MPa Compressive Strength Research Articles

Mechanical and electrothermal properties of lightweight graphite/geopolymer composites

AbstractGraphite/geopolymer composite is a promising smart material that can be used in various applications. This paper reports the design of strong self‐heating graphite/geopolymer composites with high graphite percentages up to 120 wt% of metakaolin. The physical, mechanical, electrical, and electrothermal performance of composites were investigated; the compressive strength was tested at various ages and the electrothermal performance was tested using AC and DC voltages. The results showed that a compromise between high compressive strength and high electrothermal conversion can be achieved when a specific balance between the percentage of the graphite and the water content is established. The current study specified the reason for the deterioration of the electrothermal performance of the graphite/geopolymer composites, that is, the formation of a barrier layer between the electrode and the sample surface; it has been found that this can be avoided by removing the free ions from the geopolymer via washing. A composite with 47 ± 1 MPa compressive strength and stable electrothermal performance of 98°C at 6 DC volts can be prepared using 90 wt% graphite and 57 mL water content. This work is a step in the future innovation of smart construction using self‐heating and antifreezing construction materials.

Foamed calcium sulfoaluminate cement with controlled porous network for daily or seasonal heat storage in ettringite

Calcium sulfoaluminate (CSA) cement-based materials have high ettringite content enables heat storage, enhancing the thermal inertia of buildings. This study aims to optimize the porous network of foamed CSA material in terms of porosity, permeability and mechanical strength so that they can be effective in building applications as supporting structures with heat storage capacity. To achieve these goals, a foaming process method using hydrogen peroxide (H2O2) and surfactant was used to control the porous network. The H2O2 and surfactant contents varied from 0.5% to 1.2% and 0.01% to 0.05%, respectively, and generated a wide range of material densities from 589 to 1184 kg/m3 - and hence a wide range of properties in terms of porosity (43 - 70%), permeability (2.6 10-13 - 7.1 10-12 m2) and compressive strength (0.8 -9.4 MPa). Then, an abacus correlating material properties, found by surface fitting, linking porosity, gas permeability and compressive strength, allowed the material to be optimized in accordance with the needs of each building application. The CSA paste consisting of 1% H2O2 and 0.03% surfactant, with 66% porosity, 4.1 10-12 m2 permeability, and 1.8 MPa compressive strength, was the optimal mix-design for solar storage box applications (for short-term storage). The CSA paste consisting of 0.5% H2O2 and 0.01% surfactant, with 43% porosity, 5.6 10-13 m2 permeability, 9.4 MPa compressive strength, appeared to be optimal for self-supporting wall storing solar heat (long-term storage).

Effect of manufacturing route on microstructure and micromechanical properties of AlCoCrFeNi high entropy alloy

The manufacturing route of a particular metallic alloy profoundly affects its microstructure, as well as mechanical properties. In that respect, the present research investigates the microstructure and microstructure-dependent mechanical properties of the AlCoCrFeNi high entropy alloy (HEA), that was manufactured via two different routes: (i) Atmospheric plasma spraying (APS) in the form of coating on a stainless steel subtract and (ii) vacuum arc melting (VAM) in the form of bulk material. AlCoCrFeNi HEA coating microstructure is composed of a solid solution (Ni) as a matrix, which contains different phases, as well as intermetallics and defects, such as splat boundaries. On the contrary, the microstructure of bulk AlCoCrFeNi HEA alloy is free from any secondary phases, and is homogeneous in nature, which consists of only the solid solution of Ni. The experimental results show that the strength of the bulk HEA (963.14 ± 28.58MPa of yield strength and 1005.58 ± 22.08MPa of compressive strength) is better than that of HEA coating (yield strength of 802.33 ± 43.76MPa and compressive strength of 817.73 ± 43.84MPa). The phase, as well as splat boundaries in the microstructure, are the ‘weakest link’ in the HEA coating, that serves as defect initiation site. As the bulk HEA alloy is free from these ‘weakest link’, thus, deformation of the material is guided through plastic flow of materials, in the terms of the barrelling effect.

