Increase In Compressive Strength Research Articles

Performance and failure modes of continuous fibre-reinforced energy absorption tubes by cylindrical layered 3D printing

ABSTRACT Precisely controlling the distribution of continuous fibres on a cylindrical surface is crucial for manufacturing high-performance continuous fibre-reinforced composite (CFRC) tubular structures. Existing manufacturing processes are complex, hindering the regulation of fibre orientation and content. Therefore, this study achieved unrestricted control of 3D-printed continuous fibres in terms of content and arbitrary orientation on a cylindrical surface using a cylindrical layered path planning strategy. The study investigated the impact of different fibre orientations and printing parameters on the compressive performance and energy absorption of 3D-printed CFRC tubes under quasi-static axial compression by analysing fibre distribution and failure modes. Compared to the flat layered printing strategy, the cylindrical layered printing strategy showed significant increases in compressive strength and energy absorption, by 44.3% and 85.2%, respectively. A cusp height analysis model demonstrated that the cylindrical layered printing strategy significantly enhances forming accuracy compared to the conventional flat layered method. The CFRC lightweight energy absorption tubes fabricated with this strategy demonstrated the viability of the manufacturing process. This new manufacturing technology has significant potential for producing high-performance and high-precision CFRC energy absorption tubes, applicable in aeronautics and astronautics.

Compressive stress-strain relationship of steam free reactive powder concrete at ultra-low temperatures

To explore the applicability of reactive powder concrete (RPC) as a material for LNG storage tanks, the mechanical properties of RPC at ultra-low temperatures were investigate in this paper. Forty-two axial compressive strength tests were conducted on RPC prisms at 20 °C ∼ −165 °C. The influence of temperature and steel fiber on the compressive stress-strain relationship of RPC at ultra-low temperatures was evaluated. The results showed that the axial compressive strength of RPC increases at low temperatures, with a compressive strength increase of over 70 % at −165 °C compared to room temperature. The increase in compressive strength of RPC at ultra-low temperatures is significantly greater than that of ordinary concrete. A relation for predicting the axial compressive strength development of RPC at ultra-low temperatures was also proposed. Steel fibers can increase the toughness of RPC at ultra-low temperatures to a certain extent, and effectively improve the failure mode of RPC, allowing the damaged RPC to maintain its integrity. This work provides a basis for RPC applicability as LNG storage tanks.

Research on the Performance of Steel Strand-Reinforced Reactive Powder Concrete with Mixed Steel Fibers and Basalt Fibers under the Salt Dry–Wet Erosion

In this study, the properties of steel strand-reinforced reactive powder concrete (RPC) with mixed steel fibers and basalt fibers were investigated. The volume ratios of steel fibers and basalt fibers ranged from 0% to 2%. The reinforcement ratio of steel strands was 1%. The flexural strength and toughness were measured. Moreover, the impact toughness was determined. The studies were carried out under an erosion environment with chlorides and sulfates. The electrical resistance and the ultrasonic velocity were obtained to assess the salt corrosion resistance performance of steel strand-reinforced RPC. The results show that the addition of basalt fibers and steel fibers can improve the mechanical strength, ultrasonic velocity, flexural toughness, and impact toughness and decrease the performance degradation of the steel strand-reinforced RPC under the conditions of dry–wet alternations of NaCl and Na2SO4 solutions. Basalt fibers and steel fibers can improve the steel strand-reinforced RPC’s flexural strength by rates of up to 13.1% and 28.7%, respectively. Moreover, the corresponding compressive strength increases by 10.3% and 18.3%. The flexural strength decreases by 11.2~33.6% and 7.3~22.7% after exposure to the NaCl and Na2SO4 dry–wet alternations. Meanwhile, the corresponding compressive strength decreases by 22.1~38.9% and 14.6~41.3%. The electrical resistance increases with the addition of basalt fibers and decreases with the increasing dosages of steel fibers. The steel strand-reinforced RPC with the assembly units of 1% steel fibers and 1% basalt fibers shows the optimal mechanical properties and salt resistance considering its wet–dry alternation performance. The properties of steel strand-reinforced RPC decrease more rapidly after undergoing NaCl erosion than Na2SO4 erosion.

