Split Test Research Articles

Strain-rate-dependent performance of alkali-activated binder-based ultra-high strength concrete

Ultra-high performance concrete(UHPC) is a superior protective material in impact and blast resistance, but negatively influences the environment due to the large amount of cement consumption and CO2 emissions during the preparation process. Alkali-activated binders were invented as a promising alternative to Portland cement for preparing UHPC in a method that saves energy and emits less CO2. However, the strain-rate-dependent performance of alkali-activated binder-based ultra-high strength concrete (AAB-UHSC) is still unknown. Therefore, this work focused on the strain-rate-dependent performance, e.g., dynamic mechanical properties, energy absorption and failure patterns, of AAB-UHSC materials incorporated with different steel fiber contents, as well as the microdamage at different strain rates. The quasi-static compression test, split Hopkinson pressure bar test, the sieving test and the scanning electron microscope test were carried out. The results indicated that the AAB-UHSC material is a strain rate-dependent material, the different stress-strain curves corresponding to different failure patterns vary with the strain rate, and an obvious strain rate transition zone existed for different failure patterns, as did the energy for different failure patterns. Additionally, the addition of steel fibers could effectively enhance the dynamic macromechanical performance and reduce the microdamage. An impact toughness index suitable for AAB-UHSC was defined. Eventually, a modified ZWT dynamic constitutive model with a new damage evolution equation for the AAB-UHSC material was proposed, and results show that this model can well describe the stress-strain relationship of the AAB-UHSC under impact load.

Mesoscale modeling of dynamic compressive behavior of microcapsule-based self-healing concrete under impact loading

Microcapsule-based self-healing concrete (MSC) has been widely studied, with a focus on static behavior and self-healing effectiveness. However, the dynamic mechanical properties of MSC have rarely been studied. This study presents a mesoscale numerical investigation of the dynamic compressive behavior of MSC under impact loading. In mesoscale, MSC is regarded as a four-phase composite material mainly composed of coarse aggregates, interface transition zones, cement mortar, and microcapsules. A pseudo 3D numerical model is constructed by combining a slice of a detailed mesoscale model with a homogenous 3D model. The mesoscale MSC slice models with different mass fractions of microcapsules (0%, 2%, 5%, and 8%) are constructed. Different coarse aggregate shapes (i.e., circles, ellipses, and polygons) are considered. The uniaxial dynamic compressive behaviors of MSC materials under loads of different strain rates are numerically simulated and compared with those from split Hopkinson pressure bar tests previously done by the authors. The comparison results show that the present mesoscale model can accurately predict the compressive strength and failure mode of MSC. The effects of the microcapsules ratio and strain rate on the dynamic strength are studied. Results show that the MSC compressive strength decreases with the increase in microcapsules and increases with the increase in strain rate. The dynamic increase factor (DIF) of the specimen is jointly contributed by the material DIF, inertial constraints, and heterogeneity. Different aggregate shapes have little effect on the simulation results of MSC behavior. The obtained dynamic mechanical properties of MSC may assist in designing MSC to resist collisions or explosions.

Research on the Road Performance of Ring Diamond Resin Modified Asphalt Mixture

In order to solve the problems of ineffective modification and high cost of most asphalt modifiers, a new type of high viscosity and high elasticity asphalt modifier - ring diamond resin is introduced, and this modifier is injected into 70 # base asphalt. Through high-temperature rutting, low-temperature bending, immersion Marshall and freeze-thaw splitting tests, the road performance of 70 # base asphalt and ring diamond resin modified asphalt mixture is compared and analyzed. Intended to improve the quality of asphalt pavement while reducing economic costs, thereby extending the service life of the road. The research results indicate that the ring diamond resin modifier can greatly improve the high-temperature performance of asphalt mixtures, and to a certain extent improve their low-temperature crack resistance and water stability. It is a resin modified material with great potential and high advantages. It is recommended to use a dosage of 1% in practical road engineering applications.

