optimized mix were determined to justify the strength gain in cementitious mixtures. The porosity of the OGCSM mix was estimated as 25.86% using computed tomography (CT) scanned images. The subsurface drainage design was carried out using drainage requirements in pavements (DRIP 2.0) software, and the quality of drainage was rated as good.

In tropical regions, lack of moisture-damage-resistant fillers in flexible pavements poses significant challenges for infrastructure development and maintenance. Hence, this study examined sawdust ash (SDA) for such purposes. SDA is abundant as agricultural waste in rice-producing countries like India and China. Durability assessment of SDA-enriched bituminous concrete (BC) against moisture damage is considered as state-of-art in this investigation. To implement this study, numerous laboratory tests were carried out. First, the Marshall test was carried out to estimate the optimal bitumen content (OBC) and several Marshall properties, including Marshall volumetric properties. After that, a modified Marshall immersion test, energy loss ratio test, ultrasonic pulse velocity (UPV) test, indirect tensile strength test (ITS), resilient modulus ratio test, and rutting resistance test were done to execute this investigation. Furthermore, the morphological characteristics of the studied filler were investigated by atomic force microscopy (AFM). The experimental result shows that the 8% SDA-enriched BC mix may be applied in low-volume roads in tropical regions like India with 86.94% structural integrity for the presence of ample amounts of calcium oxide ($\mathrm{CaO}$), silicon oxide (${\mathrm{SiO}}_2$), ferric oxide $({\mathrm{Fe}}_2{\mathrm{O}}_3$), and higher loss on ignition value in that ash. Moreover, the results have shown that the mixes containing 8% SDA perform exceptionally well against moisture damage with the highest energy loss ratio (63.27%) and dynamic modulus (12.1 MPa) after 14 days of immersion. Similarly, this type of mix delivers the highest tensile strength ratio (96.27%) and resilient modulus ratio (89.21%), with minimum rutting depth (9.55 mm), and performs not only in terms of moisture resistance but also in its ability to withstand rutting deformation significantly. These results make it a promising choice for asphalt pavements, to mitigate the detrimental effects of both rutting and moisture on the overall durability and longevity of the road.

Abstract

In the Chengdu-Chongqing economic circle in China, the recommended bearing capacity of a medium-weathering mudstone foundation is less than the capacity of the rock structure to withstand loads. The aim of this paper was to perform plate loading tests (PLTs) with binocular vision measurement (BVM) to obtain the accurate deformation of the foundation under vertical loading. The results revealed that vertical load–bearing foundations have a failure mode that can be reduced to that of thrust failures for thin bedded structures of mudstone foundations. By analyzing the differences in results between the PLTs and the uniaxial compressive strength tests under the same conditions, a new formalism for calculating foundation-bearing capacity was proposed; there is only a 5% difference compared to in situ tests. The results of this research provide theoretical support and a practical benchmark for the full development of the load-bearing capability of soft red rocks.

Practical Applications

As the Chengdu-Chongqing economic circle progresses toward the international urban cluster, inevitably, soft rock is used as a foundation retaining layer in the construction of superhigh and super-rise buildings in the region. However, owing to antiquated testing methods and poor intelligibility of the testing equipment, the bearing capacity of such a mass of rock has yet to be fully developed and cannot meet the dual-carbon economic goals and sustainable development of architectural design. Based on this, the study introduces a noncontact method to measure the bearing capacity of soft rock within the traditional method of in situ testing and combines the concept of big data analysis to advance an empirical method for calculating the bearing capacity accurately. Based on the results of this study, the concept of natural foundations can be adopted and the engineering dilemma that the treatment of building foundations cannot be economical and practical can be solved.

Abstract

This study examined the mechanical characteristics of recycled concrete aggregate (RCA) stabilized with lime–fly ash (LFA) and cement for utilization as a semirigid base course of low-volume roads (LVRs). Several laboratory studies, which included modified Proctor compaction, unconfined compressive strength (UCS), indirect diametrical tensile strength (IDTS), durability, indirect diametrical tensile stiffness ($M_R$), and indirect diametrical tensile fatigue tests, were considered to evaluate the performance of stabilized materials. Scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) analysis were carried out to understand the RCA morphology with stabilization at different curing periods. The test results demonstrated that RCA stabilized with a lime–fly ash content of 10% and cement content of 5% complied with a stabilized material’s strength and durability requirements for LVRs. EDS analysis found that the atomic Ca/Si ratio determined for RCA stabilized with LFA and C was less than the atomic Ca/Si ratio of RCA, which confirmed the microstructure improvement of RCA as a result of hydration products. The samples of RCA stabilized with 15% lime fly ash content were found to have higher $M_R$ and fatigue life values than those of RCA stabilized with 5% cement at the same curing period. Therefore, the performance of RCA stabilized with LFA is comparable to that of cement. The design of the pavement followed AASHTO guidelines. This research proposes a method to integrate RCA and fly ash for economical and sustainable construction of LVR.

Practical Applications

Natural aggregates from quarries have been used in the majority of road projects in India, which has resulted in the rapid depletion of nonrenewable natural resources and increased cost of construction. Simultaneously, vast amounts of construction and demolition waste (CDW) are generated in India. Therefore, the problems associated with rapid depletion of natural resources and the generation of CDW require an inexpensive and sustainable approach. LVRs constitute the major portion of the Indian road network, and generally are deprived of funds; for this reason, the use of CDW as an alternative to natural aggregate (NA) is advised for the construction of LVRs. Based on experimental results, this study provides insight into performance characteristics of RCA stabilized with lime fly ash and cement. The outcome of this study will help pavement engineering professionals. The use of RCA and fly ash in pavement applications is encouraged wherever possible to save both money and natural resources.

As the main hydration products, calcium-silicate-hydrate (C─ S─ H) and portlandite (CH) contribute significantly to the tensile strength of cementitious materials. However, the role of interface in the C─ S─ H/CH composites remains unexplored. This paper aims at elucidating the interfacial tensile properties of C─ S─ H/CH composites via molecular dynamics simulations with the ReaxFF forcefield. A method quantifying the thickness of the atomic-level interfacial transition zone in composites through potential energy analysis was proposed, with the value of $1.75–3.38\mathrm{nm}$. Results showed that all models had damages at or near the interfaces. The tensile strength of composites relied highly upon material orientations. Elevated loading speed enhanced the tensile strength of composites, and their strain rate sensitivity was more significant than either C─ S─ H or CH. Failure mechanisms were revealed via chemical bond evolution. A nanoscopic tensile constitutive model was formulated based on Morse potential function. This research sheds light on the role of the interfacial area in two-phase composites at the atomic scale, which provides essential inputs for further multiscale studies.

Abstract

To study the corrosion behavior of coupled steel bars under applied stresses, experiments on the influence of applied tensile and compressive stresses on the corrosion of coupled steel bars in simulated concrete pore solutions were conducted. The corrosion processes of the individual steel bars and coupled steel bars with different stress levels, including three tensile stress levels ($1/3f_{\mathrm{y}}$, $2/3f_{\mathrm{y}}$, and $3/3f_{\mathrm{y}}$) and three compressive stress levels ($-1/3f_{\mathrm{y}}$, $-2/3f_{\mathrm{y}}$, and $-3/3f_{\mathrm{y}}$), were monitored regularly, by several electrochemical measurements, in chloride contained simulated concrete pore solution for 45 days. The experimental results showed that applied stresses had significant effects on the corrosion of steel bars. In a chloride-free environment, the applied tensile stress was found to protect the passive film. However, once corrosion initiated, the applied tensile stress would aggravate the corrosion, while the applied compressive stress might inhibit the corrosion. Microcell corrosion and macrocell corrosion were significantly influenced by the applied stresses. The applied stresses might alter the corrosion mode. Tensile-stressed steel bars and compressive-stressed steel bars showed the susceptibility to the pitting corrosion. By comparison, steel bars with applied tensile stresses tended to corrode more uniformly; however, those with applied compressive stresses were more likely to undergo localized corrosion.

