Search Results (13)

Basalt-fiber-reinforced recycled aggregate concrete (BFRAC) produced with 100% recycled coarse aggregate is still constrained by the inferior quality of recycled aggregate and the difficulty of optimizing fiber reinforcement parameters. This study investigated the effects of basalt fiber length configuration and dosage on the mechanical performance and pore structure of recycled aggregate concrete incorporating recycled coarse aggregate subjected to two-step pretreatment with nano-silica and cement slurry. Four fiber length configurations, namely 6, 12, and 24 mm and a mixed-length system, were evaluated at volume fractions of 0.1, 0.2, and 0.3%. The reinforcing effect was assessed through compressive strength, splitting tensile strength, scanning electron microscopy, mercury intrusion porosimetry, and statistical analysis. The pretreatment improved recycled aggregate quality, reducing water absorption from 4.97% to 3.11% and crushing index from 20.5% to 13.4%. Basalt fiber incorporation generally enhanced mechanical performance, although the response depended on fiber length and dosage. At 28 days, BF24V1 achieved the highest compressive strength, whereas BFmixV1 exhibited the best overall performance by combining high compressive strength with the highest splitting tensile strength. Relative to the average performance of the corresponding single-length mixtures at the same dosage, the mixed-length system showed a positive synergistic effect. Microstructural observations indicated that this behavior was associated with more effective crack bridging and refinement of the pore-size distribution. The results demonstrate that a low-dosage mixed-length basalt fiber system provides an effective route for upgrading pretreated waste-derived aggregate into higher-performance recycled aggregate concrete. Full article

In China, a significant portion of construction and demolition waste (CDW) consists of clay bricks and concrete, which can be processed into recycled brick–concrete aggregate (RBCA). This study explores the utilization of compositely modified RBCA as a substitute for natural coarse aggregate in concrete. Two distinct composite modification methods were applied to pretreat RBCA, and then the resistance of the resulting recycled brick–concrete aggregate concrete (RBCAC) to sulfate attack and freeze–thaw cycles was systematically examined and elucidated the underlying enhancement mechanisms. The experimental data revealed a clear trend: increasing the proportion of RBCA in the concrete mix correlates with a marked decline in its durability performance. In contrast, the application of composite modification techniques yielded a significant enhancement in durability. This improvement is primarily attributed to the mitigation of weak interfacial zones and the promotion of a more compact microstructure within the interfacial transition zone (ITZ). Consequently, the observed enhancement in durability metrics can be principally ascribed to this microstructural optimization. This research offers substantive theoretical insights that can facilitate the broader adoption of compositely modified RBCA in the production of sustainable concrete, contributing to waste valorization and resource conservation. Full article

This systematic review and meta-analysis per PRISMA 2020 addresses the use of recycled concrete aggregates as a replacement for aggregates in self-consolidating concrete for structural and non-structural use. It provides a comprehensive evaluation of the available research and offers a synthesised overview of the potential use of recycled concrete aggregate in self-consolidating concrete beyond standardised replacement levels. A total of 256 research papers were obtained from different databases, and after a detailed content review, only 24 unique experimental research studies fulfilled the review criteria. Data were extracted on recycled concrete aggregate source, pre-treatment, replacement ratio, mix proportions, fresh properties, strength, stiffness, and durability. It was observed across all studies that the recycled concrete aggregates originated from precast concrete rejected elements with a low water-to-cement ratio, producing an equal or stronger concrete than the reference concrete in the studies; however, none of the studies included in this research resulted in a higher modulus of elasticity than the corresponding reference concrete. Additionally, moderate aggregate replacement (20–50%) preserved the workability, whereas high replacements (75–100%) affected fresh concrete properties as well as increased shrinkage and creep. The inclusion of fine recycled concrete aggregate in addition to coarse recycled concrete aggregate has a larger effect on lowering compressive strength and stiffness in the concrete. Overall, high-quality coarse recycled concrete aggregate (precast rejects or screened demolition waste)—an aggregate replacement level of around 50%—facilitates the production of sustainable self-consolidating concrete, whereas full replacement requires aggregate pre-treatment and a carefully optimised mix design. Full article

