To investigate the durability and damage evolution of desert sand concrete (DSC) under sulfate freeze–thaw (F–T) cycles, uniaxial compression and acoustic emission (AE) monitoring tests were conducted after F–T exposure. The effects of Na2SO4 solution mass fraction (3%, 5%, and 7%), number of F–T cycles (0, 25, 50, 75, 100, and 125), and desert sand replacement ratio (DSRR; 0%, 20%, 40%, and 60%) on the mechanical properties and AE characteristics of DSC were examined. Microstructural characterization was performed using scanning electron microscopy (SEM) for morphological analysis, nuclear magnetic resonance (NMR) for pore structure quantification, and X-ray diffraction (XRD) for phase composition analysis. The experimental results indicated that the peak stress, relative elastic modulus, dynamic elastic modulus, and peak ring count decreased monotonically with increasing F–T cycles, while they initially increased and subsequently decreased with increasing DSRR. The damage to DSC exposed to a 7% Na2SO4 solution was more severe than that observed under 3% and 5% solutions. The proportion of shear cracks increased significantly with increasing F–T cycles and Na2SO4 solution concentration. Sulfate-induced F–T action reduced the oscillation amplitude of the Ib-value curve. In addition, the damage model based on cumulative ring counts demonstrated excellent predictive accuracy. The findings provide important guidance for the engineering application of DSC in sulfate F–T environments.

Desert sand concrete (DSC) cube and beam (DSCB) specimens were prepared to investigate the influence of desert sand from Ningxia, China, on the flexural behavior of concrete beams. Specimens were produced with different desert sand replacement ratios (DSRRs), and the cubic compressive strength (CCS) of DSC cubes were measured. Digital image correlation (DIC) was applied during four-point bending tests to characterize full-field strain distributions and to track crack initiation and propagation. The results indicate that CCS peaked at a DSRR of 25%. This value represented a 6% increase relative to natural sand concrete (NSC). The ultimate flexural capacity of DSCBs reached its maximum at this DSRR. This corresponded to a 2.5% increase relative to a natural sand concrete beam (NSCB). The cracks in DSCBs developed more significantly. Failure mode of DSCBs transformed from ductile to brittle at a DSRR of 50%. The current Chinese code can provide a reference for the engineering design of DSCBs, and appropriate modifications considering the DSRR are recommended for different stress stages. These findings provide a theoretical basis and technical support for the practical application of DSC.

This study addresses the issues associated with traditional silt-based subgrade materials, such as performance degradation under high-temperature conditions, susceptibility to damage, and lack of self-healing capacity, by proposing a method for composite stabilization of silt using asphalt powder and cement. Through laboratory tests, the study focused on examining the effects of asphalt powder content and curing age on the material’s unconfined compressive strength and high-temperature self-healing performance, and systematically evaluated its thermal damage repair capacity under conditions of 55 °C. The results indicate that the strength of the composite-stabilized silt increases with curing age and asphalt powder content. The optimal performance was achieved with a mixture of 4% asphalt powder and 6% cement, yielding a strength of 1.80 MPa at 14 days—approximately 85% of the 28-day strength. Beyond 4% asphalt powder content, the increase in strength slowed.At a high temperature of 55°C, the thermoplastic properties of the asphalt powder are activated, and the material exhibits significant self-healing characteristics, enabling effective repair of microcracks and restoration of mechanical properties. The best overall high-temperature performance was achieved with a 4% asphalt powder content. The results indicate that asphalt powder-cement composite stabilized soil retains good performance recovery capabilities at 55 °C—a temperature well-below the road surface critical temperature (60 °C) and above the permitted traffic temperature (50 °C). This makes it suitable for subgrade engineering in high-temperature regions and provides important evidence for the design and optimization of soil subgrade materials.

Particle morphology is a critical parameter influencing the liquefaction resistance of coral sand. To elucidate the mechanism by which particle morphology affects the liquefaction resistance of coral sand, this study employed a dynamic image scanning technique to quantitatively analyze particle morphology. Undrained cyclic shear tests were conducted on coral sand (CS) specimens with different proportions of three particle shapes, as well as on natural quartz sand (QS), and glass ball (GB) specimens, to examine the effect of overall regularity (OR) on the liquefaction resistance of these materials. The results indicated that, under undrained conditions, CS specimens with varying OR values all reached full liquefaction and generally exhibited tensile deformation failure. With the increase in OR value, the growth rates of the double amplitude axial strain (epsilon DA) and peak transient excess pore water pressure (EPWP) displayed a 'V'-shaped development trend, whereas the liquefaction resistance followed an inverted 'V'-shaped development trend. The OR value at the turning point was found to be closely associated with the failure mode of the specimens. For CS geotechnical materials, the axial strain threshold is recommended as the liquefaction discrimination criterion. The critical curve for liquefaction discrimination of CS specimens was strongly correlated with particle morphology. Additionally, the liquefaction discrimination critical curve proposed by Seed for QS should be modified appropriately when applied to CS foundations.

