River Sand Research Articles

Effect of ICCP on tensile performance of carbon fiber bundles in seawater sea-sand cementitious matrix

Impressed current cathodic protection (ICCP), carbon fabric reinforced cementitious matrix (CFRCM) composites, and piezoresistive effect have been widely studied in delaying steel bar corrosion, strengthening steel-reinforced concrete structures, and structural health monitoring, respectively. In this study, the effect mechanism of the ICCP procedure on the tensile performance degradation of CFRCM bundles with the two types of matrix (normal matrix (i.e., sand conforming to ISO standard) and seawater sea-sand matrix), as well as the tensile performance differences between them, were investigated through carbon fiber bundle tensile tests and CFRCM bundle tensile tests. The piezoresistive effects of CFRCM with the two types of matrix after the ICCP procedure and the effect of ICCP on the piezoresistive effect were analyzed. Prediction formulas for the tensile performance were established based on the different charge densities. Based on the dual functionality of carbon fiber strengthening and self-sensing, this study lays a foundation for the development of a triple-functional system of impressed current cathodic protection, structural strengthening, and structural health monitoring (ICCP-SS-SHM). The study indicates that seawater sea-sand positively influences the delay of CFRCM degradation through ICCP. This is advantageous in tackling the issue of scarce freshwater river sand resources.

Comparison of the Use of Excavated Soil Recycled Fine Aggregate as a Substitute for River Sand in Mortar Mixing

This study comparatively investigated the performance of mortar prepared using excavated soil recycled fine aggregate (ESRFA), which mainly included fine aggregate obtained by sediment separation equipment and sieving. Scanning electron microscopy (SEM) was used to analyse the size and shape of ESRFA particles. The particle size distribution of ESRFA was uneven and its sphericality was lower than that of river sand. Two series of rendering mortar mixes were prepared using identical water/cement and aggregate/cement ratios of 0.55 and 3, respectively, using river sand as fine aggregate. ESRFA was used to replace 30%, 50%, 70%, and 100% of the river sand in each mixture. The experimental results showed that the flowability of the mortar prepared with ESRFA was lower than that of the aggregate-based mortar, but the porosity, water absorption, and mechanical properties (compressive strength, flexural strength, and drying shrinkage) increased and then decreased upon increasing the ESRFA content. In conclusion, ESRFA shows potential as a partial replacement for river sand in mortar, particularly at lower substitution rates. Further research is needed to optimize the processing and application of ESRFA in concrete to enhance its performance and sustainability.

Durability and microstructural characteristics of self-compacting concrete incorporating M-sand

ABSTRACT Self-Compacting Concrete (SCC) is characterized by increased fluidity and enhanced cohesion, leading to its growing prominence within the construction sector. Additive materials such as alccofine and silica fume can enhance the properties of SCC while concurrently mitigating the ecological footprint linked to cement manufacturing. Manufactured sand, also known as M-sand, is finely crushed aggregate sourced from rocks or quarry stones, providing a sustainable substitute for natural river sand in construction. The primary emphasis of this study revolves around evaluating the enduring compressive strength and durability attributes of SCC, wherein M-sand is employed to replace river sand to varying percentages of 0%, 25%, 50%, 75%, and 100%. Durability assessments encompass evaluations at 28, 56, 90, 180, and 365 days for water absorption, Rapid Chloride Penetration Test (RCPT), sorptivity, and Volume of Permeable Voids (VPV), all compared against the benchmarks of control concrete. Microstructural characterization studies entail the utilization of techniques such as Scanning Electron Microscope imagery (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). From the results it is observed that M-sand replacement in SCC enhanced durability of the concrete.