Harnessing iron tailings as supplementary cementitious materials in Limestone Calcined Clay Cement (LC3): An innovative approach towards sustainable construction

The increasing demand for sustainable construction materials has led to the exploration of iron tailings (ITs) as supplementary cementitious materials (SCMs) in Limestone Calcined Clay Cement (LC3). This study investigates the effects of varying ITs content in LC3 on compressive strength, microstructure, and environmental impact. Replacing 28 % of LC3 with ITs resulted in a 42 MPa compressive strength after 28 days, comparable to ordinary Portland cement (OPC), while reducing OPC content by 50 %. Microstructural analysis revealed that ITs contributed to the formation of additional C-(A)-S-H gel, enhancing the mechanical properties of the cement matrix. The findings also showed that concentrations of Zn (0.003–0.094 mg/L), Pb (0.002–0.090 mg/L), Cu (0.005–0.018 mg/L), Mn (0.115–0.712 mg/L), Ni (0.011–0.021 mg/L) in the leachates of LC3 containing ITs were below the critical limits for surface water and groundwater. Moreover, the life cycle assessment (LCA) demonstrated significant reductions in global warming potential (43.6 %), energy consumption (37.2 %), and cost (35.5 %). This study provides an innovative solution for waste utilization and environmentally friendly cement production.

Ti6Al4V Implants with Dense-Trabecular Bilayer Morphology for Bone Ingrowth: Synergy of Green Net Shaping and Sacrificial Templating.

Stress shielding in dental and orthopedic implants is a long-standing hurdle, and trabecular porous architecture to improve bone ingrowth is deemed to be a potential solution. Fabricating Ti6Al4V components with dense-porous bilayer structures is complicated with limited lab-scale and commercial success. Here, a green dough-forming technique with metal powders is successfully explored to develop heterogeneous structures with a monolith-like dense-porous interface. The porous region achieved 70% porosity with a 25 MPa compressive strength comparable to human cancellous bone. Due to its simplicity and versatility, this process is a promising solution for developing and mass-manufacturing customized designs for bone-related implants with improved bone ingrowth and osseointegration.

Performance-Based Design of Ferronickel Slag Alkali-Activated Concrete for High Thermal Load Applications.

This study aimed to develop optimized alkali-activated concrete using ferronickel slag for high-temperature applications, focusing on minimizing environmental impact while maintaining high compressive strength and slump. A response surface methodology, specifically the mixture design of experiments, was employed to optimize five components: water, FNS-based alkali-activated binder, and three aggregate sizes. Twenty concrete mixes were tested for slump and compressive strength before and after exposure to 600 °C for two hours. The optimal mix achieved 88 MPa compressive strength before heat exposure and 34 MPa after, with a slump of 140 mm. An upscaled version with improved workability (210 mm slump) maintained similar unheated strength but showed reduced post-heating strength (23.5 MPa). Replacing limestone with olivine aggregates in the upscaled mix resulted in 65 MPa unheated and 32 MPa post-heating strengths. Life Cycle Analysis revealed that the optimized ferronickel slag alkali-activated concrete's CO2 emissions were 77% lower than those of ordinary Portland cement concrete of equivalent strength. This approach demonstrated the applicability of mixture design of experiments as an alternative design methodology for alkali activated concrete, providing a valuable performance-based design tool to advance the application of alkali-activated concrete in the construction industry, where no prescriptive standards for alkali-activated ferronickel concrete mix design exist. The study concluded that the developed ferronickel slag alkali-activated concrete, obtained through a performance-based mixture design methodology, offers a promising, environmentally friendly alternative for high-strength, high-temperature applications in construction.