Practical Applications

Reinforced concrete structures usually endure various loads such as traffic and wind loads. The external loads have been proven to influence the corrosion process of steels in concrete. However, the specific principles and results of the effect of external loads on the corrosion of steels have yet to be thoroughly studied. This study aims to investigate the corrosion process of steel under different stress levels in a simulated concrete environment. Compared with an experiment in practical concrete structures, an experiment in simulated concrete pore solutions has a shorter test cycle and the experimental phenomena are more obvious. The results show that the applied tensile stress will aggravate the corrosion of steel, while the applied compressive stress will restrain the corrosion process. Based on the research results, engineers should pay attention to the effect of external loads on the durability of structures in the design stage. Moreover, this study provides a reference for further experimental studies in practical reinforced concrete structures.

Biological soil improvement techniques, such as enzyme-induced calcium precipitation (EICP), have attracted increasing attention as a sustainable and durable solution for ground improvement. However, recent life-cycle environmental assessment studies of EICP ground improvement have shown that enzyme stabilizers such as nonfat milk powder have a significant environmental impact. Hence, this study explores the potential of using sustainable biopolymer [sodium alginate (SA)] as a modifier in EICP cementing solution. The interaction effect between different EICP cementing solution constituents (calcium chloride, urease enzyme, urea, and SA) on the performance of sand-treated specimens is investigated. Response surface methodology (RSM), a design of experiments (DOE) approach, is utilized to design the testing program. In addition, RSM is adopted to model the effect of different constituents on the performance of EICP-treated soils. An optimal mix is suggested for the EICP-SA modified cementing solution with a maximum unconfined compressive strength of 1,762 kPa, compared with 460 kPa of the EICP-milk treated specimens. Moreover, the practical considerations of the SA-modified EICP solution are investigated through scanning electron microscopy, energy dispersive spectrometry, and water retention. Notably, the study demonstrated that SA-modified EICP specimens have superior water retention characteristics compared with regular EICP-treated soils due to the inclusion of SA in the EICP solution. Additionally, a set of durability tests revealed the promising performance of the SA-modified EICP-treated specimens under wetting–drying cycles, with results complying with ASTM standards. These findings suggest that the SA-modified EICP approach offers a potent and environmentally friendly alternative for soil stabilization and improvement.

Q370qENH weathering steel is widely used in railway steel bridge construction in China. However, limited research has been conducted on the high-cycle fatigue damage of the welds in weathering steel railway bridges. In this study, we conducted experimental tests to investigate the high-cycle fatigue performance of the heat-affected zone (HAZ) of Q370qENH weathering steel. First, coarse-grain heat-affected zone (CGHAZ) specimens and fine-grain heat-affected zone (FGHAZ) specimens of Q370qENH were obtained using the welding thermal simulation (WTS) method. The accuracy of the WTS method was verified through metallographic structure analysis. Subsequently, high-cycle fatigue tests were conducted on the base material and HAZ specimens. Then, probabilistic stress-life (P-S-N) curves and the fatigue strength of the Q370qENH HAZ were obtained. Finally, the fatigue extension mechanism of the Q370qENH HAZ was examined. The results indicate that the WTS method effectively produced HAZ specimens matching the welded joint. The fatigue life of the FGHAZ and CGHAZ specimens was significantly lower than that of the Q370qENH base material. The fatigue strength of HAZ was approximately 80% of that of the base material, and the fatigue strength reference of the Q370qENH HAZ was 175 MPa. Furthermore, the CGHAZ specimens were more prone to slip and had a high stress concentration at the microscopic scale, leading to their inferior fatigue performance. This study provides a valuable reference for the design and fatigue assessment of weathering steel bridges.

This study focused on how aging affected the properties of steel slag. Steel slag was treated using hydrothermal aging and pressure steaming aging techniques to improve its bulk stability. Physical and mechanical characteristics, alkalinity, and mineral constituents, as well as micromorphology of steel slag, were investigated. The results demonstrated that water absorption, crushing value, and abrasion value were all decreased by hydrothermal and pressure steam aging. The $f$-CaO particle size, total slag hydration time, and slag alkalinity were all lowered by two aging procedures. At 90°C aging for 2 days and 0.6 MPa pressure steaming for 3 h, the $\mathrm{Ca}(\mathrm{OH}{)}_2$ and ${\mathrm{CaCO}}_3$ diffraction peaks were strengthened, whereas the $f$-CaO and $f$-MgO diffraction peaks were diminished. The $f$-CaO concentration and compaction pulverization rate steadily dropped as hydrothermal days and steaming pressure increased. The water immersion swelling rate was significantly reduced, which enhanced the slag’s bulk stability. After ageing, scanning electron microscopy revealed increased ${\mathrm{CaCO}}_3$ production and enhanced steel slag stability. The optimal processes are recommended as hydrothermal treatment at 90°C for 2 days and pressure steaming at 0.6 MPa for 3 h.

This study investigates the aging mechanisms and effects of outdoor natural exposure aging (NEA) on bitumen in the Tibetan Autonomous Region of China. Unmodified bitumen (No. 90) and styrene–butadiene–styrene (SBS)-modified bitumen were exposed to natural weathering for 0, 4, and 8 months, and their aged samples were collected and analyzed. Dynamic shear rheology (DSR) and Fourier transform infrared spectroscopy (FTIR) were employed to examine the changes in rheological properties and chemical composition of the samples during NEA. The study also assessed the aging extent of bitumen using the complex modulus aging index (CMI), phase angle aging index (PAI), and rutting factor growth rate. FTIR was utilized to quantitatively evaluate the variations in functional group indices with NEA time. The correlation analysis between the conventional binder properties and functional group indices facilitated a deeper understanding of the aging behavior. The results revealed the differences in temperature sensitivity and aging resistance between unmodified bitumen (No. 90) and SBS-modified bitumen under NEA. This research offers insights into bitumen aging in high-altitude regions and emphasizes the intrinsic role of chemical functional group changes in inducing macroscopic indicator changes during NEA.

The performance of energy geostructures is dependent on the surrounding soil properties in the presence of high temperatures or thermal cycles. Change in temperature may affect many engineering parameters of soils. Sand-bentonite mixtures or bentonite, which are used as a buffer should keep their performance at design level for a long time. Purpose: In order to improve engineering behavior of soils under high temperatures thermally durable materials may be used. Volume deformation and hydraulic conductivity behavior of 30% bentonite–70% sand mixtures in the presence of fiberglass additives were investigated. Methods: Consolidation tests were performed at room and high temperatures (80°C), hydraulic conductivity tests were started at room temperature, and a temperature cycle (25°C, 50°C, and 80°C) was applied. Results: Fiberglass increased the amount of compression insignificantly under room temperature, whereas the total compression amount increased remarkably under high temperature. On the other hand, the hydraulic conductivity increased under high temperature with fiberglass additive. Conclusions: Fiberglass-added sand-bentonite mixtures can be used around energy structures as an alternative buffer material with high-temperature resistance.

