Journal of Materials in Civil Engineering

The continuous advancement in construction materials and technology demands novel admixtures to make concrete more sustainable and durable. Several supplementary cementitious materials are already being used to replace cement partially for alleviating the destructive environmental aspects. The common durability issues faced by concrete are drying shrinkage, sulfate attacks, alkali-silica reaction, and chloride attacks. This experimental study presents a solution by analysing the effect of fumed silica nanoparticles on durability, most of which are related to permeability. The fumed silica nanoparticles were incorporated in concrete as cement substitution at 0.5%, 1.0%, 1.5%, and 2.0%. Durability performance was examined by conducting the rapid chloride permeability test (RCPT), sulfate attack resistivity test, drying shrinkage test, and water absorption test. The additional tests were conducted to determine the density, void content, and compressive strength of concrete and cement mortar samples. Also, field emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDAX) were performed to understand the microstructure. The test results indicated that 2% fumed silica provided optimum results in terms of workability and mechanical performance. Compressive strength was increased by 20% and 27% in mortar and concrete, respectively. In addition, drying shrinkage was reduced by 72%, and expansion due to sulfate attack and alkali-silica were reduced by 79%, and 71% respectively. Furthermore, the rapid chloride permeability test showed that addition of 2% fumed silica resulted in overall reduction in permeability by 47%. This study corroborates that fumed silica nanoparticles-incorporated concrete is more durable than ordinary concrete. Fumed nanosilica can be effectively used in the production of performance-based cement composites. These nanoparticles have shown excellent potential in controlling drying shrinkage and permeability-related issues, including sulfate attacks and corrosion.

Chloride-based deicing salts are considered to be cost-effective and highly efficient in ensuring safe and efficient roadway and/or aircraft operation during snowy pavement conditions. However, it brings inevitable detrimental effects on the asphalt pavement. This study seeks to elucidate the influence of deicing salt type, concentration, and exposed environment on moisture susceptibility of an asphalt mixture. Immersion Marshall stability testing and freezing-thawing splitting tensile testing were employed to evaluate the moisture susceptibility of the asphalt mixture under drying-wetting and freezing-thawing cycling. Two types of compound deicing agents and three concentrations of 3%, 10%, and 20% of each salt were used to examine and compare their degrees of deterioration on the asphalt mixture. Statistical analysis was performed to establish the relationship between key indicators of moisture susceptibility and the main factors of the asphalt mixture. Microstructure analysis was carried out to elucidate the effects of those factors on the moisture susceptibility of the asphalt mixture using x-ray diffraction (XRD) analysis and scanning electron microscope (SEM) observation. Test results indicated that the moisture susceptibility of the asphalt mixture was greatly influenced by the salt concentration and conditioned drying-wetting (D/W) or freezing-thawing (F/T) cycles. With the increase of D/W or F/T cycles, the Marshall stability, Marshall modulus, and splitting tensile strength decreased while the flow value increased. The 3% salt concentration showed a significant effect on moisture susceptibility, followed by 10% and then 20%. The proposed models can effectively predict the key indicators of moisture susceptibility with high correlation coefficients over 0.9. As confirmed by the microstructural analyses, the deterioration of the asphalt mixture under simulated environmental conditions was attributed to decreased asphalt-aggregate adhesion from water ingress, salt crystallization, and/or ice formation pressure.

Extraction of recycled concrete aggregates (RCA) from construction and demolition waste is an effective way to induce sustainability in the highway sector. However, inclusions of these inferior materials could significantly deteriorate the performance of paving quality concrete (PQC) due to the presence of old adhered mortar (AM) around the RCA. Numerous techniques are available in the literature that primarily address the issues with AM for increasing the potential of RCA for concrete applications. However, the energy demand and associated emissions are higher in most of these techniques, whereas carbonation and slurry impregnation (SM) techniques are regarded as the best ways to economically enhance the characteristic of RCA for large-scale applications. The present study is the first of its kind to optimize the SM process for carbonated RCA for PQC roads; RCA was stockpiled in the natural environment in loose condition for around 12–14 months for fully carbonating the Portlandite phase. The parameters optimized are slurry material type (silica fume, fly ash, and cement), their concentrations ($20\%-60\%$), exposure duration ($4–12\mathrm{h}$), and RCA sizes (20 mm and 10 mm), whereas the porosity, toughness, absorption, and dry density were considered for process optimization. Finally, for process validation, various PQC performance parameters (fresh, mechanical, and durability) were determined. The findings suggest soaking the RCA sizes in any of the considered cementitious/waste material slurry at 40% concentration for 6 h for enhanced performance of both RCA and PQC made with treated RCA.

Basalt rock waste is a major industrial waste generated as a result of quarrying rocks and artificial sand manufacture for construction projects, and its disposal can lead to several landfill hazards. However, it shows potential to be used as a source material for the manufacture of geopolymers. This paper presents the triaxial stress-strain characteristics of a novel geopolymer developed from basalt rock waste considering partial replacement with ground granulated blast furnace slag (GGBFS) up to 30%. A detailed mix design investigation revealed the optimum molarity (M) of the sodium hydroxide solution to be 8M and the optimum ratio (R) of sodium silicate to sodium hydroxide solution to be 0.75. The axial stress-strain relationships were developed after a series of triaxial laboratory tests for low confining pressures (0 to 800 kPa) and Hoek cell tests for high confining pressures (1 to 5 MPa). A constitutive model predicting the complete stress-strain behavior is proposed. The geopolymer stress-strain behavior shows some degree of similarity to Portland cement binder; however, differences such as an increase in stiffness and reduction in ductility were observed. Scanning electron microscopy (SEM) images also suggested a dense geopolymer gel formation resulting in a homogeneous and compact microstructure. This study demonstrates that the innovative material proposed herein produced from industrial wastes has characteristics suitable for use as an alternative and sustainable construction material.

Polyurethane resins are often used in the geotechnical domain to fill fine fissures, small underground cavities, or soil pores to reduce soil permeability, improve the bearing capacity of a shallow foundation, limit the compressibility of the foundation soil, reinforce road embankments, or obtain a lifting effect of structures that have suffered differential settlements. Polyurethane resins have been widely investigated from the mechanical point of view, but the effect of long-term aging on mechanical behavior is not yet well documented. This paper aims to investigate mechanical, physical, and chemical variations following an artificial aging treatment of polyurethane resin specimens with different densities, obtained under different expansion conditions. Artificial aging was obtained in several ways, such as soaking samples in different chemical solutions or subjecting them to different environmental conditions, to simulate the long-term effect of staying in the underground environment. Besides verifying the volume stability of specimens before and after aging, uniaxial compression tests have been performed on samples with and without aging treatment to verify maintenance or any change in the mechanical properties. Accelerated aging does not seem to affect volume change or mechanical behavior of the tested polyurethane resins. Comparison of both physical and mechanical properties before and after aging allows the deduction of useful information for practical geotechnical applications. The tested polyurethane resins showed (1) very high durability under several wetting-drying cycles, (2) high stability if exposed to aggressive chemical agents, and (3) practically unchanged deformability and strength in conditions very similar to those present in the ground. Moreover, the samples that underwent the highest volume change when soaked in chemical solutions revealed no any chemical degradation under infrared spectroscopy.

This study contributes to the understanding of the chloride-induced corrosion of steel rebars embedded in various concretes. Concrete specimens were exposed to systematic wetting–drying cycles in real seawater via a platform installed on a pier. Various mixtures were designed using three different cement types and two binder dosages (therefore two water/cement ratios) with and without fly ash. The strength development and electrical conductivity of the mixtures were assessed prior to the cycles. The dimensional stability, flexural strength, compressive strength, and chloride penetration depth of plain concretes were scrutinized during the cycles. The corrosion processes of 360 RC specimens with three different cover thicknesses were monitored. The test results revealed that increasing the dosage of cement, and therefore decreasing the water/cement ratio, was a more effective corrosion-mitigation approach than was the utilization of fly ash or enhancing physical protection.

Fracture is generally the separation of an object into different pieces under the application of external stress. The fracture surface embosses the imprint of the complete deformation process subjected to a material. Hence, it is plausible to correlate fracture features and respective deformation history of a material. Two-dimensional ductile fracture complexions are quantitatively measured on the published creep-ruptured fractographs of a ferritic steel with different product dimensions at various stresses and temperatures. Intercept length measurements were performed to measure the dimple geometry on the published electron fractographs. Irrespective of test parameters and product dimensions, the fracture surface appearance persisted to be ductile transgranular in nature, which has been quantitatively analyzed by the statistical distribution of diverse-sized dimples on the fractographs. The distribution of dimple size quantified from the crept fractographs as a function of temperature and stress were monitored to estimate the nature of disparity in creep responses of the steel. It has been investigated that with the increase of the Larson-Miller parameter, the average dimple size increases as the corresponding applied stress decreases. Finally, this research brings to the fore that from the quantification of systematic crept fractographs, it is possible to reasonably deduce the creep properties/life of a ferritic steel, when the material microstructure is known.

