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The current construction industry for civil and structural engineering is considered to be one of the growing industries in the world. With the push toward a more digitized industry, emerging trends such as additive manufacturing and the use of three-dimensional (3D) printing technology, along with consumer demand, are resulting in automated development with multiple benefits. Successful applications for small-scale construction projects that have implemented 3D printing have shown improvements in cost, production time, and design freedom and complexity. However, for large-scale applications, there are various limitations and factors hindering the adoption of additive manufacturing technologies. In this paper, a systematic literature survey of recent 3D printing technologies was conducted specific to the area of construction engineering, and the various techniques, materials, software, and technical and nontechnical aspects were analyzed. The key applications and their benefits are outlined, and their potential for large-scale applications is articulated. Future research areas for these components are suggested to strengthen the technical readiness and feasibility of adopting 3D printing technology in construction engineering and industries. [ABSTRACT FROM AUTHOR]

The welded hollow sphere is formed by hot stamping of the steel plate, and the mechanical properties of the steel after hot stamping are the key to accurately evaluate the stress performance of the welded hollow sphere. In this paper, the Q235 steel used to manufacture the welded hollow sphere and the formed welded hollow spheres were made into tensile coupons. The mechanical properties of hot-stamped spherical shell Q235 steel without flattening treatment after water cooling from elevated temperature were studied by experiments. The stress–strain curves, elastic modulus, percentage elongation of fracture, yield strength, and ultimate strength of steel were analyzed. The results showed that hot stamping can improve the mechanical properties of Q235 steel to some extent. The exposure temperature and the method of water cooling have little effect on the elastic modulus of the hot-stamped spherical shell Q235 steel, but they have significant effects on the percentage elongation of fracture, yield strength, and ultimate strength. With the increase of exposure temperature, the percentage elongation of fracture presented a decreasing trend, and the higher the exposure temperature, the more obvious the decreasing trend. Before 500°C, the yield strength and ultimate strength of steel showed a decreasing trend, and it increases with the increase of exposure temperature after 500°C. Based on the experimental results, the stress–strain model and the mechanical properties calculation formula of the hot-stamped spherical shell Q235 steel after water cooling were proposed, and the mechanical properties relationship between the hot-stamped spherical shell Q235 steel and the original Q235 steel was obtained. [ABSTRACT FROM AUTHOR]

In this paper, alkali-activated materials (AAMs) were prepared combining waste coral powder (CP) and blast furnace slag (BFS) as precursors, artificial seawater and deionized water as mixing water, and blends of NaOH and sodium silicate solution as alkaline activators. The effect of CP and seawater on the fluidity, mechanical properties, and hydration was discussed. The experimental results showed that a 15% CP content effectively improved the fluidity of fresh paste while having little effect on compressive strength of the samples. Compared with deionized water, the use of seawater for sample preparation resulted in a reduction of the fluidity and mechanical properties of the samples. The pore structure could be refined by CP and seawater, but gel micropores increased significantly when the CP content reached 25%. The use of CP and seawater did not cause significant changes in the type of hydration products. Although the amount of hydration products in the early stages of the samples prepared with seawater was relatively low compared with those prepared with deionized water, it gradually surpassed that in samples prepared with deionized water with increasing curing time. Increasing the CP content led to a higher reaction degree, and a CP content of 25% resulted in a reaction degree of approximately 30%–50%, which was roughly twice that of a sample containing 5% CP. These findings have important implications for the development of sustainable construction materials for utilization in marine engineering. [ABSTRACT FROM AUTHOR]

