Journal of Materials in Civil Engineering

Ten coarse-fine mixtures (CFM) (intermediate soils) having fines contents (FC) of 0%, 12%, 20%, 30%, 40%, and plasticity indices (PI) of 5% and 15% were prepared in the laboratory by mixing different fractions of gravel, sand, nonplastic silt, kaolin, and bentonite. Index properties, volume change during saturation, specific surface area (SSA), and saturated hydraulic conductivity of CFM were investigated. For compacted CFM, a $FC=15\%$ (for $PI=5\%$) and $FC=12\%$ (for $PI=15\%$) represent the transition between coarse- and fine-dominant behavior based on intergranular void ratio. The total SSA of CFM may be estimated from the weighted average of SSA determined individually for each soil fraction since the SSA of the cohesive portion was observed to be linearly proportional to the percent fractions of kaolin and bentonite. Hydraulic conductivity estimations based on the SSA of soils proposed by the Kozeny–Carman equation underpredicted the hydraulic conductivity of CFM by one to four orders of magnitude. Alternatively, the formulations from consolidation theory and modified Hazen’s correlation utilizing effective particle size, $D_{10}$, and void ratio, e, estimated the hydraulic conductivity within an order of magnitude. Although hydraulic conductivity decreased with the increase of FC and PI, a smaller amount of decrease was observed in low plastic CFM.

The static and dynamic fracture behavior of high-strength fiber-reinforced seawater sea-sand (SWSS) concrete was investigated by conducting fracture toughness and drop-weight impact tests. The results were compared with those of freshwater normal-sand (FWNS) and SWSS plain concretes. Polypropylene (PP) and polyvinyl alcohol (PVA) fibers with different fiber ratios (0.1%–0.5%), were used for reinforcement. A poor brittle failure was found for plain SWSS and FWNS mixes. Compared with FWNS, SWSS concrete had higher fracture toughness and impact energy values. Incorporation of fibers, especially PP fiber, significantly improved both static and dynamic fracture behavior of the plain SWSS concrete. PP fiber pull-out led to a considerable enhancement of ductility, residual strength, and fracture and impact energy values. The fibers in SWSS concrete with a high percentage of PP fibers can be used as partial and, in some cases, total substitution for conventional reinforcement. On the other hand, due to their chemical bonding with cement products PVA fibers mostly improved the precracking properties of the SWSS mix, such as flexural strength and impact resistance at first crack formation, rather than postcracking properties.

High-performance equal-sized-aggregate (HPESA) concrete materials are mainly used as wall-off filling materials for underground engineering to meet the functional requirements of explosion prevention and shock absorption. However, the promotion and application of materials in underground engineering requires further understanding of its behavior in terms of damage evolution under impact load. A dynamic damage constitutive model able to describe the characteristics of material failure and deformation is thus required. According to the optimal energy-consumption ratio parameters of HPESA concrete materials, specimens that could meet the requirements of static pressure tests and split Hopkinson bar (SHPB) impact tests were prepared. The quasi-static testing parameters at a constant strain rate of $2.0\times {10}^{-5}{\mathrm{s}}^{-1}$ and the dynamic stress-strain curves at strain ratios from 25 to $155{\mathrm{s}}^{-1}$ were obtained. Then, from the bulk failure characteristics of the HPESA concrete materials under uniaxial impacting compression, the damage evolution mechanism of the material during its transformation from the structural phase to the damage phase was clarified, and an exponential model describing the evolution of damage with clear physical significance was obtained. Finally, when the damage variable of the HPESA concrete material was used in the Zhu-Wang-Tang (ZWT) rate-type constitutive equation, a uniaxial dynamic damage constitutive model that could describe the response of the HPESA concrete materials was obtained. The response characteristic parameters of the theoretical model were found by nonlinear fitting, which lays a foundation for numerical analysis of this material in underground engineering scenarios.

The high-temperature behavior of alkali-activated fly ash (AAF) geopolymers is evaluated. The physical and phase changes in the material are determined to be a function of temperature of exposure. Thermal diffusivity and compressive strength are determined to be a function of temperature. The compressive strength after high-temperature exposure is related to the phase composition changes in the sodium aluminosilicate hydrate (NASH) gel and the porosity in the AAF. Exposure to 200°C produces an increase in the NASH gel content by up to 5% and a reduction in mass due to moisture loss. The physical damage in the material on heating up to 200°C is produced by vapor pressure generated inside the material, and it results in the creation of porosity in the 100-nm range. The level of damage is higher in AAF with a lower water content because of its finer pore structure. Up to 200°C, the combined influence of additional geopolymerization and physical damage produces an increase in strength in AAF with a higher water content and a decrease in strength at lower water content. There is an increase in the thermal diffusivity with moisture loss in geopolymer pastes with high water content. There is a consistent loss of strength in the range of 25–30 MPa between 200°C and 600°C, which is produced by changes in the NASH gel. There is a reduction in the content and changes produced by silica enrichment and dehydroxylation of the NASH gel between 200°C and 600°C. There is a strength gain of 3–6 MPa between 600°C and 1,000°C, which is produced by the conversion of the amorphous NASH gel to a more crystalline form. There are no additional changes in the porosity and thermal diffusivity at temperatures higher than 200°C. The results are significant for the fire design of concrete made with geopolymers.

