Microwave-assisted crushing of coarse aggregate is a promising future development trend in the technology for producing recycled coarse aggregates. This paper presents an innovative approach that combines finite element and discrete element methods to simulate and investigate the process of microwave-assisted crushing of concrete under various conditions, including different coarse aggregate content and microwave power levels. The finite element method is utilized to examine the distribution of electromagnetic fields and temperatures within the microwave field, while the discrete element method focuses on studying the cracking mechanism of concrete in this environment. Experimental validation confirms the accuracy of simulation results and evaluates the impact of microwave-assisted crushing on concrete by determining its reduction in strength after irradiation. The study reveals that changes in coarse aggregate content and microwave power influence multiple aspects during specimen crushing, such as electric field, power density, temperature, and crack distribution evolution. Uniaxial compression tests demonstrate both the magnitude of reduction in compressive strength caused by microwave radiation and energy consumption per unit mass for a 1 MPa decrease in concrete strength. These findings indicate that pre-irradiation with microwaves can effectively reduce concrete strength during waste concrete crushing processes while facilitating resource recycling.
This study develops a cost-effective, mass-producible blast-resistant concrete (BRC) that combines high dynamic performance with excellent workability with a low steel fiber content. To improve practical applicability, locally sourced river sand was used to partially replace quartz sand. The steel fiber volume fraction was limited to 1%, enabling high flowability suitable for ready-mixed concrete production while maintaining ultra-high compressive strength exceeding 180 MPa. A two-stage experimental program was conducted. First, river sand particle size distributions were optimized based on fresh properties and quasi-static mechanical performance. Second, the effects of steel fiber geometry-micro-straight (S), hooked (H), and wavy (W)-on compressive, flexural, and tensile behavior were systematically investigated under both quasi-static and high strain-rate load conditions, including impact tests and high-speed direct tensile tests. The results demonstrate that strain rate significantly enhances strength, stiffness, and energy absorption for all mixtures. Deformed fibers substantially improve post-cracking behavior and dynamic resistance due to enhanced mechanical interlocking and fiber-matrix bonding. Compared with straight fibers, H-and W-type fibers exhibit higher dynamic peak strength, strain capacity, and toughness. Among them, W-type fibers show superior energy absorption and more stable post-peak behavior. Based on the experimental data, strain rate-dependent dynamic increase factor (DIF) models for compressive and tensile strengths were established, explicitly incorporating steel fiber type. These fiber-type-dependent DIF models constitute the main novelty of this study and provide practical input for blast-resistant structural design and numerical simulations.
Recent efforts in sustainable construction focus on reducing cement consumption while improving the performance of fiber-reinforced high-strength concrete (FRHSC). This study investigates the combined influence of ground granulated blast furnace slag (GGBS) and recycled steel fibers (RSF) on the fresh, mechanical, and durability properties of FRHSC, supported by machine learning-based strength prediction. Cement was partially replaced with GGBS at levels of 15% and 30%, while RSF were incorporated at 0.25%, 0.50%, and 0.75% by volume. Fresh properties were evaluated through workability-related tests. Mechanical performance was assessed using compressive strength (CS), splitting tensile strength (STS), and flexural strength (FS) tests at 7, 28, and 90 days. Durability was examined using sorptivity, water absorption, rapid chloride penetration, and electrical resistivity tests. The random forest (RF) and artificial neural network (ANN) models were developed to predict strength behavior. The results showed that GGBS improved workability and long-term strength due to its delayed pozzolanic activity and formation of secondary C-S-H gel, leading to a denser microstructure. RSF enhanced tensile and FS by bridging cracks and limiting crack propagation. At 90 days, the paste comprising 30% GGBS and 0.75% RSF achieved increases of 13.61% in CS, 35.73% in STS, and 31.2% in FS compared to the reference mix. Durability performance was significantly enhanced, with up to a 66.38% reduction in chloride ion penetration, attributed to pore refinement and reduced permeability. SEM analysis confirmed a compact and homogeneous microstructure in GGBS-fibermodified concrete. Among the machine learning models, the RF approach demonstrated superior predictive accuracy compared to ANN, with higher R2 values and lower prediction errors. The findings highlight the synergistic role of GGBS and recycled RSF in producing durable and high-performance concrete. The integration of machine learning further provides an efficient tool for strength prediction, reducing experimental dependency. This study offers practical guidance for developing sustainable FRHSC with enhanced mechanical performance, durability, and predictive reliability.
