Concrete Mechanisms Research Articles

Experimental study on the mechanical properties and impermeability of basalt-PVA hybrid fibre reinforced concrete

Numerous studies have indicated that the incorporation of chopped fibres can significantly improve the mechanical properties and durability of concrete. To further explore the effect of chopped basalt fibres, PVA fibres and their hybrid fibres on the improvement of concrete mechanics and impermeability, mechanical property and impermeability tests of chopped basalt fibres/PVA fibres of different lengths and hybrid ratios mixed with concrete of disparate benchmark strengths were carried out. By comparing the characteristic values of each group and their variation rules, the optimal length and hybrid ratio of the fibres were determined. The results show that the enhancement effect of chopped basalt fibres of different lengths on the mechanical and impermeability properties of concrete is different, showing a trend of first increasing and then decreasing. The enhancement effect of chopped basalt fibres on the mechanical and impermeability performance of concrete with different benchmark strengths is better than that of PVA fibres. Compared with those of the C30 plain concrete, the mechanical and impermeability properties of the chopped basalt-PVA hybrid fibre concrete significantly improve to varying degrees. When the proportion of chopped basalt fibres is greater than or equal to the proportion of PVA fibres, a positive hybrid effect on the mechanical and impermeability performance of concrete with the same benchmark strength occurs. With increasing benchmark strength, the enhancement effect of the two types of fibres on the mechanics and impermeability of the concrete decreases. The attenuation range of PVA fibres is greater than that of chopped basalt fibres, and even a reduction in the mechanical and impermeability properties of concrete occurs. This results in the enhancement effect of chopped basalt-PVA hybrid fibres on concrete mechanics as well as a significant decrease in the impermeability. The improvement rates of the compressive performance and impermeability of concrete by a single or a hybrid of the two fibres are highly similar, and the enhancement effect of the fibre compressive performance is significantly greater than that of the impermeability.

Effects of aggregate's type and orientation on stress concentration and crack propagation of modeled concrete applied a shear force

This study focused on planarizing natural modeled aggregate concrete (NMC), recycled modeled aggregate concrete (RMC), and brick modeled aggregate concrete (BMC) for analyzing the influences of aggregates on shearing failure mechanism. A designed apparatus was used to load a shear force for the specimens and analyzed the global and local strain fields near the interface transition zone (ITZ) using digital image correlation (DIC) analysis. Additionally, we employed COMSOL software simulation to understand the crack initiation process and damage evolution mechanism of related concrete. Our findings revealed that the brick aggregate leaded to the lowest modulus of elasticity and compressive strength, resulting in poor shear resistance. However, the recycled aggregate model exhibited the highest shear resistance, primarily due to the old mortar acting as a buffer layer in the ITZ. During loading, the stress in the NMC model concentrated in the load transfer zone and gradually moved to the left and right sides of the built-in aggregate model until fracture, as observed through DIC analysis. The stress distribution of the RMC was similar with those of the NMC, but the BMC showed a distinct stress distribution pattern. Furthermore, the corner of the built-in modeled aggregate significantly influenced the crack propagating path and stress distribution. Therefore, the modeled aggregate corner plays a crucial role in the shear behavior of concrete, affecting both crack propagation and overall mechanical performance. The practical implications of our study can inform the design and application of recycled concrete.

Study on mechanical properties and damage mechanism of alkali-activated slag concrete