The effects of a warm-mix agent, PN2217, on the rheological properties and thermal stability of alumina trihydrate/organic montmorillonite (ATH/OMMT) composite flame-retardant asphalt were investigated in this study. Dynamic shear rheological and multiple stress creep recovery tests were performed to investigate the high-temperature rheological properties of ATH/OMMT flame-retardant asphalts with different amounts of PN2217. Thermogravimetry–differential scanning calorimetry was performed to evaluate the thermal stability of the asphalt binders. Kinetic analyses were conducted to investigate the combustion mechanism. Fourier-transform infrared (FTIR) spectroscopy and atomic force microscopy were performed to investigate the reaction mechanism of PN2217 with the ATH/OMMT flame-retardant asphalt. The microstructure of the combustion residue was analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The FTIR spectra revealed no chemical change after the addition of PN2217 to the flame-retardant asphalt. The results indicated that PN2217 adversely affected the elastic response and rutting resistance of the ATH/OMMT asphalt because the intercalated structure formed by the intercalation of the asphalt molecules into OMMT was transformed into a phase-separated structure in the presence of PN2217. Moreover, PN2217 adversely affected the thermal stability of the ATH/OMMT asphalt by reducing the activation energy and preventing the formation of a char layer during combustion.

This paper studied the influence of ${\mathrm{CO}}_2$ curing and autoclaved aerated concrete powder on the sulfate attack of a cement sample at low temperature. The basic performance including compressive strength, mass and volume changes, and microstructure tests were analyzed by X-ray diffraction (QXRD/Rietveld), mercury intrusion porosimeter (MIP) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) analysis. Results proved that the strength of PC (Portland cement)-WAAC (waste autoclaved aerated concrete) pastes decreased after low-temperature sulfate attack; however, carbonation curing could mitigate the decrease. Compared with the strength of the uncarbonated specimens without sulfate immersion, the strengths of the ${\mathrm{CO}}_2$-cured specimens added with 0%, 10%, and 20% of WAAC after 6 months of sulfate immersion were still 3.93%, 11.90%, and 18.31% higher. The compressive strength reduction of the carbonated samples after 6 months of low-temperature sulfate immersion ($9.31\%–46.15\%$) was much lower than that of the uncarbonated specimens ($15.55\%–61.97\%$). In addition, ${\mathrm{CO}}_2$ curing decreased the porosity and improved the pore structure of the samples, thereby inhibiting sample volume expansion resulting from sulfate immersion. Carbonation curing improved the resistance of PC-WAAC specimens to low-temperature sulfate attack. After low-temperature sulfate immersion, thaumasite did not form in the carbonation curing samples. Therefore, WAAC recycling combined with carbonation curing can produce cementitious materials with good environmental sustainability and better long-term durability in sulfate erosion areas.

Abstract

Enzyme-induced calcium carbonate precipitation (EICP) is an environmentally friendly and promising method for sand treatment. However, the effect of EICP treatment alone is not sufficient to satisfy the engineering requirements for sand. The addition of fibers is an advantageous approach to enhancing the mechanical strength of EICP-treated sand. Most fibers used as reinforcement are synthetic fibers; this practice is wasteful and poses a risk of environmental pollution. The novel exploration performed in this work investigated the enhancement effect of natural fibers for EICP-treated sand. In this study, the enhancement effects of sisal, a natural fiber, and polypropylene, a synthetic fiber, on EICP-treated sand were compared. Three aspects of the enhancement effects—calcium carbonate content, strength, and toughness—were evaluated. In addition, solution analysis and microscopy observations were conducted to analyze enhancement mechanisms. The results showed that the sisal fibers did in fact contribute to the effects on EICP-treated sand, and their enhancement effect was better than that of polypropylene fibers. Specifically, with the addition of sisal and polypropylene fibers to EICP-treated sand, values of unconfined compressive strength (UCS) were 322 and 213 kPa, respectively. The solution analysis results and microscopy observations indicated that the coarser surface structure of sisal fibers resulted in stronger reinforcement than the reinforcement provided by polypropylene fibers.

Practical Applications

The mechanical properties of sand can be improved to a certain extent when sand is treated by enzyme-induced calcium carbonate precipitation. However, the enzyme-induced calcium carbonate precipitation–treated samples shown obvious brittleness, which would lead to a sudden destruction. This is unacceptable in practical projects. The application of fibers not only delays the destruction of samples but also improves the strength of enzyme-induced calcium carbonate precipitation–treated sand to a certain extent. Synthetic fibers have been widely used in soil reinforcement and brittleness reduction. This study found that natural fibers, represented by sisal fibers, can be used as a green alternative to synthetic fibers in the future. In addition, this study provided guidance for coastal zone development, island construction, and sand slope protection projects. However, it is important to note that this study was only a preliminary confirmation of the feasibility of the use of natural fibers in enzyme-induced calcium carbonate precipitation–treated sand. Natural fibers still need some modification before they can be used in practical engineering.

Coal bottom ash was pulverized into a fine powder and dispersed within a polycarboxylate-water solution to reinforce the interfacial transition zone and matrix of recycled aggregate concrete. The dispersion was used as part of a three-stage mixing sequence that included direct coating over recycled aggregate prior to, and immediately after, the application of a cement clinker coat to enhance the aggregate–cement clinker interface and the bulk matrix properties. The results suggest that when adequately dispersed, the bottom ash slurry enhances the performance of the recycled aggregate concrete system. The addition of a well-dispersed bottom ash slurry coating reinforces both the interfacial transition zone and the bulk matrix. The slurry decreases porosity and unhydrated clinker content and increases the presence of high-density Calcium-Silicate-Hydrate (C-S-H) near the interfacial transition zone. This leads to significant increases in both tensile and compressive strength and fracture toughness ($\sim 12\%$).

Asphalt aging caused by light, oxygen, water, and so forth (coupling aging) during construction and service of asphalt pavement is a major cause of pavement damage. In this study, the basic test (required in the construction regulations), rheological test, anti-fatigue test, Fourier-transform infrared spectroscopy test (FTIR), and dielectric property test of asphalt were conducted to investigate the antiaging performance and aging mechanism of matrix asphalt (90#) and styrenic block copolymers (SBS)-modified asphalt during coupling aging (including the effect of heat, oxygen, ultraviolet, and water). The method of quantitative evaluation of coupling aging process was discussed using the aforementioned tests, and the quantitative correspondence between performance and components based on dielectric properties was established, an equation was also established to predict the properties of asphalt by using dielectric constant. The results show that (1) the aging mechanisms of asphalt caused by temperature, oxygen, ultraviolet light, and water are different, so the performance of asphalt after those four kinds of aging is different; (2) the penetration, viscosity, principal curve, fatigue life, and sulfoxide index of asphalt change regularly with the increase of aging, and can be used as quantitative indexes to describe the aging degree or aging mechanism of asphalt; and (3) it is feasible to divide asphalt components, determine the aging mechanism of asphalt, and describe and predict the performance of asphalt based on the dielectric properties of asphalt. This study reveals the influence of coupling aging on the performance of asphalt from a new perspective, which has significance for the study of the mechanism of asphalt aging and the guidance of asphalt pavement construction.

Reinforcing fibers to improve the performance of asphalt mixtures have gained considerable attention recently. However, previous studies focused more on the scale of the asphalt mixture and less on the asphalt mastic, which plays a major bonding role in the asphalt mixture. This study aims to determine the optimal design of carbon fiber asphalt mastic by studying its rheological properties. Three lengths (0.5, 1, and 2 mm) and four percentage (0%, 3%, 6%, and 9% by mass of asphalt) of carbon fibers were used in this study. Frequency sweep, linear amplitude sweep, multiple stress creep recovery, elastic recovery, and bending beam rheometer tests were conducted for evaluating the linear viscoelastic properties, fatigue performance, rutting resistance, elastic recovery ability, and low-temperature performance of asphalt mastic. The test results showed that the length and content of carbon fibers positively affect the stiffness of the modified asphalt mastic, which means that the deformation resistance progressively increased with the increase of fiber length and content, as observed in the dynamic modulus master curves. Further, analysis of the phase angle master curves revealed that the asphalt mastic modified with longer and higher numbers of fibers exhibits stronger elastic properties at low and high temperatures, which is conducive to improving the asphalt’s high-temperature stability. Nonetheless, the incorporation of carbon fibers reduced the asphalt mastic’s fatigue resistance and fatigue life at medium temperatures and its cracking resistance at low temperatures. According to the elastic recovery test, asphalt mastic with a longer fiber had a higher elastic recovery capacity, whereas asphalt mastic with a shorter fiber had certain limitations. Furthermore, the temperature increase improved the low-temperature performance of asphalt mastic by increasing the creep rate. Considering the test results and modeling the performance parameters by the response surface method, the optimal proportioning proposal was determined by to 9% fiber content and 1 mm fiber length.

