Search Results (135)

As a typical solid waste, recycled fine powder from waste concrete holds significant potential for enhanced resource utilization when used in the preparation of cementitious materials through multi-solid-waste synergistic composite activation. In this study, a recycled fine powder-based multi-component composite cementitious system was established by incorporating ground granulated blast furnace slag, calcium carbide residue, and phosphogypsum. The influence of each component on the mechanical properties and microstructure of the system was systematically investigated, followed by an interaction analysis using the response surface methodology. The results indicate that the alkalinity provided by calcium carbide residue forms the foundational guarantee for activating the system’s reactivity. The ettringite formed during the hydration of phosphogypsum effectively enhances the later-age strength and structural densification. Recycled fine powder can compensate for the strength development when the dosage of ground granulated blast furnace slag is reduced. The optimized composite system achieved a maximum 28-day compressive strength of 35.2 MPa, with optimal formulation ranges of Pc = 50–70%, Ps = 50–60%, and Pp = 8–12%. The synergistic effect between Pc and Ps is the dominant factor governing compressive strength, while the phosphogypsum dosage should be controlled within a suitable range through its interaction with Ps. This work provides a novel understanding of the synergistic activation mechanism among multiple solid wastes and offers a statistically optimized mix-design guideline for practical applications. Full article

The incorporation of recycled concrete fines (F), limestone (L), and ground granulated blast-furnace slag (S) as Portland cement constituents in accordance with EN 197-6 requires the determination of naturally occurring radionuclides to ensure radiological safety from a radiation protection standpoint. This study carried out a radiological assessment of eight cement types with varying proportions of L, F, and S additions, including anhydrous cements and mortars cured for 2 and 28 days. The activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were determined by gamma-ray spectrometry using HPGe detectors and radiochemical separation. In addition, the ²²²Rn emanation fractions were measured by the accumulation method using an AlphaGuard detector. Finally, annual effective doses were calculated using the RESRAD-BUILD software for a standard dwelling of 35 m² occupied by an adult and an infant. Among the individual materials, S exhibited the highest activity in the uranium decay series (113 ± 24 Bq kg⁻¹ of ²³⁸U), while L and F showed comparably lower values. Cements containing S additions (CEM II/C-M, CEM VI (S-L), and CEM VI (S-F)) were higher than the reference average value for building materials of 50 Bq kg⁻¹, although all mortars remained below this value. Principal component analysis revealed significant correlations between S content, SiO₂, Al₂O₃, and ²³²Th. The maximum annual effective dose reached 0.32 mSv for infants (CEM VI (S-L)), with the dose due to ²²²Rn inhalation being predominant. All cements studied are radiologically safe, confirming their suitability for use within the objectives of the circular economy. Full article

Ultra-high-performance concrete (UHPC) typically contains high cement and steel-fiber contents, leading to high cost and carbon emissions. This study developed a low-carbon UHPC by partially replacing cement with industrial solid waste (ISW) composed of ground granulated blast-furnace slag and calcium carbide slag, and by partially replacing steel fibers with recycled plastic fibers (RPF). The effects of ISW and RPF on flowability, mechanical properties, hydration behavior, microstructure, carbon emissions, and raw-material cost were investigated. ISW had a limited influence on flowability, whereas RPF markedly reduced flowability. Appropriate ISW and RPF contents increased flexural and compressive strengths by up to 41.02% and 14.93%, respectively. The 30% ISW-50% RPF mixture provided the highest flexural strength, while 30% ISW-30% RPF achieved the highest compressive strength with acceptable flowability. Hydration heat, XRD, SEM, and FTIR analyses showed that moderate ISW promoted early hydration and C-S-H/C-A-S-H gel formation, whereas excessive ISW caused dilution and reduced matrix compactness. Therefore, 30% ISW-30% RPF is recommended as the balanced formulation, whereas 50% ISW-50% RPF is more suitable for carbon- and cost-sensitive applications and maintains approximately 150 MPa compressive strength. Full article