This paper evaluates the effect of the addition of nanocalcium carbonate (NC) and nanosilica (NS) on chloride-induced corrosion, chloride diffusion, chloride permeability, and service life of high-volume slag (HVS) and high-volume slag–fly ash (HVS-FA) blended concretes containing more than 70% blast furnace slag (BFS) and combined BFS and FA as the partial replacement of ordinary Portland cement (OPC). Compared to the control OPC concrete, the HVS and HVS-FA concretes containing NC and NS exhibited superior compressive strengths in all curing ages up to 365 days. Superior performance against chloride permeability, chloride diffusion, and chloride-induced corrosion are also observed in both HVS and HVS-FA concretes due to the addition of both nanomaterials. Among NS and NC, the concretes containing NC performed much better than the concrete mixes with NS. Significant extension of service life is also observed in both HVS and HVS-FA concretes by the inclusion of both nanomaterials.

In recent years, there has been unprecedented development of marine engineering construction in China. One such development has been the introduction of geopolymer (GP) concrete, which differs from portland cement in terms of durability and corrosion resistance in marine environments, and is also a low-carbon construction material. This study developed a low-shrinkage modified GP (MGP) concrete and researched its potential engineering applications . The research prototype was the Xigang seawall in the Guangdong Province of China. The effects of working performance, compressive strength, temperature rise, and strain of the concrete on the construction were assessed. The results showed that the autogenous shrinkage, chemical shrinkage, and drying shrinkage of the MGP paste were significantly lower than those of conventional GP concrete. The mechanism of shrinkage compensation of the MGP paste was discussed from the viewpoint of mesostructure and thermodynamics. The MGP concrete demonstrated smaller temperature rise and less difference between the internal and external temperatures than did portland cement concrete. Therefore, it featured a lower risk of cracking and was found to be more suitable than portland cement concrete for the rapid construction of seawalls.

This paper presents the behavior of amorphous metallic fiber (AMF)–reinforced geopolymer composites under compression, bending, and uniaxial tension loads. Comparison is also made with counterpart cement composites reinforced by AMF and steel fiber (SF)–reinforced geopolymer composites. In this study four series of composites were considered in two parts. In the first part, heat cured geopolymer (HCG) composites reinforced by 0.5%, 1.0%, and 1.5% (by volume) AMF were considered in one series, while similar volume fractions of AMF were used to reinforce conventional cement composite in another series to benchmark the observed properties. In the second part, similar volume fractions of AMF were used to reinforce ambient air cured geopolymer (ACG) composites, and the results were benchmarked with conventional SF-reinforced ACG composites. The water to cement ratio and alkali activator to binder ratios in all composites were kept constant for comparison, and all composites were tested after 28 days of curing. The results showed that the compressive strength of AMF-reinforced HCG composites was higher than that of AMF-reinforced cement and AMF-reinforced ACG composites. However, the compressive strength of SF-reinforced cement composites was slightly higher than that of AMF-reinforced ACG composites. Regardless of composite and fiber types, an increasing trend in compressive strength with an increase in the volume fraction of fibers was also observed. The results also showed higher flexural and tensile strengths for AMF-reinforced HCG composites than for counterpart cement composites. The flexural and tensile strengths of both geopolymer composites also increased with an increase in AMF volume fraction. However, both flexural and tensile strengths were higher for ACG composites when reinforced by SF than when reinforced by AMF. Microstructural observations through scanning electron microscopy showed no damage of the AMF and SF in the geopolymer composites and showed higher amounts of geopolymer matrix on the surface of AMF in HCG composites than in cement and ACG composites.

The scarcity of river sand is increasing due to worldwide fast-track urbanization and infrastructure development, which leads to high demand for fine aggregates. In recent years, the exploration and consumption of different types of fine aggregates other than natural sand in construction are growing across the globe. The existence of clay in alternative fine aggregates (AFA) is one of the formidable hurdles for their successful utilization in concrete and mortar. Clay content adversely affects the properties of concrete and mortar, such as strength, workability, and durability. Therefore, the objective of the present study represents the assessment of clay content in river sand and other types of alternative sands, such as recycled fine aggregate (RFA), crushed rock sand (CRS), and coal bottom ash (CBA), using an innovative phenol adsorption method. The activated clay effect on adsorption was also assessed. The phenol is adsorbed on the clay surface, resulting in an exothermic reaction that releases heat and causes an increase in the temperature of the solution. Standard correlation curves were developed to evaluate the clay content in different types of fine aggregates with the corresponding variation in temperature. The results were validated using a standard methylene blue value spot test, which was found in good agreement. Clay in different types of fine aggregates used in the present study was found to be less than 5%. Also found was that the activation process increases the phenol adsorption property of clay. The phenol adsorption method is relatively faster and more reliable than the methylene blue value spot test method for assessing clay content. The properties of mortar also indicated that workability and compressive strength decrease with an increase in the clay content in fine aggregates irrespective of activation. The phenol adsorption technique, which is novel, can be used to develop a sensor to evaluate the clay content in fine aggregates in the future by utilizing the exothermic property of clay.

Rapid-hardening magnesium oxysulfate (MOS) cements were prepared using a high-activity light-burned magnesia (HA-LBM) powder and boric acid (BA). The early hydration, compressive strength, phase composition, microstructure, water resistance, and solution chemistry have been studied. HA-LBM powder rapidly hydrates to form ${\mathrm{Mg}(\mathrm{OH})}_2$, and this causes rapid setting and poor mechanical properties. The addition of BA delays hydration, decreases the hydration temperature, increases setting time, promotes formation of Phase 517, and improves the physical properties. MOS cement pastes containing 1.0% by weight of BA had an initial setting time at 73 min, a final setting time at 101 min, a compressive strength after 12 h of 33.6 MPa, 28-day compressive strength of 91.4 MPa, and 28-day $R_f$ of 0.87. The research highlights the excellent properties of MOS cements manufactured using HA-LBM and BA.