This study examined the impact behavior and failure mechanism of corroded reinforced concrete (RC) beams strengthened with fiber reinforced polymers (FRP) grid-ultra-high-performance concrete (UHPC) composites. Finite element (FE) models were developed and thoroughly validated against existing experimental data. Furtherly, the effects of corrosion rate, strengthening scheme, and impact velocity were systematically analyzed. The results indicate that corrosion of longitudinal rebars concentrated flexural damage in the impact region and increased deformation. Both pure UHPC and FRP-UHPC strengthening enhanced flexural resistance and reduced sectional damage factor by up to about 44%. While minimally affecting the first peak impact force, both strengthening significantly increased the second peak. However, the high stiffness of FRP-UHPC layer induced stress concentration at the UHPC-normal concrete (NC) interface, leading to premature debonding. Transverse U-shaped anchors mitigated debonding, though local debonding might persist in unanchored zones. Increasing interfacial bond strength, simulating rebar planting, could effectively prevent interface debonding, but required approximately twice the normal strength. Therefore, a combined strategy employing interfacial rebar planting and transverse U-shaped anchors at a spacing less than 1.0h0 (h0 is the beam effective depth) is recommended to suppress debonding and fully utilize the material potential of FRP and UHPC.
Tall reinforced concrete buildings are increasingly becoming popular due to the rising housing demand and scarcity of space. These buildings need specific consideration with respect to the design and detailing. Most importantly, the dynamic behaviour and seismic damage of these buildings are considerably different compared to low-and mid-rise structures. Damaged or seismically deficient buildings can be restored with a suitable strengthening strategy, however, a pre-assessment of the lateral load behaviour of these buildings is necessary. Presently, seismic strengthening measures based on nonlinear analysis are abundant, and each of them is used according to the need or the damage level incurred in the structure or its components. However, seismic strengthening based on visible cracks or damage in the building, followed by a linear analysis to assess its performance level is also in practice. The present study is motivated towards the seismic assessment and rehabilitation of one such case study 15-storied reinforced concrete building that was hit and damaged by the M7.8 Gorkha earthquake on 25 April 2015 in Nepal. Optimal strengthening strategies for the building are suggested based on the overall improvement in its seismic performance and damage probability through nonlinear analyses.
This study presents a computational framework for modeling solid-color reinforced composite aggregates and concrete-steel bond strength using a physics-informed and data-driven simulation strategy. The approach integrates experimental observations with a structured model-development protocol that formalizes hypothesis testing, parameter calibration, and validation pathways to enhance reproducibility and transparency. The framework enables systematic investigation of interactions among silica-fume-modified cement matrices, rubberized aggregates, and steel reinforcement interfaces. A series of nonlinear computational models is established to predict compressive strength, tensile performance, and bond stress-slip relationships. The models are calibrated using experimental datasets and refined through iterative evaluation of competing constitutive assumptions, improving both predictive robustness and mechanistic interpretability. Results indicate that composite aggregate incorporation significantly modifies interfacial stress transfer mechanisms, leading to enhanced bond strength and ductility under optimized silica fume content. Compared with conventional empirical fitting approaches, the proposed modeling framework reduces parameter uncertainty and demonstrates improved generalization across material configurations. The methodology provides a scalable basis for the design and evaluation of sustainable composite concrete systems with improved structural reliability and interface performance.
This paper presents a novel approach to reducing cement consumption in concrete by using a combination of nano-silica (NS) and nano-calcium carbonate (NC) as cementitious materials-reducing admixtures (CRA). The innovation lies in the synergistic effect of NS and NC, which not only reduce cement content by 20% but also enhance concrete's mechanical properties and durability. Through a systematic optimization, the combination of 1.751% NS and 0.1% NC was found to significantly improve concrete performance compared to the control mix. Specifically, the 28-day compressive strength increased by 7.9%, the splitting tensile strength rose by 11.8%, and the chloride-ion permeability resistance decreased by 2.7%. Additionally, the optimized mix reduced the concrete cost by 11.17 CNY/ton and decreased CO2 emissions by 27.4 kg/ton. This study provides strong evidence for the practical application of NS and NC in reducing carbon emissions in concrete production, offering an environmentally friendly and economically viable alternative to traditional cement-based mixtures.
