Aggregate Replacement Rate Research Articles

Durability of Recycled Concrete after Reinforcing the Aggregates with Permeable Crystalline Materials

The utilization of recycled aggregate can significantly mitigate the extraction of natural sand and gravel. However, the practical application of recycled aggregate in engineering is impeded by its inherent characteristics, encompassing high water absorption, high crushing, and low apparent density. This study employed a soaking and air-drying method to enhance the strength of three types of aggregates with varying initial strengths by utilizing permeated crystalline materials. The durability of recycled aggregate concrete (RAC) was studied with three different aggregate replacement rates (0%, 50%, and 100%). The test results demonstrate that the slump, compressive strength, freeze resistance, and carbonation resistance of RAC exhibit a decreasing trend as the aggregate replacement rate increases. The freeze resistance and carbonation resistance of RAC are notably enhanced after incorporating permeated crystalline material. This study contributes to a sustainable and efficient solution for the treatment of construction waste, thereby enhancing the utilization rate of recycled concrete.

Experimental Study on Preparation and Characteristics of Concrete Modified by Construction Waste

With the advancement of urbanization construction, the proportion of construction waste to the total urban waste continues to increase, especially waste concrete. The treatment and reuse of waste concrete is a major trend that poses enormous pressure on environmental protection. This article focuses on the problems in the preparation of recycled aggregates from waste concrete, which has important practical value. This article presents a new type of recycled concrete prepared through surface modification of recycled coarse aggregate and design experiments to change the replacement rate of coarse aggregate. The physical properties of recycled coarse aggregate, workability of fresh concrete, and mechanical properties of recycled concrete are analyzed. The research results indicate the following: (1) Through surface modification, recycled concrete can improve the workability of fresh concrete at a fixed water cement ratio, which can meet the requirements of mixing, transportation, and pouring of fresh concrete. (2) By modifying the surface of recycled aggregates, the strong water absorption performance of recycled aggregates caused by old mortar and surface defects has been reduced. And the modification effect of recycled aggregate improves the hydration process of recycled concrete, making the surface structure dense and further enhancing the strength of recycled concrete. (3) The compressive strength of recycled concrete specifications from construction waste shows a decreasing trend with the increase in coat aggregate replacement rate. The final ratio is as follows: modular dose of 12%, modification time of 90 min, and 20% recycled aggregate content.

Study on the mechanical properties and microstructure of recycled brick aggregate concrete with waste fiber

Abstract Recycled concrete technology can promote the sustainable development of the construction industry, but the insufficient mechanical properties of recycled concrete have become a key constraint on its development. By adding waste fibers, the mechanical properties of recycled concrete can be improved, and the problem of disposing of waste polypropylene fibers can be solved. In this article, the effects of recycled brick aggregate content and waste fiber content on the mechanical properties and microstructures of recycled brick aggregate concrete through macroscopic mechanical experiments and microstructure experiments are investigated. The results show that the addition of recycled brick aggregate reduces the mechanical properties of concrete; when the content of recycled brick aggregate is 100%, the compressive strength and splitting tensile strength decrease by 22.04 and 20.00%, respectively. The addition of waste fibers can improve the mechanical properties of recycled brick aggregate concrete, but it is necessary to control the contents of waste fibers in a certain range. When the content of waste fibers is 0.08%, the best improvement effect on the mechanical properties of concrete is achieved; the compressive strength of concrete with a 50% (100%) recycled aggregate replacement rate increases by 6.06% (8.90%), while the splitting tensile strength of concrete with a 50% (100%) recycled aggregate replacement rate increases by 2.30% (6.16%). Through microstructural analysis, the mechanism by which waste fiber improves the mechanical properties of recycled brick aggregate concrete is revealed. The addition of waste fibers has the effect of strengthening the framework inside the recycled brick aggregate concrete, forming a good structural stress system and allowing the recycled brick aggregate concrete to continue to bear loads after cracking. In this study, waste brick aggregate and waste fiber are effectively utilized, which can not only reduce pollution to the environment but also realize the sustainable utilization of resources.