Research on the preparation of eco-economical ultra-high performance concrete utilizing graphite tailings resources

Ultra-High Performance Concrete (UHPC) employs river sand as its primary aggregate due to the absence of coarse aggregates, resulting in high production costs and significant ecological impacts, limiting its broader application. To mitigate these challenges, this research investigates the substitution of river sand with industrial waste graphite tailings (GT) in UHPC production. Experimental evaluations assessed changes in wet packing density, workability, mechanical properties, resistance to chloride ion penetration, and heavy metal leaching at various graphite tailings replacement rates (0 %, 25 %, 50 %, 75 %, and 100 %). The microstructural properties of UHPC were analyzed using techniques such as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), Mercury Intrusion Porosimetry (MIP), and Scanning Electron Microscopy (SEM). Results indicate that increasing the replacement rate of graphite tailings leads to a gradual decrease in UHPC workability. At a 50 % replacement rate, graphite tailings enhance the wet packing density, contributing to a 7.33 % increase in the 28-day compressive strength. Additionally, graphite tailings can decrease the carbon emissions associated with unit compressive strength by up to 6.96 % and reduce production costs by 20 %. The inclusion of graphite tailings also improves the resistance of UHPC to chloride ion penetration and reduces the leaching of heavy metal ions from the tailings. Microstructural analyses indicate that graphite tailings promote hydration reactions in UHPC without altering the types of hydration products. Additionally, these tailings improve the pore structure of the composite. This study investigates the feasibility of using graphite tailings as a substitute for river sand in the production of UHPC, providing foundational insights for subsequent studies focused on optimizing eco-friendly UHPC formulations that incorporate graphite tailings.

Mechanical properties of Al–Si alloy/Si3N4 interpenetrating phase composite based on a preform fabricated at 1200 °C

Interpenetrating phase composites with three-dimensional co-continuous architecture are promising materials for advanced structural applications due to their excellent combination of properties. In this work, a novel and low-cost Al–Si alloy/Si3N4 IPC was fabricated via squeeze infiltration of Al11Si alloy melt into a porous Si3N4 preform manufactured at a low temperature of 1200 °C using H3PO4 as pore-former and binder. Microstructures of IPC show a good infiltration quality and strong interfacial bonding between metal and ceramic phases without any intermediate reaction products. The fabricated IPC exhibited significantly higher specific hardness and stiffness than the Al11Si alloy. Moreover, an excellent damage tolerance, a substantial increase in compressive strength of 420 %, flexural strength of 168 %, and a significant reduction in wear rate of 95 % in the IPC was achieved with respect to Al11Si. The flexural strength and fracture toughness values of the fabricated IPC compare well to values of Al alloy/Si3N4 IPCs reported in the literature, despite being processed using a porous Si3N4 preform fabricated at a much lower temperature.

Developing an eco-friendly cementitious grout using paper sludge ash and steel fiber recovered from waste tires

Cement is the most important component in cementitious grout production,andtt accounts for 7% of global greenhouse gas emissions. Reducing the amount of cement used in infrastructure and buildings is a desirable way to lower the total carbon footprint associated with grout production. relatedly, developments in manufacturing and transportation lead to the production of cars in large numbers, which in turn leads to an increase in the production of byproduct waste like waste tires, which are thrown away directly without recycling. Thus, this study aims to develop a novel sustainable grout by recycling paper sludge ash waste (PSA) and waste steel fiber (WSF) as partial cement replacements. This will help reduce grout production costs, minimize environmental pollution during cement production, and enhance landfill and waste management. The Grout mixtures used in this paper were prepared using ordinary Portland cement (OPC), WSF extracted from vehicle tires, PSA, and water. Different proportions of WSF(0, 1, 2, 3%) and PSA(5, 10%) were used in the weight of cement in designing sustainable grout. The mechanical properties of the sustainable grout were evaluated by examining extensive tests including flow tables, compressive strength, and flexural strength. The results showed that partially replacing the cement with 3% WSF and 1% WSP with 5% PSA resulted in a significant improvement in workability ,as well as a clear increase in compressive and flexural strength at an early age compared to the reference mixture.