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

The accumulation of alkali residue has led to significant contamination of soil, air, and water, posing a hazardous threat to the environment. To address this issue, a technology and method for producing alkali residue–based lightweight soil were proposed to facilitate the reuse of alkali residue, and the feasibility of this method was demonstrated. Compression tests, X-ray diffraction, X-ray fluorescence spectrometry, and scanning electron microscope (SEM) were conducted to investigate the strength characteristics and hardening mechanism of the material. The results indicate that the compressive strength of the alkali residue–based lightweight soil increases linearly with wet density, age, content of portland cement, and ground granulated blast slag. The optimal water–solid ratio was determined to be 0.6. Specimens with low and high strength exhibited plastic and brittle failures, respectively. The primary contributors to the material’s compressive strength were identified as hydrated calcium silicate, ettringite, monosulfur calcium sulfoaluminate hydrate, hydrated calcium aluminate, and Friedel’s salt. The 28-d compressive strength of the alkali residue–based lightweight soil, with a water–solid ratio of 0.6 and a wet density of $800.0\mathrm{kg}/{\mathrm{m}}^3$, was measured to be 1.17 MPa, meeting the requirements for most filling projects.

Aggregate particles migrate and rearrange their spatial positions during the compaction process. To analyze the migration law, an accurate method to track migration of particles is proposed using discrete-element simulation and experimental verification. First, the coarse aggregates were generated based on realistic aggregate shapes using a three-dimensional (3D) Blu-Ray scanner. Subsequently, the fine aggregates, ranging from 0.075 to 2.36 mm, and asphalt mastic were replaced with balls with a radius of 0.7 mm. Then the three-dimensional dynamic compaction models of asphalt mixture were established using the Superpave gyratory compaction method and Marshall impact compaction method. Next, the migration tracking test of particles was developed adopting particle marking, step-by-step compaction, and CT scanning. Finally, the accuracy and efficiency of the virtual models were validated using the experimental data from the migration tracking test. The results indicate that the established compaction models can accurately track the aggregates particles and measure the migration indexes. The compaction methods have a great influence on the migration behavior. The displacement of the particles for the Superpave gyratory compaction method is greater than that for the Marshall method, and the displacement is multidirectional, whereas the displacement of particles for the Marshall impact compaction method mainly are vertical.

Improving the aging resistance of waterproof membranes is very important to extend their service life. In this paper, organic montmorillonite (OMMT) was used to enhance the aging resistance of styrene-butadiene-styrene (SBS) modified bitumen (SMB) for waterproofing. The effect of OMMT on the physical properties, chemical structure, and micromorphology of SMB membranes before and after heat aging were investigated, and the service life of the SMB membranes was predicted based on the Arrhenius model. The results indicated that the high- and low-temperature performance of SMB was improved due to the addition of OMMT, and the optimal dosage of OMMT was 3%. After 20 days of heat aging at 80°C, the alterations of softening point increment, low-temperature flexibility decrement, and viscosity aging index of OMMT/SMB decreased by 1.5°C, 3°C, and 14.7%, respectively, compared with that of SMB, which indicated that OMMT can enhance the aging resistance of SMB waterproof membranes. Fourier-transform infrared spectroscopy indicated that the change of ${\mathrm{I}}_{\mathrm{C}═\mathrm{O}}$, ${\mathrm{I}}_{\mathrm{S}═\mathrm{O}}$, and ${\mathrm{I}}_{\mathrm{C}═\mathrm{C}}$ of 3% OMMT/SMB was 53.5%, 45.6%, and 53.2% less, respectively, than SMB after 20 days of heat aging at 80°C, which shows that OMMT can inhibit the change of carbonyl, sulfoxide, and butadiene double bonds of SMB. The gel permeation chromatography showed that OMMT can hinder the degradation of SBS and polycondensation of bitumen during heat aging. The fluorescence microscope showed that OMMT/SMB maintained a more complete network structure than SMB after heat aging. According to the Arrhenius model, based on the 0°C flexibility as the damage point and the temperature of waterproof materials under sunlight being 60°C for an annual sunshine time of 1,200 h, the service life of SMB and OMMT/SMB were predicted to be 16.90 and 21.32 years, respectively.

Drainage capacity of pervious pavement mixtures is commonly measured using a falling head permeameter at hydraulic heads much higher than expected in the field. Recent advancements in computational fluid dynamics (CFD)– and X-ray computed tomography (XRCT)–based modeling eliminates the laboratory challenges of maintaining lower hydraulic heads. However, improper characterization in digital image processing (DIP) and finite-volume simulations resulted in significant errors in permeability measurements and fluid flow behavior. In addition, past studies have identified non-Darcy fluid flow characteristics in pervious pavement mixtures following the Izbash and Forchheimer laws. This paper attempts to bridge this research gap by comparing the Darcy and non-Darcy permeability parameters at different laboratory and field hydraulic heads using advanced XRCT-based modeling. It was found from the analyses that the use of laboratory hydraulic head could result in significant underestimation of permeability parameters compared with the field hydraulic heads for Darcy and Izbash equations (by up to 73%), and overestimation for Forchheimer equations (by up to 216%). Fluid flow behavior in pervious mixtures was found to be in transition flow regime (neither laminar nor turbulent) at both laboratory and field hydraulic gradients. Overall, this study can help in a better fundamental understanding of the current limitations of laboratory measurements and the need for XRCT-based numerical modeling to bridge field and laboratory permeabilities of pervious pavement mixtures.

Stiffness quantification of unbound granular materials (UGMs) is essential for designing pavement structures. This stiffness can be determined directly through the resilient modulus test, or indirectly, by correlation, with the California bearing ratio (CBR) test. Alternatively, the dynamic CBR test (dCBR) has been proposed as a simple and low-cost method for this assessment. This study investigated a new dCBR test protocol based on a novel strain-stage approach, applying 20 load cycles/stage. This testing protocol is expected to facilitate characterization and on-site control of stiffness for UGMs, including marginal granular materials (MGMs). The study characterized four MGMs using the new dCBR test protocol and the resilient modulus test; four replicate specimens manufactured by gyratory compaction were assessed per material and test. The protocol was implemented successfully for the MGMs studied to compute an equivalent resilient modulus. A methodology is proposed for calculating an adjusted equivalent resilient modulus with values similar to those of the resilient modulus. Further research is suggested to explore the relationship between the dCBR and CBR tests to advance the characterization of granular materials for pavement structures and expand the experimental data using a broader set of soils to validate the protocol.

Phosphogypsum, which contains toxic components (e.g., heavy metal elements and fluoride), is one of the byproducts of phosphoric acid production, and filling subgrade is one of the recycling methods for it. In this study, phosphogypsum was stabilized by lime to improve the mechanical properties [California bearing ratio (CBR), resilience modulus, unconfined compressive strength, and shear strength], water stability, and harmful substances dissolubility. Combined with scanning electron microscopy, the strength formation and water stability enhancement mechanism of lime-stabilized phosphogypsum (LSP) were explored. The results demonstrated that the mechanical properties of LSP were better with the lime content of 6%–10%. The CBR, resilience modulus, unconfined compressive strength, and shear strength were 3.35 times, 2.46 times, 8.61 times, and 1.39 times that of plain phosphogypsum, respectively. An intensity prediction model with a correlation of 97% was constructed. The CBR and resilience modulus softening coefficient of LSP reached best values when lime content was 6%–8%. The leaching concentration of arsenic, chromium, and lead of LSP with 2% lime met the quality standards of groundwater levels I, II, and IV, respectively. Fluoride and phosphate were not detected in LSP when lime content was greater than 6.0%. The results show that LSP is feasible as subgrade filler. Considering the mechanical properties, water stability, and dissolution of hazardous substances of LSP, it is recommended to add 6%–8% lime content to LSP as highway subgrade filler.