Investigating the Effect of Steel Wire and Carbon Black from Worn Out Tyre on the Strength of Concrete

Technology in concrete is rapidly developing to improve the quality and properties of concrete. One of the many recycled materials is worn-out tyres. Currently, the use of tires is very widespread considering the use of vehicles that increase from time to time. Piles of discarded tires can cause a lot of damage to the environment. So, by using steel wire waste (SWW) as new fiber reinforcement in concrete and with the combination with carbon black (CB), it is hoped that, by doing this, not only it could improve the quality of concrete, but also preserves the environment. Therefore, the objective of this research was, to identify the properties of fresh concrete with the addition of SWW and CB, and also to investigate the physical and mechanical properties of hardened concrete, incorporating of SWW as additional fiber reinforcement and CB. For fresh concrete, workability using a slump test was conducted. Several tests were carried out on the properties of hardened concrete. Among them were compressive strength, flexural strength, splitting tensile strength, and water absorption. The physical appearance of the concrete has also been examined and recorded. There are four batches of concrete which consist of one control batch and three batches of concrete with various weights of SWW which are in the portion of 300 g, 600 g, and 900 g, and the weight of CB is maintained at 300 g for all batches. For workability, all concrete batches with the addition of SWW and CB show acceptable workability. For the case of the density of fresh concrete, samples containing 900 g addition of SWW have the highest density which was 2520 kg/m³, as expected. Results for water absorption show that the lowest value is contributed by the control sample which was 7.6%. For compressive and flexural strength, 300 g addition of SWW has the highest value which was 28.52 MPa for compressive strength and 7.52 MPa for flexural strength. Lastly, for splitting tensile strength, the highest value was also obtained when 300 g addition of SW was added which was 5.4 MPa. To conclude, SWW and CB can be added to concrete to obtain comparable strength of concrete. However, some modifications could be made to both recycle materials to improve concrete performance.

Development of Regolith-Resin-Composite (RRC) Material for Lunar Construction

The feasible construction of lunar habitats will be strongly dependent upon the effective utilisation of resources locally available on the Moon. The Moon's surface material, otherwise known as regolith, is an obvious resource. There will, however, be the need to transport materials from Earth to be added to the regolith in order to make viable construction material. It is noted that material transported from Earth must be kept to a minimum. This paper reports the development of a potential lunar construction material that utilises regolith simulant in combination with epoxy resin (henceforth resin). The material is referred to as regolith-resin-composite (RRC), and the results of an experimental investigation are reported herein. Specific variables of the study include (i) minimum amount of resin required to achieve sufficient mixing and binding with the regolith and (ii) mechanical and analytical properties of a range of resin to regolith mix combinations. Mechanical tests consist of compressive, flexural, and tensile strength, while analytical tests comprise morphology, microstructure, and thermogravimetric analysis. It is shown that 15% by mass of resin produces a minimum viable material (based on the mix combinations considered in the study), while 20% resin content by mass produces the greatest mechanical strengths, such as 98 MPa compressive strength. The results presented in this study demonstrate that RRC has the potential to become a viable lunar construction material.

Recycled aggregate concrete using seawater: Optimizing concrete's sustainability

Concrete is the most widely used building material worldwide and causes huge carbon emissions, high water consumption and negative impacts on the environment. In this context, in order to reduce natural resources consumption and obtaining a “greener” concrete, the use of seawater and recycled aggregates becomes a promising option.In this study, the effect of the use of seawater in the composition and curing of concrete with natural aggregates (NA) and recycled aggregates (RA) applied at different ratios (0 %, 50 % and 100 %) on its mechanical and durability properties was evaluated. By applying structural equation modelling (SEM) with the R version 4.2.2, the dependence relationships between the variables were empirically evaluated.The analysis of the results has made it possible to establish the advantages and disadvantages of the manufacture of concrete with seawater and RA. It was found there is a need to increase the water/cement ratio in concrete made with seawater, the effective water/cement ratio was increased by 0.03 with respect to the control (in order to maintain workability constant) and that the use of seawater did not influence the mechanical properties of concrete made with NA. However, in concrete made with RA, the mechanical properties improved with the presence of seawater in the mixing, 39 MPa compressive strength at 28 days was obtained for concrete made with 50 % of RA. Durability properties were negatively affected by the presence of seawater and RA, with an increase in water absorption, shrinkage and carbonation depth. The seawater curing process did not influence the mechanical and durability properties of concrete.These results indicate that seawater alone does not influence the mechanical and durability properties of concrete. However, there the combined effect of seawater and RA improves the final characteristics of concrete.