Deterioration performance analysis of recycled brick concrete subjected to freezing and thawing effect

This study employed experimental and finite element modeling approaches to systematically investigate the mechanical damage mechanisms of recycled brick aggregate concrete (RAC) under freeze-thaw cycling conditions. The investigation encompassed analyses at three hierarchical levels: macroscopic, mesoscopic, and microscopic. The influence of recycled brick aggregate (RA) replacement rate and the number of freeze-thaw cycles on RAC's apparent state and mechanical performance was examined at the macroscopic level. Utilizing equipment such as electron microscopes, a comprehensive observation was conducted from mesoscopic and microscopic perspectives to elucidate the evolving patterns of the cementitious matrix, RA, and the interfacial transition zone (ITZ) within RAC during the freeze-thaw cycling process. On the one hand, more excellent internal space was inherent in RA compared to NA, enabling it to effectively accommodate the volumetric expansion resulting from water freezing. It contributed to mitigating the damage to concrete caused by freeze-thaw cycles. On the other hand, RA's rough and porous characteristics facilitated the infiltration of cement particles into its internal structure, forming a robust ITZ with RA. Concurrently, a numerical simulation of RAC's freeze-thaw cycling process was presented. This simulation generated coupled damage maps and load-deflection curves for RAC under various conditions, encompassing different levels of RA replacement rates, freeze-thaw cycle counts, and loading modes. The research results indicated that the inclusion of RA adversely affects the mechanical properties of concrete while concurrently altering the concrete's failure mode and the propagation pathways of internal cracks. Nevertheless, it was worth noting that the introduction of RA, despite diminishing the mechanical performance of concrete, effectively mitigates the rate of performance degradation during the freeze-thaw cycling process. A favorable equilibrium between freeze-thaw resistance and mechanical performance could be achieved when the replacement rate of RA for natural aggregates (NA) fell within the range of 10–30 %. By employing a finite element model to simulate the flexural performance of RAC after freeze-thaw cycles, the deviation range between the simulated and measured values fell within the range of 5.00–8.23 %. This affirmed the model's fitting solid capability and validated its effectiveness in analyzing the RAC structure's freeze-thaw-load coupled damage and lifespan prediction.

Experimental study on mechanical properties of recycled aggregate concrete with polypropylene fiber under combined compression‐shear loading

AbstractTo investigate the mechanical properties of polypropylene fiber recycled aggregate concrete (PPFRAC) under compression‐shear, 69 recycled aggregate concrete (RAC) specimens were tested with the parameters of polypropylene (PP) fiber volume content (0, 0.6, 0.9, and 1.2 kg/m3), recycled coarse aggregate (RCA) replacement rate (0%, 30%, 50%, 70%, and 100%), and normal stress (0, 3, and 6 MPa). In the tests, the failure pattern of the specimens was observed, and the effects of the polypropylene fiber content on the direct shear stress, compression‐shear stress, initial shear stiffness, and shear ductility coefficient of the PPFRAC were thoroughly investigated. The results show that as the polypropylene fiber content increases, the direct shear stress of concrete (Natural aggregate concrete and 100% recycled coarse aggregate concrete [100%RCA]) first increases and then decreases gradually. Meanwhile, the best PP fiber content is 0.9 kg/m3 in this study. Furthermore, the compression‐shear stress‐displacement curves of specimens were obtained. The compression‐shear strength under normal stress at 6 MPa is approximately 230% greater than at 0 MPa. However, the peak shear stress of concrete is almost not affected by the replacement rate of RCA. Finally, based on the Mohr circle theory, the compression‐shear calculation model of PPFRAC is verified, and the optimal calculation formula is given.

A new mesoscopic calculation model of chloride ion erosion in recycled coarse aggregate concrete (RAC): Characteristic fractal dimension of pore structure and service life prediction

This research investigates the influence of water-cement ratio and recycled aggregate content on the chlorine erosion resistance of RAC by conducting a combination of experimental and theoretical analysis. In addition, a mathematical equation is developed to represent the chloride ion transport mechanism in RAC, taking into account fluid mechanics, energy conservation, and pore structure evolution characteristics. Furthermore, mathematical analysis and modeling are used to forecast the life of the chloride ion erosion process. The results show that both the recycled coarse aggregate replacement rate and the water-cement ratio adversely affect the chloride erosion resistance of RAC. The chloride diffusion coefficient model based on pore structure characteristic parameters exhibits high prediction accuracy. This model helps increase the use of recycled aggregates and fosters the growth of the circular economy in the construction industry sector by offering a theoretical foundation for evaluating and maintaining the durability of RAC.

