Search Results (237)

The growing demand for construction materials has intensified concerns regarding natural sand depletion and the accumulation of industrial waste. Among these wastes, oil-contaminated sand (OCS) generated from petroleum-related activities presents environmental challenges while also offering potential for beneficial reuse. Previous studies have reported that low OCS contents can enhance workability and improve mechanical properties, highlighting its potential as a sustainable construction material. This study investigates the feasibility of incorporating OCS as a partial replacement for natural sand in 3D concrete printing (3DCP). Three mixes containing 0%, 0.5%, and 1% OCS were evaluated in terms of flowability, setting behaviour, printability, rheological response, hydration behaviour, mechanical performance, anisotropic response, and microstructural characteristics. The results showed that OCS incorporation had only a limited influence on flowability, while both the initial and final setting times exhibited noticeable delays. The maximum printable layers reached from 19 for the control mixture to 22 and 26 layers for the 0.5% and 1% OCS mixes, respectively, accompanied by reduced settlement and structural deformation. Rheological analysis revealed higher static yield stress and structuration rates for the OCS-modified mixes, contributing to enhanced buildability and geometric stability. Hydration calorimetry showed comparable heat-flow behaviour between the control and OCS-modified mixes, suggesting only a limited influence of OCS on cement hydration kinetics. The incorporation of OCS improved the compressive strength of the printed mixes and reduced compressive anisotropy, while SEM observations revealed a denser and more homogeneous microstructure, particularly for the 0.5% OCS mix. Thus, the findings indicate that low-level incorporation of oil-contaminated sand is a viable strategy for improving the printability and performance of 3D-printed concrete, promoting the sustainable reuse of contaminated industrial waste. Full article

To address prevalent industrial challenges, including the high cost of fabricating microstructures via photolithography and 3D printing, impurity residues easily generated by conventional physical/chemical pore-forming techniques, and the limited sensitivity of regular capacitive sensors, this paper innovatively proposes an integrated low-temperature in situ gas foaming strategy using ammonium bicarbonate for the fabrication of porous TPU-based ionic gels. Relying on the complete gaseous decomposition property of ammonium bicarbonate upon heating, a three-dimensionally interconnected continuous porous network is spontaneously constructed inside the polymer matrix. Thermoplastic polyurethane (TPU) is selected as the continuous polymer phase, and [EMIM][TFSI] imidazolium ionic liquid is blended as the ion source to synthesize composite ionic gel substrates. A PDMS composite slurry filled with graphene is employed to prepare flexible substrates, followed by low-temperature oxygen plasma surface modification to introduce polar functional groups such as hydroxyl and carboxyl onto electrode surfaces. A standard sandwich-structured ionic pressure sensor with the configuration of “top modified electrode—porous ionic gel dielectric layer—bottom modified electrode” is finally assembled. The porous framework and modified electrodes constitute a dual synergistic enhancement system: the porous structure markedly reduces the equivalent elastic modulus of the gel and improves its compressive deformation capacity; polar-modified electrodes optimize the interfacial compatibility between electrodes and gels, shorten ion migration paths and lower interfacial contact resistance. Systematic calibration of multiple batches of parallel samples reveals that the as-fabricated sensor achieves a high sensitivity of 25.3 kPa⁻¹ across the full measuring range from 0 to 1000 kPa with a linear fitting coefficient R² = 0.992. The loading response time and unloading recovery time of the device are 60 ms and 80 ms respectively, with a performance degradation of less than 3% after 1000 consecutive loading–unloading cycles, featuring low hysteresis error and excellent signal repeatability. Multi-scenario in vivo wearable tests on human subjects verify that the device can precisely capture subtle fluctuations of radial artery pulse and periodic laryngeal deformation during swallowing, distinguish characteristic waveform patterns of various English words according to differences in vocal cord vibration, and accurately detect bending motions when attached to finger joints. The entire fabrication process adopts common chemical raw materials and standard laboratory equipment without expensive micro-nano processing facilities, featuring convenient raw material procurement and high process fault tolerance, which enables large-area coating-based mass production. This work delivers a novel technical route for the low-cost large-scale production of high-performance ionic flexible sensors and bears significant industrialization reference value for applications in wearable medical monitoring, bionic robotic electronic skin, flexible human–machine interactive touch panels and other related fields. Full article