Compared to natural aggregates, recycled concrete aggregates (RCAs) which are derived from construction and demolition (C&D) waste exhibit inferior properties, such as lower density and higher water absorption. Accelerated carbonation was an effective approach to enhance the properties of RCA. This study conducted a comparative analysis on the property enhancement of both coarse recycled concrete aggregate (CRCA) and fine recycled concrete aggregate (FRCA) by utilizing four carbonation approaches: conventional carbonation, CH spraying with conventional carbonation, wet carbonation, and two-step wet carbonation. Scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) analysis, and CO₂ uptake comparison were used to investigate the microstructural properties of the RCA. Furthermore, we also evaluated the compressive strength of mortar specimens with four different replacement ratios and the density and water absorption values of different carbonation-treated aggregates. The experimental findings revealed the following: (1) All of the accelerated carbonation approaches were more effective for FRCA than CRCA due to a higher adhered mortar content. (2) The pretreatment of CH spray provided external Ca²⁺ which improved the carbonation efficiency and therefore significantly enhanced the property of FRCA. (3) Liquid–solid phase carbonation achieved higher carbonation efficiency in the inner pore areas of the adhered mortar, resulting in a high CO₂ uptake and microstructure densification compared with conventional gas–solid phase carbonation. Full article

In order to address a challenging issue in the recycling of construction debris, the impact of carbonization treatment on the characteristics of recycled aggregates (RCAs) was experimentally examined in this work. Both direct carbonization and carbonization following calcium hydroxide pretreatment were used in the study to assess the impact of carbonization on the physical characteristics of recycled aggregates. According to the findings, carbonization raised the recycled aggregates’ apparent density while drastically lowering their porosity and water absorption (by as much as 20–30%). Although the recycled aggregate’s crushing index marginally increased with age, its overall physical qualities remained excellent. Pretreatment with calcium hydroxide can improve the physical characteristics of recycled aggregates, further optimize their pore structure, and efficiently encourage the carbonation process. Furthermore, recycled aggregate’s crushing index can be considerably decreased and its quality much enhanced by the ultrasonic cavitation treatment. According to the study, the carbonation-treated recycled aggregate’s microstructure was denser in the interfacial transition zone and had a stronger link with the cement paste, improving the recycled aggregate concrete’s overall performance. XRD, infrared spectral analysis, and SEM scanning were used to determine the increased calcium carbonate content in the recycled aggregate following carbonation treatment as well as its microstructure improvement process. The findings offer fresh concepts for achieving resource efficiency and environmental preservation through the use of recycled aggregates in concrete, as well as theoretical backing for their use. Full article

In the context of sustainable construction, recycled concrete aggregates (RCAs), including both fine and coarse fractions derived from construction and demolition waste (CDW), are gaining traction due to their potential to mitigate environmental impacts by reducing reliance on natural aggregates and minimizing waste. This paper provides a comprehensive review of the effects of RCAs on the mechanical and durability properties of concrete, including compressive and tensile strengths, modulus of elasticity, and resistance to environmental degradation. The review highlights that the presence of adhered mortar and higher porosity in RCAs generally leads to reduced mechanical performance and durability. However, pretreatment methods—mechanical, chemical, and thermal—along with optimized mix designs and the use of supplementary cementitious materials (SCMs) have shown to significantly improve the concrete properties of RCAs. Additionally, recent studies on carbon dioxide (CO₂) capture through the accelerated carbonation of RCAs offer promising environmental benefits. Life cycle assessment (LCA) analyses reveal reductions in energy use, CO₂ emissions, and material costs when RCAs are properly processed and locally sourced. Despite challenges related to RCA quality variability, the review identifies pathways for the effective use of RCAs in structural applications. Full article