A comprehensive investigation on sulphate resistance of geopolymer recycled concrete: Macro and micro properties

As a potential alternative to ordinary Portland cement concrete (OPC), geopolymer recycled concrete (GRC) is provided with great research value as it not only significantly reduces carbon dioxide (CO2) emissions but also promotes the resourceful use of construction and demolition waste (CDW). However, concrete is frequently subjected to extreme circumstances such as sulphate attack during service. To comprehensively explore the structural and performance damage mechanisms of GRC caused by sulphate assault, this study is conducted to erode GRC specimens with recycled aggregate (RA) replacement rate of 0%, 30%, 50%, 70% and 100% by using magnesium sulphate solution with 10% mass fraction. The macroscopic properties of GRC subjected to sulphate attack are examined, including mass loss rate, relative modulus of elasticity and compressive strength. The microstructure and phase evolution of GRC subjected to sulphate attack is analyzed by SEM, EDS and XRD. The micro-mechanical properties of interfacial transition zones (ITZs) in GRC are measured by nanoindentation. The results show that there is no loss of mass in all GRC specimens throughout the erosion age, and the relative dynamic elastic modulus of GRC first increases and then decreases. GRC with 30% RA substitution rate has the best resistance to sulphate attack. The degradation of GRC by sulphate attack is closely related to its internal structural changes. The deterioration of the micromechanical properties of three ITZs by sulphate erosion is not significant, which indicates the RA has favorable performances with geopolymer binder contributing to excellent resistance of GRC to sulfate attack. In addition, a prediction model for the evolution of GRC resistance to sulfate erosion with erosion age for different RA substitution rates is developed, which provides a theoretical guidance for the application of GRC.

Analysis of the Performance of Recycled Insulation Concrete and Optimal Mix Ratio Design Based on Orthogonal Testing.

Construction and agricultural waste recycling have gained more and more attention recently as renewable resources. Straw and construction waste, both of which are widespread in northern Fujian, were investigated in this research. The orthogonal test was used to investigate the effects of recycled aggregate, straw, and glazed hollow beads on the mechanical and thermal properties of recycled insulation concrete. The influence of different factors on the macroscopic characteristics of recycled insulation concrete was examined using scanning electron microscopy (SEM). The optimal mix proportion for recycled insulation concrete that satisfies mechanical performance standards and provides superior insulation performance was then determined using the total efficacy coefficient method. According to the research findings, the heat conductivity of recycled insulation concrete decreases as its dried density decreases. A 100% recycled coarse aggregate replacement rate, 1% straw content, and 10% glazed hollow beads replacement rate are the optimal mix ratios for recycled insulation concrete. With a compressive strength of 20.98 MPa, a splitting tensile strength of 2.01 MPa, a thermal conductivity of 0.3776 W/(m·K), and a dry density of 1778.66 kg/m3, recycled insulation concrete has the optimal mix ratio. Recycled insulation concrete is a novel form of eco-friendly, energy-saving concrete that aims to achieve low-carbon energy savings and sustainable development by combining resource recycling with building energy savings to realize the recycling of solid waste resources, which has significant environmental, social, and economic benefits and broad market application potential.

Experimental Investigation on a Novel Temperature-Controlled Phase Change Aggregate Concrete: Thermo-Mechanical Properties and Hydration Heat Control.

