This study aims to evaluate the macro-micro-meso-mechanical properties of basalt fiber (BF)-reinforced recycled aggregate concrete (BFRAC). Firstly, the effects of BF with different contents and ...lengths on the mechanical properties of recycled aggregate concrete (RAC) at different ages were analyzed. In addition, the distribution of BF, bond between BF and matrix, failure form of BF, and element composition of the fiber interface transition zone were analyzed using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Finally, the numerical simulation of cubic compression and splitting tensile tests of RAC specimens were carried out, and the stress–strain curve and failure morphology of RAC under static loading was studied. The results show that BF content is the main factor affecting the mechanical properties of concrete within the range of test fiber content (0.1%–0.3%), and the optimal content of BF is 0.2%. The length of BF has little effect on the compressive properties of RAC, but the increase of BF length can improve the splitting tensile and flexural properties of RAC. Through SEM-EDS, the toughening and cracking resistance mechanisms of the BF are obtained. In the meso-simulation, the numerical simulation results are in high agreement with the experimental phenomenon, and this method provides an effective technical method for the prediction and establishment of RAC failure model. In summary, the research results can be used as reference for the establishment of the RAC mechanical model, performance research, and practical engineering application in the future.
Low-heat Portland cement has been extensively used in mass concrete because of its low hydration heat and high later strength. However, low-heat cement has characteristics of slow activity and low ...early strength, which affects its propagation and applications in mass concrete to a certain degree. Moreover, comprehensive theoretical research on the mechanical properties and constitutive relations of pure and modified low-heat cement concretes is lacking. In view of this, this study reviews the research progress of the mechanical properties and the damage theory of fiber-reinforced low-heat cement concrete based on analysis of the existing literature. First, the mineral composition, hydration mechanism, and performance characteristics of low-heat cement concrete are analyzed. Second, the performance traits of low-heat cement fiber concrete are examined, and the influence laws of basalt and brucite fibers on the mechanical properties of concrete are determined. Finally, the application of damage mechanics theory to fiber-reinforced concrete is summarized. This study shows that although fibers can effectively enhance the mechanical properties of low-heat cement concrete, there are limitations in the selection of fiber type. In addition, basalt and brucite fibers play significant roles in enhancing the mechanical properties of concrete; therefore, the objectives of this paper are to present the application prospects of fibers in low-heat cement concrete and propose a new concept of mixing fibers to boost the early mechanical properties of low-heat cement concrete. Combining theoretical research and analysis, it provides directions and concepts for applying the damage theory to low-heat fiber cement concrete in the future.
The strength-formation mechanism for industrial-construction residue cement stabilization of crushed aggregate (IRCSCA) is not clear. To expand the application range for recycled micro-powders in ...road engineering, the dosages of eco-friendly hybrid recycled powders (HRPs) with different proportions of RBP and RCP affecting the strengths of cement-fly ash mortar at different ages, and the strength-formation mechanism, were studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the early strength of the mortar was 2.62 times higher than that of the reference specimen when a 3/2 mass ratio of brick powder and concrete powder was mixed to form the HRP and replace some of the cement. With increasing HRP content substituted for fly ash, the strength of the cement mortar first increased and then decreased. When the HRP content was 35%, the compressive strength of the mortar was 1.56 times higher than that of the reference specimen, and the flexural strength was 1.51 times higher; XRD and SEM studies of the hydrated cement mixed with HRP showed that the amount of CH in the cement paste was reduced by the pozzolanic reaction of HRP at later hydration ages, and it was very useful in improving the compactness of the mortar. The XRD spectrum of the cement paste made with HRP indicated that the CH crystal plane orientation index R, with a diffraction angle peak of approximately 34.0, was consistent with the cement slurry strength evolution law, and this research provides a reference for the application of HRP to produce IRCSCA.
