Aggregate Replacement Rate Research Articles

Experimental study on acoustic emission of steel fiber broken pebble recycled concrete

This study investigates the mechanical properties and damage evolution of steel fiber-reinforced recycled concrete, using broken pebbles as coarse aggregates. The objective is to assess the compressive and flexural performance of the material under varying steel fiber content (0 %, 1 %, 2 %) and recycled aggregate replacement rates (0 %, 10 %, 20 %, 30 %, 40 %). The research employs Acoustic Emission (AE) technology to monitor real-time damage during compression and bending tests. The key findings reveal that increasing the steel fiber volume and aggregate replacement rate improves the interface bonding performance and enhances flexural strength, while also leading to higher initial damage. The AE signals captured during testing allowed the identification of critical damage stages, providing insight into crack initiation and propagation. This research offers valuable contributions to the understanding of recycled concrete behavior, with implications for sustainable construction and improved material design.

Carbonization test and orthogonal polynomial regression analysis of steel fiber reclaimed concrete

To enhance the carbonation resistance of reclaimed concrete, several key factors affecting its performance were investigated. An orthogonal array L16(4³×2⁶) was employed to design the carbonation tests for steel fiber (SF) reinforced concrete. The study included varying SF volume ratios, along with considerations of different concrete ages (T) and water-cement ratios (W/R). The effect of SF volume ratio, regenerated crude aggregate (RCA) replacement rate, W/R, and T on the carbonation resistance of recycled concrete was analyzed. The test results indicated a trend of increasing carbonation depth over time. However, a lower W/R ratio resulted in a reduced carbonation depth. Notably, a 50% RCA replacement rate led to a shallower carbonation depth compared to other replacement rates. After 28 d, recycled concrete containing 1% SF exhibited a carbonation depth that was 6.9%, 1.5%, 1.5%, and 9.3% lower than concrete with 0%, 0.5%, 1.5%, and 2% SF, respectively. Therefore, the incorporation of 1% SF was found to be the most effective in improving carbonation resistance. Orthogonal polynomial regression analysis was employed to develop a regression equation relating carbonation depth to SF volume ratio, RCA replacement rate, W/R, and T. The regression coefficients were calculated and tested, leading to the identification of the optimal regression equation and its corresponding confidence interval.

Study on the mechanical property and durability of alkali-activated seawater and sea sand recycled aggregate concrete

This study investigates the potential of Alkali-Activated Seawater Sea Sand Recycled Aggregate Concrete (ASSRAC) as a novel sustainable construction material. By utilizing recycled aggregates from construction and demolition waste, seawater, sea sand, and alkali-activated materials such as fly ash and blast furnace slag, this innovative concrete aims to mitigate carbon emissions from cement production and optimize resource usage. The impact of recycled aggregate replacement rate, water-to-binder ratio, and sand type on the compressive strength of ASSRAC was examined through analysis of variance. Cylindrical axial compression and prism flexural tests were conducted to evaluate the long-term performance of ASSRAC under seawater immersion. The results indicate a decrease in compressive strength with higher recycled aggregate replacement rates and water-to-binder ratios, with recycled aggregates being the primary weak link. Additionally, increasing the water-to-binder ratio hampers hydration by diluting alkali activators, weakening polycondensation reactions. Under seawater immersion, ongoing reactions foster denser C-(A)-S-H structures, enhancing compressive strength and elastic modulus over time. Moreover, higher recycled aggregate replacement rates result in improved ductility, attributed to reactions between the old mortar on recycled aggregate surfaces and slag/fly ash at interfaces. For specimens immersed for 0 and 90 days, most theoretical models accurately predict results, except for the CEB-FIP model, which only accurately reflects the stress-strain curve at 180 days. The seawater-sea sand group's flexural strength initially exceeds that of the freshwater-river sand group due to accelerated early hydration, but this advantage diminishes over time due to high salt content.