The cement industry has become one of the important sources of greenhouse gas emissions, and the alkali-activated slag (AAS) has the same mechanical properties and lower carbon emissions as cement in the production process. Therefore, it can be used as an alternative binder for low-carbon buildings. The effect of alkali concentration (mass ratio of Na2O to binder) on the macro-mechanical properties and meso-damage mechanism of alkali-activated slag concrete (AASC) under uniaxial compression was investigated in this work. Six kinds of concrete with alkali concentration of 2 %, 4 %, 6 %, 8 %, 10 % and 12 % were prepared. The microscopic characteristics of AASC were characterized by nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray energy dispersive spectroscopy (EDS); the meso-damage evolution mechanism of AASC was discussed by statistical damage theory. The results showed that the peak stress and elastic modulus of AASC specimens increased, and the microstructure became denser with the increase of alkali concentration. However, the mechanical properties of the specimen deteriorated to some extent when the alkali concentration exceeded 6 %; for example, the peak stress decreased by 24.00 MPa when the alkali concentration was increased from 6 % to 12 % at the age of 28d. Based on the statistical damage theory, the effective stress concept was introduced to quantitatively analyze the mesoscopic damage evolution of AASC. Both fracture and yielding damage modes were considered. By exploring the regular changes of the mesoscopic parameters, the connection between the macroscopic mechanical properties and the mesoscopic damage mechanism was established. Based on the above mechanical properties and mesoscopic damage results, the alkali concentration of 6 % can be used as the best mixture proportions of AASC.

Corrosion Characteristics and Durability of Bio Concrete – A Review

Abstract Concrete, is a crucial construction material widely used in infrastructure, has inherent limitations despite its versatility. It exhibits constrained ductility, low resistance to cracking, and relatively weak tensile strength. Global research has continuously sought modifications to address these issues in conventional cement concrete. Periodic exposure to harmful substances can lead to concrete corrosion, potentially causing structural failures that impact long-term operational efficiency. Studies in the literature focus on enhancing corrosion resistance, with microbiologically induced calcite precipitation (MICP) being a notable outcome. Recent research highlights specific bacterial species, like Bacillus subtilis, capable of enhancing the durability and lifespan of concrete structures. However, the actual impact on strength and properties depends on factors such as concrete mix design, bacterial concentration, and environmental conditions. Ongoing research in Bacillus subtilis application is evolving, and actual data may vary based on specific experiments and conditions. For the latest information, referring to the current scientific literature is recommended. Microbial concrete holds promise in significantly extending infrastructure service life, reducing maintenance expenses, and enhancing structural safety. This study delves into the fundamental mechanism of microbiological concrete, offering insights into factors strengthening and prolonging concrete life while presenting limitations.

Unraveling the Stray Current-Induced Interfacial Transition Zone (ITZ) Effect on Sulfate Corrosion in Concrete

The rail transit in sulfate-rich areas faces the combined effects of stray current and salt corrosion; however, the sulfate ion transport and concrete degradation mechanisms under such conditions are still unclear. To address this issue, novel sulfate transport and mesoscale splitting tests were designed, with a focus on considering the differences between the interfacial transition zone (ITZ) and cement matrix. Under the influence of stray current, the ITZ played a pivotal role in regulating the transport and mechanical failure processes of sulfate attack, while the tortuous and blocking effects of aggregates almost disappeared. This phenomenon was termed the “stray current-induced ITZ effect.” The experimental data revealed that the difference in sulfate ion transport attributed to the ITZ ranged from 1.90 to 2.31 times, while the difference in splitting strength ranged from 1.56 to 1.64 times. Through the real-time synchronization of splitting experiments and microsecond-responsive particle image velocimetry (PIV) technology, the mechanical properties were exposed to the consequences of the stray current-induced ITZ effect. The number of splitting cracks in the concrete increased, rather than along the central axis, which was significantly different from the conditions without stray current and the ideal Brazilian disk test. Furthermore, a sulfate ion mass transfer model that incorporates reactivity and electrodiffusion was meticulously constructed. The embedded finite element calculation exhibited excellent agreement with the experimental results, indicating its reliability and accuracy. Additionally, the stress field was determined utilizing analytical methods, and the mechanism underlying crack propagation was successfully obtained. Compared to the cement matrix, a stray current led to more sulfates, more microstructure degradation, and greater increases in thickness and porosity in the ITZ, which was considered to be the essence of the stray current-induced ITZ effect.

LncRNA FAM83H-AS1 Contributes to the Radio-resistance and Proliferation in Liver Cancer through Stability FAM83H Protein.