How to realize hydrophobic modification of the capillary wall of cement-based materials is still a challenge. The hydrophobic modifier in the emulsion type is more promising than the original form due to the good compatibility with cement paste for integral hydrophobic modification of cementitious materials. Their influence on cement hydration and fresh-state behavior is less concerned. In this study, low-cost and nanoscale paraffin oil emulsion (POE) was first prepared as a new hydrophobic modifier. POE was then mixed with cement pastes to investigate its influence on hydrophobicity, cement hydration, compressive strength, and fresh-state behavior. Furthermore, the absorption of POE with cement paste was studied by zeta potential measurement and organic carbon analysis to clarify the associated micromechanisms. The results indicated that the incorporated POE could improve the integral hydrophobicity of hardened cement paste and decrease the capillary water absorption as well. Meanwhile, due to the hydrogen-bond interaction between the ─ OH group of POE and the ─ OH group of cement or hydration products, POE adsorbs onto the surface of cement and results in a reduction of water demand for standard consistency of cement pastes. In addition, a decrease in cement hydration degree, prolonged setting time, and increase in workability can be observed. These findings can provide important guidelines for the development of hydrophobic cementitious materials.

Emulsified asphalt is widely acknowledged as an environmentally friendly technology that contributes to the advancement of sustainable development in road engineering by conserving resources and reducing hazardous fumes during paving. However, the stability of emulsified asphalt is crucial to its performance, especially after long-term storage or transport, which is significantly affected by the structure of the emulsifier. In this study, three dodecyl sulfonate emulsifiers [i.e., sodium dodecyl sulfonate (SDSN), sodium dodecylbenzene sulfonate (SDBS), and sodium dodecyl diphenyl ether disulfonate (SLDED)] with zero, one, and two phenyl functional groups in their lipophilic group were utilized to explore the effects of phenyl functional groups and emulsifier concentrations on the stability of dodecyl sulfonate emulsified asphalt using a storage stability test and particle size distribution test. Moreover, molecular simulation was employed to explore the underlying mechanism of the phenyl functional groups on the stability of emulsified asphalt. The results demonstrated that the incorporation of the phenyl functional group performed a negative effect on the adsorption of emulsifiers at the water–asphalt interface at low dosages of 3% and 5% by weight. Due to the steric hindrance of the phenyl functional group and the overlap of SLDED’s lipophilic and hydrophilic groups, SDBS and SLDED exhibited a stronger electrostatic potential than that of SDSN. SDBS emulsified asphalt displayed greater stability compared with SDSN emulsified asphalt, but SLDED emulsified asphalt conducted worse stability than both SDBS and SDSN emulsified asphalts because of its pronounced electrostatic potential distribution and intricate molecular structure. Therefore, it is recommended for suitable incorporation of phenyl functional groups in the emulsifiers to enhance the formation of a stable monolayer film at the water–asphalt interface.

Abstract

This study emphasized binder aging of bituminous mixtures in the field and compared it with newly developed field-simulating laboratory aging procedures. Monthly field cores from a pavement section were collected for this investigation over 2 years. After measuring the field core samples’ bulk density, the air voids were calculated to assess the densification with time due to traffic. Binder was extracted from the field core samples, and further tests were carried out to assess the rate of aging with time. Also, the bituminous specimens prepared in the laboratory at the optimal binder content were subjected to field-simulating oven-aging methods. The bituminous mixture aging process in AASHTO R30 does not match field conditions in tropical countries. Therefore, new techniques have been developed in this study to calculate the number of days required for laboratory aging to simulate field-aging conditions. The oven was modified by introducing ultraviolet bulbs and oxygen supply, termed Laboratory Oven Aging-lll (LOA-III). Test results showed that 10 days of LOA-III corresponded to 47 months in the field. The Fraass breaking point indicated that LOA-III also simulates low-temperature conditions. Experiments conducted in the laboratory revealed that LOA-III accelerates aging and can simulate field conditions in tropical countries more accurately than AASHTO R30. The field study showed that higher initial air voids in the surface layer accelerate binder aging, causing raveling and surface cracking. Therefore, it is recommended to limit the initial air voids to 8% or less immediately after construction.

Practical Applications

Bitumen aging significantly influences pavement performance, leading to raveling and cracking when coupled with heavy traffic loads. Higher initial air voids, primarily due to insufficient compaction, accelerate binder aging. Binder aging can be minimized by restricting the initial air voids to 8% or less. If the initial air voids are decreased by 1%, pavement service life is increased by 10%. The procedure given in AASHTO R30 does not simulate field aging for tropical regions. Therefore, a field-simulating laboratory method was necessary. This study indicated that aging the mixture for 10 days by introducing UV rays and oxygen in the laboratory oven-aging (LOA-III) method simulates the pressure-aging vessel (PAV) and field aging accurately for tropical regions. The developed field-replicated laboratory aging procedure can be directly adopted to study binder aging on pavement sections in tropical climatic regions with similar pavement crust thickness and traffic. The duration of aging and other factors, like oxygen supply rate and UV light intensity, may need to be modified for pavements with varying thicknesses, traffic volumes, and climatic zones.

This study investigates the effects of water/geopolymer (W/GP) solid ratio and ground granulated blast furnace slag (GGBS) content on the mechanical, elevated temperature resistance, and sorptivity properties of geopolymer concrete (GPC). In this study, two different W/GP solid ratios were used, 0.33 and 0.35, and GPC was produced by replacing fly ash (FA) with 0%, 50%, and 100% GGBS. As a result of physical, mechanical, and nondestructive tests in this GPC; strength performance and durability performance were investigated by finding slump, setting time, compressive strength, elevated temperature resistance, sorptivity, and dynamic modulus of elasticity (DME) via ultrasonic pulse velocity (UPV), a nondestructive test. In addition, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses were performed on GPC samples. As the percentage of GGBS in the mixture increased, the slump of GPC decreased but its cohesion increased. The final setting time of GP mortar containing 100% FA is approximately 80 times that of GP mortar containing 100% GGBS for both W/GP solid ratios. When the GGBS percentage in the mixture increased from 0% to 100%, the compressive strength of GPC increased about 4–5 times depending on the W/GP solid ratio. The increase in the GGBS percentage decreased the sorptivity of the GPC up to 6.5 times. The elevated temperature performance of GPC increased with the increase of the FA ratio. SEM analysis showed that a more homogeneous and denser microstructure was obtained with the increase of GGBS content in the mixture.