Turning waste concrete powder into high calcium alkali-activated cementitious materials and artificial aggregates

In order to handle the environmental pollution caused by waste concrete powder, recycled concrete powder (RCP) is utilized to prepare high calcium alkali-activated cementitious materials and artificial aggregates. This study first investigates the high calcium alkali-activated cementitious materials, exploring the effects of different mineral admixtures, liquid-to-solid ratios (L/S), RCP/slag, Na2SiO3 modulus, and Na2O content. The results illustrate that slag powder is the best mineral admixture and the most critical factor affecting cementitious materials. Increasing the slag dosage enhances the generation of C-(A)-S-H, improves the microstructure, and increases compressive strength, with a maximum compressive strength reaching 68.42 MPa. According to these test results, the impact of various factors on RCP aggregates is further explored. The results illustrate that the L/S and slag content are primary factors influencing particle size distribution and strength. Increasing these factors leads to larger aggregate particle sizes and higher strength. The compressive strength of the aggregates at 7d reaches 93.24–-99.5 % of that at 28d, with a maximum strength of 8.2 MPa. Additionally, slag content (10–30 %) and Na2O content significantly impact the physical properties of aggregates, improving apparent density and bulk density while reducing water absorption. To verify the applicability of RCP aggregates, they were used in concrete, and the effects of aggregate strength and replacement rate on concrete performance were explored. The results display that as aggregate strength rises, the mechanical properties of the concrete improve. When RCP aggregates are incorporated, the mechanical properties of the natural concrete decline only slightly (<16.70 %). The probability of aggregate damage increases with decreased RCP aggregate strength or increased RCP aggregate content under pressure. RCP aggregate concrete exhibits better shrinkage resistance compared to natural concrete. The process of utilizing RCP is low-energy, non-polluting, and results in high-performance products, making the large-scale effective utilization of RCP feasible.

Enhancing energy dissipation in mortar utilizing recycled brick fine aggregate impregnated with polymer emulsion under uniaxial cyclic load

Optimizing the damping properties of materials can enhance the energy dissipation capacity of structures and mitigate the negative effects of dynamic loads on building components. This study investigated the effects of the polymer emulsion-impregnated recycled brick fine aggregate (PRBFA) replacement rate, emulsion-impregnation treatment method, and emulsion solid content on the dynamic damping properties of PRBFA-prepared mortar (PBM). Combined with microscopic tests, the enhanced damping mechanism of PBM was discussed. The results show that under the same stress amplitude, the equivalent damping ratio and loss modulus of PBM increase with the PRBFA replacement rate and emulsion solid content. The drying treatment of PRBFA demonstrates superior damping characteristics of PBM, with the equivalent damping ratio and loss modulus increased by 84.9%–129.4 % and 71.0%–117.2 %, respectively, compared to those of PBM with undried PRBFA. The damping enhancement of PBM is attributed to the weak interface between the aggregate and cement matrix, which facilitates slippage and friction. The damping layer formed between the high viscoelastic emulsion and the aggregate, or between the emulsion and the cement matrix, is conducive to energy dissipation. The optimal PRBFA replacement rate for balancing the mechanical and damping properties of PBM is between 38% and 60 %.

Feasibility of foam concrete using recycled brick and roof tile fine aggregates

Brick (BR) and roof tile (RT) fine aggregate fractions derived from construction and demolition wastes have a low recycling rate in new construction and building materials. This article assesses their suitability for replacing the limestone aggregate in foam concrete, which helps valorise such fractions and conserve natural limestone resources. Two concrete categories containing or not silica fume (SF) were investigated, while the BR and RT aggregate replacement rates were 10%, 20% and 40%. Tested properties include flow, density, water absorption, porosity, thermal conductivity, mechanical strengths, microscopy, drying shrinkage, resistance to freeze/thaw cycles and elevated temperature. Results showed that the concrete mechanical properties improved when the limestone aggregate was replaced by 10% BR or RT but gradually curtailed at higher addition rates. Such results concorded with the density, water absorption and porosity measurements. Foamed concrete containing BR is more resistant (compared to RT) to drying shrinkage, freeze/thaw cycle, and heat exposure, which was ascribed to the relatively lower BR porosity that improves the concrete mechanical properties and durability.