Liver cancer (LC) is one of China's most common malignant tumors, with a high mortality rate, ranking third leading cause of death after gastric and esophageal cancer. Recent patents propose the LncRNA FAM83H-AS1 has been verified to perform a crucial role in the progression of LC. LncRNA FAM83H-AS1 has been verified to perform a crucial role in the progression of LC. However, the concrete mechanism remains to be pending further investigation. This study aimed to explore the embedding mechanism of FAM83H-AS1 molecules in terms of radio sensitivity of LC and provide potentially effective therapeutic targets for LC therapy. Quantitative real-time PCR (qRT-PCR) was conducted to measure the transcription levels of genes. Proliferation was determined via CCK8 and colony formation assays. Western blot was carried out to detect the relative protein expression. A xenograft mouse model was constructed to investigate the effect of LncRNA FAM83H-AS1 on tumor growth and radio-sensitivity in vivo. The levels of lncRNA FAM83H-AS1 were remarkably increased in LC. Knockdown of FAM83H-AS1 inhibited LC cell proliferation and colony survival fraction. Deletion of FAM83H-AS1 increased the sensitivity of LC cells to 4 Gy of X-ray radiation. In the xenograft model, radiotherapy combined with FAM83H-AS1 silencing significantly reduced tumor volume and weight. Overexpression of FAM83H reversed the effects of FAM83H-AS1 deletion on proliferation and colony survival fraction in LC cells. Moreover, the over-expressing of FAM83H also restored the tumor volume and weight reduction caused by the knockdown of FAM83H-AS1 or radiation in the xenograft model. Knockdown of lncRNA FAM83H-AS1 inhibited LC growth and enhanced radiosensitivity in LC. It has the potential to be a promising target for LC therapy.

Modeling of the fracture behaviors of concrete using 3D discrete element method with softening effect

Understanding the fracture mechanism of concrete is very important for the safety design of concrete structures. We develop a 3D discrete element model with softening effect to study the fracture behaviors of quasi-brittle materials. The basic ideas of our model inspired from the flat-joint concept and the cohesive crack model are implemented in the framework of MUSEN, which is an open source discrete element software with CPU–GPU accelerating computation. The placement-package-compaction method is proposed together with laser scanning technology to construct the meso-scale geometric model of concrete. The meso-parameters of 3D discrete element model developed are calibrated by uniaxial compression and splitting tension tests of concrete. The validation of the present model is verified by the laboratory test of concrete. Compared with the results predicted by the flat-joint model, the F-CMOD curves and fracture parameters simulated by our model are in good agreement with that of the laboratory tests of concrete. Finally, it is concluded that the fracture strain of bond significantly affects the fracture behavior but the softening mode does not. It is found that the linear one is better choice among three softening modes in the present model.

Study on the Effect of XYPEX Admixture on the Performance of Panel Concrete and Microscopic Mechanism

The influence of different XYPEX content on the performance of dam panel concrete was studied through laboratory tests. The test results show that a certain amount of XYPEX can improve the compressive strength and impermeability of panel concrete. According to the scanning electron microscope photos, XYPEX admixture has a good filling effect on the internal pores of concrete in the microstructure, and the macro performance is improved for impermeability, but the effect on the visible cracks on the surface of concrete is small. The research results fill the gap in the research field of XYPEX admixture in dam panel concrete, provide a new idea for improving the durability of panel concrete, and provide technical support and data support for the future application of XYPEX admixture in water conservancy and hydropower projects.