In order to study the effect of the crushing process on the fine separation of reclaimed asphalt pavement (RAP) and the mechanical properties of cement-stabilised aggregate mixed with RAP, four crushing processes, namely small mesh hammer crushing, hammer crushing, jaw crushing, and double roller crushing, were used to separate the aggregate from asphalt in RAP materials. The effect of crushing on the grading characteristics and agglomeration condition of RAP material was investigated. RAP cement-stabilised aggregates were prepared and analysed for their mechanical properties and micro-morphology using RAP materials obtained from fine separation. The relationship between the RAP material properties and the mechanical properties of the RAP-added cement-stabilised aggregate was analysed on the basis of the tests. The results showed that crushing breaks down large-size RAP materials, leading to grade refinement, and that hammer crushing was the most effective in reducing the grade variability. The highest agglomerate dissociation rate of RAP material above 4.75 mm after small mesh hammer crushing treatment was 96.9%, and the residual mass ratios of RAP material in two grades of 0~3 mm and 3~5 mm after hammer crushing were lower than 90%. The unconfined compressive strength, splitting strength, and compressive resilience modulus of RAP cement-stabilised aggregate after crushing were greater than those of the uncrushed RAP cement-stabilised aggregate, and the crushing increased the amount of RAP in the mix to 60%. Compared with the unadulterated RAP cement-stabilised aggregate, the hydration products of the RAP cement-stabilised aggregate were reduced after crushing, and there were obvious gaps and discontinuities between the RAP material and the cement paste. The RAP gradation and agglomeration condition correlated strongly with the mechanical properties of the mixes, with RAP coarse aggregate agglomerates being the main cause of gradation variability. This paper provides theoretical support for the proposal of a pretreatment process to reduce the variability of RAP-doped cement-stabilised aggregate and improve the mechanical properties, and the research results are conducive to the recycling of high-volume RAP materials in the base. Full article

The vast majority of different waste building units have negative environmental impacts around the world. Crushed building units can be recycled and utilized in the concrete industry to solve these problems and maintain natural resources. This study investigated the feasibility of employing crushed autoclaved aerated concrete (CAAC) and crushed clay brick (CCB) as a lightweight aggregate (LWA) to fabricate environmentally friendly recycled lightweight concrete (LWC). In addition, a lightweight expanded clay aggregate (LECA) was also used as an LWA, namely to study how the high porosity of an LWA can adversely affect the properties of LWC. Through the experimental program, all types of LWAs were pre-treated and strengthened with two cementitious grouts, and then the performance of the produced LWC was assessed by determining the slump of fresh concrete, the dry density, the unconfined compressive strength, and the splitting tensile strength at ages of 3, 7, 28, and 56 days. The laboratory results revealed that both CCB and CAAC can be reused as full substitutions for normal-weight coarse aggregate to manufacture LWC with appropriate properties. The obtained data show that the properties of an LECA, CCB, and CAAC were improved, and the porous structure can be strengthened by pre-treatment and coating with grouts. In the same way, the mechanical performance of produced LWC is also enhanced. Full article

Tire-derived aggregate concrete (TDAC), or rubberized concrete, is gaining ground as an eco-friendly option in civil engineering. By substituting traditional coarse aggregates with recycled rubber tires, TDAC offers a greener choice with excellent energy absorption capabilities. This leads to robust structures and reduced upkeep expenses. Nonetheless, TDAC’s lower strength than regular concrete requires a delicate balance between energy absorption and strength. This study investigates two enhancements to TDAC performance: (a) the impact of sodium hydroxide (NaOH) solution pretreatment and SikaLatex bonding agent addition on TDAC’s compressive strength, and (b) the use of varying water–cement ratios and superplasticizer to enhance TDAC’s mechanical properties. This study involves concrete cylinder compression tests and the creation of strength estimation equations. Results show that NaOH-treated tire-derived aggregate (TDA) boosts workability, increasing slump by 4.45 cm (1.75 in), yet does not significantly enhance compressive strength, causing a 34% reduction. Conversely, combining NaOH pretreatment with Sikalatex bonding agent enhances workability by 28% and boosts compressive strength by 21% at the same water-cement ratio. To optimize performance, it is advised to employ modified TDA concrete with a water–cement ratio under 0.34 and superplasticizer. These findings highlight the potential of modified TDA concrete in sustainable and seismic-resistant designs. Full article

There have been efforts to use building demolition waste as an alternative aggregate in concrete to decrease the use of natural resources for construction. The World Green Building Council estimates that the construction industry is responsible for more than 50% of all material extracted globally and that construction and demolition waste makes up 35% of global landfills. As a result, incorporating recycled aggregate (RA) in concrete production is a prudent course of action to reduce the environmental impact. This study reviews prior research on using recycled aggregate instead of conventional ingredients in concrete. The composition and morphology of different types of RA, the behavior of RA in fresh and hardened states, keyword co-occurrence and evolution analysis, and the various additives used to enhance the inferior properties of RA are discussed. The RA showed different physical properties when compared with natural aggregate. However, the addition of pozzolanic materials and various pretreatment techniques is desirable for improving the inferior properties of RA. While building waste has been utilized as a substitute for fine and coarse aggregate, prior research has demonstrated that a modified mixing approach, an adequate mixing proportion, and the optimum replacement of cementitious materials are necessary. Based on the review, the recommendation is to use RA at a replacement level of up to 30% and the addition of precoated and pozzolanic materials as a treatment to provide concrete with adequate workability, strength, and durability for structural applications. Full article