Correlation between existential form of ruthenium cocatalyst and photocatalytic hydrogen evolution of carbon nitride

Catalysts composed of nanocluster and single-atom (SA) were extensively used to enhance electrocatalytic water splitting performance, whereas study of their photocatalytic hydrogen (H2) evolution activity was limited. Herein, carbon nitride (CN) decorated by ruthenium (Ru) cocatalysts existed as SA + cluster, cluster + nanoparticles (NPs), and NPs were prepared by impregnation and calcination processes. The correlation between existential form, content of Ru cocatalyst and H2 evolution rate were carefully discussed. It was found that Ru NPs were favor for water molecule adsorption, whereas Ru SAs and clusters facilitated H2 desorption. Theoretical calculations revealed that Ru clusters + NPs cocatalyst were beneficial for H* intermediate formation. Water splitting tests found that 1.07 wt% Ru NPs + cluster modified CN showed the highest H2 evolution rate of 13.64 mmol h−1 g−1, which was 266.4 and 1.5 times higher than those of CN and Ru NPs (2.33 wt%) decorated CN, respectively. This work deeply reveals the influences of existential form of Ru cocatalysts on photocatalytic water splitting of CN, and provides thought in designing new cocatalysts to largely enhance H2 evolution.

Anti-Phospholipase A2 Receptor Antibody (Anti-PLA2R) Testing to the Rescue

Serological testing for M-type anti-phospholipase A2 receptor antibodies (antiPLA2R Ab) has abrogated the need for kidney biopsy to diagnose membranous nephropathy in the appropriate clinical setting. We report a case of a 63-year-old hypertensive male who presented with nephrotic syndrome associated with autosomal dominant polycystic kidney disease which was effectively diagnosed with the use of antiPLA2R Ab test. He achieved complete remission upon treatment with Rituximab. Hitherto, all anecdotal case reports of this uncommon association were diagnosed only by kidney biopsy. We highlight the usefulness of PLA2RAb especially in such cases of difficult-to-biopsy kidneys.

The stability of foamed asphalt concrete based on different soaking conditions

The purpose of this study is to test the water stability of foam asphalt mixture under various immersion conditions. For this purpose, experiments were conducted on warm mixed foamed asphalt and traditional hot mixed asphalt. To evaluate its water stability, Marshall tests, immersion Marshall tests, vacuum saturation Marshall tests, and freeze-thaw splitting tests were conducted. Based on surface energy theory, the water damage mechanism of asphalt mixtures was analyzed. The research results indicate that due to the adverse effects of water erosion and pressure, the water stability of the two mixtures gradually decreases. Although the failure load value of warm mixed foamed asphalt mixture is slightly lower than that of hot mixed asphalt mixture, its water stability parameters still meet the specified requirements. Therefore, warm mix foam asphalt mixture shows satisfactory water stability under different soaking conditions.

A computational approach to integrate three-dimensional peridynamics and two-dimensional higher-order classical elasticity theory for fracture analysis

AbstractAs a nonlocal alternative of classical continuum theory, peridynamics (PD) is mathematically compatible to discontinuities, making it particularly attractive for failure prediction. The PD theory on the other side can be computationally demanding due to its nonlocal interactions. A coupling between PD and refined higher-order finite element method (FEM) integrates their salient features. The present study proposes a computational approach to couple three-dimensional peridynamics with two-dimensional higher-order finite elements based on classical elasticity. The bond-based PD modeling is considered in a region where damage might appear while refined finite element modeling is used for the remaining region. The refined finite elements employed in this study are based on the 2D Carrera Unified Formulation (CUF), which provides 3D-like accuracy with optimized computational efficiency. The coupling between PD and FEM is achieved through the Lagrange multiplier method which permits physical consistency and compatibility at the interface domain. An adaptive convergence check algorithm is also proposed to achieve predetermined accuracy in the solution with minimum computational effort. Simulations of quasi-static tension tests, wedge splitting tests and L-plate cracking tests are carried out for verification. In-depth analysis shows that the present approach can reproduce the linear deformation, material degradation and crack propagation in an effective way.