Dynamic responses of rubberised concrete: A study using short-length F-shape barriers subjected to pendulum impact

This study evaluates rubberised concrete barriers' dynamic responses and failure mechanisms subjected to pendulum impacts. We constructed short-length F-shaped barriers from concrete mixed with varying proportions of steel fibres (0 %, 1 % and 2 %) and recycled crumb rubber (0 %, 30 % and 60 %). These barriers were then tested under controlled pendulum impacts, where we measured their peak impact forces, displacements, and energy absorption capacities at different impact velocities. Our findings reveal that barriers with rubber displayed significantly higher energy absorption and lower peak impact forces at low velocities than standard concrete barriers. Conversely, incorporating steel fibres into rubberised concrete increased the peak impact forces and reduced displacements, indicating enhanced stiffness. The experimental data facilitated the development of a predictive equation for peak impact forces, accounting for impact velocity and material composition. This research demonstrates rubberised concrete's less hazardous failure modes and enhanced impact resistance and energy absorption capabilities when used in roadside barriers. Our findings offer valuable insights for developing safer, more resilient infrastructure and contributing to environmental sustainability by repurposing waste materials.

Heterogeneity induced fracture characterization of concrete under fatigue loading using digital image correlation and acoustic emission techniques

Understanding the fatigue failure mechanisms in concrete is complex and remains an area of ongoing investigation. Material heterogeneity, along with the size effect, plays a significant role in specifying the crack propagation behaviour and fatigue life in case of repetitive loading conditions. In this study, the influence of material heterogeneity on the fatigue behaviour of concrete has been examined. Three different-size beam specimens with varying heterogeneity (aggregate sizes) have been considered to investigate various fracture characteristics under repetitive load conditions. Acoustic emission and digital image correlation techniques have been employed to analyse crack growth behaviour. The results revealed that stiffness degradation and crack propagation rates are faster for the specimens with smaller aggregate sizes compared to the larger aggregate size specimens of the same depth. Moreover, the fatigue life and effective crack length at failure are also higher in the case of larger aggregate sizes compared to smaller ones. Therefore, a heterogeneity-adjusted, analytical model of fatigue crack growth has been proposed. Further, the AE parameters have been utilized to characterize the tensile and shear crack dominance in different stages of fatigue crack propagation. The outcome of this study can be utilized to anticipate the crack propagation behaviour and residual fatigue life for any combination of specimen size and aggregate size.

Chemotherapy drug combinations induced maternal ovarian damage and long-term effect on fetal reproductive system in mice

With the postponement of female reproductive age and the higher incidence of cancer in young people, fertility preservation has become increasingly important in childbearing age. Chemotherapy during pregnancy is crucial for maternal cancer treatments and fetal outcomes. It is a need to further study ovarian damage caused by chemotherapy drug combinations and long-term effects on offspring development, and a detailed understanding of side effects of chemotherapy drugs.In this study, chemotherapy drug combinations significantly impacted on ovarian function, especially epirubicin/cyclophosphamide (EC) combination led to an unbalance in the development of the left and right ovary. Exposure to EC and cisplatin/paclitaxel (TP) increased the number of progenitor follicles while decreased the count of antral follicles and corpora luteum. As to the estrus cycle, EC exposure resulted in a longer estrus period and diestrus period, while TP exposure only extended the diestrus period. EC and TP affected steroid biosynthesis by reducing the expression of SF1 and P450arom.γ-H2AX was detected in both EC and TP exposure groups.As to the impact on the offspring from 4T1 tumor-bearing pregnant mice injected with EC, no significant difference was observed in the physical and neurological development compared to the control, but the ovarian weights, estrus cycles of the offspring were significantly different. Chemotherapy drug combinations exhibit ovarian toxicity, not only causing direct damage on the follicle cells but also disrupting steroid biosynthesis. The reproductive system of offspring from maternal tumor-bearing mice exposed to chemotherapy drugs was observed disorder, but the concrete mechanism still needs further exploration.

Experimental Study on the Crack Concrete Repaired via Enzyme-Induced Calcium Carbonate Precipitation (EICP).

