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.

This paper investigates the penetration resistance of Ultra-High Toughness Cementitious Composites (UHTCC, also known as ECC) and Reactive Powder Concrete (RPC, commonly referred to as UHPC) when subjected to multi-point projectile impacts at varying projectile velocities. Firstly, basic mechanical performance tests were conducted on RPC and UHTCC. Subsequently, multi-point projectile impact tests were carried out on 500 mm-thick RPC and UHTCC targets using a 14.5 mm ballistic gun at different projectile velocities and impact locations. The test results show that RPC exhibits excellent resistance against projectile penetration, with resistance approximately 2.5 times that of UHTCC under identical conditions. However, UHTCC demonstrates superior performance in reducing the crater damage on the impact surface and in resisting cracking. Under the same penetration test conditions, the crater area of UHTCC is 50% smaller than that of RPC. After multi-point projectile impacts, the penetration resistance of UHTCC decreases significantly, whereas that of RPC remains unchanged regardless of the number of impacts or projectile velocity. Finally, based on the existing test data of UHTCC and RPC, the calibrated K&C dynamic constitutive model was employed, and the restart method was used to simulate the penetration process of multi-point projectile impacts on UHTCC and RPC targets. The simulation results predicted by the calibrated K&C model correspond well with the experimental results.

To research the behavior of square concrete columns subject to small eccentric loading reinforced with Grade 600MPa steel bars, and ascertain the compressive service strength of Grade 600MPa steel bar, a total of nine corbel HSRC columns were constructed and tested. Buckling behavior of Grade 600MPa steel bar subject to compression was considered. A novel stirrup configuration was conceived and employed in these columns. Test variables conducted in this investigation mainly include the stirrup ratio, longitudinal reinforcement ratio, stirrup strength and spacing. The behaviors of HSRC columns were analyzed and discussed under small eccentric compression, such as failure mode, load-deflection relationship, load versus strain of longitudinal bar relationship, load carry-capacity and the evolution of bending moment and curvature. To guarantee the satisfactory mechanical behavior of HSRC columns subjected to small eccentric loading and ensure that Grade 600MPa steel bar can develop its full plastic strength, stirrup spacing should not exceed 5D, where D refer to as a diameter of longitudinal reinforcing bar. Simultaneously, to further understand the behavior of HSRC columns subjected to small eccentric loading, a suitable Finite element model was established and verified by test results. Based on the test results and the numerical analysis, the compressive service strength of Grade 600MPa steel bar is recommended as 570MPa. Finally, to precisely predict the load carry-capacity, a practicable method was proposed by considering the confinement effect.

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.

Early-strength polymer-modified concrete (ES-PMC) has demonstrated considerable promise for rapid repair applications, where its performance is critical to ensuring the safety and quality of concrete structure construction. This study examines the mechanical properties and stress-strain behavior of ES-PMC at various curing ages (1.5 h, 2 h, 3 h, 1 day, 3 days, 7 days, and 28 days), with early-strength concrete (ESC) serving as the control group. The results indicate that ES-PMC generally surpasses ESC in terms of cube compressive strength, uniaxial compressive strength, and flexural strength, achieving values of 35.8 MPa, 25.4 MPa, and 4.4 MPa, respectively, at 2 h. Furthermore, a strong linear correlation is observed between the cube compressive and uniaxial compressive strengths of both ESC and ES-PMC. Under uniaxial loading, as the curing age increases, both materials undergo greater damage, with peak stress, elastic modulus, and toughness increasing over time, while peak strain, ultimate strain, and relative energy absorption capacity decrease. Additionally, a modified stressstrain model for ES-PMC was developed, incorporating age-related factors to accurately depict its stress-strain behavior across different ages. This model provides a theoretical basis for promoting its application in practical engineering and predicting its performance at various stages.

This paper presents the enhancement of concrete strength and carbon dioxide sequestration through the addition of bamboo biochar. The effects of biochar addition on the compressive and flexural strength of cement mortar were optimized using response surface methodology. Biochar incorporation reduced the density of cement mortar and enhanced its water absorption capacity. The model predicted maximum compressive (35.27 MPa) and flexural strength (8.78 MPa) at 2.15 % biochar addition and a w/c ratio of 0.47. Experimental validation of the optimum point showed good agreement with the model predictions. The addition of bamboo biochar increased carbon dioxide sequestration by up to 18 % compared to the control sample. The sequestered CO2 formed carbonates within the cement mortar, enhancing compressive and flexural strength by up to 24 % and 9 %, respectively. The carbon footprint of cement mortar was reduced by up to 5.7 % with bamboo biochar addition. Furthermore, biochar addition decreased mortar density by 3 % and increased water absorption capacity by about 15 %. This study highlights the potential of bamboo biochar as an active filler in concrete, providing both structural benefits and improved carbon dioxide sequestration for sustainable construction. This advancement demonstrates promise for developing cementitious materials that contribute to carbon sequestration in the built environment.