In the high exterior temperature, the cracking possibility due to hydration heat and drying shrinkage also increases, and the ion penetration and the related corrosion increase since the ions move rapidly. In this study, the sulfate diffusion behavior with increasing temperature was evaluated and its activation energy was derived for evaluating the deterioration behavior in the NPP (Nuclear Power Plant) concrete for sulfate ion ingress. After obtaining the materials used in the NPP, concrete samples were prepared, and the temperature-dependent sulfate diffusion coefficients were obtained while elevating the temperature from 20 degrees C to 50 degrees C with 10 degrees C interval. During the process of temperature elevating, the diffusion coefficient increased to a level of 3.4 times, and the activation energy range was measured to 19.4-28.9 KJ/mol with average of 22.3 KJ/mol, which had no significant differences from the those of chloride diffusion results. Finally, the sulfate ion ingress behavior was simulated considering effect of temperature, repairing thickness, and cover depth, which showed a significant sulfate intrusion due to elevated temperature.
Most ancient city walls in China are severely damaged mainly because of the destruction of traditional pure white mortar in the walls. Traditional mortar and cement paste are typically used for restoring ancient city walls; however, traditional mortar exhibits low strength, excessive shrinkage, poor durability, and poor compatibility between the cement paste and the original mortar. Therefore, there is an urgent need to develop new repair materials for ancient building masonry. A new type of modified pure white mortar was developed in this study. Hydroxypropyl methylcellulose and calcium stearate were added to pure white mortar, and the working performance, basic mechanical properties, and shrinkage of the modified pure white mortar were investigated. The microstructures of the modified mortar were analysed using X-ray diffraction and scanning electron microscopy techniques. A 0.4% HPMC or 0.1% CS content can significantly improve the performance of the traditional mortar, and the modified mortar is suitable for ancient masonry repairs.
To ameliorate shrinkage problems in concrete, the most common route is to cut down the cementitious paste volume. This study proposed and demonstrated the strategy of filling industrial waste powder into the voids among aggregate particles in order to effectively fulfill the target of reduction in cementitious paste volume without air entrapment in concrete. The workability, strength and shrinkage of concrete mixes with 0-12.5% industrial waste powder content to replace cementitious paste at 0.35-0.60 water/cement ratio have been measured through slump, flow, cube strength, prism shrinkage tests. Results disclosed that utilization of industrial waste powder to replace cementitious paste significantly lowered the ultimate shrinkage strain by as high as 58.3% and prolong the shrinkage half-time by as high as 47.1%. In-depth analysis revealed that ultimate shrinkage strain was governed mainly by the cement content whereas shrinkage half-time was governed mainly by the water content.
This study investigates the mechanical and microstructural behavior of lightweight engineered geopolymer composites (LWEGCs) containing nano tubes under high temperatures. LWEGCs were fabricated using fly ash, silica fume, slag, metakaolin, and fly ash microspheres as binders, with ceramsite-based lightweight aggregates (LAs) such as clay-based (CBC), granulated blast furnace slag-based (GBC), and shale-based (SBC) aggregates. Compressive stress and mass loss were assessed after exposure to temperatures extending from 200 degrees C to 800 degrees C. Scanning electron microscopy (SEM), X-ray Diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to assess the phase assemblage of the produced LWEGC mixes. Results depicted that matrix compaction increased the compressive stress of LEGC-REF by 27.27% at 200 degrees C, while thermal deterioration caused a considerable decrease of 43.47% at 600 degrees C and 135.71% at 800 degrees C. With mass loss increasing to 22.54% at 800 degrees C, LEGC-CBC exhibited the lowest thermal stability, whereas LEGC-SBC had superior stability with 20.1% mass loss. The material's integrity was diminished by the development of cracks and a honeycomb structure at high temperatures, according to SEM research. By strengthening the geopolymer matrix and bridging microcracks, MWCNTs enhanced microstructural cohesiveness despite degradation. This study emphasizes how LWEGCs can be used in high-temperature applications and how LAs and MWCNTs can enhance mechanical and fire resistance.