Compressive Strength Analysis of Additively Manufactured Zirconia Honeycomb Sandwich Ceramic Parts with Different Cellular Structures

In this study, ZrO2 honeycomb sandwich structures with different cellular geometry were manufactured by SLA 3D-printing technology to analyze the compressive strength behaviour. After the printing procedure, the samples were sintered at 1450 °C for 2h. Among the samples with different cellular geometry, ZrO2 parts with circular cells were superior to that of square and triangular honeycomb structures and 1867±320 MPa compressive strength was obtained for this structure. The stress distributions in honeycomb structures were investigated using the COMSOL Multiphysics® for exposing the effect of cellular geometry on compressive strength. While more uniform stress distributions were seen on the inner wall of the circular honeycomb sample, the cellular structure of the square and triangle honeycomb samples mostly displayed compressive stress concentration on the joints of the honeycomb structure. Also, according to Rankine failure criterion, the parts with square cellular geometries were found to be more prone to failure. The highest specific compressive strength was obtained for the ZrO2 parts with circular cellular geometry. These findings demonstrated that the ZrO2 honeycomb sandwich structures with circular cellular geometry produced using SLA ceramic 3D-printing technology may be a suitable material to utilize in lightweight structural designs.

Nano-tentacled interconnected channels organic gel for rapid uranium extraction from seawater

Due to dwindling terrestrial uranium resources and escalating ecological pressures, the long-term viability of uranium supply has become a critical concern. The immense uranium reserves in seawater present a potential solution, yet extraction technology faces dual challenges of efficiency and adaptability to complex marine environments. Current interconnected porous adsorbents, despite their high flux properties, are limited by low specific surface area and weak mechanical strength, which constrain their effectiveness. Here, inspired by the unique hierarchical structures of marine organisms, we describe an organic gel adsorbent with supermacroporous and interconnected channels (10 ∼ 100 µm) adorned with "nano-tentacle" structures. This design significantly enhances the specific surface area by 18 times, increasing adsorption sites and imparting antibacterial properties. Notably, this adsorbent maintains structural integrity and superior mechanical strength (1.32 MPa tensile and 2.44 MPa compressive strength) even when fully saturated. During a 23-day trial in natural seawater, a uranium adsorption rate of 0.332 mg g⁻¹ day⁻¹ was achieved. This work offers a pioneering approach for the design and fabrication of hierarchical structured adsorbents, highlighting the immense potential of extracting uranium from seawater for sustainable energy production.

A comparative study of dynamic performance the shear-wall and bracing shapes on the tall building in seismic area

The solution to overcome earthquake loads in the seismic regions is to use resisting systems such as shear walls and braces. It can be used as an alternative design for resisting systems of tall buildings. The main purpose of this research is to compare the performance of tall buildings with resisting systems of partial shear walls and a variety of brace shapes in the seismic area of Malang City, Indonesia, by using the partial shear wall against braces of reinforced concrete in the shapes of V, inverted V (Ʌ) and X (on two floors). The mechanical properties of the materials utilized in the models are determined from laboratory testing results. They consist of 30 MPa compressive strength concrete, 250 MPa yield strength steel, and 410 MPa ultimate strength steel. To overcome the lack of bracing, position the braces on the outer side of the building and the number resisting. The several outputs reviewed are stiffness, displacement, drift, ductility, vibration period, and natural frequency. In this study, structural analysis using SAP 2000 v.20 software is used in the four models of the eight-story existing structure in Malang City. The results showed that the inverted V (Ʌ) reinforced concrete brace is the most suitable design as an alternative design for the building, compared to the partial shear wall and the other bracing shapes. The results of the study that in the X-direction the stiffness, displacement, drift, ductility, vibration period, and natural frequency respectively as follows 4.92865E+12 N/mm, 144.53 mm, 127.73 mm, 0.339, 1.12 s and 0.893 Hz. Whereas the displacement and drift in the Y-direction are 127.97 mm and 113.63mm. For practical implication, using a fully shear wall and the inverted V(Ʌ) brace creates a better performance of the structure in seismic areas.