To reduce the structural deterioration of mass concrete structures from temperature cracks, and lower energy consumption caused by the traditional mass concrete hydration heat cooling process, this paper reports the preparation of concrete temperature-controlled phase change aggregate (PCA) by a vacuum compaction method using light and high-strength black ceramite and No. 58 fully refined paraffin wax as phase change material (PCM), and the encapsulation technology of the aggregate by using superfine cement and epoxy resin. Further, through laboratory tests, the cylinder compressive strength, thermal stability and mixing breakage rate of the encapsulated PCA were tested, and the differences in mechanical properties such as compressive strength, flexural strength and splitting tensile strength between phase change aggregate concrete (PCAC) and ordinary concrete were studied. A test method was designed to test the heat storage effect of PCA, and the temperature control effect of PCAC was analyzed based on the law of conservation of energy. The research conclusions are as follows: (1) Both superfine cement and epoxy resin shells increase the strength of the aggregate, with the epoxy resin increasing it more than the superfine cement. The thermal stabilization of the PCA is good after encapsulation of superfine cement and epoxy resin. However, PCA encapsulated in superfine cement is more easily crushed than that encapsulated in epoxy resin. (2) Under the condition of water bath heating and semi-insulation, when the water bath temperature reaches 85 °C, the temperature difference between the PCA and the common stone aggregate can be up to 6 °C. Based on the law of energy conservation, the test results will be converted to mass concrete with the same volume of aggregate mixture;, the difference of PCAC and ordinary concrete temperature can be up to 10 °C, so the temperature control effect is significant. (3) The mechanical properties of PCAC with 100% aggregate replacement rate compared to ordinary concrete are reduced to varying degrees, and the performance decline of the epoxy-encapsulated PCA is smaller than that encapsulated with superfine cement; in an actual project, it is possible to improve the concrete grade to make up for this defect.

Mechanical Properties of Polypropylene Fiber Recycled Brick Aggregate Concrete and Its Influencing Factors by Gray Correlation Analysis

Making construction waste into raw materials for recycled concrete is beneficial for resource conservation and environmental protection. This paper investigated the effects of different recycled brick aggregate (RBA) replacement rates (30%, 50%, 70%, and 100%) and different contents of polypropylene fibers (PPFs) (0.08%, 0.10%, 0.12%, 0.16%, and 0.2%) on the mechanical properties of recycled brick concrete. Gray correlation was also used to analyze the degree of effect factors on the mechanical properties of concrete. The results showed that the mechanical properties decreased when the natural coarse aggregate (NCA) was replaced with RBA, while PPFs could better improve the mechanical properties of RBA concrete. The improvement of compressive and flexural properties was optimal when the PPF content was 0.12%; the improvement of tensile properties was optimal when the PPF content was 0.2%. In addition, PPFs significantly improved the toughness of RBA concrete. The gray correlation degrees between compressive strength (tensile strength, flexural strength) and NCA, RBA, and PPFs were 0.8964 (0.8691, 0.8935), 0.7301 (0.6530, 0.7074), and 0.5873 (0.5870, 0.5840), respectively.

Cyclic compressive behavior of hook-end steel and macro-polypropylene hybrid fiber reinforced recycled aggregate concrete

One widely accepted strategy is to add fiber into recycled aggregate concrete (RAC) to improve compressive strength. Few existing investigations have focused on the cyclic compressive behavior of hybrid fiber reinforced recycled aggregate concrete (HFRRAC). A total of eighteen groups of prismatic specimens with different fiber combinations and recycled coarse aggregate (RCA) replacement rates were conducted under cyclic compression to investigate the mechanical properties of hooked-end steel and macro-polypropylene hybrid fiber reinforced recycled aggregate concrete. Results indicate that specimens under cyclic loading fail similarly to those subjected to monotonic loading. The envelope curve of the cyclic stress-strain curve for HFRRAC closely resembles the corresponding monotonic stress-strain curve. RCA replacement rates and fiber combinations do not significantly affect plastic strain and stress deterioration. Fibers added to specimens mitigate stiffness degradation and improve hysteretic energy dissipation. The proposed constitutive equations can be used to describe the cyclic compressive behavior of HFRRAC. The fibers improve the density and structure of mortar and aggregate-paste interfaces from the microstructure morphologies. The fracture mechanisms of HFRRAC were also studied using mesoscale numerical models under uniaxial compression loading. The cohesive zone model is suitable for simulating the compressive behavior of HFRRAC. Numerical specimens fail in mixed fracture modes, primarily mode II fractures.

