Search

The aim of this investigation is to assess the impact of using nano‐silica (Na) at varying weight percentages of 0%, 1.5%, 3%, 4.5%, and 6% as partial cement substitute on fracture parameters of recycled aggregate concrete (RAC). A servo‐controlled testing system was employed to carry out three‐point flexure tests on 90 notched beams. Boundary effect method was used in order to interpret the fracture features. The results illustrate that adding Na increases the size‐independent fracture energy, fracture toughness and initial fracture energy of RAC by 29%, 32%, and 24% compared to that without Na, respectively. The maximum values of these parameters occur at 4.5% Na. The reference crack length (α∞*$$ {\alpha}_{\infty}^{\ast } $$) decreases from 6% to 22% by adding 1.5% to 6% Na. This shows that the RAC gets more brittle by the addition of Na. Moreover, the RAC behavior moves towards linear elastic fracture mechanics criteria by adding Na. Finally, according to the mechanical properties and test variables, multivariable models were suggested for prediction of the fracture parameters of the RAC containing Na. The models predictions were compared with experimental findings of the previous research. [ABSTRACT FROM AUTHOR]

This study developed three composite slurries for coating recycled aggregate by incorporating polyacrylate emulsion, fly ash, and gypsum into a cement-based mixture. The filling and pozzolanic effects of fly ash help to improve microcracks in the recycled aggregates. The polyacrylate emulsion forms a strong bonding layer between the cement matrix and the aggregates, enhancing the interfacial bond strength. Based on relevant studies, the following mix designs were developed: Slurry 1 consists of pure cement paste; Slurry 2 contains 15% fly ash and 3% gypsum added to the cement paste; Slurry 3 adds 22% polyacrylate emulsion to the slurry. The study first compared the effects of the three composite slurries on the crushing value and water absorption of recycled aggregates, and then analyzed their impact on the mechanical properties, permeability, and drying shrinkage of concrete. Finally, the mechanisms behind the enhancement were investigated using the Vickers Hardness Test (HV), Mercury Intrusion Porosimetry (MIP), and scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). The results showed that the polyacrylate emulsion composite slurry had the most significant improvement effect. For recycled aggregate AL, the crushing value decreased from 28.8% to 22.5% and the saturated surface–dry water absorption decreased from 15.1% to 13.8% after cement slurry modification. After coating with the composite slurry, the crushing value further dropped to 18.2% and the water absorption to 9.5%. Two aspects of the performance of recycled aggregates are enhanced with the polymer composite slurry: first, fly ash provides nucleation sites for CH, reducing the tendency for directional CH alignment. Second, the long chains of PAE (polyacrylic ester) encapsulate cementitious particles, effectively filling surface defects on the recycled aggregates, improving the bonding strength at the new-to-old interface, and significantly enhancing the performance of both recycled aggregates and recycled concrete. [ABSTRACT FROM AUTHOR]

In order to improve the quality of solid waste utilization, this study simultaneously used recycled coarse aggregate and recycled fine aggregate to prepare recycled aggregate concrete, with fly ash partially replacing cement as a binder. After the particle gradation of recycled aggregate was artificially adjusted into continuous gradation, the effects of accelerated carbonation on the performance and microstructure of recycled concrete were studied. The microstructural change was analyzed using mercury intrusion porosimetry and scanning electron microscopy–energy dispersive spectroscopy. Additionally, the environmental benefits of the recycled concrete were evaluated based on carbon emissions using the life cycle assessment method. The experimental results indicate that accelerated carbonation can increase the compressive strength of recycled concrete by up to 13%, and its microstructure becomes more compact after carbonation. The carbon emissions are reduced by more than 13% after using 20% fly ash, contributing to sustainable development. Additionally, the optimal replacement rate of recycled fine aggregate should be controlled to under 15% when both recycled coarse and fine aggregates are used. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the possibility of using recycled concrete aggregate (RCA) as an alternative to coarse natural aggregates (NAs) in warm-mix asphalt (WMA). The index engineering characteristics of the RCA used for the asphalt mixtures were determined. The physical and rheological characteristics of virgin and modified asphalt binders were specified using conventional and performance grade (PG) tests. The WMA was manufactured by two approaches. The first approach involved modifying the asphalt binder properties by incorporating Sasobit as an organic additive into the heated asphalt binder (wet process). The second approach incorporated Asphamin as a synthetic zeolite foaming additive into the aggregate during the mixing process (dry process). Nanosilica fume (NSF) was used as an economical alternative to nanomaterials to improve the investigated WMA's performance compared with a control hot-mix asphalt (HMA) containing 100% coarse RCA/100% fine NA. The performance of the asphalt mixtures in terms of Marshall, indirect tensile strength (ITS), dynamic modulus (E*), and flow number (FN) was also estimated. The Marshall test results of WMA mixtures with the two types of additives were relatively identical with the control HMA mixture with a slight difference in the optimum asphalt content (OAC). However, the NSF incorporation as a replacement to the mineral filler within the WMA mixtures led to an increase in stability values by up to 35%, especially at 40% NSF with low OAC. The tensile strength ratio (TSR) values for WMA mixes were lower than 80%, but the use of NSF showed a slight enhancement in their values to meet the minimum requirement set by Egyptian specifications. Also, the results revealed a decrease in E* and FN values for the WMA mixtures compared with those for the HMA control, whereas the addition of NSF enhanced the results significantly to outperform the HMA. Practical Applications: This research highlights the use of recycled concrete aggregate as a replacement for coarse natural aggregates for manufacturing warm-mix asphalt with two different technologies and compares their performance with hot-mix asphalt. In addition, the effect of using by-product materials such as nanosilica fume as an economical alternative to nanomaterials for raising the efficiency of warm-mix asphalt mixtures was sought. The results provide a better understanding of the performance of warm-mix asphalt mixtures, which contribute effectively to achieving environmental sustainability in the pavement industry. [ABSTRACT FROM AUTHOR]

Sustainable construction represents a pivotal aspect of contemporary engineering endeavors, which are directed towards the minimization of the detrimental impact of the construction sector on the environment. This is achieved through the efficient utilization of resources and the reduction of waste generation. The study presented an analysis of the mechanical properties of ad hoc reinforced concrete beams made of concrete with recycled and natural aggregate. The objective of this study was to assess the potential of recycled aggregates as a substitute for natural aggregates in reinforced concrete structures, with the aim of contributing to the sustainable development of construction. The experiments compared the behavior of reinforced concrete beams with the same degree of reinforcement but differing in the type of aggregate. The results demonstrated that recycled aggregate beams exhibited lower stiffness and higher deformation under load compared to natural aggregate beams, particularly at loads close to the breaking force. Nevertheless, similar failure modes and cracking patterns were observed in both types of beams, indicating that concrete with recycled aggregate could be employed effectively in specific structural applications. [ABSTRACT FROM AUTHOR]