The global coal plants are gradually decreasing to improve sustainability, resulting in the possible resource shortage of fly ash (FA) as the main raw material of engineered cementitious composite (ECC). In order to seek good candidates, this paper systematically studied the possibility of using ground granulated blast-furnace slag (or slag, GGBS) as the partial FA replacement for preparing ECC (i.e., GGBS-ECC). Using the uniaxial tensile and compressive tests, the macromechanical properties were achieved; at mesoscale, the three-point bending, single crack tensile, and single fiber pullout tests were performed to explain the tensile ductility; the microscopic techniques including gas permeation and mercury intrusion porosimetry (MIP) were applied to measure the permeability and pore structure. The results revealed that adding GGBS into ECC increased the tensile and compressive strength at either 7 days or 28 days and changed little (reduced) the tensile and compressive strain capacity at 7 days (28 days). The calculated pseudo strain hardening indices based on the mesoscale experimental results were higher, accompanied by the higher tensile strain capacity; incorporation of GGBS could improve the interfacial chemical bonding between fiber and matrix. Moreover, the GGBS-ECC exhibited a lower gas permeability and a smaller average pore size than the ECC without GGBS. Based on these findings, it was concluded that GGBS could be utilized in the development of ECC with appropriate ductility and facilitate the compactness of the matrix.

In order to solve the cracking issue of concrete under external restraint conditions, the common method is to add fibers (steel fiber, polypropylene fiber, etc.) to concrete. However, steel fiber is heavy and costly. In this paper, a slab test was carried out, and the cracking control effect of a macro-nano multiscale cracking prevention system formed by using natural green sisal fiber instead of steel fiber and nanofibrillated cellulose (NFC) on concrete is studied. A total of 14 test groups were set up, including the test groups of a single sisal fiber and single steel fiber dosage; sisal fiber combined with steel fiber with equal volume; a sisal fiber and nanofibrillated cellulose (NFC) combination; and a sisal fiber and steel fiber and nanofibrillated cellulose (NFC) hybrid combination. The early-age cracking behavior of concrete of the preceding groups were observed. The results show that the use of sisal fiber with 0.4% volume content improves the early-age cracking of concrete to the same extent as the use of steel fiber with 1% volume content. Compared with the addition of steel fiber alone, sisal fiber replacing steel fiber with equal volume can not only significantly improve the cracking resistance of concrete and reduce its cost and weight, but also protect the environment. Last but not least, results indicate that sisal fiber and nanofibrillated cellulose (NFC) also play a good synergistic role in delaying and controlling the cracking development of concrete. The macro-nano multiscale fiber by steel fiber, sisal fiber, and nanofibrillated cellulose reinforced-concrete cracking resistance mode is achieved.

A new fracture test method—the bottom-notched splitting (BNS) test—is proposed in this study to determine the $\mathrm{double}\text{-}K$ fracture parameters of concrete. In the BNS test, the concrete cube with a preset crack on the bottom surface is subjected to a line compressive load on the top surface. Numerical analyses are first carried out to simulate the stress distributions along the ligament and crack opening profiles of the BNS specimens. Then, the fitting expressions of the stress intensity factor and the crack center opening displacement are derived based on the linear elastic fracture mechanics. A series of BNS tests and three-point bending (TPB) tests with different ratios of the preset crack length to the specimen height are conducted to determine the $\mathrm{double}\text{-}K$ fracture parameters of the concrete. The results indicate that the preset cracks in the BNS tests could initiate and propagate throughout the whole cross-sections of the concrete cubes. By substituting the obtained initial fracture loads, maximum loads, and critical crack center opening displacements in the BNS tests into the fitting expressions, the $\mathrm{double}\text{-}K$ fracture parameters could be determined. By comparing with the TPB tests, the BNS tests proved to be an effective method to determine the $\mathrm{double}\text{-}K$ fracture parameters of concrete. The BNS tests are convenient to operate and can reduce the damage risk of the preset cracks. Meanwhile, they also would be appropriate for assessing the fracture properties of existing concrete structures in service because the cubes can be easily obtained from the samples core-drilled from existing concrete structures.

Automobile/industrial waste ethylene-propylene-diene monomer (EPDM) rubber has attracted considerable interest as a potential asphalt binder modifier. A rubberized asphalt binder must have adequate storage stability to assure homogeneity during storage and hauling and attain the desired performance after construction. This study focused on the application of tire pyrolytic oil (TPO) derived from the pyrolysis of scrap tires as an additive for composite modification to enhance the storage stability of the EPDM rubberized binder. Sequential and pretreatment were the two different approaches employed to produce the TPO-EPDM rubberized asphalt binders in this work. Furthermore, the effect of a crosslinking agent (sulfur) on the compatibility of the TPO-EPDM rubberized binder was investigated for both sequential and pretreatment approaches. In all total, 18 different combinations of rubberized binders with EPDM, TPO, and sulfur were fabricated for storage stability characterization. Various empirical, rheological, chemical, and microstructural analyses based separation parameters indicated that TPO usage enhanced the storage stability of rubberized asphalt binder. Both sequential and pretreatment approaches increased the storage stability of EPDM rubberized binders with an increase in TPO dosages; however, the pretreatment approach outperformed the sequential approach. The addition of sulfur further improved the compatibility of rubberized binders. The results of Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM)–based separation parameters were similar to those found using empirical and rheological tests. Grey relational analysis (GRA) was used to rank the binders according to their separation parameters. GRA showed the best results in both sequential and pretreatment approaches with and without sulfur for an optimal TPO dosage of 6%. The enhanced storage stability performance of rubberized binders with the incorporation of TPO in the pretreatment approach of binder preparation was attributed to the achieved preswelling of rubber particles during premixing and conditioning processes.

Cold-mixed epoxy asphalt (CEA) is an emerging energy-saving and environment-friendly material for steel bridge decks, overload roads, and airfield pavement. Occasionally, CEA suffers from impact with high strain rates, which will be extremely detrimental to the pavement’s safety and stability. Since little research deals with this dynamic mechanical behavior, this study aims to clarify the dynamic mechanical performance of CEA mixtures (CEAM) under high strain rates. First, this study evaluated the quasi-static strength evolution by Marshall stability tests. The Marshall stability of CEAM more than quadrupled within the first 20 h and 1.6 times up again when exposed at 60°C, while its flow value showed the opposite trend. Then, the dynamic mechanical behavior under different high strain rates and temperatures was investigated by split Hopkinson pressure bar tests. Results showed that the peak strain rate ($146–316{\mathrm{s}}^{-1}$) was 1.7–2.0 times greater than the average strain rate ($84–162{\mathrm{s}}^{-1}$). The strain–stress curves became steep as the temperature and the pressure ascended. Under the same test conditions, the peak stress and the peak dynamic modulus of CEAM were 1.7 times larger than that of cement concrete. CEAM absorbed more energy below 25°C than 60°C. All the CEAM had binder failure, and the crushed specimens had aggregates broken. The constitutive model of CEAM was established based on the statistical damage theory and the modified Weibull distribution function. Besides, multiparametric regression analysis proved a demarcation point during the impact.

The load-carrying capacity of bolted timber connections with slotted-in steel plates is a critical guide for the practical design of timber buildings. This work investigates various factors that influence the load-carrying capacity of bolted timber connections through testing and gives a comparison of the calculated load-carrying capacity from different standards. A total of 72 bolted timber connections with a range of bolt diameters and wood thicknesses were investigated during pull-out tests. The test results indicated that these connections exhibited three typical failure modes. These different failure modes can be distinguished with the slenderness ratio. The obtained initial stiffness and peak force from the measured force–deformation curves are used to define regression equations, considering the factors of wood thickness and bolt diameter. Then, an analysis formula for the calculation of load-carrying capacity is derived by considering the failure mechanism. The load-carrying capacity calculated from the analysis formula agrees with the test data, demonstrating that the derived formula is reasonable. In addition, the load-carrying capacity calculated from the analysis formula is compared with those obtained from different standards. This work enhances the understanding of the failure mechanisms of bolted timber connections with slotted-in steel plates and the factors influencing their load-carrying capacity, providing guidance for practical design.

The production of asphalt concrete depends on the use of nonrenewable resources, such as asphalt binder and crushed rocks. Nowadays, technologies exist to convert biomass into biofuels and other by-products, which are an alternative to traditional sources of energy. The by-products of biomass conversion are similar to those of petroleum distillation. Several researchers have investigated the use of bio-oils from biomass as asphalt additives, but the potential use of brewery waste has not been considered. In this project, spent grains from a local brewery were converted into bio-oil using an auger reactor. The water in the bio-oil was removed, and the biobinder was analyzed. It was found that the biobinder derived from brewer’s spent grain has an elemental composition similar to other biomass-derived biobinders. Fourier transform infrared (FTIR) spectroscopy identified multiple polar functional groups in the biobinder, including high nitrogen content (4.6% by weight). Also, thermogravimetric analysis and gas chromatography showed a higher thermal degradation rate of the biobinder and loss of volatile components. The biobinder was used to create six blends with 5%, 8%, 10%, 15%, 20%, and 25% replacement of asphalt. The performance of each of the six blends was compared with the performance of control unmodified samples. The modified binder characterization indicated that the biobinder makes the material more susceptible to permanent deformation at high temperatures, and it showed higher aging of the short-term aged residue. However, the biobinder seems to improve relaxation properties at low temperatures, which could be attributed to its high nitrogen content. The findings of this preliminary study suggest that production and use of brewer’s spent grain biobinder are feasible and could be considered a potential feedstock for further development of asphalt biomodifiers.