Experimental and numerical investigation of bias performance of steel fiber-reinforced GRC-CFFT columns

Geopolymer concrete-filled glass fiber-reinforced polymer (GFRP) tube columns show significant potential in marine engineering due to their excellent durability and mechanical properties. This study investigated the bias performance of steel fiber-reinforced geopolymer recycled aggregate concrete-filled GFRP tube (SGRC-CFFT) columns, considering variables such as load eccentricity, GFRP tube thickness, fiber winding angle, and recycled coarse aggregate (RCA) replacement rate. The failure modes, load-displacement behaviors, and strain distribution were analyzed and discussed. Furthermore, a high-precision finite element model was established based on the test data. The test results indicated that increasing load eccentricity significantly reduced both the load-bearing and axial deformation capacity of CFFT columns. When the load eccentricity reached 0.40, the peak load of the specimen was only 39 % of that of the corresponding axial compression specimen. A higher RCA replacement rate would cause a more pronounced reduction in bias-bearing capacity, with a maximum decrease of 24.6 %. Before 80 % of the peak load, the axial deformation of the column mid-span section accorded to the plane section assumption. Due to the eccentric load, the hoop deformation of the CFFT column was concentrated on the compression side. The fiber winding angle was the critical factor influencing both the peak load and the peak moment of the biased SGRC-CFFT column.

Study on the mechanical properties of recycled brick coarse aggregate concrete based on finite element modeling

In recent years, the use of recycled materials in concrete production has garnered significant attention due to their environmental and economic benefits. To promote the application of recycled aggregates, this study focuses on investigating the utilization of Recycled Brick Coarse Aggregate (RBCA) as a substitute for natural aggregate. This paper presents the development of stochastic convex polygonal RBCA through the utilization of a custom-programmed algorithm and proposes a finite element model designed to simulate the behavior of RBCA concrete under compression and splitting tensile. Numerical simulations were conducted to investigate the effects of brick aggregate Replacement Rate (RR) and porosity on the compressive and splitting tensile properties of RBCA concrete. A strong correlation was found between the Concrete Damage Plasticity (CDP) model developed in this study and experimental results, indicating high reliability. The results indicate that the replacement rate of brick aggregates has a more significant impact on the compressive strength than on the splitting tensile strength of concrete. Furthermore, the distribution of coarse aggregates and pores has a minor influence on the mechanical properties and ultimate failure mode of RBCA concrete but significantly affects the crack distribution pattern. The sequence of damage initiation in RBCA concrete was found to be: pores, old Interfacial Transition Zone (ITZ), old mortar, new ITZ, new mortar, RBCA, and Natural Coarse Aggregate (NCA). These findings contribute to a comprehensive understanding of RBCA's performance and offer valuable insights for optimizing its behavior.

Mechanical properties of steel fiber reinforced recycled concrete under compression-shear stress state

The continuous urbanization of construction has led to an increasing demand for concrete, resulting in large-scale gravel and river sand mining, which seriously affect the sustainable development of the environment. The waste concrete produced by the demolition of old buildings is processed into recycled aggregate to replace natural aggregate, and then the preparation of recycled concrete can effectively alleviate this problem. This paper investigates the mechanical properties of steel fiber reinforced recycled concrete (SFRRAC) under compression shear conditions, a compression shear test with 99 cubic specimens was designed, with the variation parameters being recycled aggregate concrete replacement rate, compressive stress, and steel fiber content. The failure mode of SFRRAC under compression-shear stress was observed, and the shear force-displacement curve was calculated. Furthermore, a thorough examination was performed to assess the mechanical characteristics of SFRRAC specimens under compression-shear stress. The findings of this study suggest that as the compressive stress increases, the failure characteristics of the specimens shift from exhibiting brittle failure to displaying ductile failure. The shear strength is most sensitive to the change in compressive stress. When the compressive stress reaches 6 MPa, the shear strength can reach 3.41 times that of the direct shear specimen. The shear strength of SFRRAC specimens is composed of the bond strength of concrete, shear expansion strength, and friction shear strength. The incorporation of steel fibers can modify the distribution of shear strength among the individual components. The adverse effect of the recycled aggregate replacement rate on the toughness index of the specimen is mainly concentrated after the peak point. Nevertheless, an elevation in compressive stress and the inclusion of steel fibers can counterbalance this detrimental influence. The shear strength calculation formula of SFRRAC in shear state is put forward, which has a reference value. This study provides an experimental reference and a theoretical basis for further examination of SFRRAC.