Recycled aggregate concrete (RAC) is a kind of five-phase composite material at the meso-level. It has a more complex interfacial transition zone (ITZ) than ordinary aggregate concrete (NAC), which ...is an important factor affecting the meso-failure of RAC. In addition, the maximum aggregate size plays an important role in the nonlinear mechanical behavior of concrete, which is closely related to the size effect. In this paper, a 2D random aggregate model of RAC is established based on meso-mechanics. The mechanical properties and failure modes of RAC under uniaxial compression are simulated using a plastic damage constitutive model. Through variable parameter analysis, the effects of the properties and thickness of ITZ on the elastic modulus and peak stress of RAC are studied, and the effect of the maximum aggregate size on the size effect of the compressive strength of RAC is discussed. The results show that the ITZ strength has a positive linear correlation with the peak stress and elastic modulus of RAC, while the ITZ thickness has a negative linear correlation with the peak stress and elastic modulus of RAC. Under the same specimen size (D = 100 mm, 150 mm, 200 mm, 300 mm), with an increase in the maximum aggregate size (dmax =20 mm, 25 mm, 30 mm, 35 mm), the nominal compressive strength of RAC increases by 6–10%, and the size effect is gradually weakened. When the maximum aggregate size reaches 30 mm, a decrease in the size effect tends to slow down compared with the maximum aggregate size of 20 mm. The classical Bažant size effect law is applicable to describe the compressive properties of RAC under different maximum aggregate sizes, and has a certain guiding significance for the prediction of the size effect of RAC in practical engineering.
The surface adhesion mortar of recycled coarse aggregate (RCA) is the main factor leading to poor aggregate quality, and it also affects the internal structure and mechanical properties of recycled ...aggregate concrete (RAC). To improve the quality of RCA and mechanical properties of RAC, self-developed mortar removal equipment was used to strengthen the RCA. Then, the RCA was soaked in 1, 2, and 3% nano-silica solutions, and the vibration-mixing process was used to improve the quality of RAC. In addition, the microstructure of the RAC was examined
scanning electron microscopy to observe its improvement effect on the microstructure of the RAC. The results indicated that the quality of the RCA was improved by mechanical and physical strengthening, and the water-absorption rate and crushing value decreased by 32.9 and 23.9%, respectively. The improvement effect of nano-immersion on the RAC was obvious. The optimal condition was a combination of physical strengthening, 2 days of immersion in 2% NS solution, and vibration stirring. The 28 day compressive strength increased by 31.3%, the splitting tensile strength increased by 23%, and the flexural strength increased by 49%. The proposed strengthening method improves the mechanical properties and microstructure of RAC. The results of this study provided a technical reference for the mechanical strengthening of RAC and promotion of the application and popularization of RAC.
The development and application of nondestructive testing technology for prestressed reinforced concrete structures in the field of infrastructure construction were summarized in this study via the ...analysis of relevant literature worldwide. The detection methods, detection principles, and detection instruments in quality evaluation of prestressed reinforced concrete structures were analyzed and compared, based on which, acoustic emission detection technology, impact echo detection technology, ultrasonic detection technology, infrared thermography detection technology, ground-penetrating radar detection technology, piezoelectric transducer detection technology, and X-ray detection technology were summarized. Additionally, the advantages, disadvantages, and application scope of each detection method were focused upon and analyzed comparatively. It is indicated that further improvement in the detection visualization, accuracy, and efficiency for most nondestructive testing technologies is available by optimizing the algorithm and combining artificial intelligence technology with neural network deep learning, precise positioning, and imaging analysis of the quality defects in prestressed reinforced concrete structures. The results of this study can provide technical reference for the further application and research of nondestructive testing technologies in the quality inspection of prestressed reinforced concrete structures.
In this study, nano-SiO
(NS) and basalt fiber (BF) were used to improve the quality of recycled aggregate concrete (RAC). The crushing value, water absorption, and apparent density of NS-modified ...recycled coarse aggregate (RA) were determined, and the effects of BF with different contents and lengths on the slump, compressive strength, splitting tensile strength, and flexural strength of RAC and BF-reinforced RAC containing NS-modified RA were analyzed. Finally, the filling effect of NS, the toughening and crack resistance mechanism of BF, and the micro-composite effect between NS and BF were analyzed based on scanning electron microscope (SEM) and energy-dispersive detector (EDS) measurement. The results show that the optimum modified concentration of NS solution is 2%, the content of BF is the main factor affecting the mechanical properties of concrete, and the optimum length and content of BF are 12 mm and 0.2%, respectively. For BF-reinforced RAC containing NS-modified RA, the 28 day compressive strength, splitting tensile strength, and flexural strength of RAC increase by 34.28, 40.55 and 54.5%, respectively. Based on SEM and EDS measuring, NS can react with Ca(OH)
crystal to form flocculent C–S–H gel, which makes RAC compact and enhances the bonding properties of the interfacial transition zone (ITZ) between BF and the matrix.
•Development in RAC reinforced by Nano-SiO2 and basalt fiber can reuse waste.•Nano-SiO2 and basalt fiber can improve interface structure of RAC.•RAC reinforced by Nano-SiO2 and basalt fiber exhibits ...excellent durability.•Some challenges for RAC reinforced by Nano-SiO2 and basalt fiber are presented.