Phosphogypsum (PG) is a byproduct of the phosphate fertilizer industry that can be used in cement mortar. However, PG mortar is known to have high water absorption. This paper proposes a new method to address this issue by using superhydrophobic phosphogypsum (SPG). PG was modified using stearic acid and sodium metasilicate. The hydrophobic mortar (H-mortar) was obtained by replacing a portion of the cement with SPG powder. The optimum water contact angle of the H-mortar was measured at 108.3°. Results from the experiment show that the water absorption of H-mortar was 19% lower than that of the reference mortar (Ref-M). Furthermore, the mechanical strength of H-mortar increased compared to Ref-M, as observed through strength testing. The study also investigated the impact of SPG addition rate on mortar corrosion resistance, and found that the addition of SPG reduces water migration and enhances resistance to chloride ion corrosion. The proposed method has the potential to utilize PG waste while improving mortar strength and corrosion resistance, making it suitable for use in marine mortar structures.

Reducing cement usage and replacing it with solid waste in high volume is one of the most important ways for the sustainable development of the cement industry. In the present work, sustainable foamed concrete with a high content of phosphogypsum (PG) was prepared through the combination activation and synergistic strengthening of waterglass, ground blast furnace slag (GBFS), and cement. The fluidity, mechanical properties, volume stability, and durability of this sustainable foamed concrete were studied and its reaction mechanisms were also investigated using hydration calorimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The results show that the early age cohesive strength for this foamed concrete is mainly derived from ettringite formation, which is a product of the pozzolanic reaction of GBFS in the presence of sulfate ions. Cement in this sustainable foamed concrete is presented as an alkali activator. Too small addition of cement would weaken its activation effect and reduce the hydration product formation, which delays the strength development of the foam concrete. High cement content would provide sufficient ${\mathrm{Ca}}^{2+}$ ions, which can also retard the GBFS hydration. The unreacted PG particles are covered by ettringite and other hydration products during the reaction process to prevent its dissolution in a moist environment and help improve the water resistance and durability of foamed concrete. The sustainable foamed concrete prepared with 15% of cement and more than 50% of PG has 7 and 28 days compressive strengths of 2.86 and 3.36 MPa, respectively. In addition, it has a water-softening coefficient of 0.81 and a volume microexpansion feature in a moist environment, which is suitable for subgrade or underground filling.

Coal is the most abundant fossil fuel and the main source of energy for the production of electricity all over the globe. Excessive utilization of coal results in the production of huge quantities of coal mining wastes called overburden (OB). In addition to occupying precious land, the disposal of these wastes poses major environmental and health risks to local communities. To establish the efficacy of locally available coal mine OB materials in the subbase and base layers of low-volume roads, a laboratory study has been conducted in the present research assessing its effectiveness in terms of mechanical and durability characteristics after stabilizing with various percentages of cement. The mechanical strength of cement-treated OB (CTOB) mixes has been evaluated through destructive tests and validated through nondestructive tests and microstructural analysis. Additionally, the durability characteristics of CTOB mixes have been investigated through the wet-dry (W-D) weathering cycle test, capillary rise (CR) test, and drying shrinkage test. The W-D weathering cycles positively impacted the mechanical strength of CTOB mixes up to 12 cycles; after that, deterioration has been observed. The microstructural study also confirmed the long-term strength development in CTOB blends after exposure to adverse weathering conditions. The CR in CTOB mixes with a cement content of 6% or more was less than 25% of the height sample within 24 h of soaking, and even after 72 h of soaking, these samples did not exhibit 100% of CR. Because 80% of final shrinkage occurs within the first 3 days of drying, a minimum of 3 days of curing is recommended to control the development of shrinkage cracks in the CTOB layers.

The mechanistic-empirical pavement design guide (M-EPDG) recommends the use of resilient modulus ($M_R$) for characterization of subgrade soils. Subgrade soils may not always have enough strength and stiffness to support the pavement structure. Therefore, a certain type of soil improvement method using cement, lime, or other stabilization techniques is often needed to enhance the strength and stiffness properties of weak subgrade soils. The cement-stabilized soils show brittle behavior under compression loading, which can induce cracking in overlying pavement layers. In general, polymer-treated soils show a semiductile or ductile behavior. It is important to look for combined cement and polymer treatments to address brittle behavior issues as well as moisture susceptibility while maintaining strength and moduli properties. A research study was conducted to understand the strength, resilient, and ductile behaviors of sandy soils treated with cement and a combination of cement and vinyl acetate ethylene (VAE) copolymer. Engineering tests such as unconfined compressive strength (UCS) and resilient modulus tests were conducted on both control and treated soil specimens cured for 7 days. Tests were conducted on specimens before and after immersing in water bath for 4 h to investigate the moisture susceptibility. In these tests, an increase in UCS was observed after cement and cement-VAE treatments as compared to control soil specimens. Results showed that cement-VAE-treated soils exhibited an increase in the axial strain at failure, indicating the semiductile behavior compared to cement-treated specimens. An improvement in the resilient moduli was observed after treatments. Subsequently, two of three-parameter models were used to analyze resilient modulus formulations with stress conditions and determined the regression constants. In conclusion, the study revealed that the use of VAE copolymer improved the stress-strain responses of cement-treated soils and imparted closer to the semiductile behavior, which will reduce cracking in overlying pavement structures.

The construction industry must adopt a sustainable and environmentally friendly approach because it heavily relies on natural resources. To tackle this issue, the utilization of industrial by-products such as fly ash (FA), ground granulated blast furnace slag (GGBS), and recycled aggregates (RAs) from building demolition waste has emerged as a significant sustainable element in the production of recycled aggregate geopolymer concretes (RAGPCs). This study evaluated the durability performance and life-cycle assessment (LCA) of FA-GGBS–based RAGPC adhering to German specifications to optimize aggregate particle packing. Six different mixes of RAGPC were developed with various alkaline-activator content (AAC)/binder ($B$) ratios, ranging from 0.3 to 0.8. The concrete was cast and then ambient cured until testing. Various tests were carried out to evaluate the performance of RAGPC. The tests included compressive strength, durability, water absorption, and volume of permeable pores. The durability was measured using water sorptivity and water permeability tests. In addition, microstructure characteristics, embodied energy, and global warming potential as part of LCA also were evaluated. It was found that ambient-cured geopolymer concretes demonstrated good strength gain, normal pore structure characteristics, and good durability. Strengths ranging from 30 to 64 MPa can be developed with RA and geopolymer binders. The durability of the RAGPC gel and its capillary porosity resulted in water absorption of less than 10%. The water permeability results indicated reduced penetration. In terms of LCA, the RAGPC had an embodied energy of 4.48% and a global warming potential of 0.083, both of which are significantly lower than those of conventional concrete.

The aim of the study is to understand and achieve storage stable, compatible plastic-modified asphalt binders. In view of global plastic accumulation, the potentiality of polymeric waste plastics is evaluated as an asphalt binder modifier; providing an alternate recycling option. However, due to phase separation issues between asphalt and plastic, the usage of waste plastic is preferred through dry mixing in asphalt mixture. In this study, the compatibility of polyethylene-modified asphalt binder was assessed along with appropriate parameters that can explain the actual phase separation occurring during storage stability testing. Two types of plastics including low-density polyethylene (LDPE) and high-density polyethylene (HDPE) were blended with a PG 58-28 neat binder after assessing their melting behavior along with polystyrene (PS) and polyethylene terephthalate (PET). The impacts of polyethylene size (2.36–1.18 mm, 0.6–0.3 mm, less than 0.3 mm), blending time (30, 60, 120, 180 min), hot storage duration (0, 24, 48 h), and compatibilizers (styrene-butadiene-styrene, nanosilica, corn oil, polyphosphoric acid) on the storage stability were assessed. ${\mathrm{G}}^{*}/\mathrm{Sin}\delta$ was used as an initial measure to assess the separation index (SI) value. The results concluded that polyethylene is observed to be inert to asphalt and phase separation persists irrespective of size and compatibilizer. Nanosilica at a dosage of 0.5% was able to partially compatibilize (SI value improved from 5.4 to 1.87) PE with asphalt. Also, in the need for better parameters to better understand the phase separation, percentage recovery, fluorescence microscopy, and black space analysis were identified as proper tests to detect phase separation.