To enhance the application effect of engineered cementitious composites in rapid repair engineering, this study prepared early strength and fast hardening sulfoaluminate cement-engineered cementitious composites (S-ECC) with sulfoaluminate cement as the matrix, fly ash, silica fume, and desulfurization gypsum as supplementary cementitious materials (SCMs), and added polyvinyl alcohol (PVA) fiber. The effects of fly ash, silica fume, and desulfurization gypsum on the performance, fiber dispersion, mechanical properties of drying shrinkage, and microscopic mechanism of S-ECC were systematically studied. The results indicate that the fiber dispersion in silica fume-S-ECC (SF-S-ECC) improves as the fly ash content increases. When the fly ash content reaches 30%, the ultimate tensile strength of SF-S-ECC at each age is the highest. The SF-S-ECC with 40% fly ash exhibited the lowest drying shrinkage of 9.3x10-5 at 28 days. The addition of silica fume enhanced the fluidity of fly ash-S-ECC (FA-S-ECC), and the ultimate tensile strength of the FA-S-ECC sample containing 5% silica fume reached 6.17 MPa after 60 days of curing. The addition of 5% and 10% desulfurization gypsum in FA-SF-S-ECC resulted in excellent tensile properties. The most important thing is to avoid reduction of the strength of the repair material in later stages. Fly ash, silica fume, and desulfurization gypsum can make up for the slow development of S-ECC strength, allowing the S-ECC of the three systems (SF-S-ECC, FA-S-ECC, FA-SF-S-ECC) to hydrate rapidly in the early stage, produce a lot of AFt and hydration product, and enhance the strength of materials. Cracks, pores, and other defects in the hardened slurry can hinder later-stage strength development.

This research focuses on creating an alternative material to Coral Gravel Limestone (CGL) for model experiments, aiming to reduce damages to marine ecosystems. High-strength, fast-setting gypsum serves as the structural framework, while low-strength clay ceramsite is utilized as a lightweight filler. The strength contrast between these components is employed to replicate the large-diameter pores characteristic of CGL. To enhance the material's adjustability, a sensitivity analysis was performed on four key factors: gypsum water-to-binder ratio, binder-to-aggregate ratio, aggregate particle size, and foaming agent content. An orthogonal experimental design guided this analysis, resulting in regression equations to predict material properties. The optimized mix ratio ( Mclay ceramsite: Mgypsum: Mwater: Mfoaming agent) was determined as 7:42:12:0.12, with a 2 mm ceramsites particle size. This composition successfully emulates the physical and mechanical properties of CGL sourced from a reef in the South China Sea, yielding dry UCS and porosity deviations of 2.6 % and 7.2 %, respectively. Furthermore, CT scans confirmed that the microporous structures of both materials are comparable, establishing a robust foundation for reef engineering model studies.

This study explores an innovative application of ultra-high-performance concrete (UHPC) by partially substituting cement with nano-zirconia (NZ) and micro-zirconia (MZ). A series of experiments were conducted to explore the influence of zirconia particle size (3860 nm and 320 nm) and varying replacement levels (0%, 0.5%, 1%, and 1.5%) on the workability, mechanical behavior, and microstructural characteristics of UHPC, utilizing the particle packing density model as a basis. Findings reveal that replacing 0.5% of the cement with MZ and NZ results in workability and mechanical performance comparable to the control mix. However, at 1.5 wt% MZ and 1.5 wt% NZ substitution levels, flowability declines by 22.01% and 24.71%, respectively, accompanied by a substantial increase in viscosity. The wet packing density of UHPC exhibits a linear rise with increasing zirconia content, with nano-sized particles exerting a more pronounced effect than their micro-sized counterparts. Specifically, at a 0.5% MZ replacement level, the 28-day compressive and flexural strengths show marginal improvements of 1.82% and 4.48%, respectively. The NZ1MZ0.5 mix achieves the highest 28-day compressive strength increase, reaching 9.45%, with an absolute gain of 11.92 MPa. Analyses using XRD, FTIR, and thermogravimetric analysis (TGA) demonstrate that zirconia incorporation has a negligible influence on the hydration process and does not alter the composition of hydration products in N-UHPC. Although zirconia effectively reduces porosity, excessive amounts (1.5%) increase pore size within the cement matrix, ultimately compromising mechanical properties. Based on these findings, the optimal NZ dosage for UHPC, when used in combination with MZ, is determined to be 0.5%.