Accurately evaluating and characterizing the performance of emulsified asphalt is the basis of its application. The rheological properties of modified emulsified asphalt residues and its material action mechanism were studied. To achieve this goal, styrene butadiene styrene (SBS)- and styrene butadiene rubber (SBR)-modified emulsified asphalt were prepared, and modified emulsified asphalt residues were prepared by the direct heating method (DHM) and two low-temperature evaporation methods (EN13074 and ASTM D7497-09). Then, the rheological properties and fatigue resistance of the modified emulsified asphalt residues were characterized through dynamic shear rheometry tests. Finally, Fourier transform infrared spectroscopy and elemental analysis were conducted to monitor the curing behavior of modified emulsified asphalt residues. The results indicated that the incorporation of SBS and SBR latex into emulsified asphalt significantly improved its viscoelastic properties, high-temperature properties, and fatigue life, and reduced its temperature sensitivity. Under different evaporation conditions, the unmodified emulsified asphalt residues and SBS-modified emulsified asphalt residues obtained by the ASTM D7497-09 evaporation method had the best rutting resistance and recovery percentage, followed by the emulsified asphalt residues obtained by EN13074 and DHM. However, the rutting resistance of SBR-modified emulsified asphalt residues was not greatly affected by the evaporation method. Though prepared with different evaporation methods, unmodified emulsified asphalt residues had similar fatigue life, and the fatigue life of modified emulsified asphalt residues were ranked as ${\mathrm{N}}_{\mathrm{f}}$ (ASTM D7497-09) ${>\mathrm{N}}_{\mathrm{f}}$ (EN13074) ${>\mathrm{N}}_{\mathrm{f}}$ (DHM). The emulsified asphalt residues obtained by DHM and EN13074 still contain moisture, and it is recommended to use the ASTM D7497-09 evaporation method to obtain emulsified asphalt residues for performance evaluation.

In order to study the effect of temperatures on the bending performance of laminated bamboo lumber (LBL), 11 temperature conditions were set to test the bending performance in radial and tangential directions ranging from $-60°\mathrm{C}$ to 200°C, and 132 specimens were tested in total. Three typical failure modes were proposed. The bending strength and bending elastic modulus for all specimens were obtained from the test, and the effects of temperatures and loading direction on them were compared. Then, the mass loss rate of the specimens was calculated, and the variation law of the load-displacement curve was analyzed. Finally, the reduction (increase) factors of bending strength and bending elastic modulus varying with temperature were calculated, and the empirical formula for reference was proposed. It was found that the temperatures had a significant influence on the bending performance of LBL, and the loading direction had little effect on it.

The flexural properties of high-performance concrete (HPC) can be enhanced by mixing two fibers with appropriate volume contents. Four-point bending tests were conducted on 48 beams to investigate the flexural behavior of steel–polyvinyl alcohol (PVA) fiber–reinforced HPC. The effects of the volume content and hybrid ratio of fibers on the flexural parameters such as strength and toughness are discussed. The synergistic effect of the two fibers reinforcing the HPC was analyzed quantitatively. The reinforcing index (${\mathrm{RI}}_v$) considering the elastic modulus and tensile strength of fibers was used to analyze the flexural parameters of steel–PVA fiber–reinforced HPC. The results indicate that addition of steel fiber or PVA fiber individually can improve the flexural properties of HPC. In steel–PVA fiber–reinforced HPC, the addition of steel fiber enhances the peak strength and toughness, and the addition of PVA fiber improves the first peak strength and deformation capacity. With 2% total fiber volume content, the best synergistic effect was achieved at 1% volume content of both steel and PVA fibers. The new model fits well with the experimental results and can be used for the ratio design of steel–PVA fiber–reinforced HPC.

The service life of porous concrete (PC) structures is severely affected by freeze–thaw damage in cold regions. However, the evaluation of freeze–thaw damage of PC using experimental tests is time-consuming and inconvenient. This paper derived an equation to evaluate the freeze–thaw damage and developed a model to predict the residual strength of PC under freeze–thaw conditions based on the Weibull distribution functions. By analyzing the experimental results, the relative dynamic elastic modulus (RDME) was identified as the damage variable, which can accurately characterize the freeze–thaw damage state of PC with the advantages of convenience and nondestructiveness. Moreover, the resistance to freeze–thaw cycles of the PC blended with basalt fibers and silica fume increased by 25% compared with that without any reinforcement. Based on the damage accumulation theory, the Weibull distribution function is appropriate to be employed to describe the freeze–thaw damage evolution of PC. The model for predicting the residual strength of PC subjected to freeze–thaw cycles was verified based on a large amount of test data and had correlation coefficients $R^2$ higher than 0.96. The proposed model also can be used to predict the residual strength of other types of PC, and provides a reference for service life prediction and safety assessment of PC structures.

The linear amplitude sweep (LAS) test is considered a useful tool for evaluating the fatigue of asphalt binders. A challenge in the LAS test is that although the strain amplitude sweep test is set to load from 0% to 30%, some high cracking-resistant asphalt binders do not show significant damage level and instead exhibit behavior within the prefailure conditions. To solve this problem, experiments can be performed by increasing the strain to a higher level or change the control mode to stress control. In this study, a 60% strain level control mode is added in addition to the standard 30% strain level control mode. The stress-controlled mode amplitude sweep test was also carried out on nine different PG grade binders at three aging conditions and four temperatures. As the results showed, when using the maximum energy level to calculate fatigue life, $N_{f}60@15\%$ is about 99% of $N_{f}30@15\%$. The fatigue life calculated based on the energy principle can well unify the results of the stress-controlled test and the strain-controlled test. The fatigue life obtained by the energy principle does not depend on the control mode of testing, which can also reflect the aging and temperature effect on the fatigue performance of asphalt binder. Comparing the fatigue parameter among the fatigue life using the energy criterion, $G^R$-based criterion, and Glover-Rowe (G-R) parameter, the fatigue life calculation method using the energy fatigue criterion can best eliminate the influence of loading history.

Stainless steel bolts are increasingly used in the semirigid connections due to their superior behavior to high-strength bolts in terms of durability, ductility, and fire resistance. Their thermomechanical properties have been implemented using a number of steady- and transient-state tests. However, their retention factors at a given temperature present a significantly scattered distribution between different previous tests, so their fully fire-induced behavior needs to be investigated considering the effects of multiple factors at a statistical level. Accordingly, their residual properties characterized by reduction factors are first compared in combination with fire-resistant bolts during or after fire according to the previously published studies. Consequently, stainless steel bolts, featuring the pronounced ductility at ambient temperature, have more significant retention of material stiffness and strength than high-strength and fire-resistant bolts beyond 600°C. Finally, the codified strength retention factors of high-strength bolts during fire, confined to an extremely specific test without response to a consistent database, are not always conservative when used for interpolation on bolts with other property classes, and the standardized reduction factors of stainless steels are hardly accurate enough for those of stainless steel bolts exposed to furnace fire. Thus, the temperature-dependent reduction models with a guaranteed rate of 95%, the prediction accuracy of which is strikingly improved compared with the commonly codified elevated temperature reduction factors in EN 1993-1-2 and AISC 360, are statistically proposed for high-strength or stainless steel bolts during and after fire. This factor contributes to the safety of structural fire resistance without highly conservative prediction.

Historical buildings made of lime material seriously deteriorate, and a sustainable repair strategy is essential. The performance requirements of the repair material should be compatible with substrate lime in terms of interfacial strength, failure modes , and carbonation of substrate lime. Therefore, this study was carried out using five types of repairing mortar mixes, and the bond performance was investigated by interfacial bond strength testing, including the carbonation test at bonded surfaces. Experimental test results revealed that lime and silica fume modification improved the bond performance with respect to tension, shear, and tension–shear. Among the repairing mixes, the lime–cement–silica fume mix indicates higher bond performance and proper cohesive failure as compared with the others that typically exhibit adhesive or substrate failure. Moreover, XRD testing reconfirms that the addition of cement and the pozzolanic material in the lime-based repair mortar mix enhances the bond strength with the formation of calcium silicate hydrate. As a result, the lime–cement–silica fume mix can guarantee good bond performance including cohesive failure at the carbonated lime substrate surface.