A low-carbon and environmentally friendly EICP method for repairing concrete cracks is presented to prolong the service life of concrete. In this study, we took concrete as the research object and quartz sand as the filling medium and employed the EICP injection method to repair concrete cracks. The internal repair effect of EICP on concrete cracks was evaluated with a combination of ultrasonic and compressive strength tests. The concrete repair mechanism of EICP was identified with a combination of EDS, XRD, and SEM tests. The results indicate that with an increase in the fracture depth, the ultrasonic sound time of the crack specimen increased gradually, and the ultrasonic wave transit time value of the crack specimen decreased significantly after EICP repair. After repair, the compressive strength rose. The highest compressive-strength recovery rate of a 0.3 mm wide specimen is 98.41%. The calcium carbonate crystal formed using EICP is vaterite. The probability density function model of the Laplace distribution was constructed, which showed good applicability and consistency in the ultrasonic sound time and compressive strength measured via experiments. The formed calcium carbonate crystals can be tightly and evenly attached to the cracks with the EICP injection repair method, resulting in a better repair effect.

Mix-mode fracture behavior in asphalt concrete: Asymmetric semi-circular bending testing and random aggregate generation-based modelling

The thermal or reflective fracture in asphalt pavement often occurs due to both shear or tension stress, simultaneously, which can be referred to the mix-mode fracture. However, most of the research in the literature focused on the pure tension or shear fracture behavior but not the hybrid effects. Therefore, this study aims to investigate the mix-mode fracture behavior and fracture resistance performance of asphalt concrete through both indoor experiments and virtual modeling methods. The Asymmetric Semi-Circular Bending (ASCB) test was employed to assess the mix-mode fracture behavior of specimens. A meso-scale virtual finite element model of the asphalt concrete was also established to simulate the mix-mode fracture process and microcrack damage evolution based on polygonal random aggregate generation method. By comparing the simulation results with indoor test results, the reliability of the finite element simulation was verified. The results indicate that virtual experiments can effectively simulate the fracture process of asphalt concrete, and the fracture process always proceeds in the direction of lower energy consumption. Meso-scale simulation experiments revealed the crack evolution mechanism of mix-mode fracture in asphalt concrete. Microcracks in the pure tension fracture mode tend to connect and form a continuous fracture surface, exhibiting lower strength and apparent brittleness. With the increase in shear proportion, the connectivity of microcracks within the specimen decreases, demonstrating higher strength. The distribution pattern of microcracks in asphalt concrete at the meso-scale was analyzed based on the failure ratio of cohesive elements and the fracture modes, and the evolution degree of mix-mode fracture and the proportion of tensile failure mode in different fracture modes were quantitatively studied, thereby revealing the meso-scale cracking mechanism of asphalt concrete.

Anchorage force transfer mechanism and bearing capacity theoretical of pawl bolt anchored in plain concrete

In this paper, the anchorage mechanism and bearing capacity of the special type of pawl bolt anchored in concrete under uplift load were studied. Static tests were carried out on two typical pawl bolts, namely 135° and 180° pawl bolts, and the effects of anchorage depth and pawl type on their failure modes were studied. The experimental results show that the uplift bearing capacity of pawl bolt is improved more effectively than that of smooth bolt. The two typical failure modes of pawl bolts under uplift load are concrete breakout failure and bolt yield failure. The concrete breakout failure exclusively occurs with anchorage depth of 5d, while the failure mode could change from concrete breakout failure to bolt yield failure with the increase of anchorage depth. The finite element model was established to elucidate the failure mechanism of anchorage bolt and concrete. The crack propagation and diffusion angle distribution of anchorage concrete can be directly judged by concrete tensile damage and stress vector in simulation analysis. Additionally, a calculation method to accurately predict the uplift bearing capacity of pawl bolt was proposed, which considered the effect of diffusion angle θi on the uplift bearing capacity and further discusses the change law of cone diffusion angle θi and concrete crack propagation. The calculated results exhibited a concordance with the experimental and numerical results, which shows that the formula presented in this paper can be considered reliable and can guide the practical engineering design.