Axial compressive behavior of low-alkalinity seawater sea-sand concrete column reinforced with hydrophobic longitudinal SFCBs and FRP hoops

To address corrosion problem of steel bars and shortage of freshwater and river sand in marine and offshore structures, a novel hydrophobic-modified longitudinal steel-FRP composite bars (SFCB) and FRP hoops reinforced low-alkalinity seawater sea-sand concrete (SWSSC) is developed. However, axial compressive behavior of hybrid SFCB and FRP reinforced columns is not clear and the applicability of existing design methods is low. Here, nine hybrid reinforced columns have been designed and tested. Typical failure modes of columns and axial compressive behavior of constituent materials (i.e., hydrophobic reinforcements and low-alkalinity SWSSC) are investigated. It is found that the synergistic confining effect formed by hybrid reinforcement are significant. The mesh confinement formed by densely distributed FRP hoops and longitudinal SFCBs improves the local buckling behavior, and effectively constrains the lateral expansion of concrete core, resulting in improved compressive strength and ductility of column. The compressive contribution of single longitudinal SFCB to ultimate load capacity of column can be enhanced effectively, up to 36.3 %, by increasing steel content of SFCB. Based on this, a prediction model of hybrid reinforced columns is proposed, which can accurately evaluate the ultimate load capacity. This work provides valuable experimental observations and load capacity model for hybrid reinforced column, which promote its design and application in marine engineering.

Porosity and hydraulic conductivity of gap graded natural sand considering shape parameters

Gap graded natural sand is widely used in hydraulic structures, foundation treatment and recharge well fillers, and it’s also common in geological structures such as landslide deposits. In order to study the influence of grain shape on its pore and permeability characteristics, river sand in Yichang (YS), standard sand in Henan (HS) and standard smooth glass beads (BZ) are selected as test materials, and the grain shape parameters of three materials are analyzed on multiple scales. Then tests on porosity and hydraulic conductivity of gap graded natural sand were conducted. On this basis, a numerical model considering grain size distribution, coarse grain content and grain shape was established. The results showed that the average values of the shape parameters increased or decreased with the increase of grain size, and the coefficients of variation for the parameters were between 0.026 and 0.208. The shape parameters showed a negative skewness distribution, but the absolute value of the skewness coefficient was small (0.254–0.616). Grain size distribution and grain shape are the main factors controlling the porosity and hydraulic conductivity of gap graded natural sand. The minimum values of porosity and hydraulic conductivity appear at about 70 % and 30 % of large grains, respectively. The closer the grains are to the sphere, the closer the material is stacked, and the smaller the porosity value is. The grain size ratio has a significant effect on the minimum porosity of the mixture and the minimum porosity increases with the increase of the grain size ratio. The porosity of gap graded natural sand obtained by numerical method is accurate, and the error is within 10 %. The hydraulic conductivity is obtained by deriving fluid grid information and the results show that the simulated value of hydraulic conductivity is highly matched with the experimental value, and the error range is roughly between 10 % and 30 %.

Sustainable use of waste glass sand and waste glass powder in alkali-activated slag foam concretes: Physico-mechanical, thermal insulation and durability characteristics

In many countries, the safe removal of the massive volume of waste glass has emerged as a major environmental priority. However, the manufacture of concrete pollutes the environment with greenhouse gasses and consumes vast amounts of natural resources. As a result, the construction industry has recently been paying more and more attention to reusing glass waste to produce environmentally friendly building materials. This work aims to manufacture environmentally friendly alkali-activated foam concrete (AAFC) by examining the combined effects of waste glass powder (GP) and waste glass sand (GS) as partial substitutes for granulated blast-furnace slag (GBFS) and river sand (RS) respectively. The present study involved the experimentation of AAFC mixtures with GP contents of 0 and 10 % as a replacement for GBFS and GS contents of 0, 25, 50 and 100 % as a replacement for RS. Eight AAFC mixtures with fixed alkaline solution-to-binder (A/B) ratio of 0.5 were fabricated and cured at 80 °C for 24 h. The effects of different GS and GP contents on the oven dry density, flowability, water absorption, porosity, sorptivity, thermal conductivity, compressive strength, flexural strength, high temperature resistance and hydrochloric acid (HCI) resistance of AAFC mixtures were evaluated. Microstructure of the mixtures was analyzed by SEM and EDS. The findings indicated that the AAFC mixture with 50 % GS exhibited the best mechanical properties with a compressive strength of 3.48 MPa, representing a 71.4 % increase over the reference mixture. The mixture with 50 %GS also exhibited the lowest sorptivity regardless of GP content. Thermal conductivity enhanced by 4.6 and 7.0 % by replacing RS with 50 % GS at 0 and 10 % GP content. Replacing RS with GS and GBFS with GP increased the high temperature and acid resistance of the AAFC mixtures and the best high temperature and acid resistance were obtained for the mixtures containing 100 %GS and 10 %GP.