Three-dimensional concrete printing (3DCP) has emerged as a promising digital construction technology that reduces material waste, eliminates formwork, and enables complex geometries. However, its sustainability remains constrained by the extensive use of ordinary Portland cement (OPC) and natural aggregates. This review comprehensively evaluates waste utilization in extrusion-based 3D printed concrete, classifying applications into three pathways: cement replacement in OPC-based systems, waste-derived precursors in alkali-activated/geopolymer binders, and fine aggregate replacement. Industrial, agricultural, and marine wastes are assessed regarding their effects on rheology, printability, mechanical performance, interlayer bonding, and durability. The reviewed literature investigated waste incorporation levels reaching up to 50% for cement replacement, up to 70% for alkali-activated/geopolymer systems, and up to 100% for aggregate replacement, depending on the material type and application pathway. Industrial wastes, particularly fly ash, slag, silica fume, and metakaolin, represent the most mature materials and generally improve printability and long-term performance. Agricultural and marine wastes show promising sustainability potential but remain insufficiently investigated. Despite encouraging laboratory-scale results, challenges related to material variability, early-age performance, standardization, and scalability continue to limit practical implementation. The review identifies critical research gaps and outlines future directions for developing sustainable and field-ready 3DCP technologies. Full article

Additive manufacturing with soil–cement mixtures is emerging as a disruptive approach to advancing sustainable manufacturing processes. However, its industrial scalability remains limited by material brittleness and a lack of process standardization. This study presents an integrative literature review that critically evaluates the influence of fiber reinforcement on the 3D printing process and the mechanical performance of soil–cement mixtures within the context of sustainable construction and circular economy principles. The analysis integrates fresh-state rheological behavior with hardened-state performance, showing that an optimized fiber dosage (0.3–0.5% by volume) shifts the failure mode from brittle to quasi-ductile while reducing crack propagation by approximately 60%. Additionally, the study compares various fiber types, including synthetic and natural alternatives. The results show that synthetic fibers used at low dosages (0.5–1.0% by volume) provide the greatest improvements in tensile strength and post-cracking ductility. In contrast, natural fibers, typically used at higher dosages (8.0–13.0% by volume), mainly improve toughness and thermal performance, with more limited gains in strength. The review also identifies key gaps in the existing literature, such as a lack of standardized protocols for measuring process parameters and the need for studies that address long-term durability and comprehensive lifecycle assessments. These findings outline a clear research roadmap to support the consolidation of reinforced soil–cement as a resilient and sustainable material for next-generation additive manufacturing. Full article

The integration of advanced additive manufacturing technologies, particularly 3D printing (3DP), also known as Additive Construction (AC), could influence a shift in the construction industry towards improved efficiency and automation. This research evaluated the effect on hardened properties of two different concrete mixes for use in 3DP based on the presence or absence of alkaline-resistant (AR) glass fibers. Furthermore, three different curing methods were evaluated: air-curing, plastic-covered curing, and spray-curing. Concrete beams were printed for flexural testing, and cores were taken from other depositions to evaluate compressive strength and split-tensile strength. An analysis of the size and location of cracks on the beams after curing was performed for the different mixes and curing methods. For beams without fibers, plastic-covered curing produced the highest flexural modulus values, and air-curing produced the lowest flexural modulus values. Plastic-cured beams with fibers had higher flexural modulus values than the air-cured beams with fibers. However, the spray-cured beams with fibers produced somewhat anomalous results, with one flexural modulus value being larger than those of the plastic-cured beams, and the other flexural modulus value being less than those of the air-cured beams. All 28-day compressive strengths and split-tensile strengths across mixes and curing conditions fell within a small band ranging between ~19.3–22.1 MPa and ~1.7–2.0 MPa (~2800–3200 psi, and 240–290 psi), respectively. There was a large amount of scatter in some of the tests. It appears that neither the presence of the AR-glass fibers, nor the type of curing had a large influence on compressive strength or split-tensile strength. Results showed that the addition of fibers and the use of the plastic during curing significantly reduced the occurrence, the width, and the depth of cracks as a result resulting from the curing process. Plastic-curing was the most effective curing method for minimizing the occurrence of cracks. Any cracks that formed during plastic-curing were extremely fine and had little or no effect on mechanical properties. Full article