Abstract

Mixed mode I–II fatigue fracture of concrete is commonly encountered in practical engineering. Accurate prediction of the fatigue crack propagation process and fatigue life is essential to evaluate the safety of concrete structures. In this study, the mixed mode I–II fatigue crack propagation process of the three-point bending (TPB) beam is investigated based on the digital image correlation (DIC) method. The results indicate that the mixed mode I–II crack propagation path under fatigue loading is consistent with that under static loading, and the stress intensity factor (SIF) corresponding to the unstable failure of concrete is constant, regardless of the fatigue load level and specimen size. Based on the experimental results, a unified model for characterizing mixed mode I–II fatigue crack propagation in concrete is developed, where the equivalent SIF amplitude composed of mode-I and mode-II SIF amplitude is introduced into Paris law, and the statistical analysis is conducted to determine the probabilistic distribution of the empirical constant in Paris law. Furthermore, the feasibility of predicting the fatigue life of concrete structures is explored using the proposed model. It is concluded that the fatigue life with different reliability can be obtained when the mixed mode I–II fatigue crack propagation path is determined based on static tests. It is expected that the developed model contributes to the prediction of fatigue life and further safety assessment of concrete structures under fatigue loading.

Practical Applications

Many concrete structures are subjected to fatigue loads in service, such as concrete pavements and bridge decks suffering from cyclic vehicle loads. Under fatigue loading, the crack gradually propagates, resulting in the fatigue failure of concrete structures. Therefore, it is critical to investigate the fatigue crack propagation process of concrete such that the safety assessment of concrete structures can be conducted. In this study, a prediction model for mixed mode I–II fatigue fracture of concrete is proposed based on the well-known Paris law. When the SIFs at the crack tip are calculated based on the finite-element method, the whole fatigue crack propagation process and fatigue life of concrete structures with different reliability can be reasonably predicted using the proposed model. Furthermore, the stability analysis of fatigue crack and the reinforcement and repair of cracked concrete structures can be conducted timely according to the predicted fatigue crack propagation length and fatigue life. In general, the proposed model is of great significance to guarantee the safety of concrete structures under fatigue loading, e.g., concrete pavements and bridge decks.

The combination of steel slag and cement to prepare green cement-based materials can help with environmental pollution issues, but the effectiveness of the products suffers versus cement without steel slag. This paper investigates the influence of cellulose fiber on the rheological properties, mechanical properties, and volume stability of steel slag cement cementitious materials. The results demonstrate that when cellulose fiber content increases, the slurry’s rheological properties improve. When the cellulose fiber content was less than 0.5%, the strength of the samples at each age increased with the increased fiber content. At the same time, compared with the control blank group, the autoclave expansion rate of the samples was reduced by a maximum of 27.31%. When the fiber volume content exceeded 0.5%, the mechanical strength of the samples started to decline. The SEM results showed that the fibers inside the samples were entirely covered by hydration products after 28 days of hydration. The hydration products were primarily $\mathrm{Ca}{(\mathrm{OH})}_2$ crystals and C-S-H, which tightly bonded the fibers and the matrix, enhancing the performance of the samples.

Four-point bending tests of self-compacting concrete with different rubber contents were conducted, and the acoustic emission (AE) technique was used to monitor the fracture process. The evolution law of rise angle (RA), average frequency (AF), and AE intensity was analyzed, and the Gaussian mixture model (GMM) was used for clustering analysis of crack mode in different loading stages. The results clarify that the safe regions of self-compacting rubberized concrete (SCRC) were proposed based on AE intensity. Both the slope of the cumulative RA–AF curve and the average value of RA and AF had a quantitative relationship with rubber content. Rubber content had little effect on crack mode. The failure process of SCRC with rubber contents of 0%–30% was dominated by the tensile crack mode, and the maximum proportion of shear cracks appeared in the postpeak loading stage (40%–20%), which can be considered as warning value of concrete bending failure. The results can provide a theoretical reference for the early warning of SCRC failure.

The present work aims to evaluate expansive soil stabilization using different additives. Twenty soil mixtures consisting of 10%, 20%, 25%, and 30% zeolitic tuff (ZT) with 2%, 4%, and 6% lime in various combinations were used to stabilize the soil for pavement subbase application. A comprehensive test program, including Atterberg’s limits, compaction, unconfined compression strength (UCS), California Bearing Ratio (CBR), resilient modulus, and permanent deformation, was performed on natural and stabilized soil specimens. Scanning electron microscopy (SEM) supplied with energy-dispersive X-ray spectroscopy (SEM/EDX) was used to confirm the study findings. Adding ZT increases the availability of the silica and alumina needed for the pozzolanic reaction; test results revealed that adding ZT increases the maximum dry unit weight, CBR, UCS, resilient modulus, decreases plasticity, and permanent deformation. As such, ZT can improve the physical and mechanical properties of lime-stabilized soil as a pavement’s subgrade and subbase layers.

Porous asphalt concrete (PAC) is commonly applied in locations with heavy rainfall. However, because of the mix’s characteristics and service environment, it is impossible to ensure the duration of its permeability performance. This paper explores the aspects that influence PAC’s permeability performance. A comprehensive clogging model is also developed, which includes PAC mix parameters. First, three clogging materials were produced. Second, the effect of nominal maximum aggregate size, porosity, and clogging material on PAC’s permeability is discussed. Finally, models are proposed to predict PAC’s clogging factor $\beta$ and clogging times $N$. The results revealed that the remaining PAC mix parameters, except for the nominal maximum aggregate size, were associated strongly with the $\beta$ and $N$. The prediction models established for $\beta$ and $N$ in PAC mixes were highly reliable, with correlation values over 0.90 in all cases. In addition, the mixture parameters that had the greatest influence on the clogging factor $\beta$ and clogging times $N$ are differed. The uniformity and curvature coefficients influenced the clogging factor $\beta$ the most, while the initial permeability coefficient affected the clogging times $N$ the most.

Unmodified epoxy adhesive is a brittle material, which limits its application in practical engineering. Adding nanomodified materials to epoxy adhesives is an effective method to improve the tensile property. In this study, the composites were artificially dispersed for 10 min, and then dispersed for 2 h in an ultrasonic cell crusher to ensure the nanoparticles were evenly dispersed in the epoxy adhesive. The influence of ${\mathrm{SiO}}_2$ and ${\mathrm{TiO}}_2$ nanoparticles (NS and NT) with different mass fractions on the tensile properties of epoxy adhesives was analyzed, and the tensile section morphology of 11 kinds of the composites was observed by scanning electron microscope (SEM). In addition, the nanomodified epoxy adhesive model was simulated using software, which was based the Python language; randomly distributed nanoparticles were generated in the two-dimensional representative volume element (RVE) model. The experimental results showed that the tensile properties of epoxy adhesive increased first and then decreased with the increase of the mass fraction of nanoparticles. When NS or NT with a mass fraction of 0.05% or 0.40% were added to epoxy adhesive, the tensile properties of the composites reached their highest value. Through the SEM observation of the colloid tensile section, it was observed that the nanoparticles could change the composites’ fracture from brittle to ductile, which achieved the purposes of strengthening and toughening. The finite-element results showed that the difference between the simulated tensile properties and the experimental value of epoxy adhesive was within 5%, and thus the software model in this study has a certain reliability.

In this paper, the corrosion resistance and mechanical properties of a coating/steel substrate system were investigated under the coupling action of the corrosive environment and load. At first, the stress corrosion tests were carried out on the coating/steel substrate specimens. Then, nanoindentation tests were used to study the elastic modulus of the coating before and after stress corrosion tests. After that, tensile tests were performed on the specimens before and after stress corrosion tests. In the tensile testing process, the evolution law of surface strain was studied by a digital image correlation method. Further, the cracking characteristics and fracture toughness of the coating/steel substrate system in the corrosion process were generated. Test results indicate that the elastic modulus of the coating/steel substrate system continuously decreases with increasing stress level. In the meantime, the critical cracking strain and fracture toughness of the coating/steel substrate system also decrease with increasing stress level. The coupling effect of the external load and corrosive environment greatly accelerate the corrosion process of the coating/steel substrate system.

Waste management is one of the most important factors in environmental protection. In the field of building, the reuse of bulk solid waste may have a great potential for the production of eco-friendly cementitious materials. The objective of this research is to assess the possibility of replacing magnesia with an admixture of magnesium bricks waste and glass powder in the preparation of magnesium potassium phosphate cement (MKPC). The MKPC mortars were produced by introducing different quantities of glass powder (0%–40% by weight). The impact of reusing waste glass material on the characteristics of the cement binder was investigated. Phase composition was evaluated using X-ray diffraction (XRD) and Fourier transform infrared (FTIR), together with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The result shows that the addition of glass powder decreased the bulk density, thereby contributing to the lightness of pastes. Replacing dead burned MgO with waste promotes the main hydrate phase (K-struvite) formation. Compressive and tensile strengths of 47 and 6.07 MPa, respectively, were obtained for the sample containing 10% by weight of glass powder. The properties of the hydration products were improved with a decrease in the waste brick/phosphate ratio. The results indicate that these types of cement can be utilized as a low-cost alternative in the field of civil engineering.