Large stone porous asphalt mixes (LSPMs) have the characteristics of large gaps, large content of coarse aggregate, and large particle size of coarse aggregate. Compared with the traditional asphalt-treated base (ATB), LSPM forms a more obvious skeleton structure in the process of bearing load. In this study, the discrete element method (DEM) model of LSPM is established, and an evaluation method for studying the bearing capacity and high-temperature performance of LSPM through an internal skeleton network is proposed. Firstly, the DEM model of asphalt mixture with different gradations is established, and the virtual uniaxial penetration test is carried out. Then, the performance of the skeleton network inside the asphalt mixture is analyzed, and the contribution of each group of aggregates to the skeleton network is further studied. The experimental results show that the bearing capacity of an asphalt mixture is closely related to the performance of internal skeleton network. The skeleton network inside the asphalt mixture is extracted by the value of the contact force, the angle between the contacts, and the contact continuity. When the skeleton network has better bearing capacity and load-transfer capacity, the asphalt mixture can bear more external load in the virtual penetration test. The contribution of different coarse aggregates to the skeleton network is analyzed from four perspectives: total contact force, vertical work, contact number, and effective coordination number. The aggregates of 19–26.5 and 4.75–9.5 mm constitute the main body of the load-transfer path and play a major role in bearing and transmitting the load in the skeleton network.

In this work, the effects of calcination temperatures ranging from 600°C to 1,000°C on the changes in mineralogical phases and mechanical characteristics of calcined impure kaolinite clay blended cement mortars were investigated. The impact of calcining temperature on pozzolanic activity of impure kaolinite clay was evaluated using direct and indirect methods. The findings demonstrated that at 700°C, kaolinite changed from a crystalline to an amorphous metakaolin phase. Specific surface, water demand, and setting time of the blended cements decreased as calcining temperature increased. The compressive strengths of blended cement mortar containing low-grade clay calcined at 700°C, 800°C, and 900°C were found to be greater than that of 600°C and 1,000°C. Based on the results of pozzolanic reactivity evaluations and compressive strength development, the most effective calcining temperature was shown to be between 800°C and 900°C.

Due to the large void ratio of porous asphalt pavement, rainwater is more likely to infiltrate through surface voids and affect the internal structure, leading to pavement damage. The objective of this study was to investigate the variation of mixture damage under different load levels and dynamic water pore pressure levels. Based on a microscopic finite-element damage model for porous asphalt concretes, the effects of repeated loadings and dynamic water pressure were introduced. Finite-element simulation models were established to analyze the pavement damage variation under loadings and the coupled effect of loadings and dynamic water pressure. The study examined the changing patterns of mixture damage under stress and revealed the mechanism of damage development in porous asphalt concretes. It was found that the damage of asphalt mastic is concentrated in the aggregate skeleton force transfer path. As the number of load cycles increase, the damage develops rapidly within 1,000 load cycles, and the damage development rate slows down. The degree of mortar damage finally stabilizes at approximately 30%. An escalation in load from 0.7 to 0.8 MPa leads to a sharp increase in damage and the mixture’s failure. With the increase of water pressure level, the change in the damage level of the model is relatively small. However, the degree of element damage increases exponentially with the increase of dynamic water pressure. Elevated dynamic water pressure intensifies the development of cracks surrounding internal voids, ultimately contributing to mixture cracking.

Abstract

This paper presents the results of a study conducted to investigate the properties of alkali-activated concrete (AAC) mixtures prepared using the optimum combinations of four precursor materials (red mud, limestone powder, silicomanganese fume, and natural pozzolana) and four activation parameters (activator to precursor ratio, silica modulus, sodium hydroxide molarity, and water to precursor ratio). In order to examine the beneficial effects of inclusion of ordinary portland cement (OPC) and curing regimes on the properties of AAC, three dosages of OPC (in the range of 10% to 30% by weight) and two types of curing (steam and air curing) were considered. Tests were conducted on the mixtures of AAC to determine different properties that included the density, void ratio, water absorption, compressive and tensile strengths, modulus of elasticity, drying shrinkage, and loss of weight and strength after exposure to acid and sulfate salt solutions. Additionally, microstructural investigations (x-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy) were conducted on the alkali-activated binders to justify the trends of the experimental data pertaining to different properties of the AAC mixtures. The results of the tests indicated that the properties of AAC were significantly affected by inclusion of OPC and curing regimes. It was found that almost all properties of the AAC were significantly enhanced when the OPC dosage was increased from 10% to 20%. Further, the AAC mixtures having more than 10% OPC exhibited better properties as compared to the traditional OPC concrete mixture.

Practical Applications

The use of OPC as a construction material is one of the major contributing factors to environmental damage. Multiple alternative materials have been suggested as a replacement for OPC such as alkali-activated industrial byproducts and natural minerals. However, these possible materials are not as well studied as OPC in terms of their strength development, volumetric stability, and resistance to extreme environments. In this work, the performance of different AAC made with natural minerals and industrial waste materials was evaluated, and we compared their performance to typical OPC concrete. The present investigation shows that the developed alternative concrete mixtures perform in a comparable or better manner to OPC concrete mixtures in terms of strength, volume change with age, acid resistance, and sulfate resistance while reducing the OPC content by 70% to 90%. The study scope, however, does not extend to study the economic viability and carbon footprint of the proposed AAC mixtures.

Steel fiber-reinforced concrete (SFRC) with hooked-end steel fibers was created for use in urban furniture to protect against blast and impact loads. Due to the variety of impact loads that these structures may experience, it is necessary to assess the impact of high strain rates on the flexural behavior of SFRC. This study involved testing SFRC beams with 1% volume content of hooked-end fibers, which were 30 mm long and had an aspect ratio of 80. The beams were tested at different strain rates and in a three-point loading configuration. Four strain rates were tested, ranging from ${10}^{-6}$ to ${10}^{-2}{\mathrm{s}}^{-1}$, and impact tests were conducted using a drop weight impact test machine and varying drop heights, corresponding to strain rates ranging from 1 to $20{\mathrm{s}}^{-1}$. Two load cells were used to measure the total impact force and one reaction force, which were then used to assess the inertial force. Two accelerometers measured the maximum acceleration at the midspan of the beams. The results included quasi-static and dynamic load-deflection relationships, dynamic flexural tensile strength, and failure mode of SFRC specimens, as well as the relationship between the inertial force and strain rate. The study revealed that deflection capacity and flexural tensile strength increased with loading rate. The study also provides dynamic to static property ratios, such as flexural tensile strength and fracture energy, which are compared with those recommended by the CEB-FIP Model Code and other researchers.