Research on Macroscopic Mechanical Behavior of Recycled Aggregate Concrete Based on Mesoscale.

Recycled concrete is a heterogeneous composite material, and the composition and volume fraction of each phase affect its macroscopic properties. In this paper, ANSYS APDL was used to construct a two-dimensional numerical model of recycled aggregate concrete with different replacement rates of recycled aggregate (0%, 25%, 50%, 75% and 100%), and a uniaxial compression test was carried out to explore the relationship between recycled aggregate content and its macroscopic mechanical behavior. On this basis, the numerical simulation of different strain rates (0.1 s-1, 0.05 s-1, 0.01 s-1, 0.005 s-1 and 0.001 s-1) was carried out. It was found that with the increase in the recycled aggregate replacement rate, the peak stress decreases first and then increases, and the peak strain increases continuously. When the replacement rate of recycled aggregate exceeds 50%, the overall damage area of the material increases rapidly. The strain rate will change the path of the micro-crack initiation and expansion of recycled concrete, as well as the process of damage accumulation and evolution. As a result, the unit area and shape of recycled concrete are different at different strain rates, and the damage degree of each phase material is also different.

Fracture behaviors of sustainable recycled aggregate concrete under compression-shear loading: Laboratory test, numerical simulation, and environmental safety analysis

A series of compression-shear tests were carried out to investigate the shear failure of sustainable recycled aggregate concrete, and shear failure surfaces were scanned by a 3D laser scanner. The effect of recycled coarse aggregate (RCA) replacement rates and normal stresses on the shear strength, failure mode, and fracture morphology were analyzed. Meanwhile, discrete element method was used to study shear behaviors at a mesoscale. Finally, the carbon emission was calculated to evaluate the effect of RCA on the environment. The result shows that the shear strength, cohesion c, and internal friction angle φ all decrease as the RCA replacement rate increases. The shear damage of RAC can be aggravated by increasing the RCA replacement rate. Fractal dimension and joint roughness coefficient of shear failure surface tend to increase with increasing RCA replacement rate and normal stress. In addition, more microcracks can be found in coarse aggregate with the increase in RCA replacement rate, and the increasing normal stress can cause more microcracks. Given the nonlinear development of stress-displacement, a modified nonlinear constitutive model is proposed. Finally, the total carbon emissions of recycled aggregate concrete are calculated considering production, transportation, and construction, the carbon emission of 100% sustainable recycled aggregate concrete is 10.2% less than that of 100% natural aggregate concrete.

Experimental study on the bond-slip behavior of steel tube-coal gangue concrete

This study investigated the bond-slip behavior at the interface between steel tubes and coal gangue concrete, considering the coal gangue coarse aggregate replacement rate, the strength grade of coal gangue concrete, and the bond length as variable parameters. Eleven groups of push out tests were conducted on steel tube coal gangue concrete specimens. The bond slip curve and the longitudinal strain distribution curve of the steel tubes were obtained, and the effects of these parameters on bond strength were analyzed. The results showed that the load-slip curves at both the loading and free ends of the specimens were similar, with slip occurring earlier at the loading end. The regularity of the test curves in repeated experiments indicated that interfacial bond stress was primarily determined by friction in the later stages. The longitudinal strain of steel tubes was approximately exponentially distributed along their length. The interfacial bond strength increased with the increase of coal gangue aggregate replacement rate and was more pronounced in specimens with higher strength coal gangue concrete. Longer bond lengths resulted in greater bond failure loads, with a lower rate of increase in higher strength coal gangue concrete specimens compared to those with lower strength. Based on the three stage bond stress-slip relationship for steel tube-concrete, a bond-slip constitutive model for steel tube-coal gangue concrete was established. This provided a reference for mechanical analysis and interface performance design of steel tube-coal gangue concrete.