The low bearing capacity of expansive soils often results in serviceability issues and premature failures of infrastructure built upon them. Various studies have demonstrated the use of different soil treatment methods using mechanical or chemical approaches to stabilize the weak ground as a precaution. Most of the reported studies are limited to either lab-based investigations or field monitoring works without the scientific connection between theory and translation. This study aims to verify the field application of a novel soil stabilization method by conducting laboratory-controlled experiments and field performance testing as verification. Enzyme–based soil stabilization was adopted for in-situ clay soil in combination with ordinary portland cement as a sustainable stabilization approach. Soil samples were collected at different regions from the field to evaluate the effectiveness and the mechanism of soil stabilization in the field by the means of replicating stabilization at the laboratory scale using identical mixing proportions of the additives. The mechanical behavior of stabilized soil was assessed through the unconfined compression strength and California bearing ratio test methods. In addition, the changes in the chemical composition of the soil due to the additives were evaluated through the X-ray diffraction testing technique and microporosity test using 2D images translated to 3D profiles from X-ray micro CT tomography. The efficacy of field stabilization was evaluated by conducting the falling weight deflectometer test in the stabilized site. Results from the study are useful to understand the efficacy of field soil stabilization and enhance the reliability of enzyme–based stabilization in practice.

Abstract

In order to assess the durability of concrete structures reinforced by different types of steel in aggressive environments, the galvanic corrosion of mill-scaled carbon steel was investigated when it was connected to AISI 304 stainless steel characterized by various cathode/anode surface area ratios ($A_{\mathrm{s}}:A_{\mathrm{c}}$) in chloride-contaminated mortars. The galvanic potential and the galvanic current density of the coupling carbon steel were measured, and the corrosion state of the mill-scaled carbon steel was inspected after 1,450 days. The results indicated that the potential of the carbon steel was slightly positively shifted by the stainless steel. High $A_{\mathrm{s}}:A_{\mathrm{c}}$ ratios promoted the passivation of the coupling carbon steel and lowered the corrosion current density in the chloride-contaminated mortars. The galvanic current densities of the carbon steel-stainless steel couples increased with $A_{\mathrm{s}}:A_{\mathrm{c}}$ ratio. Because the corrosion current density of the mill-scaled carbon steel was nearly one order of magnitude higher than the galvanic current density, the total corrosion current density of the coupling mill-scaled carbon steel generally decreased, and its overall corrosion diminished with increasing $A_{\mathrm{s}}:A_{\mathrm{c}}$ ratio. Finally, based on the results of this study, the $A_{\mathrm{s}}:A_{\mathrm{c}}$ ratio is recommended to be higher than 2:1 to ensure the sufficient durability of submerged concrete structures in an aggressive concrete environment.

Practical Applications

Corrosion of reinforcement is one of the key factors that cause the failure of marine concrete structures. The concrete structure needs to be repaired when rebar corrosion is evident. The application of stainless-steel reinforcement was thought to be a reliable method to improve the durability of the repaired concrete structures because of the high-corrosion resistance of stainless steel. However, the long-term galvanic corrosion between carbon steel and stainless steel in marine concrete structures is a major concern for engineers because of the high different potential between the two types of steel. In this study, the corrosion behavior of the mill-scaled carbon steel coupled to AISI 304 stainless steel in chloride-contaminated mortars simulating the marine environment was investigated. The results suggested that when the cathode/anode surface area ratio is higher than 2:1, the carbon steel-stainless steel couples can ensure sufficient durability of the repaired concrete structures in the simulated marine environment. The results of this study can provide guidance to the design of the repair works of corroded concrete structures by the application of stainless-steel reinforcements.

In order to study the influence of different factors on the early strength of the cold recycled emulsified asphalt mixtures, 16 different types of cold recycled mixtures were designed and produced, which were combined with different cement content, water content, and cement-water ratio. The indirect tensile strength (IDT), compressive strength (UCS), tensile strength at 15°C (TS), and indirect tensile strength ratio (ITSR) tests were used to test the early strength of the cold recycled mixture. The variance analysis method was utilized to analyze the influence of the single factor on the early strength of the cold recycled mixture. The results show that appropriate cement-water ratio content can effectively improve the early strength of cold recycled mixtures. According to the Spearman correlation coefficient and comparison of each evaluation indicator, IDT and ITSR are significantly affected by various factors, and the results are relatively stable and well-differentiated, which is recommended as indicators of early strength evaluation. Cement-water ratio is recommended as the main control factor to control the early strength of the cold recycled emulsified asphalt mixtures. The optimal cement-water ratio ranges from 0.6 to 1.0, while the cement content is controlled from 1.2% to 1.5% and the water content from 3.8% to 4.3%. This study is of great significance for promoting the design of emulsified asphalt cold regenerative mixture with cement-water ratio and improving and accelerating its early strength development.

Providing sufficient pavement surface friction (i.e., skid resistance) between vehicle tires and pavement surface throughout the pavement service life is considered to be one of the main objectives of highway design. Moreover, vehicle safety, the amount of consumed fuel, and the wearing rate of vehicle tires generally are influenced by pavement surface friction. In this study, a comprehensive experimental testing program was conducted on different aggregate sources, including calcined bauxite and five alternative local sources, to assess their friction characteristics. The testing program included a British pendulum tester (BPT) and a dynamic friction tester (DFT), which were used to evaluate the friction characteristics of the proposed aggregates, along with basic and durability properties tests. The aggregate imaging measurement system (AIMS) technique was applied to evaluate the aggregate characteristics due to Micro-Deval degradation. This study provides two empirical models for the friction characteristics of high-friction surface treatment (HFST)-application aggregates based on the experimental results. The first model correlates the friction coefficient at $20\mathrm{km}/\mathrm{h}$ (${\mathrm{DFC}}_{20}$) with the British pendulum number (BPN). The second model expresses ${\mathrm{DFC}}_{20}$ as a function of polishing resistance of aggregates, which is represented by the initial and terminal aggregate texture and angularity values measured using the AIMS device with an overall coefficient of determination ($R^2$) of 0.949. The aggregate characteristics (i.e., particle angularity and surface texture) align well with the microtexture characteristics of the investigated sources.

Metal-organic frameworks (MOFs) are beneficial in various applications such as gas separation, catalysis, wastewater treatment, and dye removal. The current study proposes a novel approach to the use of the zeolitic imidazolate framework (ZIF-67), a subfamily of MOFs, in cement composites. ZIF-67 nanoparticles were synthesized in the laboratory and analyzed using X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscope (TEM). ZIF-67 nanocrystals were incorporated in the cement matrix at a concentration of 0.3%, 0.4%, 0.5%, and 0.6% by weight of cement. The influence of ZIF-67 nanoparticles on the workability, mechanical strength, and microstructure was thoroughly investigated. The workability of cement paste was hindered by the addition of ZIF-67. The compressive strength of ZIF-67 cement composites was enhanced by 27.81% at 3 days and 20.36% at 28 days. This was attributed to the densification of microstructure. The optimum content of ZIF-67 in cement composites among the selected concentrations was determined to be 0.6% by weight of cement. The microstructure images revealed the pore-filling mechanism of ZIF-67 in cement composition as well as in providing additional nuclei sites for the hydration products. It was concluded that ZIF-67 nanoparticles act as a nonreactive filler in cement composites. There exists a huge potential for use of ZIFs in cement composites, which is yet to be explored.

The goal of this study is to investigate the dynamic mechanical properties of low yield (LY) point steels (LY100, LY160, and LY225) under high strain rates and elevated temperatures. The separate Hopkinson pressure bar system was used to conduct dynamic compression tests on LY steels at temperatures ranging from 25°C to 800°C and strain rates ranging from ${\mathrm{1,000}\mathrm{s}}^{-1}$ to ${\mathrm{5,000}\mathrm{s}}^{-1}$. The quasi-static compression tests (${0.001\mathrm{s}}^{-1}$) were conducted at the same temperatures. The stress-strain relationship of the presented three materials under various temperatures and strain rates was acquired. The test results demonstrated that LY100, LY160, and LY225 steels have an obvious temperature-softening effect. The three materials show low strain rate sensitivity under the strain rate is not more than ${\mathrm{3,000}\mathrm{s}}^{-1}$. For a given strain rate, the flow stresses of LY100 and LY160 steel are consistent at 400°C and 600°C, respectively, and both materials exhibit dynamic strain aging. Besides, LY225 steel exhibits dynamic strain aging when the temperature is above 400°C. According to the test results, a modified Johnson–Cook model of the LY point steels was established, which can reflect the material properties well. The results of this study may provide a basis for studying LY steels’ dynamic mechanical properties.