3D printing is evolving at a fast pace in both the manufacturing and construction sectors. These advancements can greatly benefit these industries. However, the 3D printing of concrete structures presents some challenges due to defects in the 3D concrete printed elements. Hence, this study systematically reviews Artificial Intelligence (AI)-driven techniques, such as Computer Vision and Machine Learning, to identify surface defects that can occur in 3D-printed cementitious material structures. The adopted methodology was the PRISMA statement with the aim of reporting the systematic review and meta-analysis. Two well-known databases, Web of Science and Scopus, were utilised for data extraction of articles published during the past 10 years, between 2014 and May 2025. The initial search provided 110 articles, both conference and journal papers; after screening, only 11 were left for the final review assessment. The smaller number of the final articles shows that much work is still needed in this area. It has been observed that various computer vision and machine learning-based methodologies were employed to classify defects in 3D concrete printed structures. Deep learning algorithms, such as YOLO and RT-DETR, were featured as the most efficient in real-time defect detection and quality monitoring. It was also observed that real-time monitoring systems attached to 3D printers help in reducing the material wastage, which is essential to meet the sustainable goals. However, more work is still required to underline the defects of 3D-printed cementitious material, probably with the involvement of AI image processing tools and techniques. This can help to automate the defects in 3D-printed structures, and by this, the productivity could be enhanced. Full article

The global construction industry urgently requires sustainable alternatives to ordinary Portland cement (OPC) to mitigate its immense carbon footprint. Red mud (RM), a highly alkaline bauxite residue, presents tremendous but challenging potential as a supplementary cementitious material. This review systematically bridges the gap between atomic-level interfacial bonding mechanisms and macroscopic engineering performance, highlighting how these properties are significantly dictated by specific RM sources (e.g., Bayer vs. Sintering processes). We first elucidate advanced pretreatment strategies, notably CO₂ mineralization, which synergistically mitigates extreme alkalinity and sequesters carbon. Crucially, the fundamental bonding mechanisms are decoded: beyond physical filling, RM integration induces significant micro-morphological densification via intense aluminosilicate depolymerization—evidenced by the Al[VI] to Al[IV] coordination shift—and the quantitative integration of approximately 40% reactive iron phases into stable Fe-S-H networks. By clearly distinguishing between traditional hydration and clinker-free alkali-activation pathways, we evaluate holistic structural parameters beyond mere 28-day compressive strength (40–67 MPa), explicitly addressing flexural capacity, modulus of elasticity, and volume stability. Environmental assessments confirm exceptional heavy metal immobilization (>95% efficiency, leaching < 0.010 mg/L) and a substantial 50–80% reduction in Global Warming Potential (GWP), provided the environmental burden of alkaline activators is rigorously accounted for. Furthermore, the long-term risk of Alkali–Silica Reaction (ASR) is evaluated as a primary durability concern. Finally, to overcome persistent rheological bottlenecks, this paper highlights transformative future trajectories, particularly data-driven Machine Learning (ML) for complex mix optimization and 3D concrete printing for advanced infrastructure. Ultimately, this review provides a robust theoretical foundation and a pragmatic roadmap for upcycling RM into safe, high-performance, and ultra-low-carbon building materials. Full article

Wound-healing and skin regeneration are the focus of intensive research, driven by a rapidly expanding global market and the growing clinical demand for more effective interventions engineered to actively direct and enhance tissue regeneration. Recent advances in biomaterial engineering and 3D bioprinting have accelerated the development of highly customized, functional constructs mimicking native tissue. Together, these innovations are reshaping therapeutic strategies and expanding the translational potential of next-generation skin substitutes. This review presents an overview of the evolution of material printing technologies and the different categories of 3D bioprinting techniques and processing methods, followed by an evaluation of the properties of natural biomaterials as bioinks for skin wound-healing and their application in skin tissue engineering. Moreover, we provide a comprehensive global market analysis, with consideration of costs, benefits, and a SWOT analysis to identify the full potential of this technology for the development of novel skin wound-healing products. Recommendations and future perspectives are provided to guide researchers, clinicians, and industry partners on the current state and potential of adopting 3D bioprinting with natural biomaterials for effective wound-healing therapies. Full article