This study aims to determine the efficiency of concrete containing multiple recycled materials, recycled concrete aggregates (RCAs) and recycled steel fibers (RSFs), and compare it with conventional concrete. Natural coarse aggregate (NCA) in the concrete mix was partially replaced with 30% RCA to achieve a target compressive strength of 30 MPa after 28 days. Different types of fibers (steel fibers, RSFs, and mixed fibers) were added at varying percentages (1.0%, 1.5%, and 2.0%) to improve the mechanical properties of the concrete mixes. The shear behavior of reinforced concrete beams containing RCA and different types of fibers was investigated. Ten concrete mixtures were designed, and 10 reinforced concrete beams were tested under a two‐point load to estimate the contribution of various fiber types to the shear resistance. The results indicate that the addition of different types of fibers significantly enhances compressive, tensile, and flexural strengths of the concrete. Specifically, the improvement in compressive strength for RSFs was 38.9% at 1.5%, tensile strength improved by 21.1%, and flexural strength by 46.2% at the same fiber percentage, thereby improving the concrete's ability to resist cracks through an increase in shear resistance. [ABSTRACT FROM AUTHOR]

A sustainable alternative to conventional concrete involves using recycled aggregates (RA) instead of natural aggregates (NA) and incorporating wheat straw ash (WSA) as a partial replacement for Portland cement. The demand for high-performance concrete (HPC) is rising due to the need for architecturally complex structures and long-span bridges, but HPC's low ductility necessitates reinforcement. Waste tire steel fibers (WTSFs) are gaining popularity for their tensile strength. However, WSA-RA concrete's low early strength is a challenge. Chemical activators like sodium sulfate can enhance early-age strength. This study evaluated the durability and strength of fiber-reinforced concrete with both inactivated and activated WSA. Tests included compressive strength, indirect tensile strength, modulus of rupture (MOR), acid attack resistance, chloride penetration, sorptivity, and water absorption. Activated WSA-RA concrete showed significantly improved early strength. The mixture with 30% RA, 40% WSA, WTSFs, and activator exhibited the highest strength at 90 days. At 60% RA content, activated concrete with 40% WSA and 2.5% WTSFs outperformed the control. Durability was enhanced with a 14–17% reduction in water absorption and sorptivity and a 25.2% decrease in chloride penetration. Acid resistance improved by 26%. X-ray diffraction (XRD) confirmed these findings with elevated hydration product peaks. This study demonstrates that chemical activation of WSA optimizes the engineering properties of WSA-modified HPC with WTSFs and RA, providing a sustainable solution to their challenges. [ABSTRACT FROM AUTHOR]

Soft computing techniques have become popular for solving complex engineering problems and developing models for evaluating structural material properties. There are limitations to the available methods, including semi-empirical equations, such as overestimating or underestimating outputs, and, more importantly, they do not provide predictive mathematical equations. Using gene expression programming (GEP) and artificial neural networks (ANNs), this study proposes models for estimating recycled aggregate concrete (RAC) properties. An experimental database compiled from parallel studies, and a large amount of literature was used to develop the models. For compressive strength prediction, GEP yielded a coefficient of determination (R²) value of 0.95, while ANN achieved an R² value of 0.93, demonstrating high reliability. The proposed predictive models are both simple and robust, enhancing the accuracy of RAC property estimation and offering a valuable tool for sustainable construction. [ABSTRACT FROM AUTHOR]

This review presents the scope of current efforts to utilize recycled construction and demolition waste in mortars for masonry. More than 100 articles are divided into groups pertaining to the type of mortar, different binder systems, the type of construction and demolition waste (CDW), and its utilization specifics. Cement-based mortars dominate this research domain, whereas recycled concrete is the main material employed to replace virgin aggregates, followed by recycled masonry and recycled mixed waste aggregates. Such application in cement-based mortars could increase water demand by 20–34% and reduce strength by 11–50%, with recycled concrete aggregates being the most favorable. Natural aggregate substitution is disadvantageous in strong mortars, whereas weaker ones, such as lime-based mortars, could benefit from this incorporation. The extent of this topic also suggests possibilities for different recycled material use cases in mortars for masonry, although the available literature is largely insufficient to infer meaningful trends. Nonetheless, the most relevant knowledge synthesized in this review offers promising and environment-conscious utilization pathways for recycled concrete and other construction and demolition waste, which brings opportunities for further research on their use in mortars for masonry and industrial-scale applications. [ABSTRACT FROM AUTHOR]

Bolivia has abundant pebbles, while the supply of crushed stone is limited and unstable. Thus, the resource utilization of local pebble as a coarse aggregate and the guarantee of concrete durability are the key scientific issues in the Sucre Highway Project. In this paper, a comparative analysis was conducted of the performance of crushed stone concrete and pebble concrete. Additionally, the impact of fly ash on the water permeability resistance of concrete was investigated. The results indicate that the apparent density, bulk density, and void ratio of pebbles are lower than those of crushed stone, and the aggregate gradation of pebbles is dispersed. The type of aggregate is the primary factor influencing the splitting tensile strength of concrete, with the main failure modes of pebble concrete being slurry cracking, aggregate crushing, and interface debonding. While aggregate and fly ash have a minor effect on compressive strength, they significantly impact flexural tensile strength; however, all concretes meet the requirements for extra-heavy, very heavy, and heavy traffic load levels. In terms of impermeability, fly ash effectively mitigates the negative impact of aggregate type on the impermeability of concrete. These findings support the application of pebble concrete in the highway project. [ABSTRACT FROM AUTHOR]

AbstractPopulation growth and urban expansion have increased impervious surfaces, leading to environmental issues such as stormwater runoff and groundwater depletion. Traditional concrete, while durable, contributes to these problems. There is a need for sustainable construction materials that can address environmental challenges and reduce the consumption of natural resources. Pervious concrete, enhanced with recycled aggregates (RCA) and supplementary cementitious materials (SCMs) like metakaolin (MK) present a potential solution. This study aims to improve the mechanical and durability properties of pervious concrete by incorporating RCA and MK, assessing their effects on workability, density, porosity, permeability, compressive strength and flexural strength. The incorporation of RCA resulted in increased aggregate porosity compared to natural aggregates. Workability was assessed using the slump test, density was measured, and porosity and permeability were evaluated. The results showed that incorporation of RCA generally decreased workability, density and strength, while the addition of MK improved these properties by refining the microstructure. Specifically, mixes with 10% MK demonstrated better performance in terms of increased compressive and flexural strengths, improved density and reduced porosity. The ANN model showed high accuracy in predicting compressive and flexural strengths. The study concludes that RCA and MK can enhance the mechanical and durability properties of pervious concrete. [ABSTRACT FROM AUTHOR]