To evaluate the potential application of desert sand concrete (DSC) in the construction industry, the evolution of its properties in the conjoint impact of sulfate corrosion and dry-wet (D-W) cycles was investigated. In this study, a range of variables were taken into account, including desert sand replacement rate (DSRR, 0,40,60%), D-W cycles (0, 30, 60, 90, 120 and 150 cycles) and mass fraction of sodium sulfate solution (3, 5 and 7%). The performance deterioration of DSC such as ultrasonic parameters, dynamic elastic modulus and damage parameters were analyzed under sulfate environment. Uniaxial compression tests ascertained the peak stress, peak strain and the compressive stress-strain curve of DSC under a range of sulfate D-W cycles. Microscopic testing techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XRD) were utilized to examine the microstructure morphology and phase composition of DSC. The experimental findings demonstrated that the ability of DSC to resist corrosion characteristics could be effectively improved under sulfate attack and D-W cycles when desert sand was added at 40%. The peak stress of DSC was improved first and then diminished with the progression of D-W cycles, attaining the maximum value at 60 D-W cycles, while peak strain gradually decreased and then increased. SEM and XRD test results revealed that sulfate crystals and continuing formation of expansive materials like gypsum (CaSO4.2 H2O) and ettringite (AFt) were the principal elements causing the degradation of DSC as the D-W cycles increased.

Rapid freeze-thaw (F-T) tests were conducted to study the frost resistance of desert sand concrete (DSC) at different stress levels (SL), desert sand replacement rate (DSRR) and the number of F-T cycles. The impact of the SL, DSRR, and number of F-T cycles on the mass loss rate, ultrasonic wave velocity, and stress-strain curve of DSC was investigated through uniaxial compression tests. Scanning electron microscope (SEM) was used to examine the microstructure of DSC. The constitutive relationship was established considering the influence of the SL and number of F-T cycles. The results indicated that the frost resistance and uniaxial compressive mechanical properties of DSC could be effectively enhanced when desert sand was added at 40%. The peak strain initially decreased and then increased as the DSRR increased. In contrast, the peak stress first increased and reached a maximum value as the DSRR increasing to 40%, followed by a gradual decrease. The F-T cycles gradually deteriorated the macroscopic properties of DSC. The proposed constitutive model of DSC was established by combining the two classical models as the ascending and descending sections, respectively. The model prediction results matched well with the experimental results, which can provide a theoretical basis for the engineering application of DSC under F-T cycles and loading environments.

Particle morphology is an important physical parameter that influences the engineering properties of coral sand, especially its compressibility. According to the quantitative analysis of particle morphology via the dynamic image analysis technology, a series of one-dimensional compression tests on coral sand and quartz sand with different particle morphology and densities were performed to reveal the effect of particle morphology on the compressibility of coral sand. The results demonstrated that the morphology of particles can be quantified using the shape-angularity group indicator (SAGI), whereas the SAGI of coral sand was greater than that of quartz sand. Coral sand exhibited a yield stress ranging from 1 to 2.5 MPa, and compressive deformations in both coral sand and quartz sand were dominated by irreversible plastic deformation. As the SAGI and densification increased, the number of particle coordination increased while the contact stress between grains decreased, which caused the yield stress of coral sand specimens to increase as well as the compression index and particle crushing rate to decrease. The SAGI of quartz sand particles remained relatively unchanged while that of coral sand particles gradually decreased after crushing, i.e., the coral sand particles developed a more regular shape after crushing.