Experimental analysis of frost resistance and failure models in engineered cementitious composites with the integration of Yellow River sand

Abstract This study investigates the potential use of Yellow River sand (YRS) sourced from the lower reaches of the Yellow River in China as a sustainable and cost-effective substitute for quartz sand in engineered cementitious composites (ECCs). This region accumulates around 400 million tons of sand annually. The study evaluates the impact of different YRS replacement percentages (0, 25, 50, 75, and 100%) on mechanical and microstructure properties under freeze-thaw conditions, focusing on assessing the ECC durability during cooling cycles. The results show that YRS exhibits a smaller normal distribution of particle sizes compared to that of quartz sand and a 5.77 times greater specific surface area, affecting the ECC particle size distribution. After 300 cooling cycles, the R25 group maintains 97.5% of the initial mass and 79.4% of flexural strength, indicating superior durability. The R25 group also demonstrates a minimal decrease of 11.5% in equivalent bending strength, reaching a level of 104.4% compared to R0. The R25 group’s porosity is 30.80%, with an average pore size of 20.47 mm, showing 1.3% and 6.7% decreases compared to the R0 group. Additionally, this study establishes a failure progression equation using the Weibull probability distribution model, with calculated values closely aligning with measured values. Overall, this study recommends using YRS as a sustainable ECC material.

Microstructure, XRD, and strength performance of ultra-high-performance lightweight concrete containing artificial lightweight fine aggregate and silica fume

Ultra-high-performance lightweight concrete (UHPLC), a sustainable and environmentally friendly concrete crafted with artificial lightweight aggregates to preserve non-renewable natural resources like river sand, has garnered significant attention due to its exceptional mechanical properties. This study explores the use of artificial lightweight fine aggregate (ALWFA) as a substitute for fine aggregate in UHPLC production, investigating both fresh properties and mechanical performance. Microstructure analysis, utilizing SEM, and crystalline phase evaluation, employing XRD, were also conducted. The study results indicated that due to the irregular shape of ALWA particles with sharp edges, increasing the content of ALWFA led to a reduction in the flowability of UHPLC. Additionally, it was found that increasing the amount of ALWFA as a replacement for fine aggregate negatively affected both the compressive and tensile strength of UHPLC. This reduction in strength can be attributed to the higher porosity and lower intrinsic strength of ALWFA particles, as well as the weaker cohesion between ALWFA particles and the matrix. SEM analysis revealed that elevating the ALWFA content as a replacement for fine aggregate resulted in an increase in both the number and dimensions of voids, which is responsible for the weaker performance of ALWFA concrete. Finally, XRD analysis showed no significant alteration in the crystalline phases as the ALWFA content increased.

Microstructure, mechanical properties and interaction mechanism of seawater sea-sand engineered cementitious composite (SS-ECC) with Glass Fiber Reinforced Polymer (GFRP) bar

With increasing demand for sustainable and long-lasting materials, seawater sea-sand engineered cementitious composite (SS-ECC) has emerged as a promising alternative to conventional concrete in near-ocean construction projects. Glass fiber reinforced polymer (GFRP) bar with excellent corrosion resistance is an ideal choice for these applications. This study evaluated the bond performance of GFRP bars embedded in normal-strength ECC with polyvinyl alcohol (PVA) fibers and high-strength ECC with polyethylene (PE) fibers through pull-out tests. Additionally, tests were conducted on GFRP bars in pristine ECC made with freshwater and river sand for comparison. Further investigation explored the structural properties and uncovered load transfer mechanisms. Results indicated that saline content facilitated early cement hydration of normal-strength ECC, resulting in finer pore structure (10.5% lower porosity and 12.5% lower sorptivity), slightly enhanced compressive performance (1.2% higher compressive strength and 8.3% higher elastic modulus), denser microstructure at GFRP-ECC interface (13.7% lower porous transition zone thickness, 19.2% narrower transition zone and 19.7% higher Ca/Si ratio), and superior bond performance (28.3% higher bond strength and 22.6% higher fracture energy). Conversely, saline content imposed a limited impact on the mechanical properties of high-strength ECC, primarily attributed to the ultra-fine microstructure and early strength characteristics exhibited by the silica fume (SF)-based cementitious binder.