Additive manufactured high-performance topology-optimized lattice structure: Compressive behavior and flow heat transfer characteristics

In this study, topological optimization techniques were employed to construct innovative TopS lattice structures, to achieve a lightweight design while simultaneously optimizing their mechanical properties and enhancing flow and heat transfer performance. Through model reconstruction and proportional scaling techniques, lightweight configurations with increased surface areas were achieved, leading to the successful fabrication of Ti-6Al-4V lattice structures via Laser Powder Bed Fusion (LPBF) technology. A comprehensive investigation combining numerical simulations and experimental testing revealed that the TopS-L16 lattice structure outperforms TopS-L1 and TopS-L4 in terms of compressive strength, demonstrating values of 386.00 MPa for compressive strength, 352.00 MPa for upper compressive yield strength, and 6938.00 MPa for elastic modulus. Furthermore, multilayer-filled lattice structures were found to effectively improve streamline distribution and vorticity, reducing boundary layers, which indicates a significant enhancement in fluid flow and heat transfer performance, with TopS-L16 exhibiting the best performance. The novelty of this work lies in its exploration of the interplay between lattice structures and their interactions with compressive deformation, energy absorption capabilities, and flow heat transfer.

Novel B4C supports for ceramic membrane filtration

Novel complex-shaped porous B4C supports were fabricated for use in ceramic membrane filtration applications, the processing of which is described in detail. Firstly, an extrudable ceramic paste was formulated and homogenised, containing a high content of B4C of super-coarse and ultrafine grades, plus water as liquid medium and various organic additives as thickener, binder, plasticiser, and lubricant. Secondly, tubular honeycomb parts (i.e., cylinders of ∼26 mm outer diameter with 30 inner channels of 3 mm diameter each) were extruded at ∼25 bar and dried in air at 120 °C for 24 h, resulting in robust green B4C membrane supports without macro- or micro-defects. Thirdly, suitable debinding conditions were identified by thermogravimetry of the paste and its components, and the dry membrane supports were debinded at 700 °C for 1.5 h in high vacuum (<0.1 Pa) confirming that they retain their shape with minimal isotropic shrinkage (∼0.13–0.15 %). And fourthly, the debinded membrane supports were pressureless sintered at 2000 °C for 3 h in inert atmosphere undergoing only an additional 1 % isotropic shrinkage, resulting in B4C membrane supports with low apparent density (∼0.89(1) g/cm3), high porosity (∼38–39 %), open interconnected micrometre pores (in the range ∼0.5–16 μm, and d50∼1.5 μm), and low skeletal density (∼2.455(1) g/cm3). Importantly, their only partial densification makes them both sufficiently strong mechanically (∼68(2) MPa compressive strength) and highly permeable to water (∼13131(418) l/(m2·h·bar) permeability at ∼1.3 bar). These attributes, together with the intrinsic lightness and durability of B4C ceramics, make these novel supports in principle very appealing for ceramic membrane filtration and other applications.

Effects of soot and plastic fibers on the performance of SCC

Self-compacting concrete is regarded as one of the newest types of concrete due to its durability, efficiency, viscosity, stability, flowability, and resistance. Today, one of the most pressing environmental challenges is the disposal of solid waste, and one of the plastic materials discarded as waste after use is plastic packaging belts. These are made on the basis of polypropylene, as well as the factory Iron smelting mines are the main source of iron oxide waste production. Studies using recycled plastic fibers (30 mm × 0.3 mm) and waste iron oxide as cost-effective additives in self-compacting concrete (SCC) are presented. The effects on fresh and hardened properties were evaluated at various additive contents. Fresh and hardened properties of self-compacting concrete (SCC) were evaluated with and without fiber and iron oxide additives. Tests included workability (slump flow, funnel), strength (compressive, tensile), and durability (ultrasonic pulse speed, permeability). Experiments revealed that increasing the amount of recycled plastic fibers and waste iron oxide in self-compacting concrete (SCC) led to higher compressive and tensile strengths at both 7 and 28 days. These strength increases ranged from 2 to 9.68 MPa for compressive strength and 1.61–7.44 MPa for tensile strength, compared to the control specimen without additives.