Steel tube filled with recycled concrete incorporating steel-fiber reinforcement and self-stressing effect

To widespread use of construction and demolition waste (CDW), an innovative steel-fiber-reinforced self-stressing recycled aggregate concrete filled steel tube (SFRCFST) is put forward. The mechanical behavior of SFRCFST under compression-bending is explored in this study. 27 specimens are conducted under eccentric compressive load, and the considered parameters are eccentricity ratio, steel tube thickness, concrete strength grade, quality replacement rates of recycled aggregate, steel fibers content and self-stress. Test results reveal that eccentric loaded SFRCFST fails in the same way of ordinary CFST columns. As the eccentric ratio is increased, the adverse impact of alternative recycled aggregates is more distinct. A double-reduction of load (Nu) and moment bearing capacities (Mu) of the specimens is observed when recycled aggregate replacement rate is increased. Introducing self-stress improves Nu and Mu with the average amount of 14.90% and 10.55%, respectively. Moreover, the flexural rigidity of SFRCFST columns is also enhanced. Moderate amount steel fibers with volume content of 1.2% ∼ 1.8% bring the improvement of Nu and Mu, as well as greater plastic development potential of SFRCFST columns. A refined FE model is proposed to simulate the eccentric loaded behavior of SFRCFST columns. Numerical results show that self-stress contributes to the confining effect throughout the loading process.

Study of recycled aggregate concrete-filled circular steel columns with H-shaped steel reinforcement

In this study, the prediction formula of the axial compressive bearing capacity of recycled aggregate concrete-filled (RAC) circular steel columns with H-shaped steel reinforcement was theoretically studied with the limit analysis method. To differentiate the restraining effect due to H-shaped steel and steel tube, the bearing capacity of the concrete is divided into two parts, i.e., recycled aggregate concrete in the H-shaped steel confined area and the recycled aggregate concrete in the steel-tube confined area. Second, the effect of inner diameter-thickness ratio of steel tube, H-shaped steel and recycled coarse aggregate replacement rate on the axial compressive bearing capacity of the column is studied. Finally, a set of calculation formulas for the axial load bearing capacity of recycled aggregate concrete stub columns with steel tubes with H-shaped steel reinforcement is proposed. The validity and accuracy of the calculation formula of the bearing capacity was assessed by comparing with test results. The error between the theoretically formula and test results was within 10%. It demonstrates the feasibility of the proposed formula and accuracy of the limit analysis method.

Calculation Method for the Cracking Resistance and Bearing Performance of SFRAC Beams.

The utilization of recycled aggregate (RCA) in preparing recycled concrete (RAC) is an effective measure to solve the increase in construction waste. Furthermore, applying RAC to flexural members is a viable practice. The addition of steel fiber to RAC to prepare steel fiber recycled concrete (SFRAC) solves the performance deterioration caused by the recycled aggregate, so it is necessary to study the effects of the recycled aggregate replacement rate and fiber-volume ratio on the crack resistance and bending performance of SFRAC beams. In this study, 13 beams were designed and manufactured, with the water-cement ratio, recycled aggregate replacement rate, and fiber-volume ratio as the primary variables, and the cracking moment and ultimate moment of the SFRAC beams were systematically studied. The results show that the cracking and ultimate moments of the SFRAC beams increased with decreases in the water-cement ratio or with increases in the fiber-volume ratio and were unaffected by the replacement rate of recycled aggregates. Based on the experimental results and theoretical analysis, a calculation model and formula for the cracking moment were established. The ultimate bearing capacity of SFRAC beams can be accurately determined using the ACI 318 and ACI 544 standards. The research results serve as a valuable reference for the design of SFRAC beams, effectively address the issue of performance degradation in RAC structural members, and promote the use of green building materials.