An indoor vibrational dissolution scouring test was designed to investigate the effects of vibrational frequency, vibrational acceleration, environmental temperature, and dissolution medium on the dissolution characteristics of cement-stabilized macadam base material during water erosion. The results showed that the dissolution damage effect exists in cement-stabilized macadam, and dissolution is an important evaluation index of its base failure. The amount of calcium ion $({\mathrm{Ca}}^{2+})$ dissolution and pH of cement stabilized gravel increased with increasing vibrational time. When the vibrational frequency was in the range of $80–180\mathrm{Hz}$, the amount of dissolved ${\mathrm{Ca}}^{2+}$ and the pH of the solution first increased, and then decreased with the vibrational frequency. The ${\mathrm{Ca}}^{2+}$ concentration and pH of the solution reached their maximum at 140 Hz for 10 h. Of the four vibrational dissolution factors considered, vibrational acceleration produced the largest degree of dissolution of cement-stabilized macadam. The leached ${\mathrm{Ca}}^{2+}$ concentration increased with increasing temperature of the dissolution medium and the concentration of ammonium chloride $({\mathrm{NH}}_4\mathrm{Cl})$ solution, while increasing pH decreased dissolution.

Recycling solid construction waste is an inevitable trend to be followed for the realization of sustainable economic development. The bond behavior of reinforcement and recycled-fiber recycled concrete is discussed in this paper based on the observations of a half-beam unidirectional pullout test. With different recycled aggregates replacement ratios and recycled fibers volume content as variables, the pullout behavior, ultimate bond stress, and bond-slip under monotonic loading are evaluated. The test comprises two parts: direct pullout test and pullout test after the attachment of strain gauges inside the reinforcement. The results show that the half-beam unidirectional pullout test can suitably reflect the bond performance between recycled-fiber recycled concrete and reinforcement. The replacement rate of recycled aggregates exhibits a significant effect on the bond behavior between reinforcement and concrete, and the bond stress reduces by 36.92% when the replacement ratio is 100%. Adding recycled fibers is proposed to improve the bond behavior between recycled concrete and reinforcement; more specifically, the addition of 0.12% recycled fibers can increase the bond stress by 11.34% when the replacement ratio of the recycled aggregates is 50%. Moreover, the bond-slip curve relationship model between recycled-fiber recycled concrete and reinforcement that suitably correlates with the experimental results is established. Finally, the bond stress distribution is nonuniform. With the increase in the pullout force, bond stress causes local stress concentration. The more recycled aggregates, the speedier the bond stress transfer; furthermore, a moderate amount of recycled fiber can alleviate the stress concentration phenomenon. This research proposes a novel method of bond behavior test; furthermore, a novel recycled-fiber recycled concrete material is proposed that could be utilized in actual construction, and the recommended dosages are provided.

Using asbestos in building materials is a risk to human health, which has driven the interest in utilizing other natural fibers, such as cellulosic fibers, in cement-based building materials. There have been studies on cement-based composites reinforced with cellulose microfibers or nanocellulose. However, to the best of our knowledge, the effect of cellulose fiber reinforcement, at different scales (micro and nano), on cement-based composite properties has not yet been studied, from raw natural fiber to nanocellulose. Moreover, comparing data from the literature on cellulose-reinforced cement composites is difficult because there are many variables (e.g., matrix, cement, sand, dosification, water:cement ratio, superplasticizer, and fabrication method) that affect the final composite performance. In the current work, different cement-based composite properties reinforced with cellulose fiber were compared using the same variables and fabrication method. After the addition of microfibers, the strength of mortar decreased compared with plain mortar, the reduction being higher as the fiber content was increased. On the other hand, after the addition of nanocellulose fiber, the density hardly changed compared with unreinforced mortar. Contrary to microfiber addition, the presence of 0.25% by weight nanocellulose in mortar slightly increased the flexural strength. The mechanical properties obtained in the current study were compared with literature data for similar systems.

Using solid waste to produce artificial aggregate (AA) to replace natural aggregate has attracted extensive research interest. This study proposes pressure granulation under minor water to produce AA. The strength formation and water-pressure synergy mechanisms are discussed by setting water and load configurations and characterizing the internal pore structure. In addition, the water damage to the AA is discussed. The results show that the squeeze-out effect caused by the synergistic effect of water and load determines AA’s physical and mechanical properties. Furthermore, the law of the squeeze-out effect is proven by the fact that the AA with a compressive strength of 19.77 MPa was obtained under a 10% water-to-powder ratio and a 55 kN load. In addition, water erosion severely affects AA’s strength, which might be relieved by decreasing the water absorption of AA.

The intrinsic brittleness of cement hydrates can bring about the potential deterioration of concrete performance, affecting the service life of cement hydrates. In this study, we introduced polyvinylpyrrolidone (PVP) coupled with in situ polymerized acrylic acid (AA) to toughen conventional cement by constructing a polymer network in the cement matrix. The flexible polymer network, intermingled with cement hydrates, offered softness to the stiff cement matrix, significantly improving its flexural strength and toughness. Compared with the control cement paste, the AA–PVP-modified cement paste displayed an increment in flexural strength up to 86% with the comparable compressive strength to the control one by adjusting the AA–PVP fraction. Cement hydration promoted the polymerization reaction of AA by releasing heat, which ensured a synergistic effect between cement hydration and polymerization. Chemical interactions between carboxyl groups and metal ions (${\mathrm{Ca}}^{2+}$ and ${\mathrm{Al}}^{3+}$) contributed to the improvement in mechanical strength. This method, the combination of polymer and in situ polymerization of monomers, exhibited extensive application prospects in toughening cement-based materials.

In this study, the usability of recycled concrete aggregates (RCAs) together with crushed aggregate (CA) in granular road base (GRB) and granular road subbase (GRSB) layers was investigated. Three different RCAs as RCA1, RCA2, and RCA3 were used according to their parent concrete compressive strength. The performance of the designs created by mixing three different RCAs with CA at 25%–50%–75% by mass was examined by laboratory tests [modified Proctor, California bearing ratio (CBR), permeability, resilient modulus, and plastic deformation]. CBR values for pure RCAs were higher than 100% and the CBR values were decreased for the mixture designs. Permeability coefficient ($k$) values of the CA and RCAs were close to each other. Resilient modulus ($M_r$) values were evaluated for three different models. In general, the lowest $M_r$ values were obtained for pure RCAs, while the highest $M_r$ value was obtained for pure CA. There was no statistically significant correlation between $M_r$ values and CBR values. The plastic deformation (${\epsilon }_p$) value of the pure CA was significantly smaller than the ${\epsilon }_p$ values obtained for the pure RCAs and mixture designs. The RCAs generally increased the ${\epsilon }_p$ values. Flexible pavement thickness and cost analyses were performed for the 50CA 50RCA2 design, which was determined to be the most suitable for GRB material, 100RCA2, and 100CA designs for comparison. The 50CA 50RCA2 design reduced the GRB cost by 13% compared to using pure CA. As a result, it was determined that 50% RCA in GRB reduced the cost and had no adverse effect considering the material properties. Recycling of concrete wastes in this way can make significant contributions to reducing environmental pollution and prevent the depletion of natural resources.

Semiflexible pavement (SFP) is gradually gaining more attention for its excellent rutting resistance and high load-bearing capacity. However, cracking damage is one of the most challenging distresses in SFP due to the brittle behavior of cement paste (CP) and insufficient adhesion between porous asphalt matrix (PAM) and hardened CP. In this study, the cement asphalt emulsion paste (CAEP) was introduced as a grouting material for SFP to overcome the shortcomings of CP. Therefore, the effect of CAEP on the cracking resistance of the SFP was studied by conducting a semicircular bending test and obtaining the full-field displacement and strain of the specimen during the whole loading process through digital image correlation (DIC). The maximum average value of full-field tensile strain was proposed to accurately determine the specimens’ fracture failure point for calculating fracture parameters. Results indicated that DIC data could identify the three fracture phases of SFP materials (i.e., crack initiation, crack propagation, and failure) precisely. In addition, incorporating the asphalt emulsion in the cement grout significantly improved the SFP material’s fracture performance by increasing the fracture energy, J-integral (Jc), and cracking resistance index (CRI) values on average by 48%, 76.1%, and 43% in SFP with CAEP20 and by 13.4%, 45.7%, and 87% in SFP with CAEP40, respectively. Overall, CAEP with an asphalt emulsion content between 20% and 40% by weight of cement is recommended as the best grout in SFP to obtain the best cracking resistance.

High-viscosity modified asphalt (HVMA) is the most commonly applied method in drainage asphalt pavements. However, some disadvantages of hot-mix HVMA, including high energy consumption and unavoidable environmental pollution, should be improved. Therefore, warm-mix additive (WMA) was introduced. In this paper, the effects of WMA on the rheological and microstructural properties of HVMA were studied to select optimum WMA conditions. WMAs mainly include foam warm mix (1%, 3%, and 5%), Sasobit (1%, 3%, and 5%), Evotherm (0.4%, 0.8%, and 1.2%), and the newly introduced warm additive glow brand (GLWBR) (0.4%, 0.8%, and 1.2%). Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were performed on HVMA after rheological processes. Also, microstructural properties were examined by Fourier transform infrared spectroscopy and scanning electron microscopy methods. Based on the obtained results, all WMAs reduced the viscosity (135°C) of HVMA and achieved warm mixing effects. However, absolute viscosity (60°C) was enhanced by Sasobit and GLWBR. In addition, GLWBR improved high-temperature rheological performance and had no significant effect on the low-temperature and aging performance of HVMA. These findings were further verified by morphological observations.