The study presents an investigation into the preparation and characterization of modified hemp fiber reinforced recycled construction waste bricks for ground and road applications. By incorporating 1 % hemp fiber and a 70/30 ratio of recycled concrete aggregate to recycled brick aggregate, the optimal combination was identified, resulting in a maximum compressive strength of 36.2 MPa, a 38.7 % improvement over the control bricks. The addition of 2 % hemp fiber increased the flexural strength by 85.7 %, while the thermal conductivity decreased by 41.5 % with the inclusion of 2 % hemp fiber and 100 % recycled brick aggregate. Scanning electron microscopy and X-ray diffraction analysis confirmed the compatibility of hemp fibers with the cement matrix and their role in enhancing the microstructure of the bricks and hydration process. These findings highlight the potential of hemp fiber-reinforced recycled waste bricks as environmentally friendly high-performance materials for sustainable ground and road construction. [ABSTRACT FROM AUTHOR]

Translation abstract Durable and sustainable bridge caps made of non‐metallic reinforcement and recycled concreteDue to chloride‐induced corrosion, bridge caps made of steel‐reinforced concrete need to be replaced regularly or more often than planned. As part of a ZIM project funded by the Federal Ministry for Economic Affairs and Climate Action, bridge caps made of non‐metallic basalt fibre reinforcement and recycled concrete were developed to mitigate the weakness of corrosion and to better utilize the materials in terms of the material cycle. To achieve this, bend reinforcement elements made of chloride‐resistant basalt fibre reinforcement and concrete with high frost‐thaw resistance were developed, consisting of up to 100 % recycled aggregate. All sub‐developments were integrated into a holistic approach, and a prototype of a resource‐efficient and durable bridge cap was successfully produced and tested. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) is widely recognized as a promising approach for recycling construction and demolition waste. However, its practical application remains limited. A contributing factor to this limitation is the incomplete understanding of RAC's durability characteristics, particularly its permeability, which is closely tied to the transport of harmful ions within the concrete matrix. Despite the critical importance of this issue, research in this area is still relatively sparse. This knowledge gap has motivated the current study, which seeks to thoroughly investigate the water permeability properties of RAC. In this comprehensive study, 84 specimens were fabricated for permeability testing. This study explores the influence of various factors, including the sources of coarse and fine recycled aggregates (RAs), the RA replacement ratios, and the water-to-binder ratio. The results indicate that the inclusion of both coarse and fine RAs reduces the impermeability of concrete. However, enhancing the quality of these RAs—specifically by increasing the compressive strength of the source concrete—can mitigate the reduction in impermeability. A statistical relationship is established between the average and maximum water permeation depths measured during permeability testing, leading to the formulation of a correlation between the permeability coefficient and the impermeability grade of RAC. Furthermore, mercury intrusion porosimetry testing was conducted to quantitatively analyze the pore structure of the mortar in RAC, providing a microscopic perspective that explains the macroscopic permeability behavior observed. Finally, a predictive model for estimating the permeability coefficient of RAC is proposed, demonstrating a high level of accuracy. [ABSTRACT FROM AUTHOR]

This study investigates the enhancement of recycled concrete aggregate (RCA) surfaces with nano-TiO2 for an improved degradation of low-concentration sulfur dioxide (SO2). Nano-TiO2 particles, known for their photocatalytic properties, were uniformly deposited on RCA surfaces. Upon exposure to SO2 under light irradiation, the functionalized RCA exhibited significantly improved degradation efficiency. This was attributed to the photo-induced oxidation of SO2 by nano-TiO2. Enhanced degradation was further observed under UV light due to increased photoactivation. The nano-TiO2 coating also showed good durability and stability, ensuring long-term effectiveness. The experimental outcomes reveal that TiO2-treated recycled aggregates exhibit an 85% retained photocatalytic activity post five cycles of reuse. Furthermore, the investigation employs a second-order polynomial-based mathematical fitting function to generate a three-dimensional trend surface, visually illustrating the inverse relationships between sulfur dioxide degradation and environmental variables, such as initial concentration and flow rates. Finally, this study demonstrates the potential of nano-TiO2-modified RCA for mitigating the environmental impact of low-concentration SO2, contributing to the development of more sustainable construction materials and broadening RCA's applications in environmental remediation. [ABSTRACT FROM AUTHOR]

In order to increase the suitability of coarse recycled concrete aggregates and improve the frost resistance of recycled coarse aggregate concrete, this study aims to investigate the effects of an antifreeze-type water-reducing admixture, air-entraining admixture, and antifreeze admixture on the frost resistance of recycled coarse aggregate concrete. The effectiveness of these admixtures is gauged by the mass loss rate and the relative dynamic modulus of elasticity (RDM). Mercury-impressed porosimetry (MIP), super depth of field microscopy, and scanning electron microscopy (SEM) were employed to characterize the hydration products, microstructure, and pore structure of recycled coarse aggregate concrete, with a view to establishing a connection between the microstructural characteristics and the macro properties and analyzing the micro-mechanism of the improvement effect of frost resistance. The test results demonstrate that the admixtures have a significant impact on the frost resistance of recycled coarse aggregate concrete. In particular, the recycled coarse aggregate concrete with an antifreeze admixture (dosage of 1%) and a water–cement ratio of 0.41 exhibited a mass loss of only 1.23% after 200 freezing and thawing cycles, a relative dynamic modulus of elasticity of up to 93.97%; however, the control group had reached the stopping condition at 150 freeze–thaw cycles with more than 10% mass loss. The recycled coarse aggregate concrete with added antifreeze admixture had a tight connection between the aggregate and the paste and a more pronounced improvement in the pore structure, indicating excellent resistance to frost damage. [ABSTRACT FROM AUTHOR]

The given text provides information on various publications, symposiums, and individuals related to the field of concrete and precast industry. The fib Bulletin 112 offers guidance on concrete durability, while the fib Bulletin 113 focuses on polymer-duct systems for post-tensioning. The fib Symposiums in Antibes and Rio de Janeiro will address key issues in concrete and innovative materials, and the fib Achievement Award recognizes young engineers for their contributions. Bruno Della Bella is recognized for his significant contributions to the precast industry, particularly in the research and development of hollow core slabs. [Extracted from the article]

The utilization of recycled concrete and glass aggregates in concrete production has emerged as a highly promising method to significantly increase the recycling rate of waste materials. However, the interaction between alkaline environment and silica present in concrete detrimentally impacts mechanical properties and durability of the concrete due to the significant silica content of the aggregates. This study aims to develop a high‐performance and sustainable concrete to resist alkali–silica reaction (ASR). The study focuses on the use of a blend of ground granulated blast furnace slag (GGBS) and fly ash (FA) as binder materials to mitigate negative effects of the ASR on the mechanical properties and and durability of concrete made with crushed glass sand and coarse recycled concrete aggregate (RCA). Various tests, including ASR expansion, flow, slump, density, compression, three‐point bending, water absorption, and chloride attack, were conducted. Furthermore, microanalysis using scanning electron microscopy and energy‐dispersive x‐ray spectroscopy was performed. Based on the results, it is found that the GGBS is less effective than the FA in reducing the ASR expansion of the concrete, with only 3%, 9%, and 12% decreased expansion as a result of the addition of 20%, 40%, and 70% GGBS to the concrete containing 30% FA, respectively. It is also shown that combining 20% GGBS with 30% FA in the RCA concrete containing glass sand develops similar compressive and flexural strengths and water absorption compared to that containing natural sand. This can be related to the pozzolanic reaction of the FA and GGBS, which helps to retain the alkalis for reducing the crack development and propagation in the concrete. However, further GGBS content leads to a decrease in the strengths and an increase in the water absorption of the concrete. The results of this study point to the significant potential of combining FA and GGBS at an optimum ratio to mitigate the ASR effect on RCA concretes containing crushed glass sand. This approach helps in minimizing the emission of greenhouse gases and other pollutants generated during cement production, thereby mitigating environmental pollution. Additionally, it helps the preservation of natural resources by reducing the depletion of natural sand and coarse aggregate. [ABSTRACT FROM AUTHOR]