Numerical and experimental study of Yellow River sand in engineered cementitious composite

Engineered cementitious composites (ECCs) represent a significant advancement in concrete technology, addressing the issues and limitations of conventional concrete and environmental challenges related to sedimentation in rivers such as the Yellow River in China. This study investigates the integration of Yellow River sand (YRS) into ECC mix designs for sustainable development. YRS replacement rates (0, 25, 50, 75 and 100%) with quartz sand are systematically analysed through flexural, compressive, uniaxial tensile and four-point bending tests. In addition, scanning electron microscopy and mercury intrusion porosimetry tests are conducted to investigate the micro-mechanical properties. The results reveal that the optimal mechanical performance with 100% YRS substitution improves the compressive and flexural strengths to 26.4 and 11.5 MPa, respectively. These values are 6.20% lower than the those of the 0% substitution rate. Notably, a 100% replacement maintains an ultimate tensile strain of 3.71%, improving the crack width and spacing compared with those at 0%. The average crack width and spacing decrease by 4.87 and 11.2%, respectively, compared with those of 0% substitution. The four-point bending test results show the highest ductility at a 75% substitution rate. Furthermore, a finite-element method model of ECC beams with YRS is developed and validated under the same loading conditions as the experimental data. This study recommends an analytical method for predicting flexural strength compared with the experimental data, enhancing its suitability for sustainable engineering applications.

3D printing of cementitious composites with seashell particles: Mechanical and microstructural analysis

Seashells are abundantly available as waste products from the seafood industry and from coastal areas. Accordingly, processed shells can be used to partially replace aggregates in traditional concrete. This paper investigates the effects of different proportions of seashell particles on the mechanical and microstructural properties of 3D-printed cementitious composites. The seashells were crushed and milled to be transformed into seashell particles, replacing the river sand at 15 wt% and 30 wt%. It was found that when the seashell particle content increased to 15 wt% and 30 wt%, the mechanical strengths all decreased significantly, which could be attributed to the increasing volumetric proportion of voids and the lower elastic modulus of seashell particles compared to river sand. However, when the seashell particle proportion further rose from 15 wt% to 30 wt%, the mechanical strengths did not continue decreasing substantially. Instead, the compressive and indirect tensile strengths nearly levelled off with minor fluctuations. Based on the microstructural analysis results, it was inferred that the fine seashell powders as part of the seashell particles, which were comprised of aragonite-based calcium carbonate, participated in the cement hydration process that could help with microstructure densification of the cement matrix. This positive effect brought by the fine seashell powders was thought to prevent the further weakening of mechanical properties. Overall, this study aims to understand the role of seashell particles on the mechanical performance of 3D-printed cementitious composites from the perspectives of microstructural characteristics, further promoting the utilisation of waste seashells in 3D concrete printing applications.

The effect of physical properties of pond ash as a partial replacement of sand in the mortar mix

The major focus of the present study is the use of pond ash to replace fine river sand in the production of plaster. In this study, the physical, mechanical, and microstructure characteristics of mortar are investigated for different replacement levels of sand with pond ash. The results show that the dry density of pond ash mixes is reduced by increasing the replacement level, which is due to the higher water absorption and pond ash’s porousness. It is worth mentioning that at a replacement rate of 20%, compressive and flexural strengths are higher than those of control specimens. On the other hand, drying shrinkage is 31% lower than the control, but the achieved strength is more than the required strength as per the Indian code. Scanning electron microscopy with energy dispersive x-ray spectroscopy shows that a rise in silicon content (12%) for samples having a 20% replacement of pond ash has a high C–S–H gel density, thus exhibiting higher compressive and flexural strengths. X-ray diffraction results show that the lower strength of 40% pond ash replacement is due to the presence of sodium sulfate. Hence, the results indicate that fine pond ash can be partially replaced with fine river sand for internal plaster and to produce mortar and blocks.