Static mechanical properties and damage evolution characteristics of selected rocks in diversion tunnel under uniaxial loading

An in-depth understanding of the mechanical properties and damage and fracture mechanism of selected rocks in a diversion tunnel plays an important role in promoting the efficient construction and safety of rock blasting excavation in a diversion tunnel. To study the mechanical properties and damage evolution characteristics of selected rocks in diversion tunnels under uniaxial loading, the uniaxial compression and uniaxial splitting tests of granite and tuff were carried out. In terms of mechanical properties, the evolution characteristics of complete stress-strain curves, instantaneous modulus-strain curves, and input energy density-strain curves were analyzed. In the aspect of damage characteristics, the macroscopic and mesoscopic failure modes were analyzed and the damage fracture mechanism was revealed. Compression-shear failure mainly occurred in granite and tuff under uniaxial compression, showing the characteristics of elastic-brittle fracture failure. Both granite and tuff showed a failure mode of coexistence of “compression-shear failure zone at the loading ends” and “tension-shear failure zone in the middle” under uniaxial splitting. The compression-shear fracture of granite was relatively smooth, and the matrix and mineral particles produced fine particles due to friction in the process of shear slip. The compression-shear fracture of tuff was relatively rough and the characteristics of shear slip were not prominent enough. The fracture failure of granite and tuff was mainly caused by the common fracture of rock matrix and mineral particles. Based on the Lemaitre equivalent strain principle, the pre-peak-post-peak two-stage damage constitutive model established by Weibull statistical distribution theory can accurately describe the static stress-strain relationships of granite and tuff under uniaxial compression.

Performance Evaluation of Self-Compacting Concrete Prepared Using Waste Foundry Sand on Engineering Properties and Life Cycle Assessment

The primary objective of this research is to utilize an industrial waste byproduct such as waste foundry sand (WFS) as an alternative for fine aggregate in self-compacting concrete (SCC). This research focuses on the use of WFS in SCC to enhance durability and mechanical properties, to find an alternative for fine aggregate in SCC, to reduce the disposal challenges of WFS, and to make SCC lightweight and environmentally friendly. Initially, WFS was treated with chemical (H2SO4), segregating, and sieving to remove the foreign matter and clay content. For this study, WFS is considered in varying percentages such as 0, 10, 20, 30, 40, and 50. For this investigation, M60 grade SCC is considered as per Indian standards and EFNARC guidelines. After that, this research focuses on tests on various fresh properties of SCC in each batch to find the flowability and passing ability of various mixes prepared using WFS. Similarly, the mechanical properties of SCC such as compressive, flexural, and split tensile strength tests were performed at 7, 28, and 90 days curing periods, respectively. Likewise, durability properties of SCC were found in all the mixes prepared using WFS such as water absorption, sorptivity, resistance to chemical attack, and chloride ion penetration; tests of these properties were performed at 28 and 90 days curing periods, respectively. Based on the experimental investigation of SCC, it was found that WFS can be used in M60 grade SCC as an alternative for fine aggregate up to 30% without compromising much on its properties. Finally, this establishes that using treated WFS in SCC helps in reducing the generation of waste and prevails as a meaningful utilization method. This research will also establish that the use of treated WFS will reduce the density and make SCC a lightweight, green, and sustainable material.

Study on acoustic emission and local deformation characteristics of feldspar vein-intrusive metagabbro at different angles of splitting

Feldspar vein-intrusive metagabbro is a special geological structure, and different stress angles have an important influence on the fracture mode and deformation characteristics of metagabbro. A Brazilian splitting test on feldspar vein-intrusive metagabbro was performed using three distinct stress angles (0°, 45°, and 90°), and acoustic emission signals and strain characteristics were monitored synchronously during the test. The results showed that the damage pattern of the feldspar vein-intrusive metagabbro was related to the feldspar mineral perforation damage on the main rupture surface. With the increase in stress angle, the percentage of high peak frequency increased gradually. The phenomenon of strain lagging stress appeared in the rock samples before the peak damage. The feldspar minerals played a controlling role in the expansion of microcracks in the feldspar vein-intrusive metagabbro. Significant differences in the local deformation coordination of rocks under different stress angles were observed. The deformation coordination of rock samples with a stress angle of 0° was much lower than that of other rock samples. This study is of great significance for the understanding of the deformation and damage laws of similar geological structures and also provides an important theoretical basis for the stability of deep chambers.