The effects of dry or saturated state, water–cement ratio, coarse aggregate type and steel fiber on the stress–strain relationship of RAC under cyclic loading were studied. What is more, the characteristics of stress–strain curve, plastic strain, stress degradation and stiffness degradation of RAC under cyclic loading were analyzed. The microstructure of RAC was analyzed. Based on the principle of surface energy, the reason for the decrease in compressive strength of wet concrete was analyzed. In addition, the envelope equation of stress–strain curve under cyclic loading, unloading and reloading curve was established. The test results showed that the peak stress of the envelope line of RAC under cyclic loading was affected by dry or saturated state, water–cement ratio and coarse aggregate type, but the addition of steel fiber could reduce the degradation rate of stress and stiffness of RAC after peak strain. The plastic strain accumulation of RAC before and after the peak stress was quite different, but dry or saturated state, water–cement ratio, coarse aggregate type and steel fiber have no obvious influence on the plastic strain accumulation of RAC. The pores and cracks of RAC provide space and channels for the moisture absorption and water absorption. The Weibull–Lognormal statistical distribution envelope model, unloading curve model and reloading curve model established were in good agreement with the experimental curves. The research results provided a reference for the study of the full curve constitutive model of RAC under cyclic loading. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) fibers are green, environmentally friendly materials. They mainly come from recycled plastic bottles and other products. The addition of PET fibers to recycled aggregate concrete (RAC) has the potential to reduce concrete damage and increase specimen toughness. In this study, the influences of recycled coarse aggregate (RCA) replacement ratio and fiber volume ratio on the impact response of PET fiber reinforced RAC at various strain rates were experimentally investigated. It was found that the compressive strength, critical strain, and toughness grew with the increasing strain rate, followed by the aggravation of the concrete damage. Owing to the strain rate effect, the failure mode of concrete specimen at a high strain rate was different from that under a quasi‐static loading. This led to the reduction of differences in the dynamic compressive strength between the natural and recycled aggregate concrete at a high strain rate. Although the replacement of natural coarse aggregates with RCAs resulted in the decrease in the dynamic compressive strength, it increased the critical strain of the specimen. To reduce the brittleness of concrete materials, flexible fibers, PET fibers were added into the concrete matrix. It was found that the addition of PET fibers increased the critical strain and significantly reduced concrete damage. The empirical equations were proposed to describe the rate‐dependent dynamic compressive strength, critical strain, and toughness based on experimental data. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete contributes to the recovery of construction and demolition waste, which is a growing societal concern. The technical feasibility of recycled aggregate concrete has been extensively tested and validated and the revisions of codes are already including clauses for recycled aggregate concrete specification and design. However, there are still doubts regarding its structural behavior. This article assesses the suitability of Eurocode 2 design clauses for concrete elements under compression when used for recycled aggregate concrete design. This is done through the analysis of model uncertainties that are estimated from a database collected from laboratory experiments on columns. Both the current version of Eurocode 2 (with and without taking confinement into account) and the upcoming (second generation) Eurocode 2 are considered. A database was collected with clearly defined criteria and includes coarse recycled aggregates produced from concrete waste, since columns made with other types of recycled aggregates are scarcely tested and do not represent the current status for structural recycled aggregate concrete design and production. The statistics of the model uncertainty for natural and recycled concrete columns were compared and it was observed that the mean model uncertainty tends to decrease slightly when recycled aggregates are used. However, a preliminary assessment of whether a partial factor for recycled aggregate concrete compression design should be used concluded that this partial factor is not necessary to ensure reliable design and the design of columns may be carried out using the same formulae used for conventional concrete. The format proposed may be used for other resistance models, provided that the partial factor is calibrated for each resistance model. [ABSTRACT FROM AUTHOR]

To study the bond properties between basalt fiber reinforced polymer (BFRP) bars and hybrid fibers which were basalt fiber (BF) and polypropylene fiber (PF) reinforced recycled concrete under freeze-thaw cycles, conducting center pull-out tests to study the effects of three factors on the bond properties: the number of freeze-thaw cycles, the volume fractions of single fiber, and the volume fractions of hybrid fibers. Based on the data obtained from the test, establishing a four-stage bond-slip constitutive relationship model. The results showed that the failure modes were pull-out failure and splitting failure. The bond strength decreased when adding the single fiber, with a maximum reduction of 13.18%, but the peak slip increased, with a maximum increase of 69.92%. When the volume fraction of BF was 0.3%, it achieved the optimal effect. The bond strength and peak slip increased when adding hybrid fibers, with maximum increases of 13.47 and 130.08%, respectively. However, excessive fiber content will reduce the increase of bond strength. The bond strength between BFRP bars and hybrid fiber-reinforced recycled aggregate concrete (HFRAC) increased when the number of freeze-thaw cycles increased but decreased when the number of freeze-thaw cycles exceeded 50. The four-stage bond-slip constitutive relationship model fitted well with the bond-slip curves. Compared with other fiber-reinforced recycled concrete specimens, this model fitted better with the curves of HFRAC specimens after freeze-thaw cycles and had the best fitting effect for the internal crack slip stage of the curves. [ABSTRACT FROM AUTHOR]

Use of 100 % recycled aggregates in concrete – report on practical applications This article reports on eight practical examples of applications for concrete with 100 % recycled aggregates. The applications include reinforced/unreinforced bored piles, foundations, load‐bearing internal/external walls, columns and floor slabs as well as balcony elements. Some components were realised as architectural concrete components. The respective project is summarised together with the results of the concrete development and concrete testing as well as the experience gained from obtaining special approvals in individual cases. Based on the findings from the various practical projects, it can be concluded that concrete with 100 % RC‐GK can be used for a large number of applications, so far limited to up to XC4 and XF3. Compressive strength for ready‐mix concrete up to C35/45 with good workability even with pumped concrete (here: pumping distance 45 m) using 100 % RC‐GK type 1 were possible without any problems. A concrete with sufficient early strength and a final strength of C40/50 was developed for precast elements. In two examples, RC‐GK type 2 was used for the coarse grain fraction and RC‐GK type 1 for the sand. All the projects presented have already been completed or are nearing completion. The feasibility of 100 % RC concrete in practice has thus been successfully demonstrated in several cases. [ABSTRACT FROM AUTHOR]