Mechanical properties of recycled aggregate concrete reinforced with steel fibers under triaxial loading

The use of steel fiber reinforced recycled concrete (SFRAC) can help achieve resourceful reuse of construction waste and environmental sustainability. However, SFRAC structural members may experience complex stress states. Therefore, triaxial compression tests were conducted on 168 cylindrical SFRAC specimens to investigate their mechanical properties. The failure modes, stress-strain behavior, strength, and deformation of SFRAC under triaxial compression were observed. The effects of lateral confining pressure, steel fiber (SF) content, and recycled coarse aggregate (RA) replacement rate on these properties were analyzed. The internal micro-morphology of SFRAC was analyzed using SEM to better understand its failure mechanism under compression. The result shows that an increase in lateral confining pressure alters the failure mode of SFRAC specimens, resulting in a significant increase in peak strength and ductility. The enhancement of the elastic modulus by steel fibers decreases as the lateral confining pressure increases, suggesting a coupling effect between the two parameters. The inclusion of steel fibers in SFRAC did not have a significant impact on its failure mode or compressive strength. And yet, it did increase the ductility and toughness of the material, with an optimal steel fiber content of 1 % (by volume). On the other hand, the addition of recycled coarse aggregate resulted in a significant reduction in the concrete's compressive strength, by almost 17 %. Finally, several common material failure criteria for concrete were used to evaluate the impact of RA substitution rate and SF content on the strength of SFRAC. The Willam-Warnke failure criterion showed a higher strength. These findings provide a theoretical basis for future engineering applications of SFRAC.

Modeling carbonation depth of recycled aggregate concrete containing chlorinated salts

The durability of recycled concrete is susceptible to degradation from both chloride salt attack and carbonation when exposed in service environment. The depth of carbonation in recycled concrete subject to chloride salt attack was studied here. This investigation assessed the effects of mineral admixture, replacement rate of recycled coarse aggregate, and quality of recycled coarse aggregate on the carbonation depth. The carbonation depth Recycled concrete was studied through accelerated simulated carbonation in the laboratory for 7d, 14d and 28d. Based on the results, the correlation analysis was conducted to investigate the relationship between depth of carbonation, mineral admixture, recycled coarse aggregate replacement rate, recycled coarse aggregate quality and the presence of chloride ions. The objective of this study was mainly to investigate the effect of internal chloride ions on the depth of carbonation of recycled concrete subjected to chloride salt attack. The study referred to previous academic research on carbonation in recycled concrete that had not been affected by chloride salts, and conducted a comparative analysis to identify the carbonation depth pattern in recycled concrete influenced by chloride salt exposure. The study discovered a negative correlation between the replacement rate of mineral admixture and recycled coarse aggregate and the carbonation resistance of concrete. Moreover, enhancing the quality of recycled coarse aggregate positively impacted the carbonation resistance of concrete. An improved model was developed that considers the effect of internal chloride salts on the carbonation depth of recycled concrete, in reference to the empirical prediction model presently available. The model demonstrated a high level of agreement with experimental outcomes, displaying an error range of between −4.32% and 8.27%. It enables an in-depth comprehension of the carbonation behavior of recycled aggregate concrete in an environment exposed to chloride salt attack. Based on the model, the service life of recycled concrete structures can be more accurately forecasted, which can provide a theoretical direction for enhancing the durability of engineering structure.

Carbonation resistance of recycled fine aggregate concrete reinforced by calcium sulfate whiskers

This study investigates mechanical and carbonation resistance tests conducted on Recycled Fine Aggregate Concrete (RFAC) with three different Recycled Fine Aggregate (RFA) replacement rates and four calcium sulfate whisker (CSW) contents, and investigates the effects of RFA replacement rate and CSW content on the mechanical properties of RFAC and the carbonation resistance of RFAC with calcium sulfate whiskers at different ages of carbonation. The microstructure of CSW-modified RFAC was observed and analyzed by SEM electron microscopy to explore further enhancement and toughening mechanisms of CSW in RFAC, as well as the optimal content of CSW in RFAC. In addition, the carbonation depth of recycled concrete with calcium sulfate beard is modeled based on a quadratic fitting formulation. The test results show that the mechanical properties and carbonation resistance of RFAC would decrease with the increase of the RFA replacement rate. Incorporating CSW can effectively improve the mechanical properties and carbonation resistance of RFAC. At 60 % RFA substitution, CSW at 2 % content has the most significant effect on the mechanical properties and carbonation resistance of RFAC. Microscopic analysis shows that CSW has a bridging effect at the micro-cracks in the concrete matrix, preventing the creation and expansion of micro-cracks in the concrete matrix, thus improving RFAC mechanical properties of RFAC and resistance to carbonation. The predicted results of the carbonation depth model which are constructed from the test data coincide with the results. We can use them to predict and analyze the carbonation depth of the carbonation resistance of recycled concrete.