Engineering properties optimization of dispersive soil by calcium silicate waste—The role of steel-making slag

Steel slag (SS) is a byproduct that comes from the production of crude steel in alkaline oxidation furnaces. Resource utilization of steel slag, a calcium-silicon solid waste, is an urgent problem. This paper investigates a solid waste disposal method that applies different steel slag contents to modify dispersive soil. The engineering properties and modification mechanisms of dispersive soil specimens are studied and revealed by performing microstructure, mineral evolution, unconfined compressive strength (UCS), and tensile strength analysis. The pinhole test, mud ball crumb test (BCT), and mud cube crumb test (CCT) were carried out to determine the dispersivity of the soil specimens. Results show that when the steel slag content increases from 1% to 10%, the unconfined compressive strength and tensile strength increase by 176.05% and 75.40%, respectively. For soil specimens without curing time under 50 mm water head, the weight loss of the specimen with 10% steel slag content decreases by 72.03% compared to specimens with 1% steel slag content. Microstructural and mineralogical analyses indicate that the hydration reaction of steel slag changes the ionic composition of the soil and generates reaction products with effects such as filling and connection. To sum up, steel slag effectively improves water stability and mechanical properties of dispersive soil.

Experimental Study on the Effect of Environmental Water on the Mechanical Properties and Deterioration Process of Underground Engineering Masonry Mortar

Urban underground engineering is generally buried at a shallow depth and suffers long-term environmental water effects such as rainfall, rivers, underground pipeline leakage, and groundwater. The mechanical properties of the structures are affected by constant deterioration, which seriously hinders the safe, healthy, and sustainable development of the city. On the basis of on-site investigation of civil defense engineering, this article simulates the water environment conditions of mortar in underground engineering in the laboratory and conducts manual sample preparation in the laboratory. Then, water, H2CO3, NaCl, and Na2CO3 solution or wet–dry cycles are used to corrode the sample, respectively. A uniaxial compression test, Brazilian splitting test, analyses of the acoustic emission signals and electromagnetic signals, and magnetic imaging testing are performed, respectively. The results show that an increase in the action time of environmental water leads to a gradual increase in the uniaxial compressive strength, tensile strength, and elastic modulus of cement mortar, but it will decrease over a long period of time. Different environmental water components can also lead to a different performance of soaked mortar. The uniaxial compressive strength R, tensile strength σt, and elastic modulus E of mortar samples exhibit values in different solutions in the order of H2CO3 solution < NaCl solution < Na2CO3 solution < water. A moderate solution soak time can enhance the mechanical properties of the mortar, but this effect decreases at long time scales. The effect of wet–dry cycles on the mechanical properties and degradation process of mortar is significant. With the increase in wet–dry cycles, the porosity of mortar continuously increases. The cumulative ringing count, energy, amplitude, and impact number of acoustic emission signals always increase when the samples are loaded to failure. The uniaxial compressive strength, tensile strength, and elastic modulus first increase and then decrease. The experimental results lay the foundation for further investigating the performance changes in mortar under complex water environments in underground engineering.

A comprehensive investigation on the effect of SiCp on microstructure and mechanical properties of Mg–5Sb-based hybrid composites

Microstructural development, strengthening mechanisms, and mechanical properties of the newly developed Mg–5Sb-xSiCp (x = 0, 1, 3, and 5) composites were studied in both as-cast and extruded states. The microstructures of composites were composed of α-Mg, in-situ Mg3Sb2, and SiCp phases. The cooling curves display that Mg3Sb2 intermetallics form as the primary phase. During solidification, the SiCp acts as heterogeneous sites for both α-Mg and intermetallics formation. The increase in SiCp content (from 0 % to 5 %) modified the as-cast grain size from 827 μm to 411 μm with the improvement of yield strength (YS) (74–97 MPa). Also, the SiC addition to as-cast facilitates the formation of a randomized texture and a significant reduction in intensity from 13.121 mrd to 6.301 mrd for SiC-Free and 5 wt% added MMCs, respectively. Grain refining and recrystallization are characterized by electron backscatter diffraction (EBSD) analysis. Grain refinement via SiCp and hot extrusion leads to substantial structural refinement, resulting in a decrease in grain size from about 411 μm down to 3.92 μm for MMC with 5 wt% of SiC. Consequently, the best combination of the ultimate tensile strength (UTS) (∼244 MPa) and total elongation (∼8.9 %) was obtained for the hot extruded composite containing 3 wt% SiCp. The prevailing strengthening mechanisms are supposed to be particle strengthening mechanism in the as-cast condition and coefficient of thermal expansion (CTE), Orowan, and Hall-Petch mechanisms in the as-extruded condition. Obviously, adding SiCp and employing hot working lead to significant increase in ultimate compressive strength (from 180 MPa to 321 MPa for 5 wt%).