To develop a sustainable geopolymer concrete (GC), the efficacy of using fine recycled concrete powder (FRCP) and recycled aggregates (RA) as partial replacements for fly ash (FA) and natural aggregates (NA), respectively, was investigated. The compressive strengths of different GCs were measured. The durability performance was assessed by means of capillary suction tests, initial surface absorption tests and acid attack performed at ambient curing. The compressive strength of the GC made with 50% RA (both coarse and fine) and FRCP was found to be comparable to that of GC made with NA. Similarly, the inclusion of FRCP in the GC mixes resulted in a pore-blocking effect, restricting water ingress to the GC through capillary suction and surface absorption, even with the use of 50% coarse RA and 25% fine RA. The results demonstrated that sustainable GC can be developed using appropriate doses of FRCP and RA. [ABSTRACT FROM AUTHOR]

To investigate the mechanical properties of recycled aggregate concrete containing brick particles (RACB), compressive strength tests were conducted on RACBs with different water/cement ratios and recycled fine aggregate substitution rates. The changes in compressive strength, elastic modulus and peak strain of RACB were analysed as a function of the proportion of substituted recycled fine aggregate, and a stress–strain equation was established. A damage model was established using ultrasonic non-destructive testing technology to reveal the damage mechanism of RACB. Results show that the basic mechanical properties of RACB are best when the replacement proportion of recycled fine aggregate (r) is 30%. The model parameter a of the stress–strain curve equation is consistent with the change of elastic modulus with r. The model parameter b has a quadratic function relationship with r, reflecting the brittleness of RACB. The initial damage of RACB is relatively large, and cracks penetrate the recycled coarse aggregate, leading to specimen failure. [ABSTRACT FROM AUTHOR]

Utilization of recycled aggregates into concrete has taken a significant stride toward achieving sustainable construction, whereas temperature remains a pivotal factor adversely affecting the diverse concrete properties during service life. Thus, when exposed to elevated temperature, enhancing and evaluating sustainable concrete properties has become essential. The present article concentrates on the physical, destructive, and nondestructive properties of concrete, incorporated with fine recycled refractory brick (RRB) as a replacement of fine aggregate in combination with polypropylene fiber as the reinforcing agent, after exposure to elevated temperatures. To accomplish this, four distinct concrete blends have been prepared, with 10%, 20%, and 30% substitution of fine aggregate with RRB including one conventional (control) mix. Moreover, 1% polypropylene fiber has been incorporated as a reinforcing agent to meet the expected strength parameters. The concrete specimens have been exposed to different temperatures, 200°C, 400°C, 600°C, 800°C, 1,000°C, and 1,200°C. After exposure, different tests (visual appearance, mass loss, density loss, stress–strain profiles and compressive strength, ultrasonic pulse velocity, dynamic modulus of elasticity, degree of damage, failure pattern, and scanning electron microscope analysis) have been conducted to assess the diverse properties of concrete. The experimental findings have conclusively indicated optimal performance when 20% fine aggregate has been replaced with RRB with a compressive strength of 35.02 MPa at ambient temperature. Whereas, the specimen with 10% fine aggregate replacement with RRB has shown a compressive strength of 38.98 MPa at 400°C. All specimens, irrespective of the RRB replacement level, indicated excellent consistency of concrete with an ultrasonic pulse velocity value greater than 4.4 km/s up to 200°C, which was then followed by stepwise degradation with further temperature increases. In the authors' opinion, natural fine aggregate partially replaced with RRB in combination with polypropylene fiber holds promising potential for the manufacturing of sustainable concrete intended for use under elevated temperature. Practical Applications: The newly developed concrete blend, designed to be both sustainable and heat-resistant, will hold the promise of safeguarding natural resources and saving Mother Earth. By incorporating a particular alternative aggregate (recycled refractory brick), this innovation will not only curtail manufacturing expenses for heat-resistant concrete but also repurpose waste effectively. This sustainable heat-resistant concrete can be applied to concrete structures and members exposed to high temperatures, protecting them from rapid deterioration caused by repeated harsh conditions. Its implementation will not only enhance durability and efficiency of these structures but also lead to significant savings on maintenance costs, particularly in steel making industries. [ABSTRACT FROM AUTHOR]

Fast consumption of conventional ingredients of concrete and waste generated due to demolishing old buildings is a multi-fold problem in the concrete industry. Hence the sustainable alternative of it is the need of the day. In this research work effect of binary blending of demolished waste and fly ash on the flexural strength of plain concrete prism is presented. The properties of aggregates and cement are evaluated. The physical and chemical properties of fly ash were determined. Recycled aggregates from demolished waste with different mix ratios (1:2:4 and 1:1.5:3) were used. Optimization of recycled aggregates; by evaluating concrete cylinders in 12 batches; showed 35% as optimum. At the optimum dosage of recycled aggregates fly ash was used from 2.5% to 15% with an increment of 2.5% to optimize its dosage. Compressive strength test of the standard-size cylinders and their comparison with control concrete showed a 10% dosage of a fly as the optimum percentage to replace the cement in the concrete matrix. Using both optimized dosages of recycled aggregates and fly ash prism specimens of 900mmx150mmx300mm were cast in four batches. The beam specimens were cured for 28 days followed by an evaluation of flexural strength and deflection under centric load in the universal testing machine. Test results of flexural strength (only 15% loss) showed good potential for both waste materials in the concrete matrix. Recycled aggregate with higher parent strength showed better performance than its other counterparts. With higher-strength recycled aggregates residual flexural strength was recorded as equal to 93%. For all specimens recorded deflection was within the allowable limits of ACI-318. [ABSTRACT FROM AUTHOR]

Present research critically investigates drying sensitivity and cement hydration resumption in recycled aggregate concrete (RAC). To determine minimum post-curing time for optimum strength resumption in RAC, a curing ratio (δ) is introduced. Curing ratio is defined as the ratio between post-curing duration and delay time before curing. Drying sensitivity of RAC is observed significantly lower than NAC. The maximum strength loss under drying conditions is 25.9% in RAC (OPC) and 23.2% in RAC (PPC). Strength criteria determine the curing ratios of RAC (OPC) and RAC (PPC) as 2.22 and 0.30. The maximum delay time for RAC (OPC) and RAC (PPC) is determined at 8 days and 21 days with a minimum post-curing for 17.76 and 6.63 days. The longest allowable delay produces ion penetration less than 1000 Coulombs, resistivity greater than 208 ohm-m, superior structural integrity and internal compactness, and sorptivity comparable to RACs cured after a shorter delay. [ABSTRACT FROM AUTHOR]