The use of recycled construction and demolition (C&D) materials as an alternative backfill in the construction of geosynthetic-reinforced structures, such as embankments and retaining walls, has been pointed out as a sustainable and effective means of attenuating the environmental impacts associated with C&D waste disposal to landfill, while also reducing natural resource depletion. Creep is an important time-dependent mechanical property that must be considered when geosynthetics are used in reinforcement applications. In this study, a series of creep rupture tests was carried out to characterize the long-term tensile response of a high-strength geotextile typically used for soil reinforcement. To assess the potential chemical and environmental degradation induced by recycled C&D aggregates on the long-term response of this geosynthetic, the creep strain and rupture behavior of fresh specimens was compared with that of specimens that were previously exposed to recycled C&D materials and a natural soil (used as a reference) for a period of 24 months, under real environmental conditions. Test results have shown that the short-term tensile strength properties of this geotextile can be considerably reduced after exposure to the backfill materials. Conversely, for long-term conditions, the exhumed specimens led to higher estimates of the retained strength at the design lifetime, implying that the use of fresh specimens for creep rupture testing is a conservative (i.e., safe) procedure with regard to the analysis of the long-term strength of this geosynthetic. Similar effects were induced by the exposure of the geotextile to the recycled C&D material and the natural soil, which supports the feasibility of using recycled C&D aggregates as a sustainable replacement to conventional backfill materials of geosynthetic-reinforced structures.

The mechanical behavior of asphalt concrete varies with temperature; therefore, researchers have been developing technologies to reduce temperature fluctuations in pavement overlays. Increasing the thermal conductivity of asphalt concrete is a key component in the realization of these technologies. Previous studies have introduced, among other additives, carbon nanotubes (CNTs), graphite, graphene nanoplatelets (GNPs), and copper slag to asphalt binders/concrete to enhance their thermal-physical properties. However, it has been challenging to assess the distribution of these additives in asphalt materials. In this paper, binary (i.e., binder/CNT and binder/GNP) and ternary (i.e., binder/CNT/GNP) composites were prepared by pretreating the additives with a surfactant and through sonication, before they were mixed into the hot binder using a mechanical shear mixer. Morphology and dispersion uniformity of CNTs and GNPs in the binders were evaluated using a digital microscope and scanning electron microscopy (SEM). The thermal conductivity of these samples was measured using Nanoflash combined with differential scanning calorimetry. The rheological properties were tested using rheometry. Results showed that our sample preparation method was able to uniformly disperse the CNTs and GNPs in the binder, as seen in the digital microscope images that offered more representative morphologies of asphalt binders than SEM. The addition of CNTs (0%–2% by weight) and/or GNPs (0%–15% by weight) improved the binder’s thermal conductivity at a limited degree, whereas the rheological properties of the CNT/GNP-modified binders remained very close to those of the control sample. Findings from this work may provide some insights into the development of new asphalt materials as well as other CNT/GNP-based composites.

Engineered cementitious composites (ECC) are distinguished by ultrahigh ductility and multiple cracking. High-strength stainless steel wire rope (HSSSWR) meshes have been successfully applied to strengthening existing structures. Taking advantage of both ECC and HSSSWR meshes, HSSSWR mesh–reinforced ECC promises to be an innovative strengthening material for significantly improving overall performance of existing structures. In order to capture the bond performance between HSSSWR meshes and ECC, direct pull-out tests on HSSSWR meshes embedded in ECC were performed considering the effects of spacing of transverse wire ropes, bond length, and nominal diameter of HSSSWR. The influence laws of the considered factors on the bond behavior between HSSSWR meshes and ECC were investigated. The failure characteristics and bond-slip relationship between HSSSWR meshes and ECC were revealed through analyses of experimental results. A bond-slip model was proposed to predict the bond-slip behavior of HSSSWR meshes in ECC, which was verified to be acceptable by comparing it with test results.

This study evaluates the potential of producing warm-mix asphalt (WMA) using a wax-based additive (Sasobit) in a binder modified using crumb rubber (CR). This binder is formulated for very hot climates and has a grade of PG 82E-16. Three proportions of Sasobit were added to the binder (1%, 2%, and 3%). In the compaction temperature range (130°C–145°C), there was 9% to 16% reduction in viscosity as a result of using 2% and 3% Sasobit. With an increased content of Sasobit, a higher dynamic modulus was identified for the 3% CR+Sasobit binder, and the rutting resistance of the binder also improved. From the fatigue tests, the use of 3% Sasobit caused noticeable reduction in fatigue life. From the nanoscale characterization conducted using Atomic Force Microscope (AFM), an island-type structure was observed for Sasobit-treated binders. This structure could be the wax crystalline phase that improved the stiffness of the binder in nano and macroscales. In addition, thermal analysis was carried out under endothermic and exothermic conditions. The binder’s melting temperature reduced and the crystallization temperature increased with the addition of Sasobit. The CR+3% Sasobit binder had the highest percentage of the Carbonyl group, which is associated with binder aging and thus reduced the fatigue life. Overall, it was observed that Sasobit (up to an addition of a 2% dosage) improved the modulus and rutting resistance without degrading the cracking resistance of binders.