Robust and exceptional thermal insulating alumina-silica aerogel composites reinforced by ultra IR-opacified ZrO2 nanofibers

Fiber-reinforced alumina-silica aerogel composites (FASA), renowned for their high-temperature resistance, low thermal conductivity, and robust mechanical properties, have emerged as a promising candidate for aerospace thermal insulation, especially in harsh environments characterized by intense vibration and oxidation. However, a significant challenge persists in homogeneously doping opacifiers and minimizing thermal conductivity of FASA at elevated temperature, which remains a thorny issue. Herein, we propose a novel fiber-reinforced and opacified (FRO) strategy to fabricate the ZrO2 fiber-reinforced alumina-silica aerogel composites (ZFASA) that boast ultra-low thermal conductivity (0.031 W·m−1·K−1 at 1100 °C) and excellent mechanical strength (0.44 MPa for compressive strength at 10 % strain and 2.1 MPa for bending strength, maintaining intact even after being rolled by a 1.7 t car). Furthermore, ZFASA exhibits remarkable thermal stability, enduring quartz lamp and butane torch tests at 1300 °C without any obvious change. This work provides a simple yet effective FRO strategy, paving a new path for the preparation of thermal insulating aerogel composites. Consequently, the highly durable and exceptional thermally insulating ZFASA we have developed is poised to better satisfy the demands of the aircraft thermal protection systems in extreme heat environments.

Preparation and characterization of UV-curable composite containing nano silica for glass-to-glass bonding

Glass is a transparent and geometrically ordered element in architecture. Glass bonding can be classified into adhesive, layered, and mechanical categories. One of the best bonding materials for glass applications is adhesive. The preparation and investigation of Ultraviolet (UV)-curable composites for glass-to-glass bonding is the goal of this research. The investigation focused on the effect of raw material type and weight percentage on mechanical properties. Epoxy acrylate resin was employed as an oligomer in this study. Trimethylolpropane triacrylate (TMPTA), tripropyleneglycol triacrylate (TPGDA), and pentaerythritol tetraacrylate (PETA) were used as monomers. As photoinitiators, were used bis (2,4,6 trimethylbenzoyl)-phenylphosphine oxide, hydroxycyclohexyl phenylketone, and 2,4,6-trimethylbenzoyl diphenyl phosphineoxide. Benzophenone, acrylic acid, nano silica, and trimethoxysilylpropyl methacrylate (TMSPMA) were used as the additives. The mechanical properties of the samples were studied using compressive and shear tests. The degree of conversion (DC) was obtained using Fourier transform infrared spectroscopy (FTIR). The mechanical behavior of the samples were measured as a function of temperature using dynamic mechanical thermal analysis (DMTA); and the distribution of nanoparticles was examined using scanning electron microscopy (SEM). The results showed that the sample containing 4 wt% nano silica, which also contained 24 wt% PETA and 7 wt% TMSPMA, has the best mechanical properties with 0.42 and 0.63 MPa compressive and shear strength, respectively. In the FTIR, was observed an increase of nano silica from the lowest (1 wt%) to the highest amount (5 wt%), the DC current decreased by 11 %. In the DMTA analysis, it was observed that an increase of nano silica from 1 to 5 wt%, the storage modulus increased by 41 %. The highest loss modulus and loss temperature were related to the samples containing 1 and 2 wt% nano silica with 221 MPa and 113.8 °C. Finally, the best distribution of nanoparticles was observed in the sample containing 1 wt% nano silica. In the SEM images, agglomeration of nanoparticles was seen in the sample containing 5 wt% nano silica.

Low carbon multi-binder composite using lithomargic soil, biomass, and calcined seashell powder for sustainable bricks