The freeze–thaw cycle test, uniaxial compressive strength test, dynamic elastic modulus test, and nuclear magnetic resonance (NMR) scanning test were carried out to study the freeze–thaw resistance of cemented sand and gravel materials in cold areas. The compressive strength, relative dynamic elastic modulus, porosity, and the most probable pore size of macroscopic degradation indexes before and after freezing and thawing were analyzed. The results show that: (1) both the compressive strength and relative elastic modulus gradually decrease with the increase of the number of freeze–thaw cycles, the porosity increases with the rise of the number of processes, and the growth rate gradually accelerates; (2) with the increase in freeze–thaw cycles, the spectral peak shifts to the larger aperture, the harmful aperture accounts for the most significant proportion, and the most probable pore size and minimum aperture increase; and (3) according to the gray entropy correlation method, the deterioration index that significantly influences the compressive strength and elastic modulus of cemented sand and gravel materials is the total porosity, and the most influential pore size range is 50–200 nm.

Red clay is a special soil that loses water and shrinks easily, which causes expansion and contraction and leads to the generation and development of cracks, weakening the strength and engineering properties of the soil. This investigation analyzed the mechanism of crack evolution and patterns of strength decay in red clay under dry–wet cycles and established a relationship between strength and crack ratio by employing image processing techniques and conducting direct shear tests on red clay with various initial moisture contents and humidification times. The results show that the crack ratio increases with the number of dry–wet cycles and eventually tends to be stable after the fourth dry–wet cycle, and the stress–displacement curve of red clay changes from weak hardening to hardening. With the progress of the dry and wet cycles, the shear strength indexes of red clay decrease extensively, displaying a negative association with the sample’s initial moisture content and the duration of humidification. Based on the experimental result, a quadratic function was established to model the relationship between soil cracking ratio and shear strength, which can predict the shear strength of red clay from the cracking ratio.

This investigation is primarily focused on addressing the prevailing uncertainty surrounding the compressive strength of three distinct types of bricks: nanomodified; simple; and commercial. Nanomodified bricks are specifically fabricated using a minute concentration of 0.01% w/w multiwalled carbon nanotubes combined with 1% sodium hexametaphosphate. However, the utilization of both materials in a single brick is currently limited. In view of this constraint, a diligent effort was made in this study to comprehend the effects of multiwalled carbon nanotubes and sodium hexametaphosphate as additive materials for brick construction. It is important to note that the compressive strength of the bricks remains the pivotal and critical characteristic under investigation, and an exhaustive analysis was undertaken employing a probabilistic approach. The findings of the study suggest that the variability observed in the compressive strength parameters of nanomodified, simple, and commercial bricks can be explained by a normal distribution at a significance level of 5%. The calculated values for the characteristic compressive strength were determined to be 24.47, 16.47, and $14.24\mathrm{N}/{\mathrm{mm}}^2$, respectively, for the three types of bricks. Further, the regression analysis conducted to assess the relationship between brick compressive strength and the independent variables yielded a cubic fit with $R^2$ (coefficient of determination) values of 0.984, 0.995, and 0.995 for nanomodified, simple, and commercial bricks, respectively. Consequently, the application of multiwalled carbon nanotubes in conjunction with sodium hexametaphosphate in fired clay bricks can be recommended to achieve enhanced compressive strength.

A nondestructive technique is lacking for the quick and accurate detection of wetting deformation in field measurements. In this study, we investigated the feasibility of using resistivity to assess wetting deformation. A modified triaxial apparatus was used to conduct wetting tests on a soil−rock mixture (SRM), with simultaneous measurement of resistivity and deformation. The results indicate that resistivity gradually decreases during consolidation and that the magnitude of resistivity changes is affected by the rock content and confining pressure. The resistivity values exhibited a gradual decrease during shearing, with the magnitude of this decrease showing a negative correlation with the rock content. In addition, there was a positive correlation between the rate of deformation and the rate of change of the resistivity. The resistivity in the wetting tests was divided into three distinct stages: prewetting, during wetting, and postwetting. Throughout these stages, a consistent decrease in resistivity was observed. The inflection points observed in the resistivity–axial strain curve can be used to determine the beginning and end of wetting. A mathematical model based on the exponential function is proposed for assessing wetting deformation via resistivity measurements. The experimental results verify the feasibility of real-time monitoring and evaluation of wetting deformation using resistivity.

Recent materials developed and applied for repairing, strengthening, and refining the performance of various structural elements are high-performance fiber-reinforced cement composites (HPFRCCs). These materials exhibit appropriate strain-hardening behavior when subjected to tensile loading. Currently, an apparent need is felt for these construction materials in all the world’s countries. The fibers used in HPFRCCs are primarily polyvinyl alcohol (PVA), polyethylene (PE), and high-tenacity polypropylene (HTPP) fibers. Due to the high cost and unavailability of the mentioned fibers, it is not possible to make HPFRCC in many parts of the world. The aim of this study is to achieve HPFRCC constructed from locally accessible ingredients and substances with proper mechanical properties, specifically increasing the tensile strain capacity and being consistent with the environment. For this purpose, 18 mixtures were examined in such a way that the written mix designs included various cases of cement type (ordinary portland cement, limestone calcined clay cement), filler type (silica sand, limestone powder, and their mixture), amount (in two ratio percentages of 0.5 and 1 concerning binders), and cases of water to solid ingredient ratios (0.2, 0.25, 0.3, 0.35, 0.4). The applied fiber in this article was ordinary polypropylene fiber, and in order to investigate the mechanical behavior of the studied mix compositions, compressive strength, direct tensile strength, a three-point bending test, and a scanning electron microscope (SEM) were used. Also, to assess the sustainability of mix designs, material sustainability indicators (MSI) were approved from the perspective of embodied energy and carbon footprint. Finally, it is shown that using local ingredients and ordinary polypropylene fiber, a green composite with a tensile strain capacity of 3.7% is possible. Moreover, replacing ordinary portland cement (OPC) with limestone calcined clay cement (LC3) in mixtures will decrease the compressive strength on average by 20%, increase the tensile strain capacity by 54%, reduce the production of carbon dioxide gas by 34%, reduce energy consumption by 18%, and increase the price by 4%.

Basalt fiber–reinforced polymer (BFRP), a composite material known for its cost-effectiveness and excellent resistance to chloride ion corrosion, combined with environmentally friendly geopolymer is expected to contribute to the development of sustainable marine engineering structures. However, concerns still remain regarding the durability of this structure in marine environments. This paper presents an experimental investigation of the durability of basalt fiber–reinforced polymer bars immersed in seawater under the combined effects of the seawater sea-sand geopolymer mortar (SSGM) covering and prestressing. The prestress level was maintained at 20% of the ultimate tensile strength of the BFRP at room temperature in the first 7 days; the alkaline content of the SSGM, represented by the mass ratio of ${\mathrm{Na}}_2\mathrm{O}$ in the alkaline activator to the precursor, was either 4% or 6%; and the seawater temperatures were room temperature, 40°C, or 60°C. The prestress losses of the BFRP bars were monitored over the entire period, and tensile tests were conducted at 30, 60, 120, and 240 days. The results show that the prestress losses of the BFRP were less than 40% after 240 days of immersion. Prestress accelerated the degradation of the BFRP performance due to fiber damage and microcracking. The alkalinity of the activator in the SSGM did not have a significant effect on the tensile strengths of the BFRP bars immersed in seawater. However, the higher the alkalinity, the higher was the compressive strength of the SSGM and the lower were the prestress losses of the BFRP, which was attributed to the increased compactness friction caused by shrinkage of the SSGM. Carbonates combined with hydrogen ions in the water to form carbonic acid, and hydroxyl groups combined with the cations in the sea sand and the SSGM to form a strongly alkaline solution; these solutions were harmful to the long-term performance of the BFRP bars.