This study investigated the underwater abrasion resistance of recycled aggregate concrete according to ASTM C1138 using recycled aggregates obtained from demolished concrete as a 100% replacement of natural aggregates. The objective was to reduce the consumption of natural resources and minimize construction and demolition waste. In addition, ground granulated blast furnace slag (BFS) was used as a supplementary cementitious material at replacement ratios of 25% and 50%. Three BFS products with Blaine fineness values of 3000, 4000, and 6000 cm²/g were used to investigate their effects on the compressive strength and underwater abrasion resistance of recycled aggregate concrete. The experimental results showed that the compressive strength of recycled aggregate concrete was approximately 7% lower than that of natural aggregate concrete. However, the underwater abrasion test according to ASTM C1138 showed that the abrasion depth of recycled aggregate concrete was comparable to that of natural aggregate concrete. After 72 h of testing, the abrasion depth of recycled aggregate concrete was only slightly higher than that of natural aggregate concrete. In contrast, recycled aggregate concrete exhibited a higher weight loss, with an average value of 2.10% compared with 1.77% for natural aggregate concrete. Among the BFS mixtures, increasing the Blaine fineness of BFS resulted in lower abrasion depth and lower mass loss. Concrete containing BFS6000 exhibited the best underwater abrasion resistance within the BFS mixtures, although all BFS mixtures showed higher abrasion depth and mass loss than recycled aggregate concrete without BFS. At the 25% replacement ratio, concrete containing BFS6000 exhibited the lowest abrasion depth (3.11 mm) and weight loss (3.37%), whereas concrete containing BFS3000 showed higher values. A similar trend was observed at the 50% replacement ratio, although both abrasion depth and weight loss slightly increased compared with the corresponding 25% mixtures. The results demonstrate that recycled aggregate concrete combined with BFS has good potential for hydraulic structures and other concrete structures exposed to underwater abrasion. Although a slight reduction in compressive strength was observed, the underwater abrasion resistance can be improved by using BFS with higher Blaine fineness together with quality-controlled recycled aggregates. These findings provide useful information for the development of sustainable recycled aggregate concrete and support the efficient utilization of recycled materials in hydraulic engineering applications. Full article

Recycled aggregate concrete (RAC) offers an effective approach to reducing the environmental burden associated with construction and demolition waste. In this study, a fiber-reinforced RAC was developed by replacing part of the cement with fly ash and ground granulated blast-furnace slag, while glass fibers or basalt fibers were incorporated as reinforcing materials. A systematic experimental program was conducted to evaluate the mechanical behavior of the proposed concrete under different saturation conditions. The results show that the best toughness performance was achieved in the natural moisture state. In comparison, compressive and flexural strengths reached their maximum values under dry conditions, whereas splitting tensile strength peaked in the natural state. Based on the experimental data, prediction equations were established for the splitting tensile and flexural strengths by considering both saturation degree and fiber content. A stress–strain model under uniaxial compression was also developed. In addition, scanning electron microscopy (SEM) was employed to examine the fiber–matrix interface and hydration products, thereby clarifying the microstructural characteristics of the concrete at different saturation levels. Full article

Mechanistic simulation and machine learning are powerful but complementary tools: physics-based simulation is interpretable yet computationally expensive and blind to real-world context, whereas machine learning is fast but data-hungry and opaque. Biological systems resolve this tension elegantly, coupling physically grounded mechanoreceptor sensing with higher-level neural interpretation that places those signals in context. Inspired by this layered architecture, we present Mechanics-AI, an open-source framework that mirrors the same sensing-then-interpretation logic computationally. A first learning layer (ML1) emulates expensive finite-element, computational fluid dynamics and multiphysics simulations to produce interpretable physical metrics such as stress, strain, shear, and thermal and moisture fields, while a second layer (ML2) fuses these metrics with heterogeneous real-world metadata to predict categorical outcomes and design recommendations. Eight algorithms are benchmarked automatically, the most accurate is selected for each task, and Shapley additive explanations expose the dominant physical drivers to preserve interpretability. The framework is demonstrated across three independent domains using a single unchanged pipeline: forensic traumatic brain injury prediction, optimisation of a bio-inspired humanoid bioreactor for tissue engineering, and a zero-emission building (ZEBAI) framework that couples thermo-hygro-mechanical simulation with Sobol-sampled surrogate modelling to design sustainable, low-carbon envelopes from recycled aggregate concrete by balancing structural safety, energy and embodied carbon. Despite entirely different physics, data and objectives, the same architecture generalises across all three, showing that bio-inspired, layered coupling of mechanistic simulation and contextual learning offers a reusable, interpretable route to cross-domain engineering prediction and sustainable design. Full article