Physico-mechanical, structural, and mineralogical analysis of composite concrete incorporating hydraulic lime and pozzolan

This study investigates alternatives to Portland cement (PC) through the utilization of pozzolanic materials like natural hydraulic lime and pozzolan in mortar and concrete production, offering both environmental and economic advantages. Natural hydraulic lime is particularly esteemed for its relevance in restoring architectural relics and preserving cultural heritage, while the incorporation of pozzolan and fine and coarse aggregates adds value to local resources. The study employs a range of comprehensive characterization techniques, including physico-chemical, mineralogical, and mechanical analyses such as X-ray fluorescence, particle size assessment, bulk density evaluation, shrinkage testing, water absorption analysis, X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and Proctor Normal and compressive strength tests, among others. Five different formulations, varying from 20 % to 40 % hydraulic lime content and a fixed 25.00 % pozzolan content, underwent testing across five curing periods (7, 14, 28, and 90 days). The results underscore the significant influence of curing time and hydraulic lime proportion on the physical, mineralogical, and mechanical characteristics of lime concrete. Scanning electron microscopy reveals a well-structured matrix in samples from various formulations, credited to effective void filling by lime and pozzolan. Furthermore, the identification of C-S-H phases through X-ray diffraction analysis enhances the concrete matrix, leading to a notable increase in compressive strength of up to 22.00 MPa. Water absorption rises with curing time due to the air curing process, fostering the formation of minor surface pores. This research assesses the environmental impact of hydraulic lime concrete across its lifecycle, underscoring the potential of pozzolans and natural hydraulic lime to produce locally-sourced, economical, and environmentally friendly construction materials, thereby contributing to global efforts in reducing carbon emissions.

Exploring engineering properties of sustainable multi‐grade concrete: Materials, structural, and environmental aspects

AbstractThrough experimental and theoretical studies, this research explores the materials, structural, and environmental aspects of multi‐grade concrete (MGC), a potentially sustainable structural concrete. The experimental part investigates the compressive, split cylinder, flexural, and shear strengths of MGC, essential parameters for the design of structural members composed of MGC. It also provides the relationships between various strengths. The compressive behavior is correlated with the cracking pattern and the confinement effect caused by the end platens. The theoretical study involves determining the carbon emissions (CEs) and modifying ASTM/ACI expressions for the flexural tensile strength (FTS) and shear capacity applicable to MGC. Three uni‐grade concretes (UGCs) with distinct materials, properties, and grades: grade 17 (G17), grade 25 (G25), and grade 30 (G30), were poured in layers of varied thicknesses to make two variants of MGC. Experimental investigations showed that the higher‐strength concrete (HSC) confined the lower‐strength concrete (LSC) part thus increasing the compressive strength. Replacing 50% of LSC with HSC led to an increase in compressive and shear strengths by 21% and 40%, respectively. The shear strength values of reinforced MGC beams observed experimentally are aligned with those obtained through the modified expressions developed by the authors. A trade‐off analysis among the strengths, CEs, and costs of UGC and MGC can aid in selecting MGC customized to specific requirements, thereby contributing to the development of sustainable structural concrete.