Bricks are manufactured using clays, which are fired at temperatures ranging from 1000 to 1200 °C. Due to the lack of quality clay, it is necessary to find alternate soils and waste materials for manufacturing bricks. The use of agricultural, aqua-cultural, and industrial wastes in the manufacturing of construction bricks leads to low-carbon material. This addresses the problem of agro-aqua-industrial waste disposal. The present study focuses on the utilization of biomass (BM) and slaked seashell powder (SSP) in compressed soil bricks made with locally available lithomargic soil (LS). The proposed soil bricks are prepared with 85% processed lithomargic soil, 12.5% biomass and 2.5% seashell powder. The reaction of multi-binder materials has been activated by one-part activation. The cast soil blocks are temperature cured at 100 °C, 250 °C, 500 °C & 750 °C to understand the effect of temperature on the hydration process of binder material. The compressed soil bricks are tested for compressive strength, initial rate of absorption, water absorption test, chloride content, sulphate content, microstructure analysis and thermal conductivity. The strength of soil bricks in bonding and in masonry, 3 prism and 4 prism tests were also conducted. Overall results indicate that bio-based alkali-activated brick masonry is superior for real-time adaptation because it reaches 10 MPa to 11.2 MPa compressive strength and 0.98 MPa to 1.2 MPa shear strength with curing at 500 °C.

Fully recycled engineered geopolymer composite: Mechanical properties and sustainability assessment

Combining the two advantages of mitigation of dependence on cement and natural sand resources and recycling waste concrete material, the utilization of recycled concrete powder (RCP) and recycled fine sand (RFS) to produce geopolymer concrete is of great value. However, the insufficient compressive strength and inherent brittleness of the existing RCP or RFS geopolymer concrete hampered its application. This paper aims to develop a high-performance engineered geopolymer composite (EGC) by maximizing the recycle amount of RCP and RFS. The effects of RCP and RFS on the physical, mechanical, and microscopic properties of EGC were investigated. The results indicated that, the less reactivity of RCP decreased the amount of gel products and compromised the strength development, while favored the multi-cracking behavior and the robust ductility. RFS showed a stronger interfacial bond with paste than quartz sand, compensating the degradation of strength driven by RCP and marginally affecting the tensile strain capacity. The developed EGC incorporating 50% RCP and 100% RFS possessed an 84 MPa compressive strength, 7.4 MPa tensile strength, and 8.1% tensile strain, which are at the highest level among the existing RCP or RFS geopolymer concretes. The main products included the coexistence of calcium aluminosilicate hydrate and alkali aluminosilicate (C(N)-A-S-H) gel and layered double hydroxide (LDH). The energy- and carbon-reduction were 16% and 57%, respectively, compared to the M45-ECC.The current findings prove the feasibility of utilizing high amounts of recycled materials to produce high value-added concrete.

Reinforcement of Insufficient Transverse Connectivity in Prestressed Concrete Box Girder Bridges Using Concrete-Filled Steel Tube Trusses and Diaphragms: A Comparative Study

To address the issue of insufficient transverse connectivity in prestressed concrete box girder (PCB) bridges, this study investigates two transverse strengthening methods—installing diaphragms and utilizing concrete-filled steel tube trusses (CFSTTs). A finite element model was developed for a typical 30 m PCB bridge and was validated by on-site load test results for reliability. Based on the deflection and load distribution of PCB bridges before and after reinforcement, as well as the maximum stress and strain of the diaphragms and the CFSTTs, comparative analyses were conducted on diaphragms of different thicknesses and materials, as well as on CFSTTs of various strength grades. The results show that the addition of a transverse partition and CFSTTs can effectively improve the load distribution of the PCB bridge and reduce the maximum deflection of the girder, especially when using the CFSTT reinforcement method. The unique structural design improves the reinforcement effect of the material in the post-elastic stage. When using CFSTTs, increasing the steel tube wall strength significantly reduces the maximum deflection of the main girder. For example, using steel tubes with yield strengths of 235 MPa and 420 MPa filled with concrete of 50 MPa compressive strength reduced the maximum deflections by 15.32% and 24.55%, respectively, and improved the load distribution coefficients by up to 7.31% and 11.57%. Additionally, steel diaphragms demonstrated better reinforcement effects compared with concrete diaphragms. The load transverse distribution coefficients for the CFSTT-reinforced PCB bridge were calculated using the hinge plate (beam) and the rigid plate (beam) methods, showing minimal differences between the two approaches. The findings of this study provide valuable insights into the design of diaphragm and CFSTT reinforcement in PCB bridges, aiding in the selection of optimal reinforcement strategies.