In order to study the damage evolution characteristics of freeze–thaw mortar materials under impact load, this paper uses cement silica powder mortar to prepare cylindrical samples, and performs freeze–thaw cycle tests on mortar samples under water saturation based on a programmable constant temperature and humidity test chamber. Combined with the analysis of scanning electron microscope and longitudinal wave velocity test results, this paper reveals the influence of freeze–thaw cycles on the deterioration of mortar mechanical parameters, performs uniaxial compression and impact tests under different strain rates on mortar samples that have undergone different freeze–thaw cycles, reveals the damage and deterioration mechanism of mortar materials under freeze–thaw cycles and impact loads, and establishes the dynamics of freeze–thaw mortars under the different strain rates compressive strength degradation prediction model. The results show that the effect of freeze–thaw cycles will aggravate the damage of mortar, continuously deteriorating its mechanical parameters, and with the constant decrease of static compressive strength and elastic modulus. The number of freeze–thaw cycles and strain rate jointly determine the dynamic compressive strength of mortar when one of the factors is constant; the dynamic compressive strength of mortar decreases exponentially with the number of freeze–thaw cycles, and linearly increases with the strain rate. The dynamic strength factor (DIF = dynamic compressive strength/static compressive strength) of mortar is affected by the number of freeze–thaw cycles and strain rate, and the latter is more significant. Finally, from the perspective of the reduction rate of the dynamic and static compressive strength of the mortar under the action of different freeze–thaw cycles, a solution for the Dongfeng Tunnel project to deal with the influence of the freeze–thaw cycle is proposed. The research results can provide theoretical reference for more engineering construction in cold regions.

Portland cement (PC) has been successfully used as an admixture in cement asphalt emulsion mixtures (CAEMs) to improve their early-age strength. However, the excessive use of PC significantly influences the environment. Thus, to reduce the PC amount to some extent, this study proposes a novel CAEM using artificial by-products, e.g., fly ash (FA) and ground-granulated blast-furnace slag (GGBS), in combination with PC. Also, the effects of different combinations of cementitious fillers on the road performance of CAEMs are examined and elucidated experimentally. The results showed that the compressive and indirect tensile strengths of CAEMs increase by 47% and 49%, respectively, by admixing 3.6 wt% PC and 0.4 wt% GGBS. It was found that artificial by-products have a positive impact on the road performance of CAEMs. In addition, the improved strength is attributed not only to the formation of hydration products and accelerated demulsification of asphalt emulsion but also to the improvement of the interface transition zone between aggregates and binders.

Porous asphalt (PA) mixture is a hot mix asphalt with an open gradation that has a high amount of air void in its structure. Although this high volume of empty space in PA has several road safety and environmental benefits, it causes some performance drawbacks like reducing PA mixes’ resistance against rutting and cracking and increasing sensitivity to aging and moisture conditions. This study aims to evaluate the rutting and intermediate-temperature cracking behavior of PA mixes modified with various percentages of nano-ZnO (NZ) (0%, 2%, 4%, 6%, and 8%) under laboratory aging conditions and freeze–thaw (F-T) cycle by performing wheel track and semicircular bending (SCB) tests. It can be inferred from the wheel track results that while the aging process positively affects the rutting behavior of the PA mixtures, the F-T cycle decreases PA mixtures’ rutting resistance because moisture deteriorates the adhesion between bitumen and aggregates. From the SCB test results, both the aging and F-T cycle negatively impact the crack resistance of the PA mix. Moreover, the results indicate that adding NZ improves PA mixtures’ performance against permanent deformation and cracking by an average of 50%. The optimum content of the NZ modifier in PA mixes was 6%.

Although there have been several studies about using recycled aggregates to construct recycled aggregate base (RAB) layers, there is a lack of information about the effects of gradation of recycled concrete aggregate (RCA) materials on the performance of such layers. There is also limited information available regarding the use of RCA and recycled asphalt pavement (RAP) materials together in RAB layers. In this study, three test cells were constructed with RAB layers using two different RCA materials with different gradations and a blend of RCA and RAP materials, and another cell was constructed with a natural aggregate base layer. Physical characteristics of the base layer aggregates were determined, and resilient modulus ($M_R$) tests were performed. A series of falling weight deflectometer (FWD) tests were performed in the field, and changes in air and soil temperatures over time were monitored. This paper contains detailed information about the evaluation of the engineering properties of recycled aggregates and the preliminary performance of the constructed RAB layers.

Phosphoaluminate cement (PAC) is a green cementing material with wide application prospects. Its main mineral compositions are calcium aluminate (CA), tricalcium phosphate $({\mathrm{C}}_3\mathrm{P})$, and calcium aluminophosphate (CAP). In this study, calcium aluminophosphate mineral was prepared in the laboratory, and its binding with chloride ions was investigated as a separate binder. The microstructure and the hydration and hardening process of the CAP paste were observed by X-ray computed tomography (XCT) and scanning electron microscopy (SEM), and the phase analysis of the hydration products before and after being soaked in sodium chloride solution was conducted using X-ray diffraction. The mechanism for the binding of the hardened CAP paste with chloride ions was also studied. The results show that the Freundlich isotherm well models the adsorption of chloride ions onto the hydration products. The binding of chloride ions with the CAP is chiefly attributed to the chemical bonding of the hydrated calcium aluminate with the ions, which is different from that with portland cement, largely caused by the physical adsorption of them onto the C─ S─ H gel.

To improve the environmental friendliness and sustainability of road deicing and snow melting, a kind of conductive ethylene–propylene–diene monomer (EPDM) rubber composite material with a thermally conductive layer, a heat-generating layer, and a heat-insulation layer is presented. It is placed under the asphalt surface to generate heat for deicing and snow melting by means of electrical heating. Vehicle load is inevitable in the road environment. To determine the feasibility of composite material long-term applications in the road environment, this paper mainly studied the durability of composite materials under vehicle load by rutting tests, resistance stability tests, mechanical properties tests, and heating tests. The results show that it has good anti-deformation durability and resistance stability under vehicle load. It has good mechanical and electrothermal durability after undergoing vehicle load. The durability of the composite material meets the requirements of safety, stability, and sustainability for long-term use in deicing under vehicle load. It is used as active deicing and snow-melting material in the road environment under vehicle load with broad application prospects.