Experimental study and prediction of the long-term strength development of high-flowability concrete made of mixed sand and high-content fly ash

To comprehensively utilize the abundant solid wastes of superfine river sand and fly ash, a mixed sand of superfine river sand with coarse manufactured sand and high-flowability concrete made of mixed sand and high-content fly ash were developed. To address the critical question about the long-term strength of this new concrete, this paper presents an experimental study on the long-term development of cubic compressive and tensile strengths of the concrete over a curing age from 7 days to 360 days. In the study, the mixed sand was a hybrid of 40 % superfine river sand and 60 % coarse manufactured sand, and the fly ash content varied from 30 % to 75 % of the total binders by weight. The law of strength development of concrete with fly ash content was analyzed, combined with explanations of the mechanism and observations of hydration exotherms and microstructures of the concrete. Equations were proposed for predicting the long-term development of cubic compressive and tensile strengths, incorporating coefficients to reflect the effects of fly ash on the binder’s compressive strength and the development tendency of concrete strength. The validity of the proposed prediction equations was verified against the test results and compared with the extended application of the equation specified in CEB-FIP MC 2010.

Recycling of contaminated waste glass in ultra-high performance concrete: Impurities impact

The feasibility of recycling clean waste glass in construction products has been demonstrated. However, the direct utilization of contaminated waste glass from consumed beverage glass bottles may negatively affect the performance of concrete. This study aimed to investigate the effect of impurities in waste glass on the properties of ultra-high-performance concrete (UHPC). Washed and unwashed waste glass powder and sand were used as cement and river sand substitutes, respectively. Light particles, clay and fine silt, organic impurities and aluminium content in waste glass were determined. The results showed that the use of washed waste glass powder (W-WGP), washed waste glass sand (W-WGS) and unwashed waste glass powder (U-WGP) had a limited negative effect on the compressive strength of UHPC. In contrast, the use of unwashed U-WGS significantly decreased the compressive strength of UHPC due to the presence of impurities (e.g., paper and metallic aluminium). However, the impurities in the unwashed waste glass could positively reduce the autogenous and drying shrinkages of UHPC. The metallic impurities reacted with an alkaline solution to generate gases, resulting in the expansion of the matrix and reduction of autogenous shrinkage at the early stage. X-ray CT and microstructural images indicated that expansion resulting from the U-WGS caused cracks in the matrix and degraded the interfacial zone between the U-WGS and the paste. However, the incorporation of waste glass did not induce any alkali-silica reaction expansion in UHPC due to its low water-cement ratio and dense structure. The UHPC prepared with 30 % U-WGP as a replacement for cement was found to achieve satisfactory performance and lower carbon emissions.

Enhancing the resistance of cementitious composites to environmental thermal fatigue using high-volume fly ash and steel slag

Daily fluctuations in environmental temperature induce thermal fatigue and cause degradation in concrete structures. This study introduces a novel approach of utilizing high-volume fly ash, steel slag fine aggregates, and basalt-polypropylene fibres to prevent degradation against environmental thermal fatigue (ETF). Five mixes were considered with variations in fine aggregate type, fibre length and volume. The compressive and flexural strengths were analysed after exposure to 60, 120, 180, 240, and 300 ETF cycles between 20 and 60 °C (at constant relative humidity). The residual compressive strength of mix with 100 % river sand and 100 % steel slag as fine aggregates was ∼106 % and ∼112 % respectively after 300 ETF cycles. The developed cementitious composites performed significantly better than the mixes utilized in the existing literature. The mix with 100 % steel slag aggregate even demonstrated a continual rise in compressive strength as opposed to mixes with river sand whose strength declined after 180 or 240 ETF cycles. Flexural strength also improved up to 180 ETF cycles and then started to decline in all mixes. A thorough microstructural analysis was also conducted using scanning electron microscopy, differential scanning calorimetry, and mercury intrusion porosimetry to gain further insights into the underlying mechanism of the newly introduced matrix composition against ETF.