Influence of GGBFS and alkali activators on macro-mechanical performance and micro-fracture mechanisms of geopolymer concrete in split Hopkinson pressure bar tests

With superior low-carbon emission and low-resource consumption, geopolymer concrete (GPC) is receiving increasing attention as an optimal alternative to conventional building materials for cleaner and sustainable construction. However, the practical application of GPC poses great challenges since its dynamic mechanical performance remains far from well understood. In this study, via a split Hopkinson pressure bar (SHPB) system, a series of dynamic compression tests at strain rates of 45 s-1 to 150 s-1are conducted on GPC specimens with different alkaline activators (AAS)-binder mass ratios (i.e., 10%, 15%, 20%, and 25%) and ground granulated blast furnace slag (GGBFS)-binder mass ratios (i.e., 0%, 30%, 50%, 70%, and 100%). Our testing results comprehensively explored the influence of mix proportions and loading rates on the dynamic mechanical performance of GPC, including the dynamic strength and deformation characteristics, energy evolution and utilization, and progressive failure behavior. The permanent strain, energy dissipation density, and dynamic strength of GPC specimens generally increase with increasing strain rate, while the average fragment size decreases. Under higher loading rates, GPC specimens are featured by denser microcracks, shorter propagation paths, and more prominent stepwise fractures. In addition, GGBFS has a greater impact on dynamic strength, strain rate sensitivity, and energy utilization than AAS. Micro-fracture effect of GPC with different mix proportions is investigated. An appropriate content of alkaline activator (i.e., 20%) and higher GGBFS content (i.e., 100%) promotes the binder depolymerization-aggregation reaction, reduces initial defects inside concrete specimens, and facilitates a more compact block structure.

Laboratory studies on the mechanical properties of sulphur-based construction material at simulated Martian temperatures

Mars is the next destination for further exploration and the hypothetical establishment of humanity's frontier. However, the planet offers very harsh environmental conditions particularly the very cold temperature in the Martian environment. Knowing that the sulphur-based construction material is perceived as one of the ideal Martian construction materials based on the identified abundant source of sulphur on Mars, its behaviour when subjected to the very cold Martian temperature is yet to be fully clarified. Therefore, this study intends to investigate the behaviour of the Martian sulphur-based construction material subjected to the simulated very cold Martian temperature whilst being compared with the simulated hot Martian temperature. Two mixture compositions of 50/50 and 60/40 comprising of sulphur and Mojave Mars simulant 1 (MMS-1) respectively were fabricated in this study characterising the simulated Martian temperature. The workability at 50 % and 60 % sulphur content was initially investigated. Subsequently, the overall mechanical properties characterising the sulphur content and simulated Martian temperature were investigated via unconfined compression, three-point bending and tensile splitting tests. Necessary factors that influence the overall mechanical properties including the internal structure and microstructural characteristics were also performed via ultrasonic pulse velocity (UPV) and scanning electron microscopy (SEM) respectively. X-ray diffraction (XRD) was also conducted to identify the chemical composition of the end product. The comparisons between this study and other previous related studies within the state-of-the-art Martian sulphur-based construction materials were also outlined. Prospects for future construction on Mars are also presented. It was found that the 60 % sulphur content exhibited higher workability due to the high amount of unreactive sulphur. The 50 % sulphur content recorded the optimal overall mechanical properties under the simulated hot and very cold Martian temperatures. The simulated very cold Martian temperature triggered non-uniform interparticle distribution and larger cavities thus dramatically reducing its overall strength and triggering higher volumetric inconsistency. The very brittle nature of unreactive crystallised sulphur binder at excessive thickness particularly at 60 % sulphur content in between filler particles also triggered volumetric inconsistency which further worsened at the simulated very cold Martian temperature. The iron sulphate hydrate found was almost in agreement with the related works and another new compound, potassium calcium magnesium sulphate was identified as well. The overall mechanical properties are comparable with the other previous related studies and the residual strength when subjected to the simulated very cold Martian temperature remains adequate in the Martian environment of low gravity. The 60 % sulphur content is suggested for structural elements built internally whereas the 50 % sulphur content demonstrated a high potential in adapting to the harsh Martian environmental conditions. The findings of this study hoped to act as the initial outlook on how such Martian sulphur-based construction material would react upon fabrication on Mars.