This research work aims to compare the strength and fracture mechanics properties of plain concretes, obtained from different coarse aggregates. During the study, mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (K I c S) and critical crack tip opening displacement (CTODc) were evaluated. The effect of the aggregates used on the brittleness of the concretes was also analyzed. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Crushed aggregates covered were basalt (BA), granite (GT), and limestone (LM), and natural peeble gravel aggregate (GL) were used in the concrete mixtures. Fracture toughness tests were performed on an MTS 810 testing machine. Due to the high strength of the rock material, the rough surface of the aggregate grains, and good bonding in the ITZ area between the aggregate and the paste, the concretes with crushed aggregates exhibited high fracture toughness. Both of the analyzed fracture mechanics parameters, i.e.,   K I c S and CTODc, increased significantly in the case of concretes which were manufactured with crushed aggregates. They amounted, in comparison to concrete based on gravel aggregate, to levels ranging from 20% for concrete with limestone aggregate to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. On the other hand, the concrete with gravel aggregate showed the lowest fracture toughness because of the smooth surface of the aggregate grains and poor bonding between the aggregate and the cement paste. However, the fracture process in each series of concrete was quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregates. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending. [ABSTRACT FROM AUTHOR]

This study explores the influence of different concentrations of recycled concrete aggregate (RCA) on the fresh and hardened properties of self-consolidating concrete (SCC) in order to assess the structural suitability of the use of RCA in a precast concrete plant. The study particularly emphasizes the early strength of the produced concrete. The RCA was sourced from crushed concrete used in roadway applications and was sieved to replicate the characteristics of natural aggregate. Five different SCC mixes were produced, with RCA substituting 0%, 10%, 30%, 50%, and 70% of the natural coarse aggregate (NCA) by weight. For each different mix design, the hardened properties tested were the compressive strength and tensile strength. The fresh properties investigated were the passing and filling ability. Additionally, aggregate properties including grain size distribution and absorption of coarse aggregate were studied. The selected mix design follows a typical well-graded self-consolidating concrete mix with 28-day strength of 8000 psi (55.16 MPa). It was found that replacing up to 50% of the NCA with RCA improves the early strength of concrete without a significant impact on the fresh and hardened concrete properties. [ABSTRACT FROM AUTHOR]

In this paper, the punching shear performance of 8 steel fiber reinforced recycled coarse aggregate concrete (SFRCAC) two-way slabs with a size of 1800 mm × 1800 mm × 150 mm was studied under local concentric load. The effects of RCA replacement ratio (rg) and SF volume fraction (Vf) on the punching shear performance of SFRCAC two-way slabs were investigated. Digital Image Correlation (DIC) measurement and Acoustic Emission (AE) technique were introduced to collect pictures and relevant data during the punching shear test. The test results show that the SFRCAC two-way slab mainly exhibits punching shear failure and flexure failure under local concentric load. The punching shear failure space area of SFRCAC two-way slab has no obvious change with increasing rg, however, show a gradual increase trend with increasing Vf. Both of the punching shear ultimate bearing capacity (Pu) and its deflection of SFRCAC two-way slab decrease with increasing rg and increase with increasing Vf, respectively. Finally, through the regression analysis of the results from this study and the data collected from related literature, the influence of rg and Vf on the Pu of two-way slabs were obtained, and the equations in GB 50010-2010, ACI 318-19, and Eurocode 2 Codes were amended, respectively. Furthermore, the amended equations were all applicable to predicted the ultimate bearing capacity of the ordinary concrete two-way slab, RCAC two-way slab, SFRC two-way slab, and SFRCAC two-way slab. [ABSTRACT FROM AUTHOR]

Sustainability plays an integral role in ensuring the continued existence of life on Earth and the protection of the natural environment. The recycling process is one of the most significant methods through which this strategy can be implemented. The potential environmental benefits of recycled concrete aggregates and polymer waste have attracted considerable interest within the asphalt industry. The present study focuses on the recycling of two materials to create asphalt mixtures. The first of these is polypropylene, which is mixed with asphalt cement at weight rates of 2%, 4%, and 6%. The second is treated and untreated Recycled Concrete Aggregate (RCA), which is substituted with coarse aggregate at weight rates of 20%, 40%, and 60%. The experimental work comprised the identification of the optimum asphalt content through the utilization of the Marshall design approach, the assessment of Marshall and volumetric characteristics, and the evaluation of moisture susceptibility through the measurement of Indirect Tensile Strength (ITS) and compressive strength. The findings indicated that all mixtures containing recycled polypropylene polymers and treated/untreated RCA exhibited a higher Tensile Strength Ratio (TSR) of approximately 6.1-14.7% and compressive strength of approximately 3.1-17.6% compared to control asphalt mixtures. This suggests that the mixture's resilience against moisture damage has been enhanced. [ABSTRACT FROM AUTHOR]

Geopolymer concrete, a cement-free concrete with recycled concrete aggregate (RCA), offers an eco-friendly solution for reducing carbon emissions from cement production and reusing a significant amount of old concrete from construction and demolition waste. This research on self-compacted, ambient-cured, and low-carbon concrete demonstrates the superior performance of one-part geopolymer concrete made from recycled materials. It is achieved by optimally replacing treated RCA with a unique method that involves coating the recycled aggregates with a one-part geopolymer slurry composed of fly ash, micro fly ash, slag, and anhydrous sodium metasilicate. The research presented in this paper introduces predictive models to assist researchers in optimising concrete mix designs based on RCA rates and treatment methods, including the incorporation of coated recycled concrete aggregates and basalt fibres. This study addresses the knowledge gap regarding geopolymer concrete based on recycled aggregate, various RCA rates, and novel RCA treatments. The novelty of the paper also lies in presenting the effectiveness of Artificial Neural Network (ANN) models in accurately predicting the compressive strength, splitting tensile strength, and modulus of elasticity for self-compacting geopolymer concrete with various rates of RCA replacement. This addresses a knowledge gap in existing research on ANN models for the prediction of geopolymer concrete properties based on RCA rate and treatment. The ANN models developed in this research predict results that are more comparable to experimental outcomes, showcasing superior accuracy compared to linear regression models. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The water environment greatly affects the creep deformation of recycled aggregate concrete (RAC). Hence, a humidity–stress–damage coupling numerical model was used for investigating the time-dependent deformation of RAC in the water environment in this study. Firstly, uniaxial compression and water absorption tests were performed to determine the calculation parameters of the creep numerical simulation of RAC in a water environment. Experimental results indicate that the elastic modulus and compressive strength drop as the water content increases. Then, the time-dependent deformation of RAC in a water environment was studied using a numerical simulation test of compressive creep when multiple stress levels were applied, and the critical stress for accelerated creep and the long-term strength of RAC were obtained. Finally, the influence of confining pressures on the long-term deformation of RAC in a water environment was discussed. When there is no confining pressure, the long-term strength of RAC is 23.53 MPa. However, when a confining pressure of 3.921 MPa is loaded onto RAC, the long-term strength of RAC is 47.052 MPa, which increases by 100%. Increasing confining pressures has an obvious effect on ensuring the long-term stable application of RAC in a water environment. Compared with the creep test, the method adopted in this study saves time and money and provides the theoretical basis for evaluating the time-dependent deformation of RAC in a water environment. [ABSTRACT FROM AUTHOR]