This PRISMA-guided scoping review examines the use of waste materials in civil engineering as a sustainable approach to reducing environmental impacts, conserving natural resources, and supporting circular economy principles. The rapid growth of urbanization, industrialization, mining, and agricultural activities generates large amounts of waste materials, including fly ash, ground granulated blast-furnace slag, bauxite residue, mining tailings, waste rock, acid-mine drainage sludge, waste plastics, post-consumer vulcanized rubber, recycled construction materials, and agricultural ashes. The disposal of these materials often creates serious environmental and land-use problems, making their reuse increasingly important. In this context, civil engineering is one of the most promising sectors for large-scale waste valorization because of its high material demand and its ability to use different waste streams into practical applications such as concrete and cementitious systems, pavement and asphalt engineering, geotechnical works, and other infrastructure sectors. This review critically evaluates the global availability, material characteristics, engineering applications, environmental and economic benefits, recent advances, and key challenges related to major industrial, mining, agricultural, polymeric, and construction-derived wastes. Although significant progress has been made in this field, wider implementation is still limited by variations in material properties, technical and environmental challenges, economic constraints, and limited field validation of long-term performance. By bringing together current knowledge from different waste streams and civil engineering sectors, this review highlights important research gaps and future directions to support more sustainable, resilient, and resource-efficient infrastructure development. The effective use of waste materials in civil engineering can play an important role in reducing carbon emissions, improving resource efficiency, and supporting global sustainability. Full article

In order to conduct a comprehensive investigation into the effects of ground granulated blast furnace slag (GGBFS) on the dynamic mechanical properties and mesoscopic damage mechanisms of recycled aggregate concrete (RAC), a combined approach integrating material testing, microscopic characterization techniques, and theoretical analysis was adopted in this study. Two GGBFS replacement rates (0% and 35%) were considered. Uniaxial compression tests were performed to obtain data at different curing ages (T = 7 d, 28 d, 56 d, and 150 d) and strain rates ($\dot{\epsilon }$ = 10⁻⁵/s, 10⁻⁴/s, 10⁻³/s, and 10⁻²/s). The obtained data were complemented by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) analyses to characterize the evolution of the microstructure and pore characteristics of the specimens. The findings demonstrated that prolonging the curing period continuously densified the microstructure of the specimens, resulting in a commensurate improvement in their initial macro-mechanical behavior. At curing ages exceeding 28 d, the secondary hydration reaction of GGBFS was found to generate additional C-S-H gel, which filled the internal microvoids within the specimens, reduced porosity, and further improved the initial macroscopic mechanical properties. Concurrently, the microstructural characteristics observed at different curing ages, in conjunction with the crack propagation and the fracture toughness effects associated with strain rate, further influenced the initiation, propagation patterns and paths of microcracks during uniaxial compression, as well as the adjustment of the effective stress framework. Furthermore, characteristic parameters describing the evolution of mesoscopic fracturing and yielding damage exhibited regular variations with curing age and strain rate. For specimens cured for 56 d, compared to those with a GGBFS replacement rate of 0%, specimens containing 35% GGBFS exhibited a 4.13% increase in peak stress and a 0.29% decrease in peak strain at $\dot{\epsilon }$ = 10⁻⁵/s. At a replacement rate of 35%, as the strain rate increased from $\dot{\epsilon }$ = 10⁻⁵/s to $\dot{\epsilon }$ = 10⁻²/s, the peak stress rose from −50.37 MPa to −60.74 MPa, whereas the peak strain dropped from −23.87 × 10⁻⁴ to −22.15 × 10⁻⁴. This study provides significant scientific evidence and a theoretical framework for the engineering application of GGBFS-modified RAC under varying strain rate conditions. Full article