A new type of shale gas reservoir—carbonate-rich shale: From laboratory mechanical characterization to field stimulation strategy

Recently, a new promising type of marine shale gas reservoir, carbonate-rich shale, has been discovered. But the mechanical properties of this type of shale were still unrevealed and the corresponding reservoir stimulation design was lack of guidance. Using the deep downhole cores of an exploratory carbonate-rich shale gas well, the physical and mechanical parameters and failure mechanism of the whole reservoir section were acquired and evaluated systematically, by performing XRD, tri-axial compression, Brazilian splitting, and fracture toughness tests. A new model was established to evaluate the reservoir brittleness based on fracture morphology and stress-strain curve. Recommended strategy for reservoir stimulation was discussed. Results showed that (1) Carbonate-rich shale possessed high compressive strength and high Young's modulus, which were improved by 10.74% and 3.37% compared to that of siliceous shale. It featured high tensile strength and fracture toughness, with insignificant anisotropy. (2) With the content of carbonate minerals increasing, the shear failure morphology transformed from sparse and wide brittle fractures to diffusely distributed and subtle plastic cracks. (3) The brittleness index order was: siliceous shale, clay-rich shale, carbonate-rich shale, and limestone. (4) The special properties of carbonate-rich shale were rooted in the inherent feature of carbonate minerals (high strength, high elastic modulus, and cleavage structure), resulting in greater challenge in reservoirs stimulation. The above findings would promote the understanding of carbonate-rich shale reservoirs and provide reference for the optimum design of reservoir stimulation.

Progressive Weakening of Granite by Piezoelectric Excitation of Quartz with Alternating Current

A promising solution to reduce energy usage and mitigate the wear of drilling and comminution tools during mining operations involves inducing vibrations within the piezoelectric phases dispersed in the structure of rocks using alternating current (AC). This paper presents experimental evidence of AC-induced weakening of Kuru granite, manifested as improvements in rock drillability and reductions of strength. Sievers’ J-miniature drill tests were used to assess surface drillability. The impact of AC treatment on the quasi-static strength of granite was assessed via three-point bending and indirect tension Brazilian disk tests. The influence of AC treatment on the dynamic tensile strength of the rock was determined using split Hopkinson bar tests, with the fragmentation process captured using in situ ultra-fast synchrotron X-ray phase contrast imaging. The quasi-static tests revealed no reduction in rock strength after the AC treatment. In contrast, reductions of 25% in hardness and 18% in dynamic tensile strength were observed. Fragmentation patterns differed between treated and non-treated rocks, with treated specimens exhibiting reduced macrocrack formation during loading.

Steel/plastic-steel hybrid fiber UHPC dynamic tensile performance: An experimental and numerical simulation study

Steel fibers (ST) in Ultra-high performance concrete (UHPC) play an important role in enhancing its mechanical strength and toughness. However, the brittleness of UHPC increases significantly under dynamic loading, while the contribution of ST to its tensile strength and fracture mode is relatively limited. In this study, Ultra-high performance hybrid fiber reinforced concrete (UHP-HFRC) was prepared using four hybrid ratios of ST and plastic steel fibers (high-performance polypropylene, PSF), and a series of quasi-static and dynamic splitting tests were conducted to investigate the effect of PSF on its dynamic tensile behavior. Additionally, X-ray computed tomography (X-CT) and SEM characterization techniques were applied to reveal the fiber synergy effect and enhancement mechanisms from the perspective of microcrack development. In addition, a novel hybrid fiber modeling method is proposed for finite element simulation of the dynamic tensile response of UHP-HFRC. The results indicate that fiber hybridization reduces the degree of damage of UHPC under dynamic loading, and its contribution is influenced by the strain rate. The increase in steel fiber content increases the dynamic tensile strength of UHP-HFRC, but the increase in PSF content contributes to the increase in energy absorption at fracture, and it is recommended to use 1 % of PSF mixed with ST. The simulation results show the constitutive relationships and failure modes that agree with the impact test results, verifying that the proposed three-dimensional mesoscopic model can effectively analyze the dynamic splitting performance of UHP-HFRC.