The construction industry faces growing pressure to adopt sustainable materials that enhance both structural performance and environmental benefits. This study investigates the potential of bamboo biochar as a sustainable filler to strengthen cement mortar while contributing to COQ sequestration. The primary objective is to evaluate the effects of bamboo biochar addition, alongside carbonation treatment, on the mechanical properties of cement mortar. The surface morphology of the biochar was characterized using scanning electron microscopy, while mortar mixes with varying water-to-cement (w/c) ratios (0.45-0.55) and biochar dosages (2 %-8 %) were prepared. Flowability, compressive, and flexural strength tests were conducted on samples cured for 7-56 days, with a control mix for comparison. Results revealed that a 6 % biochar addition with a w/c ratio of 0.45 yielded optimal performance, achieving compressive and flexural strengths of 46.98 MPa and 9.60 MPa, respectively. Carbonation further enhanced these strengths by up to 24 % and 9 %, while biochar incorporation increased COQ sequestration by 53 % compared to the control. These findings demonstrate that bamboo biochar not only improves mechanical strength through mechanisms such as internal curing, filler effect, nucleation, and improved interfacial bonding but also contributes to carbon capture. This dual benefit underscores its significance as a promising material for sustainable and resilient construction practices.

Ultra-high performance concrete (UHPC), a cementitious material without coarse aggregates, is widely used in protective engineering structures. In order to study the influence of steel fiber content(0 %, 1 %, 2 %, 3 %) on the dynamic tensile properties of UHPC, split tensile tests were conducted within the strain rate range of 1 x 10-5 s-1 to 1 x 10-2 s-1 and 5 s-1 to 20 s-1. Dynamic splitting tests at low strain rate(1 x 10-5 s-1-1 x 10-2 s-1) using an electro-hydraulic servo universal testing machine. At high strain rate (5 s-1-20 s-1) were conducted on 2 % steel fiber-reinforced UHPC using a split Hopkinson pressure bar (SHPB) system to establish the relationship between strain rate and tensile strength. During the whole dynamic testing, digital image correlation (DIC) technology was employed to analyze the failure process. Furthermore, based on dynamic splitting strength data of plain UHPC from existing studies, the strain-rate-dependent constitutive relationship for UHPC matrix was calibrated. Then, a mesoscale finite element model for UHPC reinforced with 2 % steel fiber under dynamic tension was developed and verified. Subsequently, the effect of fiber content as well as fiber inclination angle on the dynamic splitting tensile behavior at high strain rate (5 s-1-20 s-1) was analyzed with the proposed mesoscale numerical model. The results indicate that. The increase of fiber content will reduce the DIF of UHPC; Numerical simulations revealed that increasing steel fiber content enhances tensile strength but reduces the Dynamic Increase Factor (DIF) of UHPC. Fibers with 0 degrees-30 degrees inclination (nearly parallel to the loading direction) exhibit weaker bridging effects, resulting in reduced dynamic splitting strength, while fibers with 60 degrees-90 degrees inclination (perpendicular to the loading direction) significantly improve bridging stress, thereby enhancing dynamic splitting strength. The dynamic splitting strength of fibers with 30 degrees-60 degrees inclination aligns with that of randomly distributed fibers specimen.

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.

In order to investigate the effects of loading and high temperature on the uniaxial compressive properties of desert sand concrete （DSC）， the uniaxial compression experiment of DSC subjected to different loading and temperatures were carried out to obtain the stress-strain curves. The influences of loading level， temperature and cooling methods on the mass loss rate， ultrasonic velocity and axial compressive properties of DSC were analyzed. Experimental results showed that the mass loss rate of DSC gradually increased with the temperature. The uniaxial compressive strength and modulus of elasticity of DSC declined， peak strain increased greatly， and the stress-strain curve gradually became flat. The "pseudoplastic plateau" near uniaxial compressive strength of DSC stress-strain curve became more obvious. Taking into account of temperature and loading level， the stress-strain model was established to simulate the mechanical properties of DSC on the basis of two-stage constitutive model， which provided technical support for performance evaluation of DSC after high temperature.

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.

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

A method to link one- and two- dimensional diffusion coefficient models of sulfate ions in concrete is proposed. The method was established on the basis of one-dimensional as well as two- dimensional diffusion tests under different concrete strengths, different sulfate solution concentrations and different immersion periods. Based on the test results, a new one-dimensional diffusion coefficient model related to concrete strength, sulfate solution concentration and immersion period was established. Then, it was found that the two-dimensional sulfate diffusion was not simply the superimposition of two one-dimensional ones. The relationship of 1.33 times of the one-dimensional diffusion coefficient was obtained in the two-dimensional diffusion direction under multi-factor conditions. At last, based on the one-dimensional diffusion coefficient model and 1.33 times relation, a new two-dimensional diffusion coefficient model was proposed. Complying with the Fick's second law, based on the two-dimensional diffusion coefficient model established above, the sulfate ion concentration of each point under muti-factor conditions in two-dimensional diffusion direction can be obtained, which also verified the proposed diffusion coefficient model.