Numerical Study of Concrete: A Mesoscopic Scale Simulation Methodology

This study aims to understand and simulate the mechanical properties of concrete, focusing specifically on the mesoscopic scale and its relation to the macro scale. Investigating concrete at this level involves examining its composition as a heterogeneous amalgamation of mortar, aggregates, and the Interfacial Transition Zone (ITZ). Numerical models, utilizing the finite element method (FEM), are employed to thoroughly examine the structural behavior of concrete. The study uses MATLAB (2023a) programming to develop three-dimensional models, which are then subjected to FEM analysis. Various mesoscopic Representative Volume Elements (RVEs) are formulated, considering spherical aggregates with different locations and dimensions to capture the complex nature of concrete. MATLAB is used to generate files containing comprehensive information about the RVEs, which are then processed with FEM to simulate compression strength tests. As the complexity increases with the inclusion of the ITZ, prismatic RVEs are developed to better represent real-world conditions. The proposed mesoscopic model establishes a foundational framework for a numerical simulation methodology tailored to laboratory compression tests, bridging the gap between mesoscopic and macroscopic scales. This approach provides detailed insights into concrete behavior, elucidating deformation and fracture mechanisms. Although not a complete substitute for experimental methods, these models offer a cost-effective and efficient alternative, identifying vulnerable areas and exploring the effects of additional materials on concrete behavior. The progressive replacement of laboratory tests with numerical simulations using RVEs of specific compositions will make the study of concrete behavior at the mesoscopic scale increasingly sustainable, paving the way for more efficient and environmentally friendly research practices in the field.

Numerical predictions of progressive collapse in reinforced concrete beam-column sub-assemblages: A focus on 3D multiscale modeling

The progressive collapse of reinforced concrete (RC) beam-column sub-assemblage under catenary action (CA) using the alternate load path method to evaluate structures' robustness has raised much attention in the past decade, both in experimental tests and finite element (FE) simulations. However, a comprehensive multiscale method within concrete to assess structural robustness against progressive collapse, explicitly surrounding concrete matrix under CA, is generally lacking and has not been thoroughly explored in the relevant literature. This study aims to develop an FE macromodel to reliably simulate the progressive collapse resistance of seismic and non-seismic RC beam-column sub-assemblages. The proposed macroscale FE models are extensively validated by experimental results dominated by the CA and excessive deformation of RC beam-column sub-assemblages. Then, the macroscale FE model is further partitioned at the critical region with high-stress concentration to establish a sub-model and elucidate the underlying mesoscopic mechanism to motivate the CA by performing sub-modeling analysis. A 150 mm × 150 mm × 150 mm mesoscale heterogeneous model is established to be composed of aggregates, interfacial transition zone (ITZ), pores, and mortar by 3D voxel and Voronoi-based methods. The numerical predictions of the three macroscale models demonstrate good agreement of the overall deformation and load resistance trends with experimental results at both structural and sectional levels, but an overestimation of the load resistance peak is observed when concrete is crushed. Compared to the macroscale models, the sub-modeling analysis provides a more in-depth understanding of localized phenomena such as cracks and fractures. The 3D mesoscale model is further investigated with different aggregate volume fractions following the Fuller gradation. It is found that aggregates and ITZ (higher porosity, lower elastic modulus, and lower tensile strength compared to the bulk mortar) are more prone to concrete failure mechanisms without considering the role of reinforcement leading to the CA at the mesoscale, maintaining the concrete properties of the three macroscale models. In terms of the material constitutive model, the concrete damage plasticity model, and cohesive elements for mortar and ITZ, respectively, under uniaxial compression and tension behavior, the importance of interface bonding in CA of the surrounding concrete matrix is underlined. Additionally, the established mesoscale modeling method facilitates comprehension of the responses exhibited by macroscale RC sub-assemblies, ultimately shedding light on fracture initiation and propagation mechanisms.