Experimental study on dynamic direct tensile performances of steel fiber-reinforced RPC at high strain rates

Reactive power concrete (RPC) exhibits excellent mechanical properties, makes it great potential for applications. RPC has gained increasing attention in academic and engineering areas and has been used in fields such as anti-explosion engineering. The insufficient tensile strength of RPC is one of the critical reasons for its structural failure. Existing studies revealed that the strain rate effect of concrete under dynamic tension is stronger than that under dynamic compression. The existing research focuses either on dynamic splitting and spalling tests, or dynamic uniaxial tensile properties with a strain rate of 0–100/s, neither of which are representative of the effect of RPC subject to explosion. In addition, the study of the dynamic uniaxial tensile constitutive model of RPC has not been reported in the existing research. To solve the existing limitations, this study conducted dynamic direct tension tests on steel fiber-reinforced RPC with a predefined strain rate higher than 100 s−1 using a Split Hopkinson Tension Bar (SHTB) apparatus. RPC dumbbell-shaped samples, including plain RPC and steel fiber-reinforced RPC (SFRPC) with 1 % and 2 % fiber volumetric fractions, were tested at high strain rates of 98–528 s−1. Based on the test results of this study and those derived from existing publications, the relationship between dynamic direct tensile properties, steel fiber fraction, and strain rate was quantitatively analyzed, and corresponding empirical formulae were proposed. To meet the demand for numerical analysis on RPC structures subjected to explosive forces, a dynamic tensile stress-strain model for steel fiber-reinforced RPC considering steel fiber, strain rate, and dynamic toughness, was established.

Experimental investigation on the influence of temperature on the fracture surface variations of granite after Brazilian splitting tests

Understanding the variation in the morphology of rock fracture surfaces after high-temperature is of great significance for evaluating the strength, deformation, and seepage characteristics of deep engineering rock masses. In this study, the variations in the granite fracture surface roughness after exposure to different temperatures (25–800 °C) were investigated, and the damage deterioration mechanism was revealed. The results showed that the maximum fluctuation (Z) and root mean square of the first derivative (Z2) of the granite fracture surface tended to increase with increasing temperature, whereas the fractal dimension (D) decreased, suggesting that the higher temperature contributed to greater roughness of the fracture surface. The anisotropy of the fracture surface was more evident at higher temperatures and had greater roughness in the 45°–75°, 105°–135°, and 155°–170° directions after different temperatures. Physicochemical reactions, such as dehydration, quartz phase transformation, and mineral oxidation, occurred in the granite owing to high temperatures. These reactions changed the crystalline state of the minerals and facilitated the increase and expansion of microcracks, thereby weakening the cementing property between mineral particles. Fracture surfaces with higher roughness were formed after tensile failure of the rock. The research results may provide theoretical references for the construction and operation of deep engineering.

Classification of Vascular Dementia on magnetic resonance imaging using deep learning architectures

Vascular Dementia is a severe disease that results from dead nerve cells’ accumulation in blood vessels. This affects the blood flow and impairs memory and decision-making abilities. Machine learning and deep learning have been used in detecting this disease. Nevertheless, their accuracy has been inconsistent, explaining why their utilization in diagnosing patients has led to poor performance. We developed several transfer learning architectures that improve classification accuracy and diagnosis performance in assessing vascular dementia. The process first entails the preprocessing of the dataset where a random selection ensures data representation is balanced. We used a dataset containing resting-state fMRI scans to split training, testing, and validation into 80%, 10%, and 10%. We employ different Convolutional Neural Network architectures such as VGG16, VGG19, DenseNet121, and InceptionResNetV2 to enhance classification. To, enhance these, we incorporated Rectified Linear Unit and leaky activation functions for the training phase to counteract problems associated with vanishing gradient common in deep learning tasks. Our methodology ensures effective information flow throughout different layers, which is essential for a divergent information hierarchy in medical information. As such, the specifics show that our approach achieved 84.67% in accuracy in the multi-classification, which is better than the current state-of-the-art research in the same field. Therefore, the result shows that transfer learning-based approaches are suitable when combined with strategic pre-processing and activation functions in improving the diagnosis of vascular dementia using MRI images.