In this study, the potential to directly use magnesium hydroxide as an alternative binder was investigated. A compaction molding technique was employed, where magnesium hydroxide powder was mixed with water at relatively low water-to-binder ratios, compacted in a mold, then subjected to accelerated ${\mathrm{CO}}_2$ curing at room temperature to form a carbonate binder. The influence of water-to-binder ratio and compaction pressure on the mechanical and microstructural properties of compacted magnesium hydroxide systems under accelerated ${\mathrm{CO}}_2$ curing was evaluated. Results showed that compaction pressure and water-to-binder ratio have a significant effect on ${\mathrm{CO}}_2$ uptake and strength development. An optimum compaction level was found to be 3 MPa in this study, where compressive strengths of $33.5\pm 4.0$ and $70.8\pm 4.1\mathrm{MPa}$ were reached after 2 and 5 days of ${\mathrm{CO}}_2$ curing. Results highlight the potential to tailor the mechanical properties of magnesium hydroxide systems through processing, and to reach strengths comparable to those of magnesium oxide systems but with the advantage of skipping the calcination step and reducing water demand.

Degradation of ballast aggregate subjected to applied train loads can adversely influence the performance of ballasted railway tracks. Meanwhile, replacement of degraded aggregate with fresh material can engender some environmental concerns due to the necessity of implementing a scheduled maintenance program on ballasted railway tracks. Therefore, using recycled ballast material combined with fresh aggregate derived from rock quarries is characterized as an appropriate maintenance strategy. In the present study, various percentages of recycled ballast are combined with fresh aggregate, then the performance of prepared specimens against degradation is investigated by conducting a large-scale drop-weight impact loading test. Furthermore, the effect of addition of discarded crumb rubber particles on the degradation resistance of the prepared specimens is evaluated. Generally, the recycled aggregate exhibits higher level of degradation due to spitting individual particle, although the generation of fine particles considerably decreases. Likewise, the combination of various portions of recycled and fresh aggregate shows that further reduction of proportion of recycled material leads to the exacerbation of the fouling level and reduction of the breakage of single aggregate. Furthermore, the incorporation of discarded crumb rubber particles among prepared mixtures of recycled and fresh ballast aggregate evidently enhances the performance of recycled/fresh mixtures of aggregate especially for lower percentages of recycled aggregate.

To predict the fractured rock failure under deep triaxial stress, true triaxial tests were carried out using thermal infrared monitoring and acoustic emissions (AE). Based on the thermal infrared imagery, which may hold potential information for predicting rock failure, this paper proposes the infrared temperature jumping rate (ITJR) to reflect the jumpiness of the temperature field matrix and establishes an infrared advance prediction method. The results show that the high-temperature area will converge and expand gradually, and cracks propagate along a certain direction. In the sudden-temperature-reduction area, rock stripping is easy to occur. At the boundary between high- and low-temperature areas, it is easy to produce breakage cracks and form rock spalling. In the short quiet period, the rock gradually gathers strain energy, which will be released in the fracture period. By comparing the time of AE sudden increase with the time of ITJR mutation, it shows that the method has a good advance prediction effect for rock fracture.

The employment of industrial by-products with pozzolanic properties (e.g., fly ash) is a viable technique for soil stabilization purposes when a more advantageous environmental performance is sought. For routine engineering purposes, compacted soil-binder mixes are considered as isotropic materials, even though a rather cross-anisotropic material structure may be induced during the preparation process. A series of experimental shear tests at constant mean effective stress on laboratory compacted sand-fly ash-lime soil samples has been performed under drained conditions in a true triaxial apparatus. The influence of the intermediate principal stress and the effect of deviatoric linear stress path directions on the mechanical response were particularly investigated. The relative magnitude of the intermediate principal stress ratio, expressed in terms of the $b$-value, $b=({\sigma }_2^{\prime }-{\sigma }_3^{\prime })/({\sigma }_1^{\prime }-{\sigma }_3^{\prime })$, showed significant effects on the stress-strain, volumetric, and strength characteristics of the compacted sand-fly ash-lime soil. The latter decreases as $b$-value increases. However, different deviatoric linear stress-controlled paths conducted at a constant $b$-value revealed a rather isotropic response, which seemed to suggest that the cementation is erasing the inherent material anisotropy. Finally, the tested samples fitted well into the both Willam and Warnke and Kim-Lade failure criteria.

There is a scarcity of natural river sand due to the ban on mining of sand from riverbeds, attributed to environmental and ecological issues. Therefore, there are attempts to use nonorganic solid wastes and industrial by-products as sand substitutes. The paper reports experimental studies on the suitability of processed granulated blast furnace slag (PGBS) as fine aggregate in the mortars used in masonry construction. The physical and chemical characteristics of the PGBS and the properties of mortars made with PGBS, such as workability, compressive strength, water retentivity, drying shrinkage, and elastic properties, were examined. The masonry properties such as compressive strength, flexure bond strength, and stress-strain characteristics were investigated using PGBS- and sand-based mortars. The investigations show that PGBS can be a potential substitute to river sand in the masonry application. The addition of PGBS was beneficial in terms of mortar and masonry characteristics. In the case of lean mortars, the addition of PGBS showed 30% to 45% spike in compressive strength. Thermogravimetry was used to quantify hydration products formed in PGBS-based and river sand–based mortars. The experimental outcomes indicate that (1) the physical and chemical properties of PGBS were similar to those of river sand except that the PGBS may show mild pozzolanic activity and higher water absorption; and (2) the masonry compressive strength increased by $\sim 22\%$, and the flexure bond strength nearly doubled when PGBS-based mortars were used.