Mechanical properties and damage characteristics analysis on recycled aggregate concrete with glazed hollow beads after high temperatures by acoustic emission method

This research investigates the effect of high temperature on the mechanical and acoustic emission properties of recycled aggregate concrete with glazed hollow beads (GHB-RAC). Uniaxial compression tests were conducted on GHB-RAC at varying recycled coarse aggregate (RCA) substitution rates and glazed hollow beads (GHB) contents, and acoustic emission (AE) technology was used to monitor the compression-induced damage throughout the testing process. This study delves into the mechanical properties and damage characteristics of GHB-RAC when exposed to fire. The findings reveal that AE characteristic coefficients aptly delineate the three-stage nature of axial compression damage in concrete at temperatures up to 400 °C. However, these stage-specific traits vanish at temperatures exceeding 400 °C. Additionally, through the analysis of AE signals at different temperatures, the compression damage process is elucidated based on the b-value method. The RA-AF analysis indicates that the number of shear cracks exhibits an increasing trend with increasing temperature, and an increment in GHB dosage positively influences the percentage of tensile cracking during loading, with the influence being more significant at 70 % GHB content. The acoustic emission sensing can accurately detect and localise damage. With the increase in temperature, the distribution of AE signals depicting concrete damage is more dispersed and the number of AE signals is more larger. Notably, the incidence of localized damage points diminishes with a higher GHB ratio, indicating the efficacy of GHBs in mitigating thermal damage to the concrete. Furthermore, a damage constitutive model incorporating variables such as temperature, GHB dosage, and recycled coarse aggregate replacement rate was proposed. The model employed AE energy count parameters as the damage indicator. The good fitting results suggest that the mechanics behavior of GHB-RAC under uniaxial compression can be well described by the model. Consequently, the study offers invaluable insights into the damage evolution of post-fire recycled aggregate concrete with GHB admixtures.

Damage-fracture mechanism analysis of steel-polypropylene fiber reinforced recycled concrete based on acoustic emission and digital image correlation

The engineering application of recycled aggregate concrete is significant for resource conservation and environmental protection. However, the applied range of recycled aggregate concrete is greatly limited due to microscopic defects such as microcracks in recycled aggregate. Steel-polypropylene fiber reinforced recycled concrete (SPRAC) makes up for the defects brought by recycled aggregate to a certain extent due to the action of hybrid fiber. To further promote the practical application of SPRAC, it is crucial to evaluate its damage-fracture mechanic's response mechanism under different hybrid fiber admixtures and recycled aggregate replacement rates. For this purpose, the following work is carried out in this paper: firstly, SPRAC beam specimens with different substitution rates of hybrid fiber and recycled aggregate were prepared; and the damage-fracture process of specimens under four-point bending load was monitored in real-time by using acoustic emission and digital image correlation techniques to analyze the influence of hybrid fiber and recycled aggregate on the flexural properties and damage-fracture characteristics of SPRAC; the inherent relationship between the acoustic emission rise time/amplitude (RA) and the average frequency (AF) is utilized to classify the crack type of SPRAC in the course of the data analysis; the b-value is also analyzed to assess the crack evolution process in SPRAC, and the corresponding warning thresholds are given.; strain and displacement fields on the specimen surface are analyzed using the digital image correlation; finally, the microscopic results of SPRAC are also given to better understand the damage-fracture evolution mechanism of SPRAC. Results show that the flexural strength and fracture toughness of SPRAC decreased nonlinearly with the increase of recycled aggregate content; on the contrary, the addition of hybrid fiber improved the mechanical properties of SPRAC. The study in this paper provides a new method to characterize the damage-fracture mechanism of SPRAC under bending loads quantitatively. It provides a reference for the engineering application of SPRAC.