This article presents a study on the stiffness of mixtures of anthropogenic materials derived from construction or demolition waste, specifically fine recycled concrete aggregates (fRCAs) with different fine fraction (FF) contents. The study investigated small-strain shear moduli via various signal interpretation methods, examining, above all, the time domain approaches and considering the influence of FF content. However, the inconclusive results from the bender element (BE) tests highlight the complexity of factors affecting shear wave velocity, which requires further research to refine the methodology and assess long-term performance in geotechnical applications. Selecting the correct test frequency and interpretation method is crucial to obtain accurate results. The BE test method should consider all relevant factors. At low input frequencies (≤5 kHz), the near-field effect affected the received signal for fRCA mixtures. At higher frequencies (around 14 kHz), the noise levels increased, thereby interfering with the S-wave travel time determination. Intermediate input frequencies (10.0 and 12.5 kHz) provided the representative shear modulus (G) values. The small-strain shear modulus (Gmax) of the fRCA compounds from the resonant column and BE tests was found to be in good agreement, despite differences in the test procedures themselves. [ABSTRACT FROM AUTHOR]

The seismic behavior of six corroded recycled aggregate concrete (RAC) columns with ultra-high-strength bars (UHSB) was investigated through quasistatic test and numerical analysis. The main parameters include different corrosion ratios, axial load ratios (ALR), and stirrup ratios. The results revealed that: The damage development of the corroded specimen sped up with increasing corrosion ratio and ALR, and the corroded specimens suffered brittle shear failure due to the stirrup fracture or the concrete failure. The difference in carrying capacity of the specimens with low corrosion ratios and ALR was relatively small, while the deformation capacity was significantly reduced with increasing corrosion ratios and ALR. Reinforcement corrosion had a minor effect on the strength and stiffness degradation but would reduce the maximum cumulative energy dissipation capacity. By combining residual drift and residual crack width, the corroded specimens all could meet the limit of repairable residual drift and crack width before 4% drift, showing satisfactory resilient performance. Based on the modified corrosion models of materials, the numerical analysis showed the detrimental and coupling impact of the high ALR, high corrosion ratio, and low stirrup ratio on the carrying and deformation capacity. Through numerical analysis data, an equation was proposed that can satisfactorily predict the peak drift of the corroded columns with UHSB. [ABSTRACT FROM AUTHOR]

The fractal theory can effectively describe the complexity and multi-scale of concrete under impact load and provide a scientific basis for evaluating concrete's impact resistance. Therefore, based on the fractal theory, this study carried out the fragmentation size analysis by weighing the quality of SFRRAC fragments, disclosed the distribution characteristics of impact fragmentation size of steel fiber reinforced recycled aggregate concrete (SFRRAC) specimens under different recycled coarse aggregate (RCA) replacement ratio, different steel fiber (SF) contents and different impact pressures. The results indicate that the fractal dimension can describe the degree of fragmentation of the specimen. The greater the fractal dimension, the more the amount of fragmentation of the specimen subjected to impact load, the lesser the fragmentation size, and the greater the degree of fragmentation. Under the impact load, the fractal dimension of SFRRAC is between 1.36 and 2.28. As the impact pressure increases, the energy consumption increases, and the fractal dimension decreases. With the growth in replacement ratio, the fractal dimension gradually increases, and the energy consumption is negatively correlated with the fractal dimension. Along with the growth of SF content, the energy consumption gradually increases, and the fractal dimension continuously decreases. A new metric angle is provided to explore the inherent law between the impact-crushing characteristics of SFRRAC and the dynamic load, thereby offering foundational support for the application of SFRRAC in practical engineering. [ABSTRACT FROM AUTHOR]

In this paper, the possibility of utilising coarse recycled concrete aggregate (CRCA) obtained from a construction and demolition waste (CDW) plant in Delhi to make 60 MPa self-compacted concrete (SCC) was evaluated. The CRCA was used in as-collected condition and was not processed any further. The aggregate packing (bulk) density (APD) method was adopted to prepare the SCC-CRCA mixture in order to obtain an aggregate mixture exhibiting maximum bulk density/least void content (45%). In addition, SCC was made using aggregate mixtures in which the natural coarse aggregate (NCA) was replaced with CRCA at 0%, 20% and 100% of the total coarse aggregate content by weight. The cement, fly ash, silica fume and water were kept constant for all SCC mixtures. The effects of CRCA on the flow behaviour, mechanical strength, shrinkage characteristics and microstructure properties of SCC mixtures were evaluated. The test results indicated that SCC mixtures made with up to 45% CRCA replacement can be used for structural concrete, which is higher than that recommended in Indian (20%) and international specifications (35%) for traditionally vibrated (conventional) concrete. [ABSTRACT FROM AUTHOR]

The attached cement paste in recycled concrete (RC) aggregate leads to its potential reactivity against sulfate ions. Several test methods were evaluated to find a suitable, reliable, and accurate method to evaluate the potential reactivity of aggregates. Different quality RC aggregates were used to apply those methods. The studies included evaluations of concrete cores drilled from source concrete (SC), RC aggregates, recycled mortar bars under different exposures, and RC prisms exposed to external sulfate attack (ESA). The concrete core test allowed qualifying SC as potentially reactive against sulfate in a short time. Tests on recycled aggregates and recycled mortar bars showed variable sensitivity levels. Results from concrete prisms showed an effective reactivity of recycled aggregates when the replacement is higher. [ABSTRACT FROM AUTHOR]