Reusing industrial byproducts to prepare recycled aggregate concrete (RAC) is a sustainable approach that can protect the ecological environment. This study tested the possibility of preparing an eco-efficient recycled concrete containing steel slag (SS), ground-granulated blast-furnace slag (GGBS), and polypropylene (PP) fibers to avoid resource waste and depletion and decrease CO₂ emissions. To this end, 12 mix proportions were designed to analyze the effects of SS, GGBS, and PP fibers on the macro- and micro-performances of the developed RAC. The experimental results showed that increasing the SS content decreased the RAC mechanical strength, whereas partially substituting SS with GGBS in the RAC improved the mechanical properties, especially at a later stage. Adding PP fibers to the RAC containing SS and GGBS significantly increased the splitting tensile strength. However, it had little effect on the compressive strength as the PP fiber content was less than 0.6%. The microscopic experiment revealed that adding GGBS promoted the degree of hydration of SS, reduced the Ca (OH)₂ content, made the ITZ structure more compact, and optimized the pore characteristics of the RAC. Furthermore, according to the raw materials and results of mechanical properties, a hybrid Genetic Algorithm/Artificial Neural Network (GA-ANN) technique was proposed to predict the compressive strength of the RAC containing SS, GGBS, and PP fibers. We found that the proposed GA-ANN model effectively predicts the compressive strength. The findings of this study demonstrate that preparing RAC incorporating SS, GGBS, and PP fibers is promising for the reuse of industrial byproducts and construction waste. Full article

The growing demand for sustainable construction materials has led to significant advancements in ultra-high-performance concrete (UHPC), with a particular focus on geopolymer-based systems as an alternative to conventional cementitious binders. This review explores the latest developments in sustainable Ultra-High-Performance Geopolymer Concrete (UHPGPC) by analysing key material composition, mechanical, durability and microstructural properties. The incorporation of ground granulated blast furnace slag (GGBFS), silica fume (SF), and fly ash (FA) has demonstrated notable improvements in compressive strength, durability, and workability. Additionally, the use of activators such as sodium silicate and sodium hydroxide optimizes geopolymerization, resulting in a denser microstructure and enhanced mechanical performance. This review highlights the critical role of fibre reinforcement in UHPGPC, where steel fibres (SFs) and hybrid fibres significantly enhance compressive and tensile strength, as well as crack resistance. The inclusion of waste materials such as rice husk ash and recycled glass promotes sustainability by reducing CO₂ emissions while maintaining structural integrity. However, higher waste-glass content may adversely affect bonding due to its smooth surface texture. The findings highlight the potential of UHPGC as a high-performance, eco-friendly alternative to traditional cement-based UHPC. By integrating industrial by-products and alternative activation techniques, UHPGPC can contribute significantly to the global shift towards sustainable and low-carbon construction materials. Full article

This study investigates the valorization of construction and demolition (C&D) waste streams and an industrial by-product for sustainable concrete production. Recycled concrete aggregates (RCA) and recycled brick aggregates (RBA), derived from C&D wastes, together with pelletized recycled fly ash aggregates (FAA) produced from thermal power plant fly ash, were used as total replacements for natural coarse aggregates. Six concrete mixtures were prepared at a constant water-to-cement ratio of 0.50 using untreated and slag slurry–treated aggregates. A slag slurry-based two-stage mixing approach (TSMA), incorporating ground granulated blast furnace slag (GGBFS), was applied as a practical and potentially scalable treatment method to enhance aggregate quality and interfacial bonding. The results show that complete replacement of natural aggregates reduced fresh concrete unit weight by up to 17%, while meeting the minimum compressive strength requirements for structural applications. Slag slurry treatment led to statistically significant improvements in mechanical properties, reduced variability, and enhanced overall reliability. In addition, widely used code-based prediction models (TS500, ACI, Eurocode-2, NZS 3101-1:2006, and CSA A23.3-04), originally developed for conventional concrete, were evaluated for their applicability in estimating key mechanical properties of recycled and by-product aggregate concretes, and alternative regression-based models were developed to improve prediction accuracy. Overall, the findings demonstrate the potential for effective utilization of C&D wastes and industrial by-products in structural concrete, contributing to resource efficiency and reduced reliance on natural aggregates. Full article