To deal with the poor mechanical and durability of Recycled aggregate concrete (RAC), the effects of the addition of Nano-SiO2 (NS), Basalt fiber (BF), and composite addition of NS and BF are put forward. The addition of BF reduces the generation and development of early primary microcracks in RAC and prevents the generation and propagation of microcracks in the mortar. The addition of NS fills the microcracks in the concrete, which reduces the porosity, and facilitates the densification of the structure on the microscopic scale. By mixing NS and BF in experiments, NS can promote the adhesion between the fiber and matrix through the coupling effect, and effectively improve the fiber reinforcement effect. This review focuses on the effects of modified materials such as NS and BF on the interface structure, mechanical properties, carbonization resistance, freeze–thaw cycle resistance, salt erosion resistance, and high-temperature resistance of recycled concrete. The classical constitutive model, carbonization model and chloride ion diffusion model of concrete and recycled concrete are summarized. The application of current recycled concrete models is summarized, and feasible research directions are analyzed. This work also aims to understand the possible applications of nanomaterial, fiber, and fiber-nanomaterial modified recycled concrete in today's construction industry, so as to lay a theoretical foundation for the future application of recycled concrete in actual buildings and the durability evaluation of recycled concrete structures.
•137 papers are reviewed on basalt fiber-reinforced concrete (BFRC).•Influences of basalt fiber (BF) on the mechanical properties and fracture properties of BFRC are reviewed.•Effects of BF on the ...durability and the microstructure of BFRC are discussed.•Further suggestions for the research and application of BFRC are proposed.
In recent years, basalt fiber (BF) has been extensively used as a reinforced fiber to improve the mechanical properties and durability of concrete because of its excellent mechanical properties, high-temperature resistance, acid and alkali resistance, availability of raw materials, and environmentally friendly production processes. Based on a thorough review of recent literature, the current research status of basalt fiber-reinforced concrete (BFRC) in terms of the basic mechanical characteristics, fracture performance, and durability under different test conditions were reviewed in this study, and future research directions and trends were predicted and analyzed. It is shown that the reasonable addition of BF with a diameter of approximately 10–20 μm, length of approximately 12–20 mm, and an optimal volume fraction of approximately 1 % in concrete can better improve the mechanical properties of concrete. Furthermore, BF significantly improves the fracture toughness, fracture energy, and maximum deflection of concrete, effectively increasing the impermeability, resistance to concrete chloride erosion, and sulfate attack. In addition, the advancements in methods for the numerical simulation of concrete fractures and calculation of the chloride ion permeability coefficient were also summarized in this paper. Based on the shortcomings of the current study, it is suggested that future studies should focus on the mechanical properties and durability of BFRC under high-temperature and after damage. The toughening mechanism of BF on hydraulic concrete concrete should be studied, with the objective of laying the theoretical foundation for its application in practical engineering.
•Effects of content, maximum particle size, and shape of aggregate on concrete strength were simulated.•Influence law of aggregate grading and model size on compressive strength of concrete was ...revealed.•Five mesoscopic models of aggregate gradation and specimen side length were established.•Established mesoscale model improves effectiveness and efficiency of full-graded concrete modeling.
In this paper, a 2D finite element model with a mesoscale level was established. The effects of content, maximum particle size, and shape of aggregate on the strength of concrete were simulated. In addition, five mesoscopic models of aggregate gradation and specimen side length (100–450 mm) were established to investigate the influence law of aggregate grading and model size on the compressive strength of concrete. The simulation results were also compared and verified with four theoretical size-effect models. The results showed that the compressive strength shows a trend of decreasing and then increasing with the increase of aggregate content and falling with the growth of maximum aggregate size dmax. The peak stress of convex polygonal aggregates is higher than that of round and elliptical. In addition, when the ratio of model side length to the maximum aggregate particle size is about 3.5, the compressive strength gradually decreases with the increase of specimen size, up to 27.65 % decreased, showing a pronounced size effect. After comparative analysis, the simulated data in this paper fitted well with the Bažant’s Type-2, Kim’s modified, Jin’s modified, and Carpinteri’s size effect law (SEL). In addition, the data obtained from the simulation of this paper would better reflect the existing test conclusions. The mesoscale model established in this paper can significantly improve the effectiveness and efficiency of full-graded concrete modeling, and better simulate the strength difference between full-graded and wet-screened specimens. The difficulties in the mesoscale numerical simulation are solved to a certain extent.