Polyether ether ketone (PEEK) is a high-performance polymer with exceptional mechanical properties, durability and lightweight. 3D printing of PEEK can be very beneficial in the medical industry to manufacture patient-specific implants; however, there is a lack of studies regarding the fatigue behavior of 3D-printed PEEK, especially under compression, which is closely related to its potential applications. This paper investigates the static and dynamic mechanical performance of 3D-printed PEEK. Tensile and compression tests were conducted on specimens with ±45° raster orientation. Annealing at 270 °C for 5 h increased crystallinity from 34.4% to 41.4% yet unexpectedly reduced tensile strength from 60.8 MPa to 47.3 MPa, while increasing Young’s modulus from 2.51 GPa to 3.51 GPa. Micro-CT analysis revealed increased pore size after annealing. Static compression strength showed improvement post-annealing, increasing from 80.1 MPa to 126.7 MPa, with modulus rising from 1.64 GPa to 2.28 GPa. Compression–compression fatigue tests, performed at 5 Hz and 2.5 Hz with stress amplitudes of 70–95% of maximum strength (R = 0.1), enabled the construction of the first S-N curve for 3D-printed PEEK under compressive loading. Annealed specimens exhibited superior fatigue life, with infinite life achieved at 83.3 MPa (70% of static strength). Thermal imaging highlighted the role of temperature in fatigue failure, showing that annealed specimens endured higher thermal loads. These findings support the suitability of 3D-printed PEEK for load-bearing biomedical applications under cyclic compressive loads. Full article

Over the last decade, prefabrication has emerged as a strategic alternative to address the global construction industry’s challenges concerning sustainability, productivity, and the housing deficit. This study analyzes the advances, benefits, limitations, and research gaps associated with its application in real estate projects between 2015 and 2025. A systematic literature review was conducted under the PRISMA protocol, which allowed for the selection of 58 high-quality articles sourced from Scopus, Web of Science, SciELO, and Redalyc. The findings highlight Asia as the leader in innovation and industrialization, while Latin America is identified as an emerging region with applications in social housing, education, and modular infrastructure. Reported benefits include reduced time and costs, improved environmental performance, and the integration of digital technologies such as BIM, 3D printing, and digital twins. Nevertheless, regulatory gaps, cultural resistance, and limited coordination among industry, government, and academia persist. The study concludes that prefabrication constitutes a transformative engine for the real estate sector, but its consolidation requires stronger regulatory frameworks, broader empirical research in Latin America, and the adoption of circular economy and digitalization strategies to ensure a sustainable and socially accepted impact. Full article

Adipose tissue engineering (ATE) is an interdisciplinary field integrating materials science, cell biology, and engineering, aiming to construct functional artificial adipose tissue for addressing adipose tissue deficiency, metabolic disorders, and related clinical challenges. This review systematically summarizes the core advances, critical limitations, and translational potential of ATE. First, we elaborate on the three fundamental elements of ATE: scaffold materials (hydrogels, porous materials, microspheres, fibrous materials, decellularized extracellular matrix, 3D-printed/bioprinted scaffolds, and prevascularized constructs), seed cells (adipose-derived stem cells, mesenchymal stem cells, etc.), and growth factors (vascular endothelial growth factor, fibroblast growth factor, etc.), as well as their synergistic regulatory roles in adipose tissue regeneration. We then discuss the key factors influencing adipogenic differentiation and vascularization, which are pivotal for the formation of functional ATE constructs. Furthermore, we detail the construction and evaluation of in vitro and in vivo ATE models, highlighting the value of large animal models in bridging preclinical and clinical gaps. The applications of ATE in soft tissue repair and reconstruction, drug screening and disease modeling, and cultured meat manufacturing are comprehensively analyzed, with emphasis on technical challenge across different directions. Finally, we discuss the core challenges hindering ATE clinical translation, including lack of standardization of adipose-derived stem cells, immunogenicity issues, regulatory barriers, and technical limitations, and propose targeted future perspectives. This review provides a comprehensive and critical overview of ATE, offering guidance for promoting its translation from preclinical research to clinical practice and industrial application. Full article