Improving passing ability of ultra-heavy-weight concrete by optimising its packing structure

Heavy-weight concrete (HWC) is a widely adopted radiation shielding material in the nuclear industry. In this study, two kinds of high-density aggregate, namely, iron sand (IS) and steel slag coarse aggregate (SSCA), were adopted to fully replace river sand and natural coarse aggregate, respectively, producing ultra-heavy-weight concrete (UHWC) with a unit weight >3800 kg/m3, to ensure excellent radiation shielding performance. However, IS and SSCA seriously impaired the passing ability of UHWC as the cement paste could not hold the IS and SSCA as firmly as natural aggregates, owing to their high density. To overcome this, the rheology of UHWC should be optimised by partially replacing the cement with superfine silica fume (SSF) and using a suitable amount of superplasticiser (SP) to enhance the wet packing density (WPD). A total of 28 UHWC mixes with different replacement ratios of SSF and different SP dosages were tested for segregation width, flowability, L-box passing ability, unit weight and WPD. Results revealed that incorporating an appropriate quantity of SSF and SP improved the WPD of UHWC, resulting in improved segregation resistance, enhanced flowability, increased passing ability and a higher unit weight. Lastly, there is a positive correlation between flowability, passing ability and WPD.

Discrimination of tectonic provinces using zircon U-Pb ages from bedrock and detrital samples in the northern Andes

Abstract The northern Andes of southern Colombia contain a rich geologic history recorded by Proterozoic to Cenozoic metamorphic, igneous, and sedimentary rocks. The region plays a pivotal role in understanding the evolution of topography in northwestern South America and the development of large river systems, such as the Amazon, Orinoco, and Magdalena rivers. However, understanding of the basement framework has been hindered by challenging access, security concerns, tropical climate, and outcrop scarcity. Further, an insufficient geochronologic characterization of Andean basement complicates provenance interpretations of adjacent basins and restricts understanding of the paleogeographic evolution of southern Colombia. To address these issues, this paper presents a zircon U-Pb geochronological dataset derived for 24 bedrock samples and 19 modern river samples. The zircon U-Pb results reveal that the Eastern Cordillera of southern Colombia is underlain by basement rocks that originated in various tectonic events since ca. 1.5 Ga, including the accretion of discrete terranes. The oldest rocks, found in the Garzon Massif, are high-grade metamorphic rocks with contrasting Proterozoic protolith crystallization ages. Whereas the SW part of the massif formed during the Putumayo Orogeny (ca. 1.2–0.9 Ga), we report orthogneisses for the NE segment with protoliths formed at ca. 1.5 Ga, representing the NW continuation of the Rio Negro Jurena province of the Amazonian Craton. In contrast, crystalline rocks of the Central Cordillera primarily consist of Permian–Triassic (ca. 270–250 Ma) and Jurassic–Cretaceous (ca. 180–130 Ma) igneous rocks formed in a magmatic arc. In southernmost Colombia, the Putumayo Mountains mainly consist of Jurassic–Cretaceous (180–130 Ma) plutonic and volcanic rocks. Furthermore, we analyzed the heavy mineral abundances in modern river sands in southern Colombia (spanning 1°N–5°N) and found that key minerals such as garnet and epidote can be utilized to trace high-grade metamorphic and igneous lithologies, respectively, in the river catchments. The differentiation of basement ages for separate tectonic provinces, combined with heavy mineral abundances in modern sands, can serve as unique fingerprints in provenance analyses to trace the topographic and exhumational evolution of different Andean regions through time.

Cosine-enhanced tuna swarm optimized exponential entropy segmentation method for sand grain microscopic images

The feature extraction of sand grain size, color and texture is a necessary step to identify clastic components. The sand grain features are complex and various, which brings difficulties to geological identification. Aiming at these images, a cosine-enhanced tuna swarm optimized exponential entropy segmentation method is proposed, which can effectively preserve the texture features of various sand grains. Firstly, for the tuna swarm optimization (TSO) algorithm, three improvement strategies are proposed: cosine spiral movement, cosine parabolic movement and Gauss-Cauchy mutation, which improve the TSO's global and local search. This algorithm is called cosine-enhanced TSO (CETSO). Benchmark function experiments showed that the convergence accuracy and stability of CETSO are greatly improved, and the convergence speed is also slightly increased. Secondly, CETSO optimized the exponential entropy to automatically determine the segmentation thresholds, and the feasibility of the method is verified by taking the information content of the segmented image as the standard. Finally, segmentation experiments were carried out on the Yarlung Zangbo River sand microscopic image dataset, and the results show that the method has high segmentation accuracy and stability for images with high contrast, rich texture, or significant differences in the size of sand debris. Compared with TSO, the CETSO optimized exponential entropy segmented images achieved an improvement of 21% and 93% in the evaluation of the average and standard deviation of the peak signal-to-noise ratio on thirty experiments. And this method has a fast processing speed, and it only takes about 0.85s to divide an image on average, which meets the needs of engineering applications.