Mechanical Properties of Recycled Concrete with Polypropylene Fiber and Its Bonding Performance with Rebars

This paper explores the influence of polypropylene fiber on the mechanical properties of recycled concrete and the bonding performance between recycled concrete and steel bars. The results indicate that the compressive strength and splitting tensile strength of concrete decrease with the increase in the replacement rate of recycled aggregate. When the replacement rate of recycled aggregate was 100 %, the compressive strength of concrete decreased by 25.0%, while the splitting tensile strength of concrete decreased by 21.7 %. The compressive strength and splitting tensile strength of recycled aggregate concrete show a trend of first increasing and then decreasing with increasing fiber content. When the fiber content is 0.09 %, the compressive strength and tensile strength of recycled aggregate concrete are optimal. The bond strength of recycled concrete pullout specimens with fiber is higher than that of recycled concrete pullout specimens without fiber, while the slip of recycled concrete pullout specimens with fiber is lower than that of recycled concrete pullout specimens without fiber. The maximum improvement in bonding performance between recycled concrete and rebars with a 50 % recycled aggregate replacement rate is 13.7 %, and the maximum improvement in bonding performance between recycled concrete and rebars with a 100 % recycled aggregate replacement rate is 11.8 %. The bond strength shows a trend of first increasing and then decreasing with increasing fiber content, but the degree of decrease was not significant, while the slip shows a trend of first decreasing and then increasing with increasing fiber content. Compared to the compressive strength of concrete, the splitting tensile strength can better reflect the bond strength between concrete and rebar. The nonlinear relationship between the bond strength, compressive strength, and splitting tensile strength of recycled concrete is established. This study can effectively improve the mechanical properties of recycled concrete, expand the application scope of recycled concrete technology, and promote the sustainable development of the construction industry.

Replacement of Fine Aggregates in Fine-Grained Concrete by Waste Material from Cetris Boards Production

Given the increasing amount of waste in the world, it is essential not only to reduce waste generation but also to explore potential uses for the waste produced. This includes waste generated in the production of building materials. The construction industry is a significant contributor to global waste and carbon dioxide emissions, making it crucial to address these issues for sustainable development. During the production of CETRIS boards, approximately 7 600 tons of waste are generated annually. One of the waste materials obtained during the board processing is a fine powder. This waste material can potentially be reused in two ways: it can be incorporated back into the process of producing CETRIS boards or utilized in the production of building materials. This research project focuses on examining the possibility of using this waste material as a substitute for fine aggregate in fine-grained concrete. To investigate its viability, the waste material underwent testing for dry density and absorbency. Subsequently, a reference mixture and concretes with different replacement rates (50%, and 100%) of natural fine aggregate were produced to create self-healing concrete mixtures. The study examined the density, and compressive strength of these concrete samples 28 days after concreting. The findings indicated that as the amount of waste material in the concrete increased, the measured properties decreased. However, despite the decrease, the compressive strengths of the concrete remained very high, leading to the classification as high-strength concrete. Further exploration and optimization of the replacement rates could lead to the development of environmentally friendly and sustainable building materials.

Behaviour of steel-reinforced recycled aggregate concrete-filled GFRP tubular short columns under eccentric axial compression

Since the mechanical properties of recycled aggregate concrete (RAC) are different from those of natural aggregate concrete (NAC), the mechanical behaviour of reinforced RAC members has attracted great interest. Meanwhile, fibre-reinforced plastics (FRP) have been applied to improve the load capacity of concrete members owing to their good durability. This study primarily focused on the performance of glass FRP (GFRP) confined steel-reinforced RAC short columns (FCSRAC) under eccentric compression. In this study, 29 FCSRAC were used to understand the effects of the recycled coarse aggregate (RCA) replacement rate, strength of RAC, eccentric distance, fibre orientation of the GFRP tube, strength of the GFRP, and longitudinal reinforcement ratio on the eccentric compression behaviour. The results show that the longitudinal steel bar ratio and hoop strength of the GFRP tube play a critical role in the load capacity of the FCSRAC, especially at large eccentric distances. With improved steel bars and GFRP tubes, RAC can be used in core concrete to replace NAC in a column. In addition, a prediction model of the load capacity of the FCSRAC was proposed based on Samaan's model and the static equilibrium principle, introducing the eccentric distance, fibre orientation of the GFRP tube, and RCA replacement rate. The predicted results agree with the experimental results.