This paper examines the merits of using fibers derived from cigarette butts to enhance the performance of stone matrix asphalt (SMA). To this end, mechanical and environmental performances of SMA mixtures contained cigarette butt fibers were determined and compared with conventional SMA mixtures contained cellulose fibers. Two methods were applied to use cigarette butt fibers in mixtures included encapsulation with asphalt binder and mixing with hot asphalt binder for periods of three, five, and eight minutes. Performance tests included Marshall stability, asphalt binder drainage, moisture susceptibility, semicircular bending (SCB) at low and intermediate temperatures, wheel tracking tests, and toxicity characteristic leaching procedure (TCLP) were carried out on SMA mixtures contained different fibers. Mechanical test results showed that using encapsulated cigarette butts has detrimental effects on durability, low and intermediate temperature fracture resistance, and rutting performance in comparison with cellulose fibers. Nevertheless, utilization of cigarette butt fibers mixed with hot asphalt binder for 8 min improve water resistance, fracture characteristics, and rutting performance of SMA mixtures. Furthermore, by reducing the mixing duration of fibers with hot asphalt binder, moisture susceptibility and mechanical properties of mixtures were adversely impacted. TCLP test results revealed that utilization of cigarette butt fibers in SMA mixtures does not exhibit any environmental consequences. Finally, it was concluded that cigarette butt fibers mixed with hot asphalt binder for 8 min are good replacement for conventional asphalt binder stabilizers. [ABSTRACT FROM AUTHOR]

The study of alkali-activated materials as a replacement for portland cement has been growing in recent years due to the sustainable nature of these materials. Nevertheless, ternary alkali-activated pastes using waste glass as a precursor have been insufficiently studied concerning their rheological, mechanical, and microstructural properties. In addition, there is a lack of research studying alkali-activated mixtures using basic oxygen furnace (BOF) slag and glass waste as precursors. Therefore, this paper aims to study the effect of glass powder (GP) content as a precursor, the effect of the activator ratio in alkali-activated ternary pastes of BOF slag, metakaolin (MK), and GP, and the influence of the Na2SiO3/NaOH ratio on its mixtures. The activator solutions of NaOH and Na2SiO3/NaOH were used in the production of the pastes. The liquid/solid ratio was kept fixed at 0.6 and the molarity of the NaOH solution was fixed at 12 M, seeking to analyze the impact of the Na2SiO3/NaOH ratio, with adopted values of 0.75, 1.5, and 2.5. We also aimed to study the impact of the glass content in the mixture for the values of 10%, 20%, and 25%, replacing the BOF slag. The workability by the minislump test, rheology, compressive strength for 1 and 28 days, and microstructural parameters were analyzed. ANOVA was performed to determine the significance of variables in the workability and compressive strength parameters. Pastes with the highest activator ratio (Na2SiO3/NaOH=2.5) produced better compressive strength (34.74 to 36.11 MPa) and lower minislump spreads (90 to 98 mm) compared with the mixtures with Na2SiO3/NaOH=1.5 and 0.75, besides indicating a denser microstructure, linked to higher production of aluminosilicate gels. Higher GP contents generated pastes with lower mechanical performance (16.7 MPa for Na2SiO3/NaOH=0.75) and microstructural qualities, albeit with better workability (124-mm minislump spread). [ABSTRACT FROM AUTHOR]

This paper presents a pilot study on the characterization of the physical and mechanical properties of a novel green concrete with two different substituted recycled plastic aggregates. A reference mix with an average compressive strength of around 60 MPa is considered. Recycled polyethylene terephthalate (PET) powder and recycled mixed plastic [polypropylene (PP) and polyethylene (PE)] granules were adopted to substitute fine and coarse aggregates. Two different substitution strategies were employed. In the first one, the PET powder is used to substitute the fine sand by volume. In the second one, the PET powder is used to substitute the fine sand while the recycled mixed plastic granules are used to substitute the coarse sand and fine coarse aggregates by volume (50% for PET powder and 50% for recycled mixed plastic granules). Four total replacement levels (5%, 10%, 20%, and 30%) by volume were considered. The fresh concrete properties (slump and density), compressive and flexural behavior, toughness, and permeability are investigated. Finally, a microscale characterization of the plastic-paste interface is provided. An interpretation of the test results of this study by comparing them with the findings of previous studies is provided, along with the provision of two predictive equations for the compressive and flexural strength reduction factors. Results show reduced flowability for PET cases due to particle shape, slight compressive strength reduction at low substitutions, improved flexural strength at low levels, decreased permeability, and microscale enhancements. The comprehensive evaluation indicates promising physical and mechanical performance of the novel green concrete. [ABSTRACT FROM AUTHOR]