Mechanical properties of steel fiber reinforced recycled concrete under compression-shear stress state

The continuous urbanization of construction has led to an increasing demand for concrete, resulting in large-scale gravel and river sand mining, which seriously affect the sustainable development of the environment. The waste concrete produced by the demolition of old buildings is processed into recycled aggregate to replace natural aggregate, and then the preparation of recycled concrete can effectively alleviate this problem. This paper investigates the mechanical properties of steel fiber reinforced recycled concrete (SFRRAC) under compression shear conditions, a compression shear test with 99 cubic specimens was designed, with the variation parameters being recycled aggregate concrete replacement rate, compressive stress, and steel fiber content. The failure mode of SFRRAC under compression-shear stress was observed, and the shear force-displacement curve was calculated. Furthermore, a thorough examination was performed to assess the mechanical characteristics of SFRRAC specimens under compression-shear stress. The findings of this study suggest that as the compressive stress increases, the failure characteristics of the specimens shift from exhibiting brittle failure to displaying ductile failure. The shear strength is most sensitive to the change in compressive stress. When the compressive stress reaches 6 MPa, the shear strength can reach 3.41 times that of the direct shear specimen. The shear strength of SFRRAC specimens is composed of the bond strength of concrete, shear expansion strength, and friction shear strength. The incorporation of steel fibers can modify the distribution of shear strength among the individual components. The adverse effect of the recycled aggregate replacement rate on the toughness index of the specimen is mainly concentrated after the peak point. Nevertheless, an elevation in compressive stress and the inclusion of steel fibers can counterbalance this detrimental influence. The shear strength calculation formula of SFRRAC in shear state is put forward, which has a reference value. This study provides an experimental reference and a theoretical basis for further examination of SFRRAC.

Splitting Tensile Mechanical Performance and Mesoscopic Failure Mechanisms of High-Performance Concrete under 10-Year Corrosion from Salt Lake Brine

In regions characterized by the challenging combination of brine corrosion in the salt lakes and river sand with alkali silica reaction (ASR) activity in areas of the Northwest, high-performance concrete (HPC) formulated with high-volume composite mineral admixtures as ASR suppression measures has been preferred for civil engineering structures in the region. This study investigates the splitting tensile strength, corrosion products, microscopic structure characteristics, and mesoscopic mechanical mechanisms of splitting failure of such HPC under 10-year corrosion from salt lake brine. The relationship between mechanical properties and corrosion damage, as well as the characteristics of internal crack propagation paths and failure mechanisms of HPC under splitting load, are explored. The findings reveal that as the alkali content within HPC rises, corrosion damage intensifies, resulting in a reduction in splitting tensile strength. Moreover, a linear association between mechanical properties and corrosion damage is observed. Microscopic structural analysis and numerical simulation of the splitting failure process of HPC elucidate that while the substantial presence of mineral admixtures effectively suppresses the ASR risk associated with alkali-reactive aggregates in concrete, uneven ASR gel products persist. These discontinuous micro-fine interface cracks induced by the gel products and the cracks induced by the gel products around the selective alkali-active aggregate particles distributed in the local area are the initiation sources of mortar cracks in HPC splitting failure. In terms of the overall failure state observed during the concrete splitting process, mortar cracks manifest two distinct extension paths: along the coarse aggregate interface and directly through the aggregates themselves. Notably, a greater proportion of coarse aggregates are directly penetrated by mortar cracks, as opposed to the number of interface failures bypassing coarse aggregates. More importantly, the above work establishes a theoretical reference in three dimensions: macroscopic, mesoscopic, and microscopic, for studying concrete corrosion damage in complex environments such as salt lake brine corrosion and ASR inhibition.