Unavoidable cracks cause a significant reduction in the strength and longevity of concrete. Water and several harmful ions seep through the cracks, initiate corrosion of the reinforcement, and affect the self-life of concrete. Self-repaired concrete will stand for a longer period and thus is gaining interest for constructions purposes. This work was an attempt to design a microbial protein (∼28 kDa) that incorporated self-healing cementitious material for future construction needs. The protein was isolated from an alkaliphilic hot spring bacterium (BKH4) of Bakreshwar, West Bengal, India. The prepared control and protein-amended cementitious mortar samples were subjected to simulate cracks and cured under water for several days. Images and microstructures of the control and protein-incorporated samples were analyzed, which established that there was a tiny fingers-like crystalline substance developed on the cracked surfaces. The developed substance was identified as a silicate phase (Gehlenite) by energy dispersive X-ray spectroscopic analysis. The microbial protein enhanced the mechanical strengths and durability of the protein-incorporated samples that were supported by the increments of ultrasonic pulse velocity, compressive strength, and sulfate resistance as well as reduction of water permeability and slow water movement (sorptivity test) of the experimental samples. This self-healing phenomenon is eco-efficient and developed due to the bio-silicification action of the microbial protein that was incorporated in mortar samples.

The $\mathrm{EAC}+\mathrm{SMA}$ composite structure, made from epoxy asphalt concrete (EAC) with stone matrix asphalt (SMA) concrete on top, is a double-layered heterogeneous structure applied to steel bridge deck pavement (SBDP) in recent years. The interlayer bonding performance is key to the long-life application of $\mathrm{EAC}+\mathrm{SMA}$. In this study, the objective is to investigate the interlayer bonding performance of $\mathrm{EAC}+\mathrm{SMA}$ composite structure to identify its best design and construction strategy. To achieve this goal, a series of pull-off tests and interlayer shear tests under different test conditions were performed on four commonly used $\mathrm{EAC}+\mathrm{SMA}$ composite structures. The effects of design parameters, the construction conditions, and the application environment of $\mathrm{EAC}+\mathrm{SMA}$ structure on its interlayer bonding performance were evaluated. The results showed that the $\mathrm{EAC}+\mathrm{SMA}$ composite structure with SMA13 (SMA mixture with the nominal maximum aggregate size of 13.2 mm) as the wearing layer material and epoxy resin–based bonding material possessed the best interlayer bonding performance among the four composite structures. It is suggested that the bonding layer and SMA layer should be constructed after the Marshall stability of the EAC layer reaches 15 kN, and the construction interface should be clean to achieve the best interlayer bonding performance for the $\mathrm{EAC}+\mathrm{SMA}$ composite structure. In addition, the mixed-mode cohesive zone model was developed to characterize the interlayer bonding behaviors in the mechanical analysis of $\mathrm{EAC}+\mathrm{SMA}$ composite structures, and the proposed numerical characterization method could be used to obtain more accurate mechanical results for the structure design compared with the traditional numerical characterization method under the interlayer continuous assumption.

In this work, microencapsulated phase change material (MEPCM) with the eutectic mixture of stearic acid (SA) and coconut oil (CO) as the core and melamine formaldehyde (MF) as the shell was developed by emulsion-polymerization method to be applied in the gypsum plaster tile as a passive way for thermal energy storage (TES) applications. Thermal and chemical characterization, particle size distribution (PSD), and thermal resistance of the developed MEPCM were investigated. The effects of adding MEPCM on thermal conductivity, density, and mechanical strength of gypsum plaster tile were reported. The results indicated an optimum eutectic combination ratio of 20%–80% by weight of SA-CO, MF concentrations of 75% by weight with 73.5% encapsulation efficiency for the synthesized MEPCM, phase change temperature of 21°C to 28.6°C and TES of $35.04\mathrm{J}/\mathrm{g}$. The reliability and thermal stability of the produced MEPCM was proved and implied no degradation in the chemical structure of MEPCM after repeated melting and solidification processes due to protection of core materials by MF shell. The gypsum/MEPCM composite resulted acceptable mechanical strength with thermal conductivity of 0.33 W/(m · K) and density of $919\mathrm{kg}/{\mathrm{m}}^3$. The calculated extent of thermal energy storage for the simulated room that covered with G/M33 with 10% by weight of MEPCM in the interior walls and roof showed about 12% reduction in energy consumption.

This research investigated tensile creep of early age high-strength concrete (HSC) modified with superabsorbent polymer (SAP). A temperature stress test machine was utilized to investigate the influence of loading age (0.50, 0.67, 0.83, 1, 3, 5, and 7 days) on the tensile creep performance of HSC modified with SAP at early age. The experimental analyses indicated that (1) the basic tensile creep, basic tensile creep coefficient, and specific basic tensile creep of HSC modified with SAP decreased with increasing loading age, and the aging effect on the tensile creep of HSC modified with SAP was significant when the concrete was loaded within 1 day; (2) the specific basic tensile creep rate was high at early loading ages, then decreased and tended to be stable, and the earlier the loading age, the greater was the divergence between the initial creep rate and the later creep rate at the same loading age; and (3) the relative specific basic tensile creep decreased exponentially when concrete was loaded within 1 day and decreased linearly when concrete was loaded after 3 days, and the proportionality limit of specific basic tensile creep occurred at a loading age of 1.60 days, which was determined by linear and nonlinear regression analysis. A model for predicting the tensile creep of HSC modified with SAP considering loading age is proposed.