Although previous studies have broadly explored the aging process of styrene-butadiene-styrene (SBS)-modified asphalt, there still is a lack of understanding of the precise evolution patterns of its phase structure during aging, and whether aged SBS-modified asphalt retains its modified properties or reverts to conventional asphalt. To fill these gaps, this paper focused on key performance characteristics that differentiate SBS-modified asphalt from conventional asphalt, including viscosity, elasticity, and toughness properties; evaluated how aging influences mechanical properties; and examined morphological changes at different aging stages. The effective method for phase structure characterization was established. Based on the results, it was found that mechanical property variations, especially in the toughness curve, effectively indicate the phase structure. The fracture strength σB and fracture elongation εB of SBS-modified asphalt after rolling thin-film oven (RTFO) aging for 8 h closely matched those of 70# base asphalt after RTFO aging for 8 h, with values of 1,364.32 and 0.005, compared with 1,421.07 and 0.007, respectively. This curve helps determine whether aged SBS-modified asphalt remains modified or reverts to conventional asphalt. Aging primarily affected instantaneous elastic deformation, and had a minimal impact on delayed elastic deformation. Morphological analysis supported these findings, and showed that SBS polymer degradation precedes significant network disruption, and increased toughness results mainly from SBS polymer presence. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study conducted to investigate the properties of alkali-activated concrete (AAC) mixtures prepared using the optimum combinations of four precursor materials (red mud, limestone powder, silicomanganese fume, and natural pozzolana) and four activation parameters (activator to precursor ratio, silica modulus, sodium hydroxide molarity, and water to precursor ratio). In order to examine the beneficial effects of inclusion of ordinary portland cement (OPC) and curing regimes on the properties of AAC, three dosages of OPC (in the range of 10% to 30% by weight) and two types of curing (steam and air curing) were considered. Tests were conducted on the mixtures of AAC to determine different properties that included the density, void ratio, water absorption, compressive and tensile strengths, modulus of elasticity, drying shrinkage, and loss of weight and strength after exposure to acid and sulfate salt solutions. Additionally, microstructural investigations (x-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy) were conducted on the alkali-activated binders to justify the trends of the experimental data pertaining to different properties of the AAC mixtures. The results of the tests indicated that the properties of AAC were significantly affected by inclusion of OPC and curing regimes. It was found that almost all properties of the AAC were significantly enhanced when the OPC dosage was increased from 10% to 20%. Further, the AAC mixtures having more than 10% OPC exhibited better properties as compared to the traditional OPC concrete mixture. The use of OPC as a construction material is one of the major contributing factors to environmental damage. Multiple alternative materials have been suggested as a replacement for OPC such as alkali-activated industrial byproducts and natural minerals. However, these possible materials are not as well studied as OPC in terms of their strength development, volumetric stability, and resistance to extreme environments. In this work, the performance of different AAC made with natural minerals and industrial waste materials was evaluated, and we compared their performance to typical OPC concrete. The present investigation shows that the developed alternative concrete mixtures perform in a comparable or better manner to OPC concrete mixtures in terms of strength, volume change with age, acid resistance, and sulfate resistance while reducing the OPC content by 70% to 90%. The study scope, however, does not extend to study the economic viability and carbon footprint of the proposed AAC mixtures. [ABSTRACT FROM AUTHOR]