Intelligent design and seawater mixing performance of new synchronous grouting materials in a pure-solid-waste framework

Solid waste, as a reliable raw material substitute for synchronous grouting materials in shield tunneling, addresses the issue of recycling traditional waste. Additionally, geopolymer slurries utilizing waste exhibit excellent physical and chemical properties, meeting requirements for the stability and long-term performance of synchronous grouting materials. In this study, an environmentally friendly polymer grouting material based on pure solid waste was developed using sunflower stalk ash, blast furnace slag, and fly ash as raw materials. By varying the proportions of binder materials and quantity of seawater introduced, we systematically analyzed the applicability of grouting materials and reliability of seawater as a mixing medium in a comprehensive solid waste framework. We utilized an artificial intelligence integrated algorithm to predict the compressive strengths of cementitious materials with different ratios through forward performance prediction. The proportions were then inverted using a simulated annealing algorithm according to the strength required for actual engineering applications. The results demonstrated that under the dual effects of sunflower stalk ash alkalinity and seawater composite salts, more active Si and Al ions were released during the hydration process. The solid waste filling and accelerating effects of composite salt hydration can effectively improve the pore structure, resulting in a significant increase in early compressive strength. The artificial intelligence ensemble algorithm proved to be an effective model for predicting compressive strength and the simulated annealing algorithm successfully determined the optimal ratios for meeting practical production requirements. These findings provide a foundation for solid waste treatment and underground engineering using seawater resources, contribute to the preparation of high-performance slurries, and facilitate green development.

Determination of carbonation depth and pH in concrete containing crystalline waterproofing agents using the endoscopic method

The monitoring of the carbonation process plays a key role in monitoring the health of reinforced concrete structures. In this study, the carbonation depth of concrete was measured using image processing and endoscopic methods, which relied on the pH level of the concrete containing crystalline waterproofing material. The results show that the carbonation depth and pH of the concrete were estimated by the nondestructive endoscopic method-based graphical user interface, with a high accuracy of 0.99. Furthermore, it was observed that crystalline waterproofing material increased the carbonation depth of concrete. Due to the lack of direct contact between the water molecules and the Na2O, the crystalline structure could not form sufficiently to prevent CO2 penetration. This phenomenon caused porosity in the mortar, a decrease in the velocity of the ultrasonic sound, and thus a loss of strength. However, a slight increase in compressive strength after carbonation was attributed to the sodium bicarbonate filling in the voids as a result of the reactions between Na2O, water molecules, and CO2.

Synthesis and characterization of TiNbZrMo medium-entropy bio-composites: Microstructure, mechanical properties, and in vitro degradation.

This study reports the synthesis and characterization of hydroxyapatite (HA)-based bio-composites reinforced with varying amounts (by weight, 1-15 wt.%) of bio-medium entropy alloy (BioMEA) for load-bearing implant applications. BioMEA powders consisting of Ti, Nb, Zr, and Mo were mechanically alloyed for 100 h and subsequently added to HA using powder metallurgy techniques. To show the effect of BioMEA, the microstructure, density, and mechanical tests have been conducted and the synthesized BioMEA was characterized by scanning electron microscope (SEM), x-ray diffractometer (XRD), and Fourier-transform infrared spectroscopy (FTIR) analysis. In addition, in vitro degradation behavior and bioactivity analyses of bio-composites have been conducted. XRD analysis revealed the formation of BioMEA after 20 h of mechanical alloying. The highest density value of 2.47 g/cm3 was found in 15 wt.% BioMEA-reinforced bio-composite. The addition of BioMEA reinforcement led to a significant increase in hardness and tensile strength values, with the highest values observed at 15 wt.% reinforcement. Compression tests demonstrated a significant increase in compressive strength and deformation capability of the bio-composites with the highest values observed at 15 wt.% BioMEA addition. The highest toughness of 7.68 kJ/m2 was measured in 10 wt.% MEA-reinforced bio-composites. The produced bio-composite materials have an elastic modulus between 3.5-5.5 GPa, which may provide a solution to the stress shielding problems caused by the high elastic modulus of metallic implant materials. The most severe degradation occurred in 15 wt.% MEA-reinforced bio-composites, and the effect of degradation caused a decrease in Ca and an increase in Ti-Ni-Zr-Mo in all bio-composites. These findings suggest that HA/BioMEA bio-composites have the potential to be developed as advanced biomaterials with moderate mechanical and biological properties for load-bearing implant applications.