Influences of bedding angle and soaking time on the mechanical behaviour of silty mudstone: laboratory testing and theoretical modelling

Silty mudstone is highly susceptible to the influence of hot and humid environments, leading to the deterioration of its mechanical properties presenting a geohazard and even resulting in geological disasters. Accurately characterizing the effects of bedding and water–rock interaction on the mechanical behaviour of silty mudstone is a crucial prerequisite for the protection and reinforcement of silty mudstone slopes. To this end, uniaxial compression tests and Brazilian splitting tests were conducted to examine the mechanical properties of bedded silty mudstone. Based on the test results, the effects of bedding angle and soaking time on mechanical properties such as tensile strength, uniaxial compressive strength and elastic modulus of bedded silty mudstone were revealed. The test results showed that the tensile strength increased exponentially with increasing bedding angle. The observed split failure patterns of bedded silty mudstone encompassed splitting–pulling damage, shear damage and splitting damage. The uniaxial compressive strength of silty mudstone exhibited a U-shaped variation with an increase in bedding angle. The specimen with a bedding angle of 45° had the lowest uniaxial compressive strength at 7.64 MPa. Furthermore, the elastic modulus of silty mudstone was positively correlated with the bedding angle. The failure patterns of bedded silty mudstone under uniaxial compression included splitting-tension damage, shear-slip damage and splitting-shear damage. The saturated tensile strength, uniaxial compressive strength and elastic modulus of bedded silty mudstone exhibited an exponential decrease with increasing soaking time. The test data confirmed the applicability of the Jaeger equation to the uniaxial compressive strength of bedded silty mudstone. Subsequently, a modified Hoek–Brown failure criterion was derived by combining fracture mechanics theory and test results and introducing a softening factor. The parameters A , D and m in the above failure criterion decreased exponentially with increasing soaking time and an empirical Hoek–Brown failure criterion considering the soaking time was established. Compared with previous theoretical models, this model is more adaptable to the actual engineering situation, which results in more accurate calculations.

Study on Static Mechanical Properties and Numerical Simulation of Coral Aggregate Seawater Shotcrete with Reasonable Mix Proportion

This study aims to explore the static mechanical characteristics of coral aggregate seawater shotcrete (CASS) using an appropriate mix proportion. The orthogonal experiments consisting of four-factor and three-level were conducted to explore an optimal mix proportion of CASS. On a macro-scale, quasi-static compression and splitting tests of CASS with optimal mix proportion at various curing ages employed a combination of acoustic emission (AE) and digital image correlation (DIC) techniques were carried out using an electro-hydraulic servo-controlled test machine. A comparative analysis of static mechanical properties at different curing ages was conducted between the CASS and ordinary aggregate seawater shotcrete (OASS). On a micro-scale, the numerical specimens based on particle flow code (PFC) were subjected to multi-level microcracks division for quantitive analysis of the failure mechanism of specimens. The results show that the optimal mix proportion of CASS consists of 700 kg/m3 of cementitious materials content, a water–binder ratio of 0.45, a sand ratio of 60%, and a dosage of 8% for the accelerator amount. The tensile failure is the primary failure mechanism under uniaxial compression and Brazilian splitting, and the specimens will be closer to the brittle material with increased curing age. The Brazilian splitting failure caused by the arc-shaped main crack initiates from the loading points and propagates along the loading line to the center. Compared with OASS, the CASS has an approximately equal early and low later strength mainly because of the minerals’ filling or unfilling effect on coral pores. The rate of increase in CASS is swifter during the initial strength phase and decelerates during the subsequent stages of strength development. The failure in CASS is experienced primarily within the cement mortar and bonding surface between the cement mortar and aggregate.