Single-kenaf fiber-reinforced polymer composites are typically characterized by relatively low strength and stiffness properties that make them unsuitable for structural applications. However, they are lightweight, economical, and ecofriendly. This paper presents a study on the manufacturing and mechanical characterization of bidirectional kenaf (K) fiber-reinforced epoxy composites hybridized with carbon (C) fibers in various stacking sequences and the effects of hybridization on salient physical and mechanical properties. Single and hybrid fiber composites were fabricated utilizing the vacuum infusion molding technique. The density, tensile, flexural, and interlaminar shear properties in hybrid composites increased significantly when carbon fiber volume increased from 9% to 16%. Stacking sequences in a hybrid affected the mechanical properties of the composites. The highest tensile strength and modulus were shown by the seven-layer hybrid composite with an alternate K/C stacking sequence and C layers as skin layers, i.e., C/K/C/K/C/K/C, among all tested hybrid composites. Sandwich design in the hybrid (C2/K3/C2) had higher flexural strength (+300%), flexural modulus (+414%), interlaminar shear strength (+278%), lower water absorption (−46%), and thickness swelling (−30%) compared to single-fiber kenaf/epoxy composites. Density increased by 5% in hybrid composites. The highest fracture toughness (+134%) was achieved using the dual sandwich design structure hybrid (C/K2/C2/K2/C). The developed composite has applications in stairways, walkways, and bridges. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubes (CFSTs) have attracted increasing interest in research during the last decade as a construction system that increases its performance due to the use of self-stressing concrete. The efficiency and confining pressure of this construction solution mainly depends on the expansion of the concrete mixture introduced into the steel tube. This study shows the importance of the correct design of the expansive mixes and the correct selection of components. The effect of three types of chemical admixtures (air-entrained, setting retarder, and hardening accelerator) commonly used in the ready-mixed concrete industry when added to a self-stressing concrete made with a K-type calcium sulfoaluminate–based expansion agent has been analyzed. This study showed that certain chemical admixtures, added in a fixed proportion, conditioned both the compressive strength and the magnitude and kinetics of the expansion in a restricted regime of the reference self-stressing concrete mix. The efficiency of the CFST and self-stressing concrete construction solution represented by the bond failure strength and the sliding load of the concrete core against the steel tube was influenced not by the compressive strength of the expansive concrete but by the degree of restrained expansion (confinement effect) achieved. In this research, an alternative test method for measuring expansion was proposed, which allows continuous recording of positive strains (expansions), eliminating the dependence on setting time for demolding; this method even allows the exact identification of the expansion beginning. Finally, it was proposed that the ettringite detectable by the X-ray diffraction (XRD) technique was not representative of the magnitude of expansion generated from K-type calcium sulfoaluminate expansive agents because the proportion of ettringite was not related to the expansion determined by the different test methods proposed. [ABSTRACT FROM AUTHOR]

This study examined the self-cleaning and mechanical properties of basalt fiber–reinforced ground granulated blast furnace slag (GGBS)-based geopolymer mortar containing nano TiO2. The nano TiO2 and basalt fiber in mixtures were used at 0%, 0.25%, 0.5%, and 1% by weight of GGBS. The cubes (50×50×50 mm) and prisms (40×40×160 mm) samples containing nano TiO2 and basalt fiber were produced and cured in the oven for 24 h at 60°C. Then, these samples were kept at room temperature at 23°C±2°C for 28 days. Lastly, the compressive strength, flexural strength, ultrasonic pulse velocity, capillary water absorption, and self-cleaning tests of GGBS-based geopolymer mortars were carried out. In this study, the Rhodamine-B test was used to determine self-cleaning. This study showed that the compressive strength, flexural strength, and ultrasonic pulse velocity values of the GGBS-based geopolymer mortars increased as the nano TiO2 and basalt fiber ratios increased, but their capillary water absorption coefficient decreased. Also, this study found that the self-cleaning rate of GGBS-based geopolymer mortars containing 1% nano TiO2 was obtained as 50.62% at 28 days. [ABSTRACT FROM AUTHOR]