Repair mortars containing recycled concrete powder (RCP) and ground granulated blast-furnace slag (GGBFS) are promising low-carbon materials for the rapid repair of concrete structures and pavements. However, their practical use is often limited by slow early hydration, insufficient early strength, and weak bonding with existing concrete substrates. In this study, four early-strength admixtures, namely calcium formate, anhydrous sodium sulfate, calcium acetate, and triethanolamine, were incorporated into a P·I 42.5 cement-based repair mortar containing RCP and a low dosage of GGBFS. Their effects on fluidity, flexural and compressive strength, tensile bond strength, drying shrinkage, and hydration characteristics were investigated. The results showed that the suitable dosages of calcium formate, anhydrous sodium sulfate, calcium acetate, and triethanolamine were 1.5%, 1.0%, 0.8%, and 0.05% by mass of total cementitious materials, respectively. Among the four admixtures, calcium formate provided the best balance among strength enhancement, bond performance, workability retention, and dosage tolerance. Compared with the control group, the 3 d and 28 d flexural strengths of the 1.5% calcium formate group increased by 37.0% and 20.3%, respectively. Anhydrous sodium sulfate gave the highest tensile bond strength, with the 14 d value increasing by 33.15% to 1.052 MPa, but its effective dosage range was relatively narrow. Calcium acetate was more effective in reducing drying shrinkage, with a 28 d shrinkage value of 695.14 × 10⁻⁶. SEM and XRD results suggested that the admixtures mainly accelerated early hydration, while no new major crystalline phases were detected. Excessive dosages caused strength loss, bond deterioration, or increased drying shrinkage. These findings are applicable to the specific RCP–GGBFS repair mortar formulation and dosage ranges investigated here. They provide a practical basis for selecting early-strength admixtures for RCP-containing repair mortars used in concrete structure and pavement repair. Full article

The utilization of construction and demolition waste (CDW) as a supplementary cementitious material (SCM) represents a promising strategy for reducing cement consumption, minimizing environmental impacts, and promoting sustainable waste valorization. In this study, hybrid recycled powder was produced from mixed CDW obtained from a Portuguese recycling facility and processed through mechanical grinding to achieve particle size characteristics comparable to Portland cement. The ground powder was subsequently thermally activated at 600 °C and evaluated as a partial replacement for Portland cement in concrete. Concrete mixtures were prepared with recycled powder replacement contents of 5%, 15%, 25%, and 35%. The physical, mechanical, and durability properties of the concrete were investigated, including density, water absorption, compressive strength, carbonation and chloride penetration resistance. The results indicate that thermally activated recycled powder can be successfully incorporated as a partial cement replacement while maintaining satisfactory mechanical and durability performance. These findings demonstrate that thermally activated hybrid recycled powder derived from mixed CDW has significant potential as a sustainable SCM, contributing to reduced cement consumption and supporting the development of low-carbon concrete. Full article

This study extends beyond traditional single-binder assessments by developing a mechanistic framework for interpreting the behavior of multi-component geopolymer systems. It systematically examines the roles of industrial by-products (granulated blast-furnace slag), agricultural residues (barley straw ash), and construction-derived materials (recycled granite powder) when integrated into a metakaolin-based matrix, with particular emphasis on their influence on gel formation pathways, microstructural refinement, and macroscopic performance. A sustainable geopolymer concrete (SGC) system was formulated using multi-binder combinations at replacement levels ranging from 5% to 30%. Comprehensive evaluations were conducted, including fresh properties, mechanical performance, durability characteristics, thermal resistance, and microstructural features. The results demonstrate that the 70Mk–30GBFS composition facilitates the development of a dense hybrid C–(A)–S–H/N–A–S–H gel network, resulting in a 26.8% enhancement in compressive strength and a 32.0% decrease in chloride ion penetration. Rather than depending on empirical relationships, the study establishes a mechanistically grounded link between precursor chemistry, interfacial transition zone (ITZ) refinement, and performance limits. These findings contribute to a deeper understanding of multi-component geopolymer design and support the development of high-performance, sustainable concrete materials for structural applications. Full article

Waste tire disposal and high-ground-stress soft rock roadway instability are pressing global challenges. This study develops sustainable rubber granule concrete (RGC) using waste tire rubber as a key component, aiming to realize waste valorization and floor heave control. RGC’s mechanical properties (uniaxial/triaxial compression, compressibility, ductility) were systematically tested, and its pressure relief mechanism was validated via finite element analysis (ABAQUS/FLAC) and 60-day field monitoring. Results show that RGC with optimal parameters (12% rubber content, 3–4 GPa elastic modulus, 250–350 mm thickness) achieves 64% bottom stress reduction and >40% displacement control. The material’s excellent energy absorption and flexibility address the brittleness of conventional concrete, ensuring stable support in high-stress environments. This work provides a sustainable, cost-effective concrete modification strategy, bridging waste recycling and geotechnical engineering, with broad implications for low-intensity, high-toughness material applications. Full article