This study investigates the performance of concrete containing desert sand (desert sand concrete and desert sand self-compacting concrete) as overlay concrete to bond with normal-strength concrete substrate, with different bonding interfaces being considered. The impermeability of the bonding interface is determined by the electrical resistance test. Static bonding strength is tested by conventional mechanical tests. The dynamic properties of bonded specimens are also studied by dynamic response tests. Non-linear parameters, low-frequency energy parameters and ultrasonic velocity are included in the bonding interface ultrasound detection. The microstructural and chemical compositional of the overlay transition zone (OTZ) are analysed to reveal the mechanisms of bonding behaviour. The results indicate that the interface electrical resistance is positively related to bonding strength. Using concrete containing desert sand as the overlay concrete improves bonding interface adhesion for 30% at most. Bonding performance can be affected by the interface pattern and volume density in both static and dynamic conditions. The bonding strength and damping ratio with properly treated interfaces can be increased by over 300% and 38% than those of untreated groups, respectively. The dynamic response of the bonded specimens can effectively reflect the bonding performance. The non-linear ultrasound method and the ultrasound energy method are more accurate and sensitive than traditional way (ultrasonic velocities) in detecting the bonding interface. The incorporation of desert sand in the concrete or lowering W/B considerably contributes to a series of benefits to the microstructure of the bonding interface. The bonding gap width is reduced by 17% and 72% for DS incorporation and lower W/B, respectively. Characterized by Ca/Si, the OTZ width is reduced by 10% and 31% for DS incorporation and lower W/B, respectively. Characterized by micro-hardness, the OTZ width is reduced by 21% and 24% for DS incorporation and lower W/B, respectively, which provides an important reference for the engineering application of desert sand self-compacting concrete.

The significance of creep performance in Mg alloys is underscored by their widespread use as thermally conductive structural components in industries. This work investigated the influence of microstructure characteristics on the creep properties of dilute Mg-Mn-Zn alloys under varied processing conditions. The specimen designations were: AH (as-homogenized), AE (as-extruded), and AC (as-hot compressed). The creep resistance was as follows: AH > AE > AC, although AC exhibited the best mechanical properties. AH primarily exhibited cross-slip and twinning. AE displayed cross-slip and twinning for coarse non-dynamically recrystallized (non-DRXed) grains, and basal slip and pyramidal slip for fine DRXed grains. AC had basal slip and pyramidal slip. The highest creep resistance for AH resulted from the stable solid solution strengthening and the interplay between twinning and cross-slip. In contrast, AC, with the lowest creep resistance, experienced an accelerated creep strain due to precipitate coarsening and frequent grain boundary sliding. A combination of pipe diffusion-controlled and grain boundary diffusion-controlled slip contributed 57% to the steady creep rate. This work provides a considerable insight for the application of Mg alloys as thermally conductive structural components.

A method for strengthening was proposed to improve the seismic behavior of corroded reinforced concrete (RC) columns by using engineered cementitious composite (ECC) combined with a steel cage/fiber grid/carbon fibre reinforced plastics(CFRP). The corroded RC columns strengthened with ECC combined with a steel cage, fiber grid, and CFRP were subjected to low cyclic compression tests at design axial pressure ratios (n) of 0.3 and compared with corroded and uncorroded columns. Experimental results showed that ECC strengthening of corroded RC columns not only significantly improved their load-carrying capacity, displacement ductility, and energy dissipation capacity but also effectively reduced the degree of damage and stiffness degradation. The ductility coefficients of ECC/steel cage composite strengthened columns and ECC/CFRP composite strengthened columns are 35.58 % and 34.13 % higher, respectively, compared to ECC fully strengthened columns, while the ductility coefficient of ECC/fiber grid composite strengthened columns decreased by 4.33 % compared to ECC fully strengthened columns. Among them, the ECC/steel cage composite-strengthened columns exhibited the highest number of hysteresis loops, the strongest energy dissipation capacity, and the best strengthening effect. Additionally, a restoring force model for ECC-strengthened corroded RC columns was established, and its validity was verified through theoretical calculations.

Engineered Cementitious Composites are a type of advanced building materials, which have excellent ductility and can significantly enhance structural resistance. However, the expensive material cost of ECC limits its engineering applications. This study investigated the potential of replacing commonly used silica (river) sand and imported PVA fibers with the local desert sand and PVA fibers, aiming at reducing the preparation cost of ECC and improving its economic benefits and sustainability. The mixture proportion was first optimized to obtain favorable strength and ductile enhancement, using a combination of single-factor test and theoretical calculation which mentioned the slurry coating thickness of fibers and desert sand. The potential of desert sand in preparing ECC was experimentally evaluated by comparing the uniaxial tension (compression) properties and microstructures of desert sand-based ECC (DS-ECC) and those of ordinary ECC. The results indicate that optimized DS-ECC can achieve satisfactory performance even when 100