The environmental friendliness, good thermal performance and sustainable development of rammed earth structures have attracted the attention of numerous researchers and engineers in recent years. Nevertheless, the fire safety of rammed structures has not been extensively studied. The primary objective of this study is to investigate the mechanical properties of stabilized and unstabilized rammed earth exposed to direct fire under short elapsed time and high temperatures using a kiln. Rammed earth specimens with various mix designs were prepared and then exposed to high temperatures. Afterward, destructive and nondestructive tests were performed. Additionally, microstructural analysis was preceded to evaluate the change in chemical composition and microstructural of rammed earth specimens. The majority of the stabilized specimens exhibited thermal instability at 700°C. These specimens lost up to 85% of their compressive strength and 15% of their weight and change in their chemical composition. Under direct fire exposure, the rammed earth's mechanical properties were not greatly impacted due to the short elapsed time. Compressive strength was increased in unstabilized (clay) RE specimens. A correlation between destructive and nondestructive properties was proposed. This study can be considered in the mix design of RE that experiences high temperatures. [ABSTRACT FROM AUTHOR]

The use of curvilinear glass fiber‒reinforced polymer (GFRP) bars as the longitudinal reinforcement in curved reinforced concrete (RC) elements has generated significant interest. Even so, there is a lack of comprehensive data on the long-term durability of nonpultruded curvilinear GFRP bars in an alkaline environment. This study represents a pioneering effort to assess the long-term durability of nonpultruded curvilinear GFRP reinforcement, as well as its physical and mechanical properties, to address this research gap. Over 400 bar samples—including #5 curvilinear and straight GFRP bars—were prepared and tested. The physical properties were evaluated in terms of fiber content, cross-sectional area, glass-transition temperature, cure ratio, and water absorption. Tensile, transverse shear, and interlaminar shear tests were performed to assess the mechanical properties. The durability properties were investigated by submerging the samples in an alkaline solution at four different temperatures (24°C, 40°C, 50°C, and 60°C) for three different exposure durations (1,000, 3,000, and 6,000 h). Morphological studies were conducted with scanning electronic microscopy (SEM); elemental analysis was determined with energy-dispersive X-ray spectroscopy (EDS). Additionally, the bars underwent thermal analysis with differential scanning calorimetry (DSC) and chemical analysis with Fourier transform infrared spectroscopy (FTIR). Then, a long-term prediction model was developed to predict the service-life durability of the curvilinear GFRP bars in an alkaline environment. The experimental results indicate that the physical, mechanical, and durability properties of the nonpultruded curvilinear GFRP bars met all the requirements for use as reinforcing bars. In addition, the SEM, EDS, DSC, and FTIR analyses revealed that the curvilinear GFRP bars were highly durable in the alkaline environment. Furthermore, according to the long-term prediction model developed, the tensile strength retention of the curvilinear GFRP bars after 100 years of service life in an alkaline environment was >77%. [ABSTRACT FROM AUTHOR]

Increased stormwater runoff due to urbanization has highlighted the need for faster water removal. Porous concrete has high void content and porosity; however, it has poor mechanical properties. Its performance can be improved by changing parameters such as cement content, aggregate size, water-to-cement ratio, gravel-to-cement ratio, and additives. Contact surface area and aggregate interlock are the main factors to consider in the design of porous concrete. This study investigated the influence of varying aggregate size and adding polypropylene fiber on the density, mechanical properties, porosity, void ratio, and permeability of porous concrete. Twenty-six mixtures that combined different aggregate sizes and polypropylene fiber content were considered. The results revealed that increased contact surface area and void ratio using multiaggregate sizes provided adequate compressive strength and permeability performance. The best performance was achieved when aggregate sizes of 9.5–6.7 mm and 6.7–4.75 mm were combined at a 3∶1 ratio and 0.1% polypropylene fiber was added. Many applications in civil engineering might be both financially and environmentally beneficial. Compared with pond retention systems, porous concrete systems showed a major benefit in controlling stormwater runoff and avoiding soil degradation influenced by water when used as a trenching system for the upcoming water surrounding the building's foundations. Further benefits as the natural hydrological cycle restoration are achieved by infiltrating water back into the soil rather than pouring it into the sewage system. However, porous concrete relies on voids in its design, reducing its mechanical capacity, and thus cannot withstand heavy traffic. In addition, freezing and thawing cycles in cold weather countries might degrade its capacity. This article collected the aggregate sizes that could be susceptible to porous concrete production and combined at least two sizes to attain the best mechanical and permeability performance. Optimized mixes were discussed in both cases; single and combined aggregate sizes along with fiber additives to enhance the optimized mixes mechanical response and increase their bending capacity for improved traffic resistance. The optimized mixes also showed higher compressive strength than control porous concrete mixes. [ABSTRACT FROM AUTHOR]