Concretes have been the favoured material to make concrete railway sleepers due to better accessibility and weather compared to their timber counterparts. Railway sleepers are crucial infrastructure and 5% of concrete sleepers fail prematurely. Sleeper failure could result in catastrophic railway accidents. Hence, improvement is needed in the concrete sleeper mixes. Previous literature has identified two methods of improving concrete strength in concrete mixes with wastes, through replacement of concrete constituents or the use of alkali-activated materials. Use of wastes as partial concrete material replacements reduces the volume of concrete materials while alkali-activated material forms a concrete-like compound that eliminates the use of cement. These methods improve the strength performance and sustainability aspects of the concrete. While many studies have been conducted on these two types of sustainable concrete, their application in concrete railway sleepers has not been investigated. Thus, this paper looks to review the two different types of sustainable concretes through some previous literature that has been conducted on its application in concrete railway sleepers as well as those that have yet to be studied. Ultimately, identifying the best sustainable materials for concrete railway sleepers.

The desulfurized electrolytic manganese residue (DMR) was prepared by calcination and desulfurization of industrial waste electrolytic manganese residue, and the original DMR was ground to prepare DMR fine powder (GDMR) with specific surface areas of 383 m2/kg, 428 m2/kg, and 629 m2/kg. The effects of particle fineness and content of GDMR (GDMR content=0%, 10%, 20%, 30%) on the physical properties of cement and the mechanical properties of mortar were studied. After that, the leachability of heavy metal ions was tested, and the hydration products of GDMR cement were analyzed using XRD and SEM. The results show that the addition of GDMR can regulate the fluidity and water requirement for the normal consistency of cement, delay the hydration process of cement, increase the initial setting and final setting time of cement, and reduce the strength of cement mortar, especially the strength of early age mortar. As the fineness of GDMR increases, the reduction of bending strength and compressive strength decreases, and the activity index increases. The content of GDMR has a significant effect on short-term strength. With the increase in GDMR content, the strength reduction degree becomes higher and the activity index decreases. When the content of GDMR was 30%, the 3D compressive strength and bending strength decreased by 33.1% and 29%. When the content of GDMR in cement is less than 20%, the maximum limit of leachable heavy metal content in cement clinker can be met.

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.

Desulfurized manganese residue (DMR) is an industrial solid residue produced by high-temperature and high-pressure desulfurization calcination of electrolytic manganese residue (EMR). DMR not only occupies land resources but also easily causes heavy metal pollution in soil, surface water, and groundwater. Therefore, it is necessary to treat the DMR safely and effectively so that it can be used as a resource. In this paper, Ordinary Portland cement (P.O 42.5) was used as a curing agent to treat DMR harmlessly. The effects of cement content and DMR particle size on flexural strength, compressive strength, and leaching toxicity of a cement-DMR solidified body were studied. The phase composition and microscopic morphology of the solidified body were analyzed by XRD, SEM, and EDS, and the mechanism of cement-DMR solidification was discussed. The results show that the flexural strength and compressive strength of a cement-DMR solidified body can be significantly improved by increasing the cement content to 80 mesh particle size. When the cement content is 30%, the DMR particle size has a great influence on the strength of the solidified body. When the DMR particle size is 4 mesh, the DMR particles will form stress concentration points in the solidified body and reduce its strength. In the DMR leaching solution, the leaching concentration of Mn is 2.8 mg/L, and the solidification rate of Mn in the cement-DMR solidified body with 10% cement content can reach 99.8%. The results of XRD, SEM, and EDS showed that quartz (SiO2) and gypsum dihydrate (CaSO4·2H2O) were the main phases in the raw slag. Quartz and gypsum dihydrate could form ettringite (AFt) in the alkaline environment provided by cement. Mn was finally solidified by MnO2, and Mn could be solidified in C-S-H gel by isomorphic replacement.

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.

分别采用毛乌素沙漠砂和腾格里沙漠砂为细集料制备高韧性水泥基复合材料（DS-ECC），在1%、1.5%、2%的预加拉伸应变破坏下，研究了3d、7d及28d龄期的DS-ECC试件在空气和干湿循环条件下裂缝特性、自愈合后拉伸性能及自愈合产物。研究结果表明：两种沙漠砂制备的DS-ECC试件均能发生自愈合现象，干湿循环条件下自愈合现象较空气条件更加明显；残余裂缝的的最大减少量均发生在3d龄期，毛乌素沙漠砂和腾格里沙漠砂制备的DS-ECC试件残余裂缝减少量分别为89.3%和80.9%；带裂缝的DS-ECC试件自愈合后极限拉应变大多高于未带裂缝试件的极限拉应变，但最终强度有所降低，相较于空气条件，干湿循环条件下的DS-ECC试件自愈合后极限拉应变较大，最终强度降低；DS-ECC自愈合及基体混合产物主要为SiO 2 、Ca（OH） 2 和CaCO 3 。综合考虑DS-ECC的自愈合效果及自愈合后拉伸性能，毛乌素沙漠砂制备的DS-ECC试件自愈合性能较优。