Vibro-compaction is the main improvement method for hydraulic reclamation coral sand sites. Currently, the load-bearing characteristics of coral sand composite foundation reinforced by vibro-compaction have not been clarified. This paper investigates strength characteristics of coral sand composite samples (core and shell) by artificially preparing radial variable-density coral sand composite samples and performing consolidated drained triaxial tests under different area replacement rates, core-shell density ratios, and confining pressures. The results of the study show that the contribution of the core gradually increases with the increasing area replacement rate. The peak strength and peak friction angle of samples also increase gradually, but the growth tendency gradually slows down. The stress concentration coefficient of sample core is variable and follows a development pattern of first increasing and then decreasing. The secant Young's modulus of composite samples increases in a power function type with the increase of area replacement rate. The particle breakage of samples is mainly the rupture and abrasion of the 0.5-1 mm and 0.1-0.25 mm particle groups that serve as fillers. The research results can provide technical support for coral reef engineering construction.

Economical desert sand engineered cementitious composites (DS-ECCs) using a mixture of cement, fly ash, local desert sand, water, low-cost PVA fibers, and chemical additives were developed, aiming for a further enhancement in ductility and toughness. The mechanical behavior of DS-ECCs for two sand samples (from Mu Us and Tengger deserts, China) was determined using uniaxial tension/compression tests and three-/four-point bending tests. The results showed that desert sand-based ECCs with the designed mix ratios had better mechanical properties than the river sand-based ones. Compared with the river sand-based ECCs at 28 and 56 day, the DS-ECCs presented superior ultimate tensile and comparable compression strengths. The excellent ductility was characterized by ultimate tensile and compression strains of 3–7% and over 1%, respectively. Meanwhile, the DS-ECCs showed improved flexural properties with outstanding fracture and bending strengths (4–9 kN and 21–30 kN) and toughness. The findings of this study will further strengthen the mechanical performance of DS-ECCs and broaden their engineering applicability.

The strengthening effect of Engineered Cementitious Composites (ECC) on brick masonry walls is studied in this paper. Seven testing specimens including three unstrengthened and four ECC-strengthened brick masonry walls were constructed and subjected to quasi-static loading tests. The effects of aspect ratios (1, 1.5 and 2) and strengthening methods (ECC overall and frame strip strengthening) on the failure mode, failure mechanism, hysteresis characteristics and deformability capacity of brick masonry walls were studied. Research shows that the increase of the aspect ratio reduces the performance of the wall in all aspects. The ECC splint can restrain its inner brick wall dramatically, and the strengthened masonry wall convert the brittle failure mode into rocking failure or sliding failure. The ECC splint strengthening technology can effectively improve the seismic performance of the brick masonry walls. Finally, based on the strengthening effect of ECC splint, a formula for the shear capacity of brick masonry walls strengthened with ECC splint is proposed, which provides experimental and theoretical basis for seismic strengthening of masonry structures.

采用不同替代率沙漠砂制备沙漠砂混凝土,研究其高温后经二次养护抗压性能.通过高温后沙漠砂混凝土抗压强度试验,分析试件质量损失变化及温度、沙漠砂替代率对抗压强度影响;通过二次养护后抗压强度及SEM试验,分析二次养护龄期和方式对沙漠砂混凝土抗压强度和微观结构影响.试验结果表明:随温度升高,沙漠砂混凝土质量损失率逐渐增大,抗压强度逐渐减小;随沙漠砂替代率增加,抗压强度呈先增大后减小趋势;高温后沙漠砂混凝土内部孔洞、微裂缝数量增多,微观结构劣化严重.高温后沙漠砂混凝土经过二次养护,随养护龄期增加,抗压强度恢复率呈先增大,到达峰值后呈下降或持平趋势.

To study the influence of freeze-thaw cycles on the mechanical properties of concrete, compression strength experiments of concrete mixed with desert sand and fly ash（DSC） after freezing and thawing cycles at different low temperatures（-20 ℃,-30 ℃ and-40 ℃） were carried out. The influence of desert sand replacement rate（DSRR）, temperature and number of freezethaw cycles on DSC compressive strength and ultrasonic velocity was analyzed. The regression models between DSC compressive strength, ultrasonic velocity and temperature, DSRR and number of freeze-thaw cycles were established. The results show that as the number of freeze-thaw cycles increases, the DSC compressive strength and ultrasonic velocity decrease. When the temperature decreases, the DSC compressive strength and ultrasonic velocity decrease. With the increase in DSRR, DSC compressive strength firstly increase and then decrease. When the DSRR is 40%, its compressive strength reaches the maximum.