A new theoretical calculation method for the two opposite-side chloride diffusions was established, which is different from traditional diffusion calculations and the value-taking rule of error function. A new parameter, $\delta$, a diffuse constant of the object being diffused, is proposed to reflect the internal diffusion characteristics of the object, and the concrete studied in this paper has a $\delta$ value between 2 and 3—closer to 3. By performing comparison experiments with a stronger effect of superposition and accumulation in concrete under two opposite-side chloride ion, diffusion can be found, which is consistent with the calculation results. In order to improve the resistance of concrete to two opposite-side chloride codiffusion, the concrete modified by nanosilica and nanotitania was designed in this study. Due to its excellent microstructure and porosity properties, the concrete modified by nanosilica at 1.5% and nanotitania at 0.5% cement weight showed an excellent resistance to the single-side chloride ion diffusion, and the same goes for two opposite-side diffusions.

This paper studies the feasibility of replacing fly ash in cement-based grouting material with gold tailings after compound activation. Through mercury intrusion porosimetry (MIP), X-ray diffractometer (XRD), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS), the activation mechanism of gold tailings and the effect of activated gold tailings on the macroscopic properties, pore structure, hydration products, and microstructure of cement-based grouting material were studied. The results show that after the tailings are treated by compound mechanical-chemical-thermal activation, the activity index (28 days) of the cement tailings mortar is as high as 76.83%, and the pozzolanic activity meets the requirements. When activated gold tailings replace 60% fly ash in cement-based grouting material, the macroscopic properties of the grouting material reach the optimal value, the microstructure is denser, and the hydration products are calcium hydroxide, calcium–silicate–hydrate (C─ S─ H) gel, and ettringite. This research provides a new method for the effective utilization of gold tailings and a reference for the practical application of gold tailings as supplementary cementitious materials in the future.

The slab track temperature is significant with respect to the safety of the vehicle. The objective of this study was to investigate the cooling effects of solar reflective coatings (SRCs) on slab tracks. Two types of coatings were applied in the outdoor environment, and a model considering reflective coatings was subsequently established. The coatings decreased the maximum temperature and maximum temperature gradient by $8°\mathrm{C}-12°\mathrm{C}$ and $20°\mathrm{C}/\mathrm{m}-30°\mathrm{C}/\mathrm{m}$, respectively. The albedo of an SRC on a slab track was suggested to be greater than 0.6. The coatings exhibited superior cooling effects in case the wind scale was lower than Level 2.

One of the effective ways to improve the energy efficiency of buildings is the use of thermally efficient materials in the production of various building enveloped elements such as wall panels. With the increasing sustainability awareness in the construction industry and the use of cementitious materials being the most used construction materials, eco-friendly materials such as expanded glass can be utilized as lightweight aggregates to produce lightweight mortars for the construction of these elements. The novelty of this work is the results that have been obtained from the evaluation of mortars designed for the production of lightweight thermal-efficient wall panels using expanded glass as aggregates. Various proportion of expanded glass was used in the production of mortars to determine their influence on the properties of the mortar. The properties investigated are flow, thermal conductivity, compressive strength, void content, absorption, drying shrinkage, and resistance to alkali-silica reaction. Ultrasonic pulse velocity test was also utilized as a nondestructive test to assess the mortars. The findings from this study showed that it is viable to produce lightweight thermal-efficient mortars using expanded glass. The thermal conductivity of the mortars was reduced up to 78.4% when the cement to expanded glass ratio increased to $1:5$. Despite the reduction in compressive strength as a result of the presence of the expanded glass, these mortars still possess acceptable properties for the production of wall panels.

In this study, the early-age mechanical properties of a concrete mix containing ground granulated blast furnace slag (GGBFS) were investigated and incorporated in a finite-element model. The viscoelastic behavior caused by early-age tensile creep was considered using a viscoelastic analysis in which the creep strain increment was calculated using a strain superposition method. Subroutines for a FEM program (ABAQUS) were developed to predict the stress time-history considering early-age tensile and compressive creep during thermal loading and unloading. Three 1.2-m (4-ft) cubes were cast with a mix design containing 50% replacement by weight of the cement with GGBFS. The FEM predictions match well with the experimental strain measurements. The results indicate that using the proposed analysis and the measured mechanical properties obtains an accurate estimation of the maximum tensile stress for a concrete mix containing GGBFS. Engineers can use the estimated tensile stresses to take preventative measures to minimize the risk of thermal cracking on mass concrete structures.

Highly polymerized asphalt binders (HPABs) such as PG 64-40 have been increasingly used in cold regions such as Alaska in recent years. However, there are currently considerable data gaps when it comes to the characterizations of the HPABs, especially their fatigue behaviors. The objective of this study is to apply the linear amplitude sweep (LAS) test with the viscoelastic continuum damage (VECD) model to assess the fatigue resistance of HPABs. Three HPABs (PG 52-40, PG 64-40, and PG 52-46) and one unmodified binder (PG 52-28) were used in the study. The fatigue failure during LAS tests on HPABs was defined, and an analysis protocol using the VECD model was proposed based on the experimental results. The analysis protocol was validated by the agreements of the predicted and measured number of cycles to failure in the time sweep (TS) test. The results indicated that the LAS test with the selected analysis protocol can effectively predict the fatigue lives of HPABs. Both the LAS and TS test results showed that the HPABs had higher fatigue resistance than the unmodified asphalt binder. Among the four binders, the PG 64-40 binder exhibited the longest fatigue lives under repeated loadings.