Mechanical properties of short polypropylene fiber enhanced recycled concrete under cyclic compression

AbstractThis study investigated the mechanical properties and stress–strain relationship of polypropylene fiber recycled aggregate concrete (PFRAC) subjected to uniaxial cyclic compression. A total of 78 cylindrical specimens were designed for uniaxial cyclic compression test with coarse aggregate replacement rate, polypropylene fiber volume fraction, and loading rate as variation parameters. The failure process of the specimens under cyclic loading was observed and recorded. The stress–strain curve of PFRAC was summarized. The important mechanical properties of PFRAC were obtained, such as plastic strain, accumulated energy dissipation. The microstructure of PFRAC was analyzed by scanning electron microscopy, and the crack resistance mechanism of PFRAC under cyclic loading was revealed. The results show that the PFRAC under cyclic loading appeared oblique splitting failure. The compressive stress–strain curve envelope of PFRAC subjected to cyclic loading exhibited similarity to the monotonic counterpart. The addition of polypropylene fibers can improve the peak stress, peak strain, residual stress, post‐peak ductility, and accumulated energy dissipation of the recycled concrete. In addition, a constitutive relation formula for the PFRAC stress–strain curve under cyclic loading is proposed, and the fitting result is good.

An experimental investigation of the bond performance of BFRP bars with recycled-aggregate concrete of different particle sizes

The pull-out test was performed in this study to investigate the bond performance between basalt fiber reinforced polymer (BFRP) bars and recycled concrete. Three factors were considered: aggregate size (5–10 mm, 11–15 mm, and 16–20 mm), bond anchorage length of bars (3D, 5D, and 7D), and the recycled aggregate replacement rate (0%, 30%, 60%, and 100%). The bond–slip mechanism, failure mode, bond stress distribution, and bond–slip curves were all analysed. Based on the results, it was found that situations with a high recycled aggregate replacement rate, large aggregate particle sizes, or long bond lengths have an increased likelihood of experiencing splitting failure. As the aggregate size increases, the bond strength between the BFRP bars and the concrete would also increase, in ordinary concrete, a 22.54% increase was observed, whereas in recycled concrete, the maximum increase reached 48.20%. The effect would be more pronounced on recycled concrete compared to ordinary concrete, and it would also be more significant in specimens with BFRP bars compared to steel bars. Additionally, the optimal bond anchorage length was determined to be 5D. The bond strength exhibited a trend of decrease followed by an increase as the recycled aggregate replacement rate increased. The maximum reduction of 59.7% in bond strength was observed when the replacement rate of recycled aggregate reached 60%. Moreover, when the replacement rate of recycled aggregate increased to 100%, there was a decrease of 19.05% in bond strength compared to the specimen without recycled aggregates. Based on the experimental test data and existing models, an improved two-stage bond–slip constitutive model was proposed.

Improvement of Computational Efficiency and Accuracy by Firefly Algorithm and Random Forest for Compressive Strength Modeling of Recycled Concrete

It is an important direction for the sustainable development of pavement to mix the discarded concrete blocks with gradation according to a certain proportion after crushing, cleaning and other technological processes, partially or completely replace aggregate, and then add cement, water, and so on to make recycled concrete for pavement paving, but the traditional evaluation model for the compressive strength (CS) of recycled concrete cannot meet the requirements of efficient calculation. To address such issues, the present research proposed to apply the firefly algorithm (FA) to optimize the random forest (RF) model. The results were demonstrated by comparing the consistency of predicted and actual values, and also by analyzing the correlation coefficient (R) and root-mean-square error (RMSE). Higher R values (0.9756 and 0.9328) and lower RMSE values (3.0752 and 6.4369) for the training and test sets present the reliability of the FA and RF hybrid machine learning model. To understand the influence law of input indexes on the output index, the importance and sensitivity of variables are further analyzed. The results displayed that effective water-cement ratio (WC) and nominal maximum recycled concrete aggregate size (NMR) have the greatest impact on the output variable, with importance scores of 2.5947 and 2.4315, respectively, while the change in the recycled concrete aggregate replacement rate (RCA) has a weak influence, with an importance score of 0.4695. Introducing FA to RF for the compressive strength modeling of recycled concrete can significantly improve the computational efficiency and accuracy.