The interface bond strength between carbon fiber-reinforced polymer (CFRP) layers and concrete is a crucial metric for determining the mechanical properties of CFRP-reinforced concrete. This bond strength is essential for evaluating CFRP-reinforced concrete's performance and ensuring the materials' structural integrity. A database was established using the experimental data in the literature to evaluate the interface bond strength. This database comprised 360 groups of different conditions test results of CFRP-reinforced concrete, which were used to create a prediction model using an artificial neural network. The database was randomly divided into two data sets: 310 groups were used for training the neural network model and 50 for simulated prediction. A three-layer artificial neural network model was trained using the backpropagation algorithm, which is widely used in artificial neural networks. The model's input layer considered seven parameters, including the type of CFRP layer, surface form, CFRP layer thickness, anchorage length, failure mode, concrete compressive strength, and normalized concrete cover thickness. These parameters were selected based on their known influence on the interface bond strength between the CFRP layers and concrete. The output layer of the model represented the interface bond strength between the CFRP layers and concrete. The model's results indicated that the backpropagation (BP) neural network model had strong capability of prediction and generalization. The predicting error was minimal, a crucial aspect of the model's accuracy. Further, this approach allows for integrating many factors that influence the interface bond strength between the CFRP layers and concrete, providing accurate predictions of the bond strength. It can be used as a valuable tool for evaluating the performance of CFRP-reinforced concrete. This research develops an accurate method to predict the bond strength between CFRP layers and concrete using artificial neural networks. A strong bond is crucial for the structural integrity of concrete reinforced with CFRP. The neural network model considers factors like the type and thickness of CFRP used, how the concrete surface is prepared, and the concrete's strength. Engineers can use this neural network tool to evaluate how well CFRP will reinforce specific concrete mixtures and structures before construction. This allows structures to be designed and built with optimal, cost-effective use of CFRP to reinforce concrete in applications like bridges and buildings. The neural network approach integrates many technological and material factors into one predictive model, providing a useful evaluation method for the construction industry. [ABSTRACT FROM AUTHOR]

To investigate the effects of mix proportion on the compressive mechanical properties of a flexible thin spray-on liner (TSL), a series of compression tests were performed on flexible TSL specimens with different styrene-acrylic emulsion contents (ms), cement–sand ratios (mc/mq), and fiberglass contents (mF). With an increase in ms , the compressive strength of the flexible TSL first increased and then decreased, and the TSL gradually transformed from brittle to ductile. With an increase in mc/mq , the compressive strength increased. The increase of mF improved the compressive strength and elastic modulus of the TSL. Subsequently, three cyclic loading paths were selected to study the stress–strain behavior of a flexible TSL with a fixed mix proportion. The evolution characteristics of the irreversible axial strain, elastic modulus, dissipated energy, and damage variables under different cyclic loading paths were analyzed. The development of irreversible deformation accumulation reflects the characteristics of the damage evolution process under cyclic loading. Based on the experimental results, a stress–strain model is proposed to predict the stress–strain behavior of the TSL under different cyclic loading paths. The experimental results were used to calibrate and validate this model, demonstrating that the model can effectively predict the stress–strain behavior of a flexible TSL. [ABSTRACT FROM AUTHOR]