Sulphur, a major by-product of the oil and gas industry, has emerged as a promising construction material in both sulphur concrete (SC) and sulphur-extended asphalt (SEA) applications. This review examines the development, properties, and uses of these sulphur-based construction materials over a century by following PRISMA guidelines for systematic literature selection. A bibliometric analysis highlights a surge in research activity over the last two decades. The key advantages of sulphur concrete include rapid strength gain (achieving ~50 MPa within 1–2 days) and exceptional chemical durability in extreme environments. Sulphur-bound materials exhibit high corrosion resistance, low water permeability, and full recyclability upon reheating. Challenges such as thermal shrinkage-induced brittleness and temperature sensitivity have been mitigated by using polymer-modified sulphur and mix design optimisation. Sulphur-extended asphalts benefit from increased stiffness, stability, and cost savings compared to conventional mixtures. Enhanced performance has been observed at sulphur replacement levels of 20–40% in asphalt binders. The review also summarises mixed formulations, mechanical properties, durability metrics, and innovative applications ranging from acid-resistant industrial structures to sustainable pavement materials and even extraterrestrial construction. The environmental benefits, such as up to 40% GHG reduction and complete recyclability of sulphur-based concretes, align with circular economy goals. Future research directions include improving ductility, advancing 3D printing techniques, and field validation of long-term performance. Overall, sulphur by-products can be transformed into valuable construction materials that address waste management and infrastructure durability. Full article

Concrete 3D printing technology is emerging as a new way to transform the construction industry in the future. However, the existing concrete 3D printing technology still has different degrees of defects in the print molding process. The existing concrete 3D nozzles need to undergo a long motion trajectory when printing complex curved components, which leads to lower geometric accuracy of curved structures, as well as poorer overall molding quality of the printed components. The aim of this study is to design a reducer nozzle to effectively shorten the printing stroke and thus improve the printing accuracy. A reducing nozzle is proposed with multi-gear internal meshing and a rotating blade structure nozzle with an adjustable outlet caliber. The mechanical strength of the rotating blade of the nozzle and the distribution characteristics of the flow field inside the nozzle are verified through fluid–solid coupling analysis. Experimental comparison shows that compared with the existing concrete 3D printing nozzle, the variable-caliber nozzle significantly improves the surface quality of the specimen, which strongly promotes the practical application and development of concrete 3D printing technology in the engineering field. Full article

This study focuses on the design and control system of a rotating nozzle for 3D construction printers. The development of a rotating nozzle is motivated by the need to enhance control over extrusion direction and material alignment, thereby improving the mechanical performance of printed structures by the use of non-circular nozzles. The typical 3D construction printer is equipped only with a stationary circular nozzle, which prevents the use of a non-circular nozzle due to the printer’s lack of a rotational mechanical system. This, in turn, limits the opportunity to enhance mechanical properties such as tensile and compressive strengths effectively. The proposed design is developed through computer-aided design (CAD) software, and the printer’s configuration is adjusted for integration of the rotational mechanism’s control system. This design includes a full description of the rotational mechanism and integration steps for the 3D printer. Besides the main motor of the 3D printer, an additional motor is installed next to the nozzle and controlled by a new axis (parameter), which is added into the G-code. A new axis, called “U”, is responsible for the rotation of the nozzle itself. For the development of this axis design, the cosine law is applied. The calculation is based on the three consecutive points in the G-code to obtain an accurate degree of rotation for the nozzle. The effectiveness of the system was confirmed by evaluating the compressive strength depending on printhead type. Based on testing results, one trowel printhead had the highest flexural strength of 5 MPa, and a trapezoidal printhead with teeth had the highest compressive strength of 8 MPa, compared to a circular default nozzle head with 6 MPa and 2 MPa for compressive and flexural strengths, respectively. The new optimized nozzle design is implemented in existing 3D printers, which allows it not only to develop its capability in the printing process but also to make sustainable contributions in the 3D construction industry. Full article

Concrete 3D printing (3DCP) combines materials science with material processing technologies to enable automated, additive construction. This review summarizes findings from the literature and industrial practice on 3DCP mortar formulation with emphasis on the material processing chain. The workflow is examined from raw material storage through handling, mixing, and deposition. The roles of binders, aggregates, dispersed reinforcement, and chemical admixtures are discussed in relation to rheological behavior, buildability, and early-age mechanical performance. The analysis covers storage, dosing, and mixing strategies with respect to mix consistency and overall process reliability, while mortar pumping and extrusion are addressed alongside nozzle-injected additives and automation. Finally, limitations and scalability challenges are outlined with research directions such as continuous mixing, in-line monitoring, and adaptive mix formulation for on-site applications. Full article