This study investigates the long-term durability of ultra-high-performance concrete (UHC altered with metakaolin (MK) and kieselguhr earth (KE). These materials were used as sustainable alternatives to silica fume and fly ash. Four UHC pastes were developed and tested. Durability performance was evaluated through freeze-thaw resistance, chloride ion permeability, sulfate attack, and drying shrinkage under different curing regimes. All UHC pastes showed excellent freeze-thaw resistance. No mass loss and 100% relative dynamic modulus were recorded after 300 cycles. The control paste exhibited a 23% reduction in modulus of rupture after freeze-thaw exposure. In contrast, the MK and MK-KE pastes showed reductions of only 3.68% and 3.6%, respectively. Chloride permeability was significantly reduced with MK and KE incorporation. Complete replacement of fly ash with MK reduced the total charge passed by 52.9% and increased surface resistivity by 423%. The KE paste showed a 35.2% reduction in charge passed. Sulfate resistance was excellent for all pastes. Length expansion remained below 0.01% at six months, far lower than the ASTM C1012 limit of 0.10%. The MK paste showed the lowest expansion of only 0.001%. Drying shrinkage depended strongly on curing conditions. Under air-dry curing, shrinkage ranged from 748 mu epsilon to 1002 mu epsilon. The MK paste showed the lowest shrinkage, while the KE paste showed the highest. Under moist curing, shrinkage was significantly reduced. The KE paste recorded the lowest value of 215 mu epsilon at 56 days. The MK paste consistently showed the lowest cracking potential index under all curing regimes. Hence, MK and KE significantly enhance UHC durability and dimensional stability. Their combined use provides a promising pathway for sustainable and resilient UHC in aggressive environments.
This study investigates the influence of compaction mechanisms and corresponding cement paste thickness on the properties of porous concrete. Using Proctor and Marshall hammers, cylindrical specimens were compacted in both 3-layer and 5-layer configurations with 25 blows per layer. Two aggregate size ranges, 4.75-8.0 mm and 8.0-12.5 mm, were utilized. Experimental evaluations using the both compaction methods demonstrated their effectiveness in producing a uniform mix, as evidenced by consistent measurements of compressive strength, density, porosity, and permeability. While compaction energy influences void structure, cement content has a more significant effect on compressive strength, indicating that optimizing cement content is key to achieving desired strength. MATLAB image analysis showed effective cement paste thickness (d50) ranged from 0.485 mm (Marshall 5-layer) to 0.605 mm (Proctor 3-layer), with over 50% of values below 0.6 mm and a peak at 0.1 mm. Cement paste thickness is primarily controlled by cement content rather than compaction energy and shows a positive correlation with compressive strength. Overall, increasing cement paste thickness enhances strength. Furthermore, a two-factor ANOVA was performed to statistically evaluate the effects of aggregate size and compaction method, confirming that compaction method significantly influences compressive strength, while both factors significantly affect permeability. These results highlight the importance of managing compaction technique, cement paste distribution and aggregate size to balance mechanical performance and permeability in porous concrete design.
As one of the most important structural materials in the construction industry, concrete has long used Ordinary Portland Cement (OPC) as the main cementing material. However, the preparation process of cement has great problems of carbon emission and energy consumption, and a large amount of solid waste is attached, Cause serious environmental pollution. Obviously, the preparation of concrete with OPC no longer meets the requirements of "sustainable development". Therefore, the development of a new green material that can not only have the strength of cement but also can save energy and environmental protection is the current urgent need. In this paper, Mixed Coal gangue Geopolymer Concrete (MCGC) is prepared with coal gangue, fly ash and slag as raw materials. On this basis, steel fibers with different properties are selected. An experimental study on the mechanical properties of Steel Fiber reinforced Mixed Coal gangue Geopolymer Concrete (SFMCGC) was carried out, and the microstructure was analyzed by means of SEM and microhardness testing. To explore the toughening mechanism of SFMCGC, in this paper, it is found that the mechanical properties of MCGC are greatly improved by the three types of steel fibers. Through microscopic test analysis, it is found that the vertical and horizontal distribution of fibers plays a "bridge" effect, blocking the generation of micro cracks and the development of long cracks, and ensuring the integrity of the specimen. However, if the fiber content is too high, bubbles will be introduced to different degrees, which will affect the porosity and density of the specimen.