Mechanical behavior of eccentrically loaded UHPC-encased CFST medium-long columns

To study the eccentric compression performance and failure mechanism of ultra-high performance concrete (UHPC) encased concrete-filled steel tubular (CFST) medium-long columns (UC-CFST medium-long columns), a total of 27 UC-CFST column specimens were tested under eccentric compression with eccentricity and slenderness ratio as the main parameters. After verified by experimental results, the finite element (FE) analysis of UC-CFST medium-long columns with actual structural cross-sectional size under eccentric compression was further carried out. It is found that as the slenderness ratio and eccentricity increased, the bending stiffness and the ultimate bearing capacity of the UC-CFST columns decreased gradually, and the failure mode changed from strength failure to instability failure, and the smaller the proportion of encasing UHPC area, the greater the upper-bound slenderness ratio of strength failure. Moreover, the influence of eccentricity was nonlinearly coupled with slenderness ratio on the eccentric compressive bearing capacity of UC-CFST medium-long columns. Finally, a calculation method of ultimate load-bearing capacity of UC-CFST medium-long columns considering the influence of eccentricity and slenderness ratio was proposed, which had good calculation accuracy with experimental and numerical results.

Mechanical properties and hydration mechanism of low carbon concrete with recycled aggregate

Collaborative and effective disposal of construction and industrial solid waste is of great significance for protecting the ecological environment. In this paper, low carbon concrete with recycle aggregate (LCCRA) mainly made of phosphogypsum, fly ash, slag and recycled aggregate was studied. The uniaxial compression test was carried out to determine the stress-strain relationship of LCCRA and a constitutive model for LCCRA under uniaxial compressive loading was established. Scanning Electron Microscopy (SEM) was used to explore the hydration process of LCCRA. The results demonstrated that the uniaxial compressive strength of LCCRA achieved 30.8 MPa with a 100 % replacement rate of recycled coarse aggregate and a water-binder ratio of 0.54. The constitutive model of LCCRA under uniaxial compression fits well with the experimentally measured stress-strain curve. SO42− in low carbon cementitious materials reacts with [SiO4]4-, [AlO4]5- to generate C–S–H gel, C-A-S-H gel and AFt crystals, which enhance the density of LCCRA interfacial transition zone (ITZ) and thus improve its basic mechanical properties.

The preparation, property and hydration mechanism of ultra high performance concrete with metakaolin substitution for silica fume

In recent years, there has been a growing body of research on the use of metakaolin (MK) in Ultra-High Performance Concrete (UHPC) to address the issue of unstable production yields and quality of industrial by-product Silica fume (SF). However, the current scientific literature tends to focus primarily on performance enhancements, often neglecting to elucidate the underlying mechanisms responsible for these improvements. In this study, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), nuclear magnetic resonance (NMR), nanoindentation technology, and Mercury Intrusion Porosimeter (MIP) were employed to establish the correlation between mechanical properties and hydration products, microstructure, and micromechanical properties. The results indicate that the judicious addition of MK can enhance the Al/Si ratio, prolong the C-A-S-H chain length, thereby increasing the percentage of high-density C-A-S-H, reducing the volume of C-A-S-H gel pores, optimizing UHPC pore structure, and ultimately leading to improved mechanical properties.

Mechanical behavior and fiber reinforcing mechanism of high-toughness recycled aggregate concrete under high strain-rate impact loads

Fiber-reinforced recycled aggregate concrete (FRRAC) is renowned for its excellent mechanical properties and environmental benefits, making it a popular choice in construction engineering. However, the impact damage mechanisms of FRRAC remain unclear. This study leverages advanced in-situ 4D CT technology to investigate the fiber-reinforcing mechanisms of High-Toughness Recycled Aggregate Concrete (HTRAC) using construction waste as a sustainable building material. Under high strain-rate conditions, the dynamic mechanical behaviors of both plain recycled aggregate concrete (PRAC) and HTRAC were examined using the Split Hopkinson Pressure Bar (SHPB) method. The experiments revealed significant strain rate sensitivities in both materials, with HTRAC showing superior fiber reinforcement that markedly enhances its toughness. Quantitative models for dynamic increasing factors of key mechanical parameters, including peak stress, peak strain, initial elastic modulus, ultimate strain, and toughness index, were developed. These findings offer critical design insights for using HTRAC in impact load conditions and other extreme environments, promoting its wider adoption in the construction industry.