Graphite-enhanced foam cement-based materials: Mechanical properties, pore structure and electromagnetic wave absorption performance

To reduce the environmental pollution caused by electromagnetic waves (EMW), graphite-enhanced foam cement-based electromagnetic wave-absorbing materials were prepared. The effects of hydration products and pore structure on the mechanical strength and microstructure have been investigated. The results show that at a graphite content of 10 wt%, resulting in a reduction in pore size and concentration within 400μm. This led to improved material compactness, resulting in an increase in compressive strength of 32.01 % and 29.13 % for 3-day and 28-day foamed concrete, along with a 35.40 % and 29.27 % increase in flexural strength. For the 10 mm thick foamed concrete, the reflection loss is −24.08 dB with an effective absorption bandwidth of 0.466 GHz (3.762–4.228 GHz). The impedance matching increased by 129 %, moving from 8.3 to 10 mm up range to 6.1–10 mm, while the frequency range increased by 61.35 %, moving from 3.37 to 5 GHz up range to 2.37–5 GHz, compared to the control group.

Exploring enhanced high-temperature resistance: Analyzing the combined impact of fibers and nanoparticles in mortars

This study aims to explore the potential synergistic effect of polypropylene (PP) fiber and different types of nanoparticles to improve the high-temperature resistance of cementitious materials. For that, mortar samples with different PP fiber percentages, 0.6 wt% and 1.2 wt%, were produced. Different percentages of both colloidal nano-silica (CNS), 0.3 %, 0.6 %, and 0.9 %, and nano calcium carbonate (NCC), 0.5 %, 1 %, and 2 %, were used in the study. To test the resistance to elevated temperatures, mortar samples were exposed to different peak temperatures of 300°C, 600°C, and 900°C for 2 h, using unexposed samples as reference. Flexural and compressive strength, water absorption, surface electrical resistivity, and thermogravimetric analysis (TGA) of the heated and unheated samples were conducted. Results showed that, at 300°C heating regime, all samples with 0.6 % PP fiber exhibited an increase in flexural and compressive strength compared to their corresponding reference samples. For instance, specimens containing 0.6 % PP fiber and 2 % NCC content exhibited a 19 % increase in flexural strength compared to the unheated sample, whereas samples with 0.6 % PP fiber and 0.5 % NCC increased 32 % their compressive strength. In contrast, at 600°C, there was a major decline in mechanical properties in all samples, with samples containing NCC exhibiting the lowest amount (average of 61 % reduction in flexural strength and 32 % decrease in compressive strength). In general, a higher dosage of nanoparticles and lower PP fiber content will be better to resist temperatures up to 600 °C.

Strength Indicators of Fiber Reinforced Concrete with Carbon Nanomaterials

Concrete composites with low defects, dense and homogeneous, with a high degree of adhesion between the cement matrix and aggregates, as well as a high ratio between static tensile and compressive strengths and plasticity have the best crack resistance characteristics. This ratio increases in the case of the use of fiber-reinforced concrete. Modern research in nanotechnology focuses on the management of matter at the nanoscale level, which makes it possible to create materials with new properties. Due to the high aspect ratio, flexibility, high strength and rigidity, carbon nanotubes (CNTs) exhibit reinforcing properties. Due to their nanoscale features, CNTs interact with a complex network of calcium-silicate-hydrate binder (C – S – H), contribute to a decrease in porosity and compaction of the cement stone structure, increase the shear forces of matrix adhesion in the contact zone. Thus, there are all prerequisites to assert that fiber concrete with a cement matrix modified with carbon nanotubes will have the required high strength characteristics and crack resistance due to multilevel dispersed reinforcement and the efficient operation of fiber in a nanomodified concrete matrix. This article presents the results of testing samples made of cement stone, concrete and fiber concrete with carbon nanotubes. The presence of carbon nanotubes in cement stone contributes to an increase in compressive strength by 11 %, tensile strength during bending by 20 %. The test results of samples made of reinforced fiber concrete modified with nanocarbon materials have shown an increase in tensile strength during bending up to 109 %, tensile strength during splitting up to 82 %, axial tensile strength up to 78 %.