As the number of discarded tyres continues to increase, causing serious environmental problems, the need of recycling the waste tyre rubber become extremely urgent in worldwide. Today, there is an increasing focus on recyclable materials. The reuse of waste tyre rubber in concrete contributes to sustainable development. In the past 10 years, numerous experiments on the recovery of rubber from waste tyres to produce concrete products have been conducted. In this review, we conclude the major achievement of rubberized concrete (RC) durability, discuss and analyse the influence of rubber replacement rates, replacement patterns, particle size and treatment methods. Results show that an increase in rubber content can improve the chloride penetration resistance, acid and sulphate attack resistance, freeze–thaw resistance, and alkali–silica reaction damage resistance of concrete, and the content of 5–20% has a significant improvement effect. Rubber replacing fine aggregate is the best scheme for durability, followed by cement and coarse aggregate. In addition, the recommended rubber particle size is 0–3 mm. However, the rubber particle has adverse effects on abrasion resistance, impermeability, water absorption resistance and carbonation resistance. The pre-treatment of rubber or the addition of supplementary cementitious materials are effective and viable ways of improving the durability of RC. Further research is needed on the long-term durability of RC, as well as on ductility, energy absorption, and thermal and corrosion resistance. Full article

The proper disposal of used rubber tires has emerged as a primary concern for the environment all over the globe. Millions of tires are thrown away, buried and discarded every year, posing a major environmental concern owing to their slow decomposition. As a result, it is advantageous to use recycled waste rubber aggregates as an additional building resource. Recycling crushed rubber would lead to a long-term solution to the problem of decreasing natural aggregate resources while conserving the environment. This study examines the impact strength variability and reliability of preplaced aggregate concrete containing crumped rubber and fibres. Ten different mixtures were prepared by replacing natural aggregate with crumped rubber (5, 10, 15 and 20%). The crumped rubber was pretreated by the water with sodium hydroxide dilution for 30 min before usage. Hooked-end steel fibres were used at a dosage of 1.5%. The compressive strength, impact strength, impact ductility index and failure pattern were examined and discussed. In addition, a statistical method called Weibull distribution is used to analyze the scattered experimental results. The results showed that when the crumb rubber content was raised, the retained first cracking and failure impact numbers increased. As a result of substituting crumb rubber for 20% of the coarse aggregate in plain and fibrous mixes, the percentage development in first crack and failure was between 33% and 76% and 75% to 129%, respectively. Full article

In this paper, environmentally sustainable cement mortars were prepared with end-of-life tyre rubber (TR) and recycled waste porous glass (PG) as aggregates in order to obtain lightweight products characterized by renewable and not-pretreated materials specifically for indoor applications. The secondary raw materials were added as partial and/or total replacement of the conventional sand aggregate. The resulting lightweight specimens were characterized by rheological, mechanical, thermal, microstructural and wettability tests. Fine tyre rubber aggregates affected the cohesiveness of the composites, as opposite to coarse tyre rubber and porous glass. The flexural and the compressive strengths of the porous glass samples were higher than the tyre rubber samples because of the higher stiffness and good adhesion of the glass to the cement paste as observed by microstructural observations. On the contrary, an unfavorable adhesion of the tyre aggregates to the cement paste was observed, together with discrete cracks after failure without separation of the two parts of the specimens. The latter result can explain the best results obtained by tyre rubber mortars in the case of impact compression tests where the super-elastic properties of the elastomeric material were evidenced by a deep groove before complete failure. Moreover, the thermal conductivity decrease of the lightweight porous TR and PG composites was in the range of ~80–90% with respect to the sand-based samples, which suggests that they can be used as plasters and masonries, and, in the case of tyre rubber specimens, outside applications are not excluded as observed from the wettability tests. Full article