Low-carbon environmental protection and reduction of pollution have become development goals for asphalt pavement. Crumb-rubber modified asphalt binder (CRAB) made from recycled scrap tires provides an economical and practical way to salvage the natural raw materials but results in carbon and toxic emissions. Warm-mix technology has been applied to recycled CRABs, forming warm-mixed crumb-rubber asphalt binders (W-CRABs) as effective and efficient green materials to reduce energy consumption and mitigate environmental pollution. In addition, the type and dosage of warm-mix additives are key factors affecting rutting and cracking pavement distress. This study aims to correlate Superpave protocol results with those of fractional viscoelastic models to estimate the high- and low-temperature properties of W-CRABs, including recycled crumb rubber, viscosity reducer (1%, 2%, 3%), and surfactant (0.4%, 0.6%, 0.8%). Bending beam rheometer and dynamic shear rheometer tests were performed to determine experimental parameters such as complex modulus, phase angle, and the ratio of creep rate to creep stiffness ($m/S$). The fractional derivative model (a connection composed of one spring, one linear dashpot, and two Abel dashpots in series) and the generalized fractional viscoelastic model (a combination of two spring-spot fractional elements in series) were developed to investigate viscoelasticity of W-CRABs. In conclusion, by experimental and modeling methods, this study recommends that, for northwest China with significant temperature differences, the optimal resistance to cracking and rutting can be achieved by mixing 0.6% surfactant and CRABs.

Failure of high-density polyethylene (HDPE) aboveground storage tanks (ASTs) causes numerous environmental, ecological, and economic problems. Therefore, it is necessary to routinely inspect the integrity of ASTs to identify the potential defects and act before a catastrophic failure happens. This study investigated the feasibility of using infrared thermography (IRT) for routine HDPE AST inspections and how weathering impacts the properties of HDPE. Moreover, the factors affecting the IRT’s accuracy for defect detection were researched, and it was attempted to determine the minimum levels of defect detection for each weather circumstance. This study investigated the potential areas for tank failure for close inspection. Results showed that IRT is efficient in detecting shallow defects within the outer half of the wall. The smallest detectable defect size was 2.8 mm, which varied in different measurements depending on the interaction of sample geometry, initial thermal gradient, and defect location.

Abstract

Ethylene-vinyl acetate (EVA) lotion can significantly improve the interface problems caused by the physical and chemical differences between expanded polystyrene (EPS) beads and cement, which is one of the reasons why EPS cement composites are widely used in the construction field. However, the research on its problems is often limited to phenomenological engineering methods, ignoring the potential interaction mechanism in atomic structure. Therefore, in this study, the strengthening mechanism of EVA on EPS particle–cement slurry interface was systematically studied from the aspects of macromechanical properties, microstructure characteristics, chemical composition, and molecular structure. In terms of physical test, it was found that the compressive strength and flexural strength of EPS-cement-based materials containing EVA are increased by 19% and 31%, respectively, at 28 days when the content of EPS particles is the same. It was observed through an electron microscope snapshot that EVA makes a uniform and dense interface structure between EPS particles and cement. For chemical tests, EPS particle surface hardening cement was ground into powder and tested by X-ray diffraction and Fourier transform infrared spectrometer. It was comprehensively analyzed that EVA reduced the hydration product $\mathrm{Ca}(\mathrm{OH}{)}_2$ and increased calcium silicate hydrate (C-S-H) at the interface. In terms of numerical simulation, through molecular simulation modeling and calculation, it was found that the introduction of EVA can produce more stable hydrogen and ion bonds at the EPS–C-S-H interface, which plays a vital role in reducing the interface effect and increasing the interface binding energy.

Practical Applications

Cement-based materials containing expanded polystyrene beads are considered environmentally friendly, lightweight, and high-strength green building materials widely used in construction projects, such as load-bearing concrete blocks, insulation boards or walls, cladding or structural insulation panels, composite floors, structural insulated panel, pavement base material, geogrid, road barrier, and floating offshore structure. These structures have the advantages of good durability, good thermal insulation, high fire rating, low water absorption, low price, and convenient construction. In order to promote its application in practical engineering, it is necessary to solve the problems of poor adhesion of EPS/cement-based interface and uneven separation and dispersion of EPS particles in EPS cement-based composites. As an effective method, the surface modification of EPS is worth studying. This study discussed the strengthening mechanism of EPS/cement-based interface modified by ethylene-vinyl acetate lotion from multiscale by experiment and numerical simulation. It can provide a reference for preparing more stable, uniform and excellent EPS concrete.

Although basalt fiber (BF) has been used to reinforce cement composite as an eco-friendly material, its effect on basalt fiber–reinforced cement composite (BFRCC) is contradictory. BF was found to be corroded by a pore solution through scanning electron microscopy observation. Owing to the chemical alkali corrosion and physical denudation of the BF in an alkaline environment, the interface bonding between the BF and the cement matrix was weakened, and the toughening effect of the BF could not be fully exerted. Pore structure characterization was examined based on the water uptake kinetics method and image analysis of binary specimen slices. The BF was found to have a detrimental effect on the pore structure because of the inclusion of exogenous bubbles. However, basalt powder (BP) could densify the pore structures of the cementitious materials, especially in the basalt-powder-fiber-reinforced cement composite (BPFRCC), in which it further reduced the corrosion degree of the BF and enhanced the bonding between the BF and cement matrix interfaces. Therefore, BP and BF can synergistically enhance the performance of BPFRCC.

One of the most important components of box beam bridges is the shear key that connects the box beams together. The shear keys in box beam bridges often fail at the interface. In recent years, ultrahigh-performance concrete (UHPC) has been successfully used to cast these shear keys. The current study investigates the effect of temperature cycles on bond performance between a high-strength concrete (HSC) box beam and UHPC shear key. The interfacial bond performance was evaluated by subjecting specimens to 60, 120, and 180 freeze-thaw (FT) cycles representing 1, 2, and 3 years of environmental exposure. Some direct tension specimens that were subjected to 180 FT cycles were additionally subjected to 1-Hz frequency fatigue cycles with stress reversals. Using the direct tension, pull-off, slant shear, and bishear assessment methods, the test results have demonstrated that the number of FT cycles did not affect bond performance in terms of strength and failure modes. The test results also showed that standard specifications underestimate the cohesion and friction coefficients evaluated using Mohr-Coulomb’s and Carol’s approaches for concrete placed against intentionally roughened surfaces. Furthermore, it was found that fatigue loading with stress reversals did not diminish the direct tensile bond strength of the specimens.

In this study, the bearing capacity characteristics of warmed frozen soil under dynamic load were obtained by means of scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) test, and the microstructure change mechanism was evaluated. The lower the initial ambient temperature, the greater the strength of the warming frozen soil: the intensity of the $-20°\mathrm{C}$ warmed frozen soil was twice that of the $-5°\mathrm{C}$ soil. Through microscopic experiments, it was seen that the arrangement of pores in low-temperature frozen soil was more orderly than in high-temperature frozen soil. The pore distribution density in low-temperature frozen soil was large, the soil particles were more compact, the interparticle connectivity was good, and the pore area ratio increased with decreasing temperature. Under the condition of increasing temperature, the melting of ice crystal molecules in the pores and the combination of soil particles fill the large pores, so the pore volume decreases. The decrease in the pore volume was the key factor for the increase of soil accumulation deformation and the vulnerability of soil to destruction.

Catastrophic failures of tailings dams, primarily due to liquefaction, have occurred in Brazil in the last few years. Mine tailings deposited behind upstream dams are materials of low in situ densities and strengths. To avoid future disasters, chemical improvement methodologies such as deep mixing and mass stabilization technologies are being studied as alternatives to be used before decommissioning for in situ improvements of upstream tailings dams with a high risk of collapse. The present research aims to analyze the mechanical behavior of reconstituted state gold tailings specimens, in contrast to artificially cemented gold mine tailings specimens, considering the use of small and large amounts of Portland cement under a similar high void ratio. The influence of Portland cement content in the stabilization of gold tailings specimens molded with their in-situ void ratio was evaluated through saturated undrained triaxial compression tests carried out under small confining pressures. A reduced amount of Portland cement (about ${12\mathrm{kg}/\mathrm{m}}^3$) was enough to avoid liquefaction (with the generation of negative pore-pressure), keeping the same unique critical state line (CSL) for reconstituted tailings and slightly cemented tailings specimens, with a gradient $({\mathrm{M}}_{\mathrm{tc}})$ of 1.41. The use of high amounts of Portland cement insertion (75 and ${150\mathrm{kg}/\mathrm{m}}^3$) caused an alteration in the ultimate condition of the studied tailings, and ${\mathrm{M}}_{\mathrm{tc}}$ changed to 2.36. Finally, the in-situ addition of Portland cement to tailings deposited behind upstream dams is an important alternative for the safe decommissioning of such structures.