Recycled aggregates extracted from the construction and demolition waste of brick and concrete building are mixed recycled aggregates (MRA), which comprise concrete recycled aggregate (CRA) and brick recycled aggregate (BRA). The components of coarse aggregate used in concrete incorporated with MRA are natural aggregate (NA), CRA, and BRA. Due to the complex component of coarse aggregate used in mixed recycled aggregate concrete (MRC), the conventional mix design method is not suitable for MRC. The increase of coarse aggregate heterogeneity, larger total mortar volume of MRC, and the weaker strength of CRA and BRA are the primary differences between MRC and natural concrete (NC). There is no literature to propose a mix design method suitable for MRC with regard to the defects mentioned previously. To address this issue, a novel mix design method was proposed. First, the minimum density difference (MDD) method was proposed to minimize the density difference between fresh mortar and the MRA of MRC, so as to improve the homogeneity. And then the mortar volume in MRC is equal to that of NC by using the equivalent mortar volume (EMV) method. Finally, the minimum paste theory is combined with MDD and EMV methods to determine the parameters of mix proportion, so as to compensate for the defect of too little cement paste content caused by the EMV method. The experimental results showed that when the water:cement ratio is 0.5, compared with the conventional concrete mix design method, the proposed mix design method can increase the compressive strength and elastic modulus by 5% and 22.8%, respectively, and reduce the heterogeneity degree and shrinkage value (90 days) by 8.5% and 23.4%, respectively. When the water:cement ratio is 0.65, the compressive strength and elastic modulus increased by 4% and 33.5%, respectively, and the heterogeneity degree and shrinkage value (90 days) decreased by 28.44% and 23.7%, respectively. The proposed mix design method also consumed a lesser quantity of cement.

To solve the problem of the unsatisfactory effect of grouting reinforcement in broken rock mass, a cement-based composite slurry was successfully prepared by using ordinary Portland cement as the main material in this study. By conducting a single factor test, orthogonal test, and organic compound modification test, the effects of different addition ratios of fly ash, clay and waterborne polyurethane, epoxy resin, and other organic materials on the grouting performance of cement slurry were analyzed. In addition, a grouting simulation test system was used to verify the reinforcement effect of the prepared composite slurry. The results indicate that the addition ratio of clay and fly ash has a strong influence on the strength and stone rate of cement slurry. The final setting time of the best mixed slurry can be shortened to 11 h, and the compressive strength after 28 days can reach 18 MPa. The composite slurry modified by organic materials has a reinforcement coefficient of up to 4.6 for crushed sandstone, which significantly improved the brittle failure phenomenon of the reinforcement stone body and, thus, has high application value.

The fatigue resistance of an asphalt mixture is crucial to the pavement’s durability and serviceability of pavement. The pavement structure is in a three-dimensional (3D) stress state. However, the conventional fatigue-resistance design index mostly considers a one-dimensional stress state, which is different from the field conditions. In this paper, the unconfined compression test (UCT), direct tension test (DTT), and splitting test (SPT) were selected to conduct the strength and fatigue tests. Based on the Ayyagari Vural yield criterion, the strength damage surface under various loading rates was established. Furthermore, a normalized fatigue equation was developed in a 3D stress state by determining the fatigue-damaged path based on the yield criterion. Finally, the fatigue-resistance models for the structural design were proposed by combining the strength models (including the octahedral shear stress model and the Ayyagari Vural model) and the normalized fatigue equation. The results indicate that the strength damage surface model is in an elliptic form, and the surface is abducent as the loading rates increase, and the Ayyagari Vural yield criterion can describe the fatigue failure process. Both fatigue-resistance design methods for pavement resistance take the interaction among three principal stresses into consideration and comply with the failure characteristics of actual pavement structures; the equivalent stress as a design index is more feasible in its actual application. This study could provide a reference for the fatigue-resistance design of asphalt mixture layers in a complex stress state and improve the reliability in the pavement structure.

Hydraulic conductivity is a key parameter in the penetration of harmful substances, and therefore it is important to better understand microstructure-based durability performance in cementitious materials. The hydraulic conductivity of cementitious materials has typically been obtained by measuring the amount of water entry based on Darcy’s law. However, such measurement is challenging, and it is difficult to study penetration behavior along the longitudinal section of cementitious materials. In this work, a new experimental method was designed to measure the chloride penetration depth of cementitious materials and enable visual examination of hydraulic behavior in the longitudinal section of materials under a hydrostatic pressure gradient. The chloride penetration depth can be converted into hydraulic conductivity if the hydrostatic pressure applied to the materials, the chloride penetration depth, and the chloride concentration at the depth are known. As part of this work, the effect of capillary porewater on the hydraulic conductivity was examined. The result was compared with experimental data, and revealed that seawater penetrates into concrete and is mixed with capillary porewater and diluted, and the mixed water again penetrates into the concrete by hydraulic pressure.

The inclusion of recycled plastics into hot-mix asphalt is highly desirable for improved pavement performance. In this study, the need for enhanced compatibility between the components and increased mechanical performance of asphalt (AS) and polyethylene (PE) blends was addressed through the use of dispersed/exfoliated nanoclays (NC). Fourier-transform infrared (FTIR) spectroscopy showed evidence of new chemical interactions of the dispersed NC-d within the AS/PE matrix, suggesting a better-blended phase morphology. The layered silicate plate-like morphology of dispersed/exfoliated NC, identified by scanning electron microscopy, SEM, observations, promotes a greater adhesion between asphalt and polyethylene, leading to significant enhancements in all mechanical properties of viscoelastic AS/PE/NC-d blend. Indirect tensile (IDT) strength, uniaxial compression, and compression fatigue tests were performed on AS/PE blends modified by “as received” and dispersed/exfoliated NCs. The effective modification of the AS/PE blend with the dispersed/exfoliated NC-d is demonstrated by a significant improvement in IDT strength (40%), cracking tolerance index (26%), failure energy (22%), compressive strength (42%), and dynamic modulus (44%).