In construction, anchors for concrete are essential devices that connect structural and non-structural components to concrete structures. However, in many numerical analyses, anchor connections are interpreted with fixed or restrained boundary conditions, and anchors are separately evaluated for tension and shear loads according to ACI 318 standards. Numerous studies evaluating anchor performance have been conducted since the 1970s, leading to formalization and standardization based on various research findings to date. However, research on the load-displacement relationship of anchors is still insufficient, especially regarding the development of numerical models for anchor systems based on this relationship. Additionally, recent studies indicate significant degradation in anchor performance under repetitive freeze-thaw exposure conditions for post-installed anchors, whereas performance evaluations under such conditions have not been conducted for cast-in-place anchors. Therefore, this study conducted to: 1) analyze the load-displacement relationship of anchors subjected to combined tensile and shear loads, 2) analyze changes in concrete strength and anchor performance due to freeze-thaw exposure, and 3) propose and compare a numerical model for anchors that simulates the load-displacement relationship based on anchor test results. As result of this study, confirmed that concrete compressive strength varies with freeze-thaw cycles, leading to decreased performance of cast-in-place anchors. Furthermore, the proposed numerical model for anchors confirmed significant alignment with experimental results in terms of peak load and deformation energy within specific displacement ranges.
This investigation focuses on the connection between reinforced concrete beams' mechanical and corrosion-resistant qualities and the application of nanoparticles. By adding different combinations of nanomaterials to the cement mix, such as nano-magnesium oxide (NMO) and nano-metakaolin (NM), the effects of these materials on both fresh and cured concrete are examined. To assess the compressive and flexural strength, tests were conducted at intervals of 7, 14, and 28 days for cubes, prisms, and beams. The goal is to determine how concrete's mechanical qualities are affected by varying percentages of cement substitution with nanomaterials. When 3% nano-magnesium oxide is added to the concrete, the characteristics are similar to those of regular concrete. Furthermore, the study examines how resistant reinforced concrete beams containing nanoparticles are to corrosion. To ascertain the beams' resistance to corrosion, tests including resistivity, half-cell potential, and fast chloride permeability are used. Certain combinations of nanoparticles are expected to improve the concrete's mechanical qualities and, consequently, its corrosion resistance. The research's conclusions might improve the robustness and lifetime of reinforced concrete buildings in several uses.
In major projects such as wind turbine bearing platforms, temperature-induced stress cracking of massive reinforced concrete foundations poses a core hazard to the safe service of structures, and traditional analysis methods struggle to accurately quantify the regulatory effect of reinforcing bars on temperature and stress fields. This paper proposes a method for calculating the effective thermal conductivity tensor of reinforced concrete considering the heat conduction effect of rebars from the perspective of isothermal flow rate. Additionally, a method is introduced to calculate the equivalent mechanical parameters considering reinforcement bars deformation. Based on these equivalent parameter calculation methods, combined with finite element simulation, an accurate assessment of the thermodynamic performance evolution of mass reinforced concrete is conducted. By comparing the finite element simulation results obtained from detailed modeling methods and those obtained from equivalent parameter methods, the effectiveness of this approach in predicting temperature and stress field changes in reinforced concrete is demonstrated. Real-time monitoring of temperature changes in 15 wind turbine bearing platform foundations reveals the temperature development pattern and cracking risk of foundation concrete. Furthermore, based on design drawings, this paper reconstructs the three-dimensional structure of reinforcement bars in foundation and couples it with the solid model of foundation concrete using the aforementioned equivalent method for a quantitative analysis of the impact of rebars on foundation concrete temperature and stress fields. Simulation results show that under the influence of rebars, the heat exchange rate of foundation increases, and the maximum temperature rise of local concrete can be reduced by over 8 degrees C. Moreover, the maximum tensile stresses on the surface and inside of the concrete are reduced by 0 to 0.82 MPa and 0 to 1.89 MPa, respectively, thereby reducing the risk of cracking.