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

The mechanical properties of loess are strongly dependent on the environment where it is deposited. To investigate the effects of acidic, alkaline, and saline environments on the strength and deformation properties of compacted loess, the consolidation test and direct shear test were carried out on loess samples contaminated with different concentrations of acetic acid, sodium hydroxide, and sodium sulfate. In addition, changes in zeta potential, mineralogy, chemical composition, and microstructure of the loess samples at different chemical environments were also measured. The results show that the reduction in the thickness of the diffuse double layer for the loess contaminated with acetic acid leads to the aggregation of clay particles, laying the foundation for the expansion of loess pores, while the dissolution of carbonate cement and chemical cement makes the soil structure looser. Hence, the compacted loess has significantly lower shear strength and higher compressibility in an acidic environment. The mechanical properties in the saline environment show similar variation characteristics to the acidic environment, but this is mainly due to carbonate solubilization. In the alkaline environment, the degree of interparticle cementation of the loess is enhanced by the generation of calcite due to dedolomitization and the generation of colloidal flocs of Al(OH)3 , Fe(OH)3 , and H2SiO3. In addition, the pore connectivity is greatly reduced by the extensive distribution of clay particles caused by the development of a diffuse double layer. As a result, its compressibility and shear strength are improved compared to uncontaminated loess. These findings can be used as a reference for geoengineering practice in loess areas. [ABSTRACT FROM AUTHOR]

Temperature variation during the welding will cause different solid-state phase transformations in the welding area and result in a heat-affected zone (HAZ) between the weld metal (WM) and the base metal (BM). Depth-sensing indentation (DSI) is a doable technique to characterize mechanical properties of materials in the HAZ, which is usually not big enough for the fabrication of coupons for traditional tension tests. The basic idea of DSI technique is to push a hard tip into the surface of the material and then reveal its mechanical properties based on the response of the material. In this study, mechanical properties of butt welds of Q355D steel were investigated with DSI tests and reverse analytical approach. Different welding zones, including BM, subcritical HAZ, fine-grain HAZ, coarse-grain HAZ, top pass of WM and middle pass of WM, were distinguished by microstructures observed by scanning electron microscope (SEM). DSI tests were conducted on these welding zones. Mechanical properties were characterized based on load-penetration depth (P-h) curves obtained by DSI tests. These mechanical properties were adopted in finite-element (FE) simulation of DSI tests. P-h curves obtained by FE simulation agree well with results of DSI tests for all welding zones, especially for the loading curves. The agreement validates the applicability of DSI technique in characterizing mechanical properties of materials. Tension coupon tests were conducted on the BM and the middle pass of WM to verify the accuracy of the DSI technique. Variation of mechanical properties across the welding area were discussed in accordance with microstructures of materials in different welding zones. [ABSTRACT FROM AUTHOR]

The application of aeolian sand as the full aggregate to produce high-performance concrete is significant for engineering construction in desert areas. However, high-performance concrete with full aeolian sand (FA-HPC) is characterized by a low water-binder ratio, high content of cementitious materials, and no restriction of coarse aggregates, resulting in a high risk of shrinkage cracking. The main purpose of this work is to investigate the reinforcement effect of different types of fibers and their combinations on FA-HPC. Three types of fibers, i.e., steel fiber (SF), basalt fiber (BF), and polyvinyl alcohol fiber were employed in the FA-HPC matrix to explore the most promising reinforcement method. The workability, strength, shrinkage, cracking resistance, and chloride resistance of FA-HPC were investigated by laboratory tests. Moreover, the fiber-reinforcement mechanism was analyzed in terms of the micromorphology of FA-HPC. The results indicated that the incorporation of fibers could improve the previously mentioned properties except for the decrease of fluidity with content dependence, especially for 12 mm fibers. The single SF has a considerable advantage in strength enhancement and shrinkage reduction presenting a variation of 56.7% and 19.5% at 1% by volume, respectively. Moreover, the hybrid fibers exhibited better behavior in durability showing 95.88% crack reduction and 48.5% improvement in chloride resistance. Eventually, two selected schemes were recommended presenting for 1% by volume single SF and hybrid fibers (0.75% by volume SF with 0.25% by volume BF) from an integrated perspective. Furthermore, microscopic characterization revealed that the mechanism of fiber reinforcement mainly played a bonding and bridging effect, refining the pores at different scales and making the structure of FA-HPC dense. This research can optimize the material composition of FA-HPC and promote the utilization of aeolian sand resources. [ABSTRACT FROM AUTHOR]