Abstract

This research aims to investigate the impact of short- and long-term aging on the chemo-physical properties of various conventional and modified asphalt binders. The study incorporates different technologies, namely, polymers, rubber, nano, and antiaging modifiers with a combination of 11 original (unaged) asphalt binders, which were short-term aged in the rolling thin film oven, and then long-term aged in the pressure aging vessel (PAV). A comparison between the set of unaged and the two sets of aged asphalt binders was carried out using series of physical and rheological laboratory tests as well as two chemical analyses. Measured laboratory data for the three sets (33 asphalt binders) was used to study the interrelationships between the selected aging indices (AIs) using regression analysis. Results showed that styrene butadiene styrene polymer modified asphalt was one of the best asphalt binders to resist physical changes but fell in the middle range when tested chemically. The carbon nano tubes modified asphalt binder showed great resistance to aging physically and chemically. Although most antioxidant modified binders generally perform better than conventional ones in terms of aging resistance, furfural antioxidant modified asphalt showed poor resistance to rheological changes after aging, while it was superior to resist PAV aging by means of chemical analysis. According to the relationships for long-term aging indices, complex shear moduli at high and intermediate temperatures correlated the most with other physical and rheological parameters. Nonetheless, rotational viscosity and creep compliance (Jnr) correlated the most with other parameters for short-term aging. Finally, the AI of carbonyl chemical group (${\mathrm{I}}_{\mathrm{C}═\mathrm{O}}$) from the Fourier infrared spectrometry had poor correlations with most rheological indices at all aging levels. ${\mathrm{I}}_{\mathrm{C}═\mathrm{O}}$ was found to have fair to good correlations with Jnr and linear amplitude sweep test parameters after PAV aging.

Practical Applications

Asphalt binders play a crucial role in the performance and durability of asphalt pavements. Over time, asphalt binders undergo aging, which leads to changes in their rheological properties and chemical interactions. Understanding the effects of aging on asphalt binders is essential for designing long-lasting and sustainable road infrastructure. The study specifically focuses on asphalt binder’s aging incorporating different technologies. It sheds light on the complexities of asphalt binder aging and offers valuable insights for pavement design. The research outcomes provide deeper understanding of how different modifiers and aging conditions influence the chemo-physical properties of different asphalt binders, ultimately contributing to the development of more robust and sustainable pavement designs.

Abstract

Microbial induced calcium carbonate precipitation (MICCP) has applications in improving the quality of cementitious constructions by enhancing its compressive strength, reducing porosity, and increasing durability against environmental degradation. In this study, an attempt has been made to develop an in situ, online, and nondestructive ultrasonic monitoring tool to capture bacterial self-healing in cementitious materials using cheaper source of bacterial nutrition medium. Samples casted and cured in corn steep liquor (CSL) and nutrient broth (NB) demonstrated higher ultrasonic pulse transmitted signals at successive days of curing relative to water cured control (C) specimens. The rise in ultrasonic signal due to bacterial admixing and curing is due to calcite precipitation in bacterial admixed and cured specimens. The compressive strength of CSL specimens was 8.8%, 11.4%, and 11.1% higher, while in NB specimens was 13.5%, 14.6%, and 12.7% higher as compared to water casted and cured specimens at 7, 14, and 28 days, respectively. The water absorption in bacterial treated specimens was significantly reduced due to the filling of pores in the mortar matrix and a reduced sorptivity coefficient of 0.0027 and 0.0022 was observed in CSL and NB specimens respectively as compared to 0.0197 of water casted and cured C specimens. This suggests successful calcite precipitation in bacterial treated mortar specimens and ultrasonic pulse transmission monitoring technique can successfully pick up bacterial intrinsic healing and can serve as in situ and nondestructive monitoring technique in civil engineering applications.

Practical Applications

Bacterial intrinsic self-healing in cementitious materials is an inherent process and this paper highlights the successful implementation of nondestructive and in situ ultrasonic wave monitoring tool to pick the same. Commonly used nondestructive testing (NDT) techniques like ultrasonic pulse velocity (UPV), acoustic emission monitoring can capture crack initiation in cementitious structures but not its intrinsic healing. In present research, ultrasonic wave monitoring has been used to capture bacterial microstructural development in the initial curing period in MICCP. This innovative NDT technology would go a long way in developing an in situ ultrasonic monitoring technique to pick up efficacy of MICCP in concrete structures for on-site applications.

Constant advancement of the frontier of earthen building resources to meet the demands of society has been reported and reviewed down the ages. Lately, dwindling reserves of pristine clay mineral resources and the quest for better mechanical strength and weather resistance in building materials with good thermal properties have necessitated innovation in the fired clay brick (FCB) production sector. This study is aimed at optimizing the physico-mechanical properties of FCBs to improve thermal insulation using cassava peel (CP) biosolids. Raw materials were extensively examined for their physical, geotechnical, chemical, molecular, mineral, and thermal characteristics. Modeled bricks containing various percentages of CP were prepared by molding at 10-MPa compaction. The results of tests performed indicated that linear shrinkage, weight loss on ignition, and water absorption increased at 4%–16% by weight of CP. Bulk density decreased by 28.78% at 16% by weight CP and 1,000°C firing. Compressive strength decreased by 72% while thermal insulation improved by 27%. These results suggest that CP biosolid can enhance the thermal performance of FCBs. Consequently, mechanisms of CP biosolid recycling to improve the thermal performance of bricks are recommended.

The creep characteristics of a composite geomembrane under different load levels were investigated by conducting a laboratory creep test for 2,100 h under 15 load levels from 10% to 80%. Test results showed that deformation increased rapidly when a load was applied, and the change in strain decreased gradually with an increase in time. The higher the load level, the higher the creep deformation and creep rate. When the load level was lower than or equal to 40%, the creep strain of the composite geomembrane increased linearly. When the load level was higher than or equal to 45%, the creep strain increase followed a quadratic function. When the load level was 40%–45%, the creep strain changed under the influence of the deformation characteristics of the composite material. Based on the creep test data, a piecewise empirical creep model with load level and time as parameters was established. The three-parameter and four-parameter viscoelastic constitutive models reflecting the creep properties were compared and analyzed, and it was found that the four-parameter model better reflected the creep characteristics of the composite geomembrane.

Evaluating the technical conditions and performance for historic bridges is essential to ensure their structural safety and determine their need for strengthening. This study investigates the first railway steel bridge built in China in 1894, which is listed as a national preservation unit and industrial heritage site. The bridge was not only exposed to years of weather change but also suffered a geological disaster in 1976. In addition, the surroundings have changed, including the construction of new railway lines and scenic areas. Thus, it is imperative to evaluate its technical conditions and performance, particularly its material properties. To this end, evaluation procedures were formulated. First, the material composition, properties, and grades of steel were determined by microstructural analysis: the grade of nonmetallic inclusions in steel was determined by metallographic analysis; the corrosion rate of steel was obtained by electrochemical analysis; and the crystal type, size, element product of the corrosion layer, as well as the fracture type of the steel, were analyzed by phase composition and elemental analysis. Next, the static performance indices of the steel were obtained by mechanical property tests: the hardness value of the steel was obtained from hardness test; the yield and tensile strengths of the steel were obtained from tensile tests; and the fatigue properties of the steel were analyzed through fatigue tests. The S-N curve of the steel was determined by fitting the tested data. This study provides a reference for the evaluation of the technical conditions and performance of historic bridges.