The synergetic effect of steel fibers, polypropylene fibers and the hybrid effect of steel-polypropylene fibers of various concrete mixes on mechanical properties and flexural toughness was investigated. The mechanical properties include compressive strength, split tensile strength, flexural strength and modulus of elasticity. Total 16 mixes containing various concrete mixes (normal concrete of grade M35, Steel fibers - 0.5%, 1.0%, 1.5%, Polypropylene fibers (PPF) - 0.1%, 0.2%, 0.3%, hybrid fibers - each volume fraction, steel: PPF - 25%:75%, 50%:50%, 75%:25%) were cast and evaluated the mechanical properties and flexural toughness. Flexural strength, flexural toughness and indices were evaluated by using the load-deflection diagram of various concrete mixes by using the guidelines prescribed in various Codes of practices, namely, (i) ASTM C 1018 (ii) ASTM C 1609 (iii) JSCE (iv) ASTM C 1399 (v) Chinese National Standards CECS13. It was primarily observed that a concrete mix containing a fibre combination of 75% steel fibers + 25% Polypropylene fibers yielded superior mechanical properties and flexural toughness. Post peak behaviour of flexural specimens containing combination of 75% steel Fibers + 25% Polypropylene fibers found to be more ductile compared to other combinations. A method has been proposed based on the crack initiation load and percentage of peak load to determine the reserve flexural strength. Further, microstructural analysis has been carried out for the samples of plain concrete, concrete with steel fibers and concrete with hybrid fibers. It was primarily inferred from microstructural studies that due to enhanced bond between the synergy effect of steel and PPF, superior mechanical and flexural toughness were obtained.
This study performed a comparative probabilistic fragility analysis of an integral abutment bridge (IAB) in liquefied and non-liquefied soil, evaluating its seismic vulnerability to near-fault and far-fault ground motions (GMs) sources. Utilizing the OpenSees platform, incorporated p-y springs with PyLiq1 material to model the effects of soil liquefaction. A three-dimensional IAB model with a single span was developed, focusing on the susceptibility of the bridge's piles and abutments to ground vibrations. The analysis involved constructing a probabilistic seismic demand model through nonlinear time history analysis, utilizing 200 scaled earthquake sets. Fragility curves were employed to calculate the conditional probability of specific structural demands exceeding the structural capacity, with peak ground acceleration as a key parameter. The analysis results of fragility curves revealed that liquefaction had a dual impact on the seismic response of the IAB piles and abutment damage states. Liquefaction around the piles increased the probability of pile damage from slight to collapse and increased the potential for abutment collapse, while less susceptibility to abutment damage ranged from slight to extensive compared to non-liquefied soil. When considering near-fault GM in non-liquefied soil, the IAB abutment damage states increased by 2% compared to far-fault GM, while the IAB pile damage states under near-fault GM in liquefied soil decreased by 2%.
Lightweight high-strength concrete engineering structures have low dead weight and high seismic performance, but the brittleness is greater than that of traditional concrete. The inherent brittleness is bound to pose significant challenges for engineering applications. Based on the strategy of developing and improving the toughness of lightweight aggregate high-strength concrete, and unleashing the full potential of lightweight high-strength concrete in safer and more reliable structural applications, the study used ceramic particles as lightweight aggregates, mixed with basalt fibers and cellulose fibers to produce hybrid nature fiber reinforced lightweight high-strength concrete. By four-point flexural and fatigue tests, the flexural toughness and fatigue characteristics of the single/mixed nature fiber reinforced lightweight high-strength concrete under different stress levels were studied. And the fatigue life performance rules under different stress ratios were revealed, and the fatigue life equations were established with the two-parameters S-N(stress level-fatigue life) curve, considering the failure probability. The results show that under different stress levels, the fatigue life of all samples follows the two-parameter Weibull distribution probability model. The improvement of fatigue life of lightweight high-strength concrete with mixed fiber is better than that with single fiber, with the longest stable development duration and fatigue life. The fatigue strain evolution process of lightweight high-strength concrete with different fiber conforms to the development law of the third-order strain curve. The established fatigue life equation can be used to predict the flexural fatigue performance of fiber reinforced lightweight high-strength concrete under different stress levels. The improvement of fatigue toughness and service life has transformed lightweight high-strength concrete from "high strength but brittle" to "high strength and durability" and is expected to become an ideal material in earthquake engineering that combines lightweight, seismic performance, and sustainability.