When exposed to fire, load-bearing mass timber structures, such as cross-laminated timber (CLT), soften and decompose, which causes significant deformation and weakening, ultimately leading to failure. A combined experimental and modeling analysis is presented to predict the postfire residual compression properties of CLT. Multiple experimental fire exposure and postfire mechanical tests were performed under identical conditions to respectively characterize the internal and external thermal response of the CLT and assess the residual postfire compression properties. An analytical modeling strategy based on the measured through-the-thickness temperature profile during fire exposure is presented to predict the residual postfire compression properties of the CLT. X-ray computed tomography analysis revealed the charring rate to be nonconstant, which is in line with current research findings but not in line with Eurocode design suggestions. The analytical analysis revealed the transverse (cross) lamina to provide minor contribution to the axial compression properties but critically to the thermal protection and structural integrity of longitudinal (load-aligned) laminae during fire exposure. [ABSTRACT FROM AUTHOR]

Two-dimensional nano graphene oxide (GO) has attracted the attention of researchers due to its excellent high aspect ratio and intrinsic strength. However, its effectiveness in improving cement composite's performance is significantly dependent on the uniform dispersion of GO in the host matrix. In recent years, the use of pozzolans, such as fly ash, silica fume, and metakaolin, to enhance the dispersion of GO in cement medium has become a focus of research. This study considered the effect of rice husk ash (RHA) on the GO dispersion quality in simulated cement pore solution (SCPS). The findings obtained were validated by the compressive and flexural strengths of cement paste samples. According to ultraviolet–visible (UV-vis) spectroscopy, zeta potential analysis, and other measurements, this research demonstrated that the addition of RHA to SCPS minimizes the size of GO agglomerations and considerably enhances dispersion. The compressive and flexural strength results of cement paste samples incorporating RHA-GO after 56 days of curing improved by 46.7% and 38.7%, respectively, compared with those of the reference samples. The results of this study could pave the way for application of binary GO-pozzolans containing cementitious nanocomposites. [ABSTRACT FROM AUTHOR]

As a high-performance composite material, polyvinyl alcohol (PVA) fiber-reinforced engineered cementitious composites (PVA-ECCs) are often used in sub-elevated temperature environments (< 200°C) for long-term service. However, the effect of exposure time in sub-elevated temperature on the performance of PVA-ECCs is not still clear. In this study, the properties of PVA-ECCs in sub-elevated temperature environments were examined, with emphasis on the effect of exposure time (1, 3, 6, and 9 h). Furthermore, the microstructure and tensile behavior of single PVA fibers exposed to a sub-elevated temperature environment was investigated. Results showed that PVA-ECCs have enhanced tensile ductility at different sub-elevated temperature exposure times below 100°C. However, the tensile properties of PVA-ECCs at 150°C showed a strain retraction phenomenon at 6 and 9 h. The strain-hardening characteristics of PVA-ECCs gradually disappeared with the increase of the sub-elevated temperature exposure time at 200°C. The results of thermogravimetric-differential scanning calorimetry (TG-DSC), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscope (SEM) revealed that the degradation of PVA fibers was accelerated by exposure time in sub-elevated temperature, which caused the reduction of mechanical properties of PVA-ECCs. [ABSTRACT FROM AUTHOR]