Experimental study on bonding performance of GFRP bars-recycled aggregate concrete under sulfate attack environment

The sufficient bonding performance between glass fiber reinforced polymer (GFRP) bars-concrete is essential for the composite section's integrity. In addition, sulfate attack is one of the primary causes of concrete damage, which will inevitably lead to a decline in bonding performance between GFRP bars and recycled aggregate concrete (RAC). This paper uses the GFRP bar-RAC pull-out test to study the effect of recycled aggregate (RA) replacement rate and RAC protective layer thickness on bonding performance under continuous sulfate immersion. The results indicated that as the sulfate attack time increases, the bond strength of various GFRP bars-RAC specimens rises and then decreases. At the same time, as the RA substitution ratio grows, the specimen requires less time to reach its peak of bond strength, and the bond strength decreases rapidly in the later stages of erosion. When the erosion age reaches 360 days, the bond strength of specimens with recycled RA rates of 0%, 25%, 50%, and 100% drops by 12.93%, 15.18%, 17.99%, and 28.22%, respectively, compared to those without erosion. Since sulfate attacks RAC from the outside, the bond strength of the specimen with a thin protective layer thickness decreases faster after long-term erosion. Through the fitting analysis of the variation law of bond strength of 7 groups (147) specimens, a prediction model of GFRP bars-RAC bond strength is developed, considering the influence of RA substitution ratio and protective layer thickness under continuous sulfate immersion. The ratio of all predicted values to experimental values ranges between 0.94 and 1.133. It provides reliable guidance for the GFRP bar-RAC structure's durability design.

Mechanical Properties of Steel Fiber-Reinforced, Recycled, Concrete-Filled Intersecting Nodes in an Oblique Grid

The construction of high-rise oblique grid buildings requires a large amount of concrete. To save resources, an oblique grid of intersecting nodes composed of steel outer tubes and steel fiber, recycled concrete inner tubes (OGSFRCIN) has been proposed. ABAQUS is used to study the mechanical properties of the nodes under axial pressure, accounting for the effects of six parameters: the oblique angle, the thickness of the stiffening ring, the thickness of the connecting plate, the concrete strength, the recycled aggregate replacement rate, and the steel fiber content. The results show that the oblique angle, connecting plate thickness, concrete strength, and steel fiber content significantly affect the ultimate bearing capacity of specimens. The reinforcing ring thickness has a significant effect on the evolution of lateral displacement. It is not advisable to use components with a replacement rate of 100% recycled aggregate in engineering practice because of insufficient lateral stiffness and ultimate strength. The specimen’s out-of-plane displacement is tightly restricted when the connecting plate’s thickness is greater than or equal to 10 mm. In practical engineering, the connecting plate and reinforcing ring thickness should not be less than 10 mm, and the recommended steel fiber content is 1.0% to 2.0%. Through the analysis of the mechanical properties of the OGSFRCIN under monotonic axial compression and reciprocating axial tension and compression loads, it can be seen that OGSFRCIN have good mechanical properties and can be applied in engineering practice. Here, the modified formulas for calculating the bearing capacity of OGSFRCIN are put forward.

Mechanical behavior and environmental assessment of steel-bars truss slab using steel fiber-reinforced recycled concrete

Steel-bar truss slab (SBTS) is a new type of floor system with a high construction speed and environmental benefits. In this study, four-point bending tests were used to study the flexural behavior of SBTSs with eight different recycled concrete aggregate (RCA) replacement rates, steel fiber (SF) contents, concrete strengths, and slab thicknesses, including damage modes, crack development, mid-span deflection, reinforcement strains, Concrete strain and profiled steel sheeting (PSS) strain. Increasing the replacement rate of RCA (ra) resulted in decreasing trends of the cracking, yield, and ultimate loads of the SBTS. The addition of SFs could improve the flexural behavior of the SBTS while improving the crack development pattern. Based on a calculation of ordinary reinforced concrete slabs, a modified calculation method applicable to SBTS using steel fiber-reinforced recycled concrete (SFRRC) is proposed, including flexural capacity, crack width, and flexural stiffness. Cost analysis and life cycle assessment showed that the application of SFRRC to SBTS can better balance environmental and mechanical performances, which is beneficial to the sustainable development of the construction industry.