The current study examines the physical, mechanical, and durability of eco-efficient pervious concrete produced with partial and complete substitutions of natural aggregate (NA) by recycled aggregate (RA) waste from demolished concrete and porcelain. The experimental investigation assessed the workability (slump test), compressive strength, flexural strength, and tensile strength along with the concrete's water permeability, impact, and abrasion resistance. Seven mixes were examined; the first is a control mix with natural aggregate, and the other six are made with various RA ratios, including 30%, 70%, and 100%. The sand was also fully replaced by waste porcelain, even though the ratio of sand used in pervious concrete was low. The results revealed that using waste concrete and porcelain adversely affected the workability of fresh pervious concrete mixes, reducing it by approximately 14%. Furthermore, a decrease in the strength of pervious concrete was noticed, especially in the splitting tensile strength, where the reduction reached 32%. Moreover, the impact resistance of pervious concrete made with RA reduced by 29% compared to that made with NA; the same applies to durability, with an increase of 20% in weight loss. On the other hand, using both recycled concrete and recycled porcelain improved the permeability of the pervious concrete, which reached 30%. Pervious concrete made with waste concrete and porcelain can be an acceptable alternative to that made from natural aggregate due to its improved water permeability and positive environmental impact. However, further investigation is important to consider strength and durability enhancement. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The recycling of construction wastes holds significant importance both environmentally and economically. While extensive research has been conducted on aggregates derived from various wastes, the recycling of pervious concretes (PC) has been largely overlooked. This study addresses this gap by examining the porosity and mechanical properties of PC manufactured using aggregates obtained from recycled PC. The investigation focuses on three key factors: aggregate size (5/15, 10/15, and 15/25 mm size fractions), fiber inclusion (dosages of 0.1%, 0.2%, and 0.3% by volume), and aggregate type (limestone aggregate and recycled aggregate). Through image processing techniques, void characteristics including amount, structure, and homogeneity were quantified. Results indicate that the use of recycled aggregate led to a decrease in compressive strength ranging from 29% to 65%, depending on aggregate size fraction and fiber content. Porosity assessments revealed higher porosity in concrete utilizing recycled aggregate, with computer-based methods yielding values closely aligned with volumetric results. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) is not widely used in construction because of the concerns related to its quality. This paper investigates the effect of the replacement levels of recycled concrete aggregate (RCA) on bulk and hardened densities of RAC. The analysis of variance (ANOVA) was used to investigate the sensitivity of bulk and hardened densities of concrete to the replacement level of RCA. Predictive equations were developed to estimate the 3-day, 7-day, and 28-day compressive strength of RAC from its fresh properties, which are helpful for early quality control inspection of RAC. Furthermore, a predictive equation has been proposed to determine the flexural strength of RAC based on its 28-day compressive strength. The comparison of the predictive capability of the proposed and widely used code equations showed the incapability of the latter to estimate the flexural strength of RAC. In contrast, the proposed equation demonstrated a high level of prediction accuracy. [ABSTRACT FROM AUTHOR]

The administration of waste from constructing-demolition and the reuse of industrial waste materials are the main focuses of the sustainability initiatives. There are economic and environmental benefits to using recycled concrete aggregates (RCA). Nevertheless, the RCA mixes' poor performance necessitates the addition of more enhanced substances. This study investigated the moisture resistance of asphaltic mixes that included RCA and silica fume (SF). Coarse aggregates were replaced with RCA at three different percentages 15%, 30%, and 45%, which were pre-treated by immersing it in acid with a concentration of 0.1 mol. for a duration of 24 hours. Then the mixes containing RCA were incorporated with various amounts of SF, with 3%, 6%, and 9% of the binder's weight. These mixes were used to measure the Marshall characteristics and evaluate moisture resistance using indirect tensile strength, compresive strength tests. A thermal camera was employed to assess the modified asphalt's homogeneity. The thermal images demonstrated that after 30 minutes of mixing SF at 160 ℃, the asphalt cement has been uniformly distributed SF particles, as evident by the colour convergence. The findings revealed that the addition of RCA to the asphalt mix increased TSR and IRS levels by 6.68% and 8.93%, respectively, at RCA 30% compared to the original mixture. Additionally, the inclusion of silica fume led to a rise in TSR and IRS until 6%, after which there was a drop, but the levels remained above the original mix. The use of 30% RCA ratio with 6% silica fume resulted in the highest improvement in TSR and IRS, with a rise of 13.72% and 14.13%, respectively. [ABSTRACT FROM AUTHOR]

This document is a summary of a book that showcases the latest advancements in research on long-life road infrastructures. The book covers a wide range of topics, including materials and structures, performance evaluation, and modeling. The articles in the book discuss various innovative approaches and techniques for maintaining and managing rural road networks, evaluating pavement performance, and enhancing the durability and sustainability of road structures. The research presented in the book contributes to the development of more efficient and durable road systems that can withstand the demands of modern transportation networks. [Extracted from the article]

Relatively few studies have been conducted on the seismic performance of recycled aggregate concrete (RAC) shear walls with concealed bracing. To promote the development of high-performance green building structures and the application of RAC in structural components, the seismic performance of RAC shear walls under different influencing factors was tested, and low-cycle reversed loading tests were performed on ten RAC shear walls with different shear-to-span ratios. The test parameters included the recycled coarse aggregate (RCA) replacement ratio, the recycled fine aggregate (RFA) replacement ratio, the axial compression ratio, the shear span ratio and whether to set up the concealed bracing. The influence of the above variables on the seismic performance was then assessed. The results revealed that the bearing capacity, ductility, stiffness and energy dissipation capacity of the RAC shear walls decreased in line with an increase in the replacement ratio of the RFA. However, the bearing capacity, energy consumption and stiffness of the RAC shear walls decreased within 10% and the ductility decreased within 15%. The RAC shear walls were able to meet the seismic requirements of the building structure after reasonable design and use. As the axial compression ratio increased, the bearing capacity of the RAC shear walls improved, but their elastic–plastic deformation capacity was reduced. Setting the concealed bracing significantly improved the seismic performance of the RAC shear walls, such that they achieved a seismic performance close to that of the natural aggregate concrete (NAC) shear wall. After setting up the concealed bracing, the load carrying capacity of the RAC shear walls increased by up to 15%, the ductility increased by up to 20% and the energy consumption capacity increased by up to 50%. A mechanical calculation model of the RAC shear wall was then established by considering the effect of recycled aggregate, the calculated results of which were a good match with the test results. [ABSTRACT FROM AUTHOR]

The study conducted axial tensile strength tests on concrete samples that replaced conventional aggregates with recycled aggregates. In Series I, using FNG instead of FNA resulted in a reduction in compressive strength by 12.8–49.8% and tensile strength by 14.5–44.6%. If the proportion of FNG exceeds 50%, compressive strength decreases by more than 24.5% and tensile strength by more than 27.5%. In Series II, replacing CNA with CRG reduced compressive and tensile strengths by 18.4–32.8% and 5.1–24.9%, respectively; exceeding 40% CRG results in a compressive strength reduction of more than 32.8% and a tensile strength reduction of more than 24.9%. In Series III, samples made with RCA, CNA, and 20% CRG showed a compressive strength decrease of 8.8–22% and a tensile strength decrease of 10.7–26%; RCA80 samples showed maximum reductions. In Series IV, replacing CNA with RCA resulted in compressive and tensile strength reductions of 15.4–34.7% and 13.9–24.3%, respectively; RCA80 samples again showed maximum reductions. Maximum stress unit deformation values (εo) increased by 3–58.4% in Series I, 9–80% in Series II, 10–44.9% in Series III, and 9–32% in Series IV. Tensile toughness values showed the highest increase of 35.15% in the CRG40 sample and the lowest of 0.13% in the RCA40-20 sample. The use of glass aggregates in concrete is feasible, but exceeding certain ratios can significantly reduce strength. Concrete can effectively use waste glass as a partial substitute for cement, fine aggregates, or as a filler material, potentially enhancing compressive strength. [ABSTRACT FROM AUTHOR]