Suitability of using areca nut fiber as reinforcing material in compressed stabilized earth blocks (CSEB) for low-cost housing

An economical and cost-effective replacement for conventional building materials is Compressed Stabilized Earth Block (CSEB). However, they are vulnerable to erosion and cracking, particularly in humid settings. The use of natural fibers as reinforcement is found effective in overcoming this problem. Areca nut fiber which is a complete waste material in countries like Bangladesh and India is also a sturdy, adaptable, and water-resistant natural fiber that makes it the perfect choice as fiber reinforcement material for CSEBs. In this article, the strength performance analysis of areca nut fiber as a reinforcement material for CSEBs is investigated, where 0%, 0.85%, 2%, 5%, and 8% of areca nut fiber is mixed with soil that is stabilized with 10% cement. CSEB specimens of 4″ × 4″ × 4″ size have been made and tested for compressive strength, tensile strength, bulk density, and water absorption. It is observed that there is an 83.76% increase in compressive strength and an 8.89% increase in splitting tensile strength for 0.85% of areca nut fiber content specimen cured for 90 days. The water absorption was found a minimum of 9.07% for 0.85% areca nut fiber content and the minimum density of the block was observed at 1810 kg/m3 for the optimum percentage of 0.85% mix. The study indicates that using 0.85% of areca nut fiber content in stabilized CSEB shows a significant improvement in the strength characteristics of compressed stabilized earth blocks.Graphical

Mechanically suitable and osteoinductive 3D-printed composite scaffolds with hydroxyapatite nanoparticles having diverse morphologies for bone tissue engineering.

The challenge of integrating hydroxyapatite nanoparticles (nHAp) with polymers is hindered by the conflict between the hydrophilic and hygroscopic properties of nHAp and the hydrophobic properties of polymers. This conflict particularly affects the materials when calcium phosphates, including nHAp, are used as a filler in composites in thermal processing applications such as 3D printing with fused filament fabrication (FFF). To overcome this, we propose a one-step surface modification of nHAp with calcium stearate monolayer. Moreover, to build the scaffold with suitable mechanical strength, we tested the addition of nHAp with diverse morphology-spherical, plate- and rod-like nanoparticles. Our analysis showed that the composite of polycaprolactone (PCL) reinforced with nHAp with rod and plate morphologies modified with calcium stearate monolayer exhibited a significant increase in compressive strength. However, composites with spherical nHAp added to PCL showed a significant reduction in compressive modulus and compressive strength, but both parameters were within the applicability range of hard tissue scaffolds. None of the tested composite scaffolds showed cytotoxicity in L929 murine fibroblasts or MG-63 human osteoblast-like cells, supporting the proliferation of the latter. Additionally, PCL/nHAp scaffolds reinforced with spherical nHAp caused osteoactivation of bone marrow human mesenchymal stem cells, as indicated by alkaline phosphatase activity and COL1, RUNX2, and BGLAP expression. These results suggest that the calcium stearate monolayer on the surface of the nHAp particles allows the production of polymer/nHAp composites suitable for hard tissue engineering and personalized implant production in 3D printing using the FFF technique.

Study on the influence of rock bridge angle on the size effect of rock uniaxial compression.

As a basic parameter of rock, the rock bridge angle plays an important role in maintaining the stability of rock masses. To study the size effect of rock bridge angle on the uniaxial compressive strength of rocks, this paper adopts the principle of regression analysis and combines numerical simulation to carry out relevant research. The research results indicate that: (1) the uniaxial compressive strength decreases with the increase of the rock bridge angle, showing a power function relationship; (2) The uniaxial compressive strength decreases with the increase of rock size and tends to stabilize when the rock size is greater than 350 mm, showing a significant size effect. (3) The fluctuation coefficient of compressive strength increases with the increase of rock bridge angle and decreases with the increase of rock size; When the rock size is 350 mm, the fluctuation coefficient is less than 5%; (4) The characteristic compressive strength and characteristic size both